Cylinder cover parameter optimization method under heat-machine coupling condition

Abstract

The invention discloses a cylinder cover parameter optimization method under a heat-machine coupling condition, and belongs to the field of cylinder covers for internal combustion engines. The implementation method comprises the following steps of: quickly updating a cylinder cover model based on data transmission among a plurality of modules, quickly updating a cylinder cover assembly body model, drawing a high-quality self-adaptive grid of the cylinder cover, and automatically simulating and analyzing a steady-state flow field and a temperature field in the cylinder cover. The method comprises the following steps of: automatically mapping temperature distribution of the cylinder cover to rigidity and strength by using a grid model, performing simulation analysis on the rigidity and strength of the cylinder cover under a thermal-mechanical coupling condition, and repeatedly and automatically operating a performance calculation process of the cylinder cover under the thermal-mechanical coupling condition to realize comprehensive performance analysis on the cylinder covers with various different structures. And forming a sample data set representing the corresponding relationship between the cylinder cover structure and each performance of the cylinder cover under the thermal-mechanical coupling condition, and selecting an optimal parameter value from the sample data set as an optimization result, thereby realizing the performance optimization of the cylinder cover based on the joint simulation technology. The optimization precision and efficiency of the cylinder cover can be improved.

Description

Technical Field

[0001] The present invention relates to a cylinder head optimization method, and in particular to a method for optimizing cylinder head parameters based on UG, ICEM, fluent, Hypermesh, Abaqus and Isight software combined with policy technology. The method is suitable for optimizing the thermal load bearing capacity, rigidity reserve and lightweight degree of a cylinder head model under thermal-mechanical coupling conditions, and belongs to the field of energy and power engineering, and cylinder heads for internal combustion engines. Background Art

[0002] The cylinder head is one of the key components of a diesel engine. It seals the top of the cylinder and forms the combustion chamber space together with the top of the piston and the side wall of the cylinder. When the diesel engine is running, the part of the cylinder head that contacts the high-temperature gas will be subjected to a large thermal load, resulting in non-negligible thermal deformation and thermal stress. On the one hand, these thermal effects affect the sealing effect of the cylinder head, making it easy for the cylinder head to have insufficient airtightness when the design is imperfect; on the other hand, it makes the cylinder head bear a greater load on the basis of the original static stress, and puts forward higher requirements on the rigidity reserve of the cylinder head. As the design of the cylinder head continues to develop in the direction of high power density and lightweight, the effect of heat bearing capacity in the actual work of the cylinder head has become difficult to ignore, and even has become one of the decisive indicators for judging the advanced design of the cylinder head. Therefore, modern cylinder heads need to complete the performance calculation and optimization design of the model under the conditions of thermal-mechanical coupling, and more comprehensively consider the effect of thermal effects in the actual working process of the cylinder head.

[0003] The optimization design process of cylinder heads under thermal-mechanical coupling conditions has become mature, and many related cases can be found. For example, in the mature thermal-mechanical coupling simulation analysis and optimization technology of cylinder heads [1] (see Zhang Min, Zhang Yi, Zhang Qinxiu. Optimization design of cylinder head structure based on thermal-mechanical coupling [J]. Combined Machine Tools and Automation Processing Technology, 2017, (6): 126-129.), based on the design form of a basic cylinder head model, multiple groups of experiments were designed using the orthogonal experimental design method, and then the performance indicators of each experimental model were manually calculated, and the cylinder head optimization design was completed using this data. However, it can be found that the dimensions involved in such existing cases are relatively small, so the number of manual calculations required when the number of experimental planning levels is low is not large. However, as the requirements for cylinder head design continue to increase, designers may need to make more adjustments at the same time, and the total number of experiments that need to be manually calculated will also increase exponentially, resulting in a huge workload, which does not match the actual needs of efficient and fast engineering. Therefore, it is necessary to study more efficient optimization methods to adapt to the increasingly complex optimization calculation problems.

[0004] Faced with the increasing number of manual calculation requirements, many designers began to think about how to automate the cylinder head performance calculation. Coincidentally, in the face of the increasing demand for automation, software such as Isight has been used to assist in design in simple structural optimization cases in many other fields. For example, the optimization process presented in the prior art [2] (Fan Jiang, Zeng Weiwei, Wang Rongqiao, Shen Xiuli, Chen Zhiying. Optimization design of turbine blade shroud based on iSIGHT [J]. Journal of Aerospace Power, 2011, Vol. 26 (4): 745-751.) established an automated optimization process for turbine blades. However, at present, this type of design process is still rarely used in cylinder head design. The cylinder head design is different from the design of these simple geometric parts in the following ways: (1) The cylinder head geometry is relatively complex, making parametric modeling difficult and difficult to obtain a reasonable range of parameter changes; (2) The model generated by the cylinder head in each round of structural parameter changes is different. Therefore, before each round of simulation calculations, the finite element mesh of the cylinder head model and the cylinder head cooling channel model needs to be redrawn. This process can easily generate low-quality meshes, affecting the accuracy and convergence of the calculations; (3) In each round of simulation calculations, the boundary conditions and loads applied to the cylinder head need to be reassigned. Since the cylinder head mesh model used in each round of calculations is constantly changing, it is difficult to reassign the boundary conditions and loads using classic methods such as mesh number association or geometric voxel association. Summary of the invention

[0005] The purpose of the present invention is to provide a method for optimizing cylinder head parameters under thermal-mechanical coupling conditions, which realizes rapid updating of cylinder head models, rapid updating of cylinder head assembly models, high-quality adaptive grid drawing of cylinder heads, automatic simulation analysis of steady-state flow fields and temperature fields inside cylinder heads, automatic mapping of cylinder head temperature distribution to grid models for rigidity calculation, and simulation analysis of rigidity of cylinder heads under thermal-mechanical coupling conditions based on data transmission between multiple modules, and realizes comprehensive performance analysis of cylinder heads with various structures by repeatedly and automatically running the cylinder head performance calculation process under thermal-mechanical coupling conditions, forming a sample data set characterizing the corresponding relationship between the cylinder head structure and various performances of the cylinder head under thermal-mechanical coupling conditions, and selecting the optimal parameter value as the optimization result, thereby realizing cylinder head performance optimization based on joint simulation technology. The present invention can solve the problem that traditional cylinder head optimization methods require a large amount of manual operation, and at the same time, by selecting a grid data mapping method with a high degree of automation and high data transmission accuracy to build a thermal-mechanical coupling simulation environment for the cylinder head, the accuracy and efficiency of cylinder head optimization are improved.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] The present invention discloses a method for optimizing cylinder head parameters under thermal-mechanical coupling conditions. The method constructs a cylinder head geometric model based on a parametric modeling method, and uses a cylinder head expression to control the structural shape of the cylinder head geometric model, thereby realizing rapid updating of the cylinder head geometric model. The method performs finite element meshing on the cylinder head model and the cylinder head cooling channel based on an automated meshing method, and respectively draws a cylinder head body combined mesh model for flow field and temperature field calculations and a cylinder head 3D mesh model for calculating the load-bearing capacity under thermal-mechanical coupling conditions, thereby improving mesh quality and computational convergence probability. The method sets up a simulation analysis based on a cylinder head heat transfer analysis method, and uses a macro command to drive a solver to perform automated simulation analysis of the heat transfer performance of the steady-state flow field and temperature field inside the cylinder head, thereby obtaining the temperature distribution at each position on the cylinder head, and extracting key indicators that can reflect the heat transfer performance of the cylinder head. The method extracts the cylinder head temperature distribution data from the cylinder head body combined mesh model based on an automated mesh data mapping algorithm, and interpolates the data to the cylinder head 3D mesh model, thereby realizing gas The calculation results of the cylinder head temperature distribution are quickly and efficiently transmitted between different grid models; the simulation analysis is set up based on the cylinder head stiffness analysis method, and the macro command is used to drive the solver to perform automated simulation analysis of the cylinder head load-bearing performance under thermal-mechanical coupling conditions, so as to obtain the thermal-mechanical coupling stress and thermal-mechanical coupling deformation distribution of the cylinder head under service, and extract key indicators that can reflect the cylinder head load-bearing performance under thermal-mechanical coupling conditions; the sample space is constructed based on the parameter variation range of the cylinder head geometric model, and each sample point is repeatedly and independently subjected to automated simulation analysis. After filtering and removing data with non-convergence and substandard accuracy, a sample data set is obtained that characterizes the corresponding relationship between the cylinder head structure and the cylinder head load-bearing performance under thermal-mechanical coupling conditions; a comprehensive evaluation function is established to comprehensively weigh the cylinder head heat transfer performance indicators and the cylinder head load-bearing performance indicators and score the performance of each sample point, and the group of samples with the best scores are selected as the optimal cylinder head structure optimization results in the sample space, that is, to achieve cylinder head performance optimization based on joint simulation technology.

[0008] The present invention discloses a method for optimizing cylinder head parameters under thermal-mechanical coupling conditions, comprising the following steps:

[0009] Step 1: Parametrically model the cylinder head to obtain a cylinder head parametric model. The cylinder head cooling channel model is obtained through Boolean operations, and the cylinder head parametric model is associated with each identical parameter of the cylinder head cooling channel model. The initial value and upper and lower boundary values ​​of each parameter of the cylinder head parametric model are determined, and the cylinder head parametric model is gradually modified by "combining global parameter changes with modification error reporting features" until the cylinder head model meets the preset stability qualification requirements. The surfaces that need to be assigned different boundary conditions on the cylinder head parametric model and the cylinder head cooling channel model are classified, and the cylinder head parametric model and the cylinder head cooling channel model are saved in the form of surface features. By calling the API function of the UG software, the cylinder head parametric model and the cylinder head cooling channel model can be automatically updated with one click, thereby improving the update efficiency of the cylinder head parametric model and the cylinder head cooling channel model.

[0010] The specific implementation method of step one is:

[0011] S11: UG is selected as the modeling platform for parametric modeling of the cylinder head. The external features of the cylinder head are established by stretching or rotating the modeling method, and the features include the top plate, the bottom plate, and the side wall. The feature lines on the wall surfaces of the cylinder head intake and exhaust ducts are drawn by the modeling method of projection curves, and the surface features of the intake and exhaust ducts are connected by the modeling method of fitting surfaces to generate the surface features of the intake and exhaust ducts. The surface features constituting the intake and exhaust ducts are stitched to form entities, and the external features of the cylinder head are subtracted from the intake and exhaust duct entities by Boolean operations to obtain a cylinder head model that completes the airway modeling. The assembly features of the cylinder head are established by stretching, rotating, punching or rounding the modeling methods of the cylinder head that completes the airway modeling, and the features include fastening threaded holes, intake and exhaust pipe assembly holes, inlet and outlet assembly holes, injector assembly holes, and locating pin holes. The water inlet and outlet of the flow channel are drawn on the cylinder head with completed airway modeling by using the stretching modeling method. Starting from the water inlet, the flow channel geometry of the cylinder head is drawn by stretching, rotating, and stitching the surface at the position where the wall thickness on the cylinder head model is greater than the minimum wall thickness requirement of the process, until the flow channel geometry connects the water inlet and the water outlet, and the flow channel geometry is arranged at the position where the wall thickness is greater than the minimum wall thickness requirement of the process. When setting the size of the flow channel geometry, the minimum wall thickness requirement of the processing technology must be strictly met. Use Boolean operations to sum all the flow channel geometries to obtain the flow channel entity of the cylinder head model, and then use Boolean operations to subtract the cylinder head model with completed airway modeling and the flow channel entity of the cylinder head model to obtain the cylinder head model with completed airway and flow channel modeling. After the external features, airways, assembly features and runners of the cylinder head are modeled, weight-reducing geometries are established by stretching, rotating and stitching surfaces at locations on the top plate, bottom plate and side walls of the cylinder head that are not involved in assembly and sealing, and the size of the weight-reducing geometries is associated with the size of the runner geometries to always ensure that the minimum wall thickness on the cylinder head is greater than the minimum wall thickness requirement of the process. Boolean operations are used to subtract the cylinder head with completed assembly feature modeling from all weight-reducing geometries to obtain a cylinder head model that has completed parametric modeling.

[0012] S12: Obtain the cooling channel model of the cylinder head through Boolean operation. Delete the weight reduction features on the cylinder head parameterized model and save the model as copy 1; delete the weight reduction features and channel features on the cylinder head parameterized model and save the model as copy 2. Subtract the copy 1 model from the copy 2 model through Boolean operation to obtain the cooling channel model of the cylinder head. In the expression of the cylinder head cooling channel model, the parameters with the same meaning in copy 1 and copy 2 are associated, and the parameters include parameters for controlling external features and parameters for controlling air channel features, so that the parameters with the same meaning in the two sets of expressions always remain equal during the model update process. After the cylinder head cooling channel model with the same parameters associated is updated, the external features and air channel features of copy 1 and copy 2 will be updated synchronously when the parameters are updated, ensuring that the final entity obtained each time the cylinder head cooling channel model is updated is only the flow channel part of the cylinder head.

[0013] S13: Setting parameter initial values ​​and parameter boundary values ​​for structural parameters on the cylinder head parametric model and the cylinder head cooling channel model. One of the parameter boundary values ​​of the cylinder head parametric model is set to the limit parameter when the wall thickness at each position of the cylinder head is the minimum wall thickness requirement of the process, and the other is set to other limit dimensions that meet the cylinder head design requirements, the cylinder head design requirements include that the hydraulic diameter at each position of the flow channel shall not be less than the limit dimension that causes flow obstruction, the narrowest part of the cylinder head surface shall not be less than one-third of the minimum wall thickness requirement of the process, and there shall be no interference between the cylinder head flow channel, air channel, assembly feature, weight reduction feature and external wall surface. Some cylinder head dimensions are the reference dimensions set when the cylinder head parametric model is modeled. The reference dimension parameter initial value is set to the initial value used when the cylinder head parametric model is modeled, and then its boundary value is equal to the reference value. These dimensions do not change when the cylinder head parametric model is updated. After determining the upper and lower boundary values ​​of parameter changes for parameters other than the reference dimensions, the initial values ​​of the parameters other than the reference dimensions shall be set to the median of the upper and lower boundary values ​​to reduce the probability of errors when updating the cylinder head parametric model.

[0014] S14: The cylinder head parametric model is gradually modified by the method of "combining global parameter changes with error feature modification". When the cylinder head parametric model selects parameter values ​​within the parameter variation range obtained in S13 and substitutes them into the expression to update the model, and the model update exceeds the preset number of times and still does not report an error, it is determined that the stability of the cylinder head parametric model meets the conditions required for optimization. The function of this step S14 is to repeatedly test whether the cylinder head parametric model reports an error under different parameter values, and modify the error feature to gradually improve the cylinder head parametric model. Name all parameters except the reference size in the cylinder head parametric model expression, configure the data interface between Excel and UG, and import the parameter names of the cylinder head except the reference size and their corresponding parameter variation range into an Excel table, insert a random number formula to randomly select a parameter value within the variation range for all parameters except the reference size, and then select all random parameter values ​​generated by the random number formula together with the names of all parameters except the reference size as the data source of the cylinder head parametric model, and use the Excel table to drive UG to update the model many times to test the parameter stability of the cylinder head parametric model under random parameter values. The parameter stability of the cylinder head parametric model is considered qualified when no error occurs when the cylinder head parametric model is updated for a preset number of consecutive times using random parameter values; if an error occurs, the error feature prompted in the UG software is modified or the dimensional variation range corresponding to the feature is modified until the cylinder head parametric model is updated for a preset number of consecutive times using random parameter values ​​without any error.

[0015] S15: Classify the surfaces on the cylinder head parameterized model and the cylinder head cooling channel model that need to be assigned different boundary conditions, and save the cylinder head parameterized model and the cylinder head cooling channel model in the form of surface features. When performing automatic calculation of the cylinder head temperature field distribution, boundary conditions can only be automatically assigned to surface features. Extracting the surfaces of the cylinder head parameterized model and the cylinder head cooling channel model as multiple surface features based on the type of boundary condition area can achieve the effect of automatically identifying the boundary condition area in the solver. Based on the cylinder head heat transfer analysis method, the surfaces on the cylinder head parameterized model and the cylinder head cooling channel model are classified, and the surface categories include water inlet, water outlet, channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake channel wall, exhaust channel wall and fire surface. Through the modeling method of extracting geometric features, these surfaces are extracted into surface features according to categories on the cylinder head parametric model and the cylinder head cooling channel model, and the original solid models in the cylinder head parametric model and the cylinder head cooling channel model are hidden. After the cylinder head parametric model and the cylinder head cooling channel model in the form of surface features are obtained, they are saved separately, and all surface features are set to be associated with the hidden cylinder head and cylinder head cooling channel entities.

[0016] S16: Automatically update the cylinder head model by calling the API function of UG. Call the API function of UG to read the cylinder head parameterized model path and the cylinder head cooling channel model path, read the cylinder head parameterized model expression path, automatically update the cylinder head parameterized model and the cylinder head cooling channel model using the expression parameter value, and save the cylinder head parameterized model and the cylinder head cooling channel model corresponding to the new parameter value, so as to realize the one-key automatic update of the cylinder head parameterized model and the cylinder head cooling channel model.

[0017] Step 2: Using the minimum wall thickness requirement as the initial mesh size, draw a combined mesh model of the cylinder head body for flow field and temperature field calculations. Set up a simulation based on the cylinder head heat transfer analysis method, perform simulation analysis of the steady-state flow field and temperature field inside the cylinder head, and obtain the temperature distribution at each position on the cylinder head. Using the minimum wall thickness requirement as the initial mesh size, divide the 3D mesh model of the cylinder head used to calculate the load-bearing capacity under thermal-mechanical coupling conditions. Assemble the 3D mesh model of the cylinder head and various components related to the service status of the cylinder head, draw structured meshes for each component related to the service status of the cylinder head, and select mesh surfaces on the 3D mesh model of the cylinder head and the 3D mesh models of each component related to the service status of the cylinder head as the main surface and slave surface of the boundary conditions to be applied during the stiffness analysis of the cylinder head, and establish a mesh model of the cylinder head assembly. The temperature field distribution is interpolated into the stress field grid to realize the mapping of the cylinder head temperature distribution data from the cylinder head combined grid model used for flow field and temperature field calculation to the cylinder head 3D grid model used for calculating the load-bearing capacity under thermal-mechanical coupling conditions. The grid independence analysis of the cylinder head performance calculation under thermal-mechanical coupling conditions is performed, and a grid size with a short calculation time and a deviation of the stress and displacement calculation results from the calculation results under other grid sizes less than a preset threshold is selected as the finite element grid size used for optimization. The short calculation time refers to a calculation time shorter than the preset threshold.

[0018] The specific implementation method of step 2 is:

[0019] S21: Draw a combined mesh model of the cylinder head body for flow field and temperature field calculation. The mesh is drawn with the minimum wall thickness requirement size as the initial mesh size to ensure the mesh quality at the minimum position of the cylinder head wall. The cylinder head parameterized model and the cylinder head cooling channel model are imported into ICEM. The mesh size is set to the minimum wall thickness requirement size, and the surface mesh is divided using the Patch Independent meshing method to avoid the mesh drawing failure caused by geometric shape distortion at some positions. The geometric shape distortion includes the presence of broken surfaces on the cylinder head parameterized model and the cylinder head cooling channel model, narrow surfaces with a width less than the minimum wall thickness requirement of the process, or an angle between two surfaces less than 15°. Merging the mesh models of the cylinder head and the cylinder head cooling channel before calculating can achieve the simultaneous setting of the boundary conditions of the cylinder head and the cylinder head cooling channel, solving the problem that the heat transfer solver can only set the boundary conditions for one calculation target. The surface mesh models of the cylinder head and the cylinder head cooling channel are imported into ICEM successively, and the two meshes are merged to obtain the cylinder head combined surface mesh model. The quality of the surface mesh drawn automatically by ICEM is not high. If the volume mesh is drawn directly in ICEM and applied to the calculation, the calculation cannot converge. The problem can be solved by importing the merged cylinder head surface mesh model into fluent meshing to repair the mesh problem and perform volume mesh division, and the mesh quality of the volume mesh model is guaranteed to be qualified. In ICEM, the mesh areas in the merged cylinder head surface mesh model are named according to the water inlet, water outlet, flow channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake duct wall, exhaust duct wall and firepower surface. The merged cylinder head surface mesh model is imported into fluent meshing to correct the three problems of free edge, self-intersection and repeated mesh, and the mesh distortion is reduced to below the preset distortion. The volume mesh model is drawn based on the merged cylinder head surface mesh model, and the low-quality mesh is repaired based on the mesh node movement algorithm, and the inverse orthogonal quality is reduced to below the preset inverse orthogonal quality. Output the cylinder head combined mesh model for flow field and temperature field calculation.

[0020] S22: Set up simulation based on the cylinder head heat transfer analysis method, perform simulation analysis of the steady-state flow field and temperature field inside the cylinder head, and obtain the temperature distribution at each position on the cylinder head. Import the body mesh model of the cylinder head into fluent, set the scale of the simulation analysis, the calculation method used for the flow field calculation, and the material properties of the cylinder head and the coolant in the flow channel. Set the surface type of each surface on the cylinder head body mesh model, the surfaces include water inlet, water outlet, flow channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake channel wall, exhaust channel wall and fire surface, and the surface types include inlet surface, outlet surface, wall surface and interface. Set the surface type of each fluid-solid coupling surface on the cylinder head and cylinder head cooling channel mesh model to interface, and set the two fluid-solid coupling surfaces to coupling relationship, so as to solve the problem of no common nodes on the mesh of the cylinder head and cylinder head cooling channel mesh model. Set the convective heat transfer coefficient and wall initial temperature of the various surfaces. The monitoring and shutdown conditions are set for the calculation process and the simulation is initialized. The simulation calculation is submitted to obtain the temperature field simulation results of the cylinder head.

[0021] S23: Draw a 3D mesh model of the cylinder head for calculating the load-bearing capacity under thermal-mechanical coupling conditions. Use the minimum wall thickness requirement of the process as the initial mesh size for mesh drawing, import the cylinder head parametric model into Hypermesh, set the mesh size to the minimum wall thickness requirement of the process, and use the surface deviation meshing method to divide it into 2D meshes. Use the QI optimization mesh repair algorithm and the size corrected mesh repair algorithm to repair meshes with unqualified mesh quality, and use the place node method to modify the meshes that are difficult to adjust with the mesh repair algorithm to qualified mesh quality, and obtain a high-quality 2D mesh model of the cylinder head. Set the mesh size to the minimum wall thickness requirement of the process, use the tetramesh meshing method to draw a 3D mesh, and obtain a 3D mesh model of the cylinder head for calculating the load-bearing capacity under thermal-mechanical coupling conditions.

[0022] S24: Establish a mesh model of the cylinder head assembly. Import the 3D mesh model of the cylinder head used to calculate the load-bearing capacity under the condition of thermal-mechanical coupling into Hypermesh, import various components related to the service status of the cylinder head, and assemble the various components related to the service status of the cylinder head with the 3D mesh model of the cylinder head used to calculate the load-bearing capacity under the condition of thermal-mechanical coupling according to the engine assembly requirements, wherein the components include an engine body, a bushing, a gasket, and fastening bolts. Perform 2D structured mesh division on the various components related to the service status of the cylinder head using the automesh method, and perform 3D structured mesh division on the components related to the service status of the cylinder head using the solid map method, to obtain 3D mesh models of the various components related to the service status of the cylinder head. Based on the cylinder head stiffness analysis method, mesh surfaces are selected from the cylinder head 3D mesh model used to calculate the bearing capacity of the cylinder head under thermal-mechanical coupling conditions and the 3D mesh models of various components related to the service status of the cylinder head as the main surface and the secondary surface of the boundary conditions to be applied during the cylinder head stiffness analysis. The main surface and the secondary surface include the main and secondary surfaces of the contact relationship between the bolt and the cylinder head, the main and secondary surfaces of the connection relationship between the bolt and the body assembly hole, the main and secondary surfaces of the contact relationship between the cylinder head and the body, and the action surface of the explosion pressure of the combustion chamber. The material properties of the cylinder head 3D model and the 3D mesh models of various components related to the service status of the cylinder head are set and saved to obtain the mesh model of the cylinder head assembly.

[0023] S25: Interpolate the temperature field distribution into the stress field grid, and then format the obtained data file and import it into Abaqus to realize the mapping of the cylinder head temperature distribution data from the cylinder head combined grid model used for flow field and temperature field calculation to the cylinder head 3D grid model used for calculating the load-bearing capacity under thermal-mechanical coupling conditions. Extract the cylinder head grid model from the grid model of the cylinder head assembly to ensure that the grid number on the cylinder head grid model is still consistent with the grid number in the cylinder head assembly after the temperature field data is mapped to the cylinder head grid model. In fluent, based on the grid data automatic mapping algorithm, the cylinder head temperature field simulation results obtained in S22 are imported into the extracted cylinder head grid model to obtain the cylinder head temperature distribution data corresponding to the grid node layout of the cylinder head grid model. By modifying the temperature distribution data so that it can be recognized by the Abaqus solver, the modified temperature distribution data is imported into Abaqus to generate the temperature field calculation results that can be imported when Abaqus sets the calculation task.

[0024] S26: Set up simulation based on the cylinder head stiffness analysis method, perform load-bearing performance analysis under thermal-mechanical coupling conditions, and obtain the thermal-mechanical coupling stress and thermal-mechanical coupling deformation distribution at each position on the cylinder head. Import the mesh model of the cylinder head assembly into Abaqus, set the explosion pressure and bolt preload force that the cylinder head is subjected to during operation, select the contact pair between the bolt and the cylinder head and the contact pair between the cylinder head and the engine body to set the contact relationship and use the small slip and small deformation calculation method, select the connection pair between the bolt and the engine body assembly hole to set the coupling relationship and use the small slip and small deformation calculation method, and set the bottom of the engine body as a fixed support constraint. Select the simulation analysis type as static analysis, associate the Abaqus temperature field calculation results generated by S25 with the predefined temperature field, set the initial iteration step and maximum iteration step of the simulation according to the computing power conditions, submit the simulation calculation and obtain the stress distribution and displacement distribution results of the cylinder head in the service state.

[0025] S27: Perform mesh independence analysis for cylinder head performance calculation under thermal-mechanical coupling conditions. Starting from the initial value of the mesh size required for the minimum wall thickness of the process, expand or reduce the mesh size used when drawing the cylinder head combined mesh model and the cylinder head 3D mesh model, respectively calculate the temperature field simulation results of the cylinder head and the load-bearing capacity simulation results under thermal-mechanical coupling conditions, compare the effects of different mesh sizes on the calculation time and the maximum temperature, thermal-mechanical coupling stress, and thermal-mechanical coupling deformation calculation results, select a mesh size with a short calculation time and a calculation result with a deviation less than a preset threshold value under other mesh sizes as the finite element mesh size used for optimization, and complete the mesh independence analysis, wherein the short calculation time refers to a calculation time shorter than the preset threshold value.

[0026] Step 3: Adjust the structural parameters of the cylinder head model to generate a cylinder head model with parameters different from the initial values. Record the script for drawing the cylinder head body combined mesh model for flow field and temperature field calculation in ICEM and fluent meshing. Record the script for calculating the heat transfer performance of the cylinder head in fluent, and extract the index data that can characterize the heat transfer performance of the cylinder head and the quality of the cylinder head. Record the script for drawing the cylinder head 3D mesh model for calculating the load-bearing capacity under thermal-mechanical coupling conditions and the script for updating the cylinder head mesh model in the cylinder head assembly model in Hypermesh. Record the script for mapping the cylinder head temperature distribution data in Hypermesh and fluent, and use batch processing commands to realize the automatic modification of the temperature distribution data so that it can be recognized by the Abaqus solver to generate temperature field calculation results. Record the script for calculating the stiffness and strength of the cylinder head in Abaqus and extract the index data that can characterize the load-bearing performance of the cylinder head under thermal-mechanical coupling conditions.

[0027] The specific implementation method of step three is:

[0028] S31: Adjust the structural parameters of the cylinder head model, automatically update the cylinder head model and the cylinder head cooling channel model, and generate a cylinder head model with parameters different from the initial values. Modify all parameters except the reference size in the expression of the cylinder head parameterized model, call the UG API function, read the cylinder head parameterized model expression, and automatically update the cylinder head model and the cylinder head cooling channel model with one click.

[0029] S32: Record the script for drawing the cylinder head combined mesh model for flow field and temperature field calculation. Based on the mesh size determined after mesh independence analysis, start script recording in ICEM, divide the surface mesh models of the cylinder head and cylinder head cooling channel using the PatchIndependent meshing method, save the surface mesh models of the cylinder head and cylinder head cooling channel, and obtain the script for the surface meshing phase. Start script recording again in ICEM, import the surface mesh models of the cylinder head and cylinder head cooling channel, merge the two meshes, and name the mesh areas in the cylinder head surface mesh model according to the water inlet, water outlet, channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake duct wall, exhaust duct wall, and firepower surface. Obtain the script for the cylinder head combined surface mesh model and mesh merging phase. Start script recording in fluent meshing, import the merged cylinder head surface mesh model, correct the three problems of free edge, self-intersection and repeated mesh, and reduce the mesh distortion to below the preset distortion. Draw the volume mesh model of the cylinder head, and repair the low-quality mesh based on the mesh node movement algorithm to reduce the inverse orthogonal quality to below the preset inverse orthogonal quality. Output the cylinder head combined mesh model for flow field and temperature field calculation and obtain the script for the volume mesh division link.

[0030] S33: Record the script for calculating the heat transfer performance of the cylinder head. Start the script recording in Fluent, import the volume mesh model of the cylinder head, set the scale of the simulation analysis, the calculation method used for the flow field calculation, and the material properties of the cylinder head and the coolant in the flow channel. Set the surface type of each surface on the cylinder head volume mesh model, the surface includes the water inlet, water outlet, flow channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake channel wall, exhaust channel wall and fire surface, and the surface type includes the inlet surface, outlet surface, wall surface and interface. Set the surface type of each fluid-solid coupling surface on the cylinder head and cylinder head cooling channel mesh model to the interface, and set the two fluid-solid coupling surfaces to the coupling relationship. Set the convective heat transfer coefficient and the initial wall temperature of the various surfaces. Set the monitoring and shutdown conditions for the calculation process and initialize the simulation, and submit the simulation calculation to obtain the temperature field simulation results of the cylinder head. Extract the index data that can characterize the heat transfer performance of the cylinder head and the quality of the cylinder head, including the surface average convection heat transfer coefficient, surface average pressure, surface average y+ value, surface minimum y+ value, surface maximum y+ value, body average water cavity temperature, body average cylinder head temperature, body average velocity, total mass of the cylinder head, maximum temperature of the cylinder head, maximum temperature in the water cavity, maximum velocity in the water cavity, minimum temperature in the water cavity and water cavity size. Output the temperature field simulation results of the cylinder head and obtain the script for the calculation of the heat transfer performance of the cylinder head.

[0031] S34: Record the script for drawing the 3D mesh model of the cylinder head used to calculate the load-bearing capacity under the condition of thermal-mechanical coupling. Based on the mesh size determined after the mesh independence analysis, start the script recording in Hypermesh, edit the mesh quality evaluation criteria, cancel the algorithm's detection of the maximum mesh size and the minimum mesh size, and improve the repair rate of low-quality meshes. Use the surface deviation meshing method to divide the 2D mesh, repair the mesh with unqualified mesh quality based on the QI optimization mesh repair algorithm and the size corrected mesh repair algorithm, and use the placenode method to modify the mesh that is difficult to adjust by the mesh repair algorithm to a qualified mesh quality, and obtain a high-quality 2D mesh model of the cylinder head. Use the tetramesh meshing method to draw the 3D mesh and obtain the 3D mesh model of the cylinder head. Complete the drawing of the 3D mesh model of the cylinder head used to calculate the load-bearing capacity under the condition of thermal-mechanical coupling and obtain the script for drawing the 3D mesh model of the cylinder head.

[0032] S35: Record the script for updating the cylinder head mesh model in the cylinder head assembly model. Start script recording in Hypermesh, import the cylinder head assembly mesh model, replace the cylinder head mesh model in the cylinder head assembly mesh model with the cylinder head 3D mesh model with updated structure shape based on the mesh model replacement algorithm, export the new cylinder head assembly mesh model and obtain the script for updating the cylinder head mesh model.

[0033] S36: Record the script for mapping the cylinder head temperature distribution data from the cylinder head combined grid model used for flow field and temperature field calculation to the cylinder head 3D grid model used for calculating the load-bearing capacity under thermal-mechanical coupling conditions. Start the script recording in Hypermesh, extract the cylinder head grid model from the grid model of the cylinder head assembly, and ensure that the grid number on the cylinder head grid model is still consistent with the grid model of the cylinder head assembly after the temperature field data is mapped to the cylinder head grid model. Start the script recording in fluent, and import the cylinder head temperature field simulation results obtained in S33 into the extracted cylinder head grid model based on the grid data automatic mapping algorithm to obtain the cylinder head temperature distribution data corresponding to the grid node layout of the cylinder head grid model. Use the batch command to realize the automatic modification of the temperature distribution data so that the temperature distribution data can be recognized by the Abaqus solver, import the modified temperature distribution data into Abaqus, and generate a script for the mapping of the temperature field calculation results and cylinder head temperature distribution data that can be imported when setting the calculation task in Abaqus.

[0034] S37: Record the script for calculating the rigidity of the cylinder head. Start the script recording in Abaqus, import the mesh model of the cylinder head assembly into Abaqus, set the explosion pressure and bolt preload that the cylinder head is subjected to during operation, select the contact pairs between the bolts and the cylinder head and the contact pairs between the cylinder head and the engine body to set the contact relationship and use the small slip and small deformation calculation method, select the connection pairs between the bolts and the engine body assembly holes to set the coupling relationship and use the small slip and small deformation calculation method, and set the bottom of the engine body as a fixed support constraint. Select the simulation analysis type as static analysis, associate the Abaqus temperature field calculation results generated by S36 with the predefined temperature field, set the initial iteration step and maximum iteration step of the simulation according to the computing power conditions, submit the simulation calculation and obtain the stress distribution and displacement distribution results of the cylinder head under the thermal-mechanical coupling conditions.

[0035] Step 4: Based on the joint simulation technology, the cylinder head optimization model under the condition of thermal-mechanical coupling is built. The Latin hypercube algorithm is used to plan the sample space for cylinder head optimization under the condition of thermal-mechanical coupling. The script recorded during the cylinder head performance calculation process is called through the batch command to automatically run the cylinder head parameterization model update, cylinder head mesh drawing, cylinder head component update in the cylinder head assembly model, cylinder head heat transfer simulation analysis, cylinder head temperature distribution data mapping between different mesh models, cylinder head stiffness simulation analysis and cylinder head performance index data extraction under the condition of thermal-mechanical coupling in the process of cylinder head optimization design under the condition of thermal-mechanical coupling, and obtain the sample data set that characterizes the corresponding relationship between the cylinder head structure and various performances. A comprehensive evaluation function is established to comprehensively weigh multiple cylinder head performance indicators to score each sample point, select the best scoring group of samples as the optimization result, and obtain the optimal cylinder head structure in the sample space, that is, to achieve cylinder head optimization under the condition of thermal-mechanical coupling based on the joint simulation technology.

[0036] The specific implementation method of step 4 is:

[0037] S41: Build a cylinder head optimization model under thermal-mechanical coupling conditions in Isight, set the total number of samples according to the computing power conditions, and use the Latin hypercube algorithm to plan the sample space for cylinder head optimization under thermal-mechanical coupling conditions, so that the sample points are evenly distributed in the high-dimensional Euclidean space to ensure the quality of sample data. Call the script recorded during the cylinder head performance calculation process through batch commands, and use different modules to execute the cylinder head parameterization model update, cylinder head mesh drawing, cylinder head component update in the cylinder head assembly model, cylinder head heat transfer simulation analysis, cylinder head temperature distribution data mapping between different mesh models, cylinder head stiffness simulation analysis, and cylinder head performance index data extraction commands under thermal-mechanical coupling conditions. After the settings are completed, the cylinder head performance optimization model is automatically run to obtain a sample data set that characterizes the corresponding relationship between the cylinder head structure and various performances.

[0038] S42: Establish a comprehensive evaluation function, comprehensively consider the floating degree and importance of multiple cylinder head performance indicators, and score each sample point. As a preferred embodiment, the comprehensive evaluation function is shown in the following formula:

[0039]

[0040] Among them, g j is the comprehensive score of the jth evaluated sample point, λ i is the weight of the i-th evaluated indicator, y ij is the actual value of the i-th evaluated indicator of the j-th evaluated sample point, Z i is the ideal value of the i-th evaluated indicator of the evaluated sample point, σ iis the standard deviation of the i-th evaluated indicator data, and n is the total number of indicators evaluated at the sample point.

[0041] The weight of the i-th evaluated indicator can be calculated using the following formula:

[0042]

[0043] C i is the significance coefficient of the ith indicator, C i The larger the value is, the greater the impact of the i-th indicator on the comprehensive evaluation results, and the higher the weight is. i The standard deviation σ i and the correlation coefficient R i The product of is:

[0044] C i =σ i R i (3)

[0045] Standard deviation i Calculated using the following formula:

[0046]

[0047] In the formula, m is the total number of sample points used to calculate the standard deviation, x ij is the dimensionless data of the i-th performance index of the j-th sample point, is the dimensionless data average of the i-th performance indicator. The dimensionless data of the i-th performance indicator at the j-th sample point can be dimensionlessized by the following formula to obtain the data average:

[0048]

[0049] Correlation coefficient R i It can be calculated using the following formula:

[0050]

[0051] r ik is the linear correlation coefficient between the i-th indicator and the k-th indicator, which can be calculated using the following formula:

[0052]

[0053] After calculating all the above variables according to the sample data set, each sample point is scored through the comprehensive evaluation function, and the group of samples with the best scores are selected as the optimization results to obtain the optimal cylinder head structure in the sample space, that is, the cylinder head optimization under the conditions of thermal-mechanical coupling is realized based on the joint simulation technology.

[0054] The method further includes step 5, performing process adaptability design according to the optimal cylinder head structure obtained in step 4, and obtaining a cylinder head design scheme that meets production constraints. The cylinder head manufactured by the cylinder head design scheme can improve heat transfer and load-bearing performance, reduce the maximum temperature of the fire surface, reduce thermal-coupled machine deformation, reduce thermal-coupled machine stress, and improve service life compared to the cylinder head before optimization. The weight of the optimized cylinder head is reduced compared to the weight of the cylinder head before optimization, and the high power density of the engine can be improved.

[0055] Beneficial effects:

[0056] 1. The present invention discloses a method for optimizing cylinder head parameters under thermal-mechanical coupling conditions. A parametric modeling method is used to build a parametric model of the cylinder head, and then a cooling channel model of the cylinder head is obtained by Boolean operations, thereby directly controlling the structural shape of the cylinder head and the cylinder head cooling channel through the expression of the cylinder head parametric model, thereby improving the efficiency of modifying and updating the cylinder head model and the cylinder head cooling channel model.

[0057] 2. The present invention discloses a cylinder head parameter optimization method under thermal-mechanical coupling conditions, which determines the initial value and upper and lower boundary values ​​of each parameter of the cylinder head parameterized model, and gradually modifies the cylinder head parameterized model by "combining global parameter changes with modification error reporting features", thereby ensuring that the cylinder head model has sufficient stability and achieving the effect that any value of the cylinder head parameterized model expression within the parameter variation range can stably update the cylinder head parameterized model and the cylinder head cooling channel model.

[0058] 3. The present invention discloses a cylinder head parameter optimization method under thermal-mechanical coupling conditions, which realizes one-key automatic update of the cylinder head parameterized model and the cylinder head cooling channel model by calling the API function of the UG software, omitting the steps of opening the UG graphical window and then modifying the cylinder head parameterized model and the cylinder head cooling channel model, thereby improving the update efficiency of the cylinder head parameterized model and the cylinder head cooling channel model and meeting the necessary conditions for the automation of the cylinder head heat transfer calculation process.

[0059] 4. The present invention discloses a method for optimizing cylinder head parameters under thermal-mechanical coupling conditions, which performs surface mesh division on the cylinder head and the cylinder head cooling channel respectively, merges the cylinder head and the cylinder head cooling channel surface mesh models and draws the cylinder head body mesh model, and then associates the coupling surfaces of the cylinder head and the cylinder head cooling channel with each other in the cylinder head body mesh model, thereby achieving successful calculation of the coupling surfaces of the cylinder head and the cylinder head cooling channel under the premise that the meshes do not share common nodes, thereby improving the success rate of cylinder head parameter optimization under thermal-mechanical coupling conditions, and thereby improving the optimization efficiency.

[0060] 5. The present invention discloses a method for optimizing cylinder head parameters under thermal-mechanical coupling conditions. Based on a mesh model replacement algorithm, the cylinder head components in the mesh model of the cylinder head assembly are replaced with a 3D mesh model of the cylinder head with an updated structural shape, thereby realizing rapid updating of the cylinder head assembly model. This can solve the problem that the cylinder head assembly is difficult to automatically update during cylinder head simulation analysis, and significantly improve optimization efficiency.

[0061] 6. The present invention discloses a cylinder head parameter optimization method under thermal-mechanical coupling conditions. Based on a grid data automatic mapping algorithm, the cylinder head temperature distribution data is extracted from the cylinder head body grid combination model and interpolated into the cylinder head 3D grid model. While ensuring that the most suitable grid model is used in different simulation calculation links, the cylinder head temperature distribution calculation results are synchronized between different grid models. This can solve the key problem of multi-field coupled data transmission difficulty in the cylinder head thermal-mechanical coupling and improve data transmission efficiency.

[0062] 7. The present invention discloses a method for optimizing cylinder head parameters under heat-mechanical coupling conditions. By recording the scripts of mesh model division and mesh merging between the cylinder head and the cylinder head cooling channel surface in ICEM, recording the script of mesh division of the cylinder head body in fluentmeshing, and recording the scripts of heat transfer performance calculation of the cylinder head and index data extraction of the heat transfer performance of the cylinder head in fluent, the accurate reproduction and automatic operation of finite element mesh division and simulation analysis setting in the process of heat transfer performance calculation of the cylinder head can be achieved, thereby improving the efficiency of optimizing various heat transfer performances of the cylinder head.

[0063] 6. The present invention discloses a method for optimizing cylinder head parameters under thermal-mechanical coupling conditions, recording the script of cylinder head mesh drawing and the script of cylinder head component automatic updating in cylinder head assembly model in Hypermesh. Recording the script of cylinder head stiffness calculation in Abaqus and extracting performance index data that can characterize the stiffness of the cylinder head, achieving accurate reproduction and automatic operation of finite element mesh division and simulation analysis setting in the process of cylinder head load-bearing performance calculation under thermal-mechanical coupling conditions, and improving the efficiency of cylinder head load-bearing performance optimization under thermal-mechanical coupling conditions.

[0064] 8. The present invention discloses a method for optimizing cylinder head parameters under thermal-mechanical coupling conditions, which completes preliminary calculations of various cylinder head performances under the grid size required for the minimum wall thickness of the process and performs grid independence analysis of the calculations of various cylinder head performances under thermal-mechanical coupling conditions. A grid size with a short calculation time and a small deviation between the calculation results and the calculation results under other grid sizes is selected as the finite element grid size used for optimization, thereby ensuring the accuracy of the cylinder head optimization results and significantly saving the time cost of cylinder head optimization.

[0065] 9. The present invention discloses a cylinder head parameter optimization method under thermal-mechanical coupling conditions. Based on the joint simulation technology, the cylinder head performance optimization model under thermal-mechanical coupling conditions is built. The Latin hypercube algorithm is used to plan the sample space during cylinder head optimization. The total number of samples can be set according to the computing power conditions for experimental design. The sample points in the sample data set used for cylinder head optimization are sufficiently uniform, and the sample number and computing time cost are controllable.

[0066] 10. The present invention discloses a method for optimizing cylinder head parameters under thermal-mechanical coupling conditions. The cylinder head optimization model under thermal-mechanical coupling conditions is built based on the joint simulation technology. The script recorded during the calculation of various performances of the cylinder head is called through batch processing commands. The cylinder head parameterization model update, cylinder head mesh drawing, cylinder head component update in the cylinder head assembly model, cylinder head heat transfer simulation analysis, cylinder head temperature distribution data mapping between different mesh models, cylinder head stiffness simulation analysis, and cylinder head performance index data extraction operations under thermal-mechanical coupling conditions are automatically run in the process of cylinder head optimization test design under thermal-mechanical coupling conditions. The sample points in the sample space are automatically calculated to correspond to the various performances of the cylinder head, thereby improving the efficiency of cylinder head optimization. During the calculation process, the model will automatically filter out sample points that do not converge and whose mesh quality does not meet the standards to ensure the quality of the sample data set.

[0067] 11. The present invention discloses a method for optimizing cylinder head parameters under thermal-mechanical coupling conditions, establishes a comprehensive evaluation function, considers multiple cylinder head performance indicators to score the comprehensive performance of each sample point, realizes a comprehensive evaluation of the cylinder head performance, ensures that the cylinder head optimization result has the greatest improvement in comprehensive performance, and that each sub-indicator can be balanced. The cylinder head processed using the optimization result scheme selected by the comprehensive evaluation function has a longer service life, better heat transfer performance and load-bearing performance, and can be lightweight. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 It is a flow chart of a cylinder head parameter optimization method under thermal-mechanical coupling conditions of the present invention;

[0069] Figure 2 The surface feature cylinder head parameterized model and the cylinder head cooling channel model are respectively established in combination with the optimization method of the present invention, wherein: Figure 2 (a) is the parametric model of the cylinder head in the form of surface features. Figure 2 (b) The cylinder head cooling channel model in the form of surface features;

[0070] Figure 3The cylinder head combined grid model for flow field and temperature field calculation and the cylinder head 3D grid model for calculating the load-bearing capacity under thermal-mechanical coupling conditions are completed, where: Figure 3 (a) is the cylinder head combined grid model used for flow field and temperature field calculation. Figure 3 (b) 3D mesh model of the cylinder head used to calculate the load-bearing capacity under thermal-mechanical coupling conditions;

[0071] Figure 4 It is the cylinder head assembly mesh model formed after all parts are assembled and meshed;

[0072] Figure 5 This is a cloud diagram of various simulation results of the cylinder head obtained by using a 5mm grid size after the grid independence analysis in Example 1 obtains the optimal grid size of 5mm, where: Figure 5 (a) is the cylinder head temperature field distribution result, Figure 5 (b) is the thermal-mechanical coupling stress distribution result of the cylinder head. Figure 5 (c) is the thermal-mechanical coupling deformation distribution result of the cylinder head;

[0073] Figure 6 This is a workflow diagram of the cylinder head optimization model under thermal-mechanical coupling conditions built in Isight.

[0074] Figure 7 It is the optimized cylinder head model structure. DETAILED DESCRIPTION

[0075] The invention is further described below with reference to the accompanying drawings and embodiments.

[0076] Embodiment 1:

[0077] like Figure 1 As shown, the present embodiment discloses a method for optimizing cylinder head parameters under thermal-mechanical coupling conditions, and the specific implementation steps are as follows:

[0078] Step 1: Parametrically model the cylinder head to obtain a cylinder head parametric model. The cylinder head cooling channel model is obtained through Boolean operations, and the cylinder head parametric model is associated with each identical parameter of the cylinder head cooling channel model. The initial value and upper and lower boundary values ​​of each parameter of the cylinder head parametric model are determined, and the cylinder head parametric model is gradually modified by "combining global parameter changes with modification error reporting features" until the cylinder head model meets the preset stability qualification requirements. The surfaces that need to be assigned different boundary conditions on the cylinder head parametric model and the cylinder head cooling channel model are classified, and the cylinder head parametric model and the cylinder head cooling channel model are saved in the form of surface features. By calling the API function of the UG software, the cylinder head parametric model and the cylinder head cooling channel model can be automatically updated with one click, thereby improving the update efficiency of the cylinder head parametric model and the cylinder head cooling channel model.

[0079] The specific implementation method of step one includes the following steps:

[0080] Step 1.1: Use the stretching or rotation modeling method in UG to create the top plate, bottom plate and side wall of the cylinder head. Use projection curves to draw the feature lines on the cylinder head intake and exhaust duct walls, use fitting surfaces to generate the surface features of the intake and exhaust duct walls, stitch the surface features to form entities, and use Boolean operations to subtract the air duct from the cylinder head top plate, bottom plate and side wall to complete the intake and exhaust duct modeling. Use stretching, rotation, punching or rounding modeling methods to create the 22mm fastening threaded holes, 8.5mm intake and exhaust pipe assembly holes, 42mm injector assembly holes and 20mm locating pin holes of the cylinder head. The water inlet and outlet of the flow channel are drawn on the cylinder head by stretching modeling. Starting from the water inlet, 20 flow channel geometries of the cylinder head are drawn by stretching, rotating, and stitching surfaces at the position where the wall thickness of the cylinder head model is greater than 6mm, until the water inlet and the water outlet are connected and the flow channel is spread throughout the cylinder head. The flow channel geometries are summed by Boolean operation to obtain the flow channel entity of the cylinder head model. The cylinder head model with completed air channel modeling and the flow channel entity of the cylinder head model are subtracted by Boolean operation to obtain the cylinder head model with completed air channel and flow channel modeling; 6 weight reduction geometries are established by stretching, rotating, and stitching surfaces at the top plate, bottom plate, and side wall of the cylinder head where assembly and sealing are not involved, and the size of the weight reduction geometries is associated with the size of the flow channel geometries to always ensure that the minimum wall thickness on the cylinder head is greater than 6mm. The cylinder head with completed assembly feature modeling is subtracted by Boolean operation from all weight reduction geometries to obtain the cylinder head model with completed parametric modeling.

[0081] Step 1.2: Delete the weight reduction features on the cylinder head parameterized model and save the model as copy 1; delete the weight reduction features and flow channel features on the cylinder head parameterized model and save the model as copy 2. Subtract the copy 1 model from the copy 2 model by Boolean operation to obtain the cooling channel model of the cylinder head. In the expression of the cylinder head cooling channel model, the parameters with the same meaning in copy 1 and copy 2 are associated. In this embodiment, the parameters that need to be modified include the parameters that control the cylinder head shape and the parameters that control the air channel shape, a total of 53.

[0082] Step 1.3: Set the initial values ​​of the 96 reference dimension parameters constituting this embodiment as the initial values ​​used in the parametric modeling of the cylinder head, and then set their boundary values ​​equal to the reference values. These dimensions do not change when the model is updated. Among the 100 parameters other than the reference dimensions, this embodiment only optimizes the parameters controlling the flow channel shape. After determining the upper and lower boundary values ​​of the parameter changes for the 31 parameters controlling the flow channel shape, set the initial values ​​of the parameters of the 31 parameters controlling the flow channel shape to the median of the upper boundary value and the lower boundary value.

[0083] Step 1.4: Configure the data interface between Excel software and UG software, import the names of the 31 parameters that control the flow channel shape and their corresponding parameter variation ranges into the Excel table, insert a random number formula to randomly select a parameter value within the variation range for the 31 parameters that control the flow channel shape, and then select all the random parameter values ​​generated by the random number formula together with the names of the 31 parameters that control the flow channel shape as the data source of the cylinder head parametric model. Use the Excel table to drive UG to update the model to test the parameter stability of the cylinder head parametric model under random parameter values. The parameter stability of the cylinder head parametric model is considered qualified when no error occurs when the cylinder head parametric model is updated ten times in a row with random parameter values.

[0084] Step 1.5: Based on the cylinder head heat transfer analysis method, the surface feature areas of the water inlet, water outlet, channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake channel wall, exhaust channel wall and fire surface are selected on the cylinder head parametric model and cylinder head cooling channel model by extracting geometric features. All surface features are set to be associated with the hidden cylinder head and cylinder head cooling channel entities, and the original entity models in the cylinder head parametric model and cylinder head cooling channel model are hidden to obtain the cylinder head parametric model and cylinder head cooling channel model in the form of surface features. The final cylinder head parametric model in the form of surface features is as follows: Figure 2 As shown in a, the cylinder head cooling channel model in the form of surface features is as follows Figure 2 As shown in b.

[0085] Step 1.6: Call the UG API function to achieve one-key automatic update of the cylinder head parameterized model and the cylinder head cooling channel model in this embodiment.

[0086] Step 2: Using the minimum wall thickness requirement as the initial mesh size, draw a combined mesh model of the cylinder head body for flow field and temperature field calculations. Set up a simulation based on the cylinder head heat transfer analysis method, perform simulation analysis of the steady-state flow field and temperature field inside the cylinder head, and obtain the temperature distribution at each position on the cylinder head. Using the minimum wall thickness requirement as the initial mesh size, divide the 3D mesh model of the cylinder head used to calculate the load-bearing capacity under thermal-mechanical coupling conditions. Assemble the 3D mesh model of the cylinder head and various components related to the service status of the cylinder head, draw structured meshes for each component related to the service status of the cylinder head, and select mesh surfaces on the 3D mesh model of the cylinder head and the 3D mesh models of each component related to the service status of the cylinder head as the main surface and slave surface of the boundary conditions to be applied during the stiffness analysis of the cylinder head, and establish a mesh model of the cylinder head assembly. The temperature field distribution is interpolated into the stress field grid to realize the mapping of the cylinder head temperature distribution data from the cylinder head combined grid model used for flow field and temperature field calculation to the cylinder head 3D grid model used for calculating the load-bearing capacity under thermal-mechanical coupling conditions. The grid independence analysis of the cylinder head performance calculation under thermal-mechanical coupling conditions is performed, and a grid size with a short calculation time and a deviation of the stress and displacement calculation results from the calculation results under other grid sizes less than a preset threshold is selected as the finite element grid size used for optimization. The short calculation time refers to a calculation time shorter than the preset threshold.

[0087] The specific implementation method of step 2 includes the following steps:

[0088] Step 2.1: Use 6mm as the initial mesh size for mesh drawing. Import the cylinder head parameterized model and the cylinder head cooling channel model into ICEM. Set the mesh size to the minimum wall thickness requirement of the process, use the PatchIndependent meshing method to divide the surface mesh, and obtain the surface mesh model of the cylinder head and the cylinder head cooling channel. Import the surface mesh models of the cylinder head and the cylinder head cooling channel into ICEM successively, and merge the two meshes to obtain the cylinder head combined surface mesh model. In ICEM, the mesh areas in the merged cylinder head surface mesh model are named according to the water inlet, water outlet, flow channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake duct wall, exhaust duct wall and firepower surface. Import the merged cylinder head surface mesh model into fluent meshing, correct the three problems of free edges, self-intersection and repeated meshes, and reduce the mesh distortion to below 0.8. The volume mesh model of the cylinder head is drawn based on the merged cylinder head surface mesh model, and the low-quality mesh is repaired based on the mesh node movement algorithm to reduce the inverse orthogonal quality to below 0.8. The cylinder head combined mesh model for flow field and temperature field calculation is output, such as Figure 3 As shown in a.

[0089] Step 2.2: Import the body mesh model of the cylinder head into Fluent, set the simulation analysis scale to 6mm, use the SIMPLE method for flow field calculation, use the ke model for turbulence calculation, and set the material properties of the cylinder head and the coolant in the flow channel to cast iron and water, respectively. Set the water inlet, water outlet, flow channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake channel wall, exhaust channel wall and fire surface of the cylinder head body mesh model to the inlet surface, outlet surface, wall surface and interface surface, respectively, according to the needs of simulation analysis. Set the surface type of the fluid-solid coupling surface on the cylinder head and cylinder head cooling channel mesh model to the interface, and set the two fluid-solid coupling surfaces to a coupling relationship. Set the ambient temperature of the fire surface to 812℃, the heat transfer coefficient to 1582W / (m2*K); the ambient temperature of the intake duct wall to 63℃, the heat transfer coefficient to 320W / (m2*K); the ambient temperature of the exhaust duct wall to 704℃, the heat transfer coefficient to 640W / (m2*K); the water inlet temperature to 25℃, and the water outlet temperature to 70℃. Set the shutdown condition to 200 simulation iterations and initialize the simulation, submit the simulation calculation to obtain the temperature field simulation results of the cylinder head.

[0090] Step 2.3: Use 6mm as the initial mesh size for mesh drawing, import the cylinder head parametric model into Hypermesh, set the mesh size to the minimum wall thickness requirement of the process, and use the surface deviation mesh division method to divide it into 2D meshes. Use the QI optimization mesh repair algorithm and the size corrected mesh repair algorithm to repair meshes with unqualified mesh quality, and use the place node method to modify the meshes that are difficult to adjust with the mesh repair algorithm to qualified mesh quality, and obtain a high-quality cylinder head 2D mesh model. Set the mesh size to the minimum wall thickness requirement of the process, use the tetramesh mesh division method to draw a 3D mesh, and obtain the cylinder head 3D mesh model for calculating the load-bearing capacity under thermal-mechanical coupling conditions. Figure 3 As shown in b.

[0091] Step 2.4: Import the cylinder head 3D mesh model into Hypermesh, import the engine block, bushing, gasket and fastening bolts, and assemble the engine block, bushing, gasket and fastening bolts with the cylinder head 3D mesh model. Set the mesh size to 10mm, use the automesh method to perform 2D structured mesh division on the engine block, bushing, gasket and fastening bolts, and use the solid map method to perform 3D structured mesh division on the engine block, bushing, gasket and fastening bolts. Select mesh surfaces on the cylinder head 3D mesh model and the 3D mesh models of the engine block, bushing, gasket and fastening bolts as the main surface and slave surface of the boundary conditions to be applied during the cylinder head stiffness analysis. Set the material properties for the cylinder head 3D model and the 3D mesh models of each component related to the service status of the cylinder head and save them to obtain the mesh model of the cylinder head assembly as shown below. Figure 4 shown.

[0092] Step 2.5: Extract the cylinder head mesh model from the mesh model of the cylinder head assembly and import it into fluent. Based on the mesh data automatic mapping algorithm, import the cylinder head temperature field simulation results under the 6mm mesh size into the extracted cylinder head mesh model to obtain the temperature distribution data of the cylinder head corresponding to the mesh node layout of the cylinder head mesh model. Modify the temperature distribution data so that it can be recognized by the Abaqus solver, import the modified temperature distribution data into Abaqus, and generate the temperature field calculation results that can be imported when setting the calculation task in Abaqus.

[0093] Step 2.6: Import the mesh model of the cylinder head assembly into Abaqus, set the explosion pressure of the fire surface to 25Mpa, the explosion pressure of the intake and exhaust valve seats to 48Mpa and 37Mpa respectively, and the preload of the four bolts to 115000N; select the contact pair between the bolt and the cylinder head and the contact pair between the cylinder head and the engine body to set the contact relationship and use the small slip and small deformation calculation method, with a friction coefficient of 0.15; select the connection pair between the bolt and the engine body assembly hole to set the coupling relationship and use the small slip and small deformation calculation method, with a friction coefficient of 0.15; set the bottom of the engine body as a fixed support constraint. Select the simulation analysis type as static analysis, set the initial iteration step of the simulation to 0.01 and the maximum iteration step to 0.5 according to the computing power conditions, submit the simulation calculation and obtain the stress distribution and displacement distribution results of the cylinder head under the thermal-mechanical coupling conditions.

[0094] Step 2.7: Perform a mesh independence analysis of the cylinder head performance calculation under thermal-mechanical coupling conditions. Starting from the initial value of the mesh size of 6mm, expand or reduce the mesh size used when drawing the cylinder head combined mesh model and the cylinder head 3D mesh model, respectively calculate the temperature field simulation results of the cylinder head and the load-bearing capacity simulation results under thermal-mechanical coupling conditions, and compare the effects of different mesh sizes on the calculation time, maximum temperature, thermal-mechanical coupling stress, and thermal-mechanical coupling deformation calculation results. Select a mesh size with a short calculation time and a calculation result that deviates from the calculation result under other mesh sizes less than a preset threshold as the finite element mesh size used for optimization. After performing a mesh independence analysis in this embodiment, a 5mm mesh size is finally selected as the optimal mesh size that takes into account both calculation speed and calculation accuracy, and the 5mm mesh size is used in subsequent optimization. The cylinder head temperature field distribution results calculated using a 5mm mesh size are shown in the figure. Figure 5 (a) shows the thermal-mechanical coupling stress distribution of the cylinder head. Figure 5 (b) shows the thermal-mechanical coupling deformation distribution of the cylinder head. Figure 5 (c) as shown.

[0095] Step 3: Adjust the structural parameters of the cylinder head model to generate a cylinder head model with parameters different from the initial values. Record the script for drawing the combined mesh model of the cylinder head body for flow field and temperature field calculation in ICEM and fluent meshing. Record the script for calculating the heat transfer performance of the cylinder head in fluent, and extract the index data that can characterize the heat transfer performance of the cylinder head and the quality of the cylinder head. Record the script for drawing the 3D mesh model of the cylinder head for calculating the load-bearing capacity under thermal-mechanical coupling conditions and the script for updating the mesh model of the cylinder head in the cylinder head assembly model in Hypermesh. Record the script for mapping the temperature distribution data of the cylinder head in Hypermesh and fluent, and use batch processing commands to realize the automatic modification of the temperature distribution data so that it can be recognized by the Abaqus solver to generate temperature field calculation results. Record the script for calculating the stiffness and strength of the cylinder head in Abaqus and extract the index data that can characterize the load-bearing performance of the cylinder head under thermal-mechanical coupling conditions.

[0096] The specific implementation method of step three includes the following steps:

[0097] Step 3.1: Adjust the structural parameters of the cylinder head model to generate a cylinder head model whose parameters are random numbers within a variation range.

[0098] Step 3.2: Start script recording in ICEM, divide the surface mesh model of the cylinder head and the cylinder head cooling channel using the Patch Independent meshing method with a mesh size of 5mm, save the surface mesh model of the cylinder head and the cylinder head cooling channel, and obtain the script for the surface meshing link. Start script recording again in ICEM, import the surface mesh model of the cylinder head and the cylinder head cooling channel, merge the two meshes, and name the mesh areas in the cylinder head surface mesh model according to the water inlet, water outlet, channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake duct wall, exhaust duct wall and firepower surface. Obtain the script for the cylinder head combined surface mesh model and mesh merging link. Start script recording in fluent meshing, import the merged cylinder head surface mesh model, correct the three problems of free edges, self-intersection and repeated meshes, and reduce the mesh distortion to below 0.8. Draw the volume mesh model of the cylinder head, and repair the low-quality mesh based on the mesh node movement algorithm to reduce the inverse orthogonal quality to below 0.8. Output the cylinder head combined grid model for flow field and temperature field calculation and obtain the script for volume grid division. The script can be used to realize one-click automatic division of the cylinder head combined grid model.

[0099] Step 3.3: Start script recording in Fluent, import the volume mesh model of the cylinder head, set the simulation analysis scale to 5mm, use the SIMPLE method for flow field calculation, use the ke model for turbulence calculation, and set the material properties of the cylinder head and the coolant in the flow channel to cast iron and water, respectively. Set the water inlet, outlet, flow channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake channel wall, exhaust channel wall and fire surface of the cylinder head volume mesh model to the inlet surface, outlet surface, wall surface and interface surface, respectively, according to the needs of simulation analysis. Set the surface type of the fluid-solid coupling surface on the cylinder head and cylinder head cooling channel mesh model to the interface, and set the two fluid-solid coupling surfaces to the coupling relationship. Set the ambient temperature of the fire surface to 812℃ and the heat transfer coefficient to 1582W / (m2*K); the ambient temperature of the intake duct wall to 63℃ and the heat transfer coefficient to 320W / (m2*K); the ambient temperature of the exhaust duct wall to 704℃ and the heat transfer coefficient to 640W / (m2*K); the water inlet temperature is 25℃ and the water outlet temperature is 70℃. Set the shutdown condition to 200 simulation iterations and initialize the simulation, submit the simulation calculation to obtain the temperature field simulation results of the cylinder head. Extract the surface average convection heat transfer coefficient, surface average pressure, surface average y+ value, surface minimum y+ value, surface maximum y+ value, body average water cavity temperature, body average cylinder head temperature, body average velocity, total mass of the cylinder head, maximum temperature of the cylinder head, maximum temperature in the water cavity, maximum velocity in the water cavity, minimum temperature in the water cavity and water cavity size obtained by the cylinder head heat transfer performance calculation. Save the cylinder head temperature field simulation example and obtain the script for the cylinder head heat transfer performance calculation link.

[0100] Step 3.4: Start script recording in Hypermesh, edit the mesh quality criteria based on the 5mm mesh size, cancel the algorithm's detection of the maximum mesh size and the minimum mesh size, and improve the repair rate of low-quality meshes. Use the surface deviation meshing method to divide the 2D mesh, repair the meshes with unqualified mesh quality based on the QI optimization mesh repair algorithm and the size corrected mesh repair algorithm, and use the place node method to modify the meshes that are difficult to adjust by the mesh repair algorithm to qualified mesh quality, and obtain a high-quality cylinder head 2D mesh model. Use the tetramesh meshing method to draw the 3D mesh and obtain the cylinder head 3D mesh model. Complete the drawing of the cylinder head 3D mesh model for calculating the load-bearing capacity under thermal-mechanical coupling conditions and obtain the script for the cylinder head 3D mesh model drawing link.

[0101] Step 3.5: Start script recording in Hypermesh, import the cylinder head assembly mesh model, replace the cylinder head components in the cylinder head assembly mesh model with the cylinder head 3D mesh model with updated structural shape based on the mesh model replacement algorithm, export the new cylinder head assembly mesh model and obtain the script for the cylinder head mesh model update link.

[0102] Step 3.6: Start script recording in Hypermesh, extract the cylinder head mesh model from the mesh model of the cylinder head assembly, and import it into fluent. Start script recording in fluent, import the cylinder head temperature field simulation results under a 6mm mesh size into the extracted cylinder head mesh model based on the mesh data automatic mapping algorithm, and obtain the temperature distribution data of the cylinder head corresponding to the mesh node layout of the cylinder head mesh model. Use batch commands to realize the automatic modification of temperature distribution data so that the temperature distribution data can be recognized by the Abaqus solver, import the modified temperature distribution data into Abaqus, and generate a script that can import the temperature field calculation results when setting the calculation task in Abaqus and obtain the cylinder head temperature distribution data mapping link.

[0103] Step 3.7: Record the script for the cylinder head stiffness calculation. Start the script recording in Abaqus, import the cylinder head assembly mesh model, set the burst pressure of the fire surface to 25Mpa, the burst pressure of the intake and exhaust valve seats to 48Mpa and 37Mpa respectively, and the preload of the four bolts to 115000N; select the contact pair between the bolt and the cylinder head and the contact pair between the cylinder head and the engine body to set the contact relationship and use the small slip and small deformation calculation method, with a friction coefficient of 0.15; select the connection pair between the bolt and the engine body assembly hole to set the coupling relationship and use the small slip and small deformation calculation method, with a friction coefficient of 0.15; set the bottom of the engine body as a fixed support constraint. Select the simulation analysis type as static analysis, set the initial iteration step of the simulation to 0.01 and the maximum iteration step to 0.5 according to the computing power conditions, associate the temperature field calculation results that can be recognized by the Abaqus solver with the predefined temperature field, set the initial iteration step and maximum iteration step of the simulation according to the computing power conditions, submit the simulation calculation and obtain the stress distribution and displacement distribution results of the cylinder head under thermal-mechanical coupling conditions.

[0104] Step 4: Based on the joint simulation technology, the cylinder head optimization model under the condition of thermal-mechanical coupling is built. The Latin hypercube algorithm is used to plan the sample space for cylinder head optimization under the condition of thermal-mechanical coupling. The script recorded during the cylinder head performance calculation process is called through the batch command to automatically run the cylinder head parameterization model update, cylinder head mesh drawing, cylinder head component update in the cylinder head assembly model, cylinder head heat transfer simulation analysis, cylinder head temperature distribution data mapping between different mesh models, cylinder head stiffness simulation analysis and cylinder head performance index data extraction under the condition of thermal-mechanical coupling in the process of cylinder head optimization design under the condition of thermal-mechanical coupling, and obtain the sample data set that characterizes the corresponding relationship between the cylinder head structure and various performances. A comprehensive evaluation function is established to comprehensively consider multiple cylinder head performance indicators to score each sample point, select the best scoring group of samples as the optimization result, and obtain the optimal cylinder head structure in the sample space, that is, to achieve cylinder head optimization under the condition of thermal-mechanical coupling based on the joint simulation technology.

[0105] The specific implementation method of step 4 includes the following steps:

[0106] Step 4.1: Build a cylinder head optimization model under thermal-mechanical coupling conditions in Isight. The workflow can be used Figure 6 The flowchart is represented by . Based on the i5-10500CPU and 16GB memory computing device used, the total number of samples in the sample space is set to 500, and the Latin hypercube algorithm is used to plan the sample space for cylinder head optimization under thermal-mechanical coupling conditions, so that the sample points are evenly distributed in the high-dimensional Euclidean space to ensure the quality of the sample data. The script recorded during the cylinder head performance calculation process is called through batch commands, and different modules are used to execute the cylinder head parameterization model update, cylinder head mesh drawing, cylinder head component update in the cylinder head assembly model, cylinder head heat transfer simulation analysis, cylinder head temperature distribution data mapping between different mesh models, cylinder head stiffness simulation analysis, and cylinder head performance index data extraction commands under thermal-mechanical coupling conditions. After the settings are completed, the cylinder head performance optimization model is automatically run to obtain a sample data set that characterizes the corresponding relationship between the cylinder head structure and various performances.

[0107] Step 4.2: Establish a comprehensive evaluation function, comprehensively consider the floating degree and importance of multiple cylinder head performance indicators, and score the heat transfer performance of each sample point. In this embodiment, the cylinder head weight, maximum temperature, maximum thermal-mechanical coupling stress and maximum thermal-mechanical coupling deformation are selected as evaluation indicators, and the ideal value of each indicator is set to the minimum value of the indicator data. The weight of each indicator is calculated and scored using a comprehensive evaluation function. The group of samples with the best scores are selected as the optimization results to complete the optimization of the cylinder head. The final optimized cylinder head model structure is as follows: Figure 7 shown.

[0108] It also includes step 5, performing process adaptability design according to the optimal cylinder head structure obtained in step 4, and obtaining a cylinder head design scheme that meets production constraints. The cast iron cylinder head manufactured by this scheme is 9% lighter than the cylinder head before optimization, the maximum temperature is reduced from 520℃ to 446℃, the maximum thermal-mechanical coupling stress is reduced from 345.3MPa to 328.3MPa, and the maximum thermal-mechanical coupling deformation is reduced from 1.039mm to 1.025mm. It can be seen that the optimized cylinder head has improved heat transfer performance, load-bearing performance and lightweight degree.

[0109] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for optimizing cylinder head parameters under thermal-mechanical coupling conditions, characterized in that: The cylinder head geometry model is constructed based on the parametric modeling method, and the cylinder head expression is used to control the structural shape of the cylinder head geometry model to achieve rapid update of the cylinder head geometry model; the cylinder head model and cylinder head cooling channel are meshed by finite element based on the automated meshing method, and the cylinder head body combined mesh model for flow field and temperature field calculation and the cylinder head 3D mesh model for calculating the load-bearing capacity under thermal-mechanical coupling conditions are drawn respectively to improve the mesh quality and calculation convergence probability; Set up simulation analysis based on the cylinder head heat transfer analysis method, use macro commands to drive the solver to perform automatic simulation analysis of the heat transfer performance of the steady-state flow field and temperature field inside the cylinder head, obtain the temperature distribution at each position on the cylinder head, and extract key indicators that can reflect the heat transfer performance of the cylinder head; Based on the automatic mesh data mapping algorithm, the cylinder head temperature distribution data is extracted from the cylinder head body mesh combination model and interpolated into the cylinder head 3D mesh model, realizing fast and efficient data transmission of the cylinder head temperature distribution calculation results between different mesh models; The simulation analysis is set up based on the cylinder head stiffness analysis method, and the macro command is used to drive the solver to perform an automated simulation analysis of the cylinder head load-bearing performance under thermal-mechanical coupling conditions. The thermal-mechanical coupling stress and thermal-mechanical coupling deformation distribution of the cylinder head under service conditions are obtained, and key indicators that can reflect the cylinder head load-bearing performance under thermal-mechanical coupling conditions are extracted; A sample space is constructed based on the parameter variation range of the cylinder head geometric model, and automatic simulation analysis is repeatedly performed independently on each sample point. After screening and removing data with non-convergence and substandard accuracy, a sample data set is obtained that characterizes the correspondence between the cylinder head structure and the cylinder head load-bearing performance under thermal-mechanical coupling conditions. A comprehensive evaluation function is established to comprehensively weigh the cylinder head heat transfer performance index and the cylinder head load-bearing performance index, and the performance of each sample point is scored. The group of samples with the best scores are selected as the optimal cylinder head structure optimization result in the sample space, that is, to achieve cylinder head performance optimization based on joint simulation technology.

2. The method for optimizing cylinder head parameters under thermal-mechanical coupling conditions according to claim 1, characterized in that: The following steps are included: Step 1: parametrically model the cylinder head to obtain a cylinder head parametric model; obtain the cylinder head cooling channel model through Boolean operations, and associate the cylinder head parametric model with the same parameters of the cylinder head cooling channel model; determine the initial value and upper and lower boundary values ​​of each parameter of the cylinder head parametric model, and gradually modify the cylinder head parametric model by "combining global parameter changes with modification error reporting features" until the cylinder head model meets the preset stability qualification requirements; Classify the faces that need to be assigned different boundary conditions on the cylinder head parametric model and the cylinder head cooling channel model, and save the cylinder head parametric model and the cylinder head cooling channel model in the form of surface features; by calling the API function of the UG software, realize the one-click automatic update of the cylinder head parametric model and the cylinder head cooling channel model, and improve the update efficiency of the cylinder head parametric model and the cylinder head cooling channel model; Step 2: Using the minimum wall thickness requirement as the initial grid size, draw a combined grid model of the cylinder head body for flow field and temperature field calculation; set up simulation based on the cylinder head heat transfer analysis method, perform simulation analysis of the steady-state flow field and temperature field inside the cylinder head, and obtain the temperature distribution at each position on the cylinder head; using the minimum wall thickness requirement as the initial grid size, divide the cylinder head 3D grid model used to calculate the load-bearing capacity under thermal-mechanical coupling conditions; assemble the cylinder head 3D grid model and various components related to the service status of the cylinder head, and provide a reference for each cylinder head. Draw structured grids for the components related to the service status of the cylinder head, and select grid faces on the 3D grid model of the cylinder head and the 3D grid models of the components related to the service status of the cylinder head as the main face and the secondary face of the boundary conditions to be applied during the stiffness analysis of the cylinder head, so as to establish a grid model of the cylinder head assembly; interpolate the temperature field distribution into the stress field grid, and realize the mapping of the cylinder head temperature distribution data from the cylinder head combined grid model used for flow field and temperature field calculation to the cylinder head 3D grid model used for calculating the load-bearing capacity under the thermal-mechanical coupling condition; Performing mesh independence analysis of cylinder head performance calculation under thermal-mechanical coupling conditions, selecting a mesh size with a short calculation time and a stress and displacement calculation result with a deviation less than a preset threshold value from the calculation result under other mesh sizes as the finite element mesh size used in optimization, wherein the short calculation time refers to a calculation time shorter than a preset threshold value; Step 3: Adjust the structural parameters of the cylinder head model to generate a cylinder head model with parameters different from the initial values; record the script for drawing the cylinder head body combined mesh model for flow field and temperature field calculation in ICEM and fluent meshing; record the script for calculating the heat transfer performance of the cylinder head in fluent, and extract the index data that can characterize the heat transfer performance of the cylinder head and the quality of the cylinder head; record the script for drawing the cylinder head 3D mesh model for calculating the load-bearing capacity under thermal-mechanical coupling conditions and the script for updating the cylinder head mesh model in the cylinder head assembly model in Hypermesh; record the script for mapping the cylinder head temperature distribution data in Hypermesh and fluent, and use batch processing commands to realize the automatic modification of the temperature distribution data so that it can be recognized by the Abaqus solver to generate temperature field calculation results; Record the script of the cylinder head stiffness calculation in Abaqus and extract the index data that can characterize the cylinder head load-bearing performance under thermal-mechanical coupling conditions; Step 4: Based on the joint simulation technology, a cylinder head optimization model under thermal-mechanical coupling conditions is built, and the Latin hypercube algorithm is used to plan the sample space for cylinder head optimization under thermal-mechanical coupling conditions. The script recorded during the cylinder head performance calculation process is called through a batch command to automatically run the cylinder head parameterized model update, cylinder head mesh drawing, cylinder head component update in the cylinder head assembly model, cylinder head heat transfer simulation analysis, cylinder head temperature distribution data mapping between different mesh models, cylinder head stiffness simulation analysis and cylinder head performance index data extraction under thermal-mechanical coupling conditions in the cylinder head optimization design process under thermal-mechanical coupling conditions, so as to obtain a sample data set that characterizes the correspondence between the cylinder head structure and various performances; a comprehensive evaluation function is established to comprehensively weigh multiple cylinder head performance indicators to score each sample point, and a group of samples with the best scores are selected as the optimization results to obtain the optimal cylinder head structure in the sample space, that is, to achieve cylinder head optimization under thermal-mechanical coupling conditions based on joint simulation technology.

3. The method for optimizing cylinder head parameters under thermal-mechanical coupling conditions according to claim 2, characterized in that: The method also includes step 5, performing process adaptability design according to the optimal cylinder head structure obtained in step 4 to obtain a cylinder head design scheme that meets production constraints; the cylinder head manufactured by the cylinder head design scheme can improve heat transfer and load-bearing performance, reduce the maximum temperature of the fire surface, reduce thermal-coupled machine deformation, reduce thermal-coupled machine stress, and improve service life compared to the cylinder head before optimization; the weight of the optimized cylinder head is reduced compared to the weight of the cylinder head before optimization, and the high power density of the engine can be improved.

4. The method for optimizing cylinder head parameters under thermal-mechanical coupling conditions as claimed in claim 3, characterized in that: The specific implementation method of step one is: S11: Use UG as a modeling platform to perform parametric modeling of the cylinder head; use stretching or rotation modeling methods to establish the external features of the cylinder head, the features include the top plate, the bottom plate, and the side wall; use the projection curve modeling method to draw the characteristic lines on the wall surfaces of the cylinder head intake and exhaust ducts, use the fitting surface modeling method to connect the closed projection curves to generate the surface features of the intake and exhaust duct walls, sew the surface features that constitute the intake and exhaust ducts to form a solid, and use Boolean operations to calculate the difference between the external features of the cylinder head and the intake and exhaust duct entities to obtain a cylinder head model that completes the airway modeling; use stretching, rotation, punching or inverting on the cylinder head model that completes the airway modeling The rounded corner modeling method is used to establish the assembly features of the cylinder head, which include fastening threaded holes, intake and exhaust pipe assembly holes, inlet and outlet assembly holes, injector assembly holes, and locating pin holes; the stretching modeling method is used to draw the water inlet and outlet of the flow channel on the cylinder head after the airway modeling is completed, and the flow channel geometry of the cylinder head is drawn by stretching, rotating, and stitching surfaces at the position where the wall thickness on the cylinder head model is greater than the minimum wall thickness requirement of the process, starting from the water inlet, until the flow channel geometry connects the water inlet and the water outlet, and the flow channel geometry is arranged at the position where the wall thickness is greater than the minimum wall thickness requirement of the process. When setting the size of the flow channel geometry, the minimum wall thickness requirement of the processing technology must be strictly met; Use Boolean operations to sum all the flow channel geometries to obtain the flow channel entity of the cylinder head model, and then use Boolean operations to calculate the difference between the cylinder head model that has completed the air channel modeling and the flow channel entity of the cylinder head model to obtain the cylinder head model that has completed the air channel and flow channel modeling; after the external features, air channels, assembly features and flow channels of the cylinder head are modeled, use stretching, rotation, and stitching surfaces to establish weight-reducing geometries at locations on the top plate, bottom plate, and side wall of the cylinder head that do not involve assembly and sealing, and associate the size of the weight-reducing geometries with the size of the flow channel geometries to always ensure that the minimum wall thickness on the cylinder head is greater than the minimum wall thickness requirement of the process; Use Boolean operations to calculate the difference between the cylinder head that has completed the assembly feature modeling and all the weight-reducing geometries to obtain the cylinder head model that has completed the parametric modeling; S12: obtaining a cooling channel model of the cylinder head through Boolean operations; deleting the weight reduction features on the cylinder head parameterized model and saving the model as copy 1; deleting the weight reduction features and channel features on the cylinder head parameterized model and saving the model as copy 2; performing subtraction between the copy 1 model and the copy 2 model through Boolean operations to obtain a cooling channel model of the cylinder head; associating the parameters with the same meaning in copy 1 and copy 2 in the expression of the cylinder head cooling channel model, wherein the parameters include parameters for controlling external features and parameters for controlling air channel features, so that the parameters with the same meaning in the two sets of expressions always remain equal during the model update process; after completing the association of the same parameters, when updating the parameters of the cylinder head cooling channel model, the external features and air channel features of copy 1 and copy 2 will be updated synchronously, ensuring that each time the cylinder head cooling channel model is updated, the final entity obtained only has the channel part of the cylinder head; S13: setting parameter initial values ​​and parameter boundary values ​​for structural parameters on the cylinder head parameterized model and the cylinder head cooling channel model; setting one parameter boundary value of the cylinder head parameterized model to a limit parameter when the wall thickness at each position of the cylinder head is the minimum wall thickness requirement of the process, and setting the other parameter boundary value to other limit dimensions that meet the cylinder head design requirements, wherein the cylinder head design requirements include that the hydraulic diameter at each position of the channel shall not be less than the limit dimension that causes flow obstruction, the narrowest part of the cylinder head surface shall not be less than one-third of the minimum wall thickness requirement of the process, and no interference shall occur between the cylinder head channel, air channel, assembly features, weight reduction features and external wall surface; Some cylinder head dimensions are the reference dimensions set when the cylinder head parametric model is built. The initial values ​​of the reference dimension parameters are set to the initial values ​​used when the cylinder head parametric model is built, and then the boundary values ​​are equal to the reference values. These dimensions do not change when the cylinder head parametric model is updated. After the upper and lower boundary values ​​of the parameter changes are determined for the parameters other than the reference dimensions, the initial values ​​of the parameters other than the reference dimensions are set to the median of the upper and lower boundary values ​​to reduce the probability of errors when the cylinder head parametric model is updated. S14: gradually modify the cylinder head parametric model by "combining global parameter changes with error feature modification"; when the cylinder head parametric model selects parameter values ​​within the parameter variation range obtained in S13 and substitutes them into the expression to update the model, and the model update exceeds the preset number of times without error, it is determined that the stability of the cylinder head parametric model meets the conditions required for optimization; the function of this step S14 is to repeatedly test whether the cylinder head parametric model reports an error under different parameter values, and modify the error feature to gradually improve the cylinder head parametric model; name all parameters other than the reference size in the cylinder head parametric model expression, configure the data interface between Excel and UG, and import the parameter names of the cylinder head other than the reference size and their corresponding parameter variation ranges into an Excel table, insert a random number formula to randomly select a parameter value for all parameters other than the reference size within the variation range, and then select all random parameter values ​​generated by the random number formula together with the names of all parameters other than the reference size as the data source of the cylinder head parametric model, and use the Excel table to drive UG to update the model multiple times to test the parameter stability of the cylinder head parametric model under random parameter values; When the cylinder head parametric model does not report an error when the random parameter value is used continuously for the preset number of model updates, the parameter stability of the cylinder head parametric model is determined to be qualified; if an error occurs, the error feature prompted in the UG software is modified or the size variation range corresponding to the feature is modified until the cylinder head parametric model is updated continuously for the preset number of times using the random parameter value without reporting an error; S15: classifying the surfaces on the cylinder head parameterized model and the cylinder head cooling channel model that need to be assigned different boundary conditions, and saving the cylinder head parameterized model and the cylinder head cooling channel model in the form of surface features; When performing automatic calculation of cylinder head temperature field distribution, boundary conditions can only be automatically assigned to surface features. Extracting the surfaces of the cylinder head parametric model and the cylinder head cooling channel model into multiple surface features based on the type of boundary condition area can achieve the effect of automatically identifying the boundary condition area in the solver; based on the cylinder head heat transfer analysis method, the surfaces on the cylinder head parametric model and the cylinder head cooling channel model are classified, and the surface categories include water inlet, water outlet, channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake channel wall, exhaust channel wall and fire surface; through the modeling method of extracting geometric features, on the cylinder head parametric model and the cylinder head cooling channel model, these surfaces are extracted into surface features according to categories, and the original entity models in the cylinder head parametric model and the cylinder head cooling channel model are hidden. After obtaining the cylinder head parametric model and the cylinder head cooling channel model in the form of surface features, they are saved separately, and all surface features are set to be associated with the hidden cylinder head and cylinder head cooling channel entities; S16: Automatic update of the cylinder head model is realized by calling the API function of UG; calling the API function of UG to realize the functions of reading the cylinder head parameterized model path and the cylinder head cooling channel model path, reading the cylinder head parameterized model expression path, automatically updating the cylinder head parameterized model and the cylinder head cooling channel model using the expression parameter value, and saving the cylinder head parameterized model and the cylinder head cooling channel model corresponding to the new parameter value, so as to realize one-key automatic update of the cylinder head parameterized model and the cylinder head cooling channel model.

5. The method for optimizing cylinder head parameters under thermal-mechanical coupling conditions as claimed in claim 4, characterized in that: The specific implementation method of step 2 is: S21: Draw the combined mesh model of the cylinder head body for flow field and temperature field calculation; draw the mesh using the minimum wall thickness requirement of the process as the initial mesh size to ensure the mesh quality at the minimum position of the cylinder head wall; import the cylinder head parameterized model and the cylinder head cooling channel model into ICEM; The mesh size is set to the minimum wall thickness requirement of the process, and the surface mesh is divided using the Patch Independent meshing method to avoid mesh drawing failure caused by geometric shape distortion at some locations. The geometric shape distortion includes broken surfaces on the cylinder head parameterized model and the cylinder head cooling channel model, narrow surfaces with a width less than the minimum wall thickness requirement of the process, or an angle between two surfaces less than 15°; merging the mesh models of the cylinder head and the cylinder head cooling channel before calculating can achieve simultaneous setting of the boundary conditions of the cylinder head and the cylinder head cooling channel, solving the problem that the heat transfer solver can only set the boundary conditions for one calculation target; importing the surface mesh models of the cylinder head and the cylinder head cooling channel in ICEM, and merging the two meshes to obtain the cylinder head combined surface mesh model; The quality of the surface mesh automatically drawn by ICEM is not high. If the volume mesh is directly drawn in ICEM and applied to the calculation, the calculation cannot converge. Importing the merged cylinder head surface mesh model into FluentMeshing to repair the mesh problem and perform volume mesh division can solve this problem and ensure the mesh quality of the volume mesh model is qualified. In ICEM, the mesh areas in the merged cylinder head surface mesh model are named according to the water inlet, water outlet, flow channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake channel wall, exhaust channel wall and fire surface; Import the merged cylinder head surface mesh model into fluent meshing, correct the free edge, self-intersection and repeated mesh problems, and reduce the mesh distortion to below the preset distortion; Draw a volume mesh model based on the merged cylinder head surface mesh model, and repair the low-quality mesh based on the mesh node movement algorithm to reduce the inverse orthogonal quality to below the preset inverse orthogonal quality; Output the cylinder head combined mesh model for flow field and temperature field calculation; S22: Set up simulation based on the cylinder head heat transfer analysis method, perform steady-state flow field and temperature field simulation analysis inside the cylinder head, and obtain the temperature distribution at each position on the cylinder head; import the body mesh model of the cylinder head into fluent, set the scale of the simulation analysis, the calculation method used for the flow field calculation, and the material properties of the cylinder head and the coolant in the flow channel; set the surface type of each surface on the cylinder head body mesh model, including the water inlet, water outlet, flow channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake duct wall, exhaust duct wall and firepower surface, the surface types include inlet surface, outlet surface, wall surface and interface surface; the surface types of the fluid-solid coupling surfaces on the cylinder head and the cylinder head cooling channel mesh model are set as the interface surface, and the two fluid-solid coupling surfaces are set as the coupling relationship, so as to solve the problem that the meshes on the fluid-solid coupling surfaces of the cylinder head and the cylinder head cooling channel mesh model do not share common nodes; the convection heat transfer coefficients and the initial wall temperatures of the various surfaces are set; the calculation process is monitored and shutdown conditions are set and the simulation is initialized, and the simulation calculation is submitted to obtain the temperature field simulation results of the cylinder head; S23: Draw the 3D mesh model of the cylinder head used to calculate the load-bearing capacity under thermal-mechanical coupling conditions; The mesh is drawn with the minimum wall thickness requirement as the initial mesh size, the cylinder head parametric model is imported into Hypermesh, the mesh size is set to the minimum wall thickness requirement, and the surface deviation meshing method is used to divide it into 2D meshes; the meshes with unqualified mesh quality are repaired based on the QI optimization mesh repair algorithm and the size corrected mesh repair algorithm, and the place node method is used to modify the meshes that are difficult to adjust by the mesh repair algorithm to qualified mesh quality, so as to obtain a high-quality cylinder head 2D mesh model; Set the mesh size to the minimum wall thickness required by the process, use the tetramesh meshing method to draw the 3D mesh, and obtain the cylinder head 3D mesh model for calculating the load-bearing capacity under thermal-mechanical coupling conditions; S24: Establish a mesh model of the cylinder head assembly; import the 3D mesh model of the cylinder head used for calculating the load-bearing capacity under the thermal-mechanical coupling condition into Hypermesh, import various components related to the service state of the cylinder head and assemble the various components related to the service state of the cylinder head with the 3D mesh model of the cylinder head used for calculating the load-bearing capacity under the thermal-mechanical coupling condition according to the engine assembly requirements, wherein the components include an engine body, a bushing, a gasket, and a fastening bolt; perform 2D structured mesh division on the various components related to the service state of the cylinder head using the automesh method, and use solid map method to perform 3D structured mesh division on the components related to the service state of the cylinder head, and obtain the 3D mesh models of the components related to the service state of the cylinder head; based on the cylinder head stiffness analysis method, mesh surfaces are respectively selected on the cylinder head 3D mesh model used for calculating the bearing capacity of the cylinder head under the thermal-mechanical coupling condition and the 3D mesh models of the components related to the service state of the cylinder head as the main surface and the secondary surface of the boundary conditions to be applied during the stiffness analysis of the cylinder head, and the main surface and the secondary surface include the main and secondary surfaces of the contact relationship between the bolt and the cylinder head, the main and secondary surfaces of the connection relationship between the bolt and the assembly hole of the body, the main and secondary surfaces of the contact relationship between the cylinder head and the body, and the action surface of the explosion pressure of the combustion chamber; the material properties are set for the cylinder head 3D model and the 3D mesh models of the components related to the service state of the cylinder head and saved to obtain the mesh model of the cylinder head assembly; S25: interpolate the temperature field distribution into the stress field grid, then format the obtained data file and import it into Abaqus to realize the mapping of the cylinder head temperature distribution data from the cylinder head combined grid model used for flow field and temperature field calculation to the cylinder head 3D grid model used for calculating the load-bearing capacity under thermal-mechanical coupling conditions; extract the cylinder head grid model from the grid model of the cylinder head assembly to ensure that the grid number on the cylinder head grid model is still consistent with the grid number in the cylinder head assembly after the temperature field data is mapped to the cylinder head grid model; import the cylinder head temperature field simulation results obtained in S22 into the extracted cylinder head grid model based on the grid data automatic mapping algorithm in fluent to obtain the cylinder head temperature distribution data corresponding to the grid node layout of the cylinder head grid model; modify the temperature distribution data so that it can be recognized by the Abaqus solver, import the modified temperature distribution data into Abaqus, so that it generates the temperature field calculation results that can be imported when setting the calculation task in Abaqus; S26: Set up simulation based on the cylinder head stiffness analysis method, conduct load-bearing performance analysis under thermal-mechanical coupling conditions, and obtain the thermal-mechanical coupling stress and thermal-mechanical coupling deformation distribution at each position on the cylinder head; import the mesh model of the cylinder head assembly into Abaqus, set the explosion pressure and bolt preload force that the cylinder head is subjected to during operation, select the contact pair between the bolt and the cylinder head and the contact pair between the cylinder head and the engine body to set the contact relationship and use the small slip and small deformation calculation method, select the connection pair between the bolt and the engine body assembly hole to set the coupling relationship and use the small slip and small deformation calculation method, and set the bottom of the engine body as a fixed support constraint; select the simulation analysis type as static analysis, associate the Abaqus temperature field calculation results generated by S25 with the predefined temperature field, set the initial iteration step and maximum iteration step of the simulation according to the computing power conditions, submit the simulation calculation and obtain the stress distribution and displacement distribution results of the cylinder head in the service state; S27: Performing a mesh independence analysis of the cylinder head performance calculation under the thermal-mechanical coupling condition; starting from the initial value of the mesh size of the minimum wall thickness requirement of the process, expanding or reducing the mesh size used when drawing the cylinder head combined mesh model and the cylinder head 3D mesh model, respectively calculating the temperature field simulation results of the cylinder head and the load-bearing capacity simulation results under the thermal-mechanical coupling condition, comparing the effects of different mesh sizes on the calculation time and the maximum temperature, thermal-mechanical coupling stress, and thermal-mechanical coupling deformation calculation results, selecting a mesh size with a short calculation time and a calculation result with a deviation less than a preset threshold value from the calculation result under other mesh sizes as the finite element mesh size used for optimization, and completing the mesh independence analysis, wherein the short calculation time refers to a calculation time that is shorter than the preset threshold value.

6. The method for optimizing cylinder head parameters under thermal-mechanical coupling conditions according to claim 5, characterized in that: The specific implementation method of step three is: S31: adjusting the structural parameters of the cylinder head model, automatically updating the cylinder head model and the cylinder head cooling channel model, and generating a cylinder head model with parameters different from the initial values; modifying all parameters except the reference size in the expression of the cylinder head parameterized model, calling the UG API function, reading the cylinder head parameterized model expression, and automatically updating the cylinder head model and the cylinder head cooling channel model with one key; S32: Record the script for drawing the cylinder head body combined mesh model for flow field and temperature field calculation; based on the mesh size determined after mesh independence analysis, start script recording in ICEM, divide the surface mesh models of the cylinder head and the cylinder head cooling channel using the PatchIndependent meshing method, save the surface mesh models of the cylinder head and the cylinder head cooling channel, and obtain the script for the surface meshing phase; start script recording again in ICEM, import the surface mesh models of the cylinder head and the cylinder head cooling channel in turn, merge the two meshes, and name the mesh areas in the cylinder head surface mesh model according to the water inlet, water outlet, channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake duct wall, exhaust duct wall, and firepower surface; obtain the script for the cylinder head combined surface mesh model and mesh merging phase; Start script recording in Fluent Meshing, import the merged cylinder head surface mesh model, correct the three problems of free edges, self-intersection and repeated meshes, and reduce the mesh distortion to below the preset distortion; Draw the volume mesh model of the cylinder head and repair the low-quality mesh based on the mesh node movement algorithm to reduce the inverse orthogonal quality to below the preset inverse orthogonal quality; Output the cylinder head combined mesh model for flow field and temperature field calculation and obtain the script for volume mesh division; S33: Record the script for calculating the heat transfer performance of the cylinder head; start the script recording in Fluent, import the volume mesh model of the cylinder head, set the scale of the simulation analysis, the calculation method used for the flow field calculation, and the material properties of the cylinder head and the coolant in the flow channel; set the surface type of each surface on the cylinder head volume mesh model, the surfaces include water inlet, water outlet, flow channel wall, fluid-solid coupling surface, symmetry surface, outer wall, intake channel wall, exhaust channel wall and fire surface, the surface types include inlet surface, outlet surface, wall surface and interface; set the surface type of the fluid-solid coupling surface on the cylinder head and the cylinder head cooling channel mesh model to the interface, and set the two fluid-solid coupling surfaces to the coupling relationship. ; Set the convection heat transfer coefficient and initial wall temperature of the various surfaces; set monitoring and shutdown conditions for the calculation process and initialize the simulation, submit the simulation calculation to obtain the temperature field simulation result of the cylinder head; extract the index data that can characterize the heat transfer performance of the cylinder head and the quality of the cylinder head, the indexes include the surface average convection heat transfer coefficient, surface average pressure, surface average y+ value, surface minimum y+ value, surface maximum y+ value, body average water cavity temperature, body average cylinder head temperature, body average speed, total mass of the cylinder head, maximum temperature of the cylinder head, maximum temperature in the water cavity, maximum speed in the water cavity, minimum temperature in the water cavity and water cavity size; output the temperature field simulation result of the gas cylinder head and obtain the script for the calculation link of the heat transfer performance of the cylinder head; S34: Recording the script for drawing the 3D mesh model of the cylinder head used to calculate the load-bearing capacity under thermal-mechanical coupling conditions; Based on the mesh size determined after mesh independence analysis, start script recording in Hypermesh, edit the mesh quality evaluation criteria, cancel the algorithm's detection of the maximum and minimum mesh sizes, and improve the repair rate of low-quality meshes; Use the surface deviation meshing method to divide it into 2D meshes, use the QI optimization mesh repair algorithm and the size corrected mesh repair algorithm to repair meshes with unqualified mesh quality, and use the place node method to modify meshes that are difficult to adjust with the mesh repair algorithm to qualified mesh quality, so as to obtain a high-quality cylinder head 2D mesh model; use the tetramesh meshing method to draw 3D meshes to obtain a cylinder head 3D mesh model; complete the drawing of the cylinder head 3D mesh model for calculating the load-bearing capacity under thermal-mechanical coupling conditions and obtain the script for drawing the cylinder head 3D mesh model; S35: recording a script for updating the cylinder head mesh model in the cylinder head assembly model; starting script recording in Hypermesh, importing the cylinder head assembly mesh model, replacing the cylinder head mesh model in the cylinder head assembly mesh model with the cylinder head 3D mesh model after the structural shape is updated based on the mesh model replacement algorithm, exporting the new cylinder head assembly mesh model and obtaining the script for updating the cylinder head mesh model; S36: Record the script for mapping the cylinder head temperature distribution data from the cylinder head combined grid model used for flow field and temperature field calculation to the cylinder head 3D grid model used for calculating the load-bearing capacity under thermal-mechanical coupling conditions; start script recording in Hypermesh, extract the cylinder head grid model from the grid model of the cylinder head assembly, and ensure that the grid number on the cylinder head grid model is still consistent with the grid model of the cylinder head assembly after the temperature field data is mapped to the cylinder head grid model; start script recording in fluent, import the cylinder head temperature field simulation results obtained in S33 into the extracted cylinder head grid model based on the grid data automatic mapping algorithm, and obtain the cylinder head temperature distribution data corresponding to the grid node layout form of the cylinder head grid model; use batch processing commands to realize the automatic modification of temperature distribution data so that the temperature distribution data can be recognized by the Abaqus solver, import the modified temperature distribution data into Abaqus, and generate a script for mapping the temperature field calculation results and cylinder head temperature distribution data that can be imported when setting calculation tasks in Abaqus; S37: recording the script for calculating the rigidity and strength of the cylinder head; Start script recording in Abaqus, import the mesh model of the cylinder head assembly into Abaqus, set the explosion pressure and bolt preload that the cylinder head is subjected to during operation, select the contact pairs between the bolts and the cylinder head and the contact pairs between the cylinder head and the engine body to set the contact relationship and use the small slip and small deformation calculation method, select the connection pairs between the bolts and the engine body assembly holes to set the coupling relationship and use the small slip and small deformation calculation method, set the bottom of the engine body as a fixed constraint; select the simulation analysis type as static analysis, associate the Abaqus temperature field calculation results generated by S36 with the predefined temperature field, set the initial iteration step and maximum iteration step of the simulation according to the computing power conditions, submit the simulation calculation and obtain the stress distribution and displacement distribution results of the cylinder head under thermal-mechanical coupling conditions.

7. The method for optimizing cylinder head parameters under thermal-mechanical coupling conditions according to claim 6, characterized in that: The specific implementation method of step 4 is: S41: Build a cylinder head optimization model under thermal-mechanical coupling conditions in Isight, set the total number of samples according to the computing power conditions, and use the Latin hypercube algorithm to plan the sample space for cylinder head optimization under thermal-mechanical coupling conditions, so that the sample points are evenly distributed in the high-dimensional Euclidean space to ensure the quality of sample data; call the script recorded during the cylinder head performance calculation process through batch commands, and use different modules to execute the cylinder head parameterization model update, cylinder head mesh drawing, cylinder head component update in the cylinder head assembly model, cylinder head heat transfer simulation analysis, cylinder head temperature distribution data mapping between different mesh models, cylinder head stiffness simulation analysis, and cylinder head performance index data extraction commands under thermal-mechanical coupling conditions in the cylinder head optimization design process under thermal-mechanical coupling conditions; After the setup is completed, the cylinder head performance optimization model is automatically run to obtain a sample data set that characterizes the corresponding relationship between the cylinder head structure and various performances; S42: Establish a comprehensive evaluation function, comprehensively consider the floating degree and importance of multiple cylinder head performance indicators, and score each sample point. As a preferred embodiment, the comprehensive evaluation function is shown in the following formula: Among them, g j is the comprehensive score of the jth evaluated sample point, λ i is the weight of the i-th evaluated indicator, y ij is the actual value of the i-th evaluated indicator of the j-th evaluated sample point, Z i is the ideal value of the i-th evaluated indicator of the evaluated sample point, σ i is the standard deviation of the i-th evaluated indicator data, and n is the total number of indicators evaluated at the sample point. The weight of the i-th evaluated indicator is calculated using the following formula: C i is the significance coefficient of the ith indicator, C i The larger the value is, the greater the impact of the i-th indicator on the comprehensive evaluation results, and the higher the weight is. i The standard deviation σ i and the correlation coefficient R i The product of is: C i =s i R i (3) Standard deviation i Calculated using the following formula: In the formula, m is the total number of sample points used to calculate the standard deviation, x ij is the dimensionless data of the i-th performance index of the j-th sample point, is the dimensionless data average of the i-th performance indicator. The dimensionless data of the i-th performance indicator of the j-th sample point is dimensionless through the following formula, and the data average is obtained: Correlation coefficient R i Calculated using the following formula: r ik is the linear correlation coefficient between the i-th indicator and the k-th indicator, which can be calculated using the following formula: After calculating all the above variables according to the sample data set, each sample point is scored through the comprehensive evaluation function, and the group of samples with the best scores are selected as the optimization results to obtain the optimal cylinder head structure in the sample space, that is, the cylinder head optimization under the conditions of thermal-mechanical coupling is realized based on the joint simulation technology.

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