A method for optimizing parameters of a cylinder head under a thermal-mechanical coupling condition

Abstract

A kind of cylinder head parameter optimization method under the condition of thermal-mechanical coupling belongs to the field of cylinder head for internal combustion engine.The method of implementation of the present application is: based on the data transmission between multiple modules realizes the quick update of cylinder head model, the quick update of cylinder head assembly body model, the high-quality self-adapting mesh drawing of cylinder head, the automatic simulation analysis of internal steady flow field and temperature field of cylinder head, the automatic mapping of temperature distribution of cylinder head to rigid strength calculation grid model and the simulation analysis of rigid strength of cylinder head under the condition of thermal-mechanical coupling, the comprehensive performance analysis of multiple different structure cylinder heads is realized by repeatedly automatically running the performance calculation process of cylinder head under the condition of thermal-mechanical coupling, the sample data set representing the corresponding relationship between cylinder head structure and various performances of cylinder head under the condition of thermal-mechanical coupling is formed, and the optimal parameter value is selected from it as the optimization result, the performance optimization of cylinder head based on co-simulation technology is realized.The present application can improve the precision and efficiency of cylinder head optimization.

Description

TECHNICAL FIELD

[0001] The application relates to a cylinder head optimization method, in particular to a method for optimizing a cylinder head parameter based on a UG, ICEM, fluent, Hypermesh, Abaqus and Isight software combined technology, which is suitable for optimizing the heat load bearing capacity, rigidity and strength reserve and light weight degree of a cylinder head model under a thermal-mechanical coupling condition and belongs to the fields of energy and power engineering and cylinder heads for internal combustion engines. BACKGROUND

[0002] The cylinder head is one of the key components of a diesel engine, which seals the top of the cylinder and forms a 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 in contact with the high-temperature gas will bear a large thermal load, thereby generating a non-negligible thermal deformation and thermal stress. These thermal effects affect the sealing effect of the cylinder head on one hand, making the cylinder head prone to insufficient airtightness when the design is imperfect; on the other hand, they make the cylinder head bear a larger load on the basis of the original static stress, and put forward higher requirements for the rigidity and strength reserve of the cylinder head. With the continuous development of the design form of the cylinder head towards high power density and light weight, the effect of the thermal 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 advancement of the design form of the cylinder head. Therefore, the modern cylinder head needs to complete the performance calculation and optimization design of the model under the thermal-mechanical coupling condition, and more comprehensively consider the effect of thermal effects in the actual working process of the cylinder head.

[0003] The optimization design process of the cylinder head under the thermal-mechanical coupling condition has become mature, and many related cases can be found, such as the mature thermal-mechanical coupling simulation analysis and optimization technology of the cylinder head [1] (see Zhang Min, Zhang Yi, Zhang Qinxiu. Optimization design of cylinder head structure based on thermal-mechanical coupling [J]. Combination machine tool and automatic machining technology, 2017, (6): 126-129.). In the above-mentioned case, on the basis of the design form of a certain cylinder head basic model, a plurality of tests were designed by using the orthogonal test design method, and then the performance indicators of the models corresponding to each test were manually calculated, and the optimization design of the cylinder head was completed by using the data. However, it can be found that the sizes involved in the above-mentioned case are relatively small, so when the number of levels of the test planning is low, the number of manual calculations is not large. However, with the increasing requirements of the design of the cylinder head, the designer may need to adjust more at the same time, and the total number of tests that need to be manually calculated will also be doubled, thereby generating a large amount of work, which does not match the actual demand of high efficiency and speed in engineering. Therefore, a more efficient optimization method needs to be researched to adapt to the gradually complex optimization calculation problem.

[0004] In the face of increasingly large manual calculation requirements, many designers began to think about how to realize the automation of the performance calculation of the cylinder head. By coincidence, in the face of the increasing automation demand, Isight and other software are used to assist the design in the simple structure optimization cases in many other fields. For example, the prior art [2] (FAN Jiang, ZENG Wei-wei, WANG Rong-qiao, SHEN Xiu-li, CHEN Zhi-ying. Optimization design of turbine blade based on iSIGHT [J]. Journal of Aerospace Power, 2011, Vol. 26 (4): 745-751.) shows an optimization process for the turbine blade, but at present, the design process of this kind is less used in the design of the cylinder head. The design of the cylinder head is different from the design of these simple geometric parts in that: (1) the geometric shape of the cylinder head is relatively complex, and it is difficult to parameterize the modeling and obtain a reasonable parameter variation range; (2) the model generated in the process of the change of the structure parameters of the cylinder head in each round is different, so the finite element mesh of the cylinder head model and the cylinder head cooling flow channel model needs to be redrawn before each round of simulation calculation, and in this process, low-quality meshes are easily generated, which affects the accuracy and convergence of the calculation; (3) in each round of simulation calculation, the boundary conditions and loads applied to the cylinder head need to be re-assigned, and since the cylinder head mesh model used in each round of calculation is always changing, it is difficult to use the classic methods such as mesh number association or geometric voxel association to re-assign the boundary conditions and loads. SUMMARY

[0005] The purpose of the present application is to provide a cylinder head parameter optimization method under thermal-mechanical coupling conditions, which realizes the rapid update of the cylinder head model, the rapid update of the cylinder head assembly model, the high-quality adaptive mesh drawing of the cylinder head, the automatic simulation analysis of the internal steady flow field and temperature field of the cylinder head, the automatic mapping of the temperature distribution of the cylinder head to the mesh model for strength calculation, and the simulation analysis of the strength of the cylinder head under thermal-mechanical coupling conditions, and through the repeated automatic operation of the performance calculation process of the cylinder head under thermal-mechanical coupling conditions, the comprehensive performance analysis of various structures of the cylinder head is realized, the sample data set representing the corresponding relationship between the structure of the cylinder head and the performance of the cylinder head under thermal-mechanical coupling conditions is formed, and the optimal parameter value is selected as the optimization result, realizing the performance optimization of the cylinder head based on the joint simulation technology. The present application can solve the problem of the need for a large amount of manual operation in the traditional cylinder head optimization method, and through the selection of a mesh data mapping method with high automation degree and high data transmission accuracy, the thermal-mechanical coupling simulation environment of the cylinder head is built, and the accuracy and efficiency of the optimization of the cylinder head are improved.

[0006] The purpose of the present application is realized by the following technical solutions:

[0007] The application discloses a cylinder head parameter optimization method under thermal-mechanical coupling conditions, which is characterized by the following steps:

[0008] The application discloses a cylinder head parameter optimization method under thermal-mechanical coupling conditions, which is characterized by the following steps:

[0009] Step one: parameterized modeling of the cylinder head to obtain a parameterized model of the cylinder head. Obtain the cooling channel model of the cylinder head through Boolean operation, and associate the parameterized model of the cylinder head with each same parameter of the cooling channel model of the cylinder head. Determine the initial value and upper and lower boundary value of each parameter of the parameterized model of the cylinder head, and gradually modify the parameterized model of the cylinder head in a manner of "combination of global parameter variation and error reporting features" until the cylinder head model meets the predetermined stability qualification requirements. Classify the surfaces of the parameterized model of the cylinder head and the cooling channel model of the cylinder head that need to be assigned different boundary conditions, and save the parameterized model of the cylinder head and the cooling channel model of the cylinder head in the form of surface features. Through calling the API function of UG software, one-key automatic updating of the parameterized model of the cylinder head and the cooling channel model of the cylinder head is realized, and the updating efficiency of the parameterized model of the cylinder head and the cooling channel model of the cylinder head is improved.

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

[0011] S11: Select UG as a modeling platform to perform parameterized modeling of the cylinder head. Use the modeling method of stretching or rotating to establish the external features of the cylinder head, including the top plate, the bottom plate, and the side wall. Use the modeling method of projection curve to draw the characteristic lines on the wall surfaces of the intake and exhaust ports of the cylinder head, use the modeling method of fitting surface to connect the closed projection curves to generate the surface features of the intake and exhaust port walls, stitch the surface features that constitute the intake and exhaust ports to form an entity, and subtract the external features of the cylinder head from the intake and exhaust port entities through Boolean operation to obtain the cylinder head model with completed port modeling. Use the modeling methods of stretching, rotating, punching, or rounding to establish the assembly features of the cylinder head on the cylinder head model with completed port modeling, including the fastening thread holes, the intake and exhaust pipe assembly holes, the inlet and outlet water port assembly holes, the oil injection nozzle assembly holes, and the positioning pin holes. Use the modeling method of stretching to draw the inlet and outlet water ports of the flow channel on the cylinder head model with completed port modeling. From the inlet water port, use the modeling methods of stretching, rotating, and stitching surface to draw the flow channel geometry of the cylinder head at positions where the wall thickness is greater than the minimum wall thickness requirement of the process on the cylinder head model, until the flow channel geometry is connected to the inlet and outlet water ports and is arranged at positions where the wall thickness is greater than the minimum wall thickness requirement of the process. The flow channel geometry needs to strictly meet the minimum wall thickness requirement of the machining process when the size is set. Use Boolean operation to sum all the flow channel geometries to obtain the flow channel entity of the cylinder head model, and then subtract the cylinder head model with completed port modeling from the flow channel entity of the cylinder head model through Boolean operation to obtain the cylinder head model with completed port and flow channel modeling. After the external features, the ports, the assembly features, and the flow channel of the cylinder head are all modeled, use the modeling methods of stretching, rotating, and stitching surface to establish the weight-reducing geometries at positions on the top plate, the bottom plate, and the side wall of the cylinder head that are not involved in 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 operation to subtract all the weight-reducing geometries from the cylinder head with completed assembly feature modeling to obtain the cylinder head model with completed parameterized modeling.

[0012] S12: Obtain the cooling flow channel model of the cylinder head by Boolean operation. Delete the weight reduction features on the parameterized model of the cylinder head, and save the model as copy 1; delete the weight reduction features and the flow channel features on the parameterized model of the cylinder head, and save the model as copy 2. Subtract the copy 1 model from the copy 2 model by Boolean operation to obtain the cooling flow channel model of the cylinder head. In the expression of the cooling flow channel model of the cylinder head, associate the parameters of the same meaning in the copy 1 and the copy 2, including the parameters for controlling the external features and the parameters for controlling the flow channel features, so that the parameters of the same meaning in the two expressions always remain equal in the process of model updating. After the same parameter association, the cooling flow channel model of the cylinder head will update the external features and the flow channel features of the copy 1 and the copy 2 synchronously when updating the parameters, ensuring that the entity obtained after each update of the cooling flow channel model of the cylinder head is only the flow channel part of the cylinder head.

[0013] S13: Set the initial values and boundary values of the structural parameters on the parameterized model of the cylinder head and the cooling flow channel model of the cylinder head. Set one of the boundary values of the parameterized model of the cylinder head to the limit parameter when the wall thickness of the cylinder head at each position is the minimum wall thickness required by the process, and set the other to the other limit size that meets the design requirements of the cylinder head, including that the hydraulic diameter at each position of the flow channel should not be smaller than the limit size that causes flow obstruction, the narrowest part of the surface of the cylinder head should not be smaller than one-third of the minimum wall thickness required by the process, and there should be no interference between the flow channel, the air channel, the assembly feature, the weight reduction feature and the external wall surface of the cylinder head. Some sizes of the cylinder head are the reference sizes set when the parameterized model of the cylinder head is modeled. Set the initial value of the reference size parameter to the initial value used when the parameterized model of the cylinder head is modeled, and then set the boundary value of the reference size to be equal to the reference value, so that these sizes do not change when the parameterized model of the cylinder head is updated. After determining the upper and lower boundary values of the parameters other than the reference size, set the initial values of the parameters other than the reference size to the median of the upper and lower boundary values, to reduce the probability of error when the parameterized model of the cylinder head is updated.

[0014] S14: The parameterized model of the cylinder head is gradually modified by using the method of "combination of global parameter variation and error modification features". When the parameterized model of the cylinder head is updated by substituting the parameter values selected within the parameter variation range obtained in S13 into the expression, and the model update does not cause an error after a predetermined number of times, it is determined that the stability of the parameterized model of the cylinder head meets the conditions required for optimization. The purpose of this step S14 is to repeatedly test whether the parameterized model of the cylinder head causes an error under different parameter values, and to modify the error features to gradually improve the parameterized model of the cylinder head. All parameters in the expression of the parameterized model of the cylinder head except the reference dimensions are named, the data interface between Excel and UG is configured, and the parameter names and their corresponding parameter variation ranges are imported into the Excel table. A random number formula is inserted to randomly select a parameter value within the variation range for all parameters except the reference dimensions. Then, all random parameter values generated by the random number formula are selected as the data source for the parameterized model of the cylinder head together with the names of all parameters except the reference dimensions. The UG model is updated multiple times using the Excel table to test the parameter stability of the parameterized model of the cylinder head under random parameter values. When the parameterized model of the cylinder head does not cause an error after a predetermined number of model updates using random parameter values in succession, it is determined that the parameter stability of the parameterized model of the cylinder head is 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 parameterized model of the cylinder head does not cause an error after a predetermined number of model updates using random parameter values in succession.

[0015] S15: The surfaces of the parameterized model of the cylinder head and the cylinder head cooling flow passage model that need to be assigned different boundary conditions are classified, and the parameterized model of the cylinder head and the cylinder head cooling flow passage model are saved in the form of surface features. When performing automatic calculation of the temperature field distribution of the cylinder head, boundary conditions can only be automatically assigned to surface features. The surfaces of the parameterized model of the cylinder head and the cylinder head cooling flow passage model are extracted into multiple surface features based on the type of boundary condition region, which can automatically identify the boundary condition region in the solver. Based on the heat transfer analysis method of the cylinder head, the surfaces of the parameterized model of the cylinder head and the cylinder head cooling flow passage model are classified, and the surface categories include water inlet, water outlet, flow passage wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface, and fire surface. By using the modeling method of extracting geometric features, these surfaces are extracted into surface features according to the category on the parameterized model of the cylinder head and the cylinder head cooling flow passage model. The original solid models in the parameterized model of the cylinder head and the cylinder head cooling flow passage model are hidden, and the parameterized model of the cylinder head and the cylinder head cooling flow passage model in the form of surface features are obtained and saved separately. All surface features are set to be associated with the hidden cylinder head and cylinder head cooling flow passage solid.

[0016] S16: The automatic update of the cylinder cover model is realized by calling the API function of UG. The API function of UG is called to realize the functions of reading the parameterized model path of the cylinder cover and the cooling flow channel model path of the cylinder cover, reading the expression path of the parameterized model of the cylinder cover, automatically updating the parameterized model of the cylinder cover and the cooling flow channel model of the cylinder cover by using the expression parameter value, and saving the new parameter value corresponding to the parameterized model of the cylinder cover and the cooling flow channel model of the cylinder cover, so as to realize the one-key automatic update of the parameterized model of the cylinder cover and the cooling flow channel model of the cylinder cover.

[0017] Step two: The minimum wall thickness requirement size of the process is taken as the initial grid size, and the cylinder cover body combined grid model for flow field and temperature field calculation is drawn. Based on the heat transfer analysis method of the cylinder cover, the simulation is set, and the steady-state flow field and temperature field simulation analysis of the cylinder cover is carried out, so as to obtain the temperature distribution of each position on the cylinder cover. The minimum wall thickness requirement size of the process is taken as the initial grid size, and the 3D grid model of the cylinder cover for calculating the carrying capacity under the condition of thermal-mechanical coupling is divided. The 3D grid model of the cylinder cover and each part related to the service state of the cylinder cover are assembled, the structured grid of each part related to the service state of the cylinder cover is drawn, and the grid surface of the 3D grid model of the cylinder cover and each part related to the service state of the cylinder cover is selected as the main surface and the slave surface of the boundary condition to be applied in the rigid strength analysis of the cylinder cover, so as to establish the grid model of the cylinder cover assembly. The temperature field distribution is interpolated into the stress field grid, so as to realize the mapping of the temperature distribution data of the cylinder cover from the cylinder cover combined grid model for flow field and temperature field calculation to the 3D grid model of the cylinder cover for calculating the carrying capacity under the condition of thermal-mechanical coupling. The grid independence analysis of the performance calculation of the cylinder cover under the condition of thermal-mechanical coupling is carried out, and a grid size with short calculation time and stress and displacement calculation results deviating less than a preset threshold from the calculation results under other grid sizes is selected as the finite element grid size used in optimization, wherein the short calculation time refers to the calculation time shorter than the preset threshold.

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

[0019] S21: draw a cylinder head combined grid model for flow field and temperature field calculation. Grid drawing is performed with the process minimum wall thickness requirement size as the initial grid size to ensure the grid 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 grid size is set to the process minimum wall thickness requirement size, and the Patch Independent grid division method is used for face grid division to avoid grid drawing failure caused by geometric distortion at some positions, including the existence of broken surfaces, narrow surfaces with a width less than the process minimum wall thickness requirement, or the included angle between two surfaces less than 15°. Combining the grid models of the cylinder head and the cylinder head cooling channel before calculation can realize 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 face grid models of the cylinder head and the cylinder head cooling channel are imported into ICEM in sequence, and the combined face grid model of the cylinder head is obtained after combining the two grids. The quality of the face grid automatically drawn by ICEM is not high, and if the body grid is directly drawn in ICEM and used for calculation, the calculation cannot converge. Importing the combined cylinder head face grid model into fluent meshing to repair the grid problem and divide the body grid can solve this problem and ensure the grid quality of the body grid model. In ICEM, the grid regions in the combined cylinder head face grid model are named according to the water inlet, water outlet, channel wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface, and fire surface. The combined cylinder head face grid model is imported into fluent meshing, and the three problems of free edge, self-intersection, and repeated grid are corrected, and the grid distortion degree is reduced to below the preset distortion degree. Based on the combined cylinder head face grid model, the body grid model is drawn, and the low-quality grid is repaired based on the grid node movement algorithm, and the inverse orthogonal quality is reduced to below the preset inverse orthogonal quality. The cylinder head combined grid model for flow field and temperature field calculation is output.

[0020] S22: Based on the heat transfer analysis method of the cylinder head, simulation is set up, and steady-state flow field and temperature field simulation analysis of the internal cylinder head is carried out to obtain the temperature distribution of each position on the cylinder head. The body grid model of the cylinder head is imported into fluent, and the scale of simulation analysis, the calculation method used for flow field calculation and the material properties of the cooling liquid in the cylinder head and the flow channel are set. The surface types of each surface on the cylinder head body grid model are set, including the water inlet, water outlet, flow channel wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface and fire surface, and the surface types include inlet surface, outlet surface, wall surface and interface. The surface types of the fluid-structure coupling surfaces of the cylinder head and the cylinder head cooling flow channel grid model are set to the interface, and the two fluid-structure coupling surfaces are set to the coupling relationship, so as to solve the problem that the grids on the fluid-structure coupling surfaces of the cylinder head and the cylinder head cooling flow channel grid model are not shared nodes. The convective heat transfer coefficient of each surface and the initial temperature of the wall surface are set. The calculation process is set to monitor, stop condition and initialized, and the simulation is submitted to obtain the temperature field simulation result of the cylinder head.

[0021] S23: Draw the 3D grid model of the cylinder head for calculating the carrying capacity under the condition of thermal-mechanical coupling. The minimum wall thickness required size is used as the initial grid size for grid drawing, the parameterized model of the cylinder head is imported into Hypermesh, the grid size is set to the minimum wall thickness required size, and the surface deviation grid division method is used for 2D grid division. Based on the QI optimization grid repair algorithm and the size corrected grid repair algorithm, the grid quality unqualified grid is repaired, and the grid that is difficult to adjust by the grid repair algorithm is modified to the grid quality qualified by using the place node method, and the high-quality 2D grid model of the cylinder head is obtained. The grid size is set to the minimum wall thickness required size, the tetramesh grid division method is used to draw the 3D grid, and the 3D grid model of the cylinder head for calculating the carrying capacity under the condition of thermal-mechanical coupling is obtained.

[0022] S24: A mesh model of the cylinder head assembly is established. The 3D mesh model of the cylinder head for calculating the load capacity under thermal-mechanical coupling conditions is imported into Hypermesh, each component related to the service state of the cylinder head is imported, and each component related to the service state of the cylinder head is assembled with the 3D mesh model of the cylinder head for calculating the load capacity under thermal-mechanical coupling conditions according to the engine assembly requirements, the components include the engine block, the bushing, the gasket, and the fastening bolt. The 2D structured mesh division is performed on each component related to the service state of the cylinder head using the automesh method, and the 3D structured mesh division is performed on each component related to the service state of the cylinder head using the solid map method, thereby obtaining the 3D mesh model of each component related to the service state of the cylinder head. Based on the cylinder head stiffness and strength analysis method, the mesh surfaces are selected as the master surfaces and slave surfaces of the boundary conditions to be applied during the cylinder head stiffness and strength analysis on the 3D mesh model of the cylinder head for calculating the load capacity under thermal-mechanical coupling conditions and the 3D mesh model of each component related to the service state of the cylinder head, the master surfaces and slave surfaces include the contact relationship master and slave surfaces of the bolt and the cylinder head, the connection relationship master and slave surfaces of the bolt and the assembly hole of the block, the contact relationship master and slave surfaces of the cylinder head and the block, and the action surfaces of the combustion chamber explosion pressure. The material properties are set for the 3D mesh model of the cylinder head and the 3D mesh model of each component related to the service state of the cylinder head, and saved, thereby obtaining the mesh model of the cylinder head assembly.

[0023] S25: The temperature field distribution is interpolated into the stress field mesh, then the obtained data file is format processed and imported into Abaqus, thereby realizing the mapping of the cylinder head temperature distribution data from the combined mesh model of the cylinder head for flow field and temperature field calculation to the 3D mesh model of the cylinder head for calculating the load capacity under thermal-mechanical coupling conditions. The cylinder head mesh model is extracted from the mesh model of the cylinder head assembly, so that the grid number on the cylinder head mesh model after the temperature field data is mapped to the cylinder head mesh model is still uniform with the grid number in the cylinder head assembly. The cylinder head temperature field simulation result obtained in S22 is imported into the extracted cylinder head mesh model based on the grid data automatic mapping algorithm in fluent, thereby obtaining the temperature distribution data of the cylinder head corresponding to the grid node arrangement form of the cylinder head mesh model. The temperature distribution data is modified so that it can be recognized by the solver of Abaqus, the modified temperature distribution data is imported into Abaqus, so that the temperature field calculation result which can be imported when setting the calculation task in Abaqus is generated.

[0024] S26: Based on the simulation of the cylinder head stiffness and strength analysis method, the load carrying performance analysis under thermal-mechanical coupling conditions is performed to obtain the thermal-mechanical coupling stress and thermal-mechanical coupling deformation distribution of each position on the cylinder head. The mesh model of the cylinder head assembly is imported into Abaqus, the size of the blast pressure and bolt pretightening force borne by the cylinder head during operation is set, the contact relationship of the bolt and the cylinder head contact pair and the cylinder head and the engine block contact pair is set and the small slip small deformation calculation method is selected, the coupling relationship of the bolt and the engine block assembly hole connection pair is set and the small slip small deformation calculation method is selected, and the bottom of the engine block is set as a fixed constraint. The simulation analysis type is selected as static analysis, the Abaqus temperature field calculation result generated in association with S25 is pre-defined, the simulation initial iteration step and the maximum iteration step are set according to the calculation power condition, the simulation calculation is submitted and the stress distribution and displacement distribution results of the cylinder head under service condition are obtained.

[0025] S27: Perform grid independence analysis of the cylinder head performance calculation under thermal-mechanical coupling conditions. Start from the initial value of the grid size required by the minimum wall thickness of the process, expand or reduce the grid size used when drawing the cylinder head assembly grid model and the cylinder head 3D grid model, respectively calculate the temperature field simulation results and the load carrying capacity simulation results of the cylinder head under thermal-mechanical coupling conditions, compare the influence of different grid sizes on the calculation time and the highest temperature, thermal-mechanical coupling stress, thermal-mechanical coupling deformation calculation results, select a grid size with short calculation time and calculation results deviating from other grid sizes less than a preset threshold as the finite element grid size used for optimization, complete the grid independence analysis, and the short calculation time means that the calculation time is shorter than the preset threshold.

[0026] Step three: Adjust the structure parameters of the cylinder head model to generate a cylinder head model with different parameters from the initial value. Record the script for the cylinder head body assembly grid model drawing link used for flow field and temperature field calculation in ICEM and fluent meshing. Record the script for the cylinder head heat transfer performance calculation link in fluent, and extract the index data that can represent the heat transfer performance of the cylinder head and the mass of the cylinder head. Record the script for drawing the 3D grid model of the cylinder head used for calculating the load carrying capacity under thermal-mechanical coupling conditions and the script for updating the grid model of the cylinder head in the cylinder head assembly model in Hypermesh. Record the script for the temperature distribution data mapping link of the cylinder head in Hypermesh and fluent, and use the batch processing command to realize the automatic modification of the temperature distribution data, so that it can be recognized by the solver of Abaqus to generate the temperature field calculation result. Record the script for the cylinder head stiffness and strength calculation link in Abaqus and extract the index data that can represent the load carrying performance of the cylinder head under thermal-mechanical coupling conditions.

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

[0028] S31: Adjust the structure parameters of the cylinder head model, perform automatic updating of the cylinder head model and the cylinder head cooling flow channel model, and generate a cylinder head model with different parameters and initial values. Modify all parameters in the expression of the parameterized model of the cylinder head, except for the reference size, call the API function of UG, and read the expression of the parameterized model of the cylinder head to perform one-key automatic updating of the cylinder head model and the cylinder head cooling flow channel model.

[0029] S32: Record the script for the drawing link of the combined grid model of the cylinder head body for flow field and temperature field calculation. Take the grid size determined after grid independence analysis as the reference, start script recording in ICEM, divide the surface grid model of the cylinder head and the cylinder head cooling flow channel using the PatchIndependent grid division method respectively, save the surface grid model of the cylinder head and the cylinder head cooling flow channel, and obtain the script for the surface grid division link. Start script recording again in ICEM, import the surface grid model of the cylinder head and the cylinder head cooling flow channel in sequence, combine the two grids, and name the grid regions in the surface grid model of the cylinder head according to the water inlet, water outlet, flow channel wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface, and fire surface. Obtain the combined surface grid model of the cylinder head and the script for the grid combining link. Start script recording in fluent meshing, import the combined surface grid model of the cylinder head, correct the three problems of free edge, self-intersection, and repeated grid, reduce the grid twist degree to below the preset twist degree, draw the volume grid model of the cylinder head, repair low-quality grids based on the grid node movement algorithm, and reduce the inverse orthogonal quality to below the preset inverse orthogonal quality. Output the combined grid model of the cylinder head for flow field and temperature field calculation, and obtain the script for the volume grid division link.

[0030] S33: Record the script of the cylinder head heat transfer performance calculation link. Start script recording in fluent, import the body grid model of the cylinder head, set the scale of simulation analysis, the calculation method used for flow field calculation and the material properties of the cooling liquid in the cylinder head and flow channel. Set the surface type of each surface on the cylinder head body grid model, including the water inlet, water outlet, flow channel wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface and fire surface, the surface type includes inlet surface, outlet surface, wall surface and interface. Set the fluid-structure coupling surface type of each of the cylinder head and the cylinder head cooling flow channel grid model to the interface, and set the two fluid-structure coupling surfaces to the coupling relationship. Set the convective heat transfer coefficient of the various surfaces and the initial temperature of the wall surface. Set the monitoring, shutdown condition and initialize the simulation, submit the simulation calculation to obtain the temperature field simulation result of the cylinder head. Extract the index data representing the heat transfer performance of the cylinder head and the mass of the cylinder head, including the average convective heat transfer coefficient of the surface, the average pressure of the surface, the average y+ value of the surface, the minimum y+ value of the surface, the maximum y+ value of the surface, the average water cavity temperature, the average cylinder head temperature, the average velocity, the total mass of the cylinder head, the maximum temperature of the cylinder head, the maximum temperature in the water cavity, the maximum velocity in the water cavity, the minimum temperature in the water cavity and the size of the water cavity. Output the temperature field simulation result of the cylinder head and obtain the script of the cylinder head heat transfer performance calculation link.

[0031] S34: Record the script of the cylinder head 3D grid model drawing link for calculating the carrying capacity under thermal-mechanical coupling conditions. Based on the grid size determined after grid independence analysis, start script recording in Hypermesh, edit the grid quality evaluation standard, cancel the detection of the maximum grid size and the minimum grid size by the algorithm, and improve the repair rate of low-quality grids. Use the surface deviation grid division method to divide the 2D grid, repair the grid with unqualified grid quality based on the QI optimization grid repair algorithm and the size corrected grid repair algorithm, and use the place node method to modify the grid that is difficult to adjust by the grid repair algorithm to the grid with qualified grid quality, to obtain the high-quality 2D grid model of the cylinder head. Use the tetramesh grid division method to draw 3D grid to obtain the 3D grid model of the cylinder head. Complete the drawing of the 3D grid model of the cylinder head for calculating the carrying capacity under thermal-mechanical coupling conditions and obtain the script of the cylinder head 3D grid model drawing link.

[0032] S35: Record the script of the cylinder head mesh model updating link 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 3D mesh model of the cylinder head with updated structure shape based on the mesh model replacement algorithm, export the new cylinder head assembly mesh model and obtain the script of the cylinder head mesh model updating link.

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

[0034] S37: Record the script of the cylinder head stiffness and strength calculation link. Start script recording in Abaqus, import the mesh model of the cylinder head assembly into Abaqus, set the size of the explosion pressure and bolt pretightening force that the cylinder head bears during operation, set the contact relationship of the bolt and the cylinder head contact pair and the cylinder head and the engine block contact pair using small slip and small deformation calculation method, set the coupling relationship of the bolt and the engine block assembly hole connection pair using small slip and small deformation calculation method, and set the bottom of the engine block as a fixed constraint. Select the simulation analysis type as static analysis, associate the Abaqus temperature field calculation results generated in S36 in the pre-defined temperature field, set the initial iteration step and the maximum iteration step according to the calculation condition, submit the simulation calculation and obtain the stress distribution and displacement distribution results of the cylinder head under thermal-mechanical coupling conditions.

[0035] Step four: build a cylinder head optimization model under the condition of thermal-mechanical coupling based on co-simulation technology, use Latin hypercube algorithm to plan the sample space of cylinder head optimization under the condition of thermal-mechanical coupling, call the script recorded in the process of cylinder head performance calculation through batch command, automatically run the cylinder head parameterized model updating, cylinder head mesh drawing, cylinder head component updating in cylinder head assembly model, cylinder head heat transfer simulation analysis, cylinder head temperature distribution data mapping between different grid models, cylinder head stiffness and strength simulation analysis and cylinder head performance index data extraction in the process of cylinder head optimization design under the condition of thermal-mechanical coupling, and obtain the sample data set representing the corresponding relationship between cylinder head structure and performance.

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

[0037] S41: build a cylinder head optimization model under the condition of thermal-mechanical coupling in Isight, set the total number of samples according to the computing power condition, use Latin hypercube algorithm to plan the sample space of cylinder head optimization under the condition of thermal-mechanical coupling, make the sample points uniformly distributed in high-dimensional Euclidean space, and ensure the quality of sample data. Call the script recorded in the process of cylinder head performance calculation through batch command, and use different modules to execute the commands of cylinder head parameterized model updating, cylinder head mesh drawing, cylinder head component updating in cylinder head assembly model, cylinder head heat transfer simulation analysis, cylinder head temperature distribution data mapping between different grid models, cylinder head stiffness and strength simulation analysis and cylinder head performance index data extraction in the process of cylinder head optimization design under the condition of thermal-mechanical coupling. After setting, automatically run the cylinder head performance optimization model, and obtain the sample data set representing the corresponding relationship between cylinder head structure and performance.

[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 an optimization, the comprehensive evaluation function is as follows:

[0039]

[0040] Wherein, g j is the comprehensive score of the jth evaluated sample point, λ i is the weight of the ith evaluated index, y ij is the actual value of the ith evaluated index of the jth evaluated sample point, Z i is the ideal value of the ith evaluated index of the evaluated sample point, σ iis the standard deviation of the i-th evaluated index data, and n is the total number of the evaluated indexes of the sample points.

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

[0042]

[0043] C i is the significance coefficient of the i-th index, C i is larger, the greater the influence of the i-th index on the comprehensive evaluation result, and the weight is naturally higher. The significance coefficient C i can be expressed as the product of the standard deviation σ i and the correlation coefficient R i , that is:

[0044] C i = σ i R i (3)

[0045] The standard deviation σ i is calculated by 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 i-th performance index dimensionless data of the j-th sample point, is the average value of the i-th performance index dimensionless data. The i-th performance index dimensionless data of the j-th sample point can be dimensionless by the following formula, and the average value of the data is obtained:

[0048]

[0049] The correlation coefficient R i can be calculated by the following formula:

[0050]

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

[0052]

[0053] After calculating all the variables above according to the sample data set, score each sample point by the comprehensive evaluation function, select the sample with the best score as the optimization result, and obtain the optimal cylinder head structure in the sample space, that is, realize the optimization of the cylinder head under the condition of thermal-mechanical coupling based on the joint simulation technology.

[0054] Further comprising step five, process adaptability design is carried out according to the optimal cylinder cover structure obtained in step four, and a cylinder cover design scheme meeting production constraints is obtained. The cylinder cover processed and manufactured through the cylinder cover design scheme can improve heat transfer and heat exchange performance, reduce the highest temperature of the fire surface, reduce thermal-coupling machine deformation and stress, and improve service life compared with the cylinder cover before optimization. The weight of the optimized cylinder cover is lighter than that of the cylinder cover before optimization, and the high power density of the engine can be improved.

[0055] Advantages:

[0056] 1. The cylinder cover parameter optimization method under the thermal-mechanical coupling condition disclosed in the application uses a parameterized modeling method to build a parameterized model of the cylinder cover, and then uses a Boolean operation method to obtain a cooling flow channel model of the cylinder cover, so as to directly control the structure and shape of the cylinder cover and the cooling flow channel of the cylinder cover through the expression of the parameterized model of the cylinder cover, improve the efficiency of modifying and updating the cylinder cover model and the cooling flow channel model of the cylinder cover.

[0057] 2. The cylinder cover parameter optimization method under the thermal-mechanical coupling condition disclosed in the application determines the initial value and upper and lower boundary value of each parameter of the parameterized model of the cylinder cover, and gradually modifies the parameterized model of the cylinder cover in a manner of "combination of global parameter variation and modification error characteristics", so as to ensure that the cylinder cover model has sufficient stability, and realize the effect that the parameterized model of the cylinder cover and the cooling flow channel model of the cylinder cover are stably updated when the expression of the parameterized model of the cylinder cover takes any value within the parameter variation range.

[0058] 3. The cylinder cover parameter optimization method under the thermal-mechanical coupling condition disclosed in the application realizes one-key automatic updating of the parameterized model of the cylinder cover and the cooling flow channel model of the cylinder cover by calling the API function of the UG software, omits the step of opening the UG graphical window and then modifying the parameterized model of the cylinder cover and the cooling flow channel model of the cylinder cover, improves the updating efficiency of the parameterized model of the cylinder cover and the cooling flow channel model of the cylinder cover, and meets the necessary condition for automatically performing the heat transfer calculation process of the cylinder cover.

[0059] 4. The cylinder cover parameter optimization method under the thermal-mechanical coupling condition disclosed in the application performs surface mesh division on the cylinder cover and the cooling flow channel of the cylinder cover respectively, merges the surface mesh models of the cylinder cover and the cooling flow channel of the cylinder cover, and draws a cylinder cover body mesh model, and then correlates the coupling surfaces of the cylinder cover and the cooling flow channel of the cylinder cover in the cylinder cover body mesh model, so as to realize successful calculation of the coupling surfaces of the cylinder cover and the cooling flow channel of the cylinder cover under the premise that the meshes are not common nodes, improve the success rate of the cylinder cover parameter optimization under the thermal-mechanical coupling condition, and further improve the optimization efficiency.

[0060] 5. The method for optimizing the parameters of a cylinder head under thermal-mechanical coupling conditions, which is characterized in that the grid model replacement algorithm is used to replace the cylinder head component in the grid model of the cylinder head assembly with the 3D grid model of the cylinder head with updated structure shape, so that the grid model of the cylinder head assembly can be quickly updated, the problem that the grid model of the cylinder head assembly cannot be automatically updated during the simulation analysis of the cylinder head can be solved, and the optimization efficiency is significantly improved.

[0061] 6. The method for optimizing the parameters of a cylinder head under thermal-mechanical coupling conditions, which is characterized in that the grid data automatic mapping algorithm is used to extract the temperature distribution data of the cylinder head from the grid combination model of the cylinder head body and interpolate the temperature distribution data into the 3D grid model of the cylinder head, so that the most suitable grid model can be used in different simulation calculation links, the data synchronization of the calculation results of the temperature distribution of the cylinder head among different grid models is realized, the key problem that the multi-field coupling data transmission is difficult in the thermal-mechanical coupling of the cylinder head can be solved, and the data transmission efficiency is improved.

[0062] 7. The method for optimizing the parameters of a cylinder head under thermal-mechanical coupling conditions, which is characterized in that the scripts of the mesh division link and the mesh merging link of the cylinder head and the cooling flow channel surface grid model are recorded in ICEM, the script of the grid division link of the cylinder head body is recorded in fluentmeshing, and the scripts of the heat transfer performance calculation link and the index data extraction link of the heat transfer performance of the cylinder head are recorded in fluent, so that the accurate reproduction and automatic operation of the finite element grid division work and the simulation analysis setting work in the heat transfer performance calculation process of the cylinder head are realized, and the optimization efficiency of each heat transfer performance of the cylinder head is improved.

[0063] 6. The method for optimizing the parameters of a cylinder head under thermal-mechanical coupling conditions, which is characterized in that the scripts of the grid drawing link and the automatic updating link of the cylinder head component in the cylinder head assembly model are recorded in Hypermesh, and the script of the stiffness calculation link of the cylinder head is recorded in Abaqus and the performance index data capable of representing the stiffness of the cylinder head are extracted, so that the accurate reproduction and automatic operation of the finite element grid division work and the simulation analysis setting work in the load bearing performance calculation process of the cylinder head under thermal-mechanical coupling conditions are realized, and the optimization efficiency of the load bearing performance of the cylinder head under thermal-mechanical coupling conditions is improved.

[0064] 8. The method for optimizing the parameters of a cylinder head under thermal-mechanical coupling conditions, which is characterized in that the preliminary trial calculation of each performance of the cylinder head under the grid size with the minimum wall thickness requirement of the process is completed, the grid independence analysis of the calculation of each performance of the cylinder head under thermal-mechanical coupling conditions is performed, a grid size with short calculation time and small deviation from the calculation results under other grid sizes is selected as the finite element grid size used in optimization, the accuracy of the optimization results of the cylinder head is ensured, and the time cost of the optimization of the cylinder head is significantly saved.

[0065] 9. The method for optimizing the parameters of a cylinder head under thermal-mechanical coupling conditions, which is characterized in that: a performance optimization model of the cylinder head under thermal-mechanical coupling conditions is built based on joint simulation technology; a Latin hypercube algorithm is used to plan the sample space of the cylinder head optimization; and the total number of samples can be set according to the computing power condition to design the test.

[0066] 10. The method for optimizing the parameters of a cylinder head under thermal-mechanical coupling conditions, which is characterized in that: a performance optimization model of the cylinder head under thermal-mechanical coupling conditions is built based on joint simulation technology; scripts recorded during the calculation of the performance of the cylinder head are called through a batch processing command; and the following operations are automatically performed during the design of the test of the optimization of the cylinder head under thermal-mechanical coupling conditions: the updating of the parameterized model of the cylinder head, the drawing of the mesh of the cylinder head, the updating of the cylinder head components in the assembly model of the cylinder head, the simulation analysis of the heat transfer of the cylinder head, the mapping of the temperature distribution data of the cylinder head between different mesh models, the simulation analysis of the stiffness and strength of the cylinder head, and the extraction of the performance index data of the cylinder head under thermal-mechanical coupling conditions; the corresponding performance of the cylinder head of the sample points in the sample space is automatically calculated, and the efficiency of the optimization of the cylinder head is improved. During the calculation, the model automatically filters and removes the sample points with non-convergent calculation and substandard mesh quality, so as to ensure the quality of the sample data set.

[0067] 11. The method for optimizing the parameters of a cylinder head under thermal-mechanical coupling conditions, which is characterized in that: a comprehensive evaluation function is established; the comprehensive performance of each sample point is scored by considering multiple performance indicators of the cylinder head; the comprehensive evaluation of the performance of the cylinder head is realized; the optimization result has the maximum improvement in the comprehensive performance; and each performance indicator can be kept balanced. The cylinder head processed by 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 DRAWINGS

[0068] Figure 1 It is a flowchart of the method for optimizing the parameters of a cylinder head under thermal-mechanical coupling conditions.

[0069] Figure 2 It is a parameterized model of a surface feature type cylinder head and a cooling flow channel model of the cylinder head respectively established by using the optimization method. Figure 2 (a) is the parameterized model of the surface feature type cylinder head, Figure 2 (b) is the cooling flow channel model of the surface feature type cylinder head.

[0070] Figure 3is the cylinder head assembly grid model combined after all components are assembled and meshed, which is used for flow field and temperature field calculation and 3D grid model for calculating load capacity under thermal-mechanical coupling condition, wherein: Figure 3 (a) is the cylinder head assembly grid model for flow field and temperature field calculation, Figure 3 (b) is the cylinder head 3D grid model for calculating load capacity under thermal-mechanical coupling condition;

[0071] Figure 4 is the cylinder head assembly grid model combined after all components are assembled and meshed, which is used for flow field and temperature field calculation and 3D grid model for calculating load capacity under thermal-mechanical coupling condition, wherein:

[0072] Figure 5 is the cylinder head various simulation result cloud map calculated using 5mm grid size after the best grid size of 5mm is obtained by carrying out grid independence analysis on the embodiment one, wherein: Figure 5 (a) is the cylinder head temperature field distribution result, Figure 5 (b) is the cylinder head thermal-mechanical coupling stress distribution result, Figure 5 (c) is the cylinder head thermal-mechanical coupling deformation distribution result;

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

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

[0075] The content of the application will be further described below in combination with the drawings and embodiments.

[0076] Embodiment 1:

[0077] As shown in Figure 1 , the embodiment discloses a parameter optimization method of a cylinder head under thermal-mechanical coupling condition, and the specific implementation steps are as follows:

[0078] Step one: parameterized modeling of the cylinder head is performed to obtain a parameterized model of the cylinder head. A cooling channel model of the cylinder head is obtained through Boolean operation, and each identical parameter of the parameterized model of the cylinder head and the cooling channel model of the cylinder head is associated. Initial values and upper and lower boundary values of each parameter of the parameterized model of the cylinder head are determined, and the parameterized model of the cylinder head is gradually modified in a manner of “combination of global parameter variation and modification error features” until the cylinder head model meets the preset stability qualification requirements. The surfaces of the parameterized model of the cylinder head and the cooling channel model of the cylinder head that need to be assigned different boundary conditions are classified, and the parameterized model of the cylinder head and the cooling channel model of the cylinder head are saved in the form of surface features. Through calling of an API function of UG software, one-key automatic updating of the parameterized model of the cylinder head and the cooling channel model of the cylinder head is realized, and the updating efficiency of the parameterized model of the cylinder head and the cooling channel model of the cylinder head is improved.

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

[0080] Step 1.1: the top plate, bottom plate and side wall of the cylinder head are established in UG using the modeling method of stretching or rotating. The characteristic lines on the wall surfaces of the intake and exhaust ports of the cylinder head are drawn using a projection curve, and the surface features of the intake and exhaust port walls are generated using a fitting surface. After the entity is formed by stitching the surface features, the intake and exhaust ports and the top plate, bottom plate and side wall of the cylinder head are subtracted through Boolean operation to complete the modeling of the intake and exhaust ports. The 22mm fastening thread hole, 8.5mm intake and exhaust pipe assembly hole, 42mm oil nozzle assembly hole and 20mm positioning pin hole of the cylinder head are established using the modeling methods of stretching, rotating, punching or rounding. The water inlet and outlet of the flow channel are drawn on the cylinder head using the modeling method of stretching. From the water inlet, the 20 flow channel geometries of the cylinder head are drawn at positions where the wall thickness of the cylinder head model is greater than 6mm using the modeling methods of stretching, rotating and stitching surfaces until the water inlet and outlet are connected and the flow channel is distributed throughout the interior of the cylinder head. The flow channel geometries are summed using Boolean operation to obtain the flow channel entity of the cylinder head model. The cylinder head model with completed intake and exhaust port modeling and the flow channel entity of the cylinder head model are subtracted through Boolean operation to obtain the cylinder head model with completed intake and exhaust port and flow channel modeling. Six weight-reducing geometries are established on the top plate, bottom plate and side wall of the cylinder head using the modeling methods of stretching, rotating and stitching surfaces, and the sizes of the weight-reducing geometries are associated with the sizes of the flow channel geometries to always ensure that the minimum wall thickness of the cylinder head is greater than 6mm. The cylinder head with completed assembly feature modeling and all weight-reducing geometries are subtracted using Boolean operation to obtain the cylinder head model with completed parameterized modeling.

[0081] Step 1.2: delete the weight-reducing features on the parameterized model of the cylinder head, save the model as copy 1; delete the weight-reducing features and the flow channel features on the parameterized model of the cylinder head, save the model as copy 2. Subtract copy 1 model from copy 2 model by means of Boolean operation to obtain the cooling flow channel model of the cylinder head. In the expression of the cooling flow channel model of the cylinder head, associate the parameters of the same meaning in copy 1 and copy 2, in this embodiment, the parameters to be modified include 53 parameters for controlling the shape of the cylinder head and the shape of the flow channel.

[0082] Step 1.3: set the initial values of the 96 reference size parameters constituting this embodiment to the initial values used in the parameterized modeling of the cylinder head, and then set the boundary values of the reference values, so that these sizes do not change during model updating. Among the 100 parameters other than the reference sizes, this embodiment only optimizes the parameters for controlling the shape of the flow channel. After determining the upper and lower boundary values of the variation of the 31 parameters for controlling the shape of the flow channel, set the initial values of the 31 parameters for controlling the shape of the flow channel to the median of the upper and lower boundary values.

[0083] Step 1.4: configure the data interface between Excel software and UG software, import the names of the 31 parameters for controlling the shape of the flow channel and their corresponding parameter variation ranges into the Excel table, insert a random number formula to randomly select a parameter value for the 31 parameters for controlling the shape of the flow channel within the variation range, and then select all the random parameter values generated by the random number formula together with the names of the 31 parameters for controlling the shape of the flow channel as the data source of the parameterized model of the cylinder head, use the Excel table to drive UG for model updating to verify the parameter stability of the parameterized model of the cylinder head under the random parameter values. When the parameterized model of the cylinder head does not generate errors during continuous model updating using the random parameter values for ten times, it is considered that the parameter stability of the parameterized model of the cylinder head is qualified.

[0084] Step 1.5: based on the heat transfer analysis method of the cylinder head, select the face feature areas of the water inlet, the water outlet, the flow channel wall, the fluid-structure coupling surface, the symmetry surface, the outer wall surface, the intake port wall surface, the exhaust port wall surface and the fire surface on the parameterized model of the cylinder head and the cooling flow channel model of the cylinder head by extracting geometric features, set all the face features to be associated with the hidden cylinder head and the hidden cylinder head cooling flow channel entity, hide the original entity model in the parameterized model of the cylinder head and the cooling flow channel model of the cylinder head, and obtain the parameterized model of the cylinder head and the cooling flow channel model of the cylinder head in the form of face features. The final parameterized model of the cylinder head in the form of face features is shown in FIG. a, and the final cooling flow channel model of the cylinder head in the form of face features is shown in FIG. b. Figure 2 Figure 2

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

[0086] Step two: draw the cylinder head body combined grid model for flow field and temperature field calculation with the process minimum wall thickness requirement size as the initial grid size. Based on the heat transfer analysis method of the cylinder head, set the simulation, and perform the steady-state flow field and temperature field simulation analysis of the cylinder head to obtain the temperature distribution of each position on the cylinder head. Divide the 3D grid model of the cylinder head for calculating the carrying capacity under the thermal-mechanical coupling condition with the process minimum wall thickness requirement size as the initial grid size. Assemble the 3D grid model of the cylinder head and each component related to the service state of the cylinder head, draw the structured grid for each component related to the service state of the cylinder head, and select the grid surface on the 3D grid model of the cylinder head and the 3D grid model of each component related to the service state of the cylinder head as the main surface and the slave surface of the boundary conditions to be applied during the rigid strength analysis of the cylinder head, to establish the grid model of the cylinder head assembly. Interpolate the temperature field distribution into the stress field grid to realize the mapping of the temperature distribution data of the cylinder head from the cylinder head combined grid model for flow field and temperature field calculation to the 3D grid model of the cylinder head for calculating the carrying capacity under the thermal-mechanical coupling condition. Perform the grid independence analysis of the performance calculation of the cylinder head under the thermal-mechanical coupling condition, select a grid size with short calculation time and stress and displacement calculation results deviating from the calculation results under other grid sizes by less than a preset threshold as the finite element grid size used in optimization, and the short calculation time refers to the calculation time shorter than the preset threshold.

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

[0088] Step 2.1: Grid drawing with 6mm size as initial grid size. The cylinder head parameterized model and the cylinder head cooling gallery model are imported into ICEM. The grid size is set to the process minimum wall thickness requirement size, and the PatchIndependent grid division method is used to divide the surface grid of the cylinder head and the cylinder head cooling gallery. The surface grid model of the cylinder head and the cylinder head cooling gallery is obtained. The surface grid model of the cylinder head and the cylinder head cooling gallery is imported into ICEM in sequence, and the two grids are combined to obtain the combined surface grid model of the cylinder head. In ICEM, the grid area in the combined surface grid model of the cylinder head is named according to the water inlet, water outlet, flow passage wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface and fire surface. The combined surface grid model of the cylinder head is imported into fluent meshing, and the three problems of free edge, self-intersection and repeated grid are corrected, and the grid distortion is reduced to below 0.8. Based on the combined surface grid model of the cylinder head, the volume grid model of the cylinder head is drawn, and the low-quality grid is repaired based on the grid node movement algorithm, and the inverse orthogonal quality is reduced to below 0.8. The combined grid model of the cylinder head for flow field and temperature field calculation is output, as shown in FIG. 8. Figure 3

[0089] Step 2.2: The volume grid model of the cylinder head is imported into fluent, and the simulation analysis scale is set to 6mm. The calculation method used for flow field calculation is SIMPLE method, and k-e model is used for turbulence calculation. The material properties of the cylinder head and the cooling liquid in the gallery are set to cast iron and water respectively. The water inlet, water outlet, flow passage wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface and fire surface of the cylinder head volume grid model are set to inlet surface, outlet surface, wall surface and interface according to the needs of simulation analysis. The fluid-structure coupling surface types of the cylinder head and the cylinder head cooling gallery grid model are set to interface, and the two fluid-structure coupling surfaces are set to coupling relationship. The environmental temperature of the fire surface is set to 812℃, and the heat transfer coefficient is 1582W / (m2*K); the environmental temperature of the intake port wall surface is 63℃, and the heat transfer coefficient is 320W / (m2*K); the environmental temperature of the exhaust port wall surface is 704℃, and the heat transfer coefficient is 640W / (m2*K); the water inlet temperature is 25℃, and the water outlet temperature is 70℃. The stop condition is set to simulation iteration 200 steps, and the simulation is initialized. The simulation calculation is submitted to obtain the temperature field simulation result of the cylinder head.

[0090] ​Step 2.3: The cylinder head parametric model is imported into Hypermesh with 6mm size as the initial mesh size, the mesh size is set to the process minimum wall thickness requirement size, and the surface deviation mesh division method is used to divide the 2D mesh. Based on the QI optimization mesh repair algorithm and the size corrected mesh repair algorithm, the mesh with unqualified mesh quality is repaired, and the mesh that is difficult to adjust by the mesh repair algorithm is modified to the mesh with qualified mesh quality using the place node method, to obtain the high-quality 2D mesh model of the cylinder head. The mesh size is set to the process minimum wall thickness requirement size, and the tetramesh mesh division method is used to draw the 3D mesh, to obtain the 3D mesh model of the cylinder head for calculating the bearing capacity under the condition of thermal-mechanical coupling as shown in FIG. b. Figure 3

[0091] Step 2.4: The 3D mesh model of the cylinder head is imported into Hypermesh, the engine block, bushing, gasket and fastening bolt are imported and assembled with the 3D mesh model of the cylinder head. The mesh size is set to 10mm, the automesh method is used to divide the 2D structured mesh of the engine block, bushing, gasket and fastening bolt, and the solid map method is used to divide the 3D structured mesh of the engine block, bushing, gasket and fastening bolt. The mesh surface of the 3D mesh model of the cylinder head and the 3D mesh model of the engine block, bushing, gasket and fastening bolt is selected as the main surface and the slave surface of the boundary conditions to be applied during the rigid strength analysis of the cylinder head. The material properties of the 3D model of the cylinder head and the 3D mesh model of each component related to the service state of the cylinder head are set and saved, to obtain the mesh model of the cylinder head assembly as shown in FIG. b. Figure 4

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

[0093] ​​Step 2.6: The mesh model of the cylinder head assembly body is imported into Abaqus, the burst pressure of the fire surface is set to 25 MPa, the burst pressure of the intake and exhaust valve seat rings is set to 48 MPa and 37 MPa respectively, the pre-tightening force of the four bolts is set to 115,000 N; the contact relationship is set for the contact pairs of the bolts and the cylinder head and the contact pairs of the cylinder head and the engine body, and the small sliding small deformation calculation method is used, and the friction coefficient is 0.15; the coupling relationship is set for the connection pairs of the bolts and the engine assembly holes, and the small sliding small deformation calculation method is used, and the friction coefficient is 0.15; the bottom of the engine body is set as a fixed constraint. The simulation analysis type is selected as static analysis, the initial iteration step is set to 0.01, the maximum iteration step is set to 0.5 according to the computing power condition, the simulation calculation is submitted, and the stress distribution and displacement distribution results of the cylinder head under the thermal-mechanical coupling condition are obtained.

[0094] Step 2.7: Perform mesh independence analysis of the cylinder head performance calculation under the thermal-mechanical coupling condition. Starting from the initial value of the grid size of 6 mm, the grid size used when drawing the cylinder head combined grid model and the 3D grid model of the cylinder head is expanded or reduced, the temperature field simulation results and the bearing capacity simulation results of the cylinder head under the thermal-mechanical coupling condition are calculated respectively, the influence of different grid sizes on the calculation time and the highest temperature, the thermal-mechanical coupling stress, and the thermal-mechanical coupling deformation calculation results are compared, and a grid size with short calculation time and calculation results deviating from the calculation results under other grid sizes by less than a preset threshold is selected as the finite element grid size used in optimization. After the mesh independence analysis in this embodiment, the 5 mm grid size is finally selected as the optimal grid size considering the calculation speed and the calculation accuracy, and the 5 mm grid size is used in the subsequent optimization. The cylinder head temperature field distribution results calculated by using the 5 mm grid size are shown in Figure 5 (a), the cylinder head thermal-mechanical coupling stress distribution results are shown in Figure 5 (b), and the cylinder head thermal-mechanical coupling deformation distribution results are shown in Figure 5 (c).

[0095] Step three: adjust the structural parameters of the cylinder head model, generate a cylinder head model with different parameters from the initial value. Record the script of the cylinder head body combined mesh model drawing link for flow field and temperature field calculation in ICEM and fluent meshing. Record the script of the cylinder head heat transfer performance calculation link in fluent, and extract the index data that can represent the heat transfer performance of the cylinder head and the mass of the cylinder head. Record the script of the cylinder head 3D mesh model drawing link for calculating the carrying capacity under the condition of thermal-mechanical coupling in Hypermesh and the script of the cylinder head mesh model updating link in the cylinder head assembly model. Record the script of the mapping cylinder head temperature distribution data link in Hypermesh and fluent, and use the batch command to realize the automatic modification of the temperature distribution data, so that it can be recognized by the solver of Abaqus to generate the temperature field calculation result. Record the script of the cylinder head stiffness calculation link in Abaqus and extract the index data that can represent the carrying performance of the cylinder head under the condition of thermal-mechanical coupling.

[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 with a random number in the change range.

[0098] Step 3.2: Start script recording in ICEM, use Patch Independent meshing method to divide the surface mesh model of the cylinder head and the cylinder head cooling flow channel with a 5mm grid size respectively, save the surface mesh model of the cylinder head and the cylinder head cooling flow channel and obtain the script of the surface mesh division link. Start script recording again in ICEM, import the surface mesh model of the cylinder head and the cylinder head cooling flow channel in turn, combine the two meshes, and then name the mesh regions in the cylinder head surface mesh model according to the water inlet, water outlet, flow channel wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface and fire surface. Obtain the cylinder head combined surface mesh model and the script of the mesh combining link. Start script recording in fluent meshing, import the combined cylinder head surface mesh model, correct the three problems of free edge, self-intersection and repeated mesh, and reduce the mesh distortion to below 0.8. Draw the body mesh model of the cylinder head, and repair the low-quality mesh based on the mesh node movement algorithm, reduce the inverse orthogonal quality to below 0.8. Output the cylinder head combined mesh model for flow field and temperature field calculation and obtain the script of the body mesh division link. The script can realize one-key automatic division of the cylinder head combined mesh model.

[0099] Step 3.3: Start script recording in fluent, import the body grid model of the cylinder head, set the simulation scale to 5mm, the calculation method used in the flow field calculation is SIMPLE method, the turbulent flow calculation uses k-e model, the material properties of the cylinder head and the cooling liquid in the flow passage are set to cast iron and water respectively. The water inlet, water outlet, flow passage wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface and fire surface of the cylinder head body grid model are set as inlet surface, outlet surface, wall surface and interface according to the needs of simulation analysis. Set the surface type of the fluid-structure coupling surface of the cylinder head and the cooling flow passage grid model to interface, and set the two fluid-structure coupling surfaces to 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 port wall surface to 63℃, the heat transfer coefficient to 320W / (m2*K); the ambient temperature of the exhaust port wall surface 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 stop condition to 200 steps of simulation iteration and initialize the simulation, submit the simulation calculation to obtain the temperature field simulation result of the cylinder head. Extract the face average convective heat transfer coefficient, face average pressure, face average y+ value, face minimum y+ value, face maximum y+ value, body average water cavity temperature, body average cylinder head temperature, body average velocity, cylinder head total mass, cylinder head maximum temperature, water cavity maximum temperature, water cavity maximum velocity, water cavity minimum temperature and water cavity size calculated by the cylinder head heat transfer performance. Save the cylinder head temperature field simulation example and get the script of the cylinder head heat transfer performance calculation link.

[0100] Step 3.4: Start script recording in Hypermesh, edit the grid quality evaluation standard based on 5mm grid size, cancel the detection of maximum grid size and minimum grid size by the algorithm, and improve the repair rate of low-quality grids. Use surface deviation grid division method to divide 2D grid, repair the grid with unqualified grid quality based on QI optimization grid repair algorithm and size corrected grid repair algorithm, and use place node method to modify the grid that is difficult to adjust by grid repair algorithm to qualified grid quality, to obtain high-quality 2D grid model of the cylinder head. Use tetramesh grid division method to draw 3D grid, to obtain 3D grid model of the cylinder head. Complete the drawing of 3D grid model of the cylinder head for calculating the carrying capacity under thermal-mechanical coupling condition and obtain the script of 3D grid model drawing link of the cylinder head.

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

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

[0103] Step 3.7: Record the script of the cylinder head stiffness calculation link. Start script recording in Abaqus, import the cylinder head assembly grid model, set the burst pressure of the fire surface to 25Mpa, the burst pressure of the intake and exhaust valve seat ring to 48Mpa and 37Mpa respectively, and the pre-tightening force of the four bolts to 115000N; set the contact relationship of the bolt and the cylinder head and the contact relationship of the cylinder head and the engine block using small sliding small deformation calculation method, and the friction coefficient is 0.15; set the coupling relationship of the bolt and the engine block assembly hole using small sliding small deformation calculation method, and the friction coefficient is 0.15; set the bottom of the engine block as fixed constraint. Select the simulation analysis type as static analysis, set the initial iteration step of simulation to 0.01 and the maximum iteration step to 0.5 according to the computing power condition, associate the temperature field calculation results that can be recognized by Abaqus solver, set the initial iteration step and the maximum iteration step of simulation according to the computing power condition, submit simulation calculation and obtain the stress distribution and displacement distribution results of the cylinder head under the condition of thermal-mechanical coupling.

[0104] Step four: build a cylinder head optimization model under the condition of thermal-mechanical coupling based on co-simulation technology, use Latin hypercube algorithm to plan the sample space of cylinder head optimization under the condition of thermal-mechanical coupling, call the script recorded in the process of cylinder head performance calculation through batch command, automatically run the cylinder head parameterized model updating, cylinder head mesh drawing, cylinder head component updating in cylinder head assembly model, cylinder head heat transfer simulation analysis, cylinder head temperature distribution data mapping between different mesh models, cylinder head stiffness and strength simulation analysis and cylinder head performance index data extraction in the process of cylinder head optimization design under the condition of thermal-mechanical coupling, and obtain the sample data set representing the corresponding relationship between cylinder head structure and performance.

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

[0106] Step 4.1: build a cylinder head optimization model under the condition of thermal-mechanical coupling in Isight, and the workflow can be represented by the flowchart as shown in Figure 6 Based on the i5-10500 CPU and 16 GB memory computing device used, the total number of samples in the sample space is set to 500, and Latin hypercube algorithm is used to plan the sample space of cylinder head optimization under the condition of thermal-mechanical coupling, so that the sample points are uniformly distributed in high-dimensional Euclidean space, ensuring the quality of sample data. By calling the script recorded in the process of cylinder head performance calculation through batch command, different modules are used to execute the commands of cylinder head parameterized model updating, cylinder head mesh drawing, cylinder head component updating in cylinder head assembly model, cylinder head heat transfer simulation analysis, cylinder head temperature distribution data mapping between different mesh models, cylinder head stiffness and strength simulation analysis and cylinder head performance index data extraction in the process of cylinder head optimization design under the condition of thermal-mechanical coupling. After setting, the cylinder head performance optimization model is automatically run, and the sample data set representing the corresponding relationship between cylinder head structure and performance is obtained.

[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 weight, maximum temperature, maximum thermal-mechanical coupling stress and maximum thermal-mechanical coupling deformation of the cylinder head are selected as evaluation indexes, the ideal values of each index are set as the minimum value of the index data, the weight of each index is calculated and scored by using the comprehensive evaluation function, the sample with the best score is selected as the optimization result, and the optimization of the cylinder head is completed. The structure of the optimized cylinder head model is shown in Figure 7 .

[0108] Further comprising a step five, process adaptability design is carried out according to the optimal cylinder cover structure obtained in the step four, and a cylinder cover design scheme meeting production constraints is obtained. The cast iron cylinder cover processed and manufactured through the scheme is 9% lighter than the cylinder cover before optimization, the highest temperature is reduced from 520 DEG C to 446 DEG C, the highest thermal-mechanical coupling stress is reduced from 345.3 MPa to 328.3 MPa, and the maximum thermal-mechanical coupling deformation is reduced from 1.039 mm to 1.025 mm, so the optimized cylinder cover has improved in heat transfer performance, load bearing performance and lightweight degree.

[0109] The above detailed description, the purpose, technical scheme and beneficial effects of the application are further described in detail, and it should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application, and any modification, equivalent replacement, improvement, etc. within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A method for optimizing cylinder head parameters under thermo-mechanical coupling conditions, characterized in that: Comprising the following steps, Step one: parameterized modeling of the cylinder head is performed to obtain a cylinder head parameterized model; a cooling channel model of the cylinder head is obtained through Boolean operation, and each same parameter of the cylinder head parameterized model and the cooling channel model of the cylinder head is associated; initial values and upper and lower boundary values of each parameter of the cylinder head parameterized model are determined, and the cylinder head parameterized model is gradually modified in a manner of "combination of global parameter variation and modification error features", until the cylinder head model meets the preset stability qualification requirements; The surfaces of the cylinder head parameterized model and the cooling channel model of the cylinder head that need to be assigned different boundary conditions are classified, and the cylinder head parameterized model and the cooling channel model of the cylinder head are saved in the form of surface features; the API function of UG software is called to realize one-key automatic update of the cylinder head parameterized model and the cooling channel model of the cylinder head, and the update efficiency of the cylinder head parameterized model and the cooling channel model of the cylinder head is improved; Step two: the minimum wall thickness requirement size of the process is taken as the initial grid size, and a cylinder head body combined grid model for flow field and temperature field calculation is drawn; based on the heat transfer analysis method of the cylinder head, simulation is set, and internal steady-state flow field and temperature field simulation analysis of the cylinder head is performed to obtain the temperature distribution of each position on the cylinder head; the minimum wall thickness requirement size of the process is taken as the initial grid size, and a 3D grid model of the cylinder head for calculating the carrying capacity under thermal-mechanical coupling conditions is divided; the 3D grid model of the cylinder head and each component related to the service state of the cylinder head are assembled, the structured grid of each component related to the service state of the cylinder head is drawn, and the grid surfaces of the 3D grid model of the cylinder head and the 3D grid model of each component related to the service state of the cylinder head are selected as the main surface and the slave surface of the boundary conditions to be applied during the cylinder head stiffness and strength analysis, and the grid model of the cylinder head assembly is established; 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 for flow field and temperature field calculation to the 3D grid model of the cylinder head for calculating the carrying capacity under thermal-mechanical coupling conditions; Grid independence analysis for performance calculation of the cylinder head under thermal-mechanical coupling conditions is performed, and a finite element grid size with short calculation time and stress and displacement calculation results deviating from the calculation results under other grid sizes by less than a preset threshold is selected as the finite element grid size used for optimization, wherein the short calculation time refers to a calculation time shorter than a preset threshold. Step three: adjust the structural parameters of the cylinder head model to generate a cylinder head model with different parameters from the initial value; record the script for the meshing of the cylinder head body combined grid model in ICEM and fluentmeshing for flow field and temperature field calculation; record the script for the calculation of the heat transfer performance of the cylinder head in fluent, and extract the index data that can represent the heat transfer performance of the cylinder head and the mass of the cylinder head; record the script for the meshing of the cylinder head 3D grid model in Hypermesh for the calculation of the load capacity under thermal-mechanical coupling conditions and the script for the updating of the cylinder head grid model in the cylinder head assembly model; record the script for the mapping of the temperature distribution data of the cylinder head in Hypermesh and fluent, and use the batch command to realize the automatic modification of the temperature distribution data, so that it can be recognized by the solver of Abaqus to generate the calculation results of the temperature field; record the script for the calculation of the stiffness of the cylinder head in Abaqus and extract the index data that can represent the load capacity of the cylinder head under thermal-mechanical coupling conditions; Step four: based on the joint simulation technology, build an optimization model of the cylinder head under thermal-mechanical coupling conditions, use the Latin hypercube algorithm to plan the sample space for the optimization of the cylinder head under thermal-mechanical coupling conditions, and call the scripts recorded in the performance calculation process of the cylinder head through batch commands to automatically run the cylinder head parameterized model updating, cylinder head meshing, cylinder head component updating in the cylinder head assembly model, cylinder head heat transfer simulation analysis, cylinder head temperature distribution data mapping between different grid models, cylinder head stiffness simulation analysis, and cylinder head performance index data extraction under thermal-mechanical coupling conditions during the optimization design process of the cylinder head under thermal-mechanical coupling conditions, to obtain the sample data set representing the correspondence between the cylinder head structure and various performance indicators; establish a comprehensive evaluation function to weigh multiple cylinder head performance indicators and score each sample point, and select the sample with the best score as the optimization result to obtain the optimal cylinder head structure in the sample space, i.e. realize the optimization of the cylinder head under thermal-mechanical coupling conditions based on the joint simulation technology.

2. The method of claim 1, wherein: Step five: based on the optimal cylinder head structure obtained in step four, perform process adaptability design to obtain a cylinder head design scheme that meets the production constraints; the cylinder head manufactured based on the cylinder head design scheme can improve the heat transfer and load capacity, reduce the maximum temperature of the fire surface, reduce the deformation and stress of the thermal-mechanical coupling machine, and improve the service life compared to the cylinder head before optimization; the weight of the optimized cylinder head is lighter than that of the cylinder head before optimization, and the high power density of the engine can be improved.

3. The method of claim 2, wherein: The specific implementation method of step one is S11: Select UG as a modeling platform to perform parameterized modeling of the cylinder head; use a stretching or rotating modeling method to establish external features of the cylinder head, including the top plate, bottom plate, and side wall; use a projection curve modeling method to draw feature lines on the intake and exhaust port walls of the cylinder head; use a fitting surface modeling method to connect the closed projection curves to generate surface features of the intake and exhaust port walls; stitch the surface features that make up the intake and exhaust ports to form a solid, and subtract the external features of the cylinder head from the intake and exhaust port solids by means of Boolean operation to obtain a cylinder head model with completed port modeling; use a stretching, rotating, punching, or rounding corner modeling method to establish assembly features of the cylinder head on the cylinder head model with completed port modeling, including fastening thread holes, intake and exhaust pipe assembly holes, inlet and outlet water port assembly holes, oil jet assembly holes, and positioning pin holes; use a stretching modeling method to draw the inlet and outlet water ports of the flow channel on the cylinder head model with completed port modeling, and from the inlet water port, use a stretching, rotating, or stitching surface method to draw the flow channel geometry of the cylinder head on the cylinder head model at positions where the wall thickness is greater than the minimum wall thickness requirement of the process, until the flow channel geometry is connected to the inlet and outlet water ports and is arranged at positions where the wall thickness is greater than the minimum wall thickness requirement of the process, and the flow channel geometry strictly meets the minimum wall thickness requirement of the process when being sized; sum all the flow channel geometries using Boolean operation to obtain a flow channel solid of the cylinder head model, and subtract the cylinder head model with completed port modeling from the flow channel solid of the cylinder head model by means of Boolean operation to obtain a cylinder head model with completed port and flow channel modeling; after the external features, ports, assembly features, and flow channels of the cylinder head are all modeled, establish weight reduction geometries on the top plate, bottom plate, and side wall of the cylinder head at positions not involved in assembly and sealing by means of stretching, rotating, or stitching surface method, and associate the size of the weight reduction 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; subtract the cylinder head with completed assembly feature modeling from all the weight reduction geometries using Boolean operation to obtain a cylinder head model with completed parameterized modeling; S12: obtain a cooling flow channel model of the cylinder head by means of Boolean operation; delete the weight reduction features on the parameterized model of the cylinder head and save the model as copy 1; delete the weight reduction features and flow channel features on the parameterized model of the cylinder head and save the model as copy 2; subtract copy 1 model from copy 2 model by means of Boolean operation to obtain a cooling flow channel model of the cylinder head; associate parameters of the same meaning in copy 1 and copy 2 in the expression of the cooling flow channel model of the cylinder head, including parameters for controlling external features and parameters for controlling port features, so that the parameters of the same meaning in the two expressions always remain equal during the model updating process; after the same parameter association is completed, the cooling flow channel model of the cylinder head updates the external features and port features of copy 1 and copy 2 synchronously, ensuring that the entity obtained after each update of the cooling flow channel model of the cylinder head is only the flow channel part of the cylinder head; S13: Set parameter initial values and parameter boundary values for the structure parameters on the cylinder head parameterized model and the cylinder head cooling gallery model; set one of the parameter boundary values of the cylinder head parameterized model as the limit parameter when the wall thickness of each position of the cylinder head is the process minimum wall thickness requirement size, and set the other as other limit size that meets the design requirements of the cylinder head, which includes that the hydraulic diameter at each place of the gallery should not be smaller than the limit size that causes flow obstruction, the narrowest place of the cylinder head surface should not be smaller than one third of the process minimum wall thickness requirement, and there should be no interference between the gallery, the port, the assembly feature, the weight reduction feature, and the external wall surface of the cylinder head; Some cylinder head sizes are the reference sizes set when the cylinder head parameterized model is modeled, and the reference size parameter initial value is set as the initial value used when the cylinder head parameterized model is modeled, and then the boundary value is equal to the reference value, so that these sizes do not change when the cylinder head parameterized model is updated; after the upper and lower boundary values of the parameters other than the reference size are determined, the initial values of the parameters other than the reference size are all set as the median of the upper and lower boundary values, to reduce the probability of error when the cylinder head parameterized model is updated; S14: Modify the cylinder head parameterized model gradually in the manner of "combination of global parameter variation and modification error characteristics"; when the parameter values within the parameter variation range obtained in S13 are selected and substituted into the expression for model updating, and the model updating still does not cause an error after a predetermined number of times, it is determined that the stability of the cylinder head parameterized model meets the conditions required for optimization; the role of this step S14 is to repeatedly test whether the cylinder head parameterized model causes an error under different parameter values, and to modify the error characteristics, gradually improving the cylinder head parameterized model; name all parameters other than the reference size in the expression of the cylinder head parameterized model, configure the data interface of Excel and UG, and import the parameter names 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 all parameters other than the reference size, and then select all the 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 for the cylinder head parameterized model, and use the Excel table to drive UG for model updating to test the parameter stability of the cylinder head parameterized model under random parameter values; When the cylinder head parameterized model does not cause an error after a predetermined number of times of model updating using random parameter values in succession, it is determined that the parameter stability of the cylinder head parameterized model is qualified; if an error occurs, modify the error characteristics prompted in the UG software or modify the size variation range corresponding to the characteristics, until the cylinder head parameterized model does not cause an error after a predetermined number of times of model updating using random parameter values in succession; S15: Classify the surfaces of the cylinder head parameterized model and the cylinder head cooling gallery model that need to be given different boundary conditions, and save the cylinder head parameterized model and the cylinder head cooling gallery model in the form of surface characteristics; In the automatic calculation of the temperature field distribution of the cylinder head, the boundary conditions can only be automatically assigned to the surface features. The cylinder head parameterized model and the surface of the cylinder head cooling channel model are extracted into multiple surface features based on the type of the boundary condition area, so as to automatically identify the boundary condition area in the solver. The surfaces are classified based on the heat transfer analysis method of the cylinder head, including the water inlet, the water outlet, the channel wall surface, the fluid-structure coupling surface, the symmetry surface, the outer wall surface, the intake port wall surface, the exhaust port wall surface and the fire surface. The surfaces are extracted into surface features according to the classification by the modeling method of extracting geometric features. The original solid models of the cylinder head parameterized model and the cylinder head cooling channel model are hidden to obtain the cylinder head parameterized model and the cylinder head cooling channel model in the form of surface features, which are stored separately. All the surface features are set to be associated with the hidden cylinder head and the cylinder head cooling channel solid. S16: The cylinder head model is automatically updated by calling the API function of UG. The API function of UG is called to read the paths of the cylinder head parameterized model and the cylinder head cooling channel model, read the expression path of the cylinder head parameterized model, 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 one-key automatic update of the cylinder head parameterized model and the cylinder head cooling channel model.

4. The method of claim 3, wherein: The specific implementation method of step two is, S21: Draw the cylinder head body combined grid model for flow field and temperature field calculation. The grid is drawn with the process minimum wall thickness requirement size as the initial grid size to ensure the grid quality at the minimum position of the cylinder head wall surface. The cylinder head parameterized model and the cylinder head cooling channel model are imported into ICEM. The grid size is set to the process minimum wall thickness requirement size, and the Patch Independent grid division method is used for face grid division to avoid grid drawing failure caused by geometric distortion, including broken surfaces, narrow surfaces with a width less than the process minimum wall thickness requirement, or an included angle between two surfaces less than 15°. The grid models of the cylinder head and the cylinder head cooling channel are combined before calculation to realize simultaneous setting of the boundary conditions of the cylinder head and the cylinder head cooling channel, and solve the problem that the heat transfer solver can only set the boundary conditions for one calculation target. The surface grid models of the cylinder head and the cylinder head cooling channel are imported into ICEM in sequence, and the combined surface grid model of the cylinder head is obtained after combining the two grids. The quality of the surface mesh drawn automatically by ICEM is not high. If the body mesh is drawn directly in ICEM and applied to calculation, the calculation cannot converge. The problem can be solved by importing the combined surface mesh model of the cylinder head into fluent meshing to repair the mesh problem and divide the body mesh, and the quality of the body mesh model is qualified; In ICEM, the mesh regions in the combined surface mesh model of the cylinder head are named according to the water inlet, water outlet, flow passage wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface and fire surface; The combined surface mesh model of the cylinder head is imported into fluent meshing, and the three problems of free edge, self-intersection and repeated mesh are corrected, and the mesh twist is reduced to below the preset twist; Based on the combined surface mesh model of the cylinder head, the body mesh model is drawn, 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; The combined mesh model of the cylinder head for flow field and temperature field calculation is outputted; S22: Based on the cylinder head heat transfer analysis method, the simulation is set, the internal steady-state flow field and temperature field of the cylinder head are simulated and analyzed, and the temperature distribution of each position on the cylinder head is obtained. The body mesh model of the cylinder head is imported into fluent, the size of the simulation analysis, the calculation method used for flow field calculation and the material properties of the cooling liquid in the cylinder head and the flow passage are set. The surface types of each surface on the cylinder head body mesh model are set, the surfaces include water inlet, water outlet, flow passage wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface and fire surface. The surface types include inlet surface, outlet surface, wall surface and interface. The surface types of the fluid-structure coupling surfaces on the mesh models of the cylinder head and the cylinder head cooling flow passage are set as interface, and the two fluid-structure coupling surfaces are set as coupling relationship, so as to solve the problem that the meshes on the fluid-structure coupling surfaces of the cylinder head and the cylinder head cooling flow passage are not shared. The nodes. The convection heat transfer coefficient and the initial temperature of the wall surface of the various surfaces are set. The calculation process is set to monitor, stop condition and initialize the simulation, and the simulation calculation is submitted to obtain the temperature field simulation result of the cylinder head; S23: Draw the 3D mesh model of the cylinder head for calculating the carrying capacity under the condition of thermal-mechanical coupling; The minimum wall thickness required by the process is used as the initial mesh size for mesh drawing. The parameterized model of the cylinder head is imported into Hypermesh, the mesh size is set to the minimum wall thickness required by the process, and the surface deviation mesh division method is used for 2D mesh division. Based on the QI optimization mesh repair algorithm and the size corrected mesh repair algorithm, the mesh with unqualified quality is repaired, and the mesh that is difficult to adjust by the mesh repair algorithm is modified to the mesh with qualified quality by using the place node method, to obtain the high-quality 2D mesh model of the cylinder head. The grid size is set as the minimum wall thickness required by the process, a 3D grid is drawn using the tetramesh meshing method to obtain a 3D grid model of the cylinder head for calculating the load capacity under thermal-mechanical coupling conditions; S24: establishing a grid model of the cylinder head assembly; importing the 3D grid model of the cylinder head for calculating the load capacity under thermal-mechanical coupling conditions into Hypermesh, importing each component related to the service state of the cylinder head and assembling each component related to the service state of the cylinder head with the 3D grid model of the cylinder head for calculating the load capacity under thermal-mechanical coupling conditions according to the engine assembly requirements, the components including the engine block, bushing, gasket, and fastening bolt; using the automesh method to perform 2D structured meshing on each component related to the service state of the cylinder head, using the solid map method to perform 3D structured meshing on the components related to the service state of the cylinder head to obtain the 3D grid model of each component related to the service state of the cylinder head; based on the cylinder head stiffness and strength analysis method, selecting grid surfaces as master and slave surfaces of the boundary conditions to be applied during the cylinder head stiffness and strength analysis on the 3D grid model of the cylinder head for calculating the load capacity under thermal-mechanical coupling conditions and the 3D grid model of each component related to the service state of the cylinder head, the master and slave surfaces including the contact relationship master and slave surfaces of the bolt and the cylinder head, the connection relationship master and slave surfaces of the bolt and the engine assembly hole, the contact relationship master and slave surfaces of the cylinder head and the engine block, and the action surface of the combustion chamber explosion pressure; setting material properties for the 3D model of the cylinder head and the 3D grid model of each component related to the service state of the cylinder head and saving to obtain the grid model of the cylinder head assembly; S25: interpolating the temperature field distribution into the stress field grid, then performing format processing on the obtained data file, and importing 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 3D grid model of the cylinder head used for calculating the load capacity under thermal-mechanical coupling conditions; extracting 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 after the temperature field data is mapped to the cylinder head grid model is still uniform with the grid number in the cylinder head assembly; importing the cylinder head temperature field simulation result obtained in S22 into the extracted cylinder head grid model based on the grid data automatic mapping algorithm in fluent to obtain the temperature distribution data of the cylinder head corresponding to the grid node arrangement form of the cylinder head grid model; modifying the temperature distribution data so that it can be recognized by the solver of Abaqus, importing the modified temperature distribution data into Abaqus to make it generate a temperature field calculation result that can be imported when setting the calculation task in Abaqus; S26: based on the method for setting up simulation of the cylinder head stiffness strength analysis, perform load-bearing performance analysis under thermal-mechanical coupling conditions to obtain 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 magnitude of the burst pressure and bolt pretightening force borne by the cylinder head during operation, set the contact relationship of the bolt and the cylinder head and the contact relationship of the cylinder head and the engine block using the small sliding small deformation calculation method, set the coupling relationship of the bolt and the engine block assembly hole using the small sliding small deformation calculation method, and set the engine block bottom as a fixed constraint; select the simulation analysis type as static force analysis, correlate the Abaqus temperature field calculation results generated in S25 according to the predefined temperature field, set the initial iteration step and the maximum iteration step of the simulation according to the calculation power conditions, submit the simulation calculation, and obtain the stress distribution and displacement distribution results of the cylinder head under service conditions; S27: perform grid independence analysis for performance calculation of the cylinder head under thermal-mechanical coupling conditions; start from the initial value of the grid size required by the minimum wall thickness of the process, expand or reduce the grid size used when drawing the combined grid model of the cylinder head and the 3D grid model of the cylinder head, respectively calculate the temperature field simulation results and the load-bearing capacity simulation results of the cylinder head under thermal-mechanical coupling conditions, compare the influence of different grid sizes on the calculation time, the highest temperature, the thermal-mechanical coupling stress, and the thermal-mechanical coupling deformation calculation results, select a grid size with short calculation time and calculation results deviating from the calculation results under other grid sizes by less than a preset threshold as the finite element grid size used for optimization, complete the grid independence analysis, and the short calculation time refers to the calculation time being shorter than the preset threshold.

5. The method of claim 4, wherein: The specific implementation method of step three is, S31: adjust the structure parameters of the cylinder head model, perform automatic update of the cylinder head model and the cylinder head cooling flow channel model once, and generate a cylinder head model with different parameters and initial values; modify all parameters in the expression of the cylinder head parameterized model except the reference size, call the API function of UG, and read the expression of the cylinder head parameterized model to perform one-key automatic update on the cylinder head model and the cylinder head cooling flow channel model; S32: record the script for the grid drawing link of the cylinder head body combined grid model used for flow field and temperature field calculation; take the grid size determined after the grid independence analysis as the reference, start script recording in ICEM, divide the surface grid model of the cylinder head and the cylinder head cooling flow channel using the PatchIndependent grid division method respectively, save the surface grid model of the cylinder head and the cylinder head cooling flow channel, and obtain the script for the surface grid division link; start script recording again in ICEM, import the surface grid model of the cylinder head and the cylinder head cooling flow channel in sequence, combine the two grids, and name the grid regions in the cylinder head surface grid model according to the water inlet, water outlet, flow channel wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface, and fire surface; obtain the combined surface grid model of the cylinder head and the script for the grid combining link; Start script recording in fluent meshing, import the combined cylinder head surface mesh model, correct the three problems of free edge, self-intersection and repeated mesh, and reduce the mesh twist to below the preset twist; Draw the cylinder head volume mesh model, and repair low-quality mesh based on the mesh node movement algorithm to reduce the inverse orthogonal quality below the preset inverse orthogonal quality; Output the cylinder head combined mesh model for flow field and temperature field calculation and get the script for volume mesh division link; S33: Record the script for calculating the heat transfer performance of the cylinder head; Start script recording in fluent, import the volume mesh model of the cylinder head, set the scale of simulation analysis, the calculation method used for flow field calculation, and the material properties of the cylinder head and the cooling liquid in the flow passage; Set the surface type of each surface on the cylinder head volume mesh model, including the water inlet, water outlet, flow passage wall, fluid-structure coupling surface, symmetry surface, outer wall surface, intake port wall surface, exhaust port wall surface and fire surface, the surface type includes inlet surface, outlet surface, wall surface and interface surface; Set the surface type of the fluid-structure coupling surface on the cylinder head and the cylinder head cooling flow passage mesh model to interface, and set the two fluid-structure coupling surfaces to coupling relationship; Set the convective heat transfer coefficient of each surface and the initial temperature of the wall surface; Set the monitoring, shutdown condition and initialization of the simulation, submit the simulation calculation to get the temperature field simulation result of the cylinder head; Extract the index data representing the heat transfer performance of the cylinder head and the mass of the cylinder head, including the average convective heat transfer coefficient of the surface, the average pressure of the surface, the average y+ value of the surface, the minimum y+ value of the surface, the maximum y+ value of the surface, the average water cavity temperature, the average cylinder head temperature, the average velocity, the total mass of the cylinder head, the maximum temperature of the cylinder head, the maximum temperature in the water cavity, the maximum velocity in the water cavity, the minimum temperature in the water cavity and the size of the water cavity; Output the temperature field simulation result of the cylinder head and get the script for calculating the heat transfer performance of the cylinder head; S34: Record the script for drawing the 3D mesh model of the cylinder head for calculating the carrying capacity under thermal-mechanical coupling conditions; Based on the mesh size determined after mesh independence analysis, start script recording in Hypermesh, edit mesh quality evaluation criteria, cancel the detection of maximum mesh size and minimum mesh size by the algorithm, and improve the repair rate of low-quality mesh; The surface deviation mesh division method is used for 2D mesh division, the grid quality unqualified grid is repaired based on the QI optimization grid repair algorithm and the size corrected grid repair algorithm, the grid modification method is used to modify the grid which is difficult to adjust by the grid repair algorithm to the grid quality qualified, and the high-quality 2D grid model of the cylinder head is obtained; the tetramesh mesh division method is used to draw 3D grid, and the 3D grid model of the cylinder head is obtained; the drawing of the 3D grid model of the cylinder head for calculating the bearing capacity under the condition of thermal-mechanical coupling is completed, and the script of the drawing link of the 3D grid model of the cylinder head is obtained; S35: record the script of the cylinder head grid model updating link in the assembly model of the cylinder head; start script recording in Hypermesh, import the cylinder head assembly grid model, replace the cylinder head grid model in the cylinder head assembly grid model with the structure shape updated 3D grid model of the cylinder head based on the grid model replacement algorithm, export the new cylinder head assembly grid model and obtain the script of the cylinder head grid model updating link; S36: record the script of the cylinder head temperature distribution data mapping link from the cylinder head combined grid model for flow field and temperature field calculation to the 3D grid model of the cylinder head for calculating the bearing capacity under the condition of thermal-mechanical coupling; start script recording in Hypermesh, extract the cylinder head grid model from the grid model of the cylinder head assembly, ensure that the grid number on the cylinder head grid model after the temperature field data is mapped to the cylinder head grid model is still uniform with the grid model of the cylinder head assembly; start script recording in fluent, based on the grid data automatic mapping algorithm, import the cylinder head temperature field simulation result obtained in S33 into the extracted cylinder head grid model, obtain the temperature distribution data of the cylinder head corresponding to the grid node arrangement form of the cylinder head grid model; use batch processing command to realize automatic modification of temperature distribution data, so that the temperature distribution data can be recognized by the solver of Abaqus, import the modified temperature distribution data into Abaqus, generate the temperature field calculation result and the script of the temperature distribution data mapping link which can be imported when setting the calculation task in Abaqus; S37: record the script of the cylinder head stiffness and strength calculation link; Start script recording in Abaqus, import the mesh model of the cylinder head assembly into Abaqus, set the magnitude of the explosion pressure and bolt pretightening force borne by the cylinder head during the working process, select the contact pair of the bolt and the cylinder head and the contact pair of the cylinder head and the engine body to set the contact relationship and use the small sliding small deformation calculation method, select the connection pair of the bolt and the engine assembly hole to set the coupling relationship and use the small sliding small deformation calculation method, set the bottom of the engine body as a fixed constraint; select the simulation analysis type as static analysis, generate the Abaqus temperature field calculation results in association with S36, set the initial iteration step and the maximum iteration step 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 condition.

6. A method of cylinder head parameter optimization in a thermomechanical coupling condition according to claim 5, characterized in that: The specific implementation method of step four is, S41: build a cylinder head optimization model under the thermal-mechanical coupling condition in Isight, set the total number of samples according to the computing power conditions, select the Latin hypercube algorithm to plan the sample space for the cylinder head optimization under the thermal-mechanical coupling condition, make the sample points uniformly distributed in the high-dimensional Euclidean space, and ensure the quality of the sample data; call the script recorded in the cylinder head performance calculation process through the batch processing command, and 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 and strength simulation analysis, and cylinder head performance index data extraction in the cylinder head optimization design process under the thermal-mechanical coupling condition with different modules; After the settings are completed, automatically run the cylinder head performance optimization model to obtain a sample data set representing 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 an optimization, the comprehensive evaluation function is as follows: wherein g j is the comprehensive score of the jth evaluated sample point, λ i is the weight of the ith evaluated index, y ij is the actual value of the ith evaluated index of the jth evaluated sample point, Z i is the ideal value of the ith evaluated index of the evaluated sample point, σ i is the standard deviation of the data of the ith evaluated index, and n is the total number of indices evaluated for the sample point. The weight of the i-th evaluated indicator is calculated as follows: C i is the significance coefficient of the ith index, C i The greater the influence of the ith index on the comprehensive evaluation result, the higher the weight is naturally; the significance coefficient C i can be expressed as the product of the standard deviation σ i and the correlation coefficient R i , that is: C i = σ i R i (3) Standard deviation σ i is calculated with the following formula: where 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 indicator of the j-th sample point, is the average value of the dimensionless data of the i-th performance indicator; the dimensionless data of the i-th performance indicator of the j-th sample point is dimensionless by the following formula, and the average value of the data is obtained: Correlation coefficient R i was calculated using the formula: r ik The linear correlation coefficient between the ith index and the kth index can be calculated using the following formula: After calculating all the variables according to the sample data set, score each sample point through the comprehensive evaluation function, select the sample with the best score as the optimization result, and obtain the optimal cylinder head structure in the sample space, that is, realize the optimization of the cylinder head under the thermal-mechanical coupling condition based on the joint simulation technology.

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