A bidirectional fluid-structure coupling numerical simulation method for propeller-shaft coupling system

Abstract

The object of the present invention is to provide a two-way fluid-structure interaction numerical simulation method for a propeller-shaft coupling system, which comprises the following steps: numerically modeling the propeller flow field part; numerically modeling the shafting dynamics part; importing the established models into the flow field solver, wherein the shafting dynamics part is imported into the solver through a secondary development program, and after compilation, two-way coupling calculation of the flow field and the structural field within the same solver is realized; performing two-way fluid-structure interaction numerical simulation of the propeller-shaft coupling system, and in the process of solution, obtaining the excitation force of the propeller flow field and the results of the vibration displacement, velocity and acceleration of the shafting in real time. The present invention comprehensively considers conditions such as non-uniform incoming flow, propeller flow field excitation and shafting mass imbalance excitation, etc., and performs efficient and accurate numerical simulation on the dynamics of the coupling system, so as to serve for studying the transient dynamic response characteristics of the coupling system under various complex excitation conditions.

Description

Technical Field

[0001] The present invention relates to a numerical simulation method, specifically a numerical simulation method for the flow field of a ship propeller. Background Technique

[0002] The propeller - propulsion shafting coupling system is an important part of a ship's power plant. The safety and reliability of this system during operation have an important impact on the stable navigation of the ship. When the ship is sailing, due to the unevenness of the ocean inflow and the action of the hull wake, the propeller inevitably operates in a non - uniform inflow and generates periodic excitation. This excitation acting on the propulsion shafting will cause shafting vibration. Severe shafting vibration will be transmitted to the hull through the bearings, seriously affecting the quietness and comfort of the ship. Moreover, the multi - degree - of - freedom vibration of the elastic shafting will have a feedback effect on the propeller, inducing the centroid of the propeller to perform complex spatial motion. Taking the case of considering the whirling vibration of the shafting as an example, at this time, the propeller will generate the coupling of self - rotation and revolution, which affects the flow and excitation characteristics of the propeller. Therefore, there are complex fluid - structure interaction problems in the propeller - shaft system, and a numerical simulation method that can consider the two - way fluid - structure interaction effect needs to be established to conduct in - depth research on it.

[0003] The research on the hydrodynamic force and excitation force of the propeller has experienced decades of development. From the initial lift - line, lift - surface and low - order panel method (BEM) with strong assumptions about fluid flow, it has developed to the current computational fluid dynamics (CFD) method that can consider three - dimensional viscous fluid flow. For the research on shafting dynamics, the finite element method (FEM) is currently the most mainstream simulation method, which is widely used in the analysis of structural mechanics and rotor dynamics, and can accurately simulate the whirling, torsional, longitudinal and coupled vibrations of the propulsion shafting. For the fluid - structure interaction problems in the propeller - shaft system, the current research methods are mainly divided into one - way coupling methods and two - way coupling methods. One - way coupling methods are mainly used to study the dynamic response problem of the shafting under the fluid excitation of the propeller, while two - way coupling methods can be used to predict the complex dynamic behavior generated during the operation of the propeller - shaft coupling system and conduct in - depth research on the mutual influence between excitation and response.

[0004] The simulation methods for the two-way fluid-structure interaction of the propeller-shaft system are currently mainly divided into the method based on FEM / BEM and the method based on the built-in fluid-structure interaction algorithm of commercial software. The first method can accurately simulate the dynamic characteristics of the shafting. However, since the panel method is a simulation method based on the potential flow theory and makes the assumptions of inviscid and irrotational fluid flow, it cannot accurately predict the characteristics of the viscous flow of the propeller. The second method overcomes the shortcomings of the former and can accurately simulate both the flow field and the structural field. However, since the CFD and FEM solvers in commercial software are in different architectures, real-time two-way data transfer is required for two-way coupling analysis. This process is generally achieved by calling the two solvers through an intermediate program. Since the method of using an intermediate program to call the solver to achieve real-time data transfer will consume more additional computing resources, the solution speed is slow and the computing efficiency is low when using this method for two-way coupling analysis. Summary of the Invention

[0005] The object of the present invention is to provide a two-way fluid-structure coupling numerical simulation method for a propeller-shaft coupling system, which can be applied to the performance prediction and design optimization of the propulsion shafting and ship propellers, and can also be applied to the two-way fluid-structure coupling dynamics research of other fluid machinery-rotor structures except the propeller-shaft system.

[0006] The object of the present invention is achieved as follows:

[0007] A two-way fluid-structure coupling numerical simulation method for a propeller-shaft coupling system according to the present invention is characterized in that:

[0008] (1) Conduct numerical modeling of the propeller flow field part. Determine the range of the flow field domain according to the input propeller geometric model, perform spatial discretization of the flow field domain, define the boundary conditions in the flow field, and make preprocessing preparations for the propeller CFD simulation;

[0009] (2) Conduct numerical modeling of the shafting dynamics part. Establish a shafting dynamics numerical model according to the input shafting geometry and material parameters, and equivalently load the bearing supports as stiffness and damping into the model;

[0010] (3) Import the models established in steps (1) and (2) into the flow field solver. Among them, the shafting dynamics part is imported into the solver through a secondary development program, and after compilation, two-way coupling calculation of the flow field and the structural field within the same solver is realized;

[0011] (4) Perform two-way fluid-structure interaction numerical simulation on the propeller-shaft coupling system. After the flow field calculation at each time step is completed, extract the propeller excitation, load it into the shafting dynamics model for response calculation, and then feedback the obtained response results to the propeller flow field in the form of the centroid motion of the propeller to continue the flow field calculation for the next time step; during the solution process, obtain the propeller flow field excitation force and the shafting vibration displacement, velocity, and acceleration results in real time.

[0012] The present invention may further include:

[0013] 1. Specifically, step (1) is as follows:

[0014] First, determine the flow field domain range according to the input propeller geometric model, and divide it into two internal and external basins for processing. The internal basin simulates the rotation of the propeller, and the external basin simulates the oncoming flow and the motion induced by the shafting vibration; subsequently, perform spatial discretization of the flow field domain, divide the flow field calculation grid, and select the grid division parameters according to the propeller size during this process, and select the height of the first layer of grid according to the operating conditions of the propeller and the turbulence model selected for the numerical simulation; finally, define the boundary conditions in the flow field to complete the preprocessing work of the propeller CFD simulation and output the flow field model for use in subsequent steps.

[0015] 2. Specifically, step (3) is as follows:

[0016] a. Establish a numerical model for the dynamic coupling of the propeller and the shafting:

[0017] After completing the modeling process, output the mass, stiffness, and damping matrices in the model to the next step;

[0018] b. Extract the propeller fluid excitation force in the flow field simulation:

[0019] After the flow field simulation at each time step is completed, extract the pressure on each unit surface of the propeller blade, and integrate it according to the 6 degrees of freedom in the Cartesian coordinate system to obtain the fluid excitation force and moment at this time step. Transmit the obtained excitation to the dynamic response solution module, and repeat the above process after the flow field solution for the next time step is completed;

[0020] c. Solve the forced vibration response of the shafting based on the Newmark-β method:

[0021] Combine the obtained shafting dynamics model and the propeller fluid excitation, and simultaneously calculate the shafting mass imbalance excitation. Input the mass, stiffness, damping matrices of the system and the excitation data into the shafting forced vibration response solution module, and obtain the shafting dynamics response at this time step through calculation;

[0022] d. Use the centroid motion of the propeller to feedback on the flow field:

[0023] After obtaining the dynamic response of the shafting system, on the one hand, the response results and the excitation results are output to the document together, and on the other hand, the feedback effect of the dynamic response on the propeller flow field is realized, and the flow field simulation of the next time step is started; the vibration velocity results at the propeller position in the dynamic response results are extracted and assigned to the corresponding fluid domain in the propeller flow field model. In the flow field simulation of the next time step, the propeller rotates while undergoing a translational motion with the vibration velocity obtained in the previous time step as the velocity, realizing the feedback effect of the shafting dynamics on the propeller flow field.

[0024] The advantages of the present invention are as follows: When using the method of the present invention for two-way fluid-structure interaction numerical simulation of the propeller-shaft coupling system, on the one hand, the coupling effect of the viscous flow of the propeller and the multi-degree-of-freedom of the elastic shafting is considered, and at the same time, the influence of factors such as non-uniform inflow, propeller flow field excitation, and shafting mass imbalance excitation is also considered, which can accurately simulate the dynamic characteristics of the coupling system under various complex excitations; on the other hand, since the shafting dynamics model is compiled into the flow field solver by means of secondary development in the present invention, there is no additional computational resource requirement for two-way coupling simulation, and the solution speed of two-way coupling is very close to the conventional flow field solution speed. The method proposed by the present invention has a higher computational efficiency than the built-in fluid-structure interaction algorithm of commercial software. In addition, when using the method of the present invention for simulation, researchers can also obtain the propeller flow field excitation force and the results of the shafting vibration displacement, velocity, acceleration, etc. in real time, which is also very conducive to the study of the dynamic characteristics of the coupling system.

[0025] Through the method proposed by the present invention for two-way fluid-structure interaction numerical simulation analysis of the propeller-shaft coupling system, the propeller flow field and the shafting dynamics numerical model can be combined, and the shafting dynamics model is compiled into the flow field solver through a secondary development program, and two-way fluid-structure interaction simulation is carried out in the same solver. Furthermore, on the premise of saving a large amount of computational resources, rich fluid excitation and dynamic response results can be obtained for researchers to analyze. In the process of shafting dynamics modeling, the present invention can directly perform modeling through input parameters without the GUI operation in commercial software, so the process of establishing and modifying the dynamics model is very convenient. In the process of setting two-way coupling calculation, on the basis of the conventional CFD solution setting, the present invention only needs to add one step of compiling the secondary development program to complete the setting of two-way coupling in the flow field solver, which is also more convenient than the traditional method and improves the work efficiency of researchers. Brief Description of the Drawings

[0026] Figure 1 It is a schematic diagram of the propeller-shaft coupling system of the present invention;

[0027] Figure 2 It is a flow chart of the present invention;

[0028] Figure 3 Results of the propeller excitation force in the embodiments of the present invention;

[0029] Figure 4 Results of the shafting dynamic response in the embodiments of the present invention. Detailed implementation manners

[0030] The present invention will be described in more detail with reference to the accompanying drawings as follows:

[0031] Combined with Figures 1-4 the specific steps of the embodiments of the present invention are as follows:

[0032] Step 1: Perform numerical modeling on the propeller flow field part. Determine the flow field domain range according to the input propeller geometric model, perform spatial discretization of the flow field domain, define the boundary conditions in the flow field, and prepare the preprocessing for the propeller CFD simulation.

[0033] The implementation manner of this part has no significant difference from the preprocessing manner of the conventional propeller flow field simulation. First, determine the flow field domain range according to the input propeller geometric model, which needs to be processed in two inner and outer basins. The inner basin is used to simulate the rotation of the propeller, and the outer basin is used to simulate the oncoming flow and the movement induced by the shafting vibration. Subsequently, perform spatial discretization of the flow field domain, divide the flow field calculation grid, and reasonably select the grid division parameters according to the propeller size during this process. Reasonably select the height of the first layer of grid according to the operating conditions of the propeller and the turbulence model selected for the numerical simulation. Finally, it is also necessary to define the boundary conditions in the flow field, complete the preprocessing work of the propeller CFD simulation, and output the flow field model for use in the subsequent steps.

[0034] Step 2: Perform numerical modeling on the shafting dynamics part. Establish a shafting dynamics numerical model according to the input parameters such as the geometry and material of the shafting, and equivalently simulate the supports such as bearings as stiffness and damping and load them into the model.

[0035] Combined with Figure 1 Introduce the propeller-shaft coupling system. The coupling system is mainly composed of supports such as the propeller, rotating shaft, front and rear stern bearings, intermediate bearings, and thrust bearings. The shafting dynamics modeling in the present invention is based on the finite element method. Rigid disk elements are used to simulate the propeller, elastic beam elements are used to model the shaft segments, and the bearing supports are simulated by adding stiffness and damping. In the shafting dynamics modeling carried out in the present invention, the added water effect of the propeller is considered, and the added water mass and damping of the propeller are corrected in the mass and damping matrices. Through the dynamics modeling part in the program written in the present invention, only the geometric and material parameters of the shafting need to be imported into the program to complete the numerical modeling of the dynamics. When the model needs to be modified, only new parameters need to be imported again to complete. The shafting dynamics numerical modeling process in the method of the present invention is very convenient.

[0036] Step 3: Import the models established in the previous two steps into the flow field solver. The shafting dynamics part is imported into the solver through a secondary development program. After compilation, two-way coupled calculation of the flow field and the structural field within the same solver is achieved.

[0037] Achieving two-way coupled calculation of the flow field and the structural field within the same solver through the secondary development program is the core content of the present invention. The calculation method of two-way coupling and the programming implementation of secondary development are described below. Figure 2 Describe the calculation method of two-way coupling and the programming implementation of secondary development.

[0038] (1) Establish a coupled numerical model of the propeller and shafting dynamics.

[0039] The implementation method of this part has been introduced in detail above. The modeling of shafting dynamics relies on a secondary development program. After completing the first-step modeling process in the program, the mass, stiffness, and damping matrices in the model are output to the next step.

[0040] (2) Extract the propeller fluid excitation force in the flow field simulation.

[0041] After the flow field simulation at each time step is completed, the pressure on each unit surface of the propeller blade is extracted through a secondary development program. Integrate according to the 6 degrees of freedom (3 translational degrees of freedom and 3 rotational degrees of freedom) in Cartesian coordinates to obtain the fluid excitation force and moment at this time step. The obtained excitation is transmitted to the dynamic response solution module, and the dynamic response will continue to be solved and the feedback to the propeller flow field will be carried out in the subsequent steps. In this step, the program will wait for the completion of the flow field solution at the next time step and repeat the above process.

[0042] (3) Solve the forced vibration response of the shafting based on the Newmark-β method.

[0043] Combining the shafting dynamics model and the propeller fluid excitation obtained in (1) and (2) above, and simultaneously calculating the shafting mass unbalance excitation, input the data such as the mass, stiffness, damping matrices, and excitation of the system into the shafting forced vibration response solution module. After calculation, the shafting dynamics response at this time step is obtained. The reason for using the Newmark-β method is its good convergence. When the convergence coefficient is reasonably selected, the numerical solution will converge forcibly. This method is widely used in the solution of the response characteristics of various dynamic systems. The dynamic response obtained in this step will be used for the feedback to the propeller flow field and result output in the subsequent steps.

[0044] (4) Use the movement of the propeller centroid to feedback on the flow field.

[0045] After obtaining the dynamic response of the shafting system in (3), on the one hand, the response results and the excitation results are output to a document together. On the other hand, the feedback effect of the dynamic response on the propeller flow field needs to be realized, and the flow field simulation for the next time step is started. The vibration velocity results at the position of the propeller in the dynamic response results are extracted and assigned to the corresponding fluid domain in the propeller flow field model. In this way, in the flow field simulation for the next time step, the propeller will rotate and at the same time translate with the vibration velocity obtained in the previous time step as the velocity, which realizes the feedback effect of the shafting dynamics on the propeller flow field.

[0046] The processes described above all occur in the calculation of one time step. On this basis, the secondary development program of the present invention will loop until the target simulation duration ends.

[0047] Step 4: Perform two-way fluid-structure interaction numerical simulation of the propeller-shaft coupling system. The method proposed in the present invention extracts the propeller excitation after the flow field calculation at each time step, loads it into the shafting dynamics model for response calculation, and then feeds back the obtained response results to the propeller flow field in the form of the centroid motion of the propeller to continue the flow field calculation for the next time step; during the solution process, the excitation force of the propeller flow field and the results such as the vibration displacement, velocity, and acceleration of the shafting can be obtained in real time.

[0048] Combined with Figure 3 、 Figure 4 the propeller fluid excitation and the shafting dynamic response results in, it can be seen that the method proposed in the present invention realizes the functions described above. Using this method, convergent and accurate simulation results can be obtained with limited computing resources to conduct research on the two-way fluid-structure interaction dynamics of the propeller-shaft coupling system. The numerical method proposed in the present invention can be applied to the performance prediction and design optimization of the propulsion shafting and ship propellers, and can also be applied to the research on the two-way fluid-structure interaction dynamics of other fluid machinery-rotor structures except the propeller-shaft system.

Claims

1. A two-way fluid-structure interaction numerical simulation method for a propeller-shaft coupling system, characterized in that: (1) Conduct numerical modeling of the propeller flow field. Determine the flow field domain range according to the input propeller geometric model, discretize the space of the flow field domain, define the boundary conditions in the flow field, and prepare the preprocessing for the propeller CFD simulation; (2) Conduct numerical modeling of the shafting dynamics part. Establish a numerical model of shafting dynamics according to the input shafting geometry and material parameters, and equivalently load the bearing supports as stiffness and damping into the model; (3) Import the models established in steps (1) and (2) into the flow field solver. Among them, the shafting dynamics part is imported into the solver through a secondary development program, and after compilation, the two-way coupling calculation of the flow field and the structure field within the same solver is realized; a. Establish a coupled numerical model of the propeller and shafting dynamics: After completing the modeling process, output the mass, stiffness, and damping matrices in the model to the next step; b. Extract the propeller fluid excitation force in the flow field simulation: After the end of the flow field simulation at each time step, extract the pressure on each unit surface of the propeller blade, and integrate it according to the 6 degrees of freedom in Cartesian coordinates to obtain the fluid excitation force and moment at this time step. Transmit the obtained excitation to the dynamic response solution module, and repeat the above process after the flow field solution of the next time step is completed; c. Solve the forced vibration response of the shafting based on the Newmark-β method: Combine the obtained shafting dynamics model and the propeller fluid excitation, and simultaneously calculate the shafting mass imbalance excitation. Input the mass, stiffness, damping matrices of the system and the excitation data into the shafting forced vibration response solution module, and calculate the shafting dynamics response at this time step through calculation; d. Use the centroid motion of the propeller to feedback on the flow field: After obtaining the shafting dynamics response, on the one hand, output the response result and the excitation result to the document together, on the other hand, realize the feedback effect of the dynamic response on the propeller flow field, and start the flow field simulation of the next time step; extract the vibration velocity result at the position of the propeller in the dynamic response result, and assign it to the corresponding fluid domain in the propeller flow field model. In the flow field simulation of the next time step, the propeller rotates while undergoing a translational motion with the vibration velocity obtained in the previous time step as the velocity, realizing the feedback effect of the shafting dynamics on the propeller flow field; (4) Conduct a two-way fluid-structure interaction numerical simulation of the propeller-shaft coupling system. After the flow field calculation at each time step, extract the propeller excitation, load it into the shafting dynamics model for response calculation, and then feedback the obtained response result to the propeller flow field through the centroid motion of the propeller, and continue the flow field calculation of the next time step; During the solution process, obtain the propeller flow field excitation force and the shafting vibration displacement, velocity, and acceleration results in real time.

2. A two-way fluid-structure interaction numerical simulation method for a propeller-shaft coupling system according to claim 1, characterized in that: Step (1) is specifically: First, determine the flow field domain range according to the input propeller geometric model, and divide it into two basins, the inner and outer basins, for processing. The inner basin simulates the rotation of the propeller, and the outer basin simulates the oncoming flow and the movement induced by the shafting vibration; Subsequently, perform spatial discretization of the flow field domain, divide the flow field calculation grid, select the grid division parameters according to the propeller size during this process, and select the height of the first layer of grid according to the operating conditions of the propeller and the turbulence model selected for numerical simulation; Finally, define the boundary conditions in the flow field, complete the preprocessing work of the propeller CFD simulation, and output the flow field model for subsequent steps.

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