Bidirectional fluid-solid coupling CFD and modal superposition ship water elasticity acquisition method and device, computer equipment and storage medium

Abstract

The invention discloses a bidirectional fluid-solid coupling CFD and modal superposition ship water elasticity acquisition method and device, computer equipment and a storage medium, and relates to the technical field of ship water elasticity, in particular to the technical field of bidirectional fluid-solid coupling CFD and modal superposition ship water elasticity. The ship water elasticity acquisition method comprises the following steps: S1, establishing a rigid ship body drainage basin model of a target ship in a CFD solver, and performing grid discretization and physical condition setting; s2, establishing an elastic hull structure model in an FEM solver, and performing grid discretization and boundary constraint setting; s3, constructing a bidirectional coupling matching method, and associating grid information of the drainage basin model with grid information of the structure model; s4, performing numerical simulation on a coupling result to obtain a hull surface pressure field; and S5, transmitting the pressure field to the structure model, calculating a motion equation, and obtaining real-time response data reflecting water elasticity. The method is suitable for the fields of ship design, ocean engineering, water surface transportation and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of ship hydroelasticity, and in particular to the technical field of ship hydroelasticity of bidirectional fluid-solid coupling CFD and modal superposition. Background Art

[0002] As the size of ships and marine structures increases, especially the length of ships, the hull structure becomes more and more "soft", and the elastic deformation of ships and marine structures cannot be ignored. The reduction of the natural frequency of ships and marine structures makes hydroelastic responses such as vibration and flutter more likely to occur in relatively calm sea conditions. Therefore, it is particularly necessary to consider the influence of hydroelastic response. In recent years, some major container ship accidents have occurred. The main reason is that the structural fatigue damage caused by hydroelastic response was not fully considered at the beginning of structural design. Due to the large openings of container ships, the bending stiffness and torsional stiffness of the hull are relatively low. In addition, the high speed of container ships causes high-frequency vibration of the hull structure due to high-frequency encounter frequencies, which further increases the amplitude of the bending moment. In order to reduce the occurrence of accidents, it is necessary to accurately calculate the hydroelastic response of large ships. However, the traditional hydroelastic calculation method based on potential flow theory often fails to comprehensively consider the viscosity of the fluid, the nonlinearity of wave loads, the nonlinearity of structural response, and the influence of structural deformation on the flow field.

[0003] At present, the numerical simulation of ship hydroelasticity mainly adopts potential flow theory or general CFD-FEM fluid-solid coupling method. However, the potential flow theory cannot effectively simulate strong nonlinear waves, which makes the calculation of ship hydroelastic response under wave action limited to the range of linear waves and weak nonlinear waves, and does not take into account the fluid-solid coupling problem between ships and waves. In addition, the general CFD-FEM fluid-solid coupling method has high time cost and low computational efficiency. Summary of the invention

[0004] In order to solve the limitations of water elasticity calculation in the prior art and the problems of low calculation efficiency and high time cost, this application proposes the following solutions:

[0005] A method for acquiring ship hydroelasticity by bidirectional fluid-solid coupling CFD and modal superposition, the method comprising the following steps:

[0006] S1. Establishing a watershed model of a rigid hull of a target ship in a CFD solver, performing mesh discretization on the watershed model and setting physical conditions, wherein the target ship is a ship for which water elasticity is to be obtained;

[0007] S2. Establishing a structural model of the elastic hull of the target ship in the FEM solver, performing mesh discretization on the structural model and setting boundary constraints;

[0008] S3, constructing a bidirectional coupling matching method of fluid-structure grid information, which is used to associate the grid-discretized flow domain model in S1 with the grid-discretized structure model in S2, and obtain the coupling matching result;

[0009] S4, performing numerical simulation on the result of the coupling matching to obtain the surface pressure field of the hull;

[0010] S5. The surface pressure field of the hull is transmitted to the structural model described in S2 through a bidirectional fluid-solid coupling matching method and a modal transformation method, and the motion equations generated by the modal transformation are numerically superimposed to obtain real-time response data of the hull structure, wherein the corresponding data reflects the hydroelasticity of the target ship.

[0011] Furthermore, the S1 includes:

[0012] S101, creating a watershed model in a CFD solver, wherein the watershed model is a rectangular parallelepiped water area, which is composed of four side walls, a bottom surface and a top surface;

[0013] S102, importing the three-dimensional data of the hull structure into the CFD solver, and performing Boolean operations on the hull and the watershed to obtain a virtual calculation pool;

[0014] S103, using the VOF method to divide the virtual computing pool into an upper air layer, a free liquid surface layer and a lower water layer, and using a VOF-based geometric reconstruction method to calculate the volume of the grid fluid at the free liquid surface;

[0015] S104, setting a grid deformation method, using an overlapping grid method to solve the hull motion, and using a deforming grid method to solve the hull structure deformation, so as to achieve mixed deformation of the grid;

[0016] S105, meshing the watershed model, and locally encrypting the free surface layer, the hull surface mesh, and the overlapping meshes according to characteristic physical quantities of the watershed wave surface and characteristic scales of the hull;

[0017] S106, setting physical conditions for the watershed model, including: three-dimensional, implicit unsteady state, VOF wave, k-omega turbulence model, multiphase, turbulence, watershed volume, gravity, and unit mass correction model;

[0018] S107, setting conditions for the six boundaries of the flow domain, setting the four side wall surfaces and the bottom surface as velocity inlets, and setting the top surface as a pressure outlet;

[0019] S108, setting wave generation and wave elimination modes for the watershed model, using momentum source term to generate watershed waves, using force wave elimination technology to eliminate waves, and using the incoming flow velocity of the watershed as the forward speed of the ship.

[0020] Further, the S2 includes:

[0021] S201, establishing a three-dimensional finite element model of a hull structure in a FEM solver, wherein the three-dimensional finite element model of the hull structure includes a hull surface and an internal structure;

[0022] S202, meshing the three-dimensional finite element model, including meshing the hull surface and internal structure with shell elements;

[0023] S203, setting material property data of the hull surface and internal structure, wherein the material properties include mass, density, stiffness, elastic modulus, Poisson's ratio and structural damping;

[0024] S204, inputting material property data into the three-dimensional finite element model after mesh discretization to obtain the natural frequency and mode shape matrix of the hull under free vibration;

[0025] S205. According to the natural frequency and mode matrix of the hull under free vibration, gravity load is applied to all grid nodes, fluid load is applied to the grid nodes on the hull surface in contact with the external flow domain, and displacement constraints are applied to the grid nodes in combination with the degrees of freedom of the hull motion.

[0026] Further, the S3 includes:

[0027] S301, transferring the fluid load acting on the grid nodes on the hull surface to the FEM solver through the CFD solver, the FEM solver calculates the structural grid displacement on the hull surface through the modal superposition method, and returns the value to the CFD solver, the CFD solver calculates the returned value and outputs the fluid pressure and shear force on the hull surface;

[0028] S302, performing a bidirectional coupling analysis, loading the CFD output results into the fluid-solid interface of the solid finite element mesh in the form of a structural load to obtain structural deformation, feeding back the structural deformation to the CFD solver to reposition the solid wall boundary, and realizing the lifting deformation of the CFD calculation mesh;

[0029] S303. Use Gaussian surface approximation method to calculate the node forces on each structural grid in the three-dimensional finite element model of the hull structure:

[0030]

[0031] in, is the node force, X g is the g-th Gaussian node, n g is the total number of Gaussian nodes used to approximate the total nodal force, λ g is the distance weight, N iis the shape function, n is the normal vector of the structural grid unit, p is the fluid grid node pressure, σ F is the fluid stress;

[0032] S304. Constructing a bidirectional coupling matching method for fluid-structure mesh information:

[0033] First, the expression of the structural displacement vector to the fluid displacement vector is:

[0034]

[0035] Among them, F n is the fluid interface node, S n is a structural node, is the structural displacement vector, is the fluid displacement vector, is the transformation matrix from the structure nodes to the fluid interface nodes in the radial basis function, is the radial basis function matrix used to calculate the interpolation weights after the structural node values ​​are known;

[0036] Then, the normal stress at the structural node is calculated as:

[0037]

[0038] Among them, F f is the center of the fluid interface, is the transformation matrix from the center of the fluid interface to the structural node in the radial basis function, is the radial basis function matrix used to calculate the interpolation weights after the center value of the fluid interface is known. is the state variable at the center of the fluid interface;

[0039] Finally, the center displacement of the fluid interface is obtained by interpolation from the node values, expressed as:

[0040]

[0041] in, It is the transformation matrix from the structural node to the center of the fluid interface in the radial basis function.

[0042] Further, the S5 includes:

[0043] S501, transmitting the surface pressure field of the hull to the three-dimensional finite element model of the hull structure through a bidirectional fluid-solid coupling matching method and modal transformation, transferring the deformation displacement of the hull structure to the flow domain model, and recalculating the surface pressure field of the hull;

[0044] S502, presetting the calculation time step, the total simulation time and the number of data exchanges in each time step, and synchronously running the CFD solver and the FEM solver to perform numerical simulation calculations;

[0045] S503, using a modal superposition method to obtain the displacement, bending moment and shear force of any cross section of the hull, the modal superposition method being:

[0046] Considering the fluid as an inviscid compressible fluid, the equilibrium equation is obtained:

[0047]

[0048] Among them, p f is the fluid dynamic pressure, ρ f is the fluid density, γ is the volume constant for dissipative effects, is the fluid particle velocity, is the fluid particle acceleration;

[0049] Fluid pressure p and fluid bulk modulus K f The relationship between the volume strain and the

[0050]

[0051] From this we obtain the equation of motion for the fluid with respect to fluid pressure:

[0052]

[0053] The discrete finite element equation is obtained from the above formula:

[0054]

[0055] Among them, M f is the fluid inertia matrix, C f is the fluid damping matrix, K f is the fluid stiffness matrix, p is the pressure vector of the fluid node, d is the displacement vector on the fluid-solid interface, S fs is the coupling matrix;

[0056] By coupling the fluid pressure acting at the interface, the equation of motion of the structure is obtained:

[0057]

[0058] Among them, M s is the structural mass matrix, C s is the structural damping matrix, K s is the structural stiffness matrix, F f is the fluid force vector in the CFD solver, is the force acting on the structure due to fluid-structure interaction;

[0059] Get the complete finite element equation description of fluid-structure interaction:

[0060]

[0061] An auxiliary quantity ψ is introduced into the complete finite element equation of fluid-structure interaction:

[0062] ψ=p / ω 2 ,

[0063] Among them, ω is the eigenvalue;

[0064] Transforming the complete finite element equation of fluid-structure interaction into a symmetrical eigenvalue problem, we obtain the following equation:

[0065]

[0066] Compared with other structural forces, It is very small and is ignored in structural analysis, and the formula is simplified to:

[0067]

[0068] Where d is the displacement vector at the fluid-solid grid interface, expressed as:

[0069]

[0070] Where n is the modal order; is the i-th order mode shape vector, z i is the coordinate of the i-th vibration mode;

[0071] According to the orthogonality of the modal vibration shapes, the structural motion equations are decoupled:

[0072]

[0073] Among them, ω i is the natural frequency of the i-th vibration mode, ζ i is the damping ratio of the i-th vibration mode;

[0074] S504, transferring the mesh deformation of the structure obtained by mode superposition to the fluid mesh through a bidirectional fluid-solid coupling matching method to perform calculations for the next time step.

[0075] A device for calculating ship hydroelasticity using bidirectional fluid-solid coupling CFD and modal superposition, the device comprising:

[0076] A watershed model building module is used to establish a rigid hull watershed model in a CFD solver, discretize the watershed grid of the rigid hull watershed model, and set physical parameters, initial conditions, and boundary conditions;

[0077] A hull structure model building module is used to establish a three-dimensional finite element model of the hull structure in the FEM solver, discretize the structural grid of the three-dimensional finite element model of the hull structure to calculate the natural frequency and vibration mode of the hull during free vibration, and impose constraints on the structural grid;

[0078] Constructing an association module, which is used to construct a two-way coupling matching method of information from the watershed grid to the structural grid, so that each fluid grid is associated with its optimal structural unit grid;

[0079] A simulation module, used for simulating a preset hull in the CFD solver, and outputting a preset hull surface pressure field and a time history value of a preset hull motion;

[0080] A modal superposition module is used to transfer the preset hull surface pressure field to the three-dimensional finite element model of the hull structure through the information bidirectional coupling matching method and modal transformation, and numerically superimpose the modal motion equations to obtain and export the real-time response data of the preset hull structure.

[0081] A computer storage medium is used to store a computer program. When the computer program is read by a computer, the computer executes the steps in the method for obtaining the hydroelasticity of a ship described in the present invention.

[0082] The computer device comprises a processor and a storage medium. When the processor reads and runs the computer program stored in the storage medium, the processor executes the steps in the method for obtaining the hydroelasticity of a ship according to the present invention.

[0083] Furthermore, the computer device includes various intelligent processing devices, such as computers, notebooks, tablet computers, smart handheld devices, etc.

[0084] The computer program product, as a computer program, implements the steps in the method for obtaining the water elasticity of a ship described in the present invention when the computer program is read.

[0085] Beneficial effects:

[0086] (1) The present invention is a two-way fluid-solid coupling CFD and modal superposition ship hydroelastic calculation method, which combines computational fluid dynamics (CFD) with finite element method (FEM) to consider the dynamic effect of fluid on the hull and the feedback effect of the hull on the fluid in real time, making up for the deficiency of traditional potential flow theory that cannot effectively simulate the effect of fluid-solid coupling, and enhancing the calculation accuracy of hydroelastic response;

[0087] (2) The present invention provides a method for calculating the hydroelasticity of a ship using bidirectional fluid-solid coupling CFD and modal superposition. By establishing a high-precision watershed model and setting appropriate boundary conditions, the method can more accurately simulate the motion state of the ship under various sea conditions, and the calculation of the hydroelastic response is more realistic. This overcomes the problem that the calculation of the hydroelastic response in traditional methods is limited to the range of linear waves and weak nonlinear waves.

[0088] (3) The present invention provides a method for calculating the hydroelasticity of a ship using bidirectional fluid-solid coupling CFD and modal superposition. By constructing a three-dimensional finite element model, the method can accurately calculate the natural frequency and vibration mode of the hull under different loads, thus avoiding the simplified processing of the structure in traditional methods.

[0089] (4) The present invention provides a method for calculating ship hydroelasticity by combining bidirectional fluid-solid coupling CFD and modal superposition, and constructs a bidirectional coupling matching method for fluid-structure grid information, which ensures the precise matching of fluid grid and solid grid, making the information transmission between fluid and solid more efficient. Compared with the existing CFD-FEM method, it avoids the calculation error caused by grid mismatch and improves the reliability and efficiency of the overall calculation.

[0090] (5) The present invention provides a method for calculating the hydroelasticity of a ship using bidirectional fluid-solid coupling CFD and modal superposition. Through the modal superposition method, the analysis of the pressure field on the hull surface is more in-depth, and nonlinearity and frequency response can be taken into account. This overcomes the limitations of the linear assumptions in the prior art and provides a more comprehensive calculation for the dynamic behavior of the ship in a complex wave environment.

[0091] (6) The present invention provides a method for calculating ship hydroelasticity by combining bidirectional fluid-solid coupling CFD and modal superposition. By setting the calculation time step and data exchange frequency, the synchronous operation efficiency of the CFD and FEM solvers is significantly improved, the calculation time cost is reduced, and the problems of high time cost and low calculation efficiency in the prior art are solved.

[0092] The invention is applicable to the fields of ship design, marine engineering, surface transportation, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Figure 1 It is a flow chart of a hydroelastic calculation method of bidirectional fluid-solid coupling CFD and modal superposition described in the first embodiment;

[0094] Figure 2 It is a data processing principle diagram of a bidirectional fluid-solid coupling CFD and modal superposition hydroelastic calculation method described in the first embodiment;

[0095] Figure 3 It is a schematic diagram of the flow field solution using the coupled overlapping grid and VOF-based geometric reconstruction method described in the first embodiment;

[0096] Figure 4 This is the data processing method for constructing a bidirectional coupling matching method of fluid-solid grid information described in the first embodiment;

[0097] Figure 5 It is a CAD three-dimensional solid model of the hull of a luxury cruise ship described in the second implementation mode;

[0098] Figure 6 It is the numerical water pool described in the second embodiment, reference numeral 1 is the CAD three-dimensional solid model of the hull, 2 is the free surface, 3 is the air layer, and 4 is the water layer;

[0099] Figure 7 It is the grid discretization of the flow field cross section in the numerical water pool described in the second implementation mode;

[0100] Figure 8 is a side view of a surface mesh discretization of the numerical calculation model described in the second embodiment in the flow field;

[0101] Fig. 9 is a top view of the surface mesh discretization of the numerical calculation model described in the second embodiment in the flow field;

[0102] Fig.10 The surface mesh discretization of the numerical calculation model described in the second embodiment in the three-dimensional structure;

[0103] Fig.11 is a comparison between the calculation results described in the second embodiment and the heave results of the model test;

[0104] Fig.12 It is a comparison between the calculation results described in the second implementation mode and the vertical bending moment results of the model test. Implementation

[0106] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0107] Implementation Method 1

[0108] Combination Figure 1 The present embodiment is described as a method for calculating the hydroelasticity of a ship using bidirectional fluid-structure coupling CFD and modal superposition, the method comprising the following steps:

[0109] S1. Establishing a watershed model of a rigid hull in a CFD solver, discretizing the watershed grid of the watershed model, and setting the physical conditions of the watershed;

[0110] S2. Establishing a three-dimensional finite element model of the hull structure in a FEM solver, performing mesh discretization on the finite element model, obtaining the natural frequency and mode shape of the hull during free vibration, and creating boundary constraints based on the natural frequency and mode shape;

[0111] S3, construct a bidirectional coupling matching method of fluid-solid mesh information to associate the fluid mesh with the optimal solid mesh;

[0112] S4, numerically simulate the hull established in S1-S3 in the CFD solver to obtain the time-history changes of its surface pressure field and motion;

[0113] S5. The surface pressure field of the hull is transmitted to the finite element model described in S2 through a bidirectional fluid-solid coupling matching method and modal transformation, and the motion equations generated by the modal transformation are numerically superimposed to obtain a mesh deformation of the hull structure, and the mesh deformation is output to the surface pressure field of the hull to perform iteration for the next time step.

[0114] By establishing a flow domain model of a rigid hull in the CFD solver, the flow field around the hull can be accurately simulated, ensuring that the grid discretization of the flow domain adapts to the flow characteristics, optimizing the calculation accuracy, and providing a basis for subsequent fluid analysis.

[0115] A three-dimensional finite element model of the hull structure is established in the FEM solver, which can fully consider the geometric characteristics of the hull, discretize the mesh of the finite element model, and obtain the natural frequency and vibration mode of the hull during free vibration, providing key data for subsequent dynamic analysis and structural optimization.

[0116] Constructing a bidirectional coupling matching method for fluid-solid grid information to ensure efficient association between fluid grid and solid grid can effectively improve the efficiency of information transmission between fluid and structure, reduce calculation errors caused by grid mismatch, and improve overall calculation accuracy.

[0117] Numerical simulation is performed in the CFD solver to obtain the surface pressure field of the hull and the time-history changes of its motion, which can intuitively reflect the hydroelastic response, provide an important basis for subsequent analysis and optimization, and help to understand the dynamic performance of the hull under actual sea conditions.

[0118] Through the bidirectional fluid-solid coupling matching method and modal transformation, the surface pressure field of the hull is transmitted to the finite element model, and the numerical superposition of the motion equations is performed, which can achieve efficient iterative calculations. This not only improves the accuracy and stability of the calculations, but also can promptly reflect the response of the structure under dynamic loads, thereby optimizing the design and improving safety.

[0119] like Figure 2 As shown, in this implementation, the S1 specifically includes:

[0120] S101, creating a watershed model in a CFD solver, wherein the watershed model is a rectangular parallelepiped water area, which is composed of four side walls, a bottom surface and a top surface;

[0121] S102, importing the three-dimensional data of the hull structure into the CFD solver, and performing Boolean operations on the hull and the watershed to obtain a virtual calculation pool;

[0122] S103, using the VOF method to divide the virtual computing pool into an upper air layer, a free liquid surface layer and a lower water layer, and using a VOF-based geometric reconstruction method to calculate the volume of the grid fluid at the free liquid surface. The control equation of the geometric VOF method specifically includes:

[0123] The VOF method is used to solve the spatiotemporal variation of the free surface of an incompressible, incompatible multiphase fluid. The transport equation of the fluid volume is:

[0124]

[0125] Among them, f α (t) represents the indicator function of the phase distribution at time t. When the grid is full of liquid, its value is 1; when the grid is full of gas, its value is 0. u represents the velocity field.

[0126] The liquid volume within any grid is calculated using the following formula:

[0127]

[0128] Where α(t) is the liquid volume fraction at time t, and dV is the differential volume element;

[0129] In a finite time [t, t+Δt], by integrating formula (2) over time on a fixed unit and according to the divergence theorem, the evolution equation of the liquid volume fraction over time can be calculated:

[0130]

[0131] in, Represents the boundary of the grid participating in the calculation, is the external normal direction of the boundary element, dS is the grid area differential, dt is the time differential element, and the integral term represents the net flux of liquid flowing into the grid within time Δt.

[0132] The formula for calculating the volume of a fluid is defined as:

[0133]

[0134] Discretize the formula on the grid unit surface. Assuming that the grid unit has N surfaces, the area integral term on the right side is modified to:

[0135]

[0136] Among them, S k represents the kth mesh surface, Represents the direction of the outer normal of the face.

[0137] The velocity field u on the kth surface in contact with the fluid can be approximately defined as:

[0138]

[0139] Where u(x,t) is the velocity vector at spatial position x and time t, dN is the normal vector of the differential surface element, and F k is the kth surface in contact with the fluid, dS is the grid area differential, |N k | is the magnitude of the normal vector on the kth face.

[0140] Then the solution formula for volume in formula (4) (fluid volume) becomes:

[0141]

[0142] In formula (7) (the evolution equation of liquid volume fraction over time), The surface integral of represents the instantaneous area of ​​surface k immersed in the fluid, which is named A k , the formula is further simplified to:

[0143]

[0144] Among them, A k (t) represents the instantaneous immersed area of ​​the kth surface at time t.

[0145] S104, setting a grid deformation method, using an overlapping grid method to solve the hull motion, and using a deforming grid method to solve the hull structure deformation, so as to achieve mixed deformation of the grid;

[0146] S105, meshing the watershed model, and locally encrypting the free surface layer, the hull surface mesh, and the overlapping meshes according to characteristic physical quantities of the watershed wave surface and characteristic scales of the hull;

[0147] S106, setting physical conditions for the watershed model, including: three-dimensional, implicit unsteady state, VOF wave, k-omega turbulence model, multiphase, turbulence, watershed volume, gravity, and unit mass correction model;

[0148] S107, setting conditions for the six boundaries of the flow domain, setting the four side wall surfaces and the bottom surface as velocity inlets, and setting the top surface as a pressure outlet;

[0149] S108, setting wave generation and wave elimination modes for the watershed model, using momentum source term to generate watershed waves, using force wave elimination technology to eliminate waves, and using the incoming flow velocity of the watershed as the forward speed of the ship.

[0150] like Figure 2 As shown, in this embodiment, S2 specifically includes:

[0151] S201, establishing a three-dimensional finite element model of a hull structure in a FEM solver, wherein the three-dimensional finite element model of the hull structure includes a hull surface and an internal structure;

[0152] S202, meshing the three-dimensional finite element model, including meshing the hull surface and internal structure with shell elements;

[0153] S203, setting material property data of the hull surface and internal structure, wherein the material properties include mass, density, stiffness, elastic modulus, Poisson's ratio and structural damping;

[0154] S204, inputting material property data into the three-dimensional finite element model after mesh discretization to obtain the natural frequency and mode shape matrix of the hull under free vibration;

[0155] S205. Apply gravity load to all grid nodes, apply fluid load to the grid nodes on the hull surface in contact with the external flow domain, and apply displacement constraints to all grid nodes.

[0156] like Figure 3 As shown, in this embodiment, S3 specifically includes:

[0157] S301, transferring the fluid load acting on the grid nodes on the hull surface to the FEM solver through the CFD solver, the FEM solver calculates the structural grid displacement on the hull surface through the modal superposition method, and returns the value to the CFD solver, the CFD solver calculates the returned value and outputs the result;

[0158] S302, perform fluid-solid coupling analysis, load the CFD output results into the fluid-solid interface of the solid finite element mesh in the form of structural load and calculate the results, feed the calculation results of the solid finite element mesh back to the CFD solver, reposition the solid wall boundary through the CFD solver and realize the lifting deformation of the CFD calculation mesh;

[0159] S303, using the Gaussian surface approximation method to calculate the node forces on each structural grid in the three-dimensional finite element model of the hull structure, specifically:

[0160]

[0161] in, is the node force, X g is the g-th Gaussian node, n g is the total number of Gaussian nodes used to approximate the total nodal force, λ g is the distance weight, N i is the shape function, n is the normal vector of the structural grid unit, p is the fluid grid node pressure, σ F is the fluid stress;

[0162] S304, constructing a bidirectional coupling matching method of fluid-solid grid information, specifically:

[0163] First, the expression of the structural displacement vector to the fluid displacement vector is:

[0164]

[0165] Among them, F n is the fluid interface node, S n is a structural node, is the structural displacement vector, is the fluid displacement vector, is the transformation matrix from the structure nodes to the fluid interface nodes in the radial basis function, is the radial basis function matrix used to calculate the interpolation weights after the structural node values ​​are known;

[0166] The expression of the structural displacement vector to the fluid displacement vector is based on Derived,

[0167] in, represents the interpolation operator from the structure node to the fluid interface node;

[0168] Therefore, in this embodiment, the displacement vector of the structure to the displacement vector of the fluid is:

[0169]

[0170] Then, the normal stress at the structural node is calculated as:

[0171]

[0172] Among them, F f is the center of the fluid interface, is the transformation matrix from the center of the fluid interface to the structural node in the radial basis function, is the radial basis function matrix used to calculate the interpolation weights after the center value of the fluid interface is known. is the state variable at the center of the fluid interface;

[0173] The calculation formula of the normal stress of the structural node is based on Derived,

[0174] in, represents the interpolation operator from the center of the fluid interface to the structural nodes;

[0175] Therefore, the calculation formula of the normal stress of the structural node in this embodiment is:

[0176]

[0177] Finally, the center displacement of the fluid interface is obtained by interpolation from the node values, expressed as:

[0178]

[0179] in, It is the transformation matrix from the structure node to the center of the fluid interface in the radial basis function;

[0180] The interpolation of the node values ​​to obtain the center displacement of the fluid interface is based on the formula Derived,

[0181] in, To perform the node-surface interpolation matrix;

[0182] Therefore, in this embodiment, the center displacement of the fluid interface is obtained by interpolation of the node values:

[0183]

[0184] In this implementation, S4 specifically includes:

[0185] S401, set the total solution time and time step.

[0186] S402, setting the number of iterations in each time step to ensure that the calculation results of each time step converge.

[0187] S403. Setting the data exchange frequency between the fluid and structural solvers to ensure effective transmission of fluid pressure field and structural response information in each time step to achieve bidirectional coupling.

[0188] S404, determine the boundary conditions and physical properties of the initial fluid field to meet the actual situation and prepare for simulation.

[0189] S405. Use a CFD solver to perform numerical simulation and calculate the flow of fluid on and around the hull surface in each time step.

[0190] S406. Real-time monitoring of key parameters to ensure the stability of the simulation process and make adjustments based on actual conditions when necessary

[0191] S407. Obtain the surface pressure field of the hull and the time history change of the motion.

[0192] like Figure 4 As shown, in this implementation, S5 specifically includes:

[0193] S501, transmitting the surface pressure field of the hull to the three-dimensional finite element model of the hull structure through a bidirectional fluid-solid coupling matching method and modal transformation, transferring the deformation displacement of the hull structure to the flow domain model, and recalculating the surface pressure field of the hull;

[0194] S502, presetting the calculation time step, the total simulation time and the number of data exchanges in each time step, and synchronously running the CFD solver and the FEM solver to perform numerical simulation calculations;

[0195] S503, using a modal superposition method to obtain the displacement, bending moment and shear force of any cross section of the hull, wherein the modal superposition method is specifically as follows:

[0196] Considering the fluid as an inviscid compressible fluid, the equilibrium equation is obtained:

[0197]

[0198] Among them, p f is the fluid dynamic pressure, ρ f is the fluid density, γ is the volume constant for dissipative effects, is the fluid particle velocity, is the fluid particle acceleration;

[0199] Fluid pressure p and fluid bulk modulus K f The relationship between the volume strain and the

[0200]

[0201] From this we can obtain the equation of motion for the fluid with respect to fluid pressure:

[0202]

[0203] The discrete finite element equation can be obtained from the above formula:

[0204]

[0205] Among them, M f is the fluid inertia matrix, C f is the fluid damping matrix, K f is the fluid stiffness matrix, p is the pressure vector of the fluid node, d is the displacement vector on the fluid-solid interface, S fs is the coupling matrix;

[0206] By coupling the fluid pressure acting at the interface, the equation of motion of the structure is obtained:

[0207]

[0208] Among them, M s is the structural mass matrix, C s is the structural damping matrix, K s is the structural stiffness matrix, F f is the fluid force vector in the CFD solver, is the force acting on the structure due to fluid-structure interaction;

[0209] Get the complete finite element equation description of fluid-structure interaction:

[0210]

[0211] An auxiliary quantity ψ is introduced into the complete finite element equation of fluid-structure interaction:

[0212] ψ=p / ω 2 ,

[0213] Among them, ω is the eigenvalue;

[0214] Transforming the complete finite element equations of fluid-structure interaction into a symmetrical eigenvalue problem leads to the following equation:

[0215]

[0216] Compared with other structural forces, It is very small and is ignored in structural analysis, and the formula is simplified to:

[0217]

[0218] Where d is the displacement vector at the fluid-solid grid interface, expressed as:

[0219]

[0220] where n is the modal order; is the i-th order modal vibration mode vector, z i is the coordinate of the i-th order vibration mode;

[0221] According to the orthogonality of the modal vibration modes, the structural motion equation is decoupled:

[0222]

[0223] where ω i is the natural frequency of the i-th order vibration mode, and ζ i is the damping ratio of the i-th order vibration mode;

[0224] S504. Transfer the mesh deformation of the structure obtained by modal superposition to the fluid mesh through the two-way fluid-structure coupling matching method for the calculation of the next time step.

[0225] Embodiment 2

[0226] This embodiment is illustrated by a specific application scenario. A ship hydroelasticity calculation method combining two-way fluid-structure coupling CFD and modal superposition is as follows:

[0227] As Figure 5 shown, taking a certain luxury cruise ship as an example, the scale ratio of the calculation model is 1:60, the length between perpendiculars of the model is 4.966 m, the molded breadth is 0.62 m, the molded depth is 0.494 m, the draft is 0.143 m, and the displacement is 321 kg. The ship model sails at a speed of 0 kn head-on in regular waves, and the flexible deformation effect of the hull structure under the action of waves is considered during the simulation process.

[0228] In this embodiment, the CFD solver uses the OpenFOAM software, the FEM solver uses the Calculix software, and the coupling platform uses the preCICE software to perform two-way coupled data exchange between the CFD and FEM solvers.

[0229] Step 1. Establish a rigid hull domain model in the CFD solver, discretize the mesh of the domain, and set the physical conditions of the domain. In this embodiment, it specifically includes the following steps:

[0230] Establish a tank fluid domain. The tank fluid domain is a cuboid space domain surrounded by 6 faces including 4 side walls, a bottom surface and a top surface. The dimensions of the tank fluid domain in the longitudinal x-axis, transverse y-axis, and vertical z-axis of the ship are -2Lpp < x < 4Lpp, -2.5Lpp < y < 2.5Lpp, and -3.5Lpp < z < 1.5Lpp, where Lpp is the total length of the hull model.

[0231] Set the degrees of freedom, weight, center of gravity position and moment of inertia of the hull CAD 3D solid model 6, and set the position of the hull CAD 3D solid model 1 in the fluid domain. In this embodiment, only the vertical and pitching of the hull in regular waves are considered. The weight of the hull CAD 3D solid model is 321kg, the longitudinal position of the center of gravity is 2.6m from the stern column, the vertical position of the center of gravity is 0.299m from the baseline, and the rolling moment of inertia is 13.43m 4 , the pitch and yaw moments of inertia are 625.51m 4 , the intersection of the longitudinal section, the stern cross section and the still water surface in the hull CAD three-dimensional solid model is set at the coordinate origin;

[0232] like Figure 6 As shown, the volume of fluid method (VOF) is used to divide the pool fluid domain into two parts: air layer 3 and water layer 4. The vertical position of the free surface 2 is located at the height of the coordinate origin;

[0233] like Figure 7-9 As shown in the figure, the fluid domain is meshed, and the mesh is encrypted near the hull CAD 3D solid model 1 and the free surface 2. The computational domain is meshed using a hexahedral unstructured grid, and an overlapping grid scheme is used. The computational domain includes two parts: the background area and the overlapping area. In order to accurately capture the drastic changes in physical quantities such as the free surface and turbulence around the hull, local mesh encryption is performed on the free surface and around the hull. There are 10 layers of mesh in the wave height range, 60 layers of mesh in the wavelength range, and 6 layers of boundary layer mesh are set on the hull wall.

[0234] Set the mesh deformation mode, use overlapping mesh and deforming mesh technology to simulate the hull motion and structural deformation, and realize the mixed deformation of the mesh. Among them, the overlapping mesh technology is used to simulate the large movement of the hull in the waves, and the deforming mesh technology is used to simulate the elastic deformation of the hull structure;

[0235] Set boundary conditions: the four side walls and bottom of the pool fluid domain use velocity inlets, the top surface uses pressure outlets, and the outer surface of the hull uses a no-slip wall.

[0236] Set the wave generation and wave elimination modes, use the momentum source term for numerical wave generation, and use the force wave elimination technology for wave elimination;

[0237] The reverse translation speed of the fluid is set to achieve the forward speed of the ship. Since the range of the pool is limited and the ship is fixed relative to the pool, the ship's speed is achieved by applying a reverse translation speed to the fluid.

[0238] Step 2: Establish a finite element model of the hull in the FEM solver, discretize the three-dimensional finite element model of the hull structure, calculate the natural frequency and mode shape of the hull during free vibration, and create boundary constraints based on the physical motion model of the hull. In this embodiment, the following steps are specifically included:

[0239] Establish a three-dimensional finite element model of the hull structure in the FEM solver, perform finite element meshing of the hull structure, perform shell unit meshing for the hull shell, and perform beam unit meshing for the reinforcement frame;

[0240] like Fig.10 As shown, the hull structure material property definition defines the hull shell mass, density, stiffness, elastic modulus, Poisson's ratio, and structural damping. In this embodiment, the mass of each structural unit is set according to the actual hull mass distribution; the stiffness of the structural unit is set according to the actual hull stiffness distribution. The Poisson's ratio is 0.3. Using the Rayleigh damping model, it is assumed that the damping matrix can be expressed as a linear combination of the mass matrix and the stiffness matrix, and the dimensionless damping coefficient is input as 0.05;

[0241] Displacement constraints are imposed on the grid nodes in combination with the hull motion degrees of freedom. In this embodiment, only the vertical and pitching motions of the hull in regular head waves are considered, so the sway, bow pitch, roll and longitudinal displacements of each grid node are restricted;

[0242] Gravity loads are applied to all grid nodes, and corresponding fluid pressure and shear force are applied to the grid nodes on the hull surface in contact with the external flow field. This fluid load is calculated by the CFD solver.

[0243] Step 3: construct a bidirectional coupling matching method of fluid-structure grid information so that the fluid grid is associated with the optimal structural unit grid. In this embodiment, the method specifically includes the following steps:

[0244] The CFD solver transmits the fluid pressure and shear force acting on the hull surface to the FEM solver;

[0245] The FEM solver performs dynamic analysis of the hull structure based on external flow field forces, rigid body inertia forces, and structural elastic forces;

[0246] Step 4: numerically simulate the preset hull in the CFD solver, and output the preset hull surface pressure field and the time history change of the preset hull motion. In this embodiment, specifically:

[0247] The solution time was set to 15 s in the CFD solver, the time step was set to 0.001 s, the PIMPLE algorithm was used, the number of iterations in each time step was 10, the number of data exchanges between the fluid and structural solvers was 3, and the result data was output. The wave surface elevation, hull surface pressure and hull motion were output in OpenFOAM.

[0248] Step five: The surface pressure field of the hull is transmitted to the structural three-dimensional finite element model of the hull through the bidirectional interaction method of grid information and modal transformation, and the modal motion equations are numerically superimposed.

[0249] In this embodiment, the simulation results of hull heave and vertical bending moment are output in the FEM solver and the test results are shown in Figure 11-12 .

[0250] like Fig.11 As shown,

[0251] The black squares represent the test data, that is, the hull heave data obtained through actual tests.

[0252] The red broken line represents the heave result calculated by the method of the present invention.

[0253] It can be seen from the figure that the calculation results of the method of the present invention are basically consistent with the overall trend of the test data, especially when the wavelength-to-ship length ratio is in the range of 0.5 to 2, the values ​​of the two are almost the same. The closer the parts in the figure are, the more accurate the calculation results of the method are.

[0254] Fig.11 It is used to verify the accuracy of the method of the present invention in predicting the heave response of a ship. By comparing with the test data, it can be seen that the method can better simulate the heave response of a ship under the action of waves.

[0255] This shows that the proposed method has high calculation accuracy in heave and can truly reflect the vertical motion behavior of the ship under different wavelength conditions.

[0256] like Fig.12 As shown,

[0257] The black squares represent the test data and the dimensionless coefficient of the vertical bending moment obtained through actual tests.

[0258] The red broken line represents the bending moment coefficient result calculated by the method of the present invention.

[0259] It can be seen from the figure that when the wavelength-to-ship ratio is between about 1 and 1.5, the test data is highly consistent with the calculation results of the method of the present invention. When the wavelength-to-ship ratio gradually increases to more than 2, although the trend is still consistent, there are some deviations in the values. This slight deviation may be due to model simplification or calculation accuracy, but overall the degree of consistency is still high.

[0260] Fig.12 It is used to verify the effectiveness of the method of the present invention in predicting the vertical bending moment response of the ship. The agreement of the data in the figure shows that the method of the present invention can better simulate the bending moment response of the hull under the action of waves, especially showing a higher accuracy when the wavelength-to-ship length ratio is between 1 and 1.5.

[0261] The results of the method of the present invention are relatively consistent with the test data, indicating that the method has significant advantages in the accuracy of bending moment response, especially in the wavelength-to-ship length ratio range.

[0262] The technical solution provided by the present invention is further described in detail through the above specific implementation modes in order to highlight the advantages and benefits of the technical solution provided by the present invention. However, the above specific implementation modes are not intended to limit the present invention. Any reasonable modification and improvement of the present invention, combination of implementation modes and equivalent substitution within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for obtaining ship hydroelasticity based on bidirectional fluid-structure coupling CFD and modal superposition, characterized in that: The acquisition method comprises the following steps: S1. Establishing a watershed model of a rigid hull of a target ship in a CFD solver, performing mesh discretization on the watershed model and setting physical conditions, wherein the target ship is a ship for which water elasticity is to be obtained; S2. Establishing a structural model of the elastic hull of the target ship in the FEM solver, performing mesh discretization on the structural model and setting boundary constraints; S3, constructing a bidirectional coupling matching method of fluid-structure grid information, which is used to associate the grid-discretized flow domain model in S1 with the grid-discretized structure model in S2, and obtain the coupling matching result; S4, performing numerical simulation on the result of the coupling matching to obtain the surface pressure field of the hull; S5. The surface pressure field of the hull is transmitted to the structural model described in S2 through a bidirectional fluid-solid coupling matching method and a modal transformation method, and the motion equations generated by the modal transformation are numerically superimposed to obtain real-time response data of the hull structure, wherein the corresponding data reflects the hydroelasticity of the target ship.

2. The method for obtaining ship hydroelasticity by bidirectional fluid-structure coupling CFD and modal superposition according to claim 1 is characterized in that: The S1 includes: S101, creating a watershed model in a CFD solver, wherein the watershed model is a rectangular parallelepiped water area, which is composed of four side walls, a bottom surface, and a top surface; S102, importing the three-dimensional data of the hull structure into the CFD solver, and performing Boolean operations on the hull and the watershed to obtain a virtual calculation pool; S103, using the VOF method to divide the virtual computing pool into an upper air layer, a free liquid surface layer and a lower water layer, and using a VOF-based geometric reconstruction method to calculate the volume of the grid fluid at the free liquid surface; S104, setting a grid deformation mode, using an overlapping grid method to solve the hull motion, and using a deforming grid method to solve the hull structure deformation, so as to achieve mixed deformation of the grid; S105, meshing the watershed model, and locally encrypting the free surface layer, the hull surface mesh, and the overlapping meshes according to characteristic physical quantities of the watershed wave surface and characteristic scales of the hull; S106, setting physical conditions for the watershed model, including: three-dimensional, implicit unsteady state, VOF wave, k-omega turbulence model, multiphase, turbulence, watershed volume, gravity, and unit mass correction model; S107, setting conditions for the six boundaries of the flow domain, setting the four side wall surfaces and the bottom surface as velocity inlets, and setting the top surface as a pressure outlet; S108, setting wave generation and wave elimination modes for the watershed model, using momentum source term to generate watershed waves, using force wave elimination technology to eliminate waves, and using the incoming flow velocity of the watershed as the forward speed of the ship.

3. The method for obtaining ship hydroelasticity by bidirectional fluid-structure coupling CFD and modal superposition according to claim 1, characterized in that: The S2 includes: S201, establishing a three-dimensional finite element model of a hull structure in a FEM solver, wherein the three-dimensional finite element model of the hull structure includes a hull surface and an internal structure; S202, meshing the three-dimensional finite element model, including meshing the hull surface and internal structure with shell elements; S203, setting material property data of the hull surface and internal structure, wherein the material properties include mass, density, stiffness, elastic modulus, Poisson's ratio and structural damping; S204, inputting material property data into the three-dimensional finite element model after mesh discretization to obtain the natural frequency and mode shape matrix of the hull under free vibration; S205. According to the natural frequency and mode matrix of the hull under free vibration, gravity load is applied to all grid nodes, fluid load is applied to the grid nodes on the hull surface in contact with the external flow domain, and displacement constraints are applied to the grid nodes in combination with the degrees of freedom of the hull motion.

4. The method for obtaining ship hydroelasticity by bidirectional fluid-structure coupling CFD and modal superposition according to claim 1, characterized in that: The S3 includes: S301, transferring the fluid load acting on the grid nodes on the hull surface to the FEM solver through the CFD solver, the FEM solver calculates the structural grid displacement on the hull surface through the modal superposition method, and returns the value to the CFD solver, the CFD solver calculates the returned value and outputs the fluid pressure and shear force on the hull surface; S302, performing a bidirectional coupling analysis, loading the CFD output results into the fluid-solid interface of the solid finite element mesh in the form of a structural load to obtain structural deformation, feeding back the structural deformation to the CFD solver to reposition the solid wall boundary, and realizing the lifting deformation of the CFD calculation mesh; S303. Use Gaussian surface approximation method to calculate the node forces on each structural grid in the three-dimensional finite element model of the hull structure: Among them, f i e is the node force, X g is the g-th Gaussian node, n g is the total number of Gaussian nodes used to approximate the total nodal force, λ g is the distance weight, N i is the shape function, n is the normal vector of the structural grid unit, p is the fluid grid node pressure, σ F is the fluid stress; S304. Constructing a bidirectional coupling matching method for fluid-structure mesh information: First, the expression of the structural displacement vector to the fluid displacement vector is: Among them, F n is the fluid interface node, S n is a structural node, is the structural displacement vector, is the fluid displacement vector, is the transformation matrix from the structure nodes to the fluid interface nodes in the radial basis function, is the radial basis function matrix used to calculate the interpolation weights after the structural node values ​​are known; Then, the normal stress at the structural node is calculated as: Among them, F f is the center of the fluid interface, is the transformation matrix from the center of the fluid interface to the structural node in the radial basis function, is the radial basis function matrix used to calculate the interpolation weights after the center value of the fluid interface is known. is the state variable at the center of the fluid interface; Finally, the center displacement of the fluid interface is obtained by interpolation from the node values, expressed as: in, It is the transformation matrix from the structural node to the center of the fluid interface in the radial basis function.

5. The method for obtaining ship hydroelasticity by bidirectional fluid-structure coupling CFD and modal superposition according to claim 1, characterized in that: The S5 includes: S501, transmitting the surface pressure field of the hull to the three-dimensional finite element model of the hull structure through a bidirectional fluid-solid coupling matching method and modal transformation, transferring the deformation displacement of the hull structure to the flow domain model, and recalculating the surface pressure field of the hull; S502, presetting the calculation time step, the total simulation time and the number of data exchanges in each time step, and synchronously running the CFD solver and the FEM solver to perform numerical simulation calculations; S503, using a modal superposition method to obtain the displacement, bending moment and shear force of any cross section of the hull, the modal superposition method being: Considering the fluid as an inviscid compressible fluid, the equilibrium equation is obtained: Among them, p f is the fluid dynamic pressure, ρ f is the fluid density, γ is the volume constant for dissipative effects, is the fluid particle velocity, is the fluid particle acceleration; Fluid pressure p and fluid bulk modulus K f The relationship between the volume strain and the From this we obtain the equation of motion for the fluid with respect to fluid pressure: The discrete finite element equation is obtained from the above formula: Among them, M f is the fluid inertia matrix, C f is the fluid damping matrix, K f is the fluid stiffness matrix, p is the pressure vector of the fluid node, d is the displacement vector on the fluid-solid interface, S fs is the coupling matrix; By coupling the fluid pressure acting at the interface, the equation of motion of the structure is obtained: Among them, M s is the structural mass matrix, C s is the structural damping matrix, K s is the structural stiffness matrix, F f is the fluid force vector in the CFD solver, is the force acting on the structure due to fluid-structure interaction; Get the complete finite element equation description of fluid-structure interaction: An auxiliary quantity ψ is introduced into the complete finite element equation of fluid-structure interaction: ψ=p / ω 2 , Among them, ω is the eigenvalue; Transforming the complete finite element equation of fluid-structure interaction into a symmetrical eigenvalue problem, we obtain the following equation: Compared with other structural forces, It is very small and is ignored in structural analysis, and the formula is simplified to: Where d is the displacement vector at the fluid-solid grid interface, expressed as: Where n is the modal order; is the i-th order mode shape vector, z i is the coordinate of the i-th vibration mode; According to the orthogonality of the mode shapes, the structural motion equations are decoupled: Among them, ω i is the natural frequency of the i-th vibration mode, ζ i is the damping ratio of the i-th vibration mode; S504, the mesh deformation of the structure obtained by mode superposition is transferred to the fluid mesh through a two-way fluid-solid coupling matching method to perform calculations for the next time step.

6. A calculation device for ship hydroelasticity based on bidirectional fluid-solid coupling CFD and modal superposition, characterized in that: The device comprises: A watershed model building module is used to establish a rigid hull watershed model in a CFD solver, discretize the watershed grid of the rigid hull watershed model, and set physical parameters, initial conditions, and boundary conditions; A hull structure model building module is used to establish a three-dimensional finite element model of the hull structure in the FEM solver, discretize the structural grid of the three-dimensional finite element model of the hull structure to calculate the natural frequency and vibration mode of the hull during free vibration, and impose constraints on the structural grid; Constructing an association module, which is used to construct a two-way coupling matching method of information from the watershed grid to the structural grid, so that each fluid grid is associated with its optimal structural unit grid; A simulation module, used for simulating a preset hull in the CFD solver, and outputting a preset hull surface pressure field and a time history value of a preset hull motion; A modal superposition module is used to transfer the preset hull surface pressure field to the three-dimensional finite element model of the hull structure through the information bidirectional coupling matching method and modal transformation, and numerically superimpose the modal motion equations to obtain and export the real-time response data of the preset hull structure.

7. A computer storage medium for storing a computer program, characterized in that: When the computer program is read by a computer, the computer executes the steps in the method for acquiring the hydroelasticity of a ship according to any one of claims 1 to 6.

8. A computer device comprising a processor and a storage medium, characterized in that When the processor reads and runs the computer program stored in the storage medium, the processor executes the steps in the method for acquiring the hydroelasticity of a ship according to any one of claims 1 to 6.

9. A computer program product, being a computer program, characterized in that When the computer program is read, the steps in the method for obtaining the hydroelasticity of a ship as described in any one of claims 1 to 6 are implemented.

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