A hydroelastic method and system for one-way coupling CFD and modal superposition

Abstract

The present invention discloses a hydroelastic method and system of one-way coupling CFD and modal superposition, wherein the method comprises: establishing a rigid hull flow domain model in a CFD solver, and discretizing the flow domain grid; establishing a three-dimensional finite element model of the hull structure in a FEM solver, and discretizing the structural grid to calculate the natural frequency and vibration mode of the hull during free vibration; constructing an information one-way coupling matching method to associate each fluid grid with its optimal structural unit grid; simulating the hull in the CFD solver, outputting the hull surface pressure field and the time history value of the hull motion; transmitting the surface pressure to the hull structure model through the information one-way coupling matching method and modal transformation, and numerically superimposing the modal motion equation to obtain and derive the real-time response data of the hull structure. The method can accurately simulate the motion and load of the ship during navigation, and can also greatly improve the calculation efficiency of the flow-solid coupling problem of the marine structure.

Description

Technical Field

[0001] The present invention relates to the technical field of ship hydroelasticity prediction, and in particular to a ship hydroelasticity method and system for one-way coupling CFD and modal superposition. Background Art

[0002] The development of large-scale modern ships and the use of high-strength steel have made the hull structure softer, and the elastic effect of the hull under wave excitation is significant, and the traditional rigid assumption is no longer applicable. At the same time, the large opening and high speed of the ship lead to an increase in the frequency of wave encounters, significant high-frequency vibrations, and an increase in the amplitude of the ship's bending moment under wave loads. The hydroelastic theory makes more full use of the information of the flow field around the floating body than the traditional rigid body model theory, so that while predicting the motion of the rigid body, it can also obtain information such as the stress, deformation, shear force and bending moment of the floating structure, so that the ship's wave load can be predicted more accurately. Since the fluid flow around the marine structure is a strong nonlinear problem, if the hydroelasticity of the ship is not adequately evaluated during the ship design stage, it may lead to catastrophic consequences such as hull structure damage, ship capsizing, and marine environmental pollution under the action of waves. Therefore, in the design analysis of the ship, the coupling of ship motion, wave load and structural deformation should be considered comprehensively, especially when the wave encounter frequency and the natural frequency of the hull are close to each other, which will cause the hull to move significantly and the structural resonance response to increase significantly.

[0003] At present, the numerical simulation of ship hydroelasticity mainly adopts potential flow theory and coupled computational fluid dynamics / finite element method (CFD-FEM). CFD technology has the ability to model more physically based and handle nonlinear free surfaces, especially the ability to handle large amplitude waves and induced violent ship motion and breaking waves. The finite element method (FEM) can be used to study the strength and deformation effects of hull structures under wave loads. However, the potential flow theory cannot effectively simulate strong nonlinear waves, so the calculation of the hydroelastic response of ships under wave action is limited to the range of linear waves and weak nonlinear waves. In addition, the general form of CFD-FEM fluid-solid coupling method has high time cost, low computational efficiency, and high requirements for computer hardware.

[0004] Therefore, when comprehensively considering the ship structure load and hydroelastic response, there is an urgent need for a ship hydroelastic algorithm that can further improve the calculation efficiency and reduce the time cost while ensuring the calculation accuracy. Summary of the invention

[0005] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0006] To this end, an object of the present invention is to propose a ship hydroelastic method of one-way coupling CFD and modal superposition, which not only accurately simulates the motion and load of the ship during navigation, but also greatly improves the computational efficiency of the fluid-solid coupling problem of marine structures.

[0007] Another object of the present invention is to provide a ship hydroelastic system with one-way coupling CFD and modal superposition.

[0008] According to yet another aspect of the present invention, a computer device is provided.

[0009] According to another aspect of the present invention, a non-transitory computer-readable storage medium is provided.

[0010] To achieve the above-mentioned purpose, an embodiment of the present invention proposes a ship hydroelastic method of one-way coupling CFD and modal superposition, comprising the following steps: step S1, establishing a rigid hull flow domain model in a CFD solver, discretizing the flow domain grid of the rigid hull flow domain model, and setting physical parameters, initial conditions, and boundary conditions; step S2, establishing a three-dimensional finite element model of the hull structure in a FEM solver, discretizing 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 applying the structural grid constraint; step S3, constructing a one-way information coupling matching method from the watershed grid to the structural grid, so that each fluid grid is associated with its optimal structural unit grid; step S4, simulating the preset hull in the CFD solver, and outputting the preset hull surface pressure field and the time history value of the preset hull motion; step S5, transferring the preset hull surface pressure field to the three-dimensional finite element model of the hull structure through the one-way information coupling matching method and modal transformation, and numerically superimposing the modal motion equations to obtain and export the real-time response data of the preset hull structure.

[0011] The ship hydroelastic method of unidirectional coupling CFD and modal superposition in an embodiment of the present invention unidirectionally couples the CFD method with the modal superposition method, comprehensively considers the combined effects of hull motion, wave load, and structural response, and while accurately simulating the motion and load of the ship during navigation, it also greatly improves the efficiency of solving fluid-solid coupling problems.

[0012] In addition, the ship hydroelastic method of one-way coupling CFD and modal superposition according to the above embodiment of the present invention may also have the following additional technical features:

[0013] Furthermore, in one embodiment of the present invention, the CFD solver is used to simulate the wave field of the numerical water tank and the fluid flow in the area around the outside of the hull to obtain the hull surface pressure field and the hull motion history, and the FEM solver is used to simulate the structural deformation, bending moment and shear force of the hull under the action of wave force.

[0014] Further, in one embodiment of the present invention, the step S1 specifically includes: step S101, in the CFD solver, wherein the water pool fluid domain is a rectangular space domain, surrounded by four side walls, a bottom surface and a top surface; step S102, establishing a hull CAD three-dimensional solid model, performing a Boolean subtraction operation on the hull CAD three-dimensional solid model and the water pool fluid domain to obtain a calculation domain, wherein the hull CAD three-dimensional solid model includes a hull outer plate and a deck; step S103, setting the six degrees of freedom, weight, center of gravity position and moment of inertia of the hull CAD three-dimensional solid model, and the position of the hull CAD three-dimensional solid model in the water pool fluid domain; step S104, using the basin volume method to divide the calculation domain into an upper air layer, a free liquid surface layer and a lower water layer; step S105, setting the grid deformation mode, using overlapping grids and deformed grids respectively. The grid technology simulates the movement and structural deformation of the hull CAD three-dimensional solid model to achieve mixed deformation of the grid; step S106, discretize the computational domain into a watershed grid, and encrypt the free liquid surface layer and the hull CAD three-dimensional solid model; step S107, select three-dimensional, implicit unsteady state, multiphase, turbulence, watershed volume, k-epsilon turbulence, VOF wave, gravity, and unit mass correction as the physical properties of the computational domain; step S108, set the boundary conditions of the computational domain, set the four side walls and the bottom surface as velocity inlets, set the top surface as a pressure outlet, and set the outer surface of the hull as a no-slip wall; step S109, set the wave making and wave breaking methods, wherein the momentum source term is used for watershed wave making, and the force wave breaking technology is used for wave breaking; step S110, set the incoming flow velocity of the pool fluid domain to achieve the forward speed of the ship.

[0015] Further, in one embodiment of the present invention, the step S2 specifically includes: step S201, establishing a three-dimensional finite element model of the hull structure in the FEM solver, wherein the three-dimensional finite element model of the hull structure includes a hull shell and reinforcing frames; step S202, meshing the three-dimensional finite element model of the hull structure, wherein the hull shell is meshed by shell units, and the reinforcing frames are meshed by beam units; step S203, setting material properties of the hull shell and the reinforcing frames, wherein the material properties include mass, density, stiffness, elastic modulus, Poisson's ratio and structural damping; step S204, based on the mesh discretized three-dimensional finite element model of the hull structure, calculating the natural frequency and mode matrix of the hull under free vibration according to the material properties; step S205, applying gravity loads to all mesh nodes, applying fluid loads to mesh nodes on the hull surface in contact with the external flow field, and applying displacement constraints to all mesh nodes in combination with the hull motion degrees of freedom.

[0016] Furthermore, in one embodiment of the present invention, the method for constructing a one-way coupling matching method of information from a flow domain grid to a structural grid is specifically as follows: the fluid load acting on the surface of the hull is transmitted to the FEM solver through the CFD solver; and the nodal force on each structural grid in the three-dimensional finite element model of the hull structure is calculated using a Gaussian surface approximation method, wherein the nodal force at each Gaussian point is a weighted value of the pressure values ​​at the four CFD body grid nodes closest to it.

[0017] Furthermore, in one embodiment of the present invention, the Gaussian surface approximation method is used to calculate the nodes on each structural grid in the three-dimensional finite element model of the hull structure, specifically:

[0018]

[0019] 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.

[0020] Further, in one embodiment of the present invention, the step S5 specifically includes: step S501, transferring the preset hull surface pressure field to the three-dimensional finite element model of the hull structure through the information unidirectional coupling matching method and modal transformation, and performing equation decoupling; step S502, presetting the calculation time step, the total simulation time, the number of data exchanges in each time step, and synchronously running the CFD solver and the FEM solver for numerical simulation calculations; step S503, using the modal superposition method to obtain the displacement, bending moment and shear force of any cross-section of the preset hull in the time domain; step S504, outputting the real-time response data, wherein the wave surface elevation and hull surface pressure are output in the CFD solver, and the hull motion, section load, local stress and structural deformation are output in the FEM solver.

[0021] To achieve the above-mentioned purpose, another embodiment of the present invention proposes a ship hydroelastic system of unidirectional coupled CFD and modal superposition, including: a watershed model building module, which 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, which is used to establish a 3D finite element model of the hull structure in a FEM solver, discretize the structural grid of the 3D finite element model of the hull structure to calculate the natural frequency and vibration mode of the hull during free vibration, and perform structural grid discretization on the structural grid. Add constraints; construct an association module for constructing an information one-way coupling matching method from a watershed grid to a structural grid, so that each fluid grid is associated with its optimal structural unit grid; a simulation module 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 for transferring the preset hull surface pressure field to the three-dimensional finite element model of the hull structure through the information one-way coupling matching method and modal transformation, and numerically superimposing the modal motion equations to obtain and export real-time response data of the preset hull structure.

[0022] The one-way coupled CFD and modal superposition ship hydroelastic system of the embodiment of the present invention one-way couples the CFD method with the modal superposition method, comprehensively considers the combined effects of hull motion, wave load, and structural response, and while accurately simulating the motion and load of the ship during navigation, it also greatly improves the efficiency of solving fluid-solid coupling problems.

[0023] To achieve the above-mentioned purpose, another embodiment of the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the ship hydroelastic method of unidirectional coupling CFD and modal superposition as described in the above-mentioned embodiment is implemented.

[0024] To achieve the above objectives, an embodiment of the present invention also provides a non-temporary computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the ship hydroelastic method of unidirectional coupling CFD and modal superposition as described in the above embodiment is implemented.

[0025] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0027] Figure 1It is a flow chart of a ship hydroelastic method of one-way coupling CFD and modal superposition according to an embodiment of the present invention;

[0028] Figure 2 It is a schematic diagram of ship hydroelasticity execution of one-way coupled CFD and modal superposition according to an embodiment of the present invention;

[0029] Figure 3 is a schematic diagram of a geometric model of a hull shell of an embodiment of the present invention;

[0030] Figure 4 is a front view of a rigid hull watershed model simulated by a CFD solver according to an embodiment of the present invention;

[0031] Figure 5 is a side view of a rigid hull watershed model simulated by a CFD solver according to an embodiment of the present invention;

[0032] Figure 6 It is a schematic front view of the overall grid division of the computational domain in the CFD solver of one embodiment of the present invention;

[0033] Figure 7 is a schematic top view of the overall grid division of the computational domain in a CFD solver according to an embodiment of the present invention;

[0034] Figure 8 It is a front view of the meshing of the hull surface in the CFD solver of one embodiment of the present invention;

[0035] Fig. 9 is a top view of the meshing of the hull surface in a CFD solver according to an embodiment of the present invention;

[0036] Fig.10 It is a schematic diagram of a hull structure shell model in a FEM solver according to an embodiment of the present invention;

[0037] Fig.11 is a schematic diagram of a finite element mesh of a hull structure shell generated by a FEM solver according to an embodiment of the present invention;

[0038] Fig.12 is a two-dimensional schematic diagram of mesh data mapping between CFD and FEM solvers according to an embodiment of the present invention;

[0039] Fig.13 is a three-dimensional schematic diagram of mesh data mapping between CFD and FEM solvers according to an embodiment of the present invention;

[0040] Fig.14 is a schematic diagram of the motion of a ship model in waves simulated by a CFD solver according to an embodiment of the present invention;

[0041] Fig.15It is a schematic diagram comparing the numerical simulation results and the test results of the vertical bending moment of the hull section of an embodiment of the present invention;

[0042] Fig.16 2 is a schematic diagram showing a comparison between a numerical simulation result of a hull heave and a test result according to an embodiment of the present invention;

[0043] Fig.17 It is a structural schematic diagram of a ship hydroelastic device with unidirectional coupling CFD and modal superposition according to an embodiment of the present invention.

[0044] Explanation of the accompanying drawings: 1-hull CAD three-dimensional solid model, 2-free liquid surface, 3-air layer, 4-water layer, 5-CFD fluid grid, 6-FEM structural grid, 7-FEM structural grid unit, 8-Gaussian point, 100-watershed model building module, 200-hull structure model building module, 300-construction association module, 400-simulation module and modal superposition module 500. DETAILED DESCRIPTION

[0045] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0046] The following describes the ship hydroelastic method and system of one-way coupling CFD and modal superposition proposed in accordance with an embodiment of the present invention with reference to the accompanying drawings. First, the ship hydroelastic method of one-way coupling CFD and modal superposition proposed in accordance with an embodiment of the present invention will be described with reference to the accompanying drawings.

[0047] Figure 1 It is a flow chart of a ship hydroelastic method of one-way coupling CFD and modal superposition according to an embodiment of the present invention.

[0048] like Figure 1 As shown, the one-way coupled CFD and modal superposition ship hydroelastic method includes the following steps:

[0049] In step S1, a rigid hull flow domain model is established in the CFD solver, the flow domain grid of the rigid hull flow domain model is discretized, and physical parameters, initial conditions, and boundary conditions are set.

[0050] It should be noted that the CFD solver is used to simulate the wave field of the numerical water tank and the fluid flow in the area around the hull to obtain the hull surface pressure field and the hull motion history.

[0051] Furthermore, step S1 specifically includes:

[0052] Step S101, establishing a water pool fluid domain in a CFD solver, wherein the water pool fluid domain is a rectangular space domain, which is surrounded by 6 surfaces, namely, 4 side wall surfaces, 1 bottom surface and 1 top surface;

[0053] Step S102, establishing a 3D solid model of a hull CAD, performing a Boolean subtraction operation between the 3D solid model of the hull CAD and the fluid domain of the pool to obtain a calculation domain, wherein the 3D solid model of the hull CAD includes a hull outer plate and a deck;

[0054] Step S103, setting the six degrees of freedom, weight, center of gravity position and moment of inertia of the hull CAD three-dimensional solid model, and the position of the hull CAD three-dimensional solid model in the pool fluid domain;

[0055] Step S104, at the waterline of the hull CAD three-dimensional solid model, the calculation domain is divided into an upper air layer, a free liquid surface layer and a lower water layer using a basin volume method;

[0056] Step S105, setting the mesh deformation mode, using overlapping mesh and deforming mesh technology to simulate the movement and structural deformation of the hull CAD three-dimensional solid model, and realizing mixed deformation of the mesh;

[0057] Step S106, discretizing the computational domain into a watershed grid, and performing encryption processing on the free surface layer and the hull CAD three-dimensional solid model;

[0058] Step S107, selecting three-dimensional, implicit unsteady, multiphase, turbulence, flow volume, k-epsilon turbulence, VOF wave, gravity, and unit mass correction as the physical properties of the computational domain;

[0059] Step S108, setting boundary conditions of the calculation domain, setting the four side walls and the bottom surface as velocity inlets, setting the top surface as the pressure outlet, and setting the outer surface of the hull as a no-slip wall;

[0060] Step S109, setting the wave generation and wave elimination methods, wherein the momentum source term is used for basin wave generation, and the force wave elimination technology is used for wave elimination;

[0061] Step S110, setting the incoming flow velocity of the pool fluid domain to achieve the forward speed of the ship.

[0062] In step S2, a three-dimensional finite element model of the hull structure is established in the FEM solver, and the structural mesh of the three-dimensional finite element model of the hull structure is discretized to calculate the natural frequency and vibration mode of the hull during free vibration, and constraints are imposed on the structural mesh.

[0063] It should be noted that the FEM solver is used to simulate the structural deformation, bending moment and shear force of the hull under the action of wave forces.

[0064] Furthermore, step S2 specifically includes:

[0065] Step 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 shell and reinforcement frames;

[0066] Step S202, meshing the three-dimensional finite element model of the hull structure, wherein the hull shell is meshed by shell units, and the reinforcing frame is meshed by beam units;

[0067] Step S203, setting material properties of the hull shell and the reinforcement frame, wherein the material properties include mass, density, stiffness, elastic modulus, Poisson's ratio and structural damping;

[0068] Step S204, based on the three-dimensional finite element model of the hull structure after mesh discretization, calculate the natural frequency and mode shape matrix of the hull under free vibration according to material properties;

[0069] Step S205, applying gravity loads to all grid nodes, applying fluid loads to grid nodes on the hull surface in contact with the external flow field, and applying displacement constraints to all grid nodes in combination with the hull motion degrees of freedom.

[0070] In step S3, a one-way coupling matching method of information from the watershed grid to the structural grid is constructed to associate each fluid grid with its optimal structural unit grid.

[0071] Furthermore, a one-way coupling matching method of information from the watershed grid to the structural grid is constructed, specifically:

[0072] The fluid load acting on the hull surface is transmitted to the FEM solver through the CFD solver, wherein the fluid load includes fluid pressure and shear force;

[0073] The Gaussian surface approximation method is used to calculate the nodal forces on each structural grid in the three-dimensional finite element model of the hull structure, where the nodal force at each Gaussian point is the weighted value of the pressure values ​​at the four CFD volume grid nodes closest to it.

[0074] Among them, the nodal force at the Gaussian point is obtained by the approximation method, specifically:

[0075]

[0076] 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 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.

[0077] It can be understood that the environment and the overall program have been built in steps S1 to S3, and the subsequent steps S4 and S5 start using the program, wherein the CFD solver specifically uses the OpenFOAM open source software, the FEM solver specifically uses the Calculix software, and at the same time, the preCICE software is used as the coupling platform.

[0078] In step S4, the preset hull is simulated in the CFD solver, and the preset hull surface pressure field and the time history value of the preset hull motion are output.

[0079] Specifically, the preset hull is simulated by using a CFD solver in a constructed program, and the CFD solver in the constructed program also outputs the preset hull surface pressure field and the time history value of the preset hull motion.

[0080] In step S5, the preset hull surface pressure field is transferred to the three-dimensional finite element model of the hull structure through the information one-way coupling matching method and modal transformation, and the modal motion equations are numerically superimposed to obtain and export the real-time response data of the preset hull structure.

[0081] Furthermore, step S5 specifically includes:

[0082] Step S501, transferring the preset hull surface pressure field to the 3D finite element model of the hull structure through the information unidirectional coupling matching method and modal transformation, and performing equation decoupling;

[0083] Step S502, the program runs to solve, presets the calculation time step, the total simulation time, the number of data exchanges in each time step, and synchronously runs the CFD solver and the FEM solver to perform numerical simulation calculations;

[0084] Step S503, using the modal superposition method to obtain the displacement, bending moment and shear force of any cross section of the preset hull in the time domain;

[0085] Step S504, outputting real-time response data, wherein the wave surface elevation and hull surface pressure are output in the CFD solver, and the hull motion, section load, local stress, and structural deformation are output in the FEM solver.

[0086] The specific method of equation decoupling is:

[0087] Assuming that the fluid is compressible and inviscid, the equilibrium equation of fluid motion is proposed

[0088]

[0089] Among them, K f is the bulk modulus of the fluid; p rgh is the fluid dynamic pressure; γ is the volume constant of the dissipation effect; ρ f is the fluid density; is the Laplace operator;

[0090] Based on equation (2), the structural finite element discretization equation is derived as

[0091]

[0092] Among them, M f is the fluid mass matrix; C f is the fluid damping matrix; K f is the fluid restoring force matrix; p is the pressure vector of the fluid grid node, d is the displacement vector on the interface between the fluid and the structure; S fs is the effective surface area coupling matrix associated with each node on the interface;

[0093] According to the fluid pressure acting on the interface, the structural motion equation is proposed

[0094]

[0095] Among them, M s is the structural mass matrix; C s is the structural damping matrix; K s is the structural stiffness matrix; F s is the surface pressure of the structure;

[0096] According to equations (3) and (4), the complete finite element equation for the fluid-structure interaction problem in ship waves is proposed:

[0097]

[0098] Introduce auxiliary variables:

[0099] ψ=p / ω 2 (6)

[0100] Where ω is the eigenvalue of equation (4), i.e., the natural frequency of the ship;

[0101] Substituting equation (6) into equation (4), we obtain the symmetric eigenvalue equation:

[0102]

[0103] The Lanczos algorithm is used to solve equation (7) and obtain ω;

[0104] neglect The structural motion equation (4) is simplified to

[0105]

[0106] The displacement vector d on the interface between fluid and structure is defined as

[0107]

[0108] Where n is the modal order; is the i-th order vibration mode vector; z i is the coordinate of the i-th order vibration mode;

[0109] Based on the orthogonality of modal mass and stiffness, equation (8) is decoupled into

[0110]

[0111] Among them, ω i is the i-th order natural frequency; ζ i is the i-th order damping ratio.

[0112] like Figure 2 As shown, the ship hydroelastic method of one-way coupling CFD and modal superposition proposed by the present invention is further described in detail below through a specific embodiment.

[0113] Taking a certain type of luxury cruise ship as an example, the scale ratio of the calculation model is 1:60, the length between vertical lines of the model is 4.966m, the width is 0.62m, the depth is 0.494m, the draft is 0.143m, and the displacement is 321kg. The ship model sails in regular waves at a speed of 0kn. The flexible deformation effect of the hull structure under the action of waves is considered during the simulation process.

[0114] In this embodiment, the CFD solver uses OpenFOAM software, and the FEM solver uses Calculix software. The preCICE software is used as a coupling platform to perform one-way coupling data exchange between the CFD and FEM solvers.

[0115] like Figure 3-5 As shown, step 1 is to establish a numerical simulation pool model and a hull entity model (i.e., a rigid hull watershed model) in a CFD solver, obtain the watershed model through Boolean subtraction operation, set grid parameters for the watershed model, perform watershed discretization, set physical parameters, initial conditions, and boundary conditions. In this embodiment, the following steps are specifically included:

[0116] A pool fluid domain is established. The pool fluid domain is a cuboid space domain enclosed by a total of 6 faces including 4 side walls, a bottom surface, and a top surface. The dimensions of the pool 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 respectively, where Lpp is the total length of the hull model.

[0117] Set the 6 degrees of freedom, weight, center of gravity position, and moment of inertia of the hull CAD three-dimensional solid model. Set the position of the hull CAD three-dimensional solid model 1 in the fluid domain. In this embodiment, only the vertical and pitching motions of the hull in regular head waves are considered. The weight of the hull CAD three-dimensional solid model is 321 kg. The longitudinal position of the center of gravity is 2.6 m from the stern post, the vertical position of the center of gravity is 0.299 m from the baseline, the roll moment of inertia is 13.43 m4, the pitch and yaw moments of inertia are 625.51 m4, and the intersection points of the longitudinal section, stern post cross-section, and still water surface in the hull CAD three-dimensional solid model are set at the coordinate origin;

[0118] As Figure 4 and Figure 5 shown, the pool fluid domain is divided into two parts, an air layer 3 and a water layer 4, using the Volume of Fluid (VOF) method. The vertical position of the free surface 2 is at the height of the coordinate origin;

[0119] As Figure 6 and Figure 7 shown, the fluid domain is meshed, and the mesh is refined near the hull CAD three-dimensional solid model 1 and the free surface 2. As Figure 8 and Fig. 9 shown, the computational domain is meshed using hexahedral unstructured meshes. An overlapping mesh scheme is adopted, and the computational domain includes a background region and an overlapping region. To accurately capture the drastic changes in physical quantities such as the free liquid surface and the turbulence around the hull, local mesh refinement is performed at the free liquid surface and around the hull. There are 10 layers of meshes within the wave height range, 60 layers of meshes within the wavelength range, and 6 boundary layer meshes are set at the hull outer wall surface.

[0120] Set the mesh deformation method. The overlapping mesh and deformed mesh techniques are respectively used to simulate the hull motion and structural deformation, realizing the hybrid deformation of the mesh. Among them, the overlapping mesh technique is used to simulate the large-amplitude motion of the hull in waves, and the deformed mesh technique is used to simulate the elastic deformation of the hull structure;

[0121] Set the boundary conditions. The 4 side walls and the bottom surface of the pool fluid domain adopt velocity inlets, the top surface adopts a pressure outlet, and the outer surface of the hull adopts a no-slip wall surface;

[0122] Set the wave generation and wave absorption modes. Numerical wave generation is carried out using the momentum source term, and wave absorption is carried out using the force wave absorption technique;

[0123] 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.

[0124] Step 2: Establish a three-dimensional finite element model of the hull structure in the FEM solver, discretize the structural mesh of the finite element model, define the structural unit parameters, calculate the natural frequency and mode shape of the hull during free vibration, and then impose constraints on the mesh. In this embodiment, the following steps are specifically included:

[0125] like Fig.10 As shown, a three-dimensional finite element model of the hull structure is established in the FEM solver;

[0126] like Fig.11 As shown, the finite element meshing of the hull structure is performed, the shell unit meshing is performed for the hull shell, and the beam unit meshing is performed for the reinforcement frame;

[0127] 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 hull structure adopts Q355b steel, with a density of 7850kg / m3, an elastic modulus of 206GPa, and a Poisson's ratio of 0.28. The Rayleigh damping model is adopted, assuming that the damping matrix can be expressed as a linear combination of the mass matrix and the stiffness matrix, and a dimensionless damping coefficient of 0.05 is input;

[0128] 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;

[0129] 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.

[0130] Step 3: Setting a one-way coupling matching method for information from the watershed grid to the structural grid, associating each fluid grid with the most suitable structural unit grid. In this embodiment, the method specifically includes the following steps:

[0131] The CFD solver transmits the fluid pressure and shear force acting on the hull surface to the FEM solver;

[0132] The FEM solver performs dynamic analysis of the hull structure based on external flow field forces, rigid body inertia forces, and structural elastic forces;

[0133] like Fig.12 As shown, since the CFD grid unit 5 and the FEM grid unit 6 on the hull surface are not completely matched (usually the FEM structural grid is coarser than the CFD fluid grid), direct data transfer is very likely to cause data distortion;

[0134] like Fig.13 As shown, the fluid force on the FEM structure grid unit 7 can be obtained by Gaussian surface superposition approximation, and 9 Gaussian points 8 are introduced on the quadrilateral FEM grid unit 7. The fluid pressure at each Gaussian point 8 is defined as the weighted value of the pressure values ​​at the 4 CFD body grid nodes closest to it, which is obtained by the approximation method.

[0135] Step 4: simulate the hull in the CFD solver and output the pressure field on the hull surface and the time history of the hull motion. In this embodiment, specifically:

[0136] In the CFD solver, the solution time was set to 30 s, the time step was set to 0.0005 s, the PIMPLE algorithm was used, the number of iterations in each time step was 10, and the number of data exchanges between the fluid and structural solvers was 3 times;

[0137] Output result data, output wave surface elevation, hull surface pressure and hull motion in OpenFOAM, such as Fig.14 The wave field of the ship hull is shown, Fig.15 The simulation results of the vertical motion of the hull are shown compared with the test results.

[0138] Step 5: The hull surface pressure is transferred to the hull modal model through the information unidirectional coupling matching method and modal transformation, and the modal motion equation is numerically superimposed to obtain the real-time response of the hull structure and export the data. In this embodiment, the hull section load, local stress, structural deformation, vertical bending moment simulation results and test results are output in the FEM solver. Fig.16 shown.

[0139] In summary, the ship hydroelasticity method of one-way coupling CFD and modal superposition proposed in an embodiment of the present invention comprehensively considers the joint effects of hull motion, wave load, and structural response, and can accurately simulate the motion and force conditions of a ship when sailing in waves; it combines the advantages of the CFD fluid solver and the modal superposition method. Compared with the potential flow theory method, the CFD method can simulate strong nonlinear wave fields, the FEM can obtain the ship's natural frequency and vibration matrix, and the modal superposition can obtain the hull structure load and deformation, thereby fully considering the fluid-solid coupling problem between the ship and the wave; it can accurately analyze the elastic vibration and flutter response of the flexible hull under the action of strong nonlinear waves; compared with the general form of fluid-solid coupling simulation method, this method has accurate simulation of the hydroelasticity of ships with weak structural deformation, and also greatly improves the calculation efficiency, providing a reliable method for ship design and development.

[0140] Next, the ship hydroelastic system of unidirectional coupled CFD and modal superposition proposed in accordance with an embodiment of the present invention will be described with reference to the accompanying drawings.

[0141] Fig.17 It is a structural schematic diagram of a ship hydroelastic system of one-way coupled CFD and modal superposition according to an embodiment of the present invention.

[0142] like Fig.17 As shown, the system 10 includes: a watershed model construction module 100 , a hull structure model construction module 200 , a construction association module 300 , a simulation module 400 and a modal superposition module 500 .

[0143] Among them, the watershed model construction module 100 is used to establish a rigid hull watershed model in the CFD solver, discretize the watershed grid of the rigid hull watershed model, and set physical parameters, initial conditions, and boundary conditions. The hull structure model construction module 200 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. The construction association module 300 is used to construct an information one-way coupling matching method from the watershed grid to the structural grid, so that each fluid grid is associated with its optimal structural unit grid. The simulation module 400 is used to simulate the preset hull in the CFD solver, and output the preset hull surface pressure field and the time history value of the preset hull motion. The modal superposition module 500 is used to transfer the preset hull surface pressure field to the three-dimensional finite element model of the hull structure through the information one-way coupling matching method and modal transformation, and numerically superimpose the modal motion equation to obtain and export the real-time response data of the preset hull structure.

[0144] It should be noted that the aforementioned explanation of the embodiment of the ship hydroelastic method of one-way coupling CFD and modal superposition is also applicable to the system of this embodiment and will not be repeated here.

[0145] The ship hydroelastic system of one-way coupled CFD and modal superposition proposed in the embodiment of the present invention comprehensively considers the joint effects of hull motion, wave load and structural response, and can accurately simulate the motion and force conditions of a ship when sailing in waves; it combines the advantages of the CFD fluid solver and the modal superposition method. Compared with the potential flow theory method, the CFD method can simulate strong nonlinear wave fields, the FEM can obtain the ship's natural frequency and vibration mode matrix, and the modal superposition can obtain the hull structure load and deformation, thereby fully considering the fluid-solid coupling problem between the ship and the wave; it can accurately analyze the elastic vibration and flutter response of the flexible hull under the action of strong nonlinear waves; compared with the general form of fluid-solid coupling simulation method, this method has accurate simulation of the hydroelasticity of ships with weak structural deformation, and also greatly improves the calculation efficiency, providing a reliable method for ship design and development.

[0146] In order to implement the above embodiments, the present invention also proposes a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the ship hydroelastic method of one-way coupling CFD and modal superposition as described in the above embodiments is implemented.

[0147] In order to implement the above embodiments, the present invention also proposes a non-temporary computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the ship hydroelastic method of unidirectional coupling CFD and modal superposition as described in the above embodiments is implemented.

[0148] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0149] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "N" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0150] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, fragment or portion of code comprising one or more executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present invention belong.

[0151] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purpose of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or N wirings (electronic devices), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing in other suitable ways if necessary, and then stored in a computer memory.

[0152] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above embodiment, the N steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0153] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0154] In addition, each functional unit in each embodiment of the present invention may be integrated into a processing module, or each unit may exist physically separately, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0155] The storage medium mentioned above may be a read-only memory, a magnetic disk or an optical disk, etc. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. A person of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A ship hydroelastic method of one-way coupling CFD and modal superposition, characterized in that: The following steps are involved: Step S1, establishing a rigid hull watershed model in a CFD solver, discretizing the watershed grid of the rigid hull watershed model, and setting physical parameters, initial conditions, and boundary conditions; Step S2, establishing a three-dimensional finite element model of the hull structure in the FEM solver, discretizing the structural grid of the three-dimensional finite element model of the hull structure to calculate the natural frequency and mode shape of the hull during free vibration, and applying constraints to the structural grid; Step S3, constructing a one-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; Step S4, simulating the preset hull in the CFD solver, and outputting the preset hull surface pressure field and the time history value of the preset hull motion; Step S5, transferring the preset hull surface pressure field to the three-dimensional finite element model of the hull structure through the information one-way coupling matching method and modal transformation, and numerically superimposing the modal motion equations to obtain and export the real-time response data of the preset hull structure.

2. The ship hydroelastic method of one-way coupling CFD and modal superposition according to claim 1 is characterized in that: The CFD solver is used to simulate the wave field of the numerical water tank and the fluid flow in the area around the outside of the hull to obtain the hull surface pressure field and the hull motion history. The FEM solver is used to simulate the structural deformation, bending moment and shear force of the hull under the action of wave force.

3. The ship hydroelastic method of one-way coupling CFD and modal superposition according to claim 1 is characterized in that: The step S1 specifically includes: Step S101, establishing a water pool fluid domain in the CFD solver, wherein the water pool fluid domain is a rectangular space domain surrounded by four side walls, a bottom surface and a top surface; Step S102, establishing a 3D solid model of a hull CAD, performing a Boolean subtraction operation between the 3D solid model of the hull CAD and the fluid domain of the water tank to obtain a calculation domain, wherein the 3D solid model of the hull CAD includes a hull outer plate and a deck; Step S103, setting the six degrees of freedom, weight, center of gravity position and moment of inertia of the hull CAD three-dimensional solid model, and the position of the hull CAD three-dimensional solid model in the fluid domain of the water tank; Step S104, using a basin volume method to divide the calculation domain into an upper air layer, a free liquid surface layer and a lower water layer; Step S105, setting a mesh deformation mode, using overlapping mesh and deforming mesh technology to simulate the movement and structural deformation of the hull CAD three-dimensional solid model, respectively, to achieve mixed deformation of the mesh; Step S106, discretizing the computational domain into a watershed grid, and performing encryption processing on the free liquid surface layer and the hull CAD three-dimensional solid model; Step S107, selecting three-dimensional, implicit unsteady state, multiphase, turbulence, flow volume, k-epsilon turbulence, VOF wave, gravity, and unit mass correction as the physical properties of the computational domain; Step S108, setting the boundary conditions of the calculation domain, setting the four side walls and the bottom surface as velocity inlets, setting the top surface as a pressure outlet, and setting the outer surface of the hull as a no-slip wall; Step S109, setting the wave generation and wave elimination methods, wherein the momentum source term is used for basin wave generation, and the force wave elimination technology is used for wave elimination; Step S110, setting the incoming flow velocity of the pool fluid domain to achieve the forward speed of the ship.

4. The ship hydroelastic method of one-way coupling CFD and modal superposition according to claim 1 is characterized in that: The step S2 specifically includes: Step S201, establishing a three-dimensional finite element model of the hull structure in the FEM solver, wherein the three-dimensional finite element model of the hull structure includes a hull shell and reinforcement frames; Step S202, meshing the three-dimensional finite element model of the hull structure, wherein the hull shell is meshed by shell units, and the reinforcing frame is meshed by beam units; Step S203, setting the material properties of the hull shell and the reinforcing frame, wherein the material properties include mass, density, stiffness, elastic modulus, Poisson's ratio and structural damping; Step S204, based on the three-dimensional finite element model of the hull structure after mesh discretization, calculate the natural frequency and mode shape matrix of the hull under free vibration according to the material properties; Step S205, applying gravity loads to all grid nodes, applying fluid loads to grid nodes on the hull surface in contact with the external flow field, and applying displacement constraints to all grid nodes in combination with the hull motion degrees of freedom.

5. The ship hydroelastic method of one-way coupling CFD and modal superposition according to claim 1, characterized in that: The method for constructing a one-way coupling matching method of information from a watershed grid to a structural grid is specifically as follows: transmitting the fluid load acting on the hull surface to the FEM solver through the CFD solver; The nodal force on each structural grid in the three-dimensional finite element model of the hull structure is calculated using a Gaussian surface approximation method, wherein the nodal force at each Gaussian point is a weighted value of the pressure values ​​at the four CFD volume grid nodes closest to it.

6. The ship hydroelastic method of one-way coupling CFD and modal superposition according to claim 5 is characterized in that: The Gaussian surface approximation method is used to calculate the nodes on each structural grid in the three-dimensional finite element model of the hull structure, specifically: 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.

7. The ship hydroelastic method of one-way coupling CFD and modal superposition according to claim 1 is characterized in that: The step S5 specifically includes: Step S501, transferring the preset hull surface pressure field to the 3D finite element model of the hull structure through the information unidirectional coupling matching method and modal transformation, and performing equation decoupling; Step 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; Step S503, using the modal superposition method to obtain the displacement, bending moment and shear force of any cross section of the preset hull in the time domain; Step S504, outputting the real-time response data, wherein the wave surface elevation and hull surface pressure are output in the CFD solver, and the hull motion, section load, local stress, and structural deformation are output in the FEM solver.

8. A ship hydroelastic system with one-way coupling CFD and modal superposition, characterized in that: include: 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; A correlation module is constructed to construct a one-way coupling matching method of information from the flow 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; The 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 one-way 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.

9. A computer device, characterized in that: The invention comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the ship hydroelastic method of one-way coupling CFD and modal superposition as described in any one of claims 1 to 7 is implemented.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the ship hydroelastic method of one-way coupling CFD and modal superposition as described in any one of claims 1 to 7 is implemented.

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