Free liquid level geometric reconstruction method and system for coupling overlapped grids and isoVOF

Abstract

The invention discloses a free liquid level geometric reconstruction method and system for coupling overlapped grids and isoVOF, belongs to the technical field of fluid mechanics calculation, and solves the problems that an existing algebraic method cannot finely capture space-time evolution characteristics of fluids such as jet flow and the like and the problem of large deformation of the grids. The method comprises the following steps: establishing a drainage basin model of a target object according to a feature scale of the target object, and performing grid discretization on a flow field; physical condition setting is carried out on the fluid domain boundary, and initial physical condition setting is carried out on the flow field; setting a fluid control equation for the flow field; setting a fluid geometry VOF method control equation for the flow field; and creating an overlapping grid around the target object, and capturing the free liquid level by adopting a geometric VOF method to complete the free liquid level geometric reconstruction method. The method is suitable for simulation scenes of free liquid level and large-amplitude motion of objects.

Description

Technical Field

[0001] The invention belongs to the technical field of fluid mechanics calculation, and in particular relates to a free liquid surface geometry reconstruction method. Background Art

[0002] In the process of studying structures slamming into water, the complex evolution of the free surface at the gas-liquid interface in a short period of time poses a huge challenge to the fine capture of the spatiotemporal evolution of the free surface. In order to effectively solve the nonlinear and complex free-form surface, the fluid volume interface capture technology is used.

[0003] However, in the current version of ESI In the 2016 paper, the algebraic VOF method is still used to capture the free surface in the multiphase flow solver. Due to the simplification of the calculation of the unit surface volume flux in the algebraic method, the gas-liquid interface is blurred and the spatiotemporal evolution characteristics of fluids such as jets cannot be accurately captured.

[0004] In addition, the proposed isoAdvector method for sharp cross-section advection can capture the fluid precisely, but it cannot be coupled with overlapping grids. Therefore, it is more likely to diverge when the elastic body has low stiffness and large grid deformation is prone to occur.

[0005] Therefore, when the large amplitude of the structure is taken into comprehensive consideration, a method is urgently needed to ensure the fine capture of the evolution of the free liquid surface while using overlapping grids to solve the problem of large deformation of the grid. Summary of the invention

[0006] The present invention proposes a free liquid surface geometry reconstruction method and system for coupling overlapping grids and isoVOF, which aims to solve the problem that the existing algebraic method cannot accurately capture the temporal and spatial evolution characteristics of fluids such as jets and the large deformation problem of the grid.

[0007] A free liquid surface geometry reconstruction method for coupling overlay grids and isoVOF, the method comprising:

[0008] S1: Establish a flow domain model of the target object according to the characteristic scale of the target object and discretize the flow field into grids;

[0009] S2: Set physical conditions for the fluid domain boundary and set initial physical conditions for the flow field;

[0010] S3: Set the fluid control equations for the flow field;

[0011] S4: Setting the fluid geometry VOF method control equations for the flow field;

[0012] S5: creating overlapping grids around the target object, and using a geometric VOF method to capture the free liquid surface, thereby completing the free liquid surface geometric reconstruction method.

[0013] Furthermore, a preferred solution is provided: S1 comprises:

[0014] S101: Establish the pool fluid domain in the CFD solver;

[0015] S102: Perform Boolean operations on the flow field and the target object to create a calculation domain of the pool;

[0016] S103: constructing a target object model, setting parameters of the target object model, including six degrees of freedom, weight, center of gravity position and moment of inertia, and setting the position of the target object model in the fluid domain of the pool;

[0017] S104: using the basin volume method to divide the calculation domain into an air phase part and a water phase part;

[0018] S105: discretizing the flow field into a grid, and creating an object surface grid according to a characteristic scale of the target object;

[0019] S106: The fluid domain is discretized using STAR-CCM+ and the mesh is converted into a form readable by OpenFOAM using a mesh converter.

[0020] Furthermore, a preferred solution is provided: S2 includes:

[0021] S201: setting the initial physical conditions of the flow field, and selecting 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;

[0022] S202: setting boundary conditions of the calculation domain, setting the top surface as a pressure outlet, and setting the outer surface of the hull as a no-slip wall;

[0023] S203: Setting overlapping grids and creating overlapping interfaces.

[0024] Furthermore, a preferred solution is provided: the S203 includes:

[0025] Select overlapping domains according to the characteristic scale of the target object;

[0026] Create a densified region in the flow field based on the overlap domain size;

[0027] Create a surface mesh of the target object according to the surface shape of the target object;

[0028] Creating a volume mesh according to the size of the surface mesh of the object and the mesh growth ratio;

[0029] The grid size of the encrypted area in the flow field is set according to the outermost grid size of the overlapping domain to create an overlapping interface.

[0030] Furthermore, a preferred solution is provided: the fluid control equation is:

[0031]

[0032] Among them, x is the position vector, u is the velocity vector, g is the gravitational acceleration, ρ m represents the density of the mixed fluid, μ is the fluid viscosity, and p is the fluid pressure field.

[0033] Furthermore, a preferred solution is provided: the control equation of the fluid geometry VOF method is:

[0034]

[0035] Among them, f α (t) represents the indicator function of the phase distribution at time t, Represents the boundary of the grid participating in the calculation, is the external normal direction of the unit, dS is the grid area differential, the integral term represents the net flux of liquid flowing into the grid within time Δt, F k represents the kth face, N k represents the k-th face of the grid cell.

[0036] Furthermore, a preferred solution is provided: S5 includes:

[0037] S501: In the motion solver, read the data in the previous iteration step, update the object position, calculate the external force on the target object and update the motion acceleration of the target object, update the object and the grid; correct the fluid flux;

[0038] S502: In the VOF solver, read the data in the previous iteration step, initialize the volume fraction of the windward grid; set the tolerance and find the surface grid; find the isosurface and correct the volume fraction; obtain the movement of the isosurface based on the velocity field; calculate the interface boundary line according to the movement of the isosurface; calculate and correct the liquid phase volume according to the interface boundary line;

[0039] Step 503: read the physical quantity value of the previous iteration step; calculate the corrected flow field flux through the motion solver; calculate the volume fraction of each phase in the grid through the geometric VOF method; solve the momentum equation; solve the pressure equation; and perform the next iteration.

[0040] The present invention also proposes a computer device, comprising a memory and a processor, wherein a computer program is stored in the memory. When the processor runs the computer program stored in the memory, the processor executes a free liquid surface geometry reconstruction method of coupling overlapping grids and isoVOF according to any combination of the above-mentioned schemes.

[0041] The present invention also proposes a computer-readable storage medium, which is used to store a computer program, and the computer program executes the steps of a free liquid surface geometry reconstruction method for coupling overlapping grids and isoVOF described in any combination of the above solutions.

[0042] The present invention further proposes a free liquid surface geometry reconstruction system for coupling overlapping grids and isoVOF, wherein the system is implemented based on a free liquid surface geometry reconstruction method for coupling overlapping grids and isoVOF described in any one of the above solutions, and comprises:

[0043] Model building module: used to establish the watershed model of the target object according to the characteristic scale of the target object and to perform grid discretization on the flow field;

[0044] Condition setting module: used to set physical conditions for the fluid domain boundary and the initial physical conditions for the flow field;

[0045] Equation setting module: set fluid control equations for the flow field;

[0046] VOF control module: used to set the fluid geometry VOF method control equation for the flow field;

[0047] Coupling module: used to create overlapping grids around the target object and capture the free liquid surface using the geometric VOF method.

[0048] Compared with the prior art, the advantages of the present invention are:

[0049] The present invention proposes a free liquid surface geometry reconstruction method that couples overlapping grids with isoVOF. While using the geometric VOF method to finely capture the gas-liquid interface, it can also couple the overlapping grids to calculate the object motion and solve the problem of large deformation of the grid. This greatly enriches the technical means for finely capturing the rapid changes of the gas-liquid interface in a short period of time.

[0050] The method has the following advantages:

[0051] 1. Refined capture: The method uses a geometric VOF method to finely capture the gas-liquid interface, which can more accurately simulate the spatiotemporal evolution characteristics of the free liquid surface.

[0052] 2. Coupled overlapping grids: The coupled overlapping grid technology solves the grid failure problem caused by large-scale object movement and improves the stability and reliability of the calculation.

[0053] 3. Solve the problem of large mesh deformation: The application of overlapping mesh technology provides guarantee for mesh quality, especially when the object moves greatly, effectively preventing excessive deformation of the mesh.

[0054] 4. Multiphase flow control equations: The method sets the fluid control equations, taking into account the incompressibility of the fluid and the laminar flow model, thereby improving the accuracy of the simulation.

[0055] 5. Fluid volume transport equation: Use the VOF method to control the equation and calculate the change of liquid volume fraction over time through the accurate fluid volume transport equation.

[0056] 6. High computational efficiency and accuracy: By performing local mesh encryption near the surface of the object and the free liquid surface, the computational efficiency is improved while ensuring the accuracy of the calculation results.

[0057] The present invention is suitable for simulating scenes of free liquid surface and large-scale motion of objects. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0059] Figure 1 It is a flow chart of a method for studying free liquid surface geometry reconstruction by coupling overlapping grids and isoVOF according to an embodiment of the present invention;

[0060] Figure 2 is a calculation flow chart of a free liquid surface geometry reconstruction method for coupling overlapping grids and isoVOF according to an embodiment of the present invention;

[0061] Figure 3 A numerical calculation model of an embodiment of the present invention;

[0062] Figure 4 It is a flow field determination of an embodiment of the present invention, wherein 1 is a three-dimensional solid model, 2 is a free surface, 3 is an air layer, and 4 is a water layer;

[0063] Figure 5 is a grid division of a cross section of a flow field according to an embodiment of the present invention;

[0064] Figure 6 It is the surface mesh division of the numerical calculation model of one embodiment of the present invention;

[0065] Figure 7 It is the flow field capture of the cross section under the numerical calculation of one embodiment of the present invention. DETAILED DESCRIPTION

[0066] In the following description, specific details such as specific system structures and technologies are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0067] It should be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0068] It should also be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in this application specification and the appended claims, the singular forms "a", "an" and "the" are intended to include plural forms unless the context clearly indicates otherwise.

[0069] The following is a clear and complete description of the technical solutions in the embodiments of the present application in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0070] In the following description, many specific details are set forth to facilitate a full understanding of the present application, but the present application may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present application. Therefore, the present application is not limited to the specific implementation methods disclosed below.

[0071] Implementation method 1:

[0072] Reference Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 This embodiment will be described.

[0073] A free surface geometry reconstruction method for coupling overlay grids with isoVOF, comprising:

[0074] S1: In OpenFOAM software, a flow domain model of the target object is established according to the characteristic scale of the target object, and the flow field is discretized into grids;

[0075] S101: establishing a water pool fluid domain in a CFD solver, wherein the water pool fluid domain is a rectangular space domain including four side wall surfaces, a bottom surface and a top surface;

[0076] S102: Perform Boolean operations on the flow field and the target object to create a calculation domain of the pool;

[0077] S103: constructing a target object model, setting parameters of the target object model, including six degrees of freedom, weight, center of gravity position and moment of inertia, and setting the position of the target object model in the fluid domain of the pool;

[0078] S104: using the basin volume method to divide the calculation domain into an air phase part and a water phase part;

[0079] S105: discretizing the flow field into a grid, and creating an object surface grid according to a characteristic scale of the target object;

[0080] S106: Discretize the fluid domain using STAR-CCM+ and convert the mesh into a form that can be read by OpenFOAM using a mesh converter;

[0081] S2: Set physical conditions for the fluid domain boundary and set initial physical conditions for the flow field;

[0082] S201: setting the initial physical conditions of the flow field, and selecting 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;

[0083] S202: setting boundary conditions of the calculation domain, setting the top surface as a pressure outlet, and setting the outer surface of the hull as a no-slip wall;

[0084] S203: Setting overlapping grids and creating overlapping interfaces, specifically including: selecting overlapping domains according to the characteristic scale of the target object; creating a densified area in the flow field according to the size of the overlapping domain; creating an object surface grid according to the surface shape of the target object; creating a volume grid according to the size of the object surface grid and the grid growth ratio; setting the grid size of the densified area in the flow field according to the outermost grid size of the overlapping domain to create an overlapping interface.

[0085] Creation of overlapping meshes. When studying objects with large movements, the application of overlapping mesh technology provides guarantee for mesh quality. It allows the use of several overlapping meshes to handle complex or separated geometric shapes.

[0086] S3: Set the fluid control equations for the flow field;

[0087] The fluid control equation is:

[0088] Create Eulerian multiphase flow and set the fluid control equations. Due to the incompressibility of the fluid, the energy term is ignored.

[0089]

[0090] Among them, x is the position vector, u is the velocity vector, g is the gravitational acceleration, ρ m represents the density of the mixed fluid, μ is the fluid viscosity, and p is the fluid pressure field.

[0091] Since the occurrence time of the slamming problem is usually tens of milliseconds, which is much smaller than the time scale of viscosity acting on the fluid, the laminar flow model is used to close the NS equations.

[0092] S4: Setting the fluid geometry VOF method control equation for the flow field; the fluid geometry VOF method control equation is:

[0093]

[0094] Among them, f α (t) represents the indicator function of the phase distribution at time t, Represents the boundary of the grid participating in the calculation, is the external normal direction of the unit, dS is the grid area differential, the integral term represents the net flux of liquid flowing into the grid within time Δt, F k represents the kth face, N k represents the k-th face of the grid cell.

[0095] S4 sets the fluid geometric VOF method control equation for the flow field. According to the solution strategy of the fluid volume, the VOF method can be further divided into two solution methods: geometric and algebraic. In the geometric VOF method, the indicator function f α (t) is approximated by a standard reconstruction technique involving piecewise linear interface calculation (PLIC), with the interface position within each cell being explicitly defined by the plane equations. The governing equations of the VOF method are as follows:

[0096] 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:

[0097]

[0098] 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;

[0099] The liquid volume within any grid is calculated using the following formula:

[0100]

[0101] In a finite time [t, t+Δt], by integrating the above formula over time on a fixed unit and according to the divergence theorem, the evolution equation of the liquid volume fraction changing with time can be calculated:

[0102]

[0103] in, Represents the boundary of the grid participating in the calculation, is the external normal direction of the unit, dS is the differential of the grid area, and the integral term represents the net flux of liquid flowing into the grid within time Δt;

[0104] The formula for calculating the volume of a fluid is defined as:

[0105]

[0106] Discretize the above formula on the grid unit surface. Assuming that the grid unit has N surfaces, the area integral term on the right side is modified as follows:

[0107]

[0108] Among them, S k represents the kth face, Represents the direction of the external normal of the surface;

[0109] The kth face F k The available volume surface flux is approximately defined as:

[0110]

[0111] Then the solution formula for the volume becomes:

[0112]

[0113] In the above formula, 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:

[0114]

[0115] S5: creating overlapping grids around the target object, using a geometric VOF method to capture the free liquid surface, and completing the free liquid surface geometric reconstruction method;

[0116] S501: In the motion solver, read the data in the previous iteration step, update the object position, calculate the external force on the target object and update the motion acceleration of the target object, update the object and the grid; correct the fluid flux;

[0117] S502: In the VOF solver, read the data in the previous iteration step and initialize the volume fraction of the windward grid; set the tolerance and find the surface grid; find the isosurface and correct the volume fraction; obtain the movement of the isosurface during the period t to t + Δt based on the velocity field; calculate the interface boundary line according to the movement of the isosurface during the period t to t + Δt; calculate ΔV according to the interface boundary line k (t, t+Δt), using the redistribution procedure to calculate and correct the liquid volume α i (t+Δt);

[0118] S503: Read the physical quantity value of the previous iteration step; calculate the corrected flow field flux through the motion solver; calculate the volume fraction of each phase in the grid through the geometric VOF method; solve the momentum equation; solve the pressure equation; and perform the next iteration.

[0119] The method described in this embodiment uses a CFD solver to simulate the fluid flow changes in the surrounding area outside the object in the numerical water pool to obtain the surface pressure field and motion history of the object; the volume of fluid method (VOF) is used to divide the water pool fluid domain into two parts: the air layer and the water layer, which helps to more accurately simulate the position and shape of the free surface; by reasonably setting the time step and using the first-order time discrete format, the stability of the calculation and the accuracy of the calculation results are ensured; the isoVOF geometric reconstruction method is used to capture the free liquid surface and the jet, which improves the accuracy of interface capture. The method described in this embodiment is implemented based on OpenFOAM software, using existing CFD tools, which is convenient for engineering application and technology transformation.

[0120] like Figure 3 As shown, taking a three-dimensional wedge as an example, its bottom lift angle is 30°, and the wedge is in a static flow field in free fall at a certain height, the temporal and spatial evolution characteristics of the free liquid surface and the jet changes during the wedge entering the water are simulated and refined. In this embodiment, the CFD solver uses OpenFOAM software. A pool fluid domain is established, and the pool fluid domain is a rectangular space domain, which is surrounded by 6 faces, including 4 side walls, a bottom face and a top face. The 6 degrees of freedom, weight, and center of gravity position of the three-dimensional solid model of the wedge are set, and the position of the wedge in the flow field is set. In this embodiment, only the movement of the wedge in the Z direction is considered, so only the degree of freedom in one direction of the Z direction is opened, and in order to improve the calculation efficiency, the bottom vertex of the wedge is set near the free liquid surface, and the free fall part of the wedge is omitted by assigning the initial velocity of the wedge.

[0121] like Figure 4, 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 free surface 2 is located at the height of the coordinate origin. The fluid domain is meshed, and the mesh is encrypted near the hull CAD three-dimensional solid model 1 and free surface 2. The computational domain is meshed using hexahedral unstructured grids. The overlapping grid scheme is used, and the computational domain includes two parts: background area and overlapping area. In order to accurately capture the drastic changes in physical quantities such as turbulence around the free liquid surface and the hull, local mesh encryption is performed on the free liquid surface and around the hull. The number of boundary layer mesh layers of the wedge shell is 5. Set the 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 no-slip walls; set the time step. Set the solution time to 0.2s in the CFD solver, the time step is set to 0.001s, and the first-order time discretization format can be selected.

[0122] In this embodiment, the wedge body uses an overlay grid to calculate the surge, and the isoVOF geometric reconstruction method is used to capture the free liquid surface and the jet. The captured phase distribution of the cross section on the xoz surface is compared with the phase distribution captured by the traditional method. Figure 6 .

[0123] Those skilled in the art will appreciate that the above are only preferred embodiments of the present invention, and the various embodiments of the present disclosure and / or the features described in the claims may be combined or combined in various ways, even if such combinations or combinations are not explicitly described in the present disclosure. It is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art may still modify the technical solutions described in the aforementioned embodiments, or perform equivalent substitutions on some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

[0124] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0125] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

[0126] It will be appreciated by those skilled in the art that the embodiments of the present disclosure may be provided as methods, systems or computer program products. Therefore, the present disclosure may be provided in the form of a complete hardware embodiment, a complete software embodiment or an embodiment combining software and hardware. Furthermore, the present disclosure may be provided in the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0127] The present disclosure is described with reference to flowcharts and / or block diagrams of methods, devices (systems) and computer program products according to embodiments of the present disclosure. It should be understood that each process and / or block in the flowchart and / or block diagram and the combination of processes and / or blocks in the flowchart and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing device to work in a specific way, so that the instructions stored in the computer-readable memory produce a product including an instruction device, which implements the functions specified in the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0128] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0129] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present disclosure rather than to limit its protection scope. Although the present disclosure has been described in detail with reference to the above implementation modes, ordinary technicians in the relevant field should understand that after reading the present disclosure, those skilled in the art can still make various changes, modifications or equivalent substitutions to the specific implementation modes of the invention, but these changes, modifications or equivalent substitutions are all within the protection scope of the disclosed claims to be approved.

Claims

1. A free surface geometry reconstruction method for coupling overlay grids and isoVOF, characterized in that: The method comprises: S1: Establish a flow domain model of the target object according to the characteristic scale of the target object and discretize the flow field into grids; S2: Set physical conditions for the fluid domain boundary and set initial physical conditions for the flow field; S3: Set the fluid control equations for the flow field; S4: Setting the fluid geometry VOF method control equations for the flow field; S5: creating overlapping grids around the target object, and using a geometric VOF method to capture the free liquid surface, thereby completing the free liquid surface geometric reconstruction method.

2. A free surface geometry reconstruction method for coupling overlay grids and isoVOF according to claim 1, characterized in that: The S1 includes: S101: Establish the pool fluid domain in the CFD solver; S102: Perform Boolean operations on the flow field and the target object to create a calculation domain of the pool; S103: constructing a target object model, setting parameters of the target object model, including six degrees of freedom, weight, center of gravity position and moment of inertia, and setting the position of the target object model in the fluid domain of the pool; S104: using the basin volume method to divide the calculation domain into an air phase part and a water phase part; S105: discretizing the flow field into a grid, and creating an object surface grid according to a characteristic scale of the target object; S106: The fluid domain is discretized using STAR-CCM+ and the mesh is converted into a form readable by OpenFOAM using a mesh converter.

3. A free surface geometry reconstruction method for coupling overlay grids and isoVOF according to claim 2, characterized in that: The S2 includes: S201: setting the initial physical conditions of the flow field, and selecting 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; S202: setting boundary conditions of the calculation domain, setting the top surface as a pressure outlet, and setting the outer surface of the hull as a no-slip wall; S203: Setting overlapping grids and creating overlapping interfaces.

4. The free surface geometry reconstruction method of coupling overlay grid and isoVOF according to claim 3, characterized in that: The S203 includes: Select overlapping domains according to the characteristic scale of the target object; Create a densified region in the flow field based on the overlap domain size; Create a surface mesh of the target object according to the surface shape of the target object; Creating a volume mesh according to the size of the surface mesh of the object and the mesh growth ratio; The grid size of the encrypted area in the flow field is set according to the outermost grid size of the overlapping domain to create an overlapping interface.

5. The free surface geometry reconstruction method of coupling overlay grid and isoVOF according to claim 1, characterized in that: The fluid control equation is: Among them, x is the position vector, u is the velocity vector, g is the gravitational acceleration, ρ m represents the density of the mixed fluid, μ is the fluid viscosity, and p is the fluid pressure field.

6. The free surface geometry reconstruction method of coupling overlay grid and isoVOF according to claim 1, characterized in that: The fluid geometry VOF method control equation is: Among them, f α (t) represents the indicator function of the phase distribution at time t, Represents the boundary of the grid participating in the calculation, is the external normal direction of the unit, dS is the grid area differential, the integral term represents the net flux of liquid flowing into the grid within time Δt, F k represents the kth face, N k represents the k-th face of the grid cell.

7. The free surface geometry reconstruction method of coupling overlay grid and isoVOF according to claim 1, characterized in that: The S5 includes: S501: In the motion solver, read the data in the previous iteration step, update the object position, calculate the external force on the target object and update the motion acceleration of the target object, update the object and the grid; correct the fluid flux; S502: In the VOF solver, read the data in the previous iteration step, initialize the volume fraction of the windward grid; set the tolerance and find the surface grid; find the isosurface and correct the volume fraction; obtain the movement of the isosurface based on the velocity field; calculate the interface boundary line according to the movement of the isosurface; calculate and correct the liquid phase volume according to the interface boundary line; S503: Read the physical quantity value of the previous iteration step; calculate the corrected flow field flux through the motion solver; calculate the volume fraction of each phase in the grid through the geometric VOF method; solve the momentum equation; solve the pressure equation; and perform the next iteration.

8. Computer device, characterized in that The invention comprises a memory and a processor, wherein a computer program is stored in the memory, and when the processor runs the computer program stored in the memory, the processor executes a free liquid surface geometry reconstruction method for coupling overlapping grids and isoVOF according to any one of claims 1 to 7.

9. A computer-readable storage medium, characterized in that The computer-readable storage medium is used to store a computer program, and the computer program executes the steps of a free liquid surface geometry reconstruction method for coupling an overlay grid and isoVOF according to any one of claims 1 to 7.

10. A free surface geometry reconstruction system coupling overlay grid and isoVOF, characterized in that: The system comprises: Model building module: used to establish the watershed model of the target object according to the characteristic scale of the target object and to perform grid discretization on the flow field; Condition setting module: used to set physical conditions for the fluid domain boundary and the initial physical conditions for the flow field; Equation setting module: set fluid control equations for the flow field; VOF control module: used to set the fluid geometry VOF method control equation for the flow field; Coupling module: used to create overlapping grids around the target object and capture the free liquid surface using the geometric VOF method.

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