A method and system for free liquid surface geometry reconstruction using coupled overlapping meshes and isoVOF

Abstract

A method and system for geometric reconstruction of free liquid surfaces using coupled overlapping meshes and isoVOF (isoVOF) are disclosed, belonging to the field of fluid dynamics computational technology. This method addresses the limitations of existing algebraic methods in accurately capturing the spatiotemporal evolution characteristics of fluids such as jets, as well as the problem of large mesh deformation. The method includes: establishing a flow domain model of the target object based on its characteristic scale, and discretizing the flow field using a mesh; setting physical conditions for the fluid domain boundary and initial physical conditions for the flow field; setting fluid control equations for the flow field; setting fluid geometric VOF method control equations for the flow field; creating an overlapping mesh around the target object, and using the geometric VOF method to capture the free liquid surface, thus completing the geometric reconstruction of the free liquid surface. This invention is applicable to simulation scenarios involving large-amplitude movements of the free liquid surface and the object.

Description

Technical Field

[0001] This invention belongs to the field of fluid dynamics calculation technology, specifically relating to a method for geometric reconstruction of a free liquid surface. Background Technology

[0002] In studying the impact of a structure into water, the complex evolution of the free surface at the gas-liquid interface within a short timeframe poses a significant challenge to the precise capture of the spatiotemporal evolution of the free surface. To effectively solve for the complex nonlinear free-form surface, a fluid volume interface capture technique was employed.

[0003] However, in the current version of ESI In this study, the algebraic VOF method is still used to capture the free surfaces in the multiphase flow solver. However, due to the simplified calculation of the unit surface volume flux in the algebraic method, the gas-liquid interface is represented in a fuzzy manner, making it impossible to accurately capture the spatiotemporal evolution characteristics of fluids such as jets.

[0004] In addition, although the proposed isoAdvector method for advection with sharp cross sections can capture fluid precisely, it cannot be coupled with overlapping meshes. Therefore, it is prone to divergence when dealing with elastic bodies with low stiffness and large mesh deformation.

[0005] Therefore, when considering the large deformation of the structure, there is an urgent need for a method that can not only ensure the precise capture of the evolution of the liquid on the free surface, but also use overlapping meshes to solve the problem of large mesh deformation. Summary of the Invention

[0006] This invention proposes a method and system for geometric reconstruction of free liquid surfaces by coupling overlapping meshes and isoVOF. The purpose is to solve the problem that existing algebraic methods cannot accurately capture the spatiotemporal evolution characteristics of fluids such as jets, as well as the problem of large mesh deformation.

[0007] A method for geometric reconstruction of a free liquid surface coupled with overlapping meshes and isoVOF, the method comprising:

[0008] S1: Establish a flow domain model of the target object based on its characteristic scale, and discretize the flow field into a grid.

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

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

[0011] S4: Set the governing equations for the flow field using the fluid geometry VOF method;

[0012] S5: Create an overlapping mesh around the target object, and use the geometric VOF method to capture the free surface, thus completing the free surface geometric reconstruction method.

[0013] Furthermore, a preferred embodiment is provided: S1 includes:

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

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

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

[0017] S104: The computational domain is divided into an air phase and a water phase using the watershed volume method;

[0018] S105: Discretize the flow field into a mesh and create a mesh on the object surface based on the characteristic scale of the target object;

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

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

[0021] S201: Set the initial physical conditions of the flow field, and select implicit unsteady state, multiphase, turbulence, watershed volume, k-epsilon turbulence, VOF wave, gravity, and element mass correction as the physical properties of the computational domain;

[0022] S202: Set the boundary conditions of the computational domain, set the top surface as a pressure outlet, and set the outer surface of the hull as a non-slip wall;

[0023] S203: Set up overlapping grids to create overlapping interfaces.

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

[0025] The overlap region is selected based on the characteristic scale of the target object;

[0026] Create a encrypted region in the flow field based on the size of the overlapping region;

[0027] Create an object surface mesh based on the surface shape of the target object;

[0028] Create a volume mesh based on the size and growth ratio of the surface mesh of the object;

[0029] Set the mesh size of the densified region in the flow field according to the outermost mesh size of the overlapping domain, and create the overlapping interface.

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

[0031]

[0032] Where x is the position vector, u is the velocity vector, g is the gravitational acceleration, and ρ is the velocity vector. m denoted by μ, where μ is the density of the mixed fluid, and p is the fluid pressure field.

[0033] Furthermore, a preferred embodiment is provided: the governing equations of the fluid geometry VOF method are:

[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 computation. Let dS be the outward normal direction of the element, dS be the differential of the mesh area, and the integral term represent the net fluid flux into the mesh during time Δt, F. k N represents the k-th face. k This represents the k-th face of a mesh cell.

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

[0037] S501: In the motion solver, read the data from the previous iteration step, update the object position, calculate the external forces acting on the target object and update the target object's acceleration, update the object and the mesh; correct the fluid flux.

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

[0039] Step 503: Read the physical quantity values ​​from the previous iteration; calculate the corrected flow flux using the motion solver; calculate the volume fraction of each phase in the mesh using the geometric VOF method; solve the momentum equation; solve the pressure equation; and proceed to the next iteration.

[0040] The present invention also proposes a computer device, the computer device including a memory and a processor, the memory storing a computer program, and when the processor runs the computer program stored in the memory, the processor executes a free liquid surface geometry reconstruction method based on any of the above-described schemes.

[0041] The present invention also proposes a computer-readable storage medium for storing a computer program that executes the steps of a free surface geometry reconstruction method for coupled overlapping meshes and isoVOF as described in any of the above-described schemes.

[0042] This invention also proposes a free surface geometry reconstruction system based on coupled overlapping meshes and isoVOF, wherein the system is implemented based on a free surface geometry reconstruction method based on coupled overlapping meshes and isoVOF as described in any of the above-mentioned schemes, including:

[0043] Model building module: used to build a flow domain model of the target object based on the characteristic scale of the target object, and to discretize the flow field into a grid.

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

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

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

[0047] Coupling module: Used to create an overlapping mesh around the target object and capture the free surface using the geometric VOF method.

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

[0049] This invention proposes a free liquid surface geometry reconstruction method that couples overlapping meshes with isoVOF. While using the geometric VOF method to capture the gas-liquid interface in a refined manner, it can also couple overlapping meshes to calculate the motion of objects, solve the problem of large mesh deformation, and greatly enrich the technical means for 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 the geometric VOF method to refine the capture of the gas-liquid interface, which can more accurately simulate the spatiotemporal evolution characteristics of the free liquid surface.

[0052] 2. Coupled Overlapping Mesh: By using coupled overlapping mesh technology, the problem of mesh failure caused by large-scale object movement is solved, improving the stability and reliability of the calculation.

[0053] 3. Solving the problem of large mesh deformation: The application of overlapping mesh technology ensures mesh quality, especially when the object undergoes large-scale movement, effectively preventing excessive mesh deformation.

[0054] 4. Multiphase flow control equations: The method described above sets fluid control equations that take 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: Using the VOF method governing equation, the change of liquid volume fraction over time is calculated through an accurate fluid volume transport equation.

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

[0057] This invention is applicable to simulation scenarios involving free liquid surfaces and objects undergoing large-scale motion. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0059] Figure 1 This is a flowchart illustrating a method for geometric reconstruction of a free liquid surface using coupled overlapping meshes and isoVOF, according to an embodiment of the present invention.

[0060] Figure 2 This is a flowchart illustrating the calculation process of a free surface geometry reconstruction method using coupled overlapping meshes and isoVOF according to an embodiment of the present invention.

[0061] Figure 3 This is a numerical calculation model of one embodiment of the present invention;

[0062] Figure 4 This is a flow field domain determination according to 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 This is a mesh division of a cross section of the flow field according to an embodiment of the present invention;

[0064] Figure 6 This is a surface mesh division of a numerical calculation model according to an embodiment of the present invention;

[0065] Figure 7 This is a flow field capture of a cross section under numerical calculation according to an embodiment of the present invention. Detailed Implementation

[0066] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application can also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of this application with unnecessary detail.

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

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

[0069] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0070] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0071] Implementation Method 1:

[0072] Reference Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 This implementation method is described below.

[0073] A method for free liquid surface geometry reconstruction using coupled overlapping meshes and isoVOF includes:

[0074] S1: In OpenFOAM software, establish the flow domain model of the target object based on its characteristic scale, and discretize the flow field into a grid.

[0075] S101: Establish a water pool fluid domain in the CFD solver, wherein the water pool fluid domain is a cuboid space domain, including 4 side walls, a bottom surface and a top surface;

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

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

[0078] S104: The computational domain is divided into an air phase and a water phase using the watershed volume method;

[0079] S105: Discretize the flow field into a mesh and create a mesh on the object surface based on the characteristic scale of the target object;

[0080] S106: The fluid domain is discretized using STAR-CCM+, and the mesh is converted into an OpenFOAM-readable form using a mesh converter;

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

[0082] S201: Set the initial physical conditions of the flow field, and select implicit unsteady state, multiphase, turbulence, watershed volume, k-epsilon turbulence, VOF wave, gravity, and element mass correction as the physical properties of the computational domain;

[0083] S202: Set the boundary conditions of the computational domain, set the top surface as a pressure outlet, and set the outer surface of the hull as a non-slip wall;

[0084] S203: Set up overlapping meshes and create overlapping interfaces, specifically including: selecting an overlapping region based on the characteristic scale of the target object; creating a denser region in the flow field based on the size of the overlapping region; creating an object surface mesh based on the surface shape of the target object; creating a volume mesh based on the size of the object surface mesh and the mesh growth ratio; setting the mesh size of the denser region in the flow field based on the size of the outermost mesh of the overlapping region, and creating an overlapping interface.

[0085] The creation of overlapping meshes ensures mesh quality when studying objects undergoing significant motion. It allows the use of several overlapping meshes to handle complex or disjointed geometries.

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

[0087] The fluid control equation is as follows:

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

[0089]

[0090] Where x is the position vector, u is the velocity vector, g is the gravitational acceleration, and ρ is the velocity vector. m denoted by μ, where μ is the density of the mixed fluid, and p is the fluid pressure field.

[0091] Since the occurrence time of slamming problems is usually in the tens of milliseconds, which is much smaller than the time scale of viscosity acting on the fluid, a laminar flow model is chosen to close the Navier-Stokes equations.

[0092] S4: Set the governing equations for the fluid geometry VOF method for the flow field; the governing equations for the fluid geometry VOF method are:

[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 computation. Let dS be the outward normal direction of the element, dS be the differential of the mesh area, and the integral term represent the net fluid flux into the mesh during time Δt, F. k N represents the k-th face. k This represents the k-th face of a mesh cell.

[0095] S4 sets the governing equations for the fluid geometry VOF method for the flow field. Based on the solution strategy for fluid volume, the VOF method can be further divided into geometric and algebraic solutions. In the geometric VOF method, the indicator function f... α (t) is approximated using a standard reconstruction technique involving piecewise linear interface computation (PLIC), where the interface location within each cell is explicitly defined by plane equations. The governing equations of the VOF method are as follows:

[0096] The VOF method is used to solve for the spatiotemporal changes of the free surface of incompressible, immiscible multiphase fluids. The transport equation for the fluid volume is as follows:

[0097]

[0098] Among them, f α (t) represents the indicator function of the phase distribution at time t. Its value is 1 when the grid is entirely liquid and 0 when the grid is entirely gas.

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

[0100]

[0101] Over a finite time interval [t, t+Δt], by integrating the above formula over a fixed unit and applying the divergence theorem, the evolution equation of the liquid volume fraction as a function of time can be calculated:

[0102]

[0103] in, Represents the boundary of the grid participating in the computation. dS is the outward normal direction of the element, dS is the differential of the grid area, and the integral term represents the net flux of liquid flowing into the grid in time Δt.

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

[0105]

[0106] Discretizing the above formula on the mesh cell surface, assuming there are N faces in the mesh cell, the area integral term on the right side is modified as follows:

[0107]

[0108] Among them, S k Represents the k-th face. This represents the direction of the outward normal of the surface;

[0109] The kth face F k The velocity field u on the surface can be approximately defined by the surface flux of the volume as:

[0110]

[0111] The formula for calculating the volume then becomes:

[0112]

[0113] In the above formula, for The surface integral represents the instantaneous area of ​​surface k immersed in the fluid, and is named A. k The formula then simplifies further to:

[0114]

[0115] S5: Create an overlapping mesh around the target object, use the geometric VOF method to capture the free liquid surface, and complete the free liquid surface geometric reconstruction method;

[0116] S501: In the motion solver, read the data from the previous iteration step, update the object position, calculate the external forces acting on the target object and update the target object's acceleration, update the object and the mesh; correct the fluid flux.

[0117] S502: In the VOF solver, read the data from the previous iteration step, initialize the volume fraction of the windward mesh; set the tolerance and locate the surface mesh; find the isosurfaces and correct the volume fraction; obtain the motion of the isosurfaces from t to t+Δt based on the velocity field; calculate the interface boundary line based on the motion of the isosurfaces from t to t+Δt; calculate ΔV based on the interface boundary line. k (t, t+Δt), calculate and correct the liquid volume α using the redistribution procedure. i (t+Δt);

[0118] S503: Read the physical quantity values ​​from the previous iteration step; calculate the corrected flow flux using the motion solver; calculate the volume fraction of each phase in the mesh using the geometric VOF method; solve the momentum equation; solve the pressure equation; proceed to the next iteration.

[0119] The method described in this embodiment simulates the fluid flow changes in the region surrounding an object in a numerical water tank using a CFD solver, obtaining the pressure field and motion history of the object's surface. The volumetric fluid method (VOF) is used to divide the water tank fluid domain into an air layer and a water layer, which helps to more accurately simulate the position and shape of the free surface. By appropriately setting the time step and using a first-order time discretization scheme, the stability of the calculation and the accuracy of the results are ensured. The isoVOF geometric reconstruction method is used to capture the free liquid surface and jets, improving the accuracy of interface capture. The method described in this embodiment is implemented based on OpenFOAM software, utilizing existing CFD tools, which facilitates engineering applications and technology transfer.

[0120] like Figure 3 As shown, taking a three-dimensional wedge as an example, with a heave angle of 30°, the wedge falls freely from a certain height in a static flow field. The simulation refines and captures the spatiotemporal evolution characteristics of the free surface and jet changes during the wedge's impact with the water. In this embodiment, the CFD solver uses OpenFOAM software. A water pool fluid domain is established, which is a cuboid space domain enclosed by six faces: four side walls, a bottom surface, and a top surface. The six degrees of freedom, weight, and center of gravity of the three-dimensional solid model of the wedge are set. The position of the wedge in the flow field is also set. In this embodiment, only the motion of the wedge in the Z direction is considered; therefore, only the Z-direction degree of freedom is opened. To improve computational efficiency, the bottom vertex of the wedge is placed near the free surface, and the free fall portion of the wedge is omitted by assigning an initial velocity.

[0121] like Figure 4The fluid domain of the pool was divided into two parts, air layer 3 and water layer 4, using the Volume of Fluid (VOF) method. The vertical position of free surface 2 was located at the height of the origin. The fluid domain was meshed, and mesh refinement was performed near the 3D solid model 1 of the ship hull and free surface 2. A hexahedral unstructured mesh was used to mesh the computational domain, employing an overlapping mesh scheme. The computational domain included a background region and an overlapping region. To accurately capture the drastic changes in physical quantities such as turbulence around the free surface and the ship hull, local mesh refinement was performed on the free surface and around the ship hull. The boundary layer mesh number of the wedge-shaped outer shell was 5. Boundary conditions were set: the four side walls and bottom surface of the pool fluid domain were used as velocity inlets, the top surface as a pressure outlet, and the outer surface of the ship hull as a no-slip wall. The time step was set: the solution time was set to 0.2s in the CFD solver, and the time step was set to 0.001s, using a first-order time discretization scheme.

[0122] In this embodiment, the wedge-shaped body employs overlapping mesh calculations for surge, and the isoVOF geometric reconstruction method is used to capture the free surface and jet. A comparison is made between the phase distribution captured at the xoz surface cross-section and the phase distribution captured using conventional methods. Figure 6 .

[0123] Those skilled in the art will understand that the above description is merely a preferred embodiment of the present invention, and the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. This is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0124] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0125] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0126] Those skilled in the art will understand that embodiments of this disclosure can be provided as methods, systems, or computer program products. Therefore, this disclosure can take the form of a completely hardware implementation, a completely software implementation, or an implementation combining software and hardware aspects. Furthermore, this disclosure can take the form of a computer program product embodied 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] This disclosure is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart. Figure 1 One or more processes and / or boxes Figure 1 The computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to operate in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0128] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure and not to limit its protection scope. Although this disclosure has been described in detail with reference to the above embodiments, those skilled in the art should understand that after reading this disclosure, they can still make various changes, modifications or equivalent substitutions to the specific embodiments of the invention, but these changes, modifications or equivalent substitutions are all within the protection scope of the claims to be published and pending approval.

Claims

1. A method for geometric reconstruction of a free liquid surface coupled with overlapping meshes and isoVOF, characterized in that, The method includes: S1: Establish a flow domain model of the target object based on its characteristic scale, and discretize the flow field into a grid. S2: Set the physical conditions for the fluid domain boundary and the initial physical conditions for the flow field; S3: Set the fluid control equations for the flow field; S4: Set the governing equations for the flow field using the fluid geometry VOF method; S5: Create an overlapping mesh around the target object, use the geometric VOF method to capture the free liquid surface, and complete the free liquid surface geometric reconstruction method; The governing equations for the fluid geometry VOF method are: ， in, The indicator function representing the phase distribution at time t. Represents the boundary of the grid participating in the computation. The direction of the outer normal of the element. The integral term represents the time derivative of the grid area. The net flux of liquid flowing into the grid. This represents the k-th face. This represents the k-th face of a mesh cell; S5 includes: S501: In the motion solver, read the data from the previous iteration step, update the object position, calculate the external forces acting on the target object and update the target object's acceleration, update the object and the mesh; correct the fluid flux. S502: In the VOF solver, read the data from the previous iteration step, initialize the volume fraction of the windward mesh; set the tolerance and find the surface mesh; find the isosurface and correct the volume fraction; obtain the motion of the isosurface based on the velocity field; calculate the interface boundary line based on the motion of the isosurface; calculate and correct the liquid phase volume based on the interface boundary line. S503: Read the physical quantity values ​​from the previous iteration step; calculate the corrected flow flux using the motion solver; calculate the volume fraction of each phase in the mesh using the geometric VOF method; solve the momentum equation; solve the pressure equation; proceed to the next iteration.

2. The free liquid surface geometry reconstruction method according to claim 1, characterized in that, S1 includes: S101: Establish the water pool fluid domain in the CFD solver; S102: Perform Boolean operations on the flow field and the target object to create the computational domain of the pool; S103: Construct a target object model, set the parameters of the target object model, including: six degrees of freedom, weight, center of gravity position and moment of inertia, and set the position of the target object model in the fluid domain of the pool. S104: The computational domain is divided into an air phase and a water phase using the watershed volume method; S105: Discretize the flow field into a mesh and create a mesh on the object surface based on the characteristic scale of the target object; S106: The fluid domain is discretized using STAR-CCM+, and the mesh is converted into an OpenFOAM-readable form using a mesh converter.

3. The free liquid surface geometry reconstruction method according to claim 2, characterized in that, S2 includes: S201: Set the initial physical conditions of the flow field, and select implicit unsteady state, multiphase, turbulence, watershed volume, k-epsilon turbulence, VOF wave, gravity, and element mass correction as the physical properties of the computational domain; S202: Set the boundary conditions of the computational domain, set the top surface as a pressure outlet, and set the outer surface of the hull as a non-slip wall; S203: Set up overlapping grids to create overlapping interfaces.

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

5. The free liquid surface geometry reconstruction method according to claim 1, characterized in that, The fluid control equation is as follows: ， ， in, For position vectors, It is a velocity vector. It is the acceleration due to gravity. Represents the density of the mixed fluid. It is fluid viscosity. This represents the fluid pressure field.

6. A computer device, characterized in that, It includes a memory and a processor, wherein the memory stores a computer program, and when the processor runs the computer program stored in the memory, the processor executes a free surface geometry reconstruction method of coupled overlapping mesh and isoVOF according to any one of claims 1-5.

7. A computer-readable storage medium, characterized in that, The computer-readable storage medium is used to store a computer program that performs the steps of a free surface geometry reconstruction method of coupled overlapping mesh and isoVOF according to any one of claims 1-5.

8. A free liquid surface geometry reconstruction system coupled with overlapping meshes and isoVOF, characterized in that, The system is implemented based on the method of any one of claims 1 to 5, and the system comprises: Model building module: used to build a flow domain model of the target object based on the characteristic scale of the target object, and to discretize the flow field into a grid. Condition setting module: used to set physical conditions for the fluid domain boundary and to set initial physical conditions for the flow field; Equation setting module: Sets the fluid control equations for the flow field; VOF control module: used to set the governing equations for the fluid geometry VOF method in the flow field; Coupling module: Used to create an overlapping mesh around the target object and capture the free surface using the geometric VOF method.

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