Fluid-structure interaction solution method for variable diffusion extrapolation immersion boundary of complex geometry

Abstract

The invention relates to the technical field of aerospace, in particular to a complex geometry variable diffusion extrapolation immersion boundary fluid-solid coupling solving method, which comprises the following steps of: establishing a finite difference grid of a fluid-solid coupling problem and a finite element grid of a solid structure; mapping the spatial position occupied by the finite element grid to a finite difference grid, and completing the identification of a difference node; a level value set is given to the differential nodes, and then an interface normal vector is calculated; applying boundary conditions of the fluid domain to update the fluid domain; the fluid pressure is converted to a fluid load on a finite element node in the finite difference grid, and then a solid domain is updated by applying a finite element explicit algorithm; and after the solid domain is updated, interpolating fluid information around the new fluid differential node to the new fluid differential node by adopting inverse distance weighted interpolation. According to the method, partition coupling is utilized, the solid domain and the fluid domain are solved independently, the method is simple and convenient, the universality is high, and the fluid-solid coupling simulation result is good in accuracy.

Description

Technical Field

[0001] The invention relates to the field of aerospace technology, and in particular to a method for solving fluid-solid coupling of complex geometric body variable diffusion extrapolation immersed boundary. Background Art

[0002] Fluid-solid coupling technology studies the interaction between fluids and solids and is widely used in defense, military industry, aerospace, biomedicine and other fields. Fluid-solid coupling involves complex multi-physics field coupling problems, which requires solving the solid structure and fluid domain at the same time and processing the information exchange of the fluid-solid interface, and is highly nonlinear. Traditional fluid-solid coupling methods usually use unstructured grids for calculations, such as body-fitting grids or dynamic grid technologies, and their grid generation algorithms are relatively complex. The immersed boundary method uses structured grids to process the fluid-solid interface, which solves the problem of difficult grid generation and has relatively high computational efficiency. In recent years, the immersed boundary method has become one of the important fluid-solid coupling processing technologies. However, the current immersed boundary method will be numerically unstable when dealing with fluid-solid interfaces with complex shapes. For example, when there are singular positions such as corners and corners of the solid structure, numerical divergence is easy, and special numerical processing is often required to ensure the stability of the calculation. Summary of the invention

[0003] In view of the defects in the prior art, the present invention provides a method for solving fluid-solid coupling of complex geometric bodies by variable diffusion extrapolation and immersed boundary.

[0004] In order to achieve the above-mentioned purpose, the present invention provides a method for solving fluid-solid coupling of complex geometric body variable diffusion extrapolation immersed boundary, the method comprising the following steps: establishing a finite difference grid for fluid-solid coupling problem and a finite element grid for solid structure; mapping the spatial position occupied by the finite element grid to the finite difference grid, and completing the identification of the differential nodes in the finite difference grid; assigning a level value set to the differential nodes in the finite difference grid, and then calculating the interface normal vector of the fluid-solid interface; after calculating the normal vector of the fluid-solid interface, applying the boundary conditions of the fluid domain, and then updating the fluid domain; converting the fluid pressure to the fluid load on the finite element node in the finite difference grid, and then applying the finite element explicit algorithm to update the solid domain; after updating the solid domain, using inverse distance weighted interpolation to interpolate the fluid information around the new fluid differential node to the new fluid differential node. The present invention utilizes partition coupling to solve the solid domain and the fluid domain separately. The method is simple, versatile, and the accuracy of the fluid-solid coupling simulation results is good.

[0005] Optionally, mapping the spatial position occupied by the finite element grid to the finite difference grid and completing the identification of the differential nodes in the finite difference grid comprises the following steps: calculating surface normal vectors of finite element surfaces on the finite element mesh; Calculating node vectors of the differential node and the finite element node according to the surface normal vector; The angle between the node vector and the surface normal vector is calculated, thereby identifying the solid differential node and the fluid differential node.

[0006] Optionally, assigning a level value set to the difference nodes in the finite difference grid to thereby calculate an interface normal vector of the fluid-solid interface comprises the following steps: Assigning a numerical label to each of the differential nodes; According to the numerical markings, the Godunov method is used to solve the level value set reinitialization equation to obtain the level set strip contour near the fluid-solid interface; After obtaining the level set strip contour lines, the interface normal vector is calculated on the finite difference grid.

[0007] Optionally, after calculating the normal vector of the fluid-solid interface, applying the boundary conditions of the fluid domain and then updating the fluid domain comprises the following steps: Arranging tracking points on the finite element surface and calculating the tracking point velocities of the tracking points; According to the trace point velocity, the solid velocity of the solid structure near the immersed boundary is interpolated to the surrounding fluid differential nodes; By means of an extrapolation equation, the fluid information and the solid velocity stored on the fluid differential node near the immersed boundary are extrapolated to the virtual fluid node inside the solid structure to complete the extrapolation of the fluid-solid interface information; After completing the extrapolation of the fluid-solid interface information, the boundary conditions of the fluid domain at the immersed boundary are set, and then the fluid solver is applied to update the flow field to update the fluid domain.

[0008] Optionally, the interface normal vector satisfies the following relationship: in, is the interface normal vector, is the gradient of the level value set near the fluid-solid interface.

[0009] Optionally, the tracking point speed satisfies the following relationship: in, is the velocity of the tracer point, is the shape function of the kth finite element node in the finite element patch on the immersed boundary, i and j represent the row index and column index corresponding to the trace point on the finite element patch, respectively. is the velocity of the kth finite element node in the finite element patch.

[0010] Optionally, according to the tracer point velocity, the solid velocity of the solid structure near the immersed boundary is interpolated to the surrounding fluid differential nodes to satisfy the following relationship: in, The solid velocity of the solid structure near the immersed boundary is mapped to the velocity of the fluid differential node around it, is the total number of tracer points on the finite element patch involved in interpolation, is the interpolation weight coefficient of the qth tracing point on the finite element patch involved in the interpolation, is the tracking point velocity of the tracking point on the finite element patch, and i and j respectively represent the row index and column index corresponding to the tracking point on the finite element patch.

[0011] Optionally, the extrapolation equation satisfies the following relationship: in, is the variable that needs to be extrapolated. For virtual time, The finite difference grid step size is set to 0.5. is the interface normal vector, for gradient.

[0012] Optionally, the boundary condition of the fluid domain at the immersed boundary satisfies the following relationship: in, is the velocity of the virtual fluid node, is the interface normal vector, is the solid velocity, is the velocity of the fluid domain extrapolated to the virtual fluid node, is the tangent vector of the fluid-solid interface.

[0013] Optionally, the fluid load satisfies the following relationship: in, is the fluid load on the finite element node, is the surface normal vector, is the total number of the finite element nodes, is the number of segments that each edge of the finite element patch where the finite element node is located is divided into, is the sub-sheet area occupied by the qth tracing point on the finite element patch where the finite element node is located, is the fluid pressure value at the qth tracing point on the finite element patch where the finite element node is located, and i and j respectively represent the row index and column index corresponding to the tracing point on the finite element patch.

[0014] In summary, first, the present invention partitions the computational domain through the corresponding differential node marking strategy; then, the present invention uses the level value set to identify and mark the differential nodes, and uses the level set to reinitialize the equation to calculate the distance field near the fluid-solid interface, and obtains important geometric information at the fluid-solid interface, such as the interface normal vector; then, the present invention uses the interface normal vector to realize the extrapolation of fluid information to the virtual fluid node inside the solid structure, thereby conveniently defining the boundary conditions of the fluid domain. Finally, the present invention uses the fluid solver to update the fluid domain, while the solid structure uses a nonlinear finite element explicit solution method, and finally realizes the fluid-solid coupling simulation of compressible flow. It can be seen that the present invention utilizes partition coupling to solve the solid domain and the fluid domain separately. The method is simple, versatile, and the accuracy of the fluid-solid coupling simulation results is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 It is a schematic flow chart of a method for solving fluid-solid coupling of a complex geometric body variable diffusion extrapolation immersed boundary according to an embodiment of the present invention; Figure 2 A schematic diagram of surface normal vector and differential node identification according to an embodiment of the present invention; Figure 3 A schematic diagram of differential node type marking according to an embodiment of the present invention; Figure 4 A schematic diagram of tracing points on a finite element surface according to an embodiment of the present invention; Figure 5 A schematic diagram of tracing points on a finite element patch according to an embodiment of the present invention; Figure 6 A schematic diagram of converting fluid pressure to finite element nodes according to an embodiment of the present invention; Figure 7 Schematic diagram of the differential node of the new fluid according to an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are only for illustration and are not intended to limit the present invention. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details do not need to be adopted to implement the present invention. In other examples, in order to avoid confusing the present invention, known circuits, software or methods are not specifically described.

[0018] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment," "in an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combination and / or subcombination. In addition, it should be understood by those of ordinary skill in the art that the figures provided herein are for illustrative purposes and that the figures are not necessarily drawn to scale.

[0019] It should be noted in advance that, in an optional embodiment, except for independent explanations, the same symbols or letters appearing in all formulas have the same meanings and values.

[0020] In an alternative embodiment, see Figure 1 The present invention provides a method for solving fluid-solid coupling of complex geometric body variable diffusion extrapolation immersed boundary, the method comprising the following steps: S1. Establish the finite difference mesh for fluid-structure interaction problem and the finite element mesh for solid structure.

[0021] Specifically, in this embodiment, this step can be implemented by existing technical means, so it will not be described in detail here.

[0022] S2. Mapping the spatial position occupied by the finite element grid to the finite difference grid, and completing the identification of the differential nodes in the finite difference grid.

[0023] Wherein, step S2 specifically includes the following steps: S21. Calculate the surface normal vector of the finite element surface on the finite element mesh.

[0024] Specifically, in this embodiment, see Figure 2 , the cube ABCDEFGH represents a finite element on the finite element mesh, and points A to H represent the eight finite element nodes on the finite element. represents the difference nodes outside the finite element, represents a difference node located within the finite element.

[0025] More specifically, Figure 2 Take the finite element surface ABCD as an example, the normal vector of the surface is .

[0026] S22. Calculate the node vectors of the differential node and the finite element node according to the surface normal vector.

[0027] Specifically, in this embodiment, see Figure 2 , represents the difference nodes outside the finite element, Represents the differential node located in the finite element. In this embodiment, and Both are recorded as differential nodes P, and taking finite element node B as an example, the node vectors of differential node P and finite element node B are .

[0028] S23, calculating the angle between the node vector and the surface normal vector, and then identifying the solid differential node and the fluid differential node.

[0029] Specifically, in this embodiment, For example, calculate Normal vector to the cell surface Angle .

[0030] For more details, see Figure 3 ,if , then the differential node P is located outside the finite element, and this differential node P is marked as a fluid differential node; if , then the differential node P is located inside the finite element, and this differential node P is marked as a solid differential node.

[0031] Furthermore, Figure 3 Finite elements, finite element nodes, finite element mesh occupied areas, and virtual fluid nodes in solid difference nodes are also marked. Among them, the virtual fluid nodes in the solid difference nodes can be used to define the boundary conditions of the fluid domain. The number of virtual fluid nodes in each direction depends on the selected difference format. If the 5th order WENO format is used, three virtual fluid nodes are required in each direction.

[0032] S3. Assigning a level value set to the difference nodes in the finite difference grid, and then calculating the interface normal vector of the fluid-solid interface.

[0033] Wherein, step S3 specifically includes the following steps: S31. Assign a numerical label to each differential node.

[0034] Specifically, in this embodiment, the fluid differential node is marked as , label the solid difference nodes as .

[0035] S32. According to the numerical labels, the Godunov method is used to solve the level value set reinitialization equation to obtain the level set strip contour lines near the fluid-solid interface.

[0036] S33, after obtaining the level set strip contour lines, calculating the interface normal vector on the finite difference grid.

[0037] Specifically, in this embodiment, after obtaining the level set strip contour near the fluid-solid interface, the interface normal vector can be quickly calculated on the finite difference grid, and the interface normal vector satisfies the following relationship: in, is the interface normal vector, is the gradient of the horizontal value set near the fluid-solid interface.

[0038] S4. After calculating the normal vector of the fluid-solid interface, the boundary conditions of the fluid domain are applied, thereby updating the fluid domain.

[0039] Wherein, step S4 specifically includes the following steps: S41, arranging tracking points on the finite element surface, and calculating the tracking point velocities of the tracking points.

[0040] Specifically, in this embodiment, for the simulation of compressible fluid, the finite difference grid is denser than the finite element grid. In order to accurately interpolate the velocity of the finite element surface to the surrounding fluid difference node, it is necessary to arrange tracer points on the finite element surface, as shown in the following example. Figure 4 shown.

[0041] For more details, please refer to Figure 5 For any given finite element patch on the immersed boundary, put it into a cubic "bucket" with the dimensions of each coordinate axis in the spatial rectangular coordinate system Determined by the following formula: Among them, x, y and z are the three coordinate axes of the spatial rectangular coordinate system. , , and They represent the coordinate axes of the four finite element nodes on the finite element patch in the solid structure. The node coordinates on the symbol " "middle," "and" " is one, so the separate " " has no meaning, the subsequent subscript " " is interpreted the same way; in the symbol " "middle, It is also a whole.

[0042] Divide each edge of the finite element patch into segments, then the entire finite element patch can be divided into There are sub-slices, each of which has a tracer point, so the total number of tracer points on the finite element patch is .in It can be determined by the following formula: in, is the ceiling function, The difference unit and coordinate axis of the "bucket" Half the length of the parallel edges, c is a factor that can adjust the density of the shards. The smaller the c value, the denser the shards.

[0043] Furthermore, the local coordinates of the tracer point It can be determined by the following formula: in, and are the local coordinate components of the tracer point in the finite element patch, and i and j represent the row index and column index corresponding to the tracer point on the finite element patch, respectively.

[0044] Convert the local coordinates of the tracer point to global coordinates : in, is the shape function of the kth finite element node in the finite element patch on the immersed boundary, i and j represent the row index and column index of the tracer point on the finite element patch, respectively. is the velocity of the kth finite element node in the finite element patch. This is consistent with the standard bilinear shape function in finite elements. Satisfies the following relationship: in, and is the coordinate component of the kth finite element node in the finite element patch.

[0045] The tracer point velocity of the tracer point can be expressed as: in, is the velocity of the trace point shown, is the velocity of the kth finite element node in the finite element patch.

[0046] S42, interpolating the solid velocity of the solid structure near the immersed boundary to the surrounding fluid differential nodes according to the tracer point velocity.

[0047] Specifically, in this embodiment, the solid velocity of the solid structure near the immersed boundary is interpolated to the surrounding fluid differential nodes, and the interpolation is specifically performed according to the following formula: in, is the mapping of the solid velocity of the solid structure near the immersed boundary to the velocity of the surrounding fluid differential node, is the total number of tracer points on the finite element patch involved in interpolation, is the interpolation weight coefficient of the qth tracing point on the finite element patch participating in the interpolation. Satisfies the following relationship: in, , is the inverse distance coefficient of the qth tracing point on the finite element patch involved in the interpolation, is the distance from the qth tracing point on the finite element patch involved in the interpolation to the fluid differential node.

[0048] S43, using the extrapolation equation, the fluid information and the solid velocity stored on the fluid differential node near the immersed boundary are extrapolated to the virtual fluid node inside the solid structure to complete the extrapolation of the fluid-solid interface information.

[0049] Specifically, in this embodiment, the extrapolation equation satisfies the following relationship: in, is the variable that needs to be extrapolated. For virtual time, The finite difference grid step size is set to 0.5. is the interface normal vector, for According to this extrapolation equation, the fluid information and solid velocity stored on the fluid differential node near the immersed boundary are extrapolated to the virtual fluid node inside the solid structure to complete the extrapolation of the fluid-solid interface information.

[0050] S44. After completing the extrapolation of the fluid-solid interface information, the boundary conditions of the fluid domain at the immersed boundary are set, and then the fluid solver is applied to update the flow field to update the fluid domain.

[0051] Specifically, in this embodiment, in order to update the fluid domain, it is necessary to give the boundary conditions of the fluid domain at the immersed boundary. The immersed boundary belongs to a solid wall, and a slip reflection boundary condition needs to be applied. In addition, the solid structure needs to provide a velocity boundary condition for the fluid domain. The boundary conditions of the fluid domain at the immersed boundary satisfy the following relationship: in, is the velocity of the virtual fluid node, is the interface normal vector, is the solid velocity, is the velocity of the fluid domain extrapolated to the virtual fluid node, is the tangent vector of the fluid-solid interface.

[0052] Furthermore, after the boundary conditions of the fluid domain are defined, the fluid solver can be applied to update the flow field. Specifically, in the fluid solver, the convection term of the NS equations uses LF splitting and 5th-order WENO reconstruction, and the time advancement uses the 3rd-order Runge-Kutta method with TVD properties.

[0053] S5. Convert the fluid pressure to the fluid load on the finite element nodes in the finite difference grid, and then apply the finite element explicit algorithm to update the solid domain.

[0054] Specifically, in this embodiment, after the fluid domain is updated within a time step, the fluid pressure needs to be converted to the fluid load on the finite element node. Figure 6 First, the difference nodes are interpolated by inverse distance weighted interpolation. , and The fluid pressure on the surface is interpolated to the tracer points on the finite element patch The interpolation process is similar to step S42, and then the fluid pressure at the tracing point is converted into the fluid load on the four finite element nodes. Figure 6 middle, , and Differential nodes , and With tracer point The distance between is the fluid load on the kth finite element node on the finite element patch, k=1,2,3,4.

[0055] More specifically, the fluid loads on the finite element nodes satisfy the following relationship: in, is the fluid load on the finite element node, is the surface normal vector, is the total number of finite element nodes, is the number of segments that each edge of the finite element patch where the finite element node is located is divided into, is the sub-slice area occupied by the qth tracing point on the finite element patch where the finite element node is located, is the fluid pressure value at the qth tracing point on the finite element patch where the finite element node is located, and i and j represent the row index and column index corresponding to the tracing point on the finite element patch, respectively. It can be obtained by the ratio of the finite element patch area to the total number of tracer points on the surface, that is: in, is the area of ​​the finite element patch where the tracer point is located.

[0056] Furthermore, after converting the fluid pressure into fluid loads on the finite element nodes in the finite difference mesh, the finite element explicit algorithm is applied to update the solid domain.

[0057] S6. After updating the solid domain, the fluid information around the new fluid differential node is interpolated to the new fluid differential node using inverse distance weighted interpolation.

[0058] Specifically, in this embodiment, after the solid domain is updated, the position of the solid structure will change, such as Figure 7 As shown, the solid line position indicates The fluid-solid interface at time t, the dotted line indicates The fluid-solid interface at the time. The new fluid differential node is defined, that is, the surrounding fluid information is interpolated to the new fluid differential node using inverse distance weighted interpolation.

[0059] It should be noted that, in some cases, the actions described in the specification can be performed in a different order and still achieve the desired results. In this embodiment, the order of steps given is only to make the embodiment appear clearer and easier to explain, rather than to limit it.

[0060] In summary, first, the present invention partitions the computational domain through the corresponding differential node marking strategy; then, the present invention uses the level value set to identify and mark the differential nodes, and uses the level set to reinitialize the equation to calculate the distance field near the fluid-solid interface, and obtains important geometric information at the fluid-solid interface, such as the interface normal vector; then, the present invention uses the interface normal vector to realize the extrapolation of fluid information to the virtual fluid node inside the solid structure, thereby conveniently defining the boundary conditions of the fluid domain. Finally, the present invention uses the fluid solver to update the fluid domain, while the solid structure uses a nonlinear finite element explicit solution method, and finally realizes the fluid-solid coupling simulation of compressible flow. It can be seen that the present invention utilizes partition coupling to solve the solid domain and the fluid domain separately. The method is simple, versatile, and the accuracy of the fluid-solid coupling simulation results is good.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the specification of the present invention.

Claims

1. A complex geometric body variable diffusion extrapolation immersed boundary fluid-solid coupling solution method, characterized by: The steps include: Establish finite difference meshes for fluid-structure interaction problems and finite element meshes for solid structures; Mapping the spatial position occupied by the finite element grid to the finite difference grid, and completing the identification of the difference nodes in the finite difference grid; Assigning a level value set to the difference nodes in the finite difference grid, thereby calculating an interface normal vector of the fluid-solid interface; After calculating the normal vector of the fluid-solid interface, applying the boundary conditions of the fluid domain, and then updating the fluid domain; converting the fluid pressure into fluid loads on finite element nodes in the finite difference grid, and then applying a finite element explicit algorithm to update the solid domain; After the solid domain is updated, the fluid information around the new fluid differential node is interpolated to the new fluid differential node using inverse distance weighted interpolation.

2. The complex geometry variable diffusion extrapolation immersed boundary fluid-solid coupling solution method according to claim 1 is characterized in that: The step of mapping the spatial position occupied by the finite element grid to the finite difference grid and completing the identification of the differential nodes in the finite difference grid comprises the following steps: calculating surface normal vectors of finite element surfaces on the finite element mesh; Calculating node vectors of the differential node and the finite element node according to the surface normal vector; The angle between the node vector and the surface normal vector is calculated, thereby identifying the solid differential node and the fluid differential node.

3. The complex geometry variable diffusion extrapolation immersed boundary fluid-solid coupling solution method according to claim 1 is characterized in that: The step of assigning a level value set to the difference nodes in the finite difference grid and then calculating the interface normal vector of the fluid-solid interface comprises the following steps: Assigning a numerical label to each of the differential nodes; According to the numerical markings, the Godunov method is used to solve the level value set reinitialization equation to obtain the level set strip contour near the fluid-solid interface; After obtaining the level set strip contour lines, the interface normal vector is calculated on the finite difference grid.

4. The complex geometry variable diffusion extrapolation immersed boundary fluid-solid coupling solution method according to claim 2 is characterized in that: After calculating the normal vector of the fluid-solid interface, applying the boundary conditions of the fluid domain and then updating the fluid domain comprises the following steps: Arranging tracking points on the finite element surface and calculating the tracking point velocities of the tracking points; According to the trace point velocity, the solid velocity of the solid structure near the immersed boundary is interpolated to the surrounding fluid differential nodes; By means of an extrapolation equation, the fluid information and the solid velocity stored on the fluid differential node near the immersed boundary are extrapolated to the virtual fluid node inside the solid structure to complete the extrapolation of the fluid-solid interface information; After completing the extrapolation of the fluid-solid interface information, the boundary conditions of the fluid domain at the immersed boundary are set, and then the fluid solver is applied to update the flow field to update the fluid domain.

5. The complex geometry variable diffusion extrapolation immersed boundary fluid-solid coupling solution method according to claim 4 is characterized in that: The interface normal vector satisfies the following relationship: in, is the interface normal vector, is the gradient of the level value set near the fluid-solid interface.

6. The complex geometry variable diffusion extrapolation immersed boundary fluid-solid coupling solution method according to claim 4 is characterized in that: The tracking point velocity satisfies the following relationship: in, is the velocity of the tracer point, is the shape function of the kth finite element node in the finite element patch on the immersed boundary, i and j represent the row index and column index corresponding to the trace point on the finite element patch, respectively. is the velocity of the kth finite element node in the finite element patch.

7. The complex geometry variable diffusion extrapolation immersed boundary fluid-solid coupling solution method according to claim 6 is characterized in that: According to the tracking point velocity, the solid velocity of the solid structure near the immersed boundary is interpolated to the surrounding fluid differential nodes to satisfy the following relationship: in, The solid velocity of the solid structure near the immersed boundary is mapped to the velocity of the fluid differential node around it, is the total number of tracer points on the finite element patch involved in interpolation, is the interpolation weight coefficient of the qth tracing point on the finite element patch involved in the interpolation, is the tracking point velocity of the tracking point on the finite element patch, and i and j respectively represent the row index and column index corresponding to the tracking point on the finite element patch.

8. The complex geometry variable diffusion extrapolation immersed boundary fluid-solid coupling solution method according to claim 5 is characterized in that: The extrapolation equation satisfies the following relationship: in, is the variable that needs to be extrapolated. For virtual time, The finite difference grid step size is set to 0.

5. is the interface normal vector, for gradient.

9. The complex geometry variable diffusion extrapolation immersed boundary fluid-solid coupling solution method according to claim 5, characterized in that: The boundary conditions of the fluid domain at the immersed boundary satisfy the following relationship: in, is the velocity of the virtual fluid node, is the interface normal vector, is the solid velocity, is the velocity of the fluid domain extrapolated to the virtual fluid node, is the tangent vector of the fluid-solid interface.

10. The complex geometry variable diffusion extrapolation immersed boundary fluid-solid coupling solution method according to claim 4, characterized in that: The fluid load satisfies the following relationship: in, is the fluid load on the finite element node, is the surface normal vector, is the total number of the finite element nodes, is the number of segments that each edge of the finite element patch where the finite element node is located is divided into, is the sub-sheet area occupied by the qth tracing point on the finite element patch where the finite element node is located, is the fluid pressure value at the qth tracing point on the finite element patch where the finite element node is located, and i and j respectively represent the row index and column index corresponding to the tracing point on the finite element patch.

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