A wave dynamic response analysis method for marine structures based on ABAQUS-OpenFOAM

Abstract

The present invention discloses a wave dynamic response analysis method for marine structures based on ABAQUS-OpenFOAM. The present invention establishes a fluid-solid coupling algorithm based on the two calculation modules of ABAQUS and OpenFOAM, develops a fluid-solid coupling interface data transfer interface, and realizes the new function of ABAQUS-OpenFOAM coupling analysis. The present invention first uses OpenFoam to carry out wave dynamic analysis to obtain the pressure field data group of all discrete grid nodes in the fluid calculation area; then establishes KDTree to store the pressure field data group in blocks to achieve the purpose of rapid retrieval of pressure field data; then establishes a dynamic analysis model of the marine structure in ABAQUS. KDTree is used to quickly obtain the wave force at a certain spatial position, and the wave force is transferred to ABAQUS through the custom subroutines Displ() and Dload(), and applied to the surface of the marine structure as a boundary condition; finally, ABAQUS is used to analyze the dynamic response characteristics of the marine structure under the impact of waves, including displacement, pore water pressure and effective stress, and then the stability of the marine structure is evaluated.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrodynamic calculation of marine engineering structures, and in particular to an analysis method of wave dynamic response of marine structures based on ABAQUS-OpenFOAM. Background Art

[0002] Computational fluid dynamics (CFD) and computational structural mechanics (CSM) are two independent yet closely related fields, each with its own dedicated simulation software. OpenFoam, an open-source CFD software, has been widely used in the field of fluid dynamics for its powerful fluid simulation capabilities and flexible customization features. ABAQUS, on the other hand, holds a prominent position in the field of structural simulation for its superior structural mechanics analysis capabilities and nonlinear solution technology.

[0003] Fluid-structure interactions are ubiquitous in practical engineering problems, such as aeroelasticity and fluid-structure interaction vibration, requiring simultaneous consideration of both fluid and structural behavior. Geotechnical engineering encounters numerous fluid-structure interaction problems, such as evaluating the safety and stability of structures in complex marine dynamic environments. ABAQUS and OpenFOAM are not well-suited for analyzing these types of problems. Summary of the Invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a wave dynamic response analysis method of marine structures based on ABAQUS-OpenFOAM. The present invention establishes a fluid-solid coupling algorithm based on the two calculation modules of ABAQUS and OpenFOAM, develops a fluid-solid coupling interface data transmission interface, realizes the new function of ABAQUS-OpenFOAM coupling analysis, and provides a new calculation and analysis method for the wave dynamic response characteristics and stability analysis of marine structures.

[0005] The technical solution adopted to achieve the above-mentioned purpose of the present invention is:

[0006] A method for analyzing the wave dynamic response of marine structures based on ABAQUS-OpenFOAM includes the following steps:

[0007] S1. Calculate the pressure on the marine structure and seabed foundation model in the fluid working condition to be simulated using OpenFoam software, and obtain a pressure field data group for all OpenFoam grid nodes in the calculation area. The pressure field data group includes the spatial coordinates of all OpenFoam grid nodes in the calculation area and the pressure at each OpenFoam grid node;

[0008] S2. Determine the range of the calculation area by calculating the minimum and maximum values ​​of the calculation area in the X, Y, and Z directions. Divide the calculation area into 10 parts in each direction. The entire calculation area is divided into 1000 blocks. Store the OpenFoam grid nodes of the entire calculation area into 1000 blocks in the order of X, Y, and Z. Then sort and number these 1000 blocks.

[0009] S3. Re-mesh the marine structure and seabed foundation model using ABAQUS software, take any finite element mesh node as a given point, use the spatial coordinates of the given point as input parameters, calculate the block number of the given point according to the function Number_Block, and determine the block to which the given point belongs;

[0010] The formula for the Number_Block function is as follows:

[0011] Number_Block=(N z -1)*10*10+(N y -1)*10+N x

[0012] Among them, Number_Block is the number of the block to which the given point belongs, (X, Y, Z) is the spatial coordinate of the fixed point, N x 、N y and N z are all natural numbers, N x -X<1,N y -Y<1,N z -Z<1;

[0013] S4. Find the nearest point in the block to which the given point belongs, traverse the coordinates of all OpenFoam grid nodes in the block, calculate the distance to the given point, and find the OpenFoam grid node closest to the given point, that is, the nearest point;

[0014] S5. After finding the nearest point, search for the pressure data of the nearest point in the pressure field data group file calculated by the OpenFoam software in S1 according to the spatial coordinates of the nearest point;

[0015] S6. The pressure data of the nearest point is transmitted to ABAQUS through the ABAQUS custom data exchange interface subroutines Dload() and Disp();

[0016] S7. Use ABAQUS to perform solid domain calculations and obtain the wave dynamics of marine structures and seabed foundations, including displacement, pore water pressure, and effective stress, by solving the dynamic Biot equations (1)-(5);

[0017] The equilibrium equations and mass conservation equations in three dimensions:

[0018]

[0019] Where u S 、v S and w S are the displacements of the marine structure or seabed foundation in the x, y and z directions respectively; n is the porosity of the marine structure or seabed foundation; σ′ x ,σ′ y and σ′ z are the effective stresses of the marine structure or seabed foundation in the x, y and z directions respectively; τ xy , τ xz and τ yz is the shear stress of the marine structure or seabed foundation in the x, y and z directions; P is the pore fluid pressure; ρ = nρ f +(1-n)ρ s is the average density of marine structures or seabed foundations; ρ f is the fluid density; ρ s is the density of the marine structure or seabed foundation; β is the compressibility coefficient of the fluid; k is the permeability coefficient; g is the acceleration of gravity; γ w is the density of the fluid; ∈ is the volume strain of the marine structure or seabed foundation.

[0020] Furthermore, the marine structure is a composite breakwater, and the seabed foundation is a sand bed.

[0021] Furthermore, steps S2-S5 can be performed by establishing a KDTree.

[0022] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0023] 1. Currently, there is still a lack of coupled analysis models for the wave dynamic response of marine structures. Based on the calculation results of OpenFoam, the present invention obtains the pressure field data group of all discrete grid nodes in the calculation area, reads and blocks the data of the result file of the calculation area, and transmits the pressure to ABAQUS calculation through the custom data exchange interface subroutines Dload() and Disp() of ABAQUS, realizing the coupling of OpenFoam and ABAQUS. This method has high reliability and feasibility.

[0024] 2. Compared with the method of searching for the nearest point by looping through all points, the present invention adopts the method of searching for the nearest point, dividing the entire space into 1000 separate blocks, calculating the block where each given point is located according to the function, and searching for the point closest to the given point within the block. This enables the method of quickly finding the block where a given point in ABAQUS is located in OpenFoam among tens of millions of cells in the OpenFoam calculation results.

[0025] 3. The method of the present invention is simple and can be encoded into corresponding software. The software occupies little memory and is easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is an example diagram of the block division of the calculation area of ​​the OpenFoam software.

[0027] Figure 2 Schematic diagram of the composite breakwater and seabed foundation model. Figure 3 Schematic diagram of the ABAQUS_FSSI.exe program that automatically generates ABAQUS-FSSI-Step1 files.

[0028] Figure 4 Schematic diagram of the ABAQUS-FSSI-Step1 file format.

[0029] Figure 5 Schematic diagram of the finite element mesh generated for remeshing the computational domain in ABAQUS software.

[0030] Figure 6 Schematic diagram of the boundary conditions imposed by ABAQUS on the composite breakwater and seabed foundation model.

[0031] Figure 7 Submit a schematic diagram of the page for the ABAQUS case.

[0032] Figure 8 This is the dynamic response distribution diagram of the breakwater and seabed under wave load at t = 17.65s.

[0033] Figure 9 This is the displacement time history curve of the upper left corner of the breakwater caisson under wave impact. DETAILED DESCRIPTION

[0034] In order to facilitate ordinary technicians in this field to understand and implement the present invention, the present invention is further described in detail below in conjunction with specific embodiments and application examples. It should be understood that the implementation examples described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0035] Example 1

[0036] 1. Use SolidWorks software to build a model of the marine structure and seabed foundation and import it into OpenFoam software. Use OpenFoam software to calculate the pressure on the marine structure in the fluid working condition to be simulated, and obtain the pressure field data group of all OpenFoam grid nodes in the calculation area. The pressure field data group includes the spatial coordinates of all OpenFoam grid nodes in the calculation area and the pressure at each OpenFoam grid node;

[0037] S2. Establish a KDTree and determine the range of the calculation area by calculating the minimum and maximum values ​​of the area in the X, Y, and Z directions. Divide the calculation area into 10 parts in each direction. The entire space is divided into 1000 blocks. Store the OpenFoam grid nodes of the entire calculation area into 1000 blocks in the order of X, Y, and Z. Then sort and number these 1000 blocks.

[0038] S3. Re-mesh the marine structure and seabed foundation using ABAQUS software. Take any finite element mesh node as a given point, use the spatial coordinates of the given point as input parameters, calculate the block number of the given point using the Number_Block function, and determine the block to which the given point belongs.

[0039] The formula for the Number_Block function is as follows:

[0040] Number_Block=(N z -1)*10*10+(N y -1)*10+N x ,

[0041] Among them, Number_Block is the block number, (X, Y, Z) is the spatial coordinate of the fixed point, N x 、N y and N z are all natural numbers, N x -X<1,N y -Y<1,N z -Z<1.

[0042] In order to facilitate the function Number_Block, an example is given here. Dividing the calculation area of ​​the OpenFoam software into 1000 blocks is too much and not conducive to drawing. Here, the calculation area of ​​the OpenFoam software is divided into 3 parts in each direction. The entire space is divided into 27 blocks, and these 27 blocks are numbered in sequence, such as Figure 1 shown.

[0043] At this point, the formula for the Number_Block function is as follows:

[0044] Number_Block=(N z -1)*3*3+(N y -1)*3+N x ,

[0045] For the spatial coordinates of a given point in ABAQUS software (1.5, 1.5, 1.5), then N x 、N y and N z Both are equal to 2. Substituting into the function Number_Block, Number_Block = 14, the given point is located in the 14th block of the calculation area of ​​the OpenFoam software.

[0046] S4. Find the nearest point in the block, traverse the coordinates of all OpenFoam grid nodes in the block, calculate the distance to the given point, and find the OpenFoam grid node closest to the given point, that is, the nearest point.

[0047] S5. After finding the nearest point, the pressure at the given point (X, Y, Z) is searched in the pressure field data group calculated by the OpenFoam software according to the spatial coordinates of the nearest point.

[0048] S6. The pressure at the nearest point is transmitted to ABAQUS through the ABAQUS custom data exchange interface subroutines Dload() and Disp().

[0049] S7. Use ABAQUS to perform solid domain calculations and solve the dynamic Biot equation to obtain the wave dynamics of marine structures and seabed foundations, including displacement, pore water pressure, and effective stress.

[0050] The equilibrium equations and mass conservation equations in three dimensions:

[0051]

[0052] Where u S 、v S and w S are the displacements of the marine structure or seabed foundation in the x, y and z directions respectively; n is the porosity of the marine structure or seabed foundation; σ′ x ,σ′ y and σ′ z are the effective stresses of the marine structure or seabed foundation in the x, y and z directions respectively; τ xy , τ xz and τ yz is the shear stress of the marine structure or seabed foundation in the x, y and z directions; P is the pore fluid pressure; ρ = nρ f +(1-n)ρs is the average density of marine structures or seabed foundations; ρ f is the fluid density; ρ s is the density of the marine structure or seabed foundation; β is the compressibility coefficient of the fluid; k is the permeability coefficient; g is the acceleration of gravity; γ w is the density of the fluid; ∈ is the volume strain of the marine structure or seabed foundation.

[0053] The following application example uses the dynamic characteristics of a small-scale composite breakwater and its sand bed (seabed foundation) under wave loads to illustrate the specific steps as follows:

[0054] 1. Build a composite breakwater and sand bed model. The composite breakwater consists of a caisson and a rubble pile. The cross section of the caisson is square, and the cross section of the rubble pile is an isosceles trapezoid. Use SolidWorks software to build a composite breakwater and seabed foundation model. The composite breakwater and seabed foundation model is as follows: Figure 2 shown.

[0055] 2. Import the composite breakwater and sand bed model into the OpenFoam software, use the OpenFoam software to mesh the composite breakwater and sand bed model in the fluid domain, and then set the wave parameters in the OpenFoam software according to the working conditions to be simulated, as shown in Table 1 below:

[0056] Table 1 Wave and calculation model material parameters

[0057] Wave form medium H(cm) d(m) T(s) <![CDATA[G(N / m 2 )]]> ν k(m / s) n <![CDATA[d 50 (mm)]]> Sr Second-order Stokes waves Wave 5 0.32 2.2 Sand bed <![CDATA[5.0×10 8 ]]> 0.33 <![CDATA[2.3×10 -3 ]]> 0.3 0.8 0.98 pile of rubble <![CDATA[1.0×10 9 ]]> 0.24 <![CDATA[1.6×10 -1 ]]> 0.33 27 0.99 caisson <![CDATA[1.0×10 9 ]]> 0.38 0 0 - 1

[0058] 3. Run the OpenFoam software for calculation to obtain the pressure field data group of the composite breakwater and sand bed model in the calculation area at each calculation time point.

[0059] 4. Set the coupling file. First, use the automatic generation program ABAQUS_FSSI.exe of the ABAQUS-FSSI-Step1 file. The interface is as follows: Figure 3 As shown. Figure 3 The interface specifies: coupling mode (Openfoam), time interval and path of OPENFOAM results. The automatically generated file format is as follows: Figure 4 shown.

[0060] 5. Import the composite breakwater and sand bed model into ABAQUS software and re-divide the mesh. The mesh division of the structure and sand bed in the calculation domain of ABAQUS software is as follows: Figure 5 Then set the material parameters of the sand bed, caisson and rough stone (same as Table 1 above), set the analysis steps, set the boundary conditions, and apply loads to the composite breakwater and sand bed model. The boundary conditions are set as follows Figure 6 shown.

[0061] 6. Use ABAQUS to perform solid domain calculations and obtain results such as displacement, pore water pressure, and effective stress. When submitting a job in ABAQUS, specify the data interface program file path ABAQUS_FSSI_version5_final.for (the code content in the file is the content of steps S2-S5). During the calculation process, the DLOAD and DISP subroutines can be automatically called to call the OpenFOAM calculation results. The ABAQUS submission interface is as follows Figure 7 shown.

[0062] 7. ABAQUS can then be used to continue post-processing the calculation results. The example of post-processing the one-way coupling calculation results in ABAQUS is shown in the figure below. Figure 8 and Figure 9 shown.

[0063] Figure 8 The dynamic response distribution (σ′) of the breakwater and sand bed under wave load at t = 17.65s is shown. x ,σ′ y ,σ′ z , τ xz and P). From Figure 8 It can be seen that at t = 17.65s, the dynamic pore pressure P caused by the wave in the seabed and rubble pile below the wave crest is significant. The dynamic pore pressure P in the sand bed below the wave crest is positive, indicating that the wave penetration force is downward and the seabed is in a compacted state. x The distribution diagram shows that due to the rightward impact of the wave force, the breakwater always has a tendency to slide to the right. Therefore, σ′ x The left side of the rubble pile is stretched, forming a stretching zone; the right side of the rubble pile is σ′ x It is compressed, forming a compression zone. z and σ′ y Obviously larger than other places. xz The distribution diagram shows that the impact of wave forces has created a large shear stress concentration area at the interface between the caisson and the rubble pile on the lower left side. If large enough, this could cause shear failure of the breakwater. The above analysis shows that the influence of waves on the pore water pressure and effective stress in the sand foundation and breakwater is very significant.

[0064] Figure 9 The displacement time history curve of the upper left corner of the breakwater caisson under wave impact is shown. Figure 9 It can be seen that under the action of wave loads, although the displacements in the horizontal and vertical directions have only slight fluctuations, they can still be captured by the established numerical model, indicating that the established model has a high resolution for the calculation of structural displacements.

Claims

1. A method for analyzing the wave dynamic response of marine structures based on ABAQUS-OpenFOAM, characterized in that The steps include: S1. Calculate the pressure on the marine structure and seabed foundation model in the fluid working condition to be simulated using OpenFoam software, and obtain a pressure field data group for all OpenFoam grid nodes in the calculation area. The pressure field data group includes the spatial coordinates of all OpenFoam grid nodes in the calculation area and the pressure at each OpenFoam grid node; S2. Determine the range of the calculation area by calculating the minimum and maximum values ​​of the calculation area in the X, Y, and Z directions. Divide the calculation area into 10 parts in each direction. The entire calculation area is divided into 1000 blocks. Store the OpenFoam grid nodes of the entire calculation area into 1000 blocks in the order of X, Y, and Z. Then sort and number these 1000 blocks. S3. Re-mesh the marine structure and seabed foundation model using ABAQUS software, take any finite element mesh node as a given point, use the spatial coordinates of the given point as input parameters, calculate the block number of the given point according to the function Number_Block, and determine the block to which the given point belongs; The formula for the Number_Block function is as follows: Number_Block=(N z -1)*10*10+(N y -1)*10+N x Among them, Number_Block is the number of the block to which the given point belongs, (X, Y, Z) is the spatial coordinate of the fixed point, N x 、N y and N z are all natural numbers, N x - X<1,N y - Y<1,N z - Z<1; S4. Find the nearest point in the block to which the given point belongs, traverse the coordinates of all OpenFoam grid nodes in the block, calculate the distance to the given point, and find the OpenFoam grid node closest to the given point, that is, the nearest point; S5. After finding the nearest point, search for the pressure data of the nearest point in the pressure field data group file calculated by the OpenFoam software in S1 according to the spatial coordinates of the nearest point; S6. The pressure data of the nearest point is transmitted to ABAQUS through the ABAQUS custom data exchange interface subroutines Dload() and Disp(); S7. Use ABAQUS to perform solid domain calculations and obtain the wave dynamics of marine structures and seabed foundations, including displacement, pore water pressure, and effective stress, by solving the dynamic Biot equations (1)-(5); The equilibrium equations and mass conservation equations in three dimensions: （1） （2） （3） （4） （5） Where, 、 and are the displacements of the marine structure or seabed foundation in the x, y and z directions respectively; n is the porosity of the marine structure or seabed foundation; 、 and are the effective stresses of the marine structure or seabed foundation in the x, y and z directions respectively; 、 and It is the shear stress of the marine structure or seabed foundation in the x, y and z directions; is the pore fluid pressure; is the average density of marine structures or seabed foundations; is the fluid density; is the density of the marine structure or seabed foundation; is the compressibility coefficient of the fluid; k is the permeability coefficient; g is the acceleration due to gravity; is the heaviness of the fluid; It is the volumetric strain of marine structures or seabed foundations.

2. The method for analyzing wave dynamic response of marine structures based on ABAQUS-OpenFOAM according to claim 1, characterized in that: The marine structure is a composite breakwater, and the seabed foundation is a sand bed.

3. The method for analyzing wave dynamic response of marine structures based on ABAQUS-OpenFOAM according to claim 1, characterized in that: The steps S2-S5 can be performed by establishing a KDTree.

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