Hydroelastic analysis method, equipment and storage medium for bidirectional fluid-solid coupling of offshore permeable structures

Abstract

The hydroelastic analysis method, equipment and storage medium of bidirectional fluid-solid coupling of offshore permeable structures belong to the field of hydroelastic technology and solve the problem of low efficiency and accuracy of hydroelastic load prediction of cages. The method of the present invention includes: calculating the fluid load of cage rods, and processing the flow field velocity using the attenuation factor for the flow velocity attenuation effect; using the Screen model to calculate the fluid load of the lift and damping of the mesh, comprehensively considering the influence of the mesh density, inflow angle and Reynolds number on the lift coefficient and the drag coefficient, and realizing accurate calculation of the fluid load of the permeable structure mesh; mapping the lift and drag of the mesh calculated by the Screen model to the finite element structure of the rod; and using the structural solver to realize the hydroelastic dynamic response analysis of the bidirectional fluid-solid coupling of the cage. The present invention is suitable for summarizing the rules and mastering the deformation mechanism of the cage structure.

Description

Technical Field

[0001] The present application relates to the technical field of hydroelasticity, and in particular to a three-dimensional hydroelastic analysis of wave loads on offshore floating bodies. Background Art

[0002] As a typical permeable structure at sea, cages have become a key technical equipment for my country's deep-sea aquaculture industry. Due to the harsh wind and wave environment in the deep sea, the relevant technology for the design of large cages in my country is not yet mature, so accidents of cage structure damage occur from time to time, causing serious economic losses and damage to the marine environment. The prediction of wave loads and analysis of hydrodynamic performance are becoming increasingly important.

[0003] The existing dynamic analysis methods based on rigid body assumptions and the one-way fluid-solid coupling methods that only consider modal deformation cannot accurately predict the time-history maximum values ​​of wave loads and flow loads, resulting in a serious underestimation of the load extreme value prediction and the deformation of the cage structure. At present, the Morison formula has the disadvantages of low efficiency caused by a huge number of units and low applicability of mesh grouping in calculating mesh fluid loads. Foreign hydrodynamic software and commercial finite element solvers are in the initial exploration stage of pressure mapping for mesh screen models. The implementation is relatively complex, and users cannot make certain modifications and improvements based on their own functional requirements. Similarly, the CFD viscous fluid solution tool has high computational costs and is difficult to implement for a large number of discrete mesh grids. Summary of the invention

[0004] The purpose of the present invention is to solve the problem of low efficiency and accuracy of the existing prediction of hydroelastic load of cages, and to provide a bidirectional fluid-solid coupled hydroelastic analysis method, equipment and storage medium for offshore permeable structures.

[0005] The present invention is achieved through the following technical solutions. On the one hand, the present invention provides a bidirectional fluid-solid coupling hydroelastic analysis method for offshore permeable structures, the method comprising:

[0006] Step 1: Calculate the fluid load on the cage rods and use the attenuation factor to process the flow field velocity according to the velocity attenuation effect;

[0007] Step 2: Use the Screen model to calculate the fluid loads of the net's lift and damping;

[0008] Step 3: Map the lift and drag of the net calculated by the Screen model to the rod finite element structure;

[0009] Step 4: Use the structural solver to implement the hydroelastic dynamic response analysis of the cage's bidirectional fluid-solid coupling, including:

[0010] Step 4.1: Initialize a fluid load calculation model, wherein the fluid load calculation model includes the fluid load calculations of steps 1 and 3;

[0011] Step 4.2: The fluid load calculation model calculates the fluid load when the rod is regarded as a rigid body; after the calculation is stable, the fluid load is sent to the structural solver starting from the specified time step;

[0012] Step 4.3: Use the structural solver to apply the fluid load in step 4.2 to the finite element structural model, calculate the deformation of the bars of the cage and the unit nodes of the net, and return to step 4.2 until the iteration termination condition is met.

[0013] Further, step 1 comprises:

[0014] Step 1.1: Obtain the time history of the wave surface rise of the linear sine wave with finite water depth;

[0015] Step 1.2: Calculate the instantaneous buoyancy and restoring force of the cage members;

[0016] Step 1.3: Calculate the fluid loads on the cage members based on the Morison formula.

[0017] Furthermore, in step 1.1, the calculation formula for the wavefront rise is:

[0018]

[0019] Where η is the wave height, H is the regular wave height, k is the wave number, θ is the wave angle, and ω is the wave frequency. is the initial phase of the wave, x and y are the spatial coordinates of the center of the rod, and t is the time.

[0020] Furthermore, step 1.2 includes:

[0021] Divide each rod into a number of micro-segments;

[0022] When the vertical coordinate of the node at the lower end of the micro-segment is higher than the wave surface elevation, the micro-segment is not affected by the instantaneous buoyancy;

[0023] When the vertical coordinate of the upper node of the micro-segment is lower than the wave surface elevation, the instantaneous buoyancy is calculated using the total volume of the bar;

[0024] When the wave surface elevation is between the vertical coordinates of the nodes at both ends of the micro-segment, the percentage relationship between the submerged volume and the total volume of the rod is obtained, and the instantaneous buoyancy is calculated using the percentage relationship.

[0025] Further, step 1.3 includes:

[0026] The velocity u of the wave water particle wWith water flow velocity u C The total velocity u is obtained by vector superposition, and the fluid load is calculated using the Morrison formula, which is:

[0027]

[0028] In the formula, f M is the inertial force, f D is the drag force, C M is the inertia coefficient, C D is the drag force damping coefficient, A is the projected area of ​​the unit length of the rod perpendicular to the flow direction, V0 is the displacement volume, D is the rod diameter, u is the total velocity of the fluid relative to the structure after the superposition of waves and water flow, is the total acceleration of the fluid relative to the structure, and ρ is the density of water.

[0029] Furthermore, step 2 includes:

[0030] In the Screen model, the net is divided into multiple mesh panels or screen units;

[0031] The fluid load on the net is decomposed into drag and lift. D and lift F L The calculation formula is:

[0032]

[0033] Among them, C D is the drag coefficient, C L is the lift coefficient, A t is the projection area of ​​the mesh perpendicular to the flow direction, U is the velocity of the fluid at the center of mass of the mesh, and when waves and currents exist at the same time, it is approximately considered to be the superposition of the wave velocity and flow velocity of the water particle, v is the velocity of the mesh unit structure, and i D and i L is the unit normal vector.

[0034] Further, step 3 includes:

[0035] Initialize the net model, divide the entire fishing net into regions, and decompose it into many virtual plate elements;

[0036] Calculate the time history of the vector value of the wave force and fluid force at the center position of each virtual plate element;

[0037] The fluid force is mapped to the bar structural unit, including evenly distributing the concentrated force of the virtual plate element and spreading it onto the original bar unit nodes.

[0038] Furthermore, in step 4.3, the calculation of the deformation of the rods of the cage and the unit nodes of the net includes:

[0039] The finite element dynamics method is used to obtain the stress and deformation of the cage bar structure under transient loads. The basic motion equation is:

[0040]

[0041] F(t)=F 恢复力 (t)+F 杆件流体动力 +F D +F L

[0042] In the formula, and a(t) represent the node acceleration vector, node velocity vector, and node displacement vector of the system, respectively; [M], [C], [K], and F(t) represent the mass matrix, damping matrix, stiffness matrix, and node load vector of the system, respectively;

[0043] The basic equation of motion is used to solve the displacement a(t) and velocity of the structure. and acceleration

[0044] In a second aspect, the present invention provides a computer device comprising 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 steps of a bidirectional fluid-solid coupling hydroelastic analysis method for an offshore permeable structure as described above are executed.

[0045] In a third aspect, the present invention provides a computer-readable storage medium, in which a plurality of computer instructions are stored, and the plurality of computer instructions are used to enable a computer to execute a hydroelastic analysis method of bidirectional fluid-solid coupling of an offshore permeable structure as described above.

[0046] Beneficial effects of the present invention:

[0047] The present invention establishes a set of time-domain hydroelastic analysis methods for fixed permeable cages at sea with bidirectional fluid-solid coupling, and can be applied to the dynamic response analysis of floating cages at sea. It can consider the precise calculation of the buoyancy of the rods due to the instantaneous wave surface changes. It can comprehensively consider the density S of the net. n , inflow angle θ and Reynolds number Re on lift coefficient C L and the drag coefficient C DThe influence of the mesh can be accurately calculated to achieve the fluid load of the permeable structure mesh. The node force of the fluid load predicted by the mesh Screen model can be efficiently and correctly decomposed and applied to the structural model to ensure high calculation efficiency and operability. Based on the secondary development of the finite element solver, it can realize the real-time calculation of the two-way fluid-solid coupling of the mesh box with real high precision, and predict the displacement drawing of the overall deformation of the mesh at different times, the effective residual volume coefficient, the maximum value and change trend of the horizontal wave flow force. Compared with the experimental values ​​and the numerical results of other scholars, this method has reliable data accuracy, strong promotion and applicability in actual engineering.

[0048] In order to improve the efficiency and accuracy of the prediction of the hydroelastic load of the cage and achieve the goal of independent development and enriching functions, the present invention proposes a time-domain hydroelastic calculation method for bidirectional fluid-solid coupling of a floating body and a net system, which is a numerical simulation calculation method for bidirectional fluid-solid coupling of the cage based on the Screen fluid load model and the Abaqus structural solver, which can improve the accuracy of the prediction of the wave load of the cage in harsh environments and realize load pressure mapping efficiently and accurately.

[0049] The present invention is suitable for summarizing the rules and understanding the deformation mechanism of cage structures, providing reasonable and specific suggestions for their safe operation, and reducing the economic losses of offshore cage ranches. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the embodiments are briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0051] Figure 1 This is the finite element model diagram of the cage rods and net;

[0052] Figure 2 Schematic diagram of the calculation method of the immersed volume of the rod;

[0053] Figure 3 This is the basic schematic diagram of the Screen model;

[0054] Figure 4 It is the force mapping principle of Screen model;

[0055] Figure 5 It is the flow chart of the hydroelastic program for bidirectional fluid-structure coupling;

[0056] Figure 6 Comparison of the simulation results of the maximum deformation of the actual cage;

[0057] Figure 7 is the maximum deformation diagram at the initial and stable stage of iteration;

[0058] Figure 8 Comparison of peak values ​​of horizontal wave flow forces under specific working conditions;

[0059] Fig. 9 This is a comparison chart of the peak value of horizontal wave flow force at different flow velocities;

[0060] In the figure, 1 is a load ring; 2 is a floating frame body; 3 is a net; 4 is a mooring cable; and 5 is a bottom ballast weight. DETAILED DESCRIPTION

[0061] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0062] Embodiment 1: A method for analyzing hydroelasticity of a bidirectional fluid-solid coupling of an offshore permeable structure, the method comprising:

[0063] Step 1: First, derive the wave surface rise time history of a linear sine wave with limited water depth. Establish a calculation method for the instantaneous buoyancy and restoring force of the cage rod (slender structure). As the wave surface elevation changes, the instantaneous buoyancy and restoring force are calculated and updated in real time based on the ratio of the structure's submerged volume to the total volume. When the diameter of the rod is too large, the instantaneous buoyancy distribution method is used. The fluid load of the cage rod is calculated based on the Morison formula, and at the same time, the latest attenuation factor is used to refine the flow field velocity in view of the velocity attenuation effect.

[0064] Step 2: Establish a mesh fluid load calculation method based on the Screen model. Divide the mesh into many mesh panels or screen units, and comprehensively consider the consolidation ratio (density) S n The influence of three factors, inflow angle θ and Reynolds number Re, on the lift coefficient C L and the damping coefficient C D The Screen model is used to calculate the hydrodynamic load of the net, including the dual effects of waves and currents. The net resistance F is calculated according to formula (7): D and lift F L accurate forecast.

[0065] Step 3: Calculate the wave force and fluid force history at the center of each plate element after the mesh is discretized, and evenly divide the concentrated force calculated on the plate element and spread it on the original rod unit nodes, so that the calculated mesh fluid load corresponds one-to-one with the pressure mapping of the structural solver at the rod node in step 4.

[0066] Step 4: Secondary development of the structural solver to realize the hydroelastic dynamic response analysis of the cage with bidirectional fluid-solid coupling. The fluid load calculated in steps 1 and 3 is transferred unidirectionally to the finite element Abaqus structural solver, and various forces are brought into the finite element software structural dynamic equilibrium differential equation (FE equation) for solution, and the deformation of the unit nodes of the cage rods and nets is calculated. The Abaqus advanced function user subroutine User Subroutine structural solver is developed and called to realize the reverse transfer of the deformation speed and acceleration of the rods and nets from the user subroutine to the fluid load program, and the fluid load is recalculated, and the coupling iteration of the next time step is continuously performed to realize the time history prediction of the hydroelastic response of the fluid load of the cage.

[0067] This implementation method is based on the Screen fluid load model and Abaqus solid solver, considering the bidirectional coupling between the deformation of the cage structure and the flow field, and developing a set of hydroelastic analysis methods to accurately predict the wave load of the permeable structure, so as to achieve high efficiency and high precision prediction of dynamic response. Taking large cages as typical examples, the research work on deformation characteristics and wave load prediction is carried out, and the influence of various wave and flow parameters on the cage load response is fully studied.

[0068] Embodiment 2: This embodiment further defines the hydroelastic analysis method for bidirectional fluid-solid coupling of an offshore permeable structure described in Embodiment 1. In this embodiment, step 1 is further defined, specifically including:

[0069] Step 1 includes:

[0070] Step 1.1: Obtain the time history of the wave surface rise of the linear sine wave with finite water depth;

[0071] Step 1.2: Calculate the instantaneous buoyancy and restoring force of the cage members;

[0072] Step 1.3: Calculate the fluid loads on the cage members based on the Morison formula.

[0073] This embodiment provides a calculation method based on the time history of wave surface rise and the instantaneous buoyancy and restoring force of the cage rods, which can accurately calculate the fluid load of the cage rods.

[0074] Embodiment 3: This embodiment further defines the method for analyzing the hydroelasticity of a bidirectional fluid-solid coupling of an offshore permeable structure described in Embodiment 2. In this embodiment, step 1.1 is further defined, specifically including:

[0075] In step 1.1, the calculation formula for the wave surface rise is:

[0076]

[0077] Where η is the wave height, H is the regular wave height, k is the wave number, θ is the wave angle, and ω is the wave frequency. is the initial phase of the wave, x and y are the spatial coordinates of the center of the rod, and t is the time.

[0078] This embodiment provides a time history of the wavefront rise η.

[0079] Embodiment 4: This embodiment further defines the method for analyzing the hydroelasticity of a bidirectional fluid-solid coupling of an offshore permeable structure described in Embodiment 3. In this embodiment, step 1.2 is further defined, specifically including:

[0080] Step 1.2 includes:

[0081] Divide each rod into a number of micro-segments;

[0082] When the vertical coordinate of the node at the lower end of the micro-segment is higher than the wave surface elevation, the micro-segment is not affected by the instantaneous buoyancy;

[0083] When the vertical coordinate of the upper node of the micro-segment is lower than the wave surface elevation, the instantaneous buoyancy is calculated using the total volume of the bar;

[0084] When the wave surface elevation is between the vertical coordinates of the nodes at both ends of the micro-segment, the percentage relationship between the submerged volume and the total volume of the rod is obtained, and the instantaneous buoyancy is calculated using the percentage relationship.

[0085] This embodiment can take into account the precise calculation of the buoyancy of the rods due to the instantaneous wave surface changes. Because the cage structure can basically be considered to be composed of slender rods, each slender rod is divided into shorter micro-segments during the program calculation process. The buoyancy of the rod micro-segment units near the upper and lower surfaces of the wave rise η changes at all times as the wave surface rises and falls, so it can be roughly divided into three situations in this embodiment.

[0086] Furthermore, when the diameter of the rod is too large, a more accurate method for calculating the instantaneous buoyancy of the horizontal cylinder is used. The original cylinder is equivalently split into a series of thin cylinders, and the total volume and mass of these thin cylinders after accumulation and equivalent are ensured to be basically equivalent to the initial cylinder. By judging how many submerged thin cylinders are below the wave surface, the total buoyancy of the submerged thin cylinders is used to replace the initially calculated cylinder buoyancy.

[0087] Embodiment 5: This embodiment further defines the method for analyzing the hydroelasticity of a bidirectional fluid-solid coupling of an offshore permeable structure described in Embodiment 4. In this embodiment, step 1.3 is further defined, specifically including:

[0088] Step 1.3 includes:

[0089] The velocity u of the wave water particlew With water flow velocity u C The total velocity u is obtained by vector superposition, and the fluid load is calculated using the Morrison formula, which is:

[0090]

[0091] In the formula, f M is the inertial force, f D is the drag force, C M is the inertia coefficient, C D is the drag force damping coefficient, A is the projected area of ​​the unit length of the rod perpendicular to the flow direction, V0 is the displacement volume, D is the rod diameter, u is the total velocity of the fluid relative to the structure after the superposition of waves and water flow, is the total acceleration of the fluid relative to the structure, and ρ is the density of water.

[0092] In this embodiment, the diameter of the steel pipe of the truss cage is large, the inertia force cannot be ignored, and the assumption condition of the small-scale component is met. The velocity u of the wave water particle is w With water flow velocity u C The total velocity u is obtained by vector superposition, and the fluid load is calculated directly using Morrison's formula.

[0093] Embodiment 6: This embodiment further limits the hydroelastic analysis method of a bidirectional fluid-solid coupling of an offshore permeable structure described in Embodiment 1. In this embodiment, step 2 is further limited, specifically including:

[0094] Step 2 includes:

[0095] In the Screen model, the net is divided into multiple mesh panels or screen units;

[0096] The fluid load on the net is decomposed into drag and lift. D and lift F L The calculation formula is:

[0097]

[0098] Among them, C D is the drag coefficient, C L is the lift coefficient, A t is the projection area of ​​the mesh perpendicular to the flow direction, U is the velocity of the fluid at the center of mass of the mesh, and when waves and currents exist at the same time, it is approximately considered to be the superposition of the wave velocity and flow velocity of the water particle, v is the velocity of the mesh unit structure, and i D and i L is the unit normal vector.

[0099] In this embodiment, the fluid load on the net is decomposed into normal force and tangential force, or equivalently called drag and lift. This calculation method can effectively obtain the fluid load of the net's lift and damping.

[0100] Embodiment 7: This embodiment further defines the method for analyzing the hydroelasticity of a bidirectional fluid-solid coupling of an offshore permeable structure described in Embodiment 1. In this embodiment, step 3 is further defined, specifically including:

[0101] Step 3 includes:

[0102] Initialize the net model, divide the entire fishing net into regions, and decompose it into many virtual plate elements;

[0103] Calculate the time history of the vector value of the wave force and fluid force at the center position of each virtual plate element;

[0104] The fluid force is mapped to the bar structural unit, including evenly distributing the concentrated force of the virtual plate element and spreading it onto the original bar unit nodes.

[0105] In this embodiment, when modeling the net structure, in order to implement the Screen model in the existing finite element solver, it is necessary to initialize the net model first, divide the entire fishing net into regions, and decompose it into many virtual small plate elements, such as Figure 4 As shown. In the subsequent hydrodynamic program calculation process, the vector value history of the wave force and fluid force at the center position of each virtual plate element is calculated. An additional step is then performed to map the fluid force to the rod structural unit. The present invention provides an efficient and accurate processing method. The method is to evenly divide the concentrated force of the plate element and spread it on the original rod unit nodes to achieve a one-to-one correspondence between the fluid force calculation model and the structural finite element solution model. Both are rod models, which solves the problem of the existing finite element solver introducing virtual plates and shells to map pressure to linear structures. In fact, the mapping and decomposition of forces are closely related to the size of the plate element division. The number of plate elements after the mesh fluid load converges is used for the subsequent numerical calculation and analysis.

[0106] Embodiment 8: This embodiment further defines the method for analyzing the hydroelasticity of a bidirectional fluid-solid coupling of an offshore permeable structure described in Embodiment 1. In this embodiment, step 4.3 is further defined, specifically including:

[0107] In step 4.3, the calculation of the deformation of the rods of the cage and the unit nodes of the net includes:

[0108] The finite element dynamics method is used to obtain the stress and deformation of the cage bar structure under transient loads. The basic motion equation is:

[0109]

[0110] F(t)=F 恢复力 (t)+F 杆件流体动力 +F D +F L

[0111] In the formula, and a(t) represent the node acceleration vector, node velocity vector, and node displacement vector of the system, respectively; [M], [C], [K], and F(t) represent the mass matrix, damping matrix, stiffness matrix, and node load vector of the system, respectively;

[0112] The basic equation of motion is used to solve the displacement a(t) and velocity of the structure. and acceleration

[0113] This implementation method uses the central difference method to integrate the two structural motion equations in the time domain, and dynamically calculates the next incremental step from the equilibrium equation of the previous incremental step. The fluid load calculation program independently developed using the Fortran language is bidirectionally coupled with the Abaqus explicit structure solver Abaqus / Explicit. The advanced function user subroutine User Subroutine is used as a physical parameter transmission tool, and Abaqus is used to calculate the velocity and acceleration of the node unit deformation, and these two items are returned to the fluid load program to recalculate the force. In this way, the hydroelastic response prediction problem of the cage structure is solved.

[0114] Embodiment 9: This embodiment is an example of a hydroelastic analysis method for a bidirectional fluid-solid coupling of an offshore permeable structure as described above, and specifically includes:

[0115] Step 1: Calculate the fluid loads on the cage members using Morrison's formula.

[0116] The general cage structure consists of the main body of the rod, the net, the mooring rope, the load ring, the bottom ballast weight and other components, such as Figure 1 The main rod structure ensures sufficient structural strength to resist structural deformation under the action of waves and currents, and the net achieves sufficient residual volume to cultivate marine aquatic products. All components constitute a complete structure.

[0117] Step 1.1 Establish the time history of the wave surface rise η of a linear sine wave with finite water depth:

[0118]

[0119] Where: H is the wave height of regular waves, k is the wave number, θ is the wave direction angle, ω is the wave frequency, is the initial phase of the wave, x and y are the spatial coordinates of the center of the rod, and t is the time.

[0120] The velocity potential φ of the wave is calculated as shown in formula (2). By taking the first-order and second-order partial derivatives of the velocity potential, the velocity u, v and acceleration of the water particle at the center of each rod micro-end in the flow field in the horizontal and vertical directions can be obtained:

[0121] Where: d is the water depth where the cage is located, z is the vertical coordinate of the rod's position in space, and g is the acceleration due to gravity, which is generally taken as 9.8m / s^2.

[0122]

[0123] Step 1.2 Establish the calculation method of the instantaneous buoyancy and restoring force of the cage members

[0124] The cage structure can basically be considered to be composed of slender rods. In the program calculation process, each slender rod is divided into shorter micro-segments. The buoyancy of the rod micro-segment unit near the upper and lower surface of the wave rise η changes at all times with the ups and downs of the wave surface, which can be roughly divided into three situations, such as Figure 2 As shown:

[0125] (1) When the vertical coordinates of the node at the lower end of the micro-segment are higher than the wave surface elevation, the micro-segment is considered to be completely above the wave surface, that is, the micro-segment is not affected by buoyancy. (2) When the vertical coordinates of the node at the upper end of the micro-segment are lower than the wave surface elevation, the micro-segment is considered to be completely below the wave surface, and the total volume of the rod is used to calculate the buoyancy. (3) When the wave surface elevation is between the vertical coordinates of the nodes at both ends of the micro-segment, it is necessary to monitor the percentage relationship between the submerged volume and the total volume of the rod, percent = i / L, to calculate the actual buoyancy at this moment. See the schematic diagram for details. Figure 2 .

[0126] Among them, F 浮 is the buoyancy of the unit, ρ is the density of water, V 浸没 is the immersed volume, V is the total volume of the rod, i is the immersion depth of the rod, L is the actual total length of the rod, and m is the mass of the rod.

[0127] F 浮 =ρgV 浸没 =percent·V (4)

[0128] F 恢复力 =F 浮 -mg (5)

[0129] When the diameter of the rod is too large, a more accurate method for calculating the instantaneous buoyancy of the horizontal cylinder is used. The original cylinder is equivalently split into a series of thin cylinders, and the total volume and mass of these thin cylinders after accumulation and equivalent are ensured to be basically equivalent to the initial cylinder. By judging how many submerged thin cylinders are below the wave surface, the total buoyancy of the submerged thin cylinders is used to replace the initially calculated cylinder buoyancy.

[0130] Step 1.3 Establish the calculation method of fluid load on the main structural members of the cage

[0131] For truss cages with larger steel pipe diameters, the inertial force cannot be ignored. To meet the assumption of small-scale components, the velocity of the wave water particle u w With water flow velocity u C The total velocity u is obtained by vector superposition, and the fluid load is calculated directly using Morrison's formula.

[0132]

[0133] For a smaller mesh diameter, the inertial force is very small.

[0134] Where: f M is the inertial force, f D is the drag force, C M is the inertia coefficient, C D is the drag force damping coefficient, A is the projected area of ​​the unit length of the rod perpendicular to the flow direction, V0 is the displacement volume, D is the rod diameter, u is the total velocity of the fluid relative to the structure after the superposition of waves and water flow, is the total acceleration of the fluid relative to the structure.

[0135] Step 2: Establish a fluid load calculation method for the lift and damping of the net based on the Screen model

[0136] In the Screen model, the mesh is divided into many mesh panels or screen units, such as Figure 3 As shown in Figure 1, the external force on the net is decomposed into normal force and tangential force, or equivalently called drag and lift. D and lift F L The calculation formula is as follows:

[0137]

[0138] Among them, C D is the drag coefficient, C L is the lift coefficient, A t is the projection area of ​​the mesh perpendicular to the flow direction, U is the velocity of the fluid at the center of mass of the mesh, and when waves and currents exist at the same time, it can be approximately considered as the superposition of the wave velocity and flow velocity of the water particle; v is the velocity of the mesh unit structure, i D and iL is the unit normal vector.

[0139] This application considers the lift coefficient C based on the two factors of density and inflow angle in the latest "Guidelines for Marine Fisheries" (2024) published by China Classification Society. L and the drag coefficient C D Selected as a comprehensive consideration of the consolidation ratio (density) S n The function of three factors, inflow angle θ and Reynolds number Re, has been verified by experiments and numerical calculations. This experimental regression formula has high accuracy. Considering the wake effect of water flowing through permeable structures in actual production, the velocity attenuation factor r is introduced to quantitatively analyze the attenuation of the force of waves on the back cage. D and C L The coefficient calculation formula is as follows, where: U down To attenuate the water velocity of the dorsal cage, C D cyl is the cylinder drag coefficient related to the Reynolds number, C D0 and C L45 are the coefficients affected by Reynolds number and Strouhal number under 0 degree and 45 degree waves or currents respectively.

[0140]

[0141] Step 3: Project the lift and drag of the net calculated by the Screen model to the rod finite element structure

[0142] When modeling the net structure, in order to implement the Screen model in the existing finite element solver, it is necessary to initialize the net model first, divide the entire fishing net into regions, and decompose it into many virtual small plate elements, such as Figure 4 As shown, a is a schematic diagram of concentrated force of plate element, and b is a schematic diagram of uniform force of node. In the subsequent hydrodynamic program calculation process, the vector value of wave force and fluid force at the center position of each virtual plate element is calculated. An additional step is then performed to map the fluid force to the rod structural unit. The present invention provides an efficient and accurate processing method. The method is to evenly divide the concentrated force of the plate element and spread it on the original rod unit nodes to achieve a one-to-one correspondence between the fluid force calculation model and the structural finite element solution model. Both are rod models, which solves the problem of introducing virtual plates and shells in the existing finite element solver to map pressure to linear structures. In fact, the mapping and decomposition of forces are closely related to the size of the plate element division. The number of plate elements after the mesh fluid load converges is used for the subsequent numerical calculation and analysis.

[0143] Step 4: Secondary development of the structural solver to realize the hydroelastic dynamic response analysis of the cage with two-way fluid-structure coupling

[0144] Step 4.1 Fluid load calculation model initialization preprocessing

[0145] The fluid load calculation program in the main program is divided into the Morison formula module and the Screen model module. According to the different node number settings, different fluid load calculation models in step 2 and step 3 are called. During the initialization process, the structural parameters, node information, wave and flow field parameters, total calculation time, and interval step length of the cage are read through the input file, and the required fluid load calculation model is automatically identified according to the node sorting and numbering. The virtual plate element division work is performed on the net part, and the steel rod uses the Morison formula and the net uses the Screen model. Therefore, the program can be used for load prediction in pure water flow or dynamic response in pure waves, and can also be used for the calculation of pure fishing nets or pure net frame cages.

[0146] Step 4.2 Fluid load calculation and one-way transfer to the structural solver

[0147] After completing the initialization based on step 4.1, check whether the initial values ​​are input correctly. Then the program will run for 1-3 cycles to calculate the fluid load when the rod is regarded as a rigid body, including wave force, gravity, and buoyancy. After the calculation is stable, the fluid load is transferred to the user subroutine of the structural solver Abaqus starting from the specified time step as the input of the structural solver.

[0148] Step 4.3 The deformation calculated by the structural solver is transferred back to the fluid load calculation program

[0149] First, the unit in the structural solver is established using commercial modeling software, such as the Bar unit of Patran software; and the unit number, node number, node coordinates and other information of the mesh and bar structure in the initial BDF file are read by the software.

[0150] Using the Explicit module in the structural solver Abaqus, various fluid loads based on step 4.2, such as rod restoring force, rod fluid dynamics, net lift and drag, are applied to the finite element structural model to calculate the deformation of the rods of the net box and the unit nodes of the net. After waiting for the deformation speed and acceleration to be returned to the fluid load calculation program by the user subroutine, the next step of recalculating the fluid load is performed. Each alternating use is an iteration, and this is repeated. The criterion for judging the termination of the iteration is whether the time step calculated by the program meets the set total time. For details of the calculation flow chart, see Figure 5 .

[0151] The specific details of the structural solver to solve the deformation are as follows: the finite element dynamics method is used to analyze the stress and deformation of the cage bar structure under transient loads. The basic motion equation is as follows, which can solve the displacement a(t) and velocity of the structure. Acceleration

[0152]

[0153] F(t)=F 恢复力 (t)+F 杆件流体动力 +F D +F L (13)

[0154] Where: and a(t) represent the node acceleration vector, node velocity vector and node displacement vector of the system respectively; [M], [C], [K], F(t) represent the mass matrix, damping matrix, stiffness matrix and node load vector of the system respectively.

[0155] The central difference method is used to integrate the two structural motion equations in the time domain, and the next incremental step is dynamically calculated from the equilibrium equation of the previous incremental step. The fluid load calculation program independently developed using the Fortran language is bidirectionally coupled with the Abaqus explicit structure solver Abaqus / Explicit. The advanced user subroutine UserSubroutine is used as a tool for transferring physical parameters, and Abaqus is used to calculate the velocity and acceleration of the node unit deformation, and these two items are returned to the fluid load program to recalculate the force. In this way, the hydroelastic response prediction problem of the cage structure is solved.

[0156] The specific details of the structural solver user subroutines are as follows: The main subroutines involved are VDLOAD and VEXTERNALDB. VDLOAD is used in conjunction with VDISP to not only define the initial coordinate values, but also to extract the velocity, acceleration and other items on the nodes to apply time-varying fluid loads to the model to achieve one-way fluid-structure coupling. VEXTERNALDB can be used to transfer data between user subroutines in external programs, control the time increment of the analysis, and feed back the acceleration and velocity generated by the structural deformation to the fluid dynamic load program in the form of an array to perform real-time prediction of fluid loads in the time domain, thereby fully realizing the true two-way fluid-structure coupling hydroelastic dynamic response calculation.

[0157] In order to verify the effectiveness and accuracy of the numerical simulation method in this invention, two numerical examples from scholars were selected for comparative verification: (1) the full-scale test conducted by Lader in 2009; (2) the numerical simulation by Moe in 2014.

[0158] The full-scale test was carried out in the North Sea Central Tank in Hirtshals, Denmark. The tank is 21.3 meters long, 2.7 meters deep and 8 meters wide. The relevant basic parameters of the cages in the Lader test are as follows:

[0159] Table 1 Basic parameters of Lader test cage

[0160] parameter Numeric <![CDATA[Compactness S n > 0.24 Diameter D 1.75m Height L 1.95m <![CDATA[The diameter d of the network cable w > 2.42mm <![CDATA[Mesh length l w > 16.8mm Elastic modulus 350MPa Cable material density <![CDATA[1130kg / m 3 ]]>

[0161] Table 2 Wave and current parameters for specific working conditions

[0162] wave height 0.1m cycle 6s Flow rate 0.24m / s

[0163] First, the actual model of the net clothing is established, and the time step is 0.01s. After the calculation is stable, the maximum displacement deformation simulation is obtained as shown below Figure 6 , where a is the result of Moe simulation and b is the result of this application simulation. It is observed that there is a very good agreement, and the temporal trend of the residual effective volume coefficient of the cage can be seen. Figure 7 By comparing the side views of the net at the initial time and after stabilization, it can be concluded that this method can achieve accurate prediction of wave and fluid loads, and effectively and accurately simulate the displacement and deformation of the net structure with water depth. Figure 8 A comprehensive comparison was made between the experimental values ​​and the numerical results of horizontal wave flow forces of this method, and the difference was less than 3.3%, which was significantly better than Moe's numerical results. Fig. 9 The variation trend of the peak value of horizontal wave flow force with flow velocity under different flow velocities is described, which proves that the present invention can better realize the calculation and prediction of horizontal wave flow force under various flow velocities and has strong applicability.

Claims

1. A hydroelastic analysis method for bidirectional fluid-solid coupling of offshore permeable structures, characterized in that: The method comprises: Step 1: Calculate the fluid load on the cage rods and use the attenuation factor to process the flow field velocity according to the velocity attenuation effect; Step 2: Use the Screen model to calculate the fluid loads of the net's lift and damping; Step 3: Map the lift and drag of the net calculated by the Screen model to the rod finite element structure; Step 4: Use the structural solver to implement the hydroelastic dynamic response analysis of the cage's bidirectional fluid-solid coupling, including: Step 4.1: Initialize a fluid load calculation model, wherein the fluid load calculation model includes the fluid load calculations of steps 1 and 3; Step 4.2: The fluid load calculation model calculates the fluid load when the rod is regarded as a rigid body; after the calculation is stable, the fluid load is sent to the structural solver starting from the specified time step; Step 4.3: Use the structural solver to apply the fluid load in step 4.2 to the finite element structural model, calculate the deformation of the bars of the cage and the unit nodes of the net, and return to step 4.2 until the iteration termination condition is met.

2. The method for bidirectional fluid-solid coupling hydroelastic analysis of offshore permeable structures according to claim 1, characterized in that: Step 1 includes: Step 1.1: Obtain the time history of the wave surface rise of the linear sine wave with finite water depth; Step 1.2: Calculate the instantaneous buoyancy and restoring force of the cage members; Step 1.3: Calculate the fluid loads on the cage members based on the Morison formula.

3. The method for bidirectional fluid-solid coupling hydroelastic analysis of offshore permeable structures according to claim 2, characterized in that: In step 1.1, the calculation formula for the wave surface rise is: Where η is the wave height, H is the regular wave height, k is the wave number, θ is the wave angle, and ω is the wave frequency. is the initial phase of the wave, x and y are the spatial position coordinates of the center of the rod, and t is the time.

4. The method for bidirectional fluid-solid coupling hydroelastic analysis of offshore permeable structures according to claim 3 is characterized in that: Step 1.2 includes: Divide each rod into a number of micro-segments; When the vertical coordinate of the node at the lower end of the micro-segment is higher than the wave surface elevation, the micro-segment is not affected by the instantaneous buoyancy; When the vertical coordinate of the upper node of the micro-segment is lower than the wave surface elevation, the instantaneous buoyancy is calculated using the total volume of the bar; When the wave surface elevation is between the vertical coordinates of the nodes at both ends of the micro-segment, the percentage relationship between the submerged volume and the total volume of the rod is obtained, and the instantaneous buoyancy is calculated using the percentage relationship.

5. The method for bidirectional fluid-solid coupling hydroelastic analysis of offshore permeable structures according to claim 4, characterized in that: Step 1.3 includes: The velocity u of the wave water particle w With water flow velocity u C The total velocity u is obtained by vector superposition, and the fluid load is calculated using the Morrison formula, which is: In the formula, f M is the inertial force, f D is the drag force, C M is the inertia coefficient, C D is the drag force damping coefficient, A is the projected area of ​​the unit length of the rod perpendicular to the flow direction, V0 is the displacement volume, D is the rod diameter, u is the total velocity of the fluid relative to the structure after the superposition of waves and water flow, is the total acceleration of the fluid relative to the structure, ρ is the density of water; u w (t) is the velocity of the wave water particle; is the acceleration of the wave water particle.

6. The method for bidirectional fluid-solid coupling hydroelastic analysis of offshore permeable structures according to claim 1, characterized in that: Step 2 includes: In the Screen model, the net is divided into multiple mesh panels or screen units; The fluid load on the net is decomposed into drag and lift. D and lift F L The calculation formula is: Among them, C R is the drag coefficient, C L is the lift coefficient, A t is the projection area of ​​the mesh perpendicular to the flow direction, U is the velocity of the fluid at the center of mass of the mesh, and when waves and currents exist at the same time, it is approximately considered to be the superposition of the wave velocity and flow velocity of the water particle, v is the velocity of the mesh unit structure, i D and i L is the unit normal vector.

7. The method for bidirectional fluid-solid coupling hydroelastic analysis of offshore permeable structures according to claim 1, characterized in that: Step 3 includes: Initialize the net model, divide the entire fishing net into regions, and decompose it into many virtual plate elements; Calculate the time history of the vector value of the wave force and fluid force at the center position of each virtual plate element; The fluid force is mapped to the bar structural unit, including evenly distributing the concentrated force of the virtual plate element and spreading it onto the original bar unit nodes.

8. The method for bidirectional fluid-solid coupling hydroelastic analysis of offshore permeable structures according to claim 1, characterized in that: In step 4.3, the calculation of the deformation of the rods of the cage and the unit nodes of the net includes: The finite element dynamics method is used to obtain the stress and deformation of the cage bar structure under transient loads. The basic motion equation is: F(t)=F 恢复力 (t)+F 杆件流体动力 +F D +F L In the formula, and a(t) represent the node acceleration vector, node velocity vector, and node displacement vector of the system, respectively; [M], [C], [K], F(t) represent the mass matrix, damping matrix, stiffness matrix, and node load vector of the system, respectively; F 恢复力 (t) is defined as the restoring force on the unit; Using the basic equation of motion, we can solve a(t). and 9. A computer device comprising a memory and a processor, wherein a computer program is stored in the memory, wherein: When the processor runs the computer program stored in the memory, the steps of the method according to any one of claims 1 to 8 are performed.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a plurality of computer instructions, and the plurality of computer instructions are used to enable a computer to execute the method according to any one of claims 1 to 8.

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