Simulation analysis method for cleaning submarine cable soil coverings through mobile jet flow

Abstract

The invention discloses a simulation analysis method for cleaning submarine cable soil coverings through mobile jet flow. Three-dimensional design software is used for establishing a geometric model of mobile water jet flow ground breaking; a grid division tool is used for conducting grid division on the mobile water jet ground breaking geometric model, and a mobile water jet ground breaking grid model is obtained; carrying out grid coupling on the fluid domain and the solid domain; setting grid boundary conditions; defining a load, wherein the load in the experimental model is water jet; selecting an experiment failure criterion; carrying out post-processing on the simulation model, and checking a stress nephogram; according to a simulation result, various parameters are adjusted, and the steps are repeated until accurate equipment jet parameters are obtained; according to the method, simulation of submarine cable soil covering cleaning through the mobile jet technology is achieved through a simulation analysis method, various working conditions of submarine cable soil covering cleaning through the mobile jet technology in the seabed first-aid repair process are considered, the stress condition of submarine cables is also considered, and a foundation is laid for engineering application of the seabed mobile jet cleaning technology.

Description

Technical Field

[0001] The invention relates to the technical field of submarine cable repair engineering, in particular to a simulation analysis method for cleaning soil covering of a submarine cable with a moving jet. Background Art

[0002] With the increase in the mileage of submarine cable laying and the passage of laying time, the protection and emergency repair of submarine cables in the later stage are the top priority to ensure the safe operation of networking projects. Once the submarine cable is damaged, there is a possibility that the subnet and the main network will be disconnected, which can easily cause large-scale power outages. Therefore, it is necessary to establish an emergency repair mechanism plan. Before repairing the submarine cable, the soil and other coverings on the cable should be cleaned first. The jet breaking process of covering cleaning is a key step in the repair of submarine cables. In recent years, water jet technology has been widely used in various fields of people's production, life and engineering, including machinery, aerospace, construction, mining, petroleum and many other fields. As a good cutting, crushing and cleaning tool, water jet has been recognized by people, and has outstanding application prospects in the process of cleaning soil coverings during submarine cable repairs.

[0003] At present, common submarine trenching equipment includes dredgers, jet submarine trenchers, submarine trenching plows, mechanical cutting submarine trenchers, etc. Among them, the jet submarine trenching equipment has a simple structure. It usually uses a high-pressure water pump to spray water from the nozzle on the trencher to flush the sand and gravel above and around the submarine cable, thereby clearing the covering and exposing the cable to facilitate subsequent cutting. During the flushing process, it is necessary to reasonably set parameters such as the flow rate of the water flow to avoid the situation where the cable is damaged due to excessive impact force of the water flow. The existing submarine jet trenching technology is mostly used in the laying stage of submarine cables. During the laying stage, it is only necessary to erode the pre-buried width and depth of the submarine cable, and the jet conditions when the cable is repaired or in place are not considered.

[0004] At present, the global computer technology is developing rapidly, but the relevant technology of using simulation technology to simulate the cleaning of submarine cable covering by moving jets is still blank in China. The simulation of the cleaning process of submarine cable coverings is realized by simulating the action process of moving water jets on the seabed soil through LS-DYNA software. This has very important practical significance for the research of submarine cable repair technology and can ensure the rapid development of submarine cables in my country in the future. Summary of the invention

[0005] The purpose of the present invention is to provide a simulation analysis method for cleaning the soil cover of a submarine cable by a mobile jet, aiming to simulate the cleaning of the soil cover of a submarine cable by a mobile jet technology during the seabed repair process through the simulation analysis method, so as to more intuitively obtain the phenomena and key parameters in the covering cleaning process.

[0006] To achieve the above objectives, the technical solution of the present invention is:

[0007] A simulation analysis method for cleaning soil covering of submarine cables by a mobile jet, the method comprising the following steps:

[0008] S1: Model establishment: Determine the parameters of the mobile water jet soil breaking model, and establish the geometric model of the mobile water jet soil breaking using three-dimensional design software according to the determined model parameters;

[0009] S2: using a meshing tool to mesh the moving water jet soil breaking geometric model in step S1 to obtain a moving water jet soil breaking mesh model, wherein the mesh model includes a jet source domain, a nozzle domain, a water area, and a soil domain; the jet source domain, the nozzle domain, and the water area are divided by ALE meshing; the soil domain is divided by Lagrange meshing; the water area mesh and the jet source and nozzle meshes are common node meshes;

[0010] S3: Fluid-solid coupling: ALE fluid domain grid is coupled with Lagrange solid domain grid;

[0011] S4: Boundary condition setting: The bottom surface of the soil domain is set as a fixed displacement boundary, and its four sides use non-reflection boundaries to simulate infinite boundaries to reduce the workpiece material mesh definition domain. The side wall of nozzle B is a zero velocity boundary to meet the no-slip and no-penetration conditions.

[0012] S5: Define the load applied to the jet source. The water jet velocity in the experimental model is 15.92 m / s. By initializing the state equation of water, the volume internal energy is changed to apply pressure to the jet source to control the nozzle jet outlet velocity. The general form of the state equation of water is p = A (μ) + B (μ) · E, where B(μ)=(γ0+aμ), μ is the compression ratio of the medium ρ is the current density of water, ρ0 is the initial density of water at room temperature, then the relative volume v r for Assuming that the water medium in the jet source is incompressible, let the relative volume v r =1, that is, μ=0, and the pressure p=γ0·E is obtained by substituting it into the above formula. C is the speed of sound propagation in water, which is 1647m / s, a is the first-order correction of the GRUNEISEN coefficient Y0, S1, S2, and S3 are dimensionless coefficients, S1 is 1.921, S2 is -0.096, and S3 is 0; therefore, it is only necessary to change the initial internal energy of the water to add pressure to the jet source.

[0013] S6: define the failure criterion of the soil domain, the soil grid within the half-width range where the water jet force on the soil grid exceeds the preset value disappears, and the half-width refers to the radius of the jet column;

[0014] S7: The software calculates and obtains the depth and width of the scouring pit, the stress-strain cloud map of the soil, and the stress-strain cloud map of the submarine cable, and checks the stress-strain cloud map;

[0015] When the depth and width of the scouring pit meet the predetermined requirements, if the stress value in the stress-strain cloud diagram of the submarine cable does not exceed the maximum stress value that the submarine cable can withstand, the test parameters are reasonable;

[0016] If the stress value in the submarine cable stress-strain cloud diagram exceeds the maximum stress value that the submarine cable can withstand, the test parameters are unreasonable. According to the simulation results, the test parameters are adjusted and steps S1-S7 are repeated until reasonable device jet parameters are obtained.

[0017] Furthermore, the meshing of the geometric model in step S2 includes the following steps:

[0018] S21: Import the model:

[0019] Import the embedded geometry model into the hypermesh software through the Import Geometry of the hypermesh software.

[0020] S22: Coplanarity and cutting:

[0021] In the hypermesh software, the boolean operation in Solid Edit is used to merge the jet source and nozzle domain with the water area and make them coplanar, and Trim with line is used to cut the jet source, nozzle domain and water area through the boundary line.

[0022] S23: Create and move components:

[0023] Create them separately in the hypermesh software

[0024] component-sheliuyuan-penzui,component-tu components, through Organize, the collective jet source, nozzle domain and water area are moved to the corresponding component respectively.

[0025] S24: Draw the surface mesh:

[0026] In the hypermesh software, one quarter of the jet source section is divided into three groups of quadrilaterals, and surface meshes are drawn in each quadrilateral area to improve the accuracy of finite element mesh calculation. Three points are equally spaced on the edge through extract parametric in Nodes, and the points are moved to the desired position by applying Translate. The secant line is generated by connecting the points through splitsurf-line in Quick edic. The jet source is meshed through Automesh screen, and the element size is 10. The number of meshes on the opposite sides of each area is adjusted to the same value, so that each small mesh is a quadrilateral to avoid mesh deformation affecting accuracy. Move the drawn surface mesh to the newly created component-2d to facilitate its deletion after drawing the volume mesh to avoid errors during calculation.

[0027] S25: Draw the volume mesh:

[0028] In the hypermesh software, the solid map is used to draw the volume mesh along the jet source and nozzle diameter.

[0029] S26: Generate coplanar surface mesh:

[0030] In the hypermesh software, the surface mesh of the bottom surface of the solid unit of the jet source and nozzle domain is generated through Faces search. The surface mesh is applied to the water area to make the body mesh of the contact part between the jet source and nozzle domain and the water area consistent.

[0031] The drawing of the remaining volume mesh is completed through the method in steps S21-S26.

[0032] Furthermore, in the step S2, the jet source moves at a uniform speed in the horizontal direction of the submarine cable and moves at a simple harmonic speed in the horizontal direction perpendicular to the submarine cable. Where y is the displacement of the jet source in the direction perpendicular to the submarine cable, A is the amplitude of simple harmonic motion, ω is the angular frequency, It is the initial phase, which can adjust the amplitude and frequency of the jet source moving in the vertical direction.

[0033] Furthermore, the fluid-solid coupling in step S3 includes the following steps:

[0034] During meshing, the fluid domain mesh and the solid domain mesh are overlapped, and then the solid domain and the fluid domain are coupled together to achieve the transfer of mechanical parameters.

[0035] In LS-DYNA software, create part and part set collections, assemble the jet source, nozzle domain and water area into a part set collection, set the soil domain as a part, and

[0036] CONSTRAINED_LAGRANGE_IN_SOILD realizes the coupling between fluid and solid;

[0037] The specific steps include:

[0038] S31: In LS-DYNA software, select the structure of Euler unit as the main structure, define this partset collection as the main structure through MASTER, select the structure of Lagrange unit as the slave structure, and define the soil domain as the slave structure through SLAVE.

[0039] S32: In LS-DYNA software, the number of coupling points distributed on each Lagrange surface segment is set through NOUAD, mainly to control the leakage phenomenon that occurs during the jet process. The larger the value, the greater the number of couplings, but the calculation time will increase;

[0040] S33: In the LS-DYNA software, a method for setting the coupling between fluid and solid structure is provided through CTYPE. The present invention adopts an erosion penalty function for the solid unit.

[0041] S34: In LS-DYNA software, the coupling direction is set by DIREC, and the water jet soil breaking has an effect in the normal, tensile and compressive directions.

[0042] S37: In LS-DYNA software, the penalty function factor is set by PFAC to calculate the force distributed between the slave segment SLAVE and the master segment MASTER. The penalty function factor is related to the result of the entire calculation example and is a very important parameter. When the penalty function factor is too large, the grid is prone to negative volume, causing the calculation to terminate unexpectedly; and when it is too small, the coupling force between the master and slave segments is too small, and large-area grid penetration is prone to occur. After multiple debugging, the present invention selects a value of 0.1.

[0043] S38: In the LS-DYNA software, the FRCMIN value is set to 0.165 to prevent coupling penetration under high-speed collision.

[0044] Furthermore, the boundary condition setting in step S4 includes:

[0045] The soil and water bottom are fully constrained, and the normal direction of the model limits its normal translation. The top jet source is the velocity inlet, the jet target distance is 40mm, and the jet diameter is 4mm.

[0046] Furthermore, the selection of the failure criterion of step S6 includes:

[0047] The critical pressure of soil is In the formula, F cris the critical pressure of soil failure; α is the experimental correction coefficient, which is α=1.8×10 10 ; τ f is the shear strength of the soil; d 60 is the limited particle size of soil particles; d is the dry soil weight; k is the permeability coefficient of the soil; It is the soil's resistance to erosion.

[0048] The average force on the soil within the half-width of the jet is: In the formula, is the average force acting on the soil within the half-width of the flow; p0 is the nozzle outlet pressure; R0 is the nozzle outlet radius; x is the jet flow rate.

[0049] Under the impact of jet, the necessary condition for the soil to be destroyed is that the force on the soil within the half-width range is greater than the critical pressure of the soil, that is, F b >F cr , the force on the soil grid within the half-width exceeds F cr The soil grid disappears.

[0050] The beneficial effects of the present invention are:

[0051] 1. The present invention realizes the simulation of cleaning the soil cover of the submarine cable by mobile jet technology during the submarine emergency repair process through a simulation analysis method. The simulation analysis method not only takes into account the various working conditions of cleaning the soil cover of the submarine cable by mobile jet technology during the submarine emergency repair process, such as seabed soil and key jet parameters, but also takes into account the stress conditions of the submarine cable when it is in place, so as to avoid secondary damage to the submarine cable caused by high-speed jets.

[0052] 2. The present invention uses the Lagrange-Euler method to simulate the mobile jet cleaning of the soil cover of the submarine cable, and determines the method of simulating the submarine mobile water jet breaking the soil. The motion LS-DYNA display dynamics software intuitively simulates the process of the mobile water jet breaking the soil, and considers the force analysis of the submarine cable in place, which greatly saves costs and time while ensuring accuracy, and provides a theoretical basis for the engineering application of submarine mobile jet cleaning technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic diagram of the numerical simulation model of water jet soil breaking of the present invention.

[0054] Figure 2 It is a schematic diagram of the jet source domain grid of the present invention.

[0055] Figure 3 It is a schematic diagram of the nozzle domain grid of the present invention.

[0056] Figure 4It is a schematic diagram of air domain grid division of the present invention.

[0057] Figure 5 It is a schematic diagram of soil mesh division according to the present invention.

[0058] Figure 6 It is a schematic diagram of the mesh division of the fluid-solid coupling domain of the present invention.

[0059] Figure 7 It is a schematic diagram of the nozzle boundary constraint conditions of the present invention.

[0060] Figure 8 It is a schematic diagram of the mobile jet cratering morphology of the present invention.

[0061] Fig. 9 It is the nozzle velocity cloud diagram of the present invention.

[0062] Fig.10 It is the jet velocity curve at the nozzle outlet of the present invention. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical solutions and advantages of the invention clearer, the present invention is further described below with reference to the accompanying drawings.

[0064] A simulation analysis method for cleaning soil covering of submarine cables by a mobile jet comprises the following steps:

[0065] Step (1): Establishment of the model of moving water jet breaking soil: Moving water jet breaking soil means that the nozzle moves forward continuously while the jet erodes the soil. The moving direction of the nozzle is parallel to the soil surface, and the spraying direction is perpendicular to the soil surface. Water is ejected from the nozzle to flush the soil and other coverings on the submarine cable. The model data such as the determined water source pressure, nozzle inlet diameter, nozzle outlet diameter, nozzle traverse speed, length of the soil to be flushed, and width of the soil to be flushed are shown in Table 1.

[0066] Table 1 Numerical simulation parameters

[0067]

[0068] According to the determined model parameters, the simulation model of the whole process of water jet breaking soil was established using LS-DYNA simulation software.

[0069] Step (2): Meshing: The meshing of the model is as follows: Figure 1As shown, A is the jet source domain, where the jet source is defined. B is the nozzle domain, which is initially an empty material domain, C is the water area, which is initially defined as a water medium material, and D is the soil domain. Domains A, B, and C are divided by ALE meshing, and domain D is divided by Lagrange meshing. The erosion effect of the jet on the workpiece is realized by the coupling algorithm of ALE and Lagrange meshing, and the meshes of domains C and D need to overlap. High-quality hexahedral meshing is used for the entire system including the nozzle, water area, and soil. The mesh of the jet near the nozzle wall needs to be encrypted to obtain a more accurate flow field distribution. The type of mesh is an eight-node hexahedral unit.

[0070] Meshing includes the following steps:

[0071] S21: Import the model:

[0072] Import the embedded geometry model into the hypermesh software through the Import Geometry of the hypermesh software.

[0073] S22: Coplanarity and cutting:

[0074] In the hypermesh software, the boolean operation in Solid Edit is used to merge the jet source and nozzle domain with the water area and make them coplanar, and Trim with line is used to cut the jet source, nozzle domain and water area through the boundary line.

[0075] S23: Create and move components:

[0076] Create them separately in the hypermesh software

[0077] component-sheliuyuan-penzui,component-tu components, through Organize, the collective jet source, nozzle domain and water area are moved to the corresponding component respectively.

[0078] S24: Draw the surface mesh:

[0079] In the hypermesh software, one quarter of the jet source section is divided into three groups of quadrilaterals, and surface meshes are drawn in each quadrilateral area to improve the accuracy of finite element mesh calculation. Three points are equally spaced on the edge through extract parametric in Nodes, and the points are moved to the desired position by applying Translate. The secant line is generated by connecting the points through splitsurf-line in Quick edic. The jet source is meshed through Automesh screen, and the element size is 10. The number of meshes on the opposite sides of each area is adjusted to the same value, so that each small mesh is a quadrilateral to avoid mesh deformation affecting accuracy. Move the drawn surface mesh to the newly created component-2d to facilitate its deletion after drawing the volume mesh to avoid errors during calculation.

[0080] S25: Draw the volume mesh:

[0081] In the hypermesh software, the solid map is used to draw the volume mesh along the jet source and nozzle domain diameter.

[0082] S26: Generate coplanar surface mesh:

[0083] In the hypermesh software, the surface mesh of the bottom surface of the jet source and nozzle domain solid unit is generated through Faces search. The surface mesh is applied to the water area to make the body mesh of the contact part between the jet source and nozzle domain and the water area consistent.

[0084] The drawing of the remaining volume mesh is completed through the method in steps S21-S26.

[0085] The jet source is a cylinder with a size of d = 20 mm * 20 mm. The jet source wall grid is denser and uses a boundary layer grid, such as Figure 2 shown.

[0086] The shape of the nozzle will also affect the efficiency of the jet. Currently, the most widely used nozzle shapes include straight cylindrical nozzles, conical nozzles and streamlined nozzles. Among them, the streamlined nozzle has the highest efficiency, followed by the conical nozzle, and the straight cylindrical nozzle is the worst. Since the streamlined nozzle is difficult to process, the conical nozzle is currently the most widely used. When the nozzle contraction angle is 13°, the jet decays the slowest and has the highest efficiency; when the length of the nozzle parallel outlet section is 2.5 times the nozzle diameter, the jet decays the slowest and the nozzle performance is the best. The nozzle consists of three parts: the inlet section, the conical contraction section and the outlet section. Figure 3 As shown, the inlet section is a cylinder with a diameter of 20 mm and a height of 30 mm, the contraction angle of the conical contraction section is 13°, and the diameter of the outlet section is 9 mm.

[0087] The water area grid, the jet source domain and the nozzle grid form a common node grid to form the force transmission. Figure 4 As shown in the figure, the mesh of the part where the soil contacts the jet should be denser, and the mesh of the part away from the jet can be appropriately sparse to reduce the amount of calculation. The mesh division is as follows: Figure 5 shown.

[0088] Step (3): Fluid-Solid Coupling: The penalty function coupling method can be used in the Lagrangian-Euler coupling method in the model, and the interface between the master and slave materials does not need to be specially defined. The keyword *CONSTRAINED-LAGRANGE-IN-SOILD is used in the LS-DYNA program to achieve the coupling between the structure and the fluid. When using the fluid-solid coupling algorithm to simulate problems, it is often necessary to constrain the Lagrangian structure and pass the relevant parameters of the structure to the fluid unit. The Lagrangian structure grid and the Euler fluid grid in the coupling area need to overlap, such as Figure 6 shown.

[0089] In the water jet breaking model, the ALE grid of the water area C should overlap with the Lagrange grid of the lower soil D, and the coupling between the structure and the fluid is realized by defining the key letters COINSTRAINED-LAGRANGE-IN-SOLID, which is the most important keyword for realizing fluid-solid coupling. This keyword provides a way for the Lagrangian geometric entity to couple with the ALE or Eulerian geometric entity.

[0090] Create part and part set collections in LS-DYNA software, assemble the jet source and nozzle domain and the water area into a part set collection, and set the soil domain as a part; realize the coupling of fluid and solid through CONSTRAINED_LAGRANGE_IN_SOILD in LS-DYNA software.

[0091] The grid coupling specifically includes the following steps:

[0092] S31: In LS-DYNA software, select the structure of Euler unit as the main structure, define this partset collection as the main structure through MASTER, select the structure of Lagrange unit as the slave structure, and define the soil domain as the slave structure through SLAVE.

[0093] S32: In LS-DYNA software, NOUAD is used to set the number of coupling points distributed on each Lagrange surface segment. This is mainly to control the leakage phenomenon that occurs during the jet process. The larger the value, the larger the number of couplings, but the calculation time will increase. Select 2 according to the model grid size.

[0094] S33: In the LS-DYNA software, a method for setting the coupling between fluid and solid structure is provided through CTYPE. The present invention adopts an erosion penalty function for the solid unit.

[0095] S34: In LS-DYNA software, the coupling direction is set by DIREC, and the water jet soil breaking has an effect in the normal, tensile and compressive directions.

[0096] S35: In LS-DYNA software, the penalty function factor is set by PFAC to calculate the force distributed between the slave segment SLAVE and the master segment MASTER. The penalty function factor is related to the result of the entire calculation example and is a very important parameter. When the penalty function factor is too large, the grid is prone to negative volume, causing the calculation to terminate unexpectedly; and when it is too small, the coupling force between the master and slave segments is too small, and large-area grid penetration is prone to occur. After multiple debugging, the penalty function factor of the present invention is selected to be 0.1.

[0097] S36: In the LS-DYNA software, the FRCMIN value is set to 0.165 to prevent coupling penetration under high-speed collision.

[0098] Step (4): Boundary conditions: The bottom surface of workpiece D is a fixed displacement boundary, and its four sides are non-reflecting boundaries, which are used to simulate infinite boundaries to reduce the mesh definition domain of the workpiece material. The side wall of nozzle B is a zero velocity boundary, which meets the no-slip and no-penetration conditions. The soil and water bottom are fully constrained, and the model normal direction limits its normal translation. The top jet source is the velocity inlet, the jet target distance is 40mm, and the jet diameter is 4mm. After the nozzle and air domain boundary conditions are applied, Figure 7 shown.

[0099] Step (5): The water jet velocity in the experimental model is 15.92 m / s. The initialization of the water state equation changes the volume internal energy and applies pressure to the jet source to control the nozzle jet outlet velocity. The general form of the water state equation is p = A (μ) + B (μ) · E, where B(μ)=(γ0+aμ), μ is the compression ratio of the medium ρ is the current density of water, ρ0 is the initial density of water at room temperature, then the relative volume v r for Assuming that the water medium in the jet source is incompressible, let the relative volume v r =1, that is, μ = 0, and the pressure p = γ0·E is obtained by substituting it into the above formula. Therefore, it is only necessary to change the initial internal energy of the water to add pressure to the jet source. For example, the velocity cloud of the nozzle Fig. 9 As shown, the jet velocity is maximum at the outlet, which is about 15.9 m / s. Fig.10 It is the jet velocity curve at the outlet. It can be seen from the figure that the jet accelerates in the nozzle, reaches the maximum value at the outlet, and the speed is stable at 15.92m / s, which meets the jet conditions during the experiment.

[0100] Step (6): Selection of failure criteria: When using LS_DYNA to simulate water jet soil breaking, the soil will be automatically deleted after being destroyed by the water flow. Although the MAT-FHWA-SOIL model has its own maximum principal strain failure criterion, the soil will sometimes be severely distorted when the failure criterion is used during the simulation process, and even the calculation will be terminated. Therefore, the MAT-ADD-EROSION erosion failure criterion is used to control the failure of the soil material model unit. This criterion can define seven failure criteria: pressure, principal stress, principal strain, equivalent stress, shear strain, critical stress, pressure pulse failure, and time failure. At present, mobile jet soil breaking is based on the bearing capacity theory in soil mechanics. The soil is destroyed by the jet flow pressure. Therefore, the present invention uses the maximum failure pressure as the basis for judging soil failure. The bearing capacity of clay sand is 200kPa.

[0101] The failure criteria selection specifically includes:

[0102] The critical pressure of soil is In the formula, F cr is the critical pressure of soil failure; α is the experimental correction coefficient, which is α=1.8×10 10 ; τ f is the shear strength of the soil; d 60 is the limited particle size of soil particles; d is the dry soil weight; k is the permeability coefficient of the soil; It is the soil's resistance to erosion.

[0103] The average force on the soil within the half-width of the jet is: In the formula, is the average force acting on the soil within the half-width of the flow; p0 is the nozzle outlet pressure; R0 is the nozzle outlet radius; x is the jet flow rate.

[0104] Under the impact of jet, the necessary condition for the destruction of soil is that the force on the soil within the half-width range is greater than the critical pressure of the soil, that is, like Figure 8 As shown in the figure, the force on the soil grid within the half width of the soil domain exceeds F cr The soil mesh disappears, and the half-width refers to the radius of the jet column.

[0105] Step (7): Calculate using LS-DYNA software to obtain the depth and width of the scouring pit, the stress-strain cloud map of the soil, and the stress-strain cloud map of the submarine cable, and check the stress-strain cloud map;

[0106] The maximum stress value that the submarine cable can withstand is a known value. If the stress value of the submarine cable exceeds the maximum stress value that it can withstand during the process of jet scouring the soil, the submarine cable will be damaged;

[0107] Under the condition that the depth and width of the scouring pit meet the predetermined requirements, if the stress value in the stress-strain cloud diagram of the submarine cable does not exceed the maximum stress value that the submarine cable can withstand, the test parameters are reasonable;

[0108] If the stress value in the submarine cable stress-strain cloud diagram exceeds the maximum stress value that the submarine cable can withstand, the test parameters are unreasonable. According to the simulation results, the test parameters are adjusted and steps S1-S7 are repeated until reasonable device jet parameters are obtained.

[0109] In step (1), according to the seabed geological survey data of Hainan Internet Engineering, the seabed soil mainly includes low liquid limit clay, high liquid limit clay, poorly graded sand, silty sand, clay sand, etc., and the bearing capacity of the soil is between 100 and 300 kPa. The present invention takes the clay sand of Qiongzhou Strait as the research object. Table 2 shows the physical and mechanical properties of the seabed soil of Qiongzhou Strait, and the bearing capacity of the clay sand is selected as 200 kPa. According to the determination of the relevant values ​​of clay soil by referring to the relevant soil parameters and the LS-DYNA help manual, the constitutive parameters of the clay sand material in Table 2 are given below.

[0110] Table 2 Physical and mechanical properties of the seabed soil in the Qiongzhou Strait

[0111]

[0112] The relationship between the parameters of clay is as follows:

[0113]

[0114] Where τ represents the shear strength bearing capacity; σ represents the soil normal stress, which is related to the water depth of the seabed soil; represents the friction angle of the soil, which is 0.52; C represents the cohesion of the soil, which is 10 kPa. In this example, the clay sand is at a water depth of about 33 meters, and the normal stress is = 330 kPa, so the shear strength bearing capacity is = 200 kPa.

[0115] The MAT-FHWA-SOIL model is used as the constitutive model of soil material. This model is a modified Drucker-Prager plasticity model, which also includes pre-peak hardening, post-peak strain softening (damage), strain rate effect, pore water effect (moisture effect) and erosion capacity. Therefore, this model is more suitable for simulating submarine water jet breaking.

[0116] The key soil parameters in the model include: water content W, soil density ρ, bulk modulus K, shear modulus G, friction angle and cohesion C. The soil is under dynamic load and involves motion and large deformation problems, so it can be assumed that the elastic modulus in the elastic stage is consistent with the compression modulus. According to SL-237-1999 "Geotechnical Testing Regulations", the water content ω, soil density ρ, bulk modulus K, shear modulus G, friction angle, cohesion C and elastic modulus E were measured. The specific gravity of soil particles was measured by the pycnometer method, the water content was measured by the drying method, the soil density was measured by the ring knife method, the shear modulus and bulk modulus were measured by the probe and K0 consolidation test, the friction angle and cohesion were measured by the direct shear test, and the elastic modulus was measured by the indoor triaxial compression test.

[0117] The Poisson's ratio v of the seabed soil material is generally 0.3. The cohesion of seabed clay soil is generally 5kPa to 15kPa, and the cohesion of the clay sand of the present invention is 10kPa. The specific gravity of the clay soil is generally between 2.7 and 2.8, and the present invention uses 2.7. The bulk modulus K and the shear modulus G can be expressed as a function of the elastic modulus E and the Poisson's ratio v, and their expressions are as follows:

[0118]

[0119] The jet source and water area use the *MAT_NULL material model. This material allows the state equation to be considered without calculating the deviatoric stress when using solid or shell elements, and the fluid viscosity can be defined. In this model, the water density RO = 1000kg / m3 and the dynamic viscosity is 1.01×10-3Pa·s. The water state equation is described by the *EOS_Gruneisen state equation.

[0120] In step (2), the mobile jet source is set up, making full use of the free transformation characteristics of the ALE grid to allow the water area and the nozzle to move together, and a non-reflective boundary is imposed on the water area to simulate an infinitely large water area, thereby overcoming the limitations of the existing numerical simulation methods on movement due to the large and fixed flow field grid in space, and effectively reducing the amount of calculation for the entire model. The keyword for controlling the movement of the grid is *ALE_REFERENCE_SYSTEM_GROUP, which specifies how the specified grid is translated, rotated, expanded, and contracted. The setting of the mobile jet source is divided into three steps, including three keywords. First, it is necessary to use the keyword *ALE_REFERENCE_SYSTEM_GROUP during the calculation cycle of the water jet cleaning.

[0121] *DEFINE_CURVE keyword sets the movement speed function, and then passes the speed function to the key

[0122] *ALE_REFERENCE_SYSTEM_CURVE specifies the moving direction. The jet source moves at a uniform speed in the horizontal direction of the submarine cable and in a simple harmonic motion in the horizontal direction perpendicular to the submarine cable. Where y is the displacement of the jet source in the y direction perpendicular to the submarine cable, A is the amplitude of simple harmonic motion, ω is the angular frequency, is the initial phase, and the first-order derivative of the displacement is the velocity, which can adjust the amplitude and frequency of the jet source moving in the vertical direction. The velocity definition expression of the grid node coordinates is as follows:

[0123]

[0124] The first term f1, f5 and f9 on the right side of formula (4) control the translation of the grid nodes, where f1 controls the x direction, f5 controls the y direction, and f9 controls the z direction. The second term f2, f3, f4, f6, f7, f8, f10, f11, and f12 control the rotation of the grid nodes. Finally, the velocity function is loaded onto the ALE material group consisting of the jet source, nozzle, and water area through the keyword *ALE_REFERENCE_SYSTEM_GROUP to achieve the joint movement of the three.

[0125] Finally, it should be noted that the contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field. The above description is only the preferred embodiment of the present invention and is not used to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions recorded in the aforementioned embodiments, or to replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A simulation analysis method for cleaning soil covering of submarine cables by mobile jet, characterized in that , the method comprises the following steps: S1: Model establishment: Determine the parameters of the mobile water jet soil breaking model, and establish the geometric model of the mobile water jet soil breaking using three-dimensional design software according to the determined model parameters; S2: using a meshing tool to mesh the moving water jet soil breaking geometric model in step S1 to obtain a moving water jet soil breaking mesh model, wherein the mesh model includes a jet source domain (A), a nozzle domain (B), a water area (C), and a soil domain (D); the jet source domain (A), the nozzle domain (B) and the water area (C) are divided by ALE meshing; and the soil domain (D) is divided by Lagrange meshing; S3: Fluid-solid coupling: The ALE fluid domain grid formed by the jet source domain (A), nozzle domain (B) and water area (C) is coupled with the Lagrange solid domain grid of the soil domain (D); S4: Boundary condition setting: the bottom surface of the soil domain (D) is a fixed displacement boundary, its four sides are non-reflecting boundaries, and the side wall of the nozzle domain (B) is a zero velocity boundary; S5: Define the load applied to the jet source domain (A) to determine the velocity of the water jet; S6: Define the failure criterion of the soil domain (D): the soil grid disappears when the water jet force on the soil grid exceeds the preset value; S7: The software calculates and obtains the depth and width of the water jet scouring pit, the stress-strain cloud map of the soil, and the stress-strain cloud map of the submarine cable, and checks the stress-strain cloud map; When the depth and width of the scouring pit meet the predetermined requirements, if the stress value in the stress-strain cloud diagram of the submarine cable does not exceed the maximum stress value that the submarine cable can withstand, the test parameters are reasonable; If the stress value in the submarine cable stress-strain cloud diagram exceeds the maximum stress value that the submarine cable can withstand, the test parameters are unreasonable. The test parameters should be adjusted according to the simulation results, and steps S1-S7 should be repeated until reasonable equipment jet parameters are obtained.

2. A simulation analysis method for cleaning soil covering of submarine cables by a mobile jet according to claim 1, characterized in that , the meshing of the geometric model in step S2 includes the following steps: S21: import the model, import the geometric model of the moving water jet breaking the soil into the hypermesh software; S22: Coplanarity and cutting: in the hypermesh software, the jet source and nozzle domain are merged and coplanar with the water area through the Boolean operation in Solid Edit, and the jet source, nozzle domain and water area are cut through the boundary line using Trim with line; S23: Create and move components, create them separately in the hypermesh software component-sheliuyuan-penzui,component-tu element, through Organize, the collective jet source, nozzle domain and water area are moved to the corresponding component respectively; S24: Draw a surface mesh, divide a quarter of the jet source cross section into three groups of quadrilaterals in the hypermesh software, draw a surface mesh in each quadrilateral area to improve the accuracy of the finite element mesh calculation, divide three points equidistantly on the edge through extractparametric in Nodes, apply Translate to move the points to the desired position, generate secant lines with the connecting points through split surf-line in Quickedic, adjust the number of meshes on the opposite sides of each area to the same value for the jet source through Automesh screen mesh, make each small mesh a quadrilateral, and move the drawn surface mesh to the newly created component-2d; S25: Drawing a volume mesh, using Solid Map in the hypermesh software to draw a volume mesh along the jet source and nozzle domain diameter; S26: Generate a coplanar surface mesh, find the surface through Faces in the hypermesh software, generate the surface mesh of the bottom surface of the jet source and nozzle domain entity unit, and apply the surface mesh to the water area to make the body mesh of the contact part of the jet source and nozzle domain and the water area consistent; S27: Complete the drawing of the remaining volume meshes through the method of steps S21-S26.

3. The simulation analysis method for cleaning soil covering of submarine cables by mobile jet according to claim 1 is characterized in that: In step S2, the jet source moves at a uniform speed in the horizontal direction of the submarine cable and in a simple harmonic motion in the horizontal direction perpendicular to the submarine cable. Where y is the displacement of the jet source in the direction perpendicular to the submarine cable, A is the amplitude of simple harmonic motion, ω is the angular frequency, It is the initial phase.

4. The simulation analysis method for cleaning soil covering of submarine cables by mobile jet according to claim 1 is characterized in that , the fluid-solid coupling in step S3 includes the following steps: During meshing, overlap the fluid domain mesh and the solid domain mesh, couple the solid domain and the fluid domain, create part and part set collections, assemble the jet source, nozzle domain and water area into a part set collection, set the soil domain as a part, and realize the coupling between fluid and solid through CONSTRAINED_LAGRANGE_IN_SOILD in the LS-DYNA program; The specific steps include: S31: In LS-DYNA software, the structure of the Euler unit is selected as the main structure, the part set is defined as the main structure through MASTER, the structure of the Lagrange unit is selected as the slave structure, and the soil domain is defined as the slave structure through SLAVE; S32: Setting the number of coupling points distributed on each Lagrange surface segment by NOUAD in LS-DYNA software; S33: Method for setting the coupling between fluid and solid structure through CTYPE in LS-DYNA software; S34: Set the coupling direction via DIREC in LS-DYNA software; S35: Setting the penalty function factor by PFAC in the LS-DYNA software to calculate the force distributed between the slave segment SLAVE and the master segment MASTER; S36: Set FRCMIN in LS-DYNA software to prevent coupling penetration under high-speed collision.

5. The simulation analysis method for cleaning soil covering of submarine cables by mobile jet according to claim 1 is characterized in that , the boundary condition setting in step S4 includes: The soil domain and the bottom of the water area are fully constrained, the top jet source is the velocity inlet, the jet target distance is 40mm, and the jet diameter is 4mm.

6. The simulation analysis method for cleaning soil covering of submarine cables by mobile jet according to claim 1 is characterized in that , the selection of failure criteria in step S6 includes: The critical pressure of soil is In the formula, F cr is the critical pressure of soil failure; α is the experimental correction coefficient, which is α=1.8×10 10 ; τ f is the shear strength of the soil; d 60 is the limited particle size of soil particles; d is the dry soil weight; k is the permeability coefficient of the soil; is the soil's anti-erosion strength; The average force on the soil within the half-width of the jet is: In the formula, is the average force acting on the soil within the half-width of the flow; p0 is the nozzle outlet pressure; R0 is the nozzle outlet radius; x is the jet flow rate. Under the impact of jet, the necessary condition for soil to be destroyed is that the force on the soil within the half-width range is greater than the critical pressure of the soil, that is, The force on the soil grid within the half-width exceeds F cr The soil grid disappears.

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