Determination method of jet equipment for direct-buried submarine cable protection work
By measuring the physical characteristics of the soil and establishing a jet soil-breaking simulation model, and determining the key parameters of jets, the problem of unreasonable selection of jet equipment in the existing technology is solved, the scientificity and efficiency of jet equipment are achieved, and the construction cost is reduced.
Patent Information
- Application Number
- CN202211061847.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-09-01
- Publication Date
- 2025-07-01
- Estimated Expiration
- 2042-09-01
AI Technical Summary
In the existing technology, in the deprotection of direct buried submarine cables, the selection of jet equipment lacks an accurate theoretical basis, resulting in unreasonable selection, wasted resources and high construction costs.
By measuring the soil physical characteristics of the soil in the deprotected working section of the direct buried submarine cable, a jet soil breaking simulation model was established, and simulation analysis was performed using ANSYS and LS_DYNA software, key jet parameters were determined, and jet equipment selection and parameter design were guided.
The accurate determination of key jet parameters is achieved, the secondary damage of high-speed jets to submarine cables is avoided, construction costs are reduced, and equipment selection is improved scientificity and efficiency.
Smart Images
Figure CN115358085B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of submarine cable engineering and relates to a method for determining submarine cable emergency repair equipment. Background Art
[0002] Submarine cables, abbreviated as submarine cables, are an important part of the grid connection of offshore wind power, the interconnection of cross-sea international power grids, and the power supply of islands and ocean engineering. Submarine cables are vulnerable to damage by natural and human factors on the seabed. The damage of submarine cables will cause low-frequency grid accidents and is extremely likely to cause large-scale power outages. Therefore, the emergency repair work of submarine cables needs to be completed in the shortest possible time to avoid serious impacts on the economy, life, etc. The emergency repair of submarine cables is mainly divided into four parts, namely, the cleaning of submarine cable covers, the underwater cutting of submarine cables, the salvage of submarine cables, and the playback of submarine cables. The deprotection work for the cleaning of the covers of directly buried submarine cables is mainly for the submarine cables in the scouring and burying section in deep water areas, and the covers of the submarine cables in the scouring and burying section are mostly soil bodies. In the deprotection work for the cleaning of the covers of directly buried submarine cables, the method of jet erosion of the protective layer above the directly buried submarine cable by a jet device is the most efficient, economical, and safe method. By using jet erosion to erode the soil body, the submarine cable is exposed, facilitating the subsequent cutting work.
[0003] Currently, in the deprotection work of directly buried submarine cables, there are mainly two methods for selecting jet devices: one is to select the device based on experience, which has no accurate theoretical basis, often results in unreasonable selection, and causes serious waste of resources; the other is to determine the device model through a trial operation experiment. Due to the short time of the jet acting on the soil body, the water body is turbid, and it is difficult to obtain information during the jet process. Only the final jet deprotection result can be obtained, and it is difficult to conduct a mechanistic analysis on it. The experimental results have little guiding significance for actual construction and result in unnecessary construction costs. Summary of the Invention
[0004] To solve the problems described in the background art, the present invention proposes a method for determining a jet device for the deprotection work of directly buried submarine cables.
[0005] The technical solution of the present invention includes the following steps:
[0006] Step 1: Measure the soil physical properties of the soil body in the deprotection work section of the directly buried submarine cable, including: specific gravity, density, moisture content, bulk modulus, shear modulus, friction angle, cohesion, and critical failure pressure;
[0007] Step 2: Based on the soil physical properties and the necessary conditions for soil jet failure: the average force of the jet within the half-width range of the soil surface is greater than the critical failure pressure of the soil body, preliminarily estimate the key jet parameters, including: the velocity v0 at the nozzle outlet, the nozzle outlet diameter d, and the target distance L of the water jet;
[0008] Step 3: Based on the preliminary estimation of the key jet parameters, establish a jet soil-breaking model for the directly buried submarine cable in ANSYS, divide the mesh, and export the K file.
[0009] Step 4: Modify the K file in LS_PREPOST, use the ALE algorithm, define materials, boundary conditions, contacts, loads, and control equations to obtain a modified K file.
[0010] Step 5: Import the modified K file into LS_DYNA for solution analysis to obtain a simulation model.
[0011] Step 6: Perform post-processing on the simulation model in LS_PREPOS to obtain the simulation results of the directly buried submarine cable's unprotected operation.
[0012] Step 7: Analyze the simulation results. If the requirements for the directly buried submarine cable's unprotected operation are met, then use the key jet parameters estimated in Step 2 as the accurate key jet parameters. If the requirements for the directly buried submarine cable's unprotected operation are not met, then adjust the preliminarily estimated key jet parameters and re-execute Steps 3 to 6 until the accurate key jet parameters are determined.
[0013] Step 8: Determine the jet equipment parameters based on the accurate key jet parameters, including: pump head, jet diameter, nozzle installation method, and pump selection, to guide the selection and parameter design of the jet equipment.
[0014] Furthermore, in Step 1, during the determination of the soil physical properties, the specific gravity is measured using the pycnometer method, the density is measured using the core cutter method, the water content is measured using the drying method, the shear modulus and bulk modulus are measured using a penetrometer and K0 consolidation experiment, the friction angle and cohesion are measured using a direct shear experiment, and the critical failure stress is measured through a triaxial compression experiment.
[0015] Even further, in Step 2, the average force within the half-width range of the jet on the soil surface is:
[0016]
[0017] where, v0 is the velocity at the nozzle outlet, ρ is the density of seawater, d is the nozzle outlet diameter, α is the diffusion angle of the water jet from the nozzle, l0 is the length of the constant-velocity core of the water jet, and L is the target distance of the water jet.
[0018] is greater than the critical failure pressure of the soil. First, select the nozzle outlet diameter d and the target distance L of the water jet according to the actual construction process of the directly buried submarine cable's unprotected operation, then the range value of the velocity v0 at the nozzle outlet can be obtained, thereby preliminarily estimating the key jet parameters: the velocity v0 at the nozzle outlet, the nozzle outlet diameter d, and the target distance L of the water jet.
[0019] Furthermore, in the third step, when establishing the direct-buried submarine cable jetting soil-breaking model, first preliminarily establish the 1 / 2 jet model size, then adopt the SOID_164 solid element, endow 4 kinds of empty materials, make the jet source and the water area share nodes, then establish the soil body model and the submarine cable model, require the soil body and the submarine cable to share nodes, and require the model size to eliminate the influence of boundary effects; in the mesh division, conduct mesh division on the model, and encrypt the water area mesh and the soil body mesh near the jet failure.
[0020] Furthermore, in the fourth step, the steps to modify the K file are as follows:
[0021] ① Define materials: In the soil material model, input the soil physical properties obtained in the first step into the keyword *MAT_147_FHWA_SOIL and the erosion algorithm *MAT_ADD_ERODION. The soil unit algorithm adopts *SECTION_SOILD, and the parameters remain default; the material model keyword of the direct-buried submarine cable is *MAT_RIGID, including: density, Young's modulus, and Poisson's ratio. The unit algorithm of the direct-buried submarine cable adopts *SECTION_SOILD, and the parameters remain default; the keywords of the jet source and the water area model are *MAT_009_NULL, the equation of state is defined as *EOS_GRUNERSEN, and the ELFOR of the water area and the jet source unit algorithm *SECTION_SOILD is set to a fixed value, and the rest remain default; assign the above parameters to the model, and define the jet source and the water area as ALE substances respectively, with the keyword *ALE_MULTI_MATERIAL_GROUP, and adopt the ALE algorithm;
[0022] ② Define boundary conditions: Fully constrain the bottom of the soil body, restrict the translation in the normal direction of the symmetry plane of the 1 / 2 jet model, and restrict the rotation in the other two directions; apply non-reflecting boundary conditions to the sides and bottom of the soil body and the water area to simulate an infinitely large space area, with the keyword *BOUNDARY_NON_REFELECTING;
[0023] ③ Define contact: Define the fluid-structure coupling between the soil body and the direct-buried submarine cable and the jet source and the water area through the keyword *CONSTRAINED_LAGRANGE_IN_SOILD. The slave surface SLAVE is the PART composed of the soil body and the direct-buried submarine cable, and the master surface MASTER is the PART composed of the water area and the jet source;
[0024] ④ Define the load: The continuous jet injection is manifested as a continuous flow of fluid with a vertical velocity emerging from the nozzle outlet. By setting the jet velocity function curve and associating the curve with the velocity value of the jet fluid using the keyword *BOUNDARY_PRESCRIBED_MOTION_SET, a jet source for continuous injection can be achieved.
[0025] ⑤ Define the control equations: The bulk viscosity *CONTROL_BULK_VISCOSITY remains at the default value; the global control parameters *CONTROL_ALE for ALE and Euler calculations are kept at the default; the control of hourglassing *CONTROL_HOURGLASS is default; the calculation time *CONTROL_TERMINATION, the time step *CONTROL_TIMESTEP, and the output frequency *DATABASE_BINARY_D3PLOT are all determined according to the requirements of the protection work of the directly buried submarine cable.
[0026] Furthermore, in step six, the simulation results of the protection work of the directly buried submarine cable include: ① Extract the time-displacement history data of the soil elements and plot the time-displacement curve in the jet direction to obtain the soil erosion displacement; ② Measure the maximum damage width of the elements near the top of the directly buried submarine cable; ③ Extract the historical data of the stress and strain of the directly buried submarine cable elements in the model and save them as a model stress-strain file. Extract the model stress-strain file in Xyplot and plot the model stress-strain curve to obtain a comparison chart between the model stress-strain curve and the actual stress-strain curve of the directly buried submarine cable.
[0027] Furthermore, in step seven, the situations where the simulation results do not meet the requirements of the protection work of the directly buried submarine cable and the key jet parameters initially estimated need to be adjusted include: ① If the soil erosion displacement of the time-displacement curve in the jet direction does not reach the burial depth of the directly buried submarine cable, then the velocity v0 at the nozzle outlet needs to be increased or the target distance L of the water jet needs to be decreased; ② If the maximum damage width is less than the diameter of the directly buried submarine cable, then the nozzle outlet diameter d of the jet needs to be increased; ③ In the comparison chart between the model stress-strain curve and the actual stress-strain curve of the directly buried submarine cable, if the directly buried submarine cable in the model is damaged, then the velocity v0 at the nozzle outlet, the target distance of the water jet, or the nozzle outlet diameter d needs to be decreased.
[0028] Furthermore, in step eight, the pump head of the jet equipment is determined based on the velocity v0 at the nozzle outlet, the nozzle diameter of the jet equipment is determined based on the nozzle outlet diameter d, and the nozzle installation method of the jet equipment is guided based on the target distance L of the water jet; the jet flow rate can be calculated based on the jet velocity and jet diameter, so that the flow rate of the pump can be determined, guiding the selection and design of the pump of the jet equipment.
[0029] Compared with the prior art, the present invention measures the physical properties of soil during the deprotection work of direct-buried submarine cables through experimental methods, and establishes a jet erosion simulation model for the deprotection work of direct-buried submarine cables based on water jet technology. It not only takes into account the soil and water conditions of the direct-buried submarine cables during the deprotection work and the key parameters of the jet, but also conducts a stress analysis on the direct-buried submarine cables eroded by water jets to avoid secondary damage to the submarine cables by high-speed jets. The present invention accurately determines the key parameters of the jet by analyzing the simulation results of jet breaking of the direct-buried submarine cables under different working conditions, and provides an accurate and reliable basis for the selection and parameter design of jet equipment. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 It is a flow chart of the present invention.
[0031] Figure 2 Schematic diagram of the model of jet breaking through the ground for directly buried submarine cables.
[0032] Among them: 1-jet source; 2-water area; 3-soil; 4-direct buried submarine cable. DETAILED DESCRIPTION
[0033] The implementation of the present invention is described in detail below in conjunction with the accompanying drawings, but they do not constitute a limitation of the present invention, but are only examples. At the same time, through the description, the advantages of the present invention will be more clearly understood. All deformations that can be directly derived or associated with the contents disclosed by ordinary technicians in the field should be considered as the protection scope of the present invention. The positional relationships described in the embodiments are consistent with those shown in the drawings, and other parts not described in detail in the embodiments are all prior art.
[0034] Example
[0035] In this embodiment, the implementation of the present invention is further specifically described by taking the silty sand body of the South China Sea as the protective layer of the direct-buried submarine cable.
[0036] Flowchart as Figure 1 As shown, the method for determining the jet device for deprotection of the direct buried submarine cable is specifically described as follows:
[0037] (1) Determine the soil physical properties of the protective layer
[0038] In the determination of soil physical properties, the density was determined by the pycnometer method, the density was determined by the ring knife method, the moisture content was determined by the drying method, the shear modulus and bulk modulus were determined by the probe and K0 consolidation test, the friction angle and cohesion were determined by the direct shear test, and the critical failure stress was determined by the triaxial compression test.
[0039] The physical properties of the soil were measured as follows: specific gravity 2.64, moisture content 32%, density 1.88 g / cm3 The shear modulus is 2.1e-5 Mbar, the bulk modulus is 4.5e-5 Mbar, the friction angle is 0.366 rad, the cohesion is 1.5e-7 Mbar, and the ultimate stress for soil failure is 1e-6 Mbar.
[0040] (2) Preliminary estimation of key jet parameters and soil parameters
[0041] The average force of the jet within the half-width range on the soil surface is:
[0042]
[0043] wherein, v0 is the velocity at the nozzle exit, ρ is the density of seawater, d is the diameter of the nozzle exit, α is the diffusion angle of the water jet from the nozzle, l0 is the length of the constant-velocity core of the water jet, and L is the target distance of the water jet.
[0044] As known from (1), the ultimate stress for soil failure is 1e-6 Mbar, i.e., 0.1 Mpa. The condition for the soil to fail is that the average force of the jet within the half-width range on the soil surface is greater than the ultimate stress for soil failure. In this embodiment During the actual construction process, the type of nozzle is mostly a conical-straight nozzle. Then, take the diffusion angle α = 16°, and the length of the constant-velocity core l0 = (4.8 - 8)d. In this embodiment, take l0 = 4.8d. It can be seen from the above formula that the main parameters affecting the jet action are the velocity v0 at the nozzle exit, the diameter d of the nozzle exit, and the target distance L of the water jet. In this embodiment, initially take the diameter d of the nozzle exit = 0.3 cm, and the target distance L of the water jet = 1 cm, and it is necessary to satisfy Then the velocity v0 at the nozzle exit needs to be greater than 15.6 m / s. Therefore, in this embodiment, first take v0 = 33 m / s for numerical simulation, and adjust it if necessary.
[0045] In this embodiment, through calculation, it is obtained that:
[0046] Preliminary estimation of key jet parameters: the velocity v0 at the nozzle exit = 33 m / s, the diameter d of the nozzle exit = 0.3 cm, and the target distance L of the water jet = 1 cm.
[0047] (3) Making the K file
[0048] Preliminarily determine the dimensions of the 1 / 2 jet model. The dimensions of the soil 3 model are 6 cm in length, 4 cm in width, and 9 cm in height; the dimensions of the water area 2 are 5 cm in length, 5 cm in width, and 10 cm in height; the diameter of the jet source 1 is 0.3 cm, the height is 0.1 cm, and the target distance of the water jet is 1 cm; the model of the directly buried submarine cable 4 is 0.5 cm in diameter and 6 cm in length.
[0049] Mesh generation is carried out in ANSYS_APDL. Define the three-dimensional solid element SOLID_164 element and assign 4 kinds of empty materials. Co-node the jet source 1 and the water area 2, and then establish the soil model and the submarine cable model. The soil 3 and the submarine cable 4 are required to be co-noded, and the size of the soil model is required to eliminate the influence of boundary effects. Finally, mesh generation is carried out on the model, and the meshes of the water area and the soil near the jet failure should be refined. The number of elements of the jet source 1 is 95, the number of elements of the water area 2 is 240576, the number of elements of the soil 3 is 162060, and the number of elements of the directly buried submarine cable 4 is 2820. The model is as shown in Figure 2 shown, export the K file and save the model.
[0050] (3) Modify the K file
[0051] Import the K file into LS_PREPOST.
[0052] ① Define materials: In the soil material model, input the soil physical properties in step (1) into the keyword *MAT_147_FHWA_SOIL and the erosion algorithm *MAT_ADD_ERODION. The soil element algorithm uses *SECTION_SOILD, and the parameters remain default. The material model keyword of the directly buried submarine cable 4 is *MAT_RIGID. In this embodiment, the density is 2.7, the Young's modulus is 7.0, and the Poisson's ratio is 0.3. The element algorithm of the directly buried submarine cable 4 uses *SECTION_SOILD, and the parameters remain default. The material model keywords of the jet source 1 and the water area 2 are *MAT_009_NULL, and the density is 1.0. At the same time, define the equation of state *EOS_GRUNERSEN. The ELFORM of the *SECTION_SOILD of the jet source 1 and the water area 2 is set to 11, and the rest remain default. Assign the above parameters to different model PARTs. Define the ALE materials for the jet source 1 and the water area 2 respectively, with the keyword *ALE_MULTI_MATERIAL_GROUP, and use the ALE algorithm.
[0053] ② Define boundary conditions: Fully constrain the bottom of the soil, restrict the translation in the normal direction of the symmetry plane of the 1 / 2 jet model, and restrict the rotation in the other two directions; Apply non-reflecting boundary conditions to the sides and bottom of the soil 3 and the water area 2 to simulate an infinitely large space area, with the keyword *BOUNDARY_NON_REFELECTING.
[0054] ③ Define contact: Combine the soil mass 3 and the directly buried submarine cable 4 into one PART, and combine the water area 2 and the jet source 1 into one PART. Define the fluid-structure interaction between the soil mass 3 and the directly buried submarine cable 4 and the jet source 1 and the water area 2 through the keyword *CONSTRAINED_LAGRANGE_IN_SOILD. The slave surface is the PART composed of the soil mass 3 and the directly buried submarine cable 4, and the master surface is the PART composed of the water area 2 and the jet source 1.
[0055] ④ Define the load: The continuous jetting of the jet is manifested as a continuous stream of fluid with a vertical velocity emerging from the nozzle outlet. By setting the jet velocity function curve and associating the curve with the velocity value of the jet fluid through the keyword *BOUNDARY_PRESCRIBED_MOTION_SET, a continuously jetting jet source can be achieved. In this embodiment, the jet velocity is equal to the velocity at the nozzle outlet, which is 33 m / s.
[0056] ⑤ Define the control equations: The bulk viscosity *CONTROL_BULK_VISCOSITY, keep the default; For ALE and Euler calculations, set the global control parameter *CONTROL_ALE, keep the default; Control the hourglass *CONTROL_HOURGLASS, keep the default; Calculate the time *CONTROL_TERMINATION, the calculation duration is 2000 us; The time step *CONTROL_TIMESTEP, ENDTIM is 10; The output frequency *DATABASE_BINARY_D3PLOT, DT is 25.
[0057] Finally, the corrected K file is obtained.
[0058] (5) Prepare the simulation model
[0059] In the LS_DYNA software, open the Solver menu, select the Start LS_DYNA Analysis command button, and enter the corrected K file in the Start Input and Output dialog box for solution analysis. The simulation model is obtained through this simulation analysis.
[0060] (6) Obtain the simulation results
[0061] In LS_PREPOST, post-process the simulation model obtained in (5) and open the LS_DYNA Binary Plot file. First, extract the time-displacement history data of the soil elements and plot the time-displacement curve in the jet direction to observe the soil erosion displacement, which is used to determine whether the soil erosion displacement reaches the buried depth of the submarine cable. Second, measure the maximum failure width of the elements above the directly buried submarine cable 4 to compare whether the maximum failure width is greater than the diameter of the directly buried submarine cable 4. Third, extract the historical data of the stress and strain of the directly buried submarine cable 4 elements in the model, save them as the model stress-strain file, then extract the model stress-strain file in Xyplot to plot the model stress-strain curve, and compare the model stress-strain curve with the actual stress-strain curve of the directly buried submarine cable to analyze the damage condition of the submarine cable.
[0062] The simulation results can be obtained through the above post-processing.
[0063] (7) Re-determine the key jet parameters
[0064] The preliminary estimated values of the key jet parameters obtained in the above (2) are: the velocity v0 at the nozzle outlet is 33 m / s, the nozzle outlet diameter d is 0.3 cm, and the target distance L of the water jet is 1 cm. The preliminary estimated key jet parameters may not meet the requirements of the direct buried submarine cable protection work. Therefore, it is necessary to analyze the simulation results obtained from the post-processing in (6) and re-determine the key jet parameters.
[0065] Specifically, analyze the simulation results obtained from the post-processing in (6), evaluate whether the key jet parameters meet the requirements through the simulation results. If they meet the requirements of the direct buried submarine cable protection work, then take the preliminary estimated key jet parameters in step two as the accurate key jet parameters. If they do not meet the requirements of the direct buried submarine cable protection work, then adjust the preliminary estimated key jet parameters and re-execute (3) to (6) until the accurate key jet parameters are determined.
[0066] More specifically, if the soil erosion displacement of the time-displacement curve in the jet direction in (6) does not reach the burial depth of the directly buried submarine cable 4, it indicates that the jet energy is small and the cleaning task of the directly buried submarine cable 4 cannot be completed. It is necessary to increase the jet velocity or decrease the jet target distance, that is, increase the velocity v0 at the nozzle outlet or decrease the target distance L of the water jet, so as to increase the pit depth to achieve the cleaning purpose; if the maximum damage width is less than the diameter of the directly buried submarine cable 4, the cleaning task cannot be completed either, and it is necessary to increase the nozzle outlet diameter d of the jet to expand the maximum damage width; if the directly buried submarine cable 4 is damaged, it indicates that the jet energy is large, and it is necessary to decrease the jet velocity, jet target distance or jet diameter, that is, decrease the velocity v0 at the nozzle outlet, the target distance of the water jet or the nozzle outlet diameter d. According to the above analysis of the simulation results, adjust the key jet parameters, and re-execute steps (3) to (6) until the jet soil erosion displacement exceeds the burial depth of the directly buried submarine cable 4, the maximum damage width is greater than the diameter of the directly buried submarine cable 4, and the directly buried submarine cable 4 is not damaged. It can be determined that under the conditions of these key jet parameters, the requirements for the de-protection work of the directly buried submarine cable are met.
[0067] In the embodiment, the simulation results are analyzed. Within 2000 us, the jet soil erosion displacement, that is, the erosion depth, is 5 cm, the maximum damage width is 0.5 cm, and the submarine cable is not damaged, which already meets the requirements for the de-protection work of the directly buried submarine cable. There is no need to adjust the key jet parameters. The determined key jet parameters are: the velocity v0 at the nozzle outlet = 33 m / s, the nozzle outlet diameter d = 0.3 cm, and the target distance L of the water jet = 1 cm.
[0068] (8) Guide the selection of jet equipment and parameter design
[0069] Adopting a bottom-up method, among the key jet parameters determined in step (7), the velocity v0 at the nozzle outlet corresponds to the jet velocity, and thus the pump head of the jet equipment can be determined; the nozzle outlet diameter d corresponds to the jet diameter, and thus the nozzle diameter of the jet equipment can be determined; the target distance L of the water jet corresponds to the jet target distance, which can be used to guide the nozzle installation method of the jet equipment. In addition, the jet flow rate can be calculated from the jet velocity and jet diameter, thereby determining the flow rate of the pump and guiding the selection design of the pump of the jet equipment.
[0070] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings and specific embodiments. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.
Claims
1. A determination method for a jet device in the work of removing the protection of a directly buried submarine cable, characterized in that, It includes the following steps: Step 1: Measure the soil physical properties of the soil body in the directly buried submarine cable deprotection working section, including: specific gravity, density, water content, bulk modulus, shear modulus, friction angle, cohesion, and critical failure pressure; Step 2: According to the soil physical properties and the necessary conditions for soil jet failure: the average force of the jet within the half-width range of the soil surface is greater than the critical failure pressure of the soil, preliminarily estimate the key jet parameters, including: the velocity v0 at the nozzle outlet, the nozzle outlet diameter d, and the target distance L of the water jet; Step 3: Based on the preliminarily estimated key jet parameters, establish a jet soil-breaking model of the directly buried submarine cable in ANSYS, divide the mesh, and export the K file; Step 4: Modify the K file in LS_PREPOST, use the ALE algorithm, define materials, boundary conditions, contacts, loads, and control equations to obtain a modified K file; Step 5: Import the modified K file into LS_DYNA for solution analysis to obtain a simulation model; Step 6: Perform post-processing on the simulation model in LS_PREPOS to obtain the simulation results of the directly buried submarine cable deprotection work; Step 7: Analyze the simulation results. If the requirements of the directly buried submarine cable deprotection work are met, take the key jet parameters preliminarily estimated in Step 2 as the accurate key jet parameters. If the requirements of the directly buried submarine cable deprotection work are not met, adjust the preliminarily estimated key jet parameters and re-execute Steps 3 to 6 until the accurate key jet parameters are determined; Step 8: Determine the jet equipment parameters according to the accurate key jet parameters, including: pump head, jet diameter, nozzle installation method, and pump selection, to guide the selection and parameter design of the jet equipment.
2. The determination method of a jet device for the protection work of a directly buried submarine cable according to claim 1, characterized in that: In Step 1, in the measurement of soil physical properties, the specific gravity is measured by the pycnometer method, the density is measured by the cutting ring method, the water content is measured by the drying method, the shear modulus and bulk modulus are measured using a penetrometer and K0 consolidation experiment, the friction angle and cohesion are measured by direct shear experiment, and the critical failure stress is measured by triaxial compression experiment.
3. The determination method of a jet device for the protection work of a directly buried submarine cable according to claim 2, characterized in that: In the second step, the average acting force of the jet within the half-width range on the soil surface is as follows: Among them, v0 is the velocity at the nozzle outlet, ρ is the density of seawater, d is the nozzle outlet diameter, α is the water jet diffusion angle of the nozzle, l0 is the constant velocity core length of the water jet, and L is the target distance of the water jet; Greater than the critical failure pressure of the soil mass. First, select the nozzle outlet diameter d and the target distance L of the water jet according to the actual construction process of the direct-buried submarine cable protection work, then the range value of the velocity v0 at the nozzle outlet can be obtained, so as to preliminarily estimate the key jet parameters: the velocity v0 at the nozzle outlet, the nozzle outlet diameter d, and the target distance L of the water jet.
4. The determination method of a jet device for the protection work of a directly buried submarine cable according to claim 3, characterized in that: In Step 3, when establishing the jet soil-breaking model of the directly buried submarine cable, first preliminarily establish the 1 / 2 jet model size, then use the SOID_164 solid element, assign 4 kinds of empty materials, make the jet source (1) and the water area (2) share nodes, then establish the soil body model and the submarine cable model, and require the soil body (3) and the directly buried submarine cable (4) to share nodes, and require the model size to eliminate the influence of boundary effects; in the mesh division, perform mesh division on the model, and encrypt the water area mesh and the soil body mesh near the jet failure.
5. The determination method of a jet device for the protection work of a directly buried submarine cable according to claim 4, characterized in that: In Step 4, the steps to modify the K file are as follows: ① Define materials: In the soil material model, input the soil physical properties obtained in Step 1 into the keyword *MAT_147_FHWA_SOIL and the erosion algorithm *MAT_ADD_ERODION. The soil element algorithm uses *SECTION_SOILD, and the parameters remain default. The material model keyword for the directly buried submarine cable (4) is *MAT_RIGID, including density, Young's modulus, and Poisson's ratio. The element algorithm for the directly buried submarine cable (4) uses *SECTION_SOILD, and the parameters remain default. The model keywords for the jet source (1) and the water area (2) are *MAT_009_NULL, the equation of state is defined as *EOS_GRUNERSEN, and the ELFOR of the element algorithm *SECTION_SOILD for the water area (2) and the jet source (1) is set to a fixed value, and the rest remain default. Assign the above parameters to the model, and define the ALE materials for the jet source (1) and the water area (2) respectively, with the keyword *ALE_MULTI_MATERIAL_GROUP, and use the ALE algorithm. ② Define boundary conditions: Fully constrain the bottom of the soil body, restrict the translation in the normal direction of the symmetry plane of the 1 / 2 jet model, and restrict the rotation in the other two directions. Apply non-reflecting boundary conditions to the sides and bottom of the soil body (3) and the water area (2) to simulate an infinitely large space area, with the keyword *BOUNDARY_NON_REFELECTING. ③ Define contact: Define the fluid-structure interaction between the soil body (3), the directly buried submarine cable (4), the jet source (1), and the water area (2) through the keyword *CONSTRAINED_LAGRANGE_IN_SOILD. The slave surface SLAVE is the PART composed of the soil body (3) and the directly buried submarine cable (4), and the master surface MASTER is the PART composed of the jet source (1) and the water area (2). ④ Define loads: The continuous jet injection is manifested as a continuous flow of fluid with a vertical velocity emerging from the nozzle outlet. By setting the injection velocity function curve and associating the curve with the velocity value of the jet fluid through the keyword *BOUNDARY_PRESCRIBED_MOTION_SET, a jet source with continuous injection can be achieved. ⑤ Define control equations: The bulk viscosity *CONTROL_BULK_VISCOSITY remains default; the global control parameters *CONTROL_ALE for ALE and Euler calculations remain default; the control of hourglass *CONTROL_HOURGLASS remains default; the calculation time *CONTROL_TERMINATION, the time step *CONTROL_TIMESTEP, and the output frequency *DATABASE_BINARY_D3PLOT are all determined according to the requirements of the directly buried submarine cable protection work.
6. A method for determining a jet device for the protection work of a directly buried submarine cable, according to any one of claims 1-5, characterized in that: In the sixth step, the simulation results of the direct-buried submarine cable de-protection work include: ① Extract the time-displacement historical data of the soil elements, and draw the time-displacement curve in the jet direction to obtain the soil erosion displacement; ② Measure the maximum damage width of the elements above the direct-buried submarine cable (4); ③ Extract the historical data of the stress and strain of the direct-buried submarine cable (4) elements in the model and save them as a model stress-strain file. Extract the model stress-strain file in Xyplot to draw the model stress-strain curve, and obtain the comparison diagram between the model stress-strain curve and the actual direct-buried submarine cable stress-strain curve.
7. A method for determining a jet device for direct-buried submarine cable protection work according to claim 6, characterized in that: In the seventh step, the situations where the simulation results do not meet the requirements of the direct-buried submarine cable de-protection work and the key jet parameters initially estimated need to be adjusted include: ① If the soil erosion displacement of the time-displacement curve in the jet direction does not reach the burial depth of the direct-buried submarine cable (4), then it is necessary to increase the nozzle outlet velocity v0 or decrease the water jet target distance L; ② If the maximum damage width of the elements above the direct-buried submarine cable (4) is less than the diameter of the direct-buried submarine cable (4), then it is necessary to increase the nozzle outlet diameter d of the jet; ③ In the comparison diagram between the model stress-strain curve and the actual direct-buried submarine cable stress-strain curve, if the direct-buried submarine cable (4) in the model is damaged, then it is necessary to decrease the nozzle outlet velocity v0, the water jet target distance or the nozzle outlet diameter d.
8. The determination method of a jet device for the protection work of a directly buried submarine cable according to claim 7, characterized in that: In the eighth step, determine the pump head of the jet equipment according to the nozzle outlet velocity v0, determine the nozzle diameter of the jet equipment according to the nozzle outlet diameter d, and guide the nozzle installation method of the jet equipment according to the water jet target distance L; Calculate the jet flow rate according to the jet velocity and jet diameter, so as to determine the flow rate of the pump and guide the selection design of the pump of the jet equipment.