Subsea pipeline protection method, system and apparatus based on fluid mechanics analysis

Abstract

The application provides a submarine pipeline protection method, system and device based on fluid mechanics analysis, water depth, wave, sea current and soil parameters of a sea area where a submarine pipeline is located are acquired. A bottom flow velocity calculation module calculates wave bottom flow velocity and superimposes sea current flow velocity. A soil erosion calculation module calculates critical flow velocity causing soil particle movement according to soil parameters. A fluid mechanics iteration analysis module constructs a cement block model, analyzes multiple working conditions, calculates local flow velocity and compares it with the critical flow velocity, adjusts suitable cement block size, and iteratively calculates to allow the cement block size. A result output module gives a suitable treatment scheme according to the comprehensive analysis result, including end concrete block size, whether a geomembrane bag or a flexible protection pad is needed, and estimated treatment cost. The application has the beneficial effect that the suitable treatment scheme is given in the submarine pipeline treatment scheme design stage, which can significantly reduce the risk of secondary treatment of the submarine pipeline.

Description

Technical Field

[0001] This invention relates to the field of subsea pipeline protection technology, and more specifically to a subsea pipeline protection method, system, and device based on fluid dynamics analysis. Background Technology

[0002] Fishing activities, anchoring / towing operations, ship collisions, dredging operations, trenching or piling and other construction work, falling objects, and human sabotage can all damage subsea pipelines. To prevent third-party damage, post-trenching techniques are typically used during the construction phase to ensure a certain burial depth. However, due to factors such as terrain and erosion, subsea pipelines often become exposed or even suspended during operation, affecting their structural safety. Therefore, pipeline operating companies regularly conduct external pipeline inspections and employ appropriate pipeline protection technologies for remediation.

[0003] Currently, the main protection technologies include cement briquettes, cement sandbag backfilling, post-ditch excavation, flexible protective mats, geomembrane bags, and riprap protection. Among these, cement briquettes are the most commonly used technology for exposed subsea pipelines. Extensive research has been conducted on cement briquette remediation technology, including methods for placing cement briquettes on subsea pipelines, research on cement briquette laying devices, and research on the shape and spacing of cement briquettes. However, in practical applications, because cement briquettes alter the local flow field, further exposure of the subsea pipeline has occurred. These exposed areas are mainly located at the edges of the briquette-covered sections, in the gaps between briquette covers, and in the areas between briquette covers, such as... Figure 5 As shown, the extent of further exposure of the subsea pipeline is influenced by a combination of factors, including the wave and current parameters of the surrounding sea area, the seabed soil conditions, and the size of the concrete blocks. Therefore, the exposure of the concrete block ends due to the failure to comprehensively consider these factors compromises the safety of the pipeline. Summary of the Invention

[0004] This invention overcomes the shortcomings of the prior art and provides a method, system and device for protecting subsea pipelines based on fluid dynamics analysis.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] The subsea pipeline protection method based on fluid dynamics analysis includes the following steps:

[0007] Step 1: Obtain parameters for water depth, waves, ocean currents, and soil conditions;

[0008] Step 2: Water depth and wave parameters are categorized into extremely shallow water, finite water depth, and deep water. The bottom current velocity under wave action is calculated based on the water depth and wave type using the following formula.

[0009] Deep water:

[0010] Limited water depth:

[0011] Extremely shallow water depth:

[0012] Wave bottom velocity:

[0013] in: --wavelength; —Acceleration due to gravity; —Wave cycles; ——Water depth.

[0014] Step 3: Calculate the critical erosion shear stress based on the soil parameters obtained in Step 1, and calculate the shear stress generated based on the flow velocity. The specific formulas are as follows.

[0015] .

[0016] in, —Critical erosion shear stress; , — Coefficients and proportionality coefficients; —Soil particle density; —Soil density; —Soil particle size; — Angle of static friction; —Shear strength;

[0017]

[0018] in, —Shear stress caused by flow velocity; C —Chezzi coefficient.

[0019] Step 4: Establish an overall physical model. Using the bottom flow velocity calculated in Step 2 and the angle with the preset pipe direction as input parameters, simulate and calculate the local flow velocity and the shear stress caused by the corresponding flow velocity. Calculate the bottom shear stress generated by the local flow velocity in Step 3 and compare it with the critical shear stress. When the calculated bottom shear stress is greater than the critical shear stress, adjust the height of the cement block in the model and perform iterative calculations until the cement block height that meets the local flow velocity requirements is given.

[0020] Step 5: Output the results, providing the method for protecting the subsea pipeline.

[0021] In step 1, wave parameters include wave height and period; ocean current parameters include seabed current velocity; and soil parameters include soil density, particle size, internal friction angle, shear strength, and cohesion.

[0022] The specific steps of step 4 are as follows:

[0023] S1. Establish a physical model, abstract it into a mathematical and mechanical model, and determine the spatial influence area of ​​the geometry to be analyzed.

[0024] S2. Establish a CAD model of the entire geometric shape and its spatial influence area, and divide the outer surface of the geometry and the entire calculation area into spatial meshes.

[0025] S3. Add the initial conditions required for the solution, including the boundary conditions at the inlet and outlet and their corresponding flow velocity and pressure conditions;

[0026] S4. Select the K-epsilon turbulence model, set the conditions for controlling the solution process and accuracy, solve the relevant parameters, and save the data file results.

[0027] S5. Select a suitable post-processor to read the calculation result file and perform analysis and display.

[0028] In step S1, the spatial influence area of ​​the geometry is 5 times the size of the cement block.

[0029] In step S2, when the grid size of the cement block is one, the grid density within the grid ruler range of the cement block is consistent with that of the cement block; when the grid size of the cement block is greater than one, the grid density is 3-5 times the grid size of the cement block.

[0030] Step 5 uses the local flow velocity and the corresponding shear stress calculated iteratively in Step 4. When the shear stress obtained in Step 4 is less than the critical erosion shear stress obtained in Step 3, the height of the cement block corresponding to the shear stress value is obtained. It is then determined whether the height of the cement block is less than the set value. When the height of the cement block obtained by iterative calculation is less than the set value, a treatment method of hydraulic membrane bag or flexible pad is given. When the height of the cement block obtained by iterative calculation is greater than the set value, a treatment method of cement block is given.

[0031] The height of the cement block is set at 150mm.

[0032] Step 5, the method of protecting the subsea pipeline, includes the size of the end concrete block and whether geomembrane bags or flexible protective pads are needed, as well as the related estimated costs and arrangements.

[0033] The subsea pipeline protection method based on fluid dynamics analysis includes a parameter input module, a bottom flow velocity calculation module, a soil erosion calculation module, a fluid dynamics analysis module, and a result output module. The parameter input module is used to obtain the water depth, wave, ocean current, and soil parameters of the sea area where the pipeline is located. The bottom flow velocity calculation module is used to calculate the wave bottom flow velocity and superimpose the ocean current velocity. The soil erosion calculation module is used to calculate the critical flow velocity that causes soil particle movement based on the soil parameters. The fluid dynamics analysis module is used to construct a cement block model, calculate the local flow velocity and compare it with the critical flow velocity, adjust the appropriate cement block size, and iteratively calculate to the allowable cement block size. The result output module is used to provide applicable treatment solutions based on the comprehensive analysis results, including the size of the end concrete block, whether geomembrane bags or flexible protective pads are needed, and the estimated treatment cost.

[0034] A subsea pipeline protection device based on fluid dynamics analysis includes a memory and a processor, wherein the memory stores executable code, and the processor executes the executable code.

[0035] The beneficial effects of this invention are as follows: By providing an applicable treatment plan during the design phase of the subsea pipeline treatment scheme, the risks of secondary treatment of subsea pipelines can be significantly reduced. This not only saves on overall engineering treatment costs, but more importantly, ensures the safe operation of the subsea pipeline, avoiding damage from third parties and structural damage caused by partial suspension. It effectively solves the problem of high costs incurred due to secondary treatment of subsea pipelines and avoids the waste of human and financial resources. Attached Figure Description

[0036] Figure 1 This is a flowchart of the present invention;

[0037] Figure 2 It is a graph of flow velocity iteration calculation;

[0038] Figure 3 This is a typical cross-sectional diagram of cement briquettes.

[0039] Figure 4 This is a typical cross-sectional view of the membrane bag installation;

[0040] Figure 5 This is a schematic diagram showing the location of the exposed subsea pipeline;

[0041] In the diagram: 1 represents an exposed pipeline. Detailed Implementation

[0042] The technical solution of the present invention will be further described below through specific embodiments.

[0043] Example

[0044] like Figure 1As shown, the working principle of this invention is as follows: by acquiring the water depth, wave, current, and soil parameters of the sea area where the subsea pipeline is located, the wave bottom velocity and the critical velocity causing soil particle movement are calculated. A cement block model is constructed, and multi-condition analysis is performed to calculate the local velocity and compare it with the critical velocity. The appropriate cement block size is adjusted, and iterative calculations are performed until the allowable cement block size is reached. Based on the comprehensive analysis results, an applicable remediation plan is given, including the size of the end concrete block, whether geomembrane bags or flexible protective mats are needed, and the estimated remediation cost. Figure 3 and Figure 4 Structural diagrams showing typical cross-sections of cement blocks and membrane bags.

[0045] Taking a domestic subsea pipeline as an example, the marine environment conditions are as follows: water depth 7m, bottom current velocity 0.69m / s, wave height 2.21m, wave period 3.3s, soil particle size 4.5E-5m, friction angle 23.4°, and shear strength 12Kpa. Several investigations show that the overall burial depth has not changed significantly. The entire subsea pipeline shows a slight tendency for seabed erosion. Exposed pipelines are mainly located at the edges of ballast-covered sections, in the gaps between ballast covers, and in the areas between ballast covers. To prevent further exposure or even suspension, the exposed sections need to be treated. The method of this invention is used for operation, as follows:

[0046] 1. Based on water depth, wave height, and wave period, the water is determined to be of finite depth, with a wavelength of [wavelength value missing]. =16.8m, the current velocity caused by the waves is =0.31m / s.

[0047] 2. Based on soil parameters, the critical erosion shear stress The calculated value is 1.23 Pa.

[0048] 3. Calculate the bottom current velocity based on environmental conditions. In this case, the ocean current velocity is set to 0.69 m / s, the wave-induced velocity is 0.31 m / s, and the combined velocity is 1 m / s. It is assumed that the velocity and direction of the current remain constant throughout the process, and the ocean current direction is set to be perpendicular to the direction of the subsea pipeline.

[0049] 4. A CFD model was established based on the dimensions of the cement block, and a uniform flow velocity at the bottom was input. The original dimensions of the cement block (length × width × height) were 4 × 3.1 × 0.45 m. Through iterative calculation, the incoming flow at the upstream face forms a vortex at the location of the concrete block, which will cause siltation, with an affected range of 0.72 meters.

[0050] 5. At the back-flow side, the resulting eddies will cause siltation near the concrete blocks, affecting an area of ​​1.98 meters. Due to tidal fluctuations, scouring and backfilling occur on both sides of the cement blocks. Calculation results are attached. Figure 2 As shown.

[0051] 6. Through iterative calculations, when a geomembrane bag with a height of 150mm is laid at the end of the cement block, the local flow velocity is 0.3m / s, and the resulting shear stress is: The stress was 0.362 Pa, which is less than the critical shear stress of the soil (1.23 Pa). Therefore, the final treatment plan was to lay geomembrane bags with a height of 150 mm at the ends of the cement blocks.

[0052] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for protecting subsea pipelines based on fluid dynamics analysis, characterized in that... The steps include the following: Step 1: Obtain parameters for water depth, waves, ocean currents, and soil conditions; Step 2: Water depth wave parameters are categorized into extremely shallow water depth, finite water depth, and deep water. The wave bottom velocity under wave action is calculated based on the water depth and wave type using the following formula. Deep water: Limited water depth: Extremely shallow water depth: Wave bottom velocity: in: --wavelength; —Acceleration due to gravity; —Wave cycles; ——Water depth; ——wave height; Step 3: Calculate the critical erosion shear stress based on the soil parameters obtained in Step 1, and calculate the shear stress generated based on the flow velocity. The specific formulas are as follows. in, —Critical erosion shear stress; , — Coefficients and proportionality coefficients; —Soil particle density; —Soil density; —Soil particle size; — Angle of static friction; —Shear strength; in, —Shear stress caused by flow velocity; C —Checzee coefficient; Step 4: Establish a CFD model based on the size of the cement block. Use the wave bottom velocity and the angle between the wave direction and the preset pipe axis direction calculated in Step 2 as input parameters to simulate and calculate the local flow velocity around the pipe and the block, and the bottom shear stress generated by the corresponding flow velocity. Compare the calculated bottom shear stress with the critical erosion shear stress. When the calculated bottom shear stress is greater than the critical erosion shear stress, adjust the height of the cement block in the model and perform iterative calculations until the cement block height that meets the local flow velocity requirements is obtained. Step 5: Output the results, providing the method for protecting the subsea pipeline.

2. The subsea pipeline protection method based on fluid dynamics analysis according to claim 1, characterized in that: In step 1, wave parameters include wave height and period; ocean current parameters include seabed current velocity; and soil parameters include soil density, particle size, internal friction angle, shear strength, and cohesion.

3. The subsea pipeline protection method based on fluid dynamics analysis according to claim 1, characterized in that: The specific steps of step 4 are as follows: S1. Establish a physical model, abstract it into a mathematical and mechanical model, and determine the spatial influence area of ​​the geometry to be analyzed. S2. Establish a CAD model of the entire geometric shape and its spatial influence area, and divide the outer surface of the geometry and the entire calculation area into spatial meshes. S3. Add the initial conditions required for the solution, including the boundary conditions at the inlet and outlet and their corresponding flow velocity and pressure conditions; S4. Select the K-epsilon turbulence model, set the conditions to control the solution process and accuracy, solve for the relevant parameters, and save the data file results; S5. Select the post-processor to read the calculation result file and perform analysis and display.

4. The subsea pipeline protection method based on fluid dynamics analysis according to claim 3, characterized in that: In step S1, the spatial influence area of ​​the geometry is 5 times the size of the cement block.

5. The subsea pipeline protection method based on fluid dynamics analysis according to claim 3, characterized in that: In step S2, when the grid size of the cement block is one, the grid density within the grid ruler range of the cement block is consistent with that of the cement block; when the grid size of the cement block is greater than one, the grid density is 3-5 times the grid size of the cement block.

6. The subsea pipeline protection method based on fluid dynamics analysis according to claim 1, characterized in that: In step 4, the local flow velocity and the corresponding bottom shear stress are calculated iteratively. When the bottom shear stress obtained in step 4 is less than the critical erosion shear stress obtained in step 3, the height of the cement block corresponding to this bottom shear stress value is obtained. Determine whether the height of the cement block is less than the set value. If the height of the cement block obtained by iterative calculation is less than the set value, provide a treatment method of hydraulic membrane bag or flexible protective pad. If the height of the cement block obtained by iterative calculation is greater than the set value, provide a treatment method of cement block.

7. The subsea pipeline protection method based on fluid dynamics analysis according to claim 6, characterized in that: The height of the cement block is set at 150mm.

8. The subsea pipeline protection method based on fluid dynamics analysis according to claim 1, characterized in that: Step 5, the method of protecting the subsea pipeline, includes the size of the end concrete block and whether geomembrane bags or flexible protective pads are needed, as well as the related estimated costs and arrangements.

9. A subsea pipeline protection system based on fluid dynamics analysis, used to perform the subsea pipeline protection method based on fluid dynamics analysis as described in any one of claims 1-8, characterized in that: The system includes a parameter input module, a bottom current velocity calculation module, a soil erosion calculation module, a fluid dynamics analysis module, and a result output module. The parameter input module is used to obtain the water depth, wave, ocean current, and soil parameters of the sea area where the subsea pipeline is located. The bottom current velocity calculation module is used to calculate the wave bottom current velocity and superimpose the ocean current velocity. The soil erosion calculation module is used to calculate the critical velocity that causes soil particle movement based on the soil parameters. The fluid dynamics analysis module is used to construct a cement block model, calculate the local velocity and compare it with the critical velocity, adjust the appropriate cement block size, and iterate the calculation until the allowable cement block size is reached. The result output module is used to provide applicable remediation solutions based on the comprehensive analysis results, including the size of the end concrete block, whether geomembrane bags or flexible protective mats are needed, and the estimated remediation cost.

10. A subsea pipeline protection device based on fluid dynamics analysis, characterized in that: The method includes a memory and a processor, wherein the memory stores executable code, and when the processor executes the executable code, it implements the method of any one of claims 1-8.

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