A marine riser structure and a method of parameter optimization thereof

Abstract

The application provides a kind of marine riser structure, two line pipes are symmetrically arranged on both sides of the main pipe, and the line pipes are parallel to the main pipe. The application also provides a corresponding size parameter optimization method for the riser structure. First, the response relationship between the pipe diameter ratio, the spacing ratio and the incident angle at different flow rates is studied, and then the NSGA II algorithm is used for multi-objective optimization. Finally, the best size parameters are selected based on the flow rate conditions of the optimization results. Through the above structure and parameter optimization, vortex-induced vibration can be effectively suppressed and water flow resistance can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of marine pipeline technology, specifically relating to a marine riser structure and its parameter optimization method. Background Technology

[0002] A marine riser is a vertically installed pipeline in seawater, widely used on offshore drilling platforms as an oil or gas pipeline. Risers experience vortex-induced vibrations under the influence of ocean currents, and resonance can occur within a certain reduced velocity range, seriously threatening the stability and safety of the riser system. To reduce vortex-induced vibrations caused by ocean currents, a common practice is to add corresponding damping structures to the riser surface; however, this significantly increases the water flow resistance experienced by the riser, thus reducing its material lifespan. Furthermore, a riser system is not simply an oil pipeline; it also includes corresponding control lines. Some existing marine risers place the control lines inside the pipeline, which can reduce drag to some extent, but it brings significant difficulties to both initial manufacturing and subsequent maintenance. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a marine riser structure and its parameter optimization method to alleviate vibration problems caused by ocean currents affecting the riser.

[0004] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0005] A marine riser structure: two line pipes are symmetrically arranged on both sides of the main pipe, the line pipes are parallel to the main pipe, wherein the outer diameter of the main pipe is D, the outer diameter of the line pipe is d, the distance between the line pipe and the main pipe is G, and the angle of attack of the line connecting the centers of the line pipes relative to the direction of water flow is α.

[0006] Furthermore, the line pipe is fixed to the main pipe by multiple brackets, and the distance between adjacent fixing points is L.

[0007] Furthermore, L = 10D.

[0008] A parameter optimization method for the above-mentioned marine riser structure: First, obtain d / D, G / D, and α at different flow velocities U r Below for amplitude A * and resistance C D The response relationship, then with A * Minimum sum C D Multi-objective optimization is performed with the goal of minimizing, and finally d / D, G / D, and α are selected based on the optimization results.

[0009] Further, the response relationship is obtained by Box-Behnken Design and Response Surface Method analysis.

[0010] Further, the response relationship is:

[0011] A * = 0.9325 - 6.785 · d / D - 2.63833 · G / D + 0.00742778 · a + 0.1155 · U r + 0.75 · d / D · G / D - 0.049333 · d / D · a + 0.315 · d / D · U r + 0.021333 · G / D · a + 0.0775 · G / D · U r - 0.00295 · a · U r + 21.73333 · d / D 2 + 4.43333 · G / D 2 + 0.000239815 · a 2 - 0.00629167 · U r 2 ;

[0012] C D = 2.83221 - 21.73333 · d / D + 6.23667 · G / D - 0.032361 · a + 0.292 · U r - 1.6 · d / D · G / D - 0.16667 · d / D · a + 3.565 · d / D · U r + 0.12567 · G / D · a - 0.22 · G / D · U r + 0.00583333 · a · U r + 8 · d / D 2 - 12.4375 · G / D 2 + 0.0000194444 · a 2 - 0.09125 · U r 2 .

[0013] Further, the multi-objective optimization is performed by Nondominated Sorting Genetic Algorithm II genetic algorithm.

[0014] Further, when U r = 4, d / D takes the value of 0.18, G / D takes the value of 0.13, and a takes the value of 27.2°; when U r = 5, d / D takes the value of 0.15, G / D takes the value of 0.17, and a takes the value of 24.1°; when U rWhen d / D=6, d / D takes the value 0.17, G / D takes the value 0.1, and a takes the value 30°.

[0015] The present application has the following beneficial effects:

[0016] (1) The present application provides a marine riser structure, wherein two line pipes are arranged in parallel and symmetrically outside the main pipe, and through the improvement of the structure, on the one hand, vortex-induced vibration can be inhibited and drag can be reduced, and on the other hand, the external line pipes are also more conducive to later maintenance.

[0017] (2) On the basis of the marine riser structure, the present application further provides an optimization method of corresponding size parameters, wherein through the study of the response relationship between the pipe diameter ratio, the spacing ratio and the flow angle to the amplitude and the drag under different flow velocities, and further using the related optimization algorithm, the optimal parameter values are optimized under different flow velocities, so as to achieve the best balance between the amplitude and the drag.

[0018] (3) The marine riser structure and the parameter optimization method thereof have less changes in the structure level compared with some common riser vibration suppression structure technical solutions, are easier to produce and process, have little change in cost burden, and are conducive to popularization and implementation. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a marine riser structure diagram of the present application;

[0020] Figure 2 is a marine riser cross-sectional size diagram of the present application;

[0021] Fig. 3(a) is a response surface diagram between the pipe diameter ratio and the spacing ratio to the amplitude;

[0022] Fig. 3(b) is a response surface diagram between the pipe diameter ratio and the flow angle to the amplitude;

[0023] Fig. 3(c) is a response surface diagram between the spacing ratio and the flow angle to the amplitude;

[0024] Fig. 4(a) is a response surface diagram between the pipe diameter ratio and the spacing ratio to the drag;

[0025] Fig. 4(b) is a response surface diagram between the pipe diameter ratio and the flow angle to the drag;

[0026] Fig. 4(c) is a response surface diagram between the spacing ratio and the flow angle to the drag;

[0027] Figure 5 is an optimization curve diagram between the amplitude and the drag.

[0028] Reference signs:

[0029] 1-main pipe; 2-line pipe; 3-bracket. Detailed Implementation

[0030] Embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein similar or identical reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0031] I. Structural Setup

[0032] like Figure 1 and Figure 2 The marine riser shown includes a main pipe 1 and two line pipes 2. The main pipe 1 is used for oil or gas transmission, and the line pipes 2 are used to run relevant control wires. The line pipes 2 are connected and fixed to the main pipe 1 along the length direction by several supports 3. Along the axial direction of the main pipe, the distance between two adjacent fixed points is L. The two line pipes 2 are symmetrically arranged on both sides of the main pipe 1 and are parallel to the main pipe 1.

[0033] like Figure 2 As shown, the outer diameter of main pipe 1 is D, the outer diameter of pipeline pipe 2 is d, the distance between pipeline pipe 2 and main pipe 1 is G, and the angle of attack formed by the line connecting the centers of pipeline pipe 2 and main pipe 1 relative to the direction of water flow is α. Since it is a symmetrical structure, 0°≤α≤90°. The diameter ratio between pipeline pipe 2 and main pipe 1 is d / D, and the ratio of the distance between pipeline pipe 2 and main pipe 1 to the diameter of main pipe 1 is G / D.

[0034] II. Dimensional Parameter Optimization

[0035] The optimization method for the above dimensional parameters is as follows:

[0036] Step 1: The above-mentioned marine riser structure is designed and analyzed using Box-Behnken Design (BBD) and Response Surface Method (RSM) to obtain the dimensional parameters d / D, G / D, and α at different water flow velocities U. r (U r Specifically, using the dimensionless reduced velocity for amplitude A * and resistance C D The response relationship is as follows. BBD is an existing design method, and RSM is an existing analysis method. The corresponding response relationship is:

[0037] A * =0.9325-6.785·d / D-2.63833·G / D+0.00742778·α+0.1155·U r +0.75·d / D·G / D-0.049333·d / D·α+0.315·d / D·Ur +0.021333 · G / D · a + 0.0775 · G / D · U r -0.00295 · a · U r +21.73333 · d / D 2 +4.43333 · G / D 2 +0.000239815 · a 2 -0.00629167 · U r 2

[0038] C D = 2.83221 - 21.73333 · d / D + 6.23667 · G / D - 0.032361 · a + 0.292 · U r -1.6 · d / D · G / D - 0.16667 · d / D · a + 3.565 · d / D · U r +0.12567 · G / D · a - 0.22 · G / D · U r +0.00583333 · a · U r +8 · d / D 2 -12.4375 · G / D 2 +0.0000194444 · a 2 -0.09125 · U r 2

[0039] As shown in Figs. 3 and 4 are several exemplary response surface plots selected, wherein Fig. 3(a) is a response surface plot between d / D and G / D for amplitude A * ; Fig. 3(b) is a response surface plot between d / D and a for amplitude A * ; Fig. 3(c) is a response surface plot between G / D and a for amplitude A * ; Fig. 4(a) is a response surface plot between d / D and G / D for drag C D ; Fig. 4(b) is a response surface plot between d / D and a for drag C D ; Fig. 4(c) is a response surface plot between G / D and a for drag C D . Note: the parameters not listed in each of the above response surface plots take the intermediate values, specifically d / D takes the value of 0.15, G / D takes the value of 0.2, a takes the value of 15°, U r takes the value of 5; for example, Fig. 3(a) is the surface variation relationship of amplitude A r relative to d / D and G / D when a takes the value of 15°, U * takes the value of 5.

[0040] L = 10D in the above example; the response relationship formula and its response relationship surface graph are only exemplary in nature, and the response relationship obtained based on different test or test data will inevitably have slight differences.

[0041] Step 2, multi-objective optimization of the above response relationship is performed by using a second-generation genetic algorithm Nondominated Sorting Genetic Algorithm II (NSGA II), wherein the optimization parameters are d / D, G / D, a and U r , and the optimization objectives are A * min and C D min.

[0042] As Figure 5 shown are graphs of the selected exemplary three groups of different water flow velocities U r , amplitudes A * and resistances C D .

[0043] Step 3, according to the optimization results, the optimal size parameters are selected. In actual applications, since the ocean current velocity in the same sea area is relatively constant and has a small change range, that is, after the sea area where the marine riser is arranged is determined, the value of the corresponding flow velocity U can be determined, and then the optimal size parameters d / D, G / D and a are selected according to the optimization results.

[0044] Table 1 shown below respectively shows comparative test data tables of marine risers with different structural forms, wherein ① is a bare pipe scheme (i.e., a single main pipe), ② and ③ are single-line pipe schemes (i.e., only a line pipe is arranged on one side of the main pipe), ④ is the marine riser structure of the double-line pipe form of the application, and the size parameters in ④ are selected by optimization when U r = 5, and the same size parameter in the schemes ①-④ remains the same value. According to the comparison in Table 1, it can be obtained that: (1) the marine riser structure of the double-line pipe form of the application has a smaller amplitude A * and a lower resistance C D than the ordinary bare pipe structure or the single-line pipe structure (whether on the flow-encountering side or the flow-encountering side); (2) the size parameters selected by optimization when the water flow reduced velocity is 5 still have good performance effects when the reduced velocity is 4 or 6, indicating that the marine riser structure of the application can still maintain good response capability when the ocean current velocity fluctuates.

[0045] Table 1: Comparison test between double-line pipe and bare pipe and single-line pipe

[0046]

[0047]

[0048] The following Table 2 shows the performance comparison between randomly selected and optimized size parameters of the marine riser structure of the present application, wherein the column of "NSGA-II" is the A * with C D Optimal value, the column of "CFD simulation" is the A * with C D Data, the size parameters in the row of "Before optimization" are randomly selected, and the size parameters in the row of "After optimization" are selected based on the optimization results. According to the comparison in Table 2, the size parameters after optimization by the parameter optimization method of the present application can have better vibration suppression and drag reduction effects compared with the randomly selected size parameters.

[0049] Table 2: Comparison test between optimized and unoptimized size parameters of double-line pipe

[0050]

[0051] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0052] The present application is not limited to the above-mentioned embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art without departing from the essential content of the present application shall fall within the protection scope of the present application.

Claims

1. An offshore riser structure, characterized by: Two line pipes (2) are symmetrically arranged on both sides of the main pipe (1) and parallel to the main pipe (1), wherein the outer diameter of the main pipe (1) is D, the outer diameter of the line pipe (2) is d, the distance between the line pipe (2) and the main pipe (1) is G, and the angle of the line pipe (2) center line relative to the water flow direction is α. The parameters of the marine riser structure are optimized by the following method: Firstly, d / D, G / D, and a at different flow velocities U r Next, the response relationship of amplitude A * and resistance C D , then multi-objective optimization with A * min and C D min as the target, and finally select d / D, G / D, and a according to the optimization results; wherein the response relationship is: A * = 0.9325 - 6.785 · d / D - 2.63833 · G / D + 0.00742778 · a + 0.1155 · U r + 0.75 · d / D · G / D - 0.049333 · d / D · a + 0.315 · d / D · U r + 0.021333 · G / D · a + 0.0775 · G / D · U r - 0.00295 · a · U r + 21.73333 · d / D 2 + 4.43333 · G / D 2 + 0.000239815 · a 2 - 0.00629167 · U r 2 ; C D = 2.83221 - 21.73333 - d / D + 6.23667 - G / D - 0.032361 - a + 0.292 - U r - 1.6 - d / D G / D - 0.16667 d / D a + 3.565 d / D U r + 0.12567 G / D a - 0.22 G / D U r + 0.00583333 · a · U r + 8 · d / D 2 - 12.4375 · G / D 2 + 0.0000194444 · a 2 - 0.09125 · U r 2 .

2. The marine riser structure of claim 1, characterized by: The line pipe (2) and the main pipe (1) are fixed by a plurality of supports (3), and the distance between adjacent fixed points in the axial direction of the main pipe is L.

3. The marine riser structure of claim 2, characterized by: L=10D.

4. A method of parameter optimization for a marine riser structure according to any one of claims 1-3, characterized by: The response relationship is obtained by Box-Behnken Design and Response Surface Method analysis.

5. The parameter optimization method of claim 4, wherein: The multi-objective optimization is performed by Nondominated Sorting Genetic Algorithm II genetic algorithm.

6. The parameter optimization method of claim 4, wherein: When U r = 4, d / D takes the value 0.18, G / D takes the value 0.13, and a takes the value 27.2°; when U r = 5, d / D takes the value 0.15, G / D takes the value 0.17, and a takes the value 24.1°; when U r = 6, d / D takes the value 0.17, G / D takes the value 0.1, and a takes the value 30°.

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