High-throughput multi-scale integrated simulation method for mechanical properties of unbonded flexible risers

Abstract

The present invention provides a high-throughput multi-scale integrated non-bonded flexible riser mechanical property simulation method. Based on ABAQUS, RVE of riser models with different numbers of layers are established and complex periodic boundary conditions are applied using MPC to obtain the hysteresis loop of the riser; a self-proposed elastic-plastic constitutive model is used and a running program is written in FORTRAN language. By adjusting the parameters of the constitutive model, the response of the elastic-plastic constitutive model is made consistent with the hysteresis loop of the riser RVE; a UEL suitable for ABAQUS is established based on the elastic-plastic constitutive model, and a large-scale homogenized riser model is established using UEL and analyzed and studied; the function of studying the mechanical response of non-bonded flexible risers under tension, bending, torsion, and internal and external pressure loads at large scale is realized. The present invention has a more comprehensive understanding of the mechanical behavior of non-bonded riser models under complex working conditions, and provides more precise guidance for engineering design, material selection, and performance optimization.

Description

Technical Field

[0001] The present invention belongs to the technical field of marine oil and gas exploitation, and in particular relates to a high-throughput multi-scale integrated non-bonded flexible riser mechanical property simulation method. Background Art

[0002] Since the 1970s, flexible risers have been widely used in fluid delivery systems in marine environments. Compared with rigid risers, flexible risers have stronger adaptability, lower installation costs and better fatigue performance. This excellent performance comes from the structure of the flexible riser - it is composed of an alternating combination of polymer layers that provide sealing and spiral layers that provide strength, with relative sliding between layers.

[0003] However, the complex geometry and large number of contact relationships of flexible risers make the use of finite element methods extremely expensive, and the simulation of flexible risers at large scales is even more challenging. At the same time, the current use of flexible risers in more complex scenarios has led to the emergence of new failure modes, such as buckling of the spiral steel belt, which will threaten the long-term integrity of the riser system.

[0004] At the same time, the non-bonded flexible riser may be subjected to the combined effects of multiple loads in the working state, such as gravity, buoyancy, seawater pressure, medium pressure, water flow impact, etc. These loads can be uniformly simplified into five loads: tension, bending, torsion, and internal and external pressure. Analyzing the mechanical response of the flexible riser under the combined effects of these five loads can help researchers to have a more comprehensive understanding of the behavior of the riser system and provide more precise guidance for engineering design, material selection, and performance optimization. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a high-throughput multi-scale integrated non-bonded flexible riser mechanical performance simulation method for studying the mechanical response of non-bonded flexible risers under tension, bending, torsion and internal and external pressure loads at large scales.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: a high-throughput multi-scale integrated non-bonded flexible riser mechanical properties simulation method, comprising the following steps:

[0007] S1: Establish representative volume elements RVE of riser models with different numbers of layers and perform pre-processing. Apply complex periodic boundary conditions between ghost points and model nodes through multi-point constraint method MPC, and obtain the hysteresis loop of the riser through the force-displacement information of ghost points.

[0008] S2: Establish a parameterized elastic-plastic constitutive model so that the response of the elastic-plastic constitutive model is consistent with the hysteresis loop of the representative volume element RVE of the riser model;

[0009] S3: A user-defined unit UEL is established according to the elastic-plastic constitutive model of step S2, and a large-scale non-bonded homogenized flexible riser model is established using the user-defined unit UEL and analyzed.

[0010] According to the above scheme, in step S1, the representative volume element RVE is loaded by establishing random ghost points outside the riser model, and using the multi-point constraint method MPC to establish a kinematic relationship between some nodes of the discretized model and the ghost points, thereby controlling the boundary conditions of the model.

[0011] Furthermore, in step S1, it is assumed that Respectively represent the nodes described in Direction displacement, are the initial coordinates of the described node, is the material Poisson’s ratio, are the axial strain of the riser and the The curvature of the axis The curvature and alignment of the axis The curvature of the axis, is the radial strain on the inner and outer surfaces of the riser on the axial section, Respectively represent the inner surface and outer surface of the riser; in the global coordinate system, when the axial direction of the riser is parallel to the Z-axis, the control equation is as follows:

[0012] .

[0013] Furthermore, in step S1, the representative volume unit RVE is designed to have tension, bending and torsion conditions, each of which includes internal and external pressure loads; the degrees of freedom of the ghost points are respectively represented by .

[0014] According to the above scheme, in step S1, is the increment of strain energy, is the axial length of the representative volume unit, is with The corresponding torque, is the axial force, for The axial force generated by the internal and external pressure loads is and are the internal and external pressures, , and is the inner and outer radius of the riser, ; The force and displacement of the ghost point have the following relationship:

[0015] .

[0016] According to the above scheme, in step S2, set are the equivalent elastic modulus and equivalent shear model, respectively. are the equivalent cross-sectional area, equivalent moment of inertia and equivalent polar moment of inertia, respectively. They are , and The influence coefficient on hysteresis, and is the intermediate variable in the plastic evolution process; the characteristics of the elastic-plastic constitutive model are described by the following equation:

[0017]

[0018]

[0019] The response of the constitutive model is made consistent with the hysteresis loop of RVE by adjusting the parameters.

[0020] According to the above scheme, in step S3, the user-defined unit UEL is a 2-node 12-degree-of-freedom Euler-Bernoulli beam unit, each node of which contains 3 displacement degrees of freedom and 3 rotation degrees of freedom, and is used to simulate the working conditions of the riser subjected to tension, bending, torsion, and internal and external pressure loads.

[0021] Furthermore, in step S3,

[0022] set up is the beam element shape function, is the total energy of the beam element, is the beam element stiffness matrix, is the generalized displacement of the beam element; the derivation process of the UEL stiffness matrix of the user-defined element is:

[0023] .

[0024] A high-throughput multi-scale integrated non-bonded flexible riser mechanical property simulation system, the system comprising a processor and a memory, the memory storing computer instructions, the processor being used to execute the computer instructions stored in the memory, and when the computer instructions are executed by the processor, the system implements the steps of a high-throughput multi-scale integrated non-bonded flexible riser mechanical property simulation method.

[0025] A computer storage medium stores a computer program executable by a computer processor, wherein the computer program executes a high-throughput multi-scale integrated non-bonded flexible riser mechanical property simulation method.

[0026] The beneficial effects of the present invention are:

[0027] 1. The high-throughput multi-scale integrated non-bonded flexible riser mechanical properties simulation method of the present invention is based on ABAQUS to establish the RVE of the riser model with different numbers of layers and use MPC to apply complex periodic boundary conditions to obtain the hysteresis loop of the riser; a self-proposed elastic-plastic constitutive model is used and the running program is written in FORTRAN language, and the parameters of the constitutive model are adjusted to make the response of the elastic-plastic constitutive model consistent with the hysteresis loop of the riser RVE; a UEL suitable for ABAQUS is established according to the elastic-plastic constitutive model, and a large-scale homogenized riser model is established using UEL and analyzed and studied; the function of studying the mechanical response of large-scale non-bonded flexible risers under tension, bending, torsion and internal and external pressure loads is realized.

[0028] 2. The present invention establishes the RVE of the homogenized riser model and uses MPC to load complex periodic boundary conditions to obtain its hysteresis loop, eliminating the stress concentration caused by directly applying loads on the model, making the hysteresis loop more in line with the actual situation; the created elastoplastic constitutive model fully considers the influence of different loads such as tension, bending, torsion, internal and external pressure on the mechanical response of the riser, making the subsequently established UEL more universal and representative; it solves the limitations of the simulation analysis of non-bonded flexible risers in the prior art, and more comprehensively understands the mechanical behavior of the non-bonded riser model under complex working conditions, providing more precise guidance for engineering design, material selection and performance optimization.

[0029] 3. The present invention combines representative volume units with large-scale riser models, fully considering the effects of different loads such as tension, bending, torsion, internal and external pressures on the mechanical response of the riser; the created UEL is highly flexible, and while keeping the basic framework unchanged, only some parameters need to be modified to achieve the simulation of the same type of riser model; it effectively solves the problem of high computational cost of large-scale riser models, and has wide applicability and scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of an embodiment of the present invention.

[0031] Figure 2 Schematic diagram of a marine flexible riser system model according to an embodiment of the present invention.

[0032] Figure 3 1 is a finite element model diagram of an RVE according to an embodiment of the present invention.

[0033] Figure 4 It is a comparison diagram of the hysteresis curve of the RVE of the embodiment of the present invention and the calibrated elastic-plastic constitutive model.

[0034] Figure 5 It is a schematic diagram of a large-scale non-bonded flexible riser model of an embodiment of the present invention.

[0035] Figure 6 It is the axial reaction force diagram of the large-scale non-bonded flexible riser model of the embodiment of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0037] See also Figure 1 , an embodiment of the present invention comprises the following steps:

[0038] S1: Based on the simulation software ABAQUS, the RVE (representative volume element) of the riser model with different layers is established and pre-processed, MPC constraints are imposed between the ghost points and the model nodes, complex periodic boundary conditions are imposed through MPC (multi-point constraint method), and the hysteresis loop of the riser is obtained through the force-displacement information of the ghost points;

[0039] S11: MPC describes the kinematic relationship between points through control equations, establishes random ghost points outside the model, couples some nodes of the discretized model with the ghost points, and realizes the loading of RVE by controlling the boundary conditions of the ghost points. In the global coordinate system, when the axis of the riser is parallel to the Z axis, the control equation is as follows:

[0040]

[0041] in, Respectively represent the nodes described in Direction displacement, are the initial coordinates of the described node, is the material Poisson’s ratio, are the axial strain of the riser and the The curvature of the axis The curvature and alignment of the axis The curvature of the axis, is the radial strain on the inner and outer surfaces of the riser on the axial section, represent the inner and outer surfaces of the riser, respectively;

[0042] Figure 2 Schematic diagram of the marine non-bonded flexible riser system model in the present invention, Figure 3 For the RVE finite element model in the present invention, the present invention designs three working conditions for RVE, namely tension, bending and torsion, and each working condition contains the same internal and external pressure loads. In particular, The degrees of freedom of ghost points are used for representation. For this purpose, the six degrees of freedom of displacement of two ghost points can control all situations where the riser is subjected to tension, bending, torsion, and internal and external pressure loads;

[0043] For MPC, it needs to be implemented by modifying the INP file. Here is a brief introduction to its specific writing format. The example is as follows:

[0044] “*MPC, user, mode=DOF

[0045] 1,5,88888,88888,88888,99999

[0046] 2,5,88888,88888,88888,99999

[0047] 3,1,88888,88888,88888,99999

[0048] 4,1,88888,88888,88888,99999

[0049] 5,1,801,88888,88888,99999

[0050] 6,1,801,88888,88888

[0051] 7,1,801,88888,88888”

[0052] The first line "*MPC, user, mode=DOF" is the keyword of MPC. The first number of each subsequent line is the type of MPC. Seven types are set here. "88888" and "99999" represent the numbers of ghost points, and the remaining numbers represent the RVE node numbers.

[0053] S12: The hysteresis loop of RVE is obtained by extracting the force-displacement curve on the ghost point; the force and displacement of the ghost point have the following relationship:

[0054]

[0055] in, is the increment of strain energy, is the axial length of the representative volume unit, is with The corresponding torque, is the axial force, for The axial force generated by the internal and external pressure loads is and are the internal and external pressures, , and is the inner and outer radius of the riser, .

[0056] S2: Use the proposed elastic-plastic constitutive model and write a running program in FORTRAN language. By adjusting the parameters of the constitutive model, the response of the elastic-plastic constitutive model is consistent with the hysteresis loop of the riser RVE. Figure 4 Comparison between the hysteresis loop of the RVE in the present invention and the constitutive model response after calibration parameters.

[0057] The elastoplastic constitutive model is characterized by the following equations:

[0058]

[0059]

[0060] in, are the equivalent elastic modulus and equivalent shear model, respectively. are the equivalent cross-sectional area, equivalent moment of inertia and equivalent polar moment of inertia, respectively. They are , and The influence coefficient on hysteresis, and It is an intermediate variable in the plastic evolution process;

[0061] The response of the constitutive model is made consistent with the hysteresis loop of RVE by adjusting the parameters.

[0062] S3: Based on the elastoplastic constitutive model of step S2, a UEL (user-defined element) suitable for ABAQUS is established. The UEL is used to establish a large-scale non-bonded homogenized flexible riser model and conduct analysis and research. Figure 5 It is a schematic diagram of a large-scale lower riser model in the present invention, Figure 6 is the axial reaction force of the large-scale riser model under different boundary conditions.

[0063] The characteristics of UEL are: UEL is a 2-node 12-degree-of-freedom Euler-Bernoulli beam element, each node contains 3 displacement degrees of freedom and 3 rotational degrees of freedom, which can simulate the riser subjected to tension, bending, torsion and internal and external pressure loads; the derivation process of the UEL stiffness matrix is ​​as follows:

[0064]

[0065] In the formula, is the shape function, is the total energy of the beam element, is the beam element stiffness matrix, is the generalized displacement of the beam element; in the simulation software ABAQUS, the beam element is used to create a large-scale flexible riser model and perform finite element analysis to obtain the corresponding mechanical response.

[0066] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0067] The above embodiments are only used to illustrate the design ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, any equivalent changes or modifications made based on the principles and design ideas disclosed by the present invention are within the protection scope of the present invention.

Claims

1. A high-throughput multi-scale integrated non-bonded flexible riser mechanical properties simulation method, characterized by: The following steps are involved: S1: Establish representative volume elements RVE of riser models with different numbers of layers and perform pre-processing. Apply complex periodic boundary conditions between ghost points and model nodes through multi-point constraint method MPC, and obtain the hysteresis loop of the riser through the generalized force-displacement information of ghost points. The representative volume element RVE is loaded by establishing random ghost points outside the riser model and using the multi-point constraint method MPC to establish kinematic relationships between some nodes of the discretized model and the ghost points, thereby controlling the boundary conditions of the model; set up is the increment of strain energy, is the axial length of the representative volume unit, is with The corresponding torque, is the axial force, for The axial force generated by the internal and external pressure loads is and are the internal and external pressures, , and is the inner and outer radius of the riser, ; The force and displacement of the ghost point have the following relationship: ； S2: Establish a parameterized elastic-plastic constitutive model so that the response of the elastic-plastic constitutive model is consistent with the hysteresis loop of the representative volume element RVE of the riser model; S3: A user-defined beam unit UEL is established according to the elastic-plastic constitutive model of step S2, and a large-scale non-bonded homogenized flexible riser model is established using the user-defined unit UEL and analyzed.

2. The high-throughput multi-scale integrated non-bonded flexible riser mechanical properties simulation method according to claim 1 is characterized by: In the step S1, it is assumed that Respectively represent the nodes described in Direction displacement, are the initial coordinates of the described node, is the material Poisson’s ratio, are the axial strain of the riser and the The curvature of the axis The curvature and alignment of the axis The curvature of the axis, is the radial strain on the inner and outer surfaces of the riser on the axial section, Respectively represent the inner surface and outer surface of the riser; in the global coordinate system, when the axial direction of the riser is parallel to the Z-axis, the control equation is as follows: 。 3. The high-throughput multi-scale integrated non-bonded flexible riser mechanical properties simulation method according to claim 2 is characterized by: In step S1, the representative volume unit RVE is designed to include tension, bending and torsion conditions, each of which includes internal and external pressure loads; the degrees of freedom of the ghost points are respectively represented by .

4. The high-throughput multi-scale integrated non-bonded flexible riser mechanical properties simulation method according to claim 1, characterized in that: In the step S2, it is assumed that are the equivalent elastic modulus and equivalent shear model, respectively. are the equivalent cross-sectional area, equivalent moment of inertia and equivalent polar moment of inertia, respectively. They are , and The influence coefficient on hysteresis, and is the intermediate variable in the plastic evolution process; the characteristics of the elastic-plastic constitutive model are described by the following equation: The response of the constitutive model is made consistent with the hysteresis loop of RVE by adjusting the parameters.

5. The high-throughput multi-scale integrated non-bonded flexible riser mechanical properties simulation method according to claim 1, characterized in that: In the step S3, the user-defined unit UEL is a 2-node 12-degree-of-freedom Euler-Bernoulli beam unit, each node including 3 displacement degrees of freedom and 3 rotation degrees of freedom, which is used to simulate the working conditions of the riser under tension, bending, torsion and internal and external pressure loads.

6. The high-throughput multi-scale integrated non-bonded flexible riser mechanical properties simulation method according to claim 5, characterized in that: In the step S3, set up is the beam element shape function, is the total energy of the beam element, is the beam element stiffness matrix, is the generalized displacement of the beam element; the derivation process of the UEL stiffness matrix of the user-defined element is: 。 7. A high-throughput multi-scale integrated non-bonded flexible riser mechanical properties simulation system, the system comprising a processor and a memory, characterized in that: The memory stores computer instructions, and the processor is used to execute the computer instructions stored in the memory. When the computer instructions are executed by the processor, the system implements the steps of the high-throughput multi-scale integrated non-bonded flexible riser mechanical properties simulation method as described in any one of claims 1 to 6.

8. A computer storage medium, characterized in that: A computer program executable by a computer processor is stored therein, and the computer program executes the high-throughput multi-scale integrated non-bonded flexible riser mechanical property simulation method as described in any one of claims 1 to 6.

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