1. A design method of a composite flexible pipe section comprises the following steps: 1) acquiring the geometric dimension and material parameters of the flexible pipe according to the design target of the flexible pipe; it is characterized in that the preparation method is characterized in that,

2) determining the design load and failure criterion of the flexible pipe according to the operation environment of the flexible pipe, the mechanical properties of materials and the specification of a design specification;

3) establishing a finite element model and an integral analysis model of the flexible pipe, and verifying the effectiveness;

4) analyzing the alternate winding angle of the fibers of the reinforced layer of the flexible pipe, the material of the outer protective layer, the thickness of the lining layer and the thickness of the outer protective layer, and determining the basic design parameters of the flexible pipe;

5) preliminary section design, namely performing the preliminary section design of the flexible pipe under the action of single internal pressure and external pressure loads;

6) singly designing tensile load, establishing a flexible pipe integral analysis model by using the initial section fiber layer number, and respectively performing static analysis and dynamic analysis to obtain effective tension, curvature and bending moment data; calculating the single design tensile load of the flexible pipe by combining the design specification;

7) checking the strength of the flexible pipe, checking the curvature of the flexible pipe and checking the fatigue life of the flexible pipe; the section design of the flexible pipe is completed.

2. The method for designing the cross section of the composite flexible pipe according to claim 1, wherein in the step 5, the number of the reinforced layer fibers of which the cross section of the flexible pipe meets two design loads is determined, so that the number of the initial cross-section fibers is calculated through strength check, bending check and fatigue life check of the flexible pipe.

3. The design method of the cross section of the composite flexible pipe according to claim 1, wherein in the 7 th step, the strength of the flexible pipe is checked, a combined load is applied to the flexible pipe, and the stress-strain result is analyzed; and if the stress strain result exceeds the failure standard, the flexible pipe fails, and the number of the fiber layers of the initial section is reselected for analysis until the number of the fiber layers of the section enables the flexible pipe to pass through the strength check.

4. A method for designing a section of a composite flexible pipe according to claim 1, wherein, in the step 7, the curvature of the flexible pipe is checked, bending moment is applied to the flexible pipe to calculate the curvature, and the calculated curvature is compared with the allowable curvature obtained in the overall analysis; if the curvature is greater than the allowable curvature, the flexible tube material is replaced.

5. A design method of a composite flexible pipe section according to claim 1, characterized by the step 7 of checking the fatigue life of the flexible pipe, applying a fatigue load to the flexible pipe and calculating the fatigue life; if the fatigue life of the flexible pipe does not meet the design requirement, reselecting the initial number of cross-section layers until the number of cross-section fiber layers enables the flexible pipe to pass through strength check, bending check and fatigue life check; and if the fiber layer number of the cross section enables the flexible pipe to pass through all the checks, taking the fiber layer number as the final cross section fiber layer number.

Background

Flexible pipe has a number of advantages over conventional steel pipe: the marine oil gas platform has the advantages of small bending rigidity, large deformation, capability of bearing large platform movement, easiness in installation, strong corrosion resistance, recyclability and important engineering application value in the future marine oil gas development process. By adopting the same design method and a general production process and selecting different material combinations and section structures, the customized production of the flexible pipe can be realized so as to meet different application requirements in the field of oil and gas transmission.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, provides a design method of a composite flexible pipe section, aims to master the key technology of an ultra-deep water multipurpose flexible pipe in the aspects of design, analysis and production according to the requirements of oil-gas exploration and development in deep water, ultra-deep water and other complex environments, and obtains an original technology research and development result.

In order to solve the technical problems, the invention provides the following technical scheme:

a design method of a composite flexible pipe section comprises the following steps: 1) acquiring the geometric dimension and material parameters of the flexible pipe according to the design target of the flexible pipe;

2) determining the design load and failure criterion of the flexible pipe according to the operation environment of the flexible pipe and the mechanical properties of materials and in combination with the regulation of design specifications;

3) establishing a finite element model and an integral analysis model of the flexible pipe, and verifying the effectiveness of the finite element model and the integral analysis model;

4) analyzing the alternate winding angle of the fibers of the reinforced layer of the flexible pipe, the material of the outer protective layer, the thickness of the inner lining layer and the thickness of the outer protective layer, and determining the basic design parameters of the flexible pipe by combining the actual production and the design specification;

5) preliminary section design, namely performing the preliminary section design of the flexible pipe under the action of single internal pressure and external pressure loads;

6) singly designing tensile load, establishing a flexible pipe integral analysis model by using the initial section fiber layer number, and respectively performing static analysis and dynamic analysis to obtain effective tension, curvature and bending moment data; calculating the single design tensile load of the flexible pipe by combining the design specification;

7) checking the strength of the flexible pipe, checking the curvature of the flexible pipe and checking the fatigue life of the flexible pipe; the section design of the flexible pipe is completed.

Preferably, step 5, a number of reinforcing layer fiber layers is determined so that the flexible pipe section can satisfy two combined design loads at the same time. In order to allow the flexible pipe to pass through strength checking, bending checking and fatigue life checking, the number of fiber layers of the initial section is estimated.

Preferably, step 7, checking the strength of the flexible pipe, applying a combined load to the flexible pipe, and analyzing the stress-strain result; and if the stress strain result exceeds the failure standard, the flexible pipe fails, and the number of the fiber layers of the initial section is reselected for analysis until the number of the fiber layers of the section enables the flexible pipe to pass through the strength check.

Preferably, in the 7 th step, the curvature of the flexible pipe is checked, bending moment is applied to the flexible pipe to calculate the curvature of the flexible pipe, and the curvature is compared with the allowable curvature obtained in the overall analysis; if the curvature is greater than the allowable curvature, the flexible tube material is replaced and redesigned.

Preferably, 7, checking the fatigue life of the flexible pipe, and applying fatigue load to the flexible pipe to calculate the fatigue life; if the fatigue life of the flexible pipe does not meet the design requirement, reselecting the initial number of cross-section layers until the number of cross-section fiber layers enables the flexible pipe to pass through strength check, bending check and fatigue life check; and if the fiber layer number of the cross section enables the flexible pipe to pass through all the checks, taking the fiber layer number as the final cross section fiber layer number.

Compared with the prior art, the invention has the following beneficial effects:

the invention can provide guidance for the design and production of the thermoplastic fiber reinforced composite flexible pipe by researching the design method of the section of the thermoplastic fiber reinforced composite flexible pipe.

Drawings

FIG. 1 is a schematic structural view of a composite flexible pipe of the present invention;

FIG. 2 is a schematic diagram of a cylindrical coordinate system of the composite flexible pipe of the present invention;

FIG. 3 is a schematic diagram of the minimum wall thickness specification for liners of different diameters according to the national standard of the present invention;

FIG. 4 is a flow chart of an overall iterative analysis of the composite flexible pipe of the present invention;

figure 5 is a flow chart of the composite flexible pipe design of the present invention.

Detailed Description

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.

As shown in fig. 1, the thermoplastic composite flexible pipe is formed by winding and bonding a thermoplastic polymer extrusion pipe and a plurality of layers of fiber reinforced composite material strips, the cross-sectional structure of the thermoplastic composite flexible pipe is divided into four layers from inside to outside, and the functional layer is an external protective layer 1, a functional layer 2, a fiber reinforced layer 3 and an inner liner layer 4, and is a non-main bearing structure. The reinforced fiber is completely embedded into the polymer matrix, and the layers are bonded together in a heating fusion mode to form a fully-bonded composite pipeline structure. The thermoplastic polymer material can be selected from Polyethylene (PE), polypropylene (PP), nylon (PA), polyvinylidene fluoride (PVDF), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), etc.; the fiber material can be selected from glass fiber, carbon fiber, aramid fiber and the like. The flexible pipe section design process is a process of iterative iteration. In the design process, if the designed section performance is far beyond the design target, the section performance is made to just meet the design target as much as possible and the safety margin is properly reduced due to the needs of economy and actual production.

A design method of a composite flexible pipe section comprises the following steps:

1) and acquiring the geometric dimension and material parameters of the flexible pipe according to the design target of the flexible pipe.

2) And determining the design load and failure criterion of the flexible pipe according to the operating environment of the flexible pipe and the mechanical properties of materials and the regulation of the design specification on the safety factor. The design load includes design internal pressure load, design external pressure load and design tensile load. And each layer of the flexible pipe is required to respectively determine the stress-strain failure standard according to the material.

3) Establishing a finite element model of the flexible pipe in finite element software Abaqus, comparing the finite element model with experimental data, and verifying the effectiveness of the finite element model; and establishing an integral analysis model of the flexible pipe in ocean engineering dynamic analysis software Orcaflex, and verifying the section equivalence theory.

4) The alternate winding angle of the fibers of the reinforced layer of the flexible pipe, the material of the outer protective layer, the thickness of the inner lining layer and the thickness of the outer protective layer are respectively used as the unique variables of the finite element model of the flexible pipe to be analyzed one by one, and the optimal section characteristics of the flexible pipe, including the winding angle of the fibers of the reinforced layer, the optimal material of the outer protective layer, the optimal thickness of the inner lining layer and the optimal thickness of the outer protective layer, are determined by combining the analysis result with the production practice and the design specification.

5) And (3) performing preliminary section design under the action of single internal pressure and external pressure design loads. And determining the fiber layer number of the reinforcing layer of the flexible pipe, which enables the section of the flexible pipe to simultaneously meet two design loads and is called as the initial section fiber layer number, according to the failure criterion of the flexible pipe. In order to enable the flexible pipe to meet the requirement that the number of the fiber layers of the cross section is considered through load, the cross section is subjected to the subsequent combined load check, bending check and fatigue life check, and the number of the fiber layers of the cross section is estimated to be larger as much as possible through the preliminary estimation by combining with the design experience.

6) Singly designing tensile load, establishing an integral analysis model of the flexible pipe by using the number of the initial section fiber layers, respectively carrying out static analysis and dynamic analysis on the model, and recording effective tension, curvature and bending moment data of the model; and calculating the single design tensile load of the flexible pipe acting on the flexible pipe finite element model by combining the effective tension with the design specification.

7) Checking the strength of the flexible pipe, checking the curvature of the flexible pipe and checking the fatigue life of the flexible pipe; and finishing the section design of the flexible pipe.

And checking the combined load of the flexible pipe, wherein the single design tensile load can be respectively combined with the single design internal pressure load and the single design external pressure load to form two combined loads. And respectively applying the two combined loads to a flexible pipe finite element model for strength check, and analyzing the stress-strain result. And if the stress strain result exceeds the failure standard and the flexible pipe fails, reselecting the initial section fiber layer number for analysis until the section fiber layer number enables the flexible pipe to pass through the strength check.

And (4) checking the curvature of the flexible pipe, applying the bending moment load to a flexible pipe finite element model to check the curvature, and analyzing a bending deformation result. And if the bending deformation exceeds the failure standard, reselecting the flexible pipe material until the number of the cross-section fiber layers enables the flexible pipe to pass the strength check and the curvature check.

And (4) checking the fatigue life of the flexible pipe, establishing a flexible pipe fatigue analysis model by using flexible pipe finite element model parameters, and checking the fatigue life of the flexible pipe. And if the fatigue life of the flexible pipe does not meet the design requirement, reselecting the initial section layer number for analysis until the section fiber layer number enables the flexible pipe to pass through strength check, curvature check and fatigue life check. If the number of cross-sectional fiber plies is such that the flexible tube passes through all of the checks, it is referred to as the final cross-sectional fiber ply number.

And (3) section equivalence, namely obtaining the integral equivalent elastic constant of the reinforced layer by the elastic constant of the fiber band through a homogenization theory, then enabling the flexible pipe with the three-layer structure to be equivalent to a single-layer model to obtain the integral equivalent elastic constant of the flexible pipe, and providing basic parameters for the integral analysis, the vortex-induced fatigue analysis and the stability analysis of the flexible pipe.

The equivalent theory is as follows: and (3) analyzing and designing the composite layer by referring to the elastic characteristic of the enhancement layer and a P.C.Chuo multilayer board macroscopic modulus analysis method. As shown in fig. 2, the schematic diagram of the cylinder in the cylindrical coordinate system (ρ, Φ, z), wherein the direction 1 is the longitudinal direction of the fiber band, and the included angle with the circumferential direction is θ; the 2 direction is the transverse direction of the fiber belt; the direction 3 is perpendicular to the direction of the fiber band and is consistent with the radial direction of the flexible pipe. The radial direction in the cylindrical coordinate system is vertical to the plane of the fiber band, and the axial direction of the cylindrical coordinate system is coincident with the axial direction of the flexible pipe.

Because the reinforcing layer of the flexible pipe is formed by alternately winding the fiber tapes at an angle of positive and negative phases, each single-layer flexibility matrix formed by winding the fiber tapes can be obtained by the elastic constant of the fiber tapes:

the stiffness matrix of each monolayer may be obtained by inverting the compliance matrix:

[C₀]＝[S₀]^-1 (2)

the stiffness matrix of each single layer under the cylindrical coordinate system is as follows:

[S_c']^k＝[T][S₀][T]^T

(3)

where k is used to distinguish between a single layer of fiber tape wound at a positive angle (k ═ 1) and a single layer wound at a negative angle (k ═ 2), [ T ] is the coordinate transformation matrix from the material coordinate system to the cylindrical coordinate system.

Where α is the transformation angle between the material coordinate system and the cylindrical coordinate system.

The stiffness matrix of each single layer under a cylindrical coordinate system:

[C_c']^k＝[S_c']^k-1 (5)

the overall equivalent elastic constant of the reinforcement layer is related to the volume ratio of each layer, and the elements in the equivalent stiffness matrix of the reinforcement layer can be calculated by:

C_c-ij＝C_c-ji＝0(i＝1,2,3,6j＝4,5)

(6)

whereinAndis the volume fraction occupied by a single monolayer.

Wherein

The compliance matrix of the enhancement layer may be derived from the following equation:

[S_c]＝[C_c]^-1 (10)

integral elastic property of flexible pipe

The flexible pipe lining layer and the outer protective layer are made of polymers and are isotropic materials, and the flexibility matrix of the flexible pipe lining layer and the outer protective layer can be expressed as follows:

wherein E_pAnd v_pIs the modulus of elasticity and poisson's ratio of the polymer.

The stiffness matrix of the inner liner layer and the outer protective layer may be expressed as:

[C_p]＝[S_p]^-1 (12)

when the flexible pipe composed of three layers is equivalent to an equivalent section composed of one layer, the equivalent elastic performance of the equivalent section is related to the elastic performance of the inner liner layer, the reinforcing layer and the outer protective layer. Here a three-layer stiffness matrix is utilized:inner liner layer [ C]¹(i.e., [ C ]_p]) Enhancement layer [ C]²(i.e., [ C ]_c]) And an outer protective layer [ C]³(i.e., [ C ]_p]) And their volume fraction (V)₁,V₂,V₃) The elastic constant of the equivalent section of the flexible pipe is calculated. Equivalent section stiffness matrix [ C ]]Element C in (1)_ijCan be obtained by the following formula:

C_ij＝C_ji＝0(i＝1,2,3,6,j＝4,5) (14)

wherein

The flexibility matrix of the equivalent section of the flexible pipe is as follows:

the elastic constant of the equivalent section of the flexible pipe can be obtained by equation (17).

Design load and failure criteria

The thermoplastic fiber reinforced composite material flexible pipe is designed with the internal pressure load, the tensile load and the external pressure load as analysis targets, and the preliminary section design is carried out under the action of a single design load. For the tensile load, the tensile load is determined by calculation by adopting Orcaflex software and repeated iteration with Abaqus software, a safety coefficient of 1.4 is taken by reference to a specification (DNVGL RP F119-2015), and the design tensile load is calculated.

On the basis of determining the design load, the strength failure criteria of each layer of the flexible pipe are summarized as follows:

(1) the inner liner layer and the outer protective layer are made of thermoplastic materials, and whether the structure fails or not is checked according to a fourth strength theory:

(2) the fiber band is a composite material, and according to the specification, the transverse and longitudinal stress response design standards of the fiber band are shown as the formula (19):

n: controlling the stress direction; sigma_nk: the characteristic value of the local load response of the structure in the direction n;dividing the characteristic value of stress in the direction n when the matrix is cracked; gamma ray_F: a local loading factor; gamma ray_Sd: a local load model factor; gamma ray_M: a local resistance factor; gamma ray_Rd: local resistance model factor, gamma_Rd＝1.0；

According to the norm, γ_F＝1.0，γ_Sd＝1.0，γ_M＝1.2。

The flexible pipe section design comprises basic design parameters, preliminary section design and integral analysis and check.

And basic design parameters, namely analyzing the winding angle of the flexible pipe reinforcing layer, the material of the outer protective layer, the thickness of the inner liner and the outer protective layer to determine the optimal winding angle of the flexible pipe reinforcing layer, the material of the outer protective layer, the thickness of the inner liner and the outer protective layer and other basic design parameters.

And (3) establishing a flexible pipe model by adopting structural calculation analysis software such as Abaqus, taking the winding angle of the flexible pipe reinforcing layer as a unique variable, respectively applying an internal pressure load, a tensile load and an external pressure load, and determining the optimal winding angle under the action of a single design load by comparing limit load values.

And the outer protective layer material is used for respectively applying internal pressure load, tensile load and external pressure load to the flexible pipe under the condition of different outer protective layer materials, and recording the limit internal pressure load, the limit tensile load and the limit external pressure load which can be borne by the flexible pipe. And considering both the mechanical property and the economical efficiency of the outer protective layer material, and selecting the most appropriate outer protective layer material.

The thickness of the inner liner layer and the thickness of the outer protective layer are respectively recorded by adopting structural analysis software such as Abaqus to establish flexible pipe models with different thicknesses of the inner liner layer and the protective layer, respectively applying internal pressure load, tensile load and external pressure load to the flexible pipe and respectively recording the limit internal pressure load, the limit tensile load and the limit external pressure load which can be borne by the flexible pipe. On the basis, the thickness of the inner lining layer of the flexible pipe is determined by combining national standards (the second part of the coiled reinforced plastic composite pipe: the fiber reinforced thermoplastic composite continuous pipe). Generally, the outer protective layer thickness is no greater than the inner liner thickness, and thus, the outer protective layer thickness is equal to the inner liner thickness based on the calculation.

Preliminary cross section design, the thermoplastic fiber reinforced composite material flexible pipe is with internal pressure load, tensile load and external pressure load as design analysis target load, carries out preliminary cross section design under the effect of single design load. Designing internal pressure load and external pressure load according to ABS specification (Guide for building and sizing sub-sea pipeline system) and national standard (second part of the coiled reinforced plastic composite pipe: fiber reinforced thermoplastic composite continuous pipe); for the tensile load, the tensile load is determined by calculation by adopting Orcaflex software and repeated iteration with Abaqus software, a safety coefficient of 1.4 is taken by reference to a specification (DNVGL RP F119-2015), and the design tensile load is calculated.

Calculating equivalent stress of the inner layer and the outer layer of the flexible pipe, the fiber direction stress of the reinforced layer and the stress in the vertical fiber direction under the action of design load (design internal pressure load, design external pressure load and design tensile load) by using Abaqus software; and determining the geometric dimension of the section of the flexible pipe meeting the design load requirement by checking the equivalent stress of the inner liner layer and the outer protective layer and the maximum tensile stress and the maximum compressive stress of the fiber direction of the reinforced layer and the fiber direction perpendicular to the reinforced layer.

And performing integral analysis and checking, wherein the flexible pipe computational analysis software performs integral analysis, and the integral analysis comprises static analysis and dynamic analysis. On the basis of platform hydrodynamic force calculation, the flexible pipe is subjected to overall analysis, parameters such as tension, Von Mises stress and curvature are obtained, and a basis is provided for section design.

And (2) static analysis, constructing a simplified platform model by adopting structural calculation analysis software such as ANSYS (analytical system), wherein model parameters comprise the size of the platform, a floating body, a stand column, draft, the chamfering radius of the stand column, the displacement, the size of an upper module and the like, and carrying out hydrodynamic analysis on the platform model by adopting hydrodynamic analysis software such as AQWA (aqua-air analysis of water) and the like.

In the static analysis process, platform parameters, extreme hurricane sea condition data (waves, wind, tides, storm tides and the like), distribution of extreme hurricane sea condition ocean currents along water depth, seabed soil parameters (seabed rigidity, friction coefficient and the like) and other environmental parameters are considered, and the hundred-year working sea condition is adopted for calculation and analysis.

According to the density requirement of fluid conveyed in the flexible pipe, static analysis is carried out on the flexible pipe in consideration of the environment load direction of 0-360 degrees (for example, the platform and the anchoring system and the well repairing pipe are in axial symmetry, and the environment load direction can be simplified to 0-180 degrees), the tension, the Von Mises stress and the curvature of the static analysis of the flexible pipe are obtained through calculation, and the balance state configuration of the flexible pipe system under the action of gravity, buoyancy, fluid resistance and the like is obtained for the next dynamic analysis.

Dynamic analysis and flexible pipe dynamic analysis are the key of overall analysis, and on the basis of an initial configuration obtained by static analysis, the overall dynamic response of the flexible pipe in a time domain range is analyzed by referring to platform parameters, environmental parameters (extreme hurricane sea condition data, distribution of extreme hurricane sea condition ocean currents along water depth, wave parameters, seabed soil body parameters and the like), fluid density in the pipe, environmental load direction and other factors of the static analysis. The tension, curvature and Von Mises stress distribution conditions of the flexible pipe dynamic analysis are obtained by performing dynamic analysis on the flexible pipe, and are compared with static analysis to determine the maximum effective tension, curvature and Von Mises stress and provide design parameters for section design.

Checking, after the design of the initial section of the single load, carrying out strength checking on the flexible pipe, wherein the strength checking content comprises: and checking the combined load strength of stretching and external pressure, checking the combined load strength of stretching and internal pressure and checking the curvature.

The tensile load and curvature check comprises calculation results of integral analysis iteration. As shown in fig. 4, in the overall iterative analysis process, the section parameters of the flexible pipe are recalculated according to the section design result and the model equivalent parameters, so as to implement an overall-local-overall iterative procedure, and determine the section parameters of the flexible pipe through repeated calculation. If the designed flexible pipeline is heavy and too light, the pipeline installation is difficult to carry out under the empty pipe state, and under the wave current load effect, the lighter pipe is heavy and can lead to the flexible pipe to appear bigger response amplitude, considers the installation operating mode and increases corresponding counter weight. Meanwhile, the maximum effective tension of the flexible pipe is increased after the counterweight is added, and the section of the flexible pipe needs to be redesigned and checked.

And (3) fatigue analysis, wherein the safety reliability of the flexible pipe in a deep sea or ultra-deep sea environment depends on the fatigue life of the flexible pipe, and the stress fatigue analysis of the flexible pipe adopts 10 times of safety coefficient.

Establishing a flexible pipe finite element model by adopting Abaqus software, carrying out time domain Analysis on the flexible pipe according to the wave-cycle probability distribution condition of a working sea area, and calculating the Fatigue damage amount of the flexible pipe overall Analysis model by using a Fatigue Analysis module; the flexible pipe static analysis and modal analysis are carried out on the flexible pipe by adopting Orcaflex software, the calculation result is led into vortex-induced vibration (VIV) calculation software SHEAR7, the vortex-induced fatigue damage amount is calculated, and the fatigue life of the flexible pipe is predicted.

And (3) wave-induced fatigue analysis, performing overall dynamic time domain analysis on the flexible pipe according to the wave height-period probability distribution data of the working sea area, wherein the dynamic time domain analysis duration of the overall model is at least 1200s, and the analysis duration is 11300s for ensuring the stability of the calculation result. Irregular waves are selected as the wave analysis type, and Jonswap spectra are selected as the wave spectrum type. When the flexible pipe is subjected to wave-induced fatigue analysis, firstly, a load working condition for fatigue analysis is designed, and the fatigue working conditions with the environmental load directions of 180 degrees and 0 degree are subjected to key analysis.

The method comprises the steps of establishing a flexible pipe equivalent model by adopting Orcaflex software, considering the influences of waves, ocean currents, floating platform movement, fluid in the pipe and a weight layer, obtaining the integral time domain dynamic response of the flexible pipe equivalent model according to wave height-period probability distribution, calculating to obtain the comprehensive damage distribution, the wave height and probability damage distribution and the fatigue life distribution of the flexible pipe under the worst condition, and considering 10 times of fatigue safety coefficient according to the specification (API SPEC 17J-2014) to obtain the wave-induced fatigue life of the most dangerous part of the flexible pipe.

Vortex-induced fatigue analysis, VIV fatigue analysis of flexible pipes is the key point and difficulty of fatigue life analysis, and the VIV fatigue is calculated by adopting SHEAR7 software. SHEAR7 is typically used to calculate the top-tensioned flexible pipe VIV response, which is typically calculated indirectly for catenary flexible pipes using the following equivalent method: the method comprises the steps of obtaining the natural frequency, the modal shape and the modal shape curvature of the flexible pipe of the catenary by finite element software calculation, inputting specific information into a common.

The VIV fatigue life is calculated by adopting the current flow rate once a year. Establishing a flexible pipe finite element model by adopting Orcaflex software, carrying out static analysis on the flexible pipe finite element model, and directly deriving a DAT input file which can be identified by SHEAR 7; performing modal analysis on the flexible pipe, and exporting an identifiable modal input file (MDS format); two files were imported directly into SHEAR7 to calculate the VIV response of the flexible tube.

VIV fatigue analysis is carried out on the flexible pipe through VIV analysis software Shear7, and the annual damage rate, the root mean square stress and the root mean square displacement of the flexible pipe are obtained. According to the specification (API SPEC 17J-2014), a fatigue safety factor of 10 times is considered, ultimately yielding a VIV fatigue life at which the flexible pipe is most dangerous.

The above description is for the purpose of illustrating embodiments of the invention and is not intended to limit the invention, and it will be understood by those skilled in the art that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.