Steel catenary riser vortex-induced vibration characteristic analysis method considering pipe-soil contact action

Abstract

The invention discloses a steel catenary riser vortex-induced vibration characteristic analysis method considering a pipe-soil contact effect. The method comprises the following steps: S1, performing configuration simulation on a deep-sea steel catenary riser according to an external ocean current speed, a water depth of the riser, a riser fixing point position and inner and outer diameter parameters; s2, based on the virtual work and Hamiltonian variation principle, a steel catenary riser mechanical model considering the pipe-soil contact effect is established; s3, establishing a fluid force model and a wake flow vibrator model considering the influence of the inclination angle incoming flow on the vertical pipe dynamic response; and S4, coupling the established fluid force model, the established steel catenary riser mechanical model and the established wake flow vibrator model, solving the dynamic response of the steel catenary riser under the pipe-soil contact action by adopting a Newmark-beta method based on the boundary conditions of the models, and obtaining a vortex-induced vibration response rule. The method can provide reliable theoretical basis and technical support for safety evaluation and vibration control of the steel catenary riser.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas development, and in particular to a method for analyzing vortex-induced vibration characteristics of a steel catenary riser taking into account the pipe-soil contact effect. Background Art

[0002] As a key structure in offshore oil and gas development, the vortex-induced vibration problem of steel catenary risers in the marine environment has always been a research focus in the engineering field. Vortex-induced vibration is caused by the vortex shedding generated when the ocean current bypasses the riser, which causes periodic fluid force and then causes the riser to vibrate. This vibration may cause fatigue damage and structural damage to the riser, seriously affecting the safety and stability of offshore oil and gas production.

[0003] At present, the existing analysis methods are insufficient in considering the pipe-soil contact effect. In the actual marine environment, the contact between the steel catenary riser and the seabed soil will change its vibration characteristics, such as friction in the contact area, changes in constraint conditions, etc. However, traditional methods often simplify or ignore this factor, resulting in inaccurate predictions of vortex-induced vibration characteristics. In addition, the marine environment is complex and changeable, and the impact mechanism of the dynamic changes of factors such as current velocity and wave load on the vortex-induced vibration of steel catenary risers has not been fully understood and accurately simulated. Therefore, there is an urgent need for a vortex-induced vibration characteristics analysis method for steel catenary risers that can comprehensively consider the pipe-soil contact effect and various marine environmental factors to improve the design safety and reliability of marine engineering structures. Summary of the invention

[0004] The present invention aims to provide an accurate analysis method for the vortex-induced vibration characteristics of steel catenary risers taking into account the pipe-soil contact effect. By establishing a complete mathematical model, the relationship between pipe-soil contact, marine environmental factors and vortex-induced vibration characteristics is deeply studied, providing a reliable theoretical basis and technical support for the design, safety assessment and vibration control of steel catenary risers.

[0005] The present invention is implemented by adopting the following technical scheme: a method for analyzing vortex-induced vibration characteristics of a steel catenary riser considering the pipe-soil contact effect, comprising the following steps: S1: The configuration of deep-sea steel catenary riser is simulated according to the external current velocity, water depth of the riser, position of the riser fixing point and inner and outer diameter parameters; S2: Based on virtual work and Hamiltonian variational principle, a mechanical model of steel catenary riser considering pipe-soil contact is established; S3: Establish a fluid force model and a wake oscillator model that consider the influence of the inclination flow on the dynamic response of the riser; S4: The established fluid force model, steel catenary riser mechanical model and wake oscillator model are coupled, and the Newmark-β method is used based on the boundary conditions of the model to solve the dynamic response of the steel catenary riser considering the pipe-soil contact effect, and the vortex-induced vibration response law is obtained.

[0006] Furthermore, step S1 is specifically as follows: based on the catenary theory, by establishing a local coordinate system, an optimization method is used to optimize the starting point boundary, and the initial configuration of the overhang section riser is constructed: ; ; In the formula, is the riser tension; is the angle between the vertical pipe and the horizontal direction; is the seawater force per unit length of the riser; is the current load per unit length of the riser; is the seabed soil contact force per unit length of the riser; is the riser density.

[0007] Furthermore, the calculation method of the mechanical model of the steel catenary riser considering the pipe-soil contact effect is: ; Where A is the cross-sectional area of ​​the riser; I is the moment of inertia of the riser cross section; is the material density of the riser; is the additional mass coefficient; is the unit mass of the riser; is the additional unit mass; is the velocity of the fluid in the tube; Inflow Absolute displacement in direction; It is the force between the riser and the seabed soil at the bottom contact position.

[0008] Furthermore, the calculation method of the fluid force model is: ; In the formula, is the steady-state drag force coefficient; is the density of seawater; are the pulsating drag coefficient and the pulsating lift coefficient respectively.

[0009] Furthermore, the calculation method of the wake oscillator model is: ; In the formula, are dimensionless wake oscillator variables in the downstream and crossstream directions; is the vortex shedding frequency; All are dimensionless parameters determined experimentally.

[0010] Furthermore, the established fluid force model, steel catenary riser mechanical model and wake oscillator model are coupled to obtain the boundary conditions of the riser: ; In the formula, is the platform displacement; is the length of the riser; t is a certain moment.

[0011] Furthermore, the Newmark-β method is used to calculate the vibration control matrix equation of the steel catenary riser in the global coordinate system: ; In the formula, , , They are mass matrix, damping matrix and stiffness matrix respectively; , , are the riser acceleration, velocity and displacement vector respectively; It is the external fluid force load and pipe-soil contact load.

[0012] Furthermore, based on the calculated dynamic response of the steel catenary riser under the pipe-soil contact effect, the strength of the vortex-induced vibration of the riser, the magnitude of the vibration frequency and the distribution of the spatial spectrum are simulated and analyzed, and the vortex-induced vibration response law of the steel catenary riser under the pipe-soil contact effect is obtained.

[0013] The beneficial effects of the present invention are as follows: by establishing a configuration model of a steel catenary riser, the present invention conducts in-depth research on the relationship between pipe-soil contact, marine environmental factors and vortex-induced vibration characteristics, thereby providing a reliable theoretical basis and technical support for the safety assessment and vibration control of the steel catenary riser. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0015] Figure 1 This is a schematic diagram of the stress of the seawater section unit of the steel catenary riser; Figure 2 This is a schematic diagram of the ground contact section of the steel catenary riser; Figure 3 This is a schematic diagram of the py curve simulation; Figure 4 The vibration response diagram of the seawater section and the ground-touching section of the steel catenary riser; Figure 5 Vibration frequency diagram of the steel catenary riser at the midpoint and touchdown point in sea water. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0017] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0018] Some embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0019] See also Figures 1 to 3 The vortex-induced vibration characteristics analysis method of the steel catenary riser considering the pipe-soil contact effect includes the following steps: S1: The configuration of deep-sea steel catenary riser is simulated according to the external current velocity, water depth of the riser, position of the riser fixing point, inner and outer diameters and other parameters; Based on the catenary theory, by establishing a local coordinate system, the starting point boundary is optimized using the optimization method to construct the initial configuration of the suspended section riser. According to the force analysis of the modeling unit, the equilibrium equation can be obtained:

[0020] ; (1) ; (2) . (3)

[0021] In the formula, is the riser tension, N; is the angle between the vertical pipe and the horizontal direction, °; is the seawater force per unit length of the riser, N; is the current load per unit length of the riser, N; is the seabed soil contact force per unit length of the riser, N; is the riser density, kg / m.

[0022] The equation solving conditions are: ; (4) ; (5) Combining equations (1), (2), (3) and (4), we can obtain the differential control equation: ; (6) . (7)

[0023] S2: Based on virtual work and Hamiltonian variational principle, a mechanical model of steel catenary riser considering pipe-soil contact is established; According to Kirchhoff's hypothesis, the displacement function of the riser is expressed as: ; (8) In the formula, Respectively with the coordinate system The corresponding displacement field function. Considering the longitudinal and transverse coupling, the Green strain is:

[0024] ; (9) The strain energy of the riser due to structural deformation is expressed as: ; (10) In the formula, is the tube length, m; is the elastic modulus of the riser material, MPa; is the moment of inertia of the riser section, m4; is the riser tension, N; the cross-sectional area of ​​the riser , m 2 .

[0025] The total kinetic energy of the steel catenary riser system consists of the body kinetic energy, the kinetic energy of the fluid inside the pipe, and the kinetic energy of the additional mass of the flow field outside the pipe, which can be expressed as: ; (11) In the formula, is the riser length, m; is the cross-sectional area of ​​the riser, m 2 ; is the cross-sectional area of ​​the outer circle of the riser, m 2 ; is the cross-sectional area of ​​the inner circle of the riser, m 2 ; is the moment of inertia of the riser section, m 4 ; is the moment of inertia of the outer circular section of the riser, m 4 ; is the material density of the riser, kg / m 3 ; is the internal flow density, kg / m3 ; is the density of seawater, kg / m 3 ; is the additional mass coefficient, which is generally taken as 1.0 for circular cross-section pipes; is the unit mass of the riser, kg / m; is the additional unit mass, kg / m; is the velocity of the fluid in the tube, m / s; Inflow Absolute speed in direction, m / s; Inflow Displacement in direction, m.

[0026] In the steel catenary riser system, the non-conservative forces are the damping force of the riser structure, the hydrodynamic force of the external flow field, and the force of the fluid in the pipe. The damping of the pipeline structure can gradually dissipate the energy of the riser vibration, while the external flow field can excite to increase the energy of the riser system. Therefore, the variation of the work done by the non-conservative force on the riser system can be expressed as:

[0027] ; (12) In the formula, They represent the drag force in the downstream direction and the lift force in the lateral direction of the external fluid, N; is the structural damping force, N; is the vertical force of the riser, N; is the energy loss during internal flow transport, J. Among them:

[0028] ; (13) ; (14) ; (15) The load-displacement curve (py curve) of pipe-soil interaction is related to the buried depth of the pipeline and the parameters of the soil and pipeline. Divide the py curve into N segments (such as Figure 2 ), use N elastic springs to simulate the py curve (such as Figure 3 ), pipe-soil contact force It can be expressed by the following formula:

[0029] ; (16) Substituting equations (10) to (12) and (16) into equation In the simplification, we can get The governing equations for vibration in three directions are: ; (17) is the cross-sectional area of ​​the riser, m 2 ; is the moment of inertia of the riser section, m 4 ; is the material density of the riser, kg / m 3 ; is the additional mass coefficient, which is generally taken as 1.0 for circular cross-section pipes; is the unit mass of the riser, kg / m; is the additional unit mass, kg / m; is the velocity of the fluid in the tube, m / s; Inflow Absolute displacement in direction, m; is the force between the riser and the seabed soil at the bottom contact position, N.

[0030] S3: On this basis, a fluid force model and a wake oscillator model are established to consider the influence of the inclination flow on the dynamic response of the riser; First, establish the local coordinate system of the riser system, and assume that the relative velocity between the fluid and the string is , the outflow velocity of the column is Based on the steady flow, the steady drag and lift acting on the string are as follows: Figure 3 shown.

[0031] According to the Morison equation, the steady-state drag force and lift force acting on the pipe string are: ; (18) In the formula, is the steady-state drag force coefficient, is the steady-state lift coefficient, is the density of seawater, kg / m 3 .

[0032] The pulsating fluid component acting on the riser can be expressed as: ; (19) In the formula, are the pulsating drag force and pulsating lift force, N, respectively; are the pulsating drag coefficient and the pulsating lift coefficient respectively.

[0033] Since the outer cross-section of the riser is circular, the steady-state lift coefficient Usually 0, , ignoring the influence of higher-order terms, we have: ; (20) The coupling between the change of fluid force and tube vibration can be described by the wake oscillator model. The classic van der Pol nonlinear vibration equation is used to describe the shedding characteristics of the fluid vortex. The wake oscillator control equation is: ; (twenty one) In the formula, are dimensionless wake oscillator variables in the downstream and crossstream directions, is the vortex shedding frequency, both A dimensionless quantity determined experimentally.

[0034] The dimensionless wake oscillator variables in the downstream and transverse directions are and Introducing the pulsation drag coefficient and the pulsating lift coefficient In, then , the final form of the external fluid force acting on the riser can be obtained: ; (twenty two) Based on the coordinate transformation theory, the current load in the local coordinate system is transformed into the global coordinate system: So we can get: ; (twenty three) in, ; (twenty four) The matrix for transforming from unit coordinates to global coordinates can be expressed as follows: ; (25) S4: The established fluid force model, steel catenary riser mechanical model and wake oscillator model are coupled, and the Newmark-β method is used based on the boundary conditions of the model to solve the steel catenary riser mechanical model analysis method considering the pipe-soil contact effect; The heave motion of a floating platform is similar to simple harmonic motion. Its heave displacement is determined by factors such as wave height and the type, structure, and scale of the hull or platform. The motion law can be expressed as: ; (26) In the formula, is the platform displacement, m; is the wave height, m; is the wave period, s; is the ratio of heave displacement to wave height.

[0035] Both ends of the riser are hinged, and the longitudinal movement of the upper end is consistent with the platform. Its boundary conditions can be expressed as: ; (27) In the formula, is the platform displacement; is the length of the riser; t is a certain moment.

[0036] Calculation of the vibration control matrix equation of steel catenary riser in the global coordinate system using the Newmark-β method ; in , , They are mass matrix, damping matrix and stiffness matrix respectively; , , are the riser acceleration, velocity and displacement vector respectively; It is the external fluid force load and pipe-soil contact load.

[0037] S5: Based on the calculated dynamic response of the steel catenary riser under the pipe-soil contact effect, the strength of the vortex-induced vibration of the riser, the magnitude of the vibration frequency, and the distribution of the spatial spectrum are simulated and analyzed, and the vortex-induced vibration response law of the steel catenary riser under the pipe-soil contact effect is summarized. Furthermore, in S5, the differential control equation is used to calculate the vibration displacement time history of the steel catenary riser, and the vibration frequency of the riser system is obtained through Fourier transformation, and the vortex-induced vibration characteristics of the steel catenary riser under different current velocities and different fixed end positions are summarized.

[0038] The parameters of the steel catenary riser of a well were selected for the experiment. The parameters of the steel catenary riser of a certain well (detailed parameters are shown in Table 1) were selected for configuration, and the vortex-induced vibration characteristics were analyzed on this basis. Figure 4 and Figure 5 It can be seen that the riser exhibits completely different vibration characteristics in the seawater section and the bottoming section. The riser in the seawater section is mainly affected by the flow field and presents a relatively single-frequency vibration mode. Its vibration behavior is relatively simple and predictable. However, once the riser enters the bottoming area, due to the reaction force of the soil, nonlinear friction effect, and possible local vortex formation, its vibration mode changes to multi-frequency vibration. This multi-frequency vibration not only increases the complexity of the dynamic response of the riser, but may also cause more severe vibration amplitude and stress fluctuations.

[0039] .

[0040] For the aforementioned embodiments, for the sake of simplicity, they are all described as a series of action combinations, but those skilled in the art should be aware that the present application is not limited by the order of the actions described, because according to the present application, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are preferred embodiments, and the actions involved are not necessarily required by the present application.

[0041] The above embodiments describe the basic principles and main features of the present invention and the advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the changes and modifications made by those skilled in the art shall be within the scope of protection of the appended claims of the present invention without departing from the spirit and scope of the present invention.

Claims

1. A method for analyzing vortex-induced vibration characteristics of steel catenary risers considering pipe-soil contact, characterized in that: The steps include: S1: The configuration of deep-sea steel catenary riser is simulated according to the external current velocity, water depth of the riser, position of the riser fixing point and inner and outer diameter parameters; S2: Based on virtual work and Hamiltonian variational principle, a mechanical model of steel catenary riser considering pipe-soil contact is established; S3: Establish a fluid force model and a wake oscillator model that consider the influence of the inclination flow on the dynamic response of the riser; S4: The established fluid force model, steel catenary riser mechanical model and wake oscillator model are coupled, and the Newmark-β method is used based on the boundary conditions of the model to solve the dynamic response of the steel catenary riser considering the pipe-soil contact effect, and the vortex-induced vibration response law is obtained.

2. The vortex-induced vibration characteristics analysis method of steel catenary riser considering pipe-soil contact as claimed in claim 1, characterized in that: Step S1 is specifically as follows: Based on the catenary theory, a local coordinate system is established and an optimization method is used to optimize the starting point boundary to construct the initial configuration of the overhang section riser: ； ； In the formula, is the riser tension; is the angle between the vertical pipe and the horizontal direction; is the seawater force per unit length of the riser; is the current load per unit length of the riser; is the seabed soil contact force per unit length of the riser; is the riser density.

3. The vortex-induced vibration characteristics analysis method of steel catenary riser considering pipe-soil contact as claimed in claim 2, characterized in that: The calculation method of the mechanical model of the steel catenary riser considering the pipe-soil contact effect is: ； Where A is the cross-sectional area of ​​the riser; I is the moment of inertia of the riser cross section; is the material density of the riser; is the additional mass coefficient; is the unit mass of the riser; is the additional unit mass; is the velocity of the fluid in the tube; Inflow Absolute displacement in direction; It is the force between the riser and the seabed soil at the bottom contact position.

4. The vortex-induced vibration characteristic analysis method of steel catenary riser considering pipe-soil contact as claimed in claim 3, characterized in that: The calculation method of the fluid force model is: ； In the formula, is the steady-state drag force coefficient; is the density of seawater; are the pulsating drag coefficient and the pulsating lift coefficient respectively.

5. The vortex-induced vibration characteristic analysis method of steel catenary riser considering pipe-soil contact as claimed in claim 4, characterized in that: The calculation method of the wake oscillator model is: ； In the formula, are dimensionless wake oscillator variables in the downstream and crossstream directions; is the vortex shedding frequency; All are dimensionless parameters determined experimentally.

6. The method for analyzing vortex-induced vibration characteristics of steel catenary risers considering pipe-soil contact as claimed in claim 5, characterized in that: The established fluid force model, steel catenary riser mechanical model and wake oscillator model are coupled to obtain the boundary conditions of the riser: ； In the formula, is the platform displacement; is the length of the riser; t is a certain moment.

7. The method for analyzing vortex-induced vibration characteristics of steel catenary risers considering pipe-soil contact as claimed in claim 6, characterized in that: The Newmark-β method is used to calculate the vibration control matrix equation of the steel catenary riser in the global coordinate system: ； In the formula, , , They are mass matrix, damping matrix and stiffness matrix respectively; , , are the riser acceleration, velocity and displacement vector respectively; It is the external fluid force load and pipe-soil contact load.

8. The method for analyzing vortex-induced vibration characteristics of steel catenary risers considering pipe-soil contact as claimed in claim 7, characterized in that: According to the calculated dynamic response of the steel catenary riser under the pipe-soil contact effect, the strength of the vortex-induced vibration of the riser, the magnitude of the vibration frequency and the distribution of the spatial spectrum are simulated and analyzed, and the vortex-induced vibration response law of the steel catenary riser under the pipe-soil contact effect is obtained.

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