Method for predicting gas-liquid-solid three-phase flow-induced vibration of deep sea natural gas hydrate riser

Abstract

The invention discloses a gas-liquid-solid three-phase flow-induced vibration prediction method for a deep-sea natural gas hydrate riser. The method comprises the following steps: S1, introducing hypothetical conditions of nonlinear vibration of a multi-field coupling hydrate exploitation riser; s2, according to the assumed conditions, establishing a multi-field coupling hydrate exploitation riser nonlinear vibration control equation by taking a vertical axis parallel to the riser direction as a z axis and a downward positive axis, taking the upper part of the riser as an origin of coordinates, taking a direction parallel to the water flow direction as an x axis and taking a direction perpendicular to the water flow direction as a y axis; s3, establishing boundary conditions of the nonlinear vibration control equation of the multi-field coupling hydrate exploitation riser; and S4, solving the nonlinear vibration control equation of the multi-field coupling hydrate exploitation riser in combination with the boundary conditions. According to the method, the gas-liquid-solid three-phase flow-induced vibration of the deep-sea natural gas hydrate riser can be accurately predicted, and technical support is provided for ocean oil and gas resource exploitation.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas exploitation, and in particular to a method for predicting vibration caused by gas-liquid-solid three-phase flow of a deep-sea natural gas hydrate riser. Background Art

[0002] In the exploitation of marine oil and gas resources, top tension risers can quickly and efficiently transport natural gas hydrates to offshore platforms, and therefore have been widely used. The top of the top tension riser is connected to the platform, and the bottom is connected to the seabed wellhead. On the seabed, mining equipment is used to develop hydrate ore bodies in solid form, and the sediments containing hydrates are crushed into fine particles, mixed with seawater, and transported to the offshore platform using closed pipelines. On the outside of the pipeline, flow fields such as sea currents and ocean currents can excite the pipeline to vibrate, and the gas-liquid-solid multiphase flow in the pipe can also excite the pipeline to vibrate. Vibration may cause premature failure of the oil pipe string, and in severe cases may even cause the wellbore to be scrapped. Therefore, a method for predicting the vibration caused by the gas-liquid-solid three-phase flow of deep-sea natural gas hydrate risers is urgently needed. Summary of the invention

[0003] In view of the above problems, the present invention aims to provide a method for predicting gas-liquid-solid three-phase flow-induced vibration of a deep-sea natural gas hydrate riser.

[0004] The technical solution of the present invention is as follows:

[0005] A method for predicting vibration caused by gas-liquid-solid three-phase flow in a deep-sea natural gas hydrate riser comprises the following steps:

[0006] S1: Introducing the assumption of multi-field coupled nonlinear vibration of hydrate production riser;

[0007] S2: Based on the above assumptions, the vertical axis parallel to the riser direction is taken as the z-axis, the downward direction is positive, the upper part of the riser is taken as the origin of the coordinate system, the axis parallel to the water flow direction is taken as the x-axis, and the axis perpendicular to the water flow direction is taken as the y-axis, and the multi-field coupled hydrate production riser nonlinear vibration control equation is established;

[0008] S3: establishing the boundary conditions of the multi-field coupled hydrate production riser nonlinear vibration control equation;

[0009] S4: Solving the nonlinear vibration control equation of the multi-field coupled hydrate production riser in combination with the boundary conditions.

[0010] Preferably, in step S1, the assumptions include:

[0011] (1) The riser material is uniform and isotropic, the cross-sectional dimensions of the pipe do not change along the length of the pipe, and it maintains linear elasticity during movement and deformation;

[0012] (2) Both ends of the riser are hinged, and a tensioning system is provided at the top to provide pre-tension;

[0013] (3) Ignore the effect of the connection position on the bending stiffness of the riser;

[0014] (4) In the mechanical analysis, the riser is simplified as a flexible rod with uniform cross section;

[0015] (5) Under the action of internal and external loads, the riser system is a problem of small strain and large deformation;

[0016] (6) The fluid in the tube is incompressible, and the effect of changes in the pressure in the tube on the change in fluid density can be ignored.

[0017] Preferably, in step S2, the multi-field coupled hydrate production riser nonlinear vibration control equation includes:

[0018] (1) Three-degree-of-freedom vibration control equation of mining riser:

[0019]

[0020]

[0021]

[0022] Where: m υ is the unit mass of the riser, kg / m; m a is the additional unit mass, kg / m; A i is the cross-sectional area of ​​the inner circle of the riser, m 2 ; E g 、E l 、E s are gas holdup, liquid holdup, and solid content, respectively; ρ g , l , s They are respectively gas phase density, liquid phase density, and solid phase density, kg / m 3 ; β0 is the energy loss coefficient of particle collision; ρ m is the density of the mixed fluid, kg / m 3 ;υ x ,υ y ,υ z are the displacements of the riser in the x, y, and z directions, respectively; the superscript ′ indicates the first-order derivative with respect to z, the superscript ″ indicates the second-order derivative with respect to z, the superscript (4) indicates the fourth-order derivative with respect to z, the superscript · indicates the first-order derivative with respect to time t, and the superscript ·· indicates the second-order derivative with respect to time t; ρ υ is the material density of the riser, kg / m 3 ; I is the moment of inertia of the riser section, m 4 ρ ais the density of seawater, kg / m 3 ; C m is the additional mass coefficient; I o is the moment of inertia of the outer circular section of the riser, m 4 ; c is the damping coefficient of the riser; U c is the outflow velocity of the column, m / s; D o is the outer diameter of the riser, m; is the steady-state drag coefficient; E is the elastic modulus of the riser material, Pa; v g 、v l 、v s are gas phase velocity, liquid phase velocity, solid phase velocity, m / s; F T is the top tension of the riser, N; A is the cross-sectional area of ​​the riser, m 2 ; C d ′ is the pulsating drag coefficient; q x ,q y are dimensionless wake oscillator variables in the downstream and crossstream directions respectively; C l ′ is the pulsating lift coefficient; D i is the inner diameter of the riser, m; α0 is the friction loss coefficient between the internal flow and the pipe wall; v m is the velocity of the mixed fluid, m / s; f is the friction coefficient; g is the acceleration due to gravity, m / s 2 ;

[0023] (2) Wake oscillator control equation:

[0024]

[0025]

[0026] Where: ε x , ε y , A x , A y All are dimensionless parameters determined experimentally; ω s is the vortex shedding frequency; x and y are the displacement in the downstream and transverse directions, respectively, in m.

[0027] Preferably, in step S3, the boundary condition is:

[0028]

[0029] Where: (0, t) means the state where the riser depth is 0 and the time is t; (L, t) means the state where the riser depth is L and the time is t; u boat (t) is the platform displacement.

[0030] Preferably, in step S4, the linear Lagrangian function and the cubic Hermit interpolation function are used to discretize the pipe string and perform matrix assembly to obtain the pipe string vibration control matrix equation, and then the Newmark method and the Newton Raphson method are used to jointly solve the pipe string vibration control matrix equation; at the same time, the fourth-order Runge-Kutta method is used to solve the wake oscillator control equation in the multi-field coupled hydrate production riser nonlinear vibration control equation.

[0031] The beneficial effects of the present invention are:

[0032] The present invention establishes a multi-field coupled hydrate production riser nonlinear vibration control equation taking into account a variety of nonlinear factors, which can accurately predict the gas-liquid-solid three-phase flow-induced vibration of the deep-sea natural gas hydrate production riser, providing technical support for the exploitation of marine oil and gas resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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 these drawings without paying creative labor.

[0034] Figure 1 It is the coordinate system of the hydrate riser and its vibration schematic diagram;

[0035] Figure 2 is a schematic diagram of the external fluid force acting on the riser;

[0036] Figure 3 It is a schematic diagram of a solution process of a nonlinear vibration control equation of a hydrate production riser with multi-field coupling according to a specific embodiment;

[0037] Figure 4 It is a cross-flow displacement time history curve diagram of 250s to 300s at 1000m of the target riser in a specific embodiment;

[0038] Figure 5 It is a time history curve of downstream displacement of the target riser at 1000m from 150s to 200s in a specific embodiment;

[0039] Figure 6 It is a time history curve diagram of the longitudinal displacement of the target riser at 1000m from 286s to 300s in a specific embodiment. DETAILED DESCRIPTION

[0040] The present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those generally understood by those of ordinary skill in the art to which this application belongs. The words "including" or "comprising" and the like used in the disclosure of the present invention mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0041] The present invention provides a method for predicting vibration caused by gas-liquid-solid three-phase flow of a deep-sea natural gas hydrate riser, comprising the following steps:

[0042] S1: Introducing the assumption of multi-field coupled nonlinear vibration of hydrate production riser.

[0043] In a specific embodiment, the assumptions include:

[0044] (1) The riser material is uniform and isotropic, the cross-sectional dimensions of the pipe do not change along the length of the pipe, and it maintains linear elasticity during movement and deformation;

[0045] (2) Both ends of the riser are hinged, and a tensioning system is provided at the top to provide pre-tension;

[0046] (3) Ignore the effect of the connection position on the bending stiffness of the riser;

[0047] (4) In the mechanical analysis, the riser is simplified as a flexible rod with uniform cross section;

[0048] (5) Under the action of internal and external loads, the riser system is a problem of small strain and large deformation;

[0049] (6) The fluid in the tube is incompressible, and the effect of changes in the pressure in the tube on the change in fluid density can be ignored.

[0050] S2: Based on the above assumptions, the vertical axis parallel to the riser direction is taken as the z-axis, downward is positive, the upper part of the riser is taken as the coordinate origin, the x-axis parallel to the water flow direction is taken as the x-axis, and the y-axis perpendicular to the water flow direction is taken as the y-axis, and the multi-field coupled hydrate production riser nonlinear vibration control equation is established.

[0051] In a specific embodiment, the multi-field coupled hydrate production riser nonlinear vibration control equation includes:

[0052] (1) Three-degree-of-freedom vibration control equation of mining riser:

[0053]

[0054]

[0055]

[0056] Where: m υ is the unit mass of the riser, kg / m; m a is the additional unit mass, kg / m; A i is the cross-sectional area of ​​the inner circle of the riser, m 2 ; E g 、E l 、E s are gas holdup, liquid holdup, and solid content, respectively; ρ g , l , s They are respectively gas phase density, liquid phase density, and solid phase density, kg / m 3 ; β0 is the energy loss coefficient of particle collision; ρ m is the density of the mixed fluid, kg / m 3 ;υ x ,υ y ,υ z are the displacements of the riser in the x, y, and z directions, respectively; the superscript ′ indicates the first-order derivative with respect to z, the superscript ″ indicates the second-order derivative with respect to z, the superscript (4) indicates the fourth-order derivative with respect to z, the superscript · indicates the first-order derivative with respect to time t, and the superscript ·· indicates the second-order derivative with respect to time t; ρ υ is the material density of the riser, kg / m 3 ; I is the moment of inertia of the riser section, m 4 ρ a is the density of seawater, kg / m 3 ; C m is the additional mass coefficient; I o is the moment of inertia of the outer circular section of the riser, m 4 ; c is the damping coefficient of the riser; U c is the outflow velocity of the column, m / s; D o is the outer diameter of the riser, m; is the steady-state drag coefficient; E is the elastic modulus of the riser material, Pa; v g 、v l 、v s are gas phase velocity, liquid phase velocity, solid phase velocity, m / s; F T is the top tension of the riser, N; A is the cross-sectional area of ​​the riser, m 2 ; C d ′ is the pulsating drag coefficient; q x ,q y are dimensionless wake oscillator variables in the downstream and crossstream directions respectively; C l ′ is the pulsating lift coefficient; D iis the inner diameter of the riser, m; α0 is the friction loss coefficient between the internal flow and the pipe wall; v m is the velocity of the mixed fluid, m / s; f is the friction coefficient; g is the acceleration due to gravity, m / s 2 ;

[0057] (2) Wake oscillator control equation:

[0058]

[0059]

[0060] Where: ε x , ε y , A x , A y All are dimensionless parameters determined experimentally; ω s is the vortex shedding frequency; x and y are the displacement in the downstream direction and the displacement in the cross-stream direction, respectively.

[0061] In the above embodiment, the multi-field coupled hydrate production riser nonlinear vibration control equation is constructed and obtained by the following steps:

[0062] According to the assumptions, the riser is a continuous flexible structure. From the perspective of energy, the three-degree-of-freedom vibration control equation of the mining riser can be established based on the Hamilton variational principle. The Hamilton principle shows that the motion trajectory of an object in any time interval makes the action reach an extreme value. The kinetic energy and potential energy of the object are connected through the Hamilton function. The Hamilton functional of the riser system can be expressed as:

[0063]

[0064] Where: W K is the total kinetic energy of the riser system; U P is the total potential energy of the riser system; W is the work done by the non-conservative force on the riser system.

[0065] When the vertical pipe is not deformed, the vertical axis parallel to the vertical pipe is the z-axis, downward is positive, the upper part of the vertical pipe is taken as the origin of the coordinate system, the x-axis is parallel to the water flow direction (downstream), and the y-axis is perpendicular to the water flow direction (cross-flow). Figure 1 As shown, x ,υ y ,υ z They represent the displacement of the riser in the x, y, and z directions respectively.

[0066] According to Kirchhoff's hypothesis, the displacement field function of the riser can be expressed as:

[0067]

[0068] Where: u1, u2, u3 are the displacement field functions corresponding to the coordinate systems x, y, z respectively.

[0069] The Green strain considering the longitudinal and transverse coupling is:

[0070]

[0071] The potential energy generated by the riser due to structural deformation can be expressed as:

[0072]

[0073] Substituting equation (9) into equation (10) and considering the top tension, the potential energy of the riser is obtained as follows:

[0074]

[0075] Where: L is the riser depth, m.

[0076] The absolute velocities of the fluid in the tube in three directions are:

[0077]

[0078] Where: U is the velocity of the fluid in the tube; v x 、v y 、v z are the absolute velocities of the internal flow in the x, y, and z directions, respectively.

[0079] The additional mass moves with the pipeline structure and has the same speed. The total kinetic energy of the riser system consists of the kinetic energy of the pipe string, the kinetic energy of the fluid in the pipe, and the kinetic energy of the additional mass of the flow field outside the pipe, which can be expressed as:

[0080]

[0081] Where: i is the internal flow density, kg / m 3 ; C m It is the additional mass coefficient, which is generally taken as 1.0 for circular cross-section pipes.

[0082] In the current system, the non-conservative forces are the damping force of the riser structure and the hydrodynamic force of the external flow field. 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. In addition, the fluid in the pipe will also cause energy loss in the riser system during transportation. Therefore, the variation of the work done by the non-conservative force on the riser system can be expressed as:

[0083]

[0084] Where: F D ,FL They represent the drag force of the external fluid in the downstream direction and the lift in the lateral direction respectively; F cx ,F cy ,F cz is the structural damping force; w g is the vertical force of the riser; W l It is the energy loss during internal flow transport.

[0085]

[0086] c=2mωζ(16)

[0087]

[0088]

[0089] According to Hamilton's variational principle, by substituting equations (11), (13) and (14) into equation (7), we can obtain the vibration equations in three directions as the equations always hold true:

[0090]

[0091] Where: m i is the unit mass of internal flow, m / kg.

[0092] Assume the relative velocity between the fluid and the pipe string is V r , the outflow velocity of the column is U c Based on the steady flow, the steady drag and lift acting on the string are as follows: Figure 2 shown.

[0093] According to the Morison equation, the steady-state drag force and lift force acting on the pipe string are:

[0094]

[0095] Where: is the steady-state lift coefficient.

[0096] The x- and y-direction fluid force components acting on the tube can be given by Figure 2 And formula (20) we get:

[0097]

[0098] The pulsating fluid component acting on the tubing string can be expressed as:

[0099]

[0100] Where: F D ′,C D , F L ′,CL They are pulsating drag force, drag force coefficient, pulsating lift force, and lift coefficient respectively.

[0101] Combining equation (21) and equation (22) yields the external fluid force acting on the tube:

[0102]

[0103] After sorting:

[0104]

[0105] The coupling between the change of fluid force and tube vibration is described by the wake oscillator model. The coupling between structural vibration and the wake oscillator model is as follows: structural vibration affects the magnitude of lift, and in turn, lift affects the vibration of the structure. The control equation of the wake oscillator is:

[0106]

[0107] Vortex shedding frequency ω s Considering the relative velocity between the riser and the fluid in the downstream direction, it can be expressed as:

[0108]

[0109] Where: S t is the Sterthal number.

[0110] The dimensionless wake oscillator variables q in the downstream and transverse directions are x and q y Introducing the drag coefficient and lift coefficient In, then The final form of the external fluid force acting on the tube can be obtained:

[0111]

[0112] In a specific embodiment, A x =48, A y =12,ε x =1.2,ε y =0.3, C d ′=0.3,C l ′=0.4,S t =0.2.

[0113] During the lifting process of multiphase flow, the gas phase and liquid phase are prone to deformation, splitting and aggregation. Bubbles of different sizes and shapes will appear inside the pipeline, and the interface and distribution between the two phases will continue to change, which makes the flow state of the multiphase flow in the pipe very complex and has multiple flow patterns. The flow patterns of vertical pipelines can be mainly divided into: bubbly flow, slug flow, turbulent flow and annular mist flow. For different flow patterns, the excitation effect of the multiphase flow in the pipe on the pipeline will be different. Since the change of fluid density is the main reason for the vibration of the pipeline caused by the multiphase flow in the pipe, it is necessary to obtain the mixed density of the fluid in the pipe along the well depth in order to analyze the excitation effect of the flow pattern on the vertical pipe. In Hamilton's principle, the density and velocity of the fluid in the pipe will affect the kinetic energy of the fluid in the pipe.

[0114] The absolute velocities of the gas phase, liquid phase, and solid phase of the fluid in the tube in three directions can be expressed as:

[0115]

[0116]

[0117]

[0118] Where: v gx 、v gy 、v gz are the absolute velocities of the gas phase in the x, y, and z directions, m / s; v lx 、v ly 、v lz are the absolute velocities of the liquid phase in the x, y, and z directions, m / s; v sx 、v sy 、v sz are the absolute velocities of the solid phase in the x, y, and z directions, m / s, respectively.

[0119] Substituting the contents and velocities of the gas, liquid and solid phases that vary along the well depth into equation (13), the kinetic energy of the riser system can be obtained as:

[0120]

[0121] There will be energy loss in the lifting process of hydrate gas-liquid-solid three-phase flow, including friction loss between the internal flow and the pipe wall and energy loss caused by particle collision:

[0122] W l =W f +W c (32)

[0123] Where: W l is the internal flow energy loss; W f is the friction loss between the internal flow and the tube wall; Wc is the energy loss caused by particle collision.

[0124] During the transportation process, the fluid in the pipe is viscous, which will cause energy loss in the riser system. After considering the shear force between the multiphase liquid phase and the pipe wall and the shear force between the solid phase and the pipe wall, the friction loss between the internal flow and the pipe wall can be expressed as:

[0125]

[0126] in:

[0127]

[0128] Where: d s is the solid particle diameter, m; μ f Fluid dynamic viscosity; C v is the volume concentration of solid particles, mol / L; C vmax is the local maximum concentration of solid particles, mol / L.

[0129] The energy loss caused by particle collision can be expressed as:

[0130]

[0131] in:

[0132]

[0133] Where: d sp is the median particle size, m.

[0134] Substituting equation (33) and equation (35) into equation (32), we can obtain:

[0135]

[0136] By substituting the above-mentioned external fluid force, the internal flow mixing density that varies along the well depth, the internal flow mixing velocity that varies along the well depth, and the internal flow energy loss into equation (19), the multi-field coupled hydrate production riser nonlinear vibration control equation shown in equations (1) to (5) of the present invention can be obtained.

[0137] S3: Establishing the boundary conditions of the multi-field coupled hydrate production riser nonlinear vibration control equation.

[0138] In a specific embodiment, the boundary condition is:

[0139]

[0140] Where: (0, t) means the state where the riser depth is 0 and the time is t; (L, t) means the state where the riser depth is L and the time is t; u boat(t) is the platform displacement.

[0141] S4: Solving the nonlinear vibration control equation of the multi-field coupled hydrate production riser in combination with the boundary conditions.

[0142] In a specific embodiment, the pipe string is discretized into N units (a total of N+1 nodes) using a linear Lagrangian function and a cubic Hermit interpolation function, with a unit length of l, and a matrix assembly is performed to obtain a pipe string vibration control matrix equation, and then the Newmark method and the Newton Raphson method are used to jointly solve the pipe string vibration control matrix equation; at the same time, the fourth-order Runge-Kutta method is used to solve the wake oscillator control equation in the multi-field coupled hydrate production riser nonlinear vibration control equation, and the solution calculation process is as follows: Figure 3 shown.

[0143] The displacements of the pipe in the x, y, and z directions are respectively expressed as express:

[0144]

[0145] Where: represents the displacement of the string unit, Represent the vibration shape functions of the pipe string in the x, y, and z directions respectively.

[0146] in:

[0147]

[0148]

[0149]

[0150]

[0151] Substituting the displacement function (38) into the nonlinear control equation, the control equation of the pipe string expressing the longitudinal and transverse coupling of the unit using the node displacement vector is obtained as follows:

[0152]

[0153] in:

[0154]

[0155]

[0156]

[0157]

[0158] The fluid force acting on the lifting hard pipe unit is processed by finite element method, and the force on the unit is simplified. Assuming that the fluid force on the i-th unit is linearly distributed, the force on the unit string can be expressed as:

[0159]

[0160] Where: f i , f i+1 are the fluid forces at the i-th and i+1-th nodes respectively.

[0161] Then the force on the i-th unit can be expressed as:

[0162]

[0163] By matrix-assembling the unit string control equation (43), the string vibration control matrix equation can be obtained as follows:

[0164]

[0165] It can be seen from the stiffness matrix that the stiffness matrix of the pipe string model will change in real time with the displacement, which will increase the difficulty of the system's calculation convergence. At the same time, for hydrate risers with large aspect ratios, large displacements will occur in the downstream direction. Large deformations in the longitudinal and transverse coupling model will seriously affect the transverse and longitudinal vibrations, and will also lead to non-convergence of the calculation results.

[0166] In this embodiment, the incremental Newmark method and the Newton Raphson method are used to jointly solve the problem. During the gradual iteration of the Newmark method, the Newton Raphson method is used to iteratively correct the displacement, thereby improving the solution accuracy.

[0167] It should be noted that the solution method of the control equation is a prior art. In addition to the solution method used in the above embodiment, those skilled in the art may also use other equation solution methods to solve the equation. The vibration time history response of each point of the riser can be obtained according to the solution result, providing technical support for the riser vibration analysis.

[0168] In a specific embodiment, the vibration prediction method of the deep-sea natural gas hydrate riser gas-liquid-solid three-phase flow-induced vibration of the present invention is used to predict the vibration of the target riser. In this embodiment, the basic parameters related to the target riser are shown in Table 1:

[0169] Table 1 Basic parameters related to the target riser

[0170] parameter Numeric parameter Numeric Riser length 2000m Outflow speed 1.2m / s Riser outer diameter 0.44m Seawater density <![CDATA[1025kg / m 3 ]]> Riser wall thickness 0.02m Riser material density <![CDATA[7850kg / m 3 ]]> Top tension 476.198KN Density of hydrate liquid phase in tube <![CDATA[1030kg / m 3 ]]> Elastic modulus 207GPa Density of hydrate solid phase in tube <![CDATA[1350kg / m 3 ]]> Structural damping coefficient 0.01 Strouhal coefficient 0.2

[0171] The calculation code of the present invention is written using FORTRAN compiler, and the column is discretized into 280 units, the time step is 0.05s, and the final calculation result is as follows: Figure 4-Figure 6 As shown. Figure 4 It can be seen that the cross-flow vibration amplitude of the riser increases with the increase of displacement. Figure 5 It can be seen that when the displacement is small, the riser is greatly affected by the ocean outflow, resulting in a larger displacement in the downstream direction; Figure 6 It can be seen that the period of the longitudinal displacement of the riser does not change much, but the amplitude changes.

[0172] In summary, the present invention can accurately predict the gas-liquid-solid three-phase flow-induced vibration of a deep-sea natural gas hydrate riser. Compared with the prior art, the present invention is a significant improvement.

[0173] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for predicting gas-liquid-solid three-phase flow-induced vibration of a deep-sea natural gas hydrate riser, characterized in that: The following steps are involved: S1: Introducing the assumption of multi-field coupled nonlinear vibration of hydrate production riser; S2: Based on the above assumptions, the vertical axis parallel to the riser direction is taken as the z-axis, the downward direction is positive, the upper part of the riser is taken as the origin of the coordinate system, the axis parallel to the water flow direction is taken as the x-axis, and the axis perpendicular to the water flow direction is taken as the y-axis, and the multi-field coupled hydrate production riser nonlinear vibration control equation is established; S3: establishing the boundary conditions of the multi-field coupled hydrate production riser nonlinear vibration control equation; S4: Solving the nonlinear vibration control equation of the multi-field coupled hydrate production riser in combination with the boundary conditions.

2. The method for predicting gas-liquid-solid three-phase flow-induced vibration of a deep-sea natural gas hydrate riser according to claim 1, characterized in that: In step S1, the assumptions include: (1) The riser material is uniform and isotropic, the cross-sectional dimensions of the pipe do not change along the length of the pipe, and it maintains linear elasticity during movement and deformation; (2) Both ends of the riser are hinged, and a tensioning system is provided at the top to provide pre-tension; (3) Ignore the effect of the connection position on the bending stiffness of the riser; (4) In the mechanical analysis, the riser is simplified as a flexible rod with uniform cross section; (5) Under the action of internal and external loads, the riser system is a problem of small strain and large deformation; (6) The fluid in the tube is incompressible, and the effect of changes in the pressure in the tube on the change in fluid density can be ignored.

3. The method for predicting gas-liquid-solid three-phase flow-induced vibration of a deep-sea natural gas hydrate riser according to claim 2, characterized in that: In step S2, the multi-field coupled hydrate production riser nonlinear vibration control equation includes: (1) Three-degree-of-freedom vibration control equation of mining riser: Where: m υ is the unit mass of the riser, kg / m; m a is the additional unit mass, kg / m; A i is the cross-sectional area of ​​the inner circle of the riser, m 2 ; E g 、E l 、E s are gas holdup, liquid holdup, and solid content, respectively; ρ g , l , s They are respectively gas phase density, liquid phase density, and solid phase density, kg / m 3 ; β0 is the energy loss coefficient of particle collision; ρ m is the density of the mixed fluid, kg / m 3 ;υ x ,υ y ,υ z are the displacements of the riser in the x, y, and z directions, respectively; the superscript ′ indicates the first-order derivative with respect to z, the superscript ″ indicates the second-order derivative with respect to z, the superscript (4) indicates the fourth-order derivative with respect to z, the superscript · indicates the first-order derivative with respect to time t, and the superscript ·· indicates the second-order derivative with respect to time t; ρ υ is the material density of the riser, kg / m 3 ; I is the moment of inertia of the riser section, m 4 ρ a is the density of seawater, kg / m 3 ; C m is the additional mass coefficient; I o is the moment of inertia of the outer circular section of the riser, m 4 ; c is the damping coefficient of the riser; U c is the outflow velocity of the column, m / s; D o is the outer diameter of the riser, m; is the steady-state drag coefficient; E is the elastic modulus of the riser material, Pa; v g 、v l 、v s are gas phase velocity, liquid phase velocity, solid phase velocity, m / s; F T is the top tension of the riser, N; A is the cross-sectional area of ​​the riser, m 2 ; C d ′ is the pulsating drag coefficient; q x ,q y are dimensionless wake oscillator variables in the downstream and crossstream directions respectively; C l ′ is the pulsating lift coefficient; D i is the inner diameter of the riser, m; α0 is the friction loss coefficient between the internal flow and the pipe wall; v m is the velocity of the mixed fluid, m / s; f is the friction coefficient; g is the acceleration due to gravity, m / s 2 ; (2) Wake oscillator control equation: Where: ε x , ε y , A x , A y All are dimensionless parameters determined experimentally; ω s is the vortex shedding frequency; x and y are the displacement in the downstream and transverse directions, respectively, in m.

4. The method for predicting gas-liquid-solid three-phase flow-induced vibration of a deep-sea natural gas hydrate riser according to claim 3, characterized in that: In step S3, the boundary conditions are: Where: (0, t) means the state where the riser depth is 0 and the time is t; (L, t) means the state where the riser depth is L and the time is t; u boat (t) is the platform displacement.

5. The method for predicting gas-liquid-solid three-phase flow-induced vibration of a deep-sea natural gas hydrate riser according to any one of claims 1 to 4, characterized in that: In step S4, the linear Lagrangian function and the cubic Hermit interpolation function are used to discretize the pipe string and perform matrix assembly to obtain the pipe string vibration control matrix equation, and then the Newmark method and the NewtonRaphson method are used to jointly solve the pipe string vibration control matrix equation; at the same time, the fourth-order Runge-Kutta method is used to solve the wake oscillator control equation in the multi-field coupled hydrate production riser nonlinear vibration control equation.

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