阅读说明：本技术 一种基于缆索水动力特性的浮动式立柱平台模型创建方法 (Floating type upright post platform model establishing method based on hydrodynamic characteristics of cable ) 是由 朱向前 毕庆显 俞完錫 于 2021-07-22 设计创作，主要内容包括：本公开提供一种基于缆索水动力特性的浮动式立柱平台模型创建方法,涉及海洋浮动平台分析领域,基于相对速度矢量单元坐标系采用集中质量-弹簧法搭建缆索模型,解决集中质量-弹簧缆索模型的奇异性,使得浮式立柱平台及系泊系统模型的鲁棒性更强,通过对比立柱平台在X、Y向波浪作用下的运动响应,验证了所搭建缆索模型的准确性。(The invention provides a floating type upright post platform model establishing method based on hydrodynamic characteristics of cables, and relates to the field of ocean floating platform analysis.)

1. A floating type stand column platform model establishing method based on hydrodynamic characteristics of cables is characterized by comprising the following steps:

dividing the cable into a plurality of cable units based on a concentrated mass-spring model, expressing the stress of the cable based on a relative speed unit coordinate system, and creating a cable dynamic model;

dividing the stand column platform into a plurality of stand column units based on a slicing theory, acquiring the stress of the stand column platform, and creating a stand column platform numerical model;

based on a finite water depth linear wave theory, creating a wave model, and acquiring the speed and the acceleration of water particles at the node positions of the upright post unit and the cable unit to obtain the stress of the cable and the upright post platform;

and obtaining a floating type upright platform model for mooring the cable based on the upright platform numerical model and the cable dynamic model, verifying by combining a wave model, and analyzing the dynamic response of the upright platform and the cable tension under the action of the wave environment.

2. A floating mast platform model creation method based on hydrodynamic cable characteristics as claimed in claim 1 wherein the relative velocity unit coordinate system is created from cable unit direction vectors and relative velocity vectors.

3. A method of creating a floating riser platform model based on hydrodynamic characteristics of hawser as recited in claim 2 wherein the hawser forces include hawser tension, damping forces, weight in water, friedel-crafts forces and hydrodynamic drag.

4. A method of creating a floating mast platform model based on hydrodynamic characteristics of cables as claimed in claim 1 wherein the mast platform is divided into a plurality of cylindrical mast cells along its axis based on slice theory.

5. A floating mast platform model creation method based on hydrodynamic characteristics of cables as claimed in claim 1 wherein the additional mass inertial and hydrodynamic drag forces acting on each mast unit are calculated based on the position and velocity of the unit itself and the velocity and acceleration of the water particles at the location of the unit, and the moment of each unit load relative to the center origin of the mast platform is calculated.

6. A floating column platform model creation method based on hydrodynamic characteristics of hawsers according to claim 5 wherein the column platform forces further include the gravitational and buoyant forces experienced by the column platform, wherein the gravitational and buoyant forces are expressed based on a mass matrix and a restoring moment matrix.

7. The method of claim 1, wherein the separately propagating waves in X, Y directions are linearly superimposed based on finite water depth linear wave theory; and calculating the three-dimensional vector of the speed and the acceleration of the water particles at the position in real time according to the position of the unit node.

8. A method as claimed in claim 1, wherein the cables are distributed around the perimeter of the platform, one end of the cables is fixed to the seabed by a three-dimensional spring force, and the other end of the cables is connected to the platform by a rigid body-particle spherical hinge.

9. A method as claimed in claim 8, wherein a cable moored floating column platform system dynamics equation is established based on cable-column platform spherical hinge constraints, system mass matrix, column platform and cable force vectors; wherein the system mass comprises a column platform mass and a cable mass.

10. A method of creating a floating spar platform model based on hydrodynamic characteristics of cables as claimed in claim 1 wherein the spar platform heave/sway/heave/yaw and cable tension versus X and Y waves are analyzed at verification.

Technical Field

The disclosure relates to the field of ocean floating platform analysis, in particular to a floating type stand column platform model establishing method based on hydrodynamic characteristics of cables.

Background

A spar platform (spar platform) is a floating platform widely used for deep sea wind power generation and oil and gas production. Its elongated shape reduces the hydrodynamic force of the surface waves. Because the gravity center is lower than the floating center, the self-aligning moment is automatically generated when the floating center is inclined. The stability of the floating platform is one of the most concerned problems at present, and the analysis of the stability of the floating platform requires the construction of a dynamic model of the platform. The mooring force is typically simplified to three forces and three moments related to the displacement of the platform by using a quasi-static method, i.e. ignoring the non-linear hydrodynamic characteristics of the mooring lines. The oil exploitation platform is large in size, mostly adopts metal anchor chain mooring, is low in moving speed, and can ignore hydrodynamic characteristics of the anchor chain in engineering analysis.

However, the current ocean energy capture equipment widely uses small-sized floating upright platforms as carriers. Small platform motions are significant and the mooring hawsers are no longer metal hawsers but hawsers made of composite material with similar density to sea water, resulting in nonlinear hydrodynamic properties of the mooring hawsers affecting platform motions. However, the cable model established by the traditional method is easy to generate singularity, so that the robustness of the whole model is poor; and neglecting the dynamics characteristic of mooring cable, it is difficult to satisfy the research demand of floating stand platform.

Disclosure of Invention

The purpose of the present disclosure is to provide a floating type upright post platform model establishing method based on hydrodynamic characteristics of cables, which is to establish a cable model by adopting a concentrated mass method based on a relative velocity vector unit coordinate system, solve the singularity of the cable model by the concentrated mass method, make the robustness of the floating type upright post platform and a mooring system model stronger, and verify the accuracy of the established numerical model by comparing the motion response of the upright post platform under the action of X, Y waves.

In order to realize the purpose, the following technical scheme is adopted:

a floating type upright post platform model establishing method based on cable hydrodynamic characteristics comprises the following steps:

dividing the cable into a plurality of cable units based on a concentrated mass-spring model, expressing the stress of the cable based on a relative speed unit coordinate system, and creating a cable dynamic model;

dividing the stand column platform into a plurality of stand column units based on a slicing theory, acquiring the stress of the stand column platform, and creating a stand column platform numerical model;

based on a finite water depth linear wave theory, creating a wave model, and acquiring the speed and the acceleration of water particles at the node positions of the upright post unit and the cable unit to obtain the stress of the cable and the upright post platform;

and obtaining a floating type upright platform model for mooring the cable based on the upright platform numerical model and the cable dynamic model, verifying by combining a wave model, and analyzing the dynamic response of the upright platform and the cable tension under the action of the wave environment.

Further, a relative velocity unit coordinate system is created from the cable unit direction vector and the relative velocity vector.

Further, the cable forces include cable tension, damping force, weight in water, friedel-crafts force and hydrodynamic drag.

Further, based on slice theory, the column platform is divided into a plurality of cylindrical column units along the axis of the column platform.

Further, the additional mass inertia force and the hydrodynamic resistance acting on each upright unit are calculated according to the position and the speed of each upright unit and the speed and the acceleration of the water particles at the position of the upright unit, and the moment of the load of each upright unit relative to the central origin of the upright platform is calculated.

Further, the stress of the upright post platform also comprises the gravity and the buoyancy borne by the upright post platform, wherein the gravity and the buoyancy are expressed based on a mass matrix and a restoring moment matrix.

Further, based on the finite water depth linear wave theory, waves respectively propagating in X, Y directions are linearly superposed; and calculating the three-dimensional vector of the speed and the acceleration of the water particles at the position in real time according to the position of the unit node.

Furthermore, a plurality of cables are distributed on the periphery of the upright post platform, one end of each cable is fixed on the seabed through three-dimensional spring force, and the other end of each cable is connected with the upright post platform through a rigid body-particle spherical hinge.

Further, a floating type upright post platform system dynamic equation of cable mooring is established based on the spherical hinge constraint of the cable-upright post platform, the system mass matrix and the stress vectors of the upright post platform and the cable; wherein the system mass comprises a column platform mass and a cable mass.

Further, in the verification, the relation between the vertical column platform surging/swaying/heaving/yawing and the cable tension and the waves in the X direction and the Y direction is analyzed.

Compared with the prior art, the utility model has the advantages and positive effects that:

(1) based on a relative velocity vector unit coordinate system, a cable model is built by adopting a concentrated mass-spring method, the singularity of the concentrated mass-spring cable model is solved, and the robustness of the floating upright platform and the mooring system model is stronger;

(2) considering the dynamics of the cable, establishing a cable model based on a relative speed unit coordinate system, wherein the cable model not only can overcome the singularity problem generated by an Euler angle and a Frenet coordinate system, but also can effectively express the hydrodynamic force of the cable;

(3) the accuracy of the constructed numerical model is verified by comparing the motion response of the stand column platform under the action of X, Y waves.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to limit the disclosure.

Fig. 1 is a schematic view of a floating column platform model in embodiment 1 of the present disclosure;

fig. 2 is a schematic layout of a mooring cable system in embodiment 1 of the present disclosure;

fig. 3 is a schematic modeling diagram of a floating column platform and mooring cables in embodiment 1 of the present disclosure;

fig. 4 is a schematic view of a numerical model of a floating column platform and mooring cables in embodiment 1 of the present disclosure;

FIG. 5 is a schematic diagram of surging of a floating column platform over time in embodiment 1 of the present disclosure;

FIG. 6 is a schematic diagram of frequency domain analysis of the surging motion of the floating upright platform in embodiment 1 of the present disclosure;

FIG. 7 is a schematic diagram of the swaying over time of the floating upright platform in embodiment 1 of the present disclosure;

FIG. 8 is a schematic diagram of frequency domain analysis of the swaying motion of the floating upright platform in embodiment 1 of the present disclosure;

FIG. 9 is a schematic view of the heave over time of a floating column platform in accordance with embodiment 1 of the present disclosure;

FIG. 10 is a schematic diagram of frequency domain analysis of the heave motion of the floating column platform in embodiment 1 of the present disclosure;

FIG. 11 is a schematic diagram of the change of the yawing motion of the floating column platform in the embodiment 1 of the disclosure with time;

FIG. 12 is a schematic diagram of frequency domain analysis of the yawing motion of the floating-type column platform in embodiment 1 of the present disclosure;

fig. 13 is a schematic diagram of the tension of the 1 st unit of the floating upright platform system cable a in the embodiment 1 of the disclosure as a function of time;

fig. 14 is a schematic frequency domain analysis diagram of the tension of the 1 st unit of the floating upright platform system cable a in the embodiment 1 of the present disclosure;

fig. 15 is a schematic diagram of the tension of the 1 st unit of the floating upright platform system cable b in the embodiment 1 of the disclosure as a function of time;

fig. 16 is a schematic frequency domain analysis diagram of the tension of the 1 st unit of the floating upright platform system cable b in the embodiment 1 of the present disclosure.

Detailed Description

Example 1

In an exemplary embodiment of the present disclosure, as shown in fig. 1-11, a method for creating a floating-type column platform model based on hydrodynamic characteristics of cables is provided.

Based on a relative velocity vector unit coordinate system, a cable model is built by adopting a concentrated mass-spring method, the singularity of the concentrated mass-spring cable model is solved, and the robustness of the floating upright platform and the mooring system model is higher.

The model generation method comprises the following steps:

acquiring an external force acting on the stand column platform, and establishing a numerical model of the stand column platform;

dividing the cable into a plurality of cable units based on a concentrated mass-spring model, expressing the stress of the cable based on a relative speed unit coordinate system, and creating a cable dynamic model;

dividing the stand column platform into a plurality of stand column units based on a slicing theory, acquiring the stress of the stand column platform, and creating a stand column platform numerical model;

based on a finite water depth linear wave theory, creating a wave model, and acquiring the speed and the acceleration of water particles at the node positions of the upright post unit and the cable unit to obtain the stress of the cable and the upright post platform;

and obtaining a floating type upright platform model for mooring the cable based on the upright platform numerical model and the cable dynamic model, verifying by combining a wave model, and analyzing the dynamic response of the upright platform and the cable tension under the action of the wave environment.

Specifically, the model generation method is described in detail with reference to the accompanying drawings:

1. and establishing a numerical model of the stand platform based on the slice theory. The origin of the platform coordinates is located at the geometric center of the upright. Initially the three coordinate axes of the platform itself coincide with the global coordinate system and rest at the position of the trough. The column platform is divided into 100 cells along the central axis as shown in fig. 1.

External force acting on the platform of the upright column is caused by buoyancyAdditional mass inertia forceHydrodynamic resistanceAnd the relative moment generated by the unit acting force to the coordinate origin of the platformAnd (4) forming.

The expression of the external load is shown in formula (1).

Is a mass matrix of the column platform and recovers the moment coefficientAs shown in formula (2).

ρ_fAnd V₀The density of the fluid and the immersion volume of the platform in the initial condition are indicated, respectively.Is the position coordinate of the origin of the column coordinates, since the origin is located between the 50 th and 51 th elements,the expression of (b) is shown in formula (3).

Representing the additional mass inertia force acting on the jth column unit, when the jth column unit is above the water surface,is zero.Is the acceleration of the water particle at the jth pillar cell.Is the three translational accelerations of the upright platform.Represents the acceleration of the jth pillar unit, andthe moving speed of the column unit to the surrounding seawater is shown as formula (3).

V_eAnd A_eThe distribution represents the volume of the submerged column unit and the projected area in the horizontal direction.

Because the upright post platform and the cable are cylindricalAdding a mass coefficient C_AIs 1.

Representing the relative moment, vector, generated by unit acting force on the origin of coordinates of the platformRepresenting the position of the column platform unit in the column platform coordinate system, whereinRepresenting a position vectorThe diagonal matrix of (a). Finally, all unit loads are expressed at the coordinate origin of the upright platform, so that the relevant moments are expressed byAnd (4) expressing.

A₀Is the cross-sectional area of the upright platform,is the Z component of the platform center of buoyancy position.^mζ represents the wave height at which the upright is located,is a transformation matrix between the cylindrical coordinate system and the global coordinate system. Theta₁,θ₂,θ₃Is Euler's angle of rotation, and ω' represents the angular velocity of rotation of the column expressed with the column coordinates as a reference coordinate system. g is the acceleration of gravity.

2. A cable dynamics model is created based on the relative velocity unit coordinate system. In order to take cable dynamics into account, a cable model is established based on a relative velocity unit coordinate system, which not only can overcome the singularity problem generated by the euler angle and the Frenet coordinate system, but also can effectively express cable hydrodynamic force. The use of lumped mass-spring models simplifies the cable. The unit direction vector and the relative velocity are given by equation (4).Is the velocity of the water particles at the ith node.

Coordinates of unitIndicating the direction of the ith cell by normalizing the cell vectorThus obtaining the product. Coordinates of unitFrom unit coordinatesAnd relative velocityThe components are as follows. Coordinates of cells according to the right-hand rulePerpendicular toFrom unit coordinatesAnda plane of composition. The cell coordinate formula of the ith cell is given by equation (5).

The force acting on the i-th unit cable includes tensionDampingWeight in waterFroude-Krylov force (Froude-Krylov force)And hydrodynamic resistanceWhereinByAndthe composition is shown as a formula (6).Is a conversion matrixThe transposed matrix of (1), wherein

Wherein the content of the first and second substances,is the axial strain,. alphaⁱRepresents the length of the i-th cable unit, as in equation (7). The mass of the cable and the mass of an equal volume of fluid in the ith cell are respectivelyAnd

quality matrix of ith node based on global coordinate systemIs given by formula (8).The quality matrix of the ith cell expressed in reference to the cell coordinates. C_AFor the additional mass coefficient, the axial additional mass is ignored. Since the ith node is the intersection of the (i-1) th cell and the ith cell, the quality matrixUsing cell mass matricesAndand (4) showing.

Finally, the load on the unit is shared equally by the nodes at both ends. Also, the governing equation of the ith node is expressed according to the loads acting on the (i-1) th and ith cells, as shown in equation (9). One cable is divided into 20 units,representing the acceleration of the ith node.

3. And creating a wave model based on the finite water depth linear wave theory. Wave height is a function of wave position and time. The height ζ of the surface wave linearly superimposes the waves propagating in the X, Y directions, as shown in equation (10).

Upper label ()^xAnd ()^yRepresenting the values of the waves () propagating in the X and Y directions, respectively. Thus, it is possible to provideAndamplitude, ω, representing the direction of X, Y^xAnd ω^yCircular frequency, k, representing X, Y directional waves^xAnd k^yRespectively representing the wave numbers in the X, Y direction. Further, subscript ()_gRepresents the value of () calculated under a global coordinate system. The position of the water particles in the global coordinate system can be expressed as X according to the above definition_g、Y_gAnd Z_g. For finite water depth, the wave number k and the circular wave frequency ω can be obtained from equation (11).Andrespectively, representing the wave period in the direction X, Y. D_SBIs the depth of the sea bed.

Thus, when calculating the hydrodynamic load, the velocity and acceleration of the water particles can be found in equation (12) to match the cable unit and spar platform positions.

Finally, the velocity of the fluidIs the sum of the three-dimensional coordinates of the water particles, which can be obtained from formula (13)

4. The distribution model of the mooring system is characterized in that the mooring system consists of three mooring cables or four mooring cables. The current mooring system has four cables evenly distributed around the spar platform, as shown in fig. 2, the four cables connecting the cables to the fairleads of the spar platform by means of ball joints. The bottom end point of the cable is fixed to the seabed by means of spring force. Equation (14) shows the spring force at point a. Initially, the cable is a straight line without pretension. The cables a and b are respectively distributed on the + X and + Y axes. The cables c and d are respectively distributed on-X and-Y axes. According to the depth of the cable guide and the diameter of the upright post platform, the position coordinates of the cable guide a, b, c and d are respectively [ 0.5; 0; -2], [ 0; 0.5; -2], [ -0.5; 0; -2], [ 0; -0.5; -2]. A. B, C and D are the locations of anchor points on the seafloor, the radius of the current set anchor is 64 meters, so the location coordinates of A, B, C and D are [ 64; 0; -1000], [ 0; 64; -1000], [ -64; 0; -1000], [ 0; -64; -1000].

5. Floating type upright post platform and dynamic equation of mooring system thereof

A rigid body has 6 degrees of freedom in three dimensions, while a particle has only 3 translational degrees of freedom. Since the cable node has only three translational degrees of freedom, a spherical hinge expression suitable for connecting rigid body-mass points is created. The constraint equation for fairlead position a is expressed by equation (15).

Because the 1 st node of the cable is connected to the floating column platform, a position vector is usedTo construct the constraint equations. The jacobian matrix of the constraint equation is shown as equation (16).

The rotation angles of the X-Y-Z euler angle sequence are selected as generalized coordinates. G' represents the relation between the angular velocity of the platform and the Euler angular rotation speed, as shown in equation (17). Gamma ray^aConsists of the generalized coordinates and the first derivative of the generalized coordinates with respect to time, as shown in equation (18).

Finally, the equation of motion for the spar platform system with mooring cables is shown in equation (19).Is a quality matrix of the system, comprises upright post platforms and cables,Qis the external force of the surrounding environment acting on the platform and cables. Jacobian matrixIncluding constraints at fairlead locations a, b, c, and d. Matrix arrayRepresenting a Jacobian matrixThe transposed matrix of (2).

Case model verification and specific implementation:

an example model was created with the spar platform, cable and wave properties shown in tables 1, 2 and 3, respectively.

TABLE 1 column platform Attribute

TABLE 2 Cable Properties

TABLE 3 sea State attributes

Referring to the modeling method in this embodiment, a dynamic model of a floating column platform and a mooring cable system is compiled based on MATLAB, the influence of waves on six-degree-of-freedom motion of the geometric center of the column platform is analyzed, and meanwhile, a same system is built by using commercial software ProteusDS and the results of the two models are compared, so that the accuracy of a numerical model is verified, as shown in fig. 3. The simulation time was 200s and the step size was 0.01 s.

As shown in FIG. 4, the surging amplitude of the platform in the X direction is 0.8m, and the result of the numerical model is slightly larger than that of ProteusDS. With the help of fast fourier transform, fig. 5 shows the relationship of column platform X-surge versus X, Y-wave in the frequency domain, with 0.127Hz being the only prominent frequency. Since the natural frequency of the waves in the X direction is 0.125Hz, the X-direction oscillation of the column platform is mainly affected by the waves in the X direction. The Y-direction swaying motion and the associated frequencies are shown in fig. 6 and 7, respectively. The column platform was swept in the Y direction with an amplitude of 0.6m, the only prominent frequency being 0.153Hz, which coincides with the natural frequency of the Y-directed wave. Because the cables a and c are distributed in the X direction and the cables b and d are distributed in the Y direction, the surging and swaying motions of the platform are independent. The Y-direction waves have little effect on platform surging and the X-direction waves have little effect on surging. The arrangement of the mooring cables decouples the X-and Y-movements. The analysis result of the numerical model is matched with the simulation result of the ProteusDS.

The ringing and associated frequencies are shown in figures 8 and 9. The numerical model and the ProteusDS both show that the upright platform is up and down at-4.57 m, and the amplitude is 0.2 m. The heave motion couples X, Y to the wave, both of which are shown in FIG. 9 as natural frequencies. Since the X, Y forward waves have periods of 8.0s and 6.4s, respectively, the least common multiple is 32s, matching the frequency of 0.033 Hz. The analysis result of the numerical model is matched with the simulation result of the ProteusDS.

Initially the column platform is in the trough and under the action of the waves moves X, Y to the positive direction of the shaft. Without the mooring cable, it would only oscillate back and forth once in the positive direction of the X and Y axes. Due to the mooring system, the column platform moves in the negative direction of the X, Y axis, and the oscillation average value gradually changes from an amplitude value to 0, as shown in fig. 10. The column platform in the numerical model is built up from 100 axial units, and the external load of each unit acts on the geometric center of the unit. Thus, yawing motions of the spar platform are only generated by unbalanced loads of the mooring system. However, in the ProteusDS there are radial units on the column platform which generate moment arms and the hydrodynamic forces acting on the radial units of the column platform, in addition to the yawing caused by the mooring system, also generate yaw motions. Different geometries produce different external loads and slight differences in yawing motion. The yaw motion of the ProteusDS has more oscillation frequencies than the yaw motion of the numerical model, as shown in fig. 11. The frequency of 0.033Hz is significant, and 0.22Hz and 0.28Hz are the product of the frequencies of 0.033 Hz. The frequency doubling of the fundamental frequency becomes prominent due to hydrodynamic non-linear effects.

The cable has no pretightening force, and the tension is zero at the initial moment. The cable tension then varies with the wave. The tensions of the cables a and b are shown in fig. 12 and 14, respectively, and the frequencies of interest are shown in fig. 13 and 15, respectively. From the numerical model calculation, the mean tension of cable a is 8126N, while the mean tension calculated by ProteusDS is 8146N. Since the X-wave load is greater than the Y-wave, the tension of cables a and c is greater than the tension of cables b and d. The X-distributed cables are primarily affected by X-direction waves, as shown in fig. 14. Since the oscillation amplitude of the rolling motion and pitching is less than 1m and the length of a single cable is greater than 77m, the effect of the Y-direction waves on cables a and c is insignificant. Meanwhile, the Y-direction wave mainly affects the tensions of the cables b and d, and the X-direction wave does not significantly affect. The analysis result of the numerical model is matched with the simulation result of the ProteusDS.

In the embodiment, a numerical model of the floating upright platform and the mooring system is created, the hydrodynamic load of the mooring cable is considered, the accuracy of the numerical model is verified by means of commercial software ProteusDS, and the influence of X, Y directional linear waves on the stability of the system and the tension of the mooring cable is analyzed.

The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.