Floating wind power flow-structure coupling method based on computational fluid dynamics and actuator line model

Abstract

The application discloses a floating wind power fluid-structure coupling method based on computational fluid dynamics and actuator line model, obtains geometric parameters, mass-inertia properties, mooring system parameters and environmental working condition parameters of a floating wind turbine, establishes a three-dimensional multiphase flow calculation domain containing air and water phases, generates a target wave field at an inlet, solves air-water two-phase free interface evolution by using a volume of fluid method, disperses wind turbine rotor blades along a span direction into multiple actuator units, calculates rotor aerodynamic load according to local relative velocity and airfoil polar data, and projects the rotor aerodynamic load to computational fluid dynamics grid units, establishes a six-degree-of-freedom rigid body dynamics model of a floating platform, solves the floating platform motion state based on hydrodynamic load, rotor aerodynamic load, mooring load and gravity load, and performs partition-partition strong coupling between the fluid domain and the rigid body motion domain in each time step by using a PIMPLE algorithm, and updates the three-dimensional multiphase flow calculation domain by combining dynamic mesh deformation.

Description

Technical Field

[0001] This invention belongs to the field of offshore wind power numerical simulation and fluid-structure interaction calculation technology, specifically involving a floating wind power fluid-structure interaction method based on computational fluid dynamics and actuation line model. Background Technology

[0002] As offshore wind power development gradually extends to deeper and more remote areas, floating wind turbines, unaffected by the water depth limitations of fixed foundations, have become a crucial development direction for offshore wind power equipment. During operation, floating wind turbines are simultaneously subjected to wind loads, wave loads, ocean current loads, and mooring restoring forces, resulting in six degrees of freedom motion: sway, heave, roll, pitch, and bow. This motion alters the instantaneous inflow conditions of the wind turbine rotor, causing time-varying fluctuations in the rotor's aerodynamic load, wake structure, and overall turbine output performance. Therefore, accurately determining the coupling relationship between the wind field, wave field, wind turbine rotor aerodynamic load, and floating platform motion response is fundamental for load assessment, structural design, and operational performance analysis of floating wind turbines.

[0003] Existing numerical simulation methods for floating wind power typically employ blade element momentum theory, potential flow hydrodynamic models, or empirical mooring models to analyze the unit's response. These methods offer high computational efficiency and are suitable for preliminary design and parameter selection, but their ability to describe viscous hydrodynamics, nonlinear free surface variations, unsteady aerodynamic effects of the wind turbine rotor, and complex wake structures is limited. While computational fluid dynamics models using solid blades can achieve high analytical capabilities for local flows, they require high-density mesh generation for the blade surface, boundary layer, and wake region, resulting in large computational scales and difficulty in simultaneously handling the large-scale motion and long-term coupled response analysis of floating platforms.

[0004] Furthermore, in existing computational fluid dynamics simulations, air-water two-phase flow, wave generation and absorption, aerodynamic loads on wind turbine rotors, six-degree-of-freedom motion of floating platforms, and mooring loads are typically handled by different solution modules. Data exchange between these modules is prone to issues such as load lag, inconsistent boundary updates, and insufficient coupling convergence. When the floating platform experiences significant motion, the three-dimensional multiphase flow computational domain mesh will also deform with changes in boundary position. If mesh updates and the fluid solution process cannot be coordinated, it can easily affect the free surface capture and fluid load calculation results.

[0005] In view of this, the present invention provides a floating wind-current-structure coupling method based on computational fluid dynamics and actuation line model. Summary of the Invention

[0006] The purpose of this invention is to provide a floating wind power current-structure coupling method based on computational fluid dynamics and actuation line model, which solves the technical problem that existing floating wind power numerical simulation methods are unable to uniformly characterize the bidirectional strong coupling response between nonlinear waves, unsteady rotor aerodynamic loads of wind turbine rotors and six-degree-of-freedom motion of floating platforms at an acceptable computational cost.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The floating wind-current-structure interaction method based on computational fluid dynamics and actuation line model includes the following steps:

[0009] Obtain the basic geometric parameters, mass-inertia properties, mooring system parameters, and environmental condition parameters of the floating wind turbine.

[0010] A three-dimensional multiphase flow computational domain including air and water phases is established. A target wave field is generated at the entrance of the three-dimensional multiphase flow computational domain, and the waves are numerically absorbed in the exit region. The evolution state of the air-water two-phase free interface is solved by the fluid volume method.

[0011] The rotor blades of the floating wind turbine are divided into multiple actuation units along the spanwise direction. The quarter-chord position of each actuation unit is used as a control point. The rotor aerodynamic load of each actuation unit is calculated based on the local relative velocity and airfoil polar data at the control point. The rotor aerodynamic load is then projected onto the computational fluid dynamics grid cells around the control point as the momentum source term of the Navier-Stokes equation.

[0012] A six-degree-of-freedom rigid body dynamics model of the floating platform is established, and the motion state of the floating platform is solved based on the hydrodynamic load, the rotor aerodynamic load, the mooring load and the gravity load.

[0013] The PIMPLE algorithm is used to achieve strong partitioning coupling between the fluid domain and the rigid body motion domain. Multiple external iteration loops are executed in each time step. In each external iteration loop, the position and velocity of the actuator are updated according to the current motion state of the floating platform. The Navier-Stokes equations and volume fraction transport equations containing the momentum source term are solved. The hydrodynamic load is obtained by integrating the surface pressure of the floating platform. The motion state of the floating platform is updated by solving the six-degree-of-freedom rigid body dynamics model. The mesh node positions of the three-dimensional multiphase flow computation domain are updated based on dynamic mesh deformation technology until the coupling calculation in the current time step reaches the preset convergence requirement.

[0014] As a preferred technical solution of the present invention, in each external iteration cycle, the hub position, wind turbine rotor plane direction, blade azimuth angle and the position and speed of each actuation unit control point are updated according to the current position, current attitude, current translation speed and current rotation speed of the floating platform, and the spatial position of each cable guide hole is updated according to the current position and current attitude of the floating platform.

[0015] The rotor aerodynamic load is calculated based on the updated position and velocity of each actuation unit control point, and the mooring load is calculated based on the updated spatial position of each cable guide hole.

[0016] The rotor aerodynamic load, the mooring load, and the hydrodynamic load are input into the six-degree-of-freedom rigid body dynamics model to obtain the floating platform motion state for the next external iteration cycle.

[0017] As a preferred technical solution of the present invention, the three-dimensional multiphase flow computational domain includes, in sequence, an inlet region, a floating wind turbine arrangement region, and an outlet region along the wind and wave propagation direction.

[0018] Locally refined meshes are set near the free surface of the three-dimensional multiphase flow computational domain, in the action area of ​​the wind turbine rotor, around the floating platform, and in the wake development area of ​​the wind turbine rotor.

[0019] The floating platform has a grid area near the surface of its columns, pontoons and cross braces that can deform with the movement of the floating platform, and a grid size transition zone is provided between the grid area and the external fixed grid area.

[0020] As a preferred embodiment of the present invention, the target wave field is generated using Stokes' second-order wave theory or linear Airy wave theory; when Stokes' second-order wave theory is used, the free surface elevation is expressed as:

[0021] ;

[0022] in: For amplitude, For wave number, Angular frequency, ; Here are the steepness parameters; the wavenumber and frequency satisfy the dispersion relation:

[0023] Where g is the acceleration due to gravity.

[0024] As a preferred embodiment of the present invention, the fluid volume method uses volume fraction to characterize the proportion of water phase within a computational fluid dynamics grid cell, and solves for the evolution state of the gas-water two-phase free interface using a volume fraction transport equation that includes an artificial compressibility term. The volume fraction transport equation is as follows:

[0025] ;

[0026] in: For fluid velocity vector, The relative compression velocity between the two phases is perpendicular to the free surface, and its magnitude is determined by the compressibility coefficient. Decide.

[0027] As a preferred technical solution of the present invention, each actuation unit is assigned corresponding chord length, twist angle and airfoil pole data according to the blade spanwise chord length distribution, twist angle distribution and airfoil distribution, wherein the airfoil pole data includes lift coefficient and drag coefficient.

[0028] The local fluid velocity is sampled from the computational fluid dynamics grid cells around the control point of each actuation unit, and the local relative velocity is obtained by combining it with the motion velocity of the actuation unit itself.

[0029] Based on the local relative velocity, local blade chord length, local blade twist angle, and airfoil pole data, the rotor aerodynamic load of each actuation unit is calculated.

[0030] As a preferred embodiment of the present invention, the circumferential aerodynamic load and normal aerodynamic load of each actuation unit are respectively expressed as:

[0031] ;

[0032] ;

[0033] in, air density, This is the blade chord length at the corresponding position of the actuation unit. For local relative speed, The radial distance from the control point of the actuation unit to the rotor axis of the wind turbine generator. It is a circumferential discrete scale. It is an axial discrete scale. The inflow angle corresponding to the local relative velocity. The lift coefficient, This is the drag coefficient.

[0034] As a preferred technical solution of the present invention, the rotor aerodynamic load of each actuation unit is projected onto the computational fluid dynamics grid cells around each actuation unit by using a spherical Gaussian regularized kernel function; the projection range of the rotor aerodynamic load is determined according to the spacing between the actuation units and the local grid scale of the wind turbine rotor's action area; the normal force and circumferential force of all actuation units are summarized to obtain the aerodynamic thrust, aerodynamic torque of the wind turbine rotor, and rotor aerodynamic load acting on the overall structure of the floating wind turbine.

[0035] As a preferred embodiment of the present invention, the six-degree-of-freedom rigid body dynamics model is established based on the Newton-Euler equations, and the translational and rotational motion equations of the floating platform are as follows:

[0036] ;

[0037] ;

[0038] in, For the total mass of the floating platform, For the translational acceleration of the floating platform, The resultant force acting on the floating platform, For hydrodynamic loads, For rotor aerodynamic load, For mooring load, For gravity load, For the moment of inertia of the floating platform, For the rotational acceleration of the floating platform, The rotational speed of the floating platform, Let be the position vector of each load point relative to the center of mass of the floating platform. For the corresponding load, For external torque, This refers to the gyroscopic torque generated by the rotation of the wind turbine rotor.

[0039] As a preferred embodiment of the present invention, the hydrodynamic load is obtained by integrating the surface pressure and viscosity of the floating platform, the rotor aerodynamic load is provided by the actuation line model, and the mooring load is calculated using the quasi-static catenary equation.

[0040] Within each time step, the spatial position of each guide cable hole is updated according to the position and attitude of the floating platform. Then, the tension direction and magnitude of each mooring line are obtained according to the position of the guide cable hole, the position of the seabed anchor point, the total length of the mooring line and the line density of the mooring line. The tensions of each mooring line acting on the guide cable hole are combined to obtain the mooring load and mooring moment acting on the floating platform.

[0041] During the dynamic mesh deformation process, the mesh nodes near the surface of the floating platform move synchronously with the floating platform, while the outer boundary mesh nodes far from the floating platform remain fixed, and the dynamic mesh deformation process satisfies the geometric conservation law.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] This invention establishes a target wave generation and numerical absorption mechanism within the same three-dimensional multiphase flow computational domain and employs the fluid volume method to solve the evolution of the air-water two-phase free interface, reducing the interference of reflected waves on the hydrodynamic response of the floating platform. It uses an actuation line model to equivalently discretize the wind turbine rotor blades and projects the rotor aerodynamic loads onto computational fluid dynamics grid cells, avoiding the high computational overhead of solid blade boundary layer grids. By iteratively exchanging rotor aerodynamic loads, hydrodynamic loads, mooring loads, and the floating platform's motion state at each time step using the PIMPLE algorithm, and combining dynamic grid deformation to handle boundary changes caused by the six-degree-of-freedom motion of the floating platform, this invention achieves a two-way strongly coupled simulation between the wind field, wave field, wind turbine rotor aerodynamic performance, and floating platform motion response at an acceptable computational cost. This provides numerical basis for load assessment, motion response prediction, mooring system optimization, and overall performance analysis of floating wind turbine units. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0045] Figure 1 This is a flowchart of the floating wind-current-structure coupling method of the present invention;

[0046] Figure 2 This is a diagram showing the overall mesh partitioning of the three-dimensional multiphase flow computational domain in this invention;

[0047] Figure 3 This is a detailed view of the mesh division near the floating platform of the present invention;

[0048] Figure 4 This is a graph showing the variation of the motion response of the floating platform under fluid-structure interaction as a function of normalized time.

[0049] Figure 5 This is a graph showing the change of aerodynamic performance of the floating wind turbine under fluid-structure interaction state as a function of normalized time. Detailed Implementation

[0050] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. The following embodiments are used to illustrate the implementation process of the present invention and are not intended to limit the scope of protection of the present invention. Without departing from the technical concept of the present invention, those skilled in the art can adjust the size of the three-dimensional multiphase flow computational domain, mesh scale, time step and solver parameters according to the structural form, environmental conditions and computing resources of the floating wind turbine to be simulated.

[0051] A floating wind turbine consists of a floating platform, tower, nacelle, wind turbine rotor, and mooring system. The floating platform includes columns, pontoons, and cross braces, while the wind turbine rotor includes a hub and multiple blades mounted on the hub. During the calculation, solid geometric boundaries are established for the floating platform, tower, and nacelle. An actuated line model is used to treat the wind turbine rotor blades as equivalent components, thus avoiding high-density mesh generation on the solid blade surfaces and blade boundary layers.

[0052] This embodiment employs a three-dimensional multiphase flow computational domain that includes air and water phases. Within this domain, wave generation and absorption models, air-water two-phase free interface models, actuation line wind turbine rotor aerodynamic models, floating platform six-degree-of-freedom rigid body dynamic models, mooring load models, and dynamic mesh deformation models are established. The PIMPLE algorithm is used to achieve strong partitioning and coupling between the fluid domain and the rigid body motion domain.

[0053] Example 1

[0054] like Figure 1 As shown, this embodiment provides a floating wind turbine electro-structure interaction method based on computational fluid dynamics and actuation line model, used to simulate the rotor aerodynamic load, hydrodynamic load, mooring load, and six-degree-of-freedom motion response of the floating platform under the combined action of wind and waves. The method includes the following steps:

[0055] Step S101: Obtain the basic geometric parameters, mass-inertia properties, and mooring system parameters of the floating wind turbine.

[0056] The basic geometric parameters include the geometric dimensions and relative positions of each component of the floating platform, and the diameter of the wind turbine rotor. Wheel hub height The number of blades and the chord length and twist angle distribution along the blade span. The floating platform components include columns, pontoons, and cross braces. The mass-inertial properties include the total mass of the floating body. The position of the center of mass (CoM) and the principal moments of inertia about the principal axes of the center of mass. , and The mooring system parameters include the number of mooring lines and the linear density of each mooring line. Total length 1. Coordinates of the seabed anchor point and the cable guide hole.

[0057] Obtain the environmental parameters required to establish a three-dimensional multiphase flow computational domain, including water depth. Target wave height Target wave cycle Reference wind speed at wheel hub height and sea surface roughness .

[0058] Based on the acquired basic geometric parameters, a geometric model of the floating platform, tower, and engine room is established, and the mass attributes participating in rigid body motion are set according to the position of the center of mass and the principal moments of inertia. The initial connection relationship of the mooring lines is established based on the coordinates of the seabed anchor points and the guide cable holes, enabling the mooring system to generate corresponding restoring loads as the position and attitude of the floating platform change.

[0059] Step S102: Establish a three-dimensional multiphase flow calculation domain that includes air phase and water phase. The three-dimensional multiphase flow calculation domain includes an inlet region, a floating wind turbine arrangement region and an outlet region in sequence along the wind and wave propagation direction.

[0060] The inlet area is used to apply the target wind field and target wave field, the floating wind turbine layout area is used to set up the floating platform, tower, nacelle and wind turbine rotor, and the outlet area is used to numerically absorb the waves that propagate to the vicinity of the outlet to reduce the impact of reflected waves on the motion response of the floating platform and the aerodynamic load of the wind turbine rotor.

[0061] The bottom of the three-dimensional multiphase flow computational domain is set as the seabed boundary, the top of the three-dimensional multiphase flow computational domain is set as the top boundary of the air domain, the two sides of the three-dimensional multiphase flow computational domain are set as lateral boundaries, and the surfaces of the floating platform, tower, and nacelle are set as solid wall boundaries.

[0062] Mesh the computational domain for the three-dimensional multiphase flow. For example... Figure 2 As shown, locally denser grids are set near the free surface, in the area of ​​action of the wind turbine rotor, around the floating platform, and in the area where the wind turbine rotor wake develops, while larger background grids are set in areas far away from the floating wind turbine.

[0063] like Figure 2 As shown, a grid area capable of deforming with the movement of the floating platform is set near the surfaces of the columns, pontoons, and cross braces. A grid size transition zone is set between the grid area and the external fixed grid area to reduce abrupt changes in the size and shape of the grid cells during the movement of the floating platform.

[0064] The grid scale near the free surface is determined based on the wave height and wavelength of the target wave, allowing the gas-water interface to be characterized by multiple grid cells. The grid scale of the wind turbine rotor action area is determined based on the spanwise spacing of the actuation cells and the load projection range, allowing the rotor aerodynamic load of each actuation cell to be projected onto multiple computational fluid dynamics grid cells around it.

[0065] Before performing the fluid-structure interaction calculation, the mesh quality of the three-dimensional multiphase flow computation domain is checked. The check includes the non-orthogonality of mesh cells, the degree of mesh cell distortion, the transition relationship of mesh size, and the deformable range of the dynamic mesh deformation region.

[0066] The target wave field is generated at the inlet using Stokes' second-order wave theory or linear Airy wave theory, where the free surface elevation η(x,t) in Stokes' second-order wave theory is expressed as:

[0067] ;

[0068] in: For amplitude, For wave number, Angular frequency, ; Here are the steepness parameters; the wavenumber and frequency satisfy the dispersion relation:

[0069] Where g is the acceleration due to gravity.

[0070] The wave number and angular frequency are determined based on the wave height, period, and water depth of the target wave. The distribution relationship between the water phase and the air phase at the inlet is set according to the free surface elevation, so that the target wave is formed at the inlet and propagates over time.

[0071] When the nonlinearity of the target wave is low, the target wave field can be generated using linear Airy wave theory. When using linear Airy wave theory, the wave period, wave height, and propagation direction at the inlet correspond to the target environmental conditions, and the subsequent solutions for the gas-water two-phase free interface and fluid-structure interaction remain unchanged.

[0072] A numerical absorption zone is set up in the exit area. The numerical absorption zone is used to gradually attenuate the wave velocity and free surface ripples propagating to the vicinity of the exit, so that the waves are weakened before reaching the exit boundary, thereby reducing the reflected waves generated at the exit boundary.

[0073] The evolution of the gas-water two-phase free interface was solved using the fluid volume method, expressed as volume fraction. Characterizes the proportion of water phase within the computational grid cell. Water phase regions correspond to larger volume fractions, while air phase regions correspond to smaller volume fractions. The air-water free interface is located in the grid region where the volume fraction changes.

[0074] Volume fraction The transport equations include artificial compression terms to maintain the sharpness of the free surface:

[0075] ;

[0076] in: For fluid velocity vector, The relative compression velocity between the two phases is perpendicular to the free surface, and its magnitude is determined by the compressibility coefficient. Decide.

[0077] During the solution process, the distribution of air and water phases in each grid cell is updated according to the volume fraction, and the propagation and deformation state of the free surface over time are obtained in combination with the fluid velocity field.

[0078] Step S103 involves discretizing the actuation line model of the wind turbine rotor blades, dividing each blade into multiple actuation units along the spanwise direction, and using the quarter-chord length position of each actuation unit as a control point. Based on the blade's spanwise chord length distribution, torsion angle distribution, and airfoil distribution, corresponding chord length, torsion angle, and airfoil pole data are assigned to each actuation unit. The airfoil pole data includes the lift coefficient cl and the drag coefficient cd.

[0079] Within each calculation time step, based on the floating platform's current position, current attitude, current translation speed, and current rotation speed, the hub position, wind turbine rotor plane orientation, blade azimuth angle, and the position and speed of each actuation unit control point are updated.

[0080] Local fluid velocities are sampled from the computational fluid dynamics grid cells surrounding the control points of each actuation unit, and the local relative velocity W is obtained by combining it with the actuation unit's own motion velocity. Based on the local relative velocity W, the local chord length of the blade, the local twist angle of the blade, and the airfoil pole data, the rotor aerodynamic load of each actuation unit is calculated.

[0081] Circumferential force of each actuation unit and normal force The calculation formula is:

[0082] ;

[0083] ;

[0084] in, air density, This is the blade chord length at the corresponding position of the actuation unit. For local relative speed, The radial distance from the control point of the actuation unit to the rotor axis of the wind turbine generator. It is a circumferential discrete scale. It is an axial discrete scale. The inflow angle corresponding to the local relative velocity. The lift coefficient, This is the drag coefficient.

[0085] After the rotor aerodynamic load of each actuation unit is calculated, the rotor aerodynamic load is projected onto the computational fluid dynamics grid cells around each actuation unit through a spherical Gaussian regularization kernel function, and used as the momentum source term of the Navier-Stokes equation.

[0086] The spherical Gaussian regularization kernel function is used to smoothly distribute the load concentrated at the control point to the surrounding computational fluid dynamics grid cells, thereby reducing numerical oscillations caused by concentrated load application. The load projection range is determined based on the actuation cell spacing and the local grid scale of the wind turbine rotor's operating region.

[0087] After the load projection of each actuation unit is completed, the normal force and circumferential force of all actuation units are summarized to obtain the aerodynamic thrust, aerodynamic torque of the wind turbine rotor, and rotor aerodynamic load acting on the overall structure of the floating wind turbine.

[0088] Step S104: Establish a six-degree-of-freedom rigid body dynamics model of the floating platform. The six degrees of freedom include translational motion along three mutually perpendicular directions and rotational motion about three mutually perpendicular axes.

[0089] Describing the motion response of a floating platform based on the Newton-Euler equations:

[0090] ;

[0091] ;

[0092] in, For the total mass of the floating platform, For the translational acceleration of the floating platform, The resultant force acting on the floating platform, For hydrodynamic loads, For rotor aerodynamic load, For mooring load, For gravity load, For the moment of inertia of the floating platform, For the rotational acceleration of the floating platform, The rotational speed of the floating platform, Let be the position vector of each load point relative to the center of mass of the floating platform. For the corresponding load, For external torque, This refers to the gyroscopic torque generated by the rotation of the wind turbine rotor.

[0093] The hydrodynamic load is obtained by integrating the surface pressure and viscosity of the floating platform. The rotor aerodynamic load is provided by the actuation line model in step S103. The gravity load is determined based on the total mass and center of mass of the floating platform.

[0094] The mooring loads are modeled using quasi-static catenary equations. Within each calculation time step, the spatial positions of each guide hole are updated based on the floating platform's position and attitude. Then, the tension direction and magnitude of each mooring line are determined based on the guide hole positions, seabed anchor point positions, total mooring line length, and mooring line density.

[0095] The tensions acting on the guide cable holes by each mooring line are synthesized to obtain the mooring load and mooring moment acting on the floating platform, and the mooring load and mooring moment are input into a six-degree-of-freedom rigid body dynamics model.

[0096] By solving the six-degree-of-freedom rigid body dynamics model, the position, attitude, translational velocity, and rotational velocity of the floating platform under the current load are obtained, and the motion state is transferred to the actuation line model and the dynamic mesh deformation model.

[0097] Step S105: The PIMPLE algorithm is used to achieve strong coupling between the fluid domain and the rigid body motion domain. Multiple external iteration loops are executed within each time step, and the fluid load solution, rigid body motion solution, and mesh position update are completed sequentially in each external iteration loop.

[0098] At the beginning of each time step, the floating platform position, attitude, translation speed, rotation speed, fluid velocity field, pressure field and volume fraction field corresponding to the previous time step are read as the initial state of the current time step.

[0099] In each outer iteration loop of the current time step, the position and velocity of the actuation line are first updated according to the current motion state of the floating platform, so that the hub, blades and control points of each actuation unit move synchronously with the floating platform.

[0100] Subsequently, based on the updated actuation line position and velocity, the local relative velocity W is resampled, and the circumferential force of each actuation unit is calculated. and normal force The rotor aerodynamic load is projected onto the surrounding computational fluid dynamics grid cells, forming the momentum source term of the Navier-Stokes equations.

[0101] Solve the Navier-Stokes equations and volume fraction transport equations that include the momentum source term to obtain the fluid velocity field, pressure field, and air-water free interface position corresponding to the current external iteration; integrate the surface pressure of the floating platform to obtain the hydrodynamic load corresponding to the current external iteration; summarize the rotor aerodynamic load output by the actuation line model; and calculate the mooring load based on the current cable hole position.

[0102] Hydrodynamic loads, rotor aerodynamic loads, mooring loads, and gravity loads are input into a six-degree-of-freedom rigid body dynamics model to obtain the updated motion state of the floating platform. The positions of the grid nodes in the three-dimensional multiphase flow computational domain are updated based on dynamic mesh deformation technology. Grid nodes near the surface of the floating platform move synchronously with the floating platform, while grid nodes far from the outer boundary of the floating platform remain fixed, and grid nodes located between the two are adjusted in position according to the mesh deformation relationship.

[0103] After each update of the grid node positions in the three-dimensional multiphase flow computational domain, the grid cell volume and grid surface position are checked to ensure that the dynamic grid deformation process satisfies the geometric conservation law and to avoid negative volume or unacceptable distortion in the grid cells. After the dynamic grid update is completed, the updated floating platform motion state is retransmitted to the actuation line model and the next external iteration loop is entered.

[0104] When the changes in the floating platform motion state, fluid load, and rotor aerodynamic load in the continuous external iteration loop reach the preset convergence requirements, the external iteration loop in the current time step ends, and the current solution result is used as the fluid-structure interaction result of the current time step.

[0105] By executing multiple external iteration loops within each time step, the data exchange between the fluid domain and the rigid body motion domain reaches a convergence state within the same time step, thereby reducing the additional mass divergence and load lag problems in the fluid-structure interaction calculation of floating wind turbine units.

[0106] After completing the solution for all time steps within the preset calculation period, the system outputs the six-degree-of-freedom motion response of the floating platform, the surface pressure distribution of the floating platform, the hydrodynamic load, the rotor aerodynamic load, the mooring load, the mooring line tension, the wind turbine rotor aerodynamic thrust, the wind turbine rotor aerodynamic torque, the wind turbine aerodynamic performance, and the wind turbine rotor wake flow field.

[0107] This paper analyzes the sway, heave, pitch, roll, and bow changes of a floating platform under the combined action of wind and waves, based on its six-degree-of-freedom motion response. It also analyzes the impact of the floating platform's motion on the wind turbine rotor's inflow state and aerodynamic load, based on the wind turbine rotor's aerodynamic thrust, torque, and performance. Finally, it analyzes the influence of mooring system parameters on the positioning capability and motion stability of the floating wind turbine, based on mooring line tension and the floating platform's motion response.

[0108] Example 2

[0109] This embodiment uses an NREL-5MW floating wind turbine for fluid-structure interaction simulation. The basic geometric parameters, mass-inertia properties, and mooring system parameters of the floating wind turbine are obtained. The selected wind turbine is an NREL-5MW.

[0110] Table 1 Geometric parameters of the floating platform

[0111] Mass (kg) Center of mass (m) Principal moment of inertia (kg²•m) 1.3473E+7 (0,0,-13.46) (6.827E+9, 6.827E+9, 1.226E+10)

[0112] Table 2 Mooring Parameters

[0113] Linear density (kg / m³) Total length (m) Anchor point (m) Cable guide hole (m) 865.5 865.5 (-837.6,0,-200) (-40.868,0,-14)

[0114] An aerodynamic model of the wind turbine rotor was established based on the rotor diameter, hub height, blade spanwise chord length distribution, blade spanwise torsion angle distribution, and airfoil pole data of the NREL-5MW floating wind turbine. A three-dimensional multiphase flow computational domain including air and water phases was established based on the floating platform geometry, with mesh refinement applied near the free surface, around the floating platform, in the rotor's action area, and in the wake development region. Figure 2 It is evident that a locally refined grid is installed in the operating area of ​​the wind turbine rotor and near its free surface, while the floating platform is located at the interface between the air and water phases. Figure 3 As can be seen, local grid areas are set around the columns and pontoons of the floating platform, which can deform with the movement of the floating platform.

[0115] At the inlet, the target wave field is generated using Stokes' second-order wave theory, and the waves are numerically absorbed in the outlet region. The fluid volume method is used to solve the evolution of the air-water two-phase free interface. The aerodynamic load of the wind turbine rotor is calculated using the actuation line model. The mooring load is calculated using the quasi-static catenary equation. The PIMPLE algorithm is used to perform strong coupling between the fluid domain and the rigid body motion domain. The dynamic mesh deformation technique is used to handle the boundary changes of the three-dimensional multiphase flow computational domain caused by the six-degree-of-freedom motion of the floating platform.

[0116] Within each time step, the position and velocity of the actuation line are updated based on the motion state of the floating platform. The fluid control equations and volume fraction transport equations, including the momentum source term of the actuation line, are solved. The hydrodynamic load is obtained by integrating the surface pressure of the floating platform. A six-degree-of-freedom rigid body dynamics model is solved to update the motion state of the floating platform. The positions of the mesh nodes in the three-dimensional multiphase flow computational domain are then readjusted based on the updated motion state of the floating platform. Figure 4-5 It can obtain the time-varying correlation between the motion response of the floating platform and the aerodynamic performance of the wind turbine rotor, and can use the correlation for load assessment, motion response prediction, mooring system optimization design and overall performance analysis of floating wind turbines.

[0117] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A floating wind-current-structure coupling method based on computational fluid dynamics and an actuation line model, characterized in that, Includes the following steps: Obtain the basic geometric parameters, mass-inertia properties, mooring system parameters, and environmental condition parameters of the floating wind turbine. A three-dimensional multiphase flow computational domain including air and water phases is established. A target wave field is generated at the entrance of the three-dimensional multiphase flow computational domain, and the waves are numerically absorbed in the exit region. The evolution state of the air-water two-phase free interface is solved by the fluid volume method. The rotor blades of the floating wind turbine are divided into multiple actuation units along the spanwise direction. The quarter-chord position of each actuation unit is used as a control point. The rotor aerodynamic load of each actuation unit is calculated based on the local relative velocity and airfoil polar data at the control point. The rotor aerodynamic load is then projected onto the computational fluid dynamics grid cells around the control point as the momentum source term of the Navier-Stokes equation. A six-degree-of-freedom rigid body dynamics model of the floating platform is established, and the motion state of the floating platform is solved based on the hydrodynamic load, the rotor aerodynamic load, the mooring load and the gravity load. The PIMPLE algorithm is used to achieve strong partitioning coupling between the fluid domain and the rigid body motion domain. Multiple external iteration loops are executed within each time step. In each external iteration loop, the position and velocity of the actuator, the spatial position of the cable guide hole, and the mesh node position of the three-dimensional multiphase flow computation domain are updated according to the current motion state of the floating platform. The Navier-Stokes equations and volume fraction transport equations containing the momentum source term are solved. The hydrodynamic load is obtained by integrating the surface pressure of the floating platform. The mooring load is solved according to the updated spatial position of the cable guide hole. The motion state of the floating platform is updated by solving the six-degree-of-freedom rigid body dynamics model until the coupling calculation in the current time step reaches the preset convergence requirement.

2. The floating wind-current-structure coupling method based on computational fluid dynamics and actuation line model according to claim 1, characterized in that, In each outer iteration loop, based on the current position, current attitude, current translation speed and current rotation speed of the floating platform, update the hub position, wind turbine rotor plane direction, blade azimuth angle and the position and speed of each actuation unit control point, and update the spatial position of each cable guide hole based on the current position and current attitude of the floating platform. The rotor aerodynamic load is calculated based on the updated position and velocity of each actuation unit control point, and the mooring load is calculated based on the updated spatial position of each cable guide hole. The rotor aerodynamic load, the mooring load, and the hydrodynamic load are input into the six-degree-of-freedom rigid body dynamics model to obtain the floating platform motion state for the next external iteration cycle.

3. The floating wind-current-structure coupling method based on computational fluid dynamics and actuation line model according to claim 1, characterized in that, The three-dimensional multiphase flow computational domain includes, in sequence along the wind and wave propagation direction, an inlet region, a floating wind turbine arrangement region, and an outlet region; Locally refined meshes are set near the free surface of the three-dimensional multiphase flow computational domain, in the action area of ​​the wind turbine rotor, around the floating platform, and in the wake development area of ​​the wind turbine rotor. The floating platform has a grid area near the surface of its columns, pontoons and cross braces that can deform with the movement of the floating platform, and a grid size transition zone is provided between the grid area and the external fixed grid area.

4. The floating wind-current-structure coupling method based on computational fluid dynamics and actuation line model according to claim 1, characterized in that, The target wave field is generated using Stokes' second-order wave theory or linear Airy wave theory; when using Stokes' second-order wave theory, the free surface elevation is expressed as: ； in: For amplitude, For wave number, Angular frequency, ; Here are the steepness parameters; the wavenumber and frequency satisfy the dispersion relation: Where g is the acceleration due to gravity.

5. The floating wind-current-structure coupling method based on computational fluid dynamics and actuation line model according to claim 1, characterized in that, The fluid volume method uses volume fraction to characterize the proportion of water phase within the computational fluid dynamics grid cell, and solves for the evolution state of the gas-water two-phase free interface using a volume fraction transport equation that includes an artificial compressibility term. The volume fraction transport equation is as follows: ； in: For fluid velocity vector, The relative compression velocity between the two phases is perpendicular to the free surface, and its magnitude is determined by the compressibility coefficient. Decide.

6. The floating wind-current-structure coupling method based on computational fluid dynamics and actuation line model according to claim 1, characterized in that, Based on the blade spanwise chord length distribution, twist angle distribution, and airfoil distribution, each actuation unit is assigned corresponding chord length, twist angle, and airfoil pole data, including the lift coefficient and drag coefficient. The local fluid velocity is sampled from the computational fluid dynamics grid cells around the control point of each actuation unit, and the local relative velocity is obtained by combining it with the motion velocity of the actuation unit itself. Based on the local relative velocity, local blade chord length, local blade twist angle, and airfoil polar data, the circumferential and normal aerodynamic loads of each actuation unit are calculated.

7. The floating wind-current-structure coupling method based on computational fluid dynamics and actuation line model according to claim 6, characterized in that, The circumferential and normal aerodynamic loads of each actuation unit are expressed as follows: ； ； in, air density, This is the blade chord length at the corresponding position of the actuation unit. For local relative speed, The radial distance from the control point of the actuation unit to the rotor axis of the wind turbine generator. It is a circumferential discrete scale. It is an axial discrete scale. The inflow angle corresponding to the local relative velocity. The lift coefficient, This is the drag coefficient.

8. The floating wind-current-structure coupling method based on computational fluid dynamics and actuation line model according to claim 7, characterized in that, The circumferential and normal aerodynamic loads of each actuation unit are projected onto the computational fluid dynamics grid cells surrounding each actuation unit using a spherical Gaussian regularized kernel function. The projection range of the rotor aerodynamic load is determined based on the spacing between the actuation units and the local grid scale of the wind turbine rotor's action area. The circumferential and normal aerodynamic loads of all actuation units are summarized to obtain the aerodynamic thrust, aerodynamic torque, and rotor aerodynamic loads acting on the overall structure of the floating wind turbine.

9. The floating wind-current-structure coupling method based on computational fluid dynamics and actuation line model according to claim 1, characterized in that, The six-degree-of-freedom rigid body dynamics model is based on the Newton-Euler equations. The translational and rotational motion equations of the floating platform are as follows: ； ； in, For the total mass of the floating platform, For the translational acceleration of the floating platform, The resultant force acting on the floating platform, For hydrodynamic loads, For rotor aerodynamic load, For mooring load, For gravity load, For the moment of inertia of the floating platform, For the rotational acceleration of the floating platform, The rotational speed of the floating platform, Let be the position vector of each load point relative to the center of mass of the floating platform. For the corresponding load, For external torque, This refers to the gyroscopic torque generated by the rotation of the wind turbine rotor.

10. The floating wind-current-structure coupling method based on computational fluid dynamics and an actuator line model according to claim 9, characterized in that, The hydrodynamic load is obtained by integrating the surface pressure and viscosity of the floating platform; the rotor aerodynamic load is provided by the actuation line model; and the mooring load is calculated using the quasi-static catenary equation. Within each time step, the spatial position of each guide cable hole is updated according to the position and attitude of the floating platform. Then, the tension direction and magnitude of each mooring line are obtained according to the position of the guide cable hole, the position of the seabed anchor point, the total length of the mooring line and the line density of the mooring line. The tensions of each mooring line acting on the guide cable hole are combined to obtain the mooring load and mooring moment acting on the floating platform. During the dynamic mesh deformation process, the mesh nodes near the surface of the floating platform move synchronously with the floating platform, while the outer boundary mesh nodes far from the floating platform remain fixed, and the dynamic mesh deformation process satisfies the geometric conservation law. The preset convergence requirements include that the changes in floating platform displacement, attitude, fluid load, and rotor aerodynamic load are all less than the corresponding preset thresholds.

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