An integrated coupling calculation method for floating wind turbines based on OpenFAST-OpenFOAM

Abstract

The present invention discloses an integrated coupling calculation method for a floating wind turbine based on OpenFAST-OpenFOAM. The steps of the method are as follows: (1) OpenFOAM transfers the six-degree-of-freedom displacement, velocity, and acceleration of the wind turbine floating body at the previous moment to OpenFAST; (2) OpenFAST receives the motion data of the wind turbine floating body, performs time advancement, calculates the aerodynamic loads on the upper structure of the wind turbine, and then obtains the tower base loads, and solves the multi-body structure kinematic equation to obtain the motion response of the upper structure of the wind turbine; (3) OpenFAST transfers the tower base loads and applies them to the corresponding positions of the wind turbine floating body, calculates the hydrodynamic loads and mooring loads at the current time step, and updates the motion of the floating body. This method realizes the coupling calculation between the open-source wind turbine integrated analysis code OpenFAST and the computational fluid dynamics code OpenFOAM, realizes the data interaction between the motion data of the floating body of the floating wind turbine and the tower base loads, greatly reduces the running time of the CFD full-scale floating wind turbine integrated analysis, and takes into account the control of the normal power generation condition of the wind turbine and the deformation of the flexible structure.

Description

Technical Field

[0001] The present invention relates to an integrated coupling calculation method for floating wind turbines based on OpenFAST-OpenFOAM, which is mainly applied to the analysis of the structural dynamic response of floating wind turbines under complex sea conditions. Background Art

[0002] At present, most of the software for the full-coupling analysis of floating wind turbine systems is based on existing onshore wind turbine simulation programs, adding the simulation of floating platforms and mooring systems. In addition, some are adding a wind turbine aerodynamic simulation module on the basis of the original floating platform hydrodynamic simulation code. The current main research methods are as follows: 1. The combination of potential flow theory and blade element momentum theory. 2. CFD integrated numerical simulation.

[0003] At present, the wind-wave integrated analysis software for floating wind turbines based on potential flow theory and blade element momentum theory mainly includes the open-source software OpenFAST developed by the National Renewable Energy Laboratory (NREL) in the United States, Bladed developed by Det Norske Veritas (DNV) in Norway, and HAWC2 and Flex5 developed by the Technical University of Denmark (DTU). In addition, many scholars have integrated the advantages of different software through data interaction, such as OpenFAST-Orcaflex developed by NREL, Bladed-Sesam developed by DNV, and CHARM3D-FAST developed by Texas A&M University (TAMU). However, the calculation method based on potential flow theory ignores the viscosity of the fluid and cannot accurately calculate nonlinear waves such as focused waves and breaking waves.

[0004] With the rapid development of computer technology, computational fluid dynamics (CFD) has achieved rapid progress in the fields of wind turbine aerodynamics and hydrodynamics: some scholars have realized the full-scale floating wind turbine water-air coupled flow field calculation through overlapping grid and sliding grid technologies; in order to reduce the calculation cost, some scholars have also realized the full-coupling analysis of floating wind turbines by combining overlapping grids and actuator line methods. Compared with potential flow theory, the viscous CFD calculation method can more realistically restore the real flow field situation, and has the advantages of rich flow field information, high calculation accuracy, and strong accuracy, and can be used to calculate the structural response of floating wind turbines under complex sea conditions such as wave breaking and focused waves, as well as the characteristics of the flow field and hydrodynamic loads. However, its calculation efficiency is low, and it ignores the wind turbine control system and flexible structure deformation.

[0005] Based on the above considerations, there is an urgent need for an integrated coupling calculation method for floating wind turbines that can take into account calculation accuracy while also considering calculation efficiency, which is used to calculate the structural dynamic response of floating wind turbines under complex sea conditions. Summary of the Invention

[0006] Aiming at the low calculation efficiency of the CFD numerical calculation model for floating wind turbines and the lack of consideration of the related issues between the wind turbine control module and structural deformation under normal operating conditions of the wind turbine. The present invention provides an integrated coupling calculation method for floating wind turbines based on OpenFAST-OpenFOAM. The method of the present invention constructs a calculation model of the upper structure of the wind turbine and a calculation model of the wind turbine floating body in OpenFAST and OpenFOAM respectively, and completes the calculation of the structural dynamic response of the fully coupled floating wind turbine by the data interaction of the kinematic data of the floating body and the load data of the tower base, providing a reference for the operation of floating wind turbines under complex sea conditions in practical engineering.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is:

[0008] An integrated coupling calculation method for floating wind turbines based on OpenFAST-OpenFOAM, based on the model parameters of a full-scale floating wind turbine, constructs a calculation model of the upper structure of the floating wind turbine and a calculation model of the wind turbine floating body in OpenFAST&OpenFOAM respectively, calls the OpenFAST program in OpenFOAM in the form of a dynamic link library, performs coordinate system transformation on the kinematic data of the wind turbine floating body and the load data of the wind turbine tower base and then interacts and couples them, completes the aerodynamic load and multibody dynamics calculation of the upper structure of the wind turbine, updates the six-degree-of-freedom motion of the wind turbine floating body, and finally obtains data such as the power generation power of the floating wind turbine, blade thrust, rotor speed, tower displacement, six-degree-of-freedom motion of the floating body, and mooring tension.

[0009] In the above technical solution, further, the coupling calculation method is specifically as follows:

[0010] Obtain the kinematic parameters (including six-degree-of-freedom displacement, velocity, acceleration, etc.) of the wind turbine floating body in OpenFOAM at the previous time step, and convert the kinematic parameters from the global coordinate system where the OpenFOAM calculation domain is located to the local coordinate system required for OpenFAST calculation;

[0011] OpenFAST advances in time based on the kinematic parameters of the wind turbine floating body at the previous moment to obtain the six-degree-of-freedom displacement, velocity, and acceleration data of the wind turbine floating body at the current moment; based on the aerodynamic loads on the wind turbine blades at the current moment, the generalized inertial forces of the wind turbine blades, nacelle, hub, and tower are calculated respectively, so as to obtain the force and moment loads on the wind turbine tower foundation; based on the six-degree-of-freedom displacement, velocity, and acceleration data of the wind turbine floating body and the generalized inertial forces of the wind turbine blades, nacelle, hub, and tower, the multi-body structure kinematic equation is solved to obtain the floating wind turbine power generation, blade thrust, rotor speed, and tower displacement;

[0012] The force and moment loads on the wind turbine tower foundation obtained from OpenFAST are transformed from the local coordinate system to the global coordinate system of OpenFOAM and applied to the corresponding positions of the wind turbine floating body (the tower foundation is the junction of the floating body and the upper structure. After the load is transferred from the upper structure to the floating body, the coordinates of the action point are the same); the hydrodynamic loads and mooring restoring forces of the wind turbine floating body are calculated in OpenFOAM to update the motion of the wind turbine floating body at the current time step.

[0013] Furthermore, the calculation model of the upper structure of the wind turbine is as follows:

[0014] For the upper structure of the wind turbine (blades, nacelle, hub, and tower), the kinematic equation is established based on Kane's dynamics method as follows:

[0015]

[0016] where F r * is the generalized inertial force vector, and F r is the generalized active force vector.

[0017] The calculation model of the wind turbine floating body is as follows:

[0018] For the floating platform, its kinematic equation is as follows:

[0019]

[0020] where q, and are the generalized rigid body displacement, velocity, and acceleration respectively; τ is the vector of generalized forces; H is the generalized inertia matrix, which is a function of the displacement q; C is the generalized bias force matrix, which is a function of the displacement and velocity.

[0021] Furthermore, when OpenFAST and OpenFOAM exchange data, coordinate transformation of motion data and load data is required according to different coordinate systems. The specific method is as follows: Based on Euler angle transformation, the six-degree-of-freedom displacement, velocity, and acceleration data of the wind turbine floating body in the OpenFOAM computational domain are transformed from the global coordinate system to the local coordinate system based on the ReferencePoint of OpenFAST, and the force and moment load data of the wind turbine tower base in OpenFAST are transformed from the local coordinate system to the global coordinate system of OpenFOAM.

[0022] Furthermore, the hydrodynamic loads and mooring restoring forces of the wind turbine floating body are obtained in the OpenFOAM flow field calculation, and the aerodynamic loads of the upper structure of the wind turbine are calculated in OpenFAST.

[0023] Furthermore, the integrated coupling calculation method of OpenFAST-OpenFOAM for floating wind turbines can be used to calculate nonlinear waves such as breaking waves and focusing waves, and is used for the analysis of the motion response and load distribution characteristics of floating wind turbines. The deformation of the wind turbine control system and flexible structures such as blades and tower bases is considered in the coupling program.

[0024] The advantages of the present invention are as follows:

[0025] The coupling of OpenFAST and OpenFOAM can be used for the dynamic response analysis of floating wind turbines under wind-wave conditions. Compared with software based on potential flow theory such as OpenFAST / Bladed / HAWC2, the present invention can be used for the calculation of complex sea conditions such as focusing waves and breaking waves. Compared with full-scale CFD simulations, the present invention considers the deformation of the wind turbine control system and flexible structures such as blades and tower bases, and improves the calculation efficiency of the full-coupling analysis of floating wind turbines under complex sea conditions. Description of the Drawings

[0026] Figure 1 is a schematic diagram of the coupling method flow of the present invention.

[0027] Figure 2 is a schematic diagram of coordinate transformation in the coupling calculation of the present invention.

[0028] Figure 3 is the verification and comparison of the surge, heave, and pitch degrees of freedom of the floating body when the coupling calculation method of the present invention is under a rated wind speed of 11.4 m / s and a regular wave height of 7.58 m. It can be seen that the verification effect of the coupling calculation method is good.

[0029] Figure 4 is the verification and comparison of the longitudinal displacement, impeller speed, and power generation of the upper tower of the wind turbine when the coupling calculation method of the present invention is under a rated wind speed of 11.4 m / s and a regular wave height of 7.58 m. It can be seen that the results fit well with other software.

[0030] Figure 5 These are the response diagrams of the displacements and rotational motions of a floating wind turbine in three degrees of freedom, namely surge, heave, and pitch, under the working conditions of a rated wind speed of 11.4 m / s, a focused wave amplitude of 4 m, and a focused time of 100 s, using the coupling calculation method of the present invention. Detailed implementation manners

[0031] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0032] As Figure 1 is a flowchart of an integrated coupling calculation method for a floating wind turbine based on OpenFAST-OpenFOAM of the present invention. The method is as follows: construct a calculation model of the wind turbine floating body in OpenFOAM, specifically including a floating body model and a mooring model, for calculating the hydrodynamic loads and mooring restoring forces of the wind turbine floating body; construct an upper structure model of the floating wind turbine in OpenFAST, specifically including models of the upper blades, tower, nacelle, and hub of the wind turbine, for calculating the aerodynamic loads of the upper structure of the wind turbine; set the wind speed and wave inflow conditions to complete the working condition design; run OpenFOAM, and in each time step during the operation, call OpenFAST in the form of a dynamic link library. During the call, interact the kinematic data of the wind turbine floating body and the load data of the wind turbine tower base. After the interaction is completed, calculate the hydrodynamic loads and mooring restoring forces in OpenFOAM respectively and update the six degrees of freedom motion of the floating body, and calculate the aerodynamic loads and the motion responses of structures such as blades and towers in OpenFAST, and advance the time step until the calculation is completed, then the calculation and analysis of the full coupling structural dynamic response of the floating wind turbine's aerodynamic-servo-hydrodynamic-mooring can be completed.

[0033] An integrated coupling calculation method for a floating wind turbine based on OpenFAST-OpenFOAM specifically includes the following steps:

[0034] Obtain the kinematic parameters (including displacements, velocities, accelerations, etc. in six degrees of freedom) of the wind turbine floating body in OpenFOAM at the previous time step, and convert the kinematic parameters from the global coordinate system where the OpenFOAM calculation domain is located to the local coordinate system required for OpenFAST calculation;

[0035] OpenFAST advances in time based on the kinematic parameters of the wind turbine floating body at the previous moment to obtain the six-degree-of-freedom displacement, velocity, and acceleration data of the wind turbine floating body at the current moment; based on the aerodynamic loads on the wind turbine blades at the current moment, the generalized inertial forces of the wind turbine blades, nacelle, hub, and tower are calculated respectively, so as to obtain the force and moment loads on the wind turbine tower foundation; based on the six-degree-of-freedom displacement, velocity, and acceleration data of the wind turbine floating body and the generalized inertial forces of the wind turbine blades, nacelle, hub, and tower, the multi-body structure kinematic equation is solved to obtain the floating wind turbine power generation, blade thrust, rotor speed, and tower displacement;

[0036] The force and moment loads on the wind turbine tower foundation obtained from OpenFAST are converted from the local coordinate system to the global coordinate system of OpenFOAM and applied to the corresponding positions of the wind turbine floating body; the hydrodynamic loads and mooring restoring forces of the wind turbine floating body are calculated in OpenFOAM to update the motion of the wind turbine floating body at the current time step.

[0037] The calculation model of the upper structure of the wind turbine is as follows:

[0038] For the upper structure of the wind turbine, the kinematic equation is established based on Kane's dynamics method, specifically as follows:

[0039]

[0040] where F r * is the generalized inertial force vector, and F r is the generalized active force vector.

[0041] The calculation model of the wind turbine floating body is as follows:

[0042] For the floating platform, its kinematic equation is as follows:

[0043]

[0044] where q, and are the generalized rigid body displacements, velocities, and accelerations respectively; τ is the vector of generalized forces; H is the generalized inertia matrix, which is a function of the displacement q; C is the generalized bias force matrix, which is a function of the displacement and velocity.

[0045] As Figure 2, When OpenFAST and OpenFOAM exchange data, coordinate transformations of motion data and load data need to be performed according to the different coordinate systems. In OpenFOAM, numerical simulation operations are based on the global coordinate system of the computational domain, and the origin and axis directions of this coordinate system are given when drawing the computational domain grid; in OpenFAST, numerical simulation operations are based on the local coordinate system of the wind turbine motion, with the coordinate origin being the Reference Point in the OpenFAST initial settings, generally the center of the interface between the wind turbine and the water surface at the still water moment, and the axis directions are related to the tower rotation direction, as specifically shown in the OpenFAST coordinate system in the figure. Therefore, coordinate system transformations are required when transferring interactive floating body motion data and tower base load data.

[0046] It can be seen from Figure 3 and 4 that the calculation results of the method of the present invention are good, and the calculation results fit well with other software. Figure 5 Shows the displacement and rotational motion responses of the floating body in the surge, heave, and pitch degrees of freedom under the focused wave condition calculated by the method of the present invention. It can be seen from the figure that when the wind turbine encounters a focused wave under normal power generation conditions, large-amplitude motion responses can be induced in the surge and pitch degrees of freedom, posing a threat to the safe operation of the wind turbine.

[0047] Of course, the above are only specific application examples of the present invention. The present invention has other implementation manners, and all technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. An integrated coupling calculation method for floating wind turbines based on OpenFAST-OpenFOAM for focusing wave condition calculation, characterized by: Based on the parameters of the real-scale floating wind turbine model, the wind turbine superstructure calculation model and the wind turbine floating body calculation model are constructed in OpenFAST and OpenFOAM respectively; OpenFAST is called in OpenFOAM in the form of a dynamic link library to complete the data interactive coupling operation, and finally the floating wind turbine power generation, blade thrust, rotor speed, tower displacement, floating body six-degree-of-freedom motion and mooring tension data are obtained; The steps of the coupled calculation method are as follows: Obtain the kinematic parameters of the wind turbine float in OpenFOAM at the previous time step, and convert the kinematic parameters of the wind turbine float from the global coordinate system of the OpenFOAM calculation domain to the local coordinate system required for OpenFAST calculation; OpenFAST performs time advancement based on the kinematic parameters of the wind turbine float at the previous moment to obtain the six-degree-of-freedom displacement, velocity and acceleration data of the wind turbine float at the current moment; based on the aerodynamic load on the wind turbine blades at the current moment, the generalized inertia forces of the wind turbine blades, nacelle, hub and tower are calculated respectively, thereby obtaining the force and bending moment loads of the wind turbine tower base; Based on the six-degree-of-freedom displacement, velocity and acceleration data of the wind turbine floating body and the generalized inertial force of the wind turbine blades, nacelle, hub and tower, the kinematic equation of the multi-body structure is solved to obtain the floating wind turbine power generation, blade thrust, rotor speed and tower displacement; The force and moment loads of the wind turbine tower foundation obtained from OpenFAST are converted from the local coordinate system to the global coordinate system of OpenFOAM, and act on the corresponding position of the wind turbine float. The hydrodynamic load and mooring restoring force of the wind turbine float are calculated in OpenFOAM, and the movement of the wind turbine float in the current time step is updated.

2. The integrated coupling calculation method for floating wind turbines based on OpenFAST-OpenFOAM according to claim 1, characterized in that: The calculation model of the fan superstructure is: For the wind turbine superstructure, the kinematic equation is established based on the Kane dynamics method, as follows: where F r * is the generalized inertial force vector, F r is the generalized active force vector; The calculation model of the wind turbine floating body is: For a floating platform, the kinematic equation is as follows: Among them, q, as well as are the generalized rigid body displacement, velocity and acceleration respectively; τ is the vector of generalized force; H is the generalized inertia matrix, which is a function of displacement q; C is the generalized bias force matrix, which is a function of displacement and velocity.

3. The integrated coupling calculation method for floating wind turbines based on OpenFAST-OpenFOAM according to claim 1, characterized in that: When OpenFAST and OpenFOAM are coupled to calculate the kinematic parameters of the wind turbine float and the force and moment loads of the wind turbine tower foundation, it is necessary to perform coordinate transformation between the local coordinate system and the global coordinate system. The specific method is: based on the Euler angle transformation, the six-degree-of-freedom displacement, velocity and acceleration data of the wind turbine float obtained in the OpenFOAM calculation domain are transformed from the global coordinate system to the local coordinate system where OpenFAST is located; the force and moment load data of the wind turbine tower foundation obtained in OpenFAST are transformed from the local coordinate system to the global coordinate system of OpenFOAM.

4. The integrated coupling calculation method for floating wind turbines based on OpenFAST-OpenFOAM according to claim 1, characterized in that: In the coupled calculation, the hydrodynamic loads are obtained by solving the velocity and pressure field equations using the PISO algorithm, and the mooring restoring force is obtained using the mooring dynamics module based on the finite element method.

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