A multi-domain coupling simulation method for floating wind turbines based on computational fluid dynamics

Abstract

A simulation method for multi-domain coupling of floating wind turbines based on computational fluid dynamics belongs to the technical field of computational fluid dynamics multiphase flow simulation. In the multi-domain coupling simulation method of floating wind turbines, the computational domain is divided into two parts: the rotor domain and the floating wind turbine platform domain. The mutual influence between the aerodynamic characteristics of the rotor and the hydrodynamic characteristics of the floating wind turbine platform is realized through the coupling between the rotor thrust and the motion response of the floating wind turbine platform. The rotor domain and platform domain of this method are complete case models, which can complete the calculation independently, and the method can also be used to realize the coupling calculation between multiple computational domains. The simulation results of this method are in good consistency with the calculation results of traditional overall coupling methods and other studies. Under the condition of the same accuracy, the computational efficiency of this method is significantly improved compared with the traditional floating wind turbine coupling simulation method.

Description

Technical Field

[0001] The present invention belongs to the technical field of floating wind power and relates to a simulation method of multi-domain coupling of a floating wind turbine based on computational fluid dynamics. Background Art

[0002] In recent years, my country's offshore wind power industry has developed rapidly, and the application of offshore floating wind turbines has gradually moved towards the deep sea. Compared with traditional onshore wind power, offshore wind power has greater development potential and obvious advantages. As an innovative form of offshore wind energy, floating offshore wind turbines have received widespread attention and gradually been applied in recent years. Unlike traditional fixed offshore wind turbines, floating offshore wind turbines can be deployed in deeper waters, utilizing richer and more stable wind resources, and have greater development potential. However, floating offshore wind turbines face more complex environmental load challenges. The variability and uncertainty of offshore conditions, such as waves, wind speed and currents, will affect the stability of floating offshore wind turbines, resulting in complex changes in platform motion response, mooring cable loads, aerodynamic thrust, wake effects, etc.

[0003] Many researchers have used computational fluid dynamics (CFD) methods to simulate the overall coupling of floating wind turbine systems, studying motion response, aerodynamic thrust, output power, anchor chain tension, and turbine wakes. While CFD methods can comprehensively simulate the wave fields and wakes of floating wind turbines, intuitively reflecting the impact of flow fields on wind turbine systems, computational efficiency has been a key factor limiting the application of CFD methods in floating wind turbine systems. Summary of the Invention

[0004] The present invention proposes an efficient multi-domain coupling simulation method for floating wind turbines based on computational fluid dynamics. Based on the floating wind turbine coupling simulation method proposed by this invention, efficient simulation of the aerodynamic-hydrodynamic-mooring coupling model of floating wind turbines under the combined action of wind, wave and flow loads can be achieved, and the aerodynamic, hydrodynamic and mooring dynamics analysis of the wind turbine can be completed.

[0005] A computational fluid dynamics-based multi-domain coupling simulation method for floating wind turbines includes the following steps:

[0006] S1. Create the geometry file required to generate the mesh based on the shape of the simulated floating wind turbine platform;

[0007] S2. Define the dimensions of the floating wind turbine platform and rotor computational domains used for simulation in OpenFOAM. Create a specific computational mesh in the floating wind turbine platform computational domain using the geometry file from step S1. Create a refined mesh in the rotor computational domain based on computational requirements.

[0008] S3. Merge the computational domain of the floating wind turbine platform and the computational domain of the rotor, define the multiphase flow calculation phase fraction and wave field file in the computational domain of the floating wind turbine platform, and define the wind turbine cellZone in the computational domain of the rotor.

[0009] S4. Conduct multi-domain coupled simulation of floating wind turbines based on computational fluid dynamics (CFD) using the velocity-pressure coupling algorithm. The overall calculation steps include:

[0010] S41. Calculate the aerodynamic loads of the floating wind turbine under platform motion in the rotor domain. Based on the blade parameter information and platform motion information, calculate the lift and drag on the blade using the following formula:

[0011] (1)

[0012] (2)

[0013] in: represents the air density, c represents the chord length, dr represents the length of the airfoil unit on the blade, is the relative speed of the blade under the influence of platform motion and rotor rotation, and are the lift coefficient and drag coefficient of the corresponding airfoil respectively;

[0014] S42, integrating the lift and drag of all blade units calculated above along the blade radial direction to obtain the aerodynamic thrust of the fan rotor, and saving the thrust information in a dictionary file of aerodynamic loads;

[0015] S43. In the computational domain of the floating wind turbine platform, calculate the total fluid load on the floating body, including the surface pressure and viscous force on the floating wind turbine platform;

[0016] S44. Calculate the mooring load on the floating wind turbine platform by dividing the mooring cable into several mass points, each of which is connected by a massless spring. The total mass of all the mass points represents the mass of the mooring cable, the spring stiffness represents the tensile stiffness of the mooring cable, and the fluid load on the mooring unit is calculated using the Morrison equation.

[0017] S45. Calculate the motion information of the floating wind turbine platform based on the total load on the floating wind turbine platform: velocity, displacement, and acceleration. Save the information to a motion information dictionary file. Calculate the mesh node displacement using a mesh solver.

[0018] S46. In the rotor calculation domain, read the dictionary file of motion information, update the rotor rotation center position based on the global coordinate system, and calculate the position and relative speed of each segment of the blade based on the rotor local coordinate system.

[0019] Furthermore, the pre-treatment of the floating wind turbine platform includes the following steps:

[0020] a. Define the grid motion setting file based on the floating wind turbine platform parameter information;

[0021] b. Establish the aerodynamic load constraint conditions for the fan rotor and set the aerodynamic load action points.

[0022] Furthermore, the rotor calculation domain pre-processing includes the following steps:

[0023] a. Create the source item file for the rotor domain wind turbine load calculation, defining the wind turbine blade local coordinate system, blade parameter information, number of blade segments, blade load interpolation range, and blade rotation parameters;

[0024] b. Define the coupling mode between the wind turbine rotor and the floating wind turbine platform in the rotor calculation domain source item file.

[0025] Furthermore, in the multi-operating simulation of multiple platform forms and rotor forms:

[0026] Establish computational domains for multiple floating wind turbine platforms: Platform 1, Platform 2, ... Platform n;

[0027] Establish multiple rotor calculation domains: rotor 1, rotor 2... rotor n;

[0028] For a specific operating condition, the multiphase flow calculation phase fraction is defined in the floating wind turbine platform domain, and the wind turbine cellZone is defined in the rotor calculation domain. The corresponding floating wind turbine platform domain and rotor calculation domain are merged to realize multi-domain coupling calculation of a certain platform form and wind turbine form.

[0029] The beneficial effects of the present invention are as follows:

[0030] (1) The grids required for wave and wind turbine wake calculations are encrypted in the floating platform wind turbine calculation domain and the rotor calculation domain, respectively. Unnecessary grids can be easily thinned in each calculation domain to reduce the overall number of grids.

[0031] (2) The calculation of the rotor calculation domain and the floating wind turbine platform calculation domain are completed successively within one time step, and the calculation efficiency is improved superlinearly compared with the traditional method.

[0032] (3) In the calculation of multiple floating wind turbine platform forms and multiple rotor forms, each calculation domain can be reused, and the modeling efficiency is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for describing the technical solution.

[0034] Figure 1It is the flow chart of multi-domain coupled simulation.

[0035] Figure 2 Schematic diagram of the floating body domain and rotor domain in the multi-domain coupling simulation method.

[0036] Figure 3 Schematic diagram of domain merging in the efficient simulation process of the multi-domain coupled simulation method.

[0037] Figure 4 This is the surge response diagram calculated by the multi-domain coupling simulation method.

[0038] Figure 5 It is the heave response diagram calculated by the multi-domain coupling simulation method.

[0039] Figure 6 This is the pitch response diagram calculated by the multi-domain coupling simulation method.

[0040] Figure 7 It is a schematic diagram of the wake field and wave field calculated by the multi-domain coupling simulation method. DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0043] 1. The simulation steps of a single wind turbine coupling model are as follows:

[0044] a. Create the geometry file required to generate the mesh based on the shape of the floating wind turbine platform being simulated;

[0045] b. Define the computational domain and rotor dimensions of the floating wind turbine platform used for simulation in OpenFOAM, create a specific computational mesh in the computational domain of the floating platform using the geometry file in claim 1a, and create a specific refined mesh in the computational domain of the rotor according to computational requirements;

[0046] c. The pre-treatment of the floating platform includes the following steps:

[0047] c1. Define the mesh motion setting file based on the floating platform parameter information to ensure that the calculation of a single floating platform can be completed within the floating platform calculation domain;

[0048] c2. Establish the aerodynamic load constraint conditions for the fan rotor and set the aerodynamic load action points;

[0049] d. The rotor calculation domain pre-processing includes the following steps:

[0050] d1. Create the source item file for the rotor domain wind turbine load calculation, define the wind turbine blade local coordinate system, blade parameter information, number of blade segments, blade load interpolation range, and blade rotation parameters, to ensure that fixed wind turbine rotor simulation calculations can be performed;

[0051] d2. Define the coupling mode between the wind turbine rotor and the floating platform in the rotor computational domain source term file;

[0052] e. Merge the floating platform domain and the rotor calculation domain grids, define the multiphase flow calculation phase fraction and wave field file in the floating platform domain, and define the wind turbine area cellZone in the rotor calculation domain;

[0053] f. Conduct multi-domain coupled simulation of floating wind turbines based on computational fluid dynamics (CFD) using the velocity-pressure coupling algorithm. The overall calculation steps include:

[0054] f1. Calculate the aerodynamic load of the floating wind turbine under platform motion in the rotor domain. This is characterized by calculating the lift and drag on the blades using the following formula based on the blade parameter information and platform motion information:

[0055] (1)

[0056] (2)

[0057] in represents the air density, c represents the chord length, dr represents the length of the airfoil unit on the blade, is the relative speed of the blade under the influence of platform motion and rotor rotation, and are the lift and drag coefficients of the corresponding airfoil, respectively;

[0058] f2. Integrate the lift and drag of all blade units calculated in step f1 along the blade radial direction to obtain the aerodynamic thrust of the fan rotor, and save the thrust information to the dictionary file corresponding to the aerodynamic load;

[0059] f3. In the floating platform domain, calculate the total fluid load on the floating body, including the surface pressure and viscous forces acting on the floating platform;

[0060] f4. Calculate the mooring loads on the floating platform. This method involves dividing the mooring line into several mass points, each connected by a massless spring. The total mass of all the mass points represents the mass of the mooring line, and the spring stiffness represents the tensile stiffness of the mooring line. The fluid loads on the mooring unit are calculated using the Morrison equation.

[0061] f5. Calculate the motion information of the floating wind turbine platform based on the total load on the floating platform. This information, including velocity, displacement, and acceleration, is saved in the corresponding motion information dictionary file. The mesh node displacements are then calculated using a mesh solver.

[0062] f6. In the rotor computational domain, read the motion information dictionary file, update the rotor's rotation center position based on the global coordinate system, and calculate the position and relative speed of each blade segment based on the rotor's local coordinate system.

[0063] 2. In the multi-operating simulation of multiple platforms and rotors, efficient modeling and simulation include the following steps:

[0064] g. For multi-platform and multi-rotor simulations, use step c1 to establish multiple floating platform computational domains: Platform 1, Platform 2, ... Platform n;

[0065] h. For multi-platform and multi-rotor simulations, use step d1 to establish multiple rotor calculation domains: rotor 1, rotor 2, ... rotor n;

[0066] i. For multi-operating condition simulations with multiple platform and rotor types, for a specific operating condition, use step e to merge the corresponding floating platform domain and rotor calculation domain to achieve multi-domain coupling calculations for a certain platform type and wind turbine type.

[0067] The following is a detailed introduction to the implementation process of a specific case:

[0068] Build as Figure 2 The floating platform domain and rotor domain of the NREL5MW semi-submersible wind turbine are shown, and the domains are merged;

[0069] The calculation conditions used in the embodiment are a wind speed of 11.4 m / s, a wave height of 7.58 m, and a wave period of 12.1 s.

[0070] The calculated results of surge, heave and pitch are as follows: Figure 4 、 5 As shown in Figure 6, the multi-domain coupling method proposed in this invention is consistent with the calculation results of the traditional overall coupling method. The calculated wake field and wave field results are shown in Figure 6. Figure 7 shown.

[0071] In this case, the global coupling method used approximately 2.7 million meshes, with a computational time of 12 seconds per time step. The multi-domain coupling method used approximately 1.9 million meshes, with a computational time of 7 seconds per time step. Compared to the traditional global coupling method, the multi-domain coupling method reduces the number of meshes and computational time while maintaining the same accuracy, nearly doubling computational efficiency.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A simulation method for multi-domain coupling of floating wind turbines based on computational fluid dynamics, characterized in that: The following steps are involved: S1. Create the geometry file required to generate the mesh based on the shape of the simulated floating wind turbine platform; S2. Define the dimensions of the floating wind turbine platform and rotor computational domains used for simulation in OpenFOAM. Create a specific computational mesh in the floating wind turbine platform computational domain using the geometry file from step S1. Create a refined mesh in the rotor computational domain based on computational requirements. S3. Merge the computational domain of the floating wind turbine platform and the computational domain of the rotor, define the multiphase flow calculation phase fraction and wave field file in the computational domain of the floating wind turbine platform, and define the wind turbine cellZone in the computational domain of the rotor. S4. Conduct multi-domain coupled simulation of floating wind turbines based on computational fluid dynamics (CFD) using the velocity-pressure coupling algorithm. The overall calculation steps include: S41. Calculate the aerodynamic loads of the floating wind turbine under platform motion in the rotor domain. Based on the blade parameter information and platform motion information, calculate the lift and drag on the blade using the following formula: （1）； （2）； in: represents the air density, c represents the chord length, dr represents the length of the airfoil unit on the blade, is the relative speed of the blade under the influence of platform motion and rotor rotation, and are the lift coefficient and drag coefficient of the corresponding airfoil respectively; S42, integrating the lift and drag of all blade units calculated above along the blade radial direction to obtain the aerodynamic thrust of the fan rotor, and saving the thrust information in a dictionary file of aerodynamic loads; S43. In the computational domain of the floating wind turbine platform, calculate the total fluid load on the floating body, including the surface pressure and viscous force on the floating wind turbine platform; S44. Calculate the mooring load on the floating wind turbine platform by dividing the mooring cable into several mass points, each of which is connected by a massless spring. The total mass of all the mass points represents the mass of the mooring cable, the spring stiffness represents the tensile stiffness of the mooring cable, and the fluid load on the mooring unit is calculated using the Morrison equation. S45. Calculate the motion information of the floating wind turbine platform based on the total load on the floating wind turbine platform: velocity, displacement, and acceleration. Save the information to a motion information dictionary file. Calculate the mesh node displacement using a mesh solver. S46. In the rotor calculation domain, read the dictionary file of motion information, update the rotor rotation center position based on the global coordinate system, and calculate the position and relative speed of each segment of the blade based on the rotor local coordinate system.

2. The method for simulating multi-domain coupling of floating wind turbines based on computational fluid dynamics according to claim 1, characterized in that: The pre-treatment of floating wind turbine platforms includes the following steps: a. Define the grid motion setting file based on the floating wind turbine platform parameter information; b. Establish the aerodynamic load constraint conditions for the fan rotor and set the aerodynamic load action points.

3. The method for simulating multi-domain coupling of floating wind turbines based on computational fluid dynamics according to claim 2, characterized in that: The rotor calculation domain pre-processing includes the following steps: a. Create the source item file for the rotor domain wind turbine load calculation, defining the wind turbine blade local coordinate system, blade parameter information, number of blade segments, blade load interpolation range, and blade rotation parameters; b. Define the coupling mode between the wind turbine rotor and the floating wind turbine platform in the rotor calculation domain source item file.

4. The method for simulating multi-domain coupling of floating wind turbines based on computational fluid dynamics according to claim 3, characterized in that: In multi-operating simulations of multiple platforms and rotors: Establish computational domains for multiple floating wind turbine platforms: Platform 1, Platform 2, ... Platform n; Establish multiple rotor calculation domains: rotor 1, rotor 2... rotor n; For a specific operating condition, the multiphase flow calculation phase fraction is defined in the floating wind turbine platform domain, and the wind turbine cellZone is defined in the rotor calculation domain. The corresponding floating wind turbine platform domain and rotor calculation domain are merged to realize multi-domain coupling calculation of a certain platform form and wind turbine form.

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