A method for calculating the hydrodynamic coupling of the aerodynamic wake structure of a floating vertical axis wind turbine

Abstract

The application discloses a kind of floating vertical axis fan aerodynamic wake structure hydrodynamic coupling calculation method, comprising the following steps: (1) initial parameters and environmental conditions are pre-set, the structure, aerodynamic, wake load of vertical axis fan is calculated by structure module, aerodynamic module and wake module;(2) floating vertical axis fan system is decomposed into two subsystems by using loose coupling method, tower column deformation, blade large-scale rigid body motion and floating foundation motion are calculated, and then the coupling relationship of blade large-scale motion and its deformation is established;(3) in wake module, wake vortex induced velocity is transmitted to aerodynamic module for calculating aerodynamic load;(4) aerodynamic load on blade is calculated in aerodynamic module;(5) the calculated aerodynamic load is transmitted to structure module.The application can calculate the coupling response of floating vertical axis fan aerodynamic-wake-structure-hydrodynamic under various environmental loads, and provide numerical tool support for the application of floating vertical axis fan.

Description

Technical Field

[0001] This invention relates to the field of renewable energy utilization technology, and in particular to a hydrodynamic coupling calculation method for the aerodynamic wake structure of a floating vertical axis wind turbine. Background Technology

[0002] Offshore wind energy, as one of the most promising renewable energy sources, is crucial for efficient development and utilization. In the field of floating wind turbine technology, based on the arrangement of the rotor shaft, there are two main technical routes: floating horizontal axis and floating vertical axis. Floating horizontal axis wind turbines, with their technological advantages, have developed relatively mature research methods. In contrast, the development of floating vertical axis wind turbines has been relatively slow, but their unique structural advantages, such as a low center of gravity for easy maintenance, the ability to receive winds from any direction without yaw adjustment, and rapid wake recovery for compact deployment, demonstrate significant potential value in specific application scenarios. Nevertheless, unlike land-based or shallow-sea wind turbines fixed to the seabed, floating vertical axis wind turbines operate in an extremely complex environment. Their support platform sways with the waves above the sea surface, resulting in the unit constantly operating in a dynamic environment with strong coupling between aerodynamics, wake, structure, and hydrodynamics. Dynamic analysis of floating vertical axis fans often suffers from the following limitations: significant aerodynamic unsteadiness and wake interference effects, complex and highly nonlinear multiphysics coupling mechanisms, and high risk of low-frequency resonance. This results in a lack of efficient dedicated simulation tools for analyzing the coupled aerodynamic-wake-structure-hydrodynamic dynamic response, hindering its engineering application. To address these issues, a coupled calculation method is urgently needed to calculate the coupled aerodynamic-wake-structure-hydrodynamic response of floating vertical axis fans under various environmental loads, providing numerical tool support for the engineering application of floating vertical axis fans. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and to provide a coupled calculation method to calculate the coupled response of aerodynamics-wake-structure-hydrodynamics of a floating vertical axis fan under various environmental loads, thereby providing numerical tool support for the engineering application of floating vertical axis fans.

[0004] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0005] A method for hydrodynamic coupling calculation of the aerodynamic wake structure of a floating vertical axis fan includes the following steps:

[0006] (1) Before starting the simulation, the initial parameters and environmental conditions are set in advance. The structural, aerodynamic and wake loads of the vertical axis fan are calculated through the structural module, aerodynamic module and wake module.

[0007] (2) In each time step, firstly, in the structural module, the floating vertical axis wind turbine system is decomposed into two subsystems using a loose coupling method. Aerodynamic loads, hydrodynamic loads and mooring loads are applied to subsystem 1. Then, the tower deformation, large-scale rigid body motion of the blades and the floating foundation motion are calculated. Then, the coupling relationship between the large-scale motion of the blades and their own deformation is established. The large-scale rigid body motion of the blades is transferred to subsystem 2. At the same time, the floating foundation motion is transferred to the hydrodynamic module in the structural module to calculate the hydrodynamic loads and mooring loads for the next time step. Finally, the calculated blade deformation and floating foundation motion are transferred to the aerodynamic module and the wake module.

[0008] (3) In the wake module, the wake field is first divided into near field and far field. The wake velocity caused by near field particles is directly calculated using the classical Biot-Savart law, while the wake velocity caused by far field particles is solved by the improved octree algorithm. The wake vortex induced velocity is transferred to the aerodynamic module for calculating aerodynamic load.

[0009] (4) In the aerodynamic module, based on the obtained blade deformation, floating foundation motion and total induced velocity, the relative velocity and angle of attack of the blade are obtained, and then the aerodynamic load on the blade is calculated. At the same time, the induced velocity of the blade node is transmitted to the wake module for the next time step to calculate the wake field velocity.

[0010] (5) The calculated aerodynamic load is transferred to the structural module to determine the structural dynamic response of the next time step. At the same time, all vortex elements in the wake module undergo convective motion with the local induced velocity field. The newly released vortex elements will form a new wake field for the calculation of the next time step.

[0011] Furthermore, the initial parameters and environmental conditions in step (1) include incoming wind speed, fan speed, wave height, wave period, wind direction, wave direction, airfoil lift and drag coefficient table, wake cut-off length, wake update length, wake dissipation coefficient, wake hysteresis coefficient, iteration residual, relaxation factor, vortex element scale coefficient, and Taylor approximation order.

[0012] Furthermore, subsystem 1 in step (2) includes all the structures of the wind turbine. The floating foundation is treated as a rigid body, considering six degrees of freedom of motion: sway, roll, heave, pitch, pitch and yaw. The flexible tower is treated as an elastic body, and the blades are treated as equivalent mass points, considering their mass and moment of inertia. The dynamic equations of subsystem 1 are established based on the variational principle of Rhoden velocity. After considering the constraints, the final Lagrange equations are in the form of:

[0013] (1)

[0014] in, It is a quality matrix. It is a generalized external force matrix. Let Jacobi be the constraint matrix of the equations. For the Lagrange multipliers of the constraint equations, For the right-hand side of the acceleration constraint equation, Let be the generalized coordinates of all degrees of freedom of subsystem 1, including the motion of the floating foundation, the deformation of the tower column, and the motion of the blade mass points; and the coordinates of any point before the deformation of the blade. The transformed form is represented as ,but The point relative to the origin of the inertial coordinate system radius It can be represented as:

[0015] (2)

[0016] in, Let be the radius vector of the floating coordinate system of the blade relative to the inertial coordinate system. for Point relative to The radius vector, for Deformation displacement of a point, in order to describe deformation displacement The blade is treated as a flexible beam structure. Based on the finite element method, the curved blade is discretized into multiple straight beam elements. Each element node contains six degrees of freedom: bending deformation and bending angle along two transverse directions, tensile deformation along the axial direction, and torsional deformation around the axis. An element coordinate system is established on each element, based on continuum mechanics. It can be represented as:

[0017] (3)

[0018] in, Represents unit shape function, coupling term can be express, The deformation displacement is obtained by using the deformation displacement array based on the blade floating coordinate system. Then the radius vector can be described. This establishes the coupling relationship between the large-scale motion of the blade and its own deformation, transferring the large-scale rigid body motion of the blade to subsystem 2. Based on the Rhodan velocity variational principle, the dynamic equations of the flexible body of the blade in subsystem 2 can be established:

[0019] (4)

[0020] in, It is the generalized virtual power of external forces. and These are the virtual power of inertial force and the virtual power of elastic force, respectively. The modeling method for the tower column is similar to that for the blade, except that the bending angle of the beam model needs to be set to 0 during the modeling process.

[0021] Furthermore, the hydrodynamic load in step (2) is calculated based on potential flow theory, so at time t... The velocity vector of the fluid at the location It can be derived from velocity potential express:

[0022] (5)

[0023] After solving for the velocities at various positions on the wetted surface of the object in the flow field using the velocity potential, the pressure of the fluid element can be calculated based on the Bernoulli equation. After obtaining the pressure of the fluid unit Then, by integrating the pressure along the wetted surface of the object, the wave load on the structure can be calculated:

[0024] (6)

[0025] in The direction cosine of the unit's six-degree-of-freedom motion. For the wet surface of the object, the velocity potential can be considered as such during the solution process. It can be divided into three parts:

[0026] (7)

[0027] in Let be the incident velocity potential, representing the undisturbed velocity potential of the incident wave. The diffraction velocity potential represents the velocity potential generated when a wave diffracts around an object. The radiation velocity potential represents the velocity potential generated by the change in the flow field caused by the motion of the object itself. Then, the fluid pressure can be obtained. Similarly, the fluid pressure can be divided into wave incident force, wave diffraction force, and wave radiation force. In the specific calculation of wave force, the Green's function method is generally used to solve the Laplace equation with boundary value conditions. Based on the boundary element method or the surface element method, the object is treated as a surface element model. Control points are selected on each surface element, and the source-sink method is used to solve the velocity potential at each position on the surface of the object, and then the wave load is calculated.

[0028] Furthermore, the mooring load calculation in step (2) is based on the catenary theory, and a segment of the mooring cable is taken for stress analysis. The length of the segment when not stretched is... The cross-sectional area is The wet weight per unit length is Assume the axial force of the element is The hydrodynamic components in the tangential and normal directions are respectively and Through derivation, it is found that the catenary has two directions along its length. Relationship of directions:

[0029] (8)

[0030] (9)

[0031] in, and It is the equivalent axial tension Components along the horizontal and vertical directions, It is the elastic modulus. It is the density of water. It is gravitational acceleration. The vertical length of the element. The angle between the bottom of the unit and the horizontal direction is given. Integrating the above equation along the length direction to the top of the mooring cable, we can obtain:

[0032] (10)

[0033] (11)

[0034] (12)

[0035] (13)

[0036] Where X is the horizontal force on the mooring cable, Z is the vertical force on the mooring cable, and V0 is the vertical tension component at the lowest point of the suspension section. This refers to the length of the suspended portion of the mooring cable after stretching. The length of the mooring cable before tensioning the suspended portion can be written as:

[0037] (14)

[0038] in, This refers to the total length of the mooring cable when it is not stretched. This refers to the length of the section of the mooring cable lying on the bottom.

[0039] Furthermore, the classical Biot-Savart law in step (3) is:

[0040] (15)

[0041] in, It is the position vector of the source particle. It is the position vector of the target particle. It is the induction speed. is the vortex vector, and N is the number of particles. The integral along the length of the vortex element and It is the kernel function of the Biot-Savart theorem; the improved octree algorithm is as follows:

[0042] First, a large number of vortex particles are divided into a certain number of cubes, or vortex units, with the central node of each vortex unit being y. c Regarding the classical Biot-Savart law in y c Taylor approximation is used here:

[0043] (16)

[0044] Where c = {yj, j = 1, 2, …, Nc} is a particle swarm in a vortex unit, and Nc is the total number of vortex units. Since the first term is not affected by the properties of the source particles, it can be further simplified:

[0045] (17)

[0046] From this, we can obtain two key physical quantities: the Taylor coefficient. Moment of vortex particles :

[0047] (18)

[0048] (19)

[0049] Where k is the order of the Taylor approximation, and finally the induced velocity between vortex particles based on the octree method can be calculated by the improved Biot-Savart law as described below:

[0050] (20)

[0051] in, yes In y c Taylor coefficients at position k, It is the vortex element c about its center y c The k-th order moment.

[0052] Furthermore, in step (4), to obtain the relative velocity and angle of attack, the wind turbine blades need to be divided into several micro-segments along the spanwise direction in the model. For each micro-segment, the shedding vortex and wake vortex are calculated, and then the vortex core size is calculated. Based on the airfoil lift and drag coefficient table, the relative velocity and angle of attack are calculated according to the Kutzhukovsky lift principle. The Kutzhukovsky lift principle is as follows:

[0053] (twenty one)

[0054] in, It is aerodynamic lift. It is air density. It is relative velocity. It is the vortex circulation; the relative velocity of the blade is the superposition of the blade rigid body motion velocity, the blade deformation velocity and the blade aerodynamic induced velocity. The circulation of the attached vortex is calculated according to the Kutzhukovsky lift principle mentioned above. When the residual of the attached vortex circulation between the previous and next iterations is less than the iteration residual, it is judged as convergence, and the aerodynamic load of the wind turbine is further calculated; otherwise, the iteration solution continues.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] This invention employs an aerodynamic-wake coupling calculation method based on lift line theory and a free vortex wake model. It performs time-domain simulation of the dynamic induced losses of a vertical axis wind turbine under aerodynamic-wake coupling, and introduces an octree method to optimize the wake calculation process, thereby accurately solving for its aerodynamic loads. By managing the wake field hierarchically according to an octree structure, and applying approximations of appropriate precision to wake particles at different levels, the calculation efficiency is significantly improved while ensuring the accuracy of the results. Furthermore, the program is based on the rigid-flexible coupled multibody dynamics principle, considering the floating foundation and struts as rigid bodies and the tower and blades as flexible bodies. It also considers the calculation of hydrodynamic and mooring loads, and finally uses a loosely coupled method to establish a whole-machine model. This allows for the calculation of the aerodynamic-wake-structure-hydrodynamic coupling response of a floating vertical axis wind turbine under various environmental loads, providing numerical tool support for the engineering application of floating vertical axis wind turbines. Attached Figure Description

[0057] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0058] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0059] like Figure 1 As shown, a method for calculating the hydrodynamic coupling of the aerodynamic wake structure of a floating vertical axis fan includes the following steps:

[0060] (1) Before starting the simulation, the initial parameters and environmental conditions are set in advance. The structural, aerodynamic and wake loads of the vertical axis fan are calculated through the structural module, aerodynamic module and wake module.

[0061] (2) In each time step, firstly, in the structural module, the floating vertical axis wind turbine system is decomposed into two subsystems using a loose coupling method. Aerodynamic loads, hydrodynamic loads and mooring loads are applied to subsystem 1. Then, the tower deformation, large-scale rigid body motion of the blades and the floating foundation motion are calculated. Then, the coupling relationship between the large-scale motion of the blades and their own deformation is established. The large-scale rigid body motion of the blades is transferred to subsystem 2. At the same time, the floating foundation motion is transferred to the hydrodynamic module in the structural module to calculate the hydrodynamic loads and mooring loads for the next time step. Finally, the calculated blade deformation and floating foundation motion are transferred to the aerodynamic module and the wake module.

[0062] (3) In the wake module, the wake field is first divided into near field and far field. The wake velocity caused by near field particles is directly calculated using the classical Biot-Savart law, while the wake velocity caused by far field particles is solved by the improved octree algorithm. The wake vortex induced velocity is transferred to the aerodynamic module for calculating aerodynamic load.

[0063] (4) In the aerodynamic module, based on the obtained blade deformation, floating foundation motion and total induced velocity, the relative velocity and angle of attack of the blade are obtained, and then the aerodynamic load on the blade is calculated. At the same time, the induced velocity of the blade node is transmitted to the wake module for the next time step to calculate the wake field velocity.

[0064] (5) The calculated aerodynamic load is transferred to the structural module to determine the structural dynamic response of the next time step. At the same time, all vortex elements in the wake module undergo convective motion with the local induced velocity field. The newly released vortex elements will form a new wake field for the calculation of the next time step.

[0065] The specific calculation method steps of this invention are as follows:

[0066] (1) Pre-set initial parameters and environmental conditions, including incoming wind speed, fan speed, wave height, wave period, wind direction, wave direction, airfoil lift and drag coefficient table, wake cutoff length, wake update length, wake dissipation coefficient, wake hysteresis coefficient, iteration residual, relaxation factor, vortex element size coefficient, and Taylor approximation order. Calculate the structural, aerodynamic, and wake loads of the vertical axis fan using the structural module, aerodynamic module, and wake module.

[0067] (2) In each time step, the floating vertical axis wind turbine system is first decomposed into two subsystems by applying a loose coupling method in the structural module. Aerodynamic loads, hydrodynamic loads and mooring loads are applied to subsystem 1. Then, the tower deformation, the large-scale rigid body motion of the blades and the floating foundation motion are calculated, and the coupling relationship between the large-scale motion of the blades and their own deformation is established.

[0068] Subsystem 1 includes all the structures of the wind turbine. The floating foundation is treated as a rigid body, considering six degrees of freedom of motion: sway, roll, heave, pitch, and yaw. The flexible tower is treated as an elastic body, and the blades are treated as equivalent mass points, considering their mass and moment of inertia. Based on the Rhoden velocity variational principle, the dynamic equations of subsystem 1 are established. After considering constraints, the final Lagrange equations are in the following form:

[0069] (1)

[0070] in, It is a quality matrix. It is a generalized external force matrix. Let Jacobi be the constraint matrix of the equations. For the Lagrange multipliers of the constraint equations, For the right-hand side of the acceleration constraint equation, Let be the generalized coordinates of all degrees of freedom of subsystem 1, including the motion of the floating foundation, the deformation of the tower column, and the motion of the blade mass points; and the coordinates of any point before the deformation of the blade. The transformed form is represented as ,but The point relative to the origin of the inertial coordinate system radius It can be represented as:

[0071] (2)

[0072] in, Let be the radius vector of the floating coordinate system of the blade relative to the inertial coordinate system. for Point relative to The radius vector, for Deformation displacement of a point, in order to describe deformation displacement The blade is treated as a flexible beam structure. Based on the finite element method, the curved blade is discretized into multiple straight beam elements. Each element node contains six degrees of freedom: bending deformation and bending angle along two transverse directions, tensile deformation along the axial direction, and torsional deformation around the axis. An element coordinate system is established on each element, based on continuum mechanics. It can be represented as:

[0073] (3)

[0074] in, Represents unit shape function, coupling term can be express, The deformation displacement is obtained by using the deformation displacement array based on the blade floating coordinate system. Then the radius vector can be described. This establishes the coupling relationship between the large-scale movement of the blade and its own deformation.

[0075] By transferring the large-scale rigid body motion of the blade to subsystem 2, the dynamic equations of the flexible body of the blade in subsystem 2 can be established based on the Rhodan velocity variational principle:

[0076] (4)

[0077] in, It is the generalized virtual power of external forces. and These are the virtual power of inertial force and the virtual power of elastic force, respectively. The modeling method for the tower column is similar to that for the blade, except that the bending angle of the beam model needs to be set to 0 during the modeling process.

[0078] The floating foundation motion is transferred to the hydrodynamic module in the structural module to calculate the hydrodynamic load and mooring load for the next time step j. Finally, the calculated blade deformation and floating foundation motion are transferred to the aerodynamic module and wake module.

[0079] The hydrodynamic load is calculated based on the potential flow theory, which assumes that seawater is homogeneous and incompressible, and that the fluid motion is irrotational and possesses potential. Therefore, at time t... The velocity vector of the fluid at the location It can be derived from velocity potential express:

[0080] (5)

[0081] After solving for the velocities at various positions on the wetted surface of the object in the flow field using the velocity potential, the pressure of the fluid element can be calculated based on the Bernoulli equation. After obtaining the pressure of the fluid unit Then, by integrating the pressure along the wetted surface of the object, the wave load on the structure can be calculated:

[0082] (6)

[0083] in The direction cosine of the unit's six-degree-of-freedom motion. For the wet surface of the object, the velocity potential can be considered as such during the solution process. It can be divided into three parts:

[0084] (7)

[0085] in Let be the incident velocity potential, representing the undisturbed velocity potential of the incident wave. The diffraction velocity potential represents the velocity potential generated when a wave diffracts around an object. The radiation velocity potential represents the velocity potential generated by the change in the flow field caused by the motion of the object itself. Then, the fluid pressure can be obtained. Similarly, the fluid pressure can be divided into wave incident force, wave diffraction force, and wave radiation force. In the specific calculation of wave force, the Green's function method is generally used to solve the Laplace equation with boundary value conditions. Based on the boundary element method or the surface element method, the object is treated as a surface element model. Control points are selected on each surface element, and the source-sink method is used to solve the velocity potential at each position on the surface of the object, and then the wave load is calculated.

[0086] Mooring load calculations are based on catenary theory, and the mooring satisfies the following assumptions:

[0087] (1) The seabed is flat and there is no friction between the section of the mooring cable lying on the seabed and the seabed.

[0088] (2) The mooring cable moves slowly in the water, and the effects of inertia and hydrodynamics are ignored.

[0089] (3) Ignore spatial effects and consider the motion of the mooring cable in a two-dimensional plane to decouple the horizontal and vertical motions.

[0090] (4) Ignore the effects of shear stress or bending moment and only consider the tension along the mooring cable.

[0091] Force analysis is performed on a segment of the mooring cable. The length of the segment when unstretched is [length missing]. The cross-sectional area is The wet weight per unit length is Assume the axial force of the element is The hydrodynamic components in the tangential and normal directions are respectively and Through derivation, it is found that the catenary has two directions along its length. Relationship of directions:

[0092] (8)

[0093] (9)

[0094] in, and It is the equivalent axial tension Components along the horizontal and vertical directions, It is the elastic modulus. It is the density of water. It is gravitational acceleration. The vertical length of the element. The angle between the bottom of the unit and the horizontal direction is given. Integrating the above equation along the length direction to the top of the mooring cable, we can obtain:

[0095] (10)

[0096] (11)

[0097] (12)

[0098] (13)

[0099] Where X is the horizontal force on the mooring cable, Z is the vertical force on the mooring cable, and V0 is the vertical tension component at the lowest point of the suspension section. This refers to the length of the suspended portion of the mooring cable after stretching. The length of the mooring cable before tensioning the suspended portion can be written as:

[0100] (14)

[0101] in, This refers to the total length of the mooring cable when it is not stretched. This refers to the length of the section of the mooring cable lying on the bottom.

[0102] (3) In the wake module, the wake field is first divided into near field and far field. The wake velocity caused by near field particles is directly calculated using the classical Biot-Savart law, while the wake velocity caused by far field particles is solved by the improved octree algorithm. The wake vortex induced velocity is then transferred to the aerodynamic module for calculating aerodynamic loads.

[0103] The classic Biot-Savart theorem is:

[0104] (15)

[0105] in, It is the position vector of the source particle. It is the position vector of the target particle. It is the induction speed. is the vortex vector, and N is the number of particles. The integral along the length of the vortex element and It is the kernel function of the Biot-Savart theorem; the improved octree algorithm is as follows:

[0106] First, a large number of vortex particles are divided into a certain number of cubes, or vortex units, with the central node of each vortex unit being y. c Regarding the classical Biot-Savart law in y c Taylor approximation is used here:

[0107] (16)

[0108] Where c = {yj, j = 1, 2, …, Nc} is a particle swarm in a vortex unit, and Nc is the total number of vortex units. Since the first term is not affected by the properties of the source particles, it can be further simplified:

[0109] (17)

[0110] From this, we can obtain two key physical quantities: the Taylor coefficient. Moment of vortex particles :

[0111] (18)

[0112] (19)

[0113] Where k is the order of the Taylor approximation, and finally the induced velocity between vortex particles based on the octree method can be calculated by the improved Biot-Savart law as described below:

[0114] (20)

[0115] in, yes In y c Taylor coefficients at position k, It is the vortex element c about its center y c The k-th order moment.

[0116] (4) Based on the obtained blade deformation, floating foundation motion and total induced velocity, the relative velocity and angle of attack of the blade are obtained in the aerodynamic module, and then the aerodynamic load on the blade is calculated. At the same time, the induced velocity of the blade node is transmitted to the wake module for the next time step to calculate the wake field velocity.

[0117] To obtain the relative velocity and angle of attack, the wind turbine blades first need to be divided into several micro-segments along the spanwise direction in the model. For each micro-segment, the shedding vortex and wake vortex are calculated. Then, the vortex core size is calculated. Combining the airfoil lift and drag coefficient table, the relative velocity and angle of attack are calculated according to the Kutzhukovsky lift principle, which is as follows:

[0118] (twenty one)

[0119] in, It is aerodynamic lift. It is air density. It is relative velocity. It is the vortex circulation; the relative velocity of the blade is the superposition of the blade rigid body motion velocity, the blade deformation velocity and the blade aerodynamic induced velocity. The circulation of the attached vortex is calculated according to the Kutzhukovsky lift principle mentioned above. When the residual of the attached vortex circulation between the previous and next iterations is less than the iteration residual, it is judged as convergence, and the aerodynamic load of the wind turbine is further calculated; otherwise, the iteration solution continues.

[0120] (5) The calculated aerodynamic load is transferred to the structural module to determine the structural dynamic response of the next time step. At the same time, all vortex elements in the wake module undergo convective motion with the local induced velocity field. The newly released vortex elements will form a new wake field for the calculation of the next time step.

[0121] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for calculating the hydrodynamic coupling of the aerodynamic wake structure of a floating vertical axis fan, characterized in that: Includes the following steps: (1) Before starting the simulation, the initial parameters and environmental conditions are set in advance. The structural, aerodynamic and wake loads of the vertical axis fan are calculated through the structural module, aerodynamic module and wake module. (2) In each time step, firstly, in the structural module, the floating vertical axis wind turbine system is decomposed into two subsystems using a loose coupling method. Aerodynamic loads, hydrodynamic loads and mooring loads are applied to subsystem 1. Then, the tower deformation, large-scale rigid body motion of the blades and the floating foundation motion are calculated. Then, the coupling relationship between the large-scale motion of the blades and their own deformation is established. The large-scale rigid body motion of the blades is transferred to subsystem 2. At the same time, the floating foundation motion is transferred to the hydrodynamic module in the structural module to calculate the hydrodynamic loads and mooring loads for the next time step. Finally, the calculated blade deformation and floating foundation motion are transferred to the aerodynamic module and the wake module. (3) In the wake module, the wake field is first divided into near field and far field. The wake velocity caused by near field particles is directly calculated using the classical Biot-Savart law, while the wake velocity caused by far field particles is solved by the improved octree algorithm. The wake vortex induced velocity is transferred to the aerodynamic module for calculating aerodynamic load. (4) In the aerodynamic module, based on the obtained blade deformation, floating foundation motion and total induced velocity, the relative velocity and angle of attack of the blade are obtained, and then the aerodynamic load on the blade is calculated. At the same time, the induced velocity of the blade node is transmitted to the wake module for the next time step to calculate the wake field velocity. (5) The calculated aerodynamic load is transferred to the structural module to determine the structural dynamic response of the next time step. At the same time, all vortex elements in the wake module undergo convective motion with the local induced velocity field. The newly released vortex elements will form a new wake field for the calculation of the next time step.

2. The method for calculating the hydrodynamic coupling of the aerodynamic wake structure of a floating vertical axis fan according to claim 1, characterized in that: The initial parameters and environmental conditions in step (1) include incoming wind speed, wind turbine speed, wave height, wave period, wind direction, wave direction, airfoil lift and drag coefficient table, wake cut-off length, wake update length, wake dissipation coefficient, wake hysteresis coefficient, iteration residual, relaxation factor, vortex element scale coefficient, and Taylor approximation order.

3. The method for calculating the hydrodynamic coupling of the aerodynamic wake structure of a floating vertical axis fan according to claim 1, characterized in that: Subsystem 1 in step (2) includes all the structures of the wind turbine. The floating foundation is treated as a rigid body, considering six degrees of freedom of motion: sway, roll, heave, pitch, and yaw. The flexible tower is treated as an elastic body, and the blades are treated as equivalent mass points, considering their mass and moment of inertia. The dynamic equations of subsystem 1 are established based on the Rhoden velocity variational principle. After considering the constraints, the final Lagrange equations are in the form of: （1） in, It is a quality matrix. It is a generalized external force matrix. Let Jacobi be the constraint matrix of the equations. For the Lagrange multipliers of the constraint equations, For the right-hand side of the acceleration constraint equation, Let be the generalized coordinates of all degrees of freedom of subsystem 1, including the motion of the floating foundation, the deformation of the tower column, and the motion of the blade mass points; and the coordinates of any point before the deformation of the blade. The transformed form is represented as ,but The point relative to the origin of the inertial coordinate system radius It can be represented as: （2） in, Let be the radius vector of the floating coordinate system of the blade relative to the inertial coordinate system. for Point relative to The radius vector, for Deformation displacement of a point, in order to describe deformation displacement The blade is treated as a flexible beam structure. Based on the finite element method, the curved blade is discretized into multiple straight beam elements. Each element node contains six degrees of freedom: bending deformation and bending angle along two transverse directions, tensile deformation along the axial direction, and torsional deformation around the axis. An element coordinate system is established on each element, based on continuum mechanics. It can be represented as: （3） in, Represents unit shape function, coupling term can be express, The deformation displacement is obtained by using the deformation displacement array based on the blade floating coordinate system. Then the radius vector can be described. This establishes the coupling relationship between the large-scale motion of the blade and its own deformation, transferring the large-scale rigid body motion of the blade to subsystem 2. Based on the Rhodan velocity variational principle, the dynamic equations of the flexible body of the blade in subsystem 2 can be established: （4） in, It is the generalized virtual power of external forces. and These are the virtual power of inertial force and the virtual power of elastic force, respectively. The modeling method for the tower column is similar to that for the blade, except that the bending angle of the beam model needs to be set to 0 during the modeling process.

4. The method for calculating the hydrodynamic coupling of the aerodynamic wake structure of a floating vertical axis fan according to claim 1, characterized in that: The hydrodynamic load in step (2) is calculated based on potential flow theory, so at time t... The velocity vector of the fluid at the location It can be derived from velocity potential express: （5） After solving for the velocities at various positions on the wetted surface of the object in the flow field using the velocity potential, the pressure of the fluid element can be calculated based on the Bernoulli equation. After obtaining the pressure of the fluid unit Then, by integrating the pressure along the wetted surface of the object, the wave load on the structure can be calculated: （6） in The direction cosine of the unit's six-degree-of-freedom motion. For the wet surface of the object, the velocity potential can be considered as such during the solution process. It can be divided into three parts: （7） in Let be the incident velocity potential, representing the undisturbed velocity potential of the incident wave. The diffraction velocity potential represents the velocity potential generated when a wave diffracts around an object. The radiation velocity potential represents the velocity potential generated by the change in the flow field caused by the motion of the object itself. Then, the fluid pressure can be obtained. Similarly, the fluid pressure can be divided into wave incident force, wave diffraction force, and wave radiation force. In the specific calculation of wave force, the Green's function method is generally used to solve the Laplace equation with boundary value conditions. Based on the boundary element method or the surface element method, the object is treated as a surface element model. Control points are selected on each surface element, and the source-sink method is used to solve the velocity potential at each position on the surface of the object, and then the wave load is calculated.

5. The method for calculating the hydrodynamic coupling of the aerodynamic wake structure of a floating vertical axis fan according to claim 1, characterized in that: The mooring load calculation in step (2) is based on the catenary theory. A segment of the mooring cable is taken for stress analysis. The length of the segment before tension is... The cross-sectional area is The wet weight per unit length is Assume the axial force of the element is The hydrodynamic components in the tangential and normal directions are respectively and Through derivation, it is found that the catenary has two directions along its length. Relationship of directions: （8） （9） in, and It is the equivalent axial tension Components along the horizontal and vertical directions, It is the elastic modulus. It is the density of water. It is gravitational acceleration. The vertical length of the element. The angle between the bottom of the unit and the horizontal direction is given. Integrating the above equation along the length direction to the top of the mooring cable, we can obtain: （10） （11） （12） （13） Where X is the horizontal force on the mooring cable, Z is the vertical force on the mooring cable, and V0 is the vertical tension component at the lowest point of the suspension section. This refers to the length of the suspended portion of the mooring cable after stretching. The length of the mooring cable before tensioning the suspended portion can be written as: （14） in, This refers to the total length of the mooring cable when it is not stretched. This refers to the length of the section of the mooring cable lying on the bottom.

6. The method for calculating the hydrodynamic coupling of the aerodynamic wake structure of a floating vertical axis fan according to claim 1, characterized in that: The classic Biot-Savart law in step (3) is: （15） in, It is the position vector of the source particle. It is the position vector of the target particle. It is the induction speed. is the vortex vector, and N is the number of particles. The integral along the length of the vortex element and It is the kernel function of the Biot-Savart theorem; the improved octree algorithm is as follows: First, a large number of vortex particles are divided into a certain number of cubes, or vortex units, with the central node of each vortex unit being y. c Regarding the classical Biot-Savart law in y c Taylor approximation is used here: （16） Where c = {yj, j = 1, 2, …, Nc} is a particle swarm in a vortex unit, and Nc is the total number of vortex units. Since the first term is not affected by the properties of the source particles, it can be further simplified: （17） From this, we can obtain two key physical quantities: the Taylor coefficient. Moment of vortex particles : （18） （19） Where k is the order of the Taylor approximation, and finally the induced velocity between vortex particles based on the octree method can be calculated by the improved Biot-Savart law as described below: （20） in, yes In y c Taylor coefficients at position k, It is the vortex element c about its center y c The k-th order moment.

7. The method for calculating the hydrodynamic coupling of the aerodynamic wake structure of a floating vertical axis fan according to claim 1, characterized in that: To obtain the relative velocity and angle of attack in step (4), the wind turbine blades need to be divided into several micro-segments along the spanwise direction in the model. For each micro-segment, the shedding vortex and wake vortex are calculated, and then the vortex core size is calculated. The relative velocity and angle of attack are then calculated based on the Kutzhukovsky lift principle, combined with the airfoil lift and drag coefficient table. The Kutzhukovsky lift principle is as follows: （21） in, It is aerodynamic lift. It is air density. It is relative velocity. It is the vortex circulation; the relative velocity of the blade is the superposition of the blade rigid body motion velocity, the blade deformation velocity and the blade aerodynamic induced velocity. The circulation of the attached vortex is calculated according to the Kutzhukovsky lift principle mentioned above. When the residual of the attached vortex circulation between the previous and next iterations is less than the iteration residual, it is judged as convergence, and the aerodynamic load of the wind turbine is further calculated; otherwise, the iteration solution continues.

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