Floating type fan blade fatigue life calculation method and device

Abstract

The invention discloses a method and a device for calculating the fatigue life of a floating type fan blade, which are used for solving the technical problem that the accuracy of the calculated fatigue life of the blade is low due to the existing method for calculating the fatigue life of the floating type fan blade. The method comprises the steps of constructing a blade CAD model, a rigid body model and a fluid domain numerical model, and generating a fatigue load spectrum by simulating six-degree-of-freedom motion under different sea conditions and wind conditions. And then establishing a blade high-fidelity finite element model, determining fatigue crack stress distribution in combination with the obtained sea condition and wind condition occurrence probability and fracture criterion of the research sea area, and dynamically inserting into a cohesion unit to simulate intra-layer and inter-layer damage. And finally, based on the cohesion model, calculating the fatigue life of the blade through a cyclic jump method. According to the method, various sea conditions and wind conditions can be combined, fatigue cracks are taken into consideration in the calculation process, crack propagation can be simulated, and the calculation accuracy of the fatigue life of the blade can be improved while high-precision fatigue life calculation is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power generation, and in particular to a method and device for calculating the fatigue life of floating wind turbine blades. Background Art

[0002] As onshore and offshore wind power resources reach saturation, deep-sea wind power development is becoming an inevitable trend. Floating wind turbines are a key means of developing and utilizing deep-sea wind energy. As a key component of wind turbines, blades are subject to the combined effects of cyclic wind loads, centrifugal forces, inertial forces, and wave loads during long-term operation, which can lead to fatigue cracks within the material.

[0003] As operating time increases, cracks will gradually expand, eventually leading to blade failure, affecting the safe operation and service life of the wind turbine. Furthermore, as floating wind turbines become larger and deeper into the sea, their blades become longer and more flexible, and their fatigue problems become increasingly prominent. Harsh environments such as high temperature and high humidity can also reduce the fatigue properties of materials and shorten the fatigue life of blades. Therefore, it is necessary to conduct in-depth research on the motion response of floating wind turbine blades under multi-field coupling and predict their fatigue life to provide theoretical support for the structural optimization design and performance improvement of floating wind turbines.

[0004] Most existing methods for calculating the fatigue life of floating wind turbine blades only consider a single sea and wind condition. However, in the actual operating environment of floating wind turbine blades, sea and wind conditions are constantly changing, and can even combine multiple conditions. Therefore, existing technologies struggle to simulate the actual operating environment of floating wind turbine blades, resulting in low accuracy in blade fatigue life calculations. Summary of the Invention

[0005] The present invention provides a floating wind turbine blade fatigue life calculation method and device, which is used to solve the technical problem that most existing floating wind turbine blade fatigue life calculation methods only consider a single sea condition combined with a single wind condition, resulting in low accuracy of the calculated blade fatigue life.

[0006] A first aspect of the present invention provides a method for calculating fatigue life of floating wind turbine blades, comprising:

[0007] Obtaining airfoil coordinate data and airfoil geometric parameters of a floating wind turbine blade, and constructing a wind turbine blade CAD model, a floating wind turbine rigid body model, and a fluid domain numerical model based on preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size of the floating wind turbine blade, and actual operating conditions;

[0008] Under a plurality of preset sea and wind conditions, constraining the floating wind turbine rigid body model to the mooring system of the floating wind turbine blades, and coupling the floating wind turbine rigid body model with the fluid domain numerical model to generate a coupled model under each of the preset sea and wind conditions;

[0009] Solving the six-degree-of-freedom motion of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupled model under each of the preset sea and wind conditions to generate a fatigue load spectrum;

[0010] Based on the wind turbine blade CAD model, construct a high-fidelity finite element model of the wind turbine blade;

[0011] Obtaining the probability of occurrence of multiple sea and wind conditions in the study sea area, and based on the high-fidelity finite element model of the wind turbine blade, determining a target cyclic load, a target wind turbine blade root motion curve, and a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade according to the probability of occurrence of each of the sea and wind conditions, preset intra-layer and inter-layer fracture parameters, and the fatigue load spectrum;

[0012] Dynamically inserting a cohesive force unit into the high-fidelity finite element model of the wind turbine blade based on a preset blade fracture criterion and a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade;

[0013] Based on the linear stress-separation curve and the cohesive force unit, according to the target cyclic load, the target wind turbine blade root motion curve, and the preset layer interlayer fracture parameters, the target blade fatigue life of the floating wind turbine blade in the study sea area is calculated.

[0014] Optionally, constructing a wind turbine blade CAD model, a floating wind turbine rigid body model, and a fluid domain numerical model according to preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size of the floating wind turbine blade, and the actual working conditions includes:

[0015] Constructing a CAD model of a wind turbine blade according to the airfoil coordinate data and the airfoil geometric parameters;

[0016] Assigning rigid body material attributes to the wind turbine blade CAD model, and determining a wind turbine blade CAD model assigned with the rigid body material attributes;

[0017] Constructing a floating wind turbine rigid body model according to the preset boundary conditions and the wind turbine blade CAD model with the rigid body material properties assigned thereto;

[0018] Determining the size of the fluid domain according to the size of the floating wind turbine blades and actual operating conditions;

[0019] constructing a fluid domain geometric model based on the fluid domain size;

[0020] Meshing the fluid domain geometric model to generate a meshed fluid domain geometric model;

[0021] The fluid domain geometric model after meshing is pre-processed to generate a fluid domain numerical model.

[0022] Optionally, performing a six-degree-of-freedom motion solution of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupled model under each of the preset sea and wind conditions to generate a fatigue load spectrum includes:

[0023] performing a six-degree-of-freedom motion solution for the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupling models under the preset sea and wind conditions, and generating a six-degree-of-freedom motion result for the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling corresponding to the coupling models under the preset sea and wind conditions;

[0024] The fatigue load spectrum is constructed by using the wind turbine blade root motion curve and flow field pressure load in the six-degree-of-freedom motion results of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling corresponding to the coupling model under each of the preset sea and wind conditions.

[0025] Optionally, constructing a high-fidelity finite element model of the wind turbine blade based on the wind turbine blade CAD model includes:

[0026] Meshing the fan blade CAD model to generate a meshed fan blade CAD model;

[0027] The meshed wind turbine blade CAD model is given composite material properties to generate a high-fidelity finite element model of the wind turbine blade.

[0028] Optionally, the determining, based on the high-fidelity finite element model of the wind turbine blade and according to the probability of occurrence of each of the sea and wind conditions, preset intra-layer and inter-layer fracture parameters, and the fatigue load spectrum, a target cyclic load, a target wind turbine blade root motion curve, and a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade includes:

[0029] Selecting a target cyclic load and a target wind turbine blade root motion curve from the fatigue load spectrum based on the probability of occurrence of each of the sea and wind conditions;

[0030] The target wind blade root motion curve is applied to the blade root of the high-fidelity finite element model of the wind blade, the target cyclic load is applied to the blade surface of the high-fidelity finite element model of the wind blade, and based on the preset intra-layer and inter-layer fracture parameters, the high-fidelity finite element model of the wind blade is subjected to finite element calculation to determine the fatigue crack stress result corresponding to the high-fidelity finite element model of the wind blade.

[0031] Optionally, the dynamically inserting a cohesive force unit into the high-fidelity finite element model of the wind turbine blade based on a preset blade fracture criterion and a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade includes:

[0032] Determining whether a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade meets the preset blade fracture criterion;

[0033] If the conditions are met, a cohesive force unit is dynamically inserted into the high-fidelity finite element model of the wind turbine blade.

[0034] Optionally, the calculating, based on the linear stress-separation curve and the cohesive force unit, the target cyclic load, the target wind turbine blade root motion curve, and the preset intra-layer interlayer fracture parameters, of the target blade fatigue life of the floating wind turbine blade in the study sea area includes:

[0035] Based on the cohesive force unit, a fatigue damage curve of the linear stress-separation curve is used to characterize the fatigue degradation effect of the cohesive strength, thereby constructing a cohesive fatigue damage model for the wind turbine blade;

[0036] Applying the target fan blade root motion curve to the blade root of the fan blade cohesive fatigue damage model, applying the target cyclic load to the blade surface of the fan blade cohesive fatigue damage model, and performing finite element calculation on the fan blade cohesive fatigue damage model to determine the tip deflection at a current moment and the stress curve of each element;

[0037] Calculate the load application time based on the probability of occurrence of sea and wind conditions corresponding to the target cyclic load within a calculation period, and record the current time in real time;

[0038] Determining whether the current time reaches the load application time;

[0039] If yes, record the current calculation time in real time and determine whether the current calculation time reaches the preset calculation period;

[0040] If yes, selecting the maximum stress component and the minimum stress component corresponding to each unit from the stress curve of each unit, and calculating the stress amplitude of each unit based on the maximum stress component and the minimum stress component corresponding to each unit;

[0041] Using the stress amplitude of each unit, the evolution rate of the damage variable of each unit with the number of cycles is calculated;

[0042] Selecting a maximum value of the evolution rate of the damage variable with the number of cycles from the evolution rate of the damage variable with the number of cycles of each of the units, and using the maximum value of the evolution rate of the damage variable with the number of cycles to calculate the number of cycles of the jump period;

[0043] Calculating the number of jump cycles based on the sum of the number of cycles of the jump cycle and the number of load cycles corresponding to the target cyclic load within the preset calculation period;

[0044] multiplying the number of jump cycles by the preset calculation cycle to determine a fatigue life predicted based on the jump cycles;

[0045] Calculating the fatigue life of the current cycle according to the fatigue life predicted based on the jump cycle and the preset calculation cycle;

[0046] Determining whether the tip deflection at the current moment is greater than a preset maximum allowable tip deflection;

[0047] If yes, the fatigue life of the current cycle and the fatigue life of multiple historical cycles are added together to determine the target blade fatigue life of the floating wind turbine blade in the research sea area.

[0048] Optionally, it also includes:

[0049] If the current time does not reach the load application time, the process jumps to executing the step of applying the target cyclic load and the target fan blade root motion curve to the fan blade cohesive fatigue damage model, and performing finite element calculation on the fan blade cohesive fatigue damage model to determine the tip deflection at the current moment and the stress curve of each unit.

[0050] Optionally, it also includes:

[0051] If the tip deflection at the current moment is less than or equal to the preset maximum allowable tip deflection, calculating the damage variable of each unit according to the damaged area of ​​the cohesive fatigue damage model of the wind turbine blade and the area of ​​each unit;

[0052] Calculating a new damage variable of each of the units according to the number of cycles of the jump period, the damage variable of each of the units, and the evolution rate of the damage variable with the number of cycles;

[0053] updating the wind turbine blade cohesive fatigue damage model using the new damage variables of each unit to determine a new wind turbine blade cohesive fatigue damage model;

[0054] The fatigue life of the current cycle is used as the fatigue life of the historical cycle, and the step of selecting a target cyclic load and a target wind turbine blade root motion curve from the fatigue load spectrum based on the probability of occurrence of each of the sea and wind conditions is executed, until the tip deflection at the current moment is greater than the preset maximum allowable tip deflection;

[0055] The fatigue life of the current cycle determined when the tip deflection at the current moment is greater than the preset maximum allowable tip deflection and the fatigue life of multiple historical cycles are added to determine the target blade fatigue life of the floating wind turbine blade in the research sea area.

[0056] A second aspect of the present invention provides a floating wind turbine blade fatigue life calculation device, comprising:

[0057] an acquisition module for acquiring airfoil coordinate data and airfoil geometric parameters of a floating wind turbine blade, and constructing a wind turbine blade CAD model, a floating wind turbine rigid body model, and a fluid domain numerical model based on preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size of the floating wind turbine blade, and actual operating conditions;

[0058] a coupling module, configured to constrain the floating wind turbine rigid body model to the mooring system of the floating wind turbine blades under a plurality of preset sea and wind conditions, and couple the floating wind turbine rigid body model with the fluid domain numerical model to generate a coupled model under each of the preset sea and wind conditions;

[0059] A solution module, configured to solve the six-degree-of-freedom motion of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupled model under each of the preset sea and wind conditions, and generate a fatigue load spectrum;

[0060] A construction module, configured to construct a high-fidelity finite element model of the wind turbine blade based on the wind turbine blade CAD model;

[0061] a stress calculation module for obtaining the probability of occurrence of multiple sea and wind conditions in the study sea area, and determining, based on the high-fidelity finite element model of the wind turbine blade, a target cyclic load, a target wind turbine blade root motion curve, and a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade according to the probability of occurrence of each of the sea and wind conditions, preset intra-layer and inter-layer fracture parameters, and the fatigue load spectrum;

[0062] A dynamic insertion module, configured to dynamically insert a cohesive force unit into the high-fidelity finite element model of the wind turbine blade based on a preset blade fracture criterion and a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade;

[0063] A fatigue life calculation module is used to calculate the target blade fatigue life of the floating wind turbine blade in the study sea area based on the linear stress-separation curve and the cohesion unit, according to the target cyclic load, the target wind turbine blade root motion curve, and the preset layer interlayer fracture parameters.

[0064] It can be seen from the above technical solutions that the present invention has the following advantages:

[0065] The above technical solution of the present invention provides a method for calculating the fatigue life of floating wind turbine blades. First, the airfoil coordinate data and airfoil geometric parameters of the floating wind turbine blades are obtained, and according to the preset boundary conditions, airfoil coordinate data, airfoil geometric parameters, the size of the floating wind turbine blades and the actual working conditions, the wind turbine blade CAD model, the floating wind turbine rigid body model, and the fluid domain numerical model are constructed; then, under multiple preset sea and wind conditions, the floating wind turbine rigid body model is constrained on the mooring system of the floating wind turbine blades, and ... The coupling model of the solid model and the fluid domain numerical model are coupled to generate coupling models under various preset sea and wind conditions; the six-degree-of-freedom motion of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling is solved for the coupling model under various preset sea and wind conditions to generate a fatigue load spectrum; a high-fidelity finite element model of the wind turbine blade is constructed based on the CAD model of the wind turbine blade; the probability of occurrence of multiple sea and wind conditions in the study area is obtained, and based on the high-fidelity finite element model of the wind turbine blade, the target cycle is determined according to the probability of occurrence of each sea and wind condition, the preset intra-layer and inter-layer fracture parameters, and the fatigue load spectrum. load, target wind turbine blade root motion curve and fatigue crack stress results corresponding to the high-fidelity finite element model of the wind turbine blade; based on the preset blade fracture criterion and the fatigue crack stress results corresponding to the high-fidelity finite element model of the wind turbine blade, a cohesive force unit is dynamically inserted into the high-fidelity finite element model of the wind turbine blade; finally, based on the linear stress-separation curve and the cohesive force unit, the target blade fatigue life of the floating wind turbine blade in the study sea area is calculated according to the target cyclic load, the target wind turbine blade root motion curve and the preset intra-layer and inter-layer fracture parameters; Based on the above scheme, the present invention uses the wind turbine blade root motion curve and flow field pressure load calculated under multiple preset sea conditions and wind conditions to form a fatigue load spectrum, and applies it to the high-fidelity finite element model of the wind turbine blade based on the obtained probability of occurrence of multiple sea conditions and wind conditions in the study sea area to complete the fatigue life calculation process. The present invention can combine multiple sea conditions and wind conditions, take fatigue cracks into consideration in the calculation process, simulate crack propagation, and achieve high-precision fatigue life calculation while also improving the calculation accuracy of the blade fatigue life. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0067] Figure 1 A flowchart of a method for calculating fatigue life of floating wind turbine blades provided in the first embodiment of the present invention;

[0068] Figure 2A schematic diagram of the linear pull-separation law provided in the first embodiment of the present invention;

[0069] Figure 3 A schematic flow chart of a method for calculating fatigue life of floating wind turbine blades provided in the first embodiment of the present invention;

[0070] Figure 4 This is a structural block diagram of a floating wind turbine blade fatigue life calculation device provided in the second embodiment of the present invention. DETAILED DESCRIPTION

[0071] An embodiment of the present invention provides a floating wind turbine blade fatigue life calculation method and device, which is used to solve the technical problem that most existing floating wind turbine blade fatigue life calculation methods only consider a single sea condition combined with a single wind condition, resulting in low accuracy of the calculated blade fatigue life.

[0072] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, 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 embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0073] See also Figure 1 , Figure 1 This is a flowchart of the steps of a method for calculating the fatigue life of floating wind turbine blades provided in Example 1 of the present invention.

[0074] The present invention provides a method for calculating the fatigue life of floating wind turbine blades, comprising:

[0075] Step 101: Acquire the airfoil coordinate data and airfoil geometric parameters of the floating wind turbine blade, and construct a wind turbine blade CAD model, a floating wind turbine rigid body model, and a fluid domain numerical model based on preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size of the floating wind turbine blade, and the actual working conditions.

[0076] It should be noted that, based on the determined blade model to be established, the airfoil coordinate data of the floating wind turbine blade obtained are the two-dimensional coordinates of each point on the airfoil, and the airfoil geometric parameters are the chord length, torsion angle, aerodynamic center and other parameters of each airfoil.

[0077] Specifically, step 101 may include the following sub-steps:

[0078] Step S11: constructing a wind turbine blade CAD model based on the airfoil coordinate data and airfoil geometric parameters;

[0079] Step S12: assigning rigid body material attributes to the wind turbine blade CAD model, and determining the wind turbine blade CAD model assigned with the rigid body material attributes;

[0080] It should be noted that a floating wind turbine system primarily consists of structures such as a mooring system, floating foundation, tower, nacelle, blades, and power transmission and control systems. For modeling convenience, only the key components of the floating wind turbine, including the rotor, tower, and floating foundation, are modeled to construct the floating wind turbine's CAD (Computer-Aided Design) model. During modeling, it is important to ensure that the model's geometric dimensions and shape are consistent with the actual wind turbine system, particularly the dimensions and positions of key components. For example, a floating wind turbine blade CAD model typically consists of a series of complex geometric surfaces based on the airfoil. Therefore, the first step in building a floating wind turbine blade CAD model is to determine the desired blade model and obtain the relevant airfoil data (i.e., airfoil coordinate data and geometric parameters). Airfoil data can be obtained through other methods, such as Profili software, Airfoil tools, and the NACA (National Advisory Committee for Aeronautics) official website. The derived airfoil data for each blade section is the two-dimensional coordinates of each point on the airfoil. Then, based on the chord length, twist angle, aerodynamic center and other parameters of each airfoil, mathematical coordinate transformation formulas were used to calculate the three-dimensional coordinates of each point on the airfoil in real space. Finally, the lofting function in SolidWorks was used to create a CAD model of the wind turbine blade.

[0081] Step S13: constructing a floating wind turbine rigid body model according to preset boundary conditions and the wind turbine blade CAD model with rigid body material properties;

[0082] It should be noted that since the deformation of the floating wind turbine is not considered during the multi-field coupling process, rigid body material properties are assigned to each component of the floating wind turbine CAD model, and boundary conditions (preset boundary conditions) are set. The preset boundary conditions refer to setting the bottom of the floating foundation as a free float, allowing it to move in six degrees of freedom and constrained by the mooring system. The wind turbine blades are bound to the tower, and the tower is bound to the floating foundation, moving with the movement of the floating foundation. A Cartesian right-hand coordinate system is used, with the center of gravity of the wind turbine as the origin of the inertial system. The z-axis is vertically upward from the tower mid-perpendicular, and the x-axis is the projection direction of the disk normal onto the z-axis normal plane, which is consistent with the direction of the incoming flow at infinity. Based on the above steps, a rigid body model of the floating wind turbine is obtained.

[0083] Step S14: determining the size of the fluid domain according to the size of the floating wind turbine blades and actual working conditions;

[0084] Step S15: constructing a fluid domain geometric model based on the fluid domain size;

[0085] Step S16: meshing the fluid domain geometric model to generate a meshed fluid domain geometric model;

[0086] Step S17: pre-processing the fluid domain geometric model after meshing to generate a fluid domain numerical model.

[0087] It should be noted that the construction of the fluid domain numerical model mainly includes three parts: geometric modeling, meshing and pre-processing:

[0088] (1) Geometric modeling: In order to construct a fluid domain geometric model that can truly reflect the motion of the floating wind turbine and avoid the interference of fluid reflection and tail vortex on the calculation results, the size of the fluid domain should be reasonably determined according to the size of the floating wind turbine and the actual working conditions. For example, the length of the fluid domain should be at least 10 times the diameter of the wind turbine impeller, the width should be at least 5 times the diameter of the impeller, and the height should include sufficient water depth and space above the free water surface, usually more than 2 times the water depth.

[0089] (2) Meshing: Tetrahedrons or hexahedrons are used to mesh the fluid domain, and meshes are refined around the floating wind turbine and in the wake area to better capture the flow characteristics at the fluid-solid interface and the wake vortex.

[0090] (3) Pre-processing ① Fluid model setting: The present invention involves air and water. The finite volume method is used to solve the incompressible Navier-Stokes equations of two-phase flow. The volume fraction (VOF) method is combined to capture the free liquid surface to calculate the wind load on the wind turbine blades and tower and the wave load on the floating foundation. The RANS (Reynolds-Averaged Navier-Stokes) method is used to solve the fluid control equations. It is necessary to introduce a turbulence model to close the equation group. The turbulence model used in the present invention is the two-equation model k−ϵ SST. The equations of this model are provided in the main text. ② Material parameter setting: Assign material properties such as density, viscosity, etc. to the fluid domain, as well as the turbulence parameters required by the turbulence model (as shown in Table 1). ③ Boundary condition setting: Define the boundary conditions of the fluid domain. Set uniform wind speed and wave spectrum at the inlet of the fluid domain, set pressure outlet conditions at the outlet, and the remaining surfaces can be set as no-slip wall boundaries.

[0091] Specifically, the fluid domain model consists of two parts: the air domain and the seawater domain. To construct a fluid domain geometric model that accurately reflects the motion of the floating wind turbine while avoiding interference from fluid reflections and wake vortices on the calculation results, the dimensions of the fluid domain must be appropriately determined based on the size of the floating wind turbine and the actual operating conditions. For example, the length of the fluid domain should be at least 10 times the diameter of the turbine impeller, the width should be at least 5 times the diameter of the impeller, and the height should include sufficient water depth and space above the free water surface, typically at least twice the water depth. Separate fluid physical parameters (including density, viscosity, and turbulence model) are set for the air and seawater, respectively. A uniform wind speed and wave spectrum are set at the fluid domain inlet, and a pressure outlet condition is set at the outlet. No-slip wall boundaries can be set for the remaining surfaces. The fluid domain can be meshed using tetrahedrons or hexahedrons, and the mesh is refined around the floating wind turbine and in the wake to better capture the flow characteristics at the fluid-solid interface and the wake vortex.

[0092] Furthermore, wind field simulation and wave field simulation are based on the principles of aerodynamics and hydrodynamics, respectively. The finite volume method is used to solve the incompressible Navier-Stokes equations for two-phase flow (water-air). The volume fraction (VOF) method is combined to capture the free liquid surface, thereby calculating the wind loads on the wind turbine blades and tower, and the wave loads on the floating foundation. The governing equations of the fluid computational domain include the continuity equation, the momentum equation, and the phase fraction transport equation, which are expressed as follows:

[0093] ; (1)

[0094] ; (2)

[0095] ; (3)

[0096] in, and represent the fluid velocity and grid point velocity respectively; 、 、 are the fluid density, pressure and dynamic viscosity respectively; For time; is the acceleration due to gravity; is the surface tension term, , is the surface tension coefficient, The value is 0.072 N / m, is the curvature, is the volume fraction, and T is the transpose.

[0097] The movement of the fluid mesh is determined by solving the diffusion equation, where the displacement of each mesh cell is diffused from the fluid-solid interface to the stationary wall boundary. The diffusion equation can be expressed as:

[0098] ; (4)

[0099] in, is the diffusion coefficient, , 、 is a constant parameter; is the distance from the grid point to the fluid-solid interface.

[0100] Furthermore, the Reynolds-Averaged Navier-Stokes method is used to solve the fluid control equations. For the open terms in the RANS equations, a turbulence model needs to be introduced to close the equations. The present invention adopts a two-equation model widely used in engineering applications. SST. The SST model is a hybrid and A hybrid model that overcomes The model's predictions of adverse pressure gradient regions are insufficient and The model's import conditions are too sensitive, and the hybrid function can automatically Model and Automatic conversion between models. The SST model is activated by a mixing function in the region near the wall. model, and in the free flow and core area into Model.

[0101] The SST model combines the turbulence kinetic energy k and the specific turbulence dissipation rate Introduced into the transport equation:

[0102] ; (5)

[0103] ; (6)

[0104] in, is the turbulent kinetic energy; is the specific dissipation rate; is the result item; and are constants in the turbulence dissipation model, respectively and The dissipation term is related to is the kinematic viscosity; is the turbulent viscosity; and is the turbulent Prandtl number, which is related to the turbulent diffusivity; is the generation rate of turbulent kinetic energy due to the mean velocity gradient; is the invariant measure of the strain rate; is the first mixing function; is the cross diffusion coefficient.

[0105] Furthermore, the result item , strain rate invariant measure and cross-diffusion coefficient They are defined as:

[0106] ; (7)

[0107] ; (8)

[0108] ; (9)

[0109] in, is the generation term, which represents the generation term of turbulent kinetic energy due to the mean velocity gradient; is the model constant; is the strain rate tensor; To express The turbulent Prandtl number.

[0110] Mixing function for model combination , defined as follows:

[0111] ; (10)

[0112] Where y is the distance from the wall; is the empirical model constant; is the cross diffusion function CD kw The lower limit of .

[0113] The turbulent viscosity v can be obtained by equations (5) and (6): t :

[0114] ; (11)

[0115] in, is the model constant; is the second mixing function; is the modulus of the strain rate tensor.

[0116] The second mixing function Defined as:

[0117] ; (12)

[0118] Furthermore, each coefficient in the transport equation is obtained by mixing the function get:

[0119] ; (13)

[0120] in, is the coefficient of the mixed terms in the equation; For the near-wall region value; For areas away from the wall value; F is a mixing function whose value varies between 0 and 1, depending on the distance to the wall.

[0121] In addition, the values ​​of other coefficients in all equations can be found in Table 1, and the subscripts 1 and 2 of each coefficient represent Equation and The coefficients in the equation.

[0122] Table 1 Coefficients in the SST model

[0123]

[0124] Step 102: Under multiple preset sea and wind conditions, constrain the floating wind turbine rigid body model to the mooring system of the floating wind turbine blades, and couple the floating wind turbine rigid body model with the fluid domain numerical model to generate a coupled model under each preset sea and wind condition.

[0125] It should be noted that the mooring system for floating wind turbine blades typically consists of three mooring cables spaced 120° apart. The required mooring parameters can be obtained by consulting wind turbine design manuals and other relevant materials. The floating foundation is constrained by the mooring system. The mooring cable loads can be calculated using quasi-static catenary theory. The anchor chain bottoming state is determined through classification and discussion, and an iterative method is used to solve the problem.

[0126] Furthermore, to accurately simulate the actual operating environment of a floating wind turbine, it is necessary to combine multiple sea and wind conditions (i.e., multiple preset sea and wind conditions). Assume that the number of sea conditions is m and the number of wind conditions is n. The first sea condition and the first operating condition are set for the resulting fluid domain numerical model, and the floating wind turbine rigid body model is constrained to the mooring system of the floating wind turbine blades. The wind turbine rigid body model and the fluid domain numerical model are then coupled. The turbine surface is set as the fluid-structure coupling surface during the coupling process, and the coupling method is the arbitrary Lagrangian-Eulerian method.

[0127] Step 103 : Solve the six-degree-of-freedom motion of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupled model under each preset sea and wind condition to generate a fatigue load spectrum.

[0128] The preset sea and wind conditions are those for a wide sea area.

[0129] Specifically, step 103 may include the following sub-steps S31-S32:

[0130] Step S31: solving the six-degree-of-freedom motion of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupling model under each preset sea and wind condition, and generating a six-degree-of-freedom motion result of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling corresponding to the coupling model under each preset sea and wind condition;

[0131] Step S32: constructing a fatigue load spectrum using the wind turbine blade root motion curve and flow field pressure load from the six-degree-of-freedom motion results of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling corresponding to the coupling model under each preset sea and wind condition.

[0132] It should be noted that after coupling the wind turbine rigid body model and the fluid domain numerical model, the six-degree-of-freedom motion of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling is solved, and the six-degree-of-freedom motion results of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling are obtained. The wind turbine blade root motion curve and flow field pressure load in the results are stored in the database. Under the multi-field coupling effect, the dynamic equation of the floating wind turbine is as follows:

[0133] ; (14)

[0134] in, is the mass matrix of the floating wind turbine; is the additional mass matrix of the floating foundation at infinite frequency; is the acceleration vector of the wind turbine tower and floating foundation; is the damping matrix; is the velocity vector of the wind turbine tower and floating foundation; is the hydrostatic recovery stiffness matrix; is the displacement vector of the wind turbine tower and floating foundation; for The impulse function applied at the moment, R is the velocity impulse function matrix, and t is the time; for Velocity vectors of wind turbine tower and floating foundation at time t; For time delay; is the aerodynamic load; is the wind pressure load on the tower; is the wave load acting on the floating foundation; is the mooring load.

[0135] Next, set the second sea state and the second wind condition and repeat the above steps to obtain a new wind turbine blade root motion curve and flow field pressure load, which are again stored in the database. This process is repeated until the wind turbine blade root motion curve and flow field pressure load are obtained for m sea conditions and n wind conditions. This fatigue load spectrum is then formed and used as the external load for subsequent finite element analysis of floating wind turbine blades.

[0136] Step 104: construct a high-fidelity finite element model of the wind turbine blade based on the wind turbine blade CAD model.

[0137] Specifically, step 104 may include the following sub-steps S41-S42:

[0138] Step S41, meshing the wind turbine blade CAD model to generate a meshed wind turbine blade CAD model;

[0139] Step S42: assigning composite material properties to the meshed CAD model of the wind turbine blade to generate a high-fidelity finite element model of the wind turbine blade.

[0140] It should be noted that the floating wind turbine blade CAD model obtained from the above steps was imported into finite element pre-processing software and meshed. Composite material properties were then assigned and intra- and inter-laminar fracture parameters were set before the blade was laid up. Structurally, the blade can be subdivided into four major sections: the web, leading edge, main beam, and trailing edge. These sections vary in material type, ply thickness, and angle. Based on this, a high-fidelity finite element model of the wind turbine blade was constructed.

[0141] Step 105: Obtain the probability of occurrence of multiple sea conditions and wind conditions in the study sea area, and based on the high-fidelity finite element model of the wind turbine blade, determine the target cyclic load, the target wind turbine blade root motion curve, and the fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade according to the probability of occurrence of each sea condition and wind condition, the preset intra-layer and inter-layer fracture parameters, and the fatigue load spectrum.

[0142] The probability of occurrence of sea and wind conditions in the study sea area is the probability of occurrence of sea and wind conditions in a specific sea area.

[0143] Fatigue crack stress results include fiber direction stress value, crack surface normal stress component, transverse shear stress component, longitudinal shear stress component, normal equivalent stress component, and tangential equivalent stress component.

[0144] The preset intralayer and interlayer fracture parameters are intralayer and interlayer parameters, including fiber direction strength value, transverse tensile strength, transverse shear strength, longitudinal shear strength, transverse friction coefficient, longitudinal friction coefficient, normal aggregation strength, and tangential aggregation strength.

[0145] Specifically, step 105 may include the following sub-steps S51-S52:

[0146] Step S51: selecting a target cyclic load and a target wind turbine blade root motion curve from a fatigue load spectrum based on the probability of occurrence of various sea and wind conditions;

[0147] It should be noted that, based on the above steps, a fatigue load spectrum consisting of the wind turbine blade root motion curve and the flow field pressure load under m kinds of sea conditions and n kinds of wind conditions is obtained. According to actual needs, the blade root constraints and flow field pressure loads under a kind of sea condition and b kind of wind condition (a∈[1,m], b∈[1,n]) in the fatigue load spectrum are combined to obtain the target flow field pressure load (target cyclic load) and the target wind turbine blade root motion curve. Subsequently, the target wind turbine blade root motion curve is applied to the floating wind turbine blade root, and the target cyclic load is applied to the blade surface, and the blade structure is subjected to finite element calculation. Specifically, by investigating the natural environment of a certain sea area (that is, obtaining the probability of occurrence of multiple sea conditions and wind conditions in the study sea area), for example, the probability of occurrence of multiple sea conditions and wind conditions in the study sea area includes the probability of occurrence of sea condition 1 and wind condition 1 (P1), the probability of occurrence of sea condition 1 and wind condition 2 (P2), .... the probability of occurrence of sea condition a and wind condition b (P k ), then in the fatigue load spectrum, according to the probability of occurrence of sea conditions and wind conditions, select the fluid pressure load and root curve motion corresponding to sea condition 1 and wind condition 1, sea condition 1 and wind condition 2, .... the fluid pressure load and root curve motion corresponding to sea condition a and wind condition b. Assume that within a calculation cycle (i.e., a preset calculation cycle, determined according to actual needs, such as one hour), if the probability of occurrence of sea condition 1 and wind condition 1 (P1)> the probability of occurrence of sea condition 1 and wind condition 2 (P2)> ...> the probability of occurrence of sea condition a and wind condition b (P k), then in the finite element calculation process, the following operations are performed in sequence: within the time of "preset calculation period × P1", the fluid pressure load corresponding to sea state 1 and wind condition 1 (recorded as target cyclic load F1) and the target root motion curve are applied to the finite element model of the wind turbine blade; within the time of "preset calculation period × P2", the fluid pressure load corresponding to sea state 1 and wind condition 2 (recorded as target cyclic load F2) and the target root motion curve are applied to the finite element model of the wind turbine blade; ... within the time of "preset calculation period × P k ", the fluid pressure load corresponding to sea condition a and wind condition b is applied to the finite element model of the wind turbine blade (denoted as the target cycle load F k ) and target root motion curve.

[0148] Step S52: applying the target wind blade root motion curve to the blade root of the high-fidelity finite element model of the wind blade, applying the target cyclic load to the blade surface of the high-fidelity finite element model of the wind blade, and performing finite element calculation on the high-fidelity finite element model of the wind blade based on preset intra-layer and inter-layer fracture parameters to determine the fatigue crack stress result corresponding to the high-fidelity finite element model of the wind blade;

[0149] It should be noted that, during the first application process and within the application time (preset calculation cycle × maximum sea and wind condition probability), the corresponding target cyclic load and target wind turbine blade root motion curve are selected from the fatigue load spectrum according to the maximum sea and wind condition probability, and applied to the model. During the Nth application process and within the application time (preset calculation cycle × Nth largest sea and wind condition probability), the corresponding target cyclic load and target wind turbine blade root motion curve are selected from the fatigue load spectrum according to the Nth largest sea and wind condition probability, and applied to the model. The specific application process is: applying the target wind turbine blade root motion curve to the floating wind turbine blade root of the high-fidelity finite element model of the wind blade, and applying the final flow field pressure load on the blade surface of the high-fidelity finite element model of the wind blade, performing finite element calculation on the blade structure of the high-fidelity finite element model of the wind blade, and obtaining the fatigue crack stress result corresponding to the high-fidelity finite element model of the wind blade.

[0150] Step 106 : Based on the preset blade fracture criterion and the fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade, dynamically insert a cohesive force element into the high-fidelity finite element model of the wind turbine blade.

[0151] The preset blade fracture criteria include fiber fracture criterion, matrix cracking criterion and double stress criterion.

[0152] The cohesive force units include the cohesive force units dynamically inserted between the units with intra-layer fracture and the cohesive force units dynamically inserted between the units with inter-layer fracture.

[0153] Specifically, step 106 may include the following sub-steps S61-S62:

[0154] Step S61: determining whether the fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade meets the preset blade fracture criterion;

[0155] Step S62: If the conditions are met, dynamically insert cohesive force units into the high-fidelity finite element model of the wind turbine blade.

[0156] It should be noted that the fiber fracture criterion or the matrix cracking criterion is used to determine whether the blade has intralayer fracture. If intralayer fracture occurs, cohesive units are dynamically inserted between the fractured units. The fiber fracture criterion is:

[0157] ; (15)

[0158] in, is the stress value in the fiber direction; is the fiber direction strength value.

[0159] The matrix cracking criterion is:

[0160] ; (15)

[0161] ; (16)

[0162] in, 、 、 、 、 、 、 、 They are the normal stress component of the crack surface, the transverse shear stress component, the longitudinal shear stress component, the transverse tensile strength, the transverse shear strength, the longitudinal shear strength, the transverse friction coefficient, and the longitudinal friction coefficient.

[0163] Furthermore, the dual stress criterion is used to determine whether interlaminar fracture has occurred in the blade. If interlaminar fracture has occurred, cohesive elements are dynamically inserted between the fractured elements. The dual stress criterion is:

[0164] ; (17)

[0165] in, is the normal equivalent stress component; is the tangential equivalent stress component; is the normal aggregation strength; is the tangential polymerization strength.

[0166] It is worth mentioning that if the high-fidelity finite element model of the wind blade does not have interlaminar fractures and intralaminar fractures, the target flow field pressure load and the target wind blade root motion curve are reselected in the fatigue load spectrum, and then the finite element calculation is performed on the high-fidelity finite element model of the wind blade.

[0167] Step 107 : Based on the linear stress-separation curve and the cohesion unit, according to the target cyclic load, the target wind turbine blade root motion curve, and the preset intra-layer and inter-layer fracture parameters, calculate the target blade fatigue life of the floating wind turbine blade in the study sea area.

[0168] Specifically, step 107 may include the following sub-steps S71-S710:

[0169] Step S71: Based on the cohesive force unit, a fatigue damage curve of a linear stress-separation curve is used to characterize the fatigue degradation effect of the cohesive strength, and a cohesive fatigue damage model of the wind turbine blade is constructed;

[0170] It should be noted that based on the two aforementioned cohesive elements, a fatigue damage curve based on a linear stress-separation curve is used to characterize the fatigue degradation effect of cohesive strength, thereby obtaining a cohesive fatigue model for wind turbine blades. On this basis, the cyclic jump method is combined to simulate the fatigue damage process of wind turbine blades.

[0171] Step S72: applying the target fan blade root motion curve to the blade root of the fan blade cohesive fatigue damage model, applying the target cyclic load to the blade surface of the fan blade cohesive fatigue damage model, and performing finite element calculation on the fan blade cohesive fatigue damage model to determine the tip deflection and stress curve of each element at the current moment;

[0172] The stress curve of each unit is a stress curve of multiple units in the cohesive fatigue damage model of the wind blade. The multiple units in the cohesive fatigue damage model of the wind blade include cohesive units and all blade units.

[0173] Step S73: Calculate the load application time based on the probability of occurrence of sea and wind conditions corresponding to the target cyclic load within a calculation period, and record the current time in real time;

[0174] It should be noted that the load application time is calculated using the probability of occurrence of the sea and wind conditions corresponding to the target cyclic load. For example, if the probability of occurrence of the sea and wind conditions corresponding to the target cyclic load is the probability of occurrence of sea condition 1 and wind condition 1 (P1), then the load application time is the preset calculation period × P1.

[0175] Step S74: determine whether the current time reaches the load application time;

[0176] Optionally, if the current time does not reach the load application time, the process jumps to the step of applying the target cyclic load and the target fan blade root motion curve to the fan blade cohesive fatigue damage model, and performing finite element calculation on the fan blade cohesive fatigue damage model to determine the tip deflection and the stress curve of each unit at the current moment.

[0177] It should be noted that if the current time has not reached the load application time, the process jumps to step S72, that is, the currently selected target cyclic load and target wind turbine blade root motion curve continue to be applied to the wind turbine blade cohesive fatigue damage model, thereby obtaining a new tip deflection at the current moment and a new stress curve of each unit, and then obtaining a new damage variable for each unit. For example, if the currently selected target cyclic load and target wind turbine blade root motion curve are the fluid pressure load and wind turbine blade root motion curve corresponding to the probability (P1) of sea condition 1 and wind condition 1, and the current time has not reached the load application time, the fluid pressure load and the wind turbine blade root motion curve continue to be applied to the wind turbine blade cohesive fatigue damage model.

[0178] Step S75: If yes, record the current calculation time in real time and determine whether the current calculation time reaches the preset calculation period;

[0179] It should be noted that if the current calculation time does not reach the preset calculation cycle, it is necessary to update the target cyclic load and the target wind turbine blade root motion curve. Specifically, according to the probability of occurrence of multiple sea conditions and wind conditions in the study sea area, a new target cyclic load and a new target wind turbine blade root motion curve are re-selected in the fatigue load spectrum, and jump to execute step S52. For example, assuming that the probabilities of occurrence of multiple sea conditions and wind conditions in the study sea area include the probability of occurrence of sea condition 1 and wind condition 1 (P1), the probability of occurrence of sea condition 1 and wind condition 2 (P2), and the probability of occurrence of sea condition 1 and wind condition 3 (P3), and the probability of occurrence of sea condition 1 and wind condition 1 (P1)>the probability of occurrence of sea condition 1 and wind condition 2 (P2)>the probability of occurrence of sea condition 1 and wind condition 3 (P3), if the target cyclic load and the target wind turbine blade root motion curve are the fluid pressure load and the wind turbine blade root motion curve corresponding to the probability of occurrence of sea condition 1 and wind condition 1 (P1), then the new target cyclic load and the new target wind turbine blade root motion curve are the fluid pressure load and the wind turbine blade root motion curve corresponding to the probability of occurrence of sea condition 1 and wind condition 2 (P2). Similarly, after the next target cyclic load and target wind turbine blade root motion curve are updated, the new target cyclic load and new target wind turbine blade root motion curve are the fluid pressure load and wind turbine blade root motion curve corresponding to the probability (P3) of sea state 1 and wind state 3 occurring.

[0180] Step S76: If yes, select the maximum stress component and the minimum stress component corresponding to each unit in the stress curve of each unit, and calculate the stress amplitude of each unit based on the maximum stress component and the minimum stress component corresponding to each unit;

[0181] It should be noted that cycle skipping refers to calculating several load cycles within a selected interval and extrapolating the effects of these load cycles on stiffness degradation in an appropriate manner to cover the corresponding interval. The specific steps are as follows:

[0182] Based on the stress curves of all elements obtained in the above steps, the stress amplitude corresponding to each element is calculated using the following formula:

[0183] ; (18)

[0184] in, is the stress amplitude of the i-th unit; is the maximum stress component of the i-th unit; is the minimum stress component of the i-th element.

[0185] Step S77: using the stress amplitude of each unit, calculate the evolution rate of the damage variable of each unit with the number of cycles;

[0186] It should be noted that, based on the above, the evolution rate of the damage variable of the i-th unit with the number of cycles in the current calculation cycle is calculated as follows:

[0187] ; (19)

[0188] in, is the evolution rate of the damage variable of the i-th unit with the number of cycles; is the first material coefficient; is the stress amplitude of the i-th unit; is the second material coefficient.

[0189] Step S78: Select the maximum value of the evolution rate of the damage variable with the number of cycles from the evolution rate of the damage variable with the number of cycles of each unit, and use the maximum value of the evolution rate of the damage variable with the number of cycles to calculate the number of cycles of the jump period;

[0190] Step S79, calculating the number of jump cycles based on the sum of the number of jump cycles and the number of load cycles corresponding to the target cyclic load within the preset calculation period;

[0191] Step S710: multiply the number of jump cycles and the preset calculation cycle to determine the fatigue life predicted based on the jump cycle;

[0192] Step S711, calculating the fatigue life of the current cycle according to the fatigue life predicted based on the jump cycle and the preset calculation cycle;

[0193] It should be noted that the maximum value is determined by comparing the damage variable evolution rate of all units in the fan blade cohesive fatigue damage model within the calculation cycle. Then, the number of cycles that can be jumped within the calculation cycle is calculated based on formula (20), that is, the number of cycles in the jump cycle:

[0194] ; (20)

[0195] in, is the number of cycles of the i-th jump period; The preset maximum damage amount. The smaller the value, the higher the calculation accuracy. is the maximum value of the evolution rate of the damage variable with the number of cycles.

[0196] Furthermore, based on the target cyclic loads corresponding to the probability of occurrence of multiple sea and wind conditions in the study area, the number of cycles corresponding to these target cyclic loads within a preset calculation cycle (referred to as the number of load cycles) is determined. The number of jump cycles is divided by the sum of the number of load cycles corresponding to the target cyclic loads (i.e., the sum of the number of load cycles corresponding to all target cyclic loads within a preset calculation cycle) to obtain the jump cycle number. The jump cycle number is then multiplied by the preset calculation cycle to obtain the fatigue life predicted based on the jump cycle. The fatigue life predicted based on the jump cycle is then added to the preset calculation cycle (as the fatigue life predicted based on the calculation cycle) to obtain the fatigue life for the current cycle. The number of load cycles corresponding to a target cyclic load refers to the process of starting from an initial value and returning to the initial value after one cycle. The total number of load cycles within the application time of a target cyclic load is the number of load cycles corresponding to that target cyclic load. The sum of the number of load cycles corresponding to each target cyclic load within a preset calculation cycle is the total number of load cycles for that calculation cycle.

[0197] Step S712: determining whether the tip deflection at the current moment is greater than the preset maximum allowable tip deflection;

[0198] Step S713: If yes, then add the fatigue life of the current cycle and the fatigue life of multiple historical cycles to determine the target blade fatigue life of the floating wind turbine blade in the study sea area.

[0199] It should be noted that after a calculation cycle is completed, the fatigue life of the current cycle and the tip deflection at the current moment are recorded. The blade tip deflection (the tip deflection at the current moment) is then determined to see if it exceeds the maximum allowable range (the preset maximum allowable tip deflection). If so, the blade is deemed to have failed, and the fatigue life of the current cycle is added to the fatigue life of all historical cycles to obtain the final blade fatigue life (i.e., the target blade fatigue life of the floating wind turbine blade in the study area).

[0200] Optionally, it also includes:

[0201] If the tip deflection at the current moment is less than or equal to the preset maximum allowable tip deflection, the damage variable of each unit is calculated based on the damage area of ​​the wind turbine blade cohesive fatigue damage model and the area of ​​each unit;

[0202] Calculate the new damage variable of each unit according to the number of jump cycles, the damage variable of each unit and the evolution rate of the damage variable with the number of cycles;

[0203] The new damage variables of each unit are used to update the cohesive fatigue damage model of the fan blade to determine a new cohesive fatigue damage model of the fan blade;

[0204] The fatigue life of the current cycle is used as the fatigue life of the historical cycle, and the step of selecting the target cyclic load and the target wind turbine blade root motion curve in the fatigue load spectrum based on the probability of occurrence of each sea and wind condition is executed until the tip deflection at the current moment is greater than the preset maximum allowable tip deflection;

[0205] The fatigue life of the current cycle determined when the tip deflection at the current moment is greater than the preset maximum allowable tip deflection and the fatigue life of multiple historical cycles are added together to determine the target blade fatigue life of the floating wind turbine blade in the study sea area.

[0206] It should be noted that the cohesive fatigue damage model of wind turbine blades combines the traction force at the fracture interface with the crack opening. In connection, the interface where cracks may occur can be expressed as:

[0207] ;(twenty one)

[0208] in, is the traction force at the fracture interface; is the damage variable; is the strength of the interface; is the critical crack opening; is the fatigue crack opening.

[0209] Based on the above foundation, the initiation of damage is related to the strength of the interface When the area under the traction-displacement relationship is equal to the fracture toughness G C When the traction force drops to zero and a new crack surface is formed, if the linear traction-separation law is used, when the crack opening is equal to or exceeds the critical value of the crack opening, the crack will be When the new crack surface is completely formed, the linear traction-separation law is as follows Figure 2 shown; among them, is the maximum traction force when the crack opening is 0, is the crack opening when the interface is completely separated.

[0210] In the cohesive fatigue damage model of wind turbine blades, the damage variable d represents the interface strength degradation, which can be interpreted as the area of ​​the damaged area A. d The area A corresponding to one unit e The ratio between them is used to obtain the damage variable of each unit i .

[0211] Furthermore, according to formula (22), the extrapolated times The damage variable after the jump (damage variable of the next calculation cycle), that is, the new damage variable of each unit, is used to update the cohesive fatigue damage model of the fan blade using the new damage variables of all units to determine the new cohesive fatigue damage model of the fan blade, that is, the new damage variables of all units are used to define the initial state of the cohesive fatigue damage model of the fan blade; wherein, the calculation process of the new damage variable of each unit is specifically as follows:

[0212] ;(twenty two)

[0213] in, is the new damage variable of the i-th unit; is the damage variable of the ith unit.

[0214] It is worth mentioning that after the damage variable jumps, it changes from the damage variable Increase to the new damage variable , which is expressed as stiffness degradation in the blade, that is, the stiffness degradation of the blade of the fan blade cohesive fatigue damage model, thereby obtaining a new fan blade cohesive fatigue damage model.

[0215] Furthermore, if the tip deflection at the current moment is less than or equal to the preset maximum allowable tip deflection, the next calculation cycle is immediately entered, and the above steps are repeated. Specifically, the target cyclic load and target wind turbine blade root motion curve corresponding to the probability of occurrence of each sea condition and wind condition selected in the previous calculation cycle are applied to the new wind turbine blade cohesive fatigue damage model according to the logic of the above steps; for example, the previous calculation cycle selected the target cyclic load and target wind turbine blade root motion curve corresponding to the largest probability of occurrence of sea condition 1 and wind condition 1 (P1), the target cyclic load and target wind turbine blade root motion curve corresponding to the second largest probability of occurrence of sea condition 1 and wind condition 2 (P2), and the target cyclic load and target wind turbine blade root motion curve corresponding to the third largest probability of occurrence of sea condition 1 and wind condition 3 (P3) in order of the size of the probability of occurrence. After entering the current calculation cycle, the target cyclic load and target wind turbine blade root motion curve corresponding to the maximum sea state 1 and wind condition 1 probability (P1) are first selected and applied to the model. If the current time has not reached the load application time corresponding to the maximum sea state 1 and wind condition 1 probability (P1), the target cyclic load and target wind turbine blade root motion curve corresponding to the maximum sea state 1 and wind condition 1 probability (P1) are continued to be applied to the model. If the current time reaches the load application time corresponding to the maximum sea state 1 and wind condition 1 probability (P1), the target cyclic load and target wind turbine blade root motion curve corresponding to the second largest sea state 1 and wind condition 2 probability (P2) are required to be applied to the model, and the above steps are repeated to finally output the target blade fatigue life of the floating wind turbine blade in the study area.

[0216] For comparison purposes, existing technologies can be used as a reference. Predicting the fatigue life of blades on floating wind turbine platforms under multiple loads involves knowledge and techniques from multiple fields, including aerodynamics, hydrodynamics, and structural dynamics. This is a typical multi-field coupling problem. Research has found that while there is limited research on fatigue life prediction for floating wind turbine blades under multi-field coupling, scholars' research on floating wind turbines provides valuable insights and insights for this invention. For example, Luo Mengjie employed the rainflow counting method and Miner's criterion, combined with the SN curve (Stress-Number of Cycles Curve), and used Mlife software (Marine Life Fatigue Analysis Software) to conduct a short-term fatigue damage analysis of the tower top and tower base of a floating wind turbine under fully coupled loads. Ni Peng developed a rainflow counting program, combined with the SN curve and linear fatigue cumulative damage theory, to calculate the fatigue life of hot spots on the foundation of a three-buoy wind turbine under the combined effects of dynamic turbine loads, wave loads, wind loads, and flow loads. Dai Peng et al. adopted the same method as Ni Peng and combined it with the blade element momentum method and beam model to propose a fatigue life calculation method for floating offshore wind turbine blades.

[0217] Although researchers at home and abroad have conducted fatigue life calculation research on various parts of floating wind turbines under fluid-solid coupling, in the research of Luo Mengjie and Ni Peng, although the fatigue life analysis of the floating wind turbine structure was carried out, the analysis objects were the tower and foundation, and the wind turbine blades were not involved. Wind turbine blades are usually made of composite materials, and their damage mechanism is more complex. Although Dai Peng et al. proposed a calculation method for the fatigue life of floating wind turbine blades, the blade beam model they constructed is relatively simple and cannot accurately describe the geometric shape and complex laying of the blades. In addition, the fatigue damage of the blades is not considered in the calculation process, resulting in low accuracy in fatigue life calculation. In addition, most studies only consider the situation of a single sea condition combined with a single wind condition. In the actual operating environment of floating wind turbine blades, the sea conditions and wind conditions are constantly changing, and even a superposition of multiple sea conditions and wind conditions. Therefore, it is difficult for existing technologies to simulate the real working environment of floating wind turbine blades to accurately calculate the fatigue life of the blades.

[0218] To address the above issues, the present invention proposes a method for calculating the fatigue life of floating wind turbine blades. During operation, under the combined effects of wind loads, wave loads, and mooring loads, floating wind turbine blades experience intense fluid-structure coupling effects. This method is used to construct a high-precision blade fatigue life calculation method that can combine various sea and wind conditions and consider fatigue cracks. Specifically, please refer to Figure 3First, a six-degree-of-freedom motion calculation method for an aerodynamic-hydrodynamic-moored floating wind turbine under various sea and wind conditions was constructed. The calculated blade root motion curve and flow field pressure load were formed into a fatigue load spectrum, which was applied to a high-fidelity finite element model of the wind turbine blade to predict its fatigue life.

[0219] In summary, the fatigue life of existing floating wind turbine blades is mainly based on the blade element momentum method and the beam model to perform dynamic simulation to calculate the blade load, and then the life is predicted based on the fatigue life method. The fatigue life method does not take into account the progressive expansion of fatigue cracks, and the calculation accuracy is low. Compared with the existing technology, the present invention focuses on the field of wind power and innovatively proposes a high-precision fatigue life calculation method for floating wind turbine blades under aerodynamic-hydrodynamic-mooring multi-field coupling. In this method, a variety of sea conditions and wind conditions can be combined according to needs. In addition, the wind turbine blades take into account the composite material ply, and the simulation of fatigue cracks is also considered when performing finite element analysis, so that its fatigue life can be accurately calculated. The technology of the present invention can enrich the theoretical connotation of the fatigue life calculation of floating wind turbine blades, and provide support for its structural optimization design and performance improvement. The present invention can combine a variety of sea conditions and wind conditions, and consider fatigue cracks in the calculation process.

[0220] In an embodiment of the present invention, a method for calculating the fatigue life of a floating wind turbine blade is provided. First, the airfoil coordinate data and airfoil geometric parameters of the floating wind turbine blade are obtained, and according to the preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size of the floating wind turbine blade and the actual working conditions, a wind turbine blade CAD model, a floating wind turbine rigid body model, and a fluid domain numerical model are constructed; then, under multiple preset sea and wind conditions, the floating wind turbine rigid body model is constrained on the mooring system of the floating wind turbine blade, and the floating wind turbine is placed on the mooring system of the floating wind turbine blade. The rigid body model and the fluid domain numerical model are coupled to generate coupling models under various preset sea and wind conditions; the six-degree-of-freedom motion of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling is solved for the coupling models under various preset sea and wind conditions to generate a fatigue load spectrum; a high-fidelity finite element model of the wind turbine blade is constructed based on the CAD model of the wind turbine blade; the probability of occurrence of multiple sea and wind conditions in the research area is obtained, and based on the high-fidelity finite element model of the wind turbine blade, the target cycle is determined according to the probability of occurrence of each sea and wind condition, the preset intra-layer and inter-layer fracture parameters, and the fatigue load spectrum. The present invention calculates the fatigue life of the target blade of the floating wind turbine in the study area based on the target cyclic load, the target wind turbine blade root motion curve and the preset intra-layer and inter-layer fracture parameters. The fatigue load spectrum is formed by the wind turbine blade root motion curve and the flow field pressure load calculated under multiple preset sea and wind conditions, and is applied to the high-fidelity finite element model of the wind turbine blade based on the obtained probability of occurrence of multiple sea and wind conditions in the study area to complete the fatigue life calculation process. The present invention can combine multiple sea and wind conditions, take fatigue cracks into consideration during the calculation process, simulate crack propagation, and achieve high-precision fatigue life calculation while also improving the calculation accuracy of the blade fatigue life.

[0221] See also Figure 4 , Figure 4 This is a structural block diagram of a floating wind turbine blade fatigue life calculation device provided in the second embodiment of the present invention.

[0222] The present invention provides a floating wind turbine blade fatigue life calculation device, comprising:

[0223] An acquisition module 401 is configured to acquire airfoil coordinate data and airfoil geometric parameters of a floating wind turbine blade, and construct a wind turbine blade CAD model, a floating wind turbine rigid body model, and a fluid domain numerical model based on preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size of the floating wind turbine blade, and the actual operating conditions.

[0224] A coupling module 402 is configured to constrain the floating wind turbine rigid body model to the mooring system of the floating wind turbine blades under multiple preset sea and wind conditions, and couple the floating wind turbine rigid body model with the fluid domain numerical model to generate a coupled model under each preset sea and wind condition;

[0225] A solution module 403 is used to solve the six-degree-of-freedom motion of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling for the coupled model under each preset sea and wind condition, and generate a fatigue load spectrum;

[0226] A construction module 404 is used to construct a high-fidelity finite element model of the wind turbine blade based on the wind turbine blade CAD model;

[0227] The stress calculation module 405 is used to obtain the probability of occurrence of multiple sea and wind conditions in the study area, and based on the high-fidelity finite element model of the wind turbine blade, determine the target cyclic load, the target wind turbine blade root motion curve, and the fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade according to the probability of occurrence of each sea and wind condition, the preset intra-layer and inter-layer fracture parameters, and the fatigue load spectrum;

[0228] A dynamic insertion module 406 is configured to dynamically insert a cohesive force element into the high-fidelity finite element model of the wind turbine blade based on a preset blade fracture criterion and fatigue crack stress results corresponding to the high-fidelity finite element model of the wind turbine blade;

[0229] The fatigue life calculation module 407 is used to calculate the target blade fatigue life of the floating wind turbine blade in the study sea area based on the linear stress-separation curve and the cohesion unit, according to the target cyclic load, the target wind turbine blade root motion curve, and the preset intra-layer and inter-layer fracture parameters.

[0230] Furthermore, the acquisition module 401 is specifically configured to:

[0231] Construct a CAD model of the wind turbine blade based on the airfoil coordinate data and airfoil geometric parameters;

[0232] Assigning rigid body material attributes to the wind turbine blade CAD model, and determining the wind turbine blade CAD model assigned with the rigid body material attributes;

[0233] Construct a floating wind turbine rigid body model based on preset boundary conditions and a wind turbine blade CAD model with rigid body material properties;

[0234] Determine the fluid domain size based on the size of the floating wind turbine blades and actual operating conditions;

[0235] Based on the fluid domain size, a fluid domain geometric model is constructed;

[0236] Meshing the fluid domain geometric model to generate a meshed fluid domain geometric model;

[0237] The fluid domain geometric model after meshing is pre-processed to generate a fluid domain numerical model.

[0238] Furthermore, the solution module 403 is specifically configured to:

[0239] Solve the six-degree-of-freedom motion of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupled model under each preset sea and wind condition, and generate the six-degree-of-freedom motion results of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling corresponding to the coupled model under each preset sea and wind condition;

[0240] The fatigue load spectrum is constructed by using the wind turbine blade root motion curve and flow field pressure load from the six-degree-of-freedom motion results of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling corresponding to the coupling model under each preset sea and wind condition.

[0241] Furthermore, the construction module 404 is specifically configured to:

[0242] Meshing the fan blade CAD model to generate a meshed fan blade CAD model;

[0243] The meshed CAD model of the wind turbine blade is given composite material properties to generate a high-fidelity finite element model of the wind turbine blade.

[0244] Furthermore, the stress calculation module 405 is specifically configured to:

[0245] Select target cyclic loads and target wind turbine blade root motion curves from the fatigue load spectrum based on the probability of occurrence of various sea and wind conditions;

[0246] The target wind blade root motion curve is applied to the blade root of the high-fidelity finite element model of the wind blade, and the target cyclic load is applied to the blade surface of the high-fidelity finite element model of the wind blade. Based on the preset intra-layer and inter-layer fracture parameters, the high-fidelity finite element model of the wind blade is subjected to finite element calculation to determine the fatigue crack stress results corresponding to the high-fidelity finite element model of the wind blade.

[0247] Furthermore, the dynamic insertion module 406 is specifically configured to:

[0248] Determine whether the fatigue crack stress results corresponding to the high-fidelity finite element model of the wind turbine blade meet the preset blade fracture criteria;

[0249] If the conditions are met, the cohesive force elements are dynamically inserted into the high-fidelity finite element model of the wind turbine blade.

[0250] Furthermore, the fatigue life calculation module 407 is specifically configured to:

[0251] Based on the cohesive force unit, a fatigue damage curve of the linear stress-separation curve is used to characterize the fatigue degradation effect of the cohesive strength, and a cohesive fatigue damage model of the wind turbine blade is constructed.

[0252] The target fan blade root motion curve is applied to the blade root of the fan blade cohesive fatigue damage model, the target cyclic load is applied to the blade surface of the fan blade cohesive fatigue damage model, and the fan blade cohesive fatigue damage model is subjected to finite element calculation to determine the tip deflection and stress curve of each element at the current moment;

[0253] Calculate the load application time based on the probability of occurrence of sea and wind conditions corresponding to the target cyclic load within a calculation period, and record the current time in real time;

[0254] Determine whether the current time reaches the load application time;

[0255] If so, record the current calculation time in real time and determine whether the current calculation time reaches the preset calculation period;

[0256] If so, select the maximum stress component and the minimum stress component corresponding to each unit in the stress curve of each unit, and calculate the stress amplitude of each unit based on the maximum stress component and the minimum stress component corresponding to each unit;

[0257] The stress amplitude of each element is used to calculate the evolution rate of the damage variable of each element with the number of cycles;

[0258] The maximum value of the evolution rate of the damage variable with the number of cycles is selected from the evolution rate of the damage variable with the number of cycles of each unit, and the number of cycles of the jump period is calculated using the maximum value of the evolution rate of the damage variable with the number of cycles;

[0259] Calculating the number of jump cycles based on the sum of the number of jump cycles and the number of load cycles corresponding to the target cyclic load within a preset calculation period;

[0260] Multiply the number of jump cycles and the preset calculation cycle to determine the fatigue life predicted based on the jump cycle;

[0261] Calculate the fatigue life of the current cycle based on the fatigue life predicted based on the jump cycle and the preset calculation cycle;

[0262] Determine whether the tip deflection at the current moment is greater than the preset maximum allowable tip deflection;

[0263] If so, the fatigue life of the current cycle and the fatigue life of multiple historical cycles are added together to determine the target blade fatigue life of the floating wind turbine blade in the study sea area.

[0264] In an optional embodiment of the device, the device further comprises:

[0265] The first module is used to jump to the execution of applying the target cyclic load and the target fan blade root motion curve to the fan blade cohesive fatigue damage model if the current time has not reached the load application time, and performing finite element calculation on the fan blade cohesive fatigue damage model to determine the tip deflection and the stress curve of each unit at the current moment.

[0266] In an optional embodiment of the device, the device further comprises:

[0267] The second module is used to calculate the damage variable of each unit according to the damage area area of ​​the wind turbine blade cohesive fatigue damage model and the area of ​​each unit if the tip deflection at the current moment is less than or equal to the preset maximum allowable tip deflection;

[0268] The third module is used to calculate the new damage variable of each unit according to the number of jump cycles, the damage variable of each unit and the evolution rate of the damage variable with the number of cycles;

[0269] The fourth module is used to update the cohesive fatigue damage model of the fan blade using the new damage variables of each unit to determine a new cohesive fatigue damage model of the fan blade;

[0270] The fifth module is configured to use the fatigue life of the current cycle as the fatigue life of the historical cycle and jump to the step of selecting a target cyclic load and a target wind turbine blade root motion curve from the fatigue load spectrum based on the probability of occurrence of various sea and wind conditions, until the tip deflection at the current moment is greater than the preset maximum allowable tip deflection;

[0271] The sixth module is used to add the fatigue life of the current cycle determined when the tip deflection at the current moment is greater than the preset maximum allowable tip deflection and the fatigue life of multiple historical cycles to determine the target blade fatigue life of the floating wind turbine blade in the research sea area.

[0272] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the fatigue life of floating wind turbine blades, characterized in that: include: Obtaining airfoil coordinate data and airfoil geometric parameters of a floating wind turbine blade, and constructing a wind turbine blade CAD model, a floating wind turbine rigid body model, and a fluid domain numerical model based on preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size of the floating wind turbine blade, and actual operating conditions; Under a plurality of preset sea and wind conditions, constraining the floating wind turbine rigid body model to the mooring system of the floating wind turbine blades, and coupling the floating wind turbine rigid body model with the fluid domain numerical model to generate a coupled model under each of the preset sea and wind conditions; Solving the six-degree-of-freedom motion of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupled model under each of the preset sea and wind conditions to generate a fatigue load spectrum; Based on the wind turbine blade CAD model, construct a high-fidelity finite element model of the wind turbine blade; Obtaining the probability of occurrence of multiple sea and wind conditions in the study sea area, and based on the high-fidelity finite element model of the wind turbine blade, determining a target cyclic load, a target wind turbine blade root motion curve, and a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade according to the probability of occurrence of each of the sea and wind conditions, preset intra-layer and inter-layer fracture parameters, and the fatigue load spectrum; Dynamically inserting a cohesive force unit into the high-fidelity finite element model of the wind turbine blade based on a preset blade fracture criterion and a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade; Based on the linear stress-separation curve and the cohesive force unit, according to the target cyclic load, the target wind turbine blade root motion curve, and the preset layer interlayer fracture parameters, the target blade fatigue life of the floating wind turbine blade in the study sea area is calculated.

2. The method for calculating fatigue life of floating wind turbine blades according to claim 1, characterized in that: The method of constructing a wind turbine blade CAD model, a floating wind turbine rigid body model, and a fluid domain numerical model according to preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size of the floating wind turbine blade, and the actual working conditions includes: Constructing a CAD model of a wind turbine blade according to the airfoil coordinate data and the airfoil geometric parameters; Assigning rigid body material attributes to the wind turbine blade CAD model, and determining a wind turbine blade CAD model assigned with the rigid body material attributes; Constructing a floating wind turbine rigid body model according to the preset boundary conditions and the wind turbine blade CAD model with the rigid body material properties assigned thereto; Determining the size of the fluid domain according to the size of the floating wind turbine blades and actual operating conditions; constructing a fluid domain geometric model based on the fluid domain size; Meshing the fluid domain geometric model to generate a meshed fluid domain geometric model; The fluid domain geometric model after meshing is pre-processed to generate a fluid domain numerical model.

3. The method for calculating fatigue life of floating wind turbine blades according to claim 1, characterized in that: The step of solving the six-degree-of-freedom motion of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupled model under each of the preset sea and wind conditions to generate a fatigue load spectrum includes: performing a six-degree-of-freedom motion solution for the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupling models under the preset sea and wind conditions, and generating a six-degree-of-freedom motion result for the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling corresponding to the coupling models under the preset sea and wind conditions; The fatigue load spectrum is constructed by using the wind turbine blade root motion curve and flow field pressure load in the six-degree-of-freedom motion results of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling corresponding to the coupling model under each of the preset sea and wind conditions.

4. The method for calculating fatigue life of floating wind turbine blades according to claim 1, characterized in that: The step of constructing a high-fidelity finite element model of the wind blade based on the wind blade CAD model includes: Meshing the fan blade CAD model to generate a meshed fan blade CAD model; The meshed wind turbine blade CAD model is given composite material properties to generate a high-fidelity finite element model of the wind turbine blade.

5. The method for calculating fatigue life of floating wind turbine blades according to claim 1, characterized in that: The method of determining a target cyclic load, a target wind blade root motion curve, and a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind blade based on the high-fidelity finite element model of the wind blade according to the probability of occurrence of each of the sea and wind conditions, the preset intra-layer and inter-layer fracture parameters, and the fatigue load spectrum includes: Selecting a target cyclic load and a target wind turbine blade root motion curve from the fatigue load spectrum based on the probability of occurrence of each of the sea and wind conditions; The target wind blade root motion curve is applied to the blade root of the high-fidelity finite element model of the wind blade, the target cyclic load is applied to the blade surface of the high-fidelity finite element model of the wind blade, and based on the preset intra-layer and inter-layer fracture parameters, the high-fidelity finite element model of the wind blade is subjected to finite element calculation to determine the fatigue crack stress result corresponding to the high-fidelity finite element model of the wind blade.

6. The method for calculating fatigue life of floating wind turbine blades according to claim 1, characterized in that: The method of dynamically inserting a cohesive force unit into the high-fidelity finite element model of the wind turbine blade based on a preset blade fracture criterion and a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade comprises: Determining whether a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade meets the preset blade fracture criterion; If the conditions are met, a cohesive force unit is dynamically inserted into the high-fidelity finite element model of the wind turbine blade.

7. The method for calculating fatigue life of floating wind turbine blades according to claim 1, characterized in that: The calculating of the target blade fatigue life of the floating wind turbine blade in the study sea area based on the linear stress-separation curve and the cohesive force unit according to the target cyclic load, the target wind turbine blade root motion curve, and the preset intra-layer interlayer fracture parameters includes: Based on the cohesive force unit, a fatigue damage curve of the linear stress-separation curve is used to characterize the fatigue degradation effect of the cohesive strength, thereby constructing a cohesive fatigue damage model for the wind turbine blade; Applying the target fan blade root motion curve to the blade root of the fan blade cohesive fatigue damage model, applying the target cyclic load to the blade surface of the fan blade cohesive fatigue damage model, and performing finite element calculation on the fan blade cohesive fatigue damage model to determine the tip deflection at a current moment and the stress curve of each element; Calculate the load application time based on the probability of occurrence of sea and wind conditions corresponding to the target cyclic load within a calculation period, and record the current time in real time; Determining whether the current time reaches the load application time; If yes, record the current calculation time in real time and determine whether the current calculation time reaches the preset calculation period; If yes, selecting the maximum stress component and the minimum stress component corresponding to each unit from the stress curve of each unit, and calculating the stress amplitude of each unit based on the maximum stress component and the minimum stress component corresponding to each unit; Using the stress amplitude of each unit, the evolution rate of the damage variable of each unit with the number of cycles is calculated; Selecting a maximum value of the evolution rate of the damage variable with the number of cycles from the evolution rate of the damage variable with the number of cycles of each of the units, and using the maximum value of the evolution rate of the damage variable with the number of cycles to calculate the number of cycles of the jump period; Calculating the number of jump cycles based on the sum of the number of cycles of the jump cycle and the number of load cycles corresponding to the target cyclic load within the preset calculation period; multiplying the number of jump cycles by the preset calculation cycle to determine a fatigue life predicted based on the jump cycles; Calculating the fatigue life of the current cycle according to the fatigue life predicted based on the jump cycle and the preset calculation cycle; Determining whether the tip deflection at the current moment is greater than a preset maximum allowable tip deflection; If yes, the fatigue life of the current cycle and the fatigue life of multiple historical cycles are added together to determine the target blade fatigue life of the floating wind turbine blade in the research sea area.

8. The method for calculating fatigue life of floating wind turbine blades according to claim 7, characterized in that: Also includes: If the current time does not reach the load application time, the process jumps to executing the step of applying the target cyclic load and the target fan blade root motion curve to the fan blade cohesive fatigue damage model, and performing finite element calculation on the fan blade cohesive fatigue damage model to determine the tip deflection at the current moment and the stress curve of each unit.

9. The method for calculating fatigue life of floating wind turbine blades according to claim 7, characterized in that: Also includes: If the tip deflection at the current moment is less than or equal to the preset maximum allowable tip deflection, calculating the damage variable of each unit according to the damaged area of ​​the cohesive fatigue damage model of the wind turbine blade and the area of ​​each unit; Calculating a new damage variable of each of the units according to the number of cycles of the jump period, the damage variable of each of the units, and the evolution rate of the damage variable with the number of cycles; updating the wind turbine blade cohesive fatigue damage model using the new damage variables of each unit to determine a new wind turbine blade cohesive fatigue damage model; The fatigue life of the current cycle is used as the fatigue life of the historical cycle, and the step of selecting a target cyclic load and a target wind turbine blade root motion curve from the fatigue load spectrum based on the probability of occurrence of each of the sea and wind conditions is executed, until the tip deflection at the current moment is greater than the preset maximum allowable tip deflection; The fatigue life of the current cycle determined when the tip deflection at the current moment is greater than the preset maximum allowable tip deflection and the fatigue life of multiple historical cycles are added to determine the target blade fatigue life of the floating wind turbine blade in the research sea area.

10. A floating wind turbine blade fatigue life calculation device, characterized in that: include: an acquisition module for acquiring airfoil coordinate data and airfoil geometric parameters of a floating wind turbine blade, and constructing a wind turbine blade CAD model, a floating wind turbine rigid body model, and a fluid domain numerical model based on preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size of the floating wind turbine blade, and actual operating conditions; a coupling module, configured to constrain the floating wind turbine rigid body model to the mooring system of the floating wind turbine blades under a plurality of preset sea and wind conditions, and couple the floating wind turbine rigid body model with the fluid domain numerical model to generate a coupled model under each of the preset sea and wind conditions; A solution module, configured to solve the six-degree-of-freedom motion of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupled model under each of the preset sea and wind conditions, and generate a fatigue load spectrum; A construction module, configured to construct a high-fidelity finite element model of the wind turbine blade based on the wind turbine blade CAD model; a stress calculation module for obtaining the probability of occurrence of multiple sea and wind conditions in the study sea area, and determining, based on the high-fidelity finite element model of the wind turbine blade, a target cyclic load, a target wind turbine blade root motion curve, and a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade according to the probability of occurrence of each of the sea and wind conditions, preset intra-layer and inter-layer fracture parameters, and the fatigue load spectrum; A dynamic insertion module, configured to dynamically insert a cohesive force unit into the high-fidelity finite element model of the wind turbine blade based on a preset blade fracture criterion and a fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade; A fatigue life calculation module is used to calculate the target blade fatigue life of the floating wind turbine blade in the study sea area based on the linear stress-separation curve and the cohesion unit, according to the target cyclic load, the target wind turbine blade root motion curve, and the preset layer interlayer fracture parameters.

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