A method and device for calculating fatigue life of a floating wind turbine blade

Abstract

The application discloses a kind of floating fan blade fatigue life calculation method and device, to solve the technical problem that the existing floating fan blade fatigue life calculation method leads to the low accuracy of blade fatigue life calculated.Method includes constructing blade CAD model, rigid body model and fluid domain numerical model, by simulating six degrees of freedom motion under different sea conditions and generating fatigue load spectrum.Subsequently, a high-fidelity finite element model of the blade is established, combined with the probability of sea conditions and wind conditions in the study area obtained and the fracture criterion to determine the fatigue crack stress distribution, and the interlayer damage is simulated by dynamically inserting the cohesive element. Finally, based on the cohesive model, the fatigue life of the blade is calculated by the cycle hopping method. The present application can combine various sea conditions and wind conditions, consider fatigue cracks in the calculation process, simulate crack propagation, and improve the calculation accuracy of blade fatigue life while achieving high-precision fatigue life calculation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wind power generation technology, in particular to a floating wind turbine blade fatigue life calculation method and device. BACKGROUND

[0002] With the development of land and offshore wind power resources tending to saturation, deep-sea wind power development has become an inevitable trend, and the floating wind turbine is an important means to develop and utilize deep-sea wind energy. As the main component of the wind turbine, the blade will produce fatigue cracks in the material due to the combined action of periodic wind load, centrifugal force, inertia force and wave load during long-term operation.

[0003] With the increase of running time, the crack will gradually expand, eventually leading to blade failure, affecting the safe operation and service life of the wind turbine. In addition, with the large-scale and deep-sea of the floating wind turbine, the blade becomes longer and softer, and its fatigue problem becomes more prominent. High temperature, high humidity and other harsh environments will also reduce the fatigue performance of the material and shorten the fatigue life of the blade. Therefore, it is necessary to deeply study the motion response of the floating wind turbine blade under multi-field coupling and predict its fatigue life, and provide theoretical support for the structural optimization design and performance improvement of the floating wind turbine.

[0004] Most of the existing floating wind turbine blade fatigue life calculation methods only consider the case of single sea state combined with single wind condition, while in the actual operating environment of the floating wind turbine blade, the sea state and wind condition are changing all the time, even the superposition of multiple sea states and wind conditions. Therefore, the existing technology is difficult to simulate the real working environment of the floating wind turbine blade, resulting in low accuracy of the calculated blade fatigue life. SUMMARY

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

[0006] The first aspect of the present application provides a floating wind turbine blade fatigue life calculation method, comprising:

[0007] Obtaining airfoil coordinate data and airfoil geometric parameters of the 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 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 condition;

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

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

[0010] constructing a high-fidelity finite element model of the wind turbine blade based on the wind turbine blade CAD model;

[0011] obtaining a plurality of sea state and wind condition occurrence probabilities of a research sea area, and 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 based on the wind turbine blade high-fidelity finite element model, the sea state and wind condition occurrence probabilities, and preset intra-layer and inter-layer fracture parameters;

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

[0013] based on a linear stress-separation curve and the cohesive element, calculating a target blade fatigue life of the floating wind turbine blade in the research sea area according to the target cyclic load, the target wind turbine blade root motion curve, and the preset intra-layer and inter-layer fracture parameters.

[0014] Optionally, the constructing the wind turbine blade CAD model, the floating wind turbine rigid body model, and the fluid domain numerical model 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 condition comprises:

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

[0016] assigning a rigid body material attribute to the wind turbine blade CAD model to determine a wind turbine blade CAD model with a rigid body material attribute;

[0017] constructing the floating wind turbine rigid body model according to the preset boundary conditions and the wind turbine blade CAD model with the rigid body material attribute;

[0018] determining a fluid domain size according to the size of the floating wind turbine blade and the actual working condition;

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

[0020] grid the fluid domain geometry model to generate a grid-divided fluid domain geometry model;

[0021] pre-process the grid-divided fluid domain geometry model to generate a fluid domain numerical model.

[0022] Optionally, the solving the six-degree-of-freedom motion of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling of each of the preset sea state and wind condition includes:

[0023] solving the six-degree-of-freedom motion of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling of each of the preset sea state and wind condition to generate the six-degree-of-freedom motion result of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling of the coupling model corresponding to each of the preset sea state and wind condition;

[0024] adopting the wind turbine blade root motion curve and the flow field pressure load in the six-degree-of-freedom motion result of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling of the coupling model corresponding to each of the preset sea state and wind condition to constitute the fatigue load spectrum.

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

[0026] grid-dividing the wind turbine blade CAD model to generate a grid-divided wind turbine blade CAD model;

[0027] adopting the composite material attribute to the grid-divided wind turbine blade CAD model to generate the high-fidelity finite element model of the wind turbine blade.

[0028] Optionally, the determining 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 based on the sea state and wind condition occurrence probability, the preset interlayer and intralayer fracture parameters, and the fatigue load spectrum includes:

[0029] selecting the target cyclic load and the target wind turbine blade root motion curve in the fatigue load spectrum based on the sea state and wind condition occurrence probability;

[0030] applying the target wind turbine blade root motion curve to the blade root of the high-fidelity finite element model of the wind turbine blade, applying the target cyclic load to the blade surface of the high-fidelity finite element model of the wind turbine blade, and performing finite element calculation on the high-fidelity finite element model of the wind turbine blade based on the preset interlayer and intralayer fracture parameters to determine the fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade.

[0031] Optionally, the high-fidelity finite element model of the wind turbine blade is dynamically inserted with the cohesive element 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, comprising:

[0032] It is judged whether the fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade satisfies the preset blade fracture criterion;

[0033] If yes, the high-fidelity finite element model of the wind turbine blade is dynamically inserted with the cohesive element.

[0034] Optionally, the target blade fatigue life of the floating wind turbine blade in the research sea area is calculated based on the linear stress-separation amount curve, the cohesive element, the target cyclic load, the target wind turbine blade root motion curve and the preset interlayer fracture parameter, comprising:

[0035] Based on the cohesive element and the fatigue damage curve of the linear stress-separation amount curve representing the fatigue degradation effect of the cohesive strength, a wind turbine blade cohesive fatigue damage model is constructed;

[0036] The target wind turbine blade root motion curve is applied to the blade root of the wind turbine blade cohesive fatigue damage model, the target cyclic load is applied to the blade surface of the wind turbine blade cohesive fatigue damage model, and the wind turbine blade cohesive fatigue damage model is calculated by finite element method to determine the current time instant tip deflection and stress curve of each element;

[0037] According to the sea state wind occurrence probability corresponding to the target cyclic load in a calculation period, the load application time is calculated, and the current time is recorded in real time;

[0038] It is judged whether the current time reaches the load application time;

[0039] If yes, the current calculation time is recorded in real time, and it is judged whether the current calculation time reaches the preset calculation period;

[0040] If yes, the maximum stress component and the minimum stress component corresponding to each element are selected from the stress curve of each element, and the stress amplitude of each element is calculated according to the maximum stress component and the minimum stress component corresponding to each element;

[0041] The evolution rate of the damage variable with the number of cycles of each element is calculated by using the stress amplitude of each element;

[0042] 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 element, and the number of cycles of the jump period is calculated by using the maximum value of the evolution rate of the damage variable with the number of cycles.

[0043] calculating a number of skip cycles based on a number of cycles of the skip cycle and a sum of numbers of load cycles corresponding to the target cyclic load in the preset calculation period;

[0044] multiplying the number of skip cycles and the preset calculation period to determine a fatigue life predicted based on skip cycles;

[0045] calculating a fatigue life of a current period based on the fatigue life predicted based on skip cycles and the preset calculation period;

[0046] judging whether a current-time tip deflection is greater than a preset allowed maximum tip deflection;

[0047] if yes, adding the fatigue life of the current period and fatigue lives of a plurality of historical periods to determine a target blade fatigue life of the floating wind turbine blade in the research sea area.

[0048] Optionally, the method further comprises:

[0049] if the current time does not reach the load application time, jumping to perform the step of applying the target cyclic load and the target wind turbine blade root motion curve on the wind turbine blade cohesive fatigue damage model and performing finite element calculation on the wind turbine blade cohesive fatigue damage model to determine the current-time tip deflection and the stress curve of each unit.

[0050] Optionally, the method further comprises:

[0051] if the current-time tip deflection is less than or equal to the preset allowed maximum tip deflection, calculating damage variables of each unit based on an area of a damage region of the wind turbine blade cohesive fatigue damage model and areas of the units;

[0052] calculating new damage variables of each unit based on the number of cycles of the skip cycle, the damage variables of each unit and an evolution rate of the damage variables 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] taking the fatigue life of the current period as a fatigue life of a historical period and jumping to perform 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 occurrence probability of each sea state wind condition until the current-time tip deflection is greater than the preset allowed maximum tip deflection;

[0055] The fatigue life of a current period determined when the current time tip deflection is greater than the preset allowable maximum tip deflection is added to the fatigue lives of a plurality of historical periods to determine the target blade fatigue life of the floating wind turbine blade in the research sea area.

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

[0057] The acquisition module is configured to acquire 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 according to preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size of the floating wind turbine blade and actual working conditions.

[0058] The coupling module is configured to constrain the floating wind turbine rigid body model on a mooring system of the floating wind turbine blade under a plurality of preset sea state wind conditions, and couple the floating wind turbine rigid body model and the fluid domain numerical model to generate a coupled model under each of the preset sea state wind conditions.

[0059] The solving module is configured to solve 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 state wind conditions to generate a fatigue load spectrum.

[0060] The construction module is configured to construct a high-fidelity finite element model of the wind turbine blade based on the wind turbine blade CAD model.

[0061] The stress calculation module is configured to acquire occurrence probabilities of a plurality of sea state wind conditions of a research sea area, and determine 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 each of the occurrence probabilities of the sea state wind conditions, preset interlayer and intralayer fracture parameters and the fatigue load spectrum based on the high-fidelity finite element model of the wind turbine blade.

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

[0063] The fatigue life calculation module is configured to calculate the target blade fatigue life of the floating wind turbine blade in the research sea area based on a linear stress-separation curve and the cohesive element according to the target cyclic load, the target wind turbine blade root motion curve and the preset interlayer and intralayer fracture parameters.

[0064] As can be seen from the above technical solutions, the present application has the following advantages:

[0065] The technical scheme of the present application provides a floating wind turbine blade fatigue life calculation method. First, the airfoil coordinate data and airfoil geometric parameters of the floating wind turbine blade are obtained, and a wind turbine blade CAD model, a floating wind turbine rigid body model, and a fluid domain numerical model are constructed based on the preset boundary conditions, airfoil coordinate data, airfoil geometric parameters, size of the floating wind turbine blade, and actual working conditions. Then, the floating wind turbine rigid body model is constrained on the mooring system of the floating wind turbine blade under multiple preset sea state wind conditions, and the floating wind turbine rigid body model and the fluid domain numerical model are coupled to generate a coupled model under each preset sea state wind condition. The six-degree-of-freedom motion of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling is solved for each coupled model under each preset sea state wind condition to generate a fatigue load spectrum. Based on the wind turbine blade CAD model, a high-fidelity finite element model of the wind turbine blade is constructed. The occurrence probabilities of multiple sea state wind conditions in the study sea area are obtained, and based on the high-fidelity finite element model of the wind turbine blade, the target cycle load, the target wind turbine blade root motion curve, and the fatigue crack stress results corresponding to the high-fidelity finite element model of the wind turbine blade are determined according to the occurrence probabilities of the sea state wind conditions, the preset interlayer fracture parameters, and the fatigue load spectrum. 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, the high-fidelity finite element model of the wind turbine blade is dynamically inserted with a cohesive element. Finally, based on the linear stress-separation curve and the cohesive element, the target blade fatigue life of the floating wind turbine blade in the study sea area is calculated according to the target cycle load, the target wind turbine blade root motion curve, and the preset interlayer fracture parameters. Based on the above scheme, the wind turbine blade root motion curve and the flow field pressure load calculated under multiple preset sea state wind conditions are used to form a fatigue load spectrum, and the fatigue life calculation process is completed by applying the occurrence probabilities of the multiple sea state wind conditions in the study sea area to the high-fidelity finite element model of the wind turbine blade. The present application can combine multiple sea states and wind conditions, consider fatigue cracks in the calculation process, simulate crack propagation, achieve high-precision fatigue life calculation, and improve the calculation accuracy of blade fatigue life. BRIEF DESCRIPTION OF DRAWINGS

[0066] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0067] Figure 1 A step flow chart of a floating wind turbine blade fatigue life calculation method provided by the first embodiment of the present application;

[0068] Figure 2A schematic diagram of a linear traction-separation law provided for the first embodiment of the present application is shown in the figure.

[0069] Figure 3 A flowchart of a floating fan blade fatigue life calculation method provided for the first embodiment of the present application is shown in the figure.

[0070] Figure 4 A structural block diagram of a floating fan blade fatigue life calculation device provided for the second embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0071] The embodiments of the present application provide a floating fan blade fatigue life calculation method and device, which are used to solve the technical problem of low accuracy of calculated blade fatigue life caused by the fact that most of the existing floating fan blade fatigue life calculation methods only consider single sea state combined with single wind condition.

[0072] In order to make the purposes, features and advantages of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings. Obviously, the embodiments described below are only some of the embodiments of the present application, but not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0073] Please refer to Figure 1 , Figure 1 A step flowchart of a floating fan blade fatigue life calculation method provided for the first embodiment of the present application is shown in the figure.

[0074] The floating fan blade fatigue life calculation method provided by the present application comprises:

[0075] Step 101, obtaining airfoil coordinate data and airfoil geometric parameters of the floating fan blade, and constructing a fan blade CAD model, a floating fan 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 fan blade and the actual working condition.

[0076] It should be noted that the obtained airfoil coordinate data of the floating fan blade is two-dimensional coordinates of each point on the airfoil, and the airfoil geometric parameters are parameters such as chord length, twist angle and aerodynamic center of each airfoil.

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

[0078] Step S11, constructing a fan blade CAD model according to the airfoil coordinate data and the airfoil geometric parameters;

[0079] Step S12, rigid body material properties are assigned to the fan blade CAD model, and the fan blade CAD model to which the rigid body material properties are assigned is determined;

[0080] It should be noted that the floating wind turbine system mainly consists of mooring systems, floating foundations, towers, cabins, blades and other structures, as well as power transmission systems, control systems, etc. For the convenience of modeling, only the main components of the floating wind turbine including the wind wheel, tower drum, floating foundation, etc. are modeled, thereby constructing a CAD (Computer-Aided Design) model of the floating wind turbine. When modeling, it is necessary to ensure that the geometric size and shape of the model are consistent with the actual wind turbine system, especially the size and position of the key components. For example, the floating wind turbine blade CAD model is usually composed of a series of complex geometric surfaces, which are established based on airfoils. Therefore, the first step to establish the floating wind turbine blade CAD model is to determine the required blade model and obtain the relevant airfoil data (i.e. airfoil coordinate data and airfoil geometric parameters). Airfoil data can be obtained through Profili software, Airfoil tools, and NACA (National Advisory Committee for Aeronautics) website, etc. The exported blade cross-section airfoil data is the two-dimensional coordinates of each point on the airfoil. Then, according to the chord length, twist angle, aerodynamic center and other parameters of each airfoil, the three-dimensional coordinates of the points on each cross-section airfoil in the actual space are calculated using mathematical coordinate transformation formulas. Finally, the lofting function of Solidworks is used to establish the CAD model of the wind turbine blade.

[0081] Step S13, according to the pre-set boundary conditions and the fan blade CAD model to which the rigid body material properties are assigned, a floating wind turbine rigid body model is constructed;

[0082] It should be noted that, since the deformation of the floating wind turbine is not considered in the process of multi-field coupling, rigid body material properties are assigned to each component of the floating wind turbine CAD model, and boundary conditions (pre-set boundary conditions) are set. The pre-set boundary conditions refer to setting the bottom of the floating foundation as a free floating body, allowing it to move in six degrees of freedom, and being constrained by the mooring system. The fan blade is bound to the tower drum, and the tower drum is bound to the floating foundation, and moves with the floating foundation. A Cartesian-right-handed coordinate system is adopted, taking the center of gravity of the whole wind turbine as the origin of the inertial system, the z-axis is vertically upward from the vertical line of the tower, and the x-axis is projected in the z-axis plane in the direction of the normal of the disc plane, consistent with the direction of the incoming flow at infinity. Based on the above steps, the floating wind turbine rigid body model is obtained.

[0083] Step S14, according to the size of the floating wind turbine blade and the actual working condition, the size of the fluid domain is determined;

[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, preprocessing the meshed fluid domain geometric model 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 of geometric modeling, meshing and preprocessing:

[0088] (1) Geometric modeling: In order to construct a fluid domain geometric model that can truly reflect the motion state of the floating fan, and avoid the interference of fluid reflection and wake vortex on the calculation results, the size of the fluid domain should be reasonably determined according to the size and actual working condition of the floating fan. For example, the length of the fluid domain should be at least 10 times the diameter of the fan 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: The fluid domain is meshed by tetrahedron or hexahedron, and the mesh is densified around the floating fan and in the wake area, so as to better capture the flow characteristics at the fluid-structure interface and the wake vortex.

[0090] (3) Preprocessing ① Fluid model setting: The present application involves air and water, and adopts the finite volume method to solve the incompressible Navier-Stokes equation of two-phase flow, and combines the Volume of Fluid (VOF) method to capture the free surface, so as to calculate the wind load on the fan blade and tower and the wave load on the floating foundation. The RANS (Reynolds-Averaged Navier-Stokes) method is used to solve the control equation of the fluid, and a turbulence model is needed to close the equation set. The turbulence model used in the present application is a two-equation model k−ϵ SST, and the equations of the model are provided in the text. ② Material parameter setting: The fluid domain is given material properties such as density, viscosity, etc., and 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 condition at the outlet, and the rest of the surface can be set as no-slip wall boundary.

[0091] Specifically, the fluid domain model includes two parts of air domain and seawater domain. In order to construct a fluid domain geometric model which can truly reflect the motion condition of the floating wind turbine and avoid the interference of fluid reflection and wake vortex on the calculation results, the size of the fluid domain needs to be reasonably determined according to the size and actual working condition of the floating wind turbine. 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. The fluid physical parameters (including fluid density, viscosity, turbulence model, etc.) of air and seawater are set respectively, and uniform wind speed and wave spectrum are set at the inlet of the fluid domain, and pressure outlet condition is set at the outlet, and the rest of the surface can be set as no-slip wall boundary. Tetrahedron or hexahedron can be used to divide the fluid domain grid, and the grid around the floating wind turbine and the wake area is encrypted to better capture the flow characteristics at the fluid-solid interface and the wake vortex.

[0092] Further, the wind field simulation and the wave field simulation are respectively based on the principles of aerodynamics and hydrodynamics, and the finite volume method is used to solve the incompressible Navier-Stokes equation of two-phase flow (water-air), and the Volume of Fluid (VOF) method is used to capture the free surface, so as to calculate the wind load on the wind turbine blade and tower and the wave load on the floating foundation. The control equations of the fluid calculation domain include continuity equation, momentum equation and phase fraction transport equation, and their expressions are as follows:

[0093] ; (1)

[0094] ; (2)

[0095] ; (3)

[0096] wherein, and represent the fluid velocity and the grid point velocity respectively; , , are the fluid density, pressure and dynamic viscosity respectively; is the time; is the gravity acceleration; 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 a diffusion equation, where the displacement of each mesh cell diffuses from the fluid-structure interface to the stationary wall boundary. The diffusion equation can be expressed as:

[0098] (4)

[0099] where, is the diffusion coefficient, , , is a constant parameter; is the distance from the mesh point to the fluid-structure interface.

[0100] Further, the fluid governing equations are solved by using the Reynolds-Averaged Navier-Stokes (RANS) method, and a turbulence model is introduced to close the equation set for the unclosed terms in the RANS equations. The present application uses the widely used two-equation model SST. The SST model is a hybrid and model, which can overcome the shortcomings of the model in predicting the adverse pressure gradient region and the model in being too sensitive to the inlet conditions, and can automatically switch between the model and the model through a blending function. The SST model activates the model in the wall vicinity region, and switches to the model in the free stream and core region.

[0101] The SST model introduces the Turbulene kinetic energy k and the Specific dissipation rate into the transport equations:

[0102] (5)

[0103] (6)

[0104] where, is the turbulent kinetic energy; is the specific dissipation rate; is the result term; and are constants in the turbulent dissipation model, respectively and the dissipation term; is the kinematic viscosity; is the turbulent viscosity; and is the turbulent Prandtl number, 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] Further, the result term the invariant measure of the strain rate and the cross-diffusion coefficient are defined as:

[0106] ; (7)

[0107] ; (8)

[0108] ; (9)

[0109] wherein is the production term, representing the generation of turbulent kinetic energy due to the mean velocity gradient; is a model constant; is the strain rate tensor; is the turbulent Prandtl number related to .

[0110] The mixing function combined in the model is defined as:

[0111] ; (10)

[0112] wherein y is the distance to the wall; is an empirical model constant; is the lower limit value of the cross-diffusion function CD kw , .

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

[0114] ; (11)

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

[0116] Second mixing function is defined as:

[0117] (12)

[0118] Further, each coefficient in the transport equation is obtained by mixing the coefficients of the two equations

[0119] (13)

[0120] where, is the mixed coefficient of each term in the equation; is the value of near-wall region is the value of far from the wall region; F is the mixing function, which varies between 0 and 1, depending on the distance from the wall. In addition, the values of other coefficients in all equations can be seen in Table 1, and the subscripts 1 and 2 of each coefficient represent the coefficients in the

[0121] equation and the coefficients in the equation, respectively.

[0122] Table 1 Coefficients in the SST model

[0123]

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

[0125] It should be noted that the mooring system of the floating wind turbine blade is usually composed of 3 mooring cables with an interval of 120°. The required mooring parameters can be obtained by consulting the wind turbine design manual and other related materials. The floating foundation is constrained by the mooring system. The mooring load can be solved by the quasi-static catenary theory, the anchor chain lying bottom state is determined by classification discussion, and the iterative method is used for solving.

[0126] ​​​Further, in order to accurately simulate the actual working environment of the floating wind turbine, it is necessary to combine multiple sea states and wind conditions (i.e., multiple preset sea state and wind conditions). Assuming that the number of sea states is m and the number of wind conditions is n. The first sea state and the first working condition are set for the obtained fluid domain numerical model, and the rigid body model of the floating wind turbine is constrained on the mooring system of the blade of the floating wind turbine. Then the rigid body model of the wind turbine and the fluid domain numerical model are coupled, and the surface of the wind turbine is set as the fluid-structure coupling surface during the coupling process, and the coupling method is the arbitrary Lagrange-Euler method.

[0127] Step 103, solving the six-degree-of-freedom motion of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling of the coupling model under each preset sea state and wind condition, and generating a fatigue load spectrum.

[0128] The preset sea state and wind condition is the sea state and wind condition in a wide sea area.

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

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

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

[0132] It should be noted that based on the above coupling of 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, the six-degree-of-freedom motion result of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling is obtained, and the blade root motion curve and the flow field pressure load in the result are stored in the database. Under the action of multiple fields, the dynamic equation of the floating wind turbine is as follows:

[0133] ; (14)

[0134] wherein, is the mass matrix of the floating wind turbine; is the added mass matrix of the floating foundation at infinite frequency; is the acceleration vector of the wind turbine tower and the floating foundation; is the damping matrix; is the velocity vector of the wind turbine tower and the floating foundation; is the hydrostatic restoring stiffness matrix; is the displacement vector of the wind turbine tower and the floating foundation; is a pulse function applied at time t, R is a matrix of velocity pulse functions, t is time; is a velocity vector of the tower and the floating foundation at time t; is a time delay; is an aerodynamic load; is a wind pressure load on the tower; is a wave load acting on the floating foundation; is a mooring load. Next, a second sea state and a second wind condition are set, the above steps are repeated to obtain new wind turbine blade root motion curves and flow field pressure loads, which are stored in the database again. In this way, wind turbine blade root motion curves and flow field pressure loads under m sea states and n wind conditions are obtained to form a fatigue load spectrum as an external load for subsequent finite element analysis of the floating wind turbine blade.

[0135] Step 104, based on the wind turbine blade CAD model, a high-fidelity finite element model of the wind turbine blade is constructed.

[0136] Specifically, step 104 can include the following sub-steps S41-S42:

[0137] Step S41, the wind turbine blade CAD model is meshed to generate a meshed wind turbine blade CAD model;

[0138] Step S42, the meshed wind turbine blade CAD model is assigned a composite material attribute to generate a high-fidelity finite element model of the wind turbine blade.

[0139] It should be noted that the floating wind turbine blade CAD model obtained based on the above steps is imported into a finite element pre-processing software for meshing. Then, it is assigned a composite material attribute and set with interlaminar and interlaminar fracture parameters, and then the blade is layered. In terms of structure, the blade can be subdivided into four parts: web, leading edge, main beam and trailing edge. The material type, layer thickness and angle of different parts are different. Based on this, a high-fidelity finite element model of the wind turbine blade is constructed.

[0140] It should be noted that the floating wind turbine blade CAD model obtained based on the above steps is imported into a finite element pre-processing software for meshing. Then, it is assigned a composite material attribute and set with interlaminar and interlaminar fracture parameters, and then the blade is layered. In terms of structure, the blade can be subdivided into four parts: web, leading edge, main beam and trailing edge. The material type, layer thickness and angle of different parts are different. Based on this, a high-fidelity finite element model of the wind turbine blade is constructed.

[0141] Step 105, obtain the occurrence probability of a plurality of sea state 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 occurrence probability of each sea state and wind condition, the preset interlaminar and interlaminar fracture parameters, and the fatigue load spectrum.

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

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

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

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

[0146] Step S51, selecting a target cyclic load and a target wind turbine blade root movement curve in the fatigue load spectrum based on the probability of occurrence of each sea state and wind condition.

[0147] It should be noted that based on the above steps, the fatigue load spectrum composed of the wind turbine blade root movement curve and the flow field pressure load under m sea states and n wind conditions is obtained. According to actual requirements, the blade root constraint and the flow field pressure load under a sea state and b wind conditions (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 movement curve. Then the target wind turbine blade root movement curve is applied to the floating wind turbine blade root, and the target cyclic load is applied to the blade surface, and the finite element calculation of the blade structure is performed. Specifically, by investigating the natural environment of a sea area (i.e., obtaining the probability of occurrence of multiple sea states and wind conditions in the research sea area), for example, the probability of occurrence of multiple sea states and wind conditions in the research sea area includes the probability of occurrence of sea state 1 and wind condition 1 (P1), the probability of occurrence of sea state 1 and wind condition 2 (P2),..., the probability of occurrence of sea state a and wind condition b (P k ), then the fluid pressure load and root curve movement corresponding to sea state 1 and wind condition 1, sea state 1 and wind condition 2,..., sea state a and wind condition b are selected in the fatigue load spectrum in the order of sea state and wind condition occurrence probability from large to small. Assuming that in a calculation period (i.e., a preset calculation period, determined according to actual requirements, for example, one hour), if the probability of occurrence of sea state 1 and wind condition 1 (P1) > the probability of occurrence of sea state 1 and wind condition 2 (P2) > … > the probability of occurrence of sea state a and wind condition b (P k), then in the finite element calculation process, the following operations are sequentially performed: in the time of "preset calculation period × P1", the fluid pressure load corresponding to sea state 1 and wind condition 1 (denoted as target cyclic load F1) and the target root movement curve are applied to the finite element model of the wind turbine blade; in the time of "preset calculation period × P2", the fluid pressure load corresponding to sea state 1 and wind condition 2 (denoted as target cyclic load F2) and the target root movement curve are applied to the finite element model of the wind turbine blade; in the time of "preset calculation period × P k ", the fluid pressure load corresponding to sea state a and wind condition b (denoted as target cyclic load F k ) and the target root movement curve are applied to the finite element model of the wind turbine blade.

[0148] Step S52, the target wind turbine blade root movement curve is applied to the blade root of the wind turbine blade high-fidelity finite element model, the target cyclic load is applied to the blade surface of the wind turbine blade high-fidelity finite element model, and the finite element calculation is performed on the wind turbine blade high-fidelity finite element model based on the preset interlayer fracture parameter to determine the fatigue crack stress result corresponding to the wind turbine blade high-fidelity finite element model.

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

[0150] Step 106, based on the preset blade fracture criterion and the fatigue crack stress result corresponding to the wind turbine blade high-fidelity finite element model, the wind turbine blade high-fidelity finite element model is dynamically inserted with the cohesive element.

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

[0152] The cohesive element includes the cohesive element dynamically inserted between the elements that occur interlayer fracture and the cohesive element dynamically inserted between the elements that occur interlayer fracture.

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

[0154] Step S61, judging whether the fatigue crack stress result corresponding to the high-fidelity finite element model of the fan blade satisfies the preset blade fracture criterion;

[0155] Step S62, if yes, dynamically inserting the cohesive force unit to the high-fidelity finite element model of the fan blade.

[0156] It should be noted that, according to the fiber fracture criterion or the matrix cracking criterion, it is judged whether the blade has interlaminar fracture. If interlaminar fracture occurs, a cohesive force unit is dynamically inserted between the units where fracture occurs. The fiber fracture criterion is:

[0157] ; (15)

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

[0159] The matrix cracking criterion is:

[0160] ; (15)

[0161] ; (16)

[0162] wherein, , , , , , , , are the crack face normal stress component, transverse shear stress component, longitudinal shear stress component, transverse tensile strength, transverse shear strength, longitudinal shear strength, transverse friction coefficient, and longitudinal friction coefficient, respectively.

[0163] Further, according to the double stress criterion, it is judged whether the blade has interlaminar fracture. If interlaminar fracture occurs, a cohesive force unit is dynamically inserted between the units where fracture occurs. According to the double stress criterion, it is judged whether the blade has interlaminar fracture. If interlaminar fracture occurs, a cohesive force unit is dynamically inserted between the units where fracture occurs. The double stress criterion is:

[0164] ; (17)

[0165] wherein, is the normal equivalent stress component; is the tangential equivalent stress component; is the normal aggregate strength. For tangential polymerization intensity.

[0166] It is worth mentioning that if the high-fidelity finite element model of the fan blade has no interlaminar fracture and intralaminar fracture, the target flow field pressure load in the fatigue load spectrum is reselected, the target fan blade root motion curve is reselected, and the high-fidelity finite element model of the fan blade is executed again.

[0167] Step 107, based on the linear stress-separation curve and the cohesive force element, the target blade fatigue life of the floating fan blade in the study sea area is calculated according to the target cyclic load, the target fan blade root motion curve and the preset interlaminar fracture parameter.

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

[0169] Step S71, based on the cohesive force element, and using the fatigue damage curve of the linear stress-separation curve to represent the fatigue degradation effect of the cohesive strength, a fan blade cohesive fatigue damage model is constructed;

[0170] It should be noted that based on the above two kinds of cohesive force elements, the fatigue damage curve of the linear stress-separation curve is used to represent the fatigue degradation effect of the cohesive strength, thereby obtaining the fan blade cohesive fatigue model. On this basis, the cyclic jump method is combined to simulate the fatigue damage process of the fan blade.

[0171] Step S72, 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 calculated by finite element method to determine the current time tip deflection and stress curve of each element;

[0172] The stress curve of each element is the stress curve of the plurality of elements in the fan blade cohesive fatigue damage model, and the plurality of elements in the fan blade cohesive fatigue damage model include the cohesive force element and all blade elements.

[0173] Step S73, according to the probability of the corresponding sea state wind condition of the target cyclic load in a calculation period, the load time is calculated, and the current time is recorded in real time;

[0174] It should be noted that the load time is calculated by using the probability of the corresponding sea state wind condition of the target cyclic load, for example, the probability of the corresponding sea state wind condition of the target cyclic load is the probability (P1) of the occurrence of sea state 1 and wind condition 1, and the load time is the preset calculation period x P1.

[0175] Step S74, determining whether the current time reaches the load time;

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

[0177] It should be noted that if the current time does not reach the load time, the step S72 is jumped to, i.e., the current selected target cyclic load and target fan blade root motion curve are continuously applied to the fan blade cohesive fatigue damage model, so as to obtain new current time tip deflection and new stress curve of each unit, and then obtain new damage variable of each unit. For example, if the current selected target cyclic load and target fan blade root motion curve are fluid pressure load and fan blade root motion curve corresponding to the probability (P1) of occurrence of sea condition 1 and wind condition 1, and the current time does not reach the load time, the fluid pressure load and the fan blade root motion curve are continuously applied to the fan blade cohesive fatigue damage model.

[0178] In step S75, if yes, the current calculation time is recorded in real time, and it is judged 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 period, the target cyclic load and the target fan blade root motion curve need to be updated. Specifically, new target cyclic load and new target fan blade root motion curve are selected in the fatigue load spectrum according to the size of the probability of occurrence of the multiple sea conditions and wind conditions of the research sea area, and the step S52 is jumped to. For example, it is assumed that the probability of occurrence of the multiple sea conditions and wind conditions of the research sea area includes the probability (P1) of occurrence of sea condition 1 and wind condition 1, the probability (P2) of occurrence of sea condition 1 and wind condition 2, and the probability (P3) of occurrence of sea condition 1 and wind condition 3, and the probability (P1) of occurrence of sea condition 1 and wind condition 1 > the probability (P2) of occurrence of sea condition 1 and wind condition 2 > the probability (P3) of occurrence of sea condition 1 and wind condition 3. If the target cyclic load and the target fan blade root motion curve are fluid pressure load and fan blade root motion curve corresponding to the probability (P1) of occurrence of sea condition 1 and wind condition 1, the new target cyclic load and the new target fan blade root motion curve are fluid pressure load and fan blade root motion curve corresponding to the probability (P2) of occurrence of sea condition 1 and wind condition 2. Similarly, after the next target cyclic load and target fan blade root motion curve are updated, the new target cyclic load and the new target fan blade root motion curve are fluid pressure load and fan blade root motion curve corresponding to the probability (P3) of occurrence of sea condition 1 and wind condition 3.

[0180] Step S76, if yes, selecting the maximum stress component and the minimum stress component corresponding to each unit in the stress curve of each unit, and calculating the stress amplitude of each unit according to the maximum stress component and the minimum stress component corresponding to each unit;

[0181] It should be noted that the cycle jump refers to calculating a plurality of load cycles in a selected interval, and extrapolating the influence of the load cycles on the stiffness degradation in a proper manner to cover the corresponding interval. The specific steps are as follows:

[0182] Based on the stress curves of all units obtained in the above steps, the stress amplitude corresponding to each unit is calculated, and the formula is as follows:

[0183] ; (18)

[0184] wherein, 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 unit.

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

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

[0187] ; (19)

[0188] wherein, 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, selecting the maximum value of the evolution rate of the damage variable with the number of cycles in the evolution rate of the damage variable of each unit with the number of cycles, 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;

[0190] Step S79, based on the number of cycles of the jump period and the sum of the load cycle numbers corresponding to the target cyclic load in the preset calculation period, the number of jump periods is calculated;

[0191] Step S710, multiplying the number of jump periods and the preset calculation period to determine the fatigue life predicted based on the jump period;

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

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

[0194] ; (20)

[0195] Wherein, is the number of cycles of the i th jump period; is the preset maximum damage, 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] Further, according to the target cyclic load corresponding to the occurrence probability of the multiple sea state wind conditions of the research sea area, it can be known that the number of cycles corresponding to the target cyclic load in the preset calculation period (referred to as the load cycle number) is obtained by dividing the number of cycles of the jump period by the sum of the load cycle numbers corresponding to the target cyclic loads (i.e., the sum of the load cycle numbers corresponding to all target cyclic loads in a preset calculation period). The number of jump periods is obtained, and the fatigue life predicted based on the jump period is obtained by multiplying the number of jump periods by the preset calculation period. The fatigue life predicted based on the jump period is added to the fatigue life predicted based on the calculation period (as the fatigue life predicted based on the calculation period) to obtain the fatigue life of the current period. Wherein, the load cycle corresponding to the target cyclic load refers to a loading cycle, i.e., a process of starting from a certain initial value and returning to the initial value after a period. The total number of loading cycles in the loading time of a certain target cyclic load is the load cycle number corresponding to the target cyclic load. In a preset calculation period, the sum of the load cycle numbers corresponding to each target cyclic load is the total number of load cycles in the calculation period.

[0197] Step S712, determining whether the current time instant tip deflection is greater than the preset allowable maximum tip deflection;

[0198] Step S713, if yes, the fatigue life of the current period and the fatigue life of the multiple historical periods are added to determine the target blade fatigue life of the floating fan blade in the research sea area.

[0199] It should be noted that after the end of a calculation cycle, the fatigue life of the current cycle, the current time tip deflection are recorded, and then it is judged whether the blade tip deflection (current time tip deflection) exceeds the maximum allowable range (preset maximum allowable tip deflection). If it exceeds, it is determined that the blade has 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 sea area).

[0200] Optionally, it further comprises:

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

[0202] According to the cycle number of the jump cycle, the damage variable of each unit and the evolution rate of the damage variable with the cycle number, the new damage variable of each unit is calculated;

[0203] The wind turbine blade cohesive fatigue damage model is updated using the new damage variable of each unit to determine a new wind turbine blade cohesive fatigue damage model;

[0204] The fatigue life of the current cycle is taken 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 in the fatigue load spectrum based on the occurrence probability of each sea state wind condition is executed until the current time tip deflection is greater than the preset maximum allowable tip deflection;

[0205] The fatigue life of the current cycle determined when the current time tip deflection is greater than the preset maximum allowable tip deflection is added to the fatigue life of the plurality of historical cycles 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 wind turbine blade cohesive fatigue damage model relates the traction force at the fracture interface to the crack opening In connection therewith, the interface for describing the possibility of crack occurrence can be expressed as:

[0207] ; (21)

[0208] wherein, 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, the initiation of damage and the strength of the interface When the area under the traction-separation relation equals the fracture toughness G C c, the traction force drops to zero and a new crack face is formed. If a linear traction-separation law is used, the new crack face is fully formed when the crack opening displacement equals or exceeds the critical crack opening displacement c. The linear traction-separation law is shown in FIG. 6; where, Figure 2 is the maximum traction force when the crack opening displacement is 0, is the crack opening displacement when the interface is fully separated.

[0210] In the cohesive fatigue damage model of the fan blade, the damage variable d represents the degradation of the interface strength, which can be explained as the ratio between the damage area A d and the area A e corresponding to a unit, so as to obtain the damage variable d of each unit i.

[0211] Further, according to formula (22), the damage variable (the damage variable of the next calculation period) after the secondary jump is extrapolated, that is, the new damage variable of each unit, the cohesive fatigue damage model of the fan blade is updated by using the new damage variable of all units, so as to determine the new cohesive fatigue damage model of the fan blade, that is, the initial state of the cohesive fatigue damage model of the fan blade is defined by using the new damage variable of all units; wherein, the calculation process of the new damage variable of each unit is specifically:

[0212] ; (22)

[0213] wherein, is the new damage variable of the i th unit; is the damage variable of the i th unit.

[0214] It is worth mentioning that after the jump of the damage variable, the damage variable d increases to the new damage variable d , which represents the stiffness degradation in the blade, that is, the stiffness degradation of the blade of the cohesive fatigue damage model of the fan blade, so as to obtain the new cohesive fatigue damage model of the fan blade.

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

[0216] As a comparison of technical effects, reference can be made in combination with the prior art. Under the combined action of multiple loads, the blade fatigue life prediction on the floating wind turbine platform involves aerodynamics, hydrodynamics, structural dynamics and other multi-field knowledge and technology, which is a typical multi-field coupling problem. Research shows that at present, there are few studies on the fatigue life prediction of floating wind turbine blades under multi-field coupling at home and abroad, but the related research of scholars on floating wind turbines has certain enlightenment and reference significance for the present application. For example, Luo Mengjie used the rain flow counting method and the Miner criterion, combined with the S-N curve (Stress-Number of Cycles Curve, stress-life curve), and used the Mlife software (Marine Life Fatigue Analysis Software, marine structure fatigue life analysis software) to analyze the short-term fatigue damage of the tower top and tower base under the combined action of full coupling. Ni Peng calculated the fatigue life of each hot spot of the three-pontoon wind turbine foundation under the combined action of dynamic wind load, wave load, wind load and flow load by compiling a rain flow counting program, combining the S-N curve and the linear fatigue cumulative damage theory. Dai Peng et al. used the same method as Ni Peng and combined with the blade element momentum method and the beam model, and proposed a fatigue life calculation method for floating offshore wind turbine blades.

[0217] Although domestic and foreign researchers have carried out fatigue life calculation research under fluid-structure coupling for each part of the floating wind turbine, in the research of Luo Mengjie and Ni Peng, although the fatigue life of the structure of the floating wind turbine is analyzed, the analysis objects are the tower and the foundation respectively, and the wind turbine blades are not involved. The wind turbine blade is usually laid by composite materials, and its damage mechanism is more complex. Although Dai Peng et al. proposed a calculation method for the fatigue life of floating wind turbine blades, the beam model of the blade constructed by them is relatively simple and cannot accurately describe the geometric shape and complex layup of the blade, and the fatigue damage of the blade is not considered in the calculation process, resulting in low calculation accuracy of the fatigue life. In addition, most of the researches only consider the case of single sea state combined with single wind condition, while in the actual operating environment of the floating wind turbine blade, the sea state and the wind condition are changing all the time, or even the superposition of multiple sea states and wind conditions. Therefore, the prior art is difficult to simulate the real working environment of the floating wind turbine blade to accurately calculate the fatigue life of the blade.

[0218] In view of the above problems, the present application proposes a floating wind turbine blade fatigue life calculation method. Under the combined action of wind load, wave load and mooring load in the running process, the floating wind turbine blade has a severe fluid-structure coupling effect, and a high-precision blade fatigue life calculation method considering fatigue cracks is constructed, which can combine multiple sea states and wind conditions. Specifically, please refer to Figure 3, first construct the aerodynamic-hydrodynamic-mooring multi-field coupled six degrees of freedom motion calculation method of the floating wind turbine under various sea conditions and wind conditions, form the fatigue load spectrum of the calculated blade root motion curve and the flow field pressure load, apply it to the high-fidelity finite element model of the wind turbine blade, and predict the fatigue life of the wind turbine blade.

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

[0220] In the embodiment of the present application, the present application provides a floating wind turbine blade fatigue life calculation method, first, the airfoil coordinate data and the airfoil geometric parameters of the floating wind turbine blade are obtained, and the wind turbine blade CAD model, the floating wind turbine rigid body model and the fluid domain numerical model are constructed according to the preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size and the actual working condition of the floating wind turbine blade; then, the floating wind turbine rigid body model is constrained on the mooring system of the floating wind turbine blade under a plurality of preset sea conditions and wind conditions, and the floating wind turbine rigid body model and the fluid domain numerical model are coupled to generate a coupled model under each preset sea condition and wind condition; the six-degree-of-freedom motion of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling is solved for each coupled model under the preset sea condition and wind condition to generate a fatigue load spectrum; based on the wind turbine blade CAD model, a high-fidelity finite element model of the wind turbine blade is constructed; the occurrence probabilities of a plurality of sea conditions in a research sea area are obtained, and based on the high-fidelity finite element model of the wind turbine blade, the target cycle load, the target wind turbine blade root motion curve and the fatigue crack stress results corresponding to the high-fidelity finite element model of the wind turbine blade are determined according to the occurrence probabilities of the sea conditions, the preset interlayer fracture parameters and the fatigue load spectrum; 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, the high-fidelity finite element model of the wind turbine blade is dynamically inserted with a cohesive element; finally, based on the linear stress-separation amount curve and the cohesive element, the target blade fatigue life of the floating wind turbine blade in the research sea area is calculated according to the target cycle load, the target wind turbine blade root motion curve and the preset interlayer fracture parameters; based on the above scheme, the wind turbine blade root motion curve and the flow field pressure load calculated under a plurality of preset sea conditions and wind conditions can form a fatigue load spectrum, and the fatigue life calculation process is completed by applying the occurrence probabilities of a plurality of sea conditions in a research sea area to the high-fidelity finite element model of the wind turbine blade, the present application can combine a plurality of sea conditions and wind conditions, consider the fatigue crack in the calculation process, simulate crack propagation, realize high-precision fatigue life calculation, and improve the calculation accuracy of the blade fatigue life.

[0221] Please refer to Figure 4 , Figure 4 The structure block diagram of a floating wind turbine blade fatigue life calculation device provided in Embodiment Two of the present application is shown in the figure.

[0222] The floating wind turbine blade fatigue life calculation device provided by the present application comprises:

[0223] The obtaining module 401 is configured to obtain the airfoil coordinate data and the airfoil geometric parameters of the floating wind turbine blade, and construct the wind turbine blade CAD model, the floating wind turbine rigid body model and the fluid domain numerical model according to the preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size and the actual working condition of the floating wind turbine blade;

[0224] a coupling module 402, configured to constrain a floating wind turbine rigid body model on a mooring system of a floating wind turbine blade under a plurality of preset sea state and wind conditions, and to couple the floating wind turbine rigid body model and a fluid domain numerical model to generate a coupling model under each preset sea state and wind condition;

[0225] a solving module 403, configured to solve six degrees of freedom motion of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupling model under each preset sea state and wind condition to generate a fatigue load spectrum;

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

[0227] a stress calculation module 405, configured to obtain occurrence probabilities of a plurality of sea states and wind conditions in a research sea area, and to determine 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 based on the occurrence probabilities of the sea states and wind conditions, preset interlayer and intralayer fracture parameters and the fatigue load spectrum;

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

[0229] a fatigue life calculation module 407, configured to calculate a target blade fatigue life of the floating wind turbine blade in the research sea area based on a linear stress-separation curve and the cohesive element according to the target cyclic load, the target wind turbine blade root motion curve and the preset interlayer and intralayer fracture parameters.

[0230] Further, the obtaining module 401 is specifically configured to:

[0231] construct a CAD model of the wind turbine blade according to airfoil coordinate data and airfoil geometric parameters;

[0232] assign a rigid body material attribute to the CAD model of the wind turbine blade, and determine the CAD model of the wind turbine blade with the rigid body material attribute;

[0233] construct a floating wind turbine rigid body model according to preset boundary conditions and the CAD model of the wind turbine blade with the rigid body material attribute;

[0234] determine a fluid domain size according to a size and an actual working condition of the floating wind turbine blade;

[0235] construct a fluid domain geometric model based on the fluid domain size;

[0236] divide a grid for the fluid domain geometric model to generate a grid-divided fluid domain geometric model;

[0237] The fluid domain geometry model after meshing is preprocessed to generate a fluid domain numerical model.

[0238] Further, the solving module 403 is specifically configured to:

[0239] The six-degree-of-freedom motion of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling of the coupling model under each preset sea state and wind condition is solved to generate the six-degree-of-freedom motion result of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling of the coupling model under each preset sea state and wind condition.

[0240] The wind turbine blade root motion curve and the flow field pressure load in the six-degree-of-freedom motion result of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling of the coupling model under each preset sea state and wind condition are adopted to constitute a fatigue load spectrum.

[0241] Further, the constructing module 404 is specifically configured to:

[0242] The wind turbine blade CAD model is meshed to generate a meshed wind turbine blade CAD model.

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

[0244] Further, the stress calculating module 405 is specifically configured to:

[0245] Based on the occurrence probability of each sea state and wind condition, a target cyclic load and a target wind turbine blade root motion curve are selected from the fatigue load spectrum.

[0246] The target wind turbine blade root motion curve is applied to the blade root of the wind turbine blade high-fidelity finite element model, the target cyclic load is applied to the blade surface of the wind turbine blade high-fidelity finite element model, and based on preset interlayer fracture parameters, the wind turbine blade high-fidelity finite element model is calculated to determine a fatigue crack stress result corresponding to the wind turbine blade high-fidelity finite element model.

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

[0248] It is determined whether the fatigue crack stress result corresponding to the wind turbine blade high-fidelity finite element model satisfies a preset blade fracture criterion.

[0249] If yes, the wind turbine blade high-fidelity finite element model is dynamically inserted with a cohesive element.

[0250] Further, the fatigue life calculating module 407 is specifically configured to:

[0251] The fatigue damage curve of the cohesive strength is represented by a cohesive unit and a linear stress-separation curve, and a cohesive fatigue damage model of the fan blade is constructed;

[0252] A root motion curve of the target fan blade is applied to a blade root of the cohesive fatigue damage model of the fan blade, a target cyclic load is applied to a blade surface of the cohesive fatigue damage model of the fan blade, and finite element calculation is performed on the cohesive fatigue damage model of the fan blade to determine a current time instant tip deflection and stress curves of each unit;

[0253] According to a corresponding sea state wind condition occurrence probability of the target cyclic load in a calculation period, a load application time is calculated, and a current time is recorded in real time;

[0254] It is judged whether the current time reaches the load application time;

[0255] If yes, a current calculation time is recorded in real time, and it is judged whether the current calculation time reaches a preset calculation period;

[0256] If yes, the maximum stress component and the minimum stress component corresponding to each unit are selected from the stress curves of each unit, and the stress amplitude of each unit is calculated according to the maximum stress component and the minimum stress component corresponding to each unit;

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

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

[0259] The cycle number of the jump period and the sum of the load cycle numbers corresponding to the target cyclic load in the preset calculation period are used to calculate the number of jump periods;

[0260] The number of jump periods and the preset calculation period are multiplied to determine the fatigue life predicted based on the jump period;

[0261] The fatigue life of the current period is calculated according to the fatigue life predicted based on the jump period and the preset calculation period;

[0262] It is judged whether the current time instant tip deflection is greater than a preset allowable maximum tip deflection;

[0263] If yes, the fatigue life of the current period and the fatigue lives of a plurality of historical periods are added to determine the target blade fatigue life of the floating type fan blade in the research sea area.

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

[0265] The first module is configured to, if the current time does not reach the load time, jump to execute the step of applying the target cyclic load and the target fan blade root motion curve on the fan blade cohesive fatigue damage model and performing finite element calculation on the fan blade cohesive fatigue damage model to determine the current time tip deflection and the stress curve of each unit.

[0266] In an alternative device embodiment, further comprising:

[0267] The second module is configured to, if the current time tip deflection is less than or equal to the preset allowable maximum tip deflection, calculate the damage variable of each unit according to the damage area of the fan blade cohesive fatigue damage model and the area of each unit.

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

[0269] The fourth module is configured to update the fan blade cohesive fatigue damage model using the new damage variable of each unit to determine a new fan blade cohesive fatigue damage model.

[0270] The fifth module is configured to take the fatigue life of the current cycle as the fatigue life of the historical cycle, and jump to execute the step of selecting the target cyclic load and the target fan blade root motion curve in the fatigue load spectrum based on the occurrence probability of each sea state wind condition until the current time tip deflection is greater than the preset allowable maximum tip deflection.

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

[0272] The above-described embodiments are merely used to illustrate the technical solutions of the present application, rather than limit the present application; even though the present application has been described in detail with reference to the foregoing embodiments, those ordinarily skilled in the art should understand: the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalent replacements; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method of calculating fatigue life of a floating wind turbine blade, characterized by, The method comprises the following steps: 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 according to preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, the size of the floating wind turbine blade and actual working conditions; constraining the floating wind turbine rigid body model on a mooring system of the floating wind turbine blade under a plurality of preset sea state wind conditions, coupling the floating wind turbine rigid body model and the fluid domain numerical model, and generating a coupled model under each of the preset sea state wind conditions; solving 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 state wind conditions, and generating a fatigue load spectrum; constructing a high-fidelity finite element model of the wind turbine blade based on the wind turbine blade CAD model; obtaining a plurality of sea state wind condition occurrence probabilities of a research sea area, and 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 each of the sea state wind condition occurrence probabilities, preset interlayer and intralayer fracture parameters and the fatigue load spectrum based on the high-fidelity finite element model of the wind turbine blade; based on a preset blade fracture criterion and the fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade, dynamically inserting a cohesive element into the high-fidelity finite element model of the wind turbine blade; based on a linear stress-separation amount curve and the cohesive element, calculating a target blade fatigue life of the floating wind turbine blade in the research sea area according to the target cyclic load, the target wind turbine blade root motion curve and the preset interlayer and intralayer fracture parameters.

2. The floating wind turbine blade fatigue life calculation method of claim 1, wherein, The method comprises the following steps: constructing a wind turbine blade CAD model according to the airfoil coordinate data and the airfoil geometric parameters; assigning a rigid body material attribute to the wind turbine blade CAD model, and determining a wind turbine blade CAD model with the rigid body material attribute; 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 attribute; determining a fluid domain size according to the size of the floating wind turbine blade and the actual working conditions; constructing a fluid domain geometric model based on the fluid domain size; performing mesh division on the fluid domain geometric model to generate a mesh-divided fluid domain geometric model; performing pretreatment on the mesh-divided fluid domain geometric model to generate a fluid domain numerical model.

3. The floating wind turbine blade fatigue life calculation method of claim 1, wherein, The method comprises the following steps: solving 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 state wind conditions, and generating a coupled model under each of the preset sea state wind conditions; The wind turbine blade root motion curve and the flow field pressure load in the six-degree-of-freedom motion result of the floating wind turbine under the aerodynamic-hydrodynamic-mooring coupling are obtained by using the corresponding aerodynamic-hydrodynamic-mooring coupling model of each preset sea state and wind condition.

4. The floating wind turbine blade fatigue life calculation method of claim 1, wherein, The wind turbine blade high-fidelity finite element model is constructed based on the wind turbine blade CAD model, including: The wind turbine blade CAD model is meshed to generate a meshed wind turbine blade CAD model; The wind turbine blade high-fidelity finite element model is generated by assigning composite material attributes to the meshed wind turbine blade CAD model.

5. The floating wind turbine blade fatigue life calculation method of claim 1, wherein, The target cycle load, the target wind turbine blade root motion curve, and the fatigue crack stress result corresponding to the wind turbine blade high-fidelity finite element model are determined based on the sea state and wind condition occurrence probability, the preset interlayer and intralayer fracture parameters, and the fatigue load spectrum of the wind turbine blade high-fidelity finite element model, including: The target cycle load and the target wind turbine blade root motion curve are selected from the fatigue load spectrum based on the sea state and wind condition occurrence probability; The target wind turbine blade root motion curve is applied to the blade root of the wind turbine blade high-fidelity finite element model, the target cycle load is applied to the blade surface of the wind turbine blade high-fidelity finite element model, and the wind turbine blade high-fidelity finite element model is calculated based on the preset interlayer and intralayer fracture parameters to determine the fatigue crack stress result corresponding to the wind turbine blade high-fidelity finite element model.

6. The floating wind turbine blade fatigue life calculation method of claim 1, wherein, The wind turbine blade high-fidelity finite element model is dynamically inserted with a cohesive element based on the preset blade fracture criterion and the fatigue crack stress result corresponding to the wind turbine blade high-fidelity finite element model, including: It is judged whether the fatigue crack stress result corresponding to the wind turbine blade high-fidelity finite element model meets the preset blade fracture criterion; If it meets, the wind turbine blade high-fidelity finite element model is dynamically inserted with a cohesive element.

7. The floating wind turbine blade fatigue life calculation method of claim 1, wherein, The target blade fatigue life of the floating wind turbine blade in the study sea area is calculated based on the linear stress-separation amount curve and the cohesive element, the target cycle load, the target wind turbine blade root motion curve, and the preset interlayer and intralayer fracture parameters, including: A wind turbine blade cohesive fatigue damage model is constructed based on the fatigue damage curve of the linear stress-separation amount curve to represent the fatigue degradation effect of cohesive strength; The target wind turbine blade root motion curve is applied to the blade root of the wind turbine blade cohesive fatigue damage model, the target cycle load is applied to the blade surface of the wind turbine blade cohesive fatigue damage model, and the wind turbine blade cohesive fatigue damage model is calculated to determine the current time instant deflection and the stress curve of each element; The load application time is calculated according to the sea state and wind condition occurrence probability corresponding to the target cycle load in a calculation period, and the current time is recorded in real time; It is judged whether the current time reaches the load application time; If yes, the current calculation time is recorded in real time, and it is judged whether the current calculation time reaches the preset calculation period; If yes, the maximum stress component and the minimum stress component corresponding to each unit are selected from the stress curve of each unit, and the stress amplitude of each unit is calculated according to the maximum stress component and the minimum stress component corresponding to each unit; The evolution rate of the damage variable with the number of cycles of each unit is calculated by using the stress amplitude of each unit; 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 by using the maximum value of the evolution rate of the damage variable with the number of cycles; The number of jump periods is calculated based on the number of cycles of the jump period and the sum of the load cycle numbers corresponding to the target cyclic load in the preset calculation period; The fatigue life based on the jump period is determined by multiplying the number of jump periods and the preset calculation period; The fatigue life of the current period is calculated according to the fatigue life based on the jump period and the preset calculation period; It is judged whether the current time tip deflection is greater than the preset allowable maximum tip deflection; If yes, the fatigue life of the current period and the fatigue life of a plurality of historical periods are added to determine the target blade fatigue life of the floating wind turbine blade in the study sea area.

8. The floating wind turbine blade fatigue life calculation method of claim 7, wherein, Further comprising: If the current time does not reach the load application time, the step of applying the target cyclic load and the target wind turbine blade root motion curve on the wind turbine blade cohesive fatigue damage model and performing finite element calculation on the wind turbine blade cohesive fatigue damage model to determine the current time tip deflection and the stress curve of each unit is executed.

9. The floating wind turbine blade fatigue life calculation method of claim 7, wherein, Further comprising: If the current time tip deflection is less than or equal to the preset allowable maximum tip deflection, the damage variable of each unit is calculated according to the damage area of the wind turbine blade cohesive fatigue damage model and the area of each unit; The new damage variable of each unit is calculated according to the number of cycles of the jump period, the damage variable of each unit, and the evolution rate of the damage variable with the number of cycles; The new wind turbine blade cohesive fatigue damage model is determined by updating the wind turbine blade cohesive fatigue damage model using the new damage variable of each unit; The fatigue life of the current period is taken as the fatigue life of a historical period, 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 occurrence probability of each sea state wind condition is executed until the current time tip deflection is greater than the preset allowable maximum tip deflection; The fatigue life of the current period determined when the current time tip deflection is greater than the preset allowable maximum tip deflection is added to the fatigue life of a plurality of historical periods to determine the target blade fatigue life of the floating wind turbine blade in the study sea area.

10. A floating wind turbine blade fatigue life calculation device, characterized by, Comprising: The acquisition module is configured to acquire 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 according to preset boundary conditions, the airfoil coordinate data, the airfoil geometric parameters, a size of the floating wind turbine blade and an actual working condition; The coupling module is configured to constrain the floating wind turbine rigid body model on a mooring system of the floating wind turbine blade under a plurality of preset sea state and wind conditions, and couple the floating wind turbine rigid body model and the fluid domain numerical model to generate a coupling model under each of the preset sea state and wind conditions; The solving module is configured to solve six-degree-of-freedom motion of the floating wind turbine under aerodynamic-hydrodynamic-mooring coupling for the coupling model under each of the preset sea state and wind conditions to generate a fatigue load spectrum; The construction module is configured to construct a high-fidelity finite element model of the wind turbine blade based on the wind turbine blade CAD model; The stress calculation module is configured to acquire occurrence probabilities of a plurality of sea state and wind conditions of a research sea area, and determine 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 occurrence probabilities of the sea state and wind conditions, preset interlayer and intralayer fracture parameters and the fatigue load spectrum based on the high-fidelity finite element model of the wind turbine blade; The dynamic insertion module is configured to insert a cohesive element into the high-fidelity finite element model of the wind turbine blade based on a preset blade fracture criterion and the fatigue crack stress result corresponding to the high-fidelity finite element model of the wind turbine blade; The fatigue life calculation module is configured to calculate a target blade fatigue life of the floating wind turbine blade in the research sea area according to the target cyclic load, the target wind turbine blade root motion curve and the preset interlayer and intralayer fracture parameters based on a linear stress-separation curve and the cohesive element.

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