A time-domain analysis method for local stress of floating wind turbine structure foundation based on multi-body coupling analysis

Abstract

The present invention provides a method for time-domain coupling analysis of local stress of the floating foundation of an offshore floating wind power structure, which is applicable to the field of deep-sea floating wind power generation. Aiming at the problem of time-domain calculation of local stress coupling of the floating foundation of a floating wind power structure, the present invention obtains the coupled motion state of the floating wind power structure by establishing a multi-body analysis model, and then realizes the calculation of the wave distribution load of the floating foundation by replaying the wave surface time history and motion state, and combines the solution of the time-domain potential flow, and obtains the local time-domain stress of the floating foundation by load mapping and solving the control equation; then, by performing probability statistical analysis and Fourier analysis on the time-domain stress, combined with random signal reconstruction and derivation methods, the batch random propagation of local stress is realized, and then the local ultimate strength verification and local fatigue strength verification of the structure are completed by the extreme value analysis method and fatigue damage analysis theory.

Description

Technical Field

[0001] The invention belongs to the technical field of offshore wind power generation, and in particular relates to a time-domain coupling analysis method for local stress of a floating body foundation of an offshore floating wind power structure. Background Art

[0002] In recent years, offshore wind power has developed rapidly, especially the development of deep-sea wind power has become an important direction for the development of offshore wind power in the future. If the development of offshore wind power is to be expanded to deep-water areas, floating wind turbine technology must be adopted. Offshore floating wind turbine systems usually include four parts: wind turbines, towers, floating foundations, and mooring systems. Compared with land wind turbines or offshore fixed wind turbines, the dynamic response of floating wind turbines during service is more complex. In the working state, floating wind turbines not only have flexible deformations of blades, towers, and floating foundations and drive instructions of the cabin control system, but also have 6-degree-of-freedom rigid body motions of floating foundations and dynamic responses of anchor chains. During service, offshore floating wind turbines will be subjected to the combined effects of wind, waves, and ocean currents. These environmental loads do not act independently on the offshore floating wind turbine system, but have a certain coupling relationship with each other. For example, offshore floating wind turbines will produce rigid body motions under the action of environmental loads, and the rigid body motions of the floating body will affect the air loads and hydrodynamic loads on the floating wind turbines. Considering the coupling between aerodynamics, hydrodynamics, control systems and structural dynamics, accurately predicting the movement of offshore floating foundations, especially the structural stress of floating foundations under different environmental loads, has always been the focus and difficulty of research in the field of floating wind turbines.

[0003] With the launch of China's first floating wind turbine "Three Gorges Leader", domestic floating wind turbine technology has gradually transitioned from conceptual design to detailed design. The design of floating wind turbines cannot only focus on its motion response, but the stress response of the floating foundation structure is also extremely important for the optimal design of the floating foundation. The stress analysis of the floating foundation structure of floating wind turbines is mostly based on the design method of offshore oil platforms. However, there are few reports on the analysis method of its local stress. This is because the local stress coupling analysis in the pure time domain has the following difficulties:

[0004] ① The floating wind power structure is a multi-subsystem joint engineering equipment. When the wind turbine system, floating foundation and mooring system are subjected to wind, wave and current loads, the load calculation theories are different, spanning the air and water dynamics, and there are complex motion boundary coupling and force transmission between the subsystem dynamic responses.

[0005] ② The wave load calculation of floating foundations mostly adopts the frequency domain potential flow theory. In the calculation based on multi-body dynamics, the floating foundation is mostly treated as a rigid particle, which only serves as the motion coupling and force transmission medium between the upper wind turbine system and the lower mooring system. The multi-body dynamic response calculation method currently used in the industry is essentially unable to obtain the time domain local stress of the floating foundation coupled with the wind turbine system and mooring system.

[0006] ③ At present, the local strength verification of the floating foundation is carried out by transforming the Cummins equation from the frequency domain to the time domain based on the frequency domain potential flow solution. This approach is not time domain coupling because the Cummins equation cannot discuss the real motion of the floating foundation under the interaction of multiple subsystems, nor can it discuss various nonlinear problems.

[0007] ④ Many studies use computational fluid dynamics methods to conduct fully coupled stress analysis of floating foundations. This method effectively considers the viscosity problem and subsystem coupling, but it is not suitable for actual engineering. Its huge amount of calculation is an impossible task for the hundreds of working conditions that need to be verified in actual engineering. Summary of the invention

[0008] The purpose of the present invention is to provide a time-domain analysis method for local stress of a floating wind power structure foundation based on multi-body coupling analysis in view of the deficiencies in the prior art.

[0009] To this end, the above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0010] A time-domain analysis method for local stress of a floating wind power structure foundation based on multi-body coupling analysis comprises the following steps:

[0011] S1. Establishing a floating body foundation surface element model of a floating wind power structure;

[0012] S2. Calculate the basic hydrodynamic coefficient of the floating body;

[0013] Based on the mass distribution, compartment arrangement and ballast water arrangement of the floating foundation, the frequency domain potential flow solution method is used to calculate the hydrostatic restoring force coefficient, frequency-dependent additional mass coefficient, frequency-dependent additional damping coefficient, frequency-dependent first-order wave force RAOs, and frequency-dependent second-order wave force transfer function QTF of the floating foundation.

[0014] S3. Establish a multi-body coupled motion analysis model for floating wind power structures;

[0015] Establish a wind turbine tower model, a wind turbine nacelle model, a wind turbine blade model, a Morrison bar model of a floating foundation truss, and a mooring cable model, and import the floating foundation model established in step S1 and the hydrodynamic coefficients and mass properties in step S2;

[0016] S4. Perform time domain calculation of multi-body coupled motion response of floating wind turbine structure;

[0017] S5. After completing the time domain analysis of the motion response of the overall structure, derive the wave surface time history of the time domain calculation condition, the interface load time history of the wind turbine tower and the floating foundation, the mooring load time history at the fairlead hole, and the 6-DOF motion time history of the floating foundation (including displacement, velocity and acceleration);

[0018] S6, based on the wave surface time history and motion time history derived in step S5, the wave load on the floating body basic panel model at each time step is calculated by the direct solution method of Green's function in time domain of the three-dimensional Rankine source method;

[0019] S7, establish a floating foundation structure model including ribs, map the surface element wave load calculated in step S6 as a surface load to each surface unit of the structure model, map the mooring load time history at the fairlead hole obtained in step S5 as a point load to the node at the fairlead hole position of the structure model, map the interface load time history between the wind turbine tower and the floating foundation obtained in step S5 as a surface distributed load to the structure model, map the acceleration time history obtained in step S5 as an inertia load to each surface unit and rod unit of the structure model, and finally solve the following equation based on the boundary conditions to obtain the local stress time history of the structure model;

[0020]

[0021] σ=E:ε

[0022]

[0023] Where: ε is the strain tensor, u is the displacement vector, E is the elasticity tensor, σ is the stress tensor, and f is the force vector;

[0024] S8, performing probability statistical analysis on the local stress time history obtained in step S7 to obtain the first four central statistical moments thereof;

[0025] S9, performing Fourier analysis on the local stress time history obtained in step S7 to obtain a power spectrum function;

[0026] S10. Establish a third-order Hermite transformation general model based on the following equation and solve its model transformation coefficient:

[0027] Transformation model:

[0028] Model coefficients:

[0029]

[0030] Where: X is the local stress time history; X s is the standardized local stress time history; μ x is the mean value of the local stress time history; σ xis the standard deviation of the local stress time history; k, h0 is the model coefficient to be determined.

[0031] This general model is different from the traditional Hermite transformation model and can be applied to both super-Gaussian random processes with kurtosis greater than 3 and sub-Gaussian random processes with kurtosis less than 3.

[0032] S11, solving the underlying Gaussian stress power spectrum based on Rice theory, the model transformation coefficient of step S10 and the stress power spectrum of step 9;

[0033] S12, using the SRM (Spectral representation method) method to numerically multiply a large number of underlying Gaussian stresses;

[0034] S13, establishing a third-order Hermite transformation general model based on the model transformation coefficient of step S10, performing nonlinear mapping on the bottom Gaussian stress obtained in step S12, and obtaining the local structural numerical derived stress of the floating structure;

[0035] S14, extracting the maximum value in the derived stress time history obtained in step S13 as the extreme stress to determine whether it exceeds the allowable value of the structural material, thereby realizing the local ultimate strength check of the structure;

[0036] S15. Perform rain flow counting on the derived stress time history obtained in step S13, and combine it with the SN curve to obtain the fatigue cumulative damage of the structure, so as to realize the local fatigue strength verification of the structure.

[0037] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0038] As a preferred technical solution of the present invention: the step S4 specifically includes the following steps:

[0039] S401. At each time step, the aerodynamic loads suffered by the wind turbine blades are solved based on the BEM method, the first-order wave potential flow force and the second-order wave potential flow force (incident potential flow force, diffraction potential flow force and radiation potential flow force) of the floating foundation are calculated based on the hydrodynamic coefficients solved in step 2, and the wave and flow loads (including drag force and inertia force) suffered by the floating foundation truss and mooring cable are solved based on the Morrison equation, and the wind load acting on the tower is calculated. Among them, the solution of the wind turbine aerodynamic load and the tower wind load and the solution of the Morrison wave and flow load on the Morrison rod require the motion state information (displacement, velocity, acceleration) of the floating foundation structure. Therefore, the motion state information of the floating foundation in the previous time step needs to be used when solving for the first time step in each time step. For the first time step of the calculation (without the previous time step as a reference), the initial information of the floating foundation motion state (displacement, velocity, acceleration) can be set to 0.

[0040] S402. Based on multi-body dynamics analysis, at each time step, the wind turbine aerodynamic load and tower wind load will be transmitted to the floating foundation through the interface between the tower and the floating foundation, and the mooring load of the mooring system will be transmitted to the floating foundation through the fairlead hole, and then the movement of the floating foundation will be solved by the following equation.

[0041]

[0042] Where: x(t), and They represent the displacement, velocity and acceleration of the six degrees of freedom of the floating foundation; M is a 6×6 mass matrix; A ∞ is the 6×6 additional mass matrix at infinite frequency; C is the 6×6 hydrostatic restoring force matrix; F wind (t) is the wind load on the wind turbine and tower; F wave (t), F curr (t), F moor (t) are the wave load, flow load and anchor chain mooring force acting on the six degrees of freedom of the floating body; K(t) is a 6×6 time delay function matrix; the time delay function reflects the memory effect of the floating body radiation damping, which can be obtained through the floating body additional damping matrix:

[0043]

[0044] Where: B ij are the elements of the additional damping matrix;

[0045] S403. Based on multi-body dynamics analysis, at each time step, the obtained floating foundation motion result is used as the motion boundary condition of the bottom of the wind turbine tower and the motion boundary condition of the mooring cable at the fairlead hole, and steps S401 and S402 are calculated repeatedly until the newly solved floating foundation motion result converges.

[0046] As a preferred technical solution of the present invention: in step S14, the extreme value analysis can be a conventional maximum value search method, or other conventional extreme value analysis methods, such as ACER, POT method, etc.

[0047] As a preferred technical solution of the present invention: in the step 15, the stress cycle counting method used in fatigue analysis can be rain flow counting, or other methods, such as level crossing counting (LC, Level-crossing counting) method and range mean counting (RM, Range-mean counting) method.

[0048] The present invention provides a method for time-domain coupling analysis of local stress of the floating foundation of an offshore floating wind power structure, which is applicable to the field of deep-sea floating wind power generation. Aiming at the problem of time-domain calculation of local stress coupling of the floating foundation of a floating wind power structure, the present invention obtains the coupled motion state of the floating wind power structure by establishing a multi-body analysis model, and then realizes the calculation of the wave distribution load of the floating foundation by replaying the wave surface time history and motion state, and combines the solution of the time-domain potential flow, and obtains the local time-domain stress of the floating foundation by load mapping and solving the control equation; then, by performing probability statistical analysis and Fourier analysis on the time-domain stress, combined with random signal reconstruction and derivation methods, the batch random propagation of local stress is realized, and then the local ultimate strength verification and local fatigue strength verification of the structure are completed by the extreme value analysis method and fatigue damage analysis theory. The present invention proposes a time-domain analysis method for local stress of floating foundation structure based on multi-body coupling analysis, which is applied to the field of floating wind power development, so that it can realize synchronous simulation of wind, wave and current loads, synchronous analysis of dynamic response of each subsystem of the structure, time-domain coupling calculation of local stress of floating foundation structure, time-domain coupling analysis of local ultimate strength of the structure and time-domain coupling analysis of fatigue strength of the structure, and realize efficient and reliable numerical derivation of local stress, which can be applied to engineering problems such as strength verification of floating wind turbine foundation, fatigue life prediction and structural optimization.

[0049] Specifically, compared with the prior art, the present invention has the following beneficial effects:

[0050] 1) The present invention first calculates the hydrodynamic characteristic coefficient of the floating foundation through the frequency domain analysis method, and then constructs an overall motion model based on the multi-body dynamics analysis method to solve a more accurate overall coupled motion response of the structure.

[0051] 2) When solving the multi-body coupled motion response of the structure, the present invention ensures convergence of the motion coupling and force transmission between the subsystems through multi-step iterations in each time step, thereby ensuring that the load and motion solutions of each subsystem meet the consistency of the time scale and spatial state.

[0052] 3) After solving the structural motion state through coupling, the present invention will use this motion state information and the corresponding working condition information as the new solution control boundary to solve the wave load time domain of the floating foundation. In this way, the method proposed by the present invention can realize the time domain solution of the wave load of the floating foundation under the consideration of the motion coupling and force transmission of each subsystem.

[0053] 4) The present invention can further realize the local stress coupling time-domain analysis of the floating foundation under wave load, mooring load, wind turbine load and tower wind load by realizing the time-domain solution of the local wave load of the floating foundation.

[0054] 5) After obtaining the local stress time history of the floating foundation, the present invention can obtain a large amount of random stress data with the same source and nature as the numerical simulation through probability statistical analysis, Fourier analysis, random signal reconstruction and derivative technology, and then realize the local ultimate strength analysis and local fatigue strength analysis of the structure. The method proposed by the present invention avoids the problem of computing resource consumption required for extremely long simulation time in conventional time domain analysis, and greatly improves the design efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 The present invention provides a flowchart of a method for time-domain analysis of local stresses in a floating wind power structure foundation based on multi-body coupling analysis.

[0056] Figure 2 This is the stress cloud diagram of the key nodes of a floating wind turbine foundation (unit: Pa).

[0057] Figure 3 It is the hot spot stress time history of the key nodes of a floating wind turbine foundation (unit: MPa). DETAILED DESCRIPTION

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

[0059] The method for analyzing local stress of floating wind turbine structure foundation in time domain based on multi-body coupling analysis provided by the present invention mainly includes: solving the hydrodynamic coefficient of floating foundation in frequency domain, multi-body coupling time domain motion analysis of floating wind turbine, solving the dynamic water pressure of floating foundation in time domain, solving the local stress of floating foundation structure in time domain coupling, and calculating the strength and propagation of floating foundation structure.

[0060] The present invention is now described by specific embodiments:

[0061] S1. Use 3D modeling software to build a hydrodynamic surface element model of the floating body foundation. This step can use conventional software such as ANSYS, GeniE, Multisurf, or self-written programs.

[0062] S2. Import the hydrodynamic panel model into the hydrodynamic analysis software to solve the frequency domain potential flow of the floating foundation, and calculate the hydrostatic restoring force coefficient, frequency-related additional mass coefficient, frequency-related additional damping coefficient, frequency-related first-order wave force RAOs, and frequency-related second-order wave force transfer function QTF of the floating foundation. When calculating here, it is necessary to set the mass distribution information of the structure and the free surface information of the ballast water. For floating wind power structures, in water depths below 80m, it is recommended to use the full matrix QTF solution instead of the Newman approximation. This step can use conventional potential flow frequency domain analysis software such as Wamit, Wadam, Aqwa, or self-written programs.

[0063] S3. Establish a multi-body coupled motion analysis model for floating wind power structures;

[0064] Establish the wind turbine nacelle model and wind turbine blade model, including the nacelle mass distribution, wind turbine blade airfoil parameters, and blade lift and drag coefficient. This step can use aerodynamic analysis software such as Aerodyn, Bladed, Sima, or self-written programs.

[0065] Establish a wind turbine tower model, including the length, diameter, wall thickness and material constants of the tower. This step can use software such as Bladed, Orcaflex, Sima that has flexible rod wind load analysis or self-written programs.

[0066] Establish a mooring model, including mooring cable material parameters, mooring cable length, mooring radius, fairlead hole layout, anchor body selection, auxiliary buoy layout, auxiliary counterweight layout, mooring cable hydrodynamic coefficient setting, and mooring cable marine biological attachment correction. This step can use software such as Orcaflex, Riflex, etc. that have flexible unit hydrodynamic analysis or self-written programs.

[0067] S4. Integrate the wind turbine model, tower model, floating foundation model, and mooring model established in step S1 to step S3, and set environmental condition parameters, including wind, wave, current, water depth, seabed soil parameters, etc. Establish a data transmission interface for load calculation of the wind turbine model, tower model, floating foundation model, and mooring model, and perform multi-body coupling dynamic response calculation of floating wind power structure based on multi-body dynamics. This step can use software such as FAST, Sima, or self-written programs.

[0068] S5, deriving the floating body foundation motion time history, the chock load time history, the tower and floating body foundation interface load time history, and the environmental wave surface time history calculated in step S4;

[0069] S6. Replay the floating foundation motion time history and the environmental wave surface time history, solve the potential flow equation directly in the time domain, and obtain the floating foundation wave load fully coupled with the wind turbine system and mooring system. The wave load here is a distributed load, including the load time history of each surface unit on the floating foundation. This step can be achieved using Wasim or a self-written program.

[0070] S7. Establish the analysis model of the floating foundation structure, establish the transition section at the interface between the tower and the floating foundation, the ribs and stiffeners of the floating foundation, and set the plate thickness and material coefficient of each part of the floating foundation structure. This step can be achieved using GeniE or a self-written program.

[0071] The wave distribution load obtained in step S6, the load time history of the chock and the interface load time history of the tower and the floating body foundation derived in step S5, and the acceleration time history of the floating body foundation derived in step S5 are mapped to the structural analysis model established in step S7, and the local stress of the structure is solved in the time domain to obtain the time domain stress time history, such as Figure 2 , Figure 3 This step can be achieved using Sestra or a self-written program.

[0072] S8. Perform a probability statistical analysis on the local time-domain stress obtained in step S7, and calculate the first four central moments.

[0073] S9, performing Fourier analysis on the local time-domain stress obtained in step S7 to obtain a power spectrum function of the stress and calculate an autocorrelation function.

[0074] S10. Solve the third-order Hermite universal transformation model coefficients using the central moment obtained in step S8.

[0075] S11, solving the underlying Gaussian stress based on the third-order Hermite universal transformation model established in step S10, solving the underlying Gaussian stress autocorrelation function based on the local stress autocorrelation function obtained in step S9, and then converting it into a power spectrum function through Fourier transformation.

[0076] S12. Based on the underlying Gaussian stress power spectrum function obtained in step S11, a large number of derived Gaussian stresses are generated by the SRM method.

[0077] S13, mapping the derived Gaussian stress obtained in step S12 through the third-order Hermite universal transformation model obtained in step S10 to obtain the derived local time-domain stress.

[0078] S14. Perform extreme value analysis on the derived local time-domain stress and complete the ultimate strength verification.

[0079] S15. Perform rain flow counting on the derived local time domain stress and complete fatigue strength verification in combination with the material SN curve.

[0080] The above-mentioned specific implementation methods are used to explain the present invention and are only preferred embodiments of the present invention, rather than limiting the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A time-domain analysis method for local stress of floating wind power structure foundation based on multi-body coupling analysis, characterized in that: The method for analyzing local stress in the floating wind power structure foundation in the time domain based on multi-body coupling analysis comprises the following steps: S1. Establishing a floating body foundation surface element model of a floating wind power structure; S2. Calculate the basic hydrodynamic coefficient of the floating body; Based on the mass distribution, compartment arrangement and ballast water arrangement of the floating foundation, the frequency domain potential flow solution method is used to calculate the hydrostatic restoring force coefficient, frequency-dependent additional mass coefficient, frequency-dependent additional damping coefficient, frequency-dependent first-order wave force RAOs, and frequency-dependent second-order wave force transfer function QTF of the floating foundation. S3. Establish a multi-body coupled motion analysis model for floating wind power structures; Establish a wind turbine tower model, a wind turbine nacelle model, a wind turbine blade model, a Morrison bar model of a floating foundation truss, and a mooring cable model, and import the floating foundation model established in step S1 and the hydrodynamic coefficients and mass properties in step S2; S4. Perform time domain calculation of multi-body coupled motion response of floating wind turbine structure; S5. After completing the time domain analysis of the motion response of the overall structure, derive the wave surface time history of the time domain calculation condition, the interface load time history of the wind turbine tower and the floating foundation, the mooring load time history at the fairlead hole, and the 6-DOF motion time history of the floating foundation; S6, based on the wave surface time history and motion time history derived in step S5, the wave load on the floating body basic panel model at each time step is calculated by the direct solution method of Green's function in time domain of the three-dimensional Rankine source method; S7, establish a floating foundation structure model including ribs, map the surface element wave load calculated in step S6 as a surface load to each surface unit of the structure model, map the mooring load time history at the fairlead hole obtained in step S5 as a point load to the node at the fairlead hole position of the structure model, map the interface load time history between the wind turbine tower and the floating foundation obtained in step S5 as a surface distributed load to the structure model, map the acceleration time history obtained in step S5 as an inertia load to each surface unit and rod unit of the structure model, and finally solve the following equation based on the boundary conditions to obtain the local stress time history of the structure model; σ=E:ε Where: ε is the strain tensor, u is the displacement vector, E is the elasticity tensor, σ is the stress tensor, and f is the force vector; S8, performing probability statistical analysis on the local stress time history obtained in step S7 to obtain the first four central statistical moments thereof; S9, performing Fourier analysis on the local stress time history obtained in step S7 to obtain a power spectrum function; S10. Establish a third-order Hermite transformation general model based on the following equation and solve its model transformation coefficient: Transformation model: Model coefficients: Where: X is the local stress time history; X s is the standardized local stress time history; μ X is the mean value of the local stress time history; σ X is the standard deviation of the local stress time history; k, h0 is the model coefficient to be determined; S11, solving the underlying Gaussian stress power spectrum based on Rice theory, the model transformation coefficient of step S10 and the stress power spectrum of step 9; S12, using the SRM method to numerically multiply a large number of underlying Gaussian stresses; S13, establishing a third-order Hermite transformation general model based on the model transformation coefficient of step S10, performing nonlinear mapping on the bottom Gaussian stress obtained in step S12, and obtaining the local structural numerical derived stress of the floating structure; S14, extracting the maximum value in the derived stress time history obtained in step S13 as the extreme stress to determine whether it exceeds the allowable value of the structural material, thereby realizing the local ultimate strength check of the structure; S15. Perform rain flow counting on the derived stress time history obtained in step S13, and combine it with the SN curve to obtain the fatigue cumulative damage of the structure, so as to realize the local fatigue strength verification of the structure.

2. The method for local stress time domain analysis of floating wind power structure foundation based on multi-body coupling analysis according to claim 1 is characterized in that: The step S4 specifically includes the following steps: S401. At each time step, the aerodynamic loads suffered by the wind turbine blades are solved based on the BEM method, the first-order wave potential flow force and the second-order wave potential flow force of the floating foundation are calculated based on the hydrodynamic coefficients solved in step 2, the wave and flow loads suffered by the floating foundation trusses and mooring cables are solved based on the Morrison equation, and the wind loads acting on the tower are calculated; wherein, the solutions of the wind turbine aerodynamic loads and the tower wind loads and the Morrison wave and flow loads on the Morrison rods require the motion state information of the floating foundation structure, therefore, the motion state information of the floating foundation of the previous time step is required to be used in the first solution of each time step; for the first time step at the beginning of the calculation, the initial information of the motion state of the floating foundation is set to 0; S402. Based on multi-body dynamics analysis, at each time step, the wind turbine aerodynamic load and tower wind load will be transmitted to the floating foundation through the interface between the tower and the floating foundation, and the mooring load of the mooring system will be transmitted to the floating foundation through the fairlead hole, and then the motion of the floating foundation is solved by the following equation; Where: x(t), and They represent the displacement, velocity and acceleration of the six degrees of freedom of the floating foundation; M is a 6×6 mass matrix; A ∞ is the 6×6 additional mass matrix at infinite frequency; C is the 6×6 hydrostatic restoring force matrix; F wind (t) is the wind load on the wind turbine and tower; F wave (t), F curr (t), F moor (t) are the wave load, flow load and anchor chain mooring force acting on the six degrees of freedom of the floating body; K(t) is a 6×6 time delay function matrix; the time delay function reflects the memory effect of the floating body radiation damping, which can be obtained through the floating body additional damping matrix: Where: B ij are the elements of the additional damping matrix; S403. Based on multi-body dynamics analysis, at each time step, the obtained floating foundation motion result is used as the motion boundary condition of the bottom of the wind turbine tower and the motion boundary condition of the mooring cable at the fairlead hole, and steps S401 and S402 are calculated repeatedly until the newly solved floating foundation motion result converges.

3. The method for local stress time domain analysis of floating wind power structure foundation based on multi-body coupling analysis according to claim 1 is characterized in that: In step S14, the extreme value analysis may be a conventional maximum value search method or other conventional extreme value analysis methods.

4. The method for local stress time domain analysis of floating wind power structure foundation based on multi-body coupling analysis according to claim 1 is characterized in that: In step 15, the stress cycle counting method used in fatigue analysis may be rain flow counting or other methods.

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