A method and system for fatigue damage analysis of a floating wind turbine floating body structure

Abstract

The present invention relates to the technical field of fatigue analysis of floating body structures, and specifically discloses a method and system for fatigue damage analysis of a floating wind turbine floating body structure. The method includes: constructing a model of the floating wind turbine; obtaining the response of the wind load acting on the structural cross-section of the floating body structure under different wind conditions only considering the action of wind; under the condition of the wind turbine being shut down, obtaining the response of the wave load acting on the structural cross-section under different wave actions only considering the action of waves; obtaining the total load response at the structural cross-section under the corresponding marine environmental conditions; converting the total load response into local nominal stress; calculating the short-term fatigue damage under the corresponding marine environmental conditions; and calculating the long-term fatigue damage. The present invention solves the problems of large computational amount and long calculation time brought by the existing fully coupled time-domain analysis, improves the fatigue analysis efficiency while ensuring the calculation accuracy, and can quickly and accurately perform long-term fatigue assessment in engineering applications.

Description

Technical Field

[0001] The present invention relates to the technical field of fatigue damage analysis, and particularly to a fatigue damage analysis method and system for a floating wind turbine floating body structure based on decoupling of wind and waves. Background Art

[0002] Offshore floating wind turbines are long-term affected by complex environmental loads such as wind, waves, and currents, resulting in the floating body structure facing the risk of fatigue damage.

[0003] Existing fatigue analysis methods mainly adopt the fully coupled time-domain analysis method. The analysis method has high calculation accuracy, but the calculation process is complex and the calculation amount is large, which limits large-scale engineering applications. It generally includes the following parts: (1) Wind-wave coupling calculation, considering the combined action of wind force and wave loads on the floating body structure; (2) Adopting full-time-domain coupling simulation, calculating the dynamic responses under all short-term environmental conditions, and combining the rain-flow counting method and the S-N curve to calculate fatigue damage; (3) Statistically analyzing the joint probability distribution of wind and waves to estimate long-term fatigue damage.

[0004] Due to the significant wind-wave coupling effect, a large number of time-domain calculations are required for full-coupling analysis, resulting in the calculation time usually taking several weeks or even months, seriously affecting the efficiency of engineering design and optimization; and traditional full-coupling analysis methods are difficult to apply to different floating body structures. Summary of the Invention

[0005] To solve the above technical problems, one of the purposes of the present invention is to provide a fatigue damage analysis method for a floating wind turbine floating body structure. By decoupling wind and waves and respectively calculating the responses under wind load action and wave load action, the wind-wave stress is obtained to estimate short-term fatigue damage, solving the problems of large calculation amount and long calculation time brought by the existing full-coupling time-domain analysis, improving the fatigue analysis efficiency while ensuring calculation accuracy, and being able to quickly and accurately perform long-term fatigue assessment in engineering applications.

[0006] To achieve the above invention purpose, the present invention is implemented by adopting the following technical solutions:

[0007] The present application relates to a fatigue damage analysis method for a floating wind turbine floating body structure, including:

[0008] Constructing a model of a floating wind turbine, wherein the floating body structure in the floating wind turbine is modeled as a plurality of rigid body structure segments, and a structural section is formed between adjacent structure segments;

[0009] Only considering the action of wind force, obtaining the response of the wind load acting on the structural section of the floating body structure under different wind conditions;

[0010] In the state where the wind turbine is shut down, only considering the action of waves, obtaining the response of the wave load acting on the structural section under different wave actions;

[0011] Linearly superpose the responses of the wind loads and the responses of the wave loads corresponding to a single marine environmental condition to obtain the total load response at the structural section corresponding to the marine environmental condition;

[0012] Convert the total load response into local nominal stress;

[0013] Perform rainflow counting on the local nominal stress and combine it with the S-N curve to calculate the short-term fatigue damage corresponding to the marine environmental condition;

[0014] Integrate the short-term fatigue damages under all marine environmental conditions and combine with the joint distribution probability of the wind and wave parameters under the corresponding marine environmental conditions to estimate the long-term fatigue damage.

[0015] In some embodiments of the present application, correct the initial value of the linearly superposed total load response, specifically correct it to the initial value of the total load response obtained by using the traditional fully coupled time-domain analysis method.

[0016] In some embodiments of the present application, obtain the responses of the wind loads at the structural section of the floating body structure under different wind conditions, specifically:

[0017] Calculate the blade aerodynamic loads based on the blade element momentum theory, and the blade aerodynamic loads include wind excitation loads, impeller added mass loads, and aerodynamic damping loads;

[0018] Perform time-domain simulation for different wind conditions to obtain the responses of the wind loads at the structural section of the floating body structure under different wind conditions.

[0019] In some embodiments of the present application, obtain the responses of the wave loads at the structural section under different wave actions, specifically:

[0020] Calculate the floating body wave forces using the potential flow theory;

[0021] Calculate the floating body viscous damping forces based on the Morison equation;

[0022] Perform time-domain simulation for wave actions with different significant wave heights, spectral peak periods, and directions to obtain the responses of the wave loads at the structural section.

[0023] In some embodiments of the present application, convert the total load response into local nominal stress σ i , specifically:

[0024] Based on the Euler-Bernoulli beam theory, use the following formula for conversion:

[0025] ;

[0026] Among them, F x represents the axial force of the structural section, M y and M z respectively represent the bending moments of the said structural section about the y axis and z axis, A represents the cross-sectional area of the said structural section, W y and W z respectively represent the section moduli of the said structural section about the y axis and z axis.

[0027] In some embodiments of the present application, the following formula is adopted to calculate the short-term fatigue damage corresponding to the marine environmental conditions D :

[0028] ;

[0029] Among them, n represents the number of load cycles corresponding to the stress range △s, i represents the i th stress range, and N is the fatigue damage cycle number given by the S-N curve.

[0030] In some embodiments of the present application, the following formula is adopted to calculate the long-term fatigue damage D tot :

[0031] ;

[0032] Among them, p is the joint distribution probability of the wind and wave parameters, θ i represents the i th wind and wave direction, j represents the j th marine environmental condition, U w , H s and T p respectively represent the average wind speed, significant wave height and spectral peak period.

[0033] The floating wind turbine floating body structure fatigue damage analysis method involved in some embodiments provided by the present application has the following advantages and beneficial effects:

[0034] (1) Decouple the wind and wave loads, calculate the response of the wind load acting on the structural section of the floating body structure under different wind conditions and the response of the wave load acting on the structural section of the floating body structure under different wave conditions respectively, and then perform stress superposition in the post-processing stage. Compared with the full coupling of wind and waves, the computational amount is greatly reduced, and the demand for high-performance computing resources is significantly reduced;

[0035] (2) The decoupled calculation method can effectively reduce the number of working conditions, enabling the complete fatigue damage analysis of the floating body structure to be completed within a few days. Compared with the traditional full coupling analysis that takes weeks or even longer, the decoupled calculation method significantly shortens the calculation time and greatly improves the efficiency of engineering design and optimization;

[0036] (3) This application conducts fatigue damage analysis based on the structural section of the floating body structure, which is applicable to different floating body structures (such as semi-submersible, tension leg type, Spar type) and different floating body structure types (such as three-column semi-submersible type, four-column semi-submersible type), and can also be applicable to a variety of marine environmental conditions, making the fatigue damage analysis method based on wind-wave decoupling more widely used in engineering;

[0037] (4) The fatigue damage analysis method of the floating body structure based on wind-wave decoupling estimates the fatigue damage contribution under different wind and wave conditions through the statistical integration method of marine environmental conditions, improving the accuracy of long-term fatigue life assessment.

[0038] Some embodiments of this application also relate to a fatigue damage analysis system for a floating wind turbine floating body structure, including:

[0039] A unit model construction module, which is used to construct a model of the floating wind turbine. Among them, the floating body structure in the floating wind turbine is modeled as multiple rigid body structural segments, and a structural section is formed between adjacent structural segments;

[0040] A wind load acquisition module, which is used to acquire the response of the wind load acting on the structural section of the floating body structure under different wind conditions;

[0041] A wave load acquisition module, which is used to acquire the response of the wave load acting on the structural section under different waves when the wind turbine is in a shutdown state;

[0042] A total load response acquisition module, which is used to linearly superpose the response of the wind load acting and the response of the wave load acting under a single marine environmental condition to obtain the total load response at the structural section under the corresponding marine environmental condition;

[0043] A response-stress conversion module, which is used to convert the total load response into local nominal stress;

[0044] The short-term fatigue damage calculation module is used to perform rainflow counting on the local nominal stress and combine it with the S-N curve to calculate the short-term fatigue damage corresponding to the marine environmental conditions.

[0045] The long-term fatigue damage calculation module is used to integrate the short-term fatigue damages under all marine environmental conditions and combine the joint distribution probability of the wind and wave parameters under the corresponding marine environmental conditions to estimate the long-term fatigue damage.

[0046] After reading the specific embodiments of the present invention in conjunction with the accompanying drawings, other features and advantages of the present invention will become clearer. Description of the Drawings

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0048] Figure 1 is a flowchart of an embodiment of the fatigue damage analysis method for the floating wind turbine floating body structure proposed in this application;

[0049] Figure 2 is a model simulation of the floating wind turbine involved in the embodiment of the fatigue damage analysis method for the floating wind turbine floating body structure proposed in this application;

[0050] Figure 3 shows the time-domain response of the bending moment of the third structural section of the floating body structure of the wind turbine under the rated wind speed condition by using the embodiment of the fatigue damage analysis method for the floating wind turbine floating body structure proposed in this application and the time-domain response of the bending moment of the third structural section of the floating body structure of the wind turbine under the rated wind speed condition by using the traditional fully coupled time-domain analysis method M y and the time-domain response of the bending moment of the third structural section of the floating body structure of the wind turbine under the cut-out wind speed condition by using the embodiment of the fatigue damage analysis method for the floating wind turbine floating body structure proposed in this application and the time-domain response of the bending moment of the third structural section of the floating body structure of the wind turbine under the cut-out wind speed condition by using the traditional fully coupled time-domain analysis method M y comparison diagram;

[0051] Figure 4 shows the time-domain response of the bending moment of the third structural section of the floating body structure of the wind turbine under the cut-out wind speed condition by using the embodiment of the fatigue damage analysis method for the floating wind turbine floating body structure proposed in this application and the time-domain response of the bending moment of the third structural section of the floating body structure of the wind turbine under the cut-out wind speed condition by using the traditional fully coupled time-domain analysis method M y and the time-domain response of the bending moment of the third structural section of the floating body structure of the wind turbine under the cut-out wind speed condition by using the traditional fully coupled time-domain analysis method M y comparison diagram;

[0052] Figure 5Shows a comparison chart of short-term fatigue damages under different average wind speed conditions obtained at the third structural section of the floating body structure by using the fatigue damage analysis method proposed in this application and the traditional fully coupled time-domain analysis method respectively;

[0053] Figure 6 Shows a comparison chart of long-term fatigue damages at the first structural section evaluated by using the fatigue damage analysis method of this application and the traditional fully coupled time-domain analysis method at six different offshore locations;

[0054] Figure 7 Shows a comparison chart of long-term fatigue damages at the second structural section evaluated by using the fatigue damage analysis method of this application and the traditional fully coupled time-domain analysis method at six different offshore locations;

[0055] Figure 8 Shows a comparison chart of long-term fatigue damages at the third structural section evaluated by using the fatigue damage analysis method of this application and the traditional fully coupled time-domain analysis method at six different offshore locations. Detailed implementation manners

[0056] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0057] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. In the description of the present invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0058] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations. In the description of the above embodiments, specific features, structures, materials or characteristics can be combined in a suitable manner in any one or more embodiments or examples.

[0059] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0060] To solve the problems of long calculation period, large amount of calculation and inapplicability to different floating body structures brought by the traditional fully coupled time-domain analysis method when evaluating the fatigue damage of floating body structures, refer to Figure 1 , this application relates to a method for analyzing the fatigue damage of a floating wind turbine floating body structure.

[0061] Figure 1 The flowchart showing the method for analyzing the fatigue damage of a floating wind turbine floating body structure is based on a floating wind turbine floating body structure fatigue damage analysis system and is as follows. The method for analyzing the fatigue damage of a floating wind turbine floating body structure will be described in conjunction with the floating wind turbine floating body structure fatigue damage analysis system.

[0062] Refer to Figure 1 , and the method for analyzing the fatigue damage of a floating wind turbine floating body structure will be described in detail as follows.

[0063] S1: Build a model of a floating wind turbine.

[0064] The floating wind turbine mainly includes a wind turbine (including an impeller and a hub), a rotating shaft, a nacelle, a tower, a floating body structure and a mooring chain.

[0065] This model building can be achieved by using a unit model building module (not shown) in the floating wind turbine floating body structure fatigue damage analysis system.

[0066] In some embodiments of the present application, a model of a 10MW floating wind turbine is established using SIMA software. Among them, the floating body modeling is decomposed into multiple rigid body structure segments by using a multi-segment floating body modeling method, and adjacent structure segments are connected by high-stiffness beam elements for calculating the load response of the internal structure section of the floating body structure.

[0067] The modeling process of the wind turbine also provides models of other parts of the floating wind turbine except the floating body structure (including the upper unit part and the mooring system of the floating wind turbine). There is a coupling effect between the floating body structure and the upper unit part and the mooring system. Taking the floating body structure as the research object, the upper unit part and the mooring system will both bring external load effects to the floating body structure, and the load is transferred through the contact position. Therefore, when focusing on the floating body structure, the upper unit part and the mooring system provide complete boundary conditions for the floating body structure to ensure the calculation accuracy of the structural section response under the marine environment (i.e., the wind and wave environment) conditions.

[0068] The above modeling process of the wind turbine is prior art and will not be elaborated here.

[0069] Refer to the schematic diagram of the modeling of the wind turbine Figure 2 as shown. Three structural cross-sections in the floating body structure are exemplarily shown (the left yellow part shows the floating body structure, and cross-section 1 marked with data 1 on it is denoted as the first structural cross-section, cross-section 2 marked with data 2 is denoted as the second structural cross-section, and cross-section 3 marked with data 3 is denoted as the third structural cross-section). The structural cross-sections are located between adjacent structural segments, and the internal load response of the floating body structure is the stress acting on the structural cross-sections.

[0070] S2: Obtain the response of the wind load acting on the structural cross-section of the floating body structure under different wind conditions.

[0071] The obtaining of this wind load can be achieved by using the wind load obtaining module (not shown) in the fatigue damage analysis system of the floating wind turbine floating body structure.

[0072] In some embodiments of the present application, the internal load response of the floating body structure is obtained by using the wind-wave decoupling analysis method, that is, the response of the wind load acting and the response of the wave load acting are calculated separately.

[0073] In some embodiments of the present application, refer to Figure 2 the left part in. The wind turbine is set to the normal operating state, considering the wind turbine control effect, and then considering the aero-structural-control system coupling effect, without considering the wave action.

[0074] Based on the blade element momentum (BEM) theory, calculate the blade aerodynamic load, including the wind excitation load, the impeller added mass load, and the aerodynamic damping load.

[0075] Specifically, the blade aerodynamic load is calculated according to the load coefficient description in the airfoil library file and the blade element momentum theory method. This part of the technology is prior art.

[0076] Furthermore, perform time-domain simulation for different wind conditions to obtain the response of the wind load acting on the structural cross-section of the floating body structure under different wind conditions, that is, using dynamic inflow, the BEM method will give the correct time series of the rotor and blade loads (that is, the time series of the response of the internal structural cross-section of the floating body structure) under the conditions of changing the blade pitch angle, wind speed, wind direction, and tower motion.

[0077] The above-mentioned different wind conditions include the rated wind speed condition, the cut-in wind speed condition, the cut-out wind speed condition, and the shutdown wind speed condition.

[0078] As described above, for a given structural section, considering only the action of wind, the responses of wind load under different wind conditions can be obtained.

[0079] S3: Obtain the responses of wave loads at the structural section under different wave actions.

[0080] The obtaining of this wave load can be achieved by using a wave load obtaining module (not shown) in the fatigue damage analysis system of the floating wind turbine floating body structure.

[0081] In some embodiments of the present application, referring to Figure 2 the right part in, when calculating the response of wave load action, the wind turbine is set to the shutdown state, the aerodynamic load and control system effect of the wind turbine are not considered, and only the wave action is considered.

[0082] The hydrodynamic coefficients of each structural segment are calculated using the potential flow theory, including added mass, potential flow damping, and wave excitation force transfer function, and then the wave force of the floating body structure is calculated.

[0083] The viscous damping force of each structural segment is calculated based on the viscous damping force term in the Morison equation.

[0084] And further, time-domain simulations are carried out for different wave actions with significant wave height, spectral peak period, and direction (i.e., different wave actions) to obtain the responses of wave loads at the structural section.

[0085] The process of obtaining the responses of wave loads as described above is also the prior art and will not be elaborated here.

[0086] As described above, for a given structural section, in the shutdown state of the wind turbine, considering only the wave action, the responses of wave loads under different wave actions can be obtained.

[0087] S4: Obtain the total load response at the structural section corresponding to the marine environmental conditions.

[0088] The obtaining process of this total load response can be achieved by using a total load response obtaining module (not shown) in the fatigue damage analysis system of the floating wind turbine floating body structure.

[0089] The marine environmental conditions as described above are the wind-wave environmental conditions. For example, a single marine environmental condition is a wave with a significant wave height of 5m, a spectral peak period of 9s, and a wind speed of 11m / s.

[0090] For a given structural section, the responses of wind load action and wave load action corresponding to a single marine environmental condition are linearly superimposed to obtain the total load response.

[0091] As described above, through the wind-wave decoupling analysis method, the responses of wind loads under different wind conditions of a given structural section have been obtained in S2, and the responses of wave loads under different wave actions of the given structural section have been obtained in S3. Therefore, when the given structural section is under an actual single marine environmental condition, the corresponding responses of wind loads and wave loads can be linearly superimposed.

[0092] For example, for the third structural section, the total load response calculation under an actual single marine environmental condition with a significant wave height of 5m, a spectral peak period of 9s for waves, and a wind speed of 11m / s is the sum of the linear superposition of the corresponding wind load response at a wind speed of 11m / s in S2 and the wave load response corresponding to waves with a significant wave height of 5m and a spectral peak period of 9s in S3.

[0093] Therefore, the total load response of any structural section under an actual marine environmental condition can be calculated according to requirements, and then the fatigue damage of any structural section can be calculated, improving the universality of this analysis method in engineering applications. Therefore, it is applicable to different floating body structures (such as semi-submersible, tension leg type, Spar type) and different floating body structure types (such as three-column semi-submersible type, four-column semi-submersible type), and can also be applicable to a variety of marine environmental conditions.

[0094] In some embodiments of the present application, in order to avoid the repetition of the initial static response of the structural section under wind loads and wave loads, the initial value of the total load response after linear superposition is corrected to eliminate the repeated calculation effect, so as to accurately reflect the dynamic response under the combined action of wind and waves.

[0095] In some embodiments of the present application, the initial value of the total load response after the corrected linear superposition (denoted as C, for example) is equal to the initial value after linear superposition (denoted as A, for example) minus the difference between it and the initial value of the total load response obtained by using the traditional fully coupled time-domain analysis method (denoted as B, for example), that is, C = A - (A - B), that is, the initial value C of the total load response after the corrected linear superposition is the initial value B of the total load response obtained by using the traditional fully coupled time-domain analysis method.

[0096] S5: Convert the total load response to local nominal stress.

[0097] The process of obtaining this local nominal stress can be implemented by using a response-stress conversion module (not shown) in the fatigue damage analysis system of the floating wind turbine floating body structure.

[0098] In some embodiments of the present application, in order to evaluate the fatigue damage of the internal load of the floating body structure, based on the Euler-Bernoulli beam theory, the following formula (1) is used to convert the total load response to local nominal stress.

[0099] (1)

[0100] Wherein, σ i represents the local nominal stress, F x represents the axial force of the structural section (such as the third structural section), M y and M z respectively represent the bending moments of the structural section (such as the third structural section) about the y axis and z axis, A represents the cross-sectional area of the structural section (such as the third structural section), W y and W z respectively represent the section moduli of the structural section (such as the third structural section) about the y axis and z axis.

[0101] Wherein, W y = I y / R, W z = I z / R, I y and I z respectively represent the moment of inertia of the structural section (such as the third structural section) about the y axis and z axis, and R is the radius of gyration.

[0102] Wherein, xyz the coordinate system where it is located is a coordinate system established with the x direction as the axial force, y and z direction conforming to the right-hand rule.

[0103] S6: Calculate the short-term fatigue damage corresponding to the marine environmental conditions.

[0104] The process of obtaining this short-term fatigue damage can be implemented by using the short-term fatigue damage calculation module (not shown) in the fatigue damage analysis system of the floating wind turbine floating body structure.

[0105] The local nominal stress σ i obtained in S5, for the local nominal stress σ iThe rainflow meter is used to extract the load cycles, and combined with the S-N curve, the short-term fatigue damage corresponding to the marine environmental conditions is calculated using the following formula (2). D .

[0106] The S-N curve is a curve with the fatigue strength of the standard specimen of the material as the ordinate and the logarithm of the fatigue life lgN as the abscissa, which represents the relationship between the fatigue strength and the fatigue life of the standard specimen under a certain cycle characteristic, and is also called the stress-life curve.

[0107] (2)

[0108] Wherein, n represents the number of load cycles corresponding to the stress range △s, i represents the i th stress range, N is the number of fatigue damage cycles given by the S-N curve, which can be given by the S-N curve.

[0109] S7: Calculate the long-term fatigue damage.

[0110] The process of obtaining this long-term fatigue damage can be implemented by using the long-term fatigue damage calculation module (not shown) in the fatigue damage analysis system of the floating wind turbine floating body structure.

[0111] In some embodiments of the present application, by means of the statistical integration method of marine environmental conditions, combined with the joint distribution probability of wind and wave parameters, the fatigue damage contribution under different wind and wave environmental conditions is estimated to estimate the long-term fatigue damage and achieve the accuracy of long-term fatigue life assessment.

[0112] In some embodiments of the present application, the following formula (3) is used to calculate the long-term fatigue damage D tot .

[0113] (3)

[0114] Wherein, p is the joint distribution probability of wind and wave parameters, θ i represents the i th wind and wave direction, j represents the j th marine environmental condition, U w , H s and T p respectively represent the mean wind speed, significant wave height and spectral peak period.

[0115] It should be noted that the joint distribution probability pThere are existing probability distributions for each sea area in general.

[0116] See Figures 3 to 8 , which gives the comparative analysis results of the calculation results obtained by using the traditional fully coupled time-domain analysis method and the calculation results obtained by using the fatigue damage analysis method involved in this application.

[0117] See Figure 3 , which shows the time-domain response curve of the bending moment of the third structural section of the floating body structure of the wind turbine under the rated wind speed condition by using the fatigue damage analysis method of this application (that is, Figure 3 the decoupling method marked in M y ), and the time-domain response curve of the bending moment of the third structural section of the floating body structure of the wind turbine under the rated wind speed condition by using the traditional fully coupled time-domain analysis method M y (see the red curve), and the time-domain response curve of the bending moment of the third structural section of the floating body structure of the wind turbine under the rated wind speed condition by using the traditional fully coupled time-domain analysis method

[0118] See Figure 4 , which shows the time-domain response curve of the bending moment of the third structural section of the floating body structure of the wind turbine under the cut-out wind speed condition by using the fatigue damage analysis method of this application (that is, Figure 4 the decoupling method marked in M y ), and the time-domain response curve of the bending moment of the third structural section of the floating body structure of the wind turbine under the cut-out wind speed condition by using the traditional fully coupled time-domain analysis method M y (see the blue curve).

[0119] It can be seen from Figure 3 and Figure 4 that the time-domain response results of the bending moment of the third structural section M y obtained by using the fatigue analysis method involved in this application are highly consistent with the time-domain response results of the bending moment of the third structural section M y obtained by using the traditional fully coupled time-domain analysis method. Therefore, it also indirectly reflects that the fatigue damage loss method based on the decoupling of wind and waves in this application still maintains the accuracy as that of the traditional fully coupled time-domain analysis method in time-domain response calculation.

[0120] Figure 5 shows the comparison chart of short-term fatigue damage under different average wind speed conditions obtained by using the fatigue damage analysis method proposed in this application and the traditional fully coupled time-domain analysis method at the third structural section of the floating body structure, where LC1-LC15 correspond to the conditions with average wind speeds ranging from 1 m / s to 29 m / s, with a wind speed interval of 2 m / s, covering the complete condition range from the cut-in to the shutdown of the wind turbine.

[0121] Based on Figure 5 the results shown, the short-term fatigue damage involved in the present application and the short-term fatigue damage involved in the traditional fully coupled time-domain analysis method are calculated respectively. It can be known that the maximum relative difference under different average wind speed conditions is about 15%, retaining the high accuracy of the traditional fully coupled time-domain analysis method for calculating short-term fatigue damage and ensuring the accuracy of estimating short-term fatigue damage by using the method of the present application.

[0122] Figure 6 A comparison diagram showing the long-term fatigue damage at the first structural section evaluated by using the fatigue damage analysis method of the present application and the traditional fully coupled time-domain analysis method at six different offshore locations.

[0123] Figure 7 A comparison diagram showing the long-term fatigue damage at the second structural section evaluated by using the fatigue damage analysis method of the present application and the traditional fully coupled time-domain analysis method at six different offshore locations.

[0124] Figure 8 A comparison diagram showing the long-term fatigue damage at the third structural section evaluated by using the fatigue damage analysis method of the present application and the traditional fully coupled time-domain analysis method at six different offshore locations.

[0125] Among them, the six different offshore locations are selected as Norwegian North Sea 1, Norwegian North Sea 2, Norwegian North Sea 3, Norwegian North Sea 4, Norwegian North Sea 5 and the South China Sea.

[0126] See Figures 6 to 8 , for these six different offshore locations, the traditional fully coupled time-domain analysis method and the method of the present application respectively carried out 10182 and 1590 one-hour simulation analyses. The calculation cost of the method of the present application is reduced by about 84% (i.e., 1 - 1590 / 10182 = 84%), significantly reducing the calculation cost, making the demand for high-performance computing resources significantly reduced, and shortening the fatigue damage analysis cycle and improving the engineering design iteration efficiency.

[0127] Based on Figures 6 to 8 the results shown in, at the first structural section, the second structural section and the third structural section, the maximum percentage difference between the long-term fatigue damage estimated by the method of the present application and the traditional fully coupled method is about 15%, retaining the high accuracy of the traditional fully coupled time-domain analysis method for calculating long-term fatigue damage and ensuring the accuracy of estimating long-term fatigue damage by using the method of the present application.

[0128] The method provided by the present application is based on the decoupling of wind and waves. On the premise of ensuring the calculation accuracy, it greatly improves the fatigue damage assessment efficiency, providing an efficient and feasible solution for the structural optimization and engineering application of floating wind turbines.

[0129] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; 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 claimed by the present invention.

Claims

1. A method for analyzing fatigue damage of a floating wind turbine floating body structure, characterized in that, including: building a model of a floating wind turbine, wherein the floating body structure in the floating wind turbine is modeled as multiple rigid body structure segments, and a structural cross-section is formed between adjacent structure segments; only considering the action of wind force, obtaining the response of the wind force load acting on the structural cross-section of the floating body structure under different wind conditions; in the shutdown state of the wind turbine, only considering the action of waves, obtaining the response of the wave load acting on the structural cross-section under different wave actions; linearly superposing the wind force load response and the wave load response at the structural cross-section corresponding to a single marine environmental condition to obtain the total load response at the structural cross-section corresponding to the marine environmental condition; converting the total load response into local nominal stress; performing rainflow counting on the local nominal stress and combining with the S-N curve to calculate the short-term fatigue damage corresponding to the marine environmental condition; integrating the short-term fatigue damage under all marine environmental conditions and combining with the joint distribution probability of the wind-wave parameters under the corresponding marine environmental conditions to calculate the long-term fatigue damage.

2. The method for analyzing the fatigue damage of the floating body structure of a floating wind turbine according to claim 1, wherein correcting the initial value of the linearly superposed total load response, specifically correcting it to the initial value of the total load response obtained by using the traditional fully coupled time-domain analysis method.

3. The fatigue damage analysis method of the floating wind turbine floating body structure according to claim 1, wherein, Obtaining the response of the wind force load acting on the structural cross-section of the floating body structure under different wind conditions, specifically: calculating the blade aerodynamic load based on the blade element momentum theory, and the blade aerodynamic load includes wind excitation load, impeller added mass load and aerodynamic damping load; performing time-domain simulation for different wind conditions to obtain the response of the wind force load acting on the structural cross-section of the floating body structure under different wind conditions.

4. The fatigue damage analysis method for the floating wind turbine floating body structure according to claim 1, wherein, Obtaining the response of the wave load acting on the structural cross-section under different wave actions, specifically: calculating the floating body wave force by using the potential flow theory; calculating the floating body viscous damping force based on the Morison equation; performing time-domain simulation for the wave actions with different significant wave heights, spectral peak periods and directions to obtain the response of the wave load at the structural cross-section.

5. The fatigue damage analysis method of the floating wind turbine floating body structure according to claim 1, characterized in that, Convert the total load response into local nominal stress σ i , specifically: Based on the Euler-Bernoulli beam theory, the conversion is performed using the following formula: ； Among them, F x represents the axial force of the structural section, M y and M z respectively represent the bending moments of the said structural section about y axis and z axis, A represents the cross-sectional area of the said structural section, W y and W z respectively represent the section moduli of the said structural section about y axis and z axis.

6. The fatigue damage analysis method for the floating wind turbine floating body structure according to claim 1, characterized in that, Use the following formula to calculate the short-term fatigue damage corresponding to the marine environmental conditions D : ； wherein, n represents the number of load cycles corresponding to the stress range △s, i represents the i th stress range, and N is the fatigue damage cycle number given by the S-N curve.

7. The fatigue damage analysis method of the floating wind turbine floating body structure according to claim 6, wherein The long-term fatigue damage is calculated using the following formula D tot : ; Among them, p is the joint distribution probability of wind and wave parameters, θ i represents the i th wind and wave direction, j represents the j th marine environmental condition, U w , H s and T p represent the mean wind speed, significant wave height and spectral peak period respectively.

8. A fatigue damage analysis system for a floating wind turbine floating body structure, characterized in that, including: a unit model building module, which is used to build a model of a floating wind turbine, wherein the floating body structure in the floating wind turbine is modeled as multiple rigid body structure segments, and a structural cross-section is formed between adjacent structure segments; a wind force load obtaining module, which is used to only consider the action of wind force and obtain the response of the wind force load acting on the structural cross-section of the floating body structure under different wind conditions; a wave load obtaining module, which is used to only consider the action of waves in the shutdown state of the wind turbine and obtain the response of the wave load acting on the structural cross-section under different wave actions; a total load response obtaining module, which is used to linearly superpose the wind force load response and the wave load response corresponding to a single marine environmental condition to obtain the total load response at the structural cross-section corresponding to the marine environmental condition; a response-stress conversion module, which is used to convert the total load response into local nominal stress; a short-term fatigue damage calculation module, which is used to perform rainflow counting on the local nominal stress and combine with the S-N curve to calculate the short-term fatigue damage corresponding to the marine environmental condition; A long-term fatigue damage calculation module, which is used to integrate the short-term fatigue damage under all marine environmental conditions and estimate the long-term fatigue damage in combination with the joint distribution probability of the wind and wave parameters under the corresponding marine environmental conditions.

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