Method, system and equipment for predicting fatigue crack initiation position and orientation of offshore wind turbine

Abstract

The invention provides an offshore wind turbine fatigue crack initiation position and orientation prediction method, system and device. The method comprises the following steps: establishing a corresponding finite element model according to geometric features of a to-be-analyzed structure; obtaining sea condition parameters of the to-be-analyzed structure, and performing implicit stress analysis on the finite element model based on the sea condition parameters to obtain stress and strain values at the centroid of each unit in the finite element model; embedding the cohesion model into an extended finite element method framework, and calculating stress and strain values at the centroid of each unit based on a fatigue crack initiation criterion of the cohesion model so as to output a dimensionless damage index of each unit; and predicting a fatigue crack initiation position and orientation based on the dimensionless damage index. According to the method, the fatigue crack initiation position and orientation of the engineering material can be quantitatively predicted, and the limitation that a cyclic cohesion model can only accurately predict the fatigue crack propagation stage is overcome.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fatigue damage prediction of engineering materials, and relates to a method and system for predicting the fatigue crack initiation position and orientation of an offshore wind turbine, and equipment. BACKGROUND

[0002] During service, offshore wind turbines are subjected to long-term combined action of wind, wave and current, etc. multi-source cyclic loads, which leads to irreversible fatigue damage of the foundation structure. These fatigue damages will eventually lead to the initiation of fatigue cracks in the process of continuous accumulation, which seriously threatens the integrity and service safety of the wind turbine structure. In order to ensure the structural performance of offshore wind turbine foundation and other marine structures during the service period, it is urgent to introduce a scientific fatigue evaluation method in the design stage. The process of structural fatigue failure usually includes the fatigue crack initiation stage and the crack propagation stage.

[0003] Traditionally, the prediction method of fatigue crack initiation position mainly relies on experience-based judgment or critical plane method. The critical plane method is to find a certain orientation of the material micro-plane, on which the fatigue damage is the most serious, so as to predict the position and direction of the most likely crack initiation. This method usually combines stress amplitude, shear stress amplitude or energy criteria to judge the critical plane where cracks are easy to initiate. However, such methods have significant limitations in practical application. First, the critical plane method usually relies on a large number of experimental empirical coefficients, and its accuracy is strongly influenced by material type, load path and environmental factors, lacking a unified and universal model basis. Secondly, it is difficult for this method to effectively couple with advanced fracture mechanics models (such as cohesive force theory), making it difficult to capture the evolution law of micro-mechanical mechanism in the process of crack initiation.

[0004] For offshore wind turbine structures subjected to long-term action of wind, wave, flow and other multi-source complex loads, these limitations are particularly prominent. The complex stress state makes the prediction accuracy and reliability of the traditional method relying on empirical coefficients greatly reduced, making it difficult to accurately reflect the fatigue damage accumulation process under the real service environment, thereby directly affecting the safety assessment and economy of the structure in the whole life cycle.

[0005] In recent years, fracture mechanics models have developed rapidly, especially the cyclic cohesive force model in fatigue prediction, which shows significant application potential.

[0006] Current research has shown that the cyclic cohesive zone model (CCZM) has significant advantages in the simulation of fatigue crack propagation behavior. For example, Roe and Siegmund applied the model to the fatigue crack propagation analysis of a double cantilever beam specimen. By using the finite element method to calculate the stress state and local material deformation at the crack tip, they introduced them as inputs into the cyclic cohesive zone model, and then obtained the material damage evolution process and crack propagation rate. The simulation results successfully reproduced the exponential relationship between the fatigue crack propagation rate and the stress intensity factor range in the Paris formula, verifying the effectiveness and physical basis of the model in crack propagation prediction.

[0007] In addition, CN113916705A discloses a fatigue crack propagation parameter acquisition and simulation method based on the cyclic cohesive zone model. This method obtains the key damage parameters and quasi-static parameters in the cohesive zone model through crack closure tests and force-opening displacement curve measurements. Combined with the finite element method, the model can dynamically analyze the stress state, local deformation, and fatigue damage evolution at the crack tip, and is used for predicting the crack propagation path and rate.

[0008] CN112883602B discloses a simulation and prediction method for multi-scale fatigue crack initiation life. This method combines atomic-scale molecular dynamics models, micro-scale polycrystalline finite element models, and macro-scale finite element models of different scales to predict fatigue crack initiation location, direction, and life. Compared with the cyclic cohesive zone model, this method also analyzes the stress state of the local structure, but does not consider the influence of factors such as load sequence on the fatigue crack initiation life in detail.

[0009] Although the above work fully demonstrates the potential and advantages of the cyclic cohesive zone model in fatigue crack propagation analysis, it cannot be used to predict the fatigue crack initiation location and orientation. SUMMARY

[0010] The present application provides a method and system for predicting the fatigue crack initiation location and orientation of an offshore wind turbine, which can solve the technical problem of being unable to predict the fatigue crack initiation location and orientation through the load range and material change characteristics during the fatigue crack initiation process.

[0011] In a first aspect, the present application provides a method for predicting the fatigue crack initiation location and orientation of an offshore wind turbine. The method comprises:

[0012] establishing a corresponding finite element model according to the geometric characteristics of the structure to be analyzed;

[0013] acquire the sea state parameters of the structure to be analyzed, and perform implicit stress analysis on the finite element model based on the sea state parameters to acquire stress and strain values at the centroids of each element in the finite element model;

[0014] embed a cohesive zone model into a framework of extended finite element method, and calculate the stress and strain values at the centroids of each element based on a fatigue crack initiation criterion of the cohesive zone model to output a dimensionless damage index of each element;

[0015] determine whether each element is a potential position of fatigue crack initiation based on the dimensionless damage index;

[0016] calculate dimensionless damage index components of the element in different orientations, and determine an orientation corresponding to a maximum dimensionless damage index component as a fatigue crack initiation orientation.

[0017] In an implementation form of the first aspect, the calculating the stress and strain values at the centroids of each element based on the fatigue crack initiation criterion of the cohesive zone model to output a dimensionless damage index of each element comprises:

[0018] calculating a dimensionless damage parameter at the centroid of each element according to the stress and strain values at the centroid of each element; the dimensionless damage parameter comprises a normal traction, a normal cohesive strength, a tangential traction, and a tangential cohesive strength;

[0019] calculating the dimensionless damage parameter as an input of the cohesive zone model to output a dimensionless damage index of each element.

[0020] In an implementation form of the first aspect, the determining whether each element is a potential position of fatigue crack initiation based on the dimensionless damage index comprises:

[0021] determining whether the dimensionless damage index of each element is 1;

[0022] if yes, the element has initiated a fatigue crack, and the calculation of the element is stopped;

[0023] if no, the element is one of the potential positions of fatigue crack initiation.

[0024] In an implementation form of the first aspect, the calculating dimensionless damage index components of the element in different orientations comprises:

[0025] establishing a local coordinate system in the element, and calculating dimensionless damage index components of the element in different orientations through an angle parameter θ and an angle parameter defining a plurality of potential fatigue crack initiation planes, wherein the angle parameter θ represents an included angle between a normal of the potential crack initiation plane and a z-axis, and the angle parameter an angle between a projection of a normal of the potential crack initiation plane in an xOy plane and an x axis;

[0026] based on the angle parameter θ and the angle parameter calculating a dimensionless damage index component of the potential fatigue crack initiation plane.

[0027] In an implementation form of the first aspect, the dimensionless damage index comprises at least one of: a dimensionless damage index f1 based on a maximum normal traction, a dimensionless damage index f2 based on a square root traction combination, a dimensionless damage index f3 based on an improved SWT parameter criterion, a dimensionless damage index f4 based on a Findley parameter.

[0028] In an implementation form of the first aspect, an expression of the dimensionless damage index f3 based on the improved SWT parameter criterion is:

[0029]

[0030] wherein T max_n denotes a maximum normal traction, Δδ amp denotes a separation amplitude, σ max_o denotes a normal cohesive strength, δ n_o denotes a normal cohesive length;

[0031] An expression of the dimensionless damage index f4 based on the Findley parameter is:

[0032]

[0033] wherein, denotes a maximum range of tangential tractions, denotes a maximum range of normal tractions, τ max_o denotes a maximum tangential cohesive strength, σ max_o denotes a maximum normal cohesive strength, k2 is a constant factor.

[0034] In an implementation form of the first aspect, the sea state parameters are obtained for a time increment step of the structure to be analyzed; the method further comprises:

[0035] If the dimensionless damage index of the potential fatigue crack initiation position unit has reached 1, it represents that the unit has failed and fatigue crack initiation has occurred, and the calculation of the unit in the time increment step is stopped;

[0036] After the fatigue crack initiation orientation of the unit which is the potential position of fatigue crack initiation is determined, the sea state parameters of the structure to be analyzed in the next time increment step are obtained, and the unit which is the potential position of fatigue crack initiation and the fatigue crack initiation orientation of the unit are predicted and updated based on the sea state parameters in the next time increment step.

[0037] In a second aspect, the present application provides a system for predicting the position and orientation of fatigue crack initiation of offshore wind turbine. The system comprises:

[0038] a model establishing module, configured to establish a corresponding finite element model according to the geometric characteristics of the structure to be analyzed;

[0039] a stress analysis module, configured to obtain the sea state parameters of the structure to be analyzed, and perform implicit stress analysis on the finite element model based on the sea state parameters to obtain the stress and strain values at the mass centers of each unit in the finite element model;

[0040] a damage index calculation module, configured to embed a cohesive zone model into the framework of extended finite element method, and calculate the stress and strain values at the mass centers of each unit based on the fatigue crack initiation criterion of the cohesive zone model to output the dimensionless damage index of each unit;

[0041] a fatigue crack initiation position prediction module, configured to determine whether each unit is a potential position of fatigue crack initiation based on the dimensionless damage index;

[0042] an orientation prediction module, configured to calculate the dimensionless damage index components of the unit which is the potential position of fatigue crack initiation in different orientations, and determine the orientation corresponding to the maximum dimensionless damage index component as the fatigue crack initiation orientation.

[0043] In a third aspect, the present application provides an electronic device, comprising a processor and a memory, wherein the memory is configured to store a computer program, and the processor is connected in communication with the memory and configured to execute the computer program to implement the method for predicting the position and orientation of fatigue crack initiation of offshore wind turbine according to any one of the first aspect of the present application.

[0044] In a fourth aspect, the present application provides a computer readable storage medium having a computer program stored thereon, wherein the computer program is executed by a processor to implement the method for predicting the position and orientation of fatigue crack initiation of offshore wind turbine according to any one of the first aspect of the present application.

[0045] As described above, the method and system for predicting the position and orientation of fatigue crack initiation of offshore wind turbine, and the electronic device have the following beneficial effects:

[0046] The offshore wind turbine fatigue crack initiation position and orientation prediction method of the present application can quantitatively predict the fatigue crack initiation position and orientation of engineering materials, considers the damage law of materials in the fatigue crack initiation stage, realizes reasonable prediction of the fatigue crack initiation process, and overcomes the limitation that the cyclic cohesive force model can only accurately predict the fatigue crack propagation stage;

[0047] The crack initiation criterion of the present application introduces a range-dependent parameter, which is more in line with the actual material damage mechanism and enhances the physical rationality of the fatigue crack initiation position and orientation prediction model;

[0048] The present application embeds the cohesive force model into the extended finite element method framework, and the fatigue crack initiation criterion based on the cohesive force model is used to predict the structure to be analyzed, which is convenient for handling complex geometric and boundary conditions in the crack initiation and propagation process. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 A scene schematic diagram of the offshore wind turbine fatigue crack initiation position and orientation prediction method described in the embodiments of the present application is shown.

[0050] Figure 2 A flowchart of the offshore wind turbine fatigue crack initiation position and orientation prediction method described in the embodiments of the present application is shown.

[0051] Figure 3 A flowchart of the offshore wind turbine fatigue crack initiation position and orientation prediction method described in the embodiments of the present application is shown.

[0052] Figure 4 A flowchart of the offshore wind turbine fatigue crack initiation position and orientation prediction method described in the embodiments of the present application is shown.

[0053] Figure 5a A schematic diagram of the foundation connection structure of the offshore wind turbine described in the embodiments of the present application is shown.

[0054] Figure 5b A schematic diagram of the stress time history of a certain unit described in the embodiments of the present application is shown.

[0055] Figure 6a A schematic diagram of the geometric model of the foundation connection structure of the offshore wind turbine described in the embodiments of the present application is shown.

[0056] Figures 6b-6d A schematic diagram of the dimensionless damage index under different crack initiation criteria described in the embodiments of the present application is shown.

[0057] Figure 7 A local coordinate diagram of a certain region described in the embodiments of the present application is shown.

[0058] Figures 8a-8dThe angle parameter θ and the angle parameter φ described in the embodiments of the present application are shown. A schematic diagram of the dimensionless damage index component distribution under combination.

[0059] Figure 9 The structural schematic diagram of the offshore wind turbine fatigue crack initiation position and orientation prediction system described in the embodiments of the present application is shown.

[0060] Figure 10 The structural schematic diagram of the electronic device described in the embodiments of the present application is shown.

[0061] Element number explanation

[0062] 1 Offshore wind turbine fatigue crack initiation position and orientation prediction system

[0063] 11 Detection device

[0064] 12 Processor device

[0065] 13 Display device

[0066] 9 Offshore wind turbine fatigue crack initiation position and orientation prediction system

[0067] 91 Model establishing module

[0068] 92 Stress analysis module

[0069] 93 Damage index calculation module

[0070] 94 Fatigue crack initiation position prediction module

[0071] 95 Orientation prediction module

[0072] 10 Electronic device

[0073] 101 Memory

[0074] 102 Processor

[0075] 103 Display

[0076] S21-S26 Steps DETAILED DESCRIPTION

[0077] The present application will be described by specific, concrete examples. Other advantages and benefits of the present application will become apparent to those skilled in the art upon consideration of this disclosure or can be learned by practice of the application. The present application can be realized and achieved by means of the structures and combinations described in this specification. In the specification, various modifications and changes can be made based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0078] It is to be noted that the diagrams provided in the following embodiments only schematically illustrate the basic concepts of the present application, and only the components related to the present application are shown in the diagrams, not drawn according to the number, shape and size of the components in actual implementation, and the type, number and proportion of each component in actual implementation can be arbitrarily changed, and the component layout type can also be more complex.

[0079] The cyclic cohesive zone model (CCZM) is a model based on continuum mechanics, which is used to describe the cohesive behavior and damage and fracture process at the material interior or interface. It assumes that there is a cohesive zone with a certain thickness at the material interior or interface, which resists separation through cohesive force. The core of the model is the traction-separation relationship (cohesive force-separation), which describes the relationship between cohesive force and relative separation displacement at the material interior. When the material is subjected to external force, relative separation displacement occurs inside the cohesive zone, and the cohesive force changes with the increase of separation displacement, and when the critical separation displacement is reached, the material breaks.

[0080] In some technical solutions, the stress state and local material deformation at the crack tip are calculated by the finite element method, and are introduced as input into the cyclic cohesive zone model, and then the material damage evolution process and crack propagation rate are obtained; in other technical solutions, the key damage parameters and quasi-static parameters in the cohesive zone model are obtained through crack closure test and force-opening displacement curve measurement. Combined with the finite element method, the model can dynamically analyze the stress state, local deformation and fatigue damage evolution at the crack tip, and is used for predicting the crack propagation path and rate.

[0081] The above technical solutions fully embody the potential and advantages of the cyclic cohesive zone model in fatigue crack propagation analysis, but due to the limitations of the model, it has not yet realized the prediction of the fatigue crack initiation location and orientation.

[0082] At least for the above problems, the embodiments of the present application provide a method and system for predicting the fatigue crack initiation location and orientation of offshore wind turbines, and equipment. The method introduces a crack initiation criterion containing range-related parameters such as traction force variation range and separation displacement variation range, to enhance the description ability of the cohesive zone model for crack behavior under complex cyclic load. The cohesive zone model is embedded in the extended finite element method framework, and the fatigue crack initiation criterion based on the cohesive zone model is coupled to calculate the local stress state of the structure and the cohesive interface response, to realize accurate prediction of the crack initiation location and orientation.

[0083] In the prediction process, firstly, the local stress and deformation state of the offshore wind turbine foundation structure at the current time step is obtained based on the extended finite element method, and is introduced into the cohesive zone model. In the model, the fatigue damage increment is calculated according to the range change of the traction force and the separation displacement, and then the total fatigue damage value of the material is obtained by integrating the damage evolution equation. Once the damage accumulation reaches the critical value, the crack initiation can be determined, and the corresponding crack initiation position and orientation can be obtained.

[0084] Figure 1 is a kind of application scene schematic diagram of offshore wind turbine fatigue crack initiation position and orientation prediction system of the embodiment of the present application. As shown in Figure 1 , it includes detection device 11, processor equipment 12, display equipment 13.

[0085] Wherein, detection device is used to detect and save sea state parameter, and send sea state parameter to processor equipment;

[0086] Processor equipment is used to receive sea state parameter, call and execute offshore wind turbine fatigue crack initiation position and orientation prediction method described in the embodiment of the present application, to produce the prediction result of fatigue crack initiation position and orientation;

[0087] Display equipment is used to receive the prediction result of fatigue crack initiation position and orientation and display, and issue warning for corresponding fatigue crack initiation position.

[0088] The technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings in the embodiments of the present application.

[0089] Figure 2 The flow chart of offshore wind turbine fatigue crack initiation position and orientation prediction method provided by the embodiment of the present application. The offshore wind turbine fatigue crack initiation position and orientation prediction method can be applied to mobile phone processor, tablet computer processor, computer processor, etc. As shown in Figure 2 , the offshore wind turbine fatigue crack initiation position and orientation prediction method provided by the embodiment of the present application includes the following steps S21 to S25.

[0090] Step S21, according to the geometric characteristics of the structure to be analyzed, the corresponding finite element model is established.

[0091] In the embodiment, the material parameters and sea state parameters of the finite element model are defined.

[0092] When defining material parameters, considering that offshore wind turbine foundation structure usually uses high-strength steel, S355 steel is selected as the material of the structure to be analyzed in the embodiment, and the elastic modulus, Poisson's ratio and yield strength of the material are set specifically;Preferably, the elastic modulus is set to 210GPa, the Poisson's ratio is set to 0.3, and the yield strength is set to 355MPa.

[0093] In setting the sea state parameter, the load condition and the boundary condition of the finite element model are defined according to the actual working condition, and preferably, the initial load of the finite element model is set.

[0094] Step S22, the sea state parameter of the structure to be analyzed is obtained, and implicit stress analysis is performed on the finite element model based on the sea state parameter to obtain the stress and strain values at the centroids of each element in the finite element model.

[0095] It should be noted that the obtained sea state parameter is the sea state parameter of the structure to be analyzed in a certain time increment step, and the stress and strain values at the centroids of each element in the obtained finite element model are calculated as the stress and strain values in the time increment step.

[0096] Specifically, the finite element analysis program is used to take the sea state parameter (including fatigue load and boundary condition) of the structure to be analyzed corresponding to the time increment step as input, and implicit stress analysis is performed on the finite element model to obtain the stress and strain values at the centroids of each element in the finite element model.

[0097] The calculation processes in the following steps S23 to S25 are all based on the calculation of the finite element model in the time increment step, which will not be described in detail in the following steps.

[0098] Step S23, the cohesive zone model is embedded into the framework of extended finite element method, and the stress and strain values at the centroids of each element are calculated based on the fatigue crack initiation criterion of the cohesive zone model to output the dimensionless damage index of each element.

[0099] In this embodiment, the cohesive zone model is embedded into the framework of extended finite element method,

[0100] In this embodiment, the stress and strain values at the centroids of each element are calculated based on the fatigue crack initiation criterion of the cohesive zone model to output the dimensionless damage index of each element, including: calculating the dimensionless damage parameter at the centroid of each element according to the stress and strain values at the centroid of each element; the dimensionless damage parameter includes: normal traction, normal cohesive strength, tangential traction, and tangential cohesive strength; and the dimensionless damage parameter is taken as the input of the cohesive zone model to calculate and output the dimensionless damage index of each element.

[0101] In this embodiment, the dimensionless damage index includes at least one of: a dimensionless damage index f1 based on maximum normal traction, a dimensionless damage index f2 based on square root traction combination, a dimensionless damage index f3 based on improved SWT parameter criterion, and a dimensionless damage index f4 based on Findley parameter.

[0102] where the dimensionless damage index f1 is used to describe the crack initiation tendency due to normal tension, whose computational expression is as follows:

[0103]

[0104] where T n represents the normal traction, <·> represents the Macaulay bracket to ensure that only positive (tensile) tractions are considered in the calculation, σ max_o represents the normal cohesive strength.

[0105] The dimensionless damage index f2 combines the normal traction and the tangential traction to reflect the damage under the multi-axial tension-shear coupling state, whose computational expression is as follows:

[0106]

[0107] where T t represents the tangential traction, τ max_o represents the tangential cohesive strength.

[0108] The dimensionless damage index f3 can represent the combined effect of the maximum traction and the cyclic separation amplitude on crack initiation, and capture the range-dependent parameter influence, whose computational expression is as follows:

[0109]

[0110] where T max_n represents the maximum normal traction, Δδ amp represents the separation amplitude, σ max_o represents the normal cohesive strength, δ n_o represents the normal cohesive length.

[0111] The dimensionless damage index f4 combines the maximum range of the normal traction and the tangential traction and their corresponding strengths, and adjusts the relative weight of the two by adjusting the parameter k2 to reflect the contribution of the mixed mode loading to crack initiation, whose computational expression is as follows:

[0112]

[0113] where, represents the maximum range of the tangential traction, represents the maximum range of the normal traction, τ max_o represents the maximum tangential cohesive strength, σ max_o represents the maximum normal cohesive strength, and k2 is a constant coefficient.

[0114] The cohesive zone model is a theoretical model that describes how micro-cracks are generated and propagated under cyclic loading. Unlike traditional models that assume a sharp crack tip, this model considers the crack tip as a "damage process zone" with cohesive forces. By simulating the mechanical behavior of the material within this zone during repeated loading, the model predicts the accumulation of fatigue damage and the eventual formation of cracks.

[0115] Among them, the extended finite element method (XFEM) is an advanced numerical method designed specifically for efficient simulation of discontinuities such as cracks. Its core advantage lies in its ability to allow cracks to pass through the mesh arbitrarily without the need for re-meshing. XFEM can accurately describe the geometry of cracks and their influence on the mechanical behavior of structures, greatly simplifying the simulation process of crack propagation.

[0116] Step S24, judging whether each unit is a potential position of fatigue crack initiation based on the dimensionless damage index.

[0117] In this embodiment, it specifically includes: judging whether the dimensionless damage index of each unit is 1; if it is 1, the unit has failed, fatigue crack initiation occurs in the unit, and the calculation of the unit is stopped; if it is not 1, the unit is one of the potential positions of fatigue crack initiation, and the unit continues to execute the following step S25.

[0118] In this embodiment, at least one dimensionless damage index corresponding to the unit calculated in step S23 is judged. If four dimensionless damage indexes are calculated in step S23, the four dimensionless damage indexes are judged respectively.

[0119] For example, the dimensionless damage index f1, the dimensionless damage index f2, the dimensionless damage index f3 of a certain unit are all 0, and the dimensionless damage index f4 is not 0, which indicates that the unit does not occur fatigue crack initiation in the criteria of the dimensionless damage index f1, the dimensionless damage index f2, the dimensionless damage index f3, and occurs fatigue crack initiation in the criterion of the dimensionless damage index f4. Then stop the calculation of the unit in the criteria of the dimensionless damage index f1, the dimensionless damage index f2, the dimensionless damage index f3 by step S25, and continue to execute the calculation of the unit in the criterion of the dimensionless damage index f4 by step S25.

[0120] Step S25, calculating the dimensionless damage index components of the unit in different orientations which is a potential position of fatigue crack initiation, and determining the orientation corresponding to the maximum dimensionless damage index component as the fatigue crack initiation orientation.

[0121] In this embodiment, the method includes: establishing a local coordinate system within the unit, and using angle parameter θ and angle parameter... Define several potential fatigue crack initiation surfaces, where the angle parameter θ represents the angle between the normal of the potential crack initiation surface and the z-axis. This represents the angle between the projection of the normal to the potential crack initiation plane onto the xOy plane and the x-axis.

[0122] Based on angle parameter θ and angle parameter Calculate the dimensionless damage index component of the potential fatigue crack initiation plane.

[0123] The potential fatigue crack initiation surface with the largest dimensionless damage index component is extracted as the fatigue crack initiation orientation.

[0124] In some implementations, such as Figure 3 and Figure 4 As shown, the method further includes: step S26, updating to the next time step increment, that is, obtaining the sea state parameters of the structure to be analyzed within the next time step increment.

[0125] In this embodiment, the method includes: if the dimensionless damage index of the element at the potential location of fatigue crack initiation reaches 1, it indicates that the element has failed and fatigue crack initiation has occurred, and the calculation of the element at the time increment step is stopped; after the fatigue crack initiation orientation of the element at the potential location of fatigue crack initiation is determined, the sea state parameters of the structure to be analyzed in the next time increment step are obtained, and the element at the fatigue crack initiation location and the fatigue crack initiation orientation of the element are predicted and updated based on the sea state parameters in the next time increment step.

[0126] Specifically, after executing step S25, the process is updated to the next time increment step, and steps S22 to S25 are repeated. At the same time, after repeating step S25, the element at the fatigue crack initiation location and the fatigue crack initiation orientation of the element are updated until the preset time history is reached, the calculation is stopped, and the final element at the fatigue crack initiation location and the fatigue crack initiation orientation of the element are output.

[0127] The following is a detailed explanation of the method for predicting the location and orientation of fatigue crack initiation in offshore wind turbines as described in the embodiments of this application, using a practical case.

[0128] This embodiment uses the NREL5MW offshore wind turbine as the structure to be analyzed to predict the location and orientation of fatigue crack initiation. Figure 5a The diagram shows the basic connection structure of the NREL 5MW offshore wind turbine.

[0129] Execute step S21, based on Figure 5aA finite element model was established for the structure. Common sea state parameters for the area where the structure is located were selected as follows: significant wave height 7.3 m, spectral peak period 11.1 s, and wind speed 28.6 m / s. The wind speed used was the one-hour average wind speed at a height of 10 meters. Based on the international standard DNV-OS-E301, the wind speed used in the calculation was determined to be 28.6 m / s, serving as the representative input value for extreme wind load conditions of the wind turbine.

[0130] Step S22 is executed to further determine the load conditions: a floating hydrodynamic model is established using the boundary element method based on potential flow theory, and the frequency domain hydrodynamic coefficients of the wind turbine foundation under wave action are obtained. The obtained frequency domain hydrodynamic loads are used as input and imported into an open-source multibody dynamics simulation platform for time-domain dynamic response simulation, simulating the overall motion response of the wind turbine under wind-wave coupled conditions. This step yields the dynamic load time history data of the wind turbine foundation under actual service conditions. Figure 5b The figure shows the stress time history of a certain element of the structure to be analyzed, which can be decomposed into membrane stress and bending stress components. A suitable time increment step is defined to decompose the stress time history to facilitate further prediction.

[0131] In step S23, the stress and strain values ​​at the centroid of each element in the finite element model within a certain time increment are taken as input. The fatigue crack initiation criterion is calculated based on the cohesive model embedded in the extended finite element method framework. The dimensionless damage index f1, dimensionless damage index f2, dimensionless damage index f3, and dimensionless damage index f4 of each element are then output to simulate the crack initiation behavior of the wind turbine's foundation connection structure during service.

[0132] Taking a representative critical location in the foundation connection structure of a wind turbine as an example, this paper analyzes its dimensionless damage index under complex wind and wave loads. Based on the fatigue crack initiation criterion of the cohesion model, the location of the crack initiation in the foundation connection structure of the wind turbine is analyzed. Multiple representative damage assessment paths are set in the finite element model, and the damage index along the paths is quantitatively analyzed.

[0133] like Figures 6a-6d As shown, where Figure 6a The geometric model of the basic connection structure of the wind turbine is shown. Three paths at the connection points of the key structures are selected on the geometric model and named Line #1, Line #2 and Line #3, respectively, to characterize the damage evolution characteristics of the high-profit concentration area.

[0134] Obtain the dimensionless damage index distribution along each path, and extract the dimensionless damage index under different crack initiation criteria. Figure 6bIn the middle, line #1 shows its dimensionless damage index f1 and dimensionless damage index f2 are low, while dimensionless damage index f3 and dimensionless damage index f4 predict a significant upward trend at the normalized distance close to 1.0, indicating that this position is the potential crack initiation point; Figure 6c In the middle, the dimensionless damage index f1, dimensionless damage index f2, dimensionless damage index f3, and dimensionless damage index f4 of line #2 all reach the minimum near the normalized distance of 0.6-0.7, while the dimensionless damage index f3 and dimensionless damage index f4 show high damage lines at both ends of the path. Figure 6d In the middle, the dimensionless damage index f1, dimensionless damage index f2, dimensionless damage index f3, and dimensionless damage index f4 of line #3 significantly increase at the normalized distance of 0.4, which corresponds to the geometric mutation area of the fan cross support structure and is the position where structural stress concentration and fatigue cracks are prone to occur.

[0135] Step S24 is performed to determine whether each unit is a potential position for fatigue crack initiation based on the dimensionless damage index f1, dimensionless damage index f2, dimensionless damage index f3, and dimensionless damage index f4 obtained above.

[0136] Step S25 is performed to calculate the dimensionless damage index components of the unit that is a potential position for fatigue crack initiation in different orientations, and the orientation corresponding to the maximum dimensionless damage index component is determined as the fatigue crack initiation orientation.

[0137] Taking the key structural connection position in the foundation connection structure of the fan as an example, the bottom connection area is selected as the research object, which is the geometric discontinuity of the fan foundation to produce stress concentration and fatigue damage.

[0138] As shown in Figure 7 , a local coordinate system is constructed to describe the spatial crack orientation in the area, and the spatial orientation angle parameter θ and angle parameter φ of the normal of all potential fatigue crack initiation planes are considered with the analysis point as the center.

[0139] The dimensionless damage index f1, dimensionless damage index f2, dimensionless damage index f3, and dimensionless damage index f4 are used to calculate the dimensionless damage index component distribution under each angle parameter θ and angle parameter φ combination, and the results are shown in . Figures 8a to 8d

[0140] Figure 8a In the middle, the dimensionless damage index f1 shows a clear diagonal symmetry distribution, and a local maximum value appears near θ = +81°; , and the maximum dimensionless damage index f1 is 2.09 x 10 -3 ​, indicating that the direction is one of the orientations in which fatigue cracks are most likely to occur.

[0141] Figure 8b In the θ = + 80° direction, the dimensionless damage index f2 shows a multi-peak distribution characteristic, and the main extreme value appears at the θ = + 80° direction.

[0142] Figure 8c In the θ = + 80° direction, the dimensionless damage index f3 shows a similar distribution mode to the dimensionless damage index f1, but the overall value is significantly increased, and the dimensionless damage index f3 is as high as 7.98 x 10 -3 , indicating that the damage prediction is more sensitive and concentrated after considering more variables.

[0143] Figure 8d In the θ = + 80° direction, the dimensionless damage index f4 shows the same overall distribution as the dimensionless damage index f1, but the multi-peak characteristic is more pronounced, and the main extreme value is still located at the θ = + 80° direction. , the dimensionless damage index f4 is as high as 8.00 x 10 -3 , which is the highest among the four criteria, indicating that this combination of orientation angles is the most likely direction for fatigue cracks to optimally grow.

[0144] The protection scope of the offshore wind turbine fatigue crack initiation position and orientation prediction method described in the embodiments of the present application is not limited to the order of execution of the steps listed in the embodiments, and any scheme realized by adding, replacing or modifying the steps of the prior art according to the principles of the present application is included in the protection scope of the present application.

[0145] The embodiments of the present application also provide an offshore wind turbine fatigue crack initiation position and orientation prediction system, which can implement the offshore wind turbine fatigue crack initiation position and orientation prediction method described in the present application. However, the implementation device of the offshore wind turbine fatigue crack initiation position and orientation prediction method described in the present application includes but is not limited to the structure of the offshore wind turbine fatigue crack initiation position and orientation prediction system listed in the embodiments, and any structure modification and replacement of the prior art according to the principles of the present application is included in the protection scope of the present application.

[0146] As shown in Figure 9 , the embodiments provide an offshore wind turbine fatigue crack initiation position and orientation prediction system 9, which comprises:

[0147] A model establishing module 91 is configured to establish a corresponding finite element model according to the geometric characteristics of a structure to be analyzed;

[0148] A stress analysis module 92 is configured to obtain sea state parameters of the structure to be analyzed, and perform implicit stress analysis on the finite element model based on the sea state parameters to obtain stress and strain values at the centroids of each element in the finite element model.​

[0149] a damage index calculation module 93 configured to embed a cohesive zone model into a framework of extended finite element method, and calculate stress and strain values at the center of mass of each element based on a fatigue crack initiation criterion of the cohesive zone model, to output a dimensionless damage index of each element;

[0150] a fatigue crack initiation location prediction module 94 configured to determine whether each element is a potential location of fatigue crack initiation based on the dimensionless damage index;

[0151] an orientation prediction module 95 configured to calculate dimensionless damage index components of each element that is a potential location of fatigue crack initiation in different orientations, and determine an orientation corresponding to a maximum dimensionless damage index component as an orientation of fatigue crack initiation.

[0152] Since the specific implementation of the embodiment corresponds to the method embodiment described above, the same details will not be repeated here.

[0153] It should be noted that the division of each module above is only a logical division of functions, and all or part of the modules can be integrated into one physical entity, or can be physically separated. These modules can all be implemented in the form of software called by a processing element; all can be implemented in the form of hardware; or some modules can be implemented in the form of software called by a processing element, and some modules can be implemented in the form of hardware. For example, the x module can be a separately established processing element, or can be integrated into a chip of the above device, in addition, the x module can also be stored in the form of program code in the memory of the above device, and the function of the x module can be called and executed by a processing element of the above device. The implementation of other modules is similar. In addition, all or part of these modules can be integrated together, or can be independently implemented. The processing element described herein can be an integrated circuit having a signal processing capability. In the implementation process, each step of the above method or each module can be completed by integrated logic circuits or instructions in the form of software in the processing element.

[0154] For example, the above modules can be one or more integrated circuits configured to implement the above methods, such as one or more Application Specific Integrated Circuits (ASICs), or one or more Digital Signal Processors (DSPs), or one or more Field Programmable Gate Arrays (FPGAs), etc. For another example, when a certain module above is implemented in the form of a processing element scheduling code, the processing element can be a general purpose processor, such as a Central Processing Unit (CPU) or other processor that can invoke code. For another example, the modules can be integrated together to be implemented in the form of a system-on-a-chip (SOC).

[0155] The application further provides a computer readable storage medium, having stored thereon a computer program. The computer program is executed by a processor to implement the offshore wind turbine fatigue crack initiation position and orientation prediction method provided in the embodiments of the application.

[0156] In the present application, any combination of one or more storage media can be used. The storage media can be a computer readable signal medium or a computer readable storage medium. The computer readable storage medium can be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, or apparatus, or any suitable combination of the above. More specific examples (a non-exhaustive list) of the computer readable storage medium include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a RAM, a ROM, an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In this document, the computer readable storage medium can be any tangible medium that contains or stores a program that can be used by or in connection with an instruction execution system, apparatus, or device.

[0157] The embodiments of the present application can also provide a computer program product including one or more computer instructions. When the computer instructions are loaded and executed on a computing device, the processes or functions described in the embodiments of the present application are generated in whole or in part. The computer instructions can be stored in a computer readable storage medium or transferred from one computer readable storage medium to another, for example, the computer instructions can be transferred from one website, computer or data center to another website, computer or data center through wired (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (such as infrared, wireless, microwave, etc.).

[0158] The computer program product is executed by a computer, and the computer executes the method described in the foregoing method embodiments. The computer program product can be a software installation package, and when the foregoing method needs to be used, the computer program product can be downloaded and executed on the computer.

[0159] The present application also provides an electronic device, please refer to Figure 10 , which is a structural schematic diagram of an electronic device 10 in an embodiment of the present application. As Figure 10 indicated, the electronic device 10 includes at least one processor 101, a memory 102, at least one network interface 103 and a user interface 105. The various components in the electronic device 10 are coupled together through a bus system 104. It can be understood that the bus system 104 is used to realize the connection and communication between the components. In addition to including a data bus, the bus system 104 also includes a power bus, a control bus and a status signal bus. However, in order to clearly illustrate, all kinds of buses are marked as the bus system in the Figure 10 .

[0160] The user interface 105 can include a display, a keyboard, a mouse, a trackball, a click gun, a key, a button, a touchpad or a touch screen, etc.

[0161] It can be understood that the memory 102 can be a volatile memory or a non-volatile memory, and can also include both volatile and non-volatile memories. Among them, the non-volatile memory can be a read-only memory (ROM), a programmable read-only memory (PROM), which is used as an external cache. By way of example but not limitation, many forms of RAM can be used, such as static random access memory (SRAM), synchronous static random access memory (SSRAM). The memory described in the embodiments of the application is intended to include but not limited to these and any other suitable category of memory.

[0162] The memory 102 in the embodiments of the application is used to store various categories of data to support the operation of the electronic device 10. Examples of these data include: any executable program for operating on the electronic device 10, such as an operating system 1021 and an application program 1022; the operating system 1021 contains various system programs, such as a framework layer, a core library layer, a driver layer, etc., for implementing various basic services and processing hardware-based tasks. The application program 1022 can contain various application programs, such as a media player (Media Player), a browser (Browser), etc., for implementing various application services. The video decoding reconstruction method provided by the embodiments of the application can be included in the application program 1022.

[0163] The method disclosed in the above embodiments of the application can be applied in the processor 101 or implemented by the processor 101. The processor 101 can be an integrated circuit chip with a processing capability of signals. In the implementation process, each step of the above method can be completed by integrated logic circuits or instructions in the form of software in the processor 101. The processor 101 described above can be a general-purpose processor, a digital signal processor (DSP), or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. The processor 101 can implement or execute the disclosed methods, steps and logic block diagrams in the embodiments of the disclosure. The general-purpose processor 101 can be a microprocessor or any conventional processor, etc. The steps of the accessory optimization method provided in conjunction with the embodiments of the application can be directly embodied as a hardware decoding processor for execution, or executed by a combination of hardware and software modules in the decoding processor. The software module can be located in a storage medium, which is located in the memory, and the processor reads the information in the memory and combines the hardware to complete the steps of the above method.

[0164] In an exemplary embodiment, the electronic device 10 can be implemented with one or more Application Specific Integrated Circuits (ASICs), DSPs, programmable logic devices (PLDs), complex programmable logic devices (CPLDs), or the like for performing the aforementioned methods.

[0165] The above-described various figures correspond to the descriptions of the flow or structure, and the parts not described in detail in a certain flow or structure can be referred to the related description of other flow or structure.

[0166] To sum up, compared with the prior art, the offshore wind turbine fatigue crack initiation position and orientation prediction method and system and the device can quantitatively predict the fatigue crack initiation position and orientation of the engineering material, consider the damage law of the material in the fatigue crack initiation stage, realize reasonable prediction of the fatigue crack initiation process, overcome the limitation that the cyclic cohesive force model can only accurately predict the fatigue crack propagation stage, introduce the crack initiation criterion of the range-dependent parameter, which is more consistent with the actual material damage mechanism and enhances the physical rationality of the fatigue crack initiation position and orientation prediction model, embed the cohesive force model in the extended finite element method framework, and predict the structure to be analyzed based on the fatigue crack initiation criterion of the cohesive force model, which is convenient for processing the complex geometric and boundary conditions in the crack initiation and propagation process. Therefore, the present application effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0167] The above-described embodiments only exemplarily illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above-described embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought of the present application should be covered by the claims of the present application.

Claims

1. A method of predicting fatigue crack initiation location and orientation for offshore wind turbines, characterized by, The method comprises the following steps: establishing a corresponding finite element model according to the geometric characteristics of a structure to be analyzed; obtaining sea state parameters of the structure to be analyzed, and performing implicit stress analysis on the finite element model based on the sea state parameters to obtain stress and strain values at the centroids of each element in the finite element model; embedding a cohesive zone model into a framework of extended finite element method, and calculating the stress and strain values at the centroids of each element based on a fatigue crack initiation criterion of the cohesive zone model to output a dimensionless damage index of each element; judging whether each element is a potential position of fatigue crack initiation based on the dimensionless damage index; calculating dimensionless damage index components of the element in different orientations, and determining an orientation corresponding to a maximum dimensionless damage index component as a fatigue crack initiation orientation.

2. The offshore wind turbine fatigue crack initiation site and orientation prediction method according to claim 1, characterized in that, The calculation of the stress and strain values at the centroids of each element based on the fatigue crack initiation criterion of the cohesive zone model to output a dimensionless damage index of each element comprises the following steps: calculating a dimensionless damage parameter at the centroid of each element according to the stress and strain values at the centroid of each element; the dimensionless damage parameter comprises a normal traction, a normal cohesive strength, a tangential traction and a tangential cohesive strength; calculating the dimensionless damage parameter as an input of the cohesive zone model to output a dimensionless damage index of each element.

3. The offshore wind turbine fatigue crack initiation site and orientation prediction method of claim 1, wherein, The judgment of whether each element is a potential position of fatigue crack initiation based on the dimensionless damage index comprises the following steps: judging whether the dimensionless damage index of each element is 1; if the dimensionless damage index is 1, the element has occurred fatigue crack initiation, and the calculation of the element is stopped; if the dimensionless damage index is not 1, the element is one of potential positions of fatigue crack initiation.

4. The offshore wind turbine fatigue crack initiation site and orientation prediction method of claim 1, wherein, The calculation of dimensionless damage index components of the element in different orientations comprises the following steps: A local coordinate system is established in the unit and the angle parameter θ and the angle parameter define several potential fatigue crack initiation surfaces, wherein the angle parameter θ represents the angle between the normal of the potential crack initiation plane and the z-axis, the angle parameter represents the angle between the projection of the normal of the potential crack initiation plane in the xOy plane and the x-axis; based on the angle parameter θ and the angle parameter calculating a non-dimensional damage index component of the potential fatigue crack initiation plane.

5. The offshore wind turbine fatigue crack initiation site and orientation prediction method of claim 1, wherein, the dimensionless damage index comprises at least one of a dimensionless damage index f1 based on a maximum normal traction, a dimensionless damage index f2 based on a square root traction combination, a dimensionless damage index f3 based on an improved SWT parameter criterion, and a dimensionless damage index f4 based on a Findley parameter.

6. The offshore wind turbine fatigue crack initiation site and orientation prediction method according to claim 5, characterized in that, The expression of the dimensionless damage index f3 based on the improved SWT parameter criterion is as follows: where T max_n represents the maximum normal traction, Δδ amp represents the separation amplitude, σ max_o represents the normal cohesion strength, δ n_o represents the normal cohesion length; The expression of the dimensionless damage index f4 based on the Findley parameter is as follows: wherein, represents the maximum range of tangential traction force, represents the maximum range of normal traction force, τ max_o represents the maximum tangential cohesive strength, σ max_o represents the maximum normal cohesive strength, k2 is a constant coefficient.

7. The offshore wind turbine fatigue crack initiation site and orientation prediction method of claim 1, wherein, The obtained sea state parameters are sea state parameters of the structure to be analyzed in a time increment step; the method further comprises the following steps: if the dimensionless damage index of the element in the potential position of fatigue crack initiation has reached 1, it represents that the element has failed and occurred fatigue crack initiation, and the calculation of the element in the time increment step is stopped; after the fatigue crack initiation orientation of the element in the potential position of fatigue crack initiation is determined, the sea state parameters of the structure to be analyzed in a next time increment step are obtained, and the element in the potential position of fatigue crack initiation and the fatigue crack initiation orientation of the element are predicted and updated based on the sea state parameters in the next time increment step.

8. A system for predicting fatigue crack initiation location and orientation for offshore wind turbines, characterized in that, The method comprises the following steps: a model establishing module, configured to establish a corresponding finite element model according to the geometric characteristics of a structure to be analyzed; a stress analysis module configured to obtain sea state parameters of the structure to be analyzed, and perform implicit stress analysis on the finite element model based on the sea state parameters to obtain stress and strain values at the centroids of the elements in the finite element model; a damage index calculation module configured to embed a cohesive zone model into a framework of extended finite element method, and calculate the stress and strain values at the centroids of the elements based on a fatigue crack initiation criterion of the cohesive zone model to output a dimensionless damage index of each element; a fatigue crack initiation location prediction module configured to determine whether each element is a potential location of fatigue crack initiation based on the dimensionless damage index; an orientation prediction module configured to calculate dimensionless damage index components of the element that is the potential location of fatigue crack initiation in different orientations, and determine an orientation corresponding to a maximum dimensionless damage index component as an orientation of fatigue crack initiation.

9. An electronic device, comprising: The electronic device comprises: a memory storing a computer program; a processor in communication with the memory, and configured to invoke each computer program to execute the offshore wind turbine fatigue crack initiation location and orientation prediction method in any one of claims 1 to 7.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the offshore wind turbine fatigue crack initiation location and orientation prediction method in any one of claims 1 to 7.

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