Structural fatigue assessment method, system and device for tower of wind turbine, and storage medium

Abstract

The present invention relates to a structural fatigue assessment method, system and device for a tower of a wind turbine, and a storage medium. The assessment method comprises: S1, acquiring shape functions of a plurality of nodes on a target tower, wherein the plurality of nodes are obtained by means of uniformly dividing the target tower in the direction of height thereof; S2, acquiring operating data of a target wind turbine; S3, inputting the operating data and the shape function of each node into a preset wind turbine model, in order to obtain a bending moment time series corresponding to each node on the target tower; S4, on the basis of the bending moment time series of each node, determining a cumulative damage degree of each node; and S5, on the basis of the cumulative damage degree of at least one node, outputting a structural fatigue assessment result for the target tower. The assessment method enables accurate estimation of the structural fatigue condition of towers without relying on external sensors.

Description

Structural fatigue assessment methods, systems, equipment, and storage media for wind turbine towers Technical Field

[0001] This invention relates to the field of offshore wind turbines, and more particularly to a method, system, equipment, and storage medium for structural fatigue assessment of wind turbine towers. Background Technology

[0002] Offshore wind turbines are subjected to complex and variable loads during operation, including combined loads from wind, waves, and the turbine's own motion. Long-term load accumulation can cause fatigue damage to the tower structure, affecting the turbine's service life and safety.

[0003] Traditional tower load monitoring methods rely on the deployment of numerous sensors, which not only increases the manufacturing and maintenance costs of wind turbines but also suffers from problems such as short sensor lifespan and complex installation. Furthermore, because offshore wind turbines are significantly affected by the marine environment, long-term use of sensors in harsh conditions can lead to frequent failures. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method, system, equipment and storage medium for structural fatigue assessment of wind turbine towers.

[0005] The technical solution adopted by this invention to solve its technical problem is: to construct a structural fatigue assessment method for the tower of a wind turbine, comprising the following steps:

[0006] S1: Obtain the shape functions of multiple nodes on the target tower; the multiple nodes are uniformly divided along the height direction of the target tower;

[0007] S2: Obtain the operating data of the target wind turbine;

[0008] S3: Input the running data and the shape function at each node into the preset wind turbine model to obtain the bending moment time series corresponding to each node on the target tower;

[0009] S4: Determine the cumulative damage level of each node based on the bending moment time series of each node;

[0010] S5: Based on the cumulative damage level of at least one node, output the structural fatigue assessment results of the target tower.

[0011] In some embodiments, in step S1, the shape function at each node is represented as:

[0012] In the formula, For the first Each node corresponds to the relative height of the tower; a1-a5 are correlation parameters associated with the shape of the tower, L T The total height of the tower including the rigid foundation, L B This refers to the height of the rigid foundation.

[0013] In some embodiments, the method for obtaining the association parameters a1-a5 for each node includes the following steps:

[0014] S11: Obtain the reference associated parameters;

[0015] S12: Based on the reference correlation parameters, obtain the estimated correlation parameters of the target tower at the corresponding node;

[0016] S13: Based on the estimated relationship parameters, obtain the estimated bending moment at the corresponding node;

[0017] S14: Obtain the actual bending moment at the corresponding node and compare the actual bending moment with the estimated bending moment; wherein, when the difference between the estimated bending moment and the actual bending moment is within a preset error range, the estimated correlation parameter is used as the correlation parameter for calculating the bending moment at the corresponding node; when the difference between the estimated bending moment and the actual bending moment is not within the preset error range, the estimated correlation parameter is adjusted until the difference between the estimated bending moment and the actual bending moment is within the preset error range.

[0018] In some embodiments, the step of obtaining the bending moment time series of any node specifically includes:

[0019] The operating data and the shape function at each node are input into a preset wind turbine model to obtain the displacement of the tower at time t and height z.

[0020] The bending moment of the tower at time t and height z is calculated using the following formula: M(z,t)=EI(z)κ(z,t) (4)

[0021] In the formula, κ(z,t) is the curvature of the tower at time t and height z; q(z,t) is the displacement of the tower at time t and height z; EI(z) is the stiffness coefficient of the tower at height z; and M(z,t) is the bending moment of the tower at time t and height z.

[0022] By analogy, the bending moment of the tower at consecutive moments is calculated to obtain the bending moment time series of any node.

[0023] In some embodiments, the wind turbine model is a 2-DOF wind turbine model, which is related to the axial displacement of the tower and the rotation of the drive shaft.

[0024] In some embodiments, the wind turbine model is represented as follows:

[0025] In the formula, T a For aerodynamic thrust, Q a For aerodynamic torque, Q g The equivalent generator torque is given by q, and the axial displacement distance of the tower is given by q. The axial displacement velocity of the tower Let ψ be the axial displacement acceleration of the tower, and ψ be the rotation angle of the drive shaft. The rotational angular velocity of the drive shaft. Let J be the rotational angular acceleration of the drive shaft, M be the generalized mass of the wind turbine, and J be the angular acceleration of the drive shaft. X，R Let be the moment of inertia of the drive shaft about the x-axis, D be the generalized damping coefficient of the tower's axial bending, and K be the generalized stiffness coefficient of the tower's axial bending.

[0026] Alternatively, the wind turbine model can be represented as:

[0027] In the formula, F q Q is the generalized thrust acting on the tower. a For aerodynamic torque, Q g The equivalent generator torque is given by M, and the generalized mass of the wind turbine is given by M. The axial displacement acceleration of the tower. J is the rotational angular acceleration of the drive shaft. X，R Let x be the moment of inertia of the drive shaft about the x-axis.

[0028] In some embodiments, the generalized thrust F q It can be obtained through the following formula, specifically: D=2ζM e ω e (14) K = K e +K g (17) K g =K gt +K gw (19)

[0029] In the formula, f e K represents the elastic load generated by external forces acting on the tower. e K represents the elastic stiffness of the tower. g Let be the geometric deformation coefficient of the tower, and D be the generalized damping coefficient for axial bending of the tower. T is the axial displacement velocity of the tower. aFor aerodynamic thrust, M N For cabin mass, M R For rotor mass, x NG Let x be the distance between the cabin's center of gravity and the cabin's center point projected onto the x-axis. NR z is the distance between the rotor's center of gravity and the nacelle's center point projected onto the x-axis. NG The distance between the center of gravity of the nacelle and the center point of the connection between the nacelle and the tower, projected onto the z-axis. NR Let q be the distance on the z-axis projection of the rotor's center of gravity and the center point of the connection between the nacelle and the tower, and v be the axial displacement of the tower. y θ is the angle coefficient. t Let be the static angle of attack of the nacelle at time t; p(z,t) represents the axial external force acting on the tower at position z and time t; ζ is the axial bending damping coefficient of the tower, ω e M is the natural frequency of axial bending of the tower. e Let K be the mass of the tower; K be the generalized axial bending stiffness coefficient of the tower; EI(z) be the stiffness coefficient of the tower at height z; and K... gt K represents the deformation coefficient of the rotor and nacelle. gw ρ is the deformation coefficient of the tower, g is the acceleration due to gravity, m(z) is the surface mass density of the tower at height z; a For air density, A r Where V is the swept area of ​​the fan blades, V is the inflow velocity, and C is the inflow velocity. t (λ, β) is the thrust coefficient, which is a binary mapping of the tip speed ratio λ and the propeller pitch angle β; C dt D is the tower damping coefficient. t (z) is the cross-sectional diameter of the tower at height z.

[0030] In some embodiments, the generalized mass M of the wind turbine can be obtained by the following formula:

[0031] In the formula, M e For the tower mass, M N For cabin mass, M R x is the rotor mass of the generator. NG Let x be the distance between the cabin's center of gravity and the cabin's center point projected onto the x-axis. NR z is the distance between the rotor's center of gravity and the nacelle's center point projected onto the x-axis. NG The distance between the center of gravity of the nacelle and the center point of the connection between the nacelle and the tower, projected onto the z-axis. NR J is the distance on the z-axis projection of the rotor's center of gravity and the center point of the connection between the nacelle and the tower; Y，N Let J be the moment of inertia of the nacelle about the y-axis. Y，R Let v be the moment of inertia of the rotor about the y-axis. yθ is the angle coefficient; q is the axial displacement of the tower.

[0032] In some embodiments, the pneumatic torque Q a It can be obtained through the following formula, specifically:

[0033] In the formula, ρ a For air density, A r Where V is the swept area of ​​the fan blades, V is the inflow velocity, R is the radius of the impeller, and C is the cross-sectional area of ​​the impeller blades. q (λ, β) is the torque coefficient, which is a binary mapping of the tip speed ratio λ and the propeller pitch angle β;

[0034] The equivalent generator torque can be obtained by the following formula:

[0035] In the formula, N represents the electromagnetic torque of the generator. g This refers to the gearbox speed ratio.

[0036] In some embodiments, determining the cumulative damage level of each node based on the bending moment time series of each node includes:

[0037] Based on the rainflow counting method, each complete stress cycle is extracted from the bending moment time series at each node to obtain relevant data associated with the stress cycle;

[0038] The cumulative damage level of each node is obtained based on the relevant data associated with the stress cycle.

[0039] In some embodiments, the cumulative damage level of any node can be obtained by the following formula, specifically:

[0040] In the formula, This represents the cumulative damage level of a single corresponding node; n represents the total number of stress cycle types; i represents the i-th stress cycle; f i T represents the probability of the i-th stress cycle occurring; i N represents the running time of the i-th stress cycle; eq，i N represents the fatigue life under the i-th stress cycle; i * K represents the number of cycles a single corresponding node can withstand under the i-th stress cycle; SN M represents the SN curve constant for a single corresponding node; eq M represents the equivalent load of a single corresponding node; m represents the slope of the SN curve of a single corresponding node; M i N represents the amplitude of the i-th stress cycle. iThe number of stress cycles of type i is represented; T represents the total load duration.

[0041] In some embodiments, the step of outputting the structural fatigue assessment result of the target tower based on the cumulative damage degree of at least one node includes the following steps:

[0042] S51: Compare the cumulative damage level in each node with a preset threshold;

[0043] S52: When the comparison result shows that the cumulative damage degree of at least one node is greater than the preset threshold, output the result that the target tower structure exceeds the fatigue limit; when the comparison result shows that the cumulative damage degree of each node is less than the preset threshold, output the result that the target tower structure is good; when the comparison result shows that the cumulative damage degree of each node is not greater than the preset threshold, and there is at least one node whose cumulative damage degree is equal to the preset threshold, output the result that the target tower structure reaches the fatigue limit.

[0044] In some embodiments, step S5 further includes:

[0045] When the comparison result shows that the cumulative damage level of each node is less than the preset threshold, the preset interval range of the cumulative damage level that is closest to the preset threshold among all nodes is determined, and the fatigue life prediction result corresponding to the preset interval range is output.

[0046] The present invention also constructs a structural fatigue assessment system for wind turbine towers, comprising:

[0047] The first acquisition module is used to acquire the shape functions of each node of the target tower; the multiple nodes are evenly divided along the height direction of the target tower.

[0048] The second acquisition module is used to acquire the operating data of the target wind turbine.

[0049] The first calculation module is used to input the running data and the shape function at each node into a preset wind turbine model to obtain the bending moment time series corresponding to each node on the target tower.

[0050] The second calculation module is used to determine the cumulative damage degree of each node based on the bending moment time series of each node;

[0051] The output module is used to output the structural fatigue assessment results of the target tower based on the cumulative damage level of at least one node.

[0052] The present invention also constructs a structural fatigue assessment device for the tower of a wind turbine, the device comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, the computer program being configured to implement the steps of the above-described structural fatigue assessment method for the tower of a wind turbine.

[0053] The present invention also constructs a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method for structural fatigue assessment of the tower of a wind turbine.

[0054] The present invention has the following advantages: the structural fatigue assessment method for the tower of the wind turbine can accurately estimate the structural fatigue condition of the tower without relying on external sensors. Attached Figure Description

[0055] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0056] Figure 1 is a simplified flowchart of the structural fatigue assessment method for the tower of the wind turbine of the present invention in one embodiment;

[0057] Figure 2 is a flowchart of a specific embodiment of the structural fatigue assessment method for the tower of the wind turbine of the present invention;

[0058] Figure 3 is a schematic diagram of the offshore wind turbine provided in an embodiment of the present invention under static conditions;

[0059] Figure 4 is a schematic diagram of an offshore wind turbine provided in an embodiment of the present invention under tower bending.

[0060] Figure 5 is a time series diagram of the bending moments of several tower nodes provided in an embodiment of the present invention.

[0061] Attached reference numerals: 1. Tower; 2. Rigid foundation; 3. Nacelle; 4. Drive shaft; 5. Wind turbine. Detailed Implementation

[0062] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0063] It should be noted that the flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0064] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0065] This invention provides a method for structural fatigue assessment of wind turbine towers, applicable to offshore wind turbines, such as 5.5MW offshore wind turbines. Of course, this method can also be applied to onshore wind turbines.

[0066] To elaborate further, offshore wind turbines are characterized by long-duration, highly fluctuating, and large-amplitude loads. During operation, they endure complex and ever-changing loads, including combined loads from wind, waves, and the turbine's own motion. Long-term load accumulation can cause fatigue damage to the tower structure, affecting the turbine's service life and safety. Furthermore, offshore wind turbines are more susceptible to corrosion from seawater and humid moisture. This significantly shortens the fatigue life of critical components such as the tower, gearbox, and blades, resulting in a much higher failure rate compared to onshore wind turbines. Therefore, offshore wind turbines, unlike onshore wind turbines, must withstand more severe environmental factors.

[0067] In some embodiments, referring to Figure 1, the structural fatigue assessment method for wind turbine towers may include the following steps:

[0068] S1: On the target tower, divide it into multiple nodes evenly along its height direction, and obtain the shape function on each node;

[0069] S2: Obtain the operating data of the target wind turbine;

[0070] S3: Input the running data and the shape function at each node into the preset wind turbine model to obtain the bending moment time series corresponding to each node on the target tower;

[0071] S4: Determine the cumulative damage level of each node based on the bending moment time series of each node;

[0072] S5: Output the structural fatigue assessment results of the target tower based on the cumulative damage level of at least one node.

[0073] As can be understood and referenced in Figure 3, a wind turbine may include a rigid foundation 2, a tower 1 connected to the top of the rigid foundation 2, a nacelle 3 connected to the top of the tower 1, and a drive shaft 4 disposed within the nacelle 3, with a portion of the drive shaft 4 extending outside the nacelle 3. The wind turbine also includes a rotor 5, a generator, and a gearbox; the rotor 5 is mounted on the structural portion of the drive shaft 4 extending outside the nacelle 3, and includes a hub and blades disposed on the hub; the generator converts the mechanical energy generated by the rotation of the rotor 5 into electrical energy, and the gearbox is responsible for adjusting the speed and torque between the rotor 5 and the generator.

[0074] In step S1, the shape function at each node can be expressed as:

[0075] In the formula, For the first Each node corresponds to the relative height of the tower; a1-a5 are correlation parameters associated with the shape of the tower, L T The total height of the tower including the rigid foundation, L B This refers to the height of the rigid foundation.

[0076] Understandably, the tower is divided into c nodes along its height, among which c nodes can be used. Indicates the first of the tower tubes The nth node, and z representing the nth tower section. The node height of the nth node. Then, the height of the nth node... Each node corresponds to the relative height of the tower. It can be obtained using the following formula. Specifically:

[0077] Furthermore, the tower height and rigid foundation height can be obtained through measurement methods such as measuring tapes, or from the technical manual of the wind turbine.

[0078] The method for obtaining the associated parameters a1-a5 of each node of the tower can include the following steps:

[0079] S11: Obtain the reference associated parameters;

[0080] S12: Based on the reference correlation parameters, obtain the estimated correlation parameters of the target tower at the corresponding node;

[0081] S13: Based on the estimated relationship parameters, obtain the estimated bending moment at the corresponding node;

[0082] S14: Obtain the actual bending moment at the corresponding node and compare the actual bending moment with the estimated bending moment; wherein, when the difference between the estimated bending moment and the actual bending moment is within the preset error range, the estimated correlation parameter is used as the correlation parameter for calculating the bending moment at the corresponding node; when the difference between the estimated bending moment and the actual bending moment is not within the preset error range, adjust the estimated correlation parameter until the difference between the estimated bending moment and the actual bending moment is within the preset error range.

[0083] Understandably, the reference correlation parameters can be the correlation parameters of other towers with the same shape as the target tower, or they can be directly adopted from the historical correlation parameters of the target tower. After obtaining the reference correlation parameters, the estimated correlation parameters can be obtained by adjusting them based on the reference correlation parameters; this adjustment can be made by the staff based on their own experience, or it can be a regular increase or decrease.

[0084] Secondly, the true bending moment at the corresponding node can be obtained by installing measuring equipment. For example, strain gauge moment sensors can be placed at the corresponding node to measure the true bending moment. It should be noted that how to measure the bending moment using this strain gauge moment sensor can be found in relevant technologies, and will not be explained here.

[0085] One point to clarify here is that, due to the high installation difficulty and short effective measurement life of tower stress-strain measurements, this method is used to estimate the circumferential bending moment of each node of the tower, rather than using strain gauge moment sensors. Furthermore, since the associated parameters a1-a5 of each node of the tower are related to the shape of the tower and do not change with the use of the tower, these parameters can be pre-calculated before the evaluation method is executed, and can be directly used during the evaluation process. The specific method for obtaining the associated parameters is explained here only to ensure the completeness of the data source and does not require that steps S11-S14 be performed in the evaluation method.

[0086] When the difference between the estimated bending moment and the actual bending moment is within a preset error range—that is, the difference between the estimated bending moment and the actual bending moment is zero, or less than or equal to a preset error threshold—then the associated parameters a1-a5 of the target tower at the corresponding node can be determined. Subsequently, these associated parameters a1-a5 can be substituted into the above formula to obtain the shape function at the corresponding node. Repeating the above steps yields the shape function at each node.

[0087] In step S2, the wind turbine's operating data may include inflow wind speed, pitch angle, and power generation. This data can be obtained from a SCADA (Supervisory Control and Data Acquisition) system connected to the wind turbine. This SCADA system is used to collect and analyze the wind turbine's real-time operating data; its specific structure can be found in relevant technologies and will not be elaborated upon here.

[0088] In step S3, the wind turbine model is a relational model related to the axial displacement of the tower and the rotation of the drive shaft. Referring to Figure 2, the wind turbine model is a 2-DOF model, with the axial displacement of the tower and the rotation of the drive shaft being the two degrees of freedom, respectively. Furthermore, the bending moment of the tower is related to the shape function of the tower.

[0089] After inputting the operating data and the shape function at each node into the preset wind turbine model, the displacement of the tower at time t and height z can be obtained. Referring to Figure 4, this displacement refers to the axial displacement of the tower.

[0090] Then, the tower bending moment at position z at time t is calculated according to the following formula: M(z,t)=EI(z)κ(z,t) (4)

[0091] In the formula, κ(z,t) is the curvature of the tower at time t and height z; q(z,t) is the displacement of the tower at time t and height z; EI(z) is the stiffness coefficient of the tower at height z; and M(z,t) is the bending moment of the tower at time t and height z.

[0092] It should be noted that the stiffness coefficient of the tower can be obtained from the product data provided by the manufacturer.

[0093] Then, by calculating the tower bending moment at consecutive moments, the bending moment time series corresponding to each node on the tower can be obtained. Thus, the bending moment time series of each node throughout the entire operation and maintenance cycle can be obtained. For example, in this embodiment, the tower is divided into 9 nodes; see Figure 5, which shows the bending moment time series of the 9 nodes respectively.

[0094] In some embodiments, the following wind turbine model can be used for calculation, and this wind turbine model can be represented as:

[0095] This equation can be understood as the Lagrange dynamic equation for a wind turbine model. In this equation, T a For aerodynamic thrust, Q a For aerodynamic torque, Qg The equivalent generator torque is given by q, and the axial displacement distance of the tower is given by q. The axial displacement velocity of the tower Let ψ be the axial displacement acceleration of the tower, and ψ be the rotation angle of the drive shaft. The rotational angular velocity of the drive shaft. Let J be the rotational angular acceleration of the drive shaft, M be the generalized mass of the wind turbine, and J be the angular acceleration of the drive shaft. X，R Let be the moment of inertia of the drive shaft about the x-axis, D be the generalized damping coefficient of the tower's axial bending, and K be the generalized stiffness coefficient of the tower's axial bending. The specific methods for obtaining these parameters can be found below and will not be elaborated upon here.

[0096] It can be added here that the axial displacement velocity of the tower is related to both the axial displacement and time, and the axial displacement acceleration is also related to both the axial displacement velocity and time. Therefore, when calculating the axial displacement of the tower, the axial displacement velocity and / or axial displacement acceleration can be directly transformed into equations containing the axial displacement. Similarly, the rotational angular acceleration of the drive shaft is related to the aerodynamic torque and the moment of inertia of the drive shaft. The rotational angular velocity of the drive shaft can be obtained by integrating the rotational angular acceleration over time. The methods for obtaining other parameters are described below. Preferably, for the convenience of load analysis, the following wind turbine model can also be used for calculation. This wind turbine model is specifically represented as follows:

[0097] The above equation can be understood as the dynamic equation between the acceleration and load of the wind turbine model. Since this equation involves the generalized thrust on the tower, it makes load analysis more convenient.

[0098] In the formula, F q Q is the generalized thrust acting on the tower. a For aerodynamic torque, Q g The equivalent generator torque is given by M, and the generalized mass of the wind turbine is given by M. The axial displacement acceleration of the tower. J is the rotational angular acceleration of the drive shaft. X，R Let x be the moment of inertia of the drive shaft about the x-axis.

[0099] Here, it should be noted that the methods for obtaining the generalized thrust, aerodynamic torque, equivalent generator torque, and generalized mass of the wind turbine on the tower can be found below. The moment of inertia can be obtained from the product data provided by the manufacturer.

[0100] Furthermore, the aerodynamic torque Q a It can be obtained using the following formula. Specifically:

[0101] In the formula, ρa For air density, A r Where V is the swept area of ​​the fan blades, V is the inflow velocity, R is the radius of the impeller, and C is the cross-sectional area of ​​the impeller blades. q (λ, β) is the torque coefficient, which is a binary mapping of the tip speed ratio λ and the propeller pitch angle β.

[0102] It should be noted that the swept area of ​​the fan blades and the radius of the impeller can be obtained through measurement or from product data provided by the manufacturer. The tip speed ratio λ can be obtained by multiplying the fan blade's rotational speed by its length and the inflow velocity.

[0103] Secondly, the equivalent generator torque can be obtained using the following formula:

[0104] In the formula, N represents the electromagnetic torque of the generator, which can be obtained from the generator output power. g This refers to the gearbox speed ratio.

[0105] Next, the generalized mass M of the wind turbine can be obtained by the following formula. Specifically:

[0106] In the formula, M e For the tower mass, M N For cabin mass, M R x is the rotor mass of the generator. NG Let x be the distance between the cabin's center of gravity and the cabin's center point projected onto the x-axis. NR z is the distance between the rotor's center of gravity and the nacelle's center point projected onto the x-axis. NG The distance between the center of gravity of the nacelle and the center point of the connection between the nacelle and the tower, projected onto the z-axis. NR This is the distance on the z-axis projection of the center point of the rotor's center of gravity and the connection between the nacelle and the tower. These parameters can be obtained through measurement or from product data provided by the manufacturer.

[0107] J Y，N Let J be the moment of inertia of the nacelle about the y-axis. Y，R Let v be the moment of inertia of the rotor about the y-axis. y This refers to the angle coefficient; these parameters can be obtained from the product data provided by the manufacturer. Generally, v y The value is typically 0.0185.

[0108] q represents the axial displacement of the tower, which is equivalent to the displacement q(z, t) of the tower at time t and height z. y q can represent the bending angle of the tower.

[0109] Also, F aIt includes elastic loads, rigid loads, damping loads generated by external forces acting on the tower, the gravitational force of the nacelle-rotor assembly, the centrifugal force of the nacelle-rotor assembly, and the generalized torque generated by aerodynamic thrust.

[0110] The generalized thrust F q It can be obtained using the following formula. Specifically: D=2ζM e ω e (14) K = K e +K g (17) K g =K gt +K gw (19)

[0111] In equation 12-13, f e K represents the elastic load generated by external forces acting on the tower. e K represents the elastic stiffness of the tower. g Let be the geometric deformation coefficient of the tower, and D be the generalized damping coefficient for axial bending of the tower. T is the axial displacement velocity of the tower. a For aerodynamic thrust, M N For cabin mass, M R For rotor mass, x NG Let x be the distance between the cabin's center of gravity and the cabin's center point projected onto the x-axis. NR z is the distance between the rotor's center of gravity and the nacelle's center point projected onto the x-axis. NG The distance between the center of gravity of the nacelle and the center point of the connection between the nacelle and the tower, projected onto the z-axis. NR Let q be the distance on the z-axis projection of the rotor's center of gravity and the center point of the connection between the nacelle and the tower, and v be the axial displacement of the tower. y θ is the angle coefficient. t Let be the static angle of attack of the nacelle at time t; p(z,t) represents the axial external force received by the tower at position Z and time t.

[0112] In Equation 14-16, ζ is the axial bending damping coefficient of the tower, ω e M is the natural frequency of axial bending of the tower. e Let K be the mass of the tower, K be the generalized stiffness coefficient of the tower's axial bending, and m(z) be the surface density of the tower's mass at height z. It should be noted that the tower's axial bending damping coefficient, natural frequency of axial bending, and surface density can be obtained from the product data provided by the manufacturer.

[0113] In Equation 17-21, EI(z) is the stiffness coefficient of the tower at height z, and K gt K represents the deformation coefficient of the rotor and nacelle. gw Let be the deformation coefficient of the tower, and g be the acceleration due to gravity.

[0114] In Equation 22, ρ a For air density, A r Where V is the swept area of ​​the fan blades, V is the inflow velocity, and C is the inflow velocity. t (λ, β) is the thrust coefficient, which is a binary mapping of the tip speed ratio λ and the propeller pitch angle β.

[0115] In Equation 23, C dt The tower damping coefficient is related to the tower shape and material, and can be obtained from the product data provided by the manufacturer; D t (z) represents the cross-sectional diameter of the tower at height z. It can be obtained through measurement or from product data provided by the manufacturer.

[0116] Secondly, the above formula also includes the first and second derivatives of the shape function of the tower. To elaborate further, the specific equations for the first and second derivatives of the shape function of the tower are as follows:

[0117] In summary, after the operating data and the shape functions at each node are input into the preset wind turbine model, the displacement of the tower at position z at time t can be obtained. Then, by calculating the tower bending moment at position z at consecutive time points, the bending moment time series corresponding to each node on the tower can be obtained. It can be added that structural parameters, such as mass and projected distance, which are only related to the structure of the wind turbine, can be pre-input into the wind turbine model or input along with the operating data; there are no specific restrictions. As an optional solution, a database storing the structural parameters of each wind turbine can be established, which can directly import the structural parameters of the target wind turbine into the wind turbine model.

[0118] Understandably, the curves of bending moment variation over time at each node of the tower (i.e., bending moment time series) calculated using the above series of formulas are intended to simplify the irregular load history into a series of equivalent stress cycles, thereby analyzing the structural fatigue life of the tower.

[0119] Subsequently, in step S4, using the rainflow counting method, all local maxima (peaks) and local minima (valleys) are extracted from each bending moment time series, and the peaks and valleys are paired to form stress amplitude cycles. Simultaneously, incomplete stress cycles (such as edge cycles) are removed, and only complete stress cycles are considered. The relevant data associated with these stress cycles are recorded and obtained. Then, based on this relevant data, the cumulative damage degree of each node is obtained.

[0120] In some embodiments, the cumulative damage level of any node can be obtained by the following formula:

[0121] In the formula, This represents the cumulative damage level of a single corresponding node; n represents the total number of stress cycle types, with the equivalent amplitude of the same stress cycle being the same; i represents the i-th stress cycle; f i T represents the probability of the i-th stress cycle occurring; i N represents the running time of the i-th stress cycle; eq，i Let N represent the fatigue life under the i-th stress cycle, and N represent the fatigue life under the i-th stress cycle. i * K represents the number of cycles a single corresponding node can withstand under the i-th stress cycle, where fatigue life can be equated to the number of cycles; SN M represents the SN curve constant for a single corresponding node; eq M represents the equivalent load of a single corresponding node; m represents the slope of the SN curve of a single corresponding node; M i N represents the amplitude of the i-th stress cycle. i The number of stress cycles of type i is represented; T represents the total load duration.

[0122] It can be further explained here that the total number of stress cycles, the number of types, the probability of the i-th stress cycle occurring, the running time of the i-th stress cycle, the number of cycles a single corresponding node can withstand under the i-th stress cycle, the amplitude of the i-th stress cycle, the number of i-th stress cycles, and the total load duration can all be obtained from the relevant data associated with stress cycles. The probability of the i-th stress cycle occurring can be understood as follows: assuming a node's bending moment time series, according to rainflow analysis, yields 10 stress cycles, and 5 of these stress cycles have the same amplitude, then the probability of that type of stress cycle occurring is 1 / 2.

[0123] The SN curve constant and SN curve slope can be obtained from the product data provided by the manufacturer; of course, the SN curve can also be fitted from experimental data, without making any specific limitations here.

[0124] In step S5, based on the cumulative damage level of at least one node, the structural fatigue assessment result of the target tower is output, which may be:

[0125] S51: Compare the cumulative damage level in each node with a preset threshold;

[0126] S52: When the comparison result shows that the cumulative damage of at least one node is greater than the preset threshold, output the result that the tower structure has exceeded the fatigue limit;

[0127] When the cumulative damage level of each node is less than the preset threshold, the output shows that the tower structure is in good condition.

[0128] When the comparison results show that the cumulative damage level of each node is not greater than the preset threshold, and there is at least one node whose cumulative damage level is equal to the preset threshold, the output tower structure reaches the fatigue limit.

[0129] For example, when At this point, the tower structure has not yet reached its fatigue limit, meaning significant fatigue failure will not occur. Under these circumstances, the tower structure remains within its safe operating range. At this point, the cumulative damage reaches the fatigue limit. The tower structure has reached the upper limit of its design life, meaning fatigue failure is possible, requiring attention and necessary maintenance or replacement. When the cumulative damage exceeds the fatigue limit, it indicates that the tower structure has exceeded its designed fatigue life and may have experienced significant structural failure. In this case, it is recommended to immediately stop using the tower and take repair or replacement measures.

[0130] Furthermore, this method can comprehensively evaluate the equivalent fatigue load and cumulative damage rate under different stress cycles to predict the fatigue life of the tower. Understandably, the fatigue life of the tower follows the rule that the smaller the cumulative damage, the longer the fatigue life. Therefore, when the cumulative damage at each node is less than a preset threshold, the closer the cumulative damage at any node is to the preset threshold, the shorter the fatigue life of the tower. Based on this, multiple consecutive intervals can be established, each corresponding to a fatigue life prediction value. When the cumulative damage at each node is less than the preset threshold, it can be further determined which preset interval range the cumulative damage closest to the preset threshold falls within, and then the fatigue life prediction result corresponding to the preset interval range is output.

[0131] For example, when the cumulative damage level closest to the preset threshold is 0.8, the fatigue life of the tower can be estimated to be 3-4 years; when the cumulative damage level closest to the preset threshold is 0.6, the fatigue life of the tower can be estimated to be 6-8 years.

[0132] Alternatively, as shown in Figure 2, preventative maintenance guidelines can be output simultaneously when outputting the structural fatigue assessment results. Specifically, when the assessment result indicates that the tower structure has reached its fatigue limit, guidelines requiring the tower to be repaired or replaced are output; when the assessment result indicates that the tower structure has exceeded its fatigue limit, guidelines requiring the tower to be immediately taken out of service and repaired or replaced are output.

[0133] In summary, this invention estimates the bending moment time series of the tower at different nodes based on SCADA data and a 2-DOF wind turbine model. Then, it introduces the rainflow counting method to analyze the bending moment time series of the tower at different nodes, extracts stress cycles of different amplitudes, and calculates the number of cycles corresponding to each stress cycle. This allows the determination of the cumulative fatigue damage degree of the tower throughout the entire operation and maintenance cycle. Based on the cumulative fatigue damage degree, the invention assesses whether the tower structure has reached or exceeded the fatigue limit.

[0134] In this way, employers can rationally schedule preventative maintenance based on the actual fatigue status of the turbine, avoiding unnecessary downtime and high-cost repair operations, thus further improving the economic efficiency and operational reliability of offshore wind turbines. Compared with traditional sensor solutions, this invention can accurately estimate load changes at different height nodes of the tower without relying on external sensors, achieving low-cost, low-maintenance load monitoring. This technology greatly improves the reliability and economy of offshore wind turbine operation, providing technical support for the long-term stable operation of wind turbines in extreme environments.

[0135] Furthermore, the present invention also constructs a structural fatigue assessment system for wind turbine towers, which may include:

[0136] The first acquisition module is used to acquire the shape function of each node of the target tower; the node is a plurality of nodes that are uniformly divided along the height direction of the target tower.

[0137] The second acquisition module is used to acquire the operating data of the target wind turbine.

[0138] The first calculation module is used to input the running data and the shape function at each node into the preset wind turbine model to obtain the bending moment time series corresponding to each node on the target tower.

[0139] The second calculation module is used to determine the cumulative damage level of each node based on the bending moment time series of each node;

[0140] The output module is used to output the structural fatigue assessment results of the target tower based on the cumulative damage level of at least one node.

[0141] Secondly, the system may also include a storage module for the wind turbine model. The specific structure of the wind turbine model can be found above and will not be repeated here. The first computing module can connect to the storage module and access the wind turbine model within it.

[0142] Furthermore, the first acquisition module includes a first acquisition unit for acquiring the associated parameters a1-a5 of each node. It may include:

[0143] The reference parameter acquisition unit is used to acquire the reference associated parameters used as a reference.

[0144] The prediction unit is used to obtain the predicted correlation parameters of the target tower at the corresponding node based on the reference correlation parameters;

[0145] The calculation unit is used to obtain the estimated bending moment at the corresponding node based on the estimated relationship parameters;

[0146] The comparison unit is used to obtain the actual bending moment at the corresponding node and compare the actual bending moment with the estimated bending moment. When the difference between the estimated bending moment and the actual bending moment is within a preset error range, the estimated correlation parameter is used as the correlation parameter for calculating the bending moment at the corresponding node. When the difference between the estimated bending moment and the actual bending moment is not within the preset error range, the estimated correlation parameter is adjusted until the difference between the estimated bending moment and the actual bending moment is within the preset error range.

[0147] Furthermore, the second acquisition module can be connected to the SCADA system to obtain the wind turbine's operating data from the SCADA system.

[0148] Furthermore, the second calculation module is used to extract each complete stress cycle from the bending moment time series of each node according to the rainflow counting method to obtain relevant data associated with the stress cycle; and to obtain the cumulative damage degree of each node based on the relevant data associated with the stress cycle.

[0149] Furthermore, the output module is used to compare the cumulative damage level in each node with a preset threshold; wherein, when the comparison result is that the cumulative damage level of at least one node is greater than the preset threshold, the output result is that the tower structure exceeds the fatigue limit; when the comparison result is that the cumulative damage level of each node is less than the preset threshold, the output result is that the tower structure is in good condition; when the comparison result is that the cumulative damage level of each node is not greater than the preset threshold, and there is at least one node whose cumulative damage level is equal to the preset threshold, the output result is that the tower structure reaches the fatigue limit.

[0150] Optionally, the output module is also used to determine the preset range of the cumulative damage degree that is closest to the preset threshold among all nodes when the comparison result is that the cumulative damage degree of each node is less than the preset threshold, and output the fatigue life prediction result corresponding to the preset range.

[0151] Optionally, the output module is also used to simultaneously output preventive maintenance guidance when outputting structural fatigue assessment results.

[0152] Furthermore, the present invention also constructs a structural fatigue assessment device for the tower of a wind turbine, the device comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, the computer program being configured to implement the steps of the structural fatigue assessment method for the tower of a wind turbine as described above.

[0153] The present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-mentioned method for structural fatigue assessment of the tower of a wind turbine.

[0154] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A method for structural fatigue assessment of wind turbine towers, characterized in that, Includes the following steps: S1: Obtain the shape functions of multiple nodes on the target tower; the multiple nodes are uniformly divided along the height direction of the target tower; S2: Obtain the operating data of the target wind turbine; S3: Input the running data and the shape function at each node into the preset wind turbine model to obtain the bending moment time series corresponding to each node on the target tower; S4: Determine the cumulative damage level of each node based on the bending moment time series of each node; S5: Based on the cumulative damage level of at least one node, output the structural fatigue assessment results of the target tower.

2. The method for structural fatigue assessment of wind turbine towers according to claim 1, characterized in that, In step S1, the shape function at each node is represented as: In the formula, For the first Each node corresponds to the relative height of the tower; a1-a5 are correlation parameters associated with the shape of the tower, L T The total height of the tower including the rigid foundation, L B This refers to the height of the rigid foundation.

3. The method for structural fatigue assessment of wind turbine towers according to claim 2, characterized in that, The method for obtaining the associated parameters a1-a5 for each node includes the following steps: S11: Obtain the reference associated parameters; S12: Based on the reference correlation parameters, obtain the estimated correlation parameters of the target tower at the corresponding node; S13: Based on the estimated relationship parameters, obtain the estimated bending moment at the corresponding node; S14: Obtain the actual bending moment at the corresponding node and compare the actual bending moment with the estimated bending moment; wherein, when the difference between the estimated bending moment and the actual bending moment is within a preset error range, the estimated correlation parameter is used as the correlation parameter for calculating the bending moment at the corresponding node; when the difference between the estimated bending moment and the actual bending moment is not within the preset error range, the estimated correlation parameter is adjusted until the difference between the estimated bending moment and the actual bending moment is within the preset error range.

4. The method for structural fatigue assessment of wind turbine towers according to claim 1, characterized in that, The steps for obtaining the bending moment time series at any node specifically include: The operating data and the shape function at each node are input into a preset wind turbine model to obtain the displacement of the tower at time t and height z. The bending moment of the tower at time t and height z is calculated using the following formula; M(z,t)=EI(z)κ(z,t) (4) In the formula, κ(z,t) is the curvature of the tower at time t and height z; q(z,t) is the displacement of the tower at time t and height z; EI(z) is the stiffness coefficient of the tower at height z; and M(z,t) is the bending moment of the tower at time t and height z. By analogy, the bending moment of the tower at consecutive moments is calculated to obtain the bending moment time series of any node.

5. The structural fatigue assessment method for wind turbine towers according to claim 4, characterized in that, The wind turbine model is a 2-DOF model, which is related to the axial displacement of the tower and the rotation of the drive shaft.

6. The method for structural fatigue assessment of wind turbine towers according to claim 5, characterized in that, The wind turbine model is represented as follows: In the formula, T a For aerodynamic thrust, Q a For aerodynamic torque, Q g The equivalent generator torque is given by q, and the axial displacement distance of the tower is given by q. The axial displacement velocity of the tower Let ψ be the axial displacement acceleration of the tower, and ψ be the rotation angle of the drive shaft. The rotational angular velocity of the drive shaft. Let J be the rotational angular acceleration of the drive shaft, M be the generalized mass of the wind turbine, and J be the angular acceleration of the drive shaft. X，R Let be the moment of inertia of the drive shaft about the x-axis, D be the generalized damping coefficient of the tower's axial bending, and K be the generalized stiffness coefficient of the tower's axial bending. Alternatively, the wind turbine model can be represented as: In the formula, F q Q is the generalized thrust acting on the tower. a For aerodynamic torque, Q g The equivalent generator torque is given by M, and the generalized mass of the wind turbine is given by M. The axial displacement acceleration of the tower. J is the rotational angular acceleration of the drive shaft. X，R Let x be the moment of inertia of the drive shaft about the x-axis.

7. The method for structural fatigue assessment of wind turbine towers according to claim 6, characterized in that, The generalized thrust F q It can be obtained through the following formula, specifically: D=2ζM e ω e (14) K = K e +K g (17) K g =K gt +K gw (19) In the formula, f e K represents the elastic load generated by external forces acting on the tower. e K represents the elastic stiffness of the tower. g Let be the geometric deformation coefficient of the tower, and D be the generalized damping coefficient for axial bending of the tower. T is the axial displacement velocity of the tower. a For aerodynamic thrust, M N For cabin mass, M R For rotor mass, x NG Let x be the distance between the cabin's center of gravity and the cabin's center point projected onto the x-axis. NR z is the distance between the rotor's center of gravity and the nacelle's center point projected onto the x-axis. NG The distance between the center of gravity of the nacelle and the center point of the connection between the nacelle and the tower, projected onto the z-axis. NR Let q be the distance on the z-axis projection of the rotor's center of gravity and the center point of the connection between the nacelle and the tower, and v be the axial displacement of the tower. y θ is the angle coefficient. t Let be the static angle of attack of the nacelle at time t; p(z,t) represents the axial external force acting on the tower at position z and time t; ζ is the axial bending damping coefficient of the tower, ω e M is the natural frequency of axial bending of the tower. e Let K be the mass of the tower; K be the generalized axial bending stiffness coefficient of the tower; EI(z) be the stiffness coefficient of the tower at height z; and K... gt K represents the deformation coefficient of the rotor and nacelle. gw ρ is the deformation coefficient of the tower, g is the acceleration due to gravity, m(z) is the surface mass density of the tower at height z; a For air density, A r Where V is the swept area of ​​the fan blades, V is the inflow velocity, and C is the inflow velocity. t (λ, β) is the thrust coefficient, which is a binary mapping of the tip speed ratio λ and the propeller pitch angle β; C dt D is the tower damping coefficient. t (z) is the cross-sectional diameter of the tower at height z.

8. The method for structural fatigue assessment of wind turbine towers according to claim 6, characterized in that, The generalized mass M of the wind turbine can be obtained by the following formula: In the formula, M e For the tower mass, M N For cabin mass, M R x is the rotor mass of the generator. NG Let x be the distance between the cabin's center of gravity and the cabin's center point projected onto the x-axis. NR z is the distance between the rotor's center of gravity and the nacelle's center point projected onto the x-axis. NG The distance between the center of gravity of the nacelle and the center point of the connection between the nacelle and the tower, projected onto the z-axis. NR J is the distance on the z-axis projection of the rotor's center of gravity and the center point of the connection between the nacelle and the tower; Y，N Let J be the moment of inertia of the nacelle about the y-axis. Y，R Let v be the moment of inertia of the rotor about the y-axis. y θ is the angle coefficient; q is the axial displacement of the tower.

9. The method for structural fatigue assessment of wind turbine towers according to claim 6, characterized in that, The pneumatic torque Q a It can be obtained through the following formula, specifically: In the formula, ρ a For air density, A r Where V is the swept area of ​​the fan blades, V is the inflow velocity, R is the radius of the impeller, and C is the cross-sectional area of ​​the impeller blades. q (λ, β) is the torque coefficient, which is a binary mapping of the tip speed ratio λ and the propeller pitch angle β; The equivalent generator torque can be obtained by the following formula: In the formula, N represents the electromagnetic torque of the generator. g This refers to the gearbox speed ratio.

10. The method for structural fatigue assessment of wind turbine towers according to claim 1, characterized in that, The determination of the cumulative damage degree of each node based on the bending moment time series of each node includes: Based on the rainflow counting method, each complete stress cycle is extracted from the bending moment time series at each node to obtain relevant data associated with the stress cycle; The cumulative damage level of each node is obtained based on the relevant data associated with the stress cycle.

11. The method for structural fatigue assessment of wind turbine towers according to claim 10, characterized in that, The cumulative damage level of any node can be obtained by the following formula, specifically: In the formula, This represents the cumulative damage level of a single corresponding node; n represents the total number of stress cycle types; i represents the i-th stress cycle; f i T represents the probability of the i-th stress cycle occurring; i N represents the running time of the i-th stress cycle; eq，i N represents the fatigue life under the i-th stress cycle; i * K represents the number of cycles a single corresponding node can withstand under the i-th stress cycle; SN M represents the SN curve constant for a single corresponding node; eq M represents the equivalent load of a single corresponding node; m represents the slope of the SN curve of a single corresponding node; M i N represents the amplitude of the i-th stress cycle. i The number of stress cycles of type i is represented; T represents the total load duration.

12. The method for structural fatigue assessment of wind turbine towers according to claim 1, characterized in that, The step of outputting the structural fatigue assessment result of the target tower based on the cumulative damage degree of at least one node includes the following steps: S51: Compare the cumulative damage level in each node with a preset threshold; S52: When the comparison result shows that the cumulative damage degree of at least one node is greater than the preset threshold, output the result that the target tower structure exceeds the fatigue limit; when the comparison result shows that the cumulative damage degree of each node is less than the preset threshold, output the result that the target tower structure is good; when the comparison result shows that the cumulative damage degree of each node is not greater than the preset threshold, and there is at least one node whose cumulative damage degree is equal to the preset threshold, output the result that the target tower structure reaches the fatigue limit.

13. The method for structural fatigue assessment of wind turbine towers according to claim 12, characterized in that, Step S5 also includes: When the comparison result shows that the cumulative damage level of each node is less than the preset threshold, the preset interval range of the cumulative damage level that is closest to the preset threshold among all nodes is determined, and the fatigue life prediction result corresponding to the preset interval range is output.

14. A structural fatigue assessment system for wind turbine towers, characterized in that, It includes: The first acquisition module is used to acquire the shape functions of each node of the target tower. The multiple nodes are evenly divided along the height direction of the target tower. The second acquisition module is used to acquire the operating data of the target wind turbine. The first calculation module is used to input the running data and the shape function at each node into a preset wind turbine model to obtain the bending moment time series corresponding to each node on the target tower. The second calculation module is used to determine the cumulative damage degree of each node based on the bending moment time series of each node; The output module is used to output the structural fatigue assessment results of the target tower based on the cumulative damage level of at least one node.

15. A structural fatigue assessment device for the tower of a wind turbine, the device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that the computer program is configured to implement the steps of the structural fatigue assessment method for the tower of a wind turbine as described in any one of claims 1-13.

16. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the structural fatigue assessment method for the tower of the wind turbine as described in any one of claims 1-13.

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