Typhoon area offshore wind turbine load calculation correction method

Abstract

This invention discloses a method for calculating and correcting the load on offshore wind turbines in typhoon-prone areas. The method includes ultimate load correction calculations and fatigue load correction calculations. The ultimate load correction calculation corrects the ultimate load through wind resource analysis and iterative optimization calculations. The fatigue load correction calculation corrects the fatigue load through wind resource analysis and wind speed distribution model corrections, combined with iterative optimization calculations. This method for calculating and correcting the load on offshore wind turbines in typhoon-prone areas involves calculations and corrections based on air density, turbulence intensity, mud surface stiffness matrix, and wind speed distribution model, resulting in more accurate load analysis, providing data support for structural design, and ensuring structural safety and economic rationality.

Description

Technical Field

[0001] This invention belongs to the technical field of offshore wind power generation, specifically relating to a method for calculating and correcting the load of offshore wind turbines in typhoon areas. Background Technology

[0002] Offshore wind turbine blade or tower fractures are frequent occurrences in typhoon-prone areas. Wind turbine structural failure generally includes ultimate load-bearing capacity failure and fatigue damage. The structural design of wind turbine components relies on accurate assessment and calculation of wind turbine loads.

[0003] Offshore wind turbine loads mainly include ultimate loads and fatigue loads. Currently, load analysis of offshore wind power support structures in typhoon areas primarily uses air density and turbulence intensity at the local average wind speed for calculation. The stiffness matrix of the offshore wind turbine support structure at the mud surface (the constraint applied during load calculation) is calculated and extracted using the ultimate load of the wind turbine under normal power generation conditions as a reference force. Both the ultimate load and fatigue load calculations use the air density, turbulence intensity, and mud surface stiffness matrix obtained by the aforementioned method for simulation calculations. Fatigue load analysis relies entirely on the Weibull distribution wind speed distribution model for calculation and analysis.

[0004] Existing methods for calculating and analyzing the loads on offshore wind turbines in typhoon-prone areas use air density, turbulence intensity, and mud surface stiffness matrix calculated under normal power generation conditions. However, typhoons do significantly impact air density, turbulence intensity, and the mud surface stiffness matrix of offshore wind turbine support structures. Therefore, using these parameters under normal power generation conditions to calculate the ultimate load (occurring under typhoon conditions) is inaccurate. Furthermore, existing fatigue load calculations for offshore wind turbines in typhoon-prone areas use the Weibull distribution for wind speed models. Since the Weibull distribution is suitable for areas with abundant wind resources, it has limitations in simulating high-speed winds. Therefore, relying solely on the Weibull distribution for wind speed distribution in typhoon-prone areas is inaccurate.

[0005] Traditional methods for calculating the load on offshore wind turbines in typhoon-prone areas have limitations because they do not consider the impact of typhoons on air density, turbulence intensity, mud surface stiffness matrix, and wind speed distribution. Inaccurate load analysis directly affects structural design, leading to economic or safety issues. In the high-quality development stage of offshore wind power, there is an urgent need to establish a more scientific and reasonable load calculation correction method to provide more reliable technical support for the design of offshore wind turbine support structures in typhoon-prone areas. Summary of the Invention

[0006] This invention is proposed to address the above-mentioned shortcomings, and aims to provide a theoretically clear, computationally simple, logically sound, and easily applicable method for calculating and correcting the load of offshore wind turbines in typhoon areas.

[0007] To achieve the above objectives, the present invention adopts the following solution: A method for calculating and correcting the load of offshore wind turbines in typhoon areas, including calculation of ultimate load correction and calculation of fatigue load correction; The ultimate load correction calculation uses typhoon conditions as the design benchmark. By correcting the air density and turbulence intensity under typhoon conditions, the extreme typhoon load is used as the reference force to extract the mud surface stiffness matrix. The calculation is then performed by iteratively optimizing the algorithm to gradually approximate the actual load value, thereby achieving accurate calculation of the ultimate load. The fatigue load correction calculation uses normal power generation conditions as the design benchmark. By calculating the air density and turbulence intensity under normal power generation conditions, the mud surface stiffness matrix is ​​extracted using the normal power generation ultimate load as the reference force. At the same time, the high wind speed segment in the wind speed distribution model is corrected based on local historical typhoon statistics. The fatigue load is accurately calculated through iterative optimization algorithms.

[0008] Furthermore, the ultimate load correction calculation includes the following steps: S101: Based on local meteorological data, calculate the air density under normal power generation conditions, and correct the air density according to the air pressure change characteristics during the passage of the typhoon to obtain the air density under typhoon conditions. S102: Based on the measured data of the wind tower, the environmental turbulence intensity is calculated. Taking into account the wake effect between wind turbines, the effective turbulence intensity under typhoon conditions is obtained by superimposing turbulence. S103: Establish a geometric model of the wind turbine foundation and a pile-soil coupling model in the offshore wind power foundation calculation software. Apply the initial ultimate load of the offshore wind turbine as a reference force to the top of the foundation, and extract the stiffness matrix of the mud surface position through pile linearization calculation. S104: Establish a complete wind turbine model including blades, tower, foundation and control system in the offshore wind turbine design software. Use the mud surface stiffness matrix obtained in step S103 as the boundary condition. Input the air density and turbulence intensity under typhoon conditions to generate various ultimate load conditions and complete the simulation calculation to obtain time-series load data. S105: Post-process the time-series load data and select the representative value of the ultimate load from all working conditions according to the preset load extraction principle, which is used as the ultimate load of the offshore wind turbine in the first iteration. S106: Using the ultimate load obtained in step S105 as the new reference force, return to step S103 to recalculate the mud surface stiffness matrix, and execute steps S104 and S105 in sequence to complete a new round of ultimate load calculation. S107: Compare the ultimate loads calculated in two adjacent iterations. Stop the iteration when the relative deviation between the two results is less than the preset convergence threshold, and output the final ultimate load of the offshore wind turbine; otherwise, return to step S106 to continue the iteration.

[0009] Furthermore, in step S101, the method for calculating air density under typhoon conditions is as follows: First, calculate the air density ρ under normal power generation conditions using the following formula: In the formula, P is the standard atmospheric pressure, in hPa; e is the water vapor pressure, in hPa; and T is the average temperature, in K. Then, calculate the corrected air density ρ′ under typhoon conditions using the following formula: In the formula, ρ is the air density under normal power generation conditions; T is the actual temperature under typhoon conditions, in K; P is the standard atmospheric pressure; and P′ is the atmospheric pressure under typhoon conditions.

[0010] Furthermore, in step S102, the method for calculating the effective turbulence intensity under typhoon conditions is as follows: First, calculate the environmental turbulence intensity I using the following formula: In the formula, V is the average wind speed over 10 minutes, in m / s; σv is the standard deviation of the instantaneous wind speed relative to the average wind speed over 10 minutes, in m / s. Then, based on the micro-site layout of the wind turbines, the additional turbulence intensity generated by the wake between adjacent units is calculated. The environmental turbulence intensity is then superimposed with the wake turbulence intensity to obtain the effective turbulence intensity Ieff under typhoon conditions. In the formula, Iamb is the ambient turbulence intensity; Iwake is the wake turbulence intensity; and k is the coupling effect coefficient between ambient turbulence and wake turbulence.

[0011] Furthermore, in step S103, the method for calculating the mud surface stiffness matrix includes: In offshore wind power foundation calculation software, a geometric model of the wind turbine foundation is established, and the diameter, wall thickness, and mud penetration depth of the pile foundation, as well as the material properties of the steel such as density, elastic modulus, and Poisson's ratio are set. Based on the geological survey report, a pile-soil coupling model was established, and layered soil parameters were set along the pile body from the mud surface to the pile tip, including mechanical parameters such as the thickness of each soil layer, side friction, end bearing resistance and horizontal soil resistance. Set marine environmental loads, including design wave height and period, ocean current velocity and depth, and wind load parameters. A reference force is applied to the top of the wind turbine foundation to perform a linearization analysis of the pile base. The nonlinear pile-soil interaction is equivalent to a linear spring, and a 6×6 stiffness matrix containing translational stiffness, rotational stiffness, and coupling stiffness is extracted at the mud surface.

[0012] Furthermore, in step S105, the method for post-load processing is as follows: For each ultimate load case, multiple sub-cases with different random seeds are set up for simulation calculation to eliminate the influence of turbulence randomness on the calculation results; Extract the maximum value of the time sequence load for each sub-load condition, calculate the arithmetic mean of the maximum values ​​of all sub-load conditions, and select the load value that is closest to the average value as the representative value of the load condition. Iterate through all ultimate load conditions, select the maximum value from the representative values ​​of each condition, and use it as the ultimate load output of the offshore wind turbine for the current iteration.

[0013] Furthermore, in step S107, the preset convergence threshold is 1%.

[0014] Furthermore, the fatigue load correction calculation includes the following steps: S201: Calculate the air density under normal power generation conditions based on local meteorological data; S202: Calculate the environmental turbulence intensity based on the measured data of the wind tower, comprehensively consider the wake effect between wind turbines, and calculate the effective turbulence intensity under normal power generation conditions by superimposing turbulence. S203: Using the initial normal power generation ultimate load of the offshore wind turbine as the reference force, the mud surface stiffness matrix under normal power generation conditions is extracted using the same method as the ultimate load correction calculation. S204: Statistically record the wind speed and duration of local typhoons over the years, and use probabilistic statistical methods to convert historical typhoon data into annual equivalent typhoon wind speeds of different levels and their corresponding durations, and correct the high wind speed segments described by the Weibull distribution in the wind speed distribution model. S205: Establish a complete wind turbine model in the offshore wind turbine design software, use the mud surface stiffness matrix obtained in step S203 as the boundary condition, input the air density and turbulence intensity under normal power generation conditions, use the modified wind speed distribution model to generate fatigue load conditions and complete the simulation calculation. S206: Post-process the time-series load data to obtain the ultimate load and equivalent fatigue load under normal power generation conditions. S207: Using the ultimate load under normal power generation conditions obtained in step S206 as the new reference force, return to step S203 to recalculate the mud surface stiffness matrix, and execute steps S205 and S206 in sequence to complete a new round of fatigue load calculation. S208: Compare the fatigue loads calculated in two adjacent iterations. Stop the iteration when the relative deviation between the two results is less than the preset convergence threshold, and output the final offshore wind turbine fatigue load; otherwise, return to step S207 to continue the iteration.

[0015] Furthermore, in step S204, the method for correcting the wind speed distribution model is as follows: Using the Weibull distribution as the basic wind speed distribution model, its cumulative probability distribution function is: In the formula, υ is the random variable of wind speed, in m / s; c is the scale parameter; and k is the shape parameter. Statistics were compiled on typhoon events in the local area that reached or exceeded 30 m / s in the past 30 years, and the maximum wind speed and duration of each typhoon were recorded. Using the principles of probability and mathematical statistics, historical typhoon data is converted into the probability of typhoons of different levels such as 30m / s, 35m / s, 40m / s, 45m / s, and 50m / s occurring each year, as well as the corresponding average annual duration. In the fatigue load condition setting, the duration of high wind speed segments calculated using the Weibull distribution is replaced with a corrected value based on historical typhoon statistics, while the remaining wind speed segments still use the Weibull distribution calculation results.

[0016] Furthermore, in step S206, the method for post-processing fatigue load is as follows: Rainflow counting method is used to process the time-series loads of each fatigue load condition, and the amplitude of the load cycle and the corresponding number of cycles are extracted. Based on Miner's linear cumulative damage theory, load cycles of different amplitudes are converted into equivalent fatigue loads under a unified reference cycle number, which is taken as 1×10⁻⁶. 7 or 1×10 8 Second-rate; The method for extracting the ultimate load under normal power generation conditions is as follows: select the conditions that belong to the normal power generation state from the fatigue load conditions, and extract the representative value of the ultimate load under normal power generation conditions according to the ultimate load post-processing method.

[0017] Compared with the prior art, the present invention has the following beneficial effects: First, this invention establishes a comprehensive system for calculating and correcting the load on offshore wind turbines in typhoon-prone areas. Addressing the shortcomings of traditional calculation methods in parameter selection and model construction, this invention performs calculation corrections from four key dimensions: air density, turbulence intensity, mud surface stiffness matrix, and wind speed distribution model, forming a complete correction scheme covering ultimate loads and fatigue loads. This systematic correction method comprehensively reflects the impact mechanism of typhoon conditions on wind turbine loads, avoiding calculation errors that may arise from single-parameter corrections, and providing more reliable load data support for the design of offshore wind power support structures in typhoon-prone areas. The corrected calculation results accurately reflect the actual load level under typhoon conditions, ensuring that the structural design meets both safety requirements and economic rationality.

[0018] Second, this invention employs an iterative optimization algorithm to achieve gradual convergence in load calculation. During the calculation of ultimate load and fatigue load, this invention introduces an iterative optimization mechanism, using the calculated load result as a new reference force to recalculate the mud surface stiffness matrix and perform a new round of load calculation until the relative deviation between the two calculation results is less than a set threshold. This iterative convergence calculation strategy effectively eliminates the influence of the initial reference force selection on the calculation results, ensuring that the mud surface stiffness matrix matches the actual load level. The final output load value has high accuracy and stability, overcoming the problem of inconsistency between the reference force and the calculation result in traditional methods.

[0019] Third, this invention proposes a parameter correction method for typhoon conditions in the calculation of ultimate load. By introducing a pressure correction coefficient under typhoon conditions, and deriving a correction formula for air density based on the ideal gas law, it accurately reflects the impact of the low-pressure environment of a typhoon on air density. Considering the coupling effect of environmental turbulence and wind turbine wake, the effective turbulence intensity is calculated using the square root superposition method, fully reflecting the physical characteristics of enhanced turbulence under typhoon conditions. The extreme typhoon load, rather than normal generated load, is used as the reference force to calculate the mud surface stiffness matrix, making the linearization of pile-soil interaction compatible with the actual load level. This targeted parameter correction method can accurately reflect the actual physical characteristics under typhoon conditions and significantly improve the accuracy of ultimate load calculation.

[0020] Fourth, this invention proposes a method for correcting wind speed distribution models based on historical typhoon data. Addressing the limitations of the Weibull distribution in describing typhoon wind speed ranges, this invention statistically analyzes local typhoon wind speed values ​​and their durations over the past thirty years. Using principles of probability and mathematical statistics, it converts the historical typhoon data into annual equivalent wind speeds for different typhoon levels and their corresponding durations. In fatigue load scenarios, the duration of high-wind-speed ranges calculated using the Weibull distribution is replaced with corrected values ​​obtained from historical typhoon statistics, while other wind speed ranges still use the Weibull distribution calculation results. This correction method based on measured data more accurately reflects the wind speed distribution characteristics of typhoon-prone areas and improves the accuracy of fatigue load calculations.

[0021] Fifth, this invention has good engineering applicability and promotional value. Each parameter correction in this method has a clear physical meaning and calculation formula, making it easy for engineering technicians to understand and master. The calculation process is clear and standardized, and can seamlessly integrate with existing commercial software platforms. The correction parameters can be adjusted according to the actual climate conditions and historical typhoon data of different typhoon regions, making it suitable for typhoon environments of different intensities and frequencies, exhibiting strong flexibility and adaptability. Through accurate load calculations and reasonable structural design, it can effectively reduce design errors caused by load assessment deviations, reduce economic losses and safety accidents caused by improper design, and provide technical support for the safe operation of offshore wind power projects throughout their entire life cycle in typhoon-prone areas.

[0022] Sixth, this invention can generate significant economic and social benefits. Using the method of this invention for load calculation and structural design can reasonably control project costs while ensuring safety, avoiding structural safety accidents caused by underestimating loads and material waste caused by overestimating loads. Engineering practice shows that after adopting the correction method of this invention, the amount of foundation steel used only increases by about 2.2%, but the structural safety margin is significantly improved, effectively preventing the risk of structural failure under typhoon conditions. From a life-cycle perspective, reasonable load assessment and structural design can extend equipment service life, reduce operation and maintenance costs, and reduce downtime losses, resulting in considerable overall economic benefits.

[0023] In summary, this invention improves the accuracy of load calculations for offshore wind turbines in typhoon-prone areas, ensuring the safety and durability of turbines under extreme weather conditions, thereby providing a more economical and environmentally friendly solution for the offshore wind power industry. It not only optimizes turbine design and reduces operational risks but also lowers maintenance costs and extends equipment lifespan, playing a significant positive role in improving the overall economic efficiency and sustainability of wind power projects. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating a method for calculating and correcting the load on offshore wind turbines in typhoon areas according to the present invention. Figure 2 This is a schematic diagram of an offshore wind turbine structure. Figure 3 This is a schematic diagram of the Weibull model for wind speed distribution. Figure 4 This is a schematic diagram of the wind turbine load coordinate system; In the diagram, 1-wind turbine blade; 2-wind turbine tower; 3-wind turbine foundation; 4-sea surface; 5-seabed mud surface. Detailed Implementation

[0025] The following describes in detail, with reference to the accompanying drawings, the specific implementation scheme of the method for calculating and correcting the load of offshore wind turbines in typhoon areas involved in this invention.

[0026] The following example, taken at an offshore wind farm in Guangdong Province, illustrates a method for calculating and correcting the load of offshore wind turbines in typhoon-prone areas, as described in this invention.

[0027] I. Project Background and Design Conditions The offshore wind farm involved in this embodiment is located in the coastal waters of Guangdong Province, a typical typhoon-prone area. This sea area is significantly affected by tropical cyclones from the Northwest Pacific during the summer and autumn seasons each year, and has historically been directly hit by strong typhoons and super typhoons multiple times. The wind farm is planned to use 6.45MW offshore wind turbines with a rotor diameter of 180 meters and a hub height of approximately 100 meters. The turbine foundations will adopt a monopile foundation type, with pile diameters of 7 to 8 meters, and the embedment depth will be determined based on geological conditions.

[0028] like Figure 2 As shown, the offshore wind turbine structure mainly consists of wind turbine blades (1), wind turbine tower (2), and wind turbine foundation (3). The wind turbine blades are mounted on the hub, converting wind energy into mechanical energy; the wind turbine tower serves as a supporting structure, supporting the blades and nacelle at a certain height; the wind turbine foundation penetrates the sea surface (4) and inserts below the seabed mud surface (5), transferring the load of the superstructure to the foundation soil. When performing load calculations, a complete wind turbine support structure model needs to be established, and the stiffness matrix at the mud surface location needs to be extracted as the boundary condition for the load analysis model.

[0029] Based on wind resource assessment and marine environmental survey, the main design parameters of this embodiment are shown in Table 1.

[0030] Table 1 Environmental parameters for wind turbine load calculation In addition, ocean current parameters are also important for wind turbine foundation design. The ocean current velocities at different depths are shown in Table 2.

[0031] Table 2 Ocean current parameters like Figure 3As shown, the Weibull distribution is a widely used wind speed probability distribution model in the wind energy field. By statistically analyzing wind measurement data, the scale parameter A and shape parameter K of the Weibull distribution can be fitted, thus describing the wind speed distribution characteristics of the region. The probability density function of the Weibull distribution is: In the formula, υ is a random variable of wind speed in m / s; A is a scale parameter; and k is a shape parameter. In this embodiment, the scale parameter A is 9.34 m / s, the shape parameter K is 2.64, and the annual average wind speed is 8.20 m / s.

[0032] II. Ultimate Load Correction Calculation like Figure 1 As shown, the ultimate load correction calculation mainly includes steps such as calculating air density under typhoon conditions, calculating turbulence intensity under typhoon conditions, calculating the mud surface stiffness matrix, and iterative optimization calculation. This invention mainly performs correction calculations based on four boundary conditions: air density, turbulence intensity, mud surface stiffness matrix, and wind speed distribution model.

[0033] Step S101: Calculate the air density under typhoon conditions Air density is a fundamental parameter for calculating aerodynamic loads and directly affects the magnitude of wind loads acting on wind turbine blades. For offshore wind farms, the air density under normal power generation conditions must first be calculated based on local meteorological data, and then corrections must be made to account for pressure changes during typhoons.

[0034] The air density ρ under normal power generation conditions is calculated using the following formula: In the formula, P is the standard atmospheric pressure, in hPa, usually taken as 1013.25 hPa; e is the water vapor pressure, in hPa, which can be calculated based on relative humidity and saturated water vapor pressure; T is the average air temperature, in K (Kelvin), which needs to be converted from Celsius to thermodynamic temperature. This formula is derived based on the ideal gas law and takes into account the mixing effect of dry air and water vapor.

[0035] A typhoon is a powerful tropical cyclone with a central pressure significantly lower than the surrounding atmospheric pressure. Meteorological studies show that the central pressure of a strong typhoon can drop below 950 hPa, and that of a super typhoon can drop below 920 hPa. The low-pressure environment during a typhoon's passage causes changes in air density. The corrected air density ρ′ under typhoon conditions is calculated using the following formula: In the formula, ρ is the air density under normal power generation conditions, with units of kg / m³. 3T represents the actual temperature under typhoon conditions, in Kelvin (K); P represents standard atmospheric pressure, in hPa; and P′ represents atmospheric pressure under typhoon conditions, in hPa. This formula reflects the combined effect of temperature and air pressure changes on air density.

[0036] In this embodiment, based on years of observation data from the local meteorological station, the calculated air density under normal power generation conditions is 1.155 kg / m³. 3 Considering typical atmospheric pressure conditions during a typhoon's passage (taking the typhoon center pressure as approximately 970 hPa), the corrected air density for typhoon conditions is 1.149 kg / m³. 3 Although the numerical change is small, this correction is necessary for accurate load calculations.

[0037] Step S102: Calculate the turbulence intensity under typhoon conditions Turbulence intensity reflects the degree of wind speed fluctuation and is an important parameter affecting the dynamic response and fatigue load of wind turbines. Under typhoon conditions, strong atmospheric disturbances significantly increase turbulence intensity, and the wake effect between adjacent units within the wind farm is also more pronounced.

[0038] The environmental turbulence intensity I is calculated using the following formula: In the formula, V is the average wind speed over 10 minutes, in m / s; σv is the standard deviation of the instantaneous wind speed relative to the average wind speed over 10 minutes, in m / s. This definition conforms to the relevant standards of the International Electrotechnical Commission (IEC).

[0039] For wind farms, in addition to environmental turbulence, the additional turbulence generated by the turbine wake must also be considered. After the incoming flow passes the upstream turbine, a wake region forms downstream, where wind speed decreases and turbulence intensifies. Once the micro-site selection of the wind turbines is determined, the wake turbulence intensity can be calculated based on the turbine spacing and arrangement. The effective turbulence intensity Ieff under typhoon conditions is calculated using the square root superposition method: In the formula, Iamb represents the environmental turbulence intensity, calculated from measured data from the anemometer tower; Iwake represents the wake turbulence intensity, calculated based on the wake model; and k is the coupling effect coefficient between environmental turbulence and wake turbulence, typically taken as 1.0 to 1.2. The square root superposition method assumes that environmental turbulence and wake turbulence are statistically independent, and can reasonably reflect the combined effect of the two.

[0040] In this embodiment, based on the data from the meteorological tower and the wake model, the environmental turbulence intensity before correction was 0.105, and the effective turbulence intensity after correction for typhoon conditions and consideration of the wake effect was 0.129, an increase of approximately 23%. The increase in turbulence intensity means that the wind speed fluctuations are more intense, and the dynamic load on the wind turbine structure also increases accordingly.

[0041] Step S103: Calculate the mud surface stiffness matrix The mud surface stiffness matrix is ​​a key parameter describing the ability of a pile foundation to resist external forces at the mud surface. It is an important means of simplifying complex pile-soil interactions into boundary conditions. In wind turbine load simulation calculations, the mud surface stiffness matrix is ​​typically used as the boundary constraint of the foundation model to simplify the calculation model and improve computational efficiency. The mud surface stiffness matrix is ​​a concentrated representation of the pile foundation linearization results at the pile-soil interaction section (mud surface location).

[0042] The calculation of the mud surface stiffness matrix needs to be completed in specialized offshore wind power foundation calculation software (such as SACS software). The specific steps are as follows: (1) Establish the geometric model of the wind turbine foundation. Input the geometric parameters of the pile foundation into the calculation software, including pile diameter, wall thickness, and depth into the mud; set the material properties of the steel, including density, elastic modulus, Poisson's ratio (shear modulus), and yield strength. For piles with variable cross-sections or foundation structures with transition sections, it is necessary to model them in segments and ensure that the connection between each segment is correct.

[0043] (2) Establish a pile-soil coupling model. Based on the soil layer information provided in the geological survey report (geological data), set layered soil parameters along the pile body from the mud surface to the pile tip. The main parameters include: the thickness of each soil layer, soil type, side friction (tz curve), end bearing resistance (Qz curve), and horizontal soil resistance (py curve), etc. These parameters determine the mechanical properties of pile-soil interaction, and pile-soil coupling calculation is performed.

[0044] (3) Set marine environmental loads. Input design wave parameters (wave height, wavelength, and period); input ocean current parameters (current velocity and range of action); input wind parameters (wind speed, wind direction), etc. The environmental loads act on the underwater part of the pile body, and together with the wind turbine loads, they constitute the external forces acting on the foundation.

[0045] (4) Apply a reference force to perform pile baseline linearization calculation. Apply the initial ultimate load of the offshore wind turbine as a reference force at the top of the wind turbine foundation to perform pile baseline linearization calculation. That is, simplify the complex nonlinear soil-pile interaction into a linear soil-pile interaction. The resistance of the soil to the pile (side friction, horizontal soil resistance and end resistance) is transformed into a linear spring proportional to the displacement. The soil-pile interaction is characterized by the stiffness coefficient.

[0046] (5) Extract the stiffness matrix of the wind turbine foundation at the mud surface from the calculation results. The mud surface stiffness matrix is ​​a 6×6 matrix, which includes translational stiffness, rotational stiffness and coupling stiffness terms.

[0047] Before performing the first ultimate load calculation, the mud surface stiffness matrix is ​​extracted using the initial load as the reference force. The initial wind turbine load format is shown in Table 3 (the extraction location is the bottom flange of the tower, i.e., the top of the foundation): Table 3 Initial ultimate load of the wind turbine (at the bottom flange of the tower) Based on the initial load mentioned above as the reference force, after completing the pile baseline linearization calculation in SACS software, the extracted mud surface stiffness matrix [D] is shown in Table 4: Table 4 Initial mud surface stiffness matrix The mud surface stiffness matrix reflects displacement stiffness, rotational stiffness, and coupling stiffness in different directions. In subsequent wind turbine load simulation calculations, the mud surface stiffness matrix represents the constraint at the bottom of the structure. Unlike traditional methods, this invention uses the extreme typhoon load as the reference force when calculating the mud surface stiffness matrix corresponding to the ultimate load, rather than the ultimate load under normal power generation conditions. This is because pile-soil interaction exhibits significant nonlinear characteristics, and the equivalent stiffness differs under different load levels. Linearization using a reference force equivalent to the actual load level yields a more accurate stiffness matrix.

[0048] Step S104: Perform the first ultimate load calculation Using the corrected air density, turbulence intensity, and mud surface stiffness matrix calculated under the initial ultimate load conditions under typhoon conditions, the first ultimate load calculation is performed in offshore wind turbine design software (such as Bladed). The specific steps are as follows: (1) Establish a wind turbine model (blade, hub, main unit, tower) in the offshore wind turbine design software and set relevant material property parameters. At the same time, establish a generator, main shaft, gearbox and control system model.

[0049] (2) Establish a wind turbine foundation model (referring to the foundation structure below the tower) in the offshore wind turbine design software. The foundation model is only established up to the seabed mud surface, and a mud surface stiffness matrix is ​​applied at the mud surface as a constraint (that is, a simplification method is used to simplify the complex pile-soil interaction into a mud surface stiffness matrix as the boundary condition of the foundation).

[0050] (3) Input environmental parameters, including seawater density, annual average wind speed, and air density under typhoon conditions (1.149 kg / m³). 3 ) and turbulence intensity under typhoon conditions (0.129), etc.

[0051] (4) Generate all ultimate load calculation conditions in the software (combining different wind conditions, wave conditions, tide conditions, ocean current conditions, wind and wave angles, and wind turbine operating status, etc.).

[0052] (5) Complete the calculation of all ultimate load cases and obtain the time-series load values ​​of all ultimate load cases.

[0053] Step S105: Load Post-processing Post-processing is performed on the time-series load data to extract representative values ​​of the ultimate load. To eliminate the influence of random factors, each working condition typically has six sub-working conditions using different random seeds for simulation calculations. The principle for extracting the ultimate load is as follows: extract the maximum value of the time-series load for each of the six sub-working conditions, then calculate the average of these six maximum values, and select the load value closest to the average as the target value for that working condition. The maximum value of the target value is selected from all working conditions, which is the ultimate load of the offshore wind turbine obtained in the first calculation.

[0054] Steps S106-S107: Iterative optimization calculation Using the ultimate load of the offshore wind turbine calculated in the first iteration as the new reference force, return to step S103 to recalculate the mud surface stiffness matrix, and then execute steps S104 and S105 sequentially to complete a new round of ultimate load calculation. Compare the ultimate load of the offshore wind turbine calculated iteratively with the one calculated previously. If the relative deviation between the two results is less than 1%, stop the iterative calculation and output the final ultimate load calculation result; otherwise, continue iterating until convergence.

[0055] After convergence of iterative calculations, the mud surface stiffness matrix under typhoon conditions is shown in Table 5: Table 5 Mud surface stiffness matrix under typhoon conditions (unit: kN, m) The ultimate load of the wind turbine calculated using the corrected parameters is shown in Table 6: Table 6 Ultimate load of wind turbines under typhoon conditions (at the bottom flange of the tower) The calculation results of this embodiment show that the representative value of the ultimate load Myz-max obtained by the traditional calculation method is 242659.1 kNm, while the representative value of the ultimate load Myz-max obtained by the correction method of this invention is 250181.5 kNm, an increase of about 3.1%. Although this difference may seem small, for large offshore wind turbines, a 3% load increment may lead to significant adjustments to the structural design scheme, which is of great significance for ensuring structural safety.

[0056] III. Fatigue Load Correction Calculation The fatigue load correction calculation mainly includes the calculation of air density and turbulence intensity under normal power generation conditions, the calculation of mud surface stiffness matrix, the correction of wind speed distribution model, and iterative optimization calculation.

[0057] Steps S201-S202: Calculate air density and turbulence intensity under normal power generation conditions. The air density used in the fatigue load calculation adopts the parameter value under normal power generation conditions. The air density is calculated according to the basic formula in step S101, but without typhoon condition correction. In this embodiment, it is taken as 1.155 kg / m³. 3 The calculation of turbulence intensity also needs to consider the wind turbine wake effect. The environmental turbulence intensity and the wake turbulence intensity are superimposed using the square root method to obtain the effective turbulence intensity under normal power generation conditions. The turbulence intensity before correction is 0.105, and the effective turbulence intensity after correction is 0.129.

[0058] Step S203: Calculate the mud surface stiffness matrix under normal power generation conditions. The calculation method for the mud surface stiffness matrix is ​​similar to that for the ultimate load calculation, but the reference force is adjusted from the extreme typhoon load to the ultimate load under normal power generation conditions. This is because fatigue load mainly reflects the cumulative effect of cyclic loads during the long-term normal operation of the wind turbine, and using the reference force under normal power generation conditions is more in line with the actual operating conditions.

[0059] The ultimate load of the wind turbine under normal power generation conditions is shown in Table 7 (the extraction location is the bottom flange of the tower, i.e., the top of the foundation): Table 7 Ultimate load of wind turbine under normal power generation conditions (at the bottom flange of the tower) The mud surface stiffness matrix calculated based on the ultimate load under normal power generation conditions as the reference force is shown in Table 8. Table 8 Mud surface stiffness matrix under normal power generation conditions Step S204: Wind speed distribution model correction Based on the given Weibull model values ​​A and K, and the average wind speed Vave, the wind speed probability distribution can be derived. The cumulative probability distribution function of the Weibull distribution is: In the formula, υ is the random variable of wind speed, in m / s; c is the scale parameter; and k is the shape parameter. The values ​​of A and k determine the shape and scale of the distribution.

[0060] When setting fatigue load calculation conditions, it is necessary to determine the annual occurrence duration of different wind speed ranges. Taking the calculation of the annual occurrence duration of wind speed 4 m / s as an example: first, calculate the cumulative probability distribution F(5) when the wind speed is 5 m / s, and then calculate the cumulative probability distribution F(3) when the wind speed is 3 m / s. Subtracting F(3) from F(5) gives the probability of the wind speed occurring in the range of 3 m / s to 5 m / s. Multiplying the total duration (8760 hours / year) by this probability gives the annual occurrence duration of this wind speed range. Similarly, the duration of different wind speed ranges such as 0 to 50 m / s can be calculated based on the Weibull distribution.

[0061] However, due to the limitations of the Weibull distribution model, its probability distribution for fitting typhoon wind speed ranges is inaccurate, thus requiring correction. The correction method of this invention is as follows: statistically analyze the local typhoon wind speed values ​​and durations over the past 30 years, and based on the principles of probability and mathematical statistics, convert these values ​​into several different typhoon wind speed values ​​and corresponding durations each year. Specifically, the steps are: statistically analyze the number of typhoons with wind speeds above 30 m / s and their durations over the past 30 years, and using the principles of probability and mathematical statistics, convert these values ​​into different levels of typhoons occurring each year, such as 30 m / s, 35 m / s, 40 m / s, 45 m / s, and 50 m / s, and calculate the duration of each wind speed range.

[0062] In this embodiment, based on nearly 30 years of typhoon statistics for the wind farm's location, data corrections are made to the design wind speed and duration of occurrence of the high-wind-speed idling condition DLC6.4 in the fatigue conditions of offshore wind turbines as specified in the "Design Requirements for Offshore Wind Turbine Generators" (GB / T 31517-2015). Traditional methods only consider typhoon conditions with wind speeds of 35 m / s for the high-wind-speed condition DLC6.4, and the annual occurrence duration of this condition is calculated entirely based on the probability density function in the Weibull distribution. The correction method involves designing the wind speeds for the high-wind-speed condition DLC6.4 as three conditions: 30 m / s, 40 m / s, and 50 m / s. The annual occurrence time of each condition is derived from statistical processing of historical typhoon data to more accurately reflect the impact of typhoon conditions on fatigue loads. For the remaining conditions other than the high-wind-speed condition DLC6.4, the wind speed distribution is still derived using the Weibull probability distribution.

[0063] Step S205: Fatigue Load Calculation Using air density, turbulence intensity, mud surface stiffness matrix, and a modified wind speed distribution model under normal power generation conditions, the first calculation and analysis of ultimate load and fatigue load under normal power generation conditions was performed in offshore wind turbine design software. The calculation steps were similar to those for ultimate load calculation, but the operating conditions needed to cover multiple operating states such as normal power generation, start-up, shutdown, standby, and idling, as well as combinations of different wind conditions, waves, tide levels, and ocean currents.

[0064] Step S206: Post-fatigue loading treatment Post-processing was performed on the time-series loads for all fatigue load conditions. Rainflow counting was used to convert all time-series loads into load amplitudes and cycle counts. Subsequently, the load amplitudes and cycle counts were converted into equivalent fatigue loads (with the cycle count set to a fixed 1×10⁻⁶). 7 or 1×10 8 Second-rate).

[0065] The post-processing steps for the ultimate load under normal power generation conditions of offshore wind turbines are as follows: considering only the normal power generation conditions under fatigue load conditions, the ultimate load under normal power generation conditions is obtained according to the aforementioned ultimate load post-processing method.

[0066] Steps S207-S208: Iterative optimization calculation Using the initial calculated ultimate load of the offshore wind turbine as the new reference force, the process returns to step S203 to recalculate the mud surface stiffness matrix. Steps S205 and S206 are then executed sequentially to complete a new round of fatigue load calculations. The iteratively calculated fatigue load of the offshore wind turbine is compared with the previously calculated fatigue load. If the relative deviation between the two results is less than 1%, the iterative calculation stops, and the fatigue load calculation results for the offshore wind turbine are output.

[0067] After convergence of iterative calculations, the equivalent fatigue load at the bottom flange of the tower is shown in Table 9 (number of cycles 1.0 × 10⁻⁶). 8 ): Table 9 Equivalent fatigue load at the bottom flange of the tower (number of cycles 1.0 × 10⁻⁶) 8 ) The calculation results of this embodiment show that the equivalent fatigue load representative value My (with Wöhler exponent of 5) obtained by the traditional calculation method is 41691.5 kNm, while the equivalent fatigue load representative value My obtained by the correction method of this invention is 42858.9 kNm, and the equivalent fatigue load value increases by about 2.8%.

[0068] IV. Analysis of Correction Effects and Engineering Applications The ultimate load and fatigue load obtained using the typhoon-affected offshore wind turbine load calculation correction method of this invention are both greater than the corresponding load values ​​obtained by traditional calculation methods, indicating that traditional calculation methods are overly aggressive. This invention fully considers the impact of typhoons on wind turbine loads, resulting in more accurate load results.

[0069] like Figure 4The diagram shows the wind turbine load coordinate system. When performing load calculations and outputting results, it is necessary to clearly define the direction and position of each load component. The x-axis is typically defined as the alongwind direction, the y-axis as the crosswind direction, and the z-axis as vertically upward. Bending moment Mx represents the bending moment about the x-axis, and Myz represents the combined bending moment of My and Mz; these are commonly used control parameters in structural design. The ultimate load and fatigue load output by the method of this invention are both referenced to the standard coordinate system, making it convenient for designers to directly apply to subsequent structural design calculations.

[0070] Taking a certain offshore wind farm in Guangdong Province as an example, the modified calculation method was used for structural design, which increased the foundation engineering volume (by steel weight) by approximately 2.2%, ensuring a more reasonable, safe, and reliable structural design. From a life-cycle perspective, reasonable load assessment and structural design can extend equipment service life, reduce operation and maintenance costs, and reduce downtime losses caused by structural damage, resulting in considerable overall economic benefits.

[0071] The above embodiments are merely illustrative examples of the technical solution of the present invention. The method for calculating and correcting the load of offshore wind turbines in typhoon areas involved in the present invention is not limited to the content described in the above embodiments, but is subject to the scope defined by the claims. Any modifications, additions, or equivalent substitutions made by those skilled in the art based on these embodiments are within the scope of protection claimed by the claims of the present invention.

Claims

1. A method for calculating and correcting the load on offshore wind turbines in typhoon-prone areas, characterized in that, This includes calculations for ultimate load correction and fatigue load correction; The ultimate load correction calculation uses typhoon conditions as the design benchmark. By correcting the air density and turbulence intensity under typhoon conditions, the extreme typhoon load is used as the reference force to extract the mud surface stiffness matrix. The calculation is then performed by iteratively optimizing the algorithm to gradually approximate the actual load value, thereby achieving accurate calculation of the ultimate load. The fatigue load correction calculation uses normal power generation conditions as the design benchmark. By calculating the air density and turbulence intensity under normal power generation conditions, the mud surface stiffness matrix is ​​extracted using the normal power generation ultimate load as the reference force. At the same time, the high wind speed segment in the wind speed distribution model is corrected based on local historical typhoon statistics. The fatigue load is accurately calculated through iterative optimization algorithms.

2. The method for calculating and correcting offshore wind turbine loads in typhoon-prone areas according to claim 1, characterized in that, The ultimate load correction calculation includes the following steps: S101: Based on local meteorological data, calculate the air density under normal power generation conditions, and correct the air density according to the air pressure change characteristics during the passage of the typhoon to obtain the air density under typhoon conditions. S102: Based on the measured data of the wind tower, the environmental turbulence intensity is calculated. Taking into account the wake effect between wind turbines, the effective turbulence intensity under typhoon conditions is obtained by superimposing turbulence. S103: Establish a geometric model of the wind turbine foundation and a pile-soil coupling model in the offshore wind power foundation calculation software. Apply the initial ultimate load of the offshore wind turbine as a reference force to the top of the foundation, and extract the stiffness matrix of the mud surface position through pile linearization calculation. S104: Establish a complete wind turbine model including blades, tower, foundation and control system in the offshore wind turbine design software. Use the mud surface stiffness matrix obtained in step S103 as the boundary condition. Input the air density and turbulence intensity under typhoon conditions to generate various ultimate load conditions and complete the simulation calculation to obtain time-series load data. S105: Post-process the time-series load data and select the representative value of the ultimate load from all working conditions according to the preset load extraction principle, which is used as the ultimate load of the offshore wind turbine in the first iteration. S106: Using the ultimate load obtained in step S105 as the new reference force, return to step S103 to recalculate the mud surface stiffness matrix, and execute steps S104 and S105 in sequence to complete a new round of ultimate load calculation. S107: Compare the ultimate loads calculated in two adjacent iterations. Stop the iteration when the relative deviation between the two results is less than the preset convergence threshold, and output the final ultimate load of the offshore wind turbine; otherwise, return to step S106 to continue the iteration.

3. The method for calculating and correcting the load of offshore wind turbines in typhoon areas according to claim 2, characterized in that, In step S101, the method for calculating air density under typhoon conditions is as follows: First, calculate the air density ρ under normal power generation conditions using the following formula: In the formula, P is the standard atmospheric pressure, in hPa; e is the water vapor pressure, in hPa; and T is the average temperature, in K. Then, calculate the corrected air density ρ′ under typhoon conditions using the following formula: In the formula, ρ is the air density under normal power generation conditions; T represents the actual temperature under typhoon conditions, in Kelvin (K); P represents standard atmospheric pressure; and P′ represents atmospheric pressure under typhoon conditions.

4. The method for calculating and correcting the load of offshore wind turbines in typhoon areas according to claim 2, characterized in that, In step S102, the method for calculating the effective turbulence intensity under typhoon conditions is as follows: First, calculate the environmental turbulence intensity I using the following formula: In the formula, V is the average wind speed over 10 minutes, in m / s; σv is the standard deviation of the instantaneous wind speed relative to the average wind speed over 10 minutes, in m / s. Then, based on the micro-site layout of the wind turbines, the additional turbulence intensity generated by the wake between adjacent units is calculated. The environmental turbulence intensity is then superimposed with the wake turbulence intensity to obtain the effective turbulence intensity Ieff under typhoon conditions. In the formula, Iamb is the ambient turbulence intensity; Iwake is the wake turbulence intensity; and k is the coupling effect coefficient between ambient turbulence and wake turbulence.

5. The method for calculating and correcting the load of offshore wind turbines in typhoon areas according to claim 2, characterized in that, In step S103, the method for calculating the mud surface stiffness matrix includes: In offshore wind power foundation calculation software, a geometric model of the wind turbine foundation is established, and the diameter, wall thickness, and mud penetration depth of the pile foundation, as well as the material properties of the steel such as density, elastic modulus, and Poisson's ratio are set. Based on the geological survey report, a pile-soil coupling model was established, and layered soil parameters were set along the pile body from the mud surface to the pile tip, including mechanical parameters such as the thickness of each soil layer, side friction, end bearing resistance and horizontal soil resistance. Setting marine environmental loads includes design wave height and period, ocean current velocity and depth of action, and wind load parameters. A reference force is applied to the top of the wind turbine foundation to perform a linearization analysis of the pile base. The nonlinear pile-soil interaction is equivalent to a linear spring, and a 6×6 stiffness matrix containing translational stiffness, rotational stiffness, and coupling stiffness is extracted at the mud surface.

6. The method for calculating and correcting the load of offshore wind turbines in typhoon areas according to claim 2, characterized in that, In step S105, the method for post-load processing is as follows: For each ultimate load case, multiple sub-cases with different random seeds are set up for simulation calculation to eliminate the influence of turbulence randomness on the calculation results; Extract the maximum value of the time sequence load for each sub-load condition, calculate the arithmetic mean of the maximum values ​​of all sub-load conditions, and select the load value that is closest to the average value as the representative value of the load condition. Iterate through all ultimate load conditions, select the maximum value from the representative values ​​of each condition, and use it as the ultimate load output of the offshore wind turbine for the current iteration.

7. The method for calculating and correcting the load of offshore wind turbines in typhoon areas according to claim 2, characterized in that, In step S107, the preset convergence threshold is 1%.

8. The method for calculating and correcting offshore wind turbine loads in typhoon-prone areas according to claim 1, characterized in that, The fatigue load correction calculation includes the following steps: S201: Calculate the air density under normal power generation conditions based on local meteorological data; S202: Calculate the environmental turbulence intensity based on the measured data of the wind tower, comprehensively consider the wake effect between wind turbines, and calculate the effective turbulence intensity under normal power generation conditions by superimposing turbulence. S203: Using the initial normal power generation ultimate load of the offshore wind turbine as the reference force, the mud surface stiffness matrix under normal power generation conditions is extracted using the same method as the ultimate load correction calculation. S204: Statistically record the wind speed and duration of local typhoons over the years, and use probabilistic statistical methods to convert historical typhoon data into annual equivalent typhoon wind speeds of different levels and their corresponding durations, and correct the high wind speed segments described by the Weibull distribution in the wind speed distribution model. S205: Establish a complete wind turbine model in the offshore wind turbine design software, use the mud surface stiffness matrix obtained in step S203 as the boundary condition, input the air density and turbulence intensity under normal power generation conditions, use the modified wind speed distribution model to generate fatigue load conditions and complete the simulation calculation. S206: Post-process the time-series load data to obtain the ultimate load and equivalent fatigue load under normal power generation conditions. S207: Using the ultimate load under normal power generation conditions obtained in step S206 as the new reference force, return to step S203 to recalculate the mud surface stiffness matrix, and execute steps S205 and S206 in sequence to complete a new round of fatigue load calculation. S208: Compare the fatigue loads calculated in two adjacent iterations. Stop the iteration when the relative deviation between the two results is less than the preset convergence threshold, and output the final offshore wind turbine fatigue load; otherwise, return to step S207 to continue the iteration.

9. The method for calculating and correcting the load of offshore wind turbines in typhoon areas according to claim 8, characterized in that, In step S204, the method for correcting the wind speed distribution model is as follows: Using the Weibull distribution as the basic wind speed distribution model, its cumulative probability distribution function is: In the formula, υ is a random variable of wind speed, with the unit being m / s; c is the scale parameter; k is the shape parameter; Statistics were compiled on typhoon events in the area that reached or exceeded 30 m / s in the past 30 years, and the maximum wind speed and duration of each typhoon were recorded. Using the principles of probability and mathematical statistics, historical typhoon data is converted into the probability of typhoons of different levels such as 30m / s, 35m / s, 40m / s, 45m / s, and 50m / s occurring each year, as well as the corresponding average annual duration. In the fatigue load condition setting, the duration of high wind speed segments calculated using the Weibull distribution is replaced with a corrected value based on historical typhoon statistics, while the remaining wind speed segments still use the Weibull distribution calculation results.

10. The method for calculating and correcting the load of offshore wind turbines in typhoon areas according to claim 8, characterized in that, In step S206, the method for post-processing fatigue load is as follows: Rainflow counting method is used to process the time-series loads of each fatigue load condition, and the amplitude of the load cycle and the corresponding number of cycles are extracted. Based on Miner's linear cumulative damage theory, load cycles of different amplitudes are converted into equivalent fatigue loads under a unified reference cycle number, which is taken as 1×10⁻⁶. 7 Next or 1×10 8 Second-rate; The method for extracting the ultimate load under normal power generation conditions is as follows: select the conditions that belong to the normal power generation state from the fatigue load conditions, and extract the representative value of the ultimate load under normal power generation conditions according to the ultimate load post-processing method.

Images