A correction method for partial factors applicable to the structural scheme design of offshore wind turbines

Abstract

A method for modifying the partial factor of the structural scheme design of an offshore wind turbine, which belongs to the technical field of offshore wind turbine structures. Based on the reliability analysis theory, this method fully considers and quantifies the uncertain factors faced by the structural design of offshore wind turbines. By introducing partial safety factors, it ensures that the designed structure can meet the predetermined safety requirements as much as possible while approaching the target safety requirements during the service life, thereby avoiding waste of material costs caused by over-design of the structure.

Description

Technical Field

[0001] The present invention relates to a method for correcting the partial safety factor of offshore wind turbine structural design based on the principle of structural reliability, and specifically to a method for correcting the partial safety factor of offshore wind turbine structural scheme design which comprehensively considers the uncertainty factors such as structural parameters and environmental loads faced in the design stage of offshore wind turbines and fully considers the coupling effect between different loads of the overall structure of the offshore wind turbine. Background Art

[0002] At the current stage, the design of offshore wind turbine structures basically adopts the deterministic design method of traditional load-resistance partial coefficients, which mainly relies on load partial coefficients and resistance partial coefficients to characterize the uncertainty factors in the design process of offshore wind turbines. In addition, the partial safety factors in the commonly used design specifications for large offshore wind turbines are mostly derived from the traditional oil and gas industry. However, there are many differences between offshore wind turbine structures and offshore oil and gas platforms in terms of expected functions, loads borne, and service life; therefore, directly adopting the recommended partial safety factors in existing specifications during the design stage of offshore wind turbine structures usually results in over-design of wind turbine structures. Therefore, in the context of the high average cost of offshore wind power in my country, it is an objective problem that the offshore wind energy industry needs to solve urgently to make reasonable revisions to the safety partial coefficients in the current specifications. Summary of the invention

[0003] In order to reasonably correct the safety partial coefficient, the present invention proposes a correction method for the partial coefficient of offshore wind turbine structural design based on reliability. This method fully considers the coupling effect between different loads of offshore wind turbines, and can fully consider the uncertainty factors existing in the design process of offshore wind turbines. Based on this correction method, the relevant partial safety factors of the current offshore wind turbine specifications can be corrected to formulate design specifications that are more in line with the structural and functional requirements of offshore wind turbines. In addition, this method can further formulate a combination of offshore wind turbine partial safety design indicators suitable for China's offshore waters based on the unique environmental characteristics of my country's waters.

[0004] The present invention proposes a method for correcting the partial safety factor of offshore wind turbine structural design based on the principle of structural reliability. This scheme can not only take into account the coupling effect between the marine environmental load and the structure, but also simulate the offshore wind turbines under different working conditions (normal operation / shutdown), so as to achieve the purpose of systematically and comprehensively correcting the partial safety factor of the offshore wind turbine structural design.

[0005] The technical solution adopted by the present invention is: a correction method for the partial safety factor of the offshore wind turbine structural design, comprising the following steps:

[0006] S1. Determine the safety function requirements of the target designed wind turbine, and identify and quantify the load uncertainty, structural uncertainty, and accidental uncertainty existing in the design process;

[0007] S2. For the above uncertainty variables, conduct experimental design using Monte Carlo sampling, Latin hypercube sampling, or central composite sampling to obtain the sample combinations of random input variables;

[0008] S3. Establish an executable program for parametric modeling of the overall coupled model of the offshore wind turbine, and execute this program in combination with the above random sample combinations to carry out automated calculations of the fully coupled dynamic response of the offshore wind turbine structure;

[0009] S4. Combine the structural output response and random input variables to construct a mathematical surrogate model to simulate the mathematical relationship between uncertainty variables and structural response;

[0010] The constructed mathematical model:

[0011]

[0012] In the formula: a 0 , a 1 , …, a M are the coefficients of the basis functions of the regression model. For a quadratic regression model with cross terms, the value of its coefficient M satisfies

[0013] Adopt the multiple linear regression method to fit the coefficients of the quadratic polynomial based on the input variables and output responses obtained from the above steps;

[0014] S5. Combine the above mathematical surrogate model and the design safety threshold of the offshore wind turbine, and at the same time introduce partial safety factors to establish the limit state function under typical failure modes of the offshore wind turbine;

[0015] The limit state function is:

[0016] Among them, the R term represents the structural resistance, the S term represents the load effect, X represents the uncertainty variables in the structural design process, and γ m represents the partial coefficient of the structural bearing capacity, and γ f represents the partial coefficient of the structural load effect;

[0017] S6. Calculate the structural reliability index under the target failure mode, and use the classical reliability calculation method to calculate the structural reliability index of the limit state function. The calculation result is denoted as β(γ m0 , γ f0 );

[0018] Combine the obtained reliability index β(γ m , γ f)With the safety and reliability index threshold β T An optimization function is established to further correct the partial safety factors; the optimization function is:

[0019] M = (β(γ m , γ f ) - β T ) 2

[0020] The adaptive iterative optimization algorithm is used to gradually update the safety factors (γ mi , γ fi ), and then the limit state equation under typical failure modes is updated to:

[0021]

[0022] The corresponding structural reliability index is denoted as β(γ mi , γ fi ); this iterative process is continuously carried out until the minimum M value is obtained, and the corresponding (γ m , γ f ) is the optimal partial safety factor.

[0023] In step S1, the uncertainty variables are identified and quantified, and statistical analysis is carried out on the physical model test data and the measured ocean environment data using statistical principles to obtain the statistical distribution types and distribution parameters characterizing their uncertainty characteristics.

[0024] In step S3, the automated calculation of the full-coupled dynamic response of the offshore wind turbine structure is carried out based on the parametric modeling executable program of the overall coupled model of the offshore wind turbine. A parametric modeling executable program is built in the development platform using the existing full-coupled dynamic simulation tool for offshore wind turbines to achieve parametric modeling, automated calculation, and data extraction and storage of the target wind turbine structure.

[0025] Furthermore, experimental design is carried out to obtain the sample combinations of random input variables, including:

[0026] For the above-mentioned uncertainty variables, experimental design is carried out using Monte Carlo sampling to obtain the sample combinations of random input variables and output the data text;

[0027] Or, for the above-mentioned uncertainty variables, experimental design is carried out using Latin hypercube sampling to obtain the sample combinations of random input variables and output the data text;

[0028] Or, for the above-mentioned uncertainty variables, experimental design is carried out using central composite sampling to obtain the sample combinations of random input variables and output the data text;

[0029] Furthermore, based on the parameterized modeling executable program of the overall coupling model of offshore wind turbines, the fully coupled dynamic response automatic calculation of offshore wind turbine structures is carried out, including:

[0030] Based on the existing fully coupled dynamic simulation tools for offshore wind turbines such as OpenFAST, HAWC2, Bladed, etc., a parametric modeling executable program is built in the development platform to realize parametric modeling, automated calculation, and data extraction and storage of the target wind turbine structure.

[0031] Furthermore, a mathematical proxy model is constructed by combining the structural output response and the random input variables, including: developing a mathematical proxy model fitting tool through a digital simulation platform, and obtaining the relationship between the structural response and the design variables by importing the input and output data into the proxy model fitting tool.

[0032] Furthermore, the initial design partial safety factor is selected based on the current specifications, and the limit state function of typical failure modes such as tower structure stress yield is established in combination with the mathematical model obtained above. The second-order moment method, Monte Carlo method, subset simulation method and other methods are selected to calculate the structural reliability index, and the relevant data are saved.

[0033] Furthermore, the optimization index is established by combining the design target safety index with the obtained design reliability index, and the combination of partial coefficients that makes the optimization function reach the optimal value is selected within the value range of the partial coefficients, which is the final correction solution.

[0034] In summary, the present invention is a method for correcting the partial coefficient of offshore wind turbine structural design based on the reliability principle and taking into account the overall coupling effect of offshore wind turbines. Therefore, the method includes the additional function of offshore wind turbine structural reliability safety evaluation. In addition, the present invention can carry out research on the influence of conventional loads such as wind load, wave load, current load, sea ice load and earthquake load on offshore wind turbine structural design, and fully consider the influence of the above loads on the safety factor of offshore wind turbine structural design.

[0035] Based on the reliability analysis theory, the present invention fully considers and quantifies the uncertainties faced by the offshore wind turbine structure design. By introducing the partial safety factor, the designed structure is guaranteed to be as close to the target safety requirement as possible on the basis of meeting the predetermined safety requirements during the service life, thereby avoiding the waste of material costs caused by excessive structural design. The present invention has at least the following advantages:

[0036] 1. Traditional offshore wind turbine structural design and verification analysis mostly adopts semi-integral methods. Such methods usually first simplify the complex foundation structure into an equivalent single pile structure or an equivalent foundation super unit; then establish a simplified offshore wind turbine overall model of blade-hub-nacelle-equivalent foundation, carry out aeroelastic analysis, and obtain the wind turbine load at the transition point of the foundation structure; then establish a real and complex foundation structure model, apply wind turbine loads and sea state loads, carry out finite element analysis, and verify the structural safety status. The semi-integral method can consider the impact of the foundation structure on the aerodynamic load of the upper wind turbine to a certain extent, but this method has shortcomings in considering the coupling effect between different loads. In addition, when calculating the wind turbine load, wind turbine manufacturers usually consider the sea state load borne by the foundation structure. In the foundation structure design stage, the sea state load is applied again, resulting in a conservative design of the foundation structure, which in turn increases the construction cost of the wind turbine. The present invention establishes an overall coupling analysis model of offshore wind turbines based on the overall coupling simulation tool, which avoids the mutual conversion and transmission of loads between different structures of the offshore wind turbines, and can carry out overall coupling response analysis of offshore wind turbines under different load conditions such as wind, waves, currents and sea ice, and can more comprehensively simulate all working conditions that offshore wind turbines may face during their service life.

[0037] 2. This method abandons the traditional deterministic design principle and fully simulates the uncertainty factors such as structural parameters, environmental parameters, accidental errors and cognitive errors in the offshore wind turbine structure design process based on the basic principles of probability statistics, and comprehensively quantifies the influencing factors in the offshore wind turbine structure design process.

[0038] 3. The structural response obtained based on the overall coupling model of the offshore wind turbine fully considers the influence of aerodynamic damping, hydrodynamic damping and coupling effect, and also includes different operating states of the wind turbine (wind turbine shutdown, normal operation, emergency braking, fault shutdown) and different operating control methods (blade feathering, variable speed pitch, blade tip braking, high-speed drive shaft braking).

[0039] 4. Based on the reliability design principle, the present invention selects appropriate sub-item safety factors as much as possible, under the premise of ensuring that the offshore wind turbine structure meets the target structural reliability index during the service life, so that the reliability index of the designed structure is slightly higher than the target reliability index. That is, under the premise of ensuring the safety of the offshore wind turbine structure, the structural manufacturing cost is reduced as much as possible. Therefore, in the context of the high average cost of offshore wind power in my country, reasonable revision of the sub-item safety factors in the current specifications is of great guiding significance for reducing the average power generation cost in the current offshore wind energy industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0041] Figure 1 It is a design flow chart for the basic program module and interface development of the correction method for the partial factor of the structural scheme design of an offshore wind turbine considering the overall coupling effect based on the reliability principle. Detailed implementation manners

[0042] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0043] The partial safety factors applicable to the structural scheme design of an offshore wind farm in the present invention mainly include: determination of the design requirements of the target wind turbine and the characteristics of the target working environment, carrying out experimental design, coupling dynamic response analysis, establishing a mathematical surrogate model, establishing a performance function for reliability analysis, establishing and solving an optimization equation for seeking the optimal partial safety factor. The analysis methods corresponding to each part include the following steps and characteristics:

[0044] S1. Carry out experimental design based on random variables such as environmental parameters and structural parameters;

[0045] In step S1, mainly according to the design requirements of the target wind turbine and the working environment, the design variables affecting its structural performance and the target reliability index β are determined T , where the uncertainty of the structural material properties needs to be determined through mechanical experiments, and the relevant data of the environmental load variables need to be monitored on-site in the actual working sea area. Statistical analysis is carried out on the above data to obtain the best distribution function type and the corresponding distribution parameters. According to the number and distribution type of the determined random variables, experimental design is carried out to obtain the corresponding sample combinations.

[0046] S2. Establish an overall coupling model of the offshore wind turbine;

[0047] In step S2, mainly a numerical model of the target wind turbine structure is established by using a full-coupling simulation tool of aerodynamics - hydrodynamics - elasticity - servo, fully considering the coupling effects among the aerodynamic load, hydrodynamic load, structural elastic force and control load of the offshore wind turbine structure, and being able to more realistically simulate the actual working characteristics of the offshore wind turbine.

[0048] S3. Develop a parametric modeling executable program, and based on this program, implement parametric modeling of the target offshore wind turbine structure and conduct batch calculations;

[0049] The main functions of the parametric executable program mentioned in step S3 include calling the sample combinations obtained in step S1, realizing the automatic generation of relevant random variables of the overall coupled input text, outputting batch files, conducting automated calculations of the structural responses of the offshore wind turbine, and outputting the structural responses of interest.

[0050] S4. Construct a mathematical surrogate model based on the output variables and input variables to replace the complex and time-consuming numerical simulation. Based on the mathematical surrogate model, establish the limit state equation g(X) = R(X) - S(X) corresponding to the representative failure modes of the offshore wind turbine, where the R term represents the structural resistance, the S term represents the load effect, and X represents the uncertain variables in the structural design process;

[0051] Step S4 includes functions such as the construction of the mathematical surrogate model, the construction of the performance function of the typical failure mode for reliability index calculation, and the calculation of the reliability index. Among them, a mathematical model is constructed based on the input variables and output responses to characterize the complex and time-consuming numerical model of the offshore wind turbine; further, based on this mathematical model, the limit state function under the typical failure mode of the offshore wind turbine structure is constructed; further, an accurate and efficient structural reliability index calculation method is used to conduct the calculation of the structural reliability index.

[0052] S5. Based on the reliability theory, introduce partial safety factors into the limit state equation corresponding to the typical failure modes of the structure, and its expression is: where γ m represents the partial coefficient of the structural bearing capacity, and γ f represents the partial coefficient of the structural load effect;

[0053] Step S5 mainly includes selecting reasonable γ m , γ f initial values according to the existing specifications. Further, establish a limit state function for structural reliability calculation considering the partial safety factors of the structural design.

[0054] S6. Similarly, select a suitable reliability index calculation method to obtain the reliability index β(γ m , γ f ) corresponding to the updated limit state equation;

[0055] The main function of step S6 is to use an accurate and efficient structural reliability index calculation method to conduct the calculation of the structural reliability index and record the calculation results.

[0056] Furthermore, establish an optimization index equation: M = (β(γ m , γf ) - β T ) 2 ; where β T is the target reliability index. Obviously, the corresponding (γ m , γ f ) when obtaining the minimum M value is the optimal partial safety factor.

[0057] An optimization function for solving the modified solution of the partial safety factor is established, and a suitable optimization method is selected to perform iterative optimization on it until the corresponding (γ m , γ f ) when the optimization function is minimized is obtained.

[0058] Example 1

[0059] S1 Determine the target reliability index β of the designed wind turbine during its service life according to the design requirements of the wind turbine manufacturer T . Secondly, consider the uncertainty of the structural properties determined by the manufacturing errors and the non-uniformity of material properties faced by the target wind turbine during the construction process, and determine the uncertainty of the relevant loads according to the environmental characteristics of the actual installation sea area of the target wind turbine in the future. In addition, the accidental uncertainty existing in the data statistics and processing process should also be considered in the structural design stage.

[0060] S2. Adopt efficient and accurate experimental design methods, such as Latin hypercube design, Monte Carlo design, central composite design, etc., to sample and combine the random variables determined in S1, and output the random variable sample combination text.

[0061] S3. Use OpenFAST to establish an overall coupling model of the blade-nacelle-tower foundation structure, fully considering the coupling effect between different loads. Develop a parametric modeling executable program for the overall coupling model of the offshore wind turbine, and its specific functions include: realizing the parametric modeling of the input file of the OpenFAST full-coupling model, and automatically performing the full-coupling dynamic response calculation of the target wind turbine. Use this executable program to carry out a certain number of full-coupling dynamic response calculations.

[0062] S4. Select a multivariate quadratic polynomial containing cross terms that meets the engineering analysis accuracy requirements to construct a mathematical model:

[0063]

[0064] In the formula: a 0 , a 1 , …, a M are the coefficients of the basis functions of the regression model. For the quadratic regression model containing cross terms, the value of its coefficient M satisfies

[0065] Using the multiple linear regression method, the coefficients of the quadratic polynomial are fitted based on the input variables and output responses obtained from the above steps.

[0066] S5. Based on the partial safety factors recommended in the current offshore wind turbine design codes (such as IEC series, DNV series, etc.) as the initial safety factors, establish the limit state function expression considering partial safety factors under typical failure modes:

[0067]

[0068] S6. Adopt classical reliability calculation methods such as the first-order reliability method, Monte Carlo method, etc. to calculate the structural reliability index for the above formula, and the calculation result is denoted as β(γ m0 ,γ f0 ).

[0069] Based on the target reliability index β T specified by the design requirements and β(γ m ,γ f ), establish the optimization function:

[0070] M = (β(γ m ,γ f ) - β T ) 2

[0071] Adopt the adaptive iterative optimization algorithm to gradually update the safety factors (γ mi ,γ fi ), and then update the limit state equation under typical failure modes to The corresponding structural reliability index is denoted as β(γ mi ,γ fi ). Continuously carry out this iterative process until the minimum M value is obtained, and the corresponding (γ m ,γ f ) is the optimal partial safety factor.

[0072] The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for correcting the partial safety factors in the structural scheme design of offshore wind turbines, characterized in that, it includes the following steps: S1. Determine the safety function requirements of the target designed wind turbine, and identify and quantify the load uncertainties, structural uncertainties, and accidental uncertainties existing in the design process; S2. For the above uncertainty variables, conduct experimental design using Monte Carlo sampling, Latin hypercube sampling, or central composite sampling to obtain the sample combinations of random input variables; S3. Establish an executable program for parametric modeling of the overall coupled model of the offshore wind turbine, and execute this program in combination with the above random sample combinations to conduct automated calculations of the fully coupled dynamic response of the offshore wind turbine structure; S4. Combine the structural output response and random input variables to construct a mathematical surrogate model to simulate the mathematical relationship between the uncertainty variables and the structural response; The constructed mathematical model: where: a 0 , a 1 , …, a M are the coefficients of the basis functions of the regression model. For a quadratic regression model with cross terms, the value of its coefficient M satisfies Adopt the multiple linear regression method to fit the coefficients of the quadratic polynomial based on the input variables and output responses obtained in the above steps; S5. Combine the above mathematical surrogate model and the design safety threshold of the offshore wind turbine, and at the same time introduce partial safety factors to establish the limit state function under the typical failure modes of the offshore wind turbine; The limit state function is as follows: Among them, the item R represents the structural resistance, the item S represents the load effect, X represents the uncertain variables in the structural design process, and γ m represents the partial coefficient of the structural bearing capacity, and γ f represents the partial coefficient of the structural load effect; S6. Calculate the structural reliability index under the target failure mode, The structural reliability index is calculated for the limit state function using the classical reliability calculation method, and the calculation result is denoted as β(γ m ,γ f ); Combined obtained reliability index β(γ m ,γ f ) and safety reliability index threshold β T Establish an optimization objective function to further achieve the correction of partial safety factors; the optimization function is: M = (β(γ m , γ f ) - β T ) 2 The safety factors (γ mi , γ fi ) are gradually updated using an adaptive iterative optimization algorithm, and then the limit state equation under typical failure modes is updated to: The corresponding structural reliability index is denoted as β(γ mi ,γ fi ); Continuously carry out this iterative process until the minimum M value is obtained, and the corresponding (γ m ,γ f ) of this result is the optimal partial safety factor.

2. The method for correcting the partial safety factors in the structural scheme design of offshore wind turbines according to claim 1, characterized in that: In step S1, when identifying and quantifying the uncertainty variables, use statistical principles to conduct statistical analysis on the physical model test data and the measured data of the marine environment to obtain the statistical distribution type and distribution parameters characterizing their uncertainty characteristics.

3. The method for correcting the partial safety factors in the structural scheme design of offshore wind turbines according to claim 1, characterized in that: Step S3 conducts automated calculations of the fully coupled dynamic response of the offshore wind turbine structure based on the executable program for parametric modeling of the overall coupled model of the offshore wind turbine. Use the existing fully coupled dynamic simulation tool for offshore wind turbines to build an executable program for parametric modeling in the development platform to achieve parametric modeling, automated calculation, and extraction and preservation of data for the target wind turbine structure.

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