Rapid time domain fatigue calculation method for floating type fan foundation structure

Abstract

The invention discloses a rapid time-domain fatigue calculation method for a floating type wind turbine foundation structure. The rapid time-domain fatigue calculation method for the floating type wind turbine foundation structure comprises the following steps: S1, selecting an easily fatigue position in a floating type wind turbine foundation; s2, building a finite element model of an isolator in the floating fan foundation; s3, determining the main cyclic load and the acting position of the isolator; s4, independently applying a force of 1000N or 1000Nm to the position Li of the isolator model, and determining the maximum principal stress sigma 1000 of the isolator; s5, obtaining a fatigue stress factor ki corresponding to the external load cycle fi of the isolator model; s6, obtaining a stress time history curve sigma i generated by the external load cycle fi; s7, calculating a stress amplitude sigma a; s8, calculating the number of cycles; s9, obtaining a corresponding accumulated fatigue damage value D; and S10, determining the fatigue life of the key structure of the floating fan. According to the rapid time domain fatigue calculation method for the floating type wind turbine foundation structure, the calculation efficiency is improved, and calculation resources are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of fatigue calculation of floating wind turbines, and in particular relates to a fast time-domain fatigue calculation method for a floating wind turbine foundation structure. Background Art

[0002] The proportion of wind load in the environmental load borne by offshore floating wind turbines is much larger than that of traditional offshore oil and gas platforms, and the wind load itself is extremely nonlinear, causing the movement and structural stress of the floating wind turbine platform to show strong nonlinearity. The overall spectrum fatigue algorithm suitable for conventional offshore oil and gas platforms is no longer applicable to floating wind turbine platforms.

[0003] In the current wind turbine design specifications and software, wind turbine loads are obtained by traversing the time domain algorithm, which also requires classification society specifications to use time domain methods for fatigue assessment of floating platforms. At present, classification societies have only put forward requirements for time domain fatigue assessment of floating wind turbine platforms, but there is no consensus in the industry on how to implement time domain fatigue algorithms. In addition, the existing time domain fatigue calculation methods have problems such as long calculation time and occupying more computing resources.

[0004] Therefore, it is urgent to design a fast time-domain fatigue calculation method for floating wind turbine foundation structures to solve the problems mentioned above of the existing time-domain fatigue calculation methods, such as long calculation time, low efficiency, and large amount of computing resources occupied. Summary of the invention

[0005] In order to solve the technical problems mentioned in the background technology that the existing time domain fatigue calculation method has a long calculation time, low efficiency and occupies more computing resources, a fast time domain fatigue calculation method for a floating wind turbine foundation structure is provided to solve the above problems.

[0006] To achieve the above objectives, the specific technical solution of the fast time-domain fatigue calculation method of the floating wind turbine foundation structure of the present invention is as follows:

[0007] A fast time-domain fatigue calculation method for a floating wind turbine foundation structure comprises the following steps:

[0008] S1. According to the specifications and engineering experience, select the fatigue-prone position in the floating wind turbine foundation and set the structure within the relevant range as the isolation body;

[0009] S2. Use commercial finite element software to build a finite element model of the isolation body in the floating wind turbine foundation;

[0010] S3. Determine the main cyclic loads on the isolation body and the locations of these cyclic loads in the model from the data provided by the wind turbine manufacturer;

[0011] S4. Apply a force of 1000N or 1000Nm to the position L of the isolated model. i , combined with the inertia release method, the stress distribution of the isolated body model is obtained, and the maximum principal stress σ of the isolated body is determined 1000 ;

[0012] S5. Obtain the external load cycle f of the isolation model i The corresponding fatigue stress factor k i ;

[0013] S6. According to the fatigue stress factor algorithm, the external load cycle f can be obtained i The resulting stress-time curve σ i ;

[0014] S7. Omit the invalid amplitude of the stress-time curve and calculate the stress amplitude σ a ;

[0015] S8. Calculate the number of cycles of each stress amplitude when the material fails according to the stress amplitude data obtained by processing the SN curve;

[0016] S9. Using the Miner criterion of cumulative damage theory, the corresponding cumulative fatigue damage value D can be obtained;

[0017] S10. Determine the fatigue life of key structures of floating wind turbines.

[0018] Furthermore, the external load cycle f of the isolated body model is obtained i The corresponding fatigue stress factor k i The calculation formula is as follows:

[0019] k i =σ 1000 / 1000

[0020] Furthermore, according to the fatigue stress factor algorithm, the external load cycle f can be obtained. i The resulting stress-time curve σ i The calculation formula is as follows:

[0021] σ i =f i *k i

[0022] Furthermore, the stress amplitude σ is calculated by omitting the invalid amplitude of the stress time history curve. a The calculation formula is as follows:

[0023] σ a =|σ max -σ min | / 2

[0024] in,

[0025] σ max - Maximum stress value in each load cycle;

[0026] σ min - minimum stress value in each load cycle;

[0027] Furthermore, using the Miner criterion of cumulative damage theory, the corresponding calculation formula for the cumulative fatigue damage value D can be obtained as follows:

[0028]

[0029] in,

[0030] D i -The fatigue damage value caused by the i-th stress amplitude;

[0031] k-stress amplitude number;

[0032] n i -The number of cycles corresponding to the i-th stress amplitude;

[0033] N i -The number of cycles of the i-th stress amplitude at material failure;

[0034] Furthermore, the calculation formula for determining the fatigue life of the key structure of the floating wind turbine is as follows:

[0035]

[0036] in,

[0037] a- Design life.

[0038] The fast time-domain fatigue calculation method for the floating wind turbine foundation structure of the present invention has the following advantages:

[0039] By using commercial finite element software to establish a finite element model of the isolation body in the floating wind turbine foundation, the key structures that need to be fatigue checked are extracted from it according to the stiffness equivalence principle; a standard load of 1000N or 1000Nm is applied to the position where the external force acts, the fatigue stress coefficient of the key structural model is determined, and the stress-time curve of the structure is obtained; the number of cycles of each stress amplitude when the material is damaged is calculated based on the stress amplitude data obtained by processing the SN curve; the fatigue damage value is obtained by combining the Miner criterion of the cumulative damage theory, and the fatigue life of the structure is further calculated, which effectively improves the computational efficiency of the time-domain fatigue check of the floating wind turbine, reduces the mobilized computing resources, and the calculation accuracy meets the engineering requirements, with good engineering adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1A flowchart of a fast time-domain fatigue calculation method for a floating wind turbine foundation structure of the present invention;

[0041] Figure 2 Schematic diagram of the fatigue damage prone position in the isolator of the present invention Figure 1 ;

[0042] Figure 3 Schematic diagram of the fatigue damage prone position in the isolator of the present invention Figure 2 . DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0044] Those skilled in the art will appreciate that, although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present invention and form different embodiments. For example, in the claims, any one of the claimed embodiments may be used in any combination.

[0045] Please refer to the attached Figure 1 To Attachment Figure 3 The fast time domain fatigue calculation method of the floating wind turbine foundation structure of the present invention is described.

[0046] like Figure 1 As shown, the fast time domain fatigue calculation method of the floating wind turbine foundation structure in the present invention comprises the following steps:

[0047] S1. According to the specifications and engineering experience, select the fatigue-prone position in the floating wind turbine foundation and set the structure within the relevant range as the isolation body;

[0048] S2. Use commercial finite element software to build a finite element model of the isolation body in the floating wind turbine foundation;

[0049] S3. Determine the main cyclic loads {F1, F2, ..., F i ,……F n}, and the action positions of these cyclic charges in the model {L1, L2, ..., L i ,……L n};

[0050] S4. Apply a force of 1000N or 1000Nm to the position L of the isolated model. i , combined with the inertia release method, the stress distribution of the isolated body model is obtained, and the maximum principal stress σ of the isolated body is determined 1000 ,Among them, the inertia release method is an existing mature finite element calculation method and is an existing technology;

[0051] S5. Obtain the external load cycle f of the isolation model i The corresponding fatigue stress factor k i ;

[0052] S6. According to the fatigue stress factor algorithm, the external load cycle f can be obtained i The resulting stress-time curve σ i ;

[0053] S7. Omit the invalid amplitude of the stress-time curve and calculate the stress amplitude σ a ;

[0054] S8. Calculate the number of cycles for each stress amplitude when the material is damaged based on the stress amplitude data obtained through SN curve processing. The SN curve is a prior art. The SN curve is a curve that uses the fatigue strength of a standard material specimen as the ordinate and the logarithm of the fatigue life lgN as the abscissa to represent the relationship between the fatigue strength and fatigue life of a standard specimen under certain cycle characteristics. It is also called a stress-life curve.

[0055] S9. Using the Miner criterion of cumulative damage theory, the corresponding cumulative fatigue damage value D can be obtained;

[0056] S10. Determine the fatigue life of key structures of floating wind turbines.

[0057] By using commercial finite element software to establish a finite element model of the isolation body in the floating wind turbine foundation, the key structures that need to be fatigue checked are extracted from it according to the stiffness equivalence principle; a standard load of 1000N or 1000Nm is applied to the position where the external force acts, the fatigue stress coefficient of the key structural model is determined, and the stress-time curve of the structure is obtained; the number of cycles of each stress amplitude when the material is damaged is calculated based on the stress amplitude data obtained by processing the SN curve; the fatigue damage value is obtained by combining the Miner criterion of the cumulative damage theory, and the fatigue life of the structure is further calculated, which effectively improves the computational efficiency of the time-domain fatigue check of the floating wind turbine, reduces the mobilized computing resources, and the calculation accuracy meets the engineering requirements, with good engineering adaptability.

[0058] Further, if Figure 1 As shown, the external load cycle f of the isolated body model is obtained i The corresponding fatigue stress factor k i The calculation formula is as follows:

[0059] k i =σ 1000 / 1000.

[0060] Further, if Figure 1 As shown, according to the fatigue stress factor algorithm, the external load cycle f can be obtained i The resulting stress-time curve σ i The calculation formula is as follows:

[0061] σ i =f i *k i .

[0062] The fatigue stress factor algorithm is an existing technology, which is a method summarized through engineering experience and verified by actual engineering. This method applies the main cyclic loads to the finite element calculation, avoiding the process of combining the main cyclic loads in the traditional fatigue algorithm, thereby reducing the number of working conditions by several orders of magnitude.

[0063] Further, if Figure 1 As shown in the figure, the invalid amplitude is omitted from the stress time history curve, and the stress amplitude σ is calculated. a The calculation formula is as follows:

[0064] σ a =|σ min -σ min | / 2

[0065] in,

[0066] σ max - Maximum stress value in each load cycle;

[0067] σ min - Minimum stress value in each load cycle.

[0068] Further, if Figure 1 As shown, using the Miner criterion of cumulative damage theory, the corresponding calculation formula for the cumulative fatigue damage value D can be obtained as follows:

[0069]

[0070] in,

[0071] D i -The fatigue damage value caused by the i-th stress amplitude;

[0072] k-stress amplitude number;

[0073] n i -The number of cycles corresponding to the i-th stress amplitude;

[0074] Ni -The number of cycles of the ith stress amplitude before the material fails.

[0075] Further, if Figure 1 As shown in the figure, the calculation formula for determining the fatigue life of the key structure of the floating wind turbine is as follows:

[0076]

[0077] in,

[0078] a- Design life.

[0079] Through steps S1 to S10, the fatigue life of the key structure of the floating wind turbine foundation can be calculated.

[0080] like Figure 2 and Figure 3 As shown, the locations in the isolator that are prone to fatigue damage are selected for verification, and the fatigue life is shown in the following table:

[0081] Location Calculate fatigue life Standard fatigue life 1 1308 81 2 4814 81 3 10424 81 4 48830 81 5 53750 81 6 942874 81 7 3440362 81 8 14069331 81

[0082] Table 1 Fatigue life of locations prone to fatigue damage in the insulator

[0083] It can be found from Table 1 that the fatigue life of the insulator in this embodiment meets the specification requirements.

[0084] The present invention realizes the rapid time-domain fatigue calculation of the floating wind turbine foundation structure, which saves a lot of man-hours while its calculation accuracy meets the project requirements, and is suitable for floating wind turbine projects with tight construction schedules.

[0085] The computational efficiency of time-domain fatigue verification of the foundation structure of a floating wind turbine can be greatly improved, and the computational time can be reduced to 1 / 10 of the original time, and the computational accuracy meets the engineering requirements. This embodiment uses the stiffness equivalence principle to extract the finite element model of the key structure from the foundation structure of the floating wind turbine, thereby reducing the number of units in the finite element model. This embodiment uses the inertia release method to calculate the stress distribution of the finite element model of the key structure in a quasi-static state, thereby avoiding finite element solution in the time domain state and saving a lot of computational time. This embodiment introduces the fatigue factor method in fatigue verification, avoiding the combination of major loads, and reducing the original tens of thousands of working conditions to dozens of working conditions. This embodiment requires fewer computational resources, and an ordinary personal computer can complete the calculation without using a supercomputer, and has certain engineering adaptability.

[0086] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A fast time domain fatigue calculation method for a floating wind turbine foundation structure, characterized in that: The steps include: S1. According to the specifications and engineering experience, select the fatigue-prone position in the floating wind turbine foundation and set the structure within the relevant range as the isolation body; S2. Use commercial finite element software to build a finite element model of the isolation body in the floating wind turbine foundation; S3. Determine the main cyclic loads on the isolation body and the locations of these cyclic loads in the model from the data provided by the wind turbine manufacturer; S4. Apply a force of 1000N or 1000Nm to the position L of the isolated model. i , combined with the inertia release method, the stress distribution of the isolated body model is obtained, and the maximum principal stress σ of the isolated body is determined 1000 ; S5. Obtain the external load cycle f of the isolation model i The corresponding fatigue stress factor k i ; S6. According to the fatigue stress factor algorithm, the external load cycle f can be obtained i The resulting stress-time curve σ i ; S7. Omit the invalid amplitude of the stress-time curve and calculate the stress amplitude σ a ; S8. Calculate the number of cycles of each stress amplitude when the material fails according to the stress amplitude data obtained by processing the SN curve; S9. Using the Miner criterion of cumulative damage theory, the corresponding cumulative fatigue damage value D can be obtained; S10. Determine the fatigue life of key structures of floating wind turbines.

2. The fast time domain fatigue calculation method for the floating wind turbine foundation structure according to claim 1 is characterized in that: Obtain the external load cycle f of the isolated body model i The corresponding fatigue stress factor k i The calculation formula is as follows: k i =s 1000 / 1000。 3. The fast time domain fatigue calculation method for a floating wind turbine foundation structure according to claim 1 is characterized in that: According to the fatigue stress factor algorithm, the external load cycle f can be obtained i The resulting stress-time curve σ i The calculation formula is as follows: s i =f i *k i 。 4. The fast time domain fatigue calculation method for a floating wind turbine foundation structure according to claim 1 is characterized in that: Omit the invalid amplitude from the stress-time curve and calculate the stress amplitude σ a The calculation formula is as follows: s a =|s max -s min | / 2 in, σ max - Maximum stress value in each load cycle; σ min - Minimum stress value in each load cycle.

5. The fast time domain fatigue calculation method for a floating wind turbine foundation structure according to claim 1 is characterized in that: Using the Miner criterion of cumulative damage theory, the corresponding calculation formula for the cumulative fatigue damage value D can be obtained as follows: in, D i -The fatigue damage value caused by the i-th stress amplitude; k-stress amplitude number; n i -The number of cycles corresponding to the i-th stress amplitude; N i -The number of cycles of the ith stress amplitude before the material fails.

6. The fast time domain fatigue calculation method for a floating wind turbine foundation structure according to claim 1 is characterized in that: The calculation formula for determining the fatigue life of key structures of floating wind turbines is as follows: in, a- Design life.

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