AU2021106095A4 - Method for analyzing fatigue damage of offshore wind turbine foundation based on field measurement - Google Patents
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Abstract
OF THE DISCLOSURE
A method for analyzing fatigue damage of the offshore wind turbine foundation
based on field measurement is provided, which belongs to the field of safety guarantee
of marine new-energy equipment. In this method, based on the on-site monitoring
system of offshore wind turbine foundation, the structural response information is
obtained; and based on the theoretical analysis of structural dynamics and the finite
element analysis, a mathematical relationship model is established between the
characteristic parameters of hot spot stress response and the characteristic parameters of
vibration response of the foundation above the water surface. The method in the present
disclosure focuses on offshore wind plants at serve, which is to indirectly evaluate the
structural fatigue cumulative damage of the foundation in a period of time through
on-site monitoring of the structural vibration response of the wind turbine foundation. It
does not require personnel to carry out underwater detection, so the operation is simple
with a better economic efficiency. The present disclosure relates to a method for
evaluating fatigue damage based on on-site monitoring structural vibration response,
which establishes a mathematical model of structural response, and uses the linear
accumulation theory of damage and the S-N curve to get the structural damage degree in
a short time, so as to improve the fatigue damage assessment accuracy under the
combined action of multiple environmental loads, which is beneficial to the security
operation and maintenance of offshore wind plants.
ABSTRACT DRAWING - Fig 2
17988056_1 (GHMatters) P117088.AU
2/5
Analysis of structural dynamic
response characteristics
easibility analysis Load time history
By virtue of finite Measured acceleration/
element analysis 4 displacement time history response data
at structural key point
at timeT
Determine hot pot stress
response data at hot pot position
Statistical method
Extract characteristic
parameters Xi and Yi
(such as cycle times,
amplitude, standard
deviation) of two
response time histories
Establish a mathematical relationship
between Xi and Yi of different
response time histories
Damage D at the timeT
FIG2
Description
2/5
Analysis of structural dynamic response characteristics easibility analysis Load time history
By virtue of finite Measured acceleration/ element analysis 4 displacement time history response data at structural key point at timeT Determine hot pot stress response data at hot pot position
Statistical method Extract characteristic parameters Xi and Yi (such as cycle times, amplitude, standard deviation) of two response time histories
Establish a mathematical relationship between Xi and Yi of different response time histories
Damage D at the timeT
FIG2
[01] The present disclosure relates to the field of safety guarantee of marine new-energy equipment, and to a method for analyzing the fatigue damage of the offshore wind turbine foundation based on field measurement.
[02] With the rapid development of economy, the traditional energy crisis is getting serious increasingly. As a clean, pollution-free and renewable resource, offshore wind energy can effectively overcome the energy shortage crisis, so offshore wind power generation has attracted the attention of all countries in the world. As the supporting structure of offshore wind power, the wind turbine foundation has been staying in a complex ocean environment. The interaction of wind, waves, currents and sea ice in cold regions with the foundation structure produces a long-lasting alternating load, which damages the structure at different levels, thus seriously reducing the fatigue life of the foundation structure.
[03] Accurate and rapid assessment of fatigue damage of the offshore wind turbine infrastructure is an important means to ensure the safe operation of offshore wind turbines. Up to now, fatigue damage and life assessment methods of offshore structures mainly include fatigue life calculation based on load time history analysis, fatigue life calculation based on spectrum analysis, and damage degree assessment based on structural damage detection. The time history analysis method relies on load time histories obtained under different working conditions, which is a large workload and time consuming. The spectrum analysis method is mainly oriented to the estimation of overall residual life, which needs to figure out the long-term load-distribution law and has a low accuracy in fatigue damage assessment in the case of short-term and complex load coupling. However, the structural damage detection of the structure mainly aims at identifying the damage degree at the fixed position and time point, while the position of the structural hot spot stress is generally below the water surface, so the detection is weak in feasibility at a relatively high cost. Therefore, the way of quick and accurate assessment of the structural fatigue damage is of great significance to the security operation and maintenance of offshore wind plants.
[04] The present disclosure aims at providing a method for indirectly evaluating fatigue damage of the wind turbine foundation based on the field measured structural vibration response. In this method, according to the structural dynamics theory and the finite element analysis, it is to establish a mathematical model of an approximate relationship between characteristic parameters of vibration response (displacement, velocity or accelerated velocity) and hot spot stress response parameters of a structure above the water surface. The structural vibration response of the offshore wind turbine foundation is relied upon to implement the field monitoring system, so as to obtain the
1 17988056_1(GHMtters) P117088.AU structural displacement, velocity or acceleration response information in real time, and to process and analyze the collected data for obtaining characteristic parameters which are then substituted into the established mathematical model to get the stress response level of the hot spot position (below the water surface) of the wind turbine foundation. Finally, by combining the linear cumulative damage theory and the S-N curve, the degree of structural fatigue damage is further obtained.
[05] In order to achieve the above purpose, the present disclosure adopts the following technical scheme.
[06] A method for analyzing fatigue damage of offshore wind turbine foundation based on field measurement is provided, including the following steps:
[07] Step 1: The structural hot spot position and fatigue stress response information of an offshore wind turbine foundation are determined.
[08] Firstly, the offshore wind turbine foundation is analyzed for its characteristics of structural mechanics. The offshore wind turbine is structured tall and elongated, and its mechanical model can be simplified as a cantilever beam concentrating the mass at one end. Based on the field measured data and theoretical analysis, the structural vibration response of the wind turbine foundation mainly focus on the first-order mode, namely, the in-plane swing. Therefore, there is a certain approximate linear relationship between structural responses of the offshore wind turbine foundation at various positions. An on-site monitoring system oriented to security requirements of the offshore wind turbine foundation can comprehensively obtain environmental conditions, loads and structural response information of the wind turbine foundation; and a vibration sensor included in the monitoring system can obtain response data of structural vibrations and provide the data support for the structural fatigue damage calculation and analysis of the wind turbine foundation.
[09] Secondly, a finite element model of the offshore wind turbine foundation is established by ANSYS simulation software for implementing the transient structural dynamic analysis. By taking the load time history or the measured structural vibration response data as the input, the fatigue hot spot position and corresponding stress response data of the foundation are obtained.
[10] Step 2: The wind turbine foundation structural vibration response data and the hot spot stress response data are analyzed for characteristic parameters, and a mathematical relationship model is established for the two.
[11] Based on a large number of finite element numerical simulations, time history data of structural vibration response and hot spot stress response of the wind turbine foundation are obtained. The amplitude and cycle times of the structural hot spot stress are important parameters for calculating structural fatigue damage, so a standard deviation a of amplitude and a number n of cycle times are selected as characteristic parameters for analysis, so as to determine a mathematical relationship model between the structural vibration response and the hot spot stress.
[12] The analysis indicates that there is a linear relationship acc = Aas+B between the amplitude standard deviation acc of vibration acceleration response and the amplitude standard deviation as of hot spot stress response; and there is a linear relationship nacc = Cns +D between the cycle times nacc of vibration acceleration
2 17988056_1 (GHMatters) P117088.AU response and the cycle times ns of hot spot stress response. In the formula, A, B, C and D are constant coefficients.
[131 Step 3: The structural fatigue damage is calculated.
[14] According to the calculation in Step 2, the amplitude standard deviation as of hot spot stress response and the number of cycle times ns can be obtained, and the corresponding fatigue damage value of the foundation is calculated as below.
[151 Given that the stress amplitude standard deviation as is known, the damage caused by the stress amplitude corresponding to as is calculated more accurately by using the interval numbers of three parameters (INTP) method based on Gaussian distribution. According to Gaussian distribution, the probabilities of occurrence at stress intervals la,, and +2ly-3ad 3s are 68.26%, 27.19% and 4.48%, respectively. The probability is very small that a stress occurs outside 3 Ys, so it can be ignored and assumed that it will not cause any damage. During the fatigue calculation, when the stress standard deviation is treated at the above three levels, the fatigue damage calculation formula of the foundation in the ih case can be expressed as:
[161 Di = -" N + n" + " (1) 10 , N2 . Nags
[17] In the formula, nias, nzas, and n3, are respectively the actual cycle times
corresponding to las, 2asand 3as, and N1,,, N 2 ,s, and N3,, are respectively the
maximum cycle times corresponding to las, 2 (s and 3(s and required for causing fatigue damage to the foundation.
[181 In addition, in order to accurately obtain the total fatigue damage caused by different stress amplitudes, it is necessary to add up the fatigue damage caused by each stress amplitude at the hot spot of the foundation. According to the present disclosure, Miner's linear cumulative damage theory and a material S-N curve are adopted. Miner's linear cumulative damage theory means that, the resultant fatigue damage to a structure subjected to the action of multi-level constant amplitude cyclic stress load equals to the sum of fatigue damages due to separate actions of all stress amplitudes, and the calculation formula is:
[191 D = E kD = n, /N, (2)
[20] In the formula, D is the total damage of the foundation; Di is the damage caused by the ith stress amplitude to the foundation; Ni is the number of cycles required for causing fatigue damage to the foundation by the i* stress amplitude; ni is the number of actual cycles of the i* stress amplitude; and k is the number of stress amplitudes.
[21] The maximum number of cycles required for causing fatigue damage to the foundation by each stress amplitude is determined based on the S-N curve of the material. The S-N curve adopts the fatigue curve of commonly-used offshore steel
3 17988056 1 (GHMatters) P117088.AU provided by American Petroleum Institute (API), which can represent the fatigue characteristics of offshore engineering structural materials and fully consider the influence of random loads. The mathematical expression of the S-N curve is:
[221 N = 2x 106(AU/AU f)-m (3)
[231 In the formula, Aa is stress value; Aare is the limit stress amplitude, which is set to 79 MPa; m coefficient is set to 3.74; N is the maximum number of cycles required for causing fatigue damage to the foundation by the stress amplitude Aa.
[24] For calculation of the actual fatigue damage, the measured structural vibration response time history data of the wind turbine foundation is analyzed and processed to obtain the amplitude standard deviation of acceleration response and the cycle times which are then substituted into the mathematical model established in Step 2 to obtain the amplitude standard deviation of hot spot stress response and the cycle times. Then, combined with formulas (1), (2) and (3), the fatigue damage at the structural fatigue hot spot position is obtained finally.
[251 The present disclosure mainly focuses on offshore wind plants at serve, wherein the method is to indirectly evaluate the structural fatigue cumulative damage in a period of time through on-site monitoring of the structural vibration response of the offshore wind turbine foundation.
[26] According to the above analysis, in comparison to the prior art, the method for analyzing structural fatigue damage assessment by using measured vibration response information provided in the present disclosure has the following beneficial effects:
[27] 1) Compared with traditional nondestructive testing methods, the method provided by the present disclosure does not require personnel to carry out underwater detection, so the operation is simple with a better economic efficiency;
[281 2) Compared with detection technologies in the prior art based on vibration response, the method can effectively avoid errors in modality identification, and can more accurately obtain structural damage degree in a period of time;
[29] 3) The method provided by the present disclosure removes the necessity of considering multi-condition analysis of complex environmental loads, and, compared with traditional simulation analysis, it improves fatigue damage assessment accuracy under the combined action of multiple environmental loads. Therefore, this method is more convenient and reasonable in engineering applications.
[30] Fig. 1 is a schematic diagram of an on-site monitoring system of an offshore wind turbine foundation;
[311 Fig. 2 is the flow chart of fatigue damage of the offshore wind turbine foundation based on field measurement;
[321 Fig. 3 is a fmite element model diagram;
[33] Fig. 4 is a structural stress response diagram;
[341 Fig. 5 is a relational graph of the standard deviation of fitted response amplitudes;
4 17988056 1 (GHMatters) P117088.AU
[351 Fig. 6 is a relational graph of a number of fitted response cycle times.
[36] The present disclosure will be further described with reference to specific embodiments below.
[37] Step 1: The structural hot spot position and fatigue stress response information of an offshore wind turbine foundation are determined.
[38] Firstly, the offshore wind turbine foundation is analyzed for its characteristics of structural mechanics. The offshore wind turbine is structured tall and elongated, and its mechanical model can be simplified as a cantilever beam concentrating the mass at one end. Based on the field measured data and theoretical analysis, the structural vibration response of the wind turbine foundation mainly focus on the first-order mode, namely, the in-plane swing. Therefore, there is a certain approximate linear relationship between structural responses of the offshore wind turbine foundation at various positions. An on-site monitoring system oriented to security requirements of the offshore wind turbine foundation can comprehensively obtain environmental conditions, loads and structural response information of the wind turbine foundation; and a vibration sensor included in the monitoring system can obtain response data of structural vibrations and provide the data support for the structural fatigue damage calculation and analysis of the wind turbine foundation.
[39] Secondly, a finite element model of the offshore wind turbine foundation is established by ANSYS simulation software for implementing the transient structural dynamic analysis. By taking the load time history or the measured structural vibration response data as the input, the fatigue hot spot position and corresponding stress response data of the foundation are obtained.
[40] In the analysis, a single-pile wind turbine foundation is taken as an example. Since it lacks measured vibration response data, time histories under different load conditions are selected as input. The time history data of structural response is obtained after dynamic analysis by ANSYS. Since it results in too much result data, the vibration acceleration and stress response data (for about 10 seconds) under a certain load condition are intercepted herein, as shown in Table 1.
[41] Table 1 Part of response data a(m/s 2) a(rn/s 2) a(m/s 2) a(m/s 2) a(MPa) r(MPa) a(MPa) a(MPa) 0.2594 0.0940 0.0657 -0.6954 0.0843 4.2697 1.9892 2.1662 0.5437 0.1451 -0.0981 -0.3863 1.0665 3.8647 0.7982 1.3827 0.1244 0.1449 -0.1888 0.0172 4.8775 3.7737 2.7765 4.9973 -0.4908 0.0992 -0.1575 0.2768 8.2796 3.8925 3.6273 7.1713 -0.5995 0.0363 -0.0329 0.3680 7.4906 3.9564 3.6918 7.5125 -0.3104 -0.0118 0.1131 0.2490 3.5019 3.7083 3.6058 5.8100 0.0720 -0.0255 0.2101 -0.0278 0.7310 3.0384 3.9154 2.9022 0.3171 -0.0069 0.2214 -0.2924 3.7004 2.0303 4.8290 0.5119 0.3951 0.0251 0.1561 -0.3705 4.9613 0.9014 6.1366 0.2398
5 17988056 1 (GHMatters) P117088.AU
0,2659 0.0466 0.0624 -0.2568 4.2851 0,1180 7.3428 0.4838 -0.0177 0.0424 -0.0037 -0.0484 2.4689 0.8965 7.9680 1.7760 -0.2894 0.0128 -0.0099 0.1454 1.1525 1.4449 7.8047 2.6636 -0.3807 -0.0283 0.0372 0.2538 1.3958 1.8794 6.9850 2.4556 -0.2844 0.2151 0.1040 0.2467 3.0213 2.4251 5.8602 0.9728 -0.0935 0.5060 0.1493 0.1197 5.1256 1.7397 4.7971 1.4073 0.1040 0.0653 0.1480 -0.0489 6.7377 1.7421 3.9943 3.8060 0.2236 -0.5754 0.1009 -0.1486 7.0644 4.8559 3.4110 5.3311 0.1846 -0.6779 0.0327 -0.1286 5.8014 3.6760 2.8325 5.6616 0.0139 -0.3661 -0.0254 -0.0152 3.5022 0.6771 2.0241 5.1374 -0.1635 0.0342 -0.0520 0.1214 1.2849 5.0549 0.8737 4.4039 -0.2444 0.2825 -0.0457 0.2109 0.0250 7.9145 0.5496 4.0302 -0.1979 0.3561 -0.0221 0.2158 0.2957 8.8679 2.0390 4.2573 -0.0651 0.2189 -0.0041 0.1438 0.0462 7.7305 3.3598 4.9090 0.0826 -0.0718 -0.0073 0.0422 0.3463 5.3633 4.3596 5.5169 0.1724 -0.3430 -0.0340 -0.0326 0.0384 3.4861 5,0219 5.6175 0.1697 -0.4216 -0.0726 -0.0475 1.0499 3 ,1900 5,4429 5.0101 0.0920 -0.3053 -0.1059 -0.0076 2.6156 4.2655 5.7537 3.8297 -0.0027 -0.0952 0.1574 0.0545 4.0986 5.7668 6.1283 2.4316 -0.0585 0.0976 0.4700 0.0979 5.0208 6.7035 5.1468 1.1904 -0.0485 0.2027 0.0446 0.0969 5.2111 6.3939 1.1900 0.3151 0.0151 0.1927 -0.5909 0.0515 4.8370 4.6863 2.5755 0.2265
[431
[44] In the table, a is an acceleration value in m/s2 , and a is a stress value in MPa.
[45] Step 2: The wind turbine foundation structural vibration response data and the hot spot stress response data are analyzed for characteristic parameters, and a mathematical relationship model is established for the two.
[46] Based on a large number of finite element numerical simulations, time history data of structural vibration response and hot spot stress response of the wind turbine foundation are obtained. The amplitude and cycle times of the structural hot spot stress are important parameters for calculating structural fatigue damage, so a standard deviation a of amplitude and a number n of cycle times are selected as characteristic parameters for analysis, so as to determine a mathematical relationship model between the structural vibration response and the hot spot stress.
[471 According to the analysis and processing of all data, the obtained amplitude standard deviation Gac of vibration acceleration response and the amplitude standard deviation c of hot spot stress response are as shown in Table 2; and the obtained cycle times nace of vibration acceleration response and the cycle times ns of hot spot stress response are as shown in Table 3. According to data fitting, the linear relationship is obtained as follows: amplitude standard deviation as = 34.59565aacc+0.44688,and cycle
6 17988056 1 (GHMatters) P117088.AU times ns = 1.06832nacc+3.12046.
[48] Table 2 Summarized data of amplitude standard deviation of response a (m/s') S(MI~a) Gcc (m/s) 3, (MPa) 0.0120 0.4425 0.3830 13.1591 0.0436 4.7754 0.0057 0.0372 0.1026 3.8530 0.0226 1.7544 0.2003 5.0584 0.0831 4.2091 0.2434 11.0189 0.1444 6.5501 0.3735 14.4305 0.2346 6.0913 0.0134 0.6795 0.2362 8.0921 0.0381 1.3092 0.0075 0.2100 0.1212 4.1641 0.0408 1.7227 0.0129 0.5451 0.0300 1.1155 0.0424 2.1158 0.1339 6.7856 0.1029 2.7410 0.1869 7.0846 0.1205 4.1281 0.3250 10.2478
0.2650 10.3613 0.2994 12.1500
[49]
[50] Table 3 Summarized data of amplitude standard deviation of cycle times
naa(Times) n, (Times) n,,, (Times) n,(Times)
113 60 95 48 155 177 137 147 211 237 149 147 271 297 24 24 226 297 48 48 277 324 61 99 61 99 74 99 95 48 99 123 149 147 95 48
[51]
7 17988056 1 (GHMatters) P117088.AU
166 147 24 24 127 171 25 48 176 198 49 75 25 48 61 99 61 99 73 114 86 123 86 123
[521
[53] Step 3: The structural fatigue damage is calculated.
[541 According to the calculation in Step 2, the amplitude standard deviation as of hot spot stress response and the number of cycle times ns can be obtained, and the corresponding fatigue damage value of the foundation is calculated as below.
[55] Given that the stress amplitude standard deviation as is known, the damage caused by the stress amplitude corresponding to as is calculated more accurately by using the interval numbers of three parameters (INTP) method based on Gaussian distribution. According to Gaussian distribution, the probabilities of occurrence at stress intervals ls, la~2s,and 2ar 32s are 68.26%, 27.19% and 4.48%, respectively. The probability is very small that a stress occurs outside 3as, so it can be ignored and assumed that it will not cause any damage. During the fatigue calculation, when the stress standard deviation is treated at the above three levels, the fatigue damage calculation formula of the foundation in the i* case can be expressed as:
[561 Di = "+ n +` (1) NU N 2 (S Nag
[571 In the formula, nl,, n2,, and n~a, are respectively the actual cycle times
corresponding to 1ls, 2as and 3as, and Ng, N2 , and N3 , are respectively the
maximum cycle times corresponding to las, 2 as and 3as and required for causing fatigue damage to the foundation.
[58] In addition, in order to accurately obtain the total fatigue damage caused by different stress amplitudes, it is necessary to add up the fatigue damage caused by each stress amplitude at the hot spot of the foundation. According to the present disclosure, Miner's linear cumulative damage theory and a material S-N curve are adopted. Miner's linear cumulative damage theory means that, the resultant fatigue damage to a structure subjected to the action of multi-level constant amplitude cyclic stress load equals to the sum of fatigue damages due to separate actions of all stress amplitudes, and the calculation formula is:
[591 D = 1 Di = Zn, /N, (2)
8 17988056 1(GHMtters) P117088.AU
[601 In the formula, D is the total damage of the foundation; Di is the damage caused by the ith stress amplitude to the foundation; Ni is the number of cycles required for causing fatigue damage to the foundation by the i* stress amplitude; ni is the number of actual cycles of the ith stress amplitude; and K is the number of stress amplitudes.
[61] The maximum number of cycles required for causing fatigue damage to the foundation by each stress amplitude is determined based on the S-N curve of the material. The S-N curve adopts the fatigue curve of commonly-used offshore steel provided by American Petroleum Institute (API), which can represent the fatigue characteristics of offshore engineering structural materials and fully consider the influence of random loads. The mathematical expression of the S-N curve is:
[62] N = 2 X10 6 (AU/AUrf)-m (3)
[63] In the formula, Aa is stress value; Aaref is the limit stress amplitude, which is set to 79 MPa; m coefficient is set to 3.74; N is the maximum number of cycles required for causing fatigue damage to the foundation by the stress amplitude Aa.
[641 For calculation of the actual fatigue damage, it is assumed that two pieces of structural vibration response time history data is obtained of which the measured structural vibration response time duration of the wind turbine foundation is t (in second) to obtain the amplitude standard deviation of acceleration response and the cycle times which are then substituted into the mathematical model established in Step 2 to obtain the amplitude standard deviation of hot spot stress response and the cycle times. Then, combined with formulas (1), (2) and (3), the fatigue damage at the structural fatigue hot spot position is obtained finally. Calculation results are as shown in Table 4.
[651 Calculation result of the case in Table 4 Data segment 1 Data segment 2
a. 0.2 n. 290 a. 0.35 n. 140
7.37 312.93 <r, 12.56 152.69 1o, 2o, 3 o, 2, 3
7.37 14.73 22.10 12.56 25.11 37.67
213.61 85.09 14.02 104.22 41.52 6.84 Na, N2a, Nal, Ni, N2. Na, 1.43E+10 1.07E+09 2.35E+08 1.94E+09 1.45E+08 3.19E+07 Di D2
4.54E-07 5.53E-07 Total damage D = DJ+D2 7.07E-07
9 17988056 1 (GHMatters) P117088.AU
[66] The embodiments mentioned above only illustrate the implementations of the present disclosure, but they should not be understood as limiting the scope of the present disclosure. It should be noted that for those skilled in the art, without departing from the concept of the present disclosure, can make several modifications and improvements, which falls within the protection scope of the present disclosure.
[67] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.
[68] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.
10 17988056_1 (GHMatters) P117088.AU
Claims (3)
1. A method for analyzing fatigue damage of an offshore wind turbine foundation based on field measurement, which mainly focuses on offshore wind plants at serve, wherein the method is to indirectly evaluate the structural fatigue cumulative damage in a period of time through on-site monitoring of the structural vibration response of the offshore wind turbine foundation, comprising: Step 1: The structural hot spot position and fatigue stress response information of an offshore wind turbine foundation are determined. Firstly, the offshore wind turbine foundation is analyzed for its characteristics of structural mechanics, and its mechanical model is simplified as a cantilever beam concentrating the mass at one end; based on the field measured data and theoretical analysis, the structural vibration response of the wind turbine foundation mainly focus on the first-order mode, namely, the in-plane swing; therefore, there is a approximate linear relationship between structural responses of the offshore wind turbine foundation at various positions; an on-site monitoring system can obtain environmental conditions, loads and structural response information of the wind turbine foundation; and a vibration sensor included in the monitoring system can obtain response data of structural vibrations and provide the data support for the structural fatigue damage calculation and analysis of the wind turbine foundation. Secondly, a finite element model of the offshore wind turbine foundation is established by ANSYS simulation software for implementing the transient structural dynamic analysis; and by taking the load time history or the measured structural vibration response data as the input, the fatigue hot spot position and corresponding stress response data of the foundation are obtained. Step 2: The wind turbine foundation structural vibration response data and the hot spot stress response data are analyzed for characteristic parameters, and a mathematical relationship model is established for the two. Based on a large number of finite element numerical simulations, time history data of structural vibration response and hot spot stress response of the wind turbine foundation are obtained; and a standard deviation a of amplitude and a number n of cycle times are selected as characteristic parameters for analysis, so as to determine a mathematical relationship model between the structural vibration response and the hot spot stress. The analysis indicates that there is a linear relationship ac = Aas+B between the amplitude standard deviation 3ac of vibration acceleration response and the amplitude standard deviation as of hot spot stress response; and there is a linear relationship nac = Cns +D between the cycle times nacc of vibration acceleration response and the cycle times ns of hot spot stress response; wherein A, B, C and D are constant coefficients. Step 3: The structural fatigue damage is calculated. According to the calculation in Step 2, the amplitude standard deviation as of hot spot stress response and the number of cycle times ns can be obtained, and then the corresponding fatigue damage value of the foundation is calculated. Given that the stress amplitude standard deviation as is known, the damage caused
11 17988056_1(GHMtters) P117088.AU by the stress amplitude corresponding to as is calculated more accurately by using the interval numbers of three parameters (INTP) method based on Gaussian distribution; according to Gaussian distribution, the probabilities of occurrence at stress intervals las, ls~-±2s, and 2~s~-3as are 68.26%, 27.19% and 4.48%, respectively. The probability is very small that a stress occurs outside 3as, so it can be ignored and assumed that it will not cause any damage; and during the fatigue calculation, when the stress standard deviation is treated at the above three levels, the fatigue damage calculation formula of the foundation in the i case can be expressed as:
Di - n,,+ n2.,+ n, N1 s N 2 ,S Nas
In the formula, ni., n2,, and n3, are respectively the actual cycle times
corresponding to las, 2as and 3s, and Ns, N2 s, and N3as are respectively the
maximum cycle times corresponding to las, 2as and 3cs and required for causing fatigue damage to the foundation. In addition, in order to accurately obtain the total fatigue damage caused by different stress amplitudes, the fatigue damage caused by each stress amplitude at the hot spot of the foundation is added up; the maximum number of cycles required for causing fatigue damage to the foundation by each stress amplitude is determined based on the S-N curve of the material. For calculation of the actual fatigue damage, the measured structural vibration response time history data of the wind turbine foundation is analyzed and processed to obtain the amplitude standard deviation of acceleration response and the cycle times which are then substituted into the mathematical model established in Step 2 to obtain the amplitude standard deviation of hot spot stress response and the cycle times. Then, combined with formulas (1), Miner's linear cumulative damage theory and a material S-N curve, the fatigue damage at the structural fatigue hot spot position is obtained finally.
2. The method for analyzing fatigue damage of the offshore wind turbine foundation based on field measurement according to claim 1, wherein: the Miner's linear cumulative damage theory means that, the resultant fatigue damage to a structure subjected to the action of multi-level constant amplitude cyclic stress load equals to the sum of fatigue damages due to separate actions of all stress amplitudes, and the calculation formula is:
k
D = Di= ni /Ni (2)
12 17988056 1 (GHMatters) P117088.AU
In the formula, D is the total damage of the foundation; Di is the damage caused by the ith stress amplitude to the foundation; Ni is the number of cycles required for causing fatigue damage to the foundation by the i* stress amplitude; ni is the number of actual cycles of the i* stress amplitude; and K is the number of stress amplitudes.
3. The method for analyzing fatigue damage of the offshore wind turbine foundation based on field measurement according to claim 1, wherein: the S-N curve adopts the fatigue curve of commonly-used offshore steel provided by American Petroleum Institute API, which can represent the fatigue characteristics of offshore engineering structural materials and fully consider the influence of random loads; and a mathematical expression of the S-N curve is:
N = 2 X 10 6(Au/Aur)- (3)
In the formula, Aa is stress value; Aarefis the limit stress amplitude, which is set to 79 MPa; m coefficient is set to 3.74; N is the maximum number of cycles required for causing fatigue damage to the foundation by the stress amplitude A.
13 17988056 1 (GHMatters) P117088.AU
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| CN113357099B (en) * | 2021-06-07 | 2022-09-06 | 浙江大学 | Fatigue diagnosis and detection method for fan tower drum based on acceleration sensor |
| CN115982907B (en) * | 2022-12-27 | 2023-10-17 | 重庆科技学院 | Fatigue analysis method and system for marine deep water drilling guide pipe or surface casing |
| CN116306109B (en) * | 2023-02-03 | 2023-10-20 | 哈尔滨工业大学（深圳） | Marine fan soil structure interaction state identification method based on time domain model correction |
| CN117272479B (en) * | 2023-10-08 | 2024-02-23 | 山东鑫之源新材料科技有限公司 | High-strength geomembrane bursting strength prediction method based on load time course analysis |
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