TY - JOUR

T1 - Optimal wind turbine jacket structural design under ultimate loads using Powell's method

AU - Ju, Shen Haw

AU - Hsieh, Cheng Han

N1 - Funding Information:
A part of this study was supported by the National Science Council, ROC , under contract number: 109-2221-E-006-012-MY3 .
Funding Information:
As shown in Fig. 2, there are two jacket types, equilateral triangular and squared shapes, and three depths of the sea level, 35, 50, and 80 m. Moreover, DTU 10 MW (Bak et al., 2013) and IEA 15 MW OWT (Gaertner et al., 2020) support structures are included, because these two OWTs are currently the focus scales and have detailed information. Fig. 2 shows those of 10 MW cases. For 15 MW cases, the jacket shape is the same as that of 10 MW cases, and the tower top from the seabed is 181.4, 196.4, and 226.4 m for the sea level of 35, 50, and 80 m, respectively. Moreover, the pile length is 90 m for the four-leg cases and 110 m for the three-leg cases. Using Powell's method, we determined the optimal jacket shape, BBXM and DXYM, and tubular section dimensions as shown in Fig. 2 and Table 2, where BBXM is the length between the two columns at the bottom, and DXYM is the reduced length at the top. These two parameters are important for the jacket structural geometries. The optimal tubular section size, diameter × thickness, is also shown in Fig. 2, where the data inside the parentheses is that for 15 MW cases and otherwise for 10 MW cases.This section discusses the required loading cases in the ultimate design of OWT support structures, where the design load cases (DLC) of IEC 61400-3-1 (2019) as well as the seismic (DLCs 1.8 and 6.7) and tropic cyclone (DLCs I.1 and I.2) loads are used, as shown in Table 3. Although DTU 10 MB and IEA 15 MB wind turbines are suitable for IEC class IA and IB, respectively, the IEC IA with tropical cyclone effect (Vref = 57 m/s = the reference wind speed average over 10 min at the hub height) is considered in this paper. For seismic loads, the software Simqke (Gasparini and Vanmarcke, 1976) was used to generate the time-history seismic acceleration with the PGA of 0.32 g in the local X, and 0.7 and 0.3 times of that PGA in the local Y and global Z directions. Then the angle between the global X and local X directions is set to 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315° in the analysis, respectively. In the first step, the 12 cases with the initial BBXM and DXYN were analyzed under all loads of Table 3 to obtain the optimal member sizes. Then, a program was used to find all the controlled loads in the final design stage, where the controlled load means that the designed thickness of any member of all members is the largest using the member forces under this load case. Usually, the number of controlled loads is between 10 and 30, even though the number of DLCs is over a thousand, which means that using these controlled loads is enough to design the OWT support structure.An optimization procedure using Powell's method was developed in this paper, where the search parameters can be set as symbolic variables. Thus, any one or more parameters in the input data of OWT support structural analyses and steel designs can be optimal. Powell's method was then used to determine the optimal geometry, length between the bottom two columns and top shortened length, under IEC 61400-3-1, tropical cyclone, and seismic loads to minimize the overall design weight of the steel structure. The studied cases include two jacket types, equilateral triangular and squared shapes, three depths of the sea level, 35, 50, and 80 m, and DTU 10 MW and IEA 15 MW OWT support structures.A part of this study was supported by the National Science Council, ROC, under contract number: 109-2221-E-006-012-MY3.
Publisher Copyright:
© 2022 Elsevier Ltd

PY - 2022/10/15

Y1 - 2022/10/15

N2 - This paper developed an optimization procedure using Powell's method with symbolic search variables, so any one or more parameters in structural designs can be optimal. Powell's method was used to determine the optimal Offshore Wind Turbine (OWT) jacket geometry under IEC-61400-3-1 (Wind Turbines-part 3-1, Design requirements for fixed offshore wind turbines. 2019), tropical cyclone, and seismic loads to minimize the structural weight. A linear generator braking system was proposed to stop the rotor under the power production plus occurrence of fault, and analysis results indicate that this braking system can avoid the steel design dominated by this situation. When the soil resistance is strong enough, the three-leg structural type is superior; otherwise, the four-leg one is suggested. The length between two bottom legs of three-leg cases is larger than that of four-leg cases, while the average ratio of the three and four-leg cases can be set to near 1.39. The total required steel mass is roughly linearly proportional to the water depth, and it increases by around 40% from a water depth of 35 m–80 m, so the jacket type can still be used in the deep sea under not only IEC-61400-3-1 loads but also seismic and tropical cyclone loads.

AB - This paper developed an optimization procedure using Powell's method with symbolic search variables, so any one or more parameters in structural designs can be optimal. Powell's method was used to determine the optimal Offshore Wind Turbine (OWT) jacket geometry under IEC-61400-3-1 (Wind Turbines-part 3-1, Design requirements for fixed offshore wind turbines. 2019), tropical cyclone, and seismic loads to minimize the structural weight. A linear generator braking system was proposed to stop the rotor under the power production plus occurrence of fault, and analysis results indicate that this braking system can avoid the steel design dominated by this situation. When the soil resistance is strong enough, the three-leg structural type is superior; otherwise, the four-leg one is suggested. The length between two bottom legs of three-leg cases is larger than that of four-leg cases, while the average ratio of the three and four-leg cases can be set to near 1.39. The total required steel mass is roughly linearly proportional to the water depth, and it increases by around 40% from a water depth of 35 m–80 m, so the jacket type can still be used in the deep sea under not only IEC-61400-3-1 loads but also seismic and tropical cyclone loads.

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U2 - 10.1016/j.oceaneng.2022.112271

DO - 10.1016/j.oceaneng.2022.112271

M3 - Article

AN - SCOPUS:85136710595

SN - 0029-8018

VL - 262

JO - Ocean Engineering

JF - Ocean Engineering

M1 - 112271

ER -