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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