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Offshore wind turbines are divided into an upper wind turbine and a lower support structure. Offshore wind turbine system is required to secure high reliability for a variety of external environmental conditions compared to ground wind turbines because of additional periodic loads due to ocean wave and current effects. In this study, extreme load analyses have been conducted for the designed offshore wind turbine foundation with weight control functionality using computational fluid dynamics (CFD) then structural analyses have been also conducted to investigate the structural design requirement.

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This paper experimentally and numerically investigates the interference effects of the multiple arrangements of horizontal-axis wind turbines. The 1:86 scale blades of the NREL 5-MW baseline wind turbine model is accurately constructed using a 3D printer. Its torque and power are directly measured by a designed dynamometer system installed in the experimental nacelle base. The total numbers of 2 and 3 turbines are longitudinally arranged and tested for different downwind distances up to 10D (D is the rotor diameter). Some of the test cases are also modeled and analyzed using three-dimensional unsteady computational fluid dynamics (CFD), and then compared with our experimental tests. The results for the downwind interference effect on multiple wind turbine arrangements are practically presented and investigated in this study.

Structural design and analysis of a coiling arm unloading machine for submarine cable have been originally conducted in this study. Three-dimensional CAD modeling process is practically applied for the structural design in detail. Finite element method(FEM) and multi-body dynamics(MBD) analyses are also used to verify the safety and required motions of the designed coiling arm structure. The effective moving functions of the designed coiling arm with respect to rotational and radial motions are achieved by adopting bearing-roller mechanical parts and hydraulic system. Critical design loading conditions due to its self weight, carrying cables, offshore wind, and hydraulic system over operation conditions are considered for the present structural analyses. In addition, possible inclined ground conditions for the installation of the designed coiling arm are also considered to verify overturn stability. The present hydraulic type coiling arm system is originally designed and developed in this study. The developed coiling arm has been installed at a harbor, successfully tested its operational functions, and finished practical unloading mission of the submarine cable. Keywords