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a b s t r a c tHaving very strong current on the west coast with up to 10 m tidal range, there are many suitable sites for the application of tidal current power (TCP) in Korea. The turbine, which initially converts the tidal energy, is an important component because it affects the efficiency of the entire system. To design a turbine that can extract the maximum power on the site, the depth and duration of current velocity with respect to direction should be considered. To extract a significant quantity of power, a tidal current farm with a multi-arrangement is necessary in the ocean. The interactions between devices contribute significantly to the total power capacity. Thus, the study of wake propagation is necessary to understand the evolution of the wake behind a turbine. This paper introduces configuration design of horizontal axis tidal current turbine based on the blade element theory, and evaluating its performance with CFD. The maximum efficiency of the designed turbine was calculated as 40% at a tip speed ratio (TSR) of 5. The target capacity of 300 kW was generated at the design velocity, and the performance was stable over a wide range of rotating speeds. To investigate the wakes behind the turbine, unsteady simulation was carried out. The wake velocity distribution was obtained, and velocity deficit was calculated. A large and rapid recovery was observed from 2D to 8D downstream, followed by a much slower recovery beyond. The velocity was recovered up to 86% at 18D downstream.

The transmitted noise reduction (NR) of passive and active hybrid panels is experimentally studied. The concept of hybrid panels is based on a combined approach for noise controls: a passive approach for mid and high frequencies and an active approach for low frequencies. Active and passive hybrid panels are demonstrated. An active-hybrid single panel is made with a plate structure on which piezoelectric sensor/actuators are bonded in conjunction with a simple controller. Sound absorbing material is bonded on the structure to effectively reduce the transmitted noise in mid frequencies. An active-hybrid double panel is also made by using another single plate to maintain an air gap. To prove the concept of hybrid panels, an acoustic measurement experiment is performed. Instead of using the active control system, a passive shunt damping is used for the NR in low frequencies. This is called a passive-hybrid panel. The use of sound absorbing material and an air gap is effective for noise control in mid and high frequencies. Meanwhile, the active approach and the passive shunt approach are useful for noise control at lower resonance modes. These hybrid panels demonstrate the potential for NR at broadband frequencies.

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