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Sun, Hai,Ma, Chunhui,Kim, Eun Soo,Nowakowski, Gary,Mauer, Erik,Bernitsas, Michael M. Elsevier 2017 RENEWABLE ENERGY Vol.107 No.-
<P><B>Abstract</B></P> <P>Flow Induced Motions (FIMs) of rigid circular cylinders, and particularly VIV (Vortex Induced Vibrations) and galloping, are induced by alternating lift. The VIVACE (VIV for Aquatic Clean Energy) Converter uses single or multiple cylinders, in tandem, on elastic end-supports, in synergistic FIM, to convert MHK energy to electricity. Selectively distributed surface roughness is applied to enhance FIM and increase efficiency. In this paper, two cylinders are used in tandem with center-to-center spacing of 1.57, 2.0 and 2.57 diameters, harnessing damping ratio 0.00<<I>ζ</I> < 0.24, for Reynolds number 30,000 ≤ <I>Re</I> ≤ 120,000. The virtual spring-damping system V<SUB>ck</SUB> in the Marine Renewable Energy Laboratory (MRELab) enables embedded computer-controlled change of viscous-damping and spring-stiffness for fast and mathematically correct oscillator realization, without including the hydrodynamic force in the closed control loop. Experimental results for oscillatory response, energy harvesting, and efficiency are presented and the envelope of optimal power is derived. All the experiments were conducted in the Low Turbulence Free Surface Water (LTFSW) Channel of the MRELab of the University of Michigan. The main conclusions are: (1) For the tested cylinder spacing, two cylinders harness power is between 2.56 and 13.49 times the power of a single cylinder, the efficiency of two cylinders is between 2.0 and 6.68 of a single cylinder. (2) The MHK power harnessed by the upstream cylinder is increased by up to 100%, affected by the downstream cylinder. (3) The MHK power harnessed by the downstream cylinder and its FIM are affected to a lesser extent by the interaction. (4) VIVACE can harness energy from flows as slow as 0.4 m/s with no upper limit in flow velocity. (5) Close spacing and high spring stiffness yield highest harnessed power. (6) The optimal harnessed power shifts to softer springs as spacing increases.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effects of tandem spacing, spring stiffness, and damping on power harness by two circular cylinders with passive turbulence control are studied experimentally. </LI> <LI> The Vck based oscillator enables embedded computer-controlled change of viscous-damping and spring-stiffness for precise oscillator modeling and fast parametric testing. </LI> <LI> Amplitude response, frequency response, harnessed power, and efficiency are presented vs. flow velocity with spring stiffness, damping, and spacing as parameters. </LI> <LI> In the galloping range, two cylinders in synergistic flow induced motion can produce more power than the same cylinders in isolation. </LI> <LI> All the experiments were conducted in the TrSL3 (20,000<<I>Re</I><300,000) flow regime. </LI> </UL> </P>
두 원형실린더의 유동유발진동 현상을 이용하는 해양신재생에너지 변환기의 발전 효율에 발전기의 감쇠비가 미치는 영향에 관한 연구
김은수(Eun Soo Kim),박홍래(Hongrae Park),김동휘(Dong Hwi Kim),백형민(Hyung-min Baek),Michael M. Bernitsas 한국신재생에너지학회 2020 신재생에너지 Vol.16 No.1
Most countries in the world are trying to reduce the use of fossil fuels in the production of electricity and replace them with renewable energy technologies. In Korea, there are abundant ocean renewable energy sources that will play an important role in power generation in the future. This paper introduces a new tidal energy converter utilizing flow induced vibration (FIV), which can work efficiently, even in the currents slower than 1.0m/s. All tests were conducted at the Marine Renewable Energy Laboratory at the University of Michigan to examine the effects of the damping ratio of the electric generators on the power outputs and power efficiencies. In these tests, two identical circular cylinders were used, and passive turbulence controllers were applied to the surface of the cylinders to enhance the FIV. The experimental results showed that by using the two cylinders in the FIV, the power output and efficiency reached up to 31 W and 36%, respectively. In particular, the results showed that the power efficiency was higher at the relatively low flow speed (4<U<SUP>*</SUP><U or 0.45<U<0.9 ㎧). This indicates that this tidal converter can work efficiently, even at low flow speeds, and will enable the use of more tidal energy.