Key-Yong Hong

Practical Simulation of Oscillating Water Column Chamber for Wave Energy Conversion

Oscillating water column (OWC) device has been widely employed in the wave energy conversion. In the present paper, a numerical wave tank (NWT) using two-phase volume of fluid (VOF) model is utilized to simulate the generation and propagation of incident regular waves, and water column oscillation inside the chamber. The NWT consists of the continuity equation, the Reynolds-averaged Navier-Stokes equations, and the two-phase VOF functions. The standard k-ϵ turbulence model, the finite volume method, NITA-PISO algorithm, and dynamic mesh technique are employed to generate 2 Dimensional (2D) regular waves. The numerical results are compared and validated with corresponding experimental data. Effects of incident wave conditions and several structure parameters on the operating performance of OWC chamber are investigated numerically.

Review of Application of VOF-Based NWT on Integrated OWC System

Abstract - Oscillating water column is the most widely used ocean energy converting systems all over theworld. The operating performance is influenced by the efficiencies of the two converting stages in the OWCchamber-turbine integrated system. In order to consider the effects of the turbine, the orifice model are carriedout. The VOF based Numerical Wave Tank (NWT) is utilized to simulate the water column oscillation insidethe chamber and the results are compared with corresponding experimental data. This paper reviews the stateof the art in interaction among wave elevation inside the chamber and air flow rate in the duct, which are con-sidered the turbine effects. Effects of incident wave conditions and several shape parameters on the operatingperformance of OWC chamber are investigated numerically. The effects of the impulse turbine on the integratedsystem and interaction among the wave elevation, pressure and air flow velocities variations are investigated.Keywords: Integrated System(통합시스템), Numerical Wave Tank(수치조파수조), Orifice(오리피스),Oscillating Water Column(진동수주 ), Wave Energy Conversion(파력에너지변환 )

Oscillating Flow Field Analysis as Shape of Air Chamber in OWC-type Wave Energy Conversion

An OWC-type Wave Energy Conversion passes through 3 steps energy conversion process. This paper deal with the internal oscillating flow and effect of shape of air chamber and duct at setting place of turbine by numerical analysis using commercial CFD code, FLUENT. Air chamber and duct in OWC-type wave energy conversion are adopting sudden expanded and contracted form for high-efficiency. So, whole oscillating flow from OWC-type chamber to outlet duct through duct was solved by steady and unsteady analysis in order that flow efficiency of air chamber and duct was made better.

Equivalent design wave approach for structural analysis of floating pendulum wave energy converter

Offshore structures are installed in a variety of water depths, under harsh environments, for long stretches of time, and waves are the most interrelated factor directly affecting their structural integrity. Thus, such structures should be designed to satisfy the demands of wave characteristics. In the preliminary structural design phase, a method for predicting non-linear random wave characteristics and extreme wave conditions must be determined. A structural response is not a linear value corresponding to maximum wave height, due to the related periods; that is, certain waves of less than maximum height may have greater effects on a structure depending on the wave period. This study focuses on selecting design conditions that generate a significant hydrodynamic load on a floating pendulum wave energy converter (FPWEC). For this purpose, it finds an equivalent regular wave height capable of generating the same hydrodynamic load, critical wave period and wave direction by conducting a response analysis. Generally, the subsequent equivalent design wave conditions are used to investigate an FPWECs global strength. This study also applies a global structural analysis for the FPWEC using the determined equivalent design wave. The obtained results should be useful for understanding the global structural responses of FPWECs.

Performance of Oscillating Water Column type Wave Energy Converter in Oblique Waves

진동수주형 파력발전시스템의 성능은 OWC챔버의 형상 뿐만 아니라 입사파의 각도와 터빈의 효과로 인한 압력강하등과 같은 작동환경의 영향도 받는다. 기존의 대부분 연구들은 파랑에너지 흡수효율에 초점을 맞췄기 때문에 입사파 방향이 OWC챔버 입구면과 직각을 이룬다는 가정 하에 수행되었다. 하지만 실해역에서는 입사파가 해양환경에 따라 사파의 형태로 입사하게 될 것이고, 고정식 구조물인 경우에는 그 영향이 더욱 지배적이다. 본 논문은 실험 및 수치해석적인 방법으로 사파중 OWC챔버의 성능에 대하여 고찰하였다. 실험은 3차원 조파수조를 이용하여 다양한 입사파 각도조건에서 수행하였다. 터빈의 영향을 고려하기 위하여 오리피스를 적용하여 챔버내 진동수주의 수위변동을 계측하였다. VOF모델을 기반으로 한 수치조파수조를 구축하여 실험과 동일한 조건으로 계산을 수행하여 실험결과와 비교분석하여 공기실과 그 인근의 유동변화를 고찰하였다.

Application based on the strictly combined method of BEM and CADMAS-SURF

The hybrid numerical model is developed by combining BEM that can calculate the wave motion rapidly under the potential theory and CADMAS-SURF that solves Navier-Stokes equations for the free surface variation near the structure, In the hybrid model the calculation of wave motion in a wide field of wave reflection for deep water area is conducted by BEM but for shallow water area by CADMAS-SURF. Especially the hybrid model can calculate random wave motions for long term period more rapidly with almost similar accuracy than the calculation of wave motion which was carried out by CADMAS-SURF only. In this study the coupling model was applied to the calculation of the strong nonlinear wave motion such as wave runup and overtopping at the coastal structure on the mild-slope bottom and the results of numerical model were compared with the Toyosima`s experiments of regular wave runup and Goda`s design diagram of ramdom wave overtopping, respectively,