本研究內容延續莫鈞維(2013)之“利用氣壓與震盪水柱轉換波浪能量方法之研究”，以該波浪發電設計的工作原理為基礎，設計一個長6米，寬2.3米的發電設備箱體，箱體內充入液體，液體因波浪起伏造成的氣壓，而在箱體左右兩側反覆流動，進而帶動箱體中間下方置放的葉片轉動而發電，該葉片選用垂直軸式的Savonius葉型。利用CFD針對該設計之葉片及箱體進行數值模擬，本研究採用ANSYS CFX計算流體力學軟體，該軟體利用有限體積法求解三維Reynolds-Average Navier-Stokes方程式，並配合SST紊流模型進行模擬，其中網格採用ICEM軟體產生自適四面體非結構性網格。研究的重點在於探討所選用的葉片在不同流量及波浪波形等的流場及輸出性能，體積流率範圍為1m3/s至12m3/s，在不同的體積流率及不同轉速範圍下進行流場模擬，逐一討論該體積流率的操作轉速及其輸出功率。波浪的形式對輸出功率也有很大的影響，文中也對其發電輸出進一步探討，做為提供未來設計者的參考。

SUMMARY
The purpose of this study is to continue the research of Chun-Wei Mo (2013), “The Study of Converting Wave Energy by Using Air Pressure and Oscillating Water Column”, designing a 6 m-length, 2.3 m-width container with a Savonius vertical axial turbine wave energy device. From the previous study Chun-Wei Mo researched, water was filled in the generator sink. The wave motion will cause the liquid in the generator sink to reciprocate and motivate the turbine to generate. In order to obtain the performance of the blade from simulation, CFD method was employed. The software ANSYS CFX has been used in this study which is a numerical method used to solve 3-D Navier-Stokes equations with the finite volume method. The SST turbulence model was adopted to simulate the turbulent model. The self-adjusted tetrahedral non-structural grid was constructed based on the mesh generation software, ICEM. The major work in this study is to determine the operating condition for this design and discuss the power output in different wave type. Hence, the range of the volume flow from 1 m3/s to 12 m3/s has been simulated and each case is discussed, including the power output and efficiency. To determine the operating rotational speed, the method of predicting rotational speed is proposed in the simulation.

Key words: wave energy, Savonius blade, CFD, OWC

INTRODUCTION
Due to the shortage of nonrenewable energy such as petroleum and coal, development of technology related to renewable energy has accelerated recent decades. A worldwide desire to limit our dependency on fossil fuels as a means to produce power has motivated research in solar, wind and wave energy as well. Wave energy is available in a variety of forms such as marine current, tidal current, geothermal vent and waves. The most commercially viable resources studied so far are ocean current and waves. In this study, a 6 m-length, 2.3 m-width container with a Savonius vertical axial turbine physical model filled with water was set up. This device was established to be an oscillating water column and it would generate power by waves.

NUMERICAL METHOD
Nowadays, CFD modeling provides a good description of flow field analysis with details usually available through physical modeling. In this study, numerical simulations have been performed. The software ANSYS CFX was used in this study which is a numerical method solved 3-D Navier-Stokes equations with the finite volume method. Grid generation uses ANSYS ICEM CFD to generate the unstructured tetrahedral mesh. Additionally, a few prismatic layers were established near the tip area to increase the precision of the simulation. In order to achieve the accurate result, k-ωSST turbulence model was adopted since k-ωSST turbulence model has been widely used to analyze Savonius type turbine in previous researches.

RESULTS and DISCUSSION
This study is mainly aimed to analyze the output characteristics of the entire system at different volume flow rates. After the selection of the Savonius type blade, a traditional combination of a semi-cylindrical five-leaf Savonius model, flow field at 1 ~ 4m3/ s has been simulated. Based on the output characteristics and flow channel, the shape of the original blades was modified, improving the performance of the blade. To understand the physical condition of such device, and properties of the output of the modified Savonius rotor, the flow through the inlet section of the housing 1 ~ 12 m3/ s has been simulated. The results of the simulation showed the performance of the modified type blade was higher than that of the original one. In addition, the results indicated the power output is less than 30 kW at 1 ~ 5m3/ s; 30~60 kW at 6 ~ 7m3 / s and 100 ~ 300 kW at 8 ~ 12m3/ s. The value of performance efficiency is located within 0.06 to 0.08. The flow field of the whole system shows that there is a huge low pressure region with some vortex. Furthermore, this research is used to estimate the actual output performance of the wave power device based on this hydraulic turbine. As different environments caused different wave motions, this study only considered the wave period at eight seconds, and the half cycle can lead to eight tons of water flowing through the blade as physical conditions. Based on the physical conditions, 3 different types of waves were plotted to estimate a possible value of power output. The maximum volume flow rate of three different waveforms 3m3/s, 6 m3/s and 12 m3/ s, totaled to a maximum output power of 5.94 kW, 39 kW, 294.45 kW respectively. The corresponding values of the average power output during a period are 0.75 kW, 5.75 kW, and 37 kW.

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