澎湖海域潮流之數值模擬及其發電潛能評估

潮流在淺海陸棚區是困難度低、穩定性高、可完全預測的海洋能源。海流發電機組的設置可能改變當地流場的流速或流向，從而影響營養鹽類、浮游生物、稚仔魚及魚卵的分佈與通量等，這些變異可能改變原本脆弱的浮游生物群聚組成與結構，進而影響整體海洋生態系統。本研究以澎湖海域為例，建立高解析精度潮流數值模式進行潮流發電潛能評估與探討發電機組放置對當地流場造成的影響。本研究建構之高解析精度潮流數值模式推算發電潛式結果顯示，吼門水道與西嶼外垵西側海域最具發電潛能。本研究以改變摩擦係數模擬不同裝置容量之潮流渦輪機，實驗結果顯示10 倍、100 倍和1000 倍之摩擦係數約等同於設置10kW、20kW 和30kW 之理想化潮流發電機組之效果。據此將探討兩個部分，第一個部份為不同裝置容量之潮流發電機組置放對強流區造成的改變，另一個部份是以模擬示蹤劑佈放實驗探討水體交換效率的變化。強流區改變部份，於跨海大橋吼門水道中心置放發電機組後，發現於其北側產生另一強流區，南側第二渠道支流流速也增加，且隨發電機截取能量加大而增加。西嶼外垵西側海域案例中，強流區座落位置往西外移，且亦隨發電瓦數增加而愈加顯著。水體交換效率變化部份，根據示蹤劑模擬之結果，若以30kW 之理想化潮流發電機組為例，渦輪機設置前後示蹤劑傳輸擴散範圍減少了約10 km2，較未設置前約減少16%左右。再計算各濃度傳輸擴散面積所佔總傳輸擴散面積百分比，稀釋後的示蹤劑其低濃度(10%以下) 在置放發電機後傳輸擴散面積增加14.5%，高濃度(20%以上)則減少6.5%，可知內海水質傳輸擴散範圍縮減，示蹤劑受到底部渦輪機影響，高濃度的示蹤劑滯留當地，降低澎湖內海的水體交換效率。西嶼外垵西側海域的實驗中，渦輪機置放對當地水質交換的速率與比例皆無顯著影響。

關鍵字

潮流發電；澎湖海域；數值模式

並列摘要

Tidal power is a clear and constant renewable ocean energy that can be predicted accurately. With the rapid development of shallow water turbine technologies in the commercial market, the uncertainties of the investment in terms of cost-benefit assessment can be reduced. The tidal current energy conversion is considered as one of the favorable alternative in Taiwan’s energy policy. One of the crucial issues is the impacts that may be brought by the installation of turbines. As the kinetic energy is uptaken, the follow field will change and hence the transportation of nutrients, plankton and lava will altered, which leads to the direct impact of ocean ecosystem. The aim of present study is to setup a high-resolution 3-D ocean circulation model that is capable to simulate the tidal current at curvy coastline in Peng-Hu Archipelago. The numerical model system is first validated using field measured datasets. From the simulation results, it is found that the Hou-Men Channel and western Si-Yu sea area have the greatest energy potential in Peng-Hu. It is worthy to noted that the processes of tidal dynamic in the inner-bay of Peng-Hu Archipelago behave similar to a lagoon with two narrow open ends, where the effects of phase lags of major constituents is limited. The almost synchronized tidal current flow into the inner-bay from the north and south ends can be identified during flood tide and vice versa. Concerning to the approaches to simulate the effects of the installation of tidal energy conversion units, this study adopted the method of modifying the bottom drag coefficient to simulate the flow field change incurred by installing difference turbine of various capacities. Furthmore, the discussions on the change of current fields in the vicinity of installations as well as the change of water body exchange rate in the inner-bay with respect to various turbine capacities are carried out. In the Hou-Men Channel case, the location of strong current stream will move northward due to the installation of turbines, and the velocity increases in the south channel. In western Si-Yu sea area, the location of strong current stream moves westward. From the results, both Hou-Men Channel and western Si-Yu sea area entertained more severe impacts of the shifting of strong stream locations as the capacity of turbine increased. This study also compares the variation of the rates of water body exchanged at different sites through the tracer simulated experiments. For example, the setup a 30kW idealized turbine in Hou-Men Channel will inccur, the tracer spearding area reduced by 16% compared to original case. In western Si-Yu sea area, there seems no significant altering of tracer spreading with respect to different capcities of turbine.

並列關鍵字

numerical model ； Peng-Hu ； tidal current energy

參考文獻

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澎湖海域潮流之數值模擬及其發電潛能評估

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