以WRF-SWAN模擬臺灣離岸風場於颱風下之近岸波場

Abstract

隨著環境保護意識抬頭，各國接連宣布欲於2050年達到淨零碳排，加上能源需求仍不斷增加，再生能源因此蓬勃發展，臺灣也不例外。由於臺灣海峽擁有許多於世界名列前茅的優良風場，離岸風電於各種再生能源中更具有發展優勢，因此離岸風場的開拓勢在必行。不過臺灣位於易受颱風侵擾的中緯度西太平洋沿岸，颱風挾帶的極端風場及其對應生成之波浪會大幅提升離岸風機承受的負載，對離岸風電產業是一大威脅。 本研究建立一高可信度的颱風風浪模擬流程，以受廣泛使用的天氣研究與預報模式WRF (Weather Research and Forecasting)模擬颱風風場，並導入第三代近岸風浪模式SWAN (Simulating WAves Nearshore)，針對臺灣鄰近海域進行颱風風浪模擬，結合兩個模擬模型以模擬出更貼近實際結果之波況變化。 研究中選定2017年之尼莎颱風為歷史案例分析，使用WRF模擬三種不同起始時間之颱風風場，並分別導入SWAN模型中，配合海床地形資料，計算不同極端風況變化下於臺灣附近海域生成之風浪。模擬結果分析所得波場中的重要指標如：示性波高、平均週期與平均波向，並將選定浮標及竹南海洋風場觀測塔位置之結果取出與實測資料進行比對，以驗證模擬結果準確度，並瞭解臺灣竹南海洋風場(Formosa 1)在受颱風影響下近岸海域風浪變化。 總結而言，本研究之模擬流程可成功模擬出極端風場侵襲下波場的變化，且捕捉之風場與波場特性與實際結果相近，於竹南觀測塔位置模擬所得之示性波高極值高估約0.5 m，週期則高估約1 s。綜合所有比對結果可發現整體模擬趨勢與各測站觀測結果相符，兩者間相關係數最高可達0.88，均方根誤差最低則是0.53。日後可將此流程之結果波場應用於離岸風機受力分析之環境參數，以將實際波況更佳的納入考量，提高分析結果的可靠度，降低實際工程可能遇到的風險。

With growing environmental awareness, many countries have announced their commitment to achieving net-zero carbon emissions by 2050. As the demand of energy has also increased with time, this leads to the significant development in renewable energy sources worldwide, with Taiwan being no exception. Since the Taiwan Strait has many excellent wind farms that are among the best in the world, offshore wind industry has more advantages in development among other renewable energy sources. Therefore, the development of offshore wind farms is imperative. However, Taiwan’s geographical location along the western Pacific coast poses many typhoon challenges for offshore wind farms. Extreme wind and extreme wave conditions generated by typhoons significantly increase the load on offshore wind turbines, posing a substantial threat to the offshore wind energy industry. A highly reliable simulation process for typhoon-induced wind and wave conditions was established in the study. The widely used Weather Research and Forecasting (WRF) model was employed to simulate typhoon wind fields and the results were imported into the third-generation nearshore wave model, Simulating WAves Nearshore (SWAN). In this way, the wave induced by conducted typhoon wind could be well simulated in the coast areas near Taiwan. With the combination of two simulation models, the wave conditions were more accurate. Typhoon Nesat (2017) was selected as a historical case in this study. Using the WRF model, typhoon wind fields was simulated with three different initial time. These wind fields were then imported into SWAN model separately, and the bathymetric data was also taken into consideration to calculate wave conditions under three different extreme wind scenarios near Taiwan. Some characteristic wave parameters were analyzed, including significant wave height, mean wave period, and mean wave direction. Additionally, the simulation results were also compared with the measurements from selected buoys and the observation tower in Zhunan in order to validate the accuracy of the simulations, especially for the simulated wave changes in Formosa 1 offshore wind farm. In summary, the simulation process successfully captured the variations in wave conditions under extreme wind events. The simulated wind and wave characteristics closely aligned with actual observations. Notably, at the Zhunan observation tower location, the simulated significant wave height was overestimated by approximately 0.5 meters, while the period is overestimated by around 1 second. Overall, the simulation trends correlated well with the observed data, with a maximum correlation coefficient of 0.88 and a lowest root mean square error (RMSE) of 0.53. In the future, we can apply the resulting wave fields as environmental parameters for offshore wind turbine load analysis, enhancing the reliability of engineering assessments and mitigating potential risks in practical projects.