摘要
台灣海峽豐沛的風能有利於開發離岸風力發電。近年來台灣為了提高再生能源電量比例，能源局積極推動「千架風機」計畫，期許在2025年以前離岸風電達到10至17 GW裝置容量。然而目前台灣西岸海域規劃之部分離岸風場緊鄰於瀕危之海洋哺乳類中華白海豚棲息地，打樁施工所產生之水下噪音可能造成其行為改變甚至造成聽力損傷。因此本研究致力於打樁水下噪音預估，希冀可應用於噪音估算與減噪設計，使用有限元素法在頻域模擬打樁聲源，透過反傅立葉轉換成時序列訊號並計算聲曝值。量測數據為上緯新能源股份有限公司於2016年9月於台灣苗栗近海離岸風機之打樁噪音，本團隊於施工點位附近佈放底碇式聲學儀器及進行船載式噪音量測。實海域水下噪音量測結果便用於比對模擬之結果，結果顯示打樁噪音能量集中於頻率100 Hz至500 Hz，於不同貫入深度下量測與模擬之聲曝值比對誤差落於正負2 dB內，平均誤差約0.8 dB。 利用實海域量測結果驗證打樁噪音模擬之可行性後，後續採用變異數分析與迴歸分析，分別針對量測與模擬進行統計分析。量測部分為聲曝值與「樁錘能量」與「貫入深度」之統計分析，結果顯示樁錘能量對水下噪音之影響較貫入深度影響大，多參數有限元素模擬中，選用影響水下噪音之相關參數如「基樁能量」、「基樁長度」、「基樁直徑」、「基樁樁壁厚度」與「當地水深」，結果得知基樁能量與基樁樁壁厚度為主要影響之參數，其中基樁能量與水下噪音呈現正向關係，而基樁樁壁厚度與水下噪音呈現負向相關，並經由變異數分析縮減模型獲得聲曝值之迴歸公式。此公式可用於預估打樁水下噪音聲源強度，可作為未來離岸風場開發之參考依據。
並列摘要
The geographic environment and wind source around Taiwan are suitable for developing the offshore wind energy. To increase the proportion of renewable energy in total electricity in Taiwan, Bureau of Energy are actively promoting the “Thousand Wind Turbines” project which will reach 3GW offshore wind power prior to the year of 2025. However, west coast of Taiwan is a significant habitat for the endangered marine mammal, Chinese White Dolphin (Sousa chinensis). The pile driving underwater noise might cause behavior disturbance or even auditory damage to them. Therefore, the thesis aims at the pile driving underwater noise prediction, simulating the pile driving noise and analyzing the measurement data to verify the accuracy of the simulation. We utilize Finite Element method (FEM) to simulate the pile driving noise in the sound field, then using the Inverse Fourier Transform to obtain the time series sound pressure and calculating sound pressure level. In September 2016, Swancor Renewable Energy Co., Ltd constructed the offshore wind turbine, off the western coast of Miaoli, northern Taiwan, which allowed us to use bottom-mounted hydrophones and ship-measurements to record the noise created during the piling. These measurement data can be comparing with our prediction results. From the comparison, the energy of pile driving are center from 100 Hz to 500 Hz, and most case error of sound exposure level are between measurement and simulation are from 0 dB to 1.5dB and mean error are just 0.8 dB. After verifying the simulation prediction which are coherent with the measurement data, we do the analysis of variance and regression analysis on the measurement and the output of multivariable finite element simulation respectively. From the statistical analysis of measurement, the pile driving noise are dominant from hammer energy. In the simulation, we select some parameters which may be the important ones on pile driving noise. From the statistical analysis of multivariable simulation, Transfer energy and thickness are dominant variables to sound exposure level of pile driving. Transfer energy is positive relative to the noise but the thickness is negative relative to the noise. Finally we use ANOVA reduced model of simulation to get the regression equation. This equation is composed of Transfer energy, thickness, water depth. From the equation, we can predict the pile driving noise in the near field and be a reference on offshore wind farm environment assessment.
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