| Summary: | 碩士 === 國立臺灣大學 === 工程科學及海洋工程學研究所 === 107 === 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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