| Summary: | 碩士 === 國立臺灣海洋大學 === 海洋環境資訊學系 === 100 === The aim of this research is to conduct the oceanic freak wave cases on the occurrence probability and waveform from in-situ data around Taiwan.
Freak wave is unpredictable. In our study we analyze the occurrence probability of freak wave to understand a custom proportion that is helpful on the freak wave prediction advanced in the future. And then we classify the waveform of freak waves to realize the generated mechanism of freak wave.
In this study, we used buoy data from Central Weather Bureau, and we choose the Hsinchu buoy, Longdong buoy and Taitung deep sea buoy. Defined freak wave as the waves with trough to crest wave height exceeding the significant wave height by a factor of 2 and, furthermore, dangerous freak wave (DFW) means that it is not only the factor described earlier but its height higher than 2 meters. Results indicate that probability of the freak wave occurrence around Taiwan is about 1.7 ~ 2.0×10-4. That is, about 5,000 to 6,000 waves may occurs one freak wave. Finally, in the typhoon condition, the occurrence probability of DFW may rise to 2 to 5 times.
Take a step further, freak wave waveform can be contributed to various mechanisms. In this study the ratio of trough height to crest height (RTC) is used to classify three types of freak wave, high crest, deep trough and symmetric, the results shows symmetric waveform freak waves are about 80% of total freak-wave observations around Taiwan. Besides, the topic of whether freak waves hide in a wave group or not is worthy discussing. Result demonstrates that groupiness factor is unsuitable to adapt in a freak wave which occurs in a wave group. On the other hand, a simpler method to classify the freak wave waveform is considered and it shows that most of freak waves appear alone about 90% around Taiwan.
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