14:00
Hydrodynamics in Ocean II
Chair: Hua Liu
14:00
30 mins
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SCENARIOS OF FLOW FIELDS INDUCED BY POTENTIAL TSUNAMI IN SOUTH CHINA SEA
Zhiyuan Ren, Xi Zhao, Benlong Wang, Hua Liu
Abstract: Since 2004 Indian Ocean tsunami, the significant advancements of tsunami warning system and methodology had obtained more attention. As a matter of fact, the currents induced by the tsunami may bring damages, especially for ports and harbors (Lynett et al., 2012). Crescent City Harbor suffered damages of $28 million by the currents from the 2006 Kuril Islands tsunami, and $26 million from the 2011 Japan tsunami (Admire et al., 2014). At Crescent City, the observed velocities ranged from 2 to 4.5 m/s for Japan tsunami.
As Manila Trench is becoming one of the most hazardous tsunami source region (Ren et al. , 2014), the potential extreme tsunami hazards of the worst case scenario (Mw=9.3) in South China Sea are investigated numerically. Using the shallow water equations, the tsunami hazards in terms of time series of surface elevation, arrival time, maximum amplitude and velocity distribution are analyzed. The characteristics of wave amplitude and currents are presented and analyzed. The numerical results show that the most energy of tsunami wave distributes in central and north part of South China Sea, and the most tsunami-hazardous regions are southeast coast of Hainan, Guangdong, Taiwan, Philippines, and Eastern Vietnam. The maximum wave amplitude near Guangdong Province, Hainan Island, and Taiwan Island exceeds 4 m, and velocities at most measured locations near coast exceeds 2 m/s. Nested grid with high resolution is used to study the impacts of the tsunami on Hainan Island, Taiwan Island, and Lingding Bay. The regions with high level hazard are identified.
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14:30
30 mins
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TIME-DOMAIN COMPUTATION METHODS FOR A FLOATING PLATFORM OF COMPLICATED GEOMETRY WITH MULTIPLE WAVE INTERACTIONS
Yuichi Ashida, Takeshi Hara, Takuya Taniguchi, Masashi Kashiwagi
Abstract: Wave interactions are complicate and thus important in evaluating the performance of a floating platform of complicate geometry which consists of several different members of submerged structures, because generated waves will be reflected infinitely back and forth among the submerged structure members. Due to these multiple wave interactions, resulting hydrodynamic forces on the platform may fluctuate depending on the wave frequency and hence the rate of approaching zero in the damping force with increasing the wave frequency becomes slow. This is related to the slow convergence in the memory-effect function with the increase in time and also related to the increase of computation time in the time-domain direct computation for obtaining a steady state after multiple wave reflections among submerged structure members of a floating platform. These phenomena and associated difficulties in the time-domain computation methods for a floating platform of complicated geometry will be discussed in the paper. The time-domain Green function method and higher-order boundary element method will be used in the time-domain direct computation method, and obtained results are compared with corresponding results by the other method which computes a convolution integral using the memory-effect function which can be computed from the damping-force coefficient obtained in the frequency-domain problem. A numerical technique to reduce the computation time while keeping the sufficient accuracy will be proposed in the paper.
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