Hydrodynamic Resonances in Harbor Engineering (Prof. Jin S. Chung Award Lecture, 2017)
- Chiang C. Mei (Massachusetts Institute of Technology)
- Document ID
- International Society of Offshore and Polar Engineers
- International Journal of Offshore and Polar Engineering
- Publication Date
- March 2018
- Document Type
- Journal Paper
- 1 - 10
- 2018. The International Society of Offshore and Polar Engineers
- stochastic theory, wave trapping, mobile breakwater, infragravity waves, Nonlinear resonance, nonlinear dynamics, chaotic oscillations,
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We summarize the studies of two dynamical problems arising from harbor engineering. The first is on the long-period oscillations in a harbor forced by short and random incident waves. The second is on the unexpected oscillations of the mobile storm barrier designed for the Venice lagoon. In both problems nonlinearity plays a crucial role in the mathematical analysis.
PART I. LONG-PERIOD HARBOR OSCILLATIONS EXCITED BY RANDOM WIND WAVES
Harbors are designed to protect ships from storm-induced sea waves. Long-period oscillations inside a harbor are hazardous to ship operations in general and to loading and unloading of cargos in particular. They can cause excessive straining and breakage of mooring lines as well as collision of ships against piers, etc. During strong oscillations, the swift current at the entrance hammers the passing of small vessels. Early studies of harbor oscillations were focussed on the linear mechanism of synchronous resonance, which is appropriate for treating the effects of long-period tsunamis (Miles and Munk, 1961; Lee, 1971; Chen and Mei, 1974). However, many harbors in the world are troubled more often by the short incident waves generated by storms. An example is the case of Barbers Point Harbor in Hawaii (Okihiro, 1993). The wave gauge at an inside station recorded a sharp peak at the frequency of f = 0.001 Hz corresponding to the wave period of T = 100 s, which is ten times the typical wind wave period of O(10) s (see Fig. 1).
Hualien Harbor is located on the eastern (Pacific) coast of Taiwan, which is invaded by typhoons several times each year. During Typhoon Longwang on October 2, 2005, a 7000-ton cargo ship broke loose from its dock at the northern end of the basin, drifted southward for 1 km, ran aground outside the harbor, and broke in half. Figure 2 displays the wave height spectra recorded at several stations during Typhoon Tim of 1994. Those spectra at outside stations # 2 and # 5 show high peaks at quite short periods O(15) s. However, at stations #8 and #10 inside the basin, high peaks appear instead at quite long periods O(140) s.
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