Similarity relationship among non-dimensional significant wave parameters are discussed which is based upon the 3/2 power law. The characteristics of the wind wave spectra in deep water are investigated by using the parameters of JONSWAP spectrum and the 3/2 power law. From theoretical and empirical arguments, it is confirmed that a f power law exists at high frequency range, that JONSWAP spectrum parameter y and a are varied with fetch, and that parameter a and y satisfied a -1/3 power law. In shallow water region, spectral form of wind waves is varied with the shoaling coefficient. Through the analysis of the wind wave spectra, a new spectral formula is obtained.
ABSTRACTABSTRACTWhen a tsunami attacks an island, heavy damage can be caused by a trapping effect. A theoretical solution was obtained for such trapping of long waves using a conical island model. The effects of both the finite radius of the island and the refraction over a sloping beach were taken into account. Characteristic distributions of water surface elevation, runup height, and their frequency responses were studied through the theoretical solution, and the conditions pertaining to strong trapping were examined. The heights recorded in Oki and Okushiri Islands can be explained satisfactorily using the theory as verified through hydraulic experiments.Keywords: tsunami trappingtsunami refractionHokkaido Nansei-Oki earthquake
Linear and nonlinear sets of equations of long waves in the Lagrangian description are solved numerically to obtain run-up heights. Numerical results are compared with theoretical ones in case of simple topographies and the agreement is quite satisfactory. As a practical application, the computation is carried out for the Okkirai Bay in Japan. The computed run-up heighs agree fairly well with the recorded ones.
ABSTRACTABSTRACTThe feasibility of quantitatively forecasting a near-field tsunami prior to its arrival is examined, provided that the initial tsunami profile can be determined from fault parameters calculated using a method similar to that of Izutani and Hirasawa. Examination of basic equations, boundary conditions and grid lengths has led to the conclusion that the following combination is the best to perform rapid, accurate, and detailed numerical forecasting; the linear long wave theory discretized with the staggered leap-frog scheme, perfect reflection at the land boundary, and a grid length varying from 5.4 km out at deep sea to 0.2 km at the shoreline. With the aid of a super computer, tsunami heights along every 200 m of Japan's Sanriku coast (250 km long) can be obtained within 7 minutes after the occurrence of an earthquake. This method gives enough time for warning transmission and for evacuation of residents because the standard arrival time of tsunamis in this district is 25 to 30 minutes.
Linear and nonlinear sets of equations of long waves in the Lagrangian description are solved numerically to obtain run-up heights. Numerical results are compared -with theoretical ones in case of simple topographies and the agreement is quite satisfactory. As a practical application, the computation is carried out for the Okkirai Bay in Japan. The computed run-up neighs agree fairly well with the recorded ones.
Numerical calculations of shallow water waves with their disintegration into solitons are generally carried out by the Boussinesq equations. However, the Boussinesq equations do not automatically lead to wave breaking, because the frequency dispersion tends to balance the nonlinearity and to stabilize the wave profiles. Further the amplification of wave height in region just before breaking is also not sufficient due to their weak nonlinearity and dispersion. The artificial additional terms should be considered in the equations. In this study, two kind of artificial terms are investigated through comparisons between numerical and hydraulic experimental results. One is an artificial amplification term for just before the breaking region and the other is a breaking term for spilling breakers. Both artificial terms are formulated as a momentum dissipation form.
Linear and nonlinear sets of equations of long waves in the Lagrangian description are solved numerically to obtain run-up heights. Numerical results are compared -with theoretical ones in case of simple topographies and the agreement is quite satisfactory. As a practical application, the computation is carried out for the Okkirai Bay in Japan. The computed run-up neighs agree fairly well with the recorded ones.
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