Toshikazu Kitano

Stem waves along vertical wall due to random wave incidence

Abstract This study investigates stem waves, propagating along a vertical wall, due to obliquely incident random waves through laboratory experiments and numerical simulations. Attention is paid to the difference or similarity between the stem waves due to periodic waves and random waves, the nonlinear and linear characteristics, and the effect of wave breaking on the evolution of stem waves. The following were found from this study: as the incident angle of waves become large or the nonlinearity of the incident waves become small, the significant stem wave height, normalized by the incident significant wave height, becomes large. This tendency is the same as that generated by the Stokes waves or cnoidal waves. However, regardless of the nonlinearity of incident waves, the width of stem waves is almost the same. This is a different point between the stem waves due to periodic and random waves. The wave breaking suppresses the growth of the stem waves.

TRANSMISSION OF LONG WAVES INDUCED BY SHORT-WAVE GROUPS THROUGH A COMPOSITE BREAKWATER

Theoretical findings and laboratory evidences are presented regarding the transmission of long waves induced by short-wave groups through the rubble base of an infinitely long composite breakwater. Multiple-scale perturbation method is applied in describing the long-wave fields in terms of velocity potential, and an analytical solution is derived for transmitted and reflected long waves induced by wave groups. Dependency of the reflection and transmission of free long waves on several parameters is examined through the numerical calculations. It is found that the linear friction factor, the rubble-base height and the modulation of short waves affect the transmission of free long waves significantly. Theoretical results are then compared with the results from laboratory experiments. It is shown that although the conventional rubble-mound breakwaters can reflect short wave energy efficiently, a significant part of the bound long-wave energy associated with shortwave groups is transmitted to the leeward side of the breakwater as free waves.

126. DEGREE OF EXPERIENCE FOR EXTREME WAVE STATISTICS

The confidence interval for the extreme wave height of longer return period is good for nothing. Unreasonable uncertainty of estimation has been accepted. We were helpless against this difficulty. We engineers believe in a certain limitation of extrapolation , but they have been bothered with a problem: how much wide interval is no worth being considered. This study proposes a new index to use for this judgement.

DIFFRACTIVE UNCERTAINTY TOWARD THE FUTURE ESTIMATION OF RETURN WAVE HEIGHT

Freshness is very important factor, which is not exceptional for the observation data. The data ready for statistical analyses, is observed in the past, while the return period is laid on the future for the predicting return levels. It is natural that the farther ahead in the future the return level is predicted, the larger the statistical variety becomes. Thus, the freshness of the record is falling down as the pass of time. In the point of view, the statistical uncertainty becomes wide, as entering into the shadow area distinguished by the straight lines of confidence regions by the conventional method. The proposed method will give a potential trend even for the stationary model. It will be useful tool because in many cases it is very difficult to detect the faint trend in short records of wave heights and sea levels due to the climate change, as one of the applications.

A NEW ANALYSIS METHOD FOR EXTREME WAVE STATISTICS BY POISSON-GPD MODEL

This paper describes a new mothod for a frequency analysis of extreme wave heights, by employing the generalized Pareto distribution (GPD) assuming Poisson process of event occurence. A principal advantage of using GPD is the connectivity to the asymptotic extreme value distribution, whose shape parameter’s value is identical to that of GPD. The inference method is based on the maximum likelihood for estimation of return wave heights and a Goda’s spread parameter, and the confidence intervals are due to the delta method. A wave data set hindcasting off Kodiak is applied as an example. The present analysis shows that extreme value of the sample follows the FT-III distribution, which is not employed as a candidate distribution in the previous studies.