EFFICIENT LONG-PERIOD WAVE ABSORBING SUBMERGED MOUND STRUCTURE

Masashi Tanaka,Minoru Hanzawa,Akira Matsumoto

doi:10.9753/icce.v34.structures.61

Masashi Tanaka, Minoru Hanzawa + Show 1 more

Open Access

https://doi.org/10.9753/icce.v34.structures.61

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Abstract

In many Japanese ports, it has been reported that long-period waves with periods of 30 to 200s cause serious problems in cargo handling. As a countermeasure, wave absorbing mounds installed on the harbor side of breakwaters have been constructed. The crown heights of such rubble mounds are almost equal to those of the caissons. Although such structures can be expected to provide some wave absorbing performance, they are too large to apply to specific site conditions. It is important therefore to reduce the size of the structure to apply to specific site conditions. In our study, a slightly submerged mound type long-period wave absorbing structure is proposed. A series of hydraulic model experiments was carried out to evaluate the wave absorbing performance in port and stability characteristics of the armor units against wave overtopping from the sea side. Throughout this study, it became clear that submerged structures display a higher wave absorbing performance compared with those of conventional structures. Moreover, a prediction formula for the stability number for Tetrapods covering these submerged mounds is proposed.

Highlights

In many Japanese ports, long-period waves with periods of 30 to 200s can cause serious problems in cargo handling
The origins of problems in cargo handling mainly come from resonances in the periods of long waves with that of the mooring system in the harbor
In order to develop a formula for the stability of Tetrapods, the mound width BM was set to 30cm (= 2HD) or 60cm (= 4HD)

Summary

Introduction

In many Japanese ports, long-period waves with periods of 30 to 200s can cause serious problems in cargo handling. The origins of problems in cargo handling mainly come from resonances in the periods of long waves with that of the mooring system in the harbor. Hiraishi et al (1997) conducted a series of field observations to investigate the mechanism of damages by long period wave in ports. In 2002, The Ministry of Land, Infrastructure, Transport and Tourism (hereafter, referred to as MLIT) carried out interviews to uncover the actual situation of the long period wave problem. Results of these interviews can be found in the home page of MLIT. Some examples of the damage described in these interviews are as follows:

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