Evaluation of vibration characteristics of caisson-type breakwater using impact vibration tests and validation of numerical analysis model

Abstract

In this study, ambient and forced vibration tests are proposed to evaluate dynamic characteristics of a caisson-type breakwater including natural frequencies and modal damping ratios, and the feasibility of numerical analysis model with fluid-structure-soil interaction effects, which plays an important role to evaluate structural performance and safety, is investigated by comparing the numerical results with experimental results. Oryukdo breakwater in Busan, Korea is utilized as a target structure, and this breakwater was once heightened by installing additional parapet structures as amount of about 4 m to improve the harbor tranquility in 2005. Two times of vibration tests were carried out in 2000 (before heightening) and in 2011 (after heightening). In the first test, most caissons were tested while one caisson was tested in 2011. It is found that natural frequencies are reduced as amount of 1.7 - 4.3 % after heightening, and similar results are observed from the numerical analysis. It is also found that forced vibration tests can make more reasonable results than ambient vibration tests. Even though there is some degree of discrepancy between experimental and numerical results, numerical analysis can be carried out to analyze dynamic characteristics and evaluate the structural performance and safety. Copyright © 2013 by the International Society of Offshore and Polar Engineers (ISOPE).