Estimation of Force Reduction on Ocean Structures With Perforated Members

Abstract

While retrofitting and rehabilitation are usually related to strengthening of members, the presented concept is a novel attempt as it addresses decrease in the encountered forces on the members. Presence of perforated members in ocean structures reduces the wave-structure interaction significantly; breakwaters with perforated members are classical examples of such kind. This concept of encompassing the perforated outer cylinder with inner existing structure is found to be most feasible rehabilitation concept as it does not demand replacement of any damaged members. The presence of outer perforated cover alters the water particle kinematics significantly and eventually this remains the reason for the force reduction mechanism. In this study, the variation of water particle kinematics along the depth of the cylinder is estimated on the cylindrical structure with and without perforated outer cover. Forces on the inner cylinder are quantified numerically and experimentally; experimental results show a close agreement with that of the numerical ones. Velocity variations along the water depth are quantified in the form of design charts, which shall be helpful for the practicing professionals while attempting for retrofitting or re-design. Force variations derived through numerical analyses, which are functions of the water particle kinematics along the depth shall be useful in the design offices for cylindrical members encompassed with perforated outer cover. Introduction of perforated member over the existing cylindrical structure showed a significant force reduction around 60% on an average for all the wave steepness indexes considered for the study, when compared to the force on the member without perforated cover.