Model experiments on wave elevation around a four-cylinder structure

Abstract

Column-supported structures are commonly used in offshore industries. The prediction of the free surface elevation in the vicinity of the supporting columns is important for structural safety and air gap design. Because the tension leg platform is normally supported by four vertical columns, model experiments are carried out to study the diffraction of regular waves by a four-cylinder structure. The experiments are designed to measure the free surface elevation at multiple locations close to the cylinder surfaces. By analysing the measured data, the amplitudes of the first-order and second-order harmonic wave elevations are obtained. To validate the diffraction theory with regard to predicting the free surface elevation, the experimental and numerical results are compared and show that the second-order diffraction theory is effective in predicting the free surface elevation, even for steep waves. The important phenomenon of near-trapping is also investigated in the experiment. For a specific incident wave frequency, near-standing wave motion can be observed inside the structure. Different wave headings are also investigated to describe the dependence of first-order and second-order near-trapping phenomena on the incident wave direction.