Physical modelling of wave scattering around fixed FPSO-shaped bodies

•Wave-FPSO interaction tests were used to explore the effects of model length, wave steepness and incident angle on the total and scattered waves.•The highest amplitude scattered waves are obtained with the shortest model.•The linear harmonic increases as model length decreases but the nonlinear harmonics are similar for all three models.•The non-linear scattered wave increases with incident wave steepness. The incident wave angle affects the maximum crest height and wave loading.•The second order difference long-wave component is a robust feature of our experiments and needs to be considered in design of the air gap.•Contributions of the third- and fourth-harmonics should be considered to assess wave loading and structural responses for offshore structures. FPSO (Floating Production Storage and Off-loading) vessels used for offshore oil and gas production are operated in deep water, often at locations which experience severe wave loading. This paper reports on laboratory experiments on a series of simplified FPSO-shaped bodies, with the aim of understanding more about the wave-structure interaction, particularly the generation of scattered waves. These tests were carried out in the Ocean Basin at Plymouth University’s COAST Laboratory where the effects on the wave-structure interaction of model length, wave steepness and incident wave direction were investigated. All three models had semi-circular ends, separated by a box section for the 2 longer models. Input waves were based on focused wave groups generated using NewWave with an underlying JONSWAP spectrum. A general phase-based harmonic separation method was applied to separate the linear and higher-harmonic wave components of the free-surface elevation surrounding the bodies, and of relevance to the assessment of wave loads. Close to the bow of the model, the highest amplitude scattered waves are observed with the most compact model, and the third- and fourth-harmonics are significantly larger than the equivalent incident bound harmonic components. At the locations close to the stern, the linear harmonic is found to increase as the model length is decreased, although the nonlinear harmonics are similar for all three tested lengths, and the second- and third-harmonics are strongest with the medium length model. The nonlinear scattered waves increase with increasing wave steepness and a second pulse is evident in the higher-order scattered wave fields. As the incident wave angle between the waves and th