Measurements of current loads on side-by-side semi-submersibles in a wind tunnel

Abstract Numerous multi-body coupled systems are adopted in offshore operations to improve the accommodation environment and work efficiency. The current loads on a multi-body system are complex due to environmental sheltering and greatly affect operation safety and feasibility. This paper presents experimental studies on current loads, particularly the longitudinal and transverse forces acting on two side-by-side semi-submersibles in a wind tunnel. The influences of separation distance, spacing ratio, shape of columns, and draft of production platform on current loads are investigated. When the accommodation platform is upstream, the twin-body interference can generally increase the longitudinal force acting on the vessel and decrease the transverse force. The shielding effect appears when the vessel is downstream, significantly decreasing the mean transverse load coefficient by up to 80%. When separation distance decreases, the interference becomes more distinct and there is nearly a linear relationship between distance and force reduction. Once the accommodation platform turns and is shielded, the reduction in mean load coefficients becomes more noticeable as the spacing ratio decreases. The shielding effect is insensitive to drafts except for the 90°. The production platform with square columns has greater interferences (about 1.2–1.8 times) than that with cylindrical columns.