Local Structural Response of Stiffened Steel Panels due to Wave Impact: Calculated Responses From Measured Slamming Pressures Vs. Hydroelastic Measurements

Abstract

Design of offshore structures must be designed against wave impacts. The local structural integrity of the stiffened panels is often checked by finite element analysis (FEA). The design critical slamming loads used as input to the FEA is often obtained from model tests in ocean basins or towing tanks. The slamming pressure measurements and corresponding response calculations are not trivial and for practical reasons calculations do not normally account for any hydro-elastic effects, except perhaps added mass. So how accurate are such FEA calculations? This document describes a classical FEA procedure using a constant and uniform added mass. The wave impact pressures used as input to the FE response calculations were measured on a 9 × 5m2 area of a vertical column in SINTEF Ocean’s large wave tank. The FE response calculations are compared with measured responses from hydroelastic wave impacts, where the elastic panel covered the same area as the slamming force panels. The structural response is calculated for the 5 largest extreme total force events out of a total of 19 realizations of a critical sea state. The FE results of the calculations are compared statistically to measured extreme strains from the elastic panels. The FE calculation procedure is found to be conservative since calculated design strain values from FEA are significantly larger than the measured design strain values.