Local structural response to seakeeping and slamming loads: Fid-Bau Portal

Local structural response to seakeeping and slamming loads

Tuitman, Johan T. / Bosman, Theo N. / Harmsen, Eelco

Abstract A common approach to investigate the response of a structural detail such as a hatch corner is to compute the seakeeping loads using a linear 3D Boundary Element Method (BEM) and transfer the seakeeping loads to a Finite Element (FE) model of the ship structure. This approach is suitable for computations of the fatigue loading of structural details near amidships because a majority of the fatigue loading will occur in mild sea-states where the loading may be assumed linear. However, the linear seakeeping model may not hold when one investigates the ultimate response of the local bow structure of a ship which is designed to remain operational in severe conditions, for example, a frigate. A linear seakeeping analysis will significantly underpredict the loading at the bow because both the impulsive slamming loads and the non-linearities in the non-impulsive wave loads will contribute significant to the structural loading. The non-linear loads require one to first derive a short-term distribution of the local structural response before the ultimate value of the response can be derived. A method to compute the short-term distribution of a structural detail is presented in this paper. The first step is to perform seakeeping analyses which includes slamming, non-linear Froude-Kryloff and hydrostatic loads. The short-term distribution of the total hydrodynamic loading at the structural detail is obtained by simulating the seakeeping response for several hours. The response of the local structure is computed for the most severe impacts found in the seakeeping simulation. The hydrodynamic loading, including the non-linear contributions, is transfer to the structural model and the structural response is computed using the FE-method. The results of the structural analyses allow one to transform the short-term distribution of the structural loading to a short-term distribution of the response of the structural detail. A designer can obtain the ultimate structural response by entering the probability at which one accepts overloading of the structure in the short-term distribution of the response of the structural detail.

Highlights • Seakeeping response including the non-linear Froude-Kryloff and slamming forces. • Inclusion of hydro-elastic effects and coupled seakeeping and slamming computation. • Short term distributions loading at part of the bow structure is derived. • The local structural response is determined for most severe impacts. • The short-term distribution of the local response is obtained.