Linear structural stress analysis of a hull girder penetration and a short longitudinal bulkhead using finite element modeling.

Abstract

The objective of this study is to investigate structural shadow zones encountered in shipbuilding design using the I-DEAS (Integrated Design Engineering Analysis Software) software. The term 'shadow zone' refers to areas of low stress concentrations that are caused by lines of stress bending around structural discontinuities. Two ship design situations frequently encountered that result in shadow zones are hull girder penetrations and short structural longitudinal bulkheads. In both of these situations, a long-used rule of thumb is to construct a line with a slope of 1:4 originating from the. discontinuity that encompasses the area of low stress. The material within this line is then considered ineffective when computing the section modulus. This can prove to be expensive. However, powerful finite element analysis software is readily available that can analyze the shadow zones in greater detail and possibly minimize the area considered ineffective. This study uses the I-DEAS software to develop finite element models of the cited design situations for a U.S. Navy Frigate, FFG-7 class of ship. It conducts a static structural linear analysis of the ship balanced on a trochoidal wave of height 1.1 VL. The results generated in this study validate the rule of thumb in both situations