Strength Analysis for the Outer Pressure Tank of a Submersible

Abstract

There are some cases where the pressure hull of a submersible includes a partial outer pressure tank within two concentric cylinders. In this paper, the strength was calculated by two methods-FEM and some approximate theories. The calculated results were compared with the results of stress measurements made on an actual submersible. The measurements were made to find out the most accurate and efficient method of analysis for this type of structure. The FEM analysis was done in two steps. In the first step, the analysis of the whole structure model was tried in order to understand the behavior of the structure as a whole. A suitable method of partial (local) modeling was investigated to increase the efficiency of the FEM analysis. In the second step, the analysis using the partial (local) structure model made clear the stress and deformation of the structure in detail. The approximate theories, the analyses using theories by W.Hovgaard, K.Okuda and others, were also tried. From the results of these analyses and the stress measurements, the following main conclusions were reached. 1) The deformation and stress distribution for the section of this structure was nonuniform. 2) On the inner shell in the concentric cylinder area, particulary near the partial single hull, peak stress was generated. 3) The stress calculated by FEM analysis closely coincided with the measurements. 4) Concerning the location where the critical stress was generated, the results from the approximate theories (W.Hovgaard, K.Okuda, and others) underestimated the measurements, and were not within acceptable tolerance.