Ultimate Strength Assessment of Steel-Welded Hemispheres under External Hydrostatic Pressure

Sang-Rai Cho,Teguh Muttaqie,Seung Hyun Lee,Jung Min Sohn,Jaewoo Paek

doi:10.1007/s11804-020-00178-8

Abstract

This paper focusses on steel-welded hemispherical shells subjected to external hydrostatic pressure. The experimental and numerical investigations were performed to study their failure behaviour. The model was fabricated from mild steel and made through press forming and welding. We therefore considered the effect of initial shape imperfection, variation of thickness and residual stress obtained from the actual structures. Four hemisphere models designed with R/t from 50 to 130 were tested until failure. Prior to the test, the actual geometric imperfection and shell thickness were carefully measured. The comparisons of available design codes (PD 5500, ABS, DNV-GL) in calculating the collapse pressure were also highlighted against the available published test data on steel-welded hemispheres. Furthermore, the nonlinear FE simulations were also conducted to substantiate the ultimate load capacity and plastic deformation of the models that were tested. Parametric dependence of the level of sphericity, varying thickness and residual welding stresses were also numerically considered in the benchmark studies. The structure behaviour from the experiments was used to verify the numerical analysis. In this work, both collapse pressure and failure mode in the numerical model were consistent with the experimental model.

Highlights

The pressure hull is the most important structural element of submarines and submersibles
The results show that the deviation of the sphericity, including the thinning due to cold forming, and the presence of the residual welding stress exerted in the fabricated model must be considered to achieve accurate prediction of the ultimate strength
The main goal of the current paper is to assess the reliability of FE analysis for predicting the collapse pressure of the steel-welded hemisphere, enabling engineers to use that numerical tool with confidence in determining the capacity in the actual structure case

Summary

Introduction

The pressure hull is the most important structural element of submarines and submersibles. The use of titanium spherical hull type was recently considered the most effective in load-carrying capacity in the Hadal zone exploration that reaches to depths of 6000 m and beyond These are some success stories in the development of state-of-the-art manned submersible vehicles such as Jiaolong operated by China NDSC (Cui 2018), Shinkai operated by JAMSTEC, Nautile operated by IFREMER, and Consul AS37 operated by Russian Navy (Kohnen 2018). This development of deep manned submersibles represents its important contributions to the ultimate strength of spherical shells. On the other point of view, the spherical form is ineffective for managing the internal space arrangement for more complex equipment and those with higher number of crew compared with a cylinder with the same volume space

Objectives

Results

Discussion

Conclusion