Strength Analysis And Local Structural Reformation Of A Semi-submersible Drilling Platform

With the development of offshore oil industry, offshore platforms increasingly attract the global offshore oil producers' attention. The semi-submersible drilling platform which has been designed early can not meet the needs of development, so it is very necessary to upgrade for improving construction capacity.In this paper, a modified semi-submersible drilling platform is taken analyzed. The finite element model of global structure is established with the MSC.PATRAN software.The method which is recommended by ABS MODU standard is adopted to compute the loads of platform under various working conditions. The MSC.NASTRAN finite element software is used to analyze global strength of the guide platform. The yield strength is checked according to the requirements of ABS.Major work is divided into the following three parts:(1) A finite element model of the platform is established, and its static analysis is carried out under various operating conditions. The research results show that stress concentration parts of the global structure are mainly distributed as follow: 1) joints which connect the box-girder and column below the main deck and the diagonal brace; 2) the vertical and horizontal bulkheads and main skeletal material near the moonpool; 3) some connected nodes between column and brace, floating body and brace, brace and brace. Because of the large openings of moonpool sides, local stress of deck structure near the moonpool edges obviously exceeds yield stress limit.(2) The local structure of platform is analyzed based on braces, the analysis result show that: 1) The safety margin of some local structure is too large; under wave load and platform own gravity, some braces increase torsional strength of the platform structure, but the effect on the global structure strength of platform is little. 2) The newly added vertical braces which connect main deck and floating body at bow and stern have little action on global vertical strength; the newly added horizontal braces, which connect column and sponson restrict lateral motion between the two floating-body, are effective to increase transverse strength of the platform structure.(3)According to the arrangement form of braces, by comparing several reformation schemes of platform local structural, a better design which can meet the strength specifications is obtained. Some technical references are provided about the structural design of the semi-submersible drilling platform.