Design sensitivity of deck support frame structure for float-over installation

Abstract

The recent increase in size and weight of offshore plant requires the development of float-over method and the development of design technology of additional structure for safe installation. The float-over method allows the installation of over tens of thousands of tonnes of the offshore plant topside safely from the quay wall to the target offshore structure. Among the additional structures, deck support frame (DSF) to safely support heavy topside during float-over installation are to be designed in consideration of various marine environmental loads as well as operational loads. The DSF needs a weight reduction design to improve the ship motion performance and buoyancy of the topside transport vessel equipped with the DSF. In this paper, the structural design sensitivity analysis of the DSF was performed in connection with the development of the float-over method for the safe offshore operation of the 20,000-ton class topside. In order to review the structural sensitivity of the new type of DSF, design of experiments (DOE) method based on an orthogonal array was performed by considering the dimensions of the main members as three-level design factors, and setting the structural strength evaluation stress and the weight as responses. Through the sensitivity analysis, the quantitative effects on the response of each major member was analyzed, and the minimum weight design case was reviewed from the design matrix according to the DOE. ？ 2020 by the International Society of Offshore and Polar Engineers (ISOPE).