플로트오버 설치방식을 이용한 탑사이드 설치의 모형시험 연구

Abstract

Recently the float-over installation mothod is more frequently used for the installation of large-scale offshore structures. Float-over installation consists of three steps. The first step is the docking stage, during which DTV(Deck Transportation Vessel) approaches the offshore structures. The second step is the mating stage of the topside installation on jacket platform. The final step is the undocking stage of DTV after the completion of topside installation. During the mating stage, the motion of DTV and the reaction force at the interfaces are important design factors for the float-over installation. Model tests can be used to investigate the installation stability from the measured reaction force of interfaces and motion of the DTV. In this study, to evaluate the mating operation during a float-over installation in waves, model tests were designed and carried out . The experimental model consists of three main structures : a DTV, a topside structure and a jacket platform. There are various interface items such as LMU(Leg Mating Unit)s, DSU(Deck Support Unit)s, fenders, tethers and moorings. The model tests were performed at the Ocean Engineering Basin of KRISO. In the tests, four mating stages of 0%, 40%, 70%, 80% load transfer were considered. Irregular and white noise waves were tested under three different wave headings. Focus is on the dynamic forces acting on the LMUs and the motion responses of the DTV. The measured data are directly compared with the numerical simulation results which obtained by using the program KIMAPS of KRISO, and good agreements are shown in the comparisons. It is also shown that the characteristics of the impact forces on LMUs are closely related to the motion responses of the DTV. Discussions were made on the effects of wave headings, load transfer rates and center of gravity of the topside on the impact forces of LMUs and the motion response of DTV.