ABSTRACT

In this study, time-domain mating analyses were carried out to verify safety of float-over operation during various load transfer stages. Water depth of the target field is 130m. Topsides weighing 20,000 ton will be installed on fixed jacket structure by float-over using DTV (Deck Transportation Vessel) with the support of mooring lines. Five (5) operational stages from initial contact to 100% load transfer have been assessed by time domain analysis. For topsides mating analysis, DSUs, DSF Support Points, LMUs, steel-to-steel contacts at LMU points, sway fenders, mooring lines and many parts were modelled to investigate the interactions between the DTV, the topsides and the jacket. The results of analyses have been approved by a MWS.

INTRODUCTION

There are two methods for topside installation at offshore fixed structure. In case of heavy integrated topside, lifting method is limited by allowable lifting weight of crane vessels. Float-over method can handle the heavy topside by DTV's ballast system. If a topside weight is becoming heavier, the Float-over method is preferred. Since the first success of HIDECK float-over integration in 1983, many projects have been carried out with float-over method installation.

Jung et al. (2009) evaluated impact loads occurring at various load transfer during the mating phase by performing frequency domain and time domain analysis. Min He et al. (2011) analyzed the time domain using Moses and applied nonlinear spring to DSU, Fender, and LMU. Kurian et al. (2013) carried out model test and numerical calculations to confirm motion performance of the barge for the float-over installation. Magee et al. (2014) conducted a float-over installation model test. The barge motion response and the dynamic load acting on the LMU were measured and the instrumentation for the model test was described. Kim et al. (2017) carried out float-over model test in various load transfer stages.

This study is a part of research project funded by a Korean government to develop the technologies for offshore topsides installation. The research project is aimed to develop installation design package of float-over method for 20,000 ton class topsides on jacket structure.

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