Abstract

The twin-barge floatover method is promising for the offshore mega topside installation. This study presents the experimental investigation on the twin-barge floatover installation in regular waves. The sea-keeping motion characteristic of the twin-barge floatover system, together with the loads on mating units and lash lines are analyzed. In the experimental tests, the twin-barge hinged connected with the topsides was simulated. The motions of the twin-barge and the topsides were measured and investigated in detail. Results show that the twin-barges motions were as expected synchronized largely in head wave. The twin-barge motions were quite difference in both amplitude and phase in beam waves, which was caused by the shield effect and the elastic connection. The lash line experienced large forces in beam waves and should be paid attentions. The experimental results will provide valuable suggestions on the design of the twin-barge floatover system.

Introduction

The mega topside installation of the offshore platforms is a challenging task. There are two methods for the topside installation, i.e., the heavy lifting crane method and the floatover method (Gros and Lescurat, 1982; ONeill et al., 2000; Seij and Groot, 2007; Wang et al., 2010). Because of relative few costs and large capacities, the floatover installation method is much more attractive and competitive than the heavy lifting crane method, particularly for the mega topside that exceeds the lift capacity of the available heavy lift crane.

The floatover installation firstly employs the hull barge to transport the topside to the location. Then the mooring line, the fender, the winch, the monitor system and the lash line are utilized to approaching the barge into the slot of substructures. Once the weather-window is available, the topside loads are transferred on the jackets by the tide level, the barge ballast system or the jacking system. Lastly, after offloading the topside onto the jacket, the barge is separated from the topside and withdrawn from the slot of substructures. For the conventional single barge floatover installation, the installation faces several challenges, including but are not limited to, the insufficient gap between the substructures and the barge resulting in large collisions loads on the fender, the excessive motions of the topsides leading to the failure of the mating operation, and the nonlinear dynamic impact on the mating unites. The single barge floatover installation also requires the slots of substructures, which would pose some limitations of the geometries of the substructures.

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