ABSTRACT

Twin-barge floatover method can utilize two barges to install the topsides and is a promising method for the mega topsides installation. However, the complex connections between the twin barges and topsides pose great difficulties for floatover operation. The installation process involves the hydrodynamic and structual interactions of multiple bodies. In this study, a numerical model for predicting motions and loads during the floatover operations is proposed. The model considers the effects of multi-body hydrodynamic interaction, DSU and LMU structural connections, mooring systems, and fenders. The motion equations of the multiple bodies, together with the coupled stiffness matrix of the two barges and topside, are derived. The in-house code is developed to predict the coupled motions of two barges and topside, loads on DSU and LMU during different load transfer stages in time domain. The numerical results are compared with the experimental results in beam wave. Good agreement is obtained. Results indicates that the proposed numerical model can provide an accurate and reasonable predictions of the twin-barge floatover installation.

INTRODUCTION

With the develop of the offshore oil and gas industry, offshore platforms gradually become much large and intensive. Limited by the lifting capacity of crane, conventional crane lifting method is difficult to meet the installation needs of mega topside of offshore platforms, especially for 10,000-ton mega topside. To install the mega topside safely and efficiently, floatover installation method has developed rapidly in recent years. In the floaotver method, the topside of the offshore platform is carried by barges, and lowered down onto the substructures by the tide level and barge ballast adjustment, finally transferring the topsides loads onto the substructures.

The floatover methods have various configurations and can be classified according to different criteria (Qin et al. 2021). As a floatover installation method emerged in recent years, twinbarge floatover installation method is flexible in form and can use two barges to achieve the installation of topside, which has a broad engineering application prospect. In the twin-barge floatover method, the weight of topside is transferred from the twin-barge onto the jackets under wind, wave and current loads. The complexity of the system involves multi floating bodies hydrodynamic interaction, multi-body elastic connection and external restraint, load transfer, etc.

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