Hydrodynamic Performance And Motion Response Of Multi-Body System In Twin-barge Floatover

With the increasing need of the deep water oil and gas resources, more and moredrilling and production platforms are widely used in offshore oil and gas productionservice. These platforms are generally installed in the sea. So how to install theseplatforms safely and quickly has been the focus of the offshore industry. Theinstallation of the platform generally is divided traditional lift installation andfloatover method. In offshore installation work, the traditional lift installation can’tmeet the needs of deck installation and the cost becomes more and more high. Thesingle barge scheme is widely used everywhere nowadays, but the design of the jacketframe structure have to meet the demand that a single barge can enter into. Besidesthis, the weight of topside increases gradually, so the single barge scheme is oftenlimited by the draft of barges. In recent years, the twin-barge floatover has become theresearch focus in offshore topside installations.In this paper, the operation processes of floatover especially the twin-bargefloatover are introduced systematically. The key technologies in floatover installationoperation are analyzed. The research status and development trend are also introduced.Besides this, the research methods and research directions of multi-body technologyare studied in this paper.The wet surface finite element model is built, and the different body gaps andratio of water depth to draft are set in this paper. Hydrodynamic coefficients is gainedin the frequency domain. The influence of body interaction and body gap forhydrodynamic coefficients of barge is revealed. And the effect to hydrodynamiccoefficients of the ratio of water depth to draft is also studied. The body interactionand body gap have an effect on barge only in wave frequency. With the decrease ofthe ratio of water depth to draft, added mass and damping present to increase.During the topside offloading of a twin-barge floatover installation, coupleddynamic analysis is carried out to investigate the motions of the barges. Particular attention is paid to the effects on system responses with different frictionalperformance of fender and axial stiffness of the hawsers. To increase the friction offenders and the axial stiffness of hawser plays a great role in reducing the relativemotions between barges and the hawser tensions. The motion responses of barges indifferent wave heights and wave angles are also analyzed. The responses of systemare very sensitive for the environmental conditions. The relative motions and hawsertensions increase obviously with the increase of wave height and the most dangerousangle is90deg.The connection type of topside and twin-barge is investigated in this paper. Therigid connection is turned out to be the most appropriate choice. The Motion responseprediction for the twin-barge system is carried out. The natural periods of verticaldegree of freedom is obtained. The result shows that the resonance will not occurbetween substructure platform and twin-barge system in floatover.The multi-body dynamic method is carried out to simulate the multi-body systemin twin-barge floatover. The research contents will be useful for exploitations ofmulti-body hydrodynamic performance technology of ocean engineering and it ishelpful to the development of the multi-body technology. And this method should befurther approved and improved, in order to become an effective means to predict theresponses of multi-body system. The multi-body analysis method will serve themarine engineering industry better.