Hydrodynamic Interaction of Two Ships in Tandem under Current

摘要

There are various situations in the operation of ships that requirernthem to remain positioned close to another vessel at searnunder the action of environmental agents. This scenario is commonrnin the offshore oil exploitation industry, where shuttle vesselsrnattach themselves to FPSOs for offloading operations thatrnmay last for several hours. The dynamic behavior of the vesselsrnduring their exposure to the often-changeable weather is of vitalrnimportance for the safety of these operations. Having focused onrnthis problem in previous works employing mathematical modelsrnthat disregard the hydrodynamic interaction between the ships,rnwe now take on the task of incorporating these potentially importantrneffects into the analyses. Literature on this problem isrnrelatively scarce. As a point of departure, we assume that the existing,rntime-proven single-ship models should not be discarded,rnbut improved upon. We thus attempt to model the interactionrnbetween vessels through the modification of the current velocityrnfield, and thus develop a model that supplies a velocity correctionrnterm, intended for use in any of the existing models. In thisrnfirst, heuristic approach to the issue, we show that a momentumconservationrnargument can reduce the problem to that of determiningrnthe geometry of the wake of the upstream vessel. Experimentalrnresults found in the literature were used to calibrate thernparameters of the wake. The issue of the spatial averaging of thernvelocity field involved in calculating a unique correction term isrnalso discussed.