Numerical and Experimental Studies on Ship Motions Induced by Passing Ship

To investigate the ability of numerical models to simulate the behavior of moored ships subjected by ship-wake waves, use is made of scale model tests where a ship model sails with constant speed along a straight path at a constant distance from an otherwise motionless ship. The tests were carried out at one of the wave tanks of the Portuguese Civil Engineering Laboratory (LNEC). The moving ship is a self-propelled scale model of the “Aurora” chemical ship whereas the otherwise motionless ship is a scale model of the “Esso Osaka” tanker. The free-surface elevation was measured with a set of resistive wave gauges and ADVs. The tanker’s movements, induced by the wake waves, were measured along the six degrees of freedom with a gyroscope deployed inside the ship. The numerical model WAMIT provides, in the frequency domain, the quantities required to estimate the hydrodynamic forces associated to the interaction of a free-floating ship with waves. The BAS model uses those hydrodynamic forces to study in the time domain the ship interaction with any sea-waves acting on it. Wind and current actions can also be accounted for. The results of these numerical models are compared to the measurements made in the several repeats of one of those scalemodel tests, in terms of the response amplitude to several wave components. These comparisons enabled the evaluation and validation of the numerical models parameters’ calibration process. INTRODUCTION Waves can hamper cargo operations and compromise the safety of moored ships. In fact, it is not uncommon for waves inside harbors to be responsible for mooring lines’ breakage, resulting in costly damages to terminal’s structures and ship’s hulls. Such waves can be a result of extreme sea states, trapped long waves or even wake waves caused by maneuvering ships. In the first work to characterize the wave field generated by ships sailing along a straight line, Froude [1] identifies the existence of two wave systems: the transverse waves and the divergent waves. Equal phase lines of these two systems meet along two straight lines that are symmetrical with relation to the ship trajectory. The highest free-surface elevation values do occur along those lines, as well as near the ship’s bow. The theoretical wave pattern generated by a point source that moves with a constant speed obtained by Lord Kelvin [2] is similar to the ship-wake wave pattern. In that work, it is shown that the maximum of the free-surface elevation occurs along two straight lines symmetrical with relation to the point source trajectory making an angle of 38o 56’ with each other (19o 28’ with the point source trajectory). Numerical models can characterize the response of ships to waves but still depend on some parameters calibration. In that sense, physical model experiments can be of paramount Proceedings of the ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering OMAE2018 June 17-22, 2018, Madrid, Spain