Modelling of berthed ship ‚ÄövÑv¨ passing ship interaction forces and moments in shallow and confined water
Creators: name: Denehy, Shaun
Publisher: name: University of Tasmania
Year: 2023

description: When a ship transits a port environment, the pressure field surrounding it imparts interaction forces and moments on objects in the vicinity, such as berthed ships. This can cause the berthed ship to range on its moorings. These berthed ship motions can interrupt unloading/loading procedures, be a safety concern for port operators, and in extreme cases, cause damage to the ship and port infrastructure. For safe and efficient port operations, it is important to be able to predict the effect the passing ship will have on the berthed ship and implement strategies to mitigate the interaction effects. It has been shown that confined water has a significant effect on the form and magnitude of the interaction forces and moments imparted on the berthed ship by the passing ship. Most existing empirical methods do not account for the effect confined water has on the interaction forces and moments. New prediction methods are required that can accurately model the effects of very shallow and confined bathymetries in berthed ship ‚ÄövÑv¨ passing ship interactions. This thesis reports on a study into the form and magnitude of interaction forces and moments imparted on a berthed ship due to a passing ship in shallow and confined waterways. Physical model scale Experimental Fluid Dynamics (EFD) tests were conducted, and three numerical methods were developed to determine the interaction forces and moments imparted on a berthed ship due to a passing ship; ‚ÄövÑ¬¢ a double body inviscid model; ‚ÄövÑ¬¢ a double body viscous model; and, ‚ÄövÑ¬¢ a viscous model that included the free surface. The study involved a systematic variation of passing ship speeds; water depths; lateral separations between the berthed and passing ship; and near and far bank offsets. The effect that scale has on the interaction force and moment predictions was investigated using the numerical models. The newly developed numerical methods were assessed against the EFD results to determine when each method is appropriate. The flow fields around the berthed and passing ships have been analysed to better understand the effect of the independent variables during the interaction event. It was found that the form of the interaction forces and moments for laterally unrestricted, very shallow (water depths below 1.100TT) and confined (shallow and laterally restricted) cases can vary significantly from the laterally unrestricted, moderately shallow cases. A change in the form of the interaction forces and moments will change the berthed ship motions and mooring loads due to the passing ship. Most existing empirical methods are based on laterally unrestricted, moderately shallow cases, where it is assumed that the magnitude of the interaction forces and moments vary with the passing ship speed squared. For specific confined water conditions, the magnitude of the interaction surge force imparted on the berthed ship did not vary proportionally to the passing ship speed squared. The nonspeed squared proportionality of the interaction surge force imparted on the berthed ship was shown to be caused by the free surface deformation and not the viscous effects. Empirical methods based on unrestricted water cases should not be used to predict the interaction forces and moments for very shallow (below water depths of 1.100TT) cases or confined water cases. For laterally unrestricted, moderately shallow cases, model scale results can underestimate the magnitude of the interaction yaw moment imparted on the berthed ship due to the passing ship. In very shallow and confined cases, where viscous effects can be significant, predictions should be performed at full scale. A limited series of results from the experiments and numerical predictions have been used to modify an existing bank effect parameter, used to represent the influence shallow and restricted water has on a ship, to account for the effect the near and far bank offset distances have on the magnitude of the berthed ship ‚ÄövÑv¨ passing ship interaction forces and moments. These results and new numerical methods can be used to provide a more accurate estimate of the passing ship‚ÄövÑv¥s effect on the berthed ship in shallow and confined waterways. Limits of applicability of each numerical method has been presented.