Calculation of the forces on a moored ship due to a passing container ship

[摘要] ENGLISH ABSTRACT: When a sailing ship passes a moored ship the moored ship experiences forces andmoments. These forces and moments cause the moored ship to move. The resulting shipmotions due to the passing ship can sometimes be more severe than the ship motions dueto ocean waves and can cause serious accidents at moorings such as the failing of mooringlines or even the total break away of the ship from the berth. Since bulk carriers and tankerswere traditionally the largest seafaring ships, passing ship studies have focused mainly onthese vessels, but recently container ships have grown to a comparable size. In this study anexisting numerical model 'Passcat is validated with physical model measurements for aPost Panamax container ship passing a Panamax bulk carrier. Other existing mathematicalformulae are also evaluated by comparison with these model tests.In the physical model tests the passing speed (V), passing distance (G), depth draft ratio(d/D) and the presence of walls and channels were varied. It was found that the passing shipforces are proportional to the passing speed to the power of 2.32. This is slightly higher thanthe generally accepted quadratic relationship for passing ship induced forces. Similarrelationships were found for the other variables.The numerical model results were compared to the physical model measurements bydetermining agreement ratios. A perfect agreement between the numerical and physicalmodels would result in an agreement ratio of 1. Agreement ratio boundaries, whereinagreement would be regarded as good, were drawn between 0.7 and 1.3. The numericalmodel, Passcat, was found to under predict the passing ship forces. It was found thatPasscat is valid for a wide range of sensitivities and remains within the agreement ratio limitsas long as passing speed is limited to 10 knots (kt), depth draft ratio to more than 1.164,passing distance to less than four times the moored ship beam (Bm) for surge and swayestimation and passing distance to less than three times the moored ship beam for yawestimations. These limits are true for no structures in the water. For structures in the wateronly the passing speed limits are different. When quay walls are present, the surge andsway forces will only provide acceptable answers at passing speeds below 9kt. When 9Bmor 12Bm channels are present, the sway force will only provide acceptable answers atpassing speeds below 7kt. When a 6Bm channel is present, the yaw moments will onlyprovide acceptable answers at passing speeds below 6kt.From the mathematical model evaluation study it was found that empirical or semi empiricalmethods can not provide answers with good agreement to the physical model when walls orchannels are present. For the open water case, it is only the Flory method that can provideanswers with good agreement to the physical model for surge, sway and yaw forces. TheFlory method can provide answers with acceptable agreement within narrow boundaries ofpassing distance (1 to 2 times the beam of the moored ship), passing speed (4 kt to 14 kt)and depth draft ratio (less than 1.7). The numerical model, Passcat can be used with littleeffort to provide answers with better agreement to the physical model for a larger range ofvariables.

[发布机构] Stellenbosch University