ESTIMATING MANOEUVRING COEFFICIENTS OF A CONTAINER SHIP IN SHALLOW WATER USING CFD

摘要

The study of ship manoeuvring in shallow water has acquired added significance in recent times duernto increased traffic and operation of ships in inland waterways and coastal areas. The standardsrnspecified by IMO on ship manoeuvring are for deep water condition, whereas it becomes morerndemanding on the designer to come up with a vessel which meets the more stringent requirements ofrncontrollability in shallow and confined waterways. The ship manoeuvring equations of motionrncontain velocity and acceleration dependent hydrodynamic coefficients. The dynamic tests performedrnon a ship model using PMM in a towing tank yield these hydrodynamic coefficients, both linear andrnnon-linear components in uncoupled and coupled modes of sway and yaw.rnThis work presents the use of RANSE based CFD method in the determination of hydrodynamicrnderivatives in shallow water region. A container ship model has been used for the analysis in a virtualrntowing tank the size of which has been fixed based on ITTC guidelines for RANSE methods forrnmanoeuvring predictions. The objective of the present work is to study and quantify shallow waterrneffect on the manoeuvring performance of surface ships. The numerical methods for solving RANSrnequations for viscous turbulent flows have been applied here to predict the manoeuvring behaviorrnof a ship by calculating the hydrodynamic forces and moments acting on a scaled ship model duringrnforced motions. This is achieved by simulating dynamic planar motion mechanism test on a 1:36rnscale model of container ship (S 175) in a numerical towing tank.rnIn dynamic simulations, the prescribed body motions have been imposed on the hull using userdefinedrnfield functions within the commercial CFD solver STAR-CCM+ in pure sway and pure yawrnmode. Time histories of the oscillatory forces and moments have been expressed in Fourier series.rnThe terms in this series and the corresponding terms in the equations representing the mathematicalrnmodel are compared to arrive at the expressions for linear and non-linear hydrodynamic derivatives. The Fourier coefficients have been obtained through the numerical integration of the time histories ofrnforces and moments in all the modes using trapezoidal integration rule. The hydrodynamicrnderivatives hence evaluated have been compared with the experimental results and are found to be inrnreasonably good agreement. In all cases, the effect of shallow water can be seen on the values ofrnhydrodynamic derivatives.