Prediction of added resistance of a ship in waves at low speed

This paper presents predictions of the added resistance of a ship in waves at a low speed according to the IMO minimum propulsion power requirement by a hybrid Taylor expansion boundary element method(TEBEM).The flow domain is divided into two parts:the inner domain and the outer domain.The first-order TEBEM with a simple Green function is used for the solution in the inner domain and the zero order TEBEM with a transient free surface Green function is used for the solution in the outer domain.The TEBEM is applied in the numerical prediction of the motions and the added resistance in waves for three new designed commercial ships.The numerical results are compared with those obtained from the seakeeping model tests.It is shown that the prediction of the ship motions and the added resistance in waves are in good agreement with the experimental results.The comparison also indicates that the accuracy of the motion estimation is crucial for the prediction of the wave added resistance.In general,the TEBEM enjoys a satisfactory accuracy and efficiency to predict the added resistance in waves at a low speed according to the IMO minimum propulsion power requirement.

Numerical study on ship-generated unsteady waves based on a Cartesian-grid method

The added resistance of a ship in waves can be related to ship-generated unsteady waves.In the present study,the unsteady wave-pattern analysis is applied to calculate the added resistance in waves for two modified Wigley models using a Cartesian-grid method.In the present numerical method,a first-order fractional-step method is applied to the velocity-pressure coupling in the fluid domain,and one of volume-of-fluid(VOF)methods is adopted to capture the fluid interface.A ship is embedded in a Cartesian grid,and the volume fraction of the ship inside the grid is calculated by identifying whether each grid is occupied by liquid,gas,and solid body.The sensitivity to the location of measuring position of unsteady waves as well as the number of solution grids is examined.The added resistance computed by direct pressure integration and wave pattern analysis is compared with experimental data.In addition,nonlinear characteristics of the added resistance in waves are investigated by detailed analyses of unsteady flow field and resulting wave pattern.