Performance Prediction of a Blunt Ship in Oblique Waves

Abstract

On prediction of ship performance in actual seas, it is important to estimate external forces acting on a ship. The predominant factor is added resistance in waves which reduces ship speed. Therefore, added resistance in waves is required to be calculated with accuracy. In addition, since a ship sails with a drift motion due to winds and waves, it is required to estimate hydrodynamic forces and moment due to drift motion. As ocean waves is characterized their irregularity which contains various frequency and direction component, it is required to estimate added resistance in oblique waves as well as in heading waves. In this paper, it is investigated by tank tests whether the calculation method on added resistance in heading waves is applied to that in oblique waves. Furthermore, hydrodynamic forces and moment due to drift motion is calculated with appending a term of drag for wing of a small aspect ratio. The effectiveness of the calculation methods is shown by estimating decrease of ship speed in actual seas.

Study on the bow shapes above the waterline in view of the powering and greenhouse gas emissions in actual seas

“…The basic model and the large flared model have equivalent results. The coefficient C U of each model derived by the least-squares method range from In the hybrid calculation method, C U for the added resistance in oblique waves is obtained from equations (9) to (13).…”

“…The coefficient C U of each model derived by the least-squares method range from F n = 0:15 to F n = 0:247 as follows: for the wall-sided model, C U = 30:3; for the basic model, C U = 47:7; for the large flared model, C U = 45:7. In the hybrid calculation method, C U for the added resistance in oblique waves is obtained from equations ( 9) to (13).…”

“…It has been confirmed that, for both blunt ships and fine-lined ships, the added resistance could be accurately calculated by this hybrid calculation method; the method has been also validated by onboard measurements. [12][13][14] Furthermore, the hybrid calculation method can experimentally take account of the bow shapes above the waterline by introducing tank test results although the theoretical calculation method to estimate the influence of the bow shapes on the added resistance in waves has not been developed and validated. It is empirically known that the improvement in the bow shapes above the waterline reduces the added resistance in waves, and the effect can be experimentally taken into account by the hybrid calculation method.…”

Performance prediction of full-scale ship and analysis by means of on-board monitoring (Part 1 ship performance prediction in actual seas)

“…Furthermore, to Fig. 15 Averaged standard errors of longitudinal wind force coefficient (54 ships) [14] improve accuracy for the small drift angle, it has been shown that the lift-induced drag given by the small aspect ratio wing theory should be added to the resistance due to drift motion [59]. In this case, the hull drifting forces in the steady condition [resistance ( ΔR drft ), sway force (Y drft ) and yaw moment (N drft )] are expressed as Eqs.…”

Verification on the Resistance Test in Waves Using the Actual Sea Model Basin

“…For both ships the scaled models of about 6m length and 3m length are made. The resistance tests have been carried out at 400M 10) and at OEB 10), 11) for the large models and small models, respectively. The small models are used at ACT and the results of the model tests are compared with those at 400M and OEB.…”