Shukui Liu

On the prediction of the added resistance of large ships in representative seaways

ABSTRACT The importance of the sufficiently accurate prediction of the added resistance and powering of large ships in representative seaways is discussed. We introduce an updated empirical formula that may be used by engineers for the fast estimation of the added resistance of ships in waves and validate this formula for ships with LPP > 250 m operating in realistic sea conditions. The importance of the accurate prediction of added resistance of large ships is demonstrated by numerical and experimental studies on both full and fine hull forms. It is shown that for large ships sailing in representative seaways, properly quantifying the spectral contribution of the added resistance in the region of λ/LPP ≈ 0.1∼0.5 is of paramount importance and further studies are necessary to resolve this issue for large ships. This also leads to a critical discussion about the ITTC recommended experimental procedure, when assessing the overall seakeeping performance of large size ships in representative seaways.

Approximation of the added resistance of ships with small draft or in ballast condition by empirical formula

An attempt was made to extend and further tune the existing formula for approximating the added resistance in head seas to cover a wider range of speed and to account the impact of loading conditions; a new parameter based on B/T was introduced after conducting extensive parametric study to capture the influence of draft on the added resistance; the trim effect has also been investigated; Furthermore, the draft effect on the added resistance due to diffraction is further tuned and simplified. The derived formula uses only a few input, including only some ship dimensions to yield an estimation of the added resistance of ships in regular waves. Numerical results show that the added resistance of various ships in head seas at low speeds, as well as the added resistance of tankers in ballast condition and cruise ships, can be properly captured by the new formula. Hence, it meets the demand of fast examination of the minimum power; it can also be used in the early design stage of a ship for power estimation.

On Nonlinear Simulation Methods and Tools for Evaluating the Performance of Ships and Offshore Structures in Waves

This paper describes the development of alternative time domain numerical simulation methods for predicting large amplitude motions of ships and floating structures in response to incoming waves in the frame of potential theory. The developed alternative set of time domain methods simulate the hydrodynamic forces acting on ships advancing in waves with constant speed. For motions’ simulation, the diffraction forces and radiation forces are calculated up to the mean wetted surface, while the Froude-Krylov forces and hydrostatic restoring forces are calculated up to the undisturbed incident wave surface in case of large incident wave amplitude. This enables the study of the above waterline hull form effect. Characteristic case studies on simulating the hydrodynamic forces and motions of standard type of ships have been conducted for validation purpose. Good agreement with other numerical codes and experimental data has been observed. Furthermore, the added resistance of ships in waves can be calculated by the presented methods. This capability supports the increased demand of this type of tools for the proper selection of engine/propulsion systems accounting for ship’s performance in realistic sea conditions, or when optimizing ship’s sailing route for minimum fuel consumption and toxic gas emissions.