Simulation of whipping response of a large container ship fitted with a linear generator on board in irregular head seas

Abstract

There is plenty of energy contained in the ocean waves, and great efforts have been made over recent decades, to make full use of these sustainable energy resources. As a novel device to utilize ocean wave energy, the authors propose in this paper a whipping energy converter, which utilizes a linear generator extracting power from ship's whipping and springing (hull girder 2-node vibration) responses. The device is designed resonant to the hull girder 2-node vibration frequency. Numerical simulation of the responses of the whipping energy converter was carried out under irregular head sea condition, using time domain ship motion analysis by Rankine source method and subsequent 3-dimensional whole ship FE analysis, and the main parameters of the whipping energy converter was studied. A 14,000 TEU large container ship was utilized in this study, because large container ship is prone to constant whipping and springing responses in real seas. As a result, it was found that the whipping energy converter can effectively generate power from the whipping and springing responses, and at the same time, the whipping energy converter functions as a dynamic damper. With the piston weight of 5~10 tons, the whipping vibration is visibly reduced, while if the piston weight is about 100 tons, the spectral peak is reduced to less than one-third. This implies that the whipping energy converter contributes to the prevention of fatigue damage due to whipping and springing, which is an imminent concern in the design of large container ships. It was also found that larger power generation can be expected as the piston weight is heavier, and the bow is the most effective location for this device.

Predictions of Ship Extreme Hydroelastic Load Responses in Harsh Irregular Waves and Hull Girder Ultimate Strength Assessment

“…The influence of different levels of nonlinearities, which includes linear, Froude-Krylov nonlinear, body nonlinear, body exact and smooth waves methods, on symmetric hydrodynamic responses for a ship operating in harsh waves with large amplitude motions can be found in References [12,13]. On the other hand, although the computational fluid dynamics (CFD) tool, which is on the basis of solving Reynolds Averaged Navier-Stokes (RANS) equations has been incorporated into the methodology of hydroelasticity, the immensity of time cost still makes it stay at early stage and far from practical engineering application [14]. Therefore, the potential flow theory constitutes an invaluable tool in the prediction of ships hydroelastic responses.…”