Measurement of Unsteady Ship Wakes in Waves

Abstract

Although the importance of ship performance in waves has been stressed, only a few set of data of wake measurments are available in which a ship runs in waves. Adding to that, today's CFD techniques have been able to offer flow data around ships. Therefore we will need verification data of the flow field around a ship in the case when the ship runs not only in still water but also in waves. This paper is concerned with the wake measurments of a ship in regular waves. First we verified the wake measurement system by measuring the regular wave field itself and then by oscillating the probe in a still water flow field. The wake measurements were carried out with λ/L=1 and 0.5. In both conditions, the ship was towed in heave and pitch free condition and motion fixed condition. Furthermore a forced pitch conditon in still water was also carried out. Measurement data were presented by showing the change of wake fraction and mean circualtion in one encountering period and we thus showed the relation between the change in the wake and the ship motion and incident waves.