High speed video analysis of freak wave-ship model experiments

Abstract

The concept of freak waves is of importance to the maritime industry as freak wave-ship encounters can be severe, resulting in significant damage to, or loss of, the ship. Model scale testing of a ship in repeatable freak waves can be used to provide design information for the response of a ship in such conditions. The focus of this paper is the enhancement of traditional experimental data with video images to identify both the behaviour of a sea state prior to, and during, the formation of a freak wave, and the causes of severe ship responses in freak waves. Experiments were conducted using a flexible backbone model of a naval frigate, travelling at its service speed in a range of long-crested random seas which contain a freak wave. Video imagery was recorded via both a high speed camera at 200fps and a standard webcam at 30fps. Analysis of the obtained video was used to assess the phenomena (such as wave breaking) which occur during the evolution of the freak wave. Furthermore, violent flows related to the ship in freak waves (such as slamming events or green water on deck) are identified and the effect on the resultant ship responses assessed