Analysis and prediction of motions of high speed planing craft in waves

Abstract

A theoretical method has been developed to model a high speed planing craft in waves with particular emphasis on the non-linearfties associated with high speed motion. These non-linearities include, amongst others, hydrodynamic impact loading, bottom emergence and forces due to large changes in wetted surface area and wetted length.The method consists of a 2D time simulation model based on a modified stop theory approach. The hydrodynamic coefficients are usually considered to be constant for most linear applications. For planing craft in waves, the draft and wetted lengths are very time dependent and so the equations of motion are solved in the time domain.The benefits of a two-dimensional method include the ability to provide accurate solutions without the need to solve the full 3D fluid problems. The method is flexible enough to include an added resistance solution and investigation into hydroolastic responses.In order to validate the theoretical model, a high speed planing craft of simple prismatic geometry has been tested and the dynamics analysed through the use of standard towing tank equipment. However, in order to measure such effects as change in wetted area and length and spray sheet generation, a different technique is required. A new technique in data acquisition is presented whereby the data is acquired using a computer vision system. Computer vision is a technique involving the manipulation of digital pictures and object properties within the image measured and defined. The use of computer vision to analyse video footage of the high speed test provides a non-contact form of measurement; allows the experiment to be carried out repeatedly with emphasis on specified parameters with simultaneous visual observation of particular phenomena allowing cross correlation of the identified fature.