The Drift Angle Theory Applied To Ship Manoeuvring Models

Abstract

A marine vehicle manoeuvring model is concerned with the ability to simulate the status of a vehicle to various demanded controls on a digital computer. Such models have both shore based and sea going applications that are beneficial to the mariner, enhance safety of life at sea and aid in protecting the marine environment The mathematical representation of marine vehicles has generally been conducted by the measurement of the forces and moments that are experienced by a vehicle, in terms of a series of numbers collectively known as hydrodynamic coefficients. This has resulted in the non-linear force modular model which is considered to be the most accurate and versatile mathematical modelling technique. This thesis presents the results from research conducted into the construction of an accurate mathematical model of a patrol craft Picket Boat Nine. The non-linear force modular modelling technique was initially adopted. The required hydrodynamic coefficients were evaluated by the use of full scale sea trials, scale model testing techniques and by semi-empirical methodologies; by the installation of a towing tank, a data monitoring and acquisition system onboard Picket Boat Nine. An alternative new method for mathematically describing marine vehicles has also been developed based upon the drift angle theory. The existence and magnitude of the drift angle has been transformed into a set of hydrodynamic curves that mathematically represent a marine vehicle's manoeuvrability and into a method of determining the track history of a marine vehicle when underway. These two components have been developed into a new form of mathematical model This new approach to mathematical modelling has been tested by full scale sea trials in Picket Boat Nine and with comparison to a force modular model that demonstrates the stature and potential of this method. The results indicate that further research is required to include external disturbances and to prove its validity to other marine vehicles.