Computer Modelling and Experimental Study of Towed Underwater Systems

The instantaneous position of a towed body is influenced by the unsteady wave induced motion of its surface vessel, transmitted via the tow cable. In an effort to decouple this motion, a two-part tow configuration has been employed. This paper describes a three dimensional dynamic computer model developed to investigate the two-part tow, by modelling the cables separately and coupling them dynamically. This approach has been further extended to model multiple towed systems, where the underwater bodies are towed either in series or in parallel. All underwater bodies are modelled in three-dimensions with six degrees-of-freedom. The computer model is supplemented and validated using experimental results from scaled model tests and full scale trials. Since the solution to the dynamic equations is carried out using numerical techniques, the requirements for accuracy and numerical stability of the integration technique are also investigated and an acceptable time interval is presented.