University of Tasmania
whole_RanmuthugalaSusanthaDevapriya2001_thesis.pdf (17.11 MB)

Computer simulation and investigation of underwater two-part and multi tow systems

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posted on 2023-05-27, 17:16 authored by Susantha RanmuthugalaSusantha Ranmuthugala
To maximise effectiveness, towed underwater sonar bodies generally require perturbations from the steady state motion to be minimised. The instantaneous position of the towed body is influenced by the unsteady, wave-induced motion of the surface vessel, transmitted via the tow cable. This can render the trajectory of the underwater body beyond acceptable limits for sonar operations. In an effort to decouple this motion, a two-part tow configuration has been employed. This thesis describes a three-dimensional dynamic computer model developed to investigate two-part tows by modelling the individual cables separately and coupling them dynamically. This approach also enables the modelling of series and parallel multiple tow configurations. The cable system, modelled using a three degree-of freedom finite difference approach, is then coupled to the six degree-of-freedom underwater towed bodies at the appropriate locations of the cable system. The modelling of the cable as a continuous medium and the derivation of the stress wave speeds are also presented, followed by the validity and.effects of representing it as a discretised model. The solution to the dynamic equations describing the motion of the discretised tow configuration is carried out using an implicit multi-step numerical technique, subject to specific boundary conditions. This allows the values to be improved through an iterative procedure, until sufficient convergence is achieved. An introduction into the use of such numerical techniques in engineering and an analysis of the numerical procedure used in the solution are also presented. The requirements for accuracy and numerical stability of the integration technique are investigated and a guide to the time interval for the time stepping algorithm is deduced. The computer model is successfully validated using experimental results from scaled model tests in a circulating water channel. These results together with those obtained from full scale sonar trials utilising small coastal craft are used to further investigate the behaviour of the two-part tow configuration to varying parameters. The experimental results and the computer model enables the user to identify the optimum tow configuration for the prevailing conditions. The thesis also presents a detailed review of the various methods available to investigate underwater cables and vehicles, together with prediction methods for their hydrodynamic coefficients. The latter coefficients for the scaled models used in the project are obtained via experimental procedures. Although a number of investigations have been carried out dealing with aspects of underwater towing operations, the strength of this investigation lies in that it combines these aspects, i. e. mathematical modelling, computer simulation, prediction of the hydrodynamic coefficients, scaled model experiments, full scale trials, and the analysis of the numerical technique, into one study.


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Thesis (PhD)--University of Tasmania, 2001. Includes bibliographical references

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