The reports produced as a result of the program 'Propeller Hull Interactive Vibration Excitation', (PHIVE), which was carried out jointly by NMI and BSRA from 1977 to 1980, included comparisons between experiments in the water tunnel and full-scale trials on two ships. One was a 55,000 ton d.w. products tanker (PEV69), the other a 21,000 ton d.w. multiflex cargo carrier (PEV70). In both, the hull pressures produced by a cavitating propeller were measured and the cavitation photographed. The aim of these comparisons was to show the extent to which model measurements could serve as a prediction of the ship's behavior. It was concluded that the prediction of ship trial results from such tests is still in need of improvement. Although the reliability of identifying a bad hull/propeller combination is fairly high with regard to blade rate fluctuations, there is still too much uncertainty about the magnitude of the harmonics. This appears to be caused firstly by inadequate representation of the wake field and secondly by complicated scale effects in the cavitation dynamics. These conclusions are exemplified by the case of Ship PEV70 which showed excessive vibration during the builder's trials in ballast draught so that some modifications became essential. To reduce the ship's vibration, flow deflector fins - also called vortex generators - were fitted near the stern. The choice of this vessel as the object of further water tunnel studies offered additional scope for studying the problems of model scale simulation. Firstly the lack of warning of trouble from the original tunnel measurements could be investigated by repeat tests and secondly an attempt could be made to duplicate in the tunnel the benefit derived from the flow deflectors on the ship, which in turn demanded an extension of the modelling capability to deal with a hull fitted with such auxiliary surfaces. (Copyright (c) Crown Copyright, 1981.)


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    Title :

    Cavitation Induced Hull Pressures Measured in a Water Tunnel for Comparison with Ship Trials on a Single Screw Cargo Carrier


    Contributors:
    K. G. Poulton (author) / H. Ritter (author) / M. E. Davies (author) / G. E. Gadd (author)

    Publication date :

    1981


    Size :

    77 pages


    Type of media :

    Report


    Type of material :

    No indication


    Language :

    English