The importance of a good vibration climate on board ships is now generally recognised. This is reflected in the increasing number of national and international standards and regulations being put forward in this respect. Against this background it is becoming more and more common at the design stage to focus attention on both the propeller pressure impulses and the dynamic response of the hull girder and superstructure. If such investigations and calculations show that resonant frequencies of the structures are avoided in the service speed range, and if the excitation forces are kept at acceptable levels, the risk of unpleasant vibration levels will certainly be greatly reduced. A design stage vibration study according to the above has been carried out for a 33,000 tonne d.w. chemical tanker built at Sarpsborg Mekaniske Verksted A/S, followed by full scale measurements during the ship's sea trial. The results of the investigation are presented in the following report by Kristian Evensen, project engineer, Det norske Veritas (Maritime Advisory Services). The survey shows that the finite element approach to these problems is very powerful and can compute the natural frequencies of the hull girder and the superstructure with acceptable accuracy. The calculation of the forced response level is somewhat more complicated because the result depends not only on the factors determining the natural frequencies but also on the computed excitation forces and the damping chosen for the vibrating system. It is concluded that a vibration prediction program as described should be of great benefit for shipyards and shipowners in their aim of reduced vibration levels onboard future ships as demonstrated in the present case.

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    IPC Industrial Press Limited

    Dorset House, Stamford Street
    London SE1 9LU,   England 
  • Publication Date: 1980-7

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  • Accession Number: 00319476
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Oct 8 1980 12:00AM