In the authors' previous report, a numerical method was developed for calculating the hull vertical vibration using the transfer matrix, where a ship was considered as a free beam with variable cross section including shear flexibility and rotatory inertia. The method has been used in this report to calculate the natural frequencies of two tankers, four cargo liners and an ore-carrier. Comparisons of the calculated and the measured frequencies, together with the results for the bulk carriers and the destroyers treated in the previous report show that the calculated frequencies agree with measured ones within 10, of difference. Calculated mode profiles also approximately coincide with measured ones. One of the interesting results is that, for the bulk carriers, contrary to the other types of ships, the ratio of measured to calculated frequency decreases with the number of nodes. The reason is supposed to be 1) the decrease of the effective breadth of deck and bottom in the higher modes and 2) the effect of coupled vibration with such a local structure as bottom panel. A qualitative calculation has been made on the effect of the effective breadth and it is found that in the case of ships with large hatch openings and without longitudinal bulkheads, the effective breadth of deck is considerably diminished in the higher mode, which results in lowering the natural frequency. The effect of rotatory inertia on the natural frequency has been checked and found to be negligible up to 6-7 noded modes. Comparison of calculation and experiment in two model ships in air and on water shows that the Lewis-form calculation with Lewis' three-dimensional correction factor shows practically good results.(full text of report).

  • Supplemental Notes:
    • The abstract is the entire document.
  • Corporate Authors:

    Society of Naval Architects of Japan

    23 Shiba-kotohiracho, Minato-ku
    Tokyo 135,   Japan 
  • Authors:
    • Ohtaka, K
    • Takaira, F
    • Hibino, F
    • Ohji, M
  • Publication Date: 1969

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Filing Info

  • Accession Number: 00035158
  • Record Type: Publication
  • Source Agency: Society of Naval Architects of Japan
  • Files: TRIS
  • Created Date: Oct 27 1972 12:00AM