THE FUNDAMENTAL ASSUMPTIONS IN SHIP-MOTION THEORY

Some of the fundamental assumptions of ship-motion theory are examined for the purposes of elucidating the success of the heuristically derived strip theory of Korvin-Kroukovsky and of recognizing some inadequacies of that theory. The formal approach employed is a systematic slender-body expansion. In the zero-speed problem, both far-field and near-field views can be used generally to recommend the assumption that frequency of oscillation be taken as "large," in the sense that the corresponding waves have wavelength that is comparable to ship beam. This assumption leads to considerable trouble in the head-sea case, however, and this special case has not been fully solved yet. Force and moment on a ship can be computed, even in the head-sea case, through use of the Khaskind formula, but computation of the load distribution necessitates solving the diffraction problem, or, possibly, solving two-dimensional near-field problems involving the Helmholtz equation. Rationalization of the short-wave assumption is not really successful in the forward-speed case, except in terms of the observed accuracy of the motion predictions. The most thorough analyses to date of the forced-motion and head-sea diffraction problems are based on disparate assumptions about the orders of magnitude of the characteristic wavelengths, although both require the product of speed and wave frequency to be large. Some discussion is presented on the interaction between ship oscillations and the steady-motion perturbation of the incident stream.

  • Supplemental Notes:
    • Prepared for International Symposium on The Dynamics of Marine Vehicles and Structures in Waves, London, England, April 1974.
  • Corporate Authors:

    University of Michigan, Ann Arbor

    Department of Naval Architects and Marine Engineers
    Ann Arbor, MI  USA  48109
  • Authors:
    • Ogilvie, T F
  • Publication Date: 1974-2

Media Info

  • Features: References;
  • Pagination: 32 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00072753
  • Record Type: Publication
  • Source Agency: University of Michigan, Ann Arbor
  • Report/Paper Numbers: No. 148
  • Contract Numbers: NSF GK-36848
  • Files: TRIS
  • Created Date: Dec 31 1974 12:00AM