EVALUATION OF DRIFT FORCE COMPUTATION METHODS

Moored-ship and/or platform system designers are often faced with the problem of deciding between different drift force computation methods. This paper is intended to assist in this decision making by providing a comparative evaluation of the two major categories of computation methods. The methods for calculating drift forces (second order) on vessels fall into two (2) major categories. In one method, the problem is reduced to the computation of the potential far away from the vessel. This is known as the far-field approximation as described and developed by Maruo (1960), Newman (1967) and Faltinsen and Michelsen (1974). In the other method, known as the near-field or close-in approximation, the integration is performed directly on the vessel hull as developed by Salvesen (1974) and Pinkster and Van Oortmerssen (1977). Following the approach of the first mentioned category, a computer program has been prepared which calculates drift forces and moments on vessels of arbitrary hull geometry. No assumptions regarding the hull geometry are included in the underlying theory. The second category, however, includes some mild slenderness assumptions (Salvesen (1974)). Based on the drift force program outlined in this paper, some selected results for various hull geometries are presented. These results are compared, where applicable, with existing results obtained from application of the near-field method. These comparisons permit: (a) determination of the range of compatibility of the two methods, and (b) the influence of hull geometry on the applicability of the near-field approximation. Moored-ship system designers thus have a systematic procedure from which drift force calculations can be evaluated.

Media Info

  • Features: References;
  • Pagination: p. 395-400

Subject/Index Terms

Filing Info

  • Accession Number: 00329932
  • Record Type: Publication
  • Report/Paper Numbers: Volume 4 Proceeding
  • Files: TRIS
  • Created Date: Apr 15 1981 12:00AM