SCALE AND ROUGHNESS EFFECTS IN SHIP PERFORMANCE FROM THE DESIGNER'S VIEWPOINT

Evaluation of the scale effect in the absence of flow separation is usually based on two independent calculation procedures for the drag and lifting forces. Prediction of the full-scale drag forces is based on modelling of the viscous part of the resistance in accordance with the difference in Reynolds numbers. As a rule, a lifting force coefficient for full-scale bodies is treated as a lift coefficient for a model having the same Froude number. The proposed method is based on the idea that an initiation of the lifting force is associated with the viscous effects in the boundary layer. According to this approach, an estimation of the scale effect is based on a calculation of potential, boundary layer and wake flows with viscous/non-viscous interaction for given Froude and Reynolds numbers. The roughness of a surface is taken into account due to the use of special velocity profile parameters. These parameters depend on type and height roughness (casting, milling grooves, polishing, paint, fouling, acid deposit, etc). As a result, the effects of viscosity (Reynolds number) and surface roughness are determined as the difference between the drag and lift forces calculated for the model and full-scale conditions. The magnitude of the scale effect may reach 50% to 70% for the drag and 10% to 20% for the lift forces. The unusually large scale effect for the lift may play a significant role in engineering applications. Results of the systematic calculations and experimental evaluations are reported for a broad range of ship types and propellers.

  • Supplemental Notes:
    • Marine Technology, v 32 n 2, April 1995, p 126 [6 p, 19 ref, 12 fig]
  • Authors:
    • Mishkevich, V
  • Publication Date: 1995

Language

  • English

Subject/Index Terms

Filing Info

  • Accession Number: 00718724
  • Record Type: Publication
  • Source Agency: British Maritime Technology
  • Files: TRIS
  • Created Date: Mar 27 1996 12:00AM