UNSTEADY INFLUENCES ON A SURFACE-EFFECT SHIP MODEL IN A TOWING TANK
This report describes a theoretical analysis of some resistance data measured on a 1/20-scale model of a 3000-ton surface-effect ship in the High-Speed Tank at the David W. Taylor Naval Ship Research and Development Center. It was found that the model was large enough to cause important unsteady blockage effects in some conditions. For example, if measurements are attempted at a speed close to the hump, the theory predicts that the wave resistance oscillates significantly with respect to time--even though the model has achieved a steady speed. This can lead to a theoretical value of the wave resistance which is higher than the desired result by up to 14 percent. These oscillations do not occur near a depth Froude number of unity. Instead, the wave resistance approaches the steady-state value extremely slowly--taking as much as half the length of the tank to achieve it. The discrepancy in wave resistance is then +14 or -20 percent if the speed is just below, or just above, the critical value, respectively. Comparison between the experiments and the linearized theory shows that the latter may be used for predicting correction terms for tests on large models. The five computer programs used for these calculations are documented in the report.
- Distribution limited to U.S. Government Agencies only; Test and Evaluation; January 1979. Other requests for this document must be referred to the Project Manager.
David Taylor Naval Ship R&D CenterBethesda, MD United States 20084
- Doctors, L J
- Publication Date: 1979-1
- Pagination: 84 p.
- TRT Terms: Analysis; Free surface; Froude number; Information processing; Potential flow; Surface effect ships; Tanks (Containers); Towing devices; Wave resistance
- Uncontrolled Terms: Computer aided analysis
- Old TRIS Terms: Effects; Free surface effects; Model testing; Towing tanks
- Subject Areas: Design; Marine Transportation;
- Accession Number: 00188142
- Record Type: Publication
- Source Agency: David Taylor Naval Ship R&D Center
- Report/Paper Numbers: DTNSRDC-79/009
- Contract Numbers: N00014-77-C-0121
- Files: TRIS
- Created Date: Feb 27 1979 12:00AM