A Theoretical Prediction Technique for Lateral Hydrodynamic Loads on Sidewalls of Surface-Effects Ships.
Interim rept. Jul 74-Jun 75,
DAVID W TAYLOR NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER BETHESDA MD AVIATION AND SURFACE EFFECTS DEPT
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A theoretical technique is developed to predict the lateral hydrodynamic forces on low aspect-ratio, parallel, sidewalllike shapes. A free surface is assumed, and the effects of cushion pressure and seals are neglected. Two sidewall, flow-field phenomena are modeled in the present technique. They are the mutual interference of the sidewalls in the flow and contributions to the lateral forces and moments of vortices shed from the sidewall bottom edges. A three-dimensional, linear lifting-surface theory is used to predict attached flow, potential pressure distributions that reflect the mutual interference of the sidewalls in the flow field. The bound vorticity distribution is calculated form this pressure distribution and is used in a modified side-edge suction analogy to predict the force contributions due to the vortices shed from the sidewalls. The total hydrodynamic forces are the sum of the potential and the vortex induced loads. Rectangular parallel sidewalls with aspect-ratios of 0.1 and 0.2 are considered. Pressure distributions for different sidewall separation distances at yaw angles form 0 to 20 degrees are presented. Sideforce and yawing-moment coefficients are presented and are compared with experimental data for isolated rectangular wings. The influence of separation distance on the individual sidewall-force coefficients is clearly evident. Comparisons with experiment show reasonable results. The effect on the pressure distribution of a transom is investigated. The present technique predicts realistic pressure distributions for this case, using a simulated separated wake aft of the transom. Author
- Marine Engineering
- Fluid Mechanics