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Unformatted text preview: 6 CAPTIVE MEASUREMENTS Before making the decision to measure hydrodynamic derivatives, a preliminary search of the literature may turn up useful estimates. For example, test results for many hull-forms have already been published, and the basic lifting surface models are not dicult. The available computational approaches should be considered as well; these are very good for predicting added mass in particular. Finally, modern sensors and computer control systems make possible the estimation of certain coecients based on open-water tests of a model or a full-scale design. U In model tests, the Froude number F r = gL , which scales the inuence of surface waves, must be maintained between model and full-scale surface vessels. Reynolds number Re = UL , which scales the effect of viscosity, need not be matched as long as the scale model attains turbulent ow (supercritical Re ). One can use turbulence stimulators near the bow if necessary. Since the control surface(s) and propeller(s) affect the coecients, they should both be implemented in model testing. 6.1 Towtank In a towtank, tow the vehicle at different angles of attack, measuring sway force and yaw moment. The slope of the curve at zero angle determines Y v and N v respectively; higher- order...
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This note was uploaded on 02/27/2012 for the course MECHANICAL 2.154 taught by Professor Michaeltriantafyllou during the Fall '04 term at MIT.
- Fall '04