A1: 50-scale model of a submarine is to be tested in a towing tank under two conditions: motion at the free surface and motion far below the surface. the tests are performed in freshwater. on the surface, the submarine cruises at 24 knots. at what speed should the model be towed to ensure dynamic similarity?

far below the surface, the sub cruises at 0.35 knot. at what speed should the model be towed to ensure dynamic similarity? what must the drag of the model be multiplied by under each condition to give the drag of the full-scale submarine

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?