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# hw7 - Oceanographic instrument buoys should have long heave...

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10 2 40 Strouhal Number (S) 0.1 0 Reynolds Number (UD/ ) 0.2 0.3 0.4 0.47 10 3 10 4 Smooth Surface Rough Surface 10 5 10 6 10 7 Figure by MIT OCW.

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2) A fishnet is made of 1mm-diameter strings knotted together into 2cm x 2cm squares. Estimate the horsepower required to tow a 300 ft 2 of this netting at 3 knots in seawater. Assume that the net plane is normal to the direction of towing (flow). Assume the string can be modeled as a cylinder with drag coefficient 1.2, consider only viscous drag force. 3) A spar buoy is essentially a cylinder floating vertically in the water. The buoy is free to heave in the z-direction and has a heave period, T, which depends on the waterline cross-sectional area A, buoy mass m, and fluid density r. How does the period change if we double the mass? Double the water plane area?
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Unformatted text preview: Oceanographic instrument buoys should have long heave periods to avoid wave resonance. Sketch a possible long period heave buoy design. 4) An offshore riser can be modeled as a long rigid cylinder with diameter 0.25 meters. Determine the vortex shedding frequency for a current of 1.0 m/s. What is the frequency of the unsteady component of the lift force? The unsteady drag force? 5) An overhead power line is “humming” on a windy day. You are with a friend who has a very good ear and determines that the power line is vibrating at a frequency of 100 Hz. The wind is quite strong and is blowing at 8 m/s. Determine the diameter of the power line....
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