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Instrumented Full Scale Tests of a Drifting Buoy and Drogue

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Final rept. Dec 1973-Jun 1975

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The design of a full scale window shade drogue is described and illustrated. The results from a test program for measuring the drag coefficient, slippage, and dynamic response of a full scale window shade drogue are given along with a description of a dynamic motion sensing instrument, called a Force Vector Recorder FVR, which is employed during the tests. Full scale, instrumented drogue towing tests were performed in a water-filled quarry in an effort to measure the drogue drag coefficient under ideal, non-dynamic conditions. The results are interpreted and compared with the results of previously reported scale model drogue tests in a tow tank. A maximum full scale drag coefficient of 2.6 was derived for a vertically aligned drogue. In addition, the tilt angle of the top of the drogue was measured by the FVR and related to the slip velocity and towing force through a simple mathematical model of drogue drag force as a function of the tilt angle. Measured drag data agreed within or - 20 of the math model. The vertical drag coefficient of a full scale window shade drogue was measured in ocean tests by the use of the FVR. Additional ocean tests measured the dynamics of a window shade drogue supported at a mean depth of 24 meters beneath a Nova minibuoy in a drifting configuration. The data were measured and internally recorded in digital form on the FVR attached to the top spreader bar of the drogue. It was found that the FVR recorded the vertical excursion and drogue dynamics in a manner which would be useful for the verification of dynamic math models of a drogue response.

Subject Categories:

  • Marine Engineering
  • Fluid Mechanics

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