Wullenwebber antenna vibration study
Breckon, Richard Louis
Hite, Philip R.
Schmidt, L. V.
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The U.S. Navy is completing a world-wide radio directional antenna system, which has exhibited an undesirable wind induced oscillation of one of the primary structural members, resulting in physical damage and failure. This member is a horizontal beam 28 to 58 feet in length, supported 100 feet above ground, from which eight to 16 vertical wires are suspended. Oscillations at some installation have been estimated at six cycles per second, and with amplitudes of plus or minus two feet. A dynamic wind tunnel model was designed, fabricated, and tested, with the purpose of simulating the response of the various antenna designs. The installation at Winter Harbor, Maine, a two foot cylinder with one inch flanges at 90 degrees from the stagnation points, was investigated. These tests prove that, as a result of the flanges, the oscillation frequency is a function of wind velocity, so that the Strouhal number remains constant at 0.17. It is also shown that the structure's natural frequency has negligible effect upon response. As an "in the field" modification, it is recommended that the beams be rotated 90 degrees about their longitudinal axes, which should reduce the amplification of vibration by a factor of about six. this study was conducted by Lieutenant Richard L. Breckon, USN, and Lieutenant Philip r. Hite, USN, at the United States Naval Postgraduate School, Monterey, California.
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