VORTEX SHEDDING MITIGATION METHODS

THERE IS A REQUIREMENT FOR EFFECTIVE METHODS TO MITIGATE WIND INDUCED VIBRATION IN ANTENNA STRUCTURES. THESE VIBRATIONS CAUSE DISTORTION IN THE SIGNAL. CURRENT ANTENNA STRUCTURES ARE CONSTRUCTED FROM FRP TUBING BECAUSE OF ITS BENIGN ELECTROMAGNETIC PROPERTIES BUT THE MATERIAL, BECAUSE OF ITS LOW STIFFNESS AND DAMPING PROPERTIES, AGGRAVATES WIND-INDUCED VIBRATIONS. THE VIBRATIONS ARE CAUSED BY EITHER KARMAN VORTEX SHEDDING FROM THE INDIVIDUAL TUBES IN THE STRUCTURE, OR BY THE GUST RESPONSE CHARACTERISTICS OF THE STRUCTURE AS A WHOLE. A FOUR TASK PROGRAM IS OUTLINES IN WHICH BOTH OF THESE FORCING FUNCTIONS AND THEIR EFFECTS, IN TERMS OF THE SEVERITY OF VIBRATION THEY CAUSE IN THE ANTENNA, ARE TO BE INVESTIGATED. THIS WILL BE ACCOMPLISHED THROUGH A MODEL ANALYSIS OF THE ANTENNA STRUCTURE IN QUESTION BY UTILIZING FINITE ELEMENT METHODS. METHODS FOR SPOILING THE FORMATION OF THE SHED KARMAN VORTICES AS WELL AS CHANGING THE COMPLIANCY OF THE STRUCTURE AND ADDING VARIOUS DAMPING SYSTEMS WILL BE EVALUATED.