Effects of Rarefied Atmosphere on Radiation Damping in an Aluminum Euler Beam

Vehicles in the upper atmosphere travel through increasingly rarefied media. As acoustic radiation is dependent upon its media, acoustic radiation losses of vibrating structures in lower density air are investigated. An aluminum Euler beam is placed in a vacuum chamber, supported by thin nylon wires at known nodal positions, according to the excited mode. These strings are laced across a large cavity in a small steel table, effectively minimizing losses due to boundary supports. An impulse hammer excites the beam into its flexural state, while a laser vibrometer measures the velocity response. Extraction of mechanical loss factors occurs as the vacuum pressure increases (atmospheric pressure decreases) in experimental increments, thus determining the dependence of acoustic radiation losses on the rarefied media. Analysis of experimental results is presented as a topic of discussion for vibrations of launch vehicles and satellites. Other inferences and inductions are also considered.