Experimental determination of the damping ratio of a thermal insulation cover plate

Systems circulating fluids within closed boundaries generate noise produced by the circulator, turbulence in the flow, vortex shedding, etc. The ducting containing the flowing fluid acts as a generator of additional noise and as a filter amplifying the noise at discrete frequencies (i.e. normal mode of vibrations of the structural boundary).The damping ratio of these structures is an important parameter which controls the amplitude of the vibrating structure and the noise level at discrete frequencies transmitted by that structural boundary. An equally important consideration is the amplitude of the structure vibration which can cause early failure of the boundary (resonance response) or longer-term fatigue failure. The damping ratio depends on the geometrical configuration and numerous boundary conditions. It cannot be predicted accurately by analysis and must be determined experimentally. This paper describes an experiment on the measurement of the damping ratio of a commonly used structure (i.e. a square plate cover with kaowool fiber insulation backup). The measured values of the damping ratio are given for two different sizes of plate with different attachments. The effects of the configuration and attachments on the damping ratio are discussed.