Practical Problems of Assessing Damping Treatments

Abstract

This paper discusses firstly the practical situations in which damping treatments can be beneficial in attenuating noise and vibration. Brief consideration is given to systems under periodic excitation, after which randomly excited systems are considered in greater detail. Reference is made to jet-excitation vibrations of airplane structures (to the associated stress levels and transmitted noise) and also to vibrations excited by boundary-layer pressure fluctuations. The manner in which these various response quantities depend on the basic structural parameters (stiffness, damping, and mass) is discussed next with a view to defining the most desirable characteristics of an artificially damped structure. This leads to the development of certain criteria for assessing the effectiveness of damping treatments. The limitations, in this respect, of the simple flexural loss factor become apparent. The problem of selecting the best damping treatment for a given situation is then dealt with. Considered next are the difficulties of estimating the damping and stiffness of a treated reinforced-plate structure. The measurement of the damping of such systems is also discussed, and some recent work is described. Some typical values of the damping required and obtainable for airplane structures are considered. Finally, the needs for further work are outlined.