Abstract

In order to measure structural intensity in a thin‐walled structure (shell), one has to employ intensity expressions given in terms of physical quantities that (a) are measurable and (b) refer to the external surface of the shell. These quantities are surface strains and displacements or displacement derivatives—either velocities or accelerations. Intensity expressions, which can serve as a starting basis for measurements, have been established for flat plates, circular cylindrical shells, and spherical shells. The expressions are given in terms of neutral‐surface displacement and strains, which are reference quantities for any theoretical analysis and, consequently, have to be translated to the external surface domain. Intensity in a flat plate consists of two contributions: one due to extensional, the other due to flexural effects. The shell, in addition, has the influence of curvature, which couples the in‐plane and the normal components of motion. As a result, large number of strains and displacement components have to be simultaneously detected in order to produce intensity readings correctly. The number of transducers required to measure these quantities is even larger, because some of the quantities are given in a differential form, implying use of multipoint finite difference schemes in practical measurements. Furthermore, some transducers, such as accelerometers, cannot measure at the body surface but somewhat above it, which necessitates corrections in readings of in‐plane motions. This and other reasons (transducer cross‐sensitivity, surface loading) make conventional vibration transducers impractical for this work. Preference in practical measurements should go to non‐contact methods which still have to be developed. This paper describes the nature of the intensity expressions related to thin shells. Examples are given of a circular cylindrical shell in contact with an acoustic medium. Various possibilities are described for measurement of intensity using conventional transducers. Sources of measurement errors and limitations are discussed in some detail. Finally, new measurement concepts are shown, aimed at improving accuracy and reducing difficulties encountered with conventional methods.

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