ON INEXTENSIONAL VIBRATIONS OF THIN SHELLS
ARMY NATICK LABS MA OFFICE OF THE SCIENTIFIC DIRECTOR
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In this paper, the non-symmetric, free, elastic vibrations of thin domes of revolution are studied. It is assumed that the frequency is low. The asymptotic approximations previously given by the writer are used to estimate the general solution to the shell vibration equations at low frequencies. Approximations for the low natural frequencies and modes are derived systematically under a variety of edge conditions. Low natural frequencies are found only when the edge conditions impose no forces tangent to the shell surface. When the edge is free and only then Rayleighs inextensional frequencies are recovered. For certain other edge conditions new natural frequencies are found that are above Rayleighs frequencies but still low compared, e.g., with the lowest membrane frequency. The displacement modes associated with these new frequencies are mostly of inextensional type. The general results are applied to estimate these new frequencies for spherical domes.