Structural Acoustic Power Transmission By Point Moment And Force Excitation, Part I: Beam- And Frame-like Structures

Abstract The significance of moment in a combined moment and force excitation for the transmission of structural acoustic power has been analyzed for beam- and frame-like structures. The spatial variation in the proximity of discontinuities is considered and the emphasis is on the low frequency range. Asymptotic expressions, valid for small Helmholtz numbers, are derived for the point force and moment mobilities as well as for the cross-mobility from force to rotational velocity. Numerical results are presented covering a wide range of frequencies and spatial positions. The four ideal end conditions are examined, and it is found that moments must be taken into account at all frequencies if the translatory motion at the discontinuity is constrained. For discontinuities not constraining the translatory motion, moments can be disregarded. The analyses of the combined excitation near the intersection of semi-infinite beams show that the boundary condition of built-up, frame-like structures is bracketed between the simply supported and clamped cases. Moreover, the influence of moment excitation is that found for a simply supported semi-infinite beam. For low frequencies the features of a combined excitation can be exploited to cancel the active part of the power transmitted.