POWER-FLOW TO A CYLINDRICAL-SHELL WITH AN ATTACHED STRUCTURE

This paper presents an analytical framework for understanding and cont rolling the physical mechanisms which govern power flow to infinitely long cylindrical shells from applied point forces. It has been observe d by others that the power flow to an empty shell peaks dramatically w hen the excitation frequency is near the cutoff frequency of a wave in the shell. In this paper, these observations are explained and genera lized by a new analytical expression for power flow based on classic a nalyses of a shell's response to an applied point force. This expressi on quantifies the partition of power among propagating waves excited b y an applied force. Furthermore, the expression confirms that power fl ow increases dramatically as a propagating wave is excited in the vici nity of its cutoff frequency. In the context of this understanding, th e attachment of a passive structure to the shell is explored as a mean s of controlling power flow. The nonlinear problem of designing a stru cture which satisfies practical constraints and minimizes power flow i s formulated in such a way as to be solvable by a variety of optimizat ion techniques. The formulation, which can be extended to other struct ures, is based on an expression for power flow in which the impedance of the attached structure acts in mechanical parallel with the shell's impedance at the points of attachment. An example indicates that a si gnificant reduction in power flow can be achieved by the attachment of a passive structure whose parameters have been optimized by a genetic algorithm. (C) 1998 Acoustical Society of America.