A Study On Structural-acoustic Op-Timization Of Unidirectional-Ly-stiffened Sandwich Plates

Metallic sandwich plates with corrugated cores are used extensively inthe high speed transportation engineering field for their lower area density,higher specific strength and stiffness than those of a homogeneous type. Vi-bro-acoustic response of this kind of structures subject to airborne excitationhave been a concern in acoustic comfort design of high speed transportationsystems such as airplanes and express trains.This paper presents a finite element analysis of vibro-acoustic responseof sandwich plates with corrugated cores when excited by a harmonic planpressure wave on incident side.2D models are developed for the analysis offrequency-domain vibration response of whole sandwich structure and theradiated sound power into transmitting space for different cases of core to-pology and structural parameters. The structural-acoustic couplings betweenthe core elements and the fluid inside the enclosed cavities are consideredwhen carrying on the computations. The obtained results indicate that moreaccurate prediction of vibro-acoustic responses can be achieved when consi-dering these couplings in modeling the vibration response of and soundtransmission through metallic sandwich plates with corrugated cores. But formost common structures of metallic sandwich plates with corrugated cores,the acoustical-transparent assumption of stiffeners will generate negligibleerrors in the calculation of sound transmitting loss; even the internal flu-id-faceplate coupling can also be neglected and it will not bring any signifi-cant error.Because of the huge number of meshes required to model the sound transmitting of sandwich plates with corrugated cores, which increases qua-dratically with the bandwidth of the frequencies of interest, a more efficientnumerical is needed to calculate the vibro-acoustical response of sandwichplates.The spectral element method (SEM) is then given as an excellent choicefor computing the structural-acoustic response through a unidirectionalsandwich plates while ignoring the internal structural-fluid coupling effects.The spectral element formulation is deviated for the longitudinal vibration ofa rod and the flexural vibration of an Euler-Bernoulli beam. Assembly of Eu-ler-Bernoulli beams with longitudinal displacements is used to model sand-wich plates. SEM is utilized to calculate the vibration of this structure, andthe transmitted acoustic power is calculated from an approximation formula-tion of Rayleigh integration. Comparison of SEM results to FEM results in-dicates that SEM is a highly reliable and efficient method to solve the struc-tural transmitted sound of unidirectionally-stiffened sandwich plates. Basedon the effective SEM, the effect of stiffener dip angle on structural transmit-ted acoustic power is analyzed, which indicates that the transmitted acousticpower increases with the dip angle. Finally, an optimization is performed forthe minimum transmitted acoustic power through a sandwich plates withstiffener dip angles and width as the design parameters. The transmittedacoustic power of the optimized structure is much lower than the originalstructure. The high efficiency of optimization is demonstrated.