Design, Quiet Structure Based On The Minimization Of Radiated Sound Power

An approach for solving the problem of vibration-acoustic optimization from a vibrating structure by material tailoring is investigated theoretically and experimentally. A structure is optimally designed to fit a specified set of acoustic characteristics, e.g. changing sound spectrum or minimizing radiated power. The method links the disciplines of structural dynamics, acoustics and optimization into a unified methodology.Firstly, the eigen-values are considered unchanged, the design variables are the addition of masses or vibration absorbers to the structure as well as the distributions of stiffeners. In all cases, the design variables are introduced as external forces (via their impedances) in the velocity govern equation of the structure that is given as a series expansion of eigen-functions. These steps need not to solve the problems of large matrix eigen-values. The sound power generated by the simply supported plate under a harmonic force is computed with a lumped parameter / wave superposition method. A genetic algorithm is used by using MATLAB code to find optimal point mass distributions for minimum of the sound power.Secondly, the effect of material parameters and positions of the excited force on minimization of the radiated sound power are studied, a comparison between the adding masses and active structural acoustic control is also investigated.Thirdly, a finite element method is used to predict the vibration response and acoustic radiation from the flexible structure. The eigen-frequencies are changed by material tailoring. A simply supported plate is tuned by adding the masses to move the first four eigen-values into harmonic relationships. ANSYS and SYSNOISE software are used to design complex structures to match the specified requirement of acoustic characteristics.Lastly, experiments are carried to verify the validation of the theoretical method. It is shown that optimal designs are achieved through converting certain mode shapes of the structure into "quiet structure".