Synthetic Jet Actuator Cavity Acoustics: Helmholtz Versus Quarter-Wave Resonance

The impact of cavity geometry on the source of acoustic resonance (Helmholtz or quarter-wave) for synthetic jet type cavities is presented. The cavity resonance was measured through externally excited microphone measurements. It was found that, for pancake-shaped cavities, the Helmholtz resonance equation was inadequate (off by more than 130%) at predicting the acoustic cavity resonances associated with synthetic jet actuation, whereas a two-dimensional quarter-wave resonance was accurate to 15%. The changes in the geometry (cavity diameter, cavity height, and orifice length) could alter the cavity resonance by up to 50%, and a finite element solver was accurate at predicting this resonance in all cases. With better knowledge of the phenomena governing the acoustic resonance, prediction of the cavity resonance can become more accurate and improvements to current prediction tools can be made.

Numerical Analysis of Active Vibro-Acoustic Control in an Enclosed Cavity

A numerical model is applied to study the application of active vibro-acoustic control in an enclosed cavity. The vibro-acoustic problem is composed of a free-free beam, representing the windshield, coupled with a rectangular planar acoustic cavity, representing the passenger compartment. Forces at the windshield boundaries are actively applied to reduce noise due to floor panel vibrations and sound from a monopole source. Noise transfer functions are used to calculate the control forces based on their ability to minimize the acoustic energy distribution in the total region and within the region of interest. Results show that noise is substantially reduced in the low frequency range accompanied with some reduction at the higher frequencies as well. Results also show that applied forces based on partial area control have more potential in reducing noise within the region of interest than those based on global area control. It was also observed that this control strategy performs better in vibration induced noise problems than in monopole source problems. The proposed model can be applied to noise control problems involving the transmission of vibratory energy into a cavity through fluid-structural coupling that relates structural vibration to cavity acoustics.

Prediction and Analysis of Vehicle Cab Interior Noise Based on Structure-Acoustic Coupling

To study the vibration characteristics of the vehicle’s cab, finite element model of the cab was established and structural modal analysis was made. According to the internal structure of the cab, acoustic finite element modal of the cab including the seats was built and cavity acoustics modal analysis was carried out. Based on the structural modal and acoustic model of the cab, the coupled acoustic-structure model was carried. The acoustic response of the cab was calculated by mode-superposition