Acoustic pressure pulsations in piping systems can cause detrimental damage and failure of industrial components. Both the acoustic resonance and the traveling wave phenomena are of concern for industrial piping systems and there is a need to study passive damping devices and their implementation into these systems. However, there is a challenge associated with manufacturing and installation of such devices as they may be cumbersome. Therefore, the infinity tube (IT) damping device has been presented here to provide a simplified device geometry which can be easily manufactured and implemented into piping systems. A theoretical equation for the transmission loss spectra of the IT device and the frequencies of resonance have been derived as a tool for designers. Additionally, the experimental investigation has shown a considerable increase in acoustic attenuation in comparison to the conventional Herschel-Quincke device due to the significantly shorter length which the IT device can be constructed from. Acoustic pressure and phase angle measurements have elucidated that the fundamental acoustic mode of an open–open pipe can be formed within the IT device. Moreover, a parametric study is presented which has clarified practical considerations required for implementation of the IT device into piping systems for suppressing pressure pulsation.

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Acoustic transmission loss is a common parameter utilized throughout several studies to evaluate the acoustic characteristics of a given test element. Transmission loss has been frequently referred to as a source independent parameter. However, this work presents evidence that the incident acoustic pressure amplitude does, in fact, have an effect on the measured transmission loss for some passive damping devices. The transmission loss was experimentally measured utilizing the two-source location method and the specimens tested include an expansion chamber, a quarter wave resonator, a Herschel-Quincke tube and various Helmholtz resonators. When varying the power supplied to the acoustic source, it was noted that all the devices exhibited nearly constant values of transmission loss, with the exception of the Helmholtz resonators. The Helmholtz resonators had a significant variance of transmission loss with respect to the acoustic source power. This decrease in performance is caused by the "jet-flow" phenomenon occurring at the Helmholtz resonator neck, which results in increased acoustic losses. The present work illustrates that the assumption of source independence, which is often made when using transmission loss to evaluate damping devices, must be taken with caution, as this assumption is case dependent and may be crucial when scaling experimental studies to an industrial setting.

This paper presents an energy-regenerative suspension device that is able to harvest some of the wasted energy that is generated in a suspension system. For a traditional road vehicle suspension system, shock absorbers are mainly dissipating energy to reduce vibration. The dissipated energy may be collected to improve the fuel economy of road vehicles. In this research, CarSim and Simulink are used to simulate and determine the harvestable energy in a conventional shock absorber under different operating conditions. A conceptual energy-regenerative absorber is designed and tested using a fabricated prototype. A variable speed motor is implemented to adapt the change of stroke length of a mechanism due to the various road roughness. Instruments, e.g., laser tachometer, pressure gauge, ammeter, voltmeter, and stopwatch, are used to collect data. The simulation and prototype testing results indicate that the proposed energy-regenerative suspension device could harvest dissipated energy to improve vehicle fuel economy.