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This paper proposes utilizing a thin porous material coating liner on the inlet duct of the turbocharger compressor in order to absorb the incident excitation and hence, broadband reduction of the flow-induced sound wave propagation. To this end, first, a sound-absorbing inlet duct model is designed based on efficient structural parameters. Then, three different types of absorptive materials are used as coating liners to analyze the impact of varying material properties on the acoustic absorption performance of the system. Meanwhile, a sensitivity analysis is carried out to evaluate the influence of coating layer thickness on the system’s flow-induced sound insulation performance. The research involves applying a finite element approach to conducting acoustic pressure and poroacoustics studies over the desired frequency range of human hearing (1-20 kHz). In this regard, sound transmission loss (TL) and sound pressure level (SPL) are investigated for the models with and without liners. The results indicate that sound-absorbing materials can be employed to significantly diminish flow-induced sound levels in the turbocharger inlet duct. According to the results, absorptive liners would considerably increase the maximum TL and lessen the sharp drop in TL that appeared in the model without liners at around 4321Hz. In addition, the average TL has increased due to the replacement of valleys with peaks. The sensitivity analyses demonstrated that denser absorptive materials and larger liner thicknesses are associated with higher TL levels and better sound attenuation response. By adding 15 mm of rock wool liner to the designed inlet duct, the average TL and root mean square of TL were increased up to 98 and 32 dB, respectively. The proposed design procedure of this study unlocks a fundamental approach that can be practically applied to many promising fields, such as aerospace and automotive engineering.

This project outlines the effect of changing Young’s modulus, Poisson’s ratios and shear modulus on the pad natural frequencies. It aims to improve the understanding of the influence of friction material properties on the pad natural frequencies, to observe how the natural frequencies can change, with the changes in the properties of the composite brake pad friction material. In addition, two different brake pad models (Pad-A and Pad-B) were designed, using CATIA V5 software to study whether different pad aspect ratios can affect the influence of friction material properties on the natural frequencies. This study utilizes the free-free analysis on the brake pads, to investigate the natural frequencies, and the mode shapes of the first four modes, using ABAQUS software. Also, an experimental test (Tap testing) on Pad-A was carried out to verify the accuracy of the numerical analysis. The research has demonstrated that the maximum variation between the numerical and the experimental results is 5.1%, which is acceptable. Thus, the numerical analysis provided reasonable results.Furthermore, the factorial analysis was applied on the obtained natural frequencies for each pad, to find out the material properties that have the main effect on the natural frequencies, and the relationship between each property and the natural frequency, using MINITAB software. The results indicated that increasing Young’s modulus in the horizontal plane can increase the values of natural frequencies, while a decrease in Young’s modulus in the vertical plane, Poisson’s ratios, and shear modulus in all planes can increase the values of the natural frequencies. Therefore, the research deduced that Young’s modulus, and Poisson’s ratios in the horizontal plane must be taken into account, when choosing a suitable orthotropic friction material for brake pads. This relationship between the friction material properties and the natural frequency is independent of pad aspect ratios, and can be concluded for all types of pads. The natural frequency plays a significant role in triggering brake squeal. Brake squeal can occur if the pad natural frequency is coupled with the disc frequency. Therefore, determining how altering friction material properties affects the pad natural frequency, can help to propose an appropriate friction material for the pad, in order to have the pad natural frequency, which is not close to the disc frequency in the frequency range, where the brake noise occurs.