Papers by Keyword: Noise Reduction

Abstract: This research focused on noise reduction in jets using chevron passive control method, the nozzle designs with varying chevron types were subjected to CFD analysis and experimental analysis to understand pressure distribution patterns in the far field. This research distinctively analysed chevron performance through pressure distribution in the far field and not based on nozzle acoustic power dis-tribution, a surface phenomenon. Four models of nozzles namely base, chevron, wave and tabular were designed, manufactured and extensive analysis in both computational and experimental approaches was carried out. The sound pressure level (SPL) was calculated along with its percentage reduction for three models by taking the base model as reference model. The scientific results showed that among all models, wave is the least noisy with reduction of 3.3% and 1.16% SPL in computation and experiment respectively. On the other hand, the base model found to be the highest noisy model both computationally and experimentally.

Abstract: Machine learning models are effective tools for predicting and reducing noise levels in industrial gear systems. In this study, we compare different machine learning methods to investigate the effects of different gear modification parameters on noise levels. Four different predictive models was used. Random Forest Regressor, XGBoost, Gradient Boosting Machines and neural network. The study concluded that Random Forest and Gradient Boosting Machines models were the most effective. Both models achieved low mean squared error values 6.10 and 6.67. Further tests with synthetic data confirmed the stability of these models. Current sustainability trends show that the integration of machine learning into industrial applications fits well with manufacturers' objectives. However, it is currently challenging to determine which machine learning methods are most effective in optimizing noise reduction. This paper seeks to address this gap by comparing the accuracy and reliability of these models. Based on the results, the use of machine learning models is recommended to reduce noise levels in geared systems.

Abstract: The Cahn-Hilliard equation, known for describing the evolution of interfaces in multicomponent systems, can also be employed to noise reduction in mathematical functions and concentration-dependent heat transfer simulations. This work presents a finite difference method discretization of the Cahn-Hilliard equation and explores its applications. For noise reduction, three different noisy functions are simulated, demonstrating effective recovery of original functions despite significant noise levels. In heat transfer simulations, three initial temperature distributions are explored with concentration-dependent thermal diffusivity. Results show that concentration significantly affects thermal diffusivity and heat propagation, leading to non-uniform temperature distributions. Comparative simulations without concentration influence highlight the distinct impact of concentration on thermal behavior. The study underscores a reliable approach to noise reduction and insight into concentration-dependent heat transfer dynamics.

Abstract: The muffler plays a crucial role in reducing the noise generated by the internal combustion engine exhaust gases. Therefore, an effective muffler design should be capable of significantly reducing noise levels. However, we must also consider backpressure, which can negatively impact engine performance. Backpressure is the additional pressure exerted by the muffler towards the engine, and it can have adverse effects on engine performance, thus requiring minimization. These two objectives often conflict with each other. Hence, in this research, we utilize multiobjective genetic algorithms as a tool to optimize muffler design. Inspired by the natural selection process, genetic algorithms aim to find a muffler design that is not only effective in reducing noise but also produces minimal backpressure. Thus, this study aims to achieve a balance between noise reduction and backpressure minimization in muffler design. The multiobjective genetic algorithm proposes 105 muffler design solutions. These solutions are not dominated by each other against both TL and PL objectives. The design that has the best value in the TL objective is solution 1 with TL and PL values of 26.06 dBA and 2.27 kPa. The design that has the best value in the PL objective is solution 3 with TL and PL values of 8.36 dBA and 1.87 kPa. The muffler compromise design chosen was a solution 41 with TL and PL values of 17.78 dBA and 2.07 kPa.

Abstract: This research investigated the use of water treatment sludge (WTS) as an geopolymerized material. WTS with an initial SiO₂:Al₂O₃ ratio of 3.25 was thermally treated at temperatures of 105, 500, 650 and 850 °C for 1 h. The powdered WTS after calcinations was reacted with alkaline-silicate solution (ASS) with different proportion between NaOH and Na₂SiO₃ solutions. The effect of calcining temperatures on the strength’s development of WTS geopolymer was determined. Without thermal treatment of the WTS, no strength was gained during the early stages. Samples prepared from WTR calcined at 850 °C exhibited the highest strength at all curing times. When WTS geopolymer was prepared as solid plate, the test in noise reduction was explored at various sound frequencies between 1000-10000 Hz. The average noise reduction efficiency of WTS geopolymer was 63.5% closed to the case of commercial light-weight brick at the same paste’s thickness.

Abstract: This paper presents the aeroacoustics result of the trailing edge noise prepared wings two species of owl - Barn owl (Tyto alba), called “good hearing” and Northern hawk-owl (Surnia ulula), called “good seeing”. The acoustic performance comparisons between the Barn owl and Northern hawk-owl show that there are differences between the sound intensity the studied wings. These results prove that the special sound suppression characteristics of wing feather play an important role for their silent flight. Therefore the flat plates with the cutting trailing edge have been studied. At lower speeds, a better noise reduction effect was obtained for the plates with edges as elliptical arcs. On the basis of the above tests it can be concluded that other types of notches on the trailing edge (not just a sawtooth) also reduce the aerodynamic noise of flat plate.

Abstract: This paper describes the analysis on the characteristics of semi-permeable membrane sound absorber. The effects of membrane surface tension on the sound absorption characteristics were investigated. The characteristics of the membrane absorber was measured experimentally in terms of Sound Absorption Coefficient, α and Noise Reduction Coefficient, NRC. The membrane is made of thin, flexible, semi-permeable latex material and the tests were carried out by using impedance tube method according to ISO 10534-2 standard. The results showed that the surface tension has significant influence on the sound absorption characteristics. For the parameters used in the laboratory work, specimen with unstretched surface tension has the best absorption performance.

Abstract: Noise is one of the problems that often occur in urban areas due to the traffic condition. Noise in a building design depends on the choice of materials as sound absorbers. The type of sound dampening material that already exists is a porous material, a resonator, and a panel. The material often used as an absorber is porous materials, because it is relatively cheaper and lighter, especially to reduce the noise in the narrow spaces such as housing and offices. Various substitutes are made from cheap materials, such as the use of recycled materials of egg tray paper with the size of 40 x 40 centimeters. This is a quantitative research that will measure the place of egg tray paper in reducing noise, using a Sound Level Meter. The use of the egg tray paper is able to show an adequate acoustic quality as noise absorbers, with the average value of NR 22-26 dB.

Abstract: Speech processing in hearing aid often operates in noisy environments. So noise reduction algorithm is very important for hearing aid. This paper reviews conventional wiener filter algorithm and points out its remained problems----musical residual noise and low speech intelligibility for low input signal-to-noise ratios (SNR). To solve the problems, the proposed algorithm divides the frequency (0-8000 Hz) into 16 bands in Mel-frequency scale and processes the signal separately to remove musical residual noise. Meanwhile, a new Voice Activity Detector (VAD) applied for digital hearing aid is also presented. Based on the accurate judgment of speech frame, the filter processes the speech frame and non-speech frame in different ways. The method is realized in matlab to test output SNR and PESQ (Perceptual Evaluation of Speech Quality). It is also realized in android app for real-time test. Both of the experimental results demonstrate the advances of the proposed algorithm.

Abstract: Multi-Agent system (MAS) is used to control the radiation noise in a rectangular enclosure, which is surrounded by two flexible plates and four rigid plates. The noise is generateded by the vibration of the exciting flexible plane. A MAS is established to coordinate the active noise control method, and these agents are controlled by a coordination object which includes compete and cooperative rules. These agents are competitiveness, so the MAS can provide fault-tolerant capabilities for the control mechanism. Meanwhile, these agents are independent and modular, and can be used in “Plug-and-Play” control field. The formula is derivate to calculate the sound pressure in the enclosure when there some point forces applied on the flexible plates, and the simulation shows using MAS to control the noise in the cavity is effective.