The performance of various types of silencers used to reduce the micropressure waves radiated from ventilation holes and inclined shafts, which are being studied as measures to reduce micropressure waves in railway tunnels, was evaluated to find an effective silencer. In order to find the optimal silencer, the magnitude and frequency characteristics of the pressure waves emitted from the inclined shaft were analyzed to find an excellent silencer. The evaluation showed that the model with a porous cylinder and a small diameter outer tube was the simplest but performed the best.

This study aims to explore the development and current state of suppressor technology through a review of existing research and case studies, and to propose future directions for further research. Firstly, we analyze domestic and international research topics related to suppressors to determine emerging trends and research needs. Secondly, we investigate the reasons behind the discrepancies in noise reduction data from different studies that utilize identical measurement standards, proposing potential solutions to this issue. Furthermore, we examine key factors influencing suppressor performance, such as the design and shape of suppressors, including the effectiveness of baffle systems, pass-through suppressor technology, and fluid-filled suppressors. Additionally, we delve into the advancements in suppressor materials, assessing their durability, weight reduction, and thermal management capabilities, which are critical to the effectiveness and longevity of suppressors in modern warfare. This research contributes to the understanding of suppressor technology, highlighting the importance of design optimization and material innovation in enhancing both performance and practicality. The findings can guide the development of next-generation suppressors that meet the increasingly complex demands of contemporary combat environments.

Internal combustion engine is the main source of environmental pollutants and therefore advanced technology is required to reduce harmful elements from the exhaust gases all over the world. Especially, when the exhaust gas is released from the automotive muffler, exhaust noise has many bad influence on the surrounding environment. In order to reduce the exhaust noise, it is necessary that automotive muffler must be designed for best exhaust efficiency. The sound insulation room was installed for the analysis of an acoustics characteristics of the noise from automotive muffler, in this study. Exhaust gas noise, noise distribution characteristics, pressure and temperature of exhaust gas were investigated with the change of annulus temperature of air cooled annulus automotive muffler and cooled annulus automotive muffler. The following results were obtained with this study. From the frequency analysis of automotive muffler, high noise distribution was observed in the range 100~2000Hz. It means that the noise in this range has an dominate influence for the overall noise. Noise reduction of automotive muffler was affected by the temperature of annulus. It is caused the result that the high temperature and pressure of exhaust gas are changed lower by the drop of annulus temperature. The tendencies of noise, the temperature and pressure of exhaust gas are similar to the performance curve of engine. Exhaust gas pressure is determined by the r.p.m. of engine and affected by the cooling performance of automotive muffler.

In this study, the noise reduction effect of the steam vent silencer was investigated by performing a transient flow analysis applying the Loss Model, a porous flow analysis model, and calculating the noise intensity from the pressure fluctuation according to the time change. As a result of flow analysis, it was confirmed that the noise intensity decreased as the number of diffusers and the number of splitters made of foamed aluminum increased. In the case of three-stage diffusers, the noise intensity decreased by up to 33.4 dB when six foamed aluminum with a thickness of 150mm were installed.

There are many disadvantages to existing silencers used in power plants. Recently, high-performance silencers are required in society, so it is necessary to develop silencers accordingly. Therefore, in this study, to develop the flow silencer by taking advantage of the foamed aluminum, the property values such as loss coefficient and porosity were obtained through experiments, based on the Forchheimer's law. CFD analysis was performed by applying a porous modeling technique to foamed aluminum and the results were compared with experimental values. The error rate between the results of the experiment and the flow analysis is within about 2.79%, so the results of the experiment and the analysis agree relatively well. When the foamed aluminum was installed, the flow noise was reduced by about 5.14dB.

High power trends in the diesel engines due to engine downsizing do not provide noise attenuation that can be satisfied with the performance of the existing silencer on account of high frequency increases in the exhaust noise. This study improves the attenuation performance of the exhaust silencer of the diesel engine and suggests silencer structure that performs best attenuation performance, especially at the high frequency range in the exhaust noise. It proposes dual silencer structure with an average attenuation performance of 6.4 dB and a maximum of 10.7 dB in the high frequency range (over 500 Hz), and analyzes its characteristics compared with the existing silencer. The performance analysis is performed according to 'Measurements on silencers in situation–ISO 11820:1996 Acoustics' and describes the results of comparative analysis with the existing silencer.

Based on the attitude of science discovery, an industrial induction motor silencer is designed and developed, and the performance of this silencer is evaluated experimentally in this paper. The basic principle of the silencer was used as the parabola principle. During the experiment, the performance of the proposed silencer is preliminary researched using software simulation method, test analogy method, and some other methods to infer experiment was conducted to evaluate the experiment. During the simulation experiment, 25dB level can be reduced in the 12,500∼16,000Hz range. More than 35dB level was reduced in the 2,500∼5,000Hz range. When we used the silencer, the noise in the high frequency bands above 1,000Hz are reduced. In particular, 1,600Hz band is greatly reduced on average by 5dB. Some effective conclusions are obtained from the analysis of the experiment results, despite some uncertain factors in the experiment

The object of this paper is to examine the noise generating mechanism at manufacturing process of metal material products. To accomplish the object; A noise generating mechanism of high noise machine, which is mounted in the small and medium size enterprise, was investigated. The measurement method of the noise for the machine by manufacturers were investigated. The noise at the 250 point of the manufacturing procrss machine in the 40 processes of the 3 factories, 3 business fields was measured. The database of the noise was built from the measurement data. The major sound sources and frequency range for the manufacturing processes of metal product machine was investigated.

This paper describes a prototype mechanical white noise generator has a source level of more than 170.0 dB (re 1µPa at 1 m) at the frequency range of 10 Hz to 100 kHz. The results of performance evaluation of the generator are as follows. The average source level of the generator measured by a step of 15°in horizontal (0 to 360。, 25 points) was 185.2 (SD (standard deviation): 2.3) dB (re 1µPa at 1 m). The maximum and minimum source levels were appeared at the frequency range of 2.5 to 5.0 kHz and around 100 kHz, respectively. The average source levels at 0°, 90。, 180。and 270° were 162.9 (SD: 10.6), 168.4 (SD: 10.0), 162.1 (SD: 9.1) and 166.5 (SD: 11.1) dB (re 1µPa at 1 m). The average source level measured by a step of 30° in vertical was 184.9 (SD: 2.2) dB (re 1µPa at 1 m). The relative maximum variation width of the source levels in horizontal and in vertical measurement were less than 7.0 dB and 1.0 dB, respectively.