SOUND is one of the forms of mechanical energy and the two main characteristics of SOUND are intensity or power and frequency or wavelength of SOUND.their performance against the incoming SOUND wave, industrial silencers can be divided into two general groups of resonating and absorption silencers, the main difference between these silencers is the release of SOUND energy from the channeling system, which is one of the common examples of the use of resonating type silencers, their use in It is the internal combustion engines that distinguish absorption silencers from the resonator type based on the fact that the main and visible part of the act of muting the SOUND is achieved by changing SOUND energy to heat energy.The goal of this article is to design a muffler based on the breaking of SOUND frequencies resulting from the movement of fluid in the exhaust output of vehicles, which leads to a REDUCTION of at least 50 db of SOUND and gives the operator enough peace and concentration. In this article, after examining three types of mufflers, absorbent mufflers that use the properties of porous absorbent material to absorb passing SOUND and are the simplest form of mufflers, have been selected, analyzed and reviewed and are suitable for the OM457 engine of Idem Industrial Company. It designed for maximum inlet exhaust temperature is 520 and for the maximum kW power is 315 with the maximum discharge relative pressure of 185 mbar for homogenization with the standard atmosphere.

Unwanted noises and loud SOUNDs must be prevented from being transmitted to humans because they generate serious problems in the long term in terms of psychology and physiology. Helmholtz resonators are typically used as passive SOUND reducers for noise suppression in acoustic systems, such as vehicle exhaust, industry, engine intake manifolds, blowers, and more. It is a simple structure, but its performance is proper for restricting to a narrow band of frequencies due to its geometry. This work presents an adaptive Helmholtz resonator that can continuously change the effective frequency range regarding diverse SOUND sources. In this way, optimum performance over a constant point is achieved. The system includes a hollow box serving as a Helmholtz resonator, a variable orifice connected to a servomotor, and a controller. The controller receives the SOUND level and its frequency from the duct via a microphone and then adjusts the orifice area using the servomotor. This simple configuration adjusts the size of the orifice by rotating the butterfly within an effective frequency range based on the SOUND source characteristics. The experiments demonstrate that SOUND REDUCTION in frequencies lower than 1000 Hz is achieved effectively, with an approximate decrease of 46%. Moreover, during a test with a pressurized tube connected to an air compressor, the system showed a 30% REDUCTION in SOUND level. However, at high pressure, the SOUND level REDUCTION is 6.6%. Additionally, an air horn was tested as a SOUND source connected to the tube. The unbearable SOUND level is decreased by 28.5% at a high level of air pressure, although there are no significant differences in pressure.

The SOUND produced by the engine penetrates into the airplane through the structure and fuselage is still a grave concern for turboprop plane designers. The engine's propellers rotation is the main source of the SOUND in this kind of planes, the SOUND is transmitted to the fuselage through the structure and air so makes it vibrated. The decrease of noise made in the planes by dampers such as rubber, visco-elastic, and other non-dynamic absorber is not possible due to frequency low level. The present study investigates the designing of dynamic absorber for installing on the fuselage to absorb vibration and damping of the SOUND energy in the structure of the plane which makes the transmission way of vibration and SOUND possible in the structure. In the beginning, the theoretical relationship to design tunable dynamic absorber is gained, then the finite element model of the absorber is analyzed by ANSYS, and at the end, structuring and examining it for turboprop Antonov-140 is carried out.

Background and Aim: Recently, the SOUND level of military vehicles has increased significantly. Verbal communication is very important for the personnel working in these vehicles. The exchange of information between soldiers inside the vehicle as well as with the outside world, which is done using radio channels and internal communication systems, requires the ability to speak and hear properly. In military environments, armored personnel carriers (APC) are one of the most practical vehicles used, and the health and exposure to the SOUND pressure of the people inside the cabins of these tanks are very important. Therefore, the present study was conducted to evaluate the effect of different adsorbents on noise REDUCTION in armored personnel carriers. Methods: The present study was a cross-sectional and interventional study on 3 armored personnel carriers (BMP1) in 2018. SOUND pressure level inside the cabin was measured (according to BS6086-1981 [ISO5128-1980] standard) in 3 states include a. on and off mode of the tank with engine speed of 100 to 1200 rpm, b. standby mode with engine speed of 1400 rpm and c. moving mode at a speed of 15 km/hr tank with engine speed 1600 to 2000 rpm. In order to perform the intervention and reduce costs and evaluate the efficiency of adsorbents in reducing the SOUND pressure level, a room made of the main body of the tank, which was made of iron, was prepared in smaller dimensions. The SOUND was generated inside the chamber and after installing the absorbent material, the amount of SOUND pressure level REDUCTION was measured. Selected absorbent materials were included Polyurethane foam with a density of 12 kg/cm2 and thickness of 2. 5 cm, Polyurethane foam with a density of 12 kg/cm2 and thickness of 4. 2 cm, Glasswool with a density of 12 kg/cm2 and thickness of 3. 2 cm, Polyethylene foam with a density of 20 kg/cm2 and thickness of 2 cm, and felt with thickness 0. 8 cm. Data were analyzed by one-way analysis of variance (ANOVA) by SPSS software version 23 at a significance level of 0. 05. Results: The equivalent SOUND pressure level increased from 93. 8 dBA in a standstill to 101. 6 dBA in standby mode, and in the state of motion, this level increased to 107 dBA. The corresponding total SOUND pressure level increased from 93 dBA in a standstill to 98 dBA in standby mode and increased at a speed of 15 km/h to 104 dBA. The equivalent level of SOUND exposure in the chamber without adsorbent materials was considered 110 dBA, when using the felt as an absorbent material, this level dropped to 98 dBA. When the polyethylene foam was used as an adsorbent, this level dropped to 102 dBA. When the glass wall was used as an adsorbent, this level dropped to 97 dBA. When the polyurethane foam with a thickness of 2. 5 cm was used as an adsorbent, this level dropped to 95 dBA. When the polyurethane foam with a thickness of 4. 2 cm was used as an adsorbent, this level dropped to 93. 2 dBA. Conclusion: The condition of the motor of the device and the condition of the chains are the most important factors in the difference in the level of equivalent SOUND pressure in the three mentioned conditions. The best material for installation inside the cabin to reduce the SOUND pressure level is polyurethane oval foam with a density of 12 kg/m2 and 4. 2 cm thickness. This material reduces the equivalent level of SOUND exposure from 110 dBA to 94 dBA.

In this article, an attempt has been made to estimate the amount of SOUND transmission loss in a flat oval channel by applying the approach of statistical energy analysis. Correct estimation of SOUND transmission loss in an air conditioning channel is of great importance due to the harmful effects of noise pollution in the environment on human health. Simulation with the statistical energy analysis method is a powerful approach to estimate SOUND and vibration in problems in which we deal with complex and multi-part systems; is considered. In this method, first, a system is divided into several subsystems, and then by writing a matrix equation that includes the energy exchanges between subsystems and energy loss coefficients; It is investigated from the perspective of vibration and SOUND estimation.On average, the model presented in this research is able to estimate the SOUND transmission loss in different dimensions of the air conditioning channels according to the experimental results in the accuracy range of ± 2.5 dB. Considering that it seems that the results obtained from modeling with this method are in good agreement with the experimental data; The results of this research can be used as an efficient approach to estimate noise in oval shaped channels stretched in different lengths.

Inertial Navigation System (INS) is one of the navigation systems widely used in various land-based, aerial, and marine applications. Among all types of INS, Microelectromechanical System (MEMS)-based INS can be widely utilized, owing to their low cost, lightweight, and small size. However, due to the manufacturing technology, MEMS-based INS suffers from deterministic and stochastic errors, which increase positioning errors over time. In this paper, a new effective noise REDUCTION method is proposed that can provide more accurate outputs of MEMS-based inertial sensors. The intelligent method in this paper is a combined denoising method that combines Wavelet Transform (WT), Permutation Entropy (PE), Support Vector Regression (SVR), and Genetic Algorithm (GA). Firstly, WT is employed to obtain a time-frequency representation of raw data. Secondly, a four-element feature vector is formed. These four features are (1) amplitude of frequency, (2) its ratio to mean of amplitudes of all frequencies, (3) location of frequency in time-frequency representation, and (4) judgment on behaviors of frequency that is obtained by utilizing PE. Thirdly, based on the feature vector, the GA-SVR algorithm predicts amplitudes of all frequencies in the time-frequency representation of the denoised signal. Finally, by employing inverse WT the denoised signal is obtained. In this work, the outputs of the Inertial Measurement Unit (IMU) in ADIS16407 sensor, as a low-cost and MEMS-based INS, have been utilized for data collection. The proposed method has been compared with other noise REDUCTION methods and the achieved results verify superior improvement than other methods.

In this study, a three-dimensional numerical simulation of turbulent flow inside a SOUND attenuator was conducted to investigate and control the outlet SOUND. The analysis was performed using the finite volume method and ANSYS software. The aim of this research was to examine the effect of geometric parameters on the SOUND pressure difference between the inlet and outlet of the SOUND attenuator. The geometry of the diffuser and the use of rock wool, which is a type of SOUND absorber, have a significant impact on reducing the outlet SOUND, as most standards, including the AMCA standard, specify that the SOUND level at a distance of 1 meter should not exceed 85 dB. In this study, four geometric parameters were evaluated, including the diameter of the diffuser holes, the spacing between the holes, the number of holes, and the length of the rock wool region. The results indicate that increasing the diameter of the diffuser holes, the spacing between the holes, and the number of holes leads to higher SOUND jets exiting the diffuser holes and lower flow energy, resulting in a REDUCTION in the SOUND pressure difference between the inlet and outlet of the SOUND attenuator. Additionally, increasing the length of the rock wool region increases the length of the flow path and consumes more SOUND energy, ultimately resulting in a greater REDUCTION in the SOUND pressure difference. In conclusion, the maximum REDUCTION in SOUND pressure difference is associated with a hole diameter of 10 millimeters, a hole spacing of 30 millimeters, a number of holes of 20, and a rock wool length of 1400 millimeters.

Background and Aim: The interior of airport lounges is often exposed to a lot of noise, which can increase the risk to human health. Due to the dangers of high noise pollution for airport users, the present study was conducted to reduce noise pollution in the transit lounges of Ahvaz International Airport. Materials and Methods: This is an interdisciplinary, applied study that used a combination of experimental, simulation, and case study methods. First, the acoustic status of Ahwaz International Airport was determined experimentally by measuring the amount of noise pollution during the test period (8 AM to 2 PM) by the Brü el & Kjæ r SOUND level meter (model 2260 B&K) in 12 places. Then, the SOUND-absorbing plates were tested with different geometric models. After proving the validity and reliability of the research, the experiments were performed by simulation using EASE 4. 4 software. Results: In this study, the noise level of the airport lounge was considered a dependent variable and four SOUND indices including Reverberation Time (RT; the main index), Indirect SOUND Index (STI), total SOUND Pressure Level (SPL), and auditory error coefficient (ALCONSE ) were evaluated according to the international standards ISO3382 and ISO 3382-1. Conclusion: After the simulation, it was found that the use of raster pattern SOUND-absorbing plates (Model A in research) in walls and ceilings with different frequencies had the lowest SOUND pressure and the above-mentioned indices were at desirable levels. As a result, Model A had the greatest effect on reducing noise in the tested space.