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Gears are one of the important sources of vibrations and noise in industrial rotating machinery and power transmission systems. In order to design and develop an optimal and quiet geared power transmission system, this paper presents the design of an active vibration control for gear-bearing system. A dynamic model of the geared system is presented, where some undesired parameters in the design such as manufacturing errors, teeth deformations, mounting errors as well as external excitations resulting from distributions of applied torque are included. An active control system is presents in order to control and attenuate the disturbance impress on the system vibrations. The idea behind the design of this control system is to reduce vibration transmissibility by the introduction of the excitation forces in the bearing. The controller is investigated and designed by using feedback control and based on the H-infinity control approach. It can be presented as an optimization problem. To solve this optimization problem, Particle swarm optimization (PSO) algorithm is used, which is one of the optimization methods available among artificial intelligence. The simulation results are performed to investigate performance of the control system.

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Sound transmission through a double – wall circular cylindrical shell is investigated. In order to study the acoustic behavior of these kinds of thin circular cylindrical shells, an exact analytical approach is discussed in detail. Using an infinitely long thin walled circular cylindrical shell subjected to a plane wave incidence, the structure – acoustic equations based on the Donnell’s thin shell theory are obtained and transmission losses calculated by this approach are compared to the transmission losses obtained according to the Love’s theory. The comparison shows that the Donnell theory distinguishes all the frequencies in which sound transmitted inside the shell easily and it predicts the sound transmission characteristics of a thin circular cylindrical shell better than the Love’s theory especially in resonance – controlled and mass – controlled regions. Then the effects of different sound absorber materials and various gases are studied in order to fill the cylindrical shell’s gap with a material except air. The results show that high sound transmission loss and better trend can be achieved by using these sound absorber materials in double-wall circular cylindrical shells.

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Today, fast and accurate fault detection is one of the major concerns in the industry. Although many advanced algorithms have been implemented in the past decade for this purpose, they were very complicated or did not provide the desired results. Hence, in this paper, we have proposed an emerging method for deep groove ball bearing fault diagnosis and classification. In the first step, the vibration test signals, related to the normal and faulty bearings have been used for both of the drive-end and fan-end bearings of an electrical motor. After that, we have employed the one dimensional Meyer wavelet transform for signal processing in the frequency domain. Hence, the unique coefficients for each kind of fault were extracted and directed to the adaptive neuro-fuzzy system for fault classification. The intelligent adaptive neuro-fuzzy system was adopted to enhance the fault classification performance due to its flexibility and ability in dealing with uncertainty and robustness to noise. This system classifies the input data to the faults in the race or the balls of each of the fan-end and the drive-end bearings with specific fault diameters. In the final part of this study, the new experimental signals were processed in order to verify the results of the proposed method. The results reveal that this method has more accuracy and better classification performance in comparison with other methods, proposed in the literature.

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Reduction of unwanted noises is an important issue in the current societies regarding their potential negative impact on the mental and physical health of the peoples. Researchers are trying to find a new method to reduce the damage of this unwanted sound. Accordingly, the use of sound absorbing materials with appropriate acoustic properties has increased in the recent years. In this article, the production of polyurethane foam explained first and sound absorption coefficient of pure PUF has been measured. In order to improve the mechanical and acoustical properties of polyurethane foam, various quantities of Nano-Alumina powder is added to the structure of the foam. The effects of this additive material on the acoustic and mechanical properties of the foam are then measured. In this work, for the first time, the mechanical, physical and acoustical properties of the polyurethane foam improved by Nano-Alumina are studied. Finally, the change of the sound absorption coefficient of the produced composite material is analyzed based on the mechanical and physical experimental results. The sound absorption coefficient of this foam is then measured using two microphone method with Impedance tubes.

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In this study, the effects of frequency, height and wavelength of progressive gravity waves on vibration and energy absorption of the single- and two-degree of freedom Bristol oscillating cylinder systems have been investigated experimentally and numerically in different depth of water. The experiments were carried out in channel equipped with both a paddle-type wave-maker and wave features measurement tools. Numerical simulations were conducted in COMSOL software assigned to simulate interactions between physical environments for turbulent flow. Making a comparison between the numerical and experimental conclusions compared to the other researchers' results demonstrates a desired matching in a wide range of waves' parameters. It can be seen in findings that changing in depth of submerged objects from free surface of water has considerable influence on their vibration behavior, so that by rising in depth, the oscillations amplitude increases to a maximam and then decreases. The obtained results indicate the different effects of relative depth under the submerged buoy on the efficiency of the single- and two-degree of freedom systems; so that increasing water height causes rise in the efficiency of single degree of freedom systems, but it doesn't have considerable influence on two degree of freedom systems. The results also show that expanding the wave-maker frequency for a constant height of water in channel causes to rise in energy and height of the generated waves so that oscillations amplitude of submerged buoy rise in vertical and horizontal line.