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A vibration absorber is used to reduce vibration of an Euler-Bernoulli beam with elastic supports subjected to a moving oscillator. Dynamic response of the beam under moving harmonic exciter with different moving velocities and different parameters are obtained. The critical velocity of the moving oscillator is determined and absorber parameters are optimized by numerical algorithm and effect of mass and damping on the absorber performance is investigated. When absorber is applied to the beam, effect of crack occurrence on its performance is investigated. Crack is assumed to be open and is modeled by sectional flexibility increase. Two different cases considered for crack severity. In each case, optimal absorber for intact beam is applied and dynamic response of the midpoint of the beam with different velocities of moving exciter is obtained. Results show although crack can increase dynamic deflection of the beam with absorber, dynamic deflection of cracked beam without considering absorber is higher than dynamic deflection of cracked beam with absorber used. It is found that the vibration absorber designed for intact beam keeps its performance in dynamic deflection reduction after crack occurrence and changing in structural dynamic.

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The fluid induced vibration in fluid conveying pipes can cause fatigue and failure in the system. Therefore, controlling these unwanted vibrations and suppressing the vibrations of the fluid conveying pipe is important. In this paper by considering the passive vibration absorber for the fluid conveying pipe, the influence of the vibration absorber parameters on the dynamic behavior of the system is investigated. The governing equations of motion are obtained via the Newton’s second law, and analytical solutions for the characteristic equation and mode shapes of the system are obtained through the power series method. After verifying the obtained results, the effect of the vibration absorber parameters and the fluid flow velocity on the vibration behavior of the fluid conveying pipe have been investigated. Results show that by increasing the absorber mass, the effect of absorber on decreasing the oscillations amplitude is diminished. At different fluid velocities, the oscillation amplitude of the system can be reduced considerably by specifying proper values of the absorber parameters. At velocities near the critical velocity, where the oscillation amplitude reaches a maximum value, using a suitable vibration absorber may reduce the maximum oscillations amplitude of the system by 98%. The method presented in current study can be easily generalized to design passive vibration absorber for fluid conveying pipes with different boundary conditions.

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In the present article, a real mass-spring system under external excitation with time-varying frequency is studied. The external excitation causes additional oscillations in the real mass-spring system response which disrupt the path tracking procedure. Adaptive control law, which is considered for annihilating the additional oscillations, is equal to a virtual vibration absorber which its stiffness regardless of the real system and external excitation uncertainties, can be updated based on the linear absorber theory until the natural frequency of the absorber reaches the excitation frequency. The variation of the frequency is based on the step and ramp function which relatively are equal to the sudden and transient change from the initial value to the final value of the frequency. Besides, the effects of the noise with various amplitudes existed in the transient variation of the frequency on updating the virtual absorber stiffness is developed. Simulation results are presented to demonstrate that the determined adaptation law guarantees the adaptation of virtual absorber stiffness considering excitation frequency variation based on both step function and ramp function and eliminates additional vibrations of the real system.

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In this study, application of a dynamic vibration absorber system consists of two symmetric cantilever beams with tip mass and piezoelectric layer, in order to suppress undesired vibrations and harvest electrical energy, is studied. The main vibratory system is a simply supported beam, which is excited by a DC motor with rotating unbalance mass. To derive the governing electromechanical equations, the Euler-Bernoulli beam theory and the energy method are used. Then the governing electromechanical equations are experimentally validated and accommodation between theoretical and experimental results is shown using several frequency response plots. Using the non-dimensional governing equations, effect of changing the system parameters such as the tip mass, load resistance and length of the cantilever beam is studied. Then, considering ability of system to effectively suppress undesired vibrations and increase the harvested electrical energy, the proper range for selecting the non-dimensional tip mass and non-dimensional load resistance is presented. Finally, using the so-called perfection rate parameter, the best parameters, to have a good vibration suppressor and energy harvester, are obtained. Results shown that both of energy and vibration considerations can be satisfied using the system.

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Vibrations on imported fruits can cause one of the damage such as impact, wear and compression or a combination of them to the fruit. The nectarine fruit tissue is soft at the soft handling stage, which increases the susceptibility to mechanical damage during transportation and storage. In this study, the effects of simulated transport vibrations on the quality of nectarine fruit with five levels of frequency, three levels of displacement, two types of boxes, three types of adsorbent on the first, second and third rows of fruit have been studied. The root mean square vibration acceleration was considered as a measure of the vibration magnitude and the vibration transferability percentage was calculated in different treatments. In addition, the maximum stress and modulus of elasticity at the yield point were calculated. Results showed the absorbers had the highest and lowest vibration absorption in the frequency range of 5.7 to 7.5 and 8.9 Hz, respectively. The first, second and third rows of fruits had the lowest transmitted and the highest vibration absorption at accelerations of 0.8, 8.4 and 6 ms^-2, respectively. The lowest vibration absorption was obtained in the first, second and third rows at accelerations of 2.3, 5.1 and 3.4 ms^-2. Therefore, it is recommended to use cardboard boxes with paper absorbers inside to carry the fruit and do not place more than one row of fruit in each box.