Current Issue : July - September Volume : 2014 Issue Number : 3 Articles : 5 Articles
This study uses the finite element method (FEM) to analyze the excitation and dead vibration modes of two-dimensional quartz\nplates. We first simplify three-dimensional quartz plates with plane strain simplification and then compare the modes of the\nsimplified three-dimensional plates to those of two-dimensional plates. We then analyze quartz vibrating elements of AT-cut\nplates and SC-cut plates. To understand the regularity of the resonance frequency of plates that are excitable by voltage loading,\nwe compare the natural vibrations of quartz plates with the excitation frequency generated after the plates are excited by voltage\nloading....
Amplitude demodulation is a key for diagnosing bearing faults. The quality of the demodulation determines the efficiency of the\nspectrum analysis in detecting the defect. A signal analysis technique based on minimum entropy deconvolution (MED), empirical\nmode decomposition (EMD), and Teager Kaiser energy operator (TKEO) is presented.Theproposed method consists in enhancing\nthe signal by using MED, decomposing the signal in intrinsic mode functions (IMFs) and selects only the IMF which presents the\nhighest correlation coefficient with the original signal. In this study the first IMF1 was automatically selected, since it represents\nthe contribution of high frequencies which are first excited at the early stages of degradation. After that, TKEO is used to track\nthe modulation energy. The spectrum is applied to the instantaneous amplitude. Therefore, the character of the bearing faults\ncan be recognized according to the envelope spectrum. The simulation and experimental results show that an envelope spectrum\nanalysis based on MED-EMD and TKEO provides a reliable signal analysis tool.The experimental application has been developed\non acoustic emission and vibration signals recorded for bearing fault detection....
In the regions near to active faults, if the fault rupture propagation is towards the site and the shear wave propagation velocity is\nnear the velocity of fault rupture propagation, the forward directivity effect causes pulse-like long-period large-amplitude vibrations\nperpendicular to the fault plane which causes a large amount of energy to be imposed to structures in a short time. According to\nprevious investigations, the amounts of input and dissipated energies in the structure represent the general performance of the\nstructure and show the level of damage and flexibility of the structure against earthquake. Therefore, in this study, the distribution\nof damage in the structure height and its amount at the height of steel moment frames under the pulse-like vibrations in the near\nfault region has been investigated. The results of this study show that the increase rate of earthquake input energy with respect to\nincrease in the number of stories of the structure in the near field of fault is triple that in the far field of fault which then leads to a\n2ââ?¬â??2.5 times increase in the earthquake input energy in the high rise moment frames in the near field of fault with respect to that in\nthe far field of fault....
This paper presents a design method to optimize the material distribution of functionally graded beams with respect to some\nvibration and acoustic properties. The change of thematerial distribution through the beamlength alters the stiffness and the mass\nof the beam. This can be used to alter a specific beam natural frequency. It can also be used to reduce the sound power radiated\nfrom the vibrating beam. Two novel volume fraction laws are used to describe the material volume distributions through the\nlength of the FGM beam.The proposed method couples the finite elementmethod (for the modal and harmonic analysis), Lumped\nParameterModel (for calculating the power of sound radiation), and an optimization technique based on Genetic Algorithm. As a\ndemonstration of this technique, the optimization procedure is applied to maximize the fundamental frequency of FGM cantilever\nand clamped beams and to minimize the sound radiation from vibrating clamped FGM beam at a specific frequency....
Thedynamics of a light sphere in a quickly rotating inclined cylinder filled with liquid under transversal vibrations is experimentally\ninvestigated. Due to inertial oscillations of the sphere relative to the cavity, its rotation velocity differs from the cavity one. The\nintensification of the lagging motion of a sphere and the excitation of the outstripping differential rotation are possible under\nvibrations. It occurs in the resonant areas where the frequency of vibrations coincides with the fundamental frequency of the\nsystem. The position of the sphere in the center of the cylinder could be unstable. Different velocities of the sphere are matched\nwith its various quasistationary positions on the axis of rotating cavity. In tilted rotating cylinder, the axial component of the gravity\nforce appears; however, the light sphere does not float to the upper end wall but gets the stable position at a definite distance fromit.\nIt makes possible to provide a vibrational suspension of the light sphere in filled with liquid cavity rotating around the vertical axis.\nIt is found that in the wide range of the cavity inclination angles the sphere position is determined by the dimensionless velocity of\nbody differential rotation....
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