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51.
We investigate the effect of a fast vertical parametric excitation on self-excited vibrations in a delayed van der Pol oscillator. We use the method of direct partition of motion to derive the main autonomous equation governing the slow dynamic in the vicinity of the trivial equilibrium. Then, we apply the multiple scales method on this slow dynamic to derive a second-order slow flow system describing the modulation of slow dynamic. In particular we analyze the slow flow to obtain the effect of a fast excitation on the regions in parameter space where self-excited vibrations can be eliminated. We have shown that in the case where the time delay and the feedback gains are imposed, fast vertical parametric excitation can be an alternative to suppress undesirable self-excited vibrations in a delayed van der Pol oscillator. 相似文献
52.
An analysis for vibration of non-homogenous visco-elastic rectangular plate of linearly varying thickness subjected to thermal
gradient has been discussed in the present investigation. For visco-elastic, the basic elastic and viscous elements are combined.
We have taken Kelvin model for visco-elasticity that is the combination of the elastic and viscous elements in parallel. Here
the elastic element means the spring and the viscous element means the dashpot. The governing differential equation of motion
has been solved by Galerkin’s technique. Deflection, time period and logarithmic decrement at different points for the first
two modes of vibration are calculated for various values of thermal gradients, non homogeneity constant, taper constant and
aspect ratio for non-homogenous visco-elastic rectangular plate which is clamped on two parallel edges and simply supported
on remaining two edges. Comparison studies have been carried out with homogeneous visco-elastic rectangular plate to establish
the accuracy and versatility. 相似文献
53.
54.
Mural inspection by vibration measurements with TV-holography 总被引:2,自引:0,他引:2
Thomas Fricke-Begemann Gerd Gülker Klaus D. Hinsch Holger Joost 《Optics and Lasers in Engineering》2000,32(6):537-548
A commonly encountered problem in the conservation of historical murals is the identification of sections in the plaster that have detached from the wall and thus threaten to fall off. Commonly, walls are inspected by the acoustic response to a gentle finger-tapping (percussion method). Since this is a costly and cumbersome technique, means for a more automatic inspection are searched for. A TV-holography system of increased sensitivity in combination with acoustic excitation of the object is shown to be a new and powerful tool for monitoring of loose areas. It has the advantage of non-contact and remote operation which, for example, is extremely useful in large buildings. Principles of the method, experimental results obtained at an artificial wall in the laboratory, and a thorough comparison of results from historical sites gained by the traditional percussion method and the new technique are presented. The latter shows very good agreement in the assessment of wall quality and thus is evidence of the suitability of the optical equipment for tasks in conservation. 相似文献
55.
The rapid development of high-speed trains like the TGV or the ICE in recent years results in high dynamic loads causing vibrations which propagate from the train-track structure into the ground and further into nearby buildings. In this context it is important to develop rigid tracks with improved dynamic behaviour and to investigate possible means of vibration reduction. The boundary element method in frequency and time domain is used to simulate train-track structures subjected to dynamic loading and the reduction of vibrations which for instance can be achieved via a trench running parallel to the rigid track. In this context the non-causality error, which arises when the time-domain BEM algorithm is applied to mathematically concave domains, is discussed and the substructure method is proposed as a solution to this problem. A two-layered cylindrical elastic structure on a half-space with a trench is added as an example of a possible application. 相似文献
56.
57.
《中国颗粒学报》2008,6(6)
A two-dimensional discrete element model (DEM) simulation of cohesive polygonal particles has been developed to assess the benefit of point source vibration to induce flow in wedge-shaped hoppers. The particle-particle interaction model used is based on a multi-contact principle.The first part of the study investigated particle discharge under gravity without vibration to determine the critical orifice size (Be) to just sustain flow as a function of particle shape. It is shown that polygonal-shaped particles need a larger orifice than circular particles. It is also shown that Be decreases as the number of particle vertices increases. Addition of circular particles promotes flow of polygons in a linear manner.The second part of the study showed that vibration could enhance flow, effectively reducing Be. The model demonstrated the importance of vibrator location (height), consistent with previous continuum model results, and vibration amplitude in enhancing flow. 相似文献
58.
A mathematical model is developed to study periodic-impact motions and bifurcations in dynamics of a small vibro-impact pile driver. Dynamics of the small vibro-impact pile driver can be analyzed by means of a three-dimensional map, which describes free flight and sticking solutions of the vibro-impact system, between impacts, supplemented by transition conditions at the instants of impacts. Piecewise property and singularity are found to exist in the Poincaré map. The piecewise property is caused by the transitions of free flight and sticking motions of the driver and the pile immediately after the impact, and the singularity of map is generated via the grazing contact of the driver and the pile immediately before the impact. These properties of the map have been shown to exhibit particular types of sliding and grazing bifurcations of periodic-impact motions under parameter variation. The influence of piecewise property, grazing singularities and parameter variation on the performance of the vibro-impact pile driver is analyzed. The global bifurcation diagrams for the impact velocity of the driver versus the forcing frequency are plotted to predict much of the qualitative behavior of the actual physical system, which enable the practicing engineer to select excitation frequency ranges in which stable period one single-impact response can be expected to occur, and to predict the larger impact velocity and shorter impact period of such response. 相似文献
59.
《Physics letters. A》2014,378(32-33):2436-2442
The band structure of a nacreous composite material is studied by two proposed models, where an ultrawide low frequency band gap is observed. The first model (tension-shear chain model) with two phases including brick and mortar is investigated to describe the wave propagation in the nacreous composite material, and the dispersion relation is calculated by transfer matrix method and Bloch theorem. The results show that the frequency ranges of the pass bands are quite narrow, because a special tension-shear chain motion in the nacreous composite material is formed by some very slow modes. Furthermore, the second model (two-dimensional finite element model) is presented to investigate its band gap by a multi-level substructure scheme. Our findings will be of great value to the design and synthesis of vibration isolation materials in a wide and low frequency range. Finally, the transmission characteristics are calculated to verify the results. 相似文献
60.
Jessica Dubois Sofya Kulikova Lucie Hertz-Pannier Jean-François Mangin Ghislaine Dehaene-Lambertz Cyril Poupon 《Magnetic resonance imaging》2014