Topic
Critical speed
About: Critical speed is a research topic. Over the lifetime, 2764 publications have been published within this topic receiving 31365 citations.
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TL;DR: In this article, the defect of rail joint is investigated with train's critical speed, where the joints between the rails are modeled by periodic irregularities and the train is modeled as a convoy of vehicles moving with a constant speed.
Abstract: The dynamic amplification of the railway bridges caused by the passage of a train varies according to several factors. Among these factors: defaults of roughness of the rail and its joints, etc. These defects are usually encountered in railways and they influence the dynamics of the vehicle–bridge interaction, whence the importance of this study. In this paper, the defect of rail joint is investigated with train's critical speed. The joints between the rails are modeled by periodic irregularities. The bridge is modeled by a simply supported uniform beam. The train is modeled as a convoy of vehicles moving with a constant speed. The governing equations of motion for the bridge–train interaction system are derived using the Lagrangian formulation and the modal superposition technique. These equations are integrated numerically by applying the Newmark method. This paper presents a computation code in FORTRAN to analyze the effect of the above-mentioned defects on the bridge’s dynamic response. DOI: http://dx.doi.org/10.5755/j01.mech.19.1.3615
9 citations
TL;DR: In this paper, the experimental confirmation of a vibration and stability model of a thermally stressed rotating disk is presented, where the rotating-disk convective-heat-transfer problem is addressed.
Abstract: Paper presents the experimental confirmation of a vibration and stability model of a thermally stressed rotating disk. Attention is directed to the rotating-disk convective-heat-transfer problem. Measured temperature distributions are used in the computation of the theoretical characteristic frequency spectrum which is then verified by the experimental frequency spectrum. The theoretical characteristic spectrum is shown to be effective in predicting the likelihood of a critical speed instability of the thermally stressed rotating disk. Optimal control of disk operation using this model is proposed.
9 citations
01 Jun 2015
TL;DR: In this article, an increased coupling level between the degrees of freedom in the equation of motion (through additional off-diagonal terms) was introduced to deal with the effects of UHBR-engines on structural dynamics and aerodynamic stability.
Abstract: Since more and more modern civil aircraft are equipped with UHBR-engines
for reasons of fuel efficiency and environmental aspects, the need to tackle
specific engine related dynamic problems has occurred.
The request for UHBR-engines with high bypass ratio numbers and with their
intrinsic advantages of economic fuel consumption and lower acoustic emission
asks for enhanced vibration prediction capabilities.
Beside the energetic benefits such engines add to the aircraft design their rotating
large diameter fans can influence the dynamic behaviour of the complete
elastic aircraft fuselage in a very unfavourable manner.
Additional questions which arise with regard to structural dynamics and
aeroelastic stability are treated in this work.
Especially in the scenario when large rotating engine masses are to be combined with elastic
wing structures the possible occurrence of specific structural vibration
problems can be avoided by taking the gyroscopic effects into account.
As another important engine related aspect the modelling and the impact of the
engine thrust is highlighted by integrating the first order deformation
induced terms into the dynamical simulation model.
By introducing an increased coupling level between the degrees of freedom in the
equation of motion (through additional off-diagonal terms) both
eigenfrequencies and eigenmodes are affected. In the case of high engine
participation in the structural deformation we can observe a lowering of the
eigenfrequencies (in the test aeroplane up to 6[%]) and a loss in symmetry
properties in the now strongly asymmetric eigenmodes.
With the occurrence of flutter cases the critical speed had been experienced to
shift about an amount of similar magnitude. Although in the presented cases
the flutter speed moved to higher values, it was found indespensable to check
every individual aircraft configuration with regard to the stability margin.
8 citations
TL;DR: In this paper, the deformation of a thin layer of metal at the surface and eddy flow in the trapped lubricant between surfaces is calculated using the upper bound approach to calculate the power consumed by plastic deformation.
8 citations
TL;DR: In this article, a rigid smooth indentor slides at a constant sub-sonic speed on a half-space of an isotropic compressible neo-Hookean material that is initially subjected to a pre-stress aligned with the surface.
Abstract: A rigid smooth indentor slides at a constant sub-sonic speed on a half-space of an isotropic compressible neo-Hookean material that is initially subjected to a pre-stress aligned with the surface. A dynamic steady-state situation of plane strain is considered and, following Beatty and Usmani and Green and Zerna, is viewed as contact-triggered infinitesimal deformations superposed upon finite deformations due to pre-stress. The neo-Hookean material treated behaves for small strains as a linear elastic solid with Poisson's ratio 1/4. Exact solutions for both deformations are presented and, for a range of acceptable pre-stress values, these illustrate the anisotropy induced by pre-stress and a critical sliding speed corresponding to the Rayleigh speed. Imposition of the unilateral Signorini conditions of contact show that the Rayleigh speed is the upper bound for sub-sonic sliding. For pre-stress levels that fall outside this range, however, either a negative Poisson effect occurs, or a Rayleigh wave does not exist and the Signorini conditions cannot be satisfied for any sub-sonic speed.
8 citations