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, a three-dimensional model incorporating finite element (FE) meshes with infinite element (IE) boundaries for ballasted railways is proposed, where moving train loads are simulated with sliding motions of moving elements which have hard contact feature at the interface with supporting rails.
56 citations
TL;DR: In this article, the authors present the comprehensive theoretical, numerical and experimental approach adopted by EDF for crack detection in power plant rotating machinery, which consists of the derivation of a lumped cracked beam model from the three-dimensional formulation of the general problem of elasticity with unilateral contact conditions on the crack lips.
56 citations
TL;DR: In this article, the rotordynamic performance of a small rotor supported on two bump-type GFBs of length and diameter equal to 38.10 mm was analyzed and the peak amplitudes of rotor synchronous motion at the system critical speed were not proportional to the imbalance introduced.
Abstract: Gas foil bearings (GFBs) satisfy the requirements for oil-free turbomachinery, i.e., simple construction and ensuring low drag friction and reliable high speed operation. However, GFBs have a limited load capacity and minimal damping, as well as frequency and amplitude dependent stiffness and damping characteristics. This paper provides experimental results of the rotordynamic performance of a small rotor supported on two bump-type GFBs of length and diameter equal to 38.10 mm. Coast down rotor responses from 25 krpm to rest are recorded for various imbalance conditions and increasing air feed pressures. The peak amplitudes of rotor synchronous motion at the system critical speed are not proportional to the imbalance introduced. Furthermore, for the largest imbalance, the test system shows subsynchronous motions from 20.5 krpm to 15 krpm with a whirl frequency at ∼50% of shaft speed. Rotor imbalance exacerbates the severity of subsynchronous motions, thus denoting a forced nonlinearity in the GFBs. The rotor dynamic analysis with calculated GFB force coefficients predicts a critical speed at 8.5 krpm, as in the experiments; and importantly enough, unstable operation in the same speed range as the test results for the largest imbalance. Predicted imbalance responses do not agree with the rotor measurements while crossing the critical speed, except for the lowest imbalance case. Gas pressurization through the bearings' side ameliorates rotor subsynchronous motions and reduces the peak amplitudes at the critical speed. Posttest inspection reveal wear spots on the top foils and rotor surface.
56 citations
TL;DR: In this paper, the minimum gas speed for a heat exchanger (HE) at which particulate fouling is avoided is investigated, and it is found that the smallest particles in the flow deposit first on the tubes of the HE at areas of minimum flow velocities.
56 citations
TL;DR: In this article, an analytical investigation of Hopf bifurcation and hunting behavior of a rail wheelset with nonlinear primary yaw dampers and wheel-rail contact forces is presented.
Abstract: An analytical investigation of Hopf bifurcation and hunting behavior of a rail wheelset with nonlinear primary yaw dampers and wheel-rail contact forces is presented. This study is intended to complement earlier studies by True et al., where they investigated the nonlinearities stemming from creep-creep force saturation and nonlinear contacts between a realistic wheel and rail profile. The results indicate that the nonlinearities in the primary suspension and flange contact contribute significantly to the hunting behavior. Both the critical speed and the nature of bifurcation are affected by the nonlinear elements. Further, the results show that in some cases, the critical hunting speed from the nonlinear analysis is less than the critical speed from a linear analysis. This indicates that a linear analysis could predict operational speeds that in actuality include hunting.
55 citations