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Wang W.,Beijing University of Chemical Technology | Li Q.,Beijing University of Chemical Technology | Gao J.,Beijing University of Chemical Technology | Yao J.,Beijing University of Chemical Technology | Allaire P.,Rotor Bearing Solutions International
Mechanical Systems and Signal Processing | Year: 2015

Centrifugal compressor testing with magnetic bearing excitations is the last step to assure the compressor rotordynamic stability in the designed operating conditions. To meet the challenges of stability evaluation, a new method combining the rational polynomials method (RPM) with the weighted instrumental variables (WIV) estimator to fit the directional frequency response function (dFRF) is presented. Numerical simulation results show that the method suggested in this paper can identify the damping ratio of the first forward and backward modes with high accuracy, even in a severe noise environment. Experimental tests were conducted to study the effect of different bearing configurations on the stability of rotor. Furthermore, two example centrifugal compressors (a nine-stage straight-through and a six-stage back-to-back) were employed to verify the feasibility of identification method in industrial configurations as well. © 2015 Elsevier Ltd. Source

Fox C.S.,Drexel University | McKenna K.L.,Drexel University | Allaire P.E.,Rotor Bearing Solutions International | Mentzer R.M.,Cedars Sinai Medical Center | And 2 more authors.
Journal of Cardiac Surgery | Year: 2015

We present a review of the evolution of total artificial hearts (TAHs) and new directions in development, including the coupling of VADs as biventricular TAH support. © 2015 Wiley Periodicals, Inc. Source

Dousti S.,Rotor Bearing Solutions International | Dousti S.,University of Virginia | Fittro R.L.,University of Virginia
Proceedings of the ASME Turbo Expo | Year: 2015

Water lubricated bearings used in nuclear coolant pumps and sub-sea applications exhibit large lubricant inertia forces in the magnitude order of viscous forces. To model these bearings the traditional Reynolds equation is not adequate. An extended Reynolds equation is developed in this study which takes into account the turbulence and inertia effects: both convective and temporal. The most complete form of temporal inertia which applies to the turbulent regime as well, is developed that consists of primary and secondary temporal inertia terms. The convective inertia model follows Constantinescu's approach [1,2]. The turbulence model is also Constantinescu's which is tuned with a CFD work. The dynamic coefficients including the lubricant added mass coefficients of a full cylindrical fixed geometry water bearing are obtained. It is observed that the convective inertia increases the load capacity and stability of the bearing. Significant lubricant added mass coefficients comparable to the shaft mass are calculated, which exhibit destabilizing effects in general. Copyright © 2015 by ASME. Source

Cao J.,Candu Energy Inc. | Dimond T.,Rotor Bearing Solutions International | Allaire P.,University of Virginia
Proceedings of the ASME Turbo Expo | Year: 2014

This paper provides a time transient method for solving coupled lateral and torsional analysis of a flexible rotorbearing system including gyroscopic effects, nonlinear short journal bearings, nonlinear short squeeze film dampers, and external nonlinear forces/torques. The rotor is modeled as linear, and the supporting components, including bearings and dampers, are modeled as nonlinear. An implicit Runge-Kutta method is developed to solve the nonlinear equations of motion with non-constant operating speed since the unbalance force and the gyroscopic effect are related to both the rotational speed and the acceleration. The developed method is compared with previous torsional analysis first to verify the nonlinear transient solver. Then the coupled lateral and torsional analysis of a flexible 3-disk rotor with nonlinear bearings and nonlinear dampers driven by a synchronous motor is approached. The acceleration effects on lateral and torsional amplitudes is presented in the analysis. The developed method can be used to study the rotor motion with non-constant rotational speed, such as during startup, shutdown, going through critical speeds, blade loss force, or other sudden loading. Copyright © 2014 by ASME. Source

Cao J.,Cao Consulting | Dimond T.,Rotor Bearing Solutions International | Allaire P.,University of Virginia
ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) | Year: 2014

This paper presents dynamic behaviors of a flexible rotor supported on nonlinear bearings and nonlinear squeeze film dampers. The nonlinear bearing and damper forces, which depend on instantaneous nodal displacements and velocities, are calculated at each time step through closed form solutions of Reynolds equation. Such combinations of fluid film bearings and squeeze film dampers are often used in industrial machines such as compressors and steam turbines to increase system damping. No previous works have studied the nonlinear time transient analysis of a fluid film bearing and damper combination. To describe the coupled motion of shaft, bearing and squeeze film damper, a method of assembling both the linear rotor and the nonlinear components is developed. The numerical transient analyses are applied to a 3-disk rotor supported with nonlinear short plain journal bearings and nonlinear short squeeze film dampers. Squeeze film dampers, introduced to the system, increase dynamic stability of the system under a wide range of system rotational speeds, and decrease the bearing forces under severe unbalance forces. Different nonlinear rotor dynamic behavior, such as subharmonic, super-harmonic and torus orbits are shown in transient analyses. This type of analysis can be employed to study whether a centering spring is required in the damper or not. Copyright © 2014 by ASME. Source

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