The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Sagheer Ahmad - One of the best experts on this subject based on the ideXlab platform.
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Rotor Casing Contact Phenomenon in Rotor Dynamics — Literature Survey
Journal of Vibration and Control, 2010Co-Authors: Sagheer AhmadAbstract:Rubbing between a Rotor and its casing has long been recognized as a major contributor to excessive maintenance and in general to machinery failure. During contact, the high energy of the Rotor, dissipated by the frictional force, can severely damage both parts, and can lead to total destruction of the machine. The purpose of this article is to provide an overview of the state of the art on the Rotor-casing contact phenomenon in Rotor Dynamics, describing aspects of different physical parameters such as stiffness, damping, Coulomb friction, acceleration of Rotor, support structure asymmetry, thermal effects and disk flexibility etc. The intention is to summarize the results presented in literature which are beneficial for the designers of rotating machines and also a source of research inspiration for the scientists and technologists working in this field.
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Rotor casing contact phenomenon in Rotor Dynamics-literature survey
JVC Journal of Vibration and Control, 2010Co-Authors: Sagheer AhmadAbstract:Rubbing between a Rotor and its casing has long been recognized as a major contributor to excessive maintenance and in general to machinery failure. During contact, the high energy of the Rotor, dissipated by the frictional force, can severely damage both parts, and can lead to total destruction of the machine. The purpose of this article is to provide an overview of the state of the art on the Rotor-casing contact phenomenon in Rotor Dynamics, describing aspects of different physical parameters such as stiffness, damping, Coulomb friction, acceleration of Rotor, support structure asymmetry, thermal effects and disk flexibility etc. The intention is to summarize the results presented in literature which are beneficial for the designers of rotating machines and also a source of research inspiration for the scientists and technologists working in this field.
Pavel Novotný - One of the best experts on this subject based on the ideXlab platform.
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Effective thrust bearing model for simulations of transient Rotor Dynamics
International Journal of Mechanical Sciences, 2019Co-Authors: Pavel Novotný, Jozef Hrabovský, Jaroslav Juračka, Jiří Klíma, Vladimir HortAbstract:Abstract The paper introduces a new fast combined analytical and numerical computation model of thrust bearing, which can be applied to analyse the transient Rotor Dynamics of rotating machines. The bearing model is designed to allow an efficient solution to long-term processes while retaining its high-level capability to describe the bearing Dynamics and tribology. The model includes the effects of lubricant inlet temperature and pressure and also effects of temperature, shear rate and inertia of the bearing lubricant layer. This bearing model used in the virtual turbocharger allows detailed analysis of both the design of the bearing itself and the vibration and noise issues of the turbocharger. The results obtained through the bearing model are verified using Computational Fluid Dynamics (CFD) and by technical experiments on real exhaust gas turbochargers.
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The effective computational model of the hydroDynamics journal floating ring bearing for simulations of long transient regimes of turbocharger Rotor Dynamics
International Journal of Mechanical Sciences, 2018Co-Authors: Pavel Novotný, Petr Škara, Juraj HliníkAbstract:Abstract The paper presents an efficient and numerically stable calculation model of a journal plain floating ring bearing. The computational model is based on the numerical solution of the Reynolds equation in combination with the analytical description of the resulting variables. This model is used in a virtual turbocharger assembled in multibody systems. This approach allows to effectively solve transient events, such as turbocharger run-up, considering issues of Rotor Dynamics, tribology of bearings, flows of lubricant in the channels and potentially also gas flow through the sealing system. The model of the bearing includes the influence of the inlet and outlet channels and the non-cylindrical shape of the bearing surfaces. Influence of lubricant and structure temperature changes caused by shear stresses in lubrication film and related changes in the lubricant properties is also considered. The paper also presents the numerical implementation of the computational models and the verification of these models using technical experiments with the turbocharger of a diesel engine.
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Multibody Based Tool for Simulation of the Turbocharger Rotor Dynamics
Applied Mechanics and Materials, 2016Co-Authors: Jiří Knotek, Pavel Novotný, Ondřej MaršálekAbstract:The turbocharger is a unique example of the rotating machinery. Not only for its very high speed, but also because of its compact design and difficult operating conditions (i.e. high temperature, harsh vibrations, etc.). Moreover, measuring of most parameters characterizing the Rotor Dynamics is a very difficult task. Thus, it is advantageous to replace the real turbocharger by computational model and determine the turbocharger Rotor Dynamics using simulation tool. The development of such tool will be presented in this paper.
REAL DUPONT - One of the best experts on this subject based on the ideXlab platform.
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Robust Rotor Dynamics for high-speed air bearing spindles
Precision Engineering, 2015Co-Authors: REAL DUPONTAbstract:For ultra-precision machining machine tool components need to operate outside critical frequencies of the machining system to avoid insufficient surface finish caused by vibrations. This particularly applies to tooling spindles as those are generally the component of a machine tool with low stiffness and damping values. Surface finish and shape of a machined part rely directly on the overall accuracy in motion of the tooling spindle over the entire machining parameter and speed range. Thus spindle designs for an operation outside critical frequencies combined with high stiffness and damping values are crucial for ultra-precision machining. For sufficient stiffness properties bearing gaps of gas bearings have to have a size of only a few microns and show a distinct sensitivity on temperature and for journal bearings also on speed. This again means that bearing properties change with temperature and speed. Considering a spindle system comprising a rigid shaft rotating in a radial/axial bearing system with changing stiffness and damping properties leads to a resonance speed map with changing rigid mode resonance speeds. This paper treats the influence of shaft speed and temperature on bearing gaps from which rigid mode resonance speeds for a shaft spinning in a bearing system are derived. The quoted influence of centrifugal load and temperature on bearing stiffness, damping and load capacity can be applied to any kind of gas bearing. Therefore the calculation of bearing stiffness, damping or load capacity is not treated in detail. The reader will be shown that there are simple design rules for air bearing systems and shafts of high-speed tooling spindles to avoid critical speeds through the entire speed range. Finally, methods of how to prove the initial design goals and how to verify Dynamics of high-speed spindles in production will be presented to the reader. It will also be shown that there are production high-speed spindles available which do not include any critical speed within their speed range and thus show robust Rotor Dynamics with extremely low errors in motion. Procedures in design, validation and application treated in this paper shall give the reader not only design guidelines for spindles to avoid critical spindle speeds within its speed range, but also recommendations for machine tool builders and end-users for a machine operation taking machine and Rotor Dynamics into account. As the knowledge for this paper is predominantly based on the experience and work of the author himself only a few references are used. However presented testing results entirely confirm the approach presented in this paper.
Nicolò Bachschmid - One of the best experts on this subject based on the ideXlab platform.
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Increasing the robustness of fault identification in Rotor Dynamics by means of M-estimators
Mechanical Systems and Signal Processing, 2007Co-Authors: Paolo Pennacchi, Andrea Vania, Nicolò BachschmidAbstract:Abstract One of the most common problems in Rotor Dynamics is the identification of faults and model-based methods are often used for this purpose. In some applications, the least-squares (LS) estimate is used to find out the position and the severity of impending faults on the basis of experimental vibration data of rotating machinery. Anyhow LS are not very robust with respect to possible outliers (noise and gross errors) in the experimental data and to inaccuracies in the model. The introduction of weights in the LS algorithm has proven to be effective in increasing the robustness and successful experimental cases, both on test rigs and on real machines, are reported in literature. However, the arbitrary choice of the weights is normally based on operators’ experience. In this paper, an improvement is presented by introducing a method that is robust in itself, the M-estimate, which allows defining automatically the weights. This method is general and can be applied in every problem of regression or estimation, not necessarily related to Rotor Dynamics. The fundamental theoretical aspects are introduced in the first part, while several experimental test cases are presented by means of fault identification on a test rig and on a gas turbo generator in the second part of the paper. The obtained results highlight the increasing of the accuracy allowed by M-estimate.
Guang Meng - One of the best experts on this subject based on the ideXlab platform.
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Rotor Dynamics behavior of turbo-expander involving droplet impact
Mathematical and Computer Modelling of Dynamical Systems, 2016Co-Authors: Hong Guang Li, Shengtong Zhou, Xiaohu Wang, Fucai Li, Ming Li, Guang MengAbstract:ABSTRACTThis paper dedicates on the Rotor Dynamics behaviour research on the turbo-expander Rotor system involving droplet impact. A stochastic model based on Beta distribution and Bernoulli distribution of droplet generation is established and the formulations of droplet impact forces are deduced, which is applied on the Rotor Dynamics equations of the tilting pad bearing supported turbo-expander considering the temperature gradient for a further analysis. A time domain research is carried out and a conclusion that continuously droplet impact will perturb the steady vibration of the turbo-expander Rotor system is obtained. Monte Carlo method is implemented for a statistics Dynamics research and the results suggests that in the design of expander impellers, in order to decrease the uncertainty brought by droplet impact, the number of channels should be as few as possible, the droplet impact should be controlled to occur uniformly, and the collision, entrainment of the primary droplets and the stripping of...
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Rotor Dynamics behavior of turbo-expander involving droplet impact
Mathematical and Computer Modelling of Dynamical Systems, 2016Co-Authors: Shengtong Zhou, Huiyu Bai, Xiaohu Wang, Rui Zhu, Guang MengAbstract:This paper dedicates on the Rotor Dynamics behaviour research on the turbo-expander Rotor system involving droplet impact. A stochastic model based on Beta distribution and Bernoulli distribution o...
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Rotor Dynamics Behavior of Tilting Pad Bearing Supported Turbo-Expander Considering Temperature Gradient
Journal of Computational and Nonlinear Dynamics, 2015Co-Authors: Ming Li, Huiyu Bai, Hong Guang Li, Xiaohu Wang, Rui Zhu, Fucai Li, Xingxing Liu, Guang MengAbstract:This paper dedicates on the Rotor Dynamics behavior analysis on a tilting pad bearing supported turbo-expander Rotor system considering temperature gradient. Both numerical and experimental investigations are conducted intensively. The influence of the temperature gradient is modeled as the change of the lubrication oil viscosity and the length variation of the clearance due to the cryogenic thermal expansion of the journal. The analytical expressions of the tilting pad bearing oil-film force are then amended and substitute into the lumped parameter model of the turbo-expander Rotor Dynamics. Linear analysis based on this model indicates that the existence of the temperature gradient can stabilize the turbo-expander Rotor system to an extent, while the nonlinear analyses reveal that the temperature gradient will advance the occurrence of the quasi-periodic motion and break the equilibrium of the vibration between the expander side and the compressor side. Furthermore, an experimental system is established and the experimental results show that the temperature of the tilting pad bearing is influenced by the environment temperature greatly; the spectrum of the displacement of the Rotor is dominated by the synchronous frequency of the impellers and bearings. The experiment results also observe the vibration amplitude decreases when the environment temperature gets down and grows when the rotating speed increases. At the same time, the sensitivity of the vibration amplitude versus rotating speed decreases as the environment temperature rises, and vice versa.
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Nonlinear Rotor Dynamics on turbo expander with unbalanced bearing force caused by temperature difference
JOURNAL OF VIBROENGINEERING, 2015Co-Authors: Ming Li, Xianbo Liu, Hong Guang Li, Fucai Li, Cheng Li, Guang MengAbstract:This paper dedicates on the non-dimensional nonlinear Rotor Dynamics analysis of a turbo expander under unbalanced bearing forces caused by the temperature difference. The turbo expander Rotor system is abstracted to a strictly symmetric lumped parameter model. The influence of temperature difference is simplified to the ratio of oil viscosity, which is applied on Capone oil film model. 1-Dimensional and 2-Dimensional bifurcation analysis are implemented in order to obtain the dynamic characteristics of the turbo expander Rotor system. It can be concluded that the compressor wheel and the expander wheel are of the same pattern of motion in spite of the existence of the temperature difference; High temperature difference results in a high entrance point of 1-periodic motion to quasi-periodic motion, but the entrance point keeps still when the ratio of viscosity reaches some critical value. The oil-whirl, first and second order oil whip of sliding bearings are the most important factors influencing the asymmetric vibration of the compressor wheel and the expander wheel.
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turbocharger Rotor Dynamics with foundation excitation
Archive of Applied Mechanics, 2009Co-Authors: Guangchi Ying, Guang Meng, Jianping JingAbstract:To investigate the effect of foundation excitation on the dynamical behavior of a turbocharger, a dynamic model of a turbocharger Rotor-bearing system is established which includes the engine’s foundation excitation and nonlinear lubricant force. The Rotor vibration response of eccentricity is simulated by numerical calculation. The bifurcation and chaos behaviors of nonlinear Rotor Dynamics with various rotational speeds are studied. The results obtained by numerical simulation show that the differences of dynamic behavior between the turbocharger Rotor systems with/without foundation excitation are obviously. With the foundation excitation, the dynamic behavior of Rotor becomes more complicated, and develops into chaos state at a very low rotational speed.
