INTERNATIONAL JOURNAL OF ENERGY AND ENVIRONMENT SPECIAL ISSUE ON APPLIED MECHANICS RESEARCH Effect of fluid damping on vibration response of immersed rotors (original) (raw)
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Lubricants, 2016
Journal bearings are used to support rotors in a wide range of applications. In order to ensure reliable operation, accurate analyses of these rotor-bearing systems are crucial. Coupled analysis of the rotor and the journal bearing is essential in the case that the rotor is flexible. The accuracy of prediction of the model at hand depends on its comprehensiveness. In this study, we construct three bearing models of increasing modeling comprehensiveness and use these to predict the response of two different rotor-bearing systems. The main goal is to evaluate the correlation with measurement data as a function of modeling comprehensiveness: 1D versus 2D pressure prediction, distributed versus lumped thermal model, Newtonian versus non-Newtonian fluid description and non-mass-conservative versus mass-conservative cavitation description. We conclude that all three models predict the existence of critical speeds and whirl for both rotor-bearing systems. However, the two more comprehensive models in general show better correlation with measurement data in terms of frequency and amplitude. Furthermore, we conclude that a thermal network model comprising temperature predictions of the bearing surroundings is essential to obtain accurate predictions. The results of this study aid in developing accurate and computationally-efficient models of flexible rotors supported by plain journal bearings.
Self-Excited Vibrations of the Variable Mass Rotor//Fluid System
Journal of Sound and Vibration, 1998
In this paper the variable mass rotor/fluid system is considered. A rotor with variable mass is settled in hydrodynamic bearings. The dynamic properties of the rotor on which the fluid force and the impact force (due to mass variation) act are analyzed. The conditions of stable rotation are obtained applying the direct Lyapunov theorem. The self-excited vibrations are determined analytically. The Krylov-Bogolubov method is extended for solving the second order differential equation with a complex deflection function, small non-linearity and time variable parameters and a significant damping term. Analyzing the amplitude of self-excited vibrations, the conditions of unstable motion are defined. Special attention is given to the effect of interactive influence of the inertial fluid force and the impact force on the stability of rotation of the rotor. For the rotor on which the band winds up, the vibrations are obtained analytically. The results are compared with numerical ones.
Rotors of all rotating machines are always slightly imbalanced. When they rotate, the imbalance induces their lateral vibration and forces that are transmitted via the bearings into the foundations. These phenomena are significant if the rotor accelerates or decelerates and especially if it passes over the critical speeds. The vibration can be reduced if the rotor supports are equipped with damping elements. To achieve optimum performance of the damper, the damping effect must be controllable. At present time, semiactive magnetorheological squeeze film dampers are a subject of intensive research. They work on a principle of squeezing a thin film of magnetorheological liquid. If magnetic field is applied, the magnetorheological liquid starts to flow only if the shear stress between two neighbourhood layers exceeds a limit value which depends on intensity of the magnetic field. Its change enables to control the damping force. In the mathematical models, the magnetorheological liquid is usually considered as Bingham one. Application of the computer modelling method for analysis of rotors supported by rolling element bearings and magnetorheological squeeze film dampers and turning at variable angular speed requires to set up the equations of motion of the rotor and to develop a procedure for calculation of the damping force. Derivation of the equations of motion starts from the first and second impulse theorems. The pressure distribution in the thin lubricating film can be described by a Reynolds equation modified for the case of Bingham liquid. In cavitated areas, it is assumed that pressure of the medium remains constant. The hydraulic force acting on the rotor journal is then obtained by integration of the pressure distribution around the circumference and along the length of the damper. Applicability of the developed procedures was tested by means of computer simulations and influence of the control of the damping force on vibration of the rotor was analyzed.
Evaluation of bearing’s cavitation effects on the rotor dynamic behavior
Applied Mathematical Modelling, 2019
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights • Bearing's cavitation effects can affect the rotor dynamic response. • Stability threshold is changed due to bearing cavitation effects. • Cavitation effects has low influence in normal operational conditions.
International Journal of Engineering Research and Technology (IJERT), 2014
https://www.ijert.org/investigation-of-transient-response-of-an-unbalanced-aero-engine-rotor-with-semi-active-damper-system https://www.ijert.org/research/investigation-of-transient-response-of-an-unbalanced-aero-engine-rotor-with-semi-active-damper-system-IJERTV3IS10963.pdf This paper deals with dynamics and control of low pressure (LP) turbo-compressor rotor of aero-engines using electromagnetic damper system. Electro dynamically stabilized levitation for high speed rotors are essential in several rotor bearings system. The relative motion between conductor and magnetic field induces eddy currents inside the conductor, there by generating magnetic forces which are used to achieve levitation. The rotor dynamic analysis of an integral shaft over a flexible ball-bearing supports is conducted initially using finite element model. The model considers the ball-bearing contact forces, unbalance forces in compressor and turbine disks as well as gyroscopic and viscous damping terms. After predicting the critical speeds of the rotor, the design of magnetic damper begins. The parameters of the electromagnetic dampers are predicted within the operating speed range, so as to suppress the vibration amplitude at resonance conditions. Results of unbalance response are presented to illustrate the effectiveness of the controller.
Effects of Cavitation on Rotordynamic Force Matrices
When designing a turbomachine, particularly one which is to operate at high speed, it is important to be able to predict the fluid-induced forces, both steady and unsteady, acting on the various components of the machine. This paper concentrates on the fluid-induced rotordynamic forces acting upon the impeller and therefore on the bearings. Self-excited whirl, where the rotor moves away from and whirls along a trajectory eccentric to its undeflected position, can result from these fluid-induced forces. The purpose of the present work is t o study the full range of these forces so that they can be included in any rotordynamic analysis at the design stage.
The paper illustrates the experimental results obtained in several tests performed on different types of Fluid Viscous Dampers (FVDs) differentiated for load capacities, strokes and shapes. The tests were carried out on one unit for each of the three kinds of FVDs used for the structural retrofit of the Engineering Faculty Edifice A of the University of L'Aquila, peculiarly damaged by the earthquake of April 6, 2009.
Experimental analysis of the dynamic behavior of a rotating disk submerged in water
IOP Conference Series: Earth and Environmental Science, 2014
To study the dynamic behavior of turbine runners (natural frequencies and mode shapes) not only the added mass effect of still water has to be considered. Also the effect of rotation may not be neglected in the dynamic response. In the present study, the dynamic behavior of a rotating disk submerged in water is studied. For this purpose an experimental test rig has been developed. It consists of a rotating disk submerged in water that can be excited and its response can be measured from the rotating system by a slip ring system. For the excitation an impact device installed on the casing has been used. The response is measured with miniature accelerometers screwed on the disk. The influence of rotation on the dynamic response has been determined experimentally.
2018
The main objective of the research is a solution of problems, connected with increasing reliability, efficiency and safety of modern rotor machines. The class of rotary machines with varying imbalance while operating is rather diverse. These are separators, centrifuges used in chemical, food manufacturing, sugar, mining, medical industries, as well as sandblasters, washing and wringing machines and many others. On the example of washing machines within the framework of the linear theory of oscillations, the dynamics of rotor machines is investigated, and the main causes of their vibrations and noise are revealed by experimental methods. The basic problem of these machines is decreasing of their vibroactivity. We will ground the effective method of balancing rotor machines without stop during exploitation conditions – passive automatic balancing with free movement of fluid. The current work is dedicated to system research of the mentioned method, particularly for studies of fundament...