Investigations of Transient Oscillations of Rotors Supported by Magnetorheological Squeeze Film Dampers Using Bilinear Material to Model the Lubricant

2016 ◽  
Vol 821 ◽  
pp. 309-316
Author(s):  
Jaroslav Zapoměl ◽  
Jan Kozánek ◽  
Petr Ferfecki
Keyword(s):  
Squeeze Film ◽  
Lateral Vibration ◽  
Technological Solution ◽  
Damping Force ◽  
Motion Equations ◽  
Damping Effect ◽  
Squeeze Film Dampers ◽  
Nonlinear Character ◽  
Operating Regimes ◽  
Transient Oscillations

Unbalance of rotors is one of the principal causes of their lateral vibration. A technological solution frequently used to its suppression consists in placing damping devices to the rotor supports. To achieve their optimum performance their damping effect must be controllable. This is offered by squeeze film dampers utilizing the magnetorheological phenomenon to control the damping force. In mathematical models magnetorheological oils are usually represented by Bingham or Herschel-Bulkley theoretical materials. Here the magnetorheological oil is modeled by bilinear material with the yielding shear stress depending on magnetic induction. Its flow curve is continuous which contributes to reducing nonlinear character of the motion equations. The new mathematical model was applied to investigate several operating regimes of rotating machines.

Application of the Magnetorheological Squeeze Film Dampers for Reducing Energy Losses in Supports of Rotors of Rotating Machines

2017 ◽  
Author(s):  
Jaroslav Zapoměl ◽  
Petr Ferfecki
Keyword(s):  
Mathematical Model ◽  
Dynamical Analysis ◽  
Squeeze Film ◽  
Energy Losses ◽  
Damping Force ◽  
Squeeze Film Damper ◽  
Damping Effect ◽  
Wide Range ◽  
Squeeze Film Dampers ◽  
Computational Procedures

Unbalance of rotating parts is the main source of excitation of lateral oscillations of rotors, of increase of time varying forces transmitted to the rotor stationary part, and of energy losses generated in the support elements. The technological solution, which makes it possible to reduce these undesirable effects, consists in adding damping devices to the rotor supports. A simple dynamical analysis shows that to achieve their optimum performance their damping effect must be adaptable to the current operating speed. This is enabled by magnetorheological squeeze film dampers, the damping effect of which is controlled by the change of magnetic flux passing through the lubricating layer. The developed mathematical model of the magnetorheological squeeze film damper is based on assumptions of the classical theory of lubrication and on representing the magnetorheological oil by a bilinear material. The results of the carried out computational simulations show that the appropriate control of the damping force makes it possible to minimize the energy losses in a wide range of operating speeds. The development of a new mathematical model of the magnetorheological squeeze film damper, the extension of computational procedures, in which this model has been implemented, the confirmation that the magnetorheological dampers make it possible to reduce energy losses in the rotor supports, and learning more on influence of controllable dampers on behavior of rotor systems are the principal contributions of the presented paper. The carried out research highlights the possibility of reducing the energy losses by means of employing magnetorheological squeeze film dampers, which represents a new field of their prospective application.

scholarly journals A computational study on the influence of the delayed yielding phenomenon in magnetorheological oils on the steady state vibration and forces transmitted between the rotor and its frame

2018 ◽  
Vol 148 ◽  
pp. 04001
Author(s):  
Jaroslav Zapoměl ◽  
Petr Ferfecki ◽  
Jan Kozánek
Keyword(s):  
Computational Study ◽  
Practical Experience ◽  
Operating Conditions ◽  
Squeeze Film ◽  
Force Transmission ◽  
Damping Effect ◽  
Squeeze Film Dampers ◽  
Magnetorheological Damping ◽  
The Mathematical Model ◽  
Current Operating

The theoretical analyses and practical experience show that only the damping effect adaptable to the current operating conditions makes it possible to achieve optimum performance of damping devices inserted in the supports of rotating machines. This is offered by magnetorheological squeeze film dampers. The magnetorheological oils are liquids sensitive to magnetic induction. Their response to the change of a magnetic field is not instantaneous, but it is a process called the delayed yielding. The research was focused on enhancement of the mathematical model of the magnetorheological squeeze film damper by considering the delayed yielding phenomenon and on its application for the study of the influence of the delayed yielding on the force transmission between the rotor and its stationary part. The results of the computational simulations show that rising value of the delayed yielding time constant that characterizes the delayed yielding process reduces the damping effect and efficiency of the magnetorheological damping devices.

Experimental Pressures and Film Forces in a Squeeze Film Damper

1993 ◽  
Vol 115 (1) ◽  
pp. 134-140 ◽  
Author(s):  
G. L. Arauz ◽  
L. A. San Andres
Keyword(s):  
Tangential Force ◽  
Radial Force ◽  
Squeeze Film ◽  
Radial Clearance ◽  
Fluid Inertia ◽  
Damping Force ◽  
Inertia Effects ◽  
Squeeze Film Dampers ◽  
Tangential Forces ◽  
Lubricant Viscosity

The effect of whirl frequency and lubricant viscosity on the dynamic pressures and force response of an open end and a partially sealed squeeze film dampers (SFD) with a radial clearance of 0.38 mm is determined experimentally. The experiments are carried out in a damper test rig executing circular centered orbits and for whirl frequencies ranging from 33 to 83 Hz. The experimental results show that the sealed SFD configuration produces larger tangential forces than the open end SFD. The tangential (damping) force increases linearly with increasing whirl frequency. For this radial clearance fluid inertia effects in the damper are found to be negligible since the squeeze film Reynolds number is less than 1.20. Cavitation was observed in both damper configurations at high frequencies and high lubricant viscosities. This condition limited the rate of increment of the damping (tangential) force with increasing frequency and reduced the radial force when lubricant viscosity increased.

A Computational Investigation of the Steady State Vibrations of Unbalanced Flexibly Supported Rigid Rotors Damped by Short Magnetorheological Squeeze Film Dampers

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Jaroslav Zapoměl ◽  
Petr Ferfecki ◽  
Paola Forte
Keyword(s):  
Steady State ◽  
Equations Of Motion ◽  
Dynamical Behavior ◽  
Steady State Solution ◽  
Squeeze Film ◽  
Damping Force ◽  
Lateral Vibrations ◽  
Lubricating Layer ◽  
Squeeze Film Dampers ◽  
Rigid Rotors

Unbalance is the principal cause of excitation of lateral vibrations of rotors and generation of the forces transmitted through the rotor supports to the foundations. These effects can be significantly reduced if damping devices are added to the constraint elements. To achieve their optimum performance, their damping effect must be controllable. The possibility of controlling the damping force is offered by magnetorheological squeeze film dampers. This article presents an original investigation of the dynamical behavior of a rigid flexibly supported rotor loaded by its unbalance and equipped with two short magnetorheological squeeze film dampers. In the computational model, the rotor is considered as absolutely rigid and the dampers are represented by force couplings. The pressure distribution in the lubricating layer is governed by a modified Reynolds equation adapted for Bingham material, which is used to model the magnetorheological fluid. To obtain the steady state solution of the equations of motion, a collocation method is employed. Stability of the periodic vibrations is evaluated by means of the Floquet theory. The proposed approach to study the behavior of rigid rotors damped by semi-active squeeze film magnetorheological dampers and the developed efficient computational methods to calculate the system steady state response and to evaluate its stability represent new contributions of this article.

Dynamic Response and Stability of Pressurized Gas Squeeze-Film Dampers

1998 ◽  
Vol 120 (1) ◽  
pp. 306-311
Author(s):  
N. K. Arakere ◽  
B. C. Ravichandar
Keyword(s):  
High Temperature ◽  
Gas Flow ◽  
Squeeze Film ◽  
Orifice Diameter ◽  
Oil Lubrication ◽  
Damping Force ◽  
Circular Orbits ◽  
Foil Bearings ◽  
Flexible Rotors ◽  
Squeeze Film Dampers

Compressible squeeze films, an important and interesting area in gas lubrication, have been relatively neglected in recent times. Aircraft engines are being designed with light weight flexible rotors operating at high speeds and temperatures that may eventually eliminate the use of oil lubrication. A gas or air SFD might be a viable alternative to a conventional oil damper, in high temperature applications that preclude the use of oil lubrication. Oil squeeze-film dampers currently being used for rotordynamic control will not be viable at temperatures above 350°F, due to limitations on lubricant oil temperature. A good example of gas SFD application is in conjunction with high temperature gas lubricated foil bearings, which inherently have low damping. This paper presents an analysis of pressurized air dampers, similar to a hydrostatic gas bearing. Pressurized air is supplied through a series of orifices in the bearing midplane. Airflows through the orifices and the resulting pressure forces are calculated using a simple gas-flow model, as in orifice compensated hydrostatic bearings. A small perturbation analysis of the shaft center yields the stiffness and damping coefficients, for centered circular orbits. Damping characteristics are studied for a range of parameters such as supply pressure, orifice diameter, pocket volume, orbit size, number of orifices and shaft speed. Results show that maximum damping forces are generated for near choking flow conditions. The damping coefficient becomes negligible at frequencies above 350 Hz. For damping force to be present, the gas pressurization has to exert a force on the rotor opposing the instantaneous velocity, or, 90 degrees out of phase with displacement. Linear stability of unbalanced dampers undergoing centered circular orbits, is also investigated, in view of their relevance to rotordynamics. Damper design curves are presented for various parameters.

scholarly journals Imbalance Response and Damping Force Coefficients of a Rotor Supported on End Sealed Integral Squeeze Film Dampers

1999 ◽  
Author(s):  
Oscar C. De Santiago ◽  
Luis A. San Andrés
Keyword(s):  
High Performance ◽  
Effective Means ◽  
Squeeze Film ◽  
Damping Force ◽  
Damping Coefficients ◽  
Squeeze Film Dampers ◽  
Flow Through ◽  
Structural Isolation ◽  
The Impact ◽  
Severe Penalty

To this date, squeeze film dampers (SFDs) are effective means to reduce vibrations and provide structural isolation in high performance aeroengine systems. Integral squeeze film dampers (ISFDs) offer distinct advantages such as reduced overall weight, accuracy of positioning, and a split segment construction allowing easier assembly, inspection and retrofit. An experimental study is conducted to evaluate the effectiveness of integral dampers in attenuating the imbalance response of a massive test rotor. Damping coefficients for end sealed dampers are identified from the peak rotor responses due to imbalances while passing through the fundamental critical speeds. Impact response measurements at null rotor speed are also conducted to identify system damping coefficients for increasing values of the lubricant temperature. The impact tests and imbalance response measurements demonstrate that end gap seals increase effectively the ISFD viscous damping coefficients and without a severe penalty in the flow through the dampers. The experiments further demonstrate that the amplitudes of rotor synchronous response are proportional to the imbalance displacements without subsynchronous frequencies or (nonlinear) jump responses.

Transformer Eddy Current Dampers for the Vibration Control

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Andrea Tonoli ◽  
Nicola Amati ◽  
Mario Silvagni
Keyword(s):  
Vibration Control ◽  
Eddy Current ◽  
Magnetic Circuit ◽  
Design Procedure ◽  
Squeeze Film ◽  
Lateral Vibration ◽  
Geometrical Characteristics ◽  
Squeeze Film Dampers ◽  
Lorentz Forces ◽  
Moving Conductor

Eddy current dampers are promising for the passive and semiactive vibration control of mechanical structures. Among them, the “motional” types are based on Lorentz forces between a moving conductor and a stationary magnetic field. On the contrary, “transformer” ones exploit electromagnetic forces varying the reluctance of the magnetic circuit due to the motion of a part of the damper. Considering the simplicity of the layout, transformer configurations seem to be very promising as alternative to traditional rubber or squeeze film dampers to control the lateral vibration of rotating machines. The aim of the present paper is to investigate the dynamic behavior of transformer eddy current dampers integrated in a mechanical structure. The electromechanical system is modeled using the Lagrange approach in terms of the magnetic flux linkages in the electromagnets. The mathematical models have been experimentally validated using two test benches with different layouts and geometrical characteristics of the magnetic circuit. The modeling approach allows to propose a design procedure of this type of damper.

Response of Two-Disk Rotor with Squeeze Film Dampers and its Variation with Parameters

2011 ◽  
Vol 117-119 ◽  
pp. 369-372
Author(s):  
Tao Sun ◽  
Wei Yang Qin ◽  
Xu Dong Jiao
Keyword(s):  
Low Pressure ◽  
Squeeze Film ◽  
Dynamical Response ◽  
Mass Ratio ◽  
Motion Equations ◽  
Squeeze Film Damper ◽  
Rotating Speed ◽  
System Parameters ◽  
Squeeze Film Dampers ◽  
Vibration Responses

This paper investigated the variation of dynamical response of a low pressure rotor in turbo-shaft engine with its system parameters. Based on the model of low pressure rotor, a dynamical simplified model of two-disk rotor with Squeeze Film Damper at each end was built. Its motion equations were derived. The numerical method was applied to solve the 12-dimensions differential equations. The influence of some parameters, e.g., rotating speed, eccentricity and its phase angle, mass ratio of two disks, were analyzed. From simulation results, it can be seen that when phase difference of two disks’ eccentricity is π, the two disks have their minimum vibration amplitude respectively. When their phase is identical, their vibration responses reach maximum values. The larger the mass of mid-span disk is, the larger the vibrations of two disks are. When mass of mid-span is lesser than that of overhung rotor, the response of system will decrease.

Dynamic Response and Stability of Pressurized Gas Squeeze-Film Dampers

1995 ◽  
Author(s):  
Nagaraj K. Arakere ◽  
B. C. Ravichandar
Keyword(s):  
High Temperature ◽  
Gas Flow ◽  
Squeeze Film ◽  
Orifice Diameter ◽  
Oil Lubrication ◽  
Damping Force ◽  
Foil Bearings ◽  
Flexible Rotors ◽  
Squeeze Film Dampers ◽  
Damper Design

Abstract Compressible squeeze films, an important and interesting area in gas lubrication, have been relatively neglected in recent times. Aircraft engines are being designed with light weight flexible rotors operating at high speeds and temperatures that may eventually eliminate the use of oil lubrication. A gas or air SFD might be a viable alternative to a conventional oil damper, in high temperature applications that preclude the use of oil lubrication. Oil squeeze-film dampers currently being used for rotordynamic control will not be viable at temperatures above 350 °F, due to limitations on lubricant oil temperature. Gas SFD’s are well suited for use in high temperature gas lubricated foil bearings. This paper presents an analysis of pressurized air dampers, similar to a hydrostatic gas bearing. Pressurized air is supplied through a series of orifices in the bearing midplane. Air flows through the orifices and the resulting pressure forces are calculated using a simple gas-flow model, as in orifice compensated hydrostatic bearings. A small perturbation analysis of the shaft center yields the stiffness and damping coefficients, for centered circular motions. Damping characteristics are studied for a range of parameters such as supply pressure, orifice diameter, pocket volume, orbit size, number of orifices and shaft speed. Results show that maximum damping forces are generated for near choking flow conditions. The damping force becomes negligible at frequencies above 350 Hz. For damping force to be present, the gas pressurization has to exert a force on the rotor opposing the instantaneous velocity, or, 90 degrees out of phase with displacement Linear stability of unbalanced dampers undergoing centered circular orbits, is also investigated, in view of their relevance to rotordynamics. Damper design curves are presented for various parameters.

Orbit-Based Identification of Damping Coefficients for a Rotor Mounted on Off-Centered Squeeze Film Dampers and Including Support Flexibility

2000 ◽  
Author(s):  
Sergio Diaz ◽  
Luis San Andrés
Keyword(s):  
Least Square ◽  
Squeeze Film ◽  
Dramatic Improvement ◽  
Jet Engines ◽  
Damping Force ◽  
Force Coefficients ◽  
Damping Coefficients ◽  
Process Gas ◽  
Squeeze Film Dampers ◽  
Rotor Bearing

Squeeze film dampers (SFDs) provide structural isolation and energy dissipation in jet engines and process gas compressors. The determination of linearized damping force coefficients to allow the use of well-developed linear techniques is of importance in the design and reliability analysis of rotor-bearing systems dynamic response and stability. Two parameter identification techniques to estimate the linearized viscous damping coefficients of a rotor-bearing system based on the measurement of rotor displacements are presented. The first method applies a least-square curve fitting to the damping force, while the second determines the elliptic orbit that best approximates the actual one. The filtered orbit method is applied to identify the damping force coefficients from measurements of the synchronous response of a test rotor mounted on off-centered SFDs. The identified system damping coefficients (direct and cross-coupled) are found to be independent of the imbalance magnitude and shaft speed, in spite of the large amplitude rotor motions within the dampers’ clearances. A modification of the method to include the damper bearing support flexibility shows a dramatic improvement on the predicted rotor response and more reliable force coefficients.

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