Active Elimination of Oil Whip and Dry Whip Through the Use of Electromagnetic Exciter

2010 ◽  
Author(s):  
Chen-Chao Fan ◽  
Wen-Chang Tsao ◽  
Min-Chun Pan ◽  
Jhe-Wei Syu
Keyword(s):  
Root Locus ◽  
Constant Frequency ◽  
Motion Equations ◽  
Rotary Machine ◽  
Oil Whip ◽  
Fluid Handling ◽  
Excited Vibration ◽  
Small Clearance ◽  
Secondary Phenomenon ◽  
Operational Range

Oil whip induces self-excited vibration in fluid-handling machines, and what is worse, it can cause self-excited reverse precessional full annular rub, known as “dry whip”, which is a secondary phenomenon resulting from a primary cause, and may lead to a catastrophic failure of machines; that is, “coincidence of oil whip and dry whip” that occurs repeatedly with constant frequency and amplitude in small clearance cases. This paper presents a technique using an electromagnetic exciter (EE), that can raise the threshold of stability of a rotary machine and then eliminate the coincidence of oil whip and dry whip in the normal operational range. In addition, an experimental rotor rig, a general model of a rotor/beating system with an EE and corresponding governing motion equations, computation of stiffness supplied by the EE, design example, stability judged by root locus plots, and criterion for eliminating the coincidence of the oil whip and dry whip are constructed, derived and established. Experimental results demonstrate that the coincidence of oil whip and dry whip of the rotary machine can be removed effectively. These results can be used to diagnose rub and fluid-induced instability in this kind of rotary machine.

Study of Start-Up Vibration Response for Oil Whip and Dry Whip Through Hilbert Huang Transform

2011 ◽  
Author(s):  
Chen-Chao Fan ◽  
Jhe-Wei Syu ◽  
Min-Chun Pan ◽  
Wen-Chang Tsao
Keyword(s):  
Energy Concentration ◽  
Full Spectrum ◽  
Constant Frequency ◽  
Hilbert Spectrum ◽  
Hilbert Huang Transform ◽  
Oil Whip ◽  
Fluid Handling ◽  
Mode Decomposition ◽  
Excited Vibration ◽  
Concentration Changes

Oil whip induces self-excited vibration in fluid-handling machines, and what is worse, it can cause self-excited reverse precessional full annular rub, known as “dry whip” which is a secondary phenomenon resulting from a primary cause and may lead to a catastrophic failure of machines; that is, “coincidence of oil whip and dry whip” that occurs repeatedly with constant frequency and amplitude in small clearance cases of fluid-handling machines. Early detection of rub malfunction is essential to avoid damage. Hilbert Huang Transform, which included an empirical mode decomposition and Hilbert spectral analysis, is applied. Hilbert Huang Transform is a great method for analyzing non-linear and non-stationary signals, such as rotor startup signals. Hilbert Huang Transform clearly indicates instability at its initiation stage, and energy concentration changes by different stages. Malfunctions like rub can not observe by Hilbert spectrum. Hilbert spectrum combining full spectrum is developed, as know full Hilbert spectrum, to interpret the rub. The coincidence of oil whip and dry whip is observed definitely through FHS. The advantage of the full Hilbert spectrum is to offer a faster, more efficient method to diagnose fluid-induced instability.

scholarly journals STABILITY ANALYSIS OF GLOBE VALVE USING CLASSICAL TECHNIQUES

2021 ◽  
Vol 26 (4) ◽  
pp. 106-112
Author(s):  
ABORISADE DAVID OLUGBENGA ◽  
OKELOLA MUNIRU OLAJIDE ◽  
ADEWUYI PHILIP ADESOLA
Keyword(s):  
Stability Analysis ◽  
Oil And Gas ◽  
Nyquist Plot ◽  
Order System ◽  
Root Locus ◽  
Fluid Handling ◽  
Work Model ◽  
Globe Valve ◽  
And Control ◽  
Valve Model

The importance of globe valve in fluid handling and control cannot be overemphasized. It is useful in oil and gas applications. If globe valve is not properly modelled, its primary purpose of regulation of fluid flow may be defeated. In this work, model of globe valve is developed from basic mechanical principles.  The resulting model is a second order system whose response to a step input signal gives no overshoot. Further stability analysis with bode plot, Nyquist plot and root locus plot give a stable system indicating that the developed globe valve model is suitable for relevant areas of application.

The Influence of Oil-Film Journal Bearings on the Stability of Rotating Machines

1946 ◽  
Vol 13 (3) ◽  
pp. A211-A220
Author(s):  
A. C. Hagg
Keyword(s):  
Rotational Frequency ◽  
Journal Bearings ◽  
The Self ◽  
Stability Criteria ◽  
Oil Film ◽  
Oil Whip ◽  
Upper Limit ◽  
Excited Vibration ◽  
Tilting Pad ◽  
The Stability

Abstract The self-excited vibration caused by the lubricating films of journal bearings and commonly called oil-film whirl or oil whip is discussed. The upper limit of whirling frequency has been found to be one-half rotational frequency in the general case; actually the phenomenon will manifest itself at a frequency which is invariably below this limit. Stability criteria have been developed for certain common systems in terms of bearing and rotor parameters. The tilting-pad bearing of Michell has been established as a so-called “stable” or “nonwhirling” bearing. This bearing and related types are probably the only oil-film journal bearings which are incapable of exciting oil whip, regardless of the system to which they are applied. Qualitatively the results of the paper appear to be in agreement with observations. In certain cases, results have been substantiated experimentally.

Active Self-Excited Vibration Elimination of Rotating Machine With an Electromagnetic Exciter

2009 ◽  
Author(s):  
Chen-Chao Fan ◽  
Min-Chun Pan
Keyword(s):  
Journal Bearings ◽  
Rotor System ◽  
Stable Method ◽  
Rotating Machine ◽  
Oil Whip ◽  
Control Scheme ◽  
Oil Whirl ◽  
Excited Vibration ◽  
Load Carrying ◽  
Auxiliary Device

Journal bearings are commonly used in large rotary machineries because they have excellent mechanical and geometric properties as well as large load-carrying capacities. Nevertheless, the oil whirl and oil whip instabilities limit their applications due to their insufficient stiffness at high running speeds. This paper presents a method to increase the stiffness of a rotating machine using an electromagnetic exciter (EE), which can raise the threshold of instability of the rotating machine and eliminate fluid-induced instability. The EE is a controllable auxiliary device that can provide additional stiffness to the bearings to increase the operating ranges of a rotating machine, while the journal bearings act as load-carrying devices. Together, the EE complements the JB to stiffen the rotor system and raise the threshold of instability. A simple control scheme is used to calculate the amount of supplemental stiffness supplied by the EE. The experimental results demonstrate that the oil whirl and oil whip instabilities of the rotating machine can be eliminated effectively, even at higher running speeds. The advantage of the EE is to offer a faster, more stable method to eliminate fluid-induced instability.

Stabilizing Hydrodynamic Bearing Oil Whip With μ-Synthesis Control of an Active Magnetic Bearing

2015 ◽  
Author(s):  
Alexander H. Pesch ◽  
Jerzy T. Sawicki
Keyword(s):  
Rotation Speed ◽  
Stability Limit ◽  
Magnetic Bearing ◽  
Active Magnetic Bearing ◽  
Related Phenomenon ◽  
Test Rig ◽  
Hydrodynamic Bearing ◽  
Oil Whip ◽  
Oil Whirl ◽  
Excited Vibration

Oil whip is a self-excited vibration in a hydrodynamic bearing which occurs when the rotation speed is above approximately twice the first natural frequency. Because of this, the oil whip phenomenon limits the operational speed of a rotor system on hydrodynamic bearings. Below the oil whip threshold, the related phenomenon of oil whirl can cause large vibrations at frequencies below half the rotation speed. A method is presented for stabilizing oil whip and oil whirl in a hydrodynamic bearing with an active magnetic bearing (AMB). The AMB controller is designed with μ-synthesis model-based robust control utilizing the Bently-Muszynska fluid film bearing model, which predicts the unstable phenomena. Therefore, the resulting AMB controller stabilizes the natural instability in the hydrodynamic bearing. Rotor speed is taken into account by use of a parametric uncertainty such that the method is robust to changes in running speed. The proposed method is demonstrated on an experimental hydrodynamic bearing test rig. Details of the test rig and implementation of the AMB controller design are presented. Waterfall plots for the controlled and uncontrolled system are presented which demonstrate the improved stability limit.

Self-Excited Vibration of Statically Unloaded Pads in Tilting-Pad Journal Bearings

1983 ◽  
Vol 105 (3) ◽  
pp. 377-383 ◽  
Author(s):  
M. L. Adams ◽  
S. Payandeh
Keyword(s):  
Journal Bearing ◽  
Nonlinear Dynamic Analysis ◽  
Journal Bearings ◽  
Practical Significance ◽  
Oil Whip ◽  
Excited Vibration ◽  
Tilting Pad ◽  
Close Relationship ◽  
Tilting Pad Journal Bearing ◽  
Tilting Pad Journal Bearings

A time-transient nonlinear dynamic analysis is presented to study the motion of statically unloaded journal-bearing tilting pads. The major finding is that unloaded pads can exhibit a strong sub-synchronous self-excited vibration. The frequency of this periodic motion is somewhat below half the rotational speed and bears a close relationship to self-excited oil-whip vibration of rotors on lightly loaded non-tilting pad journal bearings. The identification of this type of self-excited pad vibration has practical significance to the solution of problems in applications involving damage to unloaded pads. A comprehensive parametric study is presented and shows which tilting-pad journal bearing parameters are significant to self-excited pad vibration and its elimination.

Analysis of Dynamically Loaded Floating Bush Bearing With Flexible Shaft in Flexible Anisotropic Bearing Used in Textile Application

2008 ◽  
Author(s):  
D. C. Patel ◽  
D. P. Vakharia
Keyword(s):  
Journal Bearing ◽  
Reducing Power ◽  
Design Concept ◽  
Potential Contribution ◽  
Oil Whip ◽  
Excited Vibration ◽  
Textile Machine ◽  
Minimum Film Thickness ◽  
Dynamically Loaded ◽  
Bearing Design

A FLOATING bush bearing is a kind of bearing which has a thin bush floating freely between journal and fixed bush. In recent years considerable attention has been paid to the “vibration suppressing effect” of floating us bearing. It is reported that floating bush bearing are, if properly designed, effective in suppressing both resonant vibrations at the critical speed and self excited vibration call oil whip. This study deal with performance of dynamically loaded floating ring journal bearing and investigates their feasibility for two for one textile machine application. A mathematical model is developed and its analysis for performance of floating bush journal bearing with flexible shat in flexible anisotropic bearing is conducted. The potential contribution of the floating bush journal bearing design concept to reduce vibration is assessed and its compliance with current bearing durability criteria is evaluated. The result indicates that the adoption of floating bush design concept has potential for reducing power loss and vibration in two for one (TFO) textile machine bearing. It is shown that this can be accomplished without violating minimum film thickness constraints currently accepted as criteria for successful machine bearing operation.

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