Double Overhung Disk and Parameter Effect on Rotordynamic Synchronous Instability—Morton Effect—Part I: Theory and Modeling Approach

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Xiaomeng Tong ◽  
Alan Palazzolo
Keyword(s):  
Linear Method ◽  
Response Prediction ◽  
Transient Method ◽  
Thermally Induced ◽  
Morton Effect ◽  
Nonlinear Transient ◽  
Rotating Shafts ◽  
Overhung Rotors ◽  
Different Response ◽  
Theory And Modeling

The Morton effect (ME) is a thermally induced instability problem that most commonly appears in rotating shafts with large overhung masses, outboard of the bearing span. The time-varying thermal bow due to the asymmetric journal temperature distribution may cause intolerable synchronous vibrations that exhibit a hysteresis behavior with respect to rotor speed. The fully nonlinear transient method designed for the ME prediction, in general, overhung rotors is proposed with the capability to perform the thermoelastohydrodynamic analysis for all the bearings and model the rotor thermal bow at both overhung ends with equivalent distributed unbalances. The more accurate nonlinear, coupled, double overhung approach is shown to provide significantly different response prediction relative to the more approximate linear method based using bearing coefficients and the single-overhung method, which assumes that the ME on both rotor ends can be decoupled. The flexibility of the bearing pad and pivot is investigated to demonstrate that the pivot flexibility can significantly affect the rotordynamics and ME, while the rigid pad model is generally a good approximation.

A Review of the Rotordynamic Thermally Induced Synchronous Instability (Morton) Effect

2017 ◽  
Vol 69 (6) ◽  
Author(s):  
Xiaomeng Tong ◽  
Alan Palazzolo ◽  
Junho Suh
Keyword(s):  
Case Studies ◽  
Design Stage ◽  
Trial And Error ◽  
Thermally Induced ◽  
Conventional View ◽  
Fluid Film Bearings ◽  
Morton Effect ◽  
Theoretical Predictions ◽  
Rotating Shafts ◽  
Universal Solutions

The Morton effect (ME) is a thermally induced instability problem that most commonly appears in rotating shafts with large overhung masses and supported by fluid-film bearings. The time-varying thermal bow, due to the asymmetric journal temperature distribution, may cause intolerable synchronous vibrations that exhibit a hysteresis behavior with respect to rotor speed. First discovered by Morton in the 1970s and theoretically analyzed by Keogh and Morton in the 1990s, the ME is still not fully understood by industry and academia experts. Traditional rotordynamic analysis generally fails to predict the potential existence of ME-induced instability in the design stage or troubleshooting process, and the induced excessive rotor vibrations cannot be effectively suppressed through conventional balancing, due to the continuous fluctuation of vibration amplitude and phase angle. In recent years, a fast growing number of case studies of ME have sparked academic interest in analyzing the causes and solutions of ME, and engineers have moved from an initial trial and error approach to more research inspired modification of the rotor and bearing. To facilitate the understanding of ME, the current review is intended to give the most comprehensive summary of ME in terms of symptoms, causes, prediction theories, and solutions. Published case studies in the past are also analyzed for ME diagnosis based on both the conventional view of critical speed, separation margin (SM), and the more recent view of the rotor thermal bow and instability speed band shifting. Although no universal solutions of ME are reported academically and industrially, recommendations to help avoid the ME are proposed based on both theoretical predictions and case studies.

Double Overhung Disk and Parameter Effect on Rotordynamic Synchronous Instability—Morton Effect—Part II: Occurrence and Prevention

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Xiaomeng Tong ◽  
Alan Palazzolo
Keyword(s):  
Transient Analysis ◽  
Operating Parameters ◽  
Flow Ratio ◽  
The Finite Element Method ◽  
Oil Viscosity ◽  
Testing Conditions ◽  
Bending Mode ◽  
Morton Effect ◽  
Nonlinear Transient ◽  
Parametric Studies

This paper performs the parametric studies corresponding with the theoretical Morton effect (ME) model explained in Part I of this paper, where the fully nonlinear transient analysis based on the finite element method is introduced. Operating parameters, such as oil supply temperature, bearing clearance, oil viscosity, etc., are perturbed from the testing conditions to investigate the shifting of critical speeds and ME instability onset speed (IOS). The ME is significantly affected by the rotor bending mode with large overhung deflections, and operating parameters should be adjusted to increase the separation margin between the operating speed and the corresponding critical speed for ME mitigation. Reducing the carryover flow ratio and using the asymmetric bearing pivot offset are capable to suppress the ME by reducing both the average and differential journal temperature. The heat barrier sleeve with air or ceramic isolation is designed to prevent the heat flux into the journal and can successfully mitigate the ME based on the simulations.

Thermally Induced Synchronous Instability of a Radial Inflow Overhung Turbine: Part I

1997 ◽  
Author(s):  
H. B. Faulkner ◽  
W. F. Strong ◽  
R. G. Kirk
Keyword(s):  
Thermal Expansion ◽  
Operating Speed ◽  
Lateral Motion ◽  
Turbine Wheel ◽  
Thermally Induced ◽  
Lateral Dynamics ◽  
Morton Effect ◽  
Speed Range ◽  
Differential Thermal Expansion ◽  
Rotor Dynamic

Abstract This paper is in two parts, and concerns the lateral dynamics of a large turbocharger rotor with overhung wheels. Initial rotor dynamic analysis indicated no excessive motion in the operating speed range. However, testing showed excessive motion, which was initially traced to the radial-inflow turbine wheel becoming loose on the shaft, due to transient differential thermal expansion in the wheel on startup. The attachment of the wheel was modified to eliminate this problem. The discussion up to this point is in Part I of the paper, and the remainder is in Part II. The wheel attachment modification extended the range of satisfactory operation upward considerably, but excessive lateral motion was again encountered near the upper end of the operating speed range. This behavior was traced to thermal bowing of the shaft at the turbine end, known as the Morton Effect. The turbine end bearing was modified to eliminate this problem, and satisfactory operation was then achieved throughout the operating speed range.

Stability Analysis of Two-Layered Finite Hydrodynamic Porous Journal Bearing Using Linear and Nonlinear Transient Method

2007 ◽  
Author(s):  
S. K. Kakoty ◽  
S. K. Laha ◽  
P. Mallik
Keyword(s):  
Journal Bearing ◽  
Journal Bearings ◽  
Operating Conditions ◽  
System Stability ◽  
Rigid Rotor ◽  
Transient Method ◽  
Porous Bearing ◽  
Nonlinear Transient ◽  
Linear And Nonlinear ◽  
The Stability

A theoretical analysis has been carried out to determine the stability of rigid rotor supported on two symmetrical finite two-layered porous oil journal bearings. The stability curves have been drawn for different eccentricity ratios and Sommerfeld numbers. The effect of bearing feeding parameter, L/D ratio on the stability is also investigated. This paper also deals with a theoretical investigation of stability using a non-linear transient method. This analysis gives the journal centre locus and from this the system stability can be determined. With the help of graphics, several trajectories of the journal centre have been obtained for different operating conditions. Finally a comparison between single-layered porous bearing and the two-layered porous bearing is presented here.

scholarly journals PREDICTION OF THERMAL GROWTH IN A HIGH-SPEED SPINDLE BY CONSIDERING THERMO-MECHANICAL BEHAVIOR

2021 ◽  
Vol 2021 (3) ◽  
pp. 4526-4533
Author(s):  
E. Yuksel ◽  
◽  
E. Budak ◽  
E. Ozlu ◽  
A. Oral ◽  
...  
Keyword(s):  
High Speed ◽  
Thermal Loading ◽  
Transient Behavior ◽  
Contact Analysis ◽  
Thermally Induced ◽  
Machining Errors ◽  
Thermal Growth ◽  
Continuous Rotation ◽  
Structural Deformations ◽  
Nonlinear Transient

Continuous rotation of spindle bearings and motor cause thermally induced structural deformations and thermal growth, which is one of the main reasons for machining errors. A positive feedback loop between bearing preload and heat generation causes preload variations in spindle bearings. These preload variations demonstrate a nonlinear transient behavior until the gradual expansion of outer bearing rings after which the thermally induced preload variation behaves steadily. In this study, a Finite Element (FE) framework is presented for predicting steady preload variation on spindle bearings. The method involves a thermal loading model and a transient contact analysis. In the contact analysis phase bearing contact deformations (penetration and sliding) and pressure are predicted by considering contact algorithms in an FE software. A transient spindle simulation in FE is employed to predict the bearing temperature and thermal spindle growth by using the proposed method. The performance of the method is demonstrated on a spindle prototype through bearing temperature and thermal deformation measurements. Results show that the proposed method can be a useful tool for spindle design and improvements due to its promising results and speed without the need for tests.

Tilting Pad Bearing Pivot Friction and Design Effects on Thermal Bow-Induced Rotor Vibration

2021 ◽  
Vol 143 (12) ◽  
Author(s):  
Dongil Shin ◽  
Alan B. Palazzolo
Keyword(s):  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Design Parameters ◽  
Flexible Beam ◽  
Thermally Induced ◽  
Tilting Pad ◽  
Speed Range ◽  
Transient Simulations ◽  
Nonlinear Transient ◽  
Tilting Pad Journal Bearing

Abstract The Morton effect (ME) is a thermally induced vibration problem observed in a rotor supported by hydrodynamic bearings. The journal’s synchronous orbiting induces nonuniform viscous heating on its circumference, and the ensuing thermal bow often causes unacceptable vibration levels in the rotor. This paper investigates the influence of the tilting pad journal bearing (TPJB)’s pivot design on the severity and instability speed range of ME vibration. Simulations are conducted with two different types of pivots: cylindrical (CYL) and spherical (SPH), which produce different pad degrees-of-freedom and nonlinear pivot stiffness due to their geometries. The friction between pad and pivot, which only exists with the spherical pivot, is modeled, and its impact on the ME is evaluated. The example rotor model, as obtained from the literature, is single overhung, with experimentally measured excessive vibration and large journal temperature differentials, near 8000 rpm. The bearing and journal are modeled with three-dimensional (3D) finite elements, and the shaft with flexible beam elements for ME simulation. Nonlinear transient simulations are carried out for a wide operating speed range with varying pivot design parameters. Simulation results indicate that the predicted ME instability is sensitive to the pivot shape, pivot flexibility, and pad-pivot friction.

Rotor Dynamics of Overhung Rotors: Hysteretic Dynamic Behavior

2012 ◽  
Author(s):  
Manuel A. Marin
Keyword(s):  
Dynamic Behavior ◽  
Rotor Dynamics ◽  
Journal Bearings ◽  
Body Motion ◽  
Process Industries ◽  
Morton Effect ◽  
Tilting Pad ◽  
Multistage Compressors ◽  
Overhung Rotors ◽  
Gyroscopic Effects

Overhung-configuration rotors are commonly used in the oil, gas and process industries. Examples of this type of equipment include power turbines, Fluid Catalytic Cracking (FCC) expanders, turbochargers and pipeline boosters. Generally, in overhung-configuration rotors, the mass concentration is near the bearing on the overhung end, so the rotor dynamics behavior of these overhung-configuration rotors is different than other equipments that have their mass concentrations between the bearing spans, such as multistage compressors. Among the more important characteristics that directly affect the rotor dynamics of the overhung rotors are gyroscopic effects on the higher modes and the fluid-film journal bearings. Gyroscopic effects are more significant in overhung configurations because of the relatively large overhung mass. These rotors also have a short bearing span and a relatively stiff shaft, so the first two modes are characterized by rigid body motion, as long as the bearing supports are rigid, as in most pipeline boosters. For pipeline boosters it would be typical to describe them as subcritical machines. If the bearing supports are not rigid, as at the disc end of power turbines and FCC expanders, then the first mode can be amplified, and it would not be unusual to describe them as supercritical machines. This paper will assume that the bearing supports are rigid, as in most pipeline boosters. A phenomenon observed in overhung rotors is known as the synchronous thermal instability or “Morton Effect”. The Morton Effect occurs when synchronous vibration produces non-uniform heating of the shaft under the bearing, leading the shaft end to develop a thermal bow. It is typical for this to happen on the overhung end of the rotor, where there is more unbalance to react with any thermal bow. The paper examines the hysteretic dynamic behavior observed in an overhung rotor mounted on tilting pad journal bearings, presenting a series of analysis using state-of-the-art rotor dynamics programs, and comparing analytical results with measurements, handling possible variables associated with synchronous “hysteresis” vibration.

scholarly journals A New, Iterative, Synchronous-Response Algorithm for Analyzing the Morton Effect

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Dara W. Childs ◽  
Rohit Saha
Keyword(s):  
Temperature Distribution ◽  
Circular Orbit ◽  
Elliptic Orbit ◽  
Steady Increase ◽  
Thermally Induced ◽  
Temperature Distributions ◽  
Morton Effect ◽  
Shaft Angle ◽  
The Impact ◽  
Lubricant Viscosity

Morton Effect problems involve the steady increase in rotor synchronous-response amplitudes due to differential heating across a fluid-film bearing that is induced by synchronous response. The present work presents a new computational algorithm for analyzing the Morton Effect. Previous approaches were based on Eigen or Nyquist analyses for stability studies and predicted an onset speed of instability. The present algorithm starts with a steady state elliptical orbit produced by the initial imbalance distribution, which is decomposed into a forward-precessing circular orbit and a backwards-precessing circular orbit. A separate (and numerically intensive) calculation based on the Reynolds equation plus the energy equation gives predictions for the temperature distributions induced by these separate orbits for a range of orbit radius-to-clearance ratios. Temperature distributions for the forward and backward orbits are calculated and added to produce the net temperature distribution due to the initial elliptic orbit. The temperature distribution is assumed to vary linearly across the bearing and produces a bent-shaft angle across the bearing following an analytical result due to Dimoragonas. This bent-shaft angle produces a synchronous rotor excitation in the form of equal and opposite moments acting at the bearing’s ends. For a rotor with an overhung section, the bend also produces a thermally induced imbalance. The response is due to: (1) the initial mechanical imbalance, (2) the bent-shaft excitation, and (3) the thermally-induced imbalance are added to produce a new elliptic orbit, and the process is repeated until a converged orbit is produced. For the work reported, no formal stability analysis is carried out on the converged orbit. The algorithm predicts synchronous response across the rotor’s speed range plus the speed where the response amplitudes becomes divergent by approaching the clearance. Predictions are presented for one example from the published literature, and elevated vibration levels are predicted well before the motion diverges. Synchronous-response amplitudes due to Morton Effect can be orders of magnitude greater than the response due only to mechanical imbalance, particularly near rotor critical speeds. For the example considered, bent-shaft-moment excitation produces significantly higher response levels than the mechanical imbalance induced by thermal bow. The impact of changes in: (1) bearing length-to-diameter ratio, (2) reduced lubricant viscosity, (3) bearing radius-to-clearance ratio and (4) overhung mass magnitude are investigated. Reducing lubricant viscosity and/or reducing the overhung mass are predicted to be the best remedies for Morton Effect problems.

scholarly journals Blade Tips - Clearance and Its Control

2013 ◽  
Vol 135 (08) ◽  
pp. 66-71
Author(s):  
Lee S. Langston
Keyword(s):  
Gas Turbine ◽  
Response Times ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Thermally Induced ◽  
Turbine Efficiency ◽  
Blade Tip ◽  
Different Response ◽  
Transient Operations ◽  
Blade Tip Clearance

This article focuses on studying blade tip clearance phenomena. It is important to realize that to be freely turning, a blade (or a cantilevered stator) must have a clearance gap between its tip and the engine casing (or hub). Such clearances introduce aerodynamic losses, decreasing gas turbine efficiency. Tip leakage losses in compressors can be significant and have been reviewed by the experts. During transient operations, gas turbine blade tip clearances will change based on blade/disk centrifugal loads and the different response times of engine parts to thermally induced expansions and contractions. Designers have perfected active clearance control (ACC) systems to deal with these transient conditions. ACC uses cool or hot gas path and fan air at appropriate times during transients to control the rate of expansion or contraction of internal parts adjacent to the gas path and outer casings. The research shows that continued enhancement of blade tip clearance management systems over a range of engine operating conditions has brought and will bring about gains in gas turbine efficiency.

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