proposal of rotor dynamic analysis of large industrial rotor using ansys

8/9/2019 Proposal of Rotor Dynamic Analysis of large industrial Rotor using ANSYS

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ADDIS ABABA UNIVERSITY

ADDIS ABABA INSTITUTE OF TECHNOLOGY

SCHOOL OF MECHANICAL AND INDUSTRIAL ENGINEERING

Mechanical Project Proposal

Proposal of Rotor Dynamic Analysis of large industrial Rotor using ANSYS

Mesfin Kebede

Advisor: Dr.Daniel T.

Co-Advisor: Ato Tolossa Date: 9/28/14


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9/28/2014 Thesis Proposal Mesfin kebede

Abstract

The study of rotor dynamics is essential to understand the determinant components in

engineering extensively used in industry such as Compressors, turbines and Generators

the ability to perform critical frequencies and forced response analysis is a vital role

while designing rotors of high speed it is of prime importance to consider rotor dynamics

characteristics into account considering these characteristics at the design phase may

prevent the rotor from catastrophic failures and in order to understand the levels of

stresses to which these components are subjected to during their operation .this pre design

analysis can greatly contribute to the troubleshooting the critical issues these analyses can

be a challenge due to the wide variety of components found in rotor dynamic systems

these rotor dynamic characteristics can be determined with the help of much relied finite

element method . Traditionally rotor dynamic analyses were performed with specialized

commercial tools. The most commonly used software is ANSYS the primary goal of the

thesis will be to analyze the behavior of the industrial rotors and address the critical issue

associated with them. The thesis work will also help in understanding, modeling and

simulation techniques for rotor dynamic analyses of large industrial rotors using ANSYS.


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Introduction

Rotordynamics is a discipline within mechanics, in which we study about the vibrational

behavior of axially symmetric rotating structures. The rotating structures are the pivotal

component of high speed turbo machines found in many modern day equipments ranging

from power station, automobiles, marine propulsion to high speed Jet engines. These

rotating structures are commonly referred as "Rotors" and generally spin about an axis at

high speed. The rotors when it rotates at high speed develop resonance. Resonance is the

state at which the harmonic loads are excited at their natural frequencies causing these

rotors to vibrate excessively. This vibration of larger amplitudes causes the rotors to bend

and twists significantly and leads to permanent failures. Also, deflection of shafts in

incongruous manner has a greater chance to collide with the adjacent components at its

closer proximity, and cause severe unrecoverable damages. Hence the determination of

these rotordynamics characteristics is much important.


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Statement of the problem

There are various applications on engineering, where rotors and rotating parts are of vital

importance. They play a determinant role on pumps, compressors, turbines, generators.

Due to its intrinsic dynamic state, vibration is especially relevant in this kind of

machines. Interaction between the rotating motion and the applied forces on the structure

causes some operation points to present intolerable vibration levels; the vibrational

problems in such rotating machines are prominent which necessitates the need for

analyzing their dynamic behavior and addressing these problems.

The dynamic behavior of rotating machines is characterized by their critical speeds, whirl

responses and gyroscopic effects. Due to the gyroscopic effects and the centrifugal

forces, the whirl can take place in both forward and the backward directions. The simple

rotors can be used for analyzing the rotor behavior initially; since such rotors offer ease

of modeling and simulation. A finite element analysis approach using commercial finite

element method software such as ANSYS can be viewed as a powerful solution tool that

can provide realistic information about the dynamic behavior of the rotors during their

operation. Due to the limitations of the finite element method software, it becomes

necessary to modify the calculation time and avoid large number of equations involved

by simplifying the model.


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Literature Review

In Rotordynamic analysis of industrial rotors initially requires full understanding of therotordynamic behavior of Jeffcott rotors, and the history of previous methods applied in

this field, their pros and cons considering all aspects of physical features such as

gyroscopic effect, rotor whirl instabilities, curve veering phenomenon in Campbell

diagram, etc. Studies related to these topics considering the objective of the thesis will be

studied and presented

The earliest study in the field of rotor dynamics dates back to the 18th century. J. W.

Rankin can be credited for the initial research in this field [2]. With the rapid

development in the field of rotor dynamics, the engineers felt the need for designing more

flexible and light weight rotors for meeting the ever increasing demands of the modern

industry. The focus of the research program has been to design rotors which require less

power to operate and would minimize the energy loss. However, with the development of

the flexible light weight rotors, the problem of vibrations and the resulting dynamic

stresses becomes a critical issue. The vibration analysis of the rotors plays a vital role in

their design process. In1895 by the German engineer August Fppl [1] studied amodel

consisted of a single disk, centrally located on a shaft of constant circular cross-section and with

undamped rigid bearings placed at each end of the shaft. Fppl used this model to demonstrate

that such rotor operation was still stable even when its rotating speed exceeded the critical

rotating speed, i.e. he showed that in supercritical operation, tolerable vibration levels are

observed.

In 1919, Jeffcott, a British engineer, modeled a rotor as a simple mass-spring system

consisting of a disk as a lumped mass and a massless shaft assuming an imbalance in the

rotor. He analyzed the dynamic response of the rotor on two identical rigid bearings at

high speeds [4]. A study of the rotors structural dynamics with no consideration of the

bearings was done by Stodola [5]. Biezeno and Grammel suggested the earliest methods


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for finding the critical speeds in the flexible rotors [6]. Also, the rotor dynamics analysis

considering the hydrodynamic bearings was done by Lund and Sterlicht and Lund [6].

For the first main mode shape of a rotor supported on bearings, Lund found two

corresponding critical speeds [7]. Gunter studied the stability issues in rotor dynamics [8]and his work was combined with Lunds work on the stability problems considering the

damped critical speeds within a rotor-bearing system and it initiated a great deal of

interest in this area [6]. Late in the 18th century, Karl Gustaf Patrik de Laval invented

the first steam turbine [9]. Sir Charles Algernon Parsons invented a special kind of steam

turbine that encountered considerably less vibrations in comparison with the

reciprocating engines, and were named Vibration Free Engines [10].

As mentioned earlier, Jeffcott made the first simple mass-spring rotor with a lumped disk

and a massless shaft [4]. The effect of the bearings was studied by many researchers.

Sommerfeld [11] formulated a parameter to establish the relation between the speed,

pressure and the eccentricity ratio.

The response of the rotors exhibited whirls in the forward and the backward directions

that is studied by Bhat et al. [12] using Vanderplaats method [ [13], [10]]. The effect of

the disk inertia in a rotating state on a shaft was first found by Rayleigh [3]. This

phenomenon, namely, the gyroscopic effect was studied and its effect on increasing the

forward whirl natural frequency and decreasing the backward whirl natural frequency

was analyzed by Stodola [5]. Den Hartog [14] and Timoshenko [15] studied the

gyroscopic effects on the synchronous and the non-synchronous whirls in rotors.

In 1981, Rao investigated the backward synchronous whirl in a flexible rotor with

hydrodynamic bearings [16]. Sinou, Villa and Thouverez studied the forward and

backward critical speeds in a rotor with flexible bearing support [17].

Providing a Campbell diagram for multi degree of freedom rotors using traditional

computational methods takes a long time. Genta published a fast modal analysis

technique based on splitting the gyroscopic and damping matrices into two parts and

comparing these parts with simplified conditions of rotors [18].


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In more recent days, using finite element method softwares such as ANSYS made it easy

to plot the Campbell diagram. Finite element modeling also helped the engineers to study

a variety of features in Campbell diagram such as effect of fluid film bearing properties

on the critical speeds of rotors. This work is done by Kalita and Kakoty [19].

The idea of solid or shell models of stationary structures became evident when the

casings and foundations became a part of the rotating machine and test beds became

flexible when coupled with rotors that interfered in the validating process.Stephenson and

Rouch [20] used axisymmetric solid finite elements with matrix reduction in their

analysis; Yu et al. [21] modeled shafts orbiting with 3-D solid finite elements. Neither of

these included the effects of rotation, stiffening and softening effects that go with solid

elements. Solid rotor dynamics analysis was first presented by Rao [22]. Rao et al. [23]

provided the details subsequently. Rao and Sreenivas [24] have extended the two rotor

system to a three level with the casing included in the analysis. Such an analysis enabled

practical engine rotor dynamics analysis. Surial and Kaushal [24] modeled an industrial

gas turbine en gine and validated it at Rolls Royce Canada. Due to the complexity of the

engine structure the model has been divided into four substructures using super-elements.

The first super-element represents the engine casing, the second the low pressure rotor

(LP rotor), the third the intermediate pressure rotor (IP rotor), and the fourth the high

pressure rotor (HP rotor).


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Hypothesis and Question

Question

How gyroscopic effects Modify critical speeds in large industrial Rotors?

How the critical speed of large industrial rotor related to the machine operation?

How Bearings Affect on rotor dynamics

How machine casing Affect on rotor dynamics

How applied forces and structure of machine related on rotor dynamics

Hypothesis

the amplitude of synchronous whirl increases with speed as the critical speed is

approached, and then decreases after traversing the critical speed and approaches

the value of static imbalance at supercritical speeds

Moving of machine away from the critical speed can be achieved either by

changing the operational speed or by changing the critical speed itself.

.


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Conceptual frame work

The study will be conducted on purposely chosen industrial Rotor the research will be primarily

a quantitative study. The data collection will come from two main sources: Primary and

Secondary sources. Primary data will obtain from industry. Secondary data collected from the

finite element analysis method the output of the program ANSYS. This data is used in a

corresponding manner throughout the paper with the purpose of supporting the argumentation.

Finally the data simulated from ANSYS can make possible to estimate the potential information

we want in the form of graph and simulated models to see clear information about the Rotor

Dynamic behavior of the rotor.


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Objectives of Rotordynamic analysis

There are several objectives are to be fulfilled within a standard rotordynamic analysis.

Obviously the rotor design is of prime importance in any rotordynamic analysis. Usually

the following issues are addressed:

Predict the natural frequencies and determine the mode shapes of the rotor system

at those natural frequencies.

Identify critical speeds within or near the operating speed range of a rotor system.

Make an unbalance response analysis of a rotor in order to calculate rotor

displacement and quantify the forces acting on the rotor supports that are caused

due to rotor imbalance.

Assess potential risks and operating problems in general related to the rotor-

dynamics of a given rotor system.

Although the aim of the thesis work will include The study of predicting critical speeds

and forced response analysis. Initially simple Jeffcott rotors will be studied in order to

understand the dynamic behavior of such simple rotors before dealing with largeindustrial rotors. After a consummate study on the simple rotor model, a finite element

model of a simplified industrial rotor, will be meshed and formulated in ANSYS

software. Gyroscopic effects will be considered in the analysis. Initially free vibration

analysis will be performed followed by forced vibration response due to harmonic

excitation by residual unbalance mass for a simple mode


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Method, Material and procedures

Course Related Study

In order to fulfill the requirements for Senior Thesis, graduate level courses must be

incorporated into the rotor dynamic analysis of large industrial rotor. Material from

the following courses will be utilized in the proposed Analysis to fulfill this

requirement. In MEng6005(Finite Element Method) the topics of mathematical

foundation of finite element Analysis and Developing finite element Computer

programs for engineering problems was covered. Detailed skill was performed in

using commercial Finite Element Software Packages to model and Solve practicalMechanical Engineering Problems and the class shows student how to create 2D and

3D Structure Models Using the software package ANSYS this software package used

to analyze the rotor dynamic property of a 3D modeled structure. knowledge learned

from MEng(Machine Dynamics) which covers the basic principles behind Rotor

dynamics such as continuous systems ,excitation of machine vibration and transverse

and torsional vibration of shafts and rotors will be used when evaluating the natural

frequencies and determining the mode shapes rotor system of those natural

frequencies and identifying critical speeds within or near the operating speed range of

a rotor system.


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Methodology

The methodology is outlined as follows:

1. Literature survey: The existing approaches to develop the Dynamic Model of the

rotor, to descritize the 3D Rotor model and equations the critical speed and natural

frequencies will be surveyed.

2. Simulation: Having developed the 3D model followed by the analysis of an actual

industrial rotor in order to understand its dynamic behavior which involves the

detailed analysis of the Combell diagrams, Critical speeds effect of the gyroscopic

moments etc.

3. Study and Analysis: Computer simulation results will be analyzed and the results

will be discussed.

Tools for Analysis

AutoCAD/CATIA Software will be used for the 3D modeling of the test Model and the

actual Rotor System.

ANSYS V11 Analysis Software will be used to represent and Construct the dynamic

mechanical Models.


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Work Schedule

A schedule of work is given on the next page that outlines the various tasks that need to be

completed in order to finish the thesis project outlined in the proposal above. This is only atentative schedule that is meant to be flexible and adapt to unforeseen delays or unexpected

lengths of various tasks. The only date that cannot be adjusted is the final presentation date on

October 05, 2015.


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Budget

Table 1.1 Budget estimation

No Description Unit Quantity Unit

price

Total cost

birr

1 Duplication paper ,, 1 100 100

Note book Pieces 3 25 75

flash diskettes 8GB 1 300 300

Printing of proposal first

draft and final copies and

binding

Pieces 2 70 140

Printing of research first

draft and final copies and

binding

,,3 350 1050

Pen ,, 10 5 50

For ANSYS/CATIA

Software Package

1500

Sub total 321

2

Transport

and

communicati

on cost

Transport Average

trip

125 20 2500

Internet reading hours Hours 60 12 720

Telephone communication

on average days

Days 50 15 750

Sub total 397

Total cost 718

Contingency 15 % 107Grand total 826


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References

[1] Vance J., Zeidan F. and Murphy B.,Machinery Vibration and Rotordynamics, Wiley, 2010.

[3] Rankine W. J., On the Centrifugal Force of Rotating Shafts,Engineer periodical, Vol. 27, pp.249, 1869.

[20] Rayleigh, J.W.S., Theory of Sound, MacMillan, London, 1877.

[4] Jeffcot H. H., TheLateral Vibration of Loaded Shafts in the Neighborhood of a Whirling Speed:The Effect of Want of Balance,Philosophical Magazine, Series 6, Vol 37. P. 304, 1919.

[5] Stodola A., Steam and gas turbines, New York: P. Smith, 1945.

[6] Biezeno, C.B. and Grammel, R., Technische Dynamik, Springer Verlag, 1939.

[7] Lund J. W., Rotor Bearing Dynamic Design Technology,Part III: Design Handbook for FluidFilm Bearings. Mechanical Technology Inc., Latham, New York, AFAPL-Tr-65-45, 1965.

[8] Gunter, E. J., Jr., Dynamic stability of rotor-bearing systems, NASA SP-113, 29, 1966.

[9] Smil, V. Creating the Twentieth Century: Technical Innovations of 18671914 and Their Lasting

Impact, Oxford University Press, 2005.

[10] Rao J. S.,History of Rotating Machinery Dynamics, Springer, 2011.

[11] John M. Vance,Rotordynamics of Turbomachinery, New York: Wiley, 1988.

[12] Bhat, R.B., Rao, J.S. and Sankar, T.S. Optimum Journal Bearing Parameters for MinimumUnbalance Response in Synchronous Whirl,Journal of Mechanical Design, ASME, vol. 104, p.

339, 1982.

[13] Vanderplaats, G.N., Structural Optimization by Methods of Feasible Directions, Computers

and Structures, vol. 3, p. 739, 1973.


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[14] Den Hartog, J.P.,Mechanical Vibration, McGraw-Hill Book Co, 1956.

[15] Timoshenko, S.P., Vibration Problems in Engineering, D. Van Nostrand Co. Inc., 1955.

[16] Rao J.S., Conditions for Backward Synchronous Whirl of a Flexible Rotor in HydrodynamicBearings,Mechanism and Machine Theory, Vol. 17, No. 2, 143-152, 1982.

[17] Sinou J.J., Villa C., Thouverez F., Experimental and Numerical Investigations of a Flexible

Rotor on Flexible Bearing Supports,International Journal of Rotating Machinery, Vol.3, pp. 179189, 2005.

[18] Genta G., A Fast Modal Technique For The Computation Of The Campbell Diagram Of Multi-Degree-Of-Freedom Rotors,Journal of Sound and Vibration, Vol. 155, issue 3, pp. 385-402, 1992.

[19] Madhumita K., Kakoty S.K., Analysis of whirl speeds for rotor-bearing systems supported on

fluid film bearings,Mechanical Systems and Signal Processing Vol. 18, pp. 13691380, 2004.

[20]Stephenson, R.W. and Rouch, K.E. (1993) Modeling rotating shafts using axi-symmetric solid

finite element with matrix reduction,ASME Journal of Vibration & Acoustics, vol. 115, p. 484.

[21] Yu, J., Craggs, A. and Mioduchowski, A. (1999) Modeling of shaft orbiting with 3-D solid

finite elements,International Journal of Rotating Machinery,vol. 5, p. 53.

[22]Rao, J.S. (2002) Rotor Dynamics Comes of Age, Keynote address,in Proceedings Sixth

IFToMM International Conference Rotor Dynamics,Sydney, September 30October 3, vol.I, p. 15.

[23] Rao, J.S., Sreenivas, R. and Veeresh, C.V., (2002) Solid Rotor Dynamics, inProceedingsFourteenth US National Congress of Theoretical and Applied Mechanics, Blacksburgh, VA,2328 June; (2003) Advances in Vibration Engineering, Journal of Vibration Institute of India,

vol. 2, no. 4, p. 305.

[24]Rao, J.S. and Sreenivas, R. (2003) Dynamics of a Three Level Rotor System Using SolidElements, ASME GT 2003-38783.

[25].Surial, A. and Kaushal, A. (2005) Dynamic Analysis of a Variable Speed Industrial Gas Tur-bine Engine and DrivetrainAnalysis and Testing,Advances in Vibration Engineering, vol.

4, no. 3, p. 279.


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Appendix A

List of Tables and Figures

TablesTable 1: Budget Estimation


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Appendix B

Preliminary Research

Mohammad Razi " Analysis of Rotor Dynamics Acceptance Criteria in Large Industrial Rotors

Concordia University ,Montreal Canada ,December 2013

This article discusses the numerical rotor dynamic analysis with that of ANSYS results and compare

the rotor dynamic results with Standards.

Deepak srikrishnanivas "Rotor Dynamic Analysis of RM12 Jet Engine Rotor using ANSYS

blenkinge Institute of technology Karlskrona,Sweden ,2012

This article discusses the results of rotor dynamic analysis of RM12 Jet Engine Rotor obtained

from the commercial Software ANSYS compared with that of the rotor dynamic analysis

software DyRobes.


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Submitted By

Mesfin Kebede

Student name Signature Date

Approved by

1) Dr.Daniel T.

Advisor Signature Date

2) Ato Tolossa

Co Advisor Signature Date

3) Dr.Daniel T.

School Director Signature Date

proposal of rotor dynamic analysis of large industrial rotor using ansys

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