Ozan Akkus

02-10-1995, 10:28 PM

Dear Netters,

Here are the responses to my question about modal parameter extraction

algorithms. I received three answers unfortunately less than what I

expected. I hope these will be helpful for you.

> Dear BIOMCH-L subscribers,

>

> I have been performing experimental modal analysis on curved and twisted

> beams and

> from the experimental data I have to extract certain parameters such as

> natural frequencies of the modes, loss factors of the modes and mode shapes.

> What I need exactly is an algorithm for extraction of modal parameters.

> Presently I use Kennedy-Pancu method but it is not satisfactory.

>

> Thank you very much in advance.

>

> Ozan Akkus

> Research Assistant

> Engineering Sciences Department

> Middle East Technical University

> ANKARA/TURKEY

>

From: Nikolaus Praxmarer

Dear Ozan, 1. 2. 95

Refering to your inquiry in BIOMCH-L I give a brief summary of the modal

analysis methods I am aware of. (However, I never came across Kennedy-Pancu

method which you are using.)

As I understand, the methods to analyze frequency response functions (FRFs) can

be divided into 3 classes.

1.a) Single FRF / Single Mode - analysis methods:

- Circle fit: fit a circle to the Nyquist plot of the resonance

- Inverse method: fit lines to the real and imaginary parts of the

inverse of the FRF in the vicinity of the resonance

- Bendent method: more sophisticated version of the Inverse Method; tries

to eliminate the influence of neighbouring modes

Note that you have to average the global parameters (natural frequencies,

damping factors) from the different FRFs, as they won't necessarily be

the same.

1.b) Single FRF / Several Modes - analysis methods:

If there are not well separated modes, the above methods will have

difficulties to identify them correctly.

- Rational Fraction Polynomial Method: the idea is to have an analytical

description of the FRF over an area of more than 1 mode and to

find the parameters of this description using least square methods.

2) Several FRFs / Several Modes - analysis methods:

They make use of the fact that the global parameters of a given mode

are the same for all the FRFs.

- Global Method: practically, you mark the same mode in each FRF and let

the method analyze this mode simultaneously for all FRFs.

Detailed descriptions of these methods can be found e.g in Nuno M.M. Maia,

PhD-Thesis, Imperial College, London, 1988.

There is a lot of existing software for these methods: E.g. LMS (Leuven,

Netherlands) or ICATS (Imperial College, London). There is built in software

that comes with frequency analyzers (e.g. Schlumberger). I don't know, if

there is any public domain software available from ftp-servers.

Best wishes for your work

Niko

--

Nikolaus Praxmarer

Institute of Light Weight Structures Tel.: +43 1 58801 3686

Technical University of Vienna Fax: +43 1 505 44 68

A-1040 Wien, Gusshausstrasse 27-29 E-mail: prax@ilfb03.tuwien.ac.at

Austria, Europe

----------------------------------------------------------------------------

From: "Youngman, Michael"

Read you mail-list submission.

I work for LMS, a Belgian software company that sells modal analysis

testing and analysis systems for pc's and Unix workstations. Should you

require information please send me your post address and I will send you

details.

regards

Michael Youngman

Technical Manager

LMS UK

Cheddar

England

---------------------------------------------------------------------------

From: Russell Willis

Mr. Akkus,

I've included below some infromation I was able to locate regarding

Experimental Modal Analysis. I hope you will find this information to be

helpful. I located this information by searching on 'Experimental Modal

Analysis' via Veronica.

---Russell---

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:27:54 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: tiff

TIFF

(FILE) READ.ME

(BIN) kammer72.zip

(BIN) ko72.zip

(BIN) leurid72.zip

(BIN) lieven72.zip

(BIN) nonart72.zip

(BIN) setio72.zip

(BIN) treth72.zip

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:27:24 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: ijaema.filelist

* IJAEMA FILELIST for LISTSERV@VTVM1.

*

*

* This file lists the available issue abstracts for the International

* Journal of Analytical and Experimental Modal Analysis. The files

* are in TeX-source format but are readable without processing.

*

* :::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::

*

* The GET/PUT authorization codes shown with each file entry describe

* who is authorized to GET or PUT the file:

*

* ALL = Everybody

*

*: IJA = 'JPOWELL@VTVM1'

*

* :::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::

* rec last - change

* filename filetype GET PUT -fm lrecl nrecs date time Info about...

* -------- -------- --- --- --- ----- ----- -------- -------- ---------------

------------------------

IJAEMA HELP ALL IJA V 70 74 90/12/07 13:53:05 Help file.

IJAEMA CONTENTS ALL IJA V 78 117 90/12/07 13:54:06 Bibliography of

all abstracts.

IJAEMA 1986 ALL IJA V 93 320 90/12/07 13:57:04 Abstracts, IJAE

MA, 1986 (not in TeX format).

IJAEMA 1987 ALL IJA V 77 413 90/12/07 13:58:36 Abstracts, IJAE

MA, 1987 (not in TeX format).

IJAEMA 1988 ALL IJA V 78 429 90/12/07 13:58:16 Abstracts, IJAE

MA, 1988 (not in TeX format).

IJAEMA 1989 ALL IJA V 77 393 90/12/07 13:58:00 Abstracts, IJAE

MA, 1989 (not in TeX format).

IJAEMA 1990 ALL IJA V 70 524 91/02/26 08:58:16 ABSTRACTS, IJAE

MA, 1990 (NOT IN TEX FORMAT).

IJAEMA JAN90 ALL IJA V 72 170 90/12/07 13:55:08 Abstracts, IJAE

MA, 5(1), January, 1990.

IJAEMA APR90 ALL IJA V 73 183 90/12/07 13:55:35 Abstracts, IJAE

MA, 5(2), April, 1990.

IJAEMA JUL90 ALL IJA V 119 147 90/12/07 13:55:59 Abstracts, IJAE

MA, 5(3), July, 1990.

IJAEMA OCT90 ALL IJA V 128 109 90/12/07 13:56:28 Abstracts, IJAE

MA, 5(4), October, 1990.

IJAEMA JAN91 ALL IJA V 75 112 91/01/14 10:10:00 Abstracts, IJAE

MA, 6(1), January, 1991 (not in TeX format).

IJAEMA APR91 ALL IJA V 66 157 91/06/26 09:57:55 ABSTRACTS, IJAE

MA, 6(1), APRIL, 1991 (NOT IN TEX FORMAT).

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:27:09 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: ijaema.contents

INTERNATIONAL JOURNAL of ANALYTICAL and EXPERIMENTAL MODAL ANALYSYS

Volume 5(1) FILENAME: JAN90

DYNAMIC ANALYSIS OF ASSEMBLED STRUCTURES USING FREQUENCY-

RESPONSE FUNCTIONS: IMPROVED FORMULATION OF CONSTRAINTS

by P. O. Larsson, ABB Corporate Research

EXPERIMENTAL SUBSTRUCTURE SYNTHESIS WITH

SPECIAL CONSIDERATION OF JOINTS EFFECTS

by J.H. Wang and C.M. Liou

MODELING CYLINDER ACOUSTICS OF

FLEXURAL AND SHELL MODES

by F. Ismail, University of Waterloo,

and K.R. Fyfe, University of Alberta

DIAGNOSTIC EXPERIMENTAL SPECTRAL/MODAL

ANALYSIS OF A HIGHWAY BRIDGE

by M. Biswas, A. K. Pandey and M. M. Samman, Duke University

PAREDYM--A PARAMETER REFINEMENT COMPUTER CODE

FOR STRUCTURAL DYNAMIC MODELS

by I. U. Ojalvo, T. Ting, and D. Pilon, University of Bridgeport

Volume 5(2) FILENAME: APR90

A SPECTRALLY FORMULATED FINITE ELEMENT FOR FLEXURAL WAVE

PROPAGATION IN BEAMS

by J. F. Doyle, T. N. Farris, Purdue University

ASYNCHRONOUS HARMONIC RESPONSE

ANALYSIS OF ROTOR/BEARING SYSTEMS

by C.-W. Lee and S.-W. Hong, Korea Advanced Institute

of Science and Technology

QUALIFICATION OF FREQUENCY-RESPONSE

FUNCTIONS USING THE RIGID-BODY RESPONSE

by D. O. Smallwood and J. P. Lauffer, Sandia National Laboratories

GLOBAL DAMAGE DETECTION IN SOLIDS - EXPERIMENTAL VERIFICATION

by N. Stubbs, Texas A & M University and R. Osegueda, University of

Texas at El Paso

GLOBAL NON-DESTRUCTIVE DAMAGE EVALUATION IN SOLIDS

by N. Stubbs, Texas A & M University and R. Osegueda, University of

Texas at El Paso

AN EFFECTIVE APPROACH TO DETERMINE NATURAL FREQUENCIES AND MODE

SHAPES OF CONSTRAINED BEAMS USING LAGRANGE MULTIPLIERS

by Z. Zeng and T. Huang , Tianjin University;

and J.F. Hamilton, Purdue University

Volume 5(3) FILENAME: JUL90

ACTIVE CONTROL OF STRUCTURALLY-COUPLED SOUND FIELDS IN

ELASTIC CYLINDERS BY VIBRATIONAL FORCE INPUTS

by J. D. Jones, Purdue University and C. R. Fuller, Virginia

Polytechnic Institute and State University

APPLICATION OF FINITE ELEMENT METHOD TO THE STABILITY OF

AN ECCENTRICALLY LOADED COLUMN BY SLAVE LOADS INCLUDING DAMPING

by G. M. Arif and O. Pettersson, Lund University

A SCANNING LASER DOPPLER VIBROMETER FOR MODAL TESTING

by P. Sriram, J. I. Craig and S. Hanagud, Georgia Institute of Technology

STATE-SPACE FORMULATION OF MULTI-SHAKER MODAL ANALYSIS

by Roy R. Craig, Jr., University of Texas at Austin,

Andrew J. Kurdila, Texas A&M University, and

Hyoung M. Kim, McDonnell Douglas Astronautics Co.

ESTIMATES OF VARIANCE AND CONFIDENCE BANDS FOR THE

THREE-CHANNEL FREQUENCY RESPONSE FUNCTION ESTIMATOR

by R. E. Cobb, Contract Engineer and

L. D. Mitchell, Virginia Polytechnic Institute and State University

FINITE ELEMENT ANALYSIS OF FREE VIBRATIONS OF LAMINATED

COMPOSITE PLATES

by M. J. Kim and A. Gupta, Northern Illinois University

Volume 5(4) FILENAME: OCT90

CHARACTERISTIC BEHAVIOR OF RANDOM AND SYSTEMATIC ERRORS IN

INVERSE PLANE FREQUENCY IDENTIFICATION ALGORITHMS

by J. Brandon, University of Wales College of Cardiff

IDENTIFICATION OF JOURNAL BEARING MODAL PARAMETERS

by K. A. F. Moustafa, King Fahd University of Petroleum and Minerals

and K. R. Asfar, Jordan University of Science and Technology

A SPECTRALLY FORMULATED ELEMENT FOR WAVE PROPAGATION IN 3-D FRAME

STRUCTURES

by J. F. Doyle And T. N. Farris, Purdue University

ANNULAR PLATE RESPONSE TO CIRCUMFERENTIALLY MOVING LOADS WITH SUDDEN

RADIAL POSITION CHANGES

by G. N. Weisensel And A. L. Schlack, Jr., University of Wisconsin

THE RANDOM STRUCTURAL RESPONSE OF A SDF SYSTEM WITH STIFFNESS

DEGRADATION

by S.-L. Lu And F. D. Ju, University of New Mexico

AUTHOR INDEX VOLUMES 1--5

SUBJECT INDEX VOLUMES 1--5

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:26:46 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: ijaema.apr91

================================================== ================

Maia, N. M. M., Technical University of Lisbon

6 (2): 69-80; Apr. 1991

REFLECTIONS OF SOME SINGLE-DEGREE-OF-FREEDOM (SDOF) MODAL ANALYSIS

METHODS

ABSTRACT - In the present paper, some of the most important

single-degree-of-freedom (SDOF) methods of modal analysis are

described and compared, based on experience gained while applying

them to both theoretical and experimental cases. The work is

descriptive, as the main objective is to stress and explore the

concepts involved and the existing similarities. It is believed

that a contribution is made in the sense of providing a deeper

understanding of Dobsons method relating it to the inverse method.

Mioduchowski, A., University of Alberta and W. Nadolski, Polish

Academy of Sciences

6(2): 81-88; Apr. 1991

ON TORSIONAL RESONANT DEFORMATIONS OF SIMPLIFIED NONHOMOGENEOUS

DRIVE SYSTEMS

ABSTRACT - In this paper the one-dimensional discrete - continuous

model of a simple nonhomogeneous drive system is considered. The

system consists of three rigid disks and two torsionally

deformable shafts of different materials, but such that torsional

wave speeds in both shafts are equal. Damping is taken into

account by means of an equivalent external damping of the viscous

type and an equivalent damping of the Voigt type. Numerical

results for the amplitude - frequency curves for selected cross-

sections are presented in graphical form.

Wright, J. R., University of Manchester and M. A. Al-Hadid,

Scientific Studies and Research Centre

6(2): 89-103; Apr. 1991

SENSITIVITY OF THE FORCE-STATE MAPPING APPROACH TO MEASUREMENT

ERRORS

ABSTRACT - In this paper the application of the force-state

mapping approach to the identification of nonlinear systems is

considered. In particular, the sensitivity of the basic method to

systematic amplitude and phase errors, and to random errors, in

the measurements is investigated analytically using a linear

single degree of freedom system subject to steady state

excitation. It is shown that the identified damping estimates are

very sensitive to small systematic errors in the phase of the

measured or integrated signals when the system itself is lightly

damped, and that significantly biased results can be obtained.

Other forms of error are far less important. The study highlights

the need for extremely accurate instrumentation if this

identification approach is to be used successfully in practice.

Jara-Almonte, J., Clemson University and L. D. Mitchell, Virginia

Polytechnic Institute and State University

6(2): 105-115; Apr. 1991

A HYBRID EIGENPROBLEM FORMULATION USING THE FINITE ELEMENT METHOD;

PART I: THEORY

ABSTRACT - A hybrid technique to reduce the size of finite-

element-method based eigen problems is presented in this paper.

Numerical examples using this method are presented in Part II. In

this hybrid method, a continuum transfer matrix beam element is

used as an exact dynamical element. The exact element is

incorporated into a finite element model, and is used as a

substructure, resulting in smaller matrices. The terms in the

exact dynamical representation are functions of frequency. Thus

the ensuing eigenproblem is a transcendental eigenproblem. A

frequency-scan extraction algorithm is employed to find the

eigenvalues. The eigenvectors can be reconstructed for both

finite and exact elements; however, the exact formulation yields

eigenvectors with virtually any desired spatial precision.

One result of this hybrid, finite element and transfer matrix,

method is smaller matrices, albeit with a transcendental

eigenvalue problem. Another result is that the hybrid method has

the ability to extract higher eigenfrequencies as easily and as

accurately as lower eigenfrequencies. Moreover, the formulation

allows the extraction of an average of six

eigenfrequencies/vectors for every degree of freedom in the model.

In contrast, the finite element method models usually require four

or more degrees of freedom per accurate eigenfrequency (within 5%

of the true eigenvalue).

Jara-Almonte, J., Clemson University and L. D. Mitchell, Virginia

Polytechnic Institute and State University.

6(2): 117-130; Apr. 1991

A HYBRID EIGENPROBLEM FORMULATION USING THE FINITE ELEMENT METHOD;

PART II: EXAMPLES

ABSTRACT - This paper contains numerical examples of the method

presented in Part I , which dealt with the theory. The proposed

method incorporates continuum transfer matrices into a finite

element discretization for substructuring purposes. The two

examples presented in this paper, a portal arch and Vierendeel

truss, show that the proposed method reduced the number of degrees

of freedom of the finite element models and at the same time

improved the accuracy of the predicted higher eigenvalues. These

improvements came at the expense of having to solve a

transcendental eigenproblem. The implementation and solution of

the hybrid model is also presented.

McConnell, K. G., Iowa State University and Rogers, J. D., Sandia

National Laboratories

6(2): 131-145; Apr. 1991

TUTORIAL: TRANSDUCER REQUIREMENTS FOR USE IN MODAL ANALYSIS

ABSTRACT - The art of Experimental Modal Analysis starts with the

transducers and system components used in making the required

measurements. Many different instrument systems can be used. The

objective of the first set of four papers in this tutorial series

is to understand instrumentation requirements and measurement

system characteristics as applied to experimental modal analysis.

A second set of tutorial papers will explore the requirements for

understanding and using frequency analysis. A third set of papers

will explore the art of pulling it all together in order to obtain

the natural frequencies, mode shapes, structural damping, etc.

These tutorial papers are based on a series of yearly seminars

given at the spring meetings of the Society of Experimental

Mechanics as well as current research and experience of the

authors.

The first paper is limited to the general measurement requirements

and beginning definitions used in instrumentation systems. It

addresses several topics necessary for the understanding of modal

analysis measurements. The first section gives a very brief

overview of the concepts of modal analysis. The next two sections

deal with transducer characteristics. The last five sections

discuss background material on measurements systems, operational

amplifiers, and convenient methods for dealing with complex

values. Each section was written independently from the others to

provide for convenient review as reference material. Thus, some

readers may find it more beneficial to read the background

material first, while others may choose to skip that material

entirely.

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:26:33 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: ijaema.1986

Allemang, R.J.; Brown, D.L. Multiple-input experimental modal analysis - a

survey. 1)1:37-44; Jan 1986.

ABSTRACT - The technology of experimental modal analysis is expanding

rapidly as the impact of multiple inputs, or references, is being realized.

This paper traces the development of experimental-modal-analysis

techniques while noting this current trend toward multiple-input

utilization in the estimation of system parameters. Over the past 40

years, at least four general categories of experimental-modal-analysis

methods can be identified as follows: (1) Forced-Normal-Mode Excitation,

(2) Frequency-Response Function, (3) Damped-Complex Exponential

Response, and (4) Mathematical Input-Output Modal.

Experimental-modal-analysis methods in each of these categories can

incorporated multiple-input concepts in one way or another. Historically,

the modal characteristics of mechanical systems have been estimated by

techniques that fall into either the first or second category. The

forced-normal-mode-excitation method has always included the

multiple-input concept while the frequency-response-function method,

until recently, only involved the repeated application of single inputs.

This paper reviews both of these methods with emphasis on the current

trends in the refinements of these methods involving multiple-input

concepts. The experimental-modal-analysis methods that fall into the

last two categories are composite approaches that utilize elaborate

parameter-estimation algorithms based upon structural models and

include multiple-input concepts. The current developments in these areas

are reviewed as well.

Doyle, J.F. Application of the fast-Fourier transform (FFT) to

wave-propagation problems. 1(4):18-25; Oct 1986.

ABSTRACT - The time variation of the wave signals is replaced by a

summation over its frequency components. This is done efficiently by use

of the FFT algorithm but in doing so a number of problems arise. The

procedures and problems are elucidated by considering the impact of a

beam and the resulting wave propagations.

Engles, R.C. A solution to the Craig/Bampton eigenvalue problem for

multicomponent structures. 1(2):19-24; Apr 1986.

ABSTRACT - A cost-effective technique is presented to solve the system

eigenvalue problem associated with the Craig/Brampton component-mode

synthesis method. Subspace iteration is employed in order to take

advantage of the special form of this eigenvalue problem.

Gaught, T.M.; Dobson, B.J. The transient analysis of a structure using a

modal model. 1(1):11-16; Jan 1986.

ABSTRACT - Experimental modal analysis is used to characterize the

dynamic behavior of a structure in terms of natural frequencies, mode

shapes and damping. Using the parameters extracted from this analysis a

mathematical model is generated to predict the transient behavior of the

structure subjected to an impact. A time-marching algorithm is employed

to predict the acceleration response which is compared to experimental

data. It is shown that a comparison between the measured and predicted

responses can be used to identify errors in the mode-shape parameters

extracted from the experimental modal analysis.

Haisty, B.S.; Springer, W.T. A simplified method for extracting rotational

degree-of-freedom information from modal-test data. 1(3):35-39; Jul

1986.

ABSTRACT - A method is presented which uses third-order spline curves

to approximate the deflected shape of a vibrating structure. These curves

can then be used to determine the rotational degree-of-freedom (RDOF)

contributions to the deflection curve, thereby allowing

structural-dynamics-modification (SDM) techniques requiring this

information to be correctly applied to the modal data.

Haynes, F.D. Vibration analysis of the Yamachiche lightpier. 1(2):9-18;

Apr 1986.

ABSTRACT - The Yamachiche lightpier, located in Lac St. Pierre, Quebec,

was instrumented with geophones, accelerometers and an inclinometer. In

order to determine is dynamic characteristics, 15 breakable bolts with

failure strengths from 10,000 to 101,000 lb were used to apply a step

unloading force on the pier. The damping and stiffness were obtained from

the data in the time domain. The natural frequencies and mode shapes

were obtained from the data transformed into the frequency domain. A

modal-analysis computer program was used to verify the natural

frequencies and mode shapes. A mathematical modal was developed which

includes translation, rotation and shear-beam deformation of the pier.

He, J.; Ewins, D.J. Analytical stiffness matrix correction using measured

vibration modes. 1(3):9-14; Jul 1986.

ABSTRACT - Correction of analytical stiffness and mass matrices of a

vibration structure by correlating the experimental and analytical models

has recently attracted considerable attention. This paper proposes a

method to localize the region of errors existing in the analytical stiffness

matrix and introduces an iteration concept into the model-correction

process. The methods are justified by numerically simulated results

showing that this location technique, together with the iteration process,

brings about a dramatic improvement in the correction of an analytical

stiffness matrix. Also, it becomes possible to estimate directly the

errors existing in analytical stiffness matrix by using measured modes

available, once the region of errors is pinpointed. The same methodology

can be applied to mass-matrix correction problem.

Huang, T.C.; Zhang, P.Q.; Feng, W.Q. Multiple single-input space-time

regression method in modal analysis. 1(4):1-7; Oct 1986.

ABSTRACT - The concept of the multiple single-input space-time

regression method (MS-STRM) in modal analysis is explained. Its

feasibility, advantages, and ability to deal with systems with repeated

roots, high modal density, or high damping are proved through the

identification of both computer-simulated systems and actual

experimental systems.

Ibrahim, S.R. Incipient failure detection from random-decrement time

functions. 1(2):1-8; Apr 1986.

ABSTRACT - Changes in the physical properties of structures, such as

cross sectional areas, inertias, and damping properties, can cause

measurable changes in the modal properties of these structures. Periodic

identification of the natural frequencies, damping factors, and mode

shapes institutes a credible means of nondestructive evaluation for

structural-integrity monitoring and incipient failure detection. It is

desirable that such periodic testing be performed without disrupting the

operation of the structure under test. Offshore platforms, bridges and

piping systems are among the structures that may benefit from such

procedures. This paper deals with a class of structures whose operating

responses are due to some stationary random input(s) plus some possible

harmonic excitation. These inputs need not be known or measurable. A

time-domain modal identification technique developed for a limited

number of measurements possible one, with high identification accuracy

and repeatability is suggested as the modal-identification method for this

purpose. Converting the operational responses to a form usable for

identification will be performed using the multi-measurement-multimode

random-decrement technique. The theoretical basis and possible

limitations of rht random-decrement technique are summarized. The

computational requirements for the two combined techniques are simple

and stable and could possible be implemented on minicomputers.

Leuridan, J. The use of principal inputs in multiple-input multiple-output

data analysis. 1(3):1-8; Jul 1986.

ABSTRACT - In many areas of vibration and acoustical analysis, one needs

to establish multiple-input multiple-output relations. A typical example

for structural testing is the estimation of frequency response functions

(FRFs) with simultaneous multiple-input excitation. A typical example in

acoustical analysis is the noise-ranking problem, where the contributions

of different potential noise inputs (or sources) to a given output are to be

established. Solutions for these multiple-input multiple-output problems

have been worked out for the case that the inputs are not correlated. Most

solution techniques can handle the case of some correlation between the

inputs, but fail if the inputs become very highly correlated. The aim of

this paper is to discuss techniques for verifying correlation between

multiple inputs, and between multiple inputs and one output. Classical

techniques based on ordinary, partial and multiple coherence function

calculations are reviewed. A new technique that is based on the

calculation of a set of principal inputs is introduced and is compared with

classical techniques. An example of its application is worked out to

demonstrate the new technique's feasibility and interesting features.

Matzen, V.C.; Murphy, C.E. On obtaining mass participation factors using

equivalent structures. 1(1):17-23; Jan 1986.

ABSTRACT - Mass participation factors appear in the forcing function of

modal descriptions of the behavior of structures subjected to support

excitation. Exact calculation of these factors for a given structural

discretization is theoretically possible, but it requires either the full

mass matrix or the full matrix of eigenvectors. For many applications,

both of these approaches are impractical, and the only recourse is to use

some type of approximate method. Approximate analytical methods are

based on the use of reduction schemes, which eliminate unwanted DOFs.

After the system has been reduced, the participation factors are obtained

using the same procedures as those used on the original system.

Experimental methods require either modal parameters (modal masses and

eigenvectors) or the structural response in the time domain to obtain the

participation factors. In this paper, two analytical and three

experimental methods for finding mass participation factors are

described and compared using simulated experimental data.

Mitchell, L.D. Signal processing and fast-Fourier-transform (FFT)analyzer

- a survey. 1(1):24-36; Jan 1986.

ABSTRACT - This paper will act as a tutorial for the use of

fast-Fourier-transform (FFT) techniques in the analysis of experimental

dynamic data for the purpose of the identification of the physical

characteristics of the measured system. Consideration will be given to

transducer and system calibration, signal conditioning, the relationship of

sample rate to frequency range, anti-aliasing filter processes,

time-domain windows and their data-leakage effects, channel-to-channel

crosstalk, various algorithms for computing frequency-response function,

and the coherence function. This paper should make the readers aware of

what FFT signal processing will do for them and what it will do to their

data. Recent information concerning the ability of the modalanalysis

community to make proper measurements indicates that the expert and the

novice alike need to review the basics of FFT signal processing.

Muszynska, A. Modal testing of rotor/bearing systems. 1(3):15-34; Jul

1986.

ABSTRACT - Several aspects of modal testing of rotating machines are

discussed. Advantages of the nonsynchronous perturbation technique used

for identification of rotor/bearing system parameters are outlined.

Several application examples of perturbation testing for rotating systems

are given. The obtained results are discussed. The perturbation testing of

rotor/bearing systems has revealed the existence of new modes generated

by solid/fluid interaction. These modes were unknown in classical modal

analysis.

Rogers, J.D.; McConnell, K.G. Damping in aluminum-filled epoxy using two

different flexural-testing techniques. 1(4):8-17; Oct 1986.

ABSTRACT - Two flexural-test methods were used to measure the loss

factor of a commercially available aluminum particle-filled epoxy. The

results were compared to results from the same tests performed on an

aluminum alloy. Amplitude and frequency effects on the loss factor were

considered for each material.

Shen, C.L.; Tsuei, Y.G.; Allemang, R.J.; Brown, D.L. Analytical and

experimental study of inextensional modes of a circular cylinder.

1(4):26-32; Oct 1986.

ABSTRACT - Modal analysis of a plastic cylinder, a steel cylinder and a

steel ring has been conducted. With these materials and geometries, the

lowest measurable modes under investigation are from inextensional

modes which are primarily due to flexural bending. They can be classified

into three groups: (a) cylinder surface remains prismatic, (b) cylinder

surface becomes nonprismatic, and (c) vibration of a ring due to bending in

axial direction with twist. The analytical expressions for frequencies and

modes are obtained and verified by experiments. As expected, repeated

eigenvalue occurs. For special geometry, multiplicity of four might

appear.

Snyder, V.W. Structural modification and modal analyses - a survey.

1(1):45-52; Jan 1986.

ABSTRACT - This paper discusses the mechanism for the determination of

dynamic characteristics of linear systems which has been modified. The

mechanism can be used to marry both analytical and experimental

techniques. Typically, when structural modifications are made it requires

building a new model and testing it; or running additional costly computer

runs. Complex structures may be difficult to mathematically or

physically model; the method presented here permits a very logical

substructuring to be performed. The modification technique uses the

solution already available to find the solution to the modified or combined

structure in a fast and efficient manner. The technique is effective on

systems with complex eigenvalues and eigenvectors. Many samples are

given for clarity of the technique and to show the versatility of the

method.

Stevens, K.K.; Loeps, J.B. Modal testing of circular plates with partial

viscoelastic damping treatments. 1(1):1-10; Jan 1986.

ABSTRACT - Application of modal-testing techniques to determine the

modal parameters and mode shapes of an edge-fixed circular plate with a

free-layer viscoelastic damping treatment extending over a portion of the

surface is described. The test specimen and test procedures are

discussed, and experimentally determined values of the system natural

frequencies and loss factors for varying degrees of damping treatment are

presented. These results show that partial damping treatments can be as

effective as complete treatments, while providing significant savings in

material costs and added weight. For a plate with complete damping

treatment, the values of the natural frequencies are found to compare

favorably with those predicted by a laminated plate theory. It is also

found that addition of the damping treatment had little effect upon the

flexural mode shapes of the plate.

Williams, R.; Vold, H. Multiphase-step-sine method for experimental

modal analysis. 1(2):25-34; Apr 1986.

ABSTRACT - This paper presents an approach to large-scale modal tests

that combine the multishaker methodologies of sinusoidal and random

excitation. The first phase of this method consists of verifying a single

exciter location with either stepped sine or random excitation. Then,

using closed-loop force control, a series of multishaker stepped-sine

surveys are performed, alternating polarity patterns between the surveys

(multiphase step sine). The responses in each such survey may be

considered frequency-response functions with respect to a generalized

force, since force amplitudes and polarities are controlled to be constant

within each survey. Mode-indicator functions may hence be calculated and

modal parameters can be extracted from these individual surveys, just as

for standard single-point excitation methods. From the multiple surveys

with alternating polarity patterns, a standard multiple-column FRF matrix

may also be extracted, using HI or Hv estimators. One will now normally

calculate the multivariate mode-indicator functions and the corresponding

force patterns to identify resonances and their multiplicity. From this

data set, one may either proceed to extract a modal model using

phase-separation methods or, if the situation warrants, go back to

perform a tuned-sine dwell test, with initial appropriated force patterns

from the multivariate modeindicator functions. An attractive feature of

this approach is that the decision to employ particular modal-parameter

extraction techniques can be postponed to later stages of the project.

Modal parameters may also be obtained from classical phase-resonance

techniques, guided by the insight acquired from the frequency-response function

calculations.

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:26:21 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: abstracts

ABSTRACTS

(?) Search Abstracts

(FILE) ijaema.1986

(FILE) ijaema.1987

(FILE) ijaema.1988

(FILE) ijaema.1989

(FILE) ijaema.1990

(FILE) ijaema.apr90

(FILE) ijaema.apr91

(FILE) ijaema.contents

(FILE) ijaema.filelist

(FILE) ijaema.jan90

(FILE) ijaema.jan91

(FILE) ijaema.jul90

(FILE) ijaema.list

(FILE) ijaema.oct90

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:26:08 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: IJAEMA

INTERNATIONAL JOURNAL OF ANALYTICAL AND EXPERIMENTAL MODAL ANALYSIS

(DIR) abstracts

(DIR) tiff

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:25:34 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: zhang

EXPERIMENTAL MODAL ANALYSIS OF MINIATURE OBJECTS BY OPTICAL ..

(FILE) Abstract

(IMG) ijaema.v7n4.243.gif

(IMG) ijaema.v7n4.244.gif

(IMG) ijaema.v7n4.245.gif

(IMG) ijaema.v7n4.246.gif

(IMG) ijaema.v7n4.247.gif

(IMG) ijaema.v7n4.248.gif

(IMG) ijaema.v7n4.249.gif

(IMG) ijaema.v7n4.250.gif

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(IMG) ijaema.v7n4.253.gif

(IMG) ijaema.v7n4.254.gif

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:31 1995

Date: Tue, 7 Feb 1995 21:24:48 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: 7?Experimental+Modal+Analysis+-m

Select one of:

(FILE) International Journal of Analytical and Experimental Modal Analysis

(FILE) International Journal of Analytical and Experimental Modal Analysis

(DIR) Experimental Modal Analysis of Miniature Objects by Optical ..

(DIR) Experimental Modal Analysis of Miniature Objects by Optical ..

(DIR) International Journal of Analytical and Experimental Modal Analysis

(DIR) Experimental Modal Analysis of Miniature Objects by Optical ..

(FILE) ME 5534 : EXPERIMENTAL MODAL ANALYSIS

(FILE) MEC5444 Experimental modal analysis

Here are the responses to my question about modal parameter extraction

algorithms. I received three answers unfortunately less than what I

expected. I hope these will be helpful for you.

> Dear BIOMCH-L subscribers,

>

> I have been performing experimental modal analysis on curved and twisted

> beams and

> from the experimental data I have to extract certain parameters such as

> natural frequencies of the modes, loss factors of the modes and mode shapes.

> What I need exactly is an algorithm for extraction of modal parameters.

> Presently I use Kennedy-Pancu method but it is not satisfactory.

>

> Thank you very much in advance.

>

> Ozan Akkus

> Research Assistant

> Engineering Sciences Department

> Middle East Technical University

> ANKARA/TURKEY

>

From: Nikolaus Praxmarer

Dear Ozan, 1. 2. 95

Refering to your inquiry in BIOMCH-L I give a brief summary of the modal

analysis methods I am aware of. (However, I never came across Kennedy-Pancu

method which you are using.)

As I understand, the methods to analyze frequency response functions (FRFs) can

be divided into 3 classes.

1.a) Single FRF / Single Mode - analysis methods:

- Circle fit: fit a circle to the Nyquist plot of the resonance

- Inverse method: fit lines to the real and imaginary parts of the

inverse of the FRF in the vicinity of the resonance

- Bendent method: more sophisticated version of the Inverse Method; tries

to eliminate the influence of neighbouring modes

Note that you have to average the global parameters (natural frequencies,

damping factors) from the different FRFs, as they won't necessarily be

the same.

1.b) Single FRF / Several Modes - analysis methods:

If there are not well separated modes, the above methods will have

difficulties to identify them correctly.

- Rational Fraction Polynomial Method: the idea is to have an analytical

description of the FRF over an area of more than 1 mode and to

find the parameters of this description using least square methods.

2) Several FRFs / Several Modes - analysis methods:

They make use of the fact that the global parameters of a given mode

are the same for all the FRFs.

- Global Method: practically, you mark the same mode in each FRF and let

the method analyze this mode simultaneously for all FRFs.

Detailed descriptions of these methods can be found e.g in Nuno M.M. Maia,

PhD-Thesis, Imperial College, London, 1988.

There is a lot of existing software for these methods: E.g. LMS (Leuven,

Netherlands) or ICATS (Imperial College, London). There is built in software

that comes with frequency analyzers (e.g. Schlumberger). I don't know, if

there is any public domain software available from ftp-servers.

Best wishes for your work

Niko

--

Nikolaus Praxmarer

Institute of Light Weight Structures Tel.: +43 1 58801 3686

Technical University of Vienna Fax: +43 1 505 44 68

A-1040 Wien, Gusshausstrasse 27-29 E-mail: prax@ilfb03.tuwien.ac.at

Austria, Europe

----------------------------------------------------------------------------

From: "Youngman, Michael"

Read you mail-list submission.

I work for LMS, a Belgian software company that sells modal analysis

testing and analysis systems for pc's and Unix workstations. Should you

require information please send me your post address and I will send you

details.

regards

Michael Youngman

Technical Manager

LMS UK

Cheddar

England

---------------------------------------------------------------------------

From: Russell Willis

Mr. Akkus,

I've included below some infromation I was able to locate regarding

Experimental Modal Analysis. I hope you will find this information to be

helpful. I located this information by searching on 'Experimental Modal

Analysis' via Veronica.

---Russell---

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:27:54 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: tiff

TIFF

(FILE) READ.ME

(BIN) kammer72.zip

(BIN) ko72.zip

(BIN) leurid72.zip

(BIN) lieven72.zip

(BIN) nonart72.zip

(BIN) setio72.zip

(BIN) treth72.zip

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:27:24 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: ijaema.filelist

* IJAEMA FILELIST for LISTSERV@VTVM1.

*

*

* This file lists the available issue abstracts for the International

* Journal of Analytical and Experimental Modal Analysis. The files

* are in TeX-source format but are readable without processing.

*

* :::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::

*

* The GET/PUT authorization codes shown with each file entry describe

* who is authorized to GET or PUT the file:

*

* ALL = Everybody

*

*: IJA = 'JPOWELL@VTVM1'

*

* :::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::

* rec last - change

* filename filetype GET PUT -fm lrecl nrecs date time Info about...

* -------- -------- --- --- --- ----- ----- -------- -------- ---------------

------------------------

IJAEMA HELP ALL IJA V 70 74 90/12/07 13:53:05 Help file.

IJAEMA CONTENTS ALL IJA V 78 117 90/12/07 13:54:06 Bibliography of

all abstracts.

IJAEMA 1986 ALL IJA V 93 320 90/12/07 13:57:04 Abstracts, IJAE

MA, 1986 (not in TeX format).

IJAEMA 1987 ALL IJA V 77 413 90/12/07 13:58:36 Abstracts, IJAE

MA, 1987 (not in TeX format).

IJAEMA 1988 ALL IJA V 78 429 90/12/07 13:58:16 Abstracts, IJAE

MA, 1988 (not in TeX format).

IJAEMA 1989 ALL IJA V 77 393 90/12/07 13:58:00 Abstracts, IJAE

MA, 1989 (not in TeX format).

IJAEMA 1990 ALL IJA V 70 524 91/02/26 08:58:16 ABSTRACTS, IJAE

MA, 1990 (NOT IN TEX FORMAT).

IJAEMA JAN90 ALL IJA V 72 170 90/12/07 13:55:08 Abstracts, IJAE

MA, 5(1), January, 1990.

IJAEMA APR90 ALL IJA V 73 183 90/12/07 13:55:35 Abstracts, IJAE

MA, 5(2), April, 1990.

IJAEMA JUL90 ALL IJA V 119 147 90/12/07 13:55:59 Abstracts, IJAE

MA, 5(3), July, 1990.

IJAEMA OCT90 ALL IJA V 128 109 90/12/07 13:56:28 Abstracts, IJAE

MA, 5(4), October, 1990.

IJAEMA JAN91 ALL IJA V 75 112 91/01/14 10:10:00 Abstracts, IJAE

MA, 6(1), January, 1991 (not in TeX format).

IJAEMA APR91 ALL IJA V 66 157 91/06/26 09:57:55 ABSTRACTS, IJAE

MA, 6(1), APRIL, 1991 (NOT IN TEX FORMAT).

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:27:09 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: ijaema.contents

INTERNATIONAL JOURNAL of ANALYTICAL and EXPERIMENTAL MODAL ANALYSYS

Volume 5(1) FILENAME: JAN90

DYNAMIC ANALYSIS OF ASSEMBLED STRUCTURES USING FREQUENCY-

RESPONSE FUNCTIONS: IMPROVED FORMULATION OF CONSTRAINTS

by P. O. Larsson, ABB Corporate Research

EXPERIMENTAL SUBSTRUCTURE SYNTHESIS WITH

SPECIAL CONSIDERATION OF JOINTS EFFECTS

by J.H. Wang and C.M. Liou

MODELING CYLINDER ACOUSTICS OF

FLEXURAL AND SHELL MODES

by F. Ismail, University of Waterloo,

and K.R. Fyfe, University of Alberta

DIAGNOSTIC EXPERIMENTAL SPECTRAL/MODAL

ANALYSIS OF A HIGHWAY BRIDGE

by M. Biswas, A. K. Pandey and M. M. Samman, Duke University

PAREDYM--A PARAMETER REFINEMENT COMPUTER CODE

FOR STRUCTURAL DYNAMIC MODELS

by I. U. Ojalvo, T. Ting, and D. Pilon, University of Bridgeport

Volume 5(2) FILENAME: APR90

A SPECTRALLY FORMULATED FINITE ELEMENT FOR FLEXURAL WAVE

PROPAGATION IN BEAMS

by J. F. Doyle, T. N. Farris, Purdue University

ASYNCHRONOUS HARMONIC RESPONSE

ANALYSIS OF ROTOR/BEARING SYSTEMS

by C.-W. Lee and S.-W. Hong, Korea Advanced Institute

of Science and Technology

QUALIFICATION OF FREQUENCY-RESPONSE

FUNCTIONS USING THE RIGID-BODY RESPONSE

by D. O. Smallwood and J. P. Lauffer, Sandia National Laboratories

GLOBAL DAMAGE DETECTION IN SOLIDS - EXPERIMENTAL VERIFICATION

by N. Stubbs, Texas A & M University and R. Osegueda, University of

Texas at El Paso

GLOBAL NON-DESTRUCTIVE DAMAGE EVALUATION IN SOLIDS

by N. Stubbs, Texas A & M University and R. Osegueda, University of

Texas at El Paso

AN EFFECTIVE APPROACH TO DETERMINE NATURAL FREQUENCIES AND MODE

SHAPES OF CONSTRAINED BEAMS USING LAGRANGE MULTIPLIERS

by Z. Zeng and T. Huang , Tianjin University;

and J.F. Hamilton, Purdue University

Volume 5(3) FILENAME: JUL90

ACTIVE CONTROL OF STRUCTURALLY-COUPLED SOUND FIELDS IN

ELASTIC CYLINDERS BY VIBRATIONAL FORCE INPUTS

by J. D. Jones, Purdue University and C. R. Fuller, Virginia

Polytechnic Institute and State University

APPLICATION OF FINITE ELEMENT METHOD TO THE STABILITY OF

AN ECCENTRICALLY LOADED COLUMN BY SLAVE LOADS INCLUDING DAMPING

by G. M. Arif and O. Pettersson, Lund University

A SCANNING LASER DOPPLER VIBROMETER FOR MODAL TESTING

by P. Sriram, J. I. Craig and S. Hanagud, Georgia Institute of Technology

STATE-SPACE FORMULATION OF MULTI-SHAKER MODAL ANALYSIS

by Roy R. Craig, Jr., University of Texas at Austin,

Andrew J. Kurdila, Texas A&M University, and

Hyoung M. Kim, McDonnell Douglas Astronautics Co.

ESTIMATES OF VARIANCE AND CONFIDENCE BANDS FOR THE

THREE-CHANNEL FREQUENCY RESPONSE FUNCTION ESTIMATOR

by R. E. Cobb, Contract Engineer and

L. D. Mitchell, Virginia Polytechnic Institute and State University

FINITE ELEMENT ANALYSIS OF FREE VIBRATIONS OF LAMINATED

COMPOSITE PLATES

by M. J. Kim and A. Gupta, Northern Illinois University

Volume 5(4) FILENAME: OCT90

CHARACTERISTIC BEHAVIOR OF RANDOM AND SYSTEMATIC ERRORS IN

INVERSE PLANE FREQUENCY IDENTIFICATION ALGORITHMS

by J. Brandon, University of Wales College of Cardiff

IDENTIFICATION OF JOURNAL BEARING MODAL PARAMETERS

by K. A. F. Moustafa, King Fahd University of Petroleum and Minerals

and K. R. Asfar, Jordan University of Science and Technology

A SPECTRALLY FORMULATED ELEMENT FOR WAVE PROPAGATION IN 3-D FRAME

STRUCTURES

by J. F. Doyle And T. N. Farris, Purdue University

ANNULAR PLATE RESPONSE TO CIRCUMFERENTIALLY MOVING LOADS WITH SUDDEN

RADIAL POSITION CHANGES

by G. N. Weisensel And A. L. Schlack, Jr., University of Wisconsin

THE RANDOM STRUCTURAL RESPONSE OF A SDF SYSTEM WITH STIFFNESS

DEGRADATION

by S.-L. Lu And F. D. Ju, University of New Mexico

AUTHOR INDEX VOLUMES 1--5

SUBJECT INDEX VOLUMES 1--5

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:26:46 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: ijaema.apr91

================================================== ================

Maia, N. M. M., Technical University of Lisbon

6 (2): 69-80; Apr. 1991

REFLECTIONS OF SOME SINGLE-DEGREE-OF-FREEDOM (SDOF) MODAL ANALYSIS

METHODS

ABSTRACT - In the present paper, some of the most important

single-degree-of-freedom (SDOF) methods of modal analysis are

described and compared, based on experience gained while applying

them to both theoretical and experimental cases. The work is

descriptive, as the main objective is to stress and explore the

concepts involved and the existing similarities. It is believed

that a contribution is made in the sense of providing a deeper

understanding of Dobsons method relating it to the inverse method.

Mioduchowski, A., University of Alberta and W. Nadolski, Polish

Academy of Sciences

6(2): 81-88; Apr. 1991

ON TORSIONAL RESONANT DEFORMATIONS OF SIMPLIFIED NONHOMOGENEOUS

DRIVE SYSTEMS

ABSTRACT - In this paper the one-dimensional discrete - continuous

model of a simple nonhomogeneous drive system is considered. The

system consists of three rigid disks and two torsionally

deformable shafts of different materials, but such that torsional

wave speeds in both shafts are equal. Damping is taken into

account by means of an equivalent external damping of the viscous

type and an equivalent damping of the Voigt type. Numerical

results for the amplitude - frequency curves for selected cross-

sections are presented in graphical form.

Wright, J. R., University of Manchester and M. A. Al-Hadid,

Scientific Studies and Research Centre

6(2): 89-103; Apr. 1991

SENSITIVITY OF THE FORCE-STATE MAPPING APPROACH TO MEASUREMENT

ERRORS

ABSTRACT - In this paper the application of the force-state

mapping approach to the identification of nonlinear systems is

considered. In particular, the sensitivity of the basic method to

systematic amplitude and phase errors, and to random errors, in

the measurements is investigated analytically using a linear

single degree of freedom system subject to steady state

excitation. It is shown that the identified damping estimates are

very sensitive to small systematic errors in the phase of the

measured or integrated signals when the system itself is lightly

damped, and that significantly biased results can be obtained.

Other forms of error are far less important. The study highlights

the need for extremely accurate instrumentation if this

identification approach is to be used successfully in practice.

Jara-Almonte, J., Clemson University and L. D. Mitchell, Virginia

Polytechnic Institute and State University

6(2): 105-115; Apr. 1991

A HYBRID EIGENPROBLEM FORMULATION USING THE FINITE ELEMENT METHOD;

PART I: THEORY

ABSTRACT - A hybrid technique to reduce the size of finite-

element-method based eigen problems is presented in this paper.

Numerical examples using this method are presented in Part II. In

this hybrid method, a continuum transfer matrix beam element is

used as an exact dynamical element. The exact element is

incorporated into a finite element model, and is used as a

substructure, resulting in smaller matrices. The terms in the

exact dynamical representation are functions of frequency. Thus

the ensuing eigenproblem is a transcendental eigenproblem. A

frequency-scan extraction algorithm is employed to find the

eigenvalues. The eigenvectors can be reconstructed for both

finite and exact elements; however, the exact formulation yields

eigenvectors with virtually any desired spatial precision.

One result of this hybrid, finite element and transfer matrix,

method is smaller matrices, albeit with a transcendental

eigenvalue problem. Another result is that the hybrid method has

the ability to extract higher eigenfrequencies as easily and as

accurately as lower eigenfrequencies. Moreover, the formulation

allows the extraction of an average of six

eigenfrequencies/vectors for every degree of freedom in the model.

In contrast, the finite element method models usually require four

or more degrees of freedom per accurate eigenfrequency (within 5%

of the true eigenvalue).

Jara-Almonte, J., Clemson University and L. D. Mitchell, Virginia

Polytechnic Institute and State University.

6(2): 117-130; Apr. 1991

A HYBRID EIGENPROBLEM FORMULATION USING THE FINITE ELEMENT METHOD;

PART II: EXAMPLES

ABSTRACT - This paper contains numerical examples of the method

presented in Part I , which dealt with the theory. The proposed

method incorporates continuum transfer matrices into a finite

element discretization for substructuring purposes. The two

examples presented in this paper, a portal arch and Vierendeel

truss, show that the proposed method reduced the number of degrees

of freedom of the finite element models and at the same time

improved the accuracy of the predicted higher eigenvalues. These

improvements came at the expense of having to solve a

transcendental eigenproblem. The implementation and solution of

the hybrid model is also presented.

McConnell, K. G., Iowa State University and Rogers, J. D., Sandia

National Laboratories

6(2): 131-145; Apr. 1991

TUTORIAL: TRANSDUCER REQUIREMENTS FOR USE IN MODAL ANALYSIS

ABSTRACT - The art of Experimental Modal Analysis starts with the

transducers and system components used in making the required

measurements. Many different instrument systems can be used. The

objective of the first set of four papers in this tutorial series

is to understand instrumentation requirements and measurement

system characteristics as applied to experimental modal analysis.

A second set of tutorial papers will explore the requirements for

understanding and using frequency analysis. A third set of papers

will explore the art of pulling it all together in order to obtain

the natural frequencies, mode shapes, structural damping, etc.

These tutorial papers are based on a series of yearly seminars

given at the spring meetings of the Society of Experimental

Mechanics as well as current research and experience of the

authors.

The first paper is limited to the general measurement requirements

and beginning definitions used in instrumentation systems. It

addresses several topics necessary for the understanding of modal

analysis measurements. The first section gives a very brief

overview of the concepts of modal analysis. The next two sections

deal with transducer characteristics. The last five sections

discuss background material on measurements systems, operational

amplifiers, and convenient methods for dealing with complex

values. Each section was written independently from the others to

provide for convenient review as reference material. Thus, some

readers may find it more beneficial to read the background

material first, while others may choose to skip that material

entirely.

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:26:33 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: ijaema.1986

Allemang, R.J.; Brown, D.L. Multiple-input experimental modal analysis - a

survey. 1)1:37-44; Jan 1986.

ABSTRACT - The technology of experimental modal analysis is expanding

rapidly as the impact of multiple inputs, or references, is being realized.

This paper traces the development of experimental-modal-analysis

techniques while noting this current trend toward multiple-input

utilization in the estimation of system parameters. Over the past 40

years, at least four general categories of experimental-modal-analysis

methods can be identified as follows: (1) Forced-Normal-Mode Excitation,

(2) Frequency-Response Function, (3) Damped-Complex Exponential

Response, and (4) Mathematical Input-Output Modal.

Experimental-modal-analysis methods in each of these categories can

incorporated multiple-input concepts in one way or another. Historically,

the modal characteristics of mechanical systems have been estimated by

techniques that fall into either the first or second category. The

forced-normal-mode-excitation method has always included the

multiple-input concept while the frequency-response-function method,

until recently, only involved the repeated application of single inputs.

This paper reviews both of these methods with emphasis on the current

trends in the refinements of these methods involving multiple-input

concepts. The experimental-modal-analysis methods that fall into the

last two categories are composite approaches that utilize elaborate

parameter-estimation algorithms based upon structural models and

include multiple-input concepts. The current developments in these areas

are reviewed as well.

Doyle, J.F. Application of the fast-Fourier transform (FFT) to

wave-propagation problems. 1(4):18-25; Oct 1986.

ABSTRACT - The time variation of the wave signals is replaced by a

summation over its frequency components. This is done efficiently by use

of the FFT algorithm but in doing so a number of problems arise. The

procedures and problems are elucidated by considering the impact of a

beam and the resulting wave propagations.

Engles, R.C. A solution to the Craig/Bampton eigenvalue problem for

multicomponent structures. 1(2):19-24; Apr 1986.

ABSTRACT - A cost-effective technique is presented to solve the system

eigenvalue problem associated with the Craig/Brampton component-mode

synthesis method. Subspace iteration is employed in order to take

advantage of the special form of this eigenvalue problem.

Gaught, T.M.; Dobson, B.J. The transient analysis of a structure using a

modal model. 1(1):11-16; Jan 1986.

ABSTRACT - Experimental modal analysis is used to characterize the

dynamic behavior of a structure in terms of natural frequencies, mode

shapes and damping. Using the parameters extracted from this analysis a

mathematical model is generated to predict the transient behavior of the

structure subjected to an impact. A time-marching algorithm is employed

to predict the acceleration response which is compared to experimental

data. It is shown that a comparison between the measured and predicted

responses can be used to identify errors in the mode-shape parameters

extracted from the experimental modal analysis.

Haisty, B.S.; Springer, W.T. A simplified method for extracting rotational

degree-of-freedom information from modal-test data. 1(3):35-39; Jul

1986.

ABSTRACT - A method is presented which uses third-order spline curves

to approximate the deflected shape of a vibrating structure. These curves

can then be used to determine the rotational degree-of-freedom (RDOF)

contributions to the deflection curve, thereby allowing

structural-dynamics-modification (SDM) techniques requiring this

information to be correctly applied to the modal data.

Haynes, F.D. Vibration analysis of the Yamachiche lightpier. 1(2):9-18;

Apr 1986.

ABSTRACT - The Yamachiche lightpier, located in Lac St. Pierre, Quebec,

was instrumented with geophones, accelerometers and an inclinometer. In

order to determine is dynamic characteristics, 15 breakable bolts with

failure strengths from 10,000 to 101,000 lb were used to apply a step

unloading force on the pier. The damping and stiffness were obtained from

the data in the time domain. The natural frequencies and mode shapes

were obtained from the data transformed into the frequency domain. A

modal-analysis computer program was used to verify the natural

frequencies and mode shapes. A mathematical modal was developed which

includes translation, rotation and shear-beam deformation of the pier.

He, J.; Ewins, D.J. Analytical stiffness matrix correction using measured

vibration modes. 1(3):9-14; Jul 1986.

ABSTRACT - Correction of analytical stiffness and mass matrices of a

vibration structure by correlating the experimental and analytical models

has recently attracted considerable attention. This paper proposes a

method to localize the region of errors existing in the analytical stiffness

matrix and introduces an iteration concept into the model-correction

process. The methods are justified by numerically simulated results

showing that this location technique, together with the iteration process,

brings about a dramatic improvement in the correction of an analytical

stiffness matrix. Also, it becomes possible to estimate directly the

errors existing in analytical stiffness matrix by using measured modes

available, once the region of errors is pinpointed. The same methodology

can be applied to mass-matrix correction problem.

Huang, T.C.; Zhang, P.Q.; Feng, W.Q. Multiple single-input space-time

regression method in modal analysis. 1(4):1-7; Oct 1986.

ABSTRACT - The concept of the multiple single-input space-time

regression method (MS-STRM) in modal analysis is explained. Its

feasibility, advantages, and ability to deal with systems with repeated

roots, high modal density, or high damping are proved through the

identification of both computer-simulated systems and actual

experimental systems.

Ibrahim, S.R. Incipient failure detection from random-decrement time

functions. 1(2):1-8; Apr 1986.

ABSTRACT - Changes in the physical properties of structures, such as

cross sectional areas, inertias, and damping properties, can cause

measurable changes in the modal properties of these structures. Periodic

identification of the natural frequencies, damping factors, and mode

shapes institutes a credible means of nondestructive evaluation for

structural-integrity monitoring and incipient failure detection. It is

desirable that such periodic testing be performed without disrupting the

operation of the structure under test. Offshore platforms, bridges and

piping systems are among the structures that may benefit from such

procedures. This paper deals with a class of structures whose operating

responses are due to some stationary random input(s) plus some possible

harmonic excitation. These inputs need not be known or measurable. A

time-domain modal identification technique developed for a limited

number of measurements possible one, with high identification accuracy

and repeatability is suggested as the modal-identification method for this

purpose. Converting the operational responses to a form usable for

identification will be performed using the multi-measurement-multimode

random-decrement technique. The theoretical basis and possible

limitations of rht random-decrement technique are summarized. The

computational requirements for the two combined techniques are simple

and stable and could possible be implemented on minicomputers.

Leuridan, J. The use of principal inputs in multiple-input multiple-output

data analysis. 1(3):1-8; Jul 1986.

ABSTRACT - In many areas of vibration and acoustical analysis, one needs

to establish multiple-input multiple-output relations. A typical example

for structural testing is the estimation of frequency response functions

(FRFs) with simultaneous multiple-input excitation. A typical example in

acoustical analysis is the noise-ranking problem, where the contributions

of different potential noise inputs (or sources) to a given output are to be

established. Solutions for these multiple-input multiple-output problems

have been worked out for the case that the inputs are not correlated. Most

solution techniques can handle the case of some correlation between the

inputs, but fail if the inputs become very highly correlated. The aim of

this paper is to discuss techniques for verifying correlation between

multiple inputs, and between multiple inputs and one output. Classical

techniques based on ordinary, partial and multiple coherence function

calculations are reviewed. A new technique that is based on the

calculation of a set of principal inputs is introduced and is compared with

classical techniques. An example of its application is worked out to

demonstrate the new technique's feasibility and interesting features.

Matzen, V.C.; Murphy, C.E. On obtaining mass participation factors using

equivalent structures. 1(1):17-23; Jan 1986.

ABSTRACT - Mass participation factors appear in the forcing function of

modal descriptions of the behavior of structures subjected to support

excitation. Exact calculation of these factors for a given structural

discretization is theoretically possible, but it requires either the full

mass matrix or the full matrix of eigenvectors. For many applications,

both of these approaches are impractical, and the only recourse is to use

some type of approximate method. Approximate analytical methods are

based on the use of reduction schemes, which eliminate unwanted DOFs.

After the system has been reduced, the participation factors are obtained

using the same procedures as those used on the original system.

Experimental methods require either modal parameters (modal masses and

eigenvectors) or the structural response in the time domain to obtain the

participation factors. In this paper, two analytical and three

experimental methods for finding mass participation factors are

described and compared using simulated experimental data.

Mitchell, L.D. Signal processing and fast-Fourier-transform (FFT)analyzer

- a survey. 1(1):24-36; Jan 1986.

ABSTRACT - This paper will act as a tutorial for the use of

fast-Fourier-transform (FFT) techniques in the analysis of experimental

dynamic data for the purpose of the identification of the physical

characteristics of the measured system. Consideration will be given to

transducer and system calibration, signal conditioning, the relationship of

sample rate to frequency range, anti-aliasing filter processes,

time-domain windows and their data-leakage effects, channel-to-channel

crosstalk, various algorithms for computing frequency-response function,

and the coherence function. This paper should make the readers aware of

what FFT signal processing will do for them and what it will do to their

data. Recent information concerning the ability of the modalanalysis

community to make proper measurements indicates that the expert and the

novice alike need to review the basics of FFT signal processing.

Muszynska, A. Modal testing of rotor/bearing systems. 1(3):15-34; Jul

1986.

ABSTRACT - Several aspects of modal testing of rotating machines are

discussed. Advantages of the nonsynchronous perturbation technique used

for identification of rotor/bearing system parameters are outlined.

Several application examples of perturbation testing for rotating systems

are given. The obtained results are discussed. The perturbation testing of

rotor/bearing systems has revealed the existence of new modes generated

by solid/fluid interaction. These modes were unknown in classical modal

analysis.

Rogers, J.D.; McConnell, K.G. Damping in aluminum-filled epoxy using two

different flexural-testing techniques. 1(4):8-17; Oct 1986.

ABSTRACT - Two flexural-test methods were used to measure the loss

factor of a commercially available aluminum particle-filled epoxy. The

results were compared to results from the same tests performed on an

aluminum alloy. Amplitude and frequency effects on the loss factor were

considered for each material.

Shen, C.L.; Tsuei, Y.G.; Allemang, R.J.; Brown, D.L. Analytical and

experimental study of inextensional modes of a circular cylinder.

1(4):26-32; Oct 1986.

ABSTRACT - Modal analysis of a plastic cylinder, a steel cylinder and a

steel ring has been conducted. With these materials and geometries, the

lowest measurable modes under investigation are from inextensional

modes which are primarily due to flexural bending. They can be classified

into three groups: (a) cylinder surface remains prismatic, (b) cylinder

surface becomes nonprismatic, and (c) vibration of a ring due to bending in

axial direction with twist. The analytical expressions for frequencies and

modes are obtained and verified by experiments. As expected, repeated

eigenvalue occurs. For special geometry, multiplicity of four might

appear.

Snyder, V.W. Structural modification and modal analyses - a survey.

1(1):45-52; Jan 1986.

ABSTRACT - This paper discusses the mechanism for the determination of

dynamic characteristics of linear systems which has been modified. The

mechanism can be used to marry both analytical and experimental

techniques. Typically, when structural modifications are made it requires

building a new model and testing it; or running additional costly computer

runs. Complex structures may be difficult to mathematically or

physically model; the method presented here permits a very logical

substructuring to be performed. The modification technique uses the

solution already available to find the solution to the modified or combined

structure in a fast and efficient manner. The technique is effective on

systems with complex eigenvalues and eigenvectors. Many samples are

given for clarity of the technique and to show the versatility of the

method.

Stevens, K.K.; Loeps, J.B. Modal testing of circular plates with partial

viscoelastic damping treatments. 1(1):1-10; Jan 1986.

ABSTRACT - Application of modal-testing techniques to determine the

modal parameters and mode shapes of an edge-fixed circular plate with a

free-layer viscoelastic damping treatment extending over a portion of the

surface is described. The test specimen and test procedures are

discussed, and experimentally determined values of the system natural

frequencies and loss factors for varying degrees of damping treatment are

presented. These results show that partial damping treatments can be as

effective as complete treatments, while providing significant savings in

material costs and added weight. For a plate with complete damping

treatment, the values of the natural frequencies are found to compare

favorably with those predicted by a laminated plate theory. It is also

found that addition of the damping treatment had little effect upon the

flexural mode shapes of the plate.

Williams, R.; Vold, H. Multiphase-step-sine method for experimental

modal analysis. 1(2):25-34; Apr 1986.

ABSTRACT - This paper presents an approach to large-scale modal tests

that combine the multishaker methodologies of sinusoidal and random

excitation. The first phase of this method consists of verifying a single

exciter location with either stepped sine or random excitation. Then,

using closed-loop force control, a series of multishaker stepped-sine

surveys are performed, alternating polarity patterns between the surveys

(multiphase step sine). The responses in each such survey may be

considered frequency-response functions with respect to a generalized

force, since force amplitudes and polarities are controlled to be constant

within each survey. Mode-indicator functions may hence be calculated and

modal parameters can be extracted from these individual surveys, just as

for standard single-point excitation methods. From the multiple surveys

with alternating polarity patterns, a standard multiple-column FRF matrix

may also be extracted, using HI or Hv estimators. One will now normally

calculate the multivariate mode-indicator functions and the corresponding

force patterns to identify resonances and their multiplicity. From this

data set, one may either proceed to extract a modal model using

phase-separation methods or, if the situation warrants, go back to

perform a tuned-sine dwell test, with initial appropriated force patterns

from the multivariate modeindicator functions. An attractive feature of

this approach is that the decision to employ particular modal-parameter

extraction techniques can be postponed to later stages of the project.

Modal parameters may also be obtained from classical phase-resonance

techniques, guided by the insight acquired from the frequency-response function

calculations.

>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:26:21 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: abstracts

ABSTRACTS

(?) Search Abstracts

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>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:26:08 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: IJAEMA

INTERNATIONAL JOURNAL OF ANALYTICAL AND EXPERIMENTAL MODAL ANALYSIS

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>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:30 1995

Date: Tue, 7 Feb 1995 21:25:34 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: zhang

EXPERIMENTAL MODAL ANALYSIS OF MINIATURE OBJECTS BY OPTICAL ..

(FILE) Abstract

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>From willis@garnet.acns.fsu.eduTue Feb 7 21:39:31 1995

Date: Tue, 7 Feb 1995 21:24:48 -0500

From: Russell Willis

To: willis@garnet.acns.fsu.edu

Subject: 7?Experimental+Modal+Analysis+-m

Select one of:

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(DIR) International Journal of Analytical and Experimental Modal Analysis

(DIR) Experimental Modal Analysis of Miniature Objects by Optical ..

(FILE) ME 5534 : EXPERIMENTAL MODAL ANALYSIS

(FILE) MEC5444 Experimental modal analysis