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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
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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


(DIR) abstracts
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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
(IMG) ijaema.v7n4.243.gif
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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