Upload
others
View
5
Download
0
Embed Size (px)
Citation preview
Nitin Pangavane & Brahmananda PramanikGraduate Students
Structural Dynamics [CE‐511]
The University of Mississippi
Nitin Pangavane & Brahmananda PramanikGraduate Students
Structural Dynamics [CE‐511]
The University of Mississippi
‐ This presentation aims on the experimental approaches on Modal Analysis and explains how structure vibrates.What is Modal Analysis?Why to do?For proper design and operation of structure.To check the Mathematical Model from Finite Element.How to do?Using Instruments like :‐1) Dynamic Signal Analyzer.2) Using SigLab & ME’S Scope
Modal AnalysisMode ShapesFRF(Frequency‐Response Functions)Experiments
The study of the dynamic characteristics of structuresThe Characteristics are –
Frequency Damping Mode shapes
Ratio of ‐Output Response to Input Excitation Force
Fast Fourier Transform (FFT) AnalyzerSteps to analyze FFT
Analog Signals
Anti‐aliasing Filters
Input ExcitationForce
Output Response
•Sampling•Quantization•Digitization•ADC
Digital Signals
Input
Apply WINDOW
Compute FFTOutput
Power Spectrum
Linear SpectrumInput
FrequencyResponseFunction
Input
Output
•Averagingof Samples•Computation
Cross
Output
ComputationCoherenceFunction
Magnitude Real
Phase Imaginary
Impact TestDynamic Signal AnalyzerSigLabME’scope
FRF Log –MagnitudeVsFrequency
Mode # 1@ 72.5 Hz
Mode # 2@ 382 Hz
Mode # 3@ 628 Hz
Mod
e Sh
apes
FRF Im
aginar
yW
ater
fall
Mode # 1 @ 72.5 Hz Mode # 2 @ 382 Hz Mode # 3 @ 628 Hz
Mod
e Sh
apes
FRF
Log‐Mag
nitud
e
Two different approaches for modal analysis supports each otherThis experiment shows Hammer tip to be hard enough to achieve appropriate impact excitationRight location of accelerometer to be decided early to get the correct mode shapes.
‐ Fundamentals of Structural Dynamics‐ by Roy R. Craig Jr. / Andrew J. Kurdila
‐ Class Notes ‐ Structural Dynamics [CE‐511]‐ Experimental Modal Analysis – by Peter Avitabile