TPC- Measurement Techniques

Damien Maillard, Muhammad FaizanProf. Guillermo Villanueva

Dynamical Models

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Amplitude/Phase

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Statique

Phase = 0,la masse suit la force

Inertie

Phase = -Pi,la masse ne suit plus la

force

Résonnance d’amplitude

Phase = – Pi/2

Amplitude Max

Real/Imaginary

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Résonance, ω = 5

Amplitude max

Amplitude max

Frequency Response Function (FRF)

● FRF is a ratio of output (vibrations of a mechanical structure) over input (excitation force)

● Excite structure at different points and get FRF’s to plot the mode shape

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( ) ∑= −+

==n

k kkkk

ks

kr

s

rrs jηm

ββjFjXjh

122 ) 2()(

)(ωωωωω

ωω

Objectives of the Tp

● Assembling the measurement setup (wing, hammer, accelerometer).

● Understand different settings (sampling freq, actuation time, triggering etc) of the measurement software (LabView).

● Measurement of a frequency response function of a structure.

● Study and understand the effect of mass addition to the structure.

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Procedure

● Properly mount the wing with the clamping system

● Use hammer with appropriate head to excite the wing

● Observe the time domain and frequency responses of the hammer and accelerometer

● Use FRF analysis to measure different resonance frequencies

● Attach magnets to increase the weight of the wing and again observe resonance frequencies

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Excitation System

● Hammer Headso Teflon, Metal, rubber

● Selection of hammer heado Time domain response (high no. of points on the

pulse)o Frequency domain response (flat)

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Time response Frequency response

Accelerometer

● Piezoelectric accelerometero Max displacement => Maximum force => maximum acceleration

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M

F=M a

k

Pièzo

System Block Diagram

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Données de Sortie et Affichage

Traitement de Signal

a(t)

f(t)Echantillonnage

Filtrepasse bas

Filtrepasse bas

Echantilloneur

Echantilloneur

FenètreTemporelle

FenètreTemporelle

FFT

FFT

acmplx(ω)

fcmplx(ω)

FRFimoyenne

1/n Σ (FRFi)

- Fréq. Echantillonnage- Nbre d'échantillons

Type et paramètres desfenètres temporelles - Méthode et paramètres

de Moyennage- Paramètres d'affichage

Préa

mpl

i

Niveauxd'entrée

Modal Shapes (Example)

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Tp Documentation

● All the necessary documents for the practical work can be found on the web at:http://wiki.epfl.ch/me301-tdm/tpc

● The report must be sent at the latest 2 weeks after the TP by email to damien.maillard@epfl.ch or muhammad.faizan@epfl.ch

● Do not send the scanned version of the report. Use computer to type it

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TPC- Measurement Techniques Dynamical ModelsAmplitude/PhaseReal/Imaginary Frequency Response Function (FRF)Objectives of the TpProcedureExcitation SystemAccelerometer System Block DiagramModal Shapes (Example)Tp Documentation