MECH 375 | Mechanical Vibrations Lab Experiment 4
Forced Harmonic Response of a Single DoF System Concordia
University
Lab Experiment 4
Forced Harmonic Response of a Single DoF
System
Kamal Lal | 26991459
Sheanthan Selvananthan | 26980317
Section MO
Professor Waiz Ahmed
,Conducted | 2 March 2015
Submitted | 16 March 2015
, Objective
The objective of this experiment is to analyse forced harmonic response of
a SDOF torsion vibration system and understand the importance of damping in
mechanical systems.
Introduction
Forced harmonic response occurs when a system is subjected to a periodic
external force, causing it to oscillate. This motion can be undamped or damped,
depending on the composition and properties of the system. For the first part of
this experiment, an input is provided to a shaker, which is attached to one end of
a shaft. An inertial disc is mounted on the other side and the desired frequency is
applied. Sensors record the deflection at each end and convey it to an
oscilloscope; the data obtained can be used to calculate the natural frequency,
phase angle, and amplitude ratio of the system.
The amplitude ratio is the fraction of the excitation that the steady-state
amplitude consists of. It is defined by the following equation:
∣ ∣
θss
θi
= 1
√ ( ) ( )
2 2 2
ω ω
1− ωn + 2 ζωn
The phase angle is indicative of the gap between the oscillations of the excitation
and the response. To calculate this parameter, the following equation is used:
∣ ∣
Wher
e:
2ζ ω
ωn
θss = Steady-state
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