| Modal
Test Applications
•Trouble shooting vibration problems
(Example: Ship with bridge vibrations)
•Verification of analytical models (Example: Rocket)
•Prototype test and structural modification (Example:
New car)
Modes
of Vibration
Commonly called mechanical
resonance, modes of vibration involve the natural frequencies,
damping coefficients, and corresponding mode shapes
of a structure.
Degree of Freedom
SDOF
The single degree of freedom
(SDOF) model enables us to understand the fundamental
concepts of free and forced vibration, natural frequency,
resonance and damping. Single degree of freedom systems
have only one resonant frequency with uniform amplitude
of vibration.
MDOF
For multiple degrees of freedom,
resonance may occur at a number of different frequencies,
each of which corresponds to a different pattern or
shape of the system’s motion. These are known as
the natural or normal modes of vibration, or mode shapes.
Frequency Response Function
The frequency response function
is of particular use for performing vibration analysis
and testing. A frequency response function (FRF) is
a transfer function, expressed in the frequency domain.
Frequency response functions are:
• Complex functions with real and imaginary components.
• Represented in terms of magnitude and phase.
• Formed from either measured data or analytical
functions.
(FRF) expresses the structural response to an applied
force as a function of frequency.
The
response may be given in terms of displacement, velocity,
or acceleration. Furthermore, the response parameter
may appear in the numerator or denominator of the transfer
function.
For
More Information on Modal Survey visit:
http://www.vibrationdata.com/tutorials/modal_fund.pdf
http://macl.caeds.eng.uml.edu/ |
