Modal Analysis
Domains of View
Applications
Experimental Modal Analysis Systems
Measuring vibration of a car's body
when attached to a shaker
Noise pattern . in the room when
excited by a loud speaker
example
example
Noise Engineers
Vibration Engineers
useful to
Time Domain
Frequency Domain
FFT
example
FEA
Analysis
Mode Surperposition
EOM
Converts these domains
Linear Algebra
Modes
Vibrational modal analysis:
[M]{a(t)} + [K]{x(t)} = 0
Discrete System:
[M]{a(t)} + [C]{v(t)} + [K]{x(t)} = {f(t)}
Frequency Response Functions (FRFs)
Measured In
Define
Sensors
Utilizes
Host PC to view data
Data acquisition systems
Accelerometers
Load cells
Laser vibrometer
Matricies
Stereo cameras
Multiple FRF's in matrix converted to Frequency domain
Classic Experiments
SIMO
(single-input, multiple-output)
MIMO
(multiple input/output)
Linear Combination
Linear combination of frequencies
One excitation point
Multiple excitations
Response measured at multiple points
Natural Frequencies / Eigenfrequencies
Resonance / Pattern
Produce a
Partial coherence analysis:
describes which part of a response come form which excitation source
Mode Shape
Describe
Expansion Theorem
Number of degrees of freedom ->
number of natural modes
Analog-to-digital converter to
digitize analog instrument signals
Eigenmode
Impact analysis
FEA (Olin Class)
Project teams
Degrees of Freedom