Modal
analysis and operating deflection shape testing
(ODS) are considered advanced vibration analysis
techniques. Where the analysis of vibration
usually only measures the response of a machine
or structure to unknown forces, modal analysis
provides a measure of the forces, natural
frequencies and mode shapes. A very large
percentage of machinery and most structural
vibration problems are caused by natural
frequencies excited by rotating machinery. An
analysis may include performing an ODS prior to a
Modal Test. The ODS provides a computer model of
the machine or structure that can be animated to
show how it is moving or vibrating. This is the
only tool currently available to visualize the
vibrations of actual machines and structures
A modal test requires inputting controlled and
measured forces into the structure or machine and
measuring the response. The results of the test
are a model that can be animated to show the
natural frequencies and the mode shapes. Once the
mathematical model is developed from the measured
data, the model can be modified in the software
to change the mass, stiffness and damping
properties to investigate solutions to the
problem structure or machine. This is usually
much more cost effective than attempting field
modifications in a trial and error manner. We can
make an assessment of the problem structure or
machine at no cost to determine if this is the
correct approach toward attacking the problem
