Torsional Vibration Analysis
Torsional Vibration Analysis is
the analysis of the torsional dynamic behavior of a rotating shaft system
as a result of forced vibration. Torsional vibration, or twisting, is
different from lateral vibration, or shaking. A torsional system, compressor,
driver, and coupling, are modeled as a mass-elastic system (inertia and
stiffness) to predict stresses in each component. Mass-elastic properties
of the system can be changed by adding a flywheel (additional inertia),
using a soft coupling (change in stiffness), or by viscous damping (absorb
natural frequency stimulation). Not all systems require any modification
to the mass-elastic properties to achieve a torsionally sound system.
Ariel Corporation can provide
the data for the compressor necessary to perform a torsional vibration
analysis. This
includes the torque effort curves (torque versus crank angle), mass elastic
data and fourier coefficients representing the torsional driving forces.
The torsional
analysis is the responsibility of the Packager.
Care must be taken to represent
the operating conditions the unit will see, including any partial
load conditions. Any
single acting cylinder operation
is important to include as these cases can represent the more dynamic
torque effort curves.
When applying variations in speed
and single acting cylinder configurations the torsional and acoustical
response analysis will be much simplified by applying single acting configuration
only at one given speed.
Capacity control sequencing can
be very important when considering single acting operating cases. Capacity
control sequences are discussed within the Capacity
and Load Control topic.
Ariel
Corporation Application Manual
7 March 2008