“Super Frequency” study type
There are many different types of studies
that you can run in SOLIDWORKS Simulation, such as Linear Static, Thermal,
Fatigue, Nonlinear and Drop Test, but there is one study type that is sort of a
“super” type. The super study that I’m
talking about is a Frequency study type.
Why it’s super is that it has multiple
applications where it is useful:
1 – Determining natural frequencies
The typical usage of a
Frequency analysis is to determine the natural resonances of a system, see
example listing below. You all may be
familiar with some famous examples, such as the Tacoma Narrows bridge, where a
system’s vibration will be amplified when it is excited by an external force at
(or near) one of its resonant points.
And every system theoretically has an infinite number of resonant
frequencies that are at increasingly higher values, so everything you design
has a lot of points where it can fail.
If you don’t think that your design will undergo vibration during use,
you should consider how your products get transported often by many vehicles,
either by land or air, that subject it to a wide range of external frequencies
getting to its final destination.
2 – Characteristic movement of system
Another great result to obtain
from a Frequency simulation is the characteristic shapes that the system wants
to move. This gives you an indication of
the relative stiffness in each direction, and where some areas of the design
may be “weaker” (or more susceptible to stress) than others. As you can see in the example below for an
engine mounting frame, where the engine is replaced by a remote mass point, the
first mode shape shows that has a tendency to want to rock to-and-fro and thus
tear itself away from the base. While it
cannot be determined from this analysis whether it will actually tear away, but
you can plainly see that special attention should be placed on the horizontal
braces and its bolted connections to the base.
And there are multiple characteristic shapes that can be evaluated
3 – Troubleshooting tool
One might not think of running
a simulation as a troubleshooting measure for the FEA modeling, but a Frequency
analysis can also help in this regard.
You can setup the model similarly as you would in say a linear Static
analysis; the advantage of starting it as a Frequency study is that even if you
have issues with insufficient restraints or connecting all the parts in your
assembly, it will still solve albeit with some rigid body motions yielding a
nearly 0 (zero) Hz frequency. This
information is valuable to working out the model issues. Once you have it all figured out in the
Frequency study, all the setup features can be copied to another study by
ctrl+mouse select plus drag-and-drop them into the tab (at the bottom) for that
study.
4 – Basis for many other types of analysis
A Frequency study is also the
underlying basis for the following study types: linear Buckling and the four
Linear Dynamic studies (Time History, Harmonic, Random Vibration (or PSD), and
Response Spectrum analysis). The
definition of a linear Buckling study is when the transverse stiffness goes to
zero under a compressive loading case, and this can be represented by the first
natural frequency, which for a simple column example is a half-sine wave. The combined response from summing up all of
the resonant frequencies and associated characteristic mode shapes provides a
very efficient way of performing a Linear Dynamic analysis.
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