By Jonathan Armstrong
Making sense of your frequency study results is easier than ever with the help of the new frequency response graphs. Though we've had access to information like the Mass Participation Factor before, now we can view these types of results in a graphical format that makes it easy to understand how your model is going to respond under harmonic loading.
There are a total of 3 new frequency response graphs that we now have access to; Mode Number, Effective Mass Participation Factor (EMPF) and the Cumulative Effective Mass Participation Factor (CEMPF), each providing a different insight into the behavior of the model. Each of these plots can be created by selecting the Define Frequency Response Graph option, in the right-click menu of the results folder of a frequency study.
The first and simplest of the graphs is the Frequency vs. Mode Number graph, a good first stop on our frequency analysis. With this graph we can get a good sense of the range of frequencies over which are part is likely to experience resonance.
Next is the Effective Mass Participation Factor (EMPF) graph. The EMPF represents what percentage of the mass in our model is participating in a given vibrational mode. This lets us see whether certain resonance modes are more important than others, since a mode with a high EMPF will contribute more to the dynamic response of the system. In this example we can see that the first two modes affect the largest portion of the model’s mass in the y and z directions. Modes 3 and 4, however, affect less than 1% of the mass and aren’t worth worrying about in this analysis. We can also see that for the X directed motion only the higher frequency modes 12 and 16 move a significant portion of the models mass.
Last but certainly not least on our list is the Cumulative Effective Mass Participation Factor (CEMPF) graph. The CEMPF is the sum of all mass participation factors from every mode shape so far, for a given direction. The CEMPF is used as an indication of whether we have considered a sufficiently large number of modes to ensure we are accurately representing the system’s dynamic response. As a rule of thumb, it is best to aim for a CEMPF of at least 80% in every direction. In the current example, we had considered a sufficient amount of modes after approximately 16 kHz (or mode number 20). We can now be certain that we’ve captured the important vibrational behaviour of the geometry.
All in all, the Frequency Response Graphs are a great tool that make understanding your model’s dynamic response quicker and easier. Be sure to check back soon for more simulation advice or check out our YouTube channel for tons of great SOLIDWORKS videos!
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