From the course: Autodesk Nastran In-CAD: Dynamic Analysis
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Mass participation background - Nastran In-CAD Tutorial
From the course: Autodesk Nastran In-CAD: Dynamic Analysis
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- [Narrator] In this video, we're going to look at the use of what's called modal effective mass. In modal effective mass, in normal modes analysis, we can't calculate the relative amplitude of each mode. It's just a shape, and it's not scalable. We need a response analysis to see relative amplitude, either a transient response, or a frequency response. The exception is for base motion. That's when something's connected to ground, and the ground shakes or the ground moves, and it takes the structure with it. In that particular case, if we assume unit excitation, then we can calculate a term called the modal effective mass. Modal effective mass can be calculated in normal modes analysis, and the summation of contribution from every mode in every direction should equal the actual system mass. So, we're going to run an exercise with this lamp post. And the total mass of this is 1.804 pound mass, and we'll be looking to sum the contribution in the X, the Y, and the Z direction. And the…
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