I was working with a new Simulation Professional customer recently on getting his frequency analysis model working right. He knew what the frequency should be because they had performed a physical test and he could hear the frequency it was generating; being a musician himself he knew that it was just above a D-sharp, or 311 Hz. It ends up that his model had some rigid-body modes that we took care of and got the 1st natural frequency right where he thought. (Note: A rigid-body mode, or RBM, occurs when a model is not fully constrained in one (or many) of the translational or rotational degrees-of-freedom. When animated a RBM moves the body back and forth in that direction as a single rigid unit and has a frequency of zero.)
I found the following video, which is interesting because it shows the strings of a double bass vibrate, so you can literally see what I meant above. The person who shot the video footage made these notes: “Frequency of the bass strings and high shutter speed of the camera lead to this surprising string-wobble footage. There is no slow-motion applied to the take. Sound is original. Video was filmed with a Canon 5D MarkII , Nikon 50mm lens on 1,8f.”
Watch a WMV of the video here: http://bit.ly/hzGbAo (26.1 MB, WMV file)
Download a ZIP of the video here: http://bit.ly/e8iBXE (25.1 MB, ZIP file)
Another way to see frequencies is to throw sand on say a flat plate and see where the sand accumulates in the areas where the plate is not vibrating.
Watch the original video with sound here: http://bit.ly/dLlw40 (20.5 MB, MPEG file)
Download a ZIP of it here: http://bit.ly/entbrp (19.7 MB, ZIP file)
For comparison to a frequency analysis done with our Simulation Professional package, I recreated the flat plate model restrained at the center and interspersed the original video with images of the results from the simulation. This is a good video to show how well Simulation can match real-world results. I took out the sound because it is a little annoying to the ears at higher frequencies. To create the images in Simulation, I changed the color legend to greyscale and inverted them so that the low spots would be white like the sand.
Watch the comparison video here: http://bit.ly/haGwdK (4.51 MB, WMV file)
Download a ZIP of it here: http://bit.ly/elGHI6 (4.43 MB, ZIP file)
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