Hi,
I'm trying to simulate the forced vibration of a beam that stands vertical and is supported by two simple supports that are shaken back and forth by a motor as in the attached schematic. I've also attached a model where the support separation is 335mm and the free length is 1599mm. I have a couple of questions I hope someone can help me with.
I've managed to perform the eigenfrequency study but the frequencies that result do not agree with ANSYS or my mathematical result (which do agree with each other). I also have a test rig running and observations of shuttle oscillation frequency agree with ANSYS and mathematical results. The results from the mathematical study and ansys put the first 3 frequencies at approximately 0.4Hz, 2.9Hz, and 8.3Hz. For some reason the first 3 eigenfrequencies from COMSOL are around 1Hz, 6.4Hz and 18Hz. Is someone able to shed some light on why this occurs? Is there a problem with my COMSOL model?
Also, in going ahead and just assuming that the frequencies are OK I've tried to do a frequency domain study to find the stresses in the beam using the eigenfrequencies obtained. I've tried adding a harmonic perturbation boundary load to the free end (just arbitrary for now at 10ms-2) but there is no deflection around the 6.4Hz eigenfrequency I found (I haven't tried other eigenfrequencies yet). Is the lack of damping the problem? My preference for FEA is COMSOL so I'd really like to find out how to do this. Haven't tried the stress study in ANSYS.
For some background to the project I've attached a video of the sculpture that this project concerns (skip to about half way to see it going). It is a Len Lye piece and the owner wants to build a larger version. Hence the FEA analysis.
Video:
www.youtube.com/watch?v=X2mFnXpNBwo
Any help would be much appreciated
Tim
I'm trying to simulate the forced vibration of a beam that stands vertical and is supported by two simple supports that are shaken back and forth by a motor as in the attached schematic. I've also attached a model where the support separation is 335mm and the free length is 1599mm. I have a couple of questions I hope someone can help me with.
I've managed to perform the eigenfrequency study but the frequencies that result do not agree with ANSYS or my mathematical result (which do agree with each other). I also have a test rig running and observations of shuttle oscillation frequency agree with ANSYS and mathematical results. The results from the mathematical study and ansys put the first 3 frequencies at approximately 0.4Hz, 2.9Hz, and 8.3Hz. For some reason the first 3 eigenfrequencies from COMSOL are around 1Hz, 6.4Hz and 18Hz. Is someone able to shed some light on why this occurs? Is there a problem with my COMSOL model?
Also, in going ahead and just assuming that the frequencies are OK I've tried to do a frequency domain study to find the stresses in the beam using the eigenfrequencies obtained. I've tried adding a harmonic perturbation boundary load to the free end (just arbitrary for now at 10ms-2) but there is no deflection around the 6.4Hz eigenfrequency I found (I haven't tried other eigenfrequencies yet). Is the lack of damping the problem? My preference for FEA is COMSOL so I'd really like to find out how to do this. Haven't tried the stress study in ANSYS.
For some background to the project I've attached a video of the sculpture that this project concerns (skip to about half way to see it going). It is a Len Lye piece and the owner wants to build a larger version. Hence the FEA analysis.
Video:
www.youtube.com/watch?v=X2mFnXpNBwo
Any help would be much appreciated
Tim