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Apply velocity to entire structure in 3D
Posted 6 avr. 2010, 05:52 UTC−4 1 Reply
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Hello, I should start by saying I am essentially a complete COMSOL novice.
I think my question bears some similarity to "How to specify an acceleration (caused by an EM force) in a moving mesh application mode." www.comsol.com/community/forums/general/thread/4250/
I am trying to model a linear accelerometer, which in this case is primarily a highly flexible circular membrane. The membrane is clamped on the entire boundary inside of a tube. When the device is accelerated in the normal direction, the membrane deflects and I sense this capacitively (with a fixed reference electrode within the tube).
I want to test the magnitudes of the deflections against a trapezoidal velocity profile. In other words, the device would be accelerated to the final velocity, then no acceleration would be applied so that the velocity stays constant, and then the device is given a reverse acceleration until it stops.
I am a little confused on how to define the boundary conditions and loads to describe this event. Because the whole device is moving, there is no fixed point, and I'm not sure what to do with that. Should I treat the tube as the reference frame for the velocity, and then only load the membrane? To do that I would need to apply the load at the circular boundary of the membrane, and it seems like I would have to make that boundary free, when it should be fixed to the tube.
Any help anyone can provide will be greatly appreciated, thank you! I am not sure if I provided all the information necessary for consideration, please let me know if there are any parameters I should add.
I think my question bears some similarity to "How to specify an acceleration (caused by an EM force) in a moving mesh application mode." www.comsol.com/community/forums/general/thread/4250/
I am trying to model a linear accelerometer, which in this case is primarily a highly flexible circular membrane. The membrane is clamped on the entire boundary inside of a tube. When the device is accelerated in the normal direction, the membrane deflects and I sense this capacitively (with a fixed reference electrode within the tube).
I want to test the magnitudes of the deflections against a trapezoidal velocity profile. In other words, the device would be accelerated to the final velocity, then no acceleration would be applied so that the velocity stays constant, and then the device is given a reverse acceleration until it stops.
I am a little confused on how to define the boundary conditions and loads to describe this event. Because the whole device is moving, there is no fixed point, and I'm not sure what to do with that. Should I treat the tube as the reference frame for the velocity, and then only load the membrane? To do that I would need to apply the load at the circular boundary of the membrane, and it seems like I would have to make that boundary free, when it should be fixed to the tube.
Any help anyone can provide will be greatly appreciated, thank you! I am not sure if I provided all the information necessary for consideration, please let me know if there are any parameters I should add.
1 Reply Last Post 6 avr. 2010, 11:07 UTC−4
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Posted:
1 decade ago
I believe what you'd do is go to the Physics:Subdomain Settings window and apply a Prescribed Velocity constraint to all your subdomains. In the parameter window where you enter the velocity, you'd enter time-based velocities with logical multipliers to activate the different time and velocity periods.
Something like 5[m/s]*t*(t<=t1)+10[m/s]*(t1<t<t2)+ etc...
This would give you a velocity ramp and a constant velocity, etc.
I may not have the syntax exactly right. Look at one of the COMSOL time study example problems.
-Jeff
Something like 5[m/s]*t*(t<=t1)+10[m/s]*(t1<t<t2)+ etc...
This would give you a velocity ramp and a constant velocity, etc.
I may not have the syntax exactly right. Look at one of the COMSOL time study example problems.
-Jeff