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Moving the Support over a cantilever
Posted 07.07.2020, 01:57 GMT-4 Structural & Acoustics, MEMS & Piezoelectric Devices, Structural Mechanics 3 Replies
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I am working on a Thermo-Mechanical problem. I have a cantilever kind of 2d domain, which is fixed at one end. I have done the Thermal part where the Temperature at the edge is moving down with a certain velocity from the free end to the fixed end. Used time-dependent Diritchelt condition to do the same. Now i want to move a 'support' from the free end to fixed end through the side of the cantilever. I wanted to know how we can define fixed supports which is time-dependent. Now i am able to select the complete boundary as fixed support. What i wanted to execute is to reduce the size of that fixed support continuously ( Imagine support is moving down with a certain speed) while a load is being applied in the end.)
I have gone through the 'Travelling Load' tutorial model, however, could see that there the span width is just a parameter. If support has to be changed it can be done in different simulation runs, not in single one. I also tried to define a point as a function of time so that I can move that point which will automatically make the parts below as a fixed boundary, but that was also not possible.
Request your help and kindly check the same. Appreciate your time, stay safe
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Hi,
If it is acceptable that the moving support has some finite size (at least one element), then the approach described in this blog post can be used:
https://www.comsol.com/blogs/how-to-make-boundary-conditions-conditional-in-your-simulation
Note however that a support with finite size will cause a reaction moment in a beam-like structure.
A moving point support can fairly simply be implemented in a parametric solution, but not in a time dependent study. If, however, the structural mechanics problem is not truly time dependent, it can be solved using a parametric sweep.
-------------------Henrik Sönnerlind
COMSOL
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Dear Henrik,
Thanks a lot for your reply,
May i know how a moving point support is implemented in Parametric study. Can we draw/define a point or a line which is parameter based?
- Is it possible to define the coordinates of a point or a line which is patameter based? It was only accepting Numerical values
- When aplying time dependent Diritchelt condition in thermal studies for a specific Temperature value, we use an expression like if (condition, Temp value, ht.Tvar). Similary is it possible in Structural module to define a time dependet Diritchlet condition ? ( Displacement zero). If yes may I know which variable should i use in place of ht.Tvar ?
Best Aswin
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The coordinates of a point can depend on a parameter. That is one way of moving the support if you have added a Prescribed Displacement to that point. This, of course, will require a remeshing for each parameter value, since the geometry is changed.
You can also create a mesh independent moving support, as in the attached model. There, a mesh independent point load is moved, and its value is selected so that the displacement at its location is zero. This is done using a probe, the location of which is given by a parameter.
Your last question: For a Dirichlet condition in structural mechanics, you should use one of the displacement degrees of freedom e.g. 'v'.
-------------------Henrik Sönnerlind
COMSOL
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