Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Moving the Support over a cantilever

Please login with a confirmed email address before reporting spam

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


3 Replies Last Post 13.07.2020, 07:21 GMT-4
Henrik Sönnerlind COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 4 years ago 07.07.2020, 03:46 GMT-4

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
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: 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.

Please login with a confirmed email address before reporting spam

Posted: 4 years ago 12.07.2020, 15:01 GMT-4

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?

  1. Is it possible to define the coordinates of a point or a line which is patameter based? It was only accepting Numerical values
  2. 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

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? 1. Is it possible to define the coordinates of a point or a line which is patameter based? It was only accepting Numerical values 2. 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

Henrik Sönnerlind COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 4 years ago 13.07.2020, 07:21 GMT-4

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
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'.

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.