In my study I am doing a simulation of a 2D flow , with the boundary conditions : input, output, wall , and in the other condition I want to impose a zero gradient for all variables except the Ux velocity which must have the Derechlet condition depending on the pressure ie Ux = 2 * p ^ 2 .
Is there a possibility to do it with Comsol . Thanks
Hi,
Yes, it is possible with Comsol.
You have to do :
1. Show advanced setting option
2. Tick "Advanced Physics Options"
3. Right click on flow Physic
4. Go to More > Weak constraint
5. Write in constraint expression : ux-(2*p^2)
Careful! This equation will contribute with (and not override) the wall condition.
Regards,
Alexandre
Hi,
in Comsol is possible to impose that kind of BCs however you should check the compatibility of any BC with the system under investigation in terms of saturation of degrees of freedom. In addition, theoretically speaking, some BCs are allowable only for specific kinds of flows (compressibile, incompressible, ...).
If you give me some specs of your flow I'll help you.
Paolo
Thank you,
In fact, I want to simulate the flow of water (incompressible).
So, considering you've a simulation of an incompressible flow, keep in mind that the imposition of the outflow BC is strictly related also to the solving algorithm you're using.
For example, while relying on SIMPLE algorithm, a coupled velocity - pressure BC can not be used because of the philosophy inherent in the method.
In addition, a outflow condition can not be imposed whenever an inlet pressure - based one has already been used.
For similar reasons, it is incorrect to use a vanishing pressure gradient as an outflow condition.
If you need further help, I should also know if the flow is internal or external, which solver you're going to use.
Paolo
in fact, the problem I have explained for you is just a test to learn COMSOL, but in my case I want to simulate a turbulent openflow. For this I used the k-eps model and the following boundary conditions: Volocity inlet in entry, outflow for exit, Wall at the bottom, and symmetry at the free surface. So in the free surface I want to impose a Direchlet condition Eps = k ^ 2 not zero gradient like other variables .
cordially
Hi ResearchGaters,
My COMSOL doesn't have built-in symmetry boundary condition. How can I impose it by equations? I am solving for displacement (displacement field is what COMSOL is solving for) and I'd like to force symmetry on displacement which is mathematically: The slope of displacement normal to the symmetry plane is zero.
Thanks for your help in advance.
Hossein
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