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 MasterCooler July 25, 2011 16:40

How to model a fixedValueFixedGradient boundary condition

Dear openFOAM-community,

I am still new in the simulation with openFOAM but really impressed by its potential.

Now I try to solve some simple structural problems like a beam fixed on one end. For this problem a boundary condition is required which combines fixedValue and fixedGradient (or the special case zeroGradient and zeroValue, also known as Cauchy boundary condition). So far I couldn't find a boundary condition neither in the supporting material of openFOAM nor in web discussions and articles which provides the required functionality.

To clarify the situation of understanding:
I have seen the mixed bc which switches between fixedGradient and fixedValue. But as I see there is only a switching and not really a combination applying both in a full strength a the same time.

Maybe there is a need to solve this problem on code level, isn't it? Or is there a bc which I have overlooked all the time?

Background information:
Currently I am mainly a user and I am really less experienced in interpreting code. So be careful with hints assuming a deep knowledge of programming. ;-)

Thanks in advance for any help.

Cheers
MasterCooler

 bigphil July 26, 2011 05:00

Hi,

The directionMixed boundary condition can be used to apply a fixedValue in a particular direction and a fixedGradient in the corresponding tangential direction. It can also be used to mix between both fixedValue and fixedGradient.

Also there is a boundary condition called newDirectionMixed (only in the Extend version I think) which can mix both the normal direction and the tangential direction.

In stress analysis, the directionMixed BC can be used for applying a fixed displacement in a particular direction on a patch, and applying a traction in the tangential direction (eg traction-free).

Hope it helps,
Philip

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