# How to model a fixedValueFixedGradient boundary condition

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 July 25, 2011, 16:40 How to model a fixedValueFixedGradient boundary condition #1 New Member   BT Join Date: Jan 2011 Posts: 16 Rep Power: 6 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

 July 26, 2011, 05:00 #2 Senior Member     Philip Cardiff Join Date: Mar 2009 Location: Dublin,Ireland Posts: 568 Rep Power: 19 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

 Tags boundary condition, openfoam, structural analysis

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