In this blog, quick reference notes about OpenFOAM are posted in a form of a summary to address a specific topic per post.
The directionMixed Boundary Condition
A mixed boundary condition is a combination of a fixedValue (Drichilet) and a fixedGradient (Neumann) boundaries determined by a fraction value. When fraction = 1, the BC is fixedValue and when it is set to zero the BC is fixedGradient. Values in between calculate a value in between (see code).
The directionMixed BC allows changing the fraction value for different directions. Assuming a plane-strain stress analysis that needs fixation in X-direction (Dx = 0) and free Y-direction (zeroGradient) for the displacement. Note that the Z-direction is irrelevant. The BC would look like:
The valueFraction has one rank higher than the variable (so as the gradient 
). In this case it is a symmTensor [xx xy xz yy yz zz] because the variable is a vector. The refGradient is used for all components. The Left patch in this image was set to the aforementioned BC configurations and the top patch has a fixedValue disp.
Reference: http://www.cfd-online.com/Forums/ope...-mixed-bc.html
The directionMixed BC allows changing the fraction value for different directions. Assuming a plane-strain stress analysis that needs fixation in X-direction (Dx = 0) and free Y-direction (zeroGradient) for the displacement. Note that the Z-direction is irrelevant. The BC would look like:
Quote:
PatchName
{
type directionMixed;
refValue uniform (0 0 0);
refGradient uniform (0 0 0);
valueFraction uniform (1 0 0 0 0 1);
}
{
type directionMixed;
refValue uniform (0 0 0);
refGradient uniform (0 0 0);
valueFraction uniform (1 0 0 0 0 1);
}
). In this case it is a symmTensor [xx xy xz yy yz zz] because the variable is a vector. The refGradient is used for all components. The Left patch in this image was set to the aforementioned BC configurations and the top patch has a fixedValue disp.Reference: http://www.cfd-online.com/Forums/ope...-mixed-bc.html
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