# Boundary Conditions. fixedValue and fixedGradient

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 August 22, 2014, 04:46 Boundary Conditions. fixedValue and fixedGradient #1 Member   Pratik Nanavati Join Date: May 2014 Location: Munich, Germany Posts: 40 Rep Power: 5 Hello all, I am very much confused between these two boundary conditions. - fixedValue and fixedGradient I have gone through the user guide but it just states that Value of phi and Gradient of phi are specified respectively. can anyone please explain me in detail the difference between Value and Gradient ? or If you know some good online links then please post. I need to study boundary conditions in much depth.

 August 25, 2014, 11:09 #2 Member   Join Date: Jun 2011 Posts: 53 Rep Power: 8 Hi nanavati, FixedValue means a Dirichlet boundary condition: http://en.wikipedia.org/wiki/Dirichl...dary_condition Take for example the temperature T If you give a boundary condition of your temperature field with a fixedValue at a wall WALL { type fixedValue; value uniform 300; } It means, that there is a temperature of exactly 300K at this wall. fixedGradient means a Neumann boundary condition: http://en.wikipedia.org/wiki/Neumann_boundary_condition If you give a fixedGradient at the wall WALL { type fixedGradient; value uniform 0; } or with the same meaning WALL { type zeroGradient; } Then the gradient of the Temperature dT/dx_i has this value. In this example dT/dy=0, so it is an adiabatic wall. Regards squirrel nanavati likes this.

 August 26, 2014, 03:30 #3 Member   Pratik Nanavati Join Date: May 2014 Location: Munich, Germany Posts: 40 Rep Power: 5 Many thanks for the clear cut explanation with the Examples.. My Doubt is Solved now

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