To display the Constraint Settings section in Constraint nodes, click the Show More Options button () on the Model Builder toolbar and select Advanced Physics Options in the Show More Options dialog box.
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Normal-direction constraints on a moving mesh, where the mesh motion is part of the problem. These conditions are of the type n · u − r = 0 where n = n(x) is the boundary normal, u is a vector field (displacements or velocity), and x is the mesh coordinate vector. Symmetric constraints give constraint forces not only on the equations for u but also on the equations for x, which typically are not wanted.
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Wall boundary conditions for turbulent fluid flow. For the k-ε turbulence model, this condition is of the type k − r( ε ), −n · ∇ε, where r is a given function. Bidirectional constraints for the first relation imply that the second relation cannot hold.
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