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Shawn Walker wrote:
On Mon, 15 Sep 2008, Anders Logg wrote:On Mon, Sep 15, 2008 at 11:21:59AM +0100, Garth N. Wells wrote:DOLFIN wrote:One or more new changesets pushed to the primary dolfin repository. A short summary of the last three changesets is included below. changeset: 4754:23602808c60413cb8faffca818e7a8c04527d3ec tag: tip user: Anders Logg <logg@xxxxxxxxx> date: Sun Sep 14 19:46:40 2008 +0200 files: demo/pde/elasticity/python/demo.py description: Use symmetric gradient in variational form in elasticity demoIn particular reason for this? It is simpler (and still correct) to use the gradient. GarthTo make the form and the matrix symmetric. I showed the demo to a friend (in computational mechanics) and he insisted that we replace grad(v) by epsilon(v). -- AndersIt should be epsilon(v). In the case of Stokes (or Navier-Stokes), if the velocity boundary conditions are dirichlet, then you can just use grad(v). However, if you have stress boundary conditions this is no longer true. The Dirichlet case lets you simplify the variational form from the epsilon(v) case by some integration by parts. epsilon(v) is the correct way.
This is a different story: it should be epsilon(u) where u is the trial function, but grad(v) suffices where v is the test function. For Stokes, NS, epsilon(u) is often avoided by using the incompressibility constraint.
Incidentally, this means that any "general" Navier-Stokes demos should probably be done with the epsilon(v) for the viscous term. It won't make a difference if the boundary conditions are dirichlet for velocity.
Yes, this is true. Garth
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