Question #109629 on DOLFIN changed: https://answers.launchpad.net/dolfin/+question/109629
Garth Wells proposed the following answer: On 04/05/10 19:45, Johan Hake wrote: > Question #109629 on DOLFIN changed: > https://answers.launchpad.net/dolfin/+question/109629 > > Status: Open => Answered > > Johan Hake proposed the following answer: > You are almost there: > > Try this slightly corrected code: > Also, try applying some Dirichlet bcs to the problem. Garth > Johan > > ******************************************* > from dolfin import * > mesh = UnitCube(5, 5, 5) > V = FunctionSpace(mesh, "CG", 1) > > # You want the facets not the cells > subdomains = MeshFunction("uint", mesh, mesh.topology().dim()-1) > > left, right = compile_subdomains(["(fabs(x[0])< DOLFIN_EPS)&& on_boundary", > "(fabs(x[0] - 1.0)< DOLFIN_EPS)&& on_boundary"]) > btm, top = compile_subdomains(["(fabs(x[2])< DOLFIN_EPS)&& on_boundary", > "(fabs(x[2] - 1.0)< DOLFIN_EPS)&& on_boundary"]) > > # Mark all subdomains with a number you are not using in the form > subdomains.set_all(4) > top.mark(subdomains, 1) > right.mark(subdomains, 2) > left.mark(subdomains, 3) > > v = TestFunction(V); > u = TrialFunction(V); > > > # Use Constants for, well, constants > g = Constant(1.4) > alpha=Constant(1.4*1.4/9.81) > > a = inner(grad(v), grad(u))*dx +(alpha*v*u)*ds(1) > L = g*v*ds(2)-g*v*ds(3) > > # Pass your subdomains to VariationalProblem > problem = VariationalProblem(a, L, exterior_facet_domains=subdomains) > u = problem.solve() > plot(u, interactive=True) > > On Tuesday May 4 2010 11:11:16 Thomas Ward wrote: >> New question #109629 on DOLFIN: >> https://answers.launchpad.net/dolfin/+question/109629 >> >> I am struggling with a very simple problem >> >> unit cube >> div(grad(u))=0 >> du/dn=-1.4 on x=0 >> du/dn=1.4 on x=1 >> du/dn+1.4*1.4/9.81*u=0 on z=1 >> du/dn=0 on y=0,y=1,z=0 >> >> below is my attempt with pydolfin, but it gives u=zero everywhere >> any help will be much appreciated, thanks, Tom >> >> from dolfin import * >> mesh = UnitCube(5, 5, 5) >> V = FunctionSpace(mesh, "CG", 1) >> >> subdomains = MeshFunction("uint",mesh, mesh.topology().dim()) >> left, right = compile_subdomains(["(fabs(x[0])< DOLFIN_EPS)&& >> on_boundary", "(fabs(x[0] - 1.0)< DOLFIN_EPS)&& on_boundary"]) btm, top >> = compile_subdomains(["(fabs(x[2])< DOLFIN_EPS)&& on_boundary", >> "(fabs(x[2] - 1.0)< DOLFIN_EPS)&& on_boundary"]) >> >> top.mark(subdomains, 1) >> right.mark(subdomains, 2) >> left.mark(subdomains, 3) >> >> v = TestFunction(V); >> u = TrialFunction(V); >> >> g = Expression("1.4") >> alpha=Expression("1.4*1.4/9.81") >> >> a = inner(grad(v), grad(u))*dx +(alpha*v*u)*ds(1) >> L = g*v*ds(2)-g*v*ds(3) >> >> problem = VariationalProblem(a, L) >> u = problem.solve() >> plot(u, interactive=True) > -- You received this question notification because you are a member of DOLFIN Team, which is an answer contact for DOLFIN. _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : dolfin@lists.launchpad.net Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
