Implementing Boundary Condition

Question

Hi,

I have a xml mesh and also I have some .dat file in which I have the node numbers that they are on the boundary. I like to implement Dirichlet boundary conditions at these points (zero displacement). How can i do that?

Comments

Please post short but complete example code. It's easier for someone to respond by showing you how to modify your code.

Answer 1

Here is my code. In this code since my mesh has complex geometry the MeshFunction does not work properly and do not satisfy boundary conditions well especially this line:
"bc0_2 = DirichletBC(W.sub(0), Constant((0.0, 0.0, 0.0)), facet_domains,4) #noslip"

I am looking for something rather than MeshFunction and if is possible to use the node numbers for implementing boundary conditions. It should be noted my mesh contains about 1 million element. I use this script for other geometries and works very well but for this complex one does not.

from future import print_function

from dolfin import *

Solves Stokes eqn

stablized = True

mu = Constant(1.32) #Constant(1320.0) #Constant(1.32) #viscossity

Load mesh and subdomains

mesh_filename = '/global/home/users/volume_mesh.h5'
mesh = Mesh()
mesh_in = HDF5File(mpi_comm_world(), mesh_filename, 'r')
mesh_in.read(mesh, 'mesh', False)
mesh_in.close()

Define function spaces

P2 = VectorElement("Lagrange", mesh.ufl_cell(), 2)

P1 = FiniteElement("Lagrange", mesh.ufl_cell(), 1)

TH = P2 * P1

W = FunctionSpace(mesh, TH)

V = VectorFunctionSpace(mesh, "CG", 1)
P = FunctionSpace(mesh, "CG", 1)
W = MixedFunctionSpace([V, P]) #Taylor-Hood

U_in = -100 #0.372105 #mm/s #372.105 for micron/s unit
results_dir = '/global/home/users/stokes_flow/'

BC

if MPI.rank(mpi_comm_world()) == 0:
print "Setting BC..."

bc_file = '/global/home/users/arzani/Microchannel/simple/advdif/mesh/BCnodeFacets.h5'

bc_file = '/global/home/users/BCnodeFacets.h5'
facet_domains = MeshFunction('size_t', mesh)
facet_domains_in = HDF5File(mpi_comm_world(), bc_file, 'r')
facet_domains_in.read(facet_domains, 'mesh_function')
facet_domains_in.close()

inflow = Expression((" -5(2020-x[1]x[1]-x[2]x[2])", "0.0", "0.0"))
bc0_1 = DirichletBC(W.sub(0), Constant((0.0, 0.0, 0.0)) , facet_domains,3) #noslip
bc0_2 = DirichletBC(W.sub(0), Constant((0.0, 0.0, 0.0)), facet_domains,4) #noslip
bc1_1 = DirichletBC(W.sub(0), inflow, facet_domains,1) #inlet for u

Collect boundary conditions

bcs = [bc1_1,bc0_1, bc0_2]