Hi,

I’m rather new to FeniCS and to FEM so have a hard time currently.

During solving of a first problem I get the error:

`*** Warning: Found no facets matching domain for boundary condition.`

All information in the web did not help me up to now.

I try to solve the time dependent heat convection-diffusion equation with different boundary conditions at different positions of the domain (Dirichlet and Neumann and Robin). I reduced the original code to something that might not make physical sense but looks as follows:

```
"""
Time dependent Thermal Convection-Diffusion Equation
rho*cp*grad(T,t)+rho*cp*v*grad(T,x)=div(lambda*grad(T,x),x)
T = Tc on Gamma G
T = Tc/2. on Gamma F
Temperatures in degree Celsius
Boundaries:
x: 0 --> Thick
y: 0 --> LengthT (y-Axis inverted)
x=0.0 x = Thick
0 0 0 0 0 0 0 0 0 0 0 0 0 ... 0
4 1
4 1
4 1
... ...
4 1
4 1 y = LengthM
4 2
4 2
... ...
4 2
4 2
3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 y = LengthT
"""
from fenics import *
import matplotlib.pyplot as plt
#=============================================================
# some problem parameters
rho = 7000 # kg/m**3
lmbda = 50 # W/m K
cp = 500 # J/kg K
thd = lmbda/(rho*cp) # thermal diffusivity
Tc = 1550 # degree Celsius
Thick = 0.2 # thickness
CenterX = Thick/2.0
LengthM = 0.6 # length from 0.0 to of first boundary
npThick = 20
LengthT = 3.0 # total length
npLength = 300
#=============================================================
# mesh, functionspace and boundaries
p0 = Point(0.0,0.0)
p1 = Point(Thick,LengthT)
mesh = RectangleMesh(p0,p1,npThick,npLength,'left')
V = FunctionSpace(mesh, 'P', 1)
class BoundaryG(SubDomain): # Boundary 0
tol = 1E-8
def inside(self, x, on_boundary):
if on_boundary and near(x[1],0.0,self.tol): return True
else: return False
class BoundaryF(SubDomain): # Boundary 1 (original Boundary 3 - all others removed)
tol = 1E-8
def inside(self, x, on_boundary):
if on_boundary and \
near(x[1]>LengthT,self.tol): return True
else: return False
boundary_markers = MeshFunction('size_t', mesh,dim=mesh.topology().dim()-1) #mesh.geometric_dimension()-1)
sdG = 0
sdF = 1
bG = BoundaryG()
bG.mark(boundary_markers,sdG)
bF = BoundaryF()
bF.mark(boundary_markers,sdF)
ds = Measure('ds',domain=mesh,subdomain_data=boundary_markers)
boundary_file = File("t_modell/boundaries.pvd")
boundary_file << boundary_markers
#=============================================================
# boundary conditions
u = TrialFunction(V)
v = TestFunction(V)
# default bc is Neumann
bcond = {
0:{'Dirichlet':Constant(Tc)},
1:{'Dirichlet':Constant(Tc/2.0)}
}
bcs = []
for i in bcond:
bc = DirichletBC(V,bcond[i]['Dirichlet'],boundary_markers,i)
bcs.append(bc)
#=============================================================
# Define variational problem
f0 = Constant(0) # symmetry
fD = Constant(thd) # thermal diffusivity
ts = Expression(('0.0','0.01/60.0'), degree=1) # transport speed in y direction 0.01 m/min
# weak problem
a = fD * dot(grad(u),grad(v)) * dx + dot(ts,grad(u)) * v * dx
L = f0 * v * dx
#=============================================================
# solve time dependent problem
tFinal = 60.0 # final simulation time
dt = 1.0 # time step size
# Define initial value
fI = Constant(1000) # Initial Values
u_n = interpolate(fI, V)
# Create VTK file for saving solution
vtkfile = File('t_modell/solution.pvd')
# Time-stepping
u = Function(V)
t = 0
while t < tFinal:
# Update current time
t += dt
print(t,"s /",tFinal,'s')
# Compute solution
solve(a == L, u, bcs)
# Save to file and plot solution
vtkfile << (u, t)
plot(u)
# Update previous solution
u_n.assign(u)
# Hold plot
import matplotlib.pyplot as plt
plt.show()
```

Can anyone help me and point to the lines that are not correct?