How can I use a FacetNormal in a conditional part of a form?

Question

I'm working on a 2d heat conduction problem with a deforming boundary. The material is exposed to a constant heat flux vector. My problem is that as the material deforms, part of the "exposed" boundary points away from the heat flux and is thus shielded from it. I tried using a conditional statement in the form:

n = FacetNormal(mesh)
q = conditional(gt(n[1], 0), dot(q_vector, n), Constant(0.0))
L = q*v*ds

When I look at the compile.log file I get errors saying that form header file is using undeclared identifiers 'n1' and 'n2'.

Does this idea make any sense? Is there something wrong with my implementation of it? I could remark the boundaries at every time step, but that seems excessive. Thanks.

Comments

Hi, what DOLFIN version are you running? With the code below I can't repreduce the error you mentioned

from dolfin import *

mesh = UnitSquareMesh(10, 10)

V = FunctionSpace(mesh, 'CG', 1)
v = TestFunction(V)

n = FacetNormal(mesh)
q_vector = Expression(('x[0]', 'x[1]'))
q = conditional(gt(n[1], 0), dot(q_vector, n), Constant(0.0))
# q = conditional(gt(dot(n, Constant((1, 0))), 0), dot(n, q_vector), Constant(0))
L = q*v*ds