Error 'Exp' object has no attribute '_cpp_object'

I/O
1

Hello,

I am solving a coupled flow and temperature problem, where the viscosity ‘mu’ depends on the temperature, thus forming the coupling.

I want to be able to extract the viscosity as a .pvd file, but it’s proven tricky, as viscosity is defined as

mu = exp(-Gamma*T),

where T is temperature (part of the solution) and Gamma is a constant.

I want to do something like
File(“Viscosity,pvd”) << mu

but the error I get is
File “/usr/local/lib/python3.6/dist-packages/dolfin/io/init.py”, line 21, in lshift
self.write(u)
AttributeError: ‘Exp’ object has no attribute ‘_cpp_object’

I realise that I need to interpolate or do something else to mu before just exporting it, but I haven’t been able to find out exactly what that is.

Any help would be greatly appreciated!

2

You need to project mu into an appropriate function space. There are plenty of examples in: https://bitbucket.org/fenics-project/dolfin/src/946dbd3e268dc20c64778eb5b734941ca5c343e5/python/demo/undocumented/projection-interpolation/demo_projection-interpolation.py?at=master#demo_projection-interpolation.py-1,36

3

Thank you! I was trying different versions of ‘interpolate’ but I see now that that’s for Expressions. ‘project’ worked like a charm ! (once I figured the appropriate function space).