Oldroyd-B

Here is the Oldroyd-B viscoelastic method I published in https://doi.org/10.1140/epje/s10189-020-00005-6. A Poiseuille flow test case is included.

Resolves walberla/walberla#158 (closed)

lbmpy_tests/test_oldroydb.py

@@ -7,7 +7,6 @@ from pystencils.boundaries.boundaryhandling import BoundaryHandling
 from pystencils.boundaries.boundaryconditions import Boundary, Neumann, Dirichlet
 from lbmpy.boundaries.boundaryhandling import LatticeBoltzmannBoundaryHandling
 from lbmpy.boundaries import NoSlip
-import scipy.optimize
 
 from lbmpy.oldroydb import *
 import pytest
@@ -19,6 +18,7 @@ import pytest
 
 pytest.importorskip('scipy.optimize')
 def test_oldroydb():
+    import scipy.optimize
 
     # ## Definitions