From 47e9a1a93b6cc5c55c690a16c3949942839d05e6 Mon Sep 17 00:00:00 2001
From: Michael Kuron <mkuron@icp.uni-stuttgart.de>
Date: Mon, 7 Sep 2020 18:42:31 +0200
Subject: [PATCH] Fix sign error in Schiller force model
---
lbmpy/forcemodels.py | 2 +-
lbmpy_tests/test_force.py | 9 +++++----
2 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/lbmpy/forcemodels.py b/lbmpy/forcemodels.py
index 87924699..ad57d27c 100644
--- a/lbmpy/forcemodels.py
+++ b/lbmpy/forcemodels.py
@@ -175,7 +175,7 @@ class Schiller:
omega = get_shear_relaxation_rate(lb_method)
omega_bulk = get_bulk_relaxation_rate(lb_method)
G = (u * force.transpose() + force * u.transpose() - uf * sp.Rational(2, lb_method.dim)) * sp.Rational(1, 2) * \
- (2 + omega) + uf * sp.Rational(1, lb_method.dim) * (2 + omega_bulk)
+ (2 - omega) + uf * sp.Rational(1, lb_method.dim) * (2 - omega_bulk)
result = []
for direction, w_i in zip(lb_method.stencil, lb_method.weights):
diff --git a/lbmpy_tests/test_force.py b/lbmpy_tests/test_force.py
index e7021aa4..79872b7b 100644
--- a/lbmpy_tests/test_force.py
+++ b/lbmpy_tests/test_force.py
@@ -112,15 +112,16 @@ def test_modes(stencil, force_model):
if force_model == "schiller":
num_stresses = (dim*dim-dim)//2+dim
+ lambda_s, lambda_b = -omega_s, -omega_b
# The stress moments should match eq. 47 from https://doi.org/10.1023/A:1010414013942
u = method.first_order_equilibrium_moment_symbols
def traceless(m):
tr = sp.simplify(sp.Trace(m))
return m - tr/m.shape[0]*sp.eye(m.shape[0])
- C = sp.Rational(1,2) * (2 + omega_s) * (traceless(sp.Matrix(u) * sp.Matrix(F).transpose()) + \
+ C = sp.Rational(1,2) * (2 + lambda_s) * (traceless(sp.Matrix(u) * sp.Matrix(F).transpose()) + \
traceless(sp.Matrix(F) * sp.Matrix(u).transpose())) + \
- sp.Rational(1,method.dim) * (2 + omega_b) * sp.Matrix(u).dot(F) * sp.eye(method.dim)
+ sp.Rational(1,method.dim) * (2 + lambda_b) * sp.Matrix(u).dot(F) * sp.eye(method.dim)
subs = {sp.Symbol(chr(ord("x")+i)) * sp.Symbol(chr(ord("x")+j)) : C[i,j]
for i in range(dim) for j in range(dim)}
@@ -139,7 +140,7 @@ def test_modes(stencil, force_model):
# Check eq. 4.53b from schiller2008thermal
assert [sp.simplify(sum(ff[i] * stencil[i][j] for i in range(len(stencil)))) for j in range(dim)] == F
# Check eq. 4.61a from schiller2008thermal
- ref = (2 + omega_s)/2 * (traceless(sp.Matrix(u) * sp.Matrix(F).transpose()) + \
+ ref = (2 + lambda_s)/2 * (traceless(sp.Matrix(u) * sp.Matrix(F).transpose()) + \
traceless(sp.Matrix(F) * sp.Matrix(u).transpose()))
s = sp.zeros(dim)
for i in range(0, len(stencil)):
@@ -147,7 +148,7 @@ def test_modes(stencil, force_model):
assert sp.simplify(s-ref) == sp.zeros(dim)
# Check eq. 4.61b from schiller2008thermal
assert sp.simplify(sum(ff[i] * stencil[i][a]**2 for i in range(len(stencil)) for a in range(dim))
- - (2+omega_b)*sp.Matrix(u).dot(F)) == 0
+ - (2+lambda_b)*sp.Matrix(u).dot(F)) == 0
# All other moments should be zero
assert list(force_moments[dim+1+num_stresses:]) == [0] * (len(stencil)-(dim+1+num_stresses))
--
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