def test_stokes(self):
self.system.actors.clear()
self.system.lbboundaries.clear()
self.system.actors.add(self.lbf)
# The temperature is zero.
self.system.thermostat.set_lb(kT=0)
# Setup walls
walls = [None] * 4
walls[0] = lbboundaries.LBBoundary(shape=shapes.Wall(
normal=[-1, 0, 0], dist=-(1 + box_width)), velocity=v)
walls[1] = lbboundaries.LBBoundary(
shape=shapes.Wall(
normal=[
1,
0,
0],
dist=1),
velocity=v)
walls[2] = lbboundaries.LBBoundary(shape=shapes.Wall(
normal=[0, -1, 0], dist=-(1 + box_width)), velocity=v)
walls[3] = lbboundaries.LBBoundary(
shape=shapes.Wall(
normal=[
0,
1,
0],
dist=1),
velocity=v)
for wall in walls:
self.system.lbboundaries.add(wall)
# setup sphere without slip in the middle
sphere = lbboundaries.LBBoundary(shape=shapes.Sphere(
radius=radius, center=[real_width / 2] * 2 + [box_length / 2], direction=1))
self.system.lbboundaries.add(sphere)
def size(vector):
tmp = 0
for k in vector:
tmp += k * k
return np.sqrt(tmp)
self.system.integrator.run(800)
stokes_force = 6 * np.pi * KVISC * radius * size(v)
print("Stokes' Law says: f=%f" % stokes_force)
# get force that is exerted on the sphere
for i in range(4):
self.system.integrator.run(200)
force = sphere.get_force()
print("Measured force: f=%f" % size(force))
self.assertLess(abs(1.0 - size(force) / stokes_force), 0.06)
def test(self):
self.system.actors.clear()
self.system.lbboundaries.clear()
self.system.actors.add(self.lbf)
# Setup walls
for i in range(3):
n = np.zeros(3)
n[i] = 1
self.system.lbboundaries.add(
lbboundaries.LBBoundary(shape=shapes.Wall(
normal=-n, dist=-(self.system.box_l[i] - AGRID))))
self.system.lbboundaries.add(lbboundaries.LBBoundary(
shape=shapes.Wall(
normal=n, dist=AGRID)))
# setup sphere without slip in the middle
sphere = lbboundaries.LBBoundary(shape=shapes.Sphere(
radius=RADIUS, center=self.system.box_l / 2, direction=1))
self.system.lbboundaries.add(sphere)
sphere_volume = 4. / 3. * np.pi * RADIUS**3
# Equilibration
last_force = -999999
self.system.integrator.run(100)
while True:
self.system.integrator.run(10)
force = np.linalg.norm(sphere.get_force())
if np.linalg.norm(force - last_force) < 0.01:
break
last_force = force
# Check force balance
boundary_force = np.zeros(3)
for b in self.system.lbboundaries:
boundary_force += b.get_force()
fluid_nodes = count_fluid_nodes(self.lbf)
fluid_volume = fluid_nodes * AGRID**3
applied_force = fluid_volume * np.array(LB_PARAMS['ext_force_density'])
np.testing.assert_allclose(
boundary_force,
applied_force,
atol=0.08 * np.linalg.norm(applied_force))
# Check buoyancy force on the sphere
expected_force = np.array(
[0, -sphere_volume * DENS * G, 0])
np.testing.assert_allclose(
np.copy(sphere.get_force()), expected_force,
atol=np.linalg.norm(expected_force) * 0.02)
def test_stokes(self):
self.system.actors.clear()
self.system.lbboundaries.clear()
self.system.actors.add(self.lbf)
self.system.thermostat.set_lb(LB_fluid=self.lbf, gamma=1.0)
# Setup walls
walls = [None] * 4
walls[0] = lbboundaries.LBBoundary(shape=shapes.Wall(
normal=[-1, 0, 0], dist=-(1 + box_width)),
velocity=v)
walls[1] = lbboundaries.LBBoundary(shape=shapes.Wall(normal=[1, 0, 0],
dist=1),
velocity=v)
walls[2] = lbboundaries.LBBoundary(shape=shapes.Wall(
normal=[0, -1, 0], dist=-(1 + box_width)),
velocity=v)
walls[3] = lbboundaries.LBBoundary(shape=shapes.Wall(normal=[0, 1, 0],
dist=1),
velocity=v)
for wall in walls:
self.system.lbboundaries.add(wall)
# setup sphere without slip in the middle
sphere = lbboundaries.LBBoundary(
shape=shapes.Sphere(radius=radius,
center=[real_width / 2] * 2 + [box_length / 2],
direction=1))
self.system.lbboundaries.add(sphere)
def size(vector):
tmp = 0
for k in vector:
tmp += k * k
return np.sqrt(tmp)
last_force = -1000.
dynamic_viscosity = self.lbf.viscosity * self.lbf.density
stokes_force = 6 * np.pi * dynamic_viscosity * radius * size(v)
self.system.integrator.run(35)
while True:
self.system.integrator.run(5)
force = np.linalg.norm(sphere.get_force())
if np.abs(last_force - force) < 0.01 * stokes_force:
break
last_force = force
force = np.copy(sphere.get_force())
np.testing.assert_allclose(force, [0, 0, stokes_force],
rtol=0.03,
atol=stokes_force * 0.03)
def test_stokes(self):
# System setup
agrid = 1
radius = 5.5
box_width = 54
real_width = box_width + 2 * agrid
box_length = 54
system = espressomd.System(box_l=[real_width, real_width, box_length])
system.box_l = [real_width, real_width, box_length]
system.time_step = 0.4
system.cell_system.skin = 0.4
# The temperature is zero.
system.thermostat.set_lb(kT=0)
# LB Parameters
v = [0, 0, 0.01] # The boundary slip
kinematic_visc = 5.0
# Invoke LB fluid
lbf = lb.LBFluidGPU(visc=kinematic_visc,
dens=1,
agrid=agrid,
tau=system.time_step,
fric=1)
system.actors.add(lbf)
# Setup walls
walls = [None] * 4
walls[0] = lbboundaries.LBBoundary(shape=shapes.Wall(
normal=[-1, 0, 0], dist=-(1 + box_width)),
velocity=v)
walls[1] = lbboundaries.LBBoundary(shape=shapes.Wall(normal=[1, 0, 0],
dist=1),
velocity=v)
walls[2] = lbboundaries.LBBoundary(shape=shapes.Wall(
normal=[0, -1, 0], dist=-(1 + box_width)),
velocity=v)
walls[3] = lbboundaries.LBBoundary(shape=shapes.Wall(normal=[0, 1, 0],
dist=1),
velocity=v)
for wall in walls:
system.lbboundaries.add(wall)
# setup sphere without slip in the middle
sphere = lbboundaries.LBBoundary(
shape=shapes.Sphere(radius=radius,
center=[real_width / 2] * 2 + [box_length / 2],
direction=1))
system.lbboundaries.add(sphere)
def size(vector):
tmp = 0
for k in vector:
tmp += k * k
return np.sqrt(tmp)
system.integrator.run(800)
stokes_force = 6 * np.pi * kinematic_visc * radius * size(v)
print("Stokes' Law says: f=%f" % stokes_force)
# get force that is exerted on the sphere
for i in range(5):
system.integrator.run(200)
force = sphere.get_force()
print("Measured force: f=%f" % size(force))
self.assertLess(abs(1.0 - size(force) / stokes_force), 0.06)
walls = [None] * 4
walls[0] = lbboundaries.LBBoundary(shape=shapes.Wall(normal=[-1,0,0],
dist = -(1+box_width)), velocity=v)
walls[1] = lbboundaries.LBBoundary(shape=shapes.Wall(normal=[1,0,0], dist = 1),
velocity=v)
walls[2] = lbboundaries.LBBoundary(shape=shapes.Wall(normal=[0,-1,0],
dist = -(1+box_width)), velocity=v)
walls[3] = lbboundaries.LBBoundary(shape=shapes.Wall(normal=[0,1,0], dist = 1),
velocity=v)
for wall in walls:
system.lbboundaries.add(wall)
# setup sphere without slip in the middle
sphere = lbboundaries.LBBoundary(shape=shapes.Sphere(radius=radius,
center = [real_width/2] * 2 + [box_length/2],
direction = 1))
system.lbboundaries.add(sphere)
lbf.print_vtk_boundary("./boundary.vtk")
def size(vector):
tmp = 0
for k in vector:
tmp+=k*k
return np.sqrt(tmp)
for i in range(40):
