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LB Boundary force: fix unit conversion and tests
Reference solutions for forces on shear planes and for stokes drag need dynamic viscosity, but LB uses kinetmatic viscosity. This switches the tests to dynamic viscosity and removes a 1/rho from the unit conversion in the script interface. Also, a force balance test is added, which does not depend on the density.
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| Original file line number | Diff line number | Diff line change |
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| # Copyright (C) 2010-2019 The ESPResSo project | ||
| # | ||
| # This file is part of ESPResSo. | ||
| # | ||
| # ESPResSo is free software: you can redistribute it and/or modify | ||
| # it under the terms of the GNU General Public License as published by | ||
| # the Free Software Foundation, either version 3 of the License, or | ||
| # (at your option) any later version. | ||
| # | ||
| # ESPResSo is distributed in the hope that it will be useful, | ||
| # but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| # GNU General Public License for more details. | ||
| # | ||
| # You should have received a copy of the GNU General Public License | ||
| # along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
| import unittest as ut | ||
| import unittest_decorators as utx | ||
| import numpy as np | ||
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| import espressomd.lb | ||
| import espressomd.lbboundaries | ||
| import espressomd.shapes | ||
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| """ | ||
| Checks force on lb boundaries for a fluid with a uniform volume force | ||
| """ | ||
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| AGRID = 0.5 | ||
| EXT_FORCE = np.array([-.01, 0.02, 0.03]) | ||
| VISC = 3.5 | ||
| DENS = 1.5 | ||
| TIME_STEP = 0.05 | ||
| LB_PARAMS = {'agrid': AGRID, | ||
| 'dens': DENS, | ||
| 'visc': VISC, | ||
| 'tau': TIME_STEP, | ||
| 'ext_force_density': EXT_FORCE} | ||
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| class LBBoundaryForceCommon: | ||
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| """Base class of the test that holds the test logic.""" | ||
| lbf = None | ||
| system = espressomd.System(box_l=np.array([12.0, 4.0, 4.0]) * AGRID) | ||
| system.time_step = TIME_STEP | ||
| system.cell_system.skin = 0.4 * AGRID | ||
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| def count_fluid_nodes(self): | ||
| # Count non-boundary nodes: | ||
| fluid_nodes = 0 | ||
| for n in self.lbf.nodes(): | ||
| if not n.boundary: | ||
| fluid_nodes += 1 | ||
| return fluid_nodes | ||
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| def test(self): | ||
| """ | ||
| Integrate the LB fluid until steady state is reached within a certain | ||
| accuracy. Then compare the foce balance between force exerted on fluid | ||
| and forces acting on the boundaries. | ||
| """ | ||
| self.system.actors.clear() | ||
| self.system.lbboundaries.clear() | ||
| self.system.actors.add(self.lbf) | ||
| wall_shape1 = espressomd.shapes.Wall(normal=[1, 0, 0], dist=AGRID) | ||
| wall_shape2 = espressomd.shapes.Wall( | ||
| normal=[-1, 0, 0], dist=-(self.system.box_l[0] - AGRID)) | ||
| wall1 = espressomd.lbboundaries.LBBoundary(shape=wall_shape1) | ||
| wall2 = espressomd.lbboundaries.LBBoundary(shape=wall_shape2) | ||
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| self.system.lbboundaries.add(wall1) | ||
| self.system.lbboundaries.add(wall2) | ||
| fluid_nodes = self.count_fluid_nodes() | ||
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| self.system.integrator.run(20) | ||
| diff = float("inf") | ||
| old_val = float("inf") | ||
| while diff > 0.002: | ||
| self.system.integrator.run(10) | ||
| new_val = wall1.get_force()[0] | ||
| diff = abs(new_val - old_val) | ||
| old_val = new_val | ||
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| surface_area = self.system.box_l[1] * self.system.box_l[2] | ||
| expected_force = fluid_nodes * AGRID**3 * \ | ||
| np.copy(self.lbf.ext_force_density) | ||
| measured_force = np.array(wall1.get_force()) + \ | ||
| np.array(wall2.get_force()) | ||
| np.testing.assert_allclose(measured_force, expected_force, atol=2E-2) | ||
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| @utx.skipIfMissingFeatures(['LB_BOUNDARIES', 'EXTERNAL_FORCES']) | ||
| class LBCPUBoundaryForce(ut.TestCase, LBBoundaryForceCommon): | ||
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| """Test for the CPU implementation of the LB.""" | ||
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| def setUp(self): | ||
| self.lbf = espressomd.lb.LBFluid(**LB_PARAMS) | ||
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| @utx.skipIfMissingGPU() | ||
| @utx.skipIfMissingFeatures(['LB_BOUNDARIES_GPU', 'EXTERNAL_FORCES']) | ||
| class LBGPUBoundaryForce(ut.TestCase, LBBoundaryForceCommon): | ||
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| """Test for the GPU implementation of the LB.""" | ||
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| def setUp(self): | ||
| self.lbf = espressomd.lb.LBFluidGPU(**LB_PARAMS) | ||
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| if __name__ == '__main__': | ||
| ut.main() |
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