tnormal-viscous contact model verified - sphere - GPU-based 3D discrete element method algorithm with optional fluid coupling
(HTM) git clone git://src.adamsgaard.dk/sphere
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---
(DIR) commit d951e69722dbdda4e924831e6ef544c468ad533e
(DIR) parent c62854c9bfc6be53c2155553666379bbdada700c
(HTM) Author: Anders Damsgaard <anders.damsgaard@geo.au.dk>
Date: Fri, 20 Jun 2014 12:34:28 +0200
normal-viscous contact model verified
Diffstat:
M src/contactmodels.cuh | 14 +++-----------
M tests/contactmodel.py | 64 +++++++++++++++++++++++++++++++
2 files changed, 67 insertions(+), 11 deletions(-)
---
(DIR) diff --git a/src/contactmodels.cuh b/src/contactmodels.cuh
t@@ -309,9 +309,6 @@ __device__ void contactLinear(Float3* F, Float3* T,
Float4 vel_b = dev_vel[idx_b_orig];
Float4 angvel4_b = dev_angvel[idx_b_orig];
- //printf("\n[%d,%d] vel = [+%e +%e]",
- //idx_a_orig, idx_b_orig, vel_a, vel_b);
-
// Fetch previous sum of shear displacement for the contact pair
Float4 delta_t0_4 = dev_delta_t[mempos];
t@@ -378,22 +375,17 @@ __device__ void contactLinear(Float3* F, Float3* T,
// Normal force component: Elastic - viscous damping
//f_n = (-devC_params.k_n * delta - devC_params.gamma_n * vel_n) * n;
- f_n = fmax(-devC_params.k_n * delta - devC_params.gamma_n * vel_n, 0.0) * n;
+ f_n = fmax(0.0, -devC_params.k_n*delta + devC_params.gamma_n * vel_n) * n;
+ Float f_n_length = length(f_n);
// Store energy dissipated in normal viscous component
// watt = gamma_n * vel_n * dx_n / dt
// watt = gamma_n * vel_n * vel_n * dt / dt
// watt = gamma_n * vel_n * vel_n
// watt = N*m/s = N*s/m * m/s * m/s * s / s
- *ev_dot += devC_params.gamma_n * vel_n * vel_n;
+ *ev_dot += 0.5 * devC_params.gamma_n * vel_n * vel_n;
- // Make sure the viscous damping doesn't exceed the elastic component,
- // i.e. the damping factor doesn't exceed the critical damping, 2*sqrt(m*k_n)
- if (dot(f_n, n) < 0.0f)
- f_n = MAKE_FLOAT3(0.0f, 0.0f, 0.0f);
-
- Float f_n_length = length(f_n);
// Add max. capillary force
f_c = -devC_params.kappa * sqrtf(radius_a * radius_b) * n;
(DIR) diff --git a/tests/contactmodel.py b/tests/contactmodel.py
t@@ -67,6 +67,70 @@ pytestutils.compareFloats(orig.totalKineticEnergy(), after.totalKineticEnergy(),
"Elastic normal collision (4/4):")
+## Linear viscous-elastic collisions
+
+# Normal impact: Check for conservation of momentum (sum(v_i*m_i))
+orig = sphere.sim(np=2, sid='contactmodeltest')
+after = sphere.sim(np=2, sid='contactmodeltest')
+sphere.cleanup(orig)
+orig.radius[:] = [1.0, 1.0]
+orig.x[0,:] = [5.0, 5.0, 2.0]
+orig.x[1,:] = [5.0, 5.0, 4.05]
+v_orig = 1
+orig.vel[0,2] = v_orig
+orig.defineWorldBoundaries(L=[10,10,10])
+orig.initTemporal(total = 0.1, file_dt = 0.01)
+orig.gamma_n[0] = 1.0e6
+
+orig.run(verbose=False)
+after.readlast(verbose=False)
+#print(orig.totalKineticEnergy())
+#print(after.totalKineticEnergy())
+#print(after.totalViscousNormalEnergy())
+pytestutils.test(orig.vel[0,2] > after.vel[1,2],\
+ "Viscoelastic normal collision (1/4):")
+pytestutils.compareFloats(orig.totalKineticEnergy(),
+ after.totalKineticEnergy()
+ + after.totalViscousNormalEnergy(),
+ "Viscoelastic normal collision (2/4):", tolerance=0.05)
+
+# Normal impact with different sizes: Check for conservation of momentum
+orig = sphere.sim(np=2, sid='contactmodeltest')
+after = sphere.sim(np=2, sid='contactmodeltest')
+sphere.cleanup(orig)
+orig.radius[:] = [2.0, 1.0]
+orig.x[0,:] = [5.0, 5.0, 2.0]
+orig.x[1,:] = [5.0, 5.0, 5.05]
+orig.vel[0,2] = 1.0
+orig.defineWorldBoundaries(L=[10,10,10])
+orig.initTemporal(total = 0.1, file_dt = 0.01)
+orig.gamma_n[0] = 1.0e6
+
+orig.run(verbose=False)
+after.readlast(verbose=False)
+pytestutils.compareFloats(orig.totalKineticEnergy(),
+ after.totalKineticEnergy()
+ + after.totalViscousNormalEnergy(),
+ "Viscoelastic normal collision (3/4):", tolerance=0.05)
+
+# Normal impact with different sizes: Check for conservation of momentum
+orig = sphere.sim(np=2, sid='contactmodeltest')
+after = sphere.sim(np=2, sid='contactmodeltest')
+sphere.cleanup(orig)
+orig.radius[:] = [1.0, 2.0]
+orig.x[0,:] = [5.0, 5.0, 2.0]
+orig.x[1,:] = [5.0, 5.0, 5.05]
+orig.vel[0,2] = 1.0
+orig.defineWorldBoundaries(L=[10,10,10])
+orig.initTemporal(total = 0.1, file_dt = 0.01)
+orig.gamma_n[0] = 1.0e6
+
+orig.run(verbose=False)
+after.readlast(verbose=False)
+pytestutils.compareFloats(orig.totalKineticEnergy(),
+ after.totalKineticEnergy()
+ + after.totalViscousNormalEnergy(),
+ "Viscoelastic normal collision (4/4):", tolerance=0.05)
#orig.cleanup()