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	tadd viscous and non-viscous damping - slidergrid - grid of elastic sliders on …
	git clone git://src.adamsgaard.dk/slidergrid
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	---
	commit c1d935d91f4cf966769161facb856ed8c426f859
	parent 25a1b1a29874237888551abd9d157460aedac79f
	Author: Anders Damsgaard <[email protected]>
	Date: Wed, 30 Mar 2016 10:51:54 -0700

	add viscous and non-viscous damping

	Diffstat:
	M slidergrid/main.c \| 12 ++++++++++++
	M slidergrid/simulation.c \| 2 +-
	M slidergrid/slider.c \| 66 +++++++++++++++++++++++------…
	M slidergrid/slider.h \| 8 ++++++++

	4 files changed, 71 insertions(+), 17 deletions(-)
	---
	diff --git a/slidergrid/main.c b/slidergrid/main.c
	t@@ -175,6 +175,18 @@ int main(int argc, char** argv)
	#endif
	}

	+ // add global viscous damping
	+ for (i=0; i<sim.N; i++)
	+ if (sim.sliders[i].damping_viscosity_linear > 1.0e-16 \|\|
	+ sim.sliders[i].damping_viscosity_angular > 1.0e-16)
	+ slider_global_viscous_damping(&sim.sliders[i]);
	+
	+ // add global non-viscous damping
	+ for (i=0; i<sim.N; i++)
	+ if (sim.sliders[i].damping_coefficient > 1.0e-16)
	+ slider_nonviscous_damping(&sim.sliders[i]);
	+
	+
	for (i=0; i<sim.N; i++)
	update_kinematics(&sim.sliders[i], sim.dt, sim.iteration);

	diff --git a/slidergrid/simulation.c b/slidergrid/simulation.c
	t@@ -220,7 +220,7 @@ int save_sliders_to_vtk_file(

	// angular positions
	fprintf(f, " <DataArray NumberOfComponents=\"3\" type=\"Float32\" "
	- "Name=\"Angular position [m]\" format=\"ascii\">\n");
	+ "Name=\"Angular position [rad]\" format=\"ascii\">\n");
	fprintf(f, " ");
	for (i=0; i<N; i++)
	fprintf(f, "%f %f %f ",
	diff --git a/slidergrid/slider.c b/slidergrid/slider.c
	t@@ -1,4 +1,5 @@
	#include <stdio.h>
	+#include <math.h>
	#include "typedefs.h"
	#include "slider.h"
	#include "vector_math.h"
	t@@ -31,6 +32,10 @@ void initialize_slider_values(slider* s)
	s->bond_shear_kv_stiffness = 0.0;
	s->bond_shear_kv_viscosity = 0.0;

	+ s->damping_viscosity_linear = 0.0;
	+ s->damping_viscosity_angular = 0.0;
	+ s->damping_coefficient = 0.0;
	+
	// define all entries in neighbor list as empty
	int i;
	for (i=0; i<MAX_NEIGHBORS; i++) {
	t@@ -137,14 +142,6 @@ void bond_parallel_deformation(slider* s1, const slider s…
	// relative contact interface velocity w/o rolling
	const Float3 vel_linear = subtract_float3(s1->vel, s2.vel);

	- // relative contact interface velocity with rolling
	- const Float3 vel = add_float3(vel_linear,
	- add_float3(
	- multiply_scalar_float3(dist_norm/2.,
	- cross_float3(dist, s1->angvel)),
	- multiply_scalar_float3(dist_norm/2.,
	- cross_float3(dist, s2.angvel))));
	-
	// Normal component of the relative contact interface velocity
	const Float vel_n = -1.0*dot_float3(vel_linear, n);

	t@@ -219,6 +216,15 @@ void bond_normal_deformation(slider* s1, const slider s2,
	multiply_float3(n,
	multiply_float3(n, tangential_displacement0_uncor)));

	+ // project future tangential displacement
	+
	+
	+ // determine dtangential_displacement by central differences
	+
	+
	+ // use dtangential_displacement for elastic response
	+
	+ // use vel_t for viscous response
	}


	t@@ -227,14 +233,10 @@ void bond_deformation(slider* s1, const slider s2,
	const int idx_neighbor, const int iteration)
	{
	bond_parallel_deformation(s1, s2, idx_neighbor, iteration);
	-
	-
	+ //bond_normal_deformation(s1, s2, idx_neighbor, iteration);
	}


	-
	-
	-
	void bond_parallel_kelvin_voigt(slider* s1, const slider s2,
	const int idx_neighbor)
	{
	t@@ -335,8 +337,7 @@ void bond_shear_kelvin_voigt(slider* s1, const slider s2,
	void slider_interaction(slider* s1, const slider s2, const int idx_neighbor)
	{
	bond_parallel_kelvin_voigt(s1, s2, idx_neighbor);
	-
	-
	+ //bond_normal_kelvin_voigt(s1, s2, idx_neighbor);
	}


	t@@ -360,7 +361,7 @@ void slider_neighbor_interaction(

	if (s->neighbors[idx_neighbor] != -1) {

	- slider_displacement(
	+ bond_deformation(
	s, sliders[s->neighbors[idx_neighbor]],
	idx_neighbor, iteration);

	t@@ -379,3 +380,36 @@ void slider_neighbor_interaction(
	}
	}
	}
	+
	+// add frequency-independent viscosity to sum of forces and torques to damp
	+// reflected waves from the edge of the lattice
	+// Mora and Place (1994), Place et al (2002)
	+void slider_viscous_damping(slider* s)
	+{
	+ s->force.x += - s->damping_viscosity_linear*s->vel.x;
	+ s->force.y += - s->damping_viscosity_linear*s->vel.y;
	+ s->force.z += - s->damping_viscosity_linear*s->vel.z;
	+
	+ s->torque.x += - s->damping_viscosity_angular*s->vel.x;
	+ s->torque.y += - s->damping_viscosity_angular*s->vel.y;
	+ s->torque.z += - s->damping_viscosity_angular*s->vel.z;
	+}
	+
	+// add local non-viscous damping, Potyondy and Cundall (2004)
	+void slider_nonviscous_damping(slider* s)
	+{
	+ s->force.x +=
	+ - s->damping_coefficientfabs(s->force.x)copysign(1.0, s->vel.x);
	+ s->force.y +=
	+ - s->damping_coefficientfabs(s->force.y)copysign(1.0, s->vel.y);
	+ s->force.z +=
	+ - s->damping_coefficientfabs(s->force.z)copysign(1.0, s->vel.z);
	+
	+ s->torque.x +=
	+ - s->damping_coefficientfabs(s->torque.x)copysign(1.0, s->angvel.x);
	+ s->torque.y +=
	+ - s->damping_coefficientfabs(s->torque.y)copysign(1.0, s->angvel.y);
	+ s->torque.z +=
	+ - s->damping_coefficientfabs(s->torque.z)copysign(1.0, s->angvel.z);
	+
	+}
	diff --git a/slidergrid/slider.h b/slidergrid/slider.h
	t@@ -39,6 +39,11 @@ typedef struct {
	Float bond_shear_kv_stiffness; // Hookean elastic stiffness [N/m]
	Float bond_shear_kv_viscosity; // viscosity [N/(m*s)]

	+ // Damping parameters
	+ Float damping_viscosity_linear; // Linear velocity damping [N/(m/s)]
	+ Float damping_viscosity_angular; // Angular velocity damping [N*m/(rad/s)]
	+ Float damping_coefficient; // Dimensionless damping [-]
	+
	// The uniquely identifying indexes of the slider neighbors which are bond…
	// to this slider. A value of -1 denotes an empty field. Preallocated fo…
	// speed.
	t@@ -65,4 +70,7 @@ void slider_neighbor_interaction(
	const int N,
	const int iteration);

	+void slider_viscous_damping(slider* s);
	+void slider_nonviscous_damping(slider* s);
	+
	#endif