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	tresolve twist on bond - slidergrid - grid of elastic sliders on a frictional s…
	git clone git://src.adamsgaard.dk/slidergrid
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	---
	commit bbf7010bcf7ceae41f9d8bf35c2f7d1f1e66ae78
	parent d852181baa63f618bea35aa6d8d6053763688920
	Author: Anders Damsgaard Christensen <[email protected]>
	Date: Mon, 18 Apr 2016 16:06:46 -0700

	resolve twist on bond

	Diffstat:
	M slidergrid/slider.c \| 63 ++++++++++++++++++++++++++++-…

	1 file changed, 57 insertions(+), 6 deletions(-)
	---
	diff --git a/slidergrid/slider.c b/slidergrid/slider.c
	t@@ -135,7 +135,7 @@ void update_kinematics(slider* s, Float dt, long int itera…

	// determine time step increment bond-parallel deformation (tension or
	// compression)
	-void bond_parallel_deformation(slider* s1, const slider s2,
	+void bond_tensile_deformation(slider* s1, const slider s2,
	const int idx_neighbor, const int iteration)
	{
	// vector pointing from neighbor (s2) position to this slider position (s1)
	t@@ -192,9 +192,8 @@ void bond_parallel_deformation(slider* s1, const slider s2,
	}


	-// determine time step increment bond-oblique deformation (shear, bending,
	-// and/or twist)
	-void bond_normal_deformation(slider* s1, const slider s2,
	+// determine time step increment bond-shear deformation
	+void bond_shear_deformation(slider* s1, const slider s2,
	const int idx_neighbor, const int iteration, const Float dt)
	{
	// vector pointing from neighbor (s2) position to this slider position (s1)
	t@@ -287,13 +286,65 @@ void bond_normal_deformation(slider* s1, const slider s2,
	#endif
	}

	+// determine time step increment bond twist deformation
	+void bond_twist_deformation(slider* s1, const slider s2,
	+ const int idx_neighbor, const int iteration, const Float dt)
	+{
	+ // vector pointing from neighbor (s2) position to this slider position (s1)
	+ const Float3 dist = subtract_float3(s1->pos, s2.pos);
	+
	+ // length of inter-slider vector
	+ const Float dist_norm = norm_float3(dist);
	+
	+ // unit vector pointing from neighbor (s2) to slider s1
	+ const Float3 n = divide_float3_scalar(dist, dist_norm);
	+
	+ // Get the relative angular velocity
	+ const Float3 angvel_rel = subtract_float3(s2.angvel, s1->angvel);
	+
	+ // Isolate the relative angular velocity component parallel to the bond
	+ const Float twist_vel = dot_float3(angvel_rel, n);
	+
	+ // Twist displacement happening in one time step
	+ const Float dtwist = twist_vel*dt;
	+
	+ // total relative displacement in inter-slider distance
	+ if (iteration == 0)
	+ s1->neighbor_relative_twist[idx_neighbor] = dtwist;
	+ else
	+ s1->neighbor_relative_twist[idx_neighbor] += dtwist;
	+
	+ // total relative displacement in inter-slider distance
	+ s1->neighbor_relative_twist_velocity[idx_neighbor] = twist_vel;
	+
	+#ifdef DEBUG_BOND_DEFORMATION
	+ printf("\t------\n"
	+ "\ttwist = %f %f %f\n"
	+ "\tdtwist = %f %f %f\n"
	+ "\ttwist_vel = %f %f %f\n"
	+ "\t------\n"
	+ ,
	+ twist.x,
	+ twist.y,
	+ twist.z,
	+ dtwist.x,
	+ dtwist.y,
	+ dtwist.z,
	+ twist_vel.x,
	+ twist_vel.y,
	+ twist_vel.z);
	+#endif
	+}
	+
	+

	// Find the bond deformation
	void bond_deformation(slider* s1, const slider s2,
	const int idx_neighbor, const int iteration, const Float dt)
	{
	- bond_parallel_deformation(s1, s2, idx_neighbor, iteration);
	- bond_normal_deformation(s1, s2, idx_neighbor, iteration, dt);
	+ bond_tensile_deformation(s1, s2, idx_neighbor, iteration);
	+ bond_shear_deformation(s1, s2, idx_neighbor, iteration, dt);
	+ bond_twist_deformation(s1, s2, idx_neighbor, iteration, dt);
	}