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	tgrains.c: fix and optimize grain-grain interaction - granular - granular dynam…
	git clone git://src.adamsgaard.dk/granular
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	---
	commit b5116979a34a77b651a34b8e51665749e20dd2f0
	parent f457ddb46d693870cf3f73a76057f606e94415ec
	Author: Anders Damsgaard <[email protected]>
	Date: Thu, 22 Apr 2021 13:47:47 +0200

	grains.c: fix and optimize grain-grain interaction

	Diffstat:
	M grains.c \| 16 +++++++++-------

	1 file changed, 9 insertions(+), 7 deletions(-)
	---
	diff --git a/grains.c b/grains.c
	t@@ -135,7 +135,7 @@ grains_interact(struct grain g_i, struct grain g_j, int …
	d_i, d_j,
	r_ij[3], r_ij_norm,
	m_i, m_j, m_ij,
	- E_ij, nu_ij, mu_ij,
	+ mu_ij,
	gamma_n_ij, gamma_t_ij,
	k_n_ij, k_t_ij, A_ij,
	angvel_ij[3], u_t_dot_v_ij,
	t@@ -171,14 +171,14 @@ grains_interact(struct grain g_i, struct grain g_j, in…
	v_t_ij[d] = v_ij[d] - v_n_ij[d] - 0.5 * angvel_cross_r_ij[d];
	}

	- E_ij = fmin(g_i->youngs_modulus, g_j->youngs_modulus);
	- nu_ij = fmin(g_i->poissons_ratio, g_j->poissons_ratio);
	mu_ij = fmin(g_i->friction_coeff, g_j->friction_coeff);
	gamma_n_ij = fmin(g_i->damping_n, g_j->damping_n);
	gamma_t_ij = fmin(g_i->damping_t, g_j->damping_t);

	- k_n_ij = 2.0 / 3.0 * E_ij / (1.0 - pow(nu_ij, 2.0));
	- k_t_ij = 2.0 * E_ij / (1.0 + nu_ij) * (2.0 - nu_ij);
	+ k_n_ij = fmin(grain_stiffness_normal(g_i),
	+ grain_stiffness_normal(g_j));
	+ k_t_ij = fmin(grain_stiffness_tangential(g_i),
	+ grain_stiffness_tangential(g_j));

	A_ij = sqrt(delta_ij) * sqrt(d_i * d_j / (2.0 * (d_i + d_j)));

	t@@ -204,8 +204,10 @@ grains_interact(struct grain g_i, struct grain g_j, int…
	g_i->contacts[ic].age += dt;
	u_t_dot_v_ij = dot(g_i->contacts[ic].tandisp, v_ij, 3);
	for (d = 0; d < 3; d++)
	- g_i->contacts[ic].tandisp[d] += v_t_ij[d] * dt
	- - u_t_dot_v_ij / (r_ij_norm * r_…
	+ g_i->contacts[ic].tandisp[d] += (v_t_ij[d]
	+ - u_t_dot_v_ij * r_ij[d]
	+ / (r…
	+ * dt;

	free(angvel_cross_r_ij);
	free(f_t_cross_r_ij);