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Add flex elasticity stiffness matrix to mjModel.

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PiperOrigin-RevId: 675101645
Change-Id: Ic169c108b9eece3657ea4ec211df357abe615b7e
This commit is contained in:
Alessio Quaglino
2024-09-16 04:59:55 -07:00
committed by Copybara-Service
parent c77babe046
commit 2da15cf137
12 changed files with 71 additions and 29 deletions
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test/plugin/elasticity/elasticity_test.cc
+12 -8
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@@ -148,6 +148,7 @@ TEST_F(PluginTest, ElasticEnergyMembrane) {
mj_kinematics(m, d);
mj_flex(m, d);
mjtNum* metric = m->flex_stiffness + 21 * m->flex_elemadr[0];
// check that if the entire geometry is rescaled by a factor "scale", then
// trace(strain^2) = 2*scale^2
@@ -156,15 +157,16 @@ TEST_F(PluginTest, ElasticEnergyMembrane) {
for (int t = 0; t < membrane->nt; t++) {
mjtNum energy = 0;
mjtNum volume = 1./2.;
int idx = 0;
for (int e1 = 0; e1 < 3; e1++) {
for (int e2 = 0; e2 < 3; e2++) {
for (int e2 = e1; e2 < 3; e2++) {
int idx1 = membrane->elements[t].edges[e1] + m->flex_edgeadr[0];
int idx2 = membrane->elements[t].edges[e2] + m->flex_edgeadr[0];
mjtNum elongation1 =
mjtNum elong1 =
scale * m->flexedge_length0[idx1] * m->flexedge_length0[idx1];
mjtNum elongation2 =
mjtNum elong2 =
scale * m->flexedge_length0[idx2] * m->flexedge_length0[idx2];
energy += membrane->metric[9*t+3*e2+e1] * elongation1 * elongation2;
energy += metric[21*t+idx++] * elong1 * elong2 * (e1 == e2 ? 1. : 2.);
}
}
EXPECT_NEAR(
@@ -230,6 +232,7 @@ TEST_F(ElasticityTest, ElasticEnergySolid) {
mj_kinematics(m, d);
mj_flex(m, d);
mjtNum* metric = m->flex_stiffness + 21 * m->flex_elemadr[0];
// check that if the entire geometry is rescaled by a factor "scale", then
// trace(strain^2) = 3*scale^2
@@ -238,15 +241,16 @@ TEST_F(ElasticityTest, ElasticEnergySolid) {
for (int t = 0; t < solid->nt; t++) {
mjtNum energy = 0;
mjtNum volume = 1./6.;
int idx = 0;
for (int e1 = 0; e1 < 6; e1++) {
for (int e2 = 0; e2 < 6; e2++) {
for (int e2 = e1; e2 < 6; e2++) {
int idx1 = solid->elements[t].edges[e1] + m->flex_edgeadr[0];
int idx2 = solid->elements[t].edges[e2] + m->flex_edgeadr[0];
mjtNum elongation1 =
mjtNum elong1 =
scale * m->flexedge_length0[idx1] * m->flexedge_length0[idx1];
mjtNum elongation2 =
mjtNum elong2 =
scale * m->flexedge_length0[idx2] * m->flexedge_length0[idx2];
energy += solid->metric[36*t+6*e2+e1] * elongation1 * elongation2;
energy += metric[21*t+idx++] * elong1 * elong2 * (e1 == e2 ? 1. : 2.);
}
}
EXPECT_NEAR(