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Bending stiffness for curved shells in flex.

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PiperOrigin-RevId: 796361841
Change-Id: I105ea235fe2a8e1bcbde67276d77fa92eed214a1
This commit is contained in:
Alessio Quaglino
2025-08-18 04:12:34 -07:00
committed by Copybara-Service
parent 972ffd7b90
commit b66175eba6
18 changed files with 488 additions and 250 deletions
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src/engine/engine_passive.c
+25 -5
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@@ -116,7 +116,7 @@ static void mj_springdamper(const mjModel* m, mjData* d) {
// flex elasticity
for (int f=0; f < m->nflex; f++) {
mjtNum* k = m->flex_stiffness + 21*m->flex_elemadr[f];
mjtNum* b = m->flex_bending + 16*m->flex_edgeadr[f];
mjtNum* b = m->flex_bending + 17*m->flex_edgeadr[f];
int dim = m->flex_dim[f];
if (dim == 1 || m->flex_rigid[f]) {
@@ -136,12 +136,32 @@ static void mj_springdamper(const mjModel* m, mjData* d) {
// skip boundary edges
continue;
}
// flap edges
mjtNum ed[3][3];
mju_sub3(ed[0], xpos + 3*v[1], xpos + 3*v[0]);
mju_sub3(ed[1], xpos + 3*v[2], xpos + 3*v[0]);
mju_sub3(ed[2], xpos + 3*v[3], xpos + 3*v[0]);
// forces at the vertices due to curved reference
mjtNum frc[4][3];
mju_cross(frc[1], ed[1], ed[2]);
mju_cross(frc[2], ed[2], ed[0]);
mju_cross(frc[3], ed[0], ed[1]);
frc[0][0] = -(frc[1][0] + frc[2][0] + frc[3][0]);
frc[0][1] = -(frc[1][1] + frc[2][1] + frc[3][1]);
frc[0][2] = -(frc[1][2] + frc[2][2] + frc[3][2]);
// force
mjtNum force[12] = {0};
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 4; j++) {
for (int x = 0; x < 3; x++) {
force[3*i+x] += b[16*e+4*i+j] * xpos[3*v[j]+x];
for (int x = 0; x < 3; x++) {
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 4; j++) {
// thin plate bending force
force[3*i+x] += b[17*e+4*i+j] * xpos[3*v[j]+x];
}
// curved reference contribution
force[3*i+x] += b[17*e+16] * frc[i][x];
}
}