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clamp stress for NeoHookean in singular value space

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This commit is contained in:
Xuchen Han
2019-10-11 16:24:07 -07:00
parent e87df18544
commit 9546390fd6
3 changed files with 946 additions and 2 deletions
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55
src/BulletSoftBody/btDeformableNeoHookeanForce.h
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@@ -18,6 +18,8 @@ subject to the following restrictions:
#include "btDeformableLagrangianForce.h"
#include "LinearMath/btQuickprof.h"
#include "LinearMath/btImplicitQRSVD.h"
#include "Eigen"
// This energy is as described in https://graphics.pixar.com/library/StableElasticity/paper.pdf
class btDeformableNeoHookeanForce : public btDeformableLagrangianForce
{
@@ -72,11 +74,12 @@ public:
size_t id2 = node2->index;
size_t id3 = node3->index;
btMatrix3x3 dF = DsFromVelocity(node0, node1, node2, node3) * tetra.m_Dm_inverse;
btMatrix3x3 C = dF + dF.transpose();
btMatrix3x3 dP;
// firstPiolaDampingDifferential(psb->m_tetraScratchesTn[j], dF, dP);
btMatrix3x3 I;
I.setIdentity();
dP = (dF + dF.transpose()) * m_mu_damp + I * (dF[0][0]+dF[1][1]+dF[2][2]) * m_lambda_damp;
dP = C * m_mu_damp + I * (dF[0][0]+dF[1][1]+dF[2][2]) * m_lambda_damp;
btVector3 df_on_node0 = dP * (tetra.m_Dm_inverse.transpose()*grad_N_hat_1st_col);
btMatrix3x3 df_on_node123 = dP * tetra.m_Dm_inverse.transpose();
@@ -155,6 +158,7 @@ public:
virtual void addScaledElasticForce(btScalar scale, TVStack& force)
{
// btScalar max_p = 0;
int numNodes = getNumNodes();
btAssert(numNodes <= force.size());
btVector3 grad_N_hat_1st_col = btVector3(-1,-1,-1);
@@ -166,6 +170,51 @@ public:
btSoftBody::Tetra& tetra = psb->m_tetras[j];
btMatrix3x3 P;
firstPiola(psb->m_tetraScratches[j],P);
btMatrix3x3 U, V;
btVector3 sigma;
singularValueDecomposition(P, U, sigma, V);
sigma[0] = btMin(sigma[0], (btScalar)1000);
sigma[1] = btMin(sigma[1], (btScalar)1000);
sigma[2] = btMin(sigma[2], (btScalar)1000);
sigma[0] = btMax(sigma[0], (btScalar)-1000);
sigma[1] = btMax(sigma[1], (btScalar)-1000);
sigma[2] = btMax(sigma[2], (btScalar)-1000);
btMatrix3x3 Sigma;
Sigma.setIdentity();
Sigma[0][0] = sigma[0];
Sigma[1][1] = sigma[1];
Sigma[2][2] = sigma[2];
// max_p = btMax(max_p, sigma[0]);
// max_p = btMax(max_p, sigma[1]);
// max_p = btMax(max_p, sigma[2]);
P = U * Sigma * V.transpose();
// Eigen::Matrix<double, 3,3> eigenP;
// eigenP << P[0][0], P[0][1], P[0][2],
// P[1][0],P[1][1],P[1][2],
// P[2][0],P[2][1],P[2][2];
// Eigen::JacobiSVD<Eigen::Matrix<double, 3,3> > svd(eigenP, Eigen::ComputeFullU | Eigen::ComputeFullV);
// Eigen::Matrix<double, 3,3> P_hat = svd.singularValues().asDiagonal();
// P_hat(0,0) = btMin((btScalar)P_hat(0,0), (btScalar)20);
// P_hat(1,1) = btMin((btScalar)P_hat(1,1), (btScalar)20);
// P_hat(2,2) = btMin((btScalar)P_hat(2,2), (btScalar)20);
// eigenP = svd.matrixU() * P_hat * svd.matrixV().transpose();
// max_p = btMax(max_p, (btScalar)P_hat(0,0));
// max_p = btMax(max_p, (btScalar)P_hat(1,1));
// max_p = btMax(max_p, (btScalar)P_hat(2,2));
//
// P[0][0] = eigenP(0,0);
// P[0][1] = eigenP(0,1);
// P[0][2] = eigenP(0,2);
// P[1][0] = eigenP(1,0);
// P[1][1] = eigenP(1,1);
// P[1][2] = eigenP(1,2);
// P[2][0] = eigenP(2,0);
// P[2][1] = eigenP(2,1);
// P[2][2] = eigenP(2,2);
// btVector3 force_on_node0 = P * (tetra.m_Dm_inverse.transpose()*grad_N_hat_1st_col);
btMatrix3x3 force_on_node123 = P * tetra.m_Dm_inverse.transpose();
btVector3 force_on_node0 = force_on_node123 * grad_N_hat_1st_col;
@@ -187,6 +236,7 @@ public:
force[id3] -= scale1 * force_on_node123.getColumn(2);
}
}
// std::cout << max_p << std::endl;
}
// The damping matrix is calculated using the time n state as described in https://www.math.ucla.edu/~jteran/papers/GSSJT15.pdf to allow line search
@@ -212,11 +262,12 @@ public:
size_t id2 = node2->index;
size_t id3 = node3->index;
btMatrix3x3 dF = Ds(id0, id1, id2, id3, dv) * tetra.m_Dm_inverse;
btMatrix3x3 C = dF + dF.transpose();
btMatrix3x3 dP;
// firstPiolaDampingDifferential(psb->m_tetraScratchesTn[j], dF, dP);
btMatrix3x3 I;
I.setIdentity();
dP = (dF + dF.transpose()) * m_mu_damp + I * (dF[0][0]+dF[1][1]+dF[2][2]) * m_lambda_damp;
dP = C * m_mu_damp + I * (dF[0][0]+dF[1][1]+dF[2][2]) * m_lambda_damp;
// btVector3 df_on_node0 = dP * (tetra.m_Dm_inverse.transpose()*grad_N_hat_1st_col);
btMatrix3x3 df_on_node123 = dP * tetra.m_Dm_inverse.transpose();
btVector3 df_on_node0 = df_on_node123 * grad_N_hat_1st_col;