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// 2019 © William Chèvremont <william.chevremont@univ-grenoble-alpes.fr>
#include "LubricationWithPotential.hpp"
#include <boost/python/call_method.hpp>
namespace yade {
YADE_PLUGIN((Law2_ScGeom_PotentialLubricationPhys)(GenericPotential)(CundallStrackPotential)(CundallStrackAdhesivePotential)(LinExponentialPotential))
bool Law2_ScGeom_PotentialLubricationPhys::go(shared_ptr<IGeom>& iGeom, shared_ptr<IPhys>& iPhys, Interaction* interaction)
{
// Physic & Geometry
LubricationPhys* phys = static_cast<LubricationPhys*>(iPhys.get());
ScGeom* geom = static_cast<ScGeom*>(iGeom.get());
if (!phys || !geom) {
LOG_ERROR("Wrong physics and/or geometry!");
return false;
}
// geometric parameters
Real a((geom->radius1 + geom->radius2) / 2.);
// End-of Interaction condition
if (-geom->penetrationDepth > MaxDist * a) { return false; }
// inititalization
if (phys->u == -1.) {
phys->u = -geom->penetrationDepth;
phys->delta = math::log(phys->u);
}
// Normal part
if (!solve_normalForce(-geom->penetrationDepth / a, scene->dt * a * phys->kn / (phys->nun * 3. / 2.), *phys)) {
LOG_ERROR("Unable to determine normal forces. MAYDAY MAYDAY MAYDAY!");
return false;
}
potential->applyPotential(phys->u, *phys, geom->normal); // Set contactForce, potentialForce, contact.
phys->normalLubricationForce = phys->kn * a * phys->prevDotU * geom->normal; // From implicit formulation. Prevent computing divisions.
phys->normalForce = phys->kn * (-geom->penetrationDepth - phys->u) * geom->normal; // From regularization expression.
// Get bodies properties
Body::id_t id1 = interaction->getId1();
Body::id_t id2 = interaction->getId2();
const shared_ptr<Body> b1 = Body::byId(id1, scene);
const shared_ptr<Body> b2 = Body::byId(id2, scene);
State* s1 = b1->state.get();
State* s2 = b2->state.get();
// Shear and torques
Vector3r C1 = Vector3r::Zero();
Vector3r C2 = Vector3r::Zero();
computeShearForceAndTorques_log(phys, geom, s1, s2, C1, C2);
// Apply!
scene->forces.addForce(id1, phys->normalForce + phys->shearForce);
scene->forces.addTorque(id1, C1);
scene->forces.addForce(id2, -(phys->normalForce + phys->shearForce));
scene->forces.addTorque(id2, C2);
return true;
}
CREATE_LOGGER(Law2_ScGeom_PotentialLubricationPhys);
bool Law2_ScGeom_PotentialLubricationPhys::solve_normalForce(Real const& un, Real const& dt, LubricationPhys& phys)
{
// Init
Real const& pDelta(phys.delta);
Real const& a(phys.a);
Real const ga(phys.kn * a);
Real d1(pDelta - 1.), d2(pDelta + 1.), d;
auto objf = [&, this](Real delta) -> Real {
return potential->potential(a * math::exp(delta), phys) / ga + (1. - math::exp(pDelta - delta)) / dt - un + math::exp(delta);
};
Real F1(objf(d1)), F2(objf(d2)), F;
// Seek to interval containing the zero
Real inc = (F1 < 0.) ? 1. : -1;
inc = (F1 < F2) ? inc : -inc;
while (F1 * F2 >= 0 && math::isfinite(F1) && math::isfinite(F2)) {
LOG_TRACE("d1=" << d1 << " d2=" << d2 << " F1=" << F1 << " F2=" << F2);
d1 += inc;
d2 += inc;
F1 = objf(d1);
F2 = objf(d2);
}
if (!math::isfinite(F1) || !math::isfinite(F2)) {
// Reset and search other way
LOG_DEBUG("Wrong direction");
d1 = pDelta - 1.;
d2 = pDelta + 1.;
F1 = objf(d1);
F2 = objf(d2);
inc = -inc;
while (F1 * F2 >= 0 && math::isfinite(F1) && math::isfinite(F2)) {
LOG_TRACE("d1=" << d1 << " d2=" << d2 << " F1=" << F1 << " F2=" << F2);
d1 += inc;
d2 += inc;
F1 = objf(d1);
F2 = objf(d2);
}
}
if (!math::isfinite(F1) || !math::isfinite(F2)) {
LOG_ERROR("Unable to find a start point. Abandon. d1=" << d1 << " d2=" << d2 << " F1=" << F1 << " F2=" << F2);
return false;
}
// Iterate to find a solution
uint i(MaxIter);
do {
if (F1 * F2 >= 0) {
LOG_ERROR("Boundaries have the same sign. Algorithm FAIL.");
return false;
}
d = (d1 + d2) / 2.;
F = objf(d);
if (!math::isfinite(F)) {
LOG_ERROR("Objective function return non-real value. Abandon. d=" << d << " F=" << F);
return false;
}
if (math::abs(F) < SolutionTol) break;
if (F * F1 < 0) {
d2 = d;
F2 = F;
} else {
d1 = d;
F1 = F;
}
} while (--i);
// Apply
Real up = math::exp(d);
phys.delta = d;
phys.u = a * math::exp(d);
phys.prevDotU = un - up - potential->potential(phys.u, phys) / ga; // dotu'/u'
return true;
}
Real GenericPotential::potential(Real const&, LubricationPhys const&) const { return 0; }
void GenericPotential::applyPotential(Real const&, LubricationPhys& phys, Vector3r const&)
{
phys.normalContactForce = Vector3r::Zero();
phys.normalPotentialForce = Vector3r::Zero();
phys.contact = false;
}
CREATE_LOGGER(GenericPotential);
Real CundallStrackPotential::potential(Real const& u, LubricationPhys const& phys) const { return math::min(0., -alpha * phys.kn * (phys.eps * phys.a - u)); }
void CundallStrackPotential::applyPotential(Real const& u, LubricationPhys& phys, Vector3r const& n)
{
phys.contact = u < phys.eps * phys.a;
phys.normalContactForce = (phys.contact) ? Vector3r(-alpha * phys.kn * (phys.eps * phys.a - u) * n) : Vector3r::Zero();
phys.normalPotentialForce = Vector3r::Zero();
}
CREATE_LOGGER(CundallStrackPotential);
Real CundallStrackAdhesivePotential::potential(Real const& u, LubricationPhys const& phys) const
{
Real ladh((phys.contact) ? fadh / phys.kn : 0.);
if (u < phys.eps * phys.a + ladh) return -alpha * phys.kn * (phys.eps * phys.a - u);
return 0;
}
void CundallStrackAdhesivePotential::applyPotential(Real const& u, LubricationPhys& phys, Vector3r const& n)
{
Real ladh((phys.contact) ? fadh / phys.kn : 0.);
phys.contact = u < phys.eps * phys.a + ladh;
phys.normalContactForce = (phys.contact) ? Vector3r(-alpha * phys.kn * (phys.eps * phys.a - u) * n) : Vector3r::Zero();
phys.normalPotentialForce = Vector3r::Zero();
}
CREATE_LOGGER(CundallStrackAdhesivePotential);
Real LinExponentialPotential::potential(Real const& u, LubricationPhys const& phys) const
{
return math::min(0., -alpha * phys.kn * (phys.eps * phys.a - u)) + LinExpPotential(u / phys.a);
}
void LinExponentialPotential::applyPotential(Real const& u, LubricationPhys& phys, Vector3r const& n)
{
phys.contact = u < phys.eps * phys.a;
phys.normalContactForce = (phys.contact) ? Vector3r(-alpha * phys.kn * (phys.eps * phys.a - u) * n) : Vector3r::Zero();
phys.normalPotentialForce = LinExpPotential(u / phys.a) * n;
}
void LinExponentialPotential::setParameters(Real const& x_0, Real const& x_e, Real const& k_)
{
if (x_0 >= x_e) throw std::runtime_error("x0 must be lower than xe!");
if (x_e == 0.) throw std::runtime_error("Extremum can't be at the origin.");
x0 = x_0;
xe = x_e;
k = k_;
F0 = LinExpPotential(0);
Fe = LinExpPotential(xe);
}
void LinExponentialPotential::computeParametersFromF0(Real const& F_0, Real const& x_e, Real const& k_)
{
Real rho = x_e * x_e * +4. * F_0 * x_e / k_;
if (rho <= 0) throw std::runtime_error("xe^2 + 4F0 xe/k must be positive!");
if (x_e == 0.) throw std::runtime_error("Extremum can't be at the origin.");
k = k_;
xe = x_e;
F0 = F_0;
x0 = (xe - math::sqrt(rho)) / 2.;
Fe = LinExpPotential(xe);
}
void LinExponentialPotential::computeParametersFromF0Fe(Real const& x_e, Real const& F_e, Real const& F_0)
{
using math::abs; // when used inside function it does not leak - it is safe.
if (x_e == 0.) throw std::runtime_error("Extremum can't be at the origin.");
if (F_e * F_0 < 0) {
if (x_e < 0) throw std::runtime_error("When xe < 0, F0 and Fe must be same sign!");
if (abs(F_e) <= 1.5 * abs(F_0)) throw std::runtime_error("When F0 and Fe are different sign, you must ensure |Fe| > 1.5|F0|");
} else {
if (abs(F_e) <= abs(F_0)) throw std::runtime_error("When F0 and F0 are same sign, you must ensure |Fe| > |F0|");
}
xe = x_e;
k = (F_e / (xe * math::exp(Real(-1))));
x0 = 0.;
F0 = F_0;
Fe = F_e;
for (int i(0); i < 100; i++) {
x0 = (xe - math::sqrt(xe * xe + 4. * F0 * xe / k)) / 2.;
k = Fe * xe / ((xe - x0) * (xe - x0) * exp(-xe / (xe - x0)));
// Iteration quit if relative difference is below 1%.
if (math::sqrt(
(LinExpPotential(0) - F0) * (LinExpPotential(0) - F0) / (F0 * F0)
+ (LinExpPotential(xe) - Fe) * (LinExpPotential(xe) - Fe) / (Fe * Fe))
< 0.01)
break;
}
}
Real LinExponentialPotential::LinExpPotential(Real const& u_) const { return k * ((xe - x0) / xe) * (u_ - x0) * math::exp(-u_ / (xe - x0)); }
CREATE_LOGGER(LinExponentialPotential);
} // namespace yade
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