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rAKA/ntn_contact/ntn_friction.cc
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ntn_friction.cc
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/**
* @file ntn_friction.cc
* @author David Kammer <david.kammer@epfl.ch>
* @date Fri Feb 24 15:21:44 2012
*
* @brief
*
* @section LICENSE
*
* Copyright (©) 2010-2011 EPFL (Ecole Polytechnique Fédérale de Lausanne)
* Laboratory (LSMS - Laboratoire de Simulation en Mécanique des Solides)
*
* Akantu is free software: you can redistribute it and/or modify it under the
* terms of the GNU Lesser General Public License as published by the Free
* Software Foundation, either version 3 of the License, or (at your option) any
* later version.
*
* Akantu is distributed in the hope that it will be useful, but WITHOUT ANY
* WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
* A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
* details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with Akantu. If not, see <http://www.gnu.org/licenses/>.
*
*/
/* -------------------------------------------------------------------------- */
// simtools
#include "ntn_friction.hh"
__BEGIN_SIMTOOLS__
/* -------------------------------------------------------------------------- */
NTNFriction::NTNFriction(NTNContact & contact,
const FrictionID & id,
const MemoryID & memory_id) :
Memory(memory_id), id(id),
contact(contact),
is_sticking(0,1,true,id+":is_sticking",true,"is_sticking"),
frictional_strength(0,1,0.,id+":frictional_strength",0.,"frictional_strength"),
friction_traction(0,contact.getModel().getSpatialDimension(),
0.,id+":friction_traction",0.,"friction_traction") {
//mu(0,1,0.,id+":mu",0.,"mu") {
AKANTU_DEBUG_IN();
this->contact.registerSyncronizedArray(this->is_sticking);
this->contact.registerSyncronizedArray(this->frictional_strength);
this->contact.registerSyncronizedArray(this->friction_traction);
// this->contact.registerSyncronizedArray(this->mu);
AKANTU_DEBUG_OUT();
}
/* -------------------------------------------------------------------------- */
void NTNFriction::computeFrictionTraction() {
AKANTU_DEBUG_IN();
this->computeStickTraction();
this->computeFrictionalStrength();
SolidMechanicsModel & model = this->contact.getModel();
UInt dim = model.getSpatialDimension();
UInt nb_ntn_pairs = this->contact.getNbContactNodes();
// get contact arrays
const SyncronizedArray<bool> & is_in_contact = this->contact.getIsInContact();
// compute friction traction to stop sliding
Real * contact_pressure = this->contact.getContactPressure().storage();
Real * friction_trac_p = this->friction_traction.storage();
this->is_sticking.clear(); // set to not sticking
for (UInt n=0; n<nb_ntn_pairs; ++n) {
// node pair is NOT in contact
if (is_in_contact(n)) {
// check if it is larger than frictional strength
Real abs_fric = Math::norm(dim, &(friction_trac_p[n*dim]));
if (abs_fric != 0.) {
Real alpha = this->frictional_strength(n) / abs_fric;
// larger -> sliding
if (alpha < 1.) {
for (UInt d=0; d<dim; ++d)
this->friction_traction(n,d) *= alpha;
}
else
this->is_sticking(n) = true;
}
else {
// frictional traction is already zero
this->is_sticking(n) = true;
}
}
}
AKANTU_DEBUG_OUT();
}
/* -------------------------------------------------------------------------- */
void NTNFriction::computeStickTraction() {
AKANTU_DEBUG_IN();
SolidMechanicsModel & model = this->contact.getModel();
UInt dim = model.getSpatialDimension();
Real delta_t = model.getTimeStep();
UInt nb_ntn_pairs = this->contact.getNbContactNodes();
// get contact arrays
const SyncronizedArray<Real> & impedance = this->contact.getImpedance();
const SyncronizedArray<bool> & is_in_contact = this->contact.getIsInContact();
// pre-compute the acceleration
// (not increment acceleration, because residual is still Kf)
Array<Real> acceleration(model.getFEM().getMesh().getNbNodes(),dim);
model.solveLumped(acceleration,
model.getMass(),
model.getResidual(),
model.getBoundary(),
model.getF_M2A());
// compute relative normal fields of velocity and acceleration
Array<Real> r_velo(0,dim);
Array<Real> r_acce(0,dim);
Array<Real> r_old_acce(0,dim);
this->contact.computeRelativeTangentialField(model.getVelocity(), r_velo);
this->contact.computeRelativeTangentialField(acceleration, r_acce);
this->contact.computeRelativeTangentialField(model.getAcceleration(), r_old_acce);
AKANTU_DEBUG_ASSERT(r_velo.getSize() == nb_ntn_pairs,
"computeRelativeNormalField does not give back arrays "
<< "size == nb_ntn_pairs. nb_ntn_pairs = " << nb_ntn_pairs
<< " | array size = " << r_velo.getSize());
// compute tangential gap array for all nodes
Array<Real> gap(nb_ntn_pairs, dim);
Real * gap_p = gap.storage();
Real * r_velo_p = r_velo.storage();
Real * r_acce_p = r_acce.storage();
Real * r_old_acce_p = r_old_acce.storage();
for (UInt i=0; i<nb_ntn_pairs*dim; ++i) {
*gap_p = *r_velo_p + delta_t * *r_acce_p - 0.5 * delta_t * *r_old_acce_p;
// increment pointers
gap_p++;
r_velo_p++;
r_acce_p++;
r_old_acce_p++;
}
// compute friction traction to stop sliding
Real * friction_trac_p = this->friction_traction.storage();
for (UInt n=0; n<nb_ntn_pairs; ++n) {
// node pair is NOT in contact
if (!is_in_contact(n)) {
for (UInt d=0; d<dim; ++d)
this->friction_traction(n,d) = 0.;
}
// node pair is in contact
else {
// compute friction traction
for (UInt d=0; d<dim; ++d)
this->friction_traction(n,d) = impedance(n) * gap(n,d) / 2.;
}
}
AKANTU_DEBUG_OUT();
}
/* -------------------------------------------------------------------------- */
void NTNFriction::applyFrictionTraction() {
AKANTU_DEBUG_IN();
SolidMechanicsModel & model = this->contact.getModel();
Array<Real> & residual = model.getResidual();
UInt dim = model.getSpatialDimension();
UInt nb_ntn_pairs = this->contact.getNbContactNodes();
const SyncronizedArray<UInt> & masters = this->contact.getMasters();
const SyncronizedArray<UInt> & slaves = this->contact.getSlaves();
const SyncronizedArray<Real> & lumped_boundary = this->contact.getLumpedBoundary();
for (UInt n=0; n<nb_ntn_pairs; ++n) {
UInt master = masters(n);
UInt slave = slaves(n);
for (UInt d=0; d<dim; ++d) {
residual(master,d) += lumped_boundary(n,0) * this->friction_traction(n,d);
residual(slave, d) -= lumped_boundary(n,1) * this->friction_traction(n,d);
}
}
AKANTU_DEBUG_OUT();
}
/* -------------------------------------------------------------------------- */
void NTNFriction::registerSyncronizedArray(SyncronizedArrayBase & array) {
AKANTU_DEBUG_IN();
this->frictional_strength.registerDependingArray(array);
AKANTU_DEBUG_OUT();
}
/* -------------------------------------------------------------------------- */
void NTNFriction::dumpRestart(std::string file_name) const {
AKANTU_DEBUG_IN();
this->is_sticking.dumpRestartFile(file_name);
this->frictional_strength.dumpRestartFile(file_name);
this->friction_traction.dumpRestartFile(file_name);
// this->mu.dumpRestartFile(file_name);
AKANTU_DEBUG_OUT();
}
/* -------------------------------------------------------------------------- */
void NTNFriction::readRestart(std::string file_name) {
AKANTU_DEBUG_IN();
this->is_sticking.readRestartFile(file_name);
this->frictional_strength.readRestartFile(file_name);
this->friction_traction.readRestartFile(file_name);
// this->mu.readRestartFile(file_name);
AKANTU_DEBUG_OUT();
}
/* -------------------------------------------------------------------------- */
void NTNFriction::setInternalArray(SyncronizedArray<Real> & array,
Real value) {
AKANTU_DEBUG_IN();
Real * array_p = array.storage();
Real nb_array = array.getSize();
std::fill_n(array_p, nb_array, value);
array.setDefaultValue(value);
AKANTU_DEBUG_OUT();
}
/* -------------------------------------------------------------------------- */
void NTNFriction::setInternalArray(SyncronizedArray<Real> & array,
UInt node,
Real value) {
AKANTU_DEBUG_IN();
Int index = this->contact.getNodeIndex(node);
if (index < 0) {
AKANTU_DEBUG_WARNING("Node is node a contact node. Therefore, cannot set Mu!!");
}
else {
array(index) = value;
}
AKANTU_DEBUG_OUT();
}
/* -------------------------------------------------------------------------- */
void NTNFriction::printself(std::ostream & stream, int indent) const {
AKANTU_DEBUG_IN();
std::string space;
for(Int i = 0; i < indent; i++, space += AKANTU_INDENT);
stream << space << "NTNFriction [" << std::endl;
stream << space << "]" << std::endl;
AKANTU_DEBUG_OUT();
}
__END_SIMTOOLS__
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