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pair_gran_hertzian.cpp
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Sun, Jun 30, 05:36

pair_gran_hertzian.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
http://lammps.sandia.gov, Sandia National Laboratories
Steve Plimpton, sjplimp@sandia.gov
Copyright (2003) Sandia Corporation. Under the terms of Contract
DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
certain rights in this software. This software is distributed under
the GNU General Public License.
See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */
/* ----------------------------------------------------------------------
Contributing authors: Leo Silbert (SNL), Gary Grest (SNL)
------------------------------------------------------------------------- */
#include "math.h"
#include "stdio.h"
#include "string.h"
#include "pair_gran_hertzian.h"
#include "atom.h"
#include "force.h"
#include "neigh_list.h"
using namespace LAMMPS_NS;
#define MIN(a,b) ((a) < (b) ? (a) : (b))
#define MAX(a,b) ((a) > (b) ? (a) : (b))
/* ---------------------------------------------------------------------- */
PairGranHertzian::PairGranHertzian(LAMMPS *lmp) : PairGranHistory(lmp)
{
history = 1;
}
/* ---------------------------------------------------------------------- */
void PairGranHertzian::compute(int eflag, int vflag)
{
int i,j,ii,jj,inum,jnum;
double xtmp,ytmp,ztmp,delx,dely,delz;
double radi,radj,radsum,rsq,r,rinv;
double vr1,vr2,vr3,vnnr,vn1,vn2,vn3,vt1,vt2,vt3;
double wr1,wr2,wr3;
double vtr1,vtr2,vtr3,vrel;
double xmeff,damp,ccel,ccelx,ccely,ccelz,tor1,tor2,tor3;
double fn,fs,fs1,fs2,fs3;
double shrmag,rsht,rhertz;
int *ilist,*jlist,*numneigh,**firstneigh;
int *touch,**firsttouch;
double *shear,*allshear,**firstshear;
double **f = atom->f;
double **x = atom->x;
double **v = atom->v;
double **omega = atom->omega;
double **torque = atom->torque;
double *radius = atom->radius;
double *rmass = atom->rmass;
int *mask = atom->mask;
int nlocal = atom->nlocal;
int newton_pair = force->newton_pair;
inum = list->inum;
ilist = list->ilist;
numneigh = list->numneigh;
firstneigh = list->firstneigh;
firsttouch = list->listgranhistory->firstneigh;
firstshear = list->listgranhistory->firstdouble;
// loop over neighbors of my atoms
for (ii = 0; ii < inum; ii++) {
i = ilist[ii];
xtmp = x[i][0];
ytmp = x[i][1];
ztmp = x[i][2];
radi = radius[i];
touch = firsttouch[i];
allshear = firstshear[i];
jlist = firstneigh[i];
jnum = numneigh[i];
for (jj = 0; jj < jnum; jj++) {
j = jlist[jj];
delx = xtmp - x[j][0];
dely = ytmp - x[j][1];
delz = ztmp - x[j][2];
rsq = delx*delx + dely*dely + delz*delz;
radj = radius[j];
radsum = radi + radj;
if (rsq >= radsum*radsum) {
// unset touching neighbors
touch[jj] = 0;
shear = &allshear[3*jj];
shear[0] = 0.0;
shear[1] = 0.0;
shear[2] = 0.0;
} else {
r = sqrt(rsq);
// relative translational velocity
vr1 = v[i][0] - v[j][0];
vr2 = v[i][1] - v[j][1];
vr3 = v[i][2] - v[j][2];
vr1 *= dt;
vr2 *= dt;
vr3 *= dt;
// normal component
vnnr = vr1*delx + vr2*dely + vr3*delz;
vn1 = delx*vnnr / rsq;
vn2 = dely*vnnr / rsq;
vn3 = delz*vnnr / rsq;
// tangential component
vt1 = vr1 - vn1;
vt2 = vr2 - vn2;
vt3 = vr3 - vn3;
// relative rotational velocity
wr1 = radi*omega[i][0] + radj*omega[j][0];
wr2 = radi*omega[i][1] + radj*omega[j][1];
wr3 = radi*omega[i][2] + radj*omega[j][2];
wr1 *= dt/r;
wr2 *= dt/r;
wr3 *= dt/r;
// normal damping term
// this definition of DAMP includes the extra 1/r term
xmeff = rmass[i]*rmass[j] / (rmass[i]+rmass[j]);
if (mask[i] & freeze_group_bit) xmeff = rmass[j];
if (mask[j] & freeze_group_bit) xmeff = rmass[i];
damp = xmeff*gamman_dl*vnnr/rsq;
ccel = xkk*(radsum-r)/r - damp;
rhertz = sqrt(radsum - r);
ccel = rhertz * ccel;
// relative velocities
vtr1 = vt1 - (delz*wr2-dely*wr3);
vtr2 = vt2 - (delx*wr3-delz*wr1);
vtr3 = vt3 - (dely*wr1-delx*wr2);
vrel = vtr1*vtr1 + vtr2*vtr2 + vtr3*vtr3;
vrel = sqrt(vrel);
// shear history effects
// shrmag = magnitude of shear
touch[jj] = 1;
shear = &allshear[3*jj];
shear[0] += vtr1;
shear[1] += vtr2;
shear[2] += vtr3;
shrmag = sqrt(shear[0]*shear[0] + shear[1]*shear[1] +
shear[2]*shear[2]);
// rotate shear displacements correctly
rsht = shear[0]*delx + shear[1]*dely + shear[2]*delz;
rsht /= rsq;
shear[0] -= rsht*delx;
shear[1] -= rsht*dely;
shear[2] -= rsht*delz;
// tangential forces
fs1 = -rhertz * (xkkt*shear[0] + xmeff*gammas_dl*vtr1);
fs2 = -rhertz * (xkkt*shear[1] + xmeff*gammas_dl*vtr2);
fs3 = -rhertz * (xkkt*shear[2] + xmeff*gammas_dl*vtr3);
// force normalization
// rescale frictional displacements and forces if needed
fs = sqrt(fs1*fs1 + fs2*fs2 + fs3*fs3);
fn = xmu * fabs(ccel*r);
if (fs > fn) {
if (shrmag != 0.0) {
shear[0] = (fn/fs) * (shear[0] + xmeff*gammas_dl*vtr1/xkkt) -
xmeff*gammas_dl*vtr1/xkkt;
shear[1] = (fn/fs) * (shear[1] + xmeff*gammas_dl*vtr2/xkkt) -
xmeff*gammas_dl*vtr2/xkkt;
shear[2] = (fn/fs) * (shear[2] + xmeff*gammas_dl*vtr3/xkkt) -
xmeff*gammas_dl*vtr3/xkkt;
fs1 *= fn/fs;
fs2 *= fn/fs;
fs3 *= fn/fs;
} else {
fs1 = 0.0;
fs2 = 0.0;
fs3 = 0.0;
}
}
// forces & torques
ccelx = delx*ccel + fs1;
ccely = dely*ccel + fs2;
ccelz = delz*ccel + fs3;
f[i][0] += ccelx;
f[i][1] += ccely;
f[i][2] += ccelz;
rinv = 1/r;
tor1 = rinv * (dely*fs3 - delz*fs2);
tor2 = rinv * (delz*fs1 - delx*fs3);
tor3 = rinv * (delx*fs2 - dely*fs1);
torque[i][0] -= radi*tor1;
torque[i][1] -= radi*tor2;
torque[i][2] -= radi*tor3;
if (newton_pair || j < nlocal) {
f[j][0] -= ccelx;
f[j][1] -= ccely;
f[j][2] -= ccelz;
torque[j][0] -= radj*tor1;
torque[j][1] -= radj*tor2;
torque[j][2] -= radj*tor3;
}
}
}
}
}

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