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Merge pull request #1631 from jibril-b-coulibaly/patch-2

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Bug fixes for pair style granular
This commit is contained in:
Axel Kohlmeyer
2019-10-09 14:14:48 +02:00
committed by GitHub
parent 0cf60d0c62 747bfa31f2
commit 6e244bc8dc
2 changed files with 42 additions and 54 deletions
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22
doc/src/pair_granular.txt
View File

@ -100,7 +100,7 @@ on particle {i} due to contact with particle {j} is given by:
\mathbf\{F\}_\{ne, Hooke\} = k_N \delta_\{ij\} \mathbf\{n\}
\end\{equation\}
Where \(\delta = R_i + R_j - \|\mathbf\{r\}_\{ij\}\|\) is the particle
Where \(\delta_\{ij\} = R_i + R_j - \|\mathbf\{r\}_\{ij\}\|\) is the particle
overlap, \(R_i, R_j\) are the particle radii, \(\mathbf\{r\}_\{ij\} =
\mathbf\{r\}_i - \mathbf\{r\}_j\) is the vector separating the two
particle centers (note the i-j ordering so that \(F_\{ne\}\) is
@ -177,7 +177,7 @@ following general form:
\end\{equation\}
Here, \(\mathbf\{v\}_\{n,rel\} = (\mathbf\{v\}_j - \mathbf\{v\}_i)
\cdot \mathbf\{n\}\) is the component of relative velocity along
\cdot \mathbf\{n\} \mathbf\{n\}\) is the component of relative velocity along
\(\mathbf\{n\}\).
The optional {damping} keyword to the {pair_coeff} command followed by
@ -299,8 +299,8 @@ the normal damping \(\eta_n\) (see above):
\eta_t = -x_\{\gamma,t\} \eta_n
\end\{equation\}
The normal damping prefactor \(\eta_n\) is determined by the choice of
the {damping} keyword, as discussed above. Thus, the {damping}
The normal damping prefactor \(\eta_n\) is determined by the choice
of the {damping} keyword, as discussed above. Thus, the {damping}
keyword also affects the tangential damping. The parameter
\(x_\{\gamma,t\}\) is a scaling coefficient. Several works in the
literature use \(x_\{\gamma,t\} = 1\) ("Marshall"_#Marshall2009,
@ -308,10 +308,10 @@ literature use \(x_\{\gamma,t\} = 1\) ("Marshall"_#Marshall2009,
tangential velocity at the point of contact is given by
\(\mathbf\{v\}_\{t, rel\} = \mathbf\{v\}_\{t\} - (R_i\Omega_i +
R_j\Omega_j) \times \mathbf\{n\}\), where \(\mathbf\{v\}_\{t\} =
\mathbf\{v\}_r - \mathbf\{v\}_r\cdot\mathbf\{n\}\), \(\mathbf\{v\}_r =
\mathbf\{v\}_j - \mathbf\{v\}_i\). The direction of the applied force
is \(\mathbf\{t\} =
\mathbf\{v_\{t,rel\}\}/\|\mathbf\{v_\{t,rel\}\}\|\).
\mathbf\{v\}_r - \mathbf\{v\}_r\cdot\mathbf\{n\}\{n\}\),
\(\mathbf\{v\}_r = \mathbf\{v\}_j - \mathbf\{v\}_i\).
The direction of the applied force is \(\mathbf\{t\} =
\mathbf\{v_\{t,rel\}\}/\|\mathbf\{v_\{t,rel\}\}\|\) .
The normal force value \(F_\{n0\}\) used to compute the critical force
depends on the form of the contact model. For non-cohesive models
@ -411,8 +411,8 @@ option by an additional factor of {a}, the radius of the contact region. The tan
\mathbf\{F\}_t = -min(\mu_t F_\{n0\}, \|-k_t a \mathbf\{\xi\} + \mathbf\{F\}_\mathrm\{t,damp\}\|) \mathbf\{t\}
\end\{equation\}
Here, {a} is the radius of the contact region, given by \(a = \delta
R\) for all normal contact models, except for {jkr}, where it is given
Here, {a} is the radius of the contact region, given by \(a =\sqrt\{R\delta\}\)
for all normal contact models, except for {jkr}, where it is given
implicitly by \(\delta = a^2/R - 2\sqrt\{\pi \gamma a/E\}\), see
discussion above. To match the Mindlin solution, one should set \(k_t
= 8G\), where \(G\) is the shear modulus, related to Young's modulus
@ -680,7 +680,7 @@ The single() function of these pair styles returns 0.0 for the energy
of a pairwise interaction, since energy is not conserved in these
dissipative potentials. It also returns only the normal component of
the pairwise interaction force. However, the single() function also
calculates 10 extra pairwise quantities. The first 3 are the
calculates 12 extra pairwise quantities. The first 3 are the
components of the tangential force between particles I and J, acting
on particle I. The 4th is the magnitude of this tangential force.
The next 3 (5-7) are the components of the rolling torque acting on

72
src/GRANULAR/pair_granular.cpp
View File

@ -305,7 +305,8 @@ void PairGranular::compute(int eflag, int vflag)
delta = radsum - r;
dR = delta*Reff;
if (normal_model[itype][jtype] == JKR) {
if (normal_model[itype][jtype] == JKR) {
touch[jj] = 1;
R2=Reff*Reff;
coh = normal_coeffs[itype][jtype][3];
@ -391,6 +392,7 @@ void PairGranular::compute(int eflag, int vflag)
} else {
Fncrit = fabs(Fntot);
}
Fscrit = tangential_coeffs[itype][jtype][2] * Fncrit;
//------------------------------
// tangential forces
@ -446,7 +448,6 @@ void PairGranular::compute(int eflag, int vflag)
fs3 = -k_tangential*history[2] - damp_tangential*vtr3;
// rescale frictional displacements and forces if needed
Fscrit = tangential_coeffs[itype][jtype][2] * Fncrit;
fs = sqrt(fs1*fs1 + fs2*fs2 + fs3*fs3);
if (fs > Fscrit) {
shrmag = sqrt(history[0]*history[0] + history[1]*history[1] +
@ -464,8 +465,8 @@ void PairGranular::compute(int eflag, int vflag)
} else fs1 = fs2 = fs3 = 0.0;
}
} else { // classic pair gran/hooke (no history)
fs = meff*damp_tangential*vrel;
if (vrel != 0.0) Ft = MIN(Fne,fs) / vrel;
fs = damp_tangential*vrel;
if (vrel != 0.0) Ft = MIN(Fscrit,fs) / vrel;
else Ft = 0.0;
fs1 = -Ft*vtr1;
fs2 = -Ft*vtr2;
@ -635,7 +636,7 @@ void PairGranular::compute(int eflag, int vflag)
torque[j][2] -= torroll3;
}
}
if (evflag) ev_tally_xyz(i,j,nlocal,0,
if (evflag) ev_tally_xyz(i,j,nlocal,force->newton_pair,
0.0,0.0,fx,fy,fz,delx,dely,delz);
}
}
@ -1374,22 +1375,6 @@ double PairGranular::single(int i, int j, int itype, int jtype,
vn2 = ny*vnnr;
vn3 = nz*vnnr;
double *rmass = atom->rmass;
int *mask = atom->mask;
mi = rmass[i];
mj = rmass[j];
if (fix_rigid) {
if (mass_rigid[i] > 0.0) mi = mass_rigid[i];
if (mass_rigid[j] > 0.0) mj = mass_rigid[j];
}
meff = mi*mj / (mi+mj);
if (mask[i] & freeze_group_bit) meff = mj;
if (mask[j] & freeze_group_bit) meff = mi;
delta = radsum - r;
dR = delta*Reff;
// tangential component
vt1 = vr1 - vn1;
@ -1407,6 +1392,9 @@ double PairGranular::single(int i, int j, int itype, int jtype,
// if I or J part of rigid body, use body mass
// if I or J is frozen, meff is other particle
double *rmass = atom->rmass;
int *mask = atom->mask;
mi = rmass[i];
mj = rmass[j];
if (fix_rigid) {
@ -1451,11 +1439,13 @@ double PairGranular::single(int i, int j, int itype, int jtype,
}
if (damping_model[itype][jtype] == VELOCITY) {
damp_normal = normal_coeffs[itype][jtype][1];
damp_normal = 1;
} else if (damping_model[itype][jtype] == MASS_VELOCITY) {
damp_normal = meff;
} else if (damping_model[itype][jtype] == VISCOELASTIC) {
damp_normal = normal_coeffs[itype][jtype][1]*a*meff;
damp_normal = a*meff;
} else if (damping_model[itype][jtype] == TSUJI) {
damp_normal = normal_coeffs[itype][jtype][1]*sqrt(meff*knfac);
damp_normal = sqrt(meff*knfac);
}
damp_normal_prefactor = normal_coeffs[itype][jtype][1]*damp_normal;
@ -1506,6 +1496,7 @@ double PairGranular::single(int i, int j, int itype, int jtype,
} else {
Fncrit = fabs(Fntot);
}
Fscrit = tangential_coeffs[itype][jtype][2] * Fncrit;
//------------------------------
// tangential forces
@ -1518,13 +1509,6 @@ double PairGranular::single(int i, int j, int itype, int jtype,
k_tangential *= a;
} else if (tangential_model[itype][jtype] == TANGENTIAL_MINDLIN_RESCALE) {
k_tangential *= a;
// on unloading, rescale the shear displacements
if (a < history[3]) {
double factor = a/history[3];
history[0] *= factor;
history[1] *= factor;
history[2] *= factor;
}
}
shrmag = sqrt(history[0]*history[0] + history[1]*history[1] +
@ -1535,35 +1519,34 @@ double PairGranular::single(int i, int j, int itype, int jtype,
fs2 = -k_tangential*history[1] - damp_tangential*vtr2;
fs3 = -k_tangential*history[2] - damp_tangential*vtr3;
// rescale frictional displacements and forces if needed
Fscrit = tangential_coeffs[itype][jtype][2] * Fncrit;
// rescale frictional forces if needed
fs = sqrt(fs1*fs1 + fs2*fs2 + fs3*fs3);
if (fs > Fscrit) {
if (shrmag != 0.0) {
history[0] = -1.0/k_tangential*(Fscrit*fs1/fs + damp_tangential*vtr1);
history[1] = -1.0/k_tangential*(Fscrit*fs2/fs + damp_tangential*vtr2);
history[2] = -1.0/k_tangential*(Fscrit*fs3/fs + damp_tangential*vtr3);
fs1 *= Fscrit/fs;
fs2 *= Fscrit/fs;
fs3 *= Fscrit/fs;
} else fs1 = fs2 = fs3 = 0.0;
fs *= Fscrit/fs;
} else fs1 = fs2 = fs3 = fs = 0.0;
}
// classic pair gran/hooke (no history)
} else {
fs = meff*damp_tangential*vrel;
if (vrel != 0.0) Ft = MIN(Fne,fs) / vrel;
fs = damp_tangential*vrel;
if (vrel != 0.0) Ft = MIN(Fscrit,fs) / vrel;
else Ft = 0.0;
fs1 = -Ft*vtr1;
fs2 = -Ft*vtr2;
fs3 = -Ft*vtr3;
fs = Ft*vrel;
}
//****************************************
// rolling resistance
//****************************************
if (roll_model[itype][jtype] != ROLL_NONE) {
if ((roll_model[itype][jtype] != ROLL_NONE)
|| (twist_model[itype][jtype] != TWIST_NONE)) {
relrot1 = omega[i][0] - omega[j][0];
relrot2 = omega[i][1] - omega[j][1];
relrot3 = omega[i][2] - omega[j][2];
@ -1601,7 +1584,8 @@ double PairGranular::single(int i, int j, int itype, int jtype,
fr1 *= Frcrit/fr;
fr2 *= Frcrit/fr;
fr3 *= Frcrit/fr;
} else fr1 = fr2 = fr3 = 0.0;
fr *= Frcrit/fr;
} else fr1 = fr2 = fr3 = fr = 0.0;
}
}
@ -1628,9 +1612,13 @@ double PairGranular::single(int i, int j, int itype, int jtype,
Mtcrit = mu_twist*Fncrit; // critical torque (eq 44)
if (fabs(magtortwist) > Mtcrit) {
magtortwist = -Mtcrit * signtwist; // eq 34
}
} else magtortwist = 0.0;
}
// set force and return no energy
fforce = Fntot*rinv;
// set single_extra quantities
svector[0] = fs1;