From b30c8999201ed51ed59bd9222617229bcec87d05 Mon Sep 17 00:00:00 2001
From: graham <g.macpherson@opencfd.co.uk>
Date: Tue, 31 May 2011 16:15:53 +0100
Subject: [PATCH] ENH: Cohesion force based on energy density between
particles.
---
.../PairSpringSliderDashpot.C | 29 ++++++++++++++-----
.../PairSpringSliderDashpot.H | 24 +++++++++++++++
.../constant/kinematicCloudProperties | 2 ++
.../constant/kinematicCloudProperties | 2 ++
4 files changed, 50 insertions(+), 7 deletions(-)
diff --git a/src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/PairModel/PairSpringSliderDashpot/PairSpringSliderDashpot.C b/src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/PairModel/PairSpringSliderDashpot/PairSpringSliderDashpot.C
index 3096c829d0d..812296e6f5b 100644
--- a/src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/PairModel/PairSpringSliderDashpot/PairSpringSliderDashpot.C
+++ b/src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/PairModel/PairSpringSliderDashpot/PairSpringSliderDashpot.C
@@ -2,7 +2,7 @@
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration |
- \\ / A nd | Copyright (C) 2008-2010 OpenCFD Ltd.
+ \\ / A nd | Copyright (C) 2008-2011 OpenCFD Ltd.
\\/ M anipulation |
-------------------------------------------------------------------------------
License
@@ -92,12 +92,14 @@ Foam::PairSpringSliderDashpot<CloudType>::PairSpringSliderDashpot
alpha_(readScalar(this->coeffDict().lookup("alpha"))),
b_(readScalar(this->coeffDict().lookup("b"))),
mu_(readScalar(this->coeffDict().lookup("mu"))),
+ cohesionEnergyDensity_
+ (
+ readScalar(this->coeffDict().lookup("cohesionEnergyDensity"))
+ ),
+ cohesion_(false),
collisionResolutionSteps_
(
- readScalar
- (
- this->coeffDict().lookup("collisionResolutionSteps")
- )
+ readScalar(this->coeffDict().lookup("collisionResolutionSteps"))
),
volumeFactor_(1.0),
useEquivalentSize_(Switch(this->coeffDict().lookup("useEquivalentSize")))
@@ -116,6 +118,8 @@ Foam::PairSpringSliderDashpot<CloudType>::PairSpringSliderDashpot
scalar G = E/(2.0*(1.0 + nu));
Gstar_ = G/(2.0*(2.0 - nu));
+
+ cohesion_ = (mag(cohesionEnergyDensity_) > VSMALL);
}
@@ -183,13 +187,15 @@ void Foam::PairSpringSliderDashpot<CloudType>::evaluatePair
dBEff *= cbrt(pB.nParticle()*volumeFactor_);
}
- scalar normalOverlapMag = 0.5*(dAEff + dBEff) - mag(r_AB);
+ scalar r_AB_mag = mag(r_AB);
+
+ scalar normalOverlapMag = 0.5*(dAEff + dBEff) - r_AB_mag;
if (normalOverlapMag > 0)
{
//Particles in collision
- vector rHat_AB = r_AB/(mag(r_AB) + VSMALL);
+ vector rHat_AB = r_AB/(r_AB_mag + VSMALL);
vector U_AB = pA.U() - pB.U();
@@ -208,6 +214,15 @@ void Foam::PairSpringSliderDashpot<CloudType>::evaluatePair
rHat_AB
*(kN*pow(normalOverlapMag, b_) - etaN*(U_AB & rHat_AB));
+ // Cohesion force
+ if (cohesion_)
+ {
+ fN_AB +=
+ -cohesionEnergyDensity_
+ *overlapArea(dAEff/2.0, dBEff/2.0, r_AB_mag)
+ *rHat_AB;
+ }
+
pA.f() += fN_AB;
pB.f() += -fN_AB;
diff --git a/src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/PairModel/PairSpringSliderDashpot/PairSpringSliderDashpot.H b/src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/PairModel/PairSpringSliderDashpot/PairSpringSliderDashpot.H
index d2c9071ae38..e53f80babfc 100644
--- a/src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/PairModel/PairSpringSliderDashpot/PairSpringSliderDashpot.H
+++ b/src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/PairModel/PairSpringSliderDashpot/PairSpringSliderDashpot.H
@@ -34,6 +34,7 @@ Description
#include "PairModel.H"
#include "CollisionRecordList.H"
+#include "mathematicalConstants.H"
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
@@ -67,6 +68,12 @@ class PairSpringSliderDashpot
//- Coefficient of friction in for tangential sliding
scalar mu_;
+ //- Cohesion energy density [J/m^3]
+ scalar cohesionEnergyDensity_;
+
+ // Switch cohesion on and off
+ bool cohesion_;
+
//- The number of steps over which to resolve the minimum
// harmonic approximation of the collision period
scalar collisionResolutionSteps_;
@@ -129,6 +136,23 @@ public:
return volumeFactor_;
}
+ // Return the area of overlap between two spheres of radii rA and rB,
+ // centres separated by a distance rAB. Assumes rAB < (rA + rB).
+ inline scalar overlapArea(scalar rA, scalar rB, scalar rAB) const
+ {
+ // From:
+ // http://mathworld.wolfram.com/Sphere-SphereIntersection.html
+ return
+ mathematical::pi/4.0
+ /sqr(rAB)
+ *(
+ (-rAB + rA - rB)
+ *(-rAB - rA + rB)
+ *(-rAB + rA + rB)
+ *( rAB + rA + rA)
+ );
+ }
+
//- Whether the PairModel has a timestep limit that will
// require subCycling
virtual bool controlsTimestep() const;
diff --git a/tutorials/lagrangian/icoUncoupledKinematicParcelFoam/hopper/hopperEmptying/constant/kinematicCloudProperties b/tutorials/lagrangian/icoUncoupledKinematicParcelFoam/hopper/hopperEmptying/constant/kinematicCloudProperties
index 253b3324601..7422e40c440 100644
--- a/tutorials/lagrangian/icoUncoupledKinematicParcelFoam/hopper/hopperEmptying/constant/kinematicCloudProperties
+++ b/tutorials/lagrangian/icoUncoupledKinematicParcelFoam/hopper/hopperEmptying/constant/kinematicCloudProperties
@@ -82,6 +82,7 @@ subModels
pairCollisionCoeffs
{
+ // Maximum possible particle diameter expected at any time
maxInteractionDistance 0.006;
writeReferredParticleCloud no;
@@ -94,6 +95,7 @@ subModels
alpha 0.12;
b 1.5;
mu 0.52;
+ cohesionEnergyDensity 0;
collisionResolutionSteps 12;
};
diff --git a/tutorials/lagrangian/icoUncoupledKinematicParcelFoam/hopper/hopperInitialState/constant/kinematicCloudProperties b/tutorials/lagrangian/icoUncoupledKinematicParcelFoam/hopper/hopperInitialState/constant/kinematicCloudProperties
index 93315fbd630..36448f7b307 100644
--- a/tutorials/lagrangian/icoUncoupledKinematicParcelFoam/hopper/hopperInitialState/constant/kinematicCloudProperties
+++ b/tutorials/lagrangian/icoUncoupledKinematicParcelFoam/hopper/hopperInitialState/constant/kinematicCloudProperties
@@ -91,6 +91,7 @@ subModels
pairCollisionCoeffs
{
+ // Maximum possible particle diameter expected at any time
maxInteractionDistance 0.006;
writeReferredParticleCloud no;
@@ -103,6 +104,7 @@ subModels
alpha 0.12;
b 1.5;
mu 0.52;
+ cohesionEnergyDensity 0;
collisionResolutionSteps 12;
};
--
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