From ee9e7cf0375147af1e9d57a039ad4f241bad8e4f Mon Sep 17 00:00:00 2001
From: Henry Weller <http://cfd.direct>
Date: Sat, 23 Jul 2016 11:53:48 +0100
Subject: [PATCH] lagrangian::BrownianMotionForce: Changed from a cubic to a
spherical distribution See also: StochasticDispersionRAS Resolves bug-report
http://bugs.openfoam.org/view.php?id=2153
---
.../Templates/KinematicCloud/KinematicCloud.H | 4 +--
.../KinematicCloud/KinematicCloudI.H | 2 +-
.../BrownianMotion/BrownianMotionForce.C | 29 ++++++++++++++-----
3 files changed, 25 insertions(+), 10 deletions(-)
diff --git a/src/lagrangian/intermediate/clouds/Templates/KinematicCloud/KinematicCloud.H b/src/lagrangian/intermediate/clouds/Templates/KinematicCloud/KinematicCloud.H
index 20916540674..42c3aee5f15 100644
--- a/src/lagrangian/intermediate/clouds/Templates/KinematicCloud/KinematicCloud.H
+++ b/src/lagrangian/intermediate/clouds/Templates/KinematicCloud/KinematicCloud.H
@@ -160,7 +160,7 @@ protected:
const dictionary subModelProperties_;
//- Random number generator - used by some injection routines
- cachedRandom rndGen_;
+ mutable cachedRandom rndGen_;
//- Cell occupancy information for each parcel, (demand driven)
autoPtr<List<DynamicList<parcelType*>>> cellOccupancyPtr_;
@@ -363,7 +363,7 @@ public:
// Cloud data
//- Return reference to the random object
- inline cachedRandom& rndGen();
+ inline cachedRandom& rndGen() const;
//- Return the cell occupancy information for each
// parcel, non-const access, the caller is
diff --git a/src/lagrangian/intermediate/clouds/Templates/KinematicCloud/KinematicCloudI.H b/src/lagrangian/intermediate/clouds/Templates/KinematicCloud/KinematicCloudI.H
index 37a1a43d176..53b6c713160 100644
--- a/src/lagrangian/intermediate/clouds/Templates/KinematicCloud/KinematicCloudI.H
+++ b/src/lagrangian/intermediate/clouds/Templates/KinematicCloud/KinematicCloudI.H
@@ -356,7 +356,7 @@ inline Foam::scalar Foam::KinematicCloud<CloudType>::Dmax() const
template<class CloudType>
-inline Foam::cachedRandom& Foam::KinematicCloud<CloudType>::rndGen()
+inline Foam::cachedRandom& Foam::KinematicCloud<CloudType>::rndGen() const
{
return rndGen_;
}
diff --git a/src/lagrangian/turbulence/submodels/Thermodynamic/ParticleForces/BrownianMotion/BrownianMotionForce.C b/src/lagrangian/turbulence/submodels/Thermodynamic/ParticleForces/BrownianMotion/BrownianMotionForce.C
index af762752cf7..313cbf0b171 100644
--- a/src/lagrangian/turbulence/submodels/Thermodynamic/ParticleForces/BrownianMotion/BrownianMotionForce.C
+++ b/src/lagrangian/turbulence/submodels/Thermodynamic/ParticleForces/BrownianMotion/BrownianMotionForce.C
@@ -193,13 +193,28 @@ Foam::forceSuSp Foam::BrownianMotionForce<CloudType>::calcCoupled
f = mass*sqrt(mathematical::pi*s0/dt);
}
- const scalar sqrt2 = sqrt(2.0);
- for (direction dir = 0; dir < vector::nComponents; dir++)
- {
- const scalar x = rndGen_.sample01<scalar>();
- const scalar eta = sqrt2*erfInv(2*x - 1.0);
- value.Su()[dir] = f*eta;
- }
+
+ // To generate a cubic distribution (3 independent directions) :
+ // const scalar sqrt2 = sqrt(2.0);
+ // for (direction dir = 0; dir < vector::nComponents; dir++)
+ // {
+ // const scalar x = rndGen_.sample01<scalar>();
+ // const scalar eta = sqrt2*erfInv(2*x - 1.0);
+ // value.Su()[dir] = f*eta;
+ // }
+
+
+ // To generate a spherical distribution:
+
+ cachedRandom& rnd = this->owner().rndGen();
+
+ const scalar theta = rnd.sample01<scalar>()*twoPi;
+ const scalar u = 2*rnd.sample01<scalar>() - 1;
+
+ const scalar a = sqrt(1 - sqr(u));
+ const vector dir(a*cos(theta), a*sin(theta), u);
+
+ value.Su() = f*mag(rnd.GaussNormal<scalar>())*dir;
return value;
}
--
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