New question #253112 on Yade:
https://answers.launchpad.net/yade/+question/253112
Hi all,
I modified the source code of yade to have an engine applying drag and lift
force on each particle at each time step in function of a given average
velocity field.
The fluid flow is turbulent so that I determine every dt_f also randomly a
fluid velocity fluctuation associated to each particle. (dt_f~100 dt)
To evaluate the drag and lift, I need then to pass the value of the fluctuation
associated to each particles from the python script to the C++ engine. This
takes the form of a vector of size len(O.bodies) and should then be given to
the C++ engines every dt_f
However, when the number of particle is high (~50 000), the simulation stops
after about 60s and it is written :
"processus arrêté" (processus stopped in french).
This is most probably due to the fact the process is taking too much memory.
For example a simulation of 83000 particles after 60s of virtual time simulated
takes 14GB of memory and 10GB of SWAP.
I made a test script and I found that the increase in memory consumption with
time is due to the number of time I am passing the vector with the fluctuation
associated to the particle from the python script to the C++ engine.
I have possibilities to pass a smaller vector to the C++ engine, or to evaluate
the turbulent fluctuation inside the C++ engine, however it does not seem
normal to me to have memory leakage when passing a variable from python to C++.
Any idea of what it is due to ? Is there a way to fix this problem ?
Thanks for your help !
Raphaël
Yade version : 2014-06-29.git-de4c01a
linux version : Ubuntu 12.04
Hereafter the modification of the C++ code I made.
ForceEngine.cpp :
void HydroForceEngine::action(){
FOREACH(Body::id_t id, ids){
Body* b=Body::byId(id,scene).get();
if (!b) continue;
if (!(scene->bodies->exists(id))) continue;
const Sphere* sphere = dynamic_cast<Sphere*>(b->shape.get());
if (sphere){
Vector3r posSphere = b->state->pos;//position vector of
the sphere
int p = floor((posSphere[2]-zRef)/deltaZ); //cell
number in which the particle is
if ((p<nCell)&&(p>0)) {
Vector3r liftForce = Vector3r::Zero();
Vector3r dragForce = Vector3r::Zero();
Vector3r
vFluid(vxFluid[p]+vxFluct[id],0.0,vzFluct[id]); //fluid velocity at this point
(including fluctuations)
Vector3r vPart = b->state->vel;
Vector3r vRel = vFluid - vPart;
//Drag force calculation
Real Rep =
vRel.norm()*sphere->radius*2*rhoFluid/viscoDyn;
Real A =
sphere->radius*sphere->radius*Mathr::PI; //Crossection of the sphere
if (vRel.norm()!=0.0) {
Real hindranceF =
pow(1-phiPart[p],-expoRZ); //hindrance function
Real Cd = (0.44 + 24.4/Rep)*hindranceF;
//drag coefficient
dragForce =
0.5*rhoFluid*A*Cd*vRel.squaredNorm()*vRel.normalized();
}
//lift force calculation due to difference of
pressure (Saffman lift)
int intRadius = floor(sphere->radius/deltaZ);
if
((p+intRadius<nCell)&&(p-intRadius>0)&&(lift==true)) {
Real vRelTop = vxFluid[p+intRadius] -
vPart[0]; // relative velocity of the fluid wrt the particle at the top of the
particle
Real vRelBottom = vxFluid[p-intRadius]
- vPart[0]; // same at the bottom
liftForce[2] =
0.5*rhoFluid*A*Cl*(vRelTop*vRelTop-vRelBottom*vRelBottom);
}
//Archimedes force calculation
Vector3r archimedesForce =
-4.0/3.0*Mathr::PI*sphere->radius*sphere->radius*sphere->radius*rhoFluid*gravity;
//add the force to the particle
scene->forces.addForce(id,dragForce+liftForce+archimedesForce);
}
}
}
}
ForceEngine.hpp :
class HydroForceEngine: public PartialEngine{
public:
virtual void action();
YADE_CLASS_BASE_DOC_ATTRS(HydroForceEngine,PartialEngine,"Apply drag
and lift force (and Archimedes force) due to a fluid flow vector (1D) to each
sphere. The applied force reads\n\n.. math:: F_{d}=\\frac{1}{2} C_d
A\\rho|\\vec{v_f - v}| vec{v_f - v} \n\n where $\\rho$ is the medium density
(:yref:`density<HydroForceEngine.rhoFluid>`), $v$ is particle's velocity,
$v_f$ is the velocity of the fluid at the particle center, $A$ is particle
projected area (disc), $C_d$ is the drag coefficient. The formulation of the
drag coefficient depends on the local particle reynolds number and the solid
volume fraction. The formulation of the drag is Dallavalle with a correction of
Richardson-Zaki to take into account the hindrance effect. This law is
classical in sediment transport.\n The formulation of the lift is taken from
Wiberg and Smith 1985 and is such as : \n\n.. math:: F_{L}=\\frac{1}{2} C_L
A\\rho((v_f - v)^2{top} - (v_f - v)^2{bottom}) \n\n Where the subscript top and
bottom means evaluated at the top (respectively the bottom) of the sphere
considered. This formulation of the lift is a reformulation of the so-called
saffman lift which is due to the difference of pressure inside a shear flow.",
((Real,rhoFluid,1000,,"Density of the medium (fluid or air), by
default - density of water"))
((Real,viscoDyn,1e-3,,"Dynamic viscosity of the fluid"))
((Real,zRef,,,"Position of the reference point which correspond
to the first value of the fluid velocity"))
((Real,nCell,,,"Size of the vector of the fluid velocity"))
((Real,deltaZ,,,"Size of the discretization/the cell along z"))
((Real,expoRZ,3.1,,"Value of the Richardson-Zaki exponent, for
the correction due to hindrance"))
((Real,lift,true,,"Option to activate or not the evaluation of
the lift"))
((Real,Cl,0.2,,"Value of the lift coefficient"))
((Vector3r,gravity,,,"Gravity vector"))
((vector<Real>,vxFluid,,,"Streamwise fluid velocity profile in
function of the altitude"))
((vector<Real>,phiPart,,,"Solid volume fraction profile in
function of the altitude"))
((vector<Real>,vxFluct,,,"Vector containing the value of the
fluctuation of the streamwise fluid velocity at the position of the particles
considered. The ith component of this vector correspond to the fluctuation of
fluid velocity along x at the position of particle of id i."))
((vector<Real>,vzFluct,,,"Same as
:yref:`vxFluct<DragEngineNEW.vxFluct>` but for the vertical direction z."))
);
};
REGISTER_SERIALIZABLE(HydroForceEngine);
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