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operator: use newton iteration to calculate numerical phase velocity

pull/1/head
Thorsten Liebig 2012-07-25 09:41:30 +02:00
parent 4741bcf069
commit 0ad528e6b8
2 changed files with 43 additions and 5 deletions
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46
FDTD/operator.cpp
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@ -1743,15 +1743,15 @@ void Operator::DeleteExtension(Operator_Extension* op_ext)
double Operator::CalcNumericPhaseVelocity(unsigned int start[3], unsigned int stop[3], double propDir[3], float freq) const
{
double phv=__C0__;
double average_mesh_disc[3];
// double k=2*PI*freq/__C0__;
//calculate average mesh deltas
for (int n=0;n<3;++n)
{
average_mesh_disc[n] = fabs(GetDiscLine(n,start[n])-GetDiscLine(n,stop[n]))*GetGridDelta() / (fabs(stop[n]-start[n]));
}
// if propagation is in a Cartesian direction, return analytic solution
for (int n=0;n<3;++n)
{
int nP = (n+1)%3;
@ -1763,7 +1763,45 @@ double Operator::CalcNumericPhaseVelocity(unsigned int start[3], unsigned int st
}
}
cerr << "Operator::CalcNumericPhaseVelocity: Warning, propagation direction not in Cartesian direction, assuming phase velocity to be c0" << endl;
// else, do an newton iterative estimation
double k0=2*PI*freq/__C0__;
double k=k0;
double RHS = pow(sin(2*PI*freq*dT/2)/__C0__/dT,2);
double fk=1,fdk=0;
double old_phv=0;
double phv=__C0__;
double err_est = 1e-6;
int it_count=0;
while (fabs(old_phv-phv)>err_est)
{
++it_count;
old_phv=phv;
fk=0;
fdk=0;
for (int n=0;n<3;++n)
{
fk+= pow(sin(propDir[n]*k*average_mesh_disc[n]/2)/average_mesh_disc[n],2);
fdk+= propDir[n]*sin(propDir[n]*k*average_mesh_disc[n]/2)*cos(propDir[n]*k*average_mesh_disc[n]/2)/average_mesh_disc[n];
}
fk -= RHS;
k-=fk/fdk;
// do not allow a speed greater than c0 due to a numerical inaccuracy
if (k<k0)
k=k0;
phv=2*PI*freq/k;
//abort if iteration count is getting to high!
if (it_count>99)
{
cerr << "Operator::CalcNumericPhaseVelocity: Error, newton iteration estimation can't find a solution!!" << endl;
break;
}
}
if (g_settings.GetVerboseLevel()>1)
cerr << "Operator::CalcNumericPhaseVelocity: Newton iteration estimated solution: " << phv/__C0__ << "*c0 in " << it_count << " iterations." << endl;
return phv;
}

2
matlab/Tutorials/RCS_Sphere.m
View File

@ -54,7 +54,7 @@ CSX = AddSphere(CSX,'sphere',10,[0 0 0],sphere.rad);
k_dir = [cos(inc_angle) sin(inc_angle) 0]; % plane wave direction
E_dir = [0 0 1]; % plane wave polarization --> E_z
CSX = AddPlaneWaveExcite(CSX, 'plane_wave', k_dir, E_dir);
CSX = AddPlaneWaveExcite(CSX, 'plane_wave', k_dir, E_dir, f0);
start = [-PW_Box/2 -PW_Box/2 -PW_Box/2];
stop = -start;
CSX = AddBox(CSX, 'plane_wave', 0, start, stop);