research/cantera
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

[Reactor] Use Boost's bracket_and_solve_root function

Browse source 
This algorithm is more robust than the simple Newton's method that it
replaces. Among its advantages is that it works with PureFluidPhase models.

Resolves #257
This commit is contained in:
Ray Speth 2016-10-21 19:41:55 -04:00
parent 28202f9fa2
commit 1dc0cedcd9
1 changed files with 23 additions and 31 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

54
src/zeroD/Reactor.cpp
View file

@ -10,9 +10,10 @@
#include "cantera/zeroD/ReactorNet.h"
#include "cantera/zeroD/ReactorSurface.h"
#include <cfloat>
#include <boost/math/tools/roots.hpp>
using namespace std;
namespace bmt = boost::math::tools;
namespace Cantera
{
@ -139,38 +140,29 @@ void Reactor::updateState(doublereal* y)
m_thermo->setMassFractions_NoNorm(y+3);
if (m_energy) {
// Use a damped Newton's method to determine the mixture temperature.
// Tight tolerances are required both for Jacobian evaluation and for
// sensitivity analysis to work correctly.
doublereal U = y[2];
doublereal T = temperature();
double dT = 100;
double dUprev = 1e10;
double dU = 1e10;
int i = 0;
double damp = 1.0;
while (abs(dT / T) > 10 * DBL_EPSILON) {
dUprev = dU;
double U = y[2];
// Residual function: error in internal energy as a function of T
auto u_err = [this, U](double T) {
m_thermo->setState_TR(T, m_mass / m_vol);
double dUdT = m_thermo->cv_mass() * m_mass;
dU = m_thermo->intEnergy_mass() * m_mass - U;
dT = dU / dUdT;
// Reduce the damping coefficient if the magnitude of the error
// isn't decreasing
if (std::abs(dU) < std::abs(dUprev)) {
damp = 1.0;
} else {
damp *= 0.8;
}
dT = std::min(dT, 0.5 * T) * damp;
T -= dT;
i++;
if (i > 100) {
throw CanteraError("Reactor::updateState",
"no convergence\nU/m = {}\nT = {}\nrho = {}\n",
U / m_mass, T, m_mass / m_vol);
}
return m_thermo->intEnergy_mass() * m_mass - U;
};
double T = m_thermo->temperature();
boost::uintmax_t maxiter = 100;
std::pair<double, double> TT;
try {
TT = bmt::bracket_and_solve_root(
u_err, T, 1.2, true, bmt::eps_tolerance<double>(48), maxiter);
} catch (std::exception& err) {
// Set m_thermo back to a reasonable state if root finding fails
m_thermo->setState_TR(T, m_mass / m_vol);
throw CanteraError("Reactor::updateState", err.what());
}
if (fabs(TT.first - TT.second) > 1e-7*TT.first) {
throw CanteraError("Reactor::updateState",
"bracket_and_solve_root failed");
}
m_thermo->setState_TR(TT.second, m_mass / m_vol);
} else {
m_thermo->setDensity(m_mass/m_vol);
}