mirror of
https://github.com/subsurface/subsurface.git
synced 2024-11-28 05:00:20 +00:00
3395c61bc8
A nice one - nothing to do. Introduce an std::clamp(), just because we can... Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
83 lines
2.3 KiB
C++
83 lines
2.3 KiB
C++
// SPDX-License-Identifier: GPL-2.0
|
||
/* gas-model.cpp */
|
||
/* gas compressibility model */
|
||
#include <algorithm> // std::clamp
|
||
#include <stdio.h>
|
||
#include <stdlib.h>
|
||
#include "dive.h"
|
||
|
||
/* "Virial minus one" - the virial cubic form without the initial 1.0 */
|
||
static double virial_m1(const double coeff[], double x)
|
||
{
|
||
return x*coeff[0] + x*x*coeff[1] + x*x*x*coeff[2];
|
||
}
|
||
|
||
/*
|
||
* Z = pV/nRT
|
||
*
|
||
* Cubic virial least-square coefficients for O2/N2/He based on data from
|
||
*
|
||
* PERRY’S CHEMICAL ENGINEERS’ HANDBOOK SEVENTH EDITION
|
||
*
|
||
* with the lookup and curve fitting by Lubomir.
|
||
*
|
||
* The "virial" form of the compression factor polynomial is
|
||
*
|
||
* Z = 1.0 + C[0]*P + C[1]*P^2 + C[2]*P^3 ...
|
||
*
|
||
* and these tables do not contain the initial 1.0 term.
|
||
*
|
||
* NOTE! Helium coefficients are a linear mix operation between the
|
||
* 323K and one for 273K isotherms, to make everything be at 300K.
|
||
*/
|
||
double gas_compressibility_factor(struct gasmix gas, double bar)
|
||
{
|
||
static const double o2_coefficients[3] = {
|
||
-7.18092073703e-04,
|
||
+2.81852572808e-06,
|
||
-1.50290620492e-09
|
||
};
|
||
static const double n2_coefficients[3] = {
|
||
-2.19260353292e-04,
|
||
+2.92844845532e-06,
|
||
-2.07613482075e-09
|
||
};
|
||
static const double he_coefficients[3] = {
|
||
+4.87320026468e-04,
|
||
-8.83632921053e-08,
|
||
+5.33304543646e-11
|
||
};
|
||
|
||
/*
|
||
* The curve fitting range is only [0,500] bar.
|
||
* Anything else is way out of range for cylinder
|
||
* pressures.
|
||
*/
|
||
bar = std::clamp(bar, 0.0, 500.0);
|
||
|
||
int o2 = get_o2(gas);
|
||
int he = get_he(gas);
|
||
|
||
double Z = virial_m1(o2_coefficients, bar) * o2 +
|
||
virial_m1(he_coefficients, bar) * he +
|
||
virial_m1(n2_coefficients, bar) * (1000 - o2 - he);
|
||
|
||
/*
|
||
* We add the 1.0 at the very end - the linear mixing of the
|
||
* three 1.0 terms is still 1.0 regardless of the gas mix.
|
||
*
|
||
* The * 0.001 is because we did the linear mixing using the
|
||
* raw permille gas values.
|
||
*/
|
||
return Z * 0.001 + 1.0;
|
||
}
|
||
|
||
/* Compute the new pressure when compressing (expanding) volome v1 at pressure p1 bar to volume v2
|
||
* taking into account the compressebility (to first order) */
|
||
|
||
double isothermal_pressure(struct gasmix gas, double p1, int volume1, int volume2)
|
||
{
|
||
double p_ideal = p1 * volume1 / volume2 / gas_compressibility_factor(gas, p1);
|
||
|
||
return p_ideal * gas_compressibility_factor(gas, p_ideal);
|
||
}
|