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VPM-B: Add surface decompression time.

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Now, we calculate the volume of free gas not only based on the deco
time but also time on the surface, needed for the full desaturation.

Signed-off-by: Jan Darowski <jan.darowski@gmail.com>
This commit is contained in:
Jan Darowski 2015-08-15 14:28:44 +02:00
parent c0fde4f50f
commit 499ec9af2f
3 changed files with 24 additions and 4 deletions
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24
deco.c
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@ -91,6 +91,7 @@ const double buehlmann_He_factor_expositon_one_second[] = {
#define WV_PRESSURE 0.0627 // water vapor pressure in bar
#define DECO_STOPS_MULTIPLIER_MM 3000.0
#define NITROGEN_FRACTION 0.79
double tissue_n2_sat[16];
double tissue_he_sat[16];
@ -215,6 +216,22 @@ double he_factor(int period_in_seconds, int ci)
return cache[ci].last_factor;
}
double calc_surface_phase(double surface_pressure, double he_pressure, double n2_pressure, double he_time_constant, double n2_time_constant)
{
double inspired_n2 = (surface_pressure - WV_PRESSURE) * NITROGEN_FRACTION;
if (n2_pressure > inspired_n2)
return (he_pressure / he_time_constant + (n2_pressure - inspired_n2) / n2_time_constant) / (he_pressure + n2_pressure - inspired_n2);
if (he_pressure + n2_pressure >= inspired_n2){
double gradient_decay_time = 1.0 / (n2_time_constant - he_time_constant) * log ((inspired_n2 - n2_pressure) / he_pressure);
double gradients_integral = he_pressure / he_time_constant * (1.0 - exp(-he_time_constant * gradient_decay_time)) + (n2_pressure - inspired_n2) / n2_time_constant * (1.0 - exp(-n2_time_constant * gradient_decay_time));
return gradients_integral / (he_pressure + n2_pressure - inspired_n2);
}
return 0;
}
bool is_vpmb_ok(double pressure)
{
int ci;
@ -243,15 +260,18 @@ void vpmb_start_gradient()
}
}
void vpmb_next_gradient(double deco_time)
void vpmb_next_gradient(double deco_time, double surface_pressure)
{
int ci;
double gradient_n2, gradient_he;
double n2_b, n2_c;
double he_b, he_c;
double desat_time = deco_time / 60.0;
double desat_time;
deco_time /= 60.0;
for (ci = 0; ci < 16; ++ci) {
desat_time = deco_time + calc_surface_phase(surface_pressure, tissue_he_sat[ci], tissue_n2_sat[ci], log(2.0) / buehlmann_He_t_halflife[ci], log(2.0) / buehlmann_N2_t_halflife[ci]);
n2_b = initial_n2_gradient[ci] + (vpmb_config.crit_volume_lambda * vpmb_config.surface_tension_gamma) / (vpmb_config.skin_compression_gammaC * desat_time);
he_b = initial_he_gradient[ci] + (vpmb_config.crit_volume_lambda * vpmb_config.surface_tension_gamma) / (vpmb_config.skin_compression_gammaC * desat_time);