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Adjust GFlow to apply at deepest ceiling instead of at max depth

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This moves the point where GF_low applies up which implies that at all
shallower depth (i.e. during deco) a lower GF results which makes the deco
longer compared to the previous implementation.

Of course, "GF_low" applies at first deco stop is a bit tricky since the
depth of the first deco stop again depends on GF_low, i.e. there is
another equation to solve. You can do this by inverting the equation for
the ambient pressure and use GF_low as the gradient factor. This yields

amb = (b * M_value_corrected - GF_low * a * b) / ((1-b) * GF_low + b)

Signed-off-by: Robert C. Helling helling@atdotde.de
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
This commit is contained in:
Robert C. Helling 2013-01-10 11:24:42 +01:00 • committed by Dirk Hohndel
parent 1aa3c0d514
commit 4c13f1f6b4
1 changed files with 12 additions and 0 deletions
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12
deco.c
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@ -81,6 +81,8 @@ const double buehlmann_He_factor_expositon_one_second[] = {
#define N2_IN_AIR 0.7902
#define DECO_STOPS_MULTIPLIER_MM 3000.0
#define GF_LOW_AT_MAXDEPTH 0
double tissue_n2_sat[16];
double tissue_he_sat[16];
double tissue_tolerated_ambient_pressure[16];
@ -96,6 +98,7 @@ static double tissue_tolerance_calc(const struct dive *dive)
double gf_high = buehlmann_config.gf_high;
double gf_low = buehlmann_config.gf_low;
double surface = dive->surface_pressure.mbar / 1000.0;
double lowest_ceiling;
for (ci = 0; ci < 16; ci++)
{
@ -105,6 +108,13 @@ static double tissue_tolerance_calc(const struct dive *dive)
/* tissue_tolerated_ambient_pressure[ci] = (tissue_inertgas_saturation - buehlmann_inertgas_a) * buehlmann_inertgas_b; */
#if !GF_LOW_AT_MAXDEPTH
lowest_ceiling = (buehlmann_inertgas_b * tissue_inertgas_saturation - gf_low * buehlmann_inertgas_a * buehlmann_inertgas_b) /
((1.0 - buehlmann_inertgas_b) * gf_low + buehlmann_inertgas_b);
if(lowest_ceiling > gf_low_pressure_this_dive)
gf_low_pressure_this_dive = lowest_ceiling;
#endif
tissue_tolerated_ambient_pressure[ci] = (-buehlmann_inertgas_a * buehlmann_inertgas_b * (gf_high * gf_low_pressure_this_dive - gf_low * surface) -
(1.0 - buehlmann_inertgas_b) * (gf_high - gf_low) * gf_low_pressure_this_dive * surface +
buehlmann_inertgas_b * (gf_low_pressure_this_dive - surface) * tissue_inertgas_saturation) /
@ -129,8 +139,10 @@ double add_segment(double pressure, struct gasmix *gasmix, int period_in_seconds
double ppn2 = (pressure - WV_PRESSURE) * (1000 - fo2 - gasmix->he.permille) / 1000.0;
double pphe = (pressure - WV_PRESSURE) * gasmix->he.permille / 1000.0;
#if GF_LOW_AT_MAXDEPTH
if (pressure > gf_low_pressure_this_dive)
gf_low_pressure_this_dive = pressure;
#endif
if (ccpo2 > 0.0) { /* CC */
double rel_o2_amb, f_dilutent;