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deco.c
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deco.c
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/* calculate deco values
* based on Bühlmann ZHL-16b
* based on an implemention by heinrichs weikamp for the DR5
* the original file was given to Subsurface under the GPLv2
* by Matthias Heinrichs
*
* The implementation below is a fairly complete rewrite since then
* (C) Robert C. Helling 2013 and released under the GPLv2
*
* add_segment() - add <seconds> at the given pressure, breathing gasmix
* deco_allowed_depth() - ceiling based on lead tissue, surface pressure, 3m increments or smooth
* set_gf() - set Buehlmann gradient factors
* clear_deco()
* cache_deco_state()
* restore_deco_state()
* dump_tissues()
*/
#include <math.h>
#include <string.h>
#include "dive.h"
//! Option structure for Buehlmann decompression.
struct buehlmann_config {
double satmult; //! safety at inert gas accumulation as percentage of effect (more than 100).
double desatmult; //! safety at inert gas depletion as percentage of effect (less than 100).
int last_deco_stop_in_mtr; //! depth of last_deco_stop.
double gf_high; //! gradient factor high (at surface).
double gf_low; //! gradient factor low (at bottom/start of deco calculation).
double gf_low_position_min; //! gf_low_position below surface_min_shallow.
};
struct buehlmann_config buehlmann_config = { 1.0, 1.01, 0, 0.75, 0.35, 2.0 };
const double buehlmann_N2_a[] = {1.1696, 1.0, 0.8618, 0.7562,
0.62, 0.5043, 0.441, 0.4,
0.375, 0.35, 0.3295, 0.3065,
0.2835, 0.261, 0.248, 0.2327};
const double buehlmann_N2_b[] = {0.5578, 0.6514, 0.7222, 0.7825,
0.8126, 0.8434, 0.8693, 0.8910,
0.9092, 0.9222, 0.9319, 0.9403,
0.9477, 0.9544, 0.9602, 0.9653};
const double buehlmann_N2_t_halflife[] = {5.0, 8.0, 12.5, 18.5,
27.0, 38.3, 54.3, 77.0,
109.0, 146.0, 187.0, 239.0,
305.0, 390.0, 498.0, 635.0};
const double buehlmann_N2_factor_expositon_one_second[] = {
2.30782347297664E-003, 1.44301447809736E-003, 9.23769302935806E-004, 6.24261986779007E-004,
4.27777107246730E-004, 3.01585140931371E-004, 2.12729727268379E-004, 1.50020603047807E-004,
1.05980191127841E-004, 7.91232600646508E-005, 6.17759153688224E-005, 4.83354552742732E-005,
3.78761777920511E-005, 2.96212356654113E-005, 2.31974277413727E-005, 1.81926738960225E-005};
const double buehlmann_He_a[] = { 1.6189, 1.383 , 1.1919, 1.0458,
0.922 , 0.8205, 0.7305, 0.6502,
0.595 , 0.5545, 0.5333, 0.5189,
0.5181, 0.5176, 0.5172, 0.5119};
const double buehlmann_He_b[] = {0.4770, 0.5747, 0.6527, 0.7223,
0.7582, 0.7957, 0.8279, 0.8553,
0.8757, 0.8903, 0.8997, 0.9073,
0.9122, 0.9171, 0.9217, 0.9267};
const double buehlmann_He_t_halflife[] = {1.88, 3.02, 4.72, 6.99,
10.21, 14.48, 20.53, 29.11,
41.20, 55.19, 70.69, 90.34,
115.29, 147.42, 188.24, 240.03};
const double buehlmann_He_factor_expositon_one_second[] = {
6.12608039419837E-003, 3.81800836683133E-003, 2.44456078654209E-003, 1.65134647076792E-003,
1.13084424730725E-003, 7.97503165599123E-004, 5.62552521860549E-004, 3.96776399429366E-004,
2.80360036664540E-004, 2.09299583354805E-004, 1.63410794820518E-004, 1.27869320250551E-004,
1.00198406028040E-004, 7.83611475491108E-005, 6.13689891868496E-005, 4.81280465299827E-005};
#define WV_PRESSURE 0.0627 // water vapor pressure in bar
#define DECO_STOPS_MULTIPLIER_MM 3000.0
#define GF_LOW_AT_MAXDEPTH 0
double tissue_n2_sat[16];
double tissue_he_sat[16];
int ci_pointing_to_guiding_tissue;
double gf_low_pressure_this_dive;
#define TISSUE_ARRAY_SZ sizeof(tissue_n2_sat)
static double tissue_tolerance_calc(const struct dive *dive)
{
int ci = -1;
double tissue_inertgas_saturation, buehlmann_inertgas_a, buehlmann_inertgas_b;
double ret_tolerance_limit_ambient_pressure = 0.0;
double gf_high = buehlmann_config.gf_high;
double gf_low = buehlmann_config.gf_low;
double surface = get_surface_pressure_in_mbar(dive, TRUE) / 1000.0;
double lowest_ceiling;
for (ci = 0; ci < 16; ci++)
{
double tolerated;
tissue_inertgas_saturation = tissue_n2_sat[ci] + tissue_he_sat[ci];
buehlmann_inertgas_a = ((buehlmann_N2_a[ci] * tissue_n2_sat[ci]) + (buehlmann_He_a[ci] * tissue_he_sat[ci])) / tissue_inertgas_saturation;
buehlmann_inertgas_b = ((buehlmann_N2_b[ci] * tissue_n2_sat[ci]) + (buehlmann_He_b[ci] * tissue_he_sat[ci])) / tissue_inertgas_saturation;
/* tolerated = (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
tolerated = (-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) /
(-buehlmann_inertgas_a * buehlmann_inertgas_b * (gf_high - gf_low) +
(1.0 - buehlmann_inertgas_b)*(gf_low * gf_low_pressure_this_dive - gf_high * surface) +
buehlmann_inertgas_b * (gf_low_pressure_this_dive - surface));
if (tolerated > ret_tolerance_limit_ambient_pressure)
{
ci_pointing_to_guiding_tissue = ci;
ret_tolerance_limit_ambient_pressure = tolerated;
}
}
return ret_tolerance_limit_ambient_pressure;
}
/* add period_in_seconds at the given pressure and gas to the deco calculation */
double add_segment(double pressure, const struct gasmix *gasmix, int period_in_seconds, int ccpo2, const struct dive *dive)
{
int ci;
int fo2 = get_o2(gasmix), fhe = get_he(gasmix);
double ppn2 = (pressure - WV_PRESSURE) * (1000 - fo2 - fhe) / 1000.0;
double pphe = (pressure - WV_PRESSURE) * fhe / 1000.0;
#if GF_LOW_AT_MAXDEPTH
if (pressure > gf_low_pressure_this_dive)
gf_low_pressure_this_dive = pressure;
#endif
if (ccpo2) { /* CC */
double rel_o2_amb, f_dilutent;
rel_o2_amb = ccpo2 / pressure / 1000;
f_dilutent = (1 - rel_o2_amb) / (1 - fo2 / 1000.0);
if (f_dilutent < 0) { /* setpoint is higher than ambient pressure -> pure O2 */
ppn2 = 0.0;
pphe = 0.0;
} else if (f_dilutent < 1.0) {
ppn2 *= f_dilutent;
pphe *= f_dilutent;
}
}
if (period_in_seconds == 1) { /* one second interval during dive */
for (ci = 0; ci < 16; ci++) {
if (ppn2 - tissue_n2_sat[ci] > 0)
tissue_n2_sat[ci] += buehlmann_config.satmult * (ppn2 - tissue_n2_sat[ci]) *
buehlmann_N2_factor_expositon_one_second[ci];
else
tissue_n2_sat[ci] += buehlmann_config.desatmult * (ppn2 - tissue_n2_sat[ci]) *
buehlmann_N2_factor_expositon_one_second[ci];
if (pphe - tissue_he_sat[ci] > 0)
tissue_he_sat[ci] += buehlmann_config.satmult * (pphe - tissue_he_sat[ci]) *
buehlmann_He_factor_expositon_one_second[ci];
else
tissue_he_sat[ci] += buehlmann_config.desatmult * (pphe - tissue_he_sat[ci]) *
buehlmann_He_factor_expositon_one_second[ci];
}
} else { /* all other durations */
for (ci = 0; ci < 16; ci++)
{
if (ppn2 - tissue_n2_sat[ci] > 0)
tissue_n2_sat[ci] += buehlmann_config.satmult * (ppn2 - tissue_n2_sat[ci]) *
(1 - pow(2.0,(- period_in_seconds / (buehlmann_N2_t_halflife[ci] * 60))));
else
tissue_n2_sat[ci] += buehlmann_config.desatmult * (ppn2 - tissue_n2_sat[ci]) *
(1 - pow(2.0,(- period_in_seconds / (buehlmann_N2_t_halflife[ci] * 60))));
if (pphe - tissue_he_sat[ci] > 0)
tissue_he_sat[ci] += buehlmann_config.satmult * (pphe - tissue_he_sat[ci]) *
(1 - pow(2.0,(- period_in_seconds / (buehlmann_He_t_halflife[ci] * 60))));
else
tissue_he_sat[ci] += buehlmann_config.desatmult * (pphe - tissue_he_sat[ci]) *
(1 - pow(2.0,(- period_in_seconds / (buehlmann_He_t_halflife[ci] * 60))));
}
}
return tissue_tolerance_calc(dive);
}
void dump_tissues()
{
int ci;
printf("N2 tissues:");
for (ci = 0; ci < 16; ci++)
printf(" %6.3e", tissue_n2_sat[ci]);
printf("\nHe tissues:");
for (ci = 0; ci < 16; ci++)
printf(" %6.3e", tissue_he_sat[ci]);
printf("\n");
}
void clear_deco(double surface_pressure)
{
int ci;
for (ci = 0; ci < 16; ci++) {
tissue_n2_sat[ci] = (surface_pressure - WV_PRESSURE) * N2_IN_AIR / 1000;
tissue_he_sat[ci] = 0.0;
}
gf_low_pressure_this_dive = surface_pressure + buehlmann_config.gf_low_position_min;
}
void cache_deco_state(double tissue_tolerance, char **cached_datap)
{
char *data = *cached_datap;
if (!data) {
data = malloc(2 * TISSUE_ARRAY_SZ + 2 * sizeof(double) + sizeof(int));
*cached_datap = data;
}
memcpy(data, tissue_n2_sat, TISSUE_ARRAY_SZ);
data += TISSUE_ARRAY_SZ;
memcpy(data, tissue_he_sat, TISSUE_ARRAY_SZ);
data += TISSUE_ARRAY_SZ;
memcpy(data, &gf_low_pressure_this_dive, sizeof(double));
data += sizeof(double);
memcpy(data, &tissue_tolerance, sizeof(double));
data += sizeof(double);
memcpy(data, &ci_pointing_to_guiding_tissue, sizeof(int));
}
double restore_deco_state(char *data)
{
double tissue_tolerance;
memcpy(tissue_n2_sat, data, TISSUE_ARRAY_SZ);
data += TISSUE_ARRAY_SZ;
memcpy(tissue_he_sat, data, TISSUE_ARRAY_SZ);
data += TISSUE_ARRAY_SZ;
memcpy(&gf_low_pressure_this_dive, data, sizeof(double));
data += sizeof(double);
memcpy(&tissue_tolerance, data, sizeof(double));
data += sizeof(double);
memcpy(&ci_pointing_to_guiding_tissue, data, sizeof(int));
return tissue_tolerance;
}
unsigned int deco_allowed_depth(double tissues_tolerance, double surface_pressure, struct dive *dive, gboolean smooth)
{
unsigned int depth;
double pressure_delta;
/* Avoid negative depths */
pressure_delta = tissues_tolerance > surface_pressure ? tissues_tolerance - surface_pressure : 0.0;
depth = rel_mbar_to_depth(pressure_delta * 1000, dive);
if (!smooth)
depth = ceil(depth / DECO_STOPS_MULTIPLIER_MM) * DECO_STOPS_MULTIPLIER_MM;
if (depth > 0 && depth < buehlmann_config.last_deco_stop_in_mtr * 1000)
depth = buehlmann_config.last_deco_stop_in_mtr * 1000;
return depth;
}
void set_gf(double gflow, double gfhigh)
{
if (gflow != -1.0)
buehlmann_config.gf_low = gflow;
if (gfhigh != -1.0)
buehlmann_config.gf_high = gfhigh;
}