diff options
Diffstat (limited to 'dive.c')
| -rw-r--r-- | dive.c | 31 |
1 files changed, 27 insertions, 4 deletions
@@ -286,6 +286,29 @@ static void update_min_max_temperatures(struct dive *dive, temperature_t tempera } } +/* + * At high pressures air becomes less compressible, and + * does not follow the ideal gas law any more. + * + * This tries to correct for that, becoming the same + * as to_ATM() at lower pressures. + * + * THIS IS A ROUGH APPROXIMATION! The real numbers will + * depend on the exact gas mix and temperature. + */ +double surface_volume_multiplier(pressure_t pressure) +{ + double bar = pressure.mbar / 1000.0; + + if (bar > 200) + bar = 0.00038*bar*bar + 0.51629*bar + 81.542; + return bar_to_atm(bar); +} + +int gas_volume(cylinder_t *cyl, pressure_t p) +{ + return cyl->type.size.mliter * surface_volume_multiplier(p); +} /* * If the cylinder tank pressures are within half a bar @@ -338,7 +361,7 @@ static void match_standard_cylinder(cylinder_type_t *type) return; cuft = ml_to_cuft(type->size.mliter); - cuft *= to_ATM(type->workingpressure); + cuft *= surface_volume_multiplier(type->workingpressure); psi = to_PSI(type->workingpressure); switch (psi) { @@ -381,7 +404,7 @@ static void match_standard_cylinder(cylinder_type_t *type) */ static void sanitize_cylinder_type(cylinder_type_t *type) { - double volume_of_air, atm, volume; + double volume_of_air, volume; /* If we have no working pressure, it had *better* be just a physical size! */ if (!type->workingpressure.mbar) @@ -394,8 +417,8 @@ static void sanitize_cylinder_type(cylinder_type_t *type) if (xml_parsing_units.volume == CUFT) { /* confusing - we don't really start from ml but millicuft !*/ volume_of_air = cuft_to_l(type->size.mliter); - atm = to_ATM(type->workingpressure); /* working pressure in atm */ - volume = volume_of_air / atm; /* milliliters at 1 atm: "true size" */ + /* milliliters at 1 atm: "true size" */ + volume = volume_of_air / surface_volume_multiplier(type->workingpressure); type->size.mliter = volume + 0.5; } |