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Take incompressibility of gas into account at higher pressures

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This creates a helper function called "gas_volume()" that takes the
cylinder and a particular pressure, and returns the estimated volume of
the gas at surface pressure, including proper approximation of the
incompressibility of gas.

It very much is an approximation, but it's closer to reality than
assuming a pure ideal gas.  See for example compressibility at

    http://en.wikipedia.org/wiki/Compressibility_factor

Suggested-by: Jukka Lind <jukka.lind@iki.fi>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
This commit is contained in:
Linus Torvalds 2013-02-25 15:23:16 -08:00 • committed by Dirk Hohndel
parent d53bedbed6
commit 308d71ec39
5 changed files with 58 additions and 36 deletions
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13
divelist.c
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@ -697,26 +697,19 @@ static int calculate_otu(struct dive *dive)
*/
static double calculate_airuse(struct dive *dive)
{
double airuse = 0;
int airuse = 0;
int i;
for (i = 0; i < MAX_CYLINDERS; i++) {
pressure_t start, end;
cylinder_t *cyl = dive->cylinder + i;
int size = cyl->type.size.mliter;
double kilo_atm;
if (!size)
continue;
start = cyl->start.mbar ? cyl->start : cyl->sample_start;
end = cyl->end.mbar ? cyl->end : cyl->sample_end;
kilo_atm = (to_ATM(start) - to_ATM(end)) / 1000.0;
/* Liters of air at 1 atm == milliliters at 1k atm*/
airuse += kilo_atm * size;
airuse += gas_volume(cyl, start) - gas_volume(cyl, end);
}
return airuse;
return airuse / 1000.0;
}
/* this only uses the first divecomputer to calculate the SAC rate */