Ummm... You are aware that Windows allows you to put a screen capture of the active application using the Print Screen button, right? Seriously, it's as easy as copy/paste.DYI wrote:It would be great if there was some way to take pictures of GGDT outputs that was easier than actually photographing it with a digicam and then uploading it to Photobucket.
Not necessarily....especially when barrel combustion isn't incorporated yet.pat123 wrote:I found one other thing I kept everything exactly the same except i changed the mix. At 1x it says 346 ft/s and at 3X it says 277ft/s. wouldn't 3x be alot faster?
I've seen the button, but never really understood it's function. Amazing how it could have escaped me for that long...Ummm... You are aware that Windows allows you to put a screen capture of the active application using the Print Screen button, right? Seriously, it's as easy as copy/paste.
OK, bug identified and fixed. A new version is up on the GGDT webpage for download.DYI wrote:Example:
Gun using:
-1x12" chamber
-.3" porting barrel sealing piston valve with 2 ounce piston, 0.25" porting,
1ci pilot volume
-848.3 psi hydrogen at 80 degrees fahrenheit
-0.2401" x 72" barrel
-0.24", 0.2 gram projectile
Predicted muzzle velocity: 3 250 fps.
Predicted maximum range using drag coefficient of 0.4 (perfect sphere I believe): -1 feet
There must be some problem there.
Ya, I've realized the same thing. With multiple sparks it gets real ugly real quick. I figured the only way to do it without driving myself nuts is to model the chamber as discrete volumes then scan over each volume for each time step and see if it is within the current flame front radius for any of the spark gaps. This would be an easy way to handle the flame fronts when they overlap since a particular volume element can only be burned once. That apporach would be easy to code but will probably be real slow. Currently, I'm kind of limited because I'm too lazy to take my model out of Excel and put it in a real programing language.I considered this approach for a long time and eventually went in a different direction as it seemed like the math would get nasty when multiple ignition points where thrown into the mix. In the end I went with a different approach that is admittedly less accurate for the single point ignition scenario but should be more flexible.I look at it as if there are three volumes in the chamber; (1) the unburned volume near the breech, (2) the burned volume and (3) the unburned volume on the muzzle end. For this example, all three volumes need to increase by 1% so that the fraction burned stays unchanged. (Fuel can't be "unburned" just because the total chamber volume has increased.) That means the breech end flame front moves towards the muzzle. [...] Of course, the math gets to be a PITA, especially when the flame front actually moves into the barrel.
<strike>Actually, it isn't quite the same. For GGDT Pmax and Tmax occur at time zero. For a combustion gun it occurs at some later time. P<sub>i</sub> and T<sub>i</sub> rise then fall. For a pneumatic P<sub>i</sub> and T<sub>i</sub> are always falling. Pmax and Tmax start out as maxima and fall as the chamber expands. Of course, Pmax and Tmax are really just bookkeeping devices.</strike>Obviously. This phenom is at the heart and soul of GGDT.The other thing I do is that once the spud starts to move the Tmax and Pmax have to be rescaled to take into account the expansion. In a gun in which the fuel is still burning when the projectile is moving the temperature and pressure will never reach the closed chamber Tmax and Pmax values.
It really is the same. The only difference is whether you're adding energy to the system or subtracting it or doing both at the same time. The thermodynamics are the same; it's just a superposition. Seriously, neither HGDT nor GGDT use Tmax or Pmax values even as a book keeping device. I track them strictly because people like to see the results, but nowhere do those terms show up in the programming logic that matters.jimmy101 wrote:Actually, it isn't quite the same. For GGDT Pmax and Tmax occur at time zero. For a combustion gun it occurs at some later time. P<sub>i</sub> and T<sub>i</sub> rise then fall. For a pneumatic P<sub>i</sub> and T<sub>i</sub> are always falling. Pmax and Tmax start out as maxima and fall as the chamber expands. Of course, Pmax and Tmax are really just bookkeeping devices.
Fixed (both of 'em).Carlman wrote:when you change the configuration to metric the inner diameter of the chamber stays measured in inches
and when you configure settings for projectile mass it doesn't show anything other than ounces although the number changes
Fixed._Fnord wrote:I don't get an error/warning when I set the burst pressure below the mix pressure.
Done.jimmy101 wrote:How about putting the version number in the GUI somewhere?
Yeah, I just plugged in the dimension numbers (~225 ci) for my advanced combustion to see what popped out. Projectile was a heavyish golf ball, barrel 160" long, and started running up the burst disk number. There's a massive amount of energy in there, just being able to tap it before the ball leaves the barrel is the key...high pressure disk allows that.spudfarm wrote:3x SOS?
that has to be a BIG cannon..
Do keep in mind that I'm not currently barrel combustion. On a hybrid that bursts right at max pressure, this will have zero effect on muzzle velocity. On simple combustion with a light weight projectile it will have a huge effect. Between those two extremes are shades of gray, of course.starman wrote:I'm seeing the advantage of burst disking even 1x advanced combustions, something I have already been experimenting with. A rather modest 30 psi disk will gain you a very healthy muzzle velocity, varying of course on other factors. A fairly simple addition for a big gain.
