Issues with the GGDT software

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Luke31
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Wed Mar 17, 2021 11:41 am

I am trying to use the GGDT software but im having issues. I keep getting an error stating that the projectile never cleared the barrel, but I believe I put in reasonable numbers.

The odd thing is if I increase the chamber inner diameter, it decreases the volume. If I increase the outer diameter, it increases the volume. I don't know why the outer diameter is even relevant to the experiment since its just the wall thickness.

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jackssmirkingrevenge
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Wed Mar 17, 2021 12:12 pm

"Outer Diam" is the inner diameter of your chamber tube.

"Inner Diam" is the outer diameter of your barrel for a coaxial cannon.

If your design is not a coaxial, the "Inner Diam" should be zero.
hectmarr wrote:You have to make many weapons, because this field is long and short life
Luke31
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Wed Mar 17, 2021 2:18 pm

jackssmirkingrevenge wrote:
Wed Mar 17, 2021 12:12 pm
"Outer Diam" is the inner diameter of your chamber tube.

"Inner Diam" is the outer diameter of your barrel for a coaxial cannon.

If your design is not a coaxial, the "Inner Diam" should be zero.
Man how were we supposed to know that. Anyway I'm starting to get realistic numbers now. Thanks!
Luke31
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Tue May 11, 2021 12:56 pm

Could someone explain the valve settings? My air cannon uses a 1'' ball valve, but I don't see any options in the settings for that.

What is..

Seat Diam
Chmber Seal
Generic valve
Barrel Seal
Hammer

How am I supposed to know the friction psi of my projectile. Anyway to test that?

Is psig the same as psi? Is it safe to assume 100 psi would equal 100 psig?
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jackssmirkingrevenge
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Thu May 13, 2021 9:30 am

Luke31 wrote:
Tue May 11, 2021 12:56 pm
Could someone explain the valve settings? My air cannon uses a 1'' ball valve, but I don't see any options in the settings for that.
For a ball valve, select "generic valve"

Leave the flow coefficient at 45%

Seat diameter would be 1 inch

You'll have to estimate the opening time depending on how you're opening the valve.

Dwell time is 999 if the valve stays open.

Dead volume is the total space between the base of the projectile at rest and the valve opening.
How am I supposed to know the friction psi of my projectile. Anyway to test that?
Put the projectile in the barrel and try and blow it out. If it moves then friction is less than 3 psi
Is psig the same as psi? Is it safe to assume 100 psi would equal 100 psig?
psig means psi gauge, ignoring atmospheric pressure.

For example if your gauge reads 100 psi, then it is 100 psi relative to the atmosphere but the actual pressure is 115 psi.

For practical purposes that extra 15 psi is "cancelled out" by the atmosphere.
hectmarr wrote:You have to make many weapons, because this field is long and short life
Luke31
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Thu May 13, 2021 12:09 pm

Not sure how fast I am opening the ball valve. I'm guessing 100 milliseconds.

For my application, I'm shooting multiple projectiles at once(12 6 ounce water balloons). How can I best I model this in GGDT? I just put the total weight of the projectiles in the projectile data. The balloons will scatter so the ranges will differ some, which makes it hard to model.
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