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Spudwiki help!

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Spudwiki help!

Unread postAuthor: limbeh » Thu Aug 02, 2012 12:08 pm

Well, my uni told us to go model a spudgun for a project.

I used the rough rule of thumb of calculating Cv as detailed in the Spudwiki -
http://www.spudfiles.com/spud_wiki/inde ... esign_Tool

Problem is, I can't find a proper source to cite that actually uses that. If I cited spudwiki, I'll be screwed big time.

To the experts like David Hall, PCGUY or MrCrowley, may I know where and how you guys came up with this rule? Thanks.
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Welcome to Singapore.

The laws are stricter concerning spudguns than anywhere in the West.

Even the Aussies for all they complain have it good compared to us.
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Unread postAuthor: MrCrowley » Thu Aug 02, 2012 3:37 pm

I didn't have time to read this but the abstract sounds promising:
http://www.sciencedirect.com/science/ar ... 7798100456

I assume you can get pass the paywall with your university proxy.

edit: I suspect that you wont find the formula D_Hall used (or whoever wrote that SpudWiki page) online or in journal articles because it may be a simplified formula. I'm basing that off the fact I didn't find a similar formula in a quick Google search and on the SpudWiki page it says that the formula isn't perfect but is close enough.
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Unread postAuthor: DYI » Thu Aug 02, 2012 5:43 pm

"Model a spudgun" is an awfully vague instruction...

To what level of physical accuracy does is need to be modeled? This is a project which could take anywhere from half an hour for a single person (0D, adiabatic, massless ideal gas, no flow restriction or friction) to months for a team of people (3D CFD taking into account heat transfer, viscous effects, realistic EoS).

The rule of thumb for Cv that D_Hall used in GGDT (0-D, adiabatic, massless ideal gas, valve restricts flow, projectile has const. friction) is an engineering approximation. Take a look at introductory fluid dynamics texts directed toward engineers in one of your school libraries.
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Unread postAuthor: limbeh » Thu Aug 02, 2012 9:28 pm

@DYI I'm a freshman. This is a freshman project, we're just doing extra by giving them a comparison of our experimental result versus GGDT and Launcher Range Calculator combined.

Actually I'm looking for the source of the rough rule of thumb formula on the Spudwiki site for calculating Cv:

"A rough rule of thumb for calculating the Flow Coefficient (Cv) for various valve types;

Cv = K * D2

Where D is the seat diameter in centimetres, and K is

= 1 for a sprinkler or ball valve
= 2 for a piston of QEV
= 3 for a burst disc."

I couldn't find it anywhere else.

On another note, a video link of the spudguns: http://www.youtube.com/watch?v=Q5UmqJPJ1eY
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Welcome to Singapore.

The laws are stricter concerning spudguns than anywhere in the West.

Even the Aussies for all they complain have it good compared to us.
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Unread postAuthor: jimmy101 » Sun Aug 05, 2012 11:19 am

If you can't find a suitable reference then send Dave an email. "Personal Communication" from a person that makes his living designing and building the largest and most powerful "spudguns" in the world (for the US Gov't) is a perfectly acceptable citation. You would basically cite it just like that and put the cite directly in the text (instead of as a footnote or endnote). If it is OK with Dave you would also include his affiliation (who he works for) and job title.
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Unread postAuthor: limbeh » Sun Aug 05, 2012 9:02 pm

Thanks jimmy101. I'll put that in.

DYI they actually asked for a pretty basic analysis using freshman concepts - pressure*area, work-energy theorem, etc.

We're aiming to get the highest mark in the whole batch because nobody else is giving as detailed a report as we are.
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Welcome to Singapore.

The laws are stricter concerning spudguns than anywhere in the West.

Even the Aussies for all they complain have it good compared to us.
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