Search found 380 matches

by btrettel
Sat Oct 24, 2015 1:15 pm
Forum: Pneumatic Cannons
Topic: Survey to help make better homemade water guns
Replies: 0
Views: 678

Survey to help make better homemade water guns

https://docs.google.com/forms/d/1cd9N9VPBIBtLxRCRNrI1BYXyQaKlYbyiW5ZkRDAVtMw/viewform All, I haven't participated in this community for a while due to other time commitments. But I know there are a number of people who build water guns here, and I'm running a survey for one of my websites about what...
by btrettel
Sat Mar 07, 2015 6:50 pm
Forum: General How-To & Discussion
Topic: Full Simulation of Gas Gun Systems
Replies: 5
Views: 1798

Re: Full Simulation of Gas Gun Systems

Nice work. What is GALE? I'm assuming it's a code you wrote, but I could be mistaken. How do the various codes compare against any measurements you've made? This sort of validation is really important if we want to understand how to make better launchers. I think if this comparison was done, you mig...
by btrettel
Wed Feb 06, 2013 2:14 pm
Forum: Pneumatic Cannons
Topic: The supersonic ping pong gun
Replies: 17
Views: 2074

The professor replied back to my email: Ben, I have to admit that I have some of the same questions. We're in the process of doing a straight connector with no convergent section. I'm very eager to see what happens. Eventually, I'll need to do a CFD analysis as well. Mark So, it seems that we're on ...
by btrettel
Wed Feb 06, 2013 8:57 am
Forum: Pneumatic Cannons
Topic: The supersonic ping pong gun
Replies: 17
Views: 2074

I emailed the professor. I'll post any response I get. My email is below. Hello Prof. French, I am a graduate student working in computational fluid dynamics who is also interested in the internal ballistics of compressed gas guns. I recently saw you and your students' supersonic ping-pong ball gun ...
by btrettel
Tue Feb 05, 2013 10:14 pm
Forum: Pneumatic Cannons
Topic: The supersonic ping pong gun
Replies: 17
Views: 2074

I didn't watch the video before. I watched most of it now, and I only saw one test. If anyone could point out specifically where they did an otherwise equivalent test (e.g., with the vacuum) without the nozzle, I'd be interested in knowing. It's also worth noting that the professor in the video says...
by btrettel
Mon Feb 04, 2013 9:53 pm
Forum: Pneumatic Cannons
Topic: The supersonic ping pong gun
Replies: 17
Views: 2074

As I said in the off-topic thread, I am skeptical the converging-diverging nozzle helped here. They didn't do a test without it best I can tell, so there's no solid way to know if it helped. These nozzles are mainly used when the inlet air is extremely hot to convert the heat into gas kinetic energy...
by btrettel
Mon Feb 04, 2013 7:04 pm
Forum: Off-Topic Hobbies
Topic: "Offtopic-posts-topic" NSFW
Replies: 6619
Views: 248394

I'm skeptical the convergent-divergent nozzle is necessarily helping here. They did no tests without it best I can tell. For all we know the gun would have performed better without it.
by btrettel
Wed Jan 23, 2013 8:23 pm
Forum: General How-To & Discussion
Topic: Spring Gun Design Tool Thread
Replies: 15
Views: 3084

Also what could be worth considering is forming a design programme that is made entirely from experimental data, have you ever considered such an idea yourself? It is certainly possible and attractive for the reasons you detail. However, it would be difficult even for simple low-speed pneumatics if...
by btrettel
Tue Jan 22, 2013 9:18 pm
Forum: General How-To & Discussion
Topic: Spring Gun Design Tool Thread
Replies: 15
Views: 3084

Your graph, have you tested + recorded (or similar) where an actual pressure reading of the system would be taken at? I wonder how close it would lie to the two lines. Also your equation it's perplexing me what law/scientist/rule/parrot you got it from, I will definitely use it in future but I like...
by btrettel
Tue Jan 22, 2013 7:55 am
Forum: General How-To & Discussion
Topic: Spring Gun Design Tool Thread
Replies: 15
Views: 3084

Split's right. Isothermal is demonstrably wrong even in simple cases. The higher the compression ratio, the worse the isothermal assumption is. Still, isothermal is okay if you are just getting started, but it should be corrected. I myself wrote an isothermal springer simulation back in late 2008, a...
by btrettel
Thu Jan 17, 2013 10:01 am
Forum: General How-To & Discussion
Topic: Spring Gun Design Tool Thread
Replies: 15
Views: 3084

Nice work. For the future, I would suggest learning Python or some other portable and free language instead of using Excel. Spreadsheets are okay for small jobs, but when it comes to developing a simulation you should know that debugging and testing a spreadsheet is hard.
by btrettel
Tue Sep 20, 2011 10:15 am
Forum: Pneumatic Cannons
Topic: Open source pneumatic gun simulation
Replies: 18
Views: 3759

I'm now in grad school. Long story, but I'm happy to be here. I decided to start working on the Lagrangian code again after I take the FE exam. As I recall, what I wrote before was unstable (probably due to typos, though it could be inherent to the approach) and as I haven't touched it since then, i...
by btrettel
Sun Aug 14, 2011 11:35 am
Forum: Pneumatic Cannons
Topic: Open source pneumatic gun simulation
Replies: 18
Views: 3759

A status update: Things are proceeding slower due to a change of plans. When I last posted, I was thinking I'd have to get another job, but due to some connections at my old job, I should be able to start grad school this fall. Taking care of a bunch of paperwork and cleaning has occupied most of th...
by btrettel
Sat Jul 30, 2011 8:57 am
Forum: Pneumatic Cannons
Topic: Open source pneumatic gun simulation
Replies: 18
Views: 3759

After a few days of thought, I've decided to reduce the number of goals for the first version. The first version will be written in Python. Why? Because I don't have to think about a lot of things I'll have to think about if I used a lower-level language. I already have too much on my plate. The fir...
by btrettel
Mon Jul 25, 2011 9:34 pm
Forum: Pneumatic Cannons
Topic: Open source pneumatic gun simulation
Replies: 18
Views: 3759

Well, if you haven't written anything in Java then I guess I'll start in Python as I know it can handle what we need, I know it reasonably well, and it's not too hard to pick up if you know other languages. (This is "you" in a general sense.) It sounds like you might have used a time step that was t...