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D*mn the Physics Man ! Full Speed Ahead

  1. May 31, 2007 #1
    Hello all,

    In a classic example of putting the cart before the horse...

    I have designed a underwater Vehical in a CAD program I would like to test. I have no educational physics background of any kind. I just had the idea and did it. Now that its done I would like to begin to understand how my design will behave. And what design changes are best to make.

    I am currently down loading all the EFD videos from the sticky, and understand that I must review these before continuing.

    I also understand from a cursory viewing of some of the FD videos that a Physical Model will be needed no matter what. I am capable of that, and have a scale model in mind. I have no idea yet where I will test it.

    What I would like to know is what is the best way to get my cad model into an underwater simulator software program, if possible. And what the software is called.

    Also any other input on how I should proceed is welcome, Thx.
  2. jcsd
  3. Jun 1, 2007 #2


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    I have no idea from the computer or math side of it, but why don't you just build a model and an 'aqueous wind tunnel' to see what happens?
    I have a suspicion, though, that this is a situation where the little stuff will kill you no matter how much you concentrate upon getting the big stuff right. It'll probably come down to seals, battery life, and control circuits.
  4. Jun 1, 2007 #3


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    Any fluid dynamics package will do what you need. Programs like FLUENT will be more than capable if you happen to have access to it and someone that knows how to use it. If you don't know how to create the model and know how to apply the proper boundary conditions, it will be GIGO.

    Honestly, your best bet is to build a model and test it.
  5. Jun 1, 2007 #4
    yeah danger is right. i also worked on an underwater vehicle(or something that worked under water). but yes it all comes down to how well u prepare for leakages
  6. Jun 1, 2007 #5
    Do you know of any "homemade" examples on the net I could follow. I Googled and Youtubed but couldn't find or missed any examples. Even a sketch of a proper setup would do.

    I will keep that in mind as I plan and proceed.

    I had planned to use proven systems & examples from other underwater RO/V's for the prototype. I didn't see any real reason to get exotic or experimental at first, although I would like too.

    1. Do you mean for the "Electronics Payloads" the Motors, or something else I am overlooking ? ( I think I may have a work around for the motors, but I have to do more research & may be completely off, we'll see.)

    2. I am almost certian at this point as strange as it may seem that there will be plenty of Battery space, but they will need to be custom packs fitted for the design. Again I could be completely off.

    3. Would you elaborate please ? I am unsure if I have touched on this with my research or not.

    Thank You for your reply, I have read other posts from you on the subject recently.
  7. Jun 1, 2007 #6
    Thank You. I put a call into a local Prof., waiting to hear back from him.
    Is this the right direction ?

    Get someone who knows what the h*ll they're doing, or I'm wasting my time.

    Is there a prefered Underwater Model material, should it be made of the planned prototype materials. Or just plastic.

    Thx Fred, I have also read many of your posts on the subject. I really appreciate the feedback, I have no other assets related to what I am doing other than this Forum.
  8. Jun 1, 2007 #7
    Thx ank, I was reading some of what you posted about your work.

    Compartments, Battery "Boxes", & Motor Seals right ?
  9. Jun 2, 2007 #8
    see i failed to get the seals right for 5-6 times i guess, i dont know about your model size, but mine was a little submarine(30 cm X 30 cm X 20 cm), and i used the most pathetic things that you can ever find for it. You wont believe it how i solved the water problem, i dipped all the circuitry(not circuitry actually, just a differential drive system) n motors in heavy oil(Destroy It Yourself recipe) and everything worked fine for a run of 10-15 minutes. i know, it was all stupid, but hey i am just a starter. it took about less then
    30 $ (in US currency).
    and about the aqueous wind tunnel, mythbusters used it in season3, episode 6- sea sickness cures(dont go by the name of the episode, one myth was"It is more fuel efficient to drive your pick-up truck with its tailgate down, rather than up."), so they guys put up a small aqueous wind tunnel to prove the myth wrong. it was hell of a fun (for the first time then, i was wrong in predicting whether it was busted, confirmed).. it ll solve your problem, i bet.
    and i cut a 2 ltr cola bottle in 2 halves along the length and put batteries(n other circuitry as well, i m the king of junk, haha) in it and then sealed it.
    As far as simulating it in FLUENT, what is the scale of your model? i guess bigger challenge would be to keep the whole thing as a single unit not the flow of water around it.
    anyways best of luck
  10. Jun 2, 2007 #9


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    That's the first step I would have taken. A local college prof may be your only bet. I don't know of too many companies that will open their doors and let you use some of their computing power.

    Absolutely. It is VERY easy with computer modeling to get a pretty picture that looks very official and very detailed but is absolute garbage because the model is simply not an accurate representation.

    I would think plastic would do just fine. I guess it all depends on what your testing is going to be looking for. In some aspects you would want to replicate the surface roughness of the hull as best as possible.

    You're welcome. Good luck.
  11. Jun 3, 2007 #10
    It's only a failure once you decide too quit working on solutions.

    A quick look at 1/6th puts it at about 30.85 x 15.75 x 5.75 Inches which seems like a substantial but manigable model size too me. If I am thinking correctly. ?

    From where I come from we call that adapting, improvising & overcoming. Some tasks while small have a relatively high cost to achieve the goal, accomplishing the goal is what is important.

    Thank You, that'll due.

    :) Got the job done.

    Full Scale, which is not a big problem in a CAD Prog. You just start tinkering around in it until something strikes you as too good to get rid of, then just go back take some measurements and change it on a copy of the original.

    The current CAD model is #8 of the 2nd series, the first series was good, I actually for the longest time was disapointed that I had too scrap it, and put it down for a month or better, out of frustration or disgust ?

    When I picked it back up it seemed to roll right out and turned out better than the first. So I guess you never know how things may turn out even if you feel certian of an original scraped design.

    I am really interested in the flow around the Hull, if it is acceptable, I will begin to address the concerns the three of you and myself have.

    It would probably be considered an unorthidox design by people who actually do this kind of work and dismissed out of hand. On the other hand, if it does "fly" in the aqua tunnel it would be considered an advanced hull design.

    And thats where I will need and truely appreciate the well wishes from all of you.

    We'll see, I'm sure I'll video if I get too that point. If it works I'll be excited, and post it. Otherwise I'll probably just slink off into the shadows from whince I came until the next grandiose idea strikes me ;)

    Either way Thank You all.
    Last edited: Jun 3, 2007
  12. Jun 3, 2007 #11

    Flow around the Hull is my first obstacle. If it is acceptable, then I'll move to operational systems.


    I can't say it enough, Thanks.
  13. Jun 3, 2007 #12


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    I appreciate the vote of confidence, but please note that my posts on the subject are far from authoratative. They're based upon common sense combined with some minor engineering savvy, not expertise of any sort. That's why I always defer to Fred, Astro and others once they get involved. I've pretty much exhausted that knowledge already, so I'm afraid that I can't be of much more help. Fact is, I didn't even know that the term 'aqueous wind tunnel' existed; I thought that I made it up to describe the water version of a wind tunnel.
    As for the battery situation, I wasn't referring to storage space for them. It was how long you can get them to operate that concerned me. You need a pretty high storage density such as lead/acid or gel cells. While I realize that things like lithium polymer units would be perfectly suitable, they'd be way out of the price range that you have in mind.
    Using pre-proven specialty seals should eliminate the difficulty that I foresaw there; I just wasn't sure if you were familiar with pressure seals or not.
    The controls circuitry issue just meant that you have to be sure that the thing is going to react the way that you want it to in response to your inputs, and give you adequate feedback to know what's going on. There's also the issue of how you're going to link to the unit. I've been assuming an umbilical, but you could use ultrasonics or long-wave radio.
    Anyhow, I'll continue to throw in my 2¢ worth when it seems appropriate, but you're in better hands now.
    Last edited: Jun 3, 2007
  14. Jun 4, 2007 #13
    best of luck with your work. really looking forward to see your under water vehicle video.
    and that "adapting, improvising & overcoming", it was just a money saving trick
  15. Jun 4, 2007 #14


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    Just thought of something else, which is embarrassing because it's so obvious. If you do use an umbilical, batteries aren't a problem. Just run the power from your location.
  16. Jun 4, 2007 #15
    A blind man appreciates getting pointed in the right direction even if the man directing him has Coke-bottle-bottom glasses ;)

    Also common sense & alot less engineering savy than you have got me this far, so theres something to be said for them both. All input is good as far as I'm concerned even if it doesn't become applicable.

    If you've got something to say good or bad I want too hear it all the same.

    There goes that d*mn common sense again :)

    Yes I understood your concern for the vehical was that it did end up turning into a artificial reef or makeshift anchor :surprised I would hate that.

    But I think with the available space I have that could not be utilized for anything else other than some wiring and hull surface sensors, I could stuff them with custom battery packs. And if my thinking is correct here it should be plenty for the mission times planned for it.

    Your right, as it is with most people with ideas, $$$ is gonna be a problem if left to my own devices with no outside funding. The vehical does have a working and a recreational appeal. So thats something going for it.

    I have already made a "Promotional Concept Vehical Video" with the 3D CAD program pictures and submitted it to the primary applicable company. And in the end ideally they would fund the actual prototype. The few friends I have shown it too have offered help or financing and then theres the bankers in the end.

    I usually would expect to get a "thank you for your interest, but..." response from them. But this time it is being "passed around" the company, which is making me nervous because it may be being taken seriously and I have no technical or simulation data let alone the background to speak intelligently on the subject I've presented.

    I am not up to speed on any of it, & that is why I had asked here and intended to use proven examples & systems initially so I didn't sink myself.

    Understood & appreciated. It may be a little big headed but I also want the vehical itself to understand its circumstances. I have taken examples from the like of "Solar Powered Autonomous Underwater Vehical Development by JalbertEtal2003" & "High Performance Autonomous Underwater Navigation By Mikael Bliksted Larsen" and many more too numerous to list.

    Thank You yes. It will be a ghost rider. No umbilical operation will be possible.

    I also found this last night http://www.delftship.net/ which seems pretty cool and usefull. But my old 1 & 1/2 Hamster machine doesn't have the memory to import the current vehical IGES file into it. But it's free and looks very cool.

  17. Jun 4, 2007 #16
    Thx Ank, I'll let you guys know one way or the other good or bad.
  18. Jun 4, 2007 #17
    This ended up being the understatement of the weekend for me...

    I talked to Prof. Povitsky a couple hours ago, and it turned out better than I had hoped. While not having an "Aqua Tunnel" at the University he did just install a wind tunnel and graciously offered to test and extrapulate(?) the model data for me.

    And if that wasn't enough he offered to take it to Wright Patterson A.F.B. where he works on and off for the Air Force, where they appearently have an "aqua tunnel" and finish testing there. He is there until Mid-July at which point he'll return and said to get ahold of him then.

    Unbelievably cool. Now it's crunch time for the model. I was going to get a quote from a place like this http://www.formglas.com/pattern/ for the 1/6 model (have no idea where the money will come from for it but..) and perhaps the fullsize blank if the scaled model works.

    Thanks again.
  19. Jun 5, 2007 #18


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    I gotta say, man... if you're getting that kind of response from that sort of professionals, you have one hell of a bright future. Absolutely keep us updated with your progress. And thanks for that link to Delftship. I've bookmarked it. It's late here (12:13am) and I have to be in court at 9:30 in the morning (I'll explain later), so I don't have time to really check it out. I certainly hope that the programme is Mac-friendly, because I can see having some fun with it. It's really great when outfits like that provide free tools to help people develop their dreams.
    Just promise that you'll still speak to me when you're rich and famous.
  20. Jun 5, 2007 #19


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    That's great that you found a prof. so willing to help with so much.

    If you do get to WPAFB, there are a few places I hope you can see if you can get someone to take you around a bit (I spend a fair amount of time there myself). If you are interested, there is a hangar on the base that has almost every X plane ever flown, including the XB-70. It shares a hangar with their collection of presidential aircraft.

    If you can make it over to the propulsion directorate, there are a lot of things happening over there as well.
  21. Jun 5, 2007 #20
    LOL, I hope so. But I think it's as much that Doc. Povitsky is just that cool. And I am fortunate by location. But I really do hope thats the case. Thx.


    LOL, wild child.

    I'm unsure about the Mac part, but your right. These companies allow us to pull the napkin drawings into virtual space. Putting us one step closer.

    If you liked Delftship your gonna love..
    http://www.alibre.com/xpress/software/alibre-design-xpress.asp(also free)

    I had never done CAD before, I just watched the tut's & was humming right along within a week. My limitations with it ended up being my computing power.

    Also there is a 10 part limit to assemblies on the free version, but you can get around this by using a series of sub assemblies for your final model.

    LMAO, I don't care about the famous, but the rich I could use. Aside from my obligations, what I really want the cash for is a Jet. Even if I could only own it for a year or so (with custom paint job of course;).

    If I could get my hands on a nice used T-38/F-5/F-20 for awhile, it would be a dream come true. And yes I won't forget any of you, if theres enough $$$ for a two seater I'll swing by and pick you up :biggrin:
    Last edited: Jun 5, 2007
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