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Is there any way to wrap a spiral around a spline defined revolved surface?

robert_lillyrobert_lilly Member Posts: 10
I'm trying to define a spiral cooling channel in a rocket nozzle.  This is strictly a CAD exercise - I'm trying to sketch up the thrust chamber and nozzle of the LR-101 Vernier rocket engine.  I think I understand how to do this using a spiral defined path followed by a sweep of a disc.  Unfortunately the spiral can only be defined on cylindrical and conical surfaces.  Is there any way to get a spiral to wrap around spline defined revolved surface.  This area is the throat of a supersonic nozzle, so it's converging then diverging.  

I was thinking about cutting this section in half, then trying to project a flat spiral (and there's a great discussion somewhere on the forum here on how to generate a flat spiral in the first place) onto the surface...but I don't see how to make the project fro the flat sketch onto the spline defined surface.  

Do folks have any suggestions how I might proceed?  Thanks, Bob

Best Answers

Answers

  • robert_lillyrobert_lilly Member Posts: 10
    Andrew,

    ...I'm speechless...that's brilliant!  At least, if it works.  I had not thought of creating the auger then INTERSECTING it with the desired surface.  Rueful smile.  You are crafty.  I'll try it on my own, but when you get this I suspect all I need is how to do the surface intersection.

    Bob
  • robert_lillyrobert_lilly Member Posts: 10
    Andrew,

    A bit of a head bending experience, but I did create the auger.  So cool.  Reminds me of my complex calculus class way back in the 90's (talking about Riemann surfaces and such, which is pretty close to an Auger - as I remember).  Anyway, if you get a moment to share how to do the intersection bit - because I have no idea.

    B
  • navnav Member Posts: 258 ✭✭✭✭
    @andrew_troup brilliant solution as @robert_lilly I´m also having trouble with the intersect part

    Nicolas Ariza V.
    Indaer -- Aircraft Lifecycle Solutions
  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    edited November 2015
    @robert_lilly 
    The easiest way is probably to use whichever surface overlaps the other surface to split that surface (using "Split" feature).
    If you like, you can use "Delete Part" to get rid of the excess surface (in @nav's case, it would be the outer part of the auger) to get easier visibility of the split edge at the intersection (again, in the case shown in the graphic) with the revolved surface (which you can hide), and that edge can be selected to act as your path. 
  • robert_lillyrobert_lilly Member Posts: 10
    Andrew,

    So (everybody), please forgive the messy screen grab.  I've gotten myself into a pickle on this.  The items in question are in red and blue.  I recreated the auger (had it stuck inside the defining cylinder first).  Reworked it so the spiral surface extends beyond the defining cylinder.  Lovely.  

    It won't let me split the spline defined revolution with the spiral surface (says the geometry is incorrectly generated), and in the other direction it appears to be an invalid selection.  Trying to cut back on the spiral surface using delete wipes out the auger in its entirety.

    Suggestions?  Again, what I am ultimately after is the trace that spiral leaves on the spline defined revolution (in blue).

    B


  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    edited November 2015
    @robert_lilly 
    The surface doing the splitting of the other surface needs to either overlap it at BOTH ends (or be strictly flush)
    It's not possible to see from your graphic if that's the case, also it's possible your blue surface is actually a solid (again, can't tell)
    It should preferably be a surface, (it could possibly be a single face of a solid, but I haven't got a good handle on that yet)
  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    @nav: did it work for you?
  • navnav Member Posts: 258 ✭✭✭✭
    @nav: did it work for you?
    It did but see below it was weird as you tend to select the auger as the splitting surface ,it worked the other way arround 


    Nicolas Ariza V.
    Indaer -- Aircraft Lifecycle Solutions
  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    @nav
    Thanks for that, good to know it works in practice as well as theory!
    If the auger was at least as long as the revolved surface, you should be able to use it as the splitting surface.
    If they both ended exactly flush, either surface could be used to split the other.
  • robert_lillyrobert_lilly Member Posts: 10
    Andrew,

    Unfortunately, I am still stuck.  I reworked the "surface to be divided", i.e. spline defined revolved surface .. it had been a solid, as you speculated.  The auger is larger than the spline defined revolved surface.  It doesn't work.  The diagnostic says the surface is unable to split the part.

    I don't know how to post my models cleanly like nav does, but I will share the document with you.  Perhaps you can enlighten?  (It is a bit dark in here, still).

    Thanks,

    Bob
  • navnav Member Posts: 258 ✭✭✭✭
    Do the  spiral cooling channel goes here ?



    Nicolas Ariza V.
    Indaer -- Aircraft Lifecycle Solutions
  • robert_lillyrobert_lilly Member Posts: 10
    Nav,

    Well, to be precise, a "wire" will follow the spiral on the blue surface.   A second layer will follow on top of it.  I"ve grabbed an image off the internet, just to show you what I'm hope to draw:


    So you see that the whole point of the spiral is to guide the wire (i.e. I'll be sweeping a disc to represent the wire).  The actual cooling channel was defined by the space between the loops of wire.  

    Bob
  • robert_lillyrobert_lilly Member Posts: 10
    Nav,

    So you are telling me that the helix should NOT extend beyond the spline defined revolved surface?  Err... I had thought Andrew told me that it needed to extended beyond the surface to be cut.  I'll try (I see you've already figured it out)....

    B
  • robert_lillyrobert_lilly Member Posts: 10
    Nicolas,

    Yea, pretty close.  Except that, as you can tell from the photo of the LR-101, that cooling channel has go all the way through throat and the nozzle.  Harrumph.  Well, I'll get this beasty.  I'm an obvious newbie with CAD, but even at my advanced age, I still have my dreams.... (Thanks Nic, and Andrew too!) - B
  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    edited November 2015
    Nav,

    So you are telling me that the helix should NOT extend beyond the spline defined revolved surface?  Err... I had thought Andrew told me that it needed to extended beyond the surface to be cut.  I'll try (I see you've already figured it out)....

    B
    @robert_lilly

    Well no, I didn't say (or mean) that. Apologies if I was unclear, I guess I was trying to be concise.

    Here's a dotting i's and crossing t's version of what I actually said : 

    Regardless of which surface (call it A) you are using to split the other surface (call it B ) into two surfaces :

    Surface A needs to be at least flush, or longer, than Surface B, at both ends. 

    It is an open question whether surface A should be the helix or the revolved surface.

    But in the first graphic @nav posted, which I referred to, in illustration of my point, because it was the only graphic available at the time showing a clear overlap at either end : the natural choice to use as the splitting surface A (by my rule) would be the revolved spline, and in fact his subsequent graphic :
     
    https://us.v-cdn.net/5022071/uploads/editor/c2/q28afm3i0wtd.gif

    makes it clear that it only worked when he did it that way round, in accordance with my proposed rule.
    (In other words, it only worked when he split the auger, which he called "weird", suggesting it was contrary to what his intuition suggested)

    HTH
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