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  • OT: Physics question.

    I use a machine called a wire saw for cutting concrete. You can see examples of them running on youtube for an idea. I have to use one of these with a long length of wire running submerged in sea water (~50m). My question is simple:

    I can have the 11mm wire running in open water at about 20m/sec, or running down a non-sealed 45mm ID tube in the water. The wire will draw the water along the tube obviously. Which will cause the greatest load on the wire from drag?
    Peter - novice home machinist, modern motorcycle enthusiast.

    Denford Viceroy 280 Synchro (11 x 24)
    Herbert 0V adapted to R8 by 'Sir John'.
    Monarch 10EE 1942

  • #2
    The wire in the tube will have slightly more drag. Since when is 11mm material "wire"? Sounds like bar stock to me.
    Free software for calculating bolt circles and similar: Click Here

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    • #3
      http://en.wikipedia.org/wiki/Wire_saw

      In before the ban.

      What radius does the "wire" go around as it's running?


      Roger
      Last edited by winchman; 11-29-2009, 11:40 AM.
      Any products mentioned in my posts have been endorsed by their manufacturer.

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      • #4
        The wire is only about 5mm diameter but it carries 11mm beads that are electroplated with diamond product. It can turn though quite a tight radius - say 30mm or so, but it's not optimal. Non-cutting turns are made by 80mm radius vee-pulleys.
        Peter - novice home machinist, modern motorcycle enthusiast.

        Denford Viceroy 280 Synchro (11 x 24)
        Herbert 0V adapted to R8 by 'Sir John'.
        Monarch 10EE 1942

        Comment


        • #5
          Load depends on which has the most friction, obviously, since no net movement of water is involved*. Probably that is the tube, as the transfer of energy to the water is likely to be best that way.

          Friction in all sorts of places, eddies of the water against wire, friction of water against tube, eddies as water exits tube, etc.

          Kinetic energy of the water all comes from the wire, and is dissipated in friction. if more water moves with the tube, more energy is transferred to water, and eventually lost as heat, so more drag on the wire.


          * Water going down tube is balanced by water moving up outside.

          That link has a note saying that it needs to be "wickified"... it appears to be from one commercial company, as I think one name is mentioned as a source. prime example of an unreliable (potential commercial bias) wikipedia article.
          Last edited by J Tiers; 11-29-2009, 11:54 AM.
          1601

          Keep eye on ball.
          Hashim Khan

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          • #6
            If the wire were smooth it may well have less drag in the tube because of the same type of boundary layer effect that decreases the drag of an aircraft flying in ground effect.

            However, it isn't smooth and that should bring into play the "shark skin" effect in open water which reduces the flow resistance by dragging a compliant layer of water along with the wire. A rough wire in a tube will be interacting with the boundary layer of the tube wall and create turbulence that will transfer energy from the wire to the tube so it will attempt to drag the tube with it, not just the water.
            Free software for calculating bolt circles and similar: Click Here

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            • #7
              One I found on the web not much like a wire!
              http://www.wiresawmachine.com/En/wir...ry-granite.htm

              Peter
              I have tools I don't know how to use!!

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              • #8
                Originally posted by Evan
                If the wire were smooth it may well have less drag in the tube because of the same type of boundary layer effect that decreases the drag of an aircraft flying in ground effect.

                However, it isn't smooth and that should bring into play the "shark skin" effect in open water which reduces the flow resistance by dragging a compliant layer of water along with the wire. A rough wire in a tube will be interacting with the boundary layer of the tube wall and create turbulence that will transfer energy from the wire to the tube so it will attempt to drag the tube with it, not just the water.
                The wire is indeed designed to drag water along with it for cooling and clearing purposes. Here are some pictures of wiresawing stuff.








                Peter - novice home machinist, modern motorcycle enthusiast.

                Denford Viceroy 280 Synchro (11 x 24)
                Herbert 0V adapted to R8 by 'Sir John'.
                Monarch 10EE 1942

                Comment


                • #9
                  If they were to drop that item the boys in the boat would be going for a swim...
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    Peter, nice photos. It sounds like You are going to be cutting off the piles at the bottom also or is the under water cutting for a different project?
                    What size is the saw motor?

                    Steve

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                    • #11
                      15mm beads and 45mm tube gives 15mm clearance, but it would not be evenly distributed around the wire and it would likely rub/scrape in places. That is friction and therefore drag. Then, the water flowing up/down the tube would have more frictional losses against the walls of the tube.

                      If you could pump the water at the same rate as the wire is moving it would be better, but that would take energy also. Not sure if that would be better or worse than just running the wire in open water. Only way to know for sure would be to try it.

                      If you really wanted to cut the losses, the thing to do would be to pump air or another gas into the tube. Friction against any gas would be significantly less than in any liquid. It would also be good to keep the wire from rubbing against the tube, I would think you would have to do that in any case to prevent cutting it. But I'm not real sure how to do that; perhaps small rollers every meter or so? Or use a larger tube and you could space them further apart. If it were big enough, they could be at the ends only.

                      I assume you are cutting underwater. Perhaps the thing to do would be to have some kind of motor down there and just transmit the power through the 50 meters of water. Electric, hydraulic, pneumatic? Just spit-balling here, trying to get out of the box. I’m not sure what would be best.
                      Paul A.

                      Make it fit.
                      You can't win and there is a penalty for trying!

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                      • #12
                        There won't be much difference from pulling the wire through 1 meter of water and 50. Resistance will be minimal since the wire is essentially "drafting" the wire ahead of it. The majority of free field resistance in a fluid comes from end effects and there isn't any end. Put it in a tube and now you have perpendicular end effects all around the wire.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          Originally posted by doctor demo
                          Peter, nice photos. It sounds like You are going to be cutting off the piles at the bottom also or is the under water cutting for a different project?
                          What size is the saw motor?

                          Steve
                          Saw motor is a 30cc hydraulic motor running about 200bar. Dunno what power that is.
                          This project is cutting a 1metre thick wall about 20metres below the surface. It's a tunnel portal and divers will install the wire.

                          There won't be much difference from pulling the wire through 1 meter of water and 50. Resistance will be minimal since the wire is essentially "drafting" the wire ahead of it. The majority of free field resistance in a fluid comes from end effects and there isn't any end. Put it in a tube and now you have perpendicular end effects all around the wire.
                          That's the kind of info I was looking for. The wire will run in free water, but one option was to run it through a tube. It's the matter of resistance from drag I couldn't figure out. The wire would normally run at approx 28m/sec but I'll run it slower for this application to keep the load on the crimp connectors down.
                          Peter - novice home machinist, modern motorcycle enthusiast.

                          Denford Viceroy 280 Synchro (11 x 24)
                          Herbert 0V adapted to R8 by 'Sir John'.
                          Monarch 10EE 1942

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                          • #14
                            Looks like the same stuff they use to cut granite slabs out of mountains.

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