Water Presure on a curved surface - CR4 Discussion Thread

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Smitty Power-User Join Date: Dec 2007 Location: Gulf Coast, USA Posts: 123	Water Presure on a curved surface 08/02/2008 2:37 PM
	Bare with me on this description as I can not seem to post the drawing I took from CAD and put in Microsoft WORD. Given a sheet of aluminum 30" high x 18"wide. Take the sheet and curve it (inside radius) so it it is now 30" H x 16" wide Place it in a fast moving stream of water at different angles, height always upward so water runs into the curve. The sheet wants to move backwards due to the force. How would you determine what force *in lbs,* the sheet moves backwards at , if you know the force of the current and the angle the sheet meets the water (angle of attack)? __________________ Smitty
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JohnDG Guru Join Date: May 2006 Location: Reading, Berkshire, UK. Going under cover. Posts: 9684 Good Answers: 468	#1 Re: Water Presure on a curved surface 08/02/2008 4:25 PM
	Note: This isn't an answer to your question! To get an image from CAD (or anything else, for that matter) into a CR4 post: Get the image on screen. Use [Shift-Print Screen] to copy the screen to the clipboard. Open MSPAINT. Use Edit -> Paste to paste the clipboard contents into a new image. Use the Select tool to delineate the region you want to display. Use Edit -> Copy to save the selected portion of the image. Use File -> New to create a new image area. Use Edit -> Paste to insert your image. Use File -> Save As... , and save the image as a file - I'm not sure which formats work with CR4, but JPEG definitely does. In your CR4 post, insert the image using the little green camera icon . Done. As an example, I've followed the procedure detailed, and this is the result: Best regards, John. [Edit: There are loads of other ways of doing it - I usually use Paint Shop Pro and its image grab & editing facilities - but AFAIK mspaint is shipped with OS's (up to) XP (don't know about the V-word OS), so most folk on MS systems should be able to use it. J.] __________________ "Love justice, you who rule the world" - Dante Alighieri
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Smitty Power-User Join Date: Dec 2007 Location: Gulf Coast, USA Posts: 123	#3 In reply to #1 Re: Water Presure on a curved surface 08/02/2008 7:18 PM
	Thank you. It worked straight on. Cheers Smitty __________________ Smitty
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EnviroMan Guru Join Date: Nov 2007 Location: Gone to Alabama with my banjo on my knee... Posts: 5595 Good Answers: 20	#8 In reply to #3 Re: Water Presure on a curved surface 08/05/2008 3:35 PM
	Ummm...it did? So where's the picture? __________________ Veni, vidi, video - I came, I saw, I got it on film.
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JohnDG Guru Join Date: May 2006 Location: Reading, Berkshire, UK. Going under cover. Posts: 9684 Good Answers: 468	#9 In reply to #8 Re: Water Presure on a curved surface 08/05/2008 6:28 PM
	Muss confess, I've bin asking myself the very same question for a while. __________________ "Love justice, you who rule the world" - Dante Alighieri
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Blink Guru Join Date: Aug 2006 Posts: 4484 Good Answers: 246	#10 In reply to #9 Re: Water Presure on a curved surface 08/05/2008 7:15 PM
	Ah ha! Smitty is new to the system, I think. He made another post with the picture, which I saw, and I might have responded, but it doesn't show up in my list, so maybe I did not. I'll see if I can find the other thread. __________________ There is more to life than just eating mice.
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JohnDG Guru Join Date: May 2006 Location: Reading, Berkshire, UK. Going under cover. Posts: 9684 Good Answers: 468	#11 In reply to #10 Re: Water Presure on a curved surface 08/06/2008 2:47 AM
	Found it in this thread. __________________ "Love justice, you who rule the world" - Dante Alighieri
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jdretired Guru Join Date: May 2007 Location: Australia. Posts: 1642 Good Answers: 81	#2 Re: Water Presure on a curved surface 08/02/2008 5:32 PM
	Google hydro turbine reactive forces. Regards JD.
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Smitty Power-User Join Date: Dec 2007 Location: Gulf Coast, USA Posts: 123	#4 In reply to #2 Re: Water Presure on a curved surface 08/02/2008 7:20 PM
	Thank you . I think the formulas may be over my head though. I will try to make sense of it. Smitty __________________ Smitty
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Blink Guru Join Date: Aug 2006 Posts: 4484 Good Answers: 246	#5 Re: Water Presure on a curved surface 08/03/2008 12:22 AM
	It sounds like you have created a water foil. If the entire thing is underwater and the stream is moving past on both surfaces, then you can use the formula for lift, based on the water speed, foil area, and angle of attack (from which you can derive a good estimate of coefficient of lift). If that is what you are interested in, I could run through the formula. "Lift" would be perpendicular to flow direction. Drag would be in line with the flow direction. I'm not sure which you are interested in. __________________ There is more to life than just eating mice.
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jrpeck Power-User Join Date: Jun 2007 Posts: 183 Good Answers: 3	#6 Re: Water Presure on a curved surface 08/03/2008 9:49 AM
	If the pressure is constant, such as a plate over a hole in a swimming pool, the force the pressure multiplied by the area perpendicular to the pressure. For example, let's the pressure works out to be 10 PSI (that's only about 23' deep). Then force would be: F = 10 psi X (30" x 14") = 4200 pounds If there are nozzles it works in the simular way, but it is complicated. This will get you close, but it is not exact. The applied area needs to be figured out. Then the cosine of the angle off perpendicular times pressure will be the applied pressure. Once you have that figured out, then you can apply the formula above. I hope this helps.
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RCE Guru Join Date: Dec 2007 Location: California Posts: 2363 Good Answers: 63	#7 Re: Water Presure on a curved surface 08/05/2008 11:32 AM
	Hmm, hard to visualize exactly what you are doing, but there are two forces it seesm you need to consider, hydrostatic and hydrodynamic. The hydrostatic force is just pressure do to the standing head of water. The hydrodynamic force is the force generated by the change in momentum. The momentum changes because the wtaer flow velocity is vectored in and out of the system. If the system is closed the magnitude of the momentum is conserved, though the momentum itself changes. If you do not have a closed system then switch to bernoulli equations to evaluate the pressure, because pressure, velocity and WSE are interrelated in open surface systems.
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Users who posted comments:

Blink (2); EnviroMan (1); jdretired (1); JohnDG (3); jrpeck (1); RCE (1); Smitty (2)

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