dynamic modeling of a strip valve

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WebPilot
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Re: dynamic modeling of a strip valve

Post by WebPilot » Fri Sep 26, 2008 11:16 am

Image

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Particulars:
  • dfr is 0.1
  • valve is closed at the end of the -tive pressure regime (see arrow)
  • the valve appears to oscillate 5 times to the pressure cycle's 1 time (this would most definitely shorten its lifetime due to cyclic fatigue)
  • I find this valve's behavior interesting but UNSATISFACTORY.
Image

Viv
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Re: dynamic modeling of a strip valve

Post by Viv » Fri Sep 26, 2008 12:41 pm

Hi Forrest

Do you think its possible to isolate the criteria for valve oscillation so a set of design rules could be formulated?

Viv
"Sometimes the lies you tell are less frightening than the loneliness you might feel if you stopped telling them" Brock Clarke

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Re: dynamic modeling of a strip valve

Post by WebPilot » Sat Sep 27, 2008 5:04 pm

Hi Viv,

There is no harm in trying now, is there?

continuing with my discussion ...

Image

Click here here to see image in its entirety.

Particulars:
  • dfr = 0.37
  • valve closes before end of the -tive portion of the cycle
  • theta curve appears symmetric and centered in the -tive portion of the cycle (see arrow)
  • theta curve is quite similar now to that of the pressure curve, p12, which is the pressure 'drop' across the gas flow orifice
  • I prefer this valve behavior over all of the others that I've displayed, so far.
Image

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Re: dynamic modeling of a strip valve

Post by WebPilot » Mon Sep 29, 2008 12:07 am

In summary, I have answered the following questions I posed on page one.
  • 1. What is the pressure, as a function of time, measured across the orifice? See last graph for curve of p12.
  • 3. How does the strip response vary with time. See graph, look at theta curve, and observe its units are on the right side y-axis.
  • 4. What is the relationship between the frequency of the driving force and the resonant frequency of the valve? I showed it as an iterative procedure watching the valve displacement change over one cycle as I vary the dfr.
The only question I haven't answered is 2. What is the resulting flow, Q1(t)?

Well, that is relatively simple now that I know p12(t). A simple numerical integration is all that is required.
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Re: dynamic modeling of a strip valve

Post by WebPilot » Tue Oct 14, 2008 5:07 pm

The following is a snippet from Petal valve movement distance?
WebPilot wrote:
dynajetjerry wrote: As I've mentioned before, the Dyna-Jet cycles at 230-250 cps, the 7 foot long Dyna-Fog Generator engine (the original, not today's hand-carried versions,) cycles at 115 cps, and a proof-of-concept DFG engine of 20-50 feet length ran at about 25-35 cps. They all used a stock Dyna-Jet valve head assembly and reed valve! The reed's
resonance was about 235 cps when clamped in the center and each petal was free to flex up and down. Go figure.
Hmmm. That's interesting to read Jerry.

for the 7 foot long Dyna-Fog Generator

dfr = 115/235 = 0.5

for a proof-of-concept DFG engine of 20-50 feet length

dfr = 25-35 cps / 235 cps = 0.106-0.149

Now look at the pictures for w/wn=0.1 and w/wn=0.5 in my thread, dynamic modeling of a strip valve

My theoretical model predicts valves at those driving frequency ratios, would work since they DO close properly and their openings are 0.08 and 0.14 radians, respectively.

Not bad for a relatively simple mathematical model of a petal valve, eh?
My assumptions appear to be applicable to Dyna Fog Generators, or they are acting as pulse combustors ...
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Re: dynamic modeling of a strip valve

Post by WebPilot » Tue Oct 14, 2008 11:57 pm

Image

see full image here

Ok. I am going to calculate an approximation to the resonant frequency of a dynajet petal valve using my 'strip valve'. The reader may find the final result, surprising, as I did.

I needed some dimensions concerning the dynaJet's petal valve geometry. They aren't on the drawing so I redrew the parts that I needed.
  • The 'flat' of the retainer dictates the 'free' length of the petal.
  • The red outline shows 1/2 of the petal valve.
  • The rectangle, of course, is the 'strip'. I'll show you how to deal with the 'left over', later.
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Re: dynamic modeling of a strip valve

Post by WebPilot » Wed Oct 15, 2008 3:55 pm

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Re: dynamic modeling of a strip valve

Post by WebPilot » Wed Oct 15, 2008 8:30 pm

Just a little bit more background before we can start 'plugging and chugging' ...

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Re: dynamic modeling of a strip valve

Post by WebPilot » Thu Oct 16, 2008 1:18 am

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Re: dynamic modeling of a strip valve

Post by GRIM » Thu Oct 16, 2008 2:43 pm

Hey Forrest, a truly fascinating thread , math is not my strong point , but i am following you up to now , thanks for posting , whats the story behind the binary reaper ?, he is cool anyway

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Re: dynamic modeling of a strip valve

Post by WebPilot » Thu Oct 16, 2008 7:09 pm

GRIM wrote:Hey Forrest, a truly fascinating thread , math is not my strong point , but i am following you up to now , thanks for posting , whats the story behind the binary reaper ?, he is cool anyway
Hi GRIM,

I am glad to read you're enjoying the thread and are able to follow along. I promise, more curiosities to follow. This model incorporates and makes clear many things I have read that were not so clear, when I read them.

With a 'handle' like GRIM, no wonder you like the 'binary reaper'. I am not the originator. I saw it for the first time on the Internet somewhere, many years ago. I do not know the artist's name. I was so intrigued by its conception ... and had no clue then how to draw it. I do now. This is my rendition from memory of the original. I used PSP and 'masks' and 'noise'.

I wear 'hoodies', stare at computer terminals a lot, and live in a world of 'static' at times. The animation ... is me.
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Re: dynamic modeling of a strip valve

Post by WebPilot » Thu Oct 16, 2008 11:17 pm

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Re: dynamic modeling of a strip valve

Post by WebPilot » Fri Oct 17, 2008 4:13 am

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Re: dynamic modeling of a strip valve

Post by WebPilot » Fri Oct 17, 2008 5:25 pm

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Re: dynamic modeling of a strip valve

Post by WebPilot » Sat Oct 18, 2008 4:34 am

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