dynamic modeling of a strip valve

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Mike Everman
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Re: dynamic modeling of a strip valve

Post by Mike Everman » Sun Dec 14, 2008 8:41 pm

Kinda looks like a soliton...
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Re: dynamic modeling of a strip valve

Post by WebPilot » Mon Dec 15, 2008 2:26 am

This pulse does not travel. If you measure p12 as a function of time and plot it, you get this pulse.

If you were somehow able to read a meter, real-time, you would observe:
  1. a zero signal,
  2. then a decreasing -tive signal,
  3. the signal reaches a minimum,
  4. the signal becomes less -tive, or +tive,,
  5. the signal becomes zero again for a longish period of time,
  6. the cycle repeats.
moving on ...

Image
I was able to strip the audio (with his permission) from GRIM's EVG 043.wmv film clip.

This is a spectrogram of the EVG 043 operating from video time 34 to 41 seconds. If you watch the film clip, from 33 sec to 39 sec he is panning aft (@34 sec dead aft).

The intensities, curiously, fade in and out as the engine warms and camera pans. The resolution of the spectral frequencies are fairly clear.

NOTE: There is 655 ±5 msec of beginning dead space in stripped audio file, 043.wav, so @ 37300 msec Event Time (stripped audio time), is 36.645 sec actual video time.
Image

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Re: dynamic modeling of a strip valve

Post by WebPilot » Mon Dec 15, 2008 5:05 am

8:13 PM 12/14/08

043.wav (from EVG 043.wmv)

video time
33 to 39 aft (34 dead aft)

NOTE: 655 ±5 msec of beginning dead space in stripped audio of 043.wav

Image

This is the FFT analysis of the above record @ 37300 msec Event Time (stripped audio time), or 36.645 sec actual video time. The camera is panning at the aft end of the pulse jet.

Code: Select all

Freq Band, Hz		dB

190.50 ±  2.69	-20.5	  f1
380.44 ±  5.38	-22.3	2×f1
579.60 ±  9.42	-27.8	3×f1
759.74 ± 12.11	-19.3	4×f1
937.75 ± 14.80	-30.8	5×f1
All are even or odd integral multiples of the fundamental frequency, f1; which in this case is 190.50 ± 2.69 Hz.
Image

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Re: dynamic modeling of a strip valve

Post by WebPilot » Mon Dec 15, 2008 12:55 pm

Image
This is a spectrogram of 043.wav for the interval 21-25 secs while the camera is focused at the head (23-24 secs it is dead on) of the pulse jet.

The same progression of spectral frequencies (190.50 , 380.44, 579.60, 759.74, 937.75 Hz) are there, as my model predicts from the spectral analysis of p12, the pressure drop across the orifice.

However, while the camera is focused at the intake, notice some odd things taking place in the present state of tune of the EVG-043.
  1. The intensities of the fundamental and other odd harmonics are noticeably less when compared to those of the even harmonics.
  2. Also notice that the signal strength of fourth harmonic, 4×f1, is much greater (center red) than the second harmonic, 2×f1.
Image

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Re: dynamic modeling of a strip valve

Post by WebPilot » Tue Dec 16, 2008 3:03 am

If you have been following along, the following is self-explanatory.

Image

The question is ... "why the peculiar attenuation in the EVG-043?"
Image

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Re: dynamic modeling of a strip valve

Post by WebPilot » Tue Dec 16, 2008 5:59 pm

The odd (literally) attenuation of the EVG-043 spectral frequencies in its forward wave signature really perplexed me ever since I discovered it.

Over the last several days, I've been busy with holiday stuff and trips to the stores. I also did an oil change on my mom's car, soldered some more wires on my car where a chipmunk decided to munch, and installed a new door handle assembly on the bathroom door. I'm not a carpenter, but I had to chisel out a recess on the door for the new striker plate and one on the jam for the old one. Works good!

This did give me a break and time for my mind to 'mull over' the present scenario. I thought "the only plausible explanation for attenuation is a wave form vibrating out of phase with the fundamental et alii. But from where?"

Image

Then it hit me last night ... it's the vibratory motion of the pulse jet relative to the support cradle and its motion relative to the base. Simple.
Image

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Re: dynamic modeling of a strip valve

Post by GRIM » Tue Dec 16, 2008 9:41 pm

Hi Forrest ,
You are almost certainly right about the vibration from the cradle , that carriage is mounted on ball bearing drawer runners ,

These runners are very smooth and work in a similar fashion to a linear rail , but Fail miserably as a thrust rig with Vibration , the balls seem to jam,

Good detective work,

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Re: dynamic modeling of a strip valve

Post by hinote » Wed Dec 17, 2008 3:19 am

HI Forrest:

We haven't talked in quite a while.

Thanks again for your interest in my project of some years ago (a duplicate of the now-famous Kentfield motor, with 4 intakes); your analysis and subsequent positive recommendation provided me with incentive to build a successful version of my own, and to develop and build a number of successors afterward.

The current question I have is, are you willing and able to distill the current development of your successful analysis of a "strip-valve" type intake, so we (the great unwashed) can take advantage of your discovery? There must be an eventual empirical solution that would satisfy the far more complex math you're currently working with. You could attach a limitation which would allow you to participate in any commercial application of your concept--or I'm sure there's other arrangements which would satisfy you as the source of this development. I've become a convert to the concept of "open-source" info such as this--and you would probably enjoy the fruits of real-life developments as they are likely to occur, to validate your concepts and possibly further them.

I'm enjoying the electrical theories you're applying as an analog to your solutions; in the fall of 1964 I was at UC Berkeley as a scholarship student and encountered the same concept in my Physics 1A class. Shades of my youth there!!

All the best of success in your current and future efforts.
Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

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Re: dynamic modeling of a strip valve

Post by WebPilot » Wed Dec 17, 2008 6:10 am

Bill,

Thanks for the kind words.

If I remember correctly, I never did hear from you again after I performed that analysis.

Now you ask for my Valve Glide™ technology?

No, I won't do as you ask; what you did before won't happen a second time.

~°~~°~~°~

G.,

When I first got your video, I played it over and over again in the back ground on my desktop. You have to look hard, but between 2-3 sec event time, you'll see an almost imperceptible (vector) movement to the right!

It's all a matter of seeing, isn't it?

~°~~°~~°~

OK, I don't mean to torture you, my readers, with more math, but this concept is important. If you have never taken a vibrations course, you are going to learn something quite fundamental now.

Image
Image

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Re: dynamic modeling of a strip valve

Post by Mike Everman » Wed Dec 17, 2008 4:06 pm

No torture, Forrest. I like where this is going a lot. Test stands can be so bad and the experimenter may have no idea why he's getting whacky readings. He may just conclude that his beautiful little motor has no thrust at all!
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Re: dynamic modeling of a strip valve

Post by Viv » Wed Dec 17, 2008 4:36 pm

Mike Everman wrote:No torture, Forrest. I like where this is going a lot. Test stands can be so bad and the experimenter may have no idea why he's getting whacky readings. He may just conclude that his beautiful little motor has no thrust at all!
Hi Mike

Yes agreed to that and its counterpoint for results, the application of Forrest's rigor is perfectly applicable to thrust benches of all types

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Re: dynamic modeling of a strip valve

Post by Mike Everman » Wed Dec 17, 2008 6:31 pm

Of course, the counterpoint being that you can think you have much more thrust than you have. I've always wanted to make a mount that had a tunable natural frequency, and to watch the thrust gage change just by changing the stiffness of the mount, and/or the mass.
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Re: dynamic modeling of a strip valve

Post by larry cottrill » Wed Dec 17, 2008 7:45 pm

Gentlemen -

Please explain (in simple terms) why it is an error to believe in the "common wisdom" that there will be no problem if the "unsprung mass" is simply made large enough.

Forrest -

Do you think that one useful product of your approach will be an average measurement of the power of a single impulse?

L Cottrill

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Re: dynamic modeling of a strip valve

Post by WebPilot » Wed Dec 17, 2008 8:25 pm

Mike, Viv and Larry et al,

All I was setting out to do was to attempt to explain why the spectral frequencies of the waveform emanating from the front of the pulsejet are attenuated. This can be done by use of the concept of equivalent stiffness and driving frequency ratio.

That is, if I get the chance to put it up here. Hopefully, as it evolves, your questions will be answered.

I'll interrupt my present train of thought and back up a bit.

Image

The above is not the only way, but it is a drawing of what I consider to be the essential requirements that must be addressed.
  1. the pj is mounted via cantilever arms secured to a flat cradle plate. No matter how stiff the upright cantilevers are made, there is going to be some vibratory movement of the pj relative to the cradle. I have drawn this using gray lines.
  2. the cradle rests on 4 rollers (only 2 are shown) to provide support in the upright direction and a smooth action in the for and aft directions (vector). The spring scale is attached at the aft end and a pin hole is drilled in the front. The pin essentially 'shunts' the spring; thus, making a semi-rigid connection between cradle and base.
  3. another roller is attached to each of the forward roller mounts so that the roller rests on the upper surface of the cradle. Similarly another pair are attached to the aft roller mounts. These provide the resisting moment due to a fluctuating gauge pressure inside the pj combustion chamber causing a force directed to the right (+tive gauge pressure) and to a lesser amount to the left (-tive gauge pressure).
Image

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Re: dynamic modeling of a strip valve

Post by Viv » Wed Dec 17, 2008 9:25 pm

Hi Forrest

We will keep silent at the back of the class and move the chatter over to the new thrust stand thread to keep this one clear for the maths development

Scuse

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