Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1797397 times)

Offline Rodal

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May be due to:

1) Unfamiliarity with numerical solution schemes that require double precision (and sometimes higher precision) to eliminate numerical instability in conditionally stable schemes like the central difference time-domain scheme used in Meep (of course this has nothing to do with the physical problem).

and/or

2) a warning that the input to the program (material constants, dimensions, etc.) are only known to a a much smaller precision, usually 2 or 3 digits.


People unfamiliar with #1 may think this is an issue of #2. 

However, the use of 16 digits is most likely due to the convenience of copying and pasting the whole calculated number rather than having to spend time getting rid of extra digits.

Forbearance is asked of readers, for the same reason that we don't demand attention to detail in spelling, in the interest of fast communication.

 
« Last Edit: 08/06/2015 06:38 PM by Rodal »

Offline deltaMass

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About cavity energy.

When an optimal impedance match is achieved between the RF source and its load (the cavity), all the forward power gets dissipated in the cavity walls as real ohmic heat. Thus maximum heating corresponds to maximum energy within the cavity, the condition that is being sought. Notionally then it would be possible to keep the impedance match optimal over temperature changes by simply monitoring the cavity temperature (I'm assuming that the mode does not switch). The latency of thermal feedback is slower than a 1-port or 2-port VSWR measurement, it's true, but it should nevertheless work well. And it can be made contactless.

Because there's no free lunch, a perfectly matched high-Q cavity and a perfectly matched low-Q cavity will dissipate exactly the same amount of power in ohmic heating for the same input power. At least, that's the theory.

Offline Rodal

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About cavity energy.

When an optimal impedance match is achieved between the RF source and its load (the cavity), all the forward power gets dissipated in the cavity walls as real ohmic heat. Thus maximum heating corresponds to maximum energy within the cavity, the condition that is being sought. Notionally then it would be possible to keep the impedance match optimal over temperature changes by simply monitoring the cavity temperature (I'm assuming that the mode does not switch). The latency of thermal feedback is slower than a 1-port or 2-port VSWR measurement, it's true, but it should nevertheless work well. And it can be made contactless.

Because there's no free lunch, a perfectly matched high-Q cavity and a perfectly matched low-Q cavity will dissipate exactly the same amount of power in ohmic heating for the same input power. At least, that's the theory.

What you stated is true.  Please elaborate further as to why you think that

<<The latency of thermal feedback is slower than a 1-port or 2-port VSWR measurement, it's true, but it should nevertheless work well.>>

why do you think that it should work well given the much slower thermal response ?  would be nice to elaborate on your reasoning, thanks

There seems to be some assumption of reasonable behavior such that thermal latency will not be a problem...

While the assumption of reasonable behavior applies to other known systems, the EM Drive output (non-repeatable, different by orders of magnitude between researchers) seems to not abide by that assumption
« Last Edit: 08/06/2015 06:48 PM by Rodal »

Offline RotoSequence

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I understand. I am pointing out that the number you're quoting has dubious physical significance. The last 6 digits - at least - have no effect on anything real. . That's beyond debate, so I have no problem stating these facts.

You're being pedantic about significant digits in a numerical simulation for no apparent purpose but undermining its credibility, when it really doesn't matter.

Offline deltaMass

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@Rodal: Well, because the specific heat of copper isn't zero, it takes a finite time to incur a given temperature rise for a given power input. And when there's an impedance mismatch, the dissipated power will fall and so the corresponding temperature changes will be less than in the matched condition.

On the other hand, measurable mismatch changes are sensed at the ports with response times on order  roughly the cavity dimensions divided by the speed of light. This is far faster than measurable temperature changes.

However, if the EmDrive is actually generating thrust, the statement about the equivalence of high- and low-Q dissipation may not be true. That's really the reason I'm pointing this out.
« Last Edit: 08/06/2015 06:55 PM by deltaMass »

Offline Rodal

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@Rodal: Well, because the specific heat of copper isn't zero, it takes a finite time to incur a given temperature rise for a given power input. And when there's an impedance mismatch, the dissipated power will fall and so the corresponding temperature changes will be less than in the matched condition.

On the other hand, measurable mismatch changes are sensed at the ports with response times on order  roughly the cavity dimensions divided by the speed of light. This is far faster than measurable temperature changes.

However, if the EmDrive is actually generating thrust, the statement about the equivalence of high- and low-Q dissipation may not be true. That's really the reason I'm pointing this out.

There seems to be some assumption of reasonably monotonic behavior such that thermal latency will not be a problem...

While the assumption of reasonable behavior applies to other known systems, the EM Drive output (non-repeatable, different by orders of magnitude between researchers) seems to not abide by that assumption

For example, the issue of vibrations of unknown magnitude and frequency being required to "engage" the drive, etc...
« Last Edit: 08/06/2015 07:01 PM by Rodal »

Offline deltaMass

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I take that vibration stuff in the same spirit as I take the rest of Shawyer's "physics".  :(

But you wanted me to say that, I believe. Decent setup, though 8)
« Last Edit: 08/06/2015 07:06 PM by deltaMass »

Offline SeeShells

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What mesh grid size are you guys using for those meep sims? It seems like more of a stepped cylinder than a tapered cavity, or is that intended?
The lattice is 0.2747255683428571 meters long
Oh please.

To 16 significant digits.
Size is relative. ;)

I understand. I am pointing out that the number you're quoting has dubious physical significance. The last 6 digits - at least - have no effect on anything real. . That's beyond debate, so I have no problem stating these facts.

You're being pedantic about significant digits in a numerical simulation for no apparent purpose but undermining its credibility, when it really doesn't matter.
Please bear in mind, when one does iterations with float numbers, a seemingly ridiculous accuracy can actually matter. Since float operations are limited in accuracy, each iteration, will result in more inaccurate numbers. Bottom line: It will add up and might actually be significant at the end.

Offline deltaMass

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I understand. I am pointing out that the number you're quoting has dubious physical significance. The last 6 digits - at least - have no effect on anything real. . That's beyond debate, so I have no problem stating these facts.

You're being pedantic about significant digits in a numerical simulation for no apparent purpose but undermining its credibility, when it really doesn't matter.
Please bear in mind, when one does iterations with float numbers, a seemingly ridiculous accuracy can actually matter. Since float operations are limited in accuracy, each iteration, will result in more inaccurate numbers. Bottom line: It will add up and might actually be significant at the end.
Based on that sterling observation, I withdraw my objection to this seemingly ridiculous accuracy.
« Last Edit: 08/06/2015 07:10 PM by deltaMass »

Offline SeeShells

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As I'm sitting here soaking wet I'm thinking what in the heck am I doing... lmao. The line broke on my 2100 psi industrial power washer from the wand... PANDEMONIUM insued! I couldn't get close to the power washer to shut it off as it was like a Buster Keaton skit with it flailing around spraying everything in water and soap (have a container to suck up soap). Sigh. Ran into the house about 150 foot away and shut it off squishing all the way.

I guess I need another hose. Fun times at the Egor Shop of Horrors.

BBL after I dry myself off .

So how's your day going?

Shell
http://www.gifwave.com/media/816070_halloween-young-frankenstein-igor-halloweeen-countdown_200s.gif

Offline deltaMass

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I recommend a dive into the hot tub to remind yourself that water is your friend  8)

Offline ElizabethGreene

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...The key is that when a photon reflects off something twice the photon's momentum is transferred, but this only corresponds to a tiny fraction of the photon's energy. This means the photon is barely redshifted and can continue transferring nearly the same momentum each time until: the mirror accelerates enough to cause large redshift, the photon is absorbed by a mirror which converts the energy to heat rather than directed kinetic energy, or the photon misses the reflector.

Since I was curious about the conservation of energy for a single reflection at 0 velocity (when normally equations give 0 doppler shift), I worked out the expected doppler shift. This was based off conservation of momentum and energy, keeping around terms that are normally neglected in doppler shift, since the momentum transfer to objects is negligible in most applications.

The result is:

v2/v1 = sqrt(a^2 + 4*a +1)-a-1, where  a=m*c^2/(h*v1)
where v2 is the new frequency, v1 is the starting frequency, m is the mass of the mirror that the photon reflects off, h and c are the usual constants.

To get an idea of how little energy is transferred in this case, for a photon at 3 GHz, and a mirror mass of only 1e-35 kg, the ratio is 0.999997. Any actual physical mirror with reasonable mass would result in an immeasurably small doppler shift even for much higher frequencies.

Repeated reflection just means you get to convert more of the photons energy into the desired form (kinetic energy of your craft) before the rest gets lost in some way. bolding added

On a more EM drive related note, photon drive amplification from reflections against test chamber walls was one of my first guesses at possible sources of the EM drive thrust.

Nice work.

Clearly explains why EMDrive generated Force scales with Q and why a high Q EMDrive can deliver much more Force than can a photon rocket.

In an EMDrive ....... Q Rules

Q is only half of the story.  Mr. Shawyer's force equation translates to Q times input power times (small diameter force per watt minus large diameter force per watt).

Theoretically you can increase the small diameter force per watt exponentially by approaching the cut-off size of the equivalent waveguide.

I played with the numbers yesterday for F=2P/Vg -> F=2*P*Sqrt(1-(c/(2*(a+x)*f))^2) and found ...

for 2a = lambda, f =2.45e9, P=1
xF
x>=lambda/22/C 6.6e-9
10e-21.3e-8
10e-33.73e-8
10e-61.16e-6
10e-93.6e-4
Note: 10e-9 refers to the calculator version of e. i.e. 2*10e-9 = 2*10^-9

By carefully controlling the wide dimension of the reflector you can increase the resultant force by 4 orders of magnitude.

Caution:I haven't sanity or double checked these numbers.

Submicrometer (10e-6) precision is likely impossible to recognize in a physical system.  Thermal distortion = flooby dust interference.  It also seems pointless if you are using a wideband Rf source.

... so that would be a nifty way to add a couple of orders of magnitude of thrust to your flashlight+skateboard photon rocket.

Disclaiming again, I probably broke the math.

Offline Rodal

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As I'm sitting here soaking wet I'm thinking what in the heck am I doing... lmao. The line broke on my 2100 psi industrial power washer from the wand... PANDEMONIUM insued! I couldn't get close to the power washer to shut it off as it was like a Buster Keaton skit with it flailing around spraying everything in water and soap (have a container to suck up soap). Sigh. Ran into the house about 150 foot away and shut it off squishing all the way.

I guess I need another hose. Fun times at the Egor Shop of Horrors.

BBL after I dry myself off ..

So how's your day going?

Shell
http://www.gifwave.com/media/816070_halloween-young-frankenstein-igor-halloweeen-countdown_200s.gif

Please be careful, as we are all worried about your safety. It would be nice to have somebody helping  you in case something goes wrong: for example you could have slipped on the wet floor etc.  Please don't work alone.  Safety first. :)

Offline deltaMass

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I've been going over the figures here again
http://emdrive.wiki/Experimental_Results
Yang is ahead of the pack by a very decent margin on both thrust and specific thrust (N/W).

Consider:
- Yang is at a Chinese establishment with ties to the military.
- Yang does not respond to questions about her experiment.
- It does not seem unreasonable to imagine that disinformation is at work here.
- A perfect conspiratorial excuse for any such data is "military secrecy".

So I'll just state flat out that I don't give Yang's results any credence.
I also know that nobody here can prove me wrong unless they reproduce her results.

Offline aero

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As I'm sitting here soaking wet I'm thinking what in the heck am I doing... lmao. The line broke on my 2100 psi industrial power washer from the wand... PANDEMONIUM insued! I couldn't get close to the power washer to shut it off as it was like a Buster Keaton skit with it flailing around spraying everything in water and soap (have a container to suck up soap). Sigh. Ran into the house about 150 foot away and shut it off squishing all the way.

I guess I need another hose. Fun times at the Egor Shop of Horrors.

BBL after I dry myself off .

So how's your day going?

Shell
http://www.gifwave.com/media/816070_halloween-young-frankenstein-igor-halloweeen-countdown_200s.gif

Well, I'm happy for you that your experimental setup wasn't further along. I hope you didn't manage to destroy anything of significance?
Retired, working interesting problems

Offline Rodal

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...In an EMDrive ....... Q Rules[/b]

Q is only half of the story.  Mr. Shawyer's force equation translates to Q times input power times (small diameter force per watt minus large diameter force per watt).

Theoretically you can increase the small diameter force per watt exponentially by approaching the cut-off size of the equivalent waveguide.

I played with the numbers yesterday for F=2P/Vg -> F=2*P*Sqrt(1-(c/(2*(a+x)*f))^2) and found ...

for 2a = lambda, f =2.45e9, P=1
xF
x>=lambda/22/C 6.6e-9
10e-21.3e-8
10e-33.73e-8
10e-61.16e-6
10e-93.6e-4
Note: 10e-9 refers to the calculator version of e. i.e. 2*10e-9 = 2*10^-9

By carefully controlling the wide dimension of the reflector you can increase the resultant force by 4 orders of magnitude.

Caution:I haven't sanity or double checked these numbers.

Submicrometer (10e-6) precision is likely impossible to recognize in a physical system.  Thermal distortion = flooby dust interference.  It also seems pointless if you are using a wideband Rf source.

... so that would be a nifty way to add a couple of orders of magnitude of thrust to your flashlight+skateboard photon rocket.

Disclaiming again, I probably broke the math.

I doubt that even a devout follower of Shawyer like TheTraveller really believes the cut-off prescription to the point that it applies to that level of accuracy.   I think that it is just an engineering prescription due to the fact that after cut-off the mode persists in the wider section of the cavity but not as much in the extended section, so that the extended section is wasted for Q resonance purposes.  It is part of Shawyer's "cooking instructions" it should not be seen as a scientific prescription but as a cooking recipe, which is not meant to apply that precisely.
« Last Edit: 08/06/2015 07:44 PM by Rodal »

Offline SeeShells

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As I'm sitting here soaking wet I'm thinking what in the heck am I doing... lmao. The line broke on my 2100 psi industrial power washer from the wand... PANDEMONIUM insued! I couldn't get close to the power washer to shut it off as it was like a Buster Keaton skit with it flailing around spraying everything in water and soap (have a container to suck up soap). Sigh. Ran into the house about 150 foot away and shut it off squishing all the way.

I guess I need another hose. Fun times at the Egor Shop of Horrors.

BBL after I dry myself off ..

So how's your day going?

Shell
http://www.gifwave.com/media/816070_halloween-young-frankenstein-igor-halloweeen-countdown_200s.gif

Please be careful, as we are all worried about your safety. It would be nice to have somebody helping  you in case something goes wrong: for example you could have slipped on the wet floor etc.  Please don't work alone.  Safety first. :)

Ya ya ya I hear ya. I would have had help if the person helping would have gotten up off the floor from a uncontrollable fit of laughing.

Thanks for the concern and I try to be very careful all the time.

Shell

Offline SeeShells

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As I'm sitting here soaking wet I'm thinking what in the heck am I doing... lmao. The line broke on my 2100 psi industrial power washer from the wand... PANDEMONIUM insued! I couldn't get close to the power washer to shut it off as it was like a Buster Keaton skit with it flailing around spraying everything in water and soap (have a container to suck up soap). Sigh. Ran into the house about 150 foot away and shut it off squishing all the way.

I guess I need another hose. Fun times at the Egor Shop of Horrors.

BBL after I dry myself off .

So how's your day going?

Shell
http://www.gifwave.com/media/816070_halloween-young-frankenstein-igor-halloweeen-countdown_200s.gif

Well, I'm happy for you that your experimental setup wasn't further along. I hope you didn't manage to destroy anything of significance?
No, I was lucky, I'd cleared out the area before so just walls and floors... and soap.

Thanks Aero,
Shell

Offline SeeShells

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Ok, going to go clean up the mess. I'll be back later.

Shell

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