Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1800703 times)

Online flux_capacitor

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And whatever makes you think that the Woodward Effect is "accepted physics"?

@deltaMass, I know you know a loooooot about Woodward's theory and experiments so what I write below is not directly for your but for all others.

Basically, I think @DeWeave claimed "accepted physics" about Woodward because Mach's principle explains inertia as a gravitational effect within general relativity, as per Einstein and Wheeler, on strong theoretical grounds. For the EmDrive on the other hand, we have very speculative ideas, and McCulloch's MiHsC states some quantum fields are required to explain inertia.

To summarize, inertia according to Mach's principle is "plain vanilla" GR, while MiHsC is a ZPF theory, which adds unnecessary complication.

I'm not arguing about Woodward's experimental MLTs and METs test articles, more the fundamental basis of inertia in Machian GR, theoretically explored already by Sciama, Barbour, Bondi, Hoyle… BTW I found the full paper Heidi Fearn (Woodward's coworker) is about to present at the IAAA conference, along Tajmar's paper on the EmDrive:

Fearn, Heidi (July 2015). "New Theoretical Results for the Mach Effect Thruster", AIAA: Joint Propulsion conference, Orlando Florida.

Paper attached. It represents the latest news on the Woodward front.
« Last Edit: 07/21/2015 09:05 PM by flux_capacitor »

Offline DrBagelBites

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Meepers...here's a video that describes my antenna placement in NSF-1701:



Looking great!  I have a design suggestion, though.

You could attach the magnetron to a removable strip of copper. That way you can test all locations from the center to the edge and we can hopefully see some relationship of R to thrust as well as top/bottom to thrust.

-I


Offline X_RaY

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Another thougth.

upon reflection light undergoes a 180 degree phase change on metal surfaces

Yes, and this situation is modeled by a traveling wave with reverse propagation and exactly 180 degrees of phase difference producing a destructive interference exactly at the mirror position.
With two mirrors one has to satisfy the destructive interference at two points simultaneously, and this condition defines the possibles modes on "cavity".
This is a example of superposition  principle to model boundary conditions.

There isn't destructive interference at all (otherwise there isn't a propagating wave...). ;)
Into the direction of the small diameter there will be a gain in the field strength (see horn antennas)
« Last Edit: 07/22/2015 06:14 AM by X_RaY »

Offline rq3

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...Reading Woodwards description of transient mass fluctuation, makes it sound very similar to what is being discussed here.  Is there a possibility that all of standing waves and power being pumped into the copper fulstrum is making it mimic one of Woodwards capacitors? 

Would provide a (relatively) clean way to try to tie the effect back into the realm of accepted physics.  But again, I may just be oversimplifying it.

My take on it, if it's for real, is that it behaves like an animation I saw on (the only?) youtube lecture by Woodward; a rocket with a spring and brick on back bouncing its way forward, sort of like a squid.

Unlike the Woodward effect which relies on the charged capacitor having more inertia than an uncharged one, the "Shawyer Effect" I call a "Sagnac Ratchet"; the force in the forward, and impedance in the reverse directions are the result the frustrum's asymmetrical dispersion, group velocity, and sum/difference frequency filtering characteristics.

Maybe Shawyer would have gotten a different response if he made it clear it was acting as a ratchet, so CoM wouldn't have been the issue.

Exactly. And let's not forget that the "average homebrew" magnetron is running from a half-wave rectified high voltage supply. The magnetron output goes to zero 50-60 times per second.

Offline Ricvil

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1) I have confirmed that the fact that the stress is much higher at the small base than the big base for Yang Shell has nothing to do with the RF feed being on.  It is due to the standing waves

2) I don't understand at the moment how these forces are going to be balanced in the conical lateral walls.  That's one of the reasons that I wrote my own code to examine this.  I am going to examine what is happening with the stress at the conical walls.

3) It seems to me that to balance the greater force at the small end, the stress at the conical walls has to be a suction instead of a pressure (in order to give an axial component to balance the forces) or else there has to be a huge shear force to balance the greater force at the small end

4) I understand that Coulomb forces due to the Magnetic Field producing eddy currents can result in a suction force.

5) Regardless of the nature of the suction/and/or/shear stress necessary to balance the forces at the ends. I propose that it may be very easy to disrupt these forces.  It seems to me that it may be much easier to maintain pressure than suction, and to maintain pressure than shear. 

WARNING: not a well-formed idea follows:

6) Perhaps the "ratcheting" effect of the EM Drive is all due to the momentary disruption of these boundary conditions.  In other words: set-up an electromagnetic field whereby there is greater force at the small end than the force at the big end. If the pressure at the small end is much greater, this has to be counterbalanced by a suction and/or shear on the conical lateral walls.  While it may be possible to have suction and/or/shear due to the Magnetic field and eddy -currents,  it may be easy to disrupt them, hence the ratcheting effect.  It would be like disrupting boundary conditions in a submarine propeller with cavitation or disrupting the no-slip boundary condition in a fluid-elastic viscous flow (in this last case, resulting in stick-slip at the boundary oscillating between plug flow and viscous flow).

Don't forget the force on the antenna. Calculate using closed surface with the antenna inside and with outward normal.
The antenna is a metallic dipole, right?
« Last Edit: 07/21/2015 09:32 PM by Ricvil »

Offline rq3

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1) I have confirmed that the fact that the stress is much higher at the small base than the big base for Yang Shell has nothing to do with the RF feed being on.  It is due to the standing waves


How do you get standing waves with no RF feed? Some kind of Casimir effect? ;)
« Last Edit: 07/21/2015 09:43 PM by rq3 »

Online Rodal

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1) I have confirmed that the fact that the stress is much higher at the small base than the big base for Yang Shell has nothing to do with the RF feed being on.  It is due to the standing waves


How do you get standing waves with no RF feed? Some kind of Casimir effect ;)
No.  It is similar to what happens when you strike a bell, and it continues to resonate when you are not hitting it.  It is just oscillation at a natural frequency.   The higher the Q the longer it will continue to resonate.  The only reason why it stops resonating has to do with damping:  damping is inversely proportional to Q.
« Last Edit: 07/21/2015 09:48 PM by Rodal »

Offline Ricvil

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See that. :)

Another thougth.

upon reflection light undergoes a 180 degree phase change on metal surfaces

Yes, and this situation is modeled by a traveling wave with reverse propagation and exactly 180 degrees of phase difference producing a destructive interference exactly at the mirror position.
With two mirrors one has to satisfy the destructive interference at two points simultaneously, and this condition defines the possibles modes on "cavity".
This is a example of superposition  principle to model boundary conditions.

There isn't destructive interference at all (otherwise there isn't a propagating wave...). ;)
Into the direction of the small diameter there will be a gain in the field strength (see horn antennas)
I think the difference between a resonator and a waveguide is: (pre sign of the field
,see picture-example for TE011)

please correct me if i am wrong


Offline lmbfan

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I'm back from vacation, and have just finished reading a weeks worth of posts.  Y'all talk too much :) .  I have downloaded and run the NSF-1701.ctl at home while I'm at work, for benchmarking and verification with existing output.  I'll work on adapting my hexagonal cone to the same standards, using similar naming conventions and outputs.

Some observations and notes related to meep:

Back at the beginning of my readings, someone had to switch (set! ...) with (define ...) to get meep to run.  This is bad.  It most likely indicates a bad Scheme install.  The "set" commands modify meep defined variables to control the output.  If these are overridden by local defines, the calculations are not guaranteed to match the changed variables.  Swapping set with define was, if I recall correctly, done on the google (maybe amazon?) host, so this would need to be corrected before that option would be viable, in my opinion.

As far as punching holes in the walls (hi Shell!), the biggest problem I see with this is that the mesh density would have to increase a great deal.  Meep automagically sub-divides the mesh into voxels, which means that in order to model holes of a certain size, the voxels should be at least 1/2 the radius of the hole, but that's pushing it (no numerical analysis, just my gut feeling).  For 3/16" holes (I think that's what they were), the current meep sub-divisions are right at that threshold.  For better analysis, 2 or 3 times the number of subdivisions will be needed, which drives simulation times way up.  If a comparison between solid an perforated sheets is all that is desired, then that can be done relatively easily, but it remains to be seen how long it will take to run.  I'll see if I can work up some meep geometry for that.  If there is a simpler model than the hex cone that I could use, that would help out too, maybe something square-shaped.

Meep natively has an option to start the output from a specific time.  So, it can relatively quickly run thru the simulation up to a time, then start outputting data.  I mention this because the currently hard-to-obtain goal of 1,000 times longer run time may be substantially shortened by using this method if all y'all are interested in is the last 300-400 time slices.  This also dramatically reduces the storage requirements from 1 TB to 1GB per file per run.

Meep also allows a source (antenna) to be turned off at a specific time via the "end-time" parameter on the
"src-time" classes such as "continuous-src" and "gaussian-src".  I could run this when I get home tonight if no one beats me to the punch.

Offline mwvp

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...What I want to see is some of the qualitative behavior surmised by some (Traveler I think?) where the wave dissipates into the big end, aliasing into the wall as dissipation (ultimately) into thermal energy, creating a kind of momentum sink.  If I understand correctly - we would need to model the dissipative wall effects in meep explicitly in the boundary condition, as this isn't a "multi-physics" package as was pointed out.  We'd have whatever surface currents exist in the walls creating a dissipation into heat based on material characteristics, certainly do-able.

Do I have this right? Is it important in the presumed phenomenology?

I posited filter-selected sideband thermal dissipation a couple months back:
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1380201#msg1380201

I still think its a significant, as I discussed. I'm not a pan-gloss; I'm guessing a 50-50 chance of this being for real. If I was more certain, I would no doubt spend more time, effort and money like Traveler.

Thanks so much for helping out notarget! Looking forward to resolving this mystery, and moving on. I'm not going to make a business of it.

Offline tidux

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The git repository is up!

Web Interface: http://git.emdrive.science/

Please send your SSH keys if you'd like commit access.  I'm still working on read-only anonymous access, so that's not ready yet.

Offline mwvp

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upon reflection light undergoes a 180 degree phase change on metal surfaces

Yes, and this situation is modeled by a traveling wave with reverse propagation and exactly 180 degrees of phase difference producing a destructive interference exactly at the mirror position.
With two mirrors one has to satisfy the destructive interference at two points simultaneously, and this condition defines the possibles modes on "cavity".
This is a example of superposition  principle to model boundary conditions.

Know anything about increased skin depth and attenuation with evanescent modes? I read somewhere bends in the waveguide cause increased RF penetration and loss, and evanescent modes came to mind. Googled around for it briefly but didn't find anything. That would help explain selective sideband attenuation, but the big end, rather than the small end (with the low cutoff) is what's been observed to get hot.

Offline notarget

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Well, yes but when the antenna is on the axis of rotation and either a point source or axial in length, the frustum is rotationally symmetric. Meep also allows specification of mirror symmetry which reduces run time significantly but does not address the granularity issue.
Hey - as I was thinking about this, I think a cylindrical 2D model could be *very* helpful in understanding the qualitative behavior if Todd's theories or the ratchet theory are involved here.  We could do the sims in (1/261)th the time.  With a 2D cyl, we would assume a circular plate source (a line in the 2D plane)....  I'll check it out unless you beat me to it...

Offline rq3

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1) I have confirmed that the fact that the stress is much higher at the small base than the big base for Yang Shell has nothing to do with the RF feed being on.  It is due to the standing waves


How do you get standing waves with no RF feed? Some kind of Casimir effect ;)
No.  It is similar to what happens when you strike a bell, and it continues to resonate when you are not hitting it.  It is just oscillation at a natural frequency.   The higher the Q the longer it will continue to resonate.  The only reason why it stops resonating has to do with damping:  damping is inversely proportional to Q.

OK. True. I'll buy that. A well designed quartz oscillator aiming for extremely low phase noise can take several SECONDS just to turn on, let alone stabilize. It's easily visible on a 'scope. But as I understand it, due to computation time, no-one has ever run a MEEP simulation over several ON-OFF (20-100 millisecond) cycles of a typical magnetron source running from a half-wave rectified high voltage power supply. I've mentioned this in previous posts. I'm seeing this thread getting wrapped up in software.

So why are folks relying on MEEP to model a physical process that, according to known physics, is impossible? MEEP is a model itself, and must have been designed to give reliable results according to known physics. Attempting to warp the model to fit unknown physics seems like a phenomenal waste of time, especially when no one can replicate the effect of the unknown physics on a reliable basis.

Good science goes:
1) I believe that x may be true (hypothesis)
2) Based on what I know, if I do y I should see z, proving or disproving x for this reason (theory)
3) Do 2 above, with controls (experiment)
4) Modify 1 based on results of 3 (new hypothesis)

With MEEP:
1) I believe that x may be true (hypothesis)
DO
2) Based on what I THINK I know, run a computer simulation of x, with uncontrolled variables
3) When I don't get the results I expect, modify the computer simulation
LOOP

Until someone has a reliable, physical, and functional Emdrive with a signal (at least 4 sigma, not asking for the moon here) above noise, MEEP is worthless. Sorry folks. For those building hardware, keep it up. For those doing MEEP, stand by for useful data to plug in to your model.

Offline mwvp

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3) It seems to me that to balance the greater force at the small end, the stress at the conical walls has to be a suction instead of a pressure (in order to give an axial component to balance the forces) or else there has to be a huge shear force to balance the greater force at the small end

I read (somewhere lately) that if a TM mode cylindrical cavity is compressed from the outside-top/bottom inward, the field potential energy is reduced, and the frequency is reduced. As would be expected with the plates of a capacitor.

If the cavity is bent inwards from the sides, the frequency is increased. As one would expect from compressing the B field and increasing its intensity.,

It also makes me think there is an attractive force between the can top and bottom, and internal pressure (pondermotive force) against the sidewalls, inside-out.

One would expect reciprocal behavior in a TE mode cavity? Magnetic pressure against the top and bottom, and internal electrostatic suction on the sidewalls.

Offline lmbfan

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<snip>

So why are folks relying on MEEP to model a physical process that, according to known physics, is impossible? MEEP is a model itself, and must have been designed to give reliable results according to known physics. Attempting to warp the model to fit unknown physics seems like a phenomenal waste of time, especially when no one can replicate the effect of the unknown physics on a reliable basis.

Good science goes:
1) I believe that x may be true (hypothesis)
2) Based on what I know, if I do y I should see z, proving or disproving x for this reason (theory)
3) Do 2 above, with controls (experiment)
4) Modify 1 based on results of 3 (new hypothesis)

With MEEP:
1) I believe that x may be true (hypothesis)
DO
2) Based on what I THINK I know, run a computer simulation of x, with uncontrolled variables
3) When I don't get the results I expect, modify the computer simulation
LOOP

Until someone has a reliable, physical, and functional Emdrive with a signal (at least 4 sigma, not asking for the moon here) above noise, MEEP is worthless. Sorry folks. For those building hardware, keep it up. For those doing MEEP, stand by for useful data to plug in to your model.

There are a number of more qualified people to speak to these points, but as someone who is trying to help by using meep, I feel like you are grossly mischaracterizing what is happening.  People with the knowledge, experience, technical know-how, and money required to actually build and test microwave devices are in short supply.  People who know how to use a computer and can run simulations are more plentiful.  Simulations that are designed to reveal what, using currently known physics, is actually happening inside the cavities.  The tweaking being done is not to build "unknown physics" models.  No modifications to the code are being made that would entail changing physics to match something (to match what? I don't even know what results we "expect." There is no a priori goal here.).  There is no "warp[ing] the model to fit unknown physics " using meep going on in this thread.

In addition, there are several experiments that HAVE been done, and HAVE produced results, and we have "useful data to plug in to your model" as you said.  So we are plugging, and seeing what comes out. The first, intuitive explanations (as proposed by other theorists) have proven inaccurate (no simple standing waves, asymmetric Poynting vectors, etc.).  I would argue that simulation is required if we want to understand what is going on, as the behavior of the cavity is complex and poorly understood.

I, for one, am curious to help and to see what others are doing.  I don't have the time/money/experience/etc. to build a physical device.  I would rather be helping out with meep than just sitting passively by, waiting.

Offline Prunesquallor

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...Maybe Shawyer would have gotten a different response if he made it clear it was acting as a ratchet, so CoM wouldn't have been the issue.

"asymmetrical dispersion, group velocity, and sum/difference frequency filtering characteristics"

don't really get around the Conservation of Momentum issue in a frame-indifferent Universe.

It isn't a matter of getting around CoM, it's a matter of how its conforming with it.

...Conservation of Momentum issues remain, and as often remarked by Frobnicat and deltaMass, even more disturbing issues related to conservation of energy are brought forth.

Yes, I followed that exchange a few days back, and felt like a naive sucker for trusting the rocket-scientists at Eagleworks' figures - 4N/kW, 2 week mars trips, et. I haven't had the heart, patience or time to do the math myself, but I get specifying constant force/power can result in CoE violation. Shame on them.

And I know EW is testing several devices with several different theories and they have a few theories of their own. But don't fling Eagleworks' 4N/kW rottting, dead, CoM-violating cat at Shawyer, because he does point out he believes his gadget looses power with acceleration and conforms with CoE and CoM. This adds to his credibility. Eagleworks credibility should be questioned for sighting such figures as they have without qualification.

I have NOT seen ANY proposed thruster operational characteristic that does not violate CoM as usually construed.
Retired, yet... not

Offline tleach

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What I want to see is some of the qualitative behavior surmised by some where the wave dissipates into the big end, aliasing into the wall as dissipation (ultimately) into thermal energy, creating a kind of momentum sink.

"Momentum Sink" 

I like it.  If the frustum acts as a Momentum Sink, soaking ALL of the radiation's (microwaves') momentum up and converting it into momentum of the frustum, then we avoid the conservation of momentum issues, right?
« Last Edit: 07/21/2015 11:22 PM by tleach »
T. Thor Leach

Online Rodal

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It is not just the gross mischaracterization of what is happening,  accompanied by an obvious misunderstanding of how the scientific process works , but the sheer pomposity of pretending to teach others how science should be conducted.  The question asked, has been answered repeatedly in this thread.  The people doing the testing (rfmwguy, SeeShells, etc.) have worked together with the people doing these simulations, whose object has been to understand the mode shapes, electromagnetic fields, flux and stresses excited in the microwave cavity, just like Prof. Yang conducted computer simulations (prior to her test results: the highest forces ever reported) and just like it has been done in all R&D since WWII.

The hubris of somebody that just joined this 600 pages long thread telling others to "stand by", is just outstanding.

All done anonymously, of course.
« Last Edit: 07/22/2015 01:20 AM by Rodal »

Offline frobnicat

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What I want to see is some of the qualitative behavior surmised by some where the wave dissipates into the big end, aliasing into the wall as dissipation (ultimately) into thermal energy, creating a kind of momentum sink.

"Momentum Sink" 

I like it.  If the frustum acts as a Momentum Sink, soaking ALL of the radiation's (microwaves') momentum up and converting it into momentum of the frustum, then we avoid the conservation of momentum issues, right?

An astronaut leaving right side of a space station (by pushing with feet, or repulsing with magnet, whatever) and coasting through and being "soaked" (grabbing) on the left side will move the space station to the right (by a few centimetres or millimetres), but that don't yield an acquired deltaV at end of the exercise. It is trivial to move a box "propellentless" by moving things (mass or energy) inside the box, but the centre of mass of the whole system (box + content of box) is not departing from inertial trajectory (no move overall). And this is one shot, can't be cycled for added displacement (can't be used to "crawl").

http://forum.nasaspaceflight.com/index.php?topic=37642.msg1402428#msg1402428
( for a 2kg 2m sized spacecraft on lithium ion battery such mass_energy displacement amounts for a one shot of one tenth of an angström... and it couldn't possibly exceed the size of the spacecraft even with antimatter batteries)

This is for deep space flat spacetime. In curved spacetime things can be a bit different and cycling can yield added displacement, but this is a very small magnitude effect : swimming in spacetime
(was already mentioned in thread 1)
The curvature of spacetime is very slight, so the ability to swim in spacetime is unlikely to  lead  to  new  propulsion  devices.  For  a meter-sized   object   performing   meter-sized deformations at the surface of the Earth, the displacement is of order 10^-23m

More accessible illustrated sciam article on the principle.  ( the article on the publisher's site is paywalled, not sure if this full length article copy is legit )

edited:left/right blunder
« Last Edit: 07/22/2015 12:14 AM by frobnicat »

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