Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1804619 times)

Offline aero

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@SeeShell -
Are you planning to use an antenna or a waveguide for cavity excitation? I had a thought about using a waveguide, and questions of course.

First, I am thinking of a square cross section and short length, one end excited by a dipole antenna with a noisy (magnetron) source, and the other fixed to the cavity model at the specified center location. Questions:

What would be viable dimensions for this waveguide model?
What would be the attachment point of choice
What would be the injection angle of the wave guide relative to the cavity x, y, z coordinates?

The last question is to point out that with a wave guide, the signal could be injected parallel to the lateral axis and perpendicular to the axis of rotation, but it need not be. The signal could also be injected toward the big or small base, nearly parallel with the axis of rotation, or it could be injected nearly tangentially to the circumference of the cavity, that is nearly perpendicular to a lateral axis. Or of course it could be injected at any combination of those directions. I hope all here understand this question. Mentally, I am using a fire hose model of the injected energy, but the direction of the injected wave will make a difference in the field patterns in the cavity. won't it?
Retired, working interesting problems

Offline WarpTech

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Thanks for taking the time to explain this.  With the ends closed (as claimed by Shawyer) how can anything get out to result in acceleration of the closed truncated cone without violating conservation of momentum? (if so what gets out and how does it get out?).  If nothing gets out, it appears that acceleration of the copper cone would imply a violation of CoM.

Or are you considering that the use of choke joints (  https://en.wikipedia.org/wiki/Waveguide_flange#Choke_connection  ) (hat tip R. L. for the references) may allow emission out of the frustum thus preserving conservation of momentum?

First, does anyone know why the Formatting tools on here don't work anymore? I'm using Safari browser on a Mac. They used to work, but haven't worked for the past couple of weeks.



As I've said for a long time, dissipative systems are not conservative. The question of, "How does it generate a force many orders of magnitude greater than a photon rocket?", has been answered. There is a force acting on the stored energy that goes as 1/r^2, toward the big end. This is many orders of magnitude greater than a photon rocket, near the cut-off frequency.

The question of, "How does the momentum get out?", is a different answer. Obviously, it would have more thrust if the big end were open. Any momentum reflecting off the big end plate will negate the momentum gained in getting there. However, in a dissipative system, after each bounce the wave rotates the momentum a little more into the "x" direction, but loses energy due to dissipation of heat into the copper. That means that when it reaches the back wall, it has less momentum than it should have. The NET is not zero because something was lost along the way.

Alternatively, or in addition to, any DC circulating currents generated at the small end, will produce magnetic flux that experiences the same 1/r^2 force toward the big end. DC magnetic flux can pass through the copper. The flux will be pushed out the big end by this force. It is an inductance gradient. So a DC offset in the copper can and will escape. In doing so, it exerts a lorentz force on the cone walls that push the cone forward.

The essential component in understanding this new force is that the cone geometry (not the end plates) causes a rotation of the k-vector from;

k2 = (ky2 +  kz2) -> k2 = kx2

This rotation occurs in both oscillating and DC fields, where k is the direction of the magnetic gauge vector-field and current density, i.e., the vector parallel to the electron waves. I'm thinking it is taking Feynman's EM angular momentum, p = q*A, and rotating it into linear momentum in a way that has never been shown before.

This is why it's taking me so long to write this paper. It's complicated to understand the Math from so many different view points, but that's what I'm good at. It's like merging 5 string theories into M-Theory. :) So far, everything is moving along consistently, which is a good sign.
Todd

Offline WarpTech

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@SeeShell -
Are you planning to use an antenna or a waveguide for cavity excitation? I had a thought about using a waveguide, and questions of course.

First, I am thinking of a square cross section and short length, one end excited by a dipole antenna with a noisy (magnetron) source, and the other fixed to the cavity model at the specified center location. Questions:

What would be viable dimensions for this waveguide model?
What would be the attachment point of choice
What would be the injection angle of the wave guide relative to the cavity x, y, z coordinates?

The last question is to point out that with a wave guide, the signal could be injected parallel to the lateral axis and perpendicular to the axis of rotation, but it need not be. The signal could also be injected toward the big or small base, nearly parallel with the axis of rotation, or it could be injected nearly tangentially to the circumference of the cavity, that is nearly perpendicular to a lateral axis. Or of course it could be injected at any combination of those directions. I hope all here understand this question. Mentally, I am using a fire hose model of the injected energy, but the direction of the injected wave will make a difference in the field patterns in the cavity. won't it?

I think the waveguide should just merge right into the small end and expand from there. You want the cutoff of the waveguide to be as close to the input frequency as possible, so that the waves move very slow through he waveguide and build up stored energy before entering the frustum, tapered part of the guide.

Theoretically, there should be no major VSWR reflected back down the input waveguide because the waves will have expanded beyond the cut-off as soon as they enter the frustum section. Giving up that energy as thrust.
Todd

Online Rodal

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did a search and did not find this... hope it was not posted yet


Quote
AIAA Propulsion and Energy Forum and Exposition
27–29 July 2015
Hilton Orlando, Orlando, Florida
...
TUESDAY, JULY 28, 2015
NFF-04. Future Flight Propulsion Systems
Chair(s): Gregory Meholic (The Aerospace Corporation)
Co-Chair(s): Heidi Fearn (California State University, Fullerton)
2:30 PM - 5:30 PM; Lake Nona A
...
3:30 PM - 4:00 PM
Design and First Measurements of a Superconducting Gravity-Impulse-Generator
Istvan Lörincz; Martin Tajmar

4:00 PM - 4:30 PM
Replication and Experimental Characterization of the Wallace Dynamic Force Field Generator
Martin Tajmar

4:30 PM - 5:00 PM
New Theoretical Results for the Mach Effect Thruster
Heidi Fearn

5:00 PM - 5:30 PM
Direct Thrust Measurements of an EMDrive and Evaluation of Possible Side-Effects
Martin Tajmar


I wonder if someone from this thread could attend the conference and if there is a following Q/A, even mention some of the experiments discussed here, ask questions, etc.

I am looking forward to this presentation.  Unfortunately, I won't be attending.  I have tried to find out, from several different second-hand sources what has been the nature of Martin Tajmar's experiments.  It is my personal understanding that his EM Drive experiments have shown  very low force/InputPower readings for an EM Drive in a partial vacuum: less than a few dozen or so times the force/InputPower of a perfectly collimated photon rocket, thus much lower thrust force/InputPower than Yang (who reported 300,000  times a photon rocket) and Shawyer (25,000 to 70,000 times) have reported.  I understand that the quality factor of resonance (Q) in the experiments is extremely low, much lower than any researcher has reported up to now. 

Regarding possible questions to ask if anybody attends, one suggestion (if this is what is reported) is to ask why is his experimental  Q so low (less than 100): how could the experiments have been conducted under resonance if the Q was so low?. Another question: what was responsible for such a low Q in the experiments, and whether Tajmar thinks that the discrepancy with other researchers has to do with the different Q reported from different researchers.
« Last Edit: 07/04/2015 11:23 PM by Rodal »

Offline SeeShells

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@SeeShell -
Are you planning to use an antenna or a waveguide for cavity excitation? I had a thought about using a waveguide, and questions of course.

First, I am thinking of a square cross section and short length, one end excited by a dipole antenna with a noisy (magnetron) source, and the other fixed to the cavity model at the specified center location. Questions:

What would be viable dimensions for this waveguide model?
What would be the attachment point of choice
What would be the injection angle of the wave guide relative to the cavity x, y, z coordinates?

The last question is to point out that with a wave guide, the signal could be injected parallel to the lateral axis and perpendicular to the axis of rotation, but it need not be. The signal could also be injected toward the big or small base, nearly parallel with the axis of rotation, or it could be injected nearly tangentially to the circumference of the cavity, that is nearly perpendicular to a lateral axis. Or of course it could be injected at any combination of those directions. I hope all here understand this question. Mentally, I am using a fire hose model of the injected energy, but the direction of the injected wave will make a difference in the field patterns in the cavity. won't it?

Antenna first, of course. With the split cavity design I can change antennas from dipoles to loop to helicals and place anywhere I want for testing. First off this is a testing jig to evaluate different configurations for cavity lengths reflective materials, endplate configurations and whether a CD will act a a good endplate (sorry... :) ) .

The thing I can't do is do a waveguide insertion site and vary position, rotation, direction, phase. IF we really knew with no questions why this works the way it does and what effect we want to amplify where to put this wouldn't be a issue. So it's like the CD as an endplate, one of the last things I test.

After finding the optimal insertion point and if one is needed (remember the helical?) I was planning to do a waveguide but right now the only clue I have or can give you is Yang used a waveguide. If you do use a waveguide you might not want to place it so the wave guide physical guide inserts into the cavity, as it would cause wave pattern interference.

So RS inserted his I believe like this. http://www.emdrive.com/IAC-08-C4-4-7.pdf

Yang did this. http://cdni.wired.co.uk/1920x1280/d_f/Emdrive-Yang.jpg

But where i really think it should go is Dr. White's concept.
http://4.bp.blogspot.com/-ifFlwFvt4rM/VSQUAHcmhWI/AAAAAAAA8yo/0wZ4pI1aZcQ/s1600/onehundredkwthousandn.jpg

Maybe like him I have a few issues doing a microwave insertion into a asymmetrical point on the cone. It would seem better and I'm not sure of this to insert along the length from the small end centered in the reflective plate through a matching choke through a hole in the small plate. It would be like a RF megahorn very clean and lead to a very nice Q.

Hoped I help and I do like the feed into the end, so much cleaner.

Shell

Offline cej

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(...)
but I'm going to add something else:  I personally see no way that any physics simulation software, FEM, FDM, BEM, or anything else, will show any meaningful thrust on the device.

And in fact, it's worse that that.  If you did see thrust with meep, what is more likely:

1) It has accurately predicted emdrive thrust from traditional physics.

2) The simulation was wrong.   

I've done plenty of work with numerical methods and written enough FDM codes myself to know that you don't always get exactly what you expect.  That's the nature of approximation, especially understanding how error can propagate from grid point to grid point or element to element.

Maybe I have this wrong, but I've gotten the impression that some people feel that all this confusion can be solved with MEEP.  If MEEP showed use something that we didn't already know, ie. a net thrust greater than a photon rocket, I wouldn't consider that a plus for the EMdrive.  I would consider it a negative for MEEP.     

I do not recall anyone here claiming that a simulation (meep) can prove thrust. What it does do, however, is let us quickly test our intuition of how to correctly apply theory to predict the behavior of an EM field in the cavity. For example, it appears to be incorrect to assume a standing wave in the EM Drive.

If the simulation predicts no thrust, then we have ruled out even more "what ifs" questioning whether there might still be a corner case that allows for thrust using conventional physics. And if it does suggest thrust, it will hopefully give us something more specific to test for in an experiment.

Offline SeeShells

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@SeeShell -
Are you planning to use an antenna or a waveguide for cavity excitation? I had a thought about using a waveguide, and questions of course.

First, I am thinking of a square cross section and short length, one end excited by a dipole antenna with a noisy (magnetron) source, and the other fixed to the cavity model at the specified center location. Questions:

What would be viable dimensions for this waveguide model?
What would be the attachment point of choice
What would be the injection angle of the wave guide relative to the cavity x, y, z coordinates?

The last question is to point out that with a wave guide, the signal could be injected parallel to the lateral axis and perpendicular to the axis of rotation, but it need not be. The signal could also be injected toward the big or small base, nearly parallel with the axis of rotation, or it could be injected nearly tangentially to the circumference of the cavity, that is nearly perpendicular to a lateral axis. Or of course it could be injected at any combination of those directions. I hope all here understand this question. Mentally, I am using a fire hose model of the injected energy, but the direction of the injected wave will make a difference in the field patterns in the cavity. won't it?

(sorry was awake most of the night last night... restless hours and just got up after a long 4th o July nap.)
 
If you're going to build the wave guide yourself what are you going to use? For these powers you need not to consider building a waveguide from old beer cans. There is a much easier fix.

Use the parts from a old microwave, the electronics, Mag, brackets and housings that attaches into the microwave cavity.

But if you insist full DYI I would machine it.

Here are some links for the numbers.
http://www.microwaves101.com/encyclopedias/waveguide-mathematics
Quick calculator and it agrees with MW101 site for what you want to do. I ran them and it's good.
http://www.myteron.de/wavehan/waveguide/antenna2calc.php

When I was a little fuzzier and wrote to you I ran over all the different injection points from satisfactory tested I could find. Dr. White's wasn't but I still like his insertion method. What mode were you trying to meet TE or TM?

I've never seen a meep simulation where the large end was used for the placement of the dipole or waveguide.

Offline WarpTech

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but I'm going to add something else:  I personally see no way that any physics simulation software, FEM, FDM, BEM, or anything else, will show any meaningful thrust on the device.

And in fact, it's worse that that.  If you did see thrust with meep, what is more likely:

1) It has accurately predicted emdrive thrust from traditional physics.

2) The simulation was wrong.   

I've done plenty of work with numerical methods and written enough FDM codes myself to know that you don't always get exactly what you expect.  That's the nature of approximation, especially understanding how error can propagate from grid point to grid point or element to element.

Maybe I have this wrong, but I've gotten the impression that some people feel that all this confusion can be solved with MEEP.  If MEEP showed use something that we didn't already know, ie. a net thrust greater than a photon rocket, I wouldn't consider that a plus for the EMdrive.  I would consider it a negative for MEEP.     

I do not recall anyone here claiming that a simulation (meep) can prove thrust. What it does do, however, is let us quickly test our intuition of how to correctly apply theory to predict the behavior of an EM field in the cavity. For example, it appears to be incorrect to assume a standing wave in the EM Drive.

If the simulation predicts no thrust, then we have ruled out even more "what ifs" questioning whether there might still be a corner case that allows for thrust using conventional physics. And if it does suggest thrust, it will hopefully give us something more specific to test for in an experiment.

Meep has already output sections of E and B for the interior. It would only need to Sum(E^2 + B^2) at the copper boundary for the entire interior surface area. If that sum is 0, then No NET Thrust. If that sum is not 0? Well, then we have a start. It is best to calculate it in 3 parts. Big end, small end, and conical wall. That way, if they are not zero, we know which direction the thrust is directed.

(May also want to include the sum over the surface area of the antenna too, as forces will act on it as well, depending on constructive and destructive interference.)

Todd

Offline SeeShells

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@SeeShell -

I think the waveguide should just merge right into the small end and expand from there. You want the cutoff of the waveguide to be as close to the input frequency as possible, so that the waves move very slow through he waveguide and build up stored energy before entering the frustum, tapered part of the guide.

Theoretically, there should be no major VSWR reflected back down the input waveguide because the waves will have expanded beyond the cut-off as soon as they enter the frustum section. Giving up that energy as thrust.
Todd
Ack you make it sound so simple Todd. Well done.
Shell

Offline wallofwolfstreet

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but I'm going to add something else:  I personally see no way that any physics simulation software, FEM, FDM, BEM, or anything else, will show any meaningful thrust on the device.

And in fact, it's worse that that.  If you did see thrust with meep, what is more likely:

1) It has accurately predicted emdrive thrust from traditional physics.

2) The simulation was wrong.   

I've done plenty of work with numerical methods and written enough FDM codes myself to know that you don't always get exactly what you expect.  That's the nature of approximation, especially understanding how error can propagate from grid point to grid point or element to element.

Maybe I have this wrong, but I've gotten the impression that some people feel that all this confusion can be solved with MEEP.  If MEEP showed use something that we didn't already know, ie. a net thrust greater than a photon rocket, I wouldn't consider that a plus for the EMdrive.  I would consider it a negative for MEEP.     

I do not recall anyone here claiming that a simulation (meep) can prove thrust. What it does do, however, is let us quickly test our intuition of how to correctly apply theory to predict the behavior of an EM field in the cavity. For example, it appears to be incorrect to assume a standing wave in the EM Drive.

If the simulation predicts no thrust, then we have ruled out even more "what ifs" questioning whether there might still be a corner case that allows for thrust using conventional physics. And if it does suggest thrust, it will hopefully give us something more specific to test for in an experiment.

I wasn't trying to denigrate the importance of the MEEP work being done.  I'm sorry if it came across that way. 

In many ways, I was addressing that comment more to the people reading this thread than to fellow posters.  After all, there are maybe 30-40 NSF contributors here that post on any kind of regular basis.  However, this thread has been read 438,431 times.  For every contributor, there are 10,000 people just reading.

I know that after a few posts between Aero and Rodal on the finer details of MEEP, I stopped paying attention.  Sorry, but FEM analysis is not how I want to spend my free brain time.  I'd imagine many of the forums readers zoned out a bit too.  So I guess I felt that maybe a few people coming back to the forum, or coming to the forum for the first time, might have seen the awesome visuals that have been posted for the last dozen pages and concluded more than they ought to.

Like I said, great visuals and deeply important results for refining intuition, but it really constitutes a "first step" on the road to understanding this thing.
« Last Edit: 07/04/2015 10:38 PM by wallofwolfstreet »

Online Rodal

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...
I do not recall anyone here claiming that a simulation (meep) can prove thrust. What it does do, however, is let us quickly test our intuition of how to correctly apply theory to predict the behavior of an EM field in the cavity. For example, it appears to be incorrect to assume a standing wave in the EM Drive.

If the simulation predicts no thrust, then we have ruled out even more "what ifs" questioning whether there might still be a corner case that allows for thrust using conventional physics. And if it does suggest thrust, it will hopefully give us something more specific to test for in an experiment.
Excellent summary  !!!.  I could not have written it better.  Thanks
« Last Edit: 07/04/2015 10:44 PM by Rodal »

Online Rodal

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@Dr. Rodal - You wrote
To double check this all that is needed is to provide other circular cross-sections: I would favor one at the antenna location, another one close to it, within the same longitudinal wave-pattern, and another one in the next longitudinal wave pattern away from it towards the big base.

Would you care to look at a csv file  with x,y or x,z and tell which row (x dimension is rows, isn't it?) that contains the fields you want to see? I can then take slices of the y,z plane containing those rows. Slicing the cavity in the y,z plane, and uploading to Google drive is faster than doing same for the other two planes, so more slices will not be a big burden.

I think that the best y-z plane (with normal x) cross-sections would be at the following two locations:


A) 150 in the x direction from the left end, (the end nearest the big base)

B) 209 in the x direction from the left end, (the end nearest the big base)


These cross sections are located near the small end (the 209 location is located near the antenna).

It appears that the matrix is not square in this case (wasn't it square before when it had half the number of entries in each direction?): 

the x direction has 247 entries

while the y and the z directions have 264 entries. 

Is that in agreement with what you intended?


This will be useful not only to double check the results, and see the circumferential distribution of the Power surface-density flux (the Poynting vector) at those locations
« Last Edit: 07/05/2015 12:02 AM by Rodal »

Offline SeeShells

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You guys tickle me pink. It doesn't matter where you put the antenna if you are using Maxwell/Poynting to figure that out. That theory says that you get zero thrust. You're better off with a Hail Mary. It's logical.

You have overstated your case.  There is nothing in Maxwell's or Poynting's theory saying that one should get zero thrust out of anything.  Actually, Maxwell was the first scientist to derive the equations predicting that electromagnetic radiation can produce stresses, and the stress-energy tensor carries his name to honor that achievement.

Case in point: if there is a net Poynting vector due to energy that gets dissipated into heat asymetrically, there maybe asymmetric heat transfer (by convection and/or radiation)  resulting in asymmetric forces: "thrust".  That is fully consistent with Maxwell's and Poynting's equations as well as consistent with Newton's equations. 

A correct statement you could make is that you, personally, don't see a way that enough thrust/InputPower can result from an asymmetric microwave cavity that is in excess of a perfect photon rocket thrust/inputPower by several orders of magnitude, but that is not the statement you made. 

Quote from: Anson Mount
I'm an enemy of exposition. I feel there's no need to overstate.
 

While saying "Maxwell predicts zero thrust" is an overstatement, I have to agree with deltamass here.  I will also throw my hat into the ring by saying I don't personally see a way "that thrust/InputPower can result from an asymmetric microwave cavity that is in excess of a perfect photon rocket thrust/inputPower by several orders of magnitude", but I'm going to add something else:  I personally see no way that any physics simulation software, FEM, FDM, BEM, or anything else, will show any meaningful thrust on the device.

And in fact, it's worse that that.  If you did see thrust with meep, what is more likely:

1) It has accurately predicted emdrive thrust from traditional physics.

2) The simulation was wrong.   

I've done plenty of work with numerical methods and written enough FDM codes myself to know that you don't always get exactly what you expect.  That's the nature of approximation, especially understanding how error can propagate from grid point to grid point or element to element.

Maybe I have this wrong, but I've gotten the impression that some people feel that all this confusion can be solved with MEEP.  If MEEP showed use something that we didn't already know, ie. a net thrust greater than a photon rocket, I wouldn't consider that a plus for the EMdrive.  I would consider it a negative for MEEP.     

So... using standard physics in simulations will not give us any foundations to go on? Fact. The numerical simulations have been used for years, the're used in the designing of CERN, fiber optic communications, and in cad and in just about every aspect of numerical modeling in engineering and physics I can think of. They are not perfect but I remember getting my slide rule out and using cheaters to see the divisions better. Yes, they are not perfect but it is what we have other than our gray matter and a pencil and that sucks. ;)

Let's back up and regroup so I can feel better because I'm feeling pretty funky right now. I believe there is enough empirical data in such widely varying test beds and that this is just enough out of the noise of chance that there is something going on and it deserves further testing. Agreed? Maybe? Why are you here? Just a little hope? Ya, I knew it you really don't want us laying in the dirt to look at the stars. That's cool.

We have worlds of ideology clashing into this thing. Standard Physics, you know ohms law, speed of light, gravity. wait...um gravity doesn't belong there, damn, we still are not sure how it works, so out it goes...poof. So we have Einstein's work, CoM, CoE Maxwell's and a beautiful host of other that fit perfectly into our standard model. What, they all don't, we still have questions? Poo.

Ok I got it now I can fix this! What makes all these very nice and obeyed laws work so beautifully (well kinda)? Quantum MECHANICS QV QM QED PMS and lets just throw in a black hole so we can suck it all up so nothing matters. Sorry, it does matter, I was kidding. They all matter but they are like the kid under the stairs a little freaky with glowing eyes and they are so different than the standard model. But, but, but, they make the standard model work. Phew, now here we are trying to figure out how to go backwards from normal physics and a can of microwaves down to quantum world to make thrust, to make it go, to understand. You know it's not easy. Things will not click and work quite like they should and we need to be diligent and have hope.

Is it worth it, you bet, will they be questions, yep. And every bit of it it worth it. So bring your doubting on and your questions and your blind faith and we'll do this, we'll kick this can.

And a Happy 4th Of July to all that are celebrating it.

Shell

Offline wallofwolfstreet

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So... using standard physics in simulations will not give us any foundations to go on? Fact. The numerical simulations have been used for years, the're used in the designing of CERN, fiber optic communications, and in cad and in just about every aspect of numerical modeling in engineering and physics I can think of. They are not perfect but I remember getting my slide rule out and using cheaters to see the divisions better. Yes, they are not perfect but it is what we have other than our gray matter and a pencil and that sucks. ;)

Let's back up and regroup so I can feel better because I'm feeling pretty funky right now. I believe there is enough empirical data in such widely varying test beds and that this is just enough out of the noise of chance that there is something going on and it deserves further testing. Agreed? Maybe? Why are you here? Just a little hope? Ya, I knew it you really don't want us laying in the dirt to look at the stars. That's cool.

We have worlds of ideology clashing into this thing. Standard Physics, you know ohms law, speed of light, gravity. wait...um gravity doesn't belong there, damn, we still are not sure how it works, so out it goes...poof. So we have Einstein's work, CoM, CoE Maxwell's and a beautiful host of other that fit perfectly into our standard model. What, they all don't, we still have questions? Poo.

Ok I got it now I can fix this! What makes all these very nice and obeyed laws work so beautifully (well kinda)? Quantum MECHANICS QV QM QED PMS and lets just throw in a black hole so we can suck it all up so nothing matters. Sorry, it does matter, I was kidding. They all matter but they are like the kid under the stairs a little freaky with glowing eyes and they are so different than the standard model. But, but, but, they make the standard model work. Phew, now here we are trying to figure out how to go backwards from normal physics and a can of microwaves down to quantum world to make thrust, to make it go, to understand. You know it's not easy. Things will not click and work quite like they should and we need to be diligent and have hope.

Is it worth it, you bet, will they be questions, yep. And every bit of it it worth it. So bring your doubting on and your questions and your blind faith and we'll do this, we'll kick this can.

And a Happy 4th Of July to all that are celebrating it.

Shell

I'll be the first to admit there is something going on and it deserves further testing.  I have never advocated, and never will, that testing should be abandoned.  However, I have always been clear that I feel the likelihood that that something is propellantless thrust to be very low.  Finding the exact quirk that gives the appearance of propellantless thrust is a worthwhile scientific endeavor in it's own right though.

Quote
I believe there is enough empirical data in such widely varying test beds and that this is just enough out of the noise of chance that there is something going on and it deserves further testing.

This right here is probably where you and I, and everyone else who has a different take on the emdrive from 100% likelihood to 0% likelihood, differ.  When the emdrive first popped back into the news last august, I always heard the word replication being thrown around.  Nasa has replicated a propellantless drive!  It was replicated by the Chinese!  UK inventor has drive replicated by Nasa and Chinese Labs!  These were the kinds of headlines I saw.  However, when you actually read through the individual papers, something practically explodes out at you.  None of the experiments are actually replications of any of the others:

The chinese got higher thrust from lower Q than Shawyer - goes against Shaywer's theory

Nasa didn't get thrust from a frustum without a dielectric - goes against Chinese and Shawyer's experimental results, goes against Shawyers theory.

Shawyer has gotten different thrust directions from different set-ups (dielectric vs. none) - goes against theory, just outright strange

So far, every experiment has used a drastically different apparatus, with different variable inputs and gotten massively different results.  Thrust direction has not even remained constant.  So when you look at the experiments in that light, the empirical data becomes rather sketchy.  To date, as far as I know, no lab has truly replicated any other, and that's a problem.

Edit:  A problem that may be be solved by all the DIY yourself projects that are coming online this month.  I may have to retire this criticism in a few weeks if strong data comes out of some of the replication attempts.
« Last Edit: 07/05/2015 02:28 AM by wallofwolfstreet »

Offline frobnicat

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...
The question of, "How does the momentum get out?", is a different answer. Obviously, it would have more thrust if the big end were open. Any momentum reflecting off the big end plate will negate the momentum gained in getting there. However, in a dissipative system, after each bounce the wave rotates the momentum a little more into the "x" direction, but loses energy due to dissipation of heat into the copper. That means that when it reaches the back wall, it has less momentum than it should have. The NET is not zero because something was lost along the way.
...

Sorry, please explain to the Newtonian guy in me : how a play of throwing and bouncing and catching balls within a free floating box could give any persistent deltaV to the box ? deltaX I see, but not deltaV at the end of the story (when the game stops). At one end of the box you have a source of energy, the energy flows in some arbitrary geometry and after long or short path ends absorbed asymmetrically by some inner walls. Some walls (patches) will have received more energy, some less. A source full of energy (loaded battery, or fresh radioisotopes generator) weighs more than when depleted. A hot wall patch weighs more than a cold one. All that has happened is a (tiny) displacement of the centre of mass within the box, following the displacement of conserved energy. A corresponding tiny deltaX in the opposite direction will be observed from the outside of the box, no deltaV between start and end of "discharge". That is, unless the inner walls bleed thermal IR outside, with photon rocket efficiency as an upper bound.

Do you really say that the mechanism you propose here would allow a system fully enclosed in an ideal perfect thermal blanket to gain an ultimate deltaV, i.e. without bleeding any radiation having permanently (asymptotically after switch off) changed its velocity relative to its initial inertial rest frame, as good as the velocity acquired by a  chemical thruster burst is still there indefinitely after power off of said thruster ?

Not addressing the later hypothesis involving DC components, just this specific part quoted, as you seem to imply that it could be valid by itself and independently.

Offline WarpTech

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...
The question of, "How does the momentum get out?", is a different answer. Obviously, it would have more thrust if the big end were open. Any momentum reflecting off the big end plate will negate the momentum gained in getting there. However, in a dissipative system, after each bounce the wave rotates the momentum a little more into the "x" direction, but loses energy due to dissipation of heat into the copper. That means that when it reaches the back wall, it has less momentum than it should have. The NET is not zero because something was lost along the way.
...

Sorry, please explain to the Newtonian guy in me : how a play of throwing and bouncing and catching balls within a free floating box could give any persistent deltaV to the box ? deltaX I see, but not deltaV at the end of the story (when the game stops). At one end of the box you have a source of energy, the energy flows in some arbitrary geometry and after long or short path ends absorbed asymmetrically by some inner walls. Some walls (patches) will have received more energy, some less. A source full of energy (loaded battery, or fresh radioisotopes generator) weighs more than when depleted. A hot wall patch weighs more than a cold one. All that has happened is a (tiny) displacement of the centre of mass within the box, following the displacement of conserved energy. A corresponding tiny deltaX in the opposite direction will be observed from the outside of the box, no deltaV between start and end of "discharge". That is, unless the inner walls bleed thermal IR outside, with photon rocket efficiency as an upper bound.

Do you really say that the mechanism you propose here would allow a system fully enclosed in an ideal perfect thermal blanket to gain an ultimate deltaV, i.e. without bleeding any radiation having permanently (asymptotically after switch off) changed its velocity relative to its initial inertial rest frame, as good as the velocity acquired by a  chemical thruster burst is still there indefinitely after power off of said thruster ?

Not addressing the later hypothesis involving DC components, just this specific part quoted, as you seem to imply that it could be valid by itself and independently.

"... throwing and bouncing and catching balls within a free floating box..."  Is a linear equation of momentum. The momentum coming out of the waveguide is a non-linear equation, with a force exerted as 1/r^2. The momentum transferred by the wave is proportional to the phase velocity, not c. So there is more momentum exchange at the small end due to higher phase velocity, than there is at the big end.  A photon rocket in free space is a linear equation. Inside a tapered wave guide, it is non-linear. It can't be explained in terms of billiard balls. The question you are asking is the one I am trying to resolve mathematically. My theory is not quite there yet.

This is where I'm at... The attached image is the derivation of the Photon Rocket equation, for an open-ended circular waveguide. So anyone who says a photon rocket can only exert a maximum force of F = 2P/c, is only correct in free space but not when confined to a waveguide. The thrust-to-power ratio is much, much larger near the cut-off.
Todd



Online Rodal

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...First, does anyone know why the Formatting tools on here don't work anymore? I'm using Safari browser on a Mac. They used to work, but haven't worked for the past couple of weeks.
...

You are right, the formatting stopped working a couple of weeks ago for Google Chrome as well.  Very annoying.

I have found that the formatting still works if you use Mozilla's Firefox as a browser.

https://www.mozilla.org/en-US/firefox/new/
« Last Edit: 07/05/2015 02:26 AM by Rodal »

Offline aero

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@Dr. Rodal - You wrote
To double check this all that is needed is to provide other circular cross-sections: I would favor one at the antenna location, another one close to it, within the same longitudinal wave-pattern, and another one in the next longitudinal wave pattern away from it towards the big base.

Would you care to look at a csv file  with x,y or x,z and tell which row (x dimension is rows, isn't it?) that contains the fields you want to see? I can then take slices of the y,z plane containing those rows. Slicing the cavity in the y,z plane, and uploading to Google drive is faster than doing same for the other two planes, so more slices will not be a big burden.

I think that the best y-z plane (with normal x) cross-sections would be at the following two locations:


A) 150 in the x direction from the left end, (the end nearest the big base)

B) 209 in the x direction from the left end, (the end nearest the big base)


These cross sections are located near the small end (the 209 location is located near the antenna).

It appears that the matrix is not square in this case (wasn't it square before when it had half the number of entries in each direction?): 

the x direction has 247 entries

while the y and the z directions have 264 entries. 

Is that in agreement with what you intended?


This will be useful not only to double check the results, and see the circumferential distribution of the Power surface-density flux (the Poynting vector) at those locations

The file got bigger when I increased the resolution from 100 to 250. The file contains the complete lattice which is dimensioned as the maximum diameter and height of the frustum, plus a fixed space all around. The diameter is bigger than the height so the lattice is not square in views where both are seen. When you look at the yz view, you see two diameters, so the lattice projects as a square in that view. But xy and xz show the height and a diameter so not square.

I'll get around to making those csv files ...
Retired, working interesting problems

Online Rodal

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...
"... throwing and bouncing and catching balls within a free floating box..."  Is a linear equation of momentum. The momentum coming out of the waveguide is a non-linear equation, with a force exerted as 1/r^2. The momentum transferred by the wave is proportional to the phase velocity, not c. So there is more momentum exchange at the small end due to higher phase velocity, than there is at the big end.  A photon rocket in free space is a linear equation. Inside a tapered wave guide, it is non-linear. It can't be explained in terms of billiard balls. The question you are asking is the one I am trying to resolve mathematically. My theory is not quite there yet.

...

I would like to point out that Meep takes into account many possible solutions to Maxwell's equations, including travelling, standing and evanescent waves, and other forms that are not simple.  That is the power of a time-domain analysis: that it can analyze nonlinear problems that are not subject to exact solutions in terms of well-known functions like harmonic solutions.

I'm not sure that everybody has appreciated the fact that the Poyinting vector field shown in this message: http://forum.nasaspaceflight.com/index.php?topic=37642.msg1399795#msg1399795 shows a very non-harmonic, asymmetric nonlinear time response cycle and its implications:  see how the Poynting vector field diminishes with time from its peak in a monotone gradual manner until step TS07 where it reaches minimum and then suddenly it jumps to peak value:


1st cycle
TS03 = peak flux (pointing from small base towards big base)
TS04 = flux (pointing from small base towards big base)
TS05 = flux (pointing from small base towards big base)
TS06 =  significantly less flux (pointing from small base towards big base)
TS07 = minimum flux (pointing from small base towards big base)
2nd cycle
TS08 = peak flux (pointing from small base towards big base)
TS09 = flux (pointing from small base towards big base)
TS10 = flux (pointing from small base towards big base)
TS11 = significantly less flux (pointing from small base towards big base)
TS12 = minimum flux (pointing from small base towards big base)
3rd cycle
TS13 = peak flux (pointing from small base towards big base)

This non-harmonic, nonlinear time response is also shown in the movies of the electromagnetic fields.

It is not just a case of the Poynting vector summing up to a finite value over integer number of periods, the reason for this is that the time rate of the Poynting vector through time is not symmetric during a cycle:  it jumps from minimum to maximum value much faster than it goes from maximum to minimum.

Those familiar with nonlinear problems will get where this is going.  I'll plot this later.

« Last Edit: 07/05/2015 03:35 AM by Rodal »

Offline Ricvil

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This guys think another way

http://arxiv.org/abs/0708.3519

:)



quote author=WarpTech link=topic=37642.msg1400231#msg1400231 date=1436058596]
...
The question of, "How does the momentum get out?", is a different answer. Obviously, it would have more thrust if the big end were open. Any momentum reflecting off the big end plate will negate the momentum gained in getting there. However, in a dissipative system, after each bounce the wave rotates the momentum a little more into the "x" direction, but loses energy due to dissipation of heat into the copper. That means that when it reaches the back wall, it has less momentum than it should have. The NET is not zero because something was lost along the way.
...

Sorry, please explain to the Newtonian guy in me : how a play of throwing and bouncing and catching balls within a free floating box could give any persistent deltaV to the box ? deltaX I see, but not deltaV at the end of the story (when the game stops). At one end of the box you have a source of energy, the energy flows in some arbitrary geometry and after long or short path ends absorbed asymmetrically by some inner walls. Some walls (patches) will have received more energy, some less. A source full of energy (loaded battery, or fresh radioisotopes generator) weighs more than when depleted. A hot wall patch weighs more than a cold one. All that has happened is a (tiny) displacement of the centre of mass within the box, following the displacement of conserved energy. A corresponding tiny deltaX in the opposite direction will be observed from the outside of the box, no deltaV between start and end of "discharge". That is, unless the inner walls bleed thermal IR outside, with photon rocket efficiency as an upper bound.

Do you really say that the mechanism you propose here would allow a system fully enclosed in an ideal perfect thermal blanket to gain an ultimate deltaV, i.e. without bleeding any radiation having permanently (asymptotically after switch off) changed its velocity relative to its initial inertial rest frame, as good as the velocity acquired by a  chemical thruster burst is still there indefinitely after power off of said thruster ?

Not addressing the later hypothesis involving DC components, just this specific part quoted, as you seem to imply that it could be valid by itself and independently.

"... throwing and bouncing and catching balls within a free floating box..."  Is a linear equation of momentum. The momentum coming out of the waveguide is a non-linear equation, with a force exerted as 1/r^2. The momentum transferred by the wave is proportional to the phase velocity, not c. So there is more momentum exchange at the small end due to higher phase velocity, than there is at the big end.  A photon rocket in free space is a linear equation. Inside a tapered wave guide, it is non-linear. It can't be explained in terms of billiard balls. The question you are asking is the one I am trying to resolve mathematically. My theory is not quite there yet.

This is where I'm at... The attached image is the derivation of the Photon Rocket equation, for an open-ended circular waveguide. So anyone who says a photon rocket can only exert a maximum force of F = 2P/c, is only correct in free space but not when confined to a waveguide. The thrust-to-power ratio is much, much larger near the cut-off.
Todd



[/quote]


« Last Edit: 07/05/2015 03:38 AM by Ricvil »

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