Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1802180 times)

Offline aero

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Looking for Harminv Q calculation formula - here
https://github.com/stevengj/harminv

I found this,
Quote
You can get the "quality factor" Q (pi |freq| / decay) by:

does that make any sense to anyone?

I'd rather not guess what it means, but there is a hint that what is now labelled as the imaginary frequency was previously labelled "decay".  Here is the line of output for the latest Harminv run for SeeShell's axially oriented antenna 1/4 wavelength from the big end.

Yang-Shell            harminv0:    frequency              imag. freq.       Q                        |amp|                      
big end axial ant.   harminv0:   2.464865332   -2.07E-008           59,477,392    3.6868535094   
                           amplitude                                          error
 3.1499611941641876-1.9158896823060045i    4.470790574981857e-11+0.0i
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Online Rodal

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Offline aero

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@Rodal and SeeShell,

Rerun csv files are uploaded, here

https://drive.google.com/folderview?id=0B1XizxEfB23tflNPTnJEcWVZNkVJSUhuUkUtdzJEaWlSRWR0R2xsdmN4Y05mdlBzRHAza28&usp=sharing
Did you make any changes other than to output different locations (like changed mesh, time step, time slices, scaling factor, material Drude model, antenna location and type, etc.) ?

No, I just re-sliced the existing .h5 files which I had saved. I did not re-run meep.
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Offline Star One

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A bit of an update - can't release details from Tajmar yet, but keep watching...

http://www.wired.co.uk/news/archive/2015-07/24/emdrive-space-drive-pluto-mission

Look at this:

http://forum.nasaspaceflight.com/index.php?topic=37642.msg1408539#msg1408539

I find the extremely small force/InputPower measured by Tajmar NOT to be something that Shawyer should be so  encouraged about, for the reasons in my post.  I don't see anything in Tajmar's results pointing towards the practicality of an EM Drive mission to Pluto in 18 months anytime soon.  We will see...

It certainly would be nice to find out I'm wrong about this :)

You might want to see what he actual says. I wish people would stop reporting on stories where the actual results haven't been published yet.

Offline X_RaY

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To get more control about the transmission factor into the resonator and get impedance matching against the magnetron there may be a (relative) simple way.
For that one need a 3 stub tuner, 50 Ohm broadband load, two high voltage schottky diodes and a xy-oscilloscope.
If the coupling is realized as a waveguide(the magnetron is), it is possible to use 2 schottky in a small distance(i think the needed was 45 deg? of phaseshift inside the waveguide) to get I,Q signal. Power schottky are available for high voltages (for example 170V) but it would be important to use a verry short length of the schottky stub-antenna inside the high power waveguide otherwise the magnetron kill the diode.
The signals on the diodes will generated by signal mixing of the forward(45deg) and reflected(also 45deg) wave component. That results in 2 canals with 90 deg phase difference --> Inphase and Quadrature

Use a xy-oscilloscope, put the load at the end of the magnetron and tuner line (unused tuner, screws as out as possible). Put the RF on. Measure the Voltage of the diodes. Tune both channels to be null Volt DC with the scope offsets. Switch the RF off.
After this, place the waveguide antenna feed onto the cavity.
Switch the RF on again and use the waveguidtuner to get impedance matching (the scope have to show null Volts for both channels as you are calibrated before)
tadaaa   Z=~50 Ohm  ;D 8)

Tuner:
Take a (rectangular) waveguide for the frequency of interest.
Calculate the wavelength using the dimensions of your waveguide.
Drill 3 holes into the waveguide at the middle of the a-axis, the first is random, the next two have to be in a distance of, i think it was for example(take a look of some design rules..) 1*lambda/8, 3*lambda/8, or 5*lambda/8 or something like that. Take some screws and put they into the holes

Detector diodes:
Same game, drill a hole (random) in a waveguide (some half wavelength away from the tuner) and a second in a distance of Lambda/8 to the first (or lambda/4? can't remember exactly) than stick one wire of the diode into the hole and fix it. This technique is also be used in gunn oscillator transceivers (CW).

I have tested the   procedure for commercial µW-sensors, it will work  8)
good luck and have fun while testing
« Last Edit: 07/24/2015 10:35 PM by X_RaY »

Offline aero

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@Rodal and SeeShell,

Rerun csv files are uploaded, here

https://drive.google.com/folderview?id=0B1XizxEfB23tflNPTnJEcWVZNkVJSUhuUkUtdzJEaWlSRWR0R2xsdmN4Y05mdlBzRHAza28&usp=sharing

Time slice 10 is totally missing

So it is. Give me a minute. Ok - They should be there now.
I'll need to fix my bash shell file some more. Once I get it right, it should stay right.
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Online Rodal

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Looking for Harminv Q calculation formula - here
https://github.com/stevengj/harminv

I found this,
Quote
You can get the "quality factor" Q (pi |freq| / decay) by:

does that make any sense to anyone?

I'd rather not guess what it means, but there is a hint that what is now labelled as the imaginary frequency was previously labelled "decay".  Here is the line of output for the latest Harminv run for SeeShell's axially oriented antenna 1/4 wavelength from the big end.

Yang-Shell            harminv0:    frequency              imag. freq.       Q                        |amp|                      
big end axial ant.   harminv0:   2.464865332   -2.07E-008           59,477,392    3.6868535094   
                           amplitude                                          error
 3.1499611941641876-1.9158896823060045i    4.470790574981857e-11+0.0i

The quality factor Q can be expressed as  2 Pi times the exponential decay time (https://en.wikipedia.org/wiki/Exponential_decay) of the stored energy times the natural frequency or by

where   and is the stored energy in the cavity

Since the time dependence is exponential , - e(- beta t )/( d( e(- t/exponentialDecayTime )/dt) = exponentialDecayTime

so

Q = 2 * Pi * frequency * exponentialDecayTime
« Last Edit: 07/24/2015 11:34 PM by Rodal »

Offline Star One

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A bit of an update - can't release details from Tajmar yet, but keep watching...

http://www.wired.co.uk/news/archive/2015-07/24/emdrive-space-drive-pluto-mission

Look at this:

http://forum.nasaspaceflight.com/index.php?topic=37642.msg1408539#msg1408539

I find the extremely small force/InputPower measured by Tajmar NOT to be something that Shawyer should be so  encouraged about, for the reasons in my post.  I don't see anything in Tajmar's results pointing towards the practicality of an EM Drive mission to Pluto in 18 months anytime soon.  We will see...

It certainly would be nice to find out I'm wrong about this :)

You might want to see what he actual says. I wish people would stop reporting on stories where the actual results haven't been published yet.
Dr. Bagelbytes posted that he was going to be attending the conference, and he asked for people in this thread to contribute questions, weeks ago.  I dedicated my own time to inquire about what is going to be presented, from various trustworthy, knowlegeable sources and to carefully formulate suggested questions for Dr.Bagelbytes to ask at the session based on the testing results I heard have been obtained at The Technische Universität Dresden.  Of course nobody can predict what Prof. Tajmar is exactly going to say, that's why it is a live presentation and not a recorded presentation, I even stated that obvious fact in my previous posts, besides the fact that any testing information I received may be stale by the time of the presentation.

You on the other hand neglected to formulate any questions as per Dr. Bagelbytes request, and now you are complaining that you don't like reading about unpublished results.  It is a live presentation, not a publication.  If you don't like reading the post nobody is forcing you to read this thread.

My comments about publishing articles on unpublished results was more a function of my disappointment at Wired doing this.

Offline deltaMass

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I'm sure New Scientist will attempt to out-sensationalise Wired in due course.

Offline birchoff

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A bit of an update - can't release details from Tajmar yet, but keep watching...

http://www.wired.co.uk/news/archive/2015-07/24/emdrive-space-drive-pluto-mission

Look at this:

http://forum.nasaspaceflight.com/index.php?topic=37642.msg1408539#msg1408539

I find the extremely small force/InputPower measured by Tajmar NOT to be something that Shawyer should be so  encouraged about, for the reasons in my post.  I don't see anything in Tajmar's results pointing towards the practicality of an EM Drive mission to Pluto in 18 months anytime soon.  We will see...

It certainly would be nice to find out I'm wrong about this :)

You might want to see what he actual says. I wish people would stop reporting on stories where the actual results haven't been published yet.
Dr. Bagelbytes posted that he was going to be attending the conference, and he asked for people in this thread to contribute questions, weeks ago.  I dedicated my own time to inquire about what is going to be presented, from various trustworthy, knowlegeable sources and to carefully formulate suggested questions for Dr.Bagelbytes to ask at the session based on the testing results I heard have been obtained at The Technische Universität Dresden.  Of course nobody can predict what Prof. Tajmar is exactly going to say, that's why it is a live presentation and not a recorded presentation, I even stated that obvious fact in my previous posts, besides the fact that any testing information I received may be stale by the time of the presentation.

It is a live presentation, not a publication.  If you don't like reading the post nobody is forcing you to read this thread.

I saw the questions you proposed. What is perplexing is you seem to make reference to test results and I cannot find any information anywhere on what tajmar's results were. Are you holding out on us Dr.???<jk/>

My real question is, did I miss something and are the experimental results avialable somewhere I missed.

Online Rodal

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...

I saw the questions you proposed. What is perplexing is you seem to make reference to test results and I cannot find any information anywhere on what tajmar's results were. Are you holding out on us Dr.???<jk/>

My real question is, did I miss something and are the experimental results avialable somewhere I missed.

As I said in this post (which I now removed after Star-One's explanation) and in previous posts:

Quote
  I dedicated my own time to inquire about what is going to be presented, from various trustworthy, knowlegeable sources and to carefully formulate suggested questions for Dr.Bagelbytes to ask at the session based on the testing results I heard have been obtained at The Technische Universität Dresden.

I repeat: " based on the testing results I heard have been obtained at The Technische Universität Dresden"  from various trustworthy, knowlegeable sources.

No, the results are not yet available from the AIAA.  They will be available from the AIAA at and after the conference, and hopefully we will get a first hand report from Dr. BagelBytes :)



« Last Edit: 07/25/2015 01:30 AM by Rodal »

Offline rq3

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To get more control about the transmission factor into the resonator and get impedance matching against the magnetron there may be a (relative) simple way.
For that one need a 3 stub tuner, 50 Ohm broadband load, two high voltage schottky diodes and a xy-oscilloscope.
If the coupling is realized as a waveguide(the magnetron is), it is possible to use 2 schottky in a small distance(i think the needed was 45 deg? of phaseshift inside the waveguide) to get I,Q signal. Power schottky are available for high voltages (for example 170V) but it would be important to use a verry short length of the schottky stub-antenna inside the high power waveguide otherwise the magnetron kill the diode.
The signals on the diodes will generated by signal mixing of the forward(45deg) and reflected(also 45deg) wave component. That results in 2 canals with 90 deg phase difference --> Inphase and Quadrature

Use a xy-oscilloscope, put the load at the end of the magnetron and tuner line (unused tuner, screws as out as possible). Put the RF on. Measure the Voltage of the diodes. Tune both channels to be null Volt DC with the scope offsets. Switch the RF off.
After this, place the waveguide antenna feed onto the cavity.
Switch the RF on again and use the waveguidtuner to get impedance matching (the scope have to show null Volts for both channels as you are calibrated before)
tadaaa   Z=~50 Ohm  ;D 8)

Tuner:
Take a (rectangular) waveguide for the frequency of interest.
Calculate the wavelength using the dimensions of your waveguide.
Drill 3 holes into the waveguide at the middle of the a-axis, the first is random, the next two have to be in a distance of, i think it was for example(take a look of some design rules..) 1*lambda/8, 3*lambda/8, or 5*lambda/8 or something like that. Take some screws and put they into the holes

Detector diodes:
Same game, drill a hole (random) in a waveguide (some half wavelength away from the tuner) and a second in a distance of Lambda/8 to the first (or lambda/4? can't remember exactly) than stick one wire of the diode into the hole and fix it. This technique is also be used in gunn oscillator transceivers (CW).

I have tested the   procedure for commercial µW-sensors, it will work  8)
good luck and have fun while testing

This is a great idea, and will indeed work, BUT. It uses a "pure" 50 ohm load as the "reference". The frustum is very likely nowhere near a 50 ohm load, nor is that the load that the magnetron is expecting to see for maximum radiated power ( best match) in all likelyhood.

My own thought is that trying to design a cavity (frustum) "tuned" to a spectrally noisy source like a magnetron is a thankless task. How about designing the cavity (frustum) to a "best practices" standard. OFHC walls and ends, internally silver plated. Later you could even niobium plate it for superconducting tests. I'd consider making the frustum capable of at least 60 PSI internal pressure, or internal hard vacuum  for later filling with arc suppressors, maser gain media for higher frequency designs, or testing under vacuum.

The source would be a klystron (or other high power/high gain/relatively low phase noise amplifier  of your choice - NOT a noisy oscillator like a magnetron), coupled to the frustum via a crossguide or other well matched dual-directional coupler. This would almost take the frustum out of the equation, leaving you with a microwave source, driving the klystron, that could be a good lab quality microwave synthesizer. This gives you control over frequency, modulation (AM/FM,perhaps even phase), and power. The coupler gives you direct forward and reflected power, allowing direct match and Q measurement via power meters or spectrum analysis (or even a VNA), and the sampled signals could be used to directly phase or frequency lock the synthesizer at any point of interest (like measured thrust). Most modern lab quality synthesizers can be easily phase locked to a coupler output with a bit of signal conditioning.

I know this kind of turns the approach "on its head". Experimenters seem to be trying to make the perfect frustum for a very imperfect source. I think SeaShell has recognized this by making a frustum that can be relatively easily modified, and may negate atmospheric effects. I submit it's the microwave source that needs control, not the frustum. In other words, there's nothing "magic" about a magnetron. There may be something about the inherent modulation of an easily available magnetron (they're inherently very low Q oscillators, and amplitude modulate 100% at 50 or 60 Hertz if they are powered by a microwave oven supply).

This could be (relatively) easily tested with a fully controllable source, with the frustum itself as a "fixed" element in the experimental protocol.

Just some thoughts.
« Last Edit: 07/24/2015 11:37 PM by rq3 »

Offline rq3

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SNIP > While not a dielectric fan

You don't have Barium Titanate blades? I'm sorry, engineering humor.  ;)
« Last Edit: 07/24/2015 11:45 PM by rq3 »

Offline aero

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Looking for Harminv Q calculation formula - here
https://github.com/stevengj/harminv

I found this,
Quote
You can get the "quality factor" Q (pi |freq| / decay) by:

does that make any sense to anyone?

I'd rather not guess what it means, but there is a hint that what is now labelled as the imaginary frequency was previously labelled "decay".  Here is the line of output for the latest Harminv run for SeeShell's axially oriented antenna 1/4 wavelength from the big end.

Yang-Shell            harminv0:    frequency              imag. freq.       Q                        |amp|                      
big end axial ant.   harminv0:   2.464865332   -2.07E-008           59,477,392    3.6868535094   
                           amplitude                                          error
 3.1499611941641876-1.9158896823060045i    4.470790574981857e-11+0.0i

The quality factor Q can be expressed as  2 Pi times the exponential decay time (https://en.wikipedia.org/wiki/Exponential_decay) of the stored energy times the natural frequency or by

where   and is the stored energy in the cavity

Since the time dependence is exponential , - e(- beta t )/( d( e(- t/exponentialDecayTime )/dt) = exponentialDecayTime

so

Q = 2 * Pi * frequency * exponentialDecayTime

Well great, that obviously means something to you.  :) 
So can you use this to relate the number Harminv provides to the Q that you calculate? If so, what is the numerical value that results from the Harminv number above, and what calculation do I put into my spread sheet to produce that numerical value? Or is one of the terms determined on a case by case basis?
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Offline Silversheep2011

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Is this article of any interest to the experimenter's on the em thread?
I see a lot of talk about  material selection. brass sheets, copper, copper perforation shapes angles, total surface areas and frustum point
design. And at danger of not know 'if' its of any real value [moderators feel free to delete]

 https://www.newscientist.com/article/mg22630235.400-spacecraft-built-from-graphene-could-run-on-nothing-but-sunlight

this part  of article interest me as it seems to be related- to quote:

"But how was this movement happening? One explanation is that the material acts like a solar sail. Photons can transfer momentum to an object and propel it forwards, and in the vacuum of space this tiny effect can build up enough thrust to move a spacecraft. Just last week, the Planetary Society in Pasadena, California, launched a small solar sail to test the technology. But the forces the team saw were too large to come from photons alone.
The team also ruled out the idea that the laser vaporises some of the graphene and makes it spit out carbon atoms.
Instead, they think the graphene absorbs laser energy and builds up a charge of electrons. Eventually it can’t hold any more, and extra electrons are released, pushing the sponge in the opposite direction. Although it’s not clear why the electrons don’t fly off randomly, the team was able to confirm a current flowing away from the graphene as it was exposed to a laser, suggesting this hypothesis is correct (arxiv.org/abs/1505.04254).
Graphene sponge could be used to make a light-powered propulsion system for spacecraft that would beat solar sails. “While the propulsion force is still smaller than conventional chemical rockets, it is already several orders larger than that from light pressure,” they write."

So is a Cone in Graphene sponge a 'possibility' in this sort of application?

Online Rodal

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Looking for Harminv Q calculation formula - here
https://github.com/stevengj/harminv

I found this,
Quote
You can get the "quality factor" Q (pi |freq| / decay) by:

does that make any sense to anyone?

I'd rather not guess what it means, but there is a hint that what is now labelled as the imaginary frequency was previously labelled "decay".  Here is the line of output for the latest Harminv run for SeeShell's axially oriented antenna 1/4 wavelength from the big end.

Yang-Shell            harminv0:    frequency              imag. freq.       Q                        |amp|                      
big end axial ant.   harminv0:   2.464865332   -2.07E-008           59,477,392    3.6868535094   
                           amplitude                                          error
 3.1499611941641876-1.9158896823060045i    4.470790574981857e-11+0.0i

The quality factor Q can be expressed as  2 Pi times the exponential decay time (https://en.wikipedia.org/wiki/Exponential_decay) of the stored energy times the natural frequency or by

where   and is the stored energy in the cavity

Since the time dependence is exponential , - e(- beta t )/( d( e(- t/exponentialDecayTime )/dt) = exponentialDecayTime

so

Q = 2 * Pi * frequency * exponentialDecayTime

Well great, that obviously means something to you.  :) 
So can you use this to relate the number Harminv provides to the Q that you calculate? If so, what is the numerical value that results from the Harminv number above, and what calculation do I put into my spread sheet to produce that numerical value? Or is one of the terms determined on a case by case basis?

What Steve Ng wrote is correct (except he forgot the factor of 2 in 2 Pi).  You can get Q from:

Q = 2 * Pi * frequency * exponentialDecayTime

You know what is Pi, and you know what is the frequency.  You need the exponential decay time to calculate Q. 
(I suspect that when doing so you will get the same Q that was output).
Since your calculated Q was 59,477,392, then the decay number you are looking for is

59,477,392/(2 Pi 2.46 *10^9 1/sec) = 3.840*10^(-3) sec

and remember that Meep time = a/c = 10^(-9)

Please look at your output for what is the decay time.  If you did not output it, then you may have to request its value to be output.

In other words: where is the decay time ?

If HarmInv is trying to get a decay time from this transient response, all such attempts are futile as the Borgs say.

There is no decay during this transient, on the contrary, the response is exponentially increasing with time.

To get a decay, you have to turn the RF feed off.
« Last Edit: 07/25/2015 01:25 AM by Rodal »

Offline dustinthewind

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If I have a cavity that is in resonance with the light inside, so that there is current flowing in the cavity, then if I get an external metal plate close to the cavity (less than a 1/4 wavelength), will there be counter currents developed in the external metal plate?

Online Rodal

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We continue the program started with posts

http://forum.nasaspaceflight.com/index.php?topic=37642.msg1403629#msg1403629
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1404000#msg1404000
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1404004#msg1404004
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1404005#msg1404005
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1404006#msg1404006
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1404754#msg1404754
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1404783#msg1404783
http://forum.nasaspaceflight.com/index.php?topic=37642.msg1406306#msg1406306

showing the stress (force/unitArea) on the small and the big Base for what is believed to be Yang's EM Drive geometry:  (Db=0.201m,Ds=0.1492m,L=0.24m), with the dipole antenna previously used by aero for the RFMWGUY and the Yang/Shell geometry, but this time located near the big end in the longitudinal instead of the transverse direction: dipole 0.058 m long in the axis of axi-symmetry x of the truncated cone.
 

The stress tensor σxx (*) component is obtained using Wolfram Mathematica ( http://www.wolfram.com/mathematica/ ) , post-processed from the transient Finite Difference (using Meep) solution for RF feed ON.

The stress component σxx  has a negative magnitude, at the Big Base: it is compressive.  Since it has a negative magnitude it points in the direction from the small base to the big base.  From the interior to the surface.  In other words, the electromagnetic field exerts a pressure.

The stress is distributed in the shape of a spike at the big base (very narrowly distributed over its central portion).   The stress is practically zero at the small base.  This distribution is quite different from the distribution in the case of rfmwguy/NSF -1701 and Yang/Shell cases with the antenna located in the transverse direction.

In order to compare the stresses to the previous case of Yang/Shell with the antenna in the transverse direction, I have shown all plots to the same numerical scale.  This means that the huge spike produced by the antenna had to be clipped (the magnitude of this stress spike is much higher).

The Finite Difference mesh identical to the one used for the previous Yang/Shell model that had the dipole antenna in the transverse direction.
The antenna overwhelms the natural TM113 mode that would occur otherwise:  there is no trace of the two crescent shapes this time at the big base because the antenna is so near the big base.


______________________________






(*)  (we denote by σxx= T11 the contravariant component of the tensor acting along the longitudinal direction "x" of the EM Drive, normal to the the plane yz having normal x, where direction "1" is "x")

(**) For the copper diamagnetism is assumed such that the magnetization M is assumed proportional to the applied magnetic field such that for free space it is assumed that M is zero in free space in the relationship 

(***) The Stress calculations are for an Input Power of 43 Watts (similar to the value used by NASA in some of their runs).  The Stress values are proportional to the Input Power, so for example, if the Input Power were 860 Watts, that means that the calculated values for Stress are 860 Watts/ 43 Watts = 20 times greater than shown in the plots.    In other words, for 860 Watts InputPower, the values for Stress in the plots need to be multiplied by a factor of 20.
« Last Edit: 07/25/2015 12:39 AM by Rodal »

Online Rodal

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The stress at the small base.  It clearly shows a transverse magnetic TM11 m=1, n=1 mode shape, same mode shape as previously shown for the antenna in the transverse direction.  Compare with this:  http://forum.nasaspaceflight.com/index.php?topic=37642.msg1406307#msg1406307
« Last Edit: 07/25/2015 01:19 AM by Rodal »

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EM DRIVE FORCE vs. TIME

Compare with http://forum.nasaspaceflight.com/index.php?topic=37642.msg1406309#msg1406309

The force difference between the big and small faces is almost self-cancelling.

The net force difference for the case with the antenna in the transverse direction was much larger (not self-cancelling). 

The time response is such that the big base leads and the small base follows.  The time phase difference is due to the fact that the antenna is next to the big base, that leads the response.

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Quote from: aero


Yang-Shell - 229x196x196

This is the final summary output from the log file.

run 0 finished at t = 13.054 (6527 timesteps)

Total number of slices 14, the last 14 of 32 full cycles, or periods at 0.1 period intervals. That is, at 30.7, 30.8 and so forth to 32.0 periods of the drive center frequency.
Number of time steps, 6527 and total meep time = 13.054 time units.
« Last Edit: 07/25/2015 02:59 AM by Rodal »

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