Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1799201 times)

Offline aero

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@Rodal.
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the Finite Difference mesh is coarser for the smaller big diameter of the Yang model (0.201m) than the big diameter of rfmwguy's model (0.2794 m): a less precise FD mesh with less nodes in the cross-section.  The actual physical distance between nodes was kept practically the same.  But what matters for a numerical discretization of a partial differential equation is the number of nodes to characterize the fields in the solution to the partial differential equation.  For the same natural frequency mode shape it would be best to keep the same mesh regardless of the actual physical size. ]

I don't know why you say that. It is not correct. The actual Meep pixel separation is identical at 0.004 and the time step is identical at 0.002 between the Yang-Shell model and rfmwguy's NSF-1701 model. I use the same code, setting a switch to select the Yang-Shell model dimensions and antenna location. When creating the lattice, the control file is designed to use only a large enough lattice to include the model and a fixed space around the model. Because the Yang-Shell frustum has a significantly smaller big base diameter, the lattice is significantly smaller in the y and z coordinate directions, but the step size and node separation within the cavity is identical between the two models. The drive center frequency and noise bandwidth is identical between models so there are an identical number of nodes per wavelength and an identical number of time steps per period. The mesh is NOT courser. It is identical. The difference is that the Yang-Shell frustum is smaller, so the lattice surrounding the frustum is smaller.

I see what you are saying that you expected perhaps to excite a lower mode with less of a field variation.  That you expected perhaps to excite a 01 mode instead of a 11 mode.  But one doesn't know the solution ahead of time, otherwise one would not be using a numerical solution to solve the problem.  In this case the indication (the two crescent shapes characteristic of mode 11) is that mode 11 was excited, not 01.  Even if you expected to excite m=0 (constant in the circumferential direction), TE01 still has n=1 requiring the same discretization in the diameter direction as TM11 for example, they both have n=1.
No - I have absolutely no expectation as to what will be produced and certainly no desire to color the analysis by "adjusting" to achieve some desired result. That is exactly what I do NOT want to do.
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The FD mesh you used is coarser:

NSF-1701 - 245x261x261
Yang-Shell - 229x196x196


245 is larger than 229
261 is larger than 196
261 is larger than 196

Multiplying all the numbers, the mesh is 1.89 times coarser .   The mesh for RFMWGUY had 1.89 times more nodes.  Using the same FD operator.  That's what matters.

The FD mesh is the number of nodes per side.  That's it.

<<The actual Meep pixel separation is identical at 0.004 >><< node separation within the cavity is identical between the two models.>> yes, that's what I said.  That's the physical distance between the nodes (in meters) .

What matters is the discretization of the fields.

A smaller EM Drive, operating at the same mode shape at higher frequency should require the same mesh discretization not the same physical distance between the nodes. If one carries this to the absurdum: if one insists on the separation between nodes in meters as being significant, you would be saying that something smaller than the distance between the nodes would require no nodes to be modeled.

To model something that is nanometers long still requires a fine mesh if it has strong field variation.

Partial differential equations are solved by the FD method at the FD nodes.  (Keeping the same type of FD operator, for example for a central-difference operator being used in both cases) The number of nodes is what matters.
You still have it wrong Dr. Rodal, perhaps its terminology.
courser
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adjective, Mathematics
1.
of or relating to a topology on a topological space whose open sets are included among the open sets of a second specified topology on the space.
Compare finer.

But you said that The FD mesh I used is coarser:

NSF-1701 - 245x261x261
Yang-Shell - 229x196x196

No - NSF-1701 is bigger than Yang-Shell. That is all there is to it.

You also said, "What matters is the discretization of the fields." That is true. In both cases above, the frequency was identical at 2.45 GHz, the node separation was identical at 0.004 meep lengths and the time discretization was 0.002 meep time units per step. Therefore, the fields were propagated identically within the cavities. Any numerical errors were therefore identical per time /space step.

My point is that differences in your calculated results for the two models can not be laid at the feet of differences in the meep calculations. The two models are calculated/propagated as identically can be. If you continue to assume that the runs were somehow different you color your own thought process with an erroneous assumption which may lead you in a direction different from what your results are truly showing.
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Offline aero

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...
Regarding SeeShell's question?

Was the same antenna dimensions and orientation and Io=1 amp used for Yang-Shell as for RFMWGUY NSF-1701 ? Was all you changed (regarding the antenna) the location to be near the big end?

Yes. The antenna location and the name of the run log file.
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Offline aero

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What about the momentum back-reaction on the antenna feed?

Radiation is symmetrically emitted from the antenna. All back reactions cancel at the antenna.
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Offline leomillert

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I think there is miscommunication here.
Is "mesh coarseness" and "mesh density" the same things?
It is important to define terms before discussing them. Doesn't the MEEP manual talk about this subject? I personally couldn't find it.

Offline apoc2021

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I think there is miscommunication here.
Is "mesh coarseness" and "mesh density" the same things?
It is important to define terms before discussing them. Doesn't the MEEP manual talk about this subject? I personally couldn't find it.
Yes.. isn't the 'coarser' mesh as it is because its modeled cavity is smaller, thus requiring fewer points? My understanding was that meep plants a mesh on the model plus some fixed distance around that model.

Perhaps a disagreement of definitions.

Online Rodal

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I think there is miscommunication here.
Is "mesh coarseness" and "mesh density" the same things?
It is important to define terms before discussing them. Doesn't the MEEP manual talk about this subject? I personally couldn't find it.
Yes.. isn't the 'coarser' mesh as it is because its modeled cavity is smaller, thus requiring fewer points? My understanding was that meep plants a mesh on the model plus some fixed distance around that model.

Perhaps a disagreement of definitions.
So accordingly something smaller deserves less Finite Difference nodes just on the basis of being smaller?

So accordingly the Baby EM Drive could be analyzed with Meep using a Finite Difference mesh with much less nodes than the NASA EM Drive truncated cone?. And something smaller than the present (arbitrarily chosen) distance between nodes could be analyzed with no nodes at all?  Of course not.

This is not  a disagreement about definitions.  This pertains to an understanding  of how the Finite Difference model solves the partial differential equations.

The required number of nodes in a given direction has to do with the examined field variation in that direction, and not just a function of the physical size of the object.

If you need to analyze the same mode shape for the Baby EM Drive than for NASA's EM Drive, you should use the same number of nodes, despite the much smaller sizer of the Baby EM Drive. 

In this case, the mesh should be chosen on the basis of the highest mode shapes [*] that can possibly be excited in the bandwidth of interest.

[*] I emphasize mode shapes, not frequencies ! .  Higher mode shapes require more node spatial discretization to characterize their field variations in space, regardless of the physical size of the object.  Higher frequency requires smaller finite difference time steps.  For conditionally stable operators the discretization in time is related to discretization in space due to stability consideration.
« Last Edit: 07/19/2015 05:29 PM by Rodal »

Offline wallofwolfstreet

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I think there is miscommunication here.
Is "mesh coarseness" and "mesh density" the same things?
It is important to define terms before discussing them. Doesn't the MEEP manual talk about this subject? I personally couldn't find it.
Yes.. isn't the 'coarser' mesh as it is because its modeled cavity is smaller, thus requiring fewer points? My understanding was that meep plants a mesh on the model plus some fixed distance around that model.

Perhaps a disagreement of definitions.
So accordingly something smaller deserves less Finite Difference nodes just on the basis of being smaller?

So accordingly the Baby EM Drive could be analyzed with Meep using a Finite Difference mesh with much less nodes than the NASA EM Drive truncated cone?  Of course not.

This is not  a disagreement about definitions.  This pertains to an understanding  of how the Finite Difference model solves the partial differential equations.

Have to agree with Rodal here, smaller objects don't have fewer grid points.  The number of grid points shouldn't scale by size.

Mesh coarseness and mesh density are the inverse of one another, in that a coarse mesh has a low density and a "fine" mesh a high density.  In my experience, I always used and heard people use mesh coarseness over mesh density.

Online dustinthewind

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Yes, we cringed.
...dynamic characteristics such as the rate that Power is consumed to the rate of Acceleration and Velocity increase.

...I decided to abandon doing Static testing as I want to explore the Power to Acceleration & Velocity relationships as if there is any new physics, that is where it may show up.

...

In my opinion any serious EMDrive experimenter should be doing rotary testing...

I can't say your wrong to explore that.  One thing caught my attention when you mentioned rotary testing.  I don't think the radiation necessarily rotates with the cavity when the cavity is rotated.  As a result I would think the Q of the cavity should drop in relation to its rate of rotation.  Similar to when moving a metal sheet with respect to a magnet and the magnet induces currents that resist the motion.  The reflected waves should still be bouncing in a direction and then as the cavity rotates they should experience slight changes in dimension and react accordingly.  I have to admit that considering the time to reach resonance and your rate of rotation that the effect may be negligible.  Then again, depending on the field strengths inside maybe it's not negligible. 
« Last Edit: 07/19/2015 05:42 PM by dustinthewind »

Offline deltaMass

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Seems to me that in general the value of A/B should remain approximately constant between models, where
A = # nodes per unit length
B = some measure of dE/dx or dB/dx.
In other words the number of nodes per unit length should be sufficient to capture the spatial differentials.

Online Rodal

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Seems to me that in general the value of A/B should remain approximately constant between models, where
A = # nodes per unit length
B = some measure of dE/dx or dB/dx.
In other words the number of nodes per unit length should be sufficient to capture the spatial differentials.
Yes, and the issue is that higher mode shapes have higher variation of dE/dx etc.  (the lowest mode shape m=0 is constant in the azimuthal direction).  The issue is that in a given bandwidth there are several mode shapes, some having significantly higher m, than others.  The number of nodes thus should be based on the highest mode that can possibly be excited in a given bandwith.

Offline deltaMass

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Seems to me that in general the value of A/B should remain approximately constant between models, where
A = # nodes per unit length
B = some measure of dE/dx or dB/dx.
In other words the number of nodes per unit length should be sufficient to capture the spatial differentials.
Yes, and the issue is that higher mode shapes have higher variation of dE/dx etc.  (the lowest mode shape m=0 is constant in the azimuthal direction).  The issue is that in a given bandwidth there are several mode shapes, some having significantly higher m, than others.  The number of nodes thus should be based on the highest mode that can possibly be excited in a given bandwith.
Roger that, Captain!  :D

Offline SeeShells

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What about the momentum back-reaction on the antenna feed?

Radiation is symmetrically emitted from the antenna. All back reactions cancel at the antenna.
The run you have just did was for the Yang size with the antenna in the large end dipole parallel and centered in the plate.
All you need to do now to help me complete my analysis of antenna placements is the same run but flip the Dipole 90 degrees to excite the TE 012 mode. This will be just like the Yang's device.

Dr. Rodal would you be so kind as to run your magic Wolfram calculations when Aero is done?

As you all know I've set up this EMDrive test to be narrowing down what is causing the thrust. It will be interesting to compare meep, Wolfram and real world tests. This is picking it apart bit by bit.

I've started my physical build and the first test will be the best chance of thrust scenario measuring the pressure in a static test with a digital scale and the beam riding on a V shaped knife edge.

The second series will be run with the beam and fulcrum being allowed to move giving acceleration curves. All I have to do is replace the Carbon fiber Tube with another I have bought that will allow Stainless Steel Cabling to connect to the pivot point, calibrate and run while all the other test hardware remains the same.

The first test drawing is about done, just a few tweaks but I wanted to post it anyway.

Online Rodal

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Yes, and aero, please just change one thing at a time.  Just change the antenna orientation, keep the same mesh.  We'll deal with the mesh convergence at a later time.

EDIT: Yet another run will be required with the antenna at the same proportionally scaled distance to the smalll base as rfmwguy in the same orientation to know whether the change in thrust direction is due to the antenna distance to the bases or is it due to the geometry of Yang vs NASA/rfmwguy
« Last Edit: 07/19/2015 06:08 PM by Rodal »

Offline aero

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I think there is miscommunication here.
Is "mesh coarseness" and "mesh density" the same things?
It is important to define terms before discussing them. Doesn't the MEEP manual talk about this subject? I personally couldn't find it.
Yes.. isn't the 'coarser' mesh as it is because its modeled cavity is smaller, thus requiring fewer points? My understanding was that meep plants a mesh on the model plus some fixed distance around that model.

Perhaps a disagreement of definitions.
So accordingly something smaller deserves less Finite Difference nodes just on the basis of being smaller?

So accordingly the Baby EM Drive could be analyzed with Meep using a Finite Difference mesh with much less nodes than the NASA EM Drive truncated cone?  Of course not.

This is not  a disagreement about definitions.  This pertains to an understanding  of how the Finite Difference model solves the partial differential equations.

Have to agree with Rodal here, smaller objects don't have fewer grid points.  The number of grid points shouldn't scale by size.

Mesh coarseness and mesh density are the inverse of one another, in that a coarse mesh has a low density and a "fine" mesh a high density.  In my experience, I always used and heard people use mesh coarseness over mesh density.

Of course the number of grid points scale by size all else being equal as they are for NSF-1701 and Yang-Shell models. Rodal's example of the Baby EM drive is a red herring.  The cavity is much smaller but operates at ~10 times higher frequency.  So all else is not equal for that cavity. To properly model the Baby EM drive one would certainly adjust the meep resolution, perhaps increase it by a factor of 10. Node spacing  = 1/resolution. = 1/250 =0.004 currently. The scale factor could be adjusted for convenience but if left at 0.3 then to use the same number of time steps per period would require resolution = 2500. 

The number of grid points scale by size just like the number of node points in a window screen scale by window size. Of course you could use different screens on bigger windows, and maintain the number of nodes equal. That is, until the bugs came in through the screen.
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Online Rodal

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... Rodal's example of the Baby EM drive is a red herring. ...
Not a red herring but a didactic way for people to understand that it is incorrect to determine the number of nodes solely on the basis of physical size.  It should be based as per my prior posts that I will not repeat.  You are entitled to your own personal opinions on this matter.   I don't agree with them.
On with EM Drive Developments - related to space flight applications :)
« Last Edit: 07/19/2015 06:36 PM by Rodal »

Online dustinthewind

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What about the momentum back-reaction on the antenna feed?

Radiation is symmetrically emitted from the antenna. All back reactions cancel at the antenna.

I don't know that I would assume all back reactions cancel at the antenna if non-symmetric dissipation is going on inside the frustum.  A phase array antenna which can steer projected radiation with out any moving parts uses simple antennas.  Though they emit symmetrically, as a whole they do not and a resulting force is experienced. 
« Last Edit: 07/19/2015 06:22 PM by dustinthewind »

Online Rodal

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What about the momentum back-reaction on the antenna feed?

Radiation is symmetrically emitted from the antenna. All back reactions cancel at the antenna.

I don't know that I would assume all back reactions cancel at the antenna if dissipation is going on inside the frustum.  A phase array antenna which can steer projected radiation with out any moving parts uses simple antennas.  Though they emit symmetrically, as a whole they do not and a resulting force is experienced.
Some of your initial posts had to do with phase shift between the small base and the big base.  Have you had a chance to see the phase shift in the force between the big base and the small base for the Meep/Wolfram Mathematica model for rfmwguy?

The antenna is close to the small base and the force at the small base leads.
« Last Edit: 07/19/2015 06:26 PM by Rodal »

Offline rfmwguy

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You guys are in luck, as NSF-1701 is easily reconfigurable. Here's what I propose. Assymetrical placement of monopole in both the small base and big base. This will not be frustum side insertion, but parallel to axis, offset from centerline for assymetry. My reccomendation is 1/4 wavelength from frustum sidewall to realize 50 ohm match. It will be more like nasa insertion but not a perpendicular coupling loop. For now, polarity is parallel to frustum length axis...the easiest way to swap ends for insertion tests. I'll start at a large diameter insertion for static temp testing of magnetron core. Now, off to get some more solder...IR thermometer arrives mid week, will video static test. Max core temp is 160C. Exceeding that typifies poor impedance match according to my research. If matched properly, power-up can exceed 5 minutes.

Online dustinthewind

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What about the momentum back-reaction on the antenna feed?

Radiation is symmetrically emitted from the antenna. All back reactions cancel at the antenna.

I don't know that I would assume all back reactions cancel at the antenna if dissipation is going on inside the frustum.  A phase array antenna which can steer projected radiation with out any moving parts uses simple antennas.  Though they emit symmetrically, as a whole they do not and a resulting force is experienced.
Some of your initial posts had to do with phase shift between the small base and the big base.  Have you had a chance to see the phase shift in the force between the big base and the small base for the Meep/Wolfram Mathematica model for rfmwguy?

I think i saw your post.  I thought it interesting that there was a phase shift between the forces and a net force on the two bases in a single direction.  It appears it is still open as to the net force on the side walls and the antenna. 

I think in the diagram I was using of interacting currents [block diagram], even though there was a phase shift in current, the force given was not phase shifted.  I think what matters is if there is a net-force in a single direction.  The diagram I used didn't take into account charge separation (in a wire) which fights against the magnetic interaction (for propulsion) but still, the static field appears to lose out in the case of a phase array antenna, leaving the weak photon propulsion. 

The reason I drew the model of the two cavities out of phase was to minimize the distance between plates with currents out of phase so as to maximize their interaction.  My idea was to eliminate the charge separation and so I suggested the two cylindrical cavities in a TE mode so that current circulates around the axis of the circular plates in a way that eliminates charge separation.  It would appear then energy alternates between the currents in the plates and the light stored in the cavity.  The phase relationship between the cavities when brought close should have near field interaction and one cavity should lose radiation to the other and possibly allow radiation not only to tunnel from one to the other but possibly to tunnel out of both cavities in one direction.  At least that is what I am imagining in my head for all the good that does me. 

If only magnetic interaction between the plates doesn't provide the propulsion Edit:(then) the other alternative would be transverse magnetic where charge separation does occur and then we have both magnetic and static electric field interaction between the cavities.  My suspicion is that one of these would provide more propulsion than the other. 
« Last Edit: 07/19/2015 07:07 PM by dustinthewind »

Offline X_RaY

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What about the momentum back-reaction on the antenna feed?

Radiation is symmetrically emitted from the antenna. All back reactions cancel at the antenna.

I don't know that I would assume all back reactions cancel at the antenna if dissipation is going on inside the frustum.  A phase array antenna which can steer projected radiation with out any moving parts uses simple antennas.  Though they emit symmetrically, as a whole they do not and a resulting force is experienced.
Some of your initial posts had to do with phase shift between the small base and the big base.  Have you had a chance to see the phase shift in the force between the big base and the small base for the Meep/Wolfram Mathematica model for rfmwguy?

I think i saw your post.  I thought it interesting that there was a phase shift between the forces and a net force on the two bases in a single direction.  It appears it is still open as to the net force on the side walls and the antenna. 

I think in the diagram I was using of interacting currents [block diagram], even though there was a phase shift in current, the force given was not phase shifted.  I think what matters is if there is a net-force in a single direction.  The diagram I used didn't take into account charge separation (in a wire) which fights against the magnetic interaction (for propulsion) but still, the static field appears to lose out in the case of a phase array antenna, leaving the weak photon propulsion. 

The reason I drew the model of the two cavities out of phase was to minimize the distance between plates with currents out of phase so as to maximize their interaction.  My idea was to eliminate the charge separation and so I suggested the two cylindrical cavities in a TE mode so that current circulates around the axis of the circular plates in a way that eliminates charge separation.  It would appear then energy alternates between the currents in the plates and the light stored in the cavity.  The phase relationship between the cavities when brought close should have near field interaction and one cavity should lose radiation to the other and possibly allow radiation not only to tunnel from one to the other but possibly to tunnel out of both cavities in one direction.  At least that is what I am imagining in my head for all the good that does me. 

If only magnetic interaction between the plates doesn't provide the propulsion Edit:(then) the other alternative would be transverse magnetic where charge separation does occur and then we have both magnetic and static electric field interaction between the cavities.  My suspicion is that one of these would provide more propulsion than the other.

I have got a question. Are these cavities of a pure dielectrically type (non metallic plates between them)? If not there may be a problem with that idea: If there are metallic plates the penetration depth is only a few m..
Was your idea to transform the SHORT at the end plate to be an OPEN a quarter wavelength away? I think there is a physically short at the end plate of the second cavity because there is a metallic plate also(boundary conditions). The currents are not at the outside of a metallic cavity resonator(for this high frequencies).
Time average of any thrust will be zero even there is a phase shift.
« Last Edit: 07/19/2015 07:36 PM by X_RaY »

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