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#1300 by rfmwguy on 08 Oct, 2016 14:24
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For future calculations I will need some defined data:
This will be more difficult to obtain as time progresses and general acceptance grows. Believe it is best to research this for yourself here and elsewhere for prior information disclosed by builders (I removed my info from EmDrive.wiki however). Little is being disclosed now...for better or for worse, that's the way seems to be headed.
- frustum: shape/ dimensions, material
- possible dielectric: shape/ dimensions, dielectric constants
- frequency or frequency band (start-stop)
- source: type, position and direction, for wg-port mode shape and impedance
- input power
- defined requests about measurements, for example: magnitude current at plate X for a defined frequency Y
- maybe some more informations, I will ask for if needed
I doesn't make sense to ask for results without define some input data.
Thanks
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#1301 by WarpTech on 08 Oct, 2016 15:37
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For future calculations I will need some defined data:
- frustum: shape/ dimensions, material
- possible dielectric: shape/ dimensions, dielectric constants
- frequency or frequency band (start-stop)
- source: type, position and direction, for wg-port mode shape and impedance
- input power
- defined requests about measurements, for example: magnitude current at plate X for a defined frequency Y
- maybe some more informations, I will ask for if needed
I doesn't make sense to ask for results without define some input data.
Thanks
From my own thrust equation derivation, I find that the length of the cavity has the most significant effect on the thrust. Given the same end plate dimensions, how short can you make the length and still achieve a resonance at the desired frequency? A frustum shaped more like a flying saucer (wide and flat) should produce about an order of magnitude more thrust than anything tried so far. I'll get back to you when I've worked out the dimensions and parameters to model for this.
For those worried about CoM, you can forget all about the momentum of the EM fields inside the frustum. They cancel out as required by Maxwell's equations. However, what has not been considered is the power dissipation. If we have a perfect conducting cavity or superconductor with no heat losses, the Q will be enormous. The energy put into the cavity will be sustained indefinitely. As long as the cavity is sealed, the energy stored can't decay to a lower energy state. In that sense, the cavity is in a "ground state".
However, if we have a normal copper shell cavity, the energy put into the cavity will be stored temporarily, even if the cavity is sealed. Eventually, the energy inside decays to a lower energy state and eventually all the energy is lost as heat in the copper. In this case, the energy in the frustum has a "gravitational potential energy" just like an object suspended above the Earth. As the energy inside the frustum decays, the rate of decay is asymmetrical. The big end dissipates more power and absorbs more losses than the small end. So the energy inside seems to flow toward the big end. This creates a gradient in the field, just like gravity. As the energy inside is attracted to the big end where it is lost by heating the copper, the frustum accelerates the other way to balance the gradient, just like gravity. So if you want to consider CoM, you must consider how it works in a gravitational field, and not simply Maxwell's equations and photons.
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#1302 by Bob012345 on 08 Oct, 2016 16:03
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Bob012345, I think you are are missing some important details about what is being said about CoE and why Woodward's paper is very wrong. First from a previous post, you asked:
...
You said you are a physics major, but you clearly have forgotten some of the basic physics relevant to this discussion. P = F*v is literally one form of the definition of power in classical mechanics, so yes, that is true as long as you include all relevant energy.
Finally, are you saying that the power delivered to the device from a rocket's chemical fuel or an EmDrive' electrical energy is always exactly equal to F*V?
(Note: I have an engineering degree, which came with a physics heavy curriculum)
There is no problem with constant force, there is a problem with trying to claim that the power required to generate that force is constant. Every text on classical mechanics shows as I stated above, the power to apply constant force is P=F*v. After this it is trivially obvious that the power required to apply a constant force must increase with time."Critics" say if Professor Woodward provides some input energy to the spaceship with MET, and the spaceship ends up with much higher output energy, this violates CoE.
That's what they say. They don't say one can't have a constant force acting as long as you want. That's basic mechanics. They worry about how much energy it takes to generate that force. I've never seen that worry expressed in any text on classical mechanics.
(emphasis mine)He says for each of the 10 intervals, in each of the 10 different frames, he provides 1/10 of the input energy, and end up with much lower output energy for each interval in each different frame, each does not violate CoE.
Yes. He says you can define the proper interval up to the point where the energies are equal.I say if he sums up the ten 1/10 input energy he ends up with the same input energy; but if he sum up the 10 much lower output energy for each interval and each frame, the summation, no more than the total input energy, does not match the total output energy, so his treatment is wrong.
I think you are missing something here. Woodward is merely stating that in each interval, the total input energy must equal the kinetic energy as seen from a frame where the acceleration started from rest. He's basically saying one can always find such an interval for a given energy input and force. He's saying that's all that matters and his critics are simply wrong about CoE. Of course when you add up the effect of the frames the overall kinetic energy builds exponentially while the energy input grows only linearly. But Woodward correctly points out that this is not unique to MET's but is a property built into Classical mechanics for any constant force. It doesn't typically come up since problems usually involve an outside constant force applied in the observer frame and not a force generated in and by the accelerating ship.
No, he is the one that is wrong about CoE, and very blatantly.
First, he is adding energy across reference frames, which doesn't make sense as you have pointed out before, but you seem to think it is fine when Woodward does it.
Second, finding a single interval where things ad up doesn't change the fact that physics still has to work in between.
Third, "overall kinetic energy builds exponentially while the energy input grows only linearly. But Woodward correctly points out that this is not unique to MET's but is a property built into Classical mechanics for any constant force." is wrong on 2 counts:
-the overally kinetic energy grows quadratically, not exponentially, I assume this is a typo.
-energy input doesn't grow linearly in classical mechanics. There is no such thing as a constant force/power ratio by definition in classical mechanics. The introduction of a device that does directly contradicts classical mechanics.The critics have to show how the ship frame knows what it's velocity is and what mechanism is invoked by nature to reduce the force and thus acceleration to comply with the critics view of CoE. If that's been done please point me to it. I don't think it has. At least you are consistent in you belief that because of CoE, the device would not work at all in any frame under any circumstance. But then your problem is to justify why won't work at least as well as radiation pressure.
You keep asking for the critics to explain the mechanism by which the device could work when the whole point is that a device cannot work as described, or it is a source of free energy. It is up to the person claiming the device works to propose a way that it could obey conservation of energy.
How many times do I have to explain that it is the energy stored in the observer frame in the battery, so it is not confusing frames?You seems to believe if he sums up the ten 1/10 input energy he ends up with the same input energy, and the final output energy is much higher than my summation, indeed, is equal to the critics' calculation. It seems you defeat Professor Woodward's treatment and agree with the "critics".
There might be some confusion because of the example you gave of the cannon. In that example, the whole problem was already assumed to be within the bounds of Woodward's condition. In other words, the total input energy does equal the total kinetic energy. Breaking up that problem into steps is not necessary but I did it only to illustrate that it can be done. Yet you seemed to object how I did that which had nothing to do with MET's or EmDrives but just simply mechanics. Each frame is faster than the previous and when you take that into account it all ads up. Woodward says when the input energy is less than the kinetic energy, consider an interval where they are equal. It's just a way of looking at the problem.
In general, equating energy input in the ships frame with kinetic energy in the observers frame is confusing frames in my view.
What Woodward does changing references frames every time that energy goes overunity in the last part of his paper is badly confusing frames. Also, just to be sure, energy conservation is broken completely, not just after a certain amount of time. Energy disappearing into nothing is also a problem, and that is what happens as soon as you turn the device on, unless it can be explained where that energy goes (and you can't just say losses, you have to be specific)
And one final time, since this is the point you seem to be missing in this last post: Constant force is not a problem at all in classical mechanics. Constant power providing a constant force is where things break. Woodward's entire paper is trying to show that a device can generate constant force using constant power, but this is simply and completely inconsistent with classical mechanics. (Special relativity tweaks the definition of energy, which in turn tweaks the definition of power, so a constant force/power ratio becomes allowed, but it is strictly limited to a ratio of 1/c, or lower with inefficiencies.)
I'll give a more detailed response later but for now, I suspect that not everyone here agrees with you and Tellmeagain esp. About prof. Woodward whom you two seem to think a complete fool. I strongly suspect that those here building devices actually think they will ultimately work and will work with a constant input power.
It would be nice to hear from you all who respect and admire prof. Woodward and know he has been thinking through these issues for nearly three decades. Thanks.
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#1303 by Gilbertdrive on 08 Oct, 2016 16:09
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Yes, it is 110VAC to the power supply which does the -4kV conversion. I am convinced I saw something real, but I do have to appreciate the high level of doubt there is about something so dramatic. This is the reason I did not publish a test report, was unable to complete the # of tests I wanted to. It did seem to me that there was no thermal change within 4 inches of the frustum, and therefore no expansion of the leads.
p.s. I guess I was not active posting on NSF during the testing this summer. For the record, I stated I would only continue working with EmDrive if I got near my 100x displacement improvement and became convinced it was an actual effect. I did both and therefore decided to progress to Gen III with solid state & batteries.
If I understand correctly, your Magnetron failed before you could do the test with polymer insert ? Am I correct ? As it was told earlier, the polymer insert can help to see the reality of the thrust, since most undesired effects should be the same with, and without the insert. Heat, Lorentz Forces...
Solid State and Batteries is a great thing to do, but IMHO, the dimensions of the frustrum have to be more precise with solid state
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#1304 by Rodal on 08 Oct, 2016 16:10
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....From my own thrust equation derivation, I find that the length of the cavity has the most significant effect on the thrust. Given the same end plate dimensions, how short can you make the length and still achieve a resonance at the desired frequency? A frustum shaped more like a flying saucer (wide and flat) should produce about an order of magnitude more thrust than anything tried so far. I'll get back to you when I've worked out the dimensions and parameters to model for this...
Do you mean shaped more like the Cannae device, but asymmetric, one side flat with a larger OD and the other side having a smaller diameter?
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#1305 by meberbs on 08 Oct, 2016 16:33
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I'll give a more detailed response later but for now, I suspect that not everyone here agrees with you and Tellmeagain esp. About prof. Woodward whom you two seem to think a complete fool. I strongly suspect that those here building devices actually think they will ultimately work and will work with a constant input power.
My impression about Woodward from what people here had been saying was fairly positive before I read that paper. I have not read anything else from him, and maybe everything else he has written is reasonable, but that paper is full of numerous, basic mistakes. The paper as a whole is completely, indefensibly wrong.
It would be nice to hear from you all who respect and admire prof. Woodward and know he has been thinking through these issues for nearly three decades. Thanks. -
#1306 by WarpTech on 08 Oct, 2016 16:36
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....From my own thrust equation derivation, I find that the length of the cavity has the most significant effect on the thrust. Given the same end plate dimensions, how short can you make the length and still achieve a resonance at the desired frequency? A frustum shaped more like a flying saucer (wide and flat) should produce about an order of magnitude more thrust than anything tried so far. I'll get back to you when I've worked out the dimensions and parameters to model for this...
Do you mean shaped more like the Cannae device, but asymmetric, one side flat with a larger OD and the other side having a smaller diameter?
Yes, exactly, like a tapered pill-box. I'm using MathCAD now to optimize the cavity dimensions. I'll let you know what I come up with. I also think that driving it from the small end to prevent VSWR from feeding back to the amplifier, is the best location. Like Cannae has it because the small end is more reflective and therefore, less power will couple back to the antenna or Magnetron. The equation also shows that we want the lowest order mode harmonic.
All of this agrees with @Notsosureofit's model as well.
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#1307 by WarpTech on 08 Oct, 2016 16:38
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I'll give a more detailed response later but for now, I suspect that not everyone here agrees with you and Tellmeagain esp. About prof. Woodward whom you two seem to think a complete fool. I strongly suspect that those here building devices actually think they will ultimately work and will work with a constant input power.
My impression about Woodward from what people here had been saying was fairly positive before I read that paper. I have not read anything else from him, and maybe everything else he has written is reasonable, but that paper is full of numerous, basic mistakes. The paper as a whole is completely, indefensibly wrong.
It would be nice to hear from you all who respect and admire prof. Woodward and know he has been thinking through these issues for nearly three decades. Thanks.
You should read the papers by Dr. Heidi Fern. They are on Researchgate. The derivations are not too difficult to follow and are rock solid physics.
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#1308 by dustinthewind on 08 Oct, 2016 16:42
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For future calculations I will need some defined data:
- frustum: shape/ dimensions, material
- possible dielectric: shape/ dimensions, dielectric constants
- frequency or frequency band (start-stop)
- source: type, position and direction, for wg-port mode shape and impedance
- input power
- defined requests about measurements, for example: magnitude current at plate X for a defined frequency Y
- maybe some more informations, I will ask for if needed
I doesn't make sense to ask for results without define some input data.
Thanks
From my own thrust equation derivation, I find that the length of the cavity has the most significant effect on the thrust. Given the same end plate dimensions, how short can you make the length and still achieve a resonance at the desired frequency? A frustum shaped more like a flying saucer (wide and flat) should produce about an order of magnitude more thrust than anything tried so far. I'll get back to you when I've worked out the dimensions and parameters to model for this.
For those worried about CoM, you can forget all about the momentum of the EM fields inside the frustum. They cancel out as required by Maxwell's equations. However, what has not been considered is the power dissipation. If we have a perfect conducting cavity or superconductor with no heat losses, the Q will be enormous. The energy put into the cavity will be sustained indefinitely. As long as the cavity is sealed, the energy stored can't decay to a lower energy state. In that sense, the cavity is in a "ground state".
However, if we have a normal copper shell cavity, the energy put into the cavity will be stored temporarily, even if the cavity is sealed. Eventually, the energy inside decays to a lower energy state and eventually all the energy is lost as heat in the copper. In this case, the energy in the frustum has a "gravitational potential energy" just like an object suspended above the Earth. As the energy inside the frustum decays, the rate of decay is asymmetrical. The big end dissipates more power and absorbs more losses than the small end. So the energy inside seems to flow toward the big end. This creates a gradient in the field, just like gravity. As the energy inside is attracted to the big end where it is lost by heating the copper, the frustum accelerates the other way to balance the gradient, just like gravity. So if you want to consider CoM, you must consider how it works in a gravitational field, and not simply Maxwell's equations and photons.
I remember also wondering if thermal gradients could be a form of propulsion. Here is where I was wondering if this might be the case. I would think it might have an effect on the light generated by the currents also.
https://forum.nasaspaceflight.com/index.php?topic=39772.msg1553736#msg1553736Quoteon: 06/24/2016 05:17 PM ... On another note, I was thinking about what would happen if we had the frustum back half as a more resistant material like aluminum and then the front half as copper. Or maybe the back half as silver and the front half as superconducting. The idea being to keep a decent Q or reflective nature of the cavity but have an imbalance in the resistance to current.
wikipedia.org
Superconductor should be near zero
Copper Electrical resistivity 16.78 nΩ·m (at 20 °C)
Aluminum Electrical resistivity 28.2 nΩ·m (at 20 °C)
Silver Electrical resistivity 15.87 nΩ·m (at 20 °C)
Wouldn't this lead to a heat imbalance between the front and back half? If current is more free to accelerate with out resistance does this mean there is more of a push from the light than materials with greater resistance, or does the skin depth of penetration for the light in the material cancel out any difference in push in the long run?
The idea being some difference in push exists * Q. If Q is 10,000 then (delta_push)*10,000/2.
I remember you mentioning something similar just recently and it struck a cord with me.
Another thought I was wondering about was energy loss. If we measured power in and used a thermal bath to measure a change in temperature of water then would the power put in match the rise in temperature of the water or would there be some missing energy that seemed to be escaping. I get the impression that you would expect there to be no difference in energy put in and the energy in the thermal bath. -
#1309 by Rodal on 08 Oct, 2016 16:45
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... The equation also shows that we want the lowest order mode harmonic...
That makes sense. The lowest fundamental frequencies should have the highest amplitudes.
All of this agrees with @Notsosureofit's model as well.
Higher mode shapes like TE013 instead of TE011 have been emphasized by some following Shawyer. One justification for that is that (if one does not have other means to provide an asymmetry, like electrostrictive inserts or ferromagnetic ends) TE013 has the maximum energy density closer to the small end than TE012 (which has the maximum energy density towards the middle of the longitudinal direction). -
#1310 by WarpTech on 08 Oct, 2016 16:51
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... The equation also shows that we want the lowest order mode harmonic...
That makes sense. The lowest fundamental frequencies should have the highest amplitudes.
All of this agrees with @Notsosureofit's model as well.
Higher mode shapes like TE013 instead of TE011 have been emphasized by some following Shawyer. One justification for that is that (if one does not have other means to provide an asymmetry, like electrostrictive inserts or ferromagnetic ends) TE013 has the maximum energy density closer to the small end than TE012 (which has the maximum energy density towards the middle of the longitudinal direction).
Exactly. Energy density at the small end will persist longer than energy density at the big end, due to higher dissipation at the big end. The flow of energy due to dissipation will be from small end to big end "as if" it were attracted by gravity toward the big end. Likewise, the frustum moves the other way to balance the gravitational effect.
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#1311 by Star One on 08 Oct, 2016 16:59
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Just as a side comment if the modifications to our understanding of how gravity works resultant from producing a theory on how this device operates puts to the sword the idea of dark matter/energy then I will be greatly happy.
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#1312 by rfmwguy on 08 Oct, 2016 17:42
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Yes, I never used an insert. I had several reservations including possible out-gassing, phase change, lower Q and a lack of solid evidence that an insert was the only way to go. It might help, I just don't know. Tell you one thing, the only reason I'd ever seen for a dielectric insert was to change the dielectric constant of a cavity filter, which yields a smaller size for a given frequency...IOW, a space-saving technique where Q was not an issue. For every material, there is a positive and negative. Inserts just seemed more of a negative. Others look at it differently and that's OK.
Yes, it is 110VAC to the power supply which does the -4kV conversion. I am convinced I saw something real, but I do have to appreciate the high level of doubt there is about something so dramatic. This is the reason I did not publish a test report, was unable to complete the # of tests I wanted to. It did seem to me that there was no thermal change within 4 inches of the frustum, and therefore no expansion of the leads.
p.s. I guess I was not active posting on NSF during the testing this summer. For the record, I stated I would only continue working with EmDrive if I got near my 100x displacement improvement and became convinced it was an actual effect. I did both and therefore decided to progress to Gen III with solid state & batteries.
If I understand correctly, your Magnetron failed before you could do the test with polymer insert ? Am I correct ? As it was told earlier, the polymer insert can help to see the reality of the thrust, since most undesired effects should be the same with, and without the insert. Heat, Lorentz Forces...
Solid State and Batteries is a great thing to do, but IMHO, the dimensions of the frustrum have to be more precise with solid state -
#1313 by Bob012345 on 08 Oct, 2016 18:01
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I'll give a more detailed response later but for now, I suspect that not everyone here agrees with you and Tellmeagain esp. About prof. Woodward whom you two seem to think a complete fool. I strongly suspect that those here building devices actually think they will ultimately work and will work with a constant input power.
My impression about Woodward from what people here had been saying was fairly positive before I read that paper. I have not read anything else from him, and maybe everything else he has written is reasonable, but that paper is full of numerous, basic mistakes. The paper as a whole is completely, indefensibly wrong.
It would be nice to hear from you all who respect and admire prof. Woodward and know he has been thinking through these issues for nearly three decades. Thanks.
To quote my favorite character, Dr. Sheldon Cooper, "That's your opinion".
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#1314 by Gilbertdrive on 08 Oct, 2016 18:12
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Yes, I never used an insert. I had several reservations including possible out-gassing, phase change, lower Q and a lack of solid evidence that an insert was the only way to go. It might help, I just don't know. Tell you one thing, the only reason I'd ever seen for a dielectric insert was to change the dielectric constant of a cavity filter, which yields a smaller size for a given frequency...IOW, a space-saving technique where Q was not an issue. For every material, there is a positive and negative. Inserts just seemed more of a negative. Others look at it differently and that's OK.
Yes, it is 110VAC to the power supply which does the -4kV conversion. I am convinced I saw something real, but I do have to appreciate the high level of doubt there is about something so dramatic. This is the reason I did not publish a test report, was unable to complete the # of tests I wanted to. It did seem to me that there was no thermal change within 4 inches of the frustum, and therefore no expansion of the leads.
p.s. I guess I was not active posting on NSF during the testing this summer. For the record, I stated I would only continue working with EmDrive if I got near my 100x displacement improvement and became convinced it was an actual effect. I did both and therefore decided to progress to Gen III with solid state & batteries.
If I understand correctly, your Magnetron failed before you could do the test with polymer insert ? Am I correct ? As it was told earlier, the polymer insert can help to see the reality of the thrust, since most undesired effects should be the same with, and without the insert. Heat, Lorentz Forces...
Solid State and Batteries is a great thing to do, but IMHO, the dimensions of the frustrum have to be more precise with solid state
Thanks very much for the detailed information
In fact, the aim of the insert in my idea was not at all to improve the thrust. If the insert, at the opposive, was reducing the thrust measurements, it would have been a strong argument that the thrust that you measured without the insert was not coming from heating cable, thermal winds or from other artifacts. That was my idea. Using the insert as a control
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#1315 by X_RaY on 08 Oct, 2016 18:31
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@ WarpTech
Todd, you asked for surface current density for the Brady cone without dielectric and using an idealised 100W source.
What I find you can see in the pic below. Mode is TE012 @ 2.1805GHz, I hope the numbers can help you somehow.
Please note, the upper right diagram was generated using
"no power scaling" option in the power settings menu to find the exact resonance frequency. When "total source power (no mismatch)" is applied, the power over frequency plot shows a straight line at 100W, therefore no peak can be find.
Your idea to shorten the length of the frustum sounds interesting. Which mode do you suggest, TE011 or an other?
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#1316 by meberbs on 08 Oct, 2016 18:39
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His paper being wrong is no more a matter of opinion than 1+1=2 being a matter of opinion.I'll give a more detailed response later but for now, I suspect that not everyone here agrees with you and Tellmeagain esp. About prof. Woodward whom you two seem to think a complete fool. I strongly suspect that those here building devices actually think they will ultimately work and will work with a constant input power.
My impression about Woodward from what people here had been saying was fairly positive before I read that paper. I have not read anything else from him, and maybe everything else he has written is reasonable, but that paper is full of numerous, basic mistakes. The paper as a whole is completely, indefensibly wrong.
It would be nice to hear from you all who respect and admire prof. Woodward and know he has been thinking through these issues for nearly three decades. Thanks.
To quote my favorite character, Dr. Sheldon Cooper, "That's your opinion". -
#1317 by RotoSequence on 08 Oct, 2016 18:42
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His paper being wrong is no more a matter of opinion than 1+1=2 being a matter of opinion.
I must admit that I've been skimming the thread a bit as of late due to the rate and volume of updates; have you gone into the specifics of the mistakes contained in the Woodward paper in prior posts? -
#1318 by SeeShells on 08 Oct, 2016 19:02
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... The equation also shows that we want the lowest order mode harmonic...
That makes sense. The lowest fundamental frequencies should have the highest amplitudes.
All of this agrees with @Notsosureofit's model as well.
Higher mode shapes like TE013 instead of TE011 have been emphasized by some following Shawyer. One justification for that is that (if one does not have other means to provide an asymmetry, like electrostrictive inserts or ferromagnetic ends) TE013 has the maximum energy density closer to the small end than TE012 (which has the maximum energy density towards the middle of the longitudinal direction).QuoteTE013 has the maximum energy density closer to the small end than TE012 (which has the maximum energy density towards the middle of the longitudinal direction).
[/color]
This is one reason I'm pursuing TE013.
I've reached the limits in the home lab with vibration and noise and EM interference. I'm starting on a program over the next 6 weeks to set up a new lab. Separate power, EMI shielded and vibration isolated along with some new and better equipment.
Before I can put up this cute little building for the Space Lab I have my work cut out for me.
This attached pic is the area next to the house I'm going to be clearing off to set this lab. I've got to Split and move all the wood, grade and level the ground and pour the concrete. Erect the building, insulate it, wire it, EMI shield and heat it. Then comes the real work, moving in and setting up the test equipment and start to test. I guess you could ask why I'm doing this? Simple, error bars and to get myself from two prancing 135 pound Great Pyrenees and on stable ground.
Oh thank goodness I have a tractor with a loader and can grade. I want this to be done by Thanksgiving by adding some sweat and blisters.
Back to work!
My Best,
Shell
PS: Many more details in the construction and lab isolation I've not included.
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#1319 by WarpTech on 08 Oct, 2016 19:16
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@ WarpTech
Todd, you asked for surface current density for the Brady cone without dielectric and using an idealised 100W source.
What I find you can see in the pic below. Mode is TE012 @ 2.1805GHz, I hope the numbers can help you somehow.
Your idea to shorten the length of the frustum sounds interesting. Which mode do you suggest, TE011 or an other?
Thank you sir! Much appreciated. I will review it and let you know how it works out. TE011 should have the highest power and lowest frequency, so I would start there.
I've just now run some optimization plots on MathCAD. What I found to Maximize the thrust to power ratio is the following;
1. The ratio of the radii, Rb/Rs = 1.500. This is the maximum. Smaller than this the thrust drops off very quickly. Larger than this the thrust drops off more slowly and is probably okay if it's not too much larger than this.
2. The length L should be no longer than Rs is wide, shorter is better and the performance improves as 1/L. Assuming you can find a resonance there.
3. Shoot for the lowest frequency resonance possible. It will have the highest thrust and the performance improves as 1/f, for a constant set of cavity dimensions.
4. The big end needs to have more dissipation than the small end. I would consider adding a mass or fins on the outside of the big end to act as a heatsink, to draw the heat out of the frustum so it doesn't melt, then crank up the power!
5. There must be a compromise between higher Q and higher dissipation. I still need to work out the details on this point, regarding dielectric inserts and other materials that could be used, but I predict that superconductivity and eliminating the power dissipation, should eliminate the thrust as well.
Enjoy,
Todd
