.....I have to think again about all that. ...
I've probably got the thickness of the frustum walls wrong but it's difficult to gauge because where the frustum walls flare out at the bottom and attach to the base cap they appear to be thinner than where they flare out at the top and attach to the top cap. I wish the photo was from a lower point of view so we could see beneath the top rim of the thing.At any rate I can't get the dimensions of the inner cavity in the photo to jive with Shawyer's numbers. So I'm at a loss. I will say that it's a pretty remarkable coincidence that his numbers work precisely with the measurements in the photo if we use the diameters of the base and top caps, rather than the estimated diameters of the inner cavity, whatever they may be.I'll post the chart just for the sake of having it visible. Like I said, the two diameter scales must be incorrect. My best guess for "overall" diameter of the top, would be 189mm.
Quote from: frobnicat on 02/25/2015 10:15 amQuote from: Rodal on 02/25/2015 01:00 amQuote from: frobnicat on 02/25/2015 12:49 am....Later on thread 2 (related to spaceflight) while explaining why the buckling analysed by Rodal ... would make a ... thrust in opposite direction to the one observed by the pendulum, ...That's incorrect.Maybe, but it appears Paul March in this post says that it is opposite, and I don't see that this disagreement was acknowledged ... (Bold added for emphasis)The fact that the thermal instability (buckling force) cannot be used to nullify the EM Drive thrust, was explicitly acknowledged by me and explained here http://forum.nasaspaceflight.com/index.php?topic=36313.msg1336196#msg1336196:Quote Dr. Rodal analyzed possible thermal instability (thermal buckling of the flat ends) as a cause for the measured thrust and reported this at NSF and at ResearchGate (https://www.researchgate.net/publication/268804028_NASA%27S_MICROWAVE_PROPELLANT-LESS_THRUSTER_ANOMALOUS_RESULTS_CONSIDERATION_OF_A_THERMO-MECHANICAL_EFFECT). A thermo-mechanical effect (thermal buckling) is shown that occurs in less than 1 second (for the copper thickness employed for the microwave cavity), with a temperature increase of a degree C or less and that results in forces of the same magnitude as reportedly measured by NASA. Moreover, this thermal instability produces forces in the same direction as measured, and it will occur in a vacuum (since the heating can be due either to induction heating from the axial magnetic field in a TE mode or resistive heating due to the axial electric field in a TM mode). However, this effect can only explain the initial impulsive force and cannot explain the longer 30 to 40 second measured force. Thus the thrust force measured for up to 40 second is not nullified by this explanation either.Thermal expansion effect as posited by a team from Oak Ridge National Labs for another propellant-less set of experiments was also eliminated as a possible source by the NSF contributors because it would result in forces in the complete opposite direction as the forces measured by NASA. (Bold and color added for emphasis)
Quote from: Rodal on 02/25/2015 01:00 amQuote from: frobnicat on 02/25/2015 12:49 am....Later on thread 2 (related to spaceflight) while explaining why the buckling analysed by Rodal ... would make a ... thrust in opposite direction to the one observed by the pendulum, ...That's incorrect.Maybe, but it appears Paul March in this post says that it is opposite, and I don't see that this disagreement was acknowledged ...
Quote from: frobnicat on 02/25/2015 12:49 am....Later on thread 2 (related to spaceflight) while explaining why the buckling analysed by Rodal ... would make a ... thrust in opposite direction to the one observed by the pendulum, ...That's incorrect.
....Later on thread 2 (related to spaceflight) while explaining why the buckling analysed by Rodal ... would make a ... thrust in opposite direction to the one observed by the pendulum, ...
Dr. Rodal analyzed possible thermal instability (thermal buckling of the flat ends) as a cause for the measured thrust and reported this at NSF and at ResearchGate (https://www.researchgate.net/publication/268804028_NASA%27S_MICROWAVE_PROPELLANT-LESS_THRUSTER_ANOMALOUS_RESULTS_CONSIDERATION_OF_A_THERMO-MECHANICAL_EFFECT). A thermo-mechanical effect (thermal buckling) is shown that occurs in less than 1 second (for the copper thickness employed for the microwave cavity), with a temperature increase of a degree C or less and that results in forces of the same magnitude as reportedly measured by NASA. Moreover, this thermal instability produces forces in the same direction as measured, and it will occur in a vacuum (since the heating can be due either to induction heating from the axial magnetic field in a TE mode or resistive heating due to the axial electric field in a TM mode). However, this effect can only explain the initial impulsive force and cannot explain the longer 30 to 40 second measured force. Thus the thrust force measured for up to 40 second is not nullified by this explanation either.Thermal expansion effect as posited by a team from Oak Ridge National Labs for another propellant-less set of experiments was also eliminated as a possible source by the NSF contributors because it would result in forces in the complete opposite direction as the forces measured by NASA.
...Now Newton's third law still states that for every action there is an equal and opposite reaction. So when the copper frustum's large OD end-cap's prompt and inward oil canning action, followed by the slower frustum cone thermal expansions, they both push the copper frustum's Center of Mass (CoM) to the left as viewed from the front of the Eagleworks' vacuum chamber looking back at the test article and torque pendulum, while noting how the copper frustum is bolted on to the T.P.. These thermally induced actions to the left requires the torque pendulum's arm to move to the right to maintain the balance of the torque pendulum's arm in the lab's 1.0 gee gravity field, since we also use the Earth's g-field to help null the pendulum's movements. ...
....So to make my position explicit in regard to observables : I predict that the consequence of an "inward oil canning" is a sharp plunge on the record charts (or to add a sharp plunge term to other possible effects that move the arm). And I also think Paul March sees that the same way. Will take time to further reply of your next post, unless other contributors feel it clutters the main thread and we could discuss that by PM.
Quote from: frobnicat on 02/25/2015 10:15 am.....I have to think again about all that. ...The mathematical equations I used are in the aforementioned paper, if you object to any of the equations and assumptions we would have a better basis for discussion.To state that the buckling forces produces a force (towards the right in the picture), in the opposite direction to the measured movement and force of the EM Drive (towards the left in the picture) is, I think, untenable....
FYIAnytime I hear the term "Two-Photon Loss"...........http://arxiv.org/pdf/1412.4633v1.pdf"In conclusion, we have realized a non-linearly driven-dissipative oscillator which spontaneously evolves towards the quantum manifold spanned by two coherent states."And"This was achieved by attaining the regime in which the photon pair exchange rate is of the same order as the single photon decay rate. The ratio between these two rates can be further improved within the present technology by using a higher Q oscillator and increasing its on-linear coupling to the bath."For whatever it's worth. (requires non-linear elements. surface ? also ignored some terms ?)
@FlybyThe second type distortion you refer to is a perspective distortion. All of that is true and in addition the camera wasn't held on a flat level when the photo was taken. I've rotated it a few degrees clockwise to compensate for this problem but I might still be off of the horizontal by a fraction of a degree. At any rate my experience is that these distortions are so small that they don't significantly affect the accuracy of the estimate, which is a just that, a rough estimate give or take a couple mms.If you have the software and are able to correct for some of the distortion, I'll recalculate. I'm not sure that it matters much but I'd be happy to do so.
FYIAnytime I hear the term "Two-Photon Loss"...........
Quote from: lasoi on 02/25/2015 03:24 pm@FlybyThe second type distortion you refer to is a perspective distortion. All of that is true and in addition the camera wasn't held on a flat level when the photo was taken. I've rotated it a few degrees clockwise to compensate for this problem but I might still be off of the horizontal by a fraction of a degree. At any rate my experience is that these distortions are so small that they don't significantly affect the accuracy of the estimate, which is a just that, a rough estimate give or take a couple mms.If you have the software and are able to correct for some of the distortion, I'll recalculate. I'm not sure that it matters much but I'd be happy to do so.Well, it might be interesting to pretend we do not know the real dimensions and see if such a photo-touch up can be used to make more accurate measures.. or... that it proves to be totally useless...I do feel a bit uncomfortable about the tilt-correction, but ignoring it would mean you have to resort to a 3 point perspective, which is highly uncomfortable (horizon points far far away) considering you have a near 1-point perspective...but... let's give it a spin...if it hits a wall, then we'll know...
Quote from: frobnicat on 02/25/2015 10:15 am.....I have to think again about all that. ...The mathematical equations I used are in the aforementioned paper, if you object to any of the equations and assumptions we would have a better basis for discussion.
To state that the buckling forces produces a force (towards the right in the picture), in the opposite direction to the measured movement and force of the EM Drive (towards the left in the picture) is, I think, untenable.Here are two tenable positions that can be taken:1) The buckling force cannot produce any motion of the center of mass of an unconstrained EM Drive free-floating in space. If one assumes simply supported boundary conditions at the edges of the big diameter plate, just before instability takes place, the end plate is flat and hence the membrane forces are balanced by the rigid circular rim. These membrane forces are directed radially from the rim towards the center, they are self-balanced. There are no forces perpendicular to the plate. If one assumes that the buckling instability takes place instantaneously , superluminally, in the buckled state, there are no membrane forces if the plate is infinitesimally thin, such that it will take whatever bent position is necessary to accommodate the required membrane thermal expansion. Since there are no membrane forces in the final buckled state, there are no forces at the simply supported edges at all in the buckled state. Hence there are no forces to move the EM Drive before and after the buckled state, and that's all, because the buckling motion is assumed to take place instantaneously (hence there are no forces to be considered to take place in between the initial flat state and the final buckled state).
2) If one assumes that buckling cannot take place instantaneously, but that its maximum speed has to be limited by the velocity of stress waves in the material, that is, by the speed of sound in the material, then the minimum time interval for buckling to take place is governed by the speed of sound. In the paper I derived a speed and acceleration for the buckling motion under some assumptions that are explicitly stated (see equations). Those assumptions can indeed be criticized. The equations can also be criticized, and you are invited to do so. The derived speed is below the speed of sound in the material, so it satisfies this physical condition (that the buckling speed should be lower than the speed of sound in the material). After the onset of buckling, and during this (short time) buckling motion, the membrane force decreases, from a maximum at the onset of buckling to a minimum at the final buckling state. During this (short time) the plate is in a bent condition, with increased bending shape with time. At the edges of the plate, the bending of the plate produces a slope at the simply supported edges. The membrane force at the edges can be decomposed into two directions: A) a component that is in the original flat direction. This component is self-balanced. B) The other force vector component is directed in the same direction (towards the left) as the motion of the EM Drive. This is a very short-time impulsive force, calculated to be of the same magnitude as the initial transient rise force in the experiments.
...That's what I have in mind when I say that inward buckling to the left will appear as a kick to the right for the system :....From 3 to 4 : the consequence of an "inward oil canning" alone is a kick to the right initially. Do I have to write down equations ? For me this is more a matter of proper forces orientation conventions than anything else. I hope this is clear enough as to why I said that buckling would kick opposite to the observed thrust. So, what's wrong with this way of seeing orientations ?
Quote from: frobnicat on 02/25/2015 06:51 pm...That's what I have in mind when I say that inward buckling to the left will appear as a kick to the right for the system :....From 3 to 4 : the consequence of an "inward oil canning" alone is a kick to the right initially. Do I have to write down equations ? For me this is more a matter of proper forces orientation conventions than anything else. I hope this is clear enough as to why I said that buckling would kick opposite to the observed thrust. So, what's wrong with this way of seeing orientations ?Get rid of the pendulum and everything else for the time being, as it further muddles the picture. Just consider the flat plate and a rigid ring around it and ask yourself in which direction you have to push the plate's center for the plate's center to move towards the left. Of course that one has to have a force moving to the left.
All those words and images above are associated with a discussion of a reaction from the pendulum. You could use all those words to also talk about a reaction from the pendulum concerning EM Drive's thrust, and get into a similar mambo jambo as Shawyer's discussion of thrust in EM Drives.
First you have to address in which direction is the movement of the buckled shape (it is towards the left), and when it moves towards the left , in which direction it is pulling the supports (towards the left). The buckled material cannot move towards the left without pulling on the supports towards the left: it is all connected.
What you are discussing instead is what is the effect of the buckling force pulling the supports to the left, on the pendulum. That is an entirely different question. You can ask yourself exactly the same question regarding what is the effect of the EM Drive moving towards the left, with a force pulling towards the left, on the pendulum.
After you have accepted that fact, you can talk about the reaction, which involves elastic deformation, and it is also present for the EM Drive thrust.And, it is unclear why you think that this is so relevant, because the flat plate can theoretically buckle towards the left or towards the right (if there would be no plastic insulation on the outside and if the copper would be very thin) depending on initial imperfections. An even if you think that when the buckled plate moves towards the left it gives a force towards the right (which is a misscommunication based on the fact that you are focusing on the pendulum's reaction rather than the buckling force itself, but for argument sake's) then even per your admission then if the plate buckles towards the right according to you would produce a force towards the left.
It seems to me that if you wanted to argue about this for intellectual reasons, a much safer ground would be to say that the buckling force is self-balanced and that it produces no forces on the center of mass, either to the left or to the right (for the aforementioned reasons in my above post).
EDIT: And having said that, the thermal expansion explanation by Oak Ridge does not make any sense in this case for the HD PE (to think that an unrestrained, homogeneous, isotropic, free to expand material, will produce a force when expanding. Thermal expansion changes the VOLUME of a material. The mass stays the same. If free to expand, then the density of the HD PE will change (larger volume, same mass = lower density). Thermal expansion produces forces only when there is a thermal gradient through the material or the material is anisotropic, or the most general case: when the material is constrained so that it cannot expand !!!!! )
...
... When thermal expansion displaces a part of a system relative to the rest of a system, the rest of the system will recoil. Whatever displaces a part of a system relative to the rest of the system, this displacement implies a force F_system_part. The rest of the system will recoil. Recoil is the acceleration due to the opposite force (F_part_system). An unrestrained, homogeneous, isotropic, free to expand but in one direction material, will produce a force when expanding against the wall against which it rests.Why is it so hard to reach consensus now ?