...Now, in this case, the entire chamber is in the near field of these 15 cm waves. Near fields can be pretty non-intuitive (for example, not weakening as 1/R^2). I would be especially wary of what's going on in the reactive near field (within 2 cm or so of the drive), which is likely to be non-intuitive even for near-fields.Do we know if MEEP adequately models the reactive near field? I don't see signs of it in the plots, but I do not trust my intituition, so things may be fine, but I thought I would ask.
...Also, please don't forget that static fields can cause forces. "It would be nice" to see a breakdown of force by cause here.
While this single run detected only 1/3 of the experimental measured value, I will brazenly write that I think we can forget about axions and dark matter. We can forget about exotic theory and consider that the thrust force likely results from a little understood characteristic of evanescent waves and the forces they generate.
Well, partly perhaps, but lets wait until I run the same model without the vacuum chamber. I have ran enough cases already that I feel confident that there will be forces in that case to.
Quote from: aero on 02/15/2015 09:04 pmWhile this single run detected only 1/3 of the experimental measured value, I will brazenly write that I think we can forget about axions and dark matter. We can forget about exotic theory and consider that the thrust force likely results from a little understood characteristic of evanescent waves and the forces they generate.Quote from: aero on 02/15/2015 11:13 pmWell, partly perhaps, but lets wait until I run the same model without the vacuum chamber. I have ran enough cases already that I feel confident that there will be forces in that case to.Pardon the ignorance of this non-scientist, but with these results are you suggesting that the drive's thrust is only an interaction with the testing apparatus? In the second quote you say that you are confident that forces will be generated without a vacuum chamber. Does this mean that the drive would produce thrust in free space?
In these particular runs (which I believe is just the Drive and the chamber) the reactive near field is probably irrelevant, but for modeling the Drive + pendulum suspension it won't be.Does MEEP support variable mesh sizes? It may be necessary to decrease the mesh size near structures.And, for that matter, what is the mesh size in these plots? I think the rule of thumb is < lambda / 40, which is a little less than 4 mm.(Note, by the way, that evanescent, or exponentially decaying, waves are just one part of near field behavior and not all near field waves have to rapidly decay, particularly if you have something like a waveguide set up.)
...As for whether or not meep integrates the equations, I think it is a matter of terminology...
Pardon the ignorance of this non-scientist, but with these results are you suggesting that the drive's thrust is only an interaction with the testing apparatus? In the second quote you say that you are confident that forces will be generated without a vacuum chamber. Does this mean that the drive would produce thrust in free space?
Quote from: aero on 02/16/2015 02:00 pm...As for whether or not meep integrates the equations, I think it is a matter of terminology...Numerical Integration involves approximating definite integrals by summing discretized areas. This is not what the Finite Difference method does. I point the difference because it is important to understand the convergence problems with Finite Difference methods (as opposed to integration methods like the Boundary Element method, for example, or methods based on variational principles like the Finite Element Method).What the Finite Difference method does is instead to approximate solutions to differential equations using finite differences to approximate derivatives. The idea of a finite difference method is the transformation of a continuity domain to a discrete set of points, the mesh. In every grid point the given differential operator is approximated by a difference-operator. The Finite Difference method is a very old method (references going back to the 19th century) but great progress was made using it during and after World War II, due to the development of the digital computer, due to Von Neuman and Friederichs.At MIT's ASRL very complex Finite Difference codes were developed, for example the PETROS code:http://bit.ly/1AJ5Vgt in addition to Finite Element and other types of numerical analyses.
1.) "are you suggesting that the drive's thrust is only an interaction with the testing apparatus?" I personally feel that that is the way to bet. In any case, such interactions must be exhaustively ruled out before we can consider this to be a "real" (i.e., new physics) effect. This is a small effect (10 micronewtons is the force a 1 mm chunk of ice exerts sitting on your hand), and this will not be trivial.
Including the vacuum chamber requires a lattice size of 26x31 x no-size, so all runs will be 2D with the vacuum chamber included. I tried to run a 3D but ran out of memory before resolution got as large as 10. That is not enough resolution to detect small features of the thruster cavity model and so is not useful for our purposes. ....
...No - meep does not support variable mesh size. ..
That's useful information, as a uniform Finite Difference mesh size implies extremely long computer running times to get convergence in regions of steep gradient of the electromagnetic field. Otherwise steep gradient regions will not be well modeled.
I've been following this thread as a lurker for a little while, but my knowledge is serverely lacking and have a lot of difficulty understanding what is being said. Is it the consensus at this point that it isn't a real effect, but merely experimental artefact?
Well, you can calculate it, or you can try and devise better experiments (e.g., the same test in a fiberglass chamber). In the end, I suspect it will take a test in space to really be sure, but that's expensive, so it is entirely proper to make it jump through all kinds of hoops here on the ground first. (And, note, it is quite possible that it will either be rejected or just fade away in the process.)
I can think of 3 ways to test the evanescent wave theory. 1) Is the measured thrust the same with the chamber door open and closed? 2) Is the thrust still there when the test article is rolled out of the chamber. Not sure if 2 is possible.....3) Change the conditions near the resonant cavity; like wrap the thing in thick foam and then wrap all that with foil, see what the thrust does. ...
Marshall, how about these methods proposed by Mulletron to test whether the EM Drive thrust is due to evanescent wave interaction:
Change the conditions near the resonant cavity; like wrap the thing in thick foam and then wrap all that with foil, see what the thrust does.