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[#751] resistivity in lare3d

Submitted By: David Tsiklauri

Open Date 2012-07-03 19:01:08
Priority: Medium	Assignee: Nobody
Status: Open
Summary resistivity in lare3d
Details perhaps this better suits support rather than bugs section... coming back to the pulse issue, after increasing the pulse width almost 10 times, from 0.3 to 2.5 it is now well resolved but with resistive_mhd = .TRUE. eta_background = 5.0e-4_num by 20 Alfven times pulse does not dissipate at all (it does phase-mix but not dissipate in the gradient regions). attachments show it all. if you have any ideas what further tests to make I would appreciate that. thank you.
Details perhaps this better suits support rather than bugs section... coming back to the pulse issue, after increasing the pulse width almost 10 times, from 0.3 to 2.5 it is now well resolved but with resistive_mhd = .TRUE. eta_background = 5.0e-4_num by 20 Alfven times pulse does not dissipate at all (it does phase-mix but not dissipate in the gradient regions). attachments show it all. if you have any ideas what further tests to make I would appreciate that. thank you.

Follow-ups
Submitted By: Tony Arber Adddate: 2012-07-04 08:57:25 The diffusive timescale is length^2 / resistivity. So for your case isn't this 2.5^2 / 5e-4 = 1.25e4 so nothing should happen by t=20.
Submitted By: David Tsiklauri Adddate: 2012-07-17 17:08:45 finally got down to the bottom of this. it was error on my side in using the wrong analytical expression coefficient and also a problem with not choosing the sufficient resolution. I am happy to report that I tested lared3d on 2pix2pix2pi with 768x768x768 grids on essentially 2D Alfven pulse problem. (I am testing 3D code becuase next I'm going to use it for 3D magnetic fields). Attached figure (fig_final.eps) showns that accuracy is 1%, this still seems a bit high error because code is 2nd order accurate, so (2pi/768)^2 = 0.007% but then you ran it for 5.5 alfven times hence 0.04% error (crosses are simulation results, *'s are Hood et al (2002) or Tsiklauri, Rowlands, Nakariakov (2003) analytical formula and solid line is the analytical powerlaw (with properly calulated coefficient)). This means that the new (current) version of lare3d has been tested beyond "basic sanity tests". Please close this tracker item. Thank you.
Submitted By: Tony Arber Adddate: 2012-07-24 09:44:43 The resistivie diffusion time of the pulse is 2.5^2/5.e-4=12,500 so this won't dissipate. I assume you mean there is no dissipation in the phase mixing region? What is the typical transverse scale (s) in this region? The dissipation should occur on s^2/\eta

File Name	File Type	File Size	Posted By
initial_conditions.f90	text/x-fortran	2498	David Tsiklauri
control.f90	text/x-fortran	6173	David Tsiklauri
fig1.eps	image/x-eps	216756	David Tsiklauri
fig_final.eps	application/postscript	7579	David Tsiklauri

Change Date	User Id	Field Name	Old Value	New Value
2012-07-03 19:01:07	David Tsiklauri	_created_		resistivity in lare3d

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