Opened 10 years ago

Last modified 7 years ago

#37 new defect - etc

very large Av models do not conserve energy

Reported by: Gary J. Ferland Owned by: Gary J. Ferland
Priority: major Milestone: C13 branch
Component: radiative transfer Version:
Keywords: energy conservation Cc:

Description (last modified by Gary J. Ferland)

the sim grains_conserve.in was added to auto by gjf on 08 may 31 - this exposes this bug clearly and quickly. The sim is irradiated by an STE blackbody at 500K and sphere is set to all radiation should go into the outward direction. The grains should remain at 500K across the cloud. They start at 500K but cool down to 400K as energy is lost.

this was posted by Nick in the developer's page

We need to improve the way in which Cloudy treats the radiative transfer of IR dust emission in models which go out to large AV. Once Cloudy goes to the point where all atoms are in molecular form, then Cloudy starts to use large zone sizes until the stopping criteria is reached. One consequence of this is a given zone becomes optically thick in the IR. This can lead to energy conservation issues. All the luminosity should be in the form of FIR deep in a molecular cloud, or at least all the luminosity be in the IR. However, if you compare the total luminosity at the illuminated face to the total luminosity in the final zone, the final zone luminosity is orders of magnitude lower.

To see this effect, all you have to do is run a model such as orion_hii_pdr.in and run the calculation out to Av = 1,000 or 10,00 mag. Compare the total intensity given at the beginning of the output to the total FIR intensity. You will need to run the model for at least two iterations, and also be sure to use the emergent intensity.

One way I have found to at least partially get around this issue is to artificially decrease the zone thickness deep in the model. If I run a model at constant density, and I know the AV/NH ratio, then I can set a value of maximum zone thickness "set drmax xxx", such that the change in AV is never greater than 1-2. This assures that no zone is optically thick in the IR. This does get the total luminosity to be correct to within 5%, which in a model where all IR = FIR should be reasonable in getting the FIR correct. Additionally, plots of the dust spectrum seem to agree reasonably well with observation. However, this is by no means a final fix. Something about the dust RT needs to be modified. Some combination of improved zone logic, the RT of the dust continuum, etc. needs to be worked out. There should be a way to take larger zone sizes by improved RT methods. My workaround of this issue takes a long time to finish a single model (~5000 - 10000 zones), which is highly inefficient.

Attachments (1)

grains_conserve.in (824 bytes) - added by Gary J. Ferland 9 years ago.
sim from test suite exposng bug

Download all attachments as: .zip

Change History (10)

comment:1 Changed 10 years ago by peter

Component: grainsradiative transfer
Owner: changed from peter to nobody

comment:2 Changed 10 years ago by peter

Owner: changed from nobody to Gary J. Ferland

Changed 9 years ago by Gary J. Ferland

Attachment: grains_conserve.in added

sim from test suite exposng bug

comment:3 Changed 9 years ago by Gary J. Ferland

Description: modified (diff)

comment:4 Changed 9 years ago by peter

PR #41 may be a duplicate of this PR.

comment:5 Changed 8 years ago by Gary J. Ferland

Milestone: C08.01C10 branch

comment:6 Changed 8 years ago by rjrw

source:/branches/rt2 opened to investigate possible solutions.

Use of alternate form for continuum advance fixes energy densities in grains_conserve_pp and grains_conserve_sp -- however energy conservation tests in various blr_xxx runs then fail.

=> finite zone optical depth is a significant effect to be dealt with.

comment:7 Changed 8 years ago by Gary J. Ferland

Milestone: C10 branchC12 release

comment:8 Changed 8 years ago by Gary J. Ferland

Priority: blockermajor

in tests done by gjf and Nick this problem is much smaller, < 10%, in the deepest sims tested. we may have unknowingly corrected something contributing to the problem.

there is no reason to think that the current RT should pass this test since it was designed for the H+ region of PN and HII regions. this is still a major, but not critical, issue.

change from blocker and major problem. there are many parts of the code that are not accurate to 10%.

comment:9 Changed 7 years ago by Gary J. Ferland

Milestone: C12 releaseC12 branch

Milestone C12 release deleted

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