LTRANS and wetting and drying

[lcbernardo]

Dear all,

Lately I have become interested in using the LTRANS model to run particle tracking simulations. I've been able to get it to run successfully using a ROMS simulation with wetting and drying turned off. However, when I tried a similar simulation with wetting and drying turned on, I received an error message and the model would not run. I'm trying to investigate further, but does anyone know whether the current version of LTRANS (v.2b) supports the wetting and drying feature? Would appreciate any help!

Lawrence

[ian]

What is the error code you are receiving?

LTRANS should not work with wetting/drying, as it loads the boundary information from the gridfile, and is static after that.

You may still be able to successfully run your simulation, if the particles do not interact with that area of the domain, or if the velocities in the newly dry cells are zero, and you accept it as appropriate behaviour for the particles to move into those areas and freeze until they become wet again.

[lcbernardo]

Hi Ian,

Thank you for your reply, and for the clarification on how LTRANS uses the grid information. I think I can now understand what seems to be happening. I can run make successfully, and the error I get upon running LTRANS.EXE is the following:

****** BEGIN ITERATIONS *******
write output to file, day = 4.16666666666666644E-002
write output to file, day = 8.33333333333333287E-002
existing matrix,stepf= 4
write output to file, day = 0.12500000000000000
existing matrix,stepf= 5
write output to file, day = 0.16666666666666666
existing matrix,stepf= 6
write output to file, day = 0.20833333333333331
existing matrix,stepf= 7
write output to file, day = 0.25000000000000000
existing matrix,stepf= 8
ERROR: Particle Outside Main Boundaries After intersect_reflect
Model Run Cannot Continue

Previous Location:
x: 168470.81138245956 y: 166696.24361807349
lon: 124.26183999999989 lat: 24.397490000000030

Current Location:
x: 168475.68509459964 y: 1.78147872375898568E+038
lon: 128.10016473381091 lat: 1.60036394110602449E+033

If I remember correctly from one of the posts in the ROMS forum, the velocities in newly dry cells are not zero but some very large value. Could this be the reason for the particle emerging outside the main boundaries after intersect_reflect?

[ian]

Yes, that would do it. I believe the code will only reflect a particle 3 times before it gives up and calls it out of bounds.

If you would like to ignore these particles, you can change the error flag towards the bottom of LTRANS.data to 3. It will set those particles out of bounds, but continue to run the rest instead of halting the run.

[johnluick]

Lawrence have you considered doing the particle tracking in ROMS? While I am asking, I wonder if anyone has compared the accuracies of the two approaches. I have always assumed the ROMS approach could be more accurate, since the positions would usually be updated more frequently than one would save for LTRANS.

[lcbernardo]

Yes, that would do it. I believe the code will only reflect a particle 3 times before it gives up and calls it out of bounds.

If you would like to ignore these particles, you can change the error flag towards the bottom of LTRANS.data to 3. It will set those particles out of bounds, but continue to run the rest instead of halting the run.

Hi Ian,

Thanks for the suggestion. I'm not sure I'd like to ignore these particles, but I'll check to see what happens with the error flag set to 3.

[lcbernardo]

Lawrence have you considered doing the particle tracking in ROMS? While I am asking, I wonder if anyone has compared the accuracies of the two approaches. I have always assumed the ROMS approach could be more accurate, since the positions would usually be updated more frequently than one would save for LTRANS.

Hi John,

I haven't considered the particle tracking in ROMS as I've been more familiar/comfortable with offline particle tracking codes, mainly to economize in terms of computing time. But I think I'd be interested to see what happens when wetting and drying is used though.