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2nd order conservative remapping on unstructured grid

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2nd order conservative remapping on unstructured grid

Posted by Anonymous at October 19. 2020

Good morning oasis team,

At AWI we are currently using GAUSWGT remapping with GSSPOS global conservative flux residual redistribution for D->U remapping. A colleague of mine is interested in testing out the 2nd order locally conservative remapping. I had a quick look into the manual but I'm not 100% sure it would work for us based on what I read there. It says:

CONSERV performs 1st or 2nd order conservative remapping, which means that the weight of a source cell is proportional to area intersected by the target cell (plus some other terms proportional to the gradient of the field in the longitudinal and latitudinal directions for the second order).The configuring line is:# SCRIPR (for CONSERV) $CMETH $CGRS $CFTYP $REST $NBIN $NORM $ORDER

where: $CMETH = CONSERV. $CGRS is the source grid type: LR, D and U. Note that the grid corners have to given by the user in the grid data file grids.nc or by the code itself in the initialisation phase by calling routine oasiswritecorner

Which would imply that unstructured grids are supported. However I also find:

If the SCRIPR/CONSERV remapping is specified, longitudes and latitudes for the source and target grid corners must also be available in the grids.nc file as double precision REAL arrays dimensioned(nx,ny,4) or (nbrpts,1,4) where 4 is the number of corners (in the counter-clockwize sense, starting by any corner).

Does this mean 4 ist just an example? Or does it mean it has to be 4 corners? On our U mesh have a variable number of corners between 3 and ~10.
Best regards,
Jan

Re: 2nd order conservative remapping on unstructured grid

Posted by Anonymous at October 19. 2020

Dear Jan,

Indeed there is an error in the User Guide. The number of corners/vertices can be anything but must be the same for all cells. If your cells have a varying number of corners/vertices, you should used the largest number and just repeat the last one as needed.

Finally, please pay attention to the fact that for second order conservative remapping, it is the model that must provide the gradients of the field. This is explained in details in section 2.2.7, on p. 19.

Please note that we made a correction to the user guide in this paragraph about two months ago so you should make sure to use an up-to-date version. I hope this helps and please do not hesitate if you have additional questions,

Regards, Sophie

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