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+Refactor set_viscous_BBL and add non-trigonometric find_L_open option #543

Merged
merged 5 commits into from
Mar 6, 2024
Merged

+Refactor set_viscous_BBL and add non-trigonometric find_L_open option #543

merged 5 commits into from
Mar 6, 2024

Commits on Mar 5, 2024

  1. Refactor set_viscous_BBL channel drag calculations 

      Refactored set_viscous_BBL to separate out the routines setting the open
interface lengths used for the channel drag, shortening a 1070 line long routine
to 915 lines and reducing the scope of a number of temporary variables.  A
number of logical branch points have been moved outside of the innermost do
loops.  This refactoring will also make it easier to provide alternatives to
some of the solvers that do not use the trigonometric functions to solve for the
roots of a cubic expression and avoiding the issues noted at
NOAA-GFDL/issues/483.  All answers are bitwise identical and public
interfaces are unchanged.
    @Hallberg-NOAA
    Hallberg-NOAA committed Mar 5, 2024
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  2. +Add find_L_open_concave_iterative 

      Added the new routine find_L_open_concave_iterative to use iterative Newton's
method approaches with appropriate limits to solve the cubic equation for the
fractional open face lengths at interfaces that are used by the CHANNEL_DRAG
code.  These solutions are analogous to those given by the previous expressions
that are now in find_L_open_concave_trigonometric, and the two differ at close
to roundoff, but the new method is completely independent of the transcendental
function library, thereby addressing dev/gfdl MOM6 issue mom-ocean#483.  This new routine
is called when the new runtime parameter TRIG_CHANNEL_DRAG_WIDTHS is set to
false, but by default the previous answers are recovered.  By default all
answers are bitwise identical, but there is a new runtime parameter in some
MOM_parameter_doc files.
    @Hallberg-NOAA
    Hallberg-NOAA committed Mar 5, 2024
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  3. Add the debugging routine test_L_open_concave 

      Added the new debugging or testing subroutine test_L_open_concave along with
extra calls when DEBUG = True that can be used to demonstrate that the iterative
solver in find_L_open_concave_iterative is substantially more accurate but
mathematically equivalent to the solver in find_L_open_concave_trigonometric.
This extra code is only called in debugging mode, and it probably should be
deleted in a separate commit after find_L_open_concave_iterative has been
accepted onto the dev/gfdl branch of MOM6.  All answers are bitwise identical
and no output or input is changed.
    @Hallberg-NOAA
    Hallberg-NOAA committed Mar 5, 2024
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  4. Minor refactoring in set_viscous_BBL 

      Carried out minor refactoring in set_viscous_BBL as suggested by the reviews
of this PR, including the elimination of some unnecessary error handling and the
replacement of C2pi_3 as an argument to find_L_open_concave_trigonometric with
an internal parameter.  All answers are bitwise identical and there are no
changes to publicly visible interfaces.
    @Hallberg-NOAA
    Hallberg-NOAA committed Mar 5, 2024
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  5. Merge branch 'dev/gfdl' into nontrig_set_viscosity

    @marshallward
    marshallward authored Mar 5, 2024
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