Version 15 (modified by gm, 3 years ago) (diff)

ENHANCE-5_Gurvan — RK-3 time stepping

Summary

Action ENHANCE-5_Gurvan — RK-3 time stepping
PI(S) Gurvan Madec

Digest

Introduce an optional RK3 time-stepping scheme. The scheme will:

  1. be a valuable alternative to the current Modified Leap-Frog (MLF, Leclair and Madec OM2009) scheme,
  2. prepare the futur introduction of a compensated time-space scheme,
  3. allow AGRIF to be exactly conservative, and
  4. make much more easier to use time coarsening of TRC and OFF-line variable volume calculation
  5. make feasible to properly implement an implicit computation of top and bottom friction (properly means consistent with the ssh time splitting scheme)

As such a change will impact many module of OPA, it has been preferred to develop the RK3 version in a separate directory, RK3_SRC, put at the same level as OPA_SRC and being a copy of OPA_SRC as starting point.

In addition to the RK3 scheme, a Forward-Bacward Scheme (FBS) will be introduced. The goals associated with FBS are the following:

(i) FB scheme is also a two levels time-stepping scheme but much simpler than a RK3. Its implementation will prepare all the required environment for the RK3 scheme, while been much easier to develop and test.

(ii) FB scheme may be a valuable alternative for low resolution simulations (in particular ORCA 2° and 1°) which do not necessarily need a high order time-stepping scheme, although FB scheme requires to used UBS scheme on advection of both dynamics and tracers.

In practice the work done in 2017 is :

  • start from the trunk, updated with HPC09 branch (i.e. ZDF modifications)
  • update with the ICEMODEL branch (i.e. new sea-ice model)
  • update with the dev_rev8689_LIM3_RST branch (improved sea-ice restart read/write)
  • linear dynamics option and no selection of dyn_adv scheme by default
  • add a NONE case fort dyn/tra/trc logicals on advection and diffusion and no selection by default
  • remove split explicit vertical advection option on tracer and dynamics
  • remove all work_nemo from DOM, DYN, LDF, and TRA
  • replace nn_timing by ln_timing (in TRA, DYN, DOM and ZDF)
  • CFL criteria re-rewritten a,d now controlled by ln_diacfl logical


Postponed to 2018 workplan:

  • create RK3_SRC directory a a copy of OPA_SRC
  • implement the FB scheme in a stp_fbs routine (found either in step.F90 or in stpfbs.F90), i.e. changes in most of SBC, TRA, DYN and ZDF modules
  • implement the RK3 scheme in a stp_rk3 routine (found either in step.F90 or stprk3.F90)
Dependencies no
Target 2017 merge party
Trac Ticket #1911
SVN branch dev_r7881_ENHANCE09_RK3
Previewer(s) Names
Reviewer(s) Names
Status Started and ongoing : RK3 directory not updated in the ENHANCE09_RK3, and not added in the dev_merge_2017
Link

'.' => '/nemo/wiki/2017WP/ENHANCE-05_Gurvan-RK3'

Abstract

This section should be completed before starting to develop the code, in order to find agreement on the method beforehand.

Description

Implementation

Reference manual and web pages updates

Updated on 11/29/2017 12:19:21 by gm

Once the PI has completed this section, he should send a mail to the previewer(s) asking them to preview the work within two weeks.

Preview

Since the preview step must be completed before the PI starts the coding, the previewer(s) answers are expected to be completed within the two weeks after the PI has sent his request.
For each question, an iterative process should take place between PI and previewer(s) in order to reach a "YES" answer for each of the following questions.

Questions Answer Comment
Does the previewer agree with the proposed methodology?
Does the previewer agree with the proposed flowchart and list of routines to be changed?
Does the previewer agree with the proposed new list of variables, including agreement with coding rules?
Does the previewer agree with the proposed summary of updates in reference manual?
… … …

Updated on 11/25/2020 06:47:35 by anonymous

Once all "YES" have been reached, the PI can start the development into his development branch.

Tests

Once the development is done, the PI should complete this section below and ask the reviewers to start their review in the lower section.

Questions Answer Comment
Can this change be shown to produce expected impact? (if option activated)?
Can this change be shown to have a null impact? (if option not activated)
Detailed results of restartability and reproducibility when the option is activated. Please indicate the configuration used for this test
Detailed results of SETTE tests (restartability and reproducibility for each of the reference configuration)
Results of the required bit comparability tests been run: Are there no differences when activating the development?
If some differences appear, is reason for the change valid/understood?
If some differences appear, is the !ticket describing in detail the impact this change will have on model configurations?
Is this change expected to preserve all diagnostics?
If no, is reason for the change valid/understood?
Are there significant changes in run time/memory?
… … …

Updated on 11/25/2020 06:47:35 by anonymous

Review

A successful review is needed to schedule the merge of this development into the future NEMO release during next Merge Party (usually in November).

Code changes and documentation

Question Answer Comment
Is the proposed methodology now implemented?
Are the code changes in agreement with the flowchart defined at Preview step?
Are the code changes in agreement with list of routines and variables as proposed at Preview step?
If not, are the discrepancies acceptable?
Is the in-line documentation accurate and sufficient?
Do the code changes comply with NEMO coding standards?
Is the !ticket of development documented with sufficient details for others to understand the impact of the change?
Are the reference manual tex files now updated following the proposed summary in preview section?
Is there a need for some documentation on the web pages (in addition to in-line and reference manual)?
If yes, please describe and ask PI. A yes answer must include all documentation available.
… … …

Review Summary

Is the review fully successful?

Updated on 11/25/2020 06:47:35 by anonymous

Once review is successful, the development must be scheduled for merge during next Merge Party Meeting.