Hi Isaac,

I noticed that your optimization file session.opt is basically empty:

<?xml version="1.0" encoding="utf-8" ?>

</NEKTAR>

So, my understanding is that in this case, no optimization is going to be performed at the beginning of your run. You can check if nektar++ is performing an optimization at the beginning of your run by using the –verbose option

srun IncNavierStokesSolver session.xml --io-format Hdf5 --use-hdf5-node-comm --verbose

I would simply recommend deleting your empty session.opt file and try again. If a session.opt already exist, nektar++ will simply read the existing optfile. You can also specify the name of the optfile to use by using the –useoptfile option as in

srun IncNavierStokesSolver session.xml --io-format Hdf5 --use-hdf5-node-comm --useoptfile optfile.opt

Best,

Jacques

From: nektar-users-bounces@imperial.ac.uk <nektar-users-bounces@imperial.ac.uk> On Behalf Of Isaac Rosin
Sent: Wednesday, August 9, 2023 2:09 AM
To: nektar-users@imperial.ac.uk
Cc: Maziyar Hassanpour <maziyar.hassanpour@ucalgary.ca>
Subject: [Nektar-users] Optimisation Issues

This email from isaac.rosin1@ucalgary.ca originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list to disable email stamping for this address.

Hello Nektar Community,

I am running a full 3D DNS simulation at Re=400 of a flow past a rectangular prism using the incompressible solver. This flow is laminar but 3D effects are present. I am using a structured mesh generated using gmsh with a p order of 4 which comes to roughly 2.6 million degrees of freedom. A colleague is able to run a similar but slightly more complex DNS simulation at Re=3900 on 1/8 the number of processors and he still obtains results much faster. All signs indicate I should be able to use far fewer resources than I currently am, but neither of us can figure out how to optimise further than I already have. I followed the optimisation section of the Nektar user guide, tweaked my mesh several times, changed the time step size, etc., but all of these adjustments showed marginal improvements at best. I would be very grateful if anyone has any suggestions. I am providing my case files here: https://drive.google.com/drive/folders/1iT0GvZgE0MyfmjNe1GYMlAKJp-8fh57X?usp=sharing the slurm file called P4.sh has the script I normally use on clusters.

I look forward to hearing from you!

All the best,

Isaac