Hi Isaac, I noticed that your optimization file session.opt is basically empty: <?xml version="1.0" encoding="utf-8" ?> <NEKTAR> <COLLECTIONS /> </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<mailto: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<https://spam.ic.ac.uk/SpamConsole/Senders.aspx> 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... 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