July 2025 - Nektar-users - imperial.ac.uk

Question on Restarting APE Solver from Checkpoint Files
by dxz324＠student.bham.ac.uk 30 Jul '25

30 Jul '25

******************* This email 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. ******************* Dear Nektar++ Development Team, I hope you are doing well. I am currently running the APE solver of Nektar++ on the ARCHER2 supercomputing platform. I have already enabled checkpointing and successfully generated .chk files during my simulation runs. However, I could not find detailed instructions in the user guide on how to restart the solver from these checkpoint files automatically, once the allocated job time expires. Could you please advise on the correct way to configure the solver (e.g., input files or command-line options) so that it restarts from a given checkpoint file rather than starting from the initial conditions? Thank you for your time and support. Best regards, Dao

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CWIPI Version Mismatch and Forcing Newer CWIPI in Nektar++
by dxz324＠student.bham.ac.uk 29 Jul '25

29 Jul '25

******************* This email 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. ******************* Dear Nektar++ Team, I have two questions about using CWIPI coupling in Nektar++ 5.2.0 on ARCHER2: Can a mismatch between the CWIPI library versions (the coupling application using CWIPI 1.3.0 vs. Nektar++ loading its bundled CWIPI 0.11.1) cause the MPI data exchange to deadlock at initialization? If so, what’s the recommended way to override Nektar++’s default CWIPI 0.11.1 at build/install time so it links against an external CWIPI 1.3.0 (or later) instead? For context, I’ve observed that on startup Nektar++ prints many: cwipi 0.11.1 initializing lines, while the external coupling application prints: cwipi 1.3.0 initializing and neither ever progresses to the “Coupling Config:” stage. I tried pointing -DCMAKE_PREFIX_PATH at my CWIPI 1.3.0 install, but ldd AcousticSolver still shows libcwp.so.0.11.1. I also attempted manually replacing libcwp.so.0.11.1 with a symlink to libcwipi.so.1, without success. Could you please confirm: Whether version mismatch alone can block the CWIPI handshake? The exact CMake or install steps needed to force Nektar++ to use an external CWIPI 1.3.0 instead of its internal copy? Thank you for your guidance. Best wishes, Dao

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Merging two or more solvers: Electrohydrodynamics
by Ananth Narayan S am24d038 23 Jul '25

23 Jul '25

******************* This email 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. ******************* Dear Nektar users, I am new to Nektar and planning to incorporate the IncNavierStokesSolver with ADRSolver- Poisson. I am currently working on Electrohydrodynamics, where Navier Stokes, Poisson equation (for potential difference) and species transport (for positive and negative species with custom forcing term). [image: image.png] As a first step, I am trying to solve Navier Stokes with Poisson equation (not coupled), further solve the species equation then couple the force (\rho_e\vec{E}) in the momentum equation. I have already written this solver in OpenFOAM, so I can grasp the concepts at earliest. Since the coding style is completely different, I need support on implementing this solver. I have seen the documentation on implementing the scalar transport along with IncNavierStokes, but found no examples or other documentation on implementation. Regarding the coding part, I am not sure where to add Poisson solver as soon as Navier stokes is solved for a time step. Thank you Ananth Narayan PhD, Fluid Mechanics IIT Madras

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2D stability analysis question
by Ben 15 Jul '25

15 Jul '25

******************* This email 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 everyone, I have encountered some problems while calculating 2D linear stability analysis. Anyone can provide suggestions. 1. The extension does not take effect in direct and adjoint, but only in the calculation of the baseflow. The meaning is that the dat grids of direct and adjoint are not encrypted according to the settings in the extension.Set as follows <EXPANSIONS>         <E COMPOSITE="C[37]" NUMMODES="3, 3" BASISTYPE="Modified_A,Modified_A" POINTSTYPE="GaussLobattoLegendre,GaussLobattoLegendre"   NUMPOINTS="4,4" FIELDS="u,v" />         <E COMPOSITE="C[37]" NUMMODES="2, 2" BASISTYPE="Modified_A,Modified_A" POINTSTYPE="GaussLobattoLegendre,GaussLobattoLegendre"   NUMPOINTS="4,4" FIELDS="p" />     </EXPANSIONS> 2. The vorticity and modal plots in tecplot are very blurry. Do I need to perform additional post-processing on the results (such as C0Projection) or increase the grid order for recalculation? Ben

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Basic questions related to Nektar++ Steady State Solver
by Gaurav Gupta 10 Jul '25

10 Jul '25

******************* This email 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, I am a new user of Nektar++ and will be using the Linear Stability Analysis solver. I have been able to run simulations successfully and I have a few basic questions related to post-processing in Nektar++. I would be grateful if someone could help me with the following questions: 1. What are the headers of the ConvergenceHistory.txt file ? There are 5 columns where I understand the first three are iteration number, simulation time, computation time. Are the other two Linf and L2 ? 2. I had run the solver in parallel which generates folders with n chk/fld files for n processes. Is there any way I can combine these n files into a single vtu file for post-processing ? I couldn't find answers to the above questions in user-guide as well as in the email archive. Hence, I am posting this email. Thanks! Sincerely, *Gaurav Gupta* Senior Undergrad Student Dept. of Aerospace Engineering Indian Institute of Space Science and Technology

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