March 2024 - Nektar-users - imperial.ac.uk

BndLayerSurface IDs in step file for mesh generation with NekMesh
by Alexander Schukmann 02 Apr '24

02 Apr '24

******************* 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, to gain experience with NekMesh I first decided to generate a simple 3D boundary layer mesh after working my way through the very helpful tutorials. I started with creating a square duct in Gmsh, exporting the geometry as a STEP file (as recommended in the user guide) and finally feeding it to the mesh configuration file (MCF) and it worked very well. However, since in my case it is necessary to pass the parameter “BndLayerSurfaces” within the MCF, I tried to figure out where this information is stored inside the STEP file. Of course, to first set up the MCF I used the surface information written in the GEO file provided by Gmsh, but I wondered what would happen if I didn’t have a GEO but only a STEP file, e.g. of a more complex geometry created with a more sophisticated CAD tool? How would I know the necessary “BndLayerSurfaces” IDs in such a case? Thanks in advance and all the best, Alex

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Questions about the plane of rotational periodic symmetry
by 谢亚广 01 Apr '24

01 Apr '24

******************* 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 attempting to use Nektar++'s rotational periodic boundary conditions. After generating the mesh, surfaces 5 and 6 in the .msh file can be joined together by rotating around the z-axis by Pi/6. However, when I use the command provided in the help documentation: NekMesh -m peralign:surf1=5:surf2=6:dir=z:rot=PI/6 test.xml test_align.xml the process always fails, displaying the following warning: [ProcessPerAlign] WARNING: Could not find matching edge for surface element 3. Skipping periodic alignment. I have been unable to resolve this issue on my own. If anyone could provide assistance, I would be extremely grateful. Attached to this email, you will find the corresponding .geo, .msh, and .xml files that I have been using for testing. Thank you very much for your help. Best regards, Yaguang

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Problem with MPI + Quasi-3D + AWGN initialization for ICNS solver
by Alexander Schukmann 25 Mar '24

25 Mar '24

******************* 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 everybody, I am currently running parallel quasi-3D simulations (Hom1D) with the incompressible Navier-Stokes solver within Nektar++ version 5.3.0 and the data transfer at the partition boundaries appears to be faulty when initializing the velocity field in the homogeneous z-direction with additive white Gaussian noise as can be seen here: [g853.png] I don't know if this problem still exists in the current Nektar version, but I couldn't find anything about it in the user archives and therefore wanted to draw attention to this. All the best, Alex

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Incompressible NS solver with DG projection
by Alexander Schukmann 25 Mar '24

25 Mar '24

******************* 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 a quick question regarding the user guide entry for the ICNS solver. The table of possible values for the EqType tag under 11.3.2 in the 5.5.0 user guide does not list "DG" as a projection for the unsteady NS equations (only CG and CG-DG, i.e. mixed projection). However, under 11.3.3 under "Driver" it says DG for the Standard driver. I am a little bit confused as to whether the ICNS solver can be used with DG projection or not and would appreciate some clarification. All the best and thanks a lot! Alexander Sicher versendet mit [Proton Mail](https://proton.me/).

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The 8th Nektar++ Workshop - Registration is Open
by Mohsen Lahooti 13 Mar '24

13 Mar '24

******************* 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 All, Registration for the 8th Nektar++ workshop is now open Please visit the link below to register. https://www.eventbrite.co.uk/e/nektar-workshop-2024-tickets-860475053047 Workshop details are available at the link below. Please visit this link frequently for the updates https://www.nektar.info/community/workshops/nektar-workshop-2024/ The workshop will be run as a hybrid event, meaning attendees can be in-person or remote. We do, however, encourage attendance in person! Please provide a provisional title for your talk/poster during the registration if you are presenting at the workshop The workshop is free to attend, and lunch and refreshments will be provided during the sessions. A workshop dinner will be on 12th June, but self-payment will be required. Hope to see you all at the workshop. Cheers, Mohsen

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explicit time integration on a subset of DOFs
by Mesgarnejad, Ataollah 10 Mar '24

10 Mar '24

******************* 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. ******************* Hi, I’m interested in performing the explicit time integration but only on a subset of DOFs, i.e., having the current solution for every DOF I like to obtain the next time step only for a subset of DOFs. Needless to say I want to obtain this solution without advancing all DOFs and extracting the solution of my subset. I’m working with Prof. Babaee at U Pitt and our goal is to implement CUR algorithm for UQ regardless of the solver type in Nektar++ if possible; however, I’m most interested in performing above for the compressible navier stokes solver. Thank you, Ata Mesgarnejad, PhD Visiting Scholar, Department of Mechanical Engineering, University of Pitssburgh Department of Physics, Northeastern University

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Filters in Acoustic Solver
by Nande, Ishan A. 07 Mar '24

07 Mar '24

******************* 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 trying to set-up a "HistoryPoints" filter in the AcousticSolver which is solving Linearized Euler Equations. Unfotunately, this filter is never activated. The system is set-up to solve for 100 time steps and I wish to record values at points as well as lines. To start with, I played around with the points filter setup and this the format which I have used: <FILTERS> <FILTER TYPE="HistoryPoints"> <PARAM NAME="OutputFrequency">1</PARAM> <PARAM NAME="Points"> -100 0 0 </PARAM> </FILTER> <FILTER TYPE="Checkpoint"> <PARAM NAME="OutputFile">IntermediateFields</PARAM> <PARAM NAME="OutputFrequency">1</PARAM> </FILTER> </FILTERS> For some reason, the .his files are never written but .chk files are. What could I be doing wrong in my setup ? Regards, Ishan

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Re-start settings and base flow input for LEE solver
by Nande, Ishan A. 04 Mar '24

04 Mar '24

******************* 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 hope all is well with you. I am using Nektar++ to solve for Linearized Euler Equations(LEE) using the Acoustic Solver. I have tried to play around a bit w.r.t to the following issues but have been un-successful: 1. I have found a few tutorials where the solution re-start can be accomplished using .rst file which is supplied under the Initial Conditions field in the XML files. I have made a similar setup for the Acoustic Solver but I get this warning when I run the solver: Fatal : Level 0 assertion violation m_timestep < 0. This doesn't seem right because my time step is not less than zero. The .rst file was generated from .chk file of the last time step and, this file was supplied as the file from which the remaining time-steps should start. 2. Secondly, how can I generate a .bse file? Is this also a .chk or .fld file whose extension has been renamed ? 3. Is it possible to generate a .bse file with data from an external source ? What would be the right way to approach this ? 4. What would be the right way to convert 1D Gmsh to Nektar++ mesh using NekMesh ? I have got errors while doing this. 5. Finally, is there a forum where users can post questions ? Thanks a lot for taking the time to read my email. Regards, Ishan PGR University of Leicester

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