September 2022 - Nektar-users

how to set a a forced oscillating cylinder by nektar++, in which the cylinder's velocity and displacement are read from a file.
by hongfu2233 29 Sep '22

29 Sep '22

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Some questions about Nektar++ in the VIV simulation
by Zhipeng Yu 28 Sep '22

28 Sep '22

******************* 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 sir I am a PHD student from Tsinghua Univerity in China. I am writing this letter to enquire some questions about Nektar++ v5.2.0. When the simulation about the VIV of a rigid cylinder are carried out by Nektar++, the Dis_y showed the same value in z direction. However, the Vel_y and Acel_y presented different values in z direction at the same time is quite different. It seems that the Vel_y and Acel_y should be the same value in the z direction for a rigid cylinder. The results are presented as follow. # Time z Disp_x Vel_x Acel_x Disp_y Vel_y Acel_y 400 0 0 0 0 0.00419954 -0.0018539027 -0.0046684539 400 0.19635 0 0 0 0.00419954 -0.0018539026 -0.0046731296 400 0.392699 0 0 0 0.00419954 -0.0018539025 -0.004678392 400 0.589049 0 0 0 0.00419954 -0.0018539025 -0.0046851524 400 0.785398 0 0 0 0.00419954 -0.0018539025 -0.0046888038 400 0.981748 0 0 0 0.00419954 -0.0018539025 -0.004685259 400 1.1781 0 0 0 0.00419954 -0.0018539026 -0.0046771037 400 1.37445 0 0 0 0.00419954 -0.0018539027 -0.00466885 400 1.5708 0 0 0 0.00419954 -0.0018539028 -0.0046617006 400 1.76715 0 0 0 0.00419954 -0.0018539029 -0.004654695 400 1.9635 0 0 0 0.00419954 -0.0018539029 -0.0046481107 400 2.15984 0 0 0 0.00419954 -0.001853903 -0.0046443416 400 2.35619 0 0 0 0.00419954 -0.001853903 -0.0046429716 400 2.55254 0 0 0 0.00419954 -0.0018539029 -0.0046455258 400 2.74889 0 0 0 0.00419954 -0.0018539029 -0.0046517606 400 2.94524 0 0 0 0.00419954 -0.0018539028 -0.0046603436 Thank you for your patient. Best regards.

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Checkpoint fields filter StartTime
by Guillermo Suarez 22 Sep '22

22 Sep '22

******************* 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 think nektar++ can really benefit from using a "StartTime" for writing the .chk files. Say that I want to generate several .chk during a period of a vortex shedding. Right now I have two possibilities: (a) start from initial conditions=0 which will generate a lot of unnecessary .chk files because of the transient, or (b) run the simulation (without writing any .chk) and then do a restart from the .fld and write the .chk files. Because the transient will now be shorter, the number of generated unnecessary .chk files will also be smaller. In that sense, I think the Checkpoint fields filter could implement some parameter to control the time step when to start writing the chk files -- exactly the same (code) as for the aeroforces filter. Cheers, Guillermo

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¿How do I get ASCII files?
by Octavio Morales 20 Sep '22

20 Sep '22

******************* 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 dear Nektar++ community. I've been trying to obtain Graphicable files, so, I used the "FieldConvert test.xml test.fld test.dat" command to get readable data (ASCII). Unfortunately, all I get is a confusing weird-looking file. Is there any other command to get ASCII data besides the FieldConvert command written above and that gives the data in a column-arrangement type format? I am using NCAR Graphics to draw my graphics. Thanks for your time, any help is welcomed and highly appreciated. Greetings, Octavio.

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(no subject)
by Sekar Verma 17 Sep '22

17 Sep '22

******************* 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 and team, Hello, I have just started working with Nektar++. Currently, I'm trying to use the Nektar++ to conduct global sensitivity analysis on the cylinder flow at Re=100. The SFD base flow file is generated through the examples given in *solvers/IncNavierStokesSolver/Tests/**Cyl_AdaptiveSFD.xml*. After that, I change the session file according to the tutorials to get the direct and adjoint modes. But I can only get the direct modes correctly. I don't know whether there are some problems with my settings in the adjoint session file (in the attachment). Can anyone help me? Looking forward to your reply! Sincerely, Sekar Verma

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NekMesh projectcad
by Andrew N Guarendi 17 Sep '22

17 Sep '22

******************* 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 new to Nektar++, and have attempted to follow the tutorial on converting a Pointwise mesh to Nektar (nektar.info/mesh-conversion-from-gridgen-pointwise-to-nektar/), however when running NekMesh as indicated I get an error "No such module: Process: projectcad". I have Nektar++ version 5.3.0. Has this capability not yet been implemented? Thanks! Andrew

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Issue with History points
by Octavio Morales 12 Sep '22

12 Sep '22

******************* 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 dear Nektar++ community, I've been trying to execute the HistoryPoints filter but I'm still not getting the so called session.his file. This is the syntax I'm using: ***************************************************************************************************************** <NEKTAR> <FILTER TYPE="HistoryPoints"> <PARAM NAME="OutputFile">TimeValues</PARAM> <PARAM NAME="OutputFrequency">1000</PARAM> <PARAM NAME="Points"> 1.3 0 0 1.5 0 0 0 0.5 0 0 -0.5 0 0.5 0.5 0 0.5 -0.5 0 </PARAM> </FILTER> </NEKTAR> ***************************************************************************************************************** Thanks for your attention, any help is highly appreciated. Kind regards, Octavio.

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CoupledLNS
by A.P. 05 Sep '22

05 Sep '22

******************* 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 using CoupledLinearisedNS solver for 2D stabiblty analysis. To do this, it is needed to set the imaginary eigenvalue shift. Now it is possible only in 3D with a homogeneous direction. I set an appropriate 3D case and the BetaZero property that overrides LHom. As a result, eigenvalues look nice, but eigenfunctions are not. The eigenfunctions are not two-dimensional. How I can get the eigenfunctions? Or my proposition about the BetaZero property is wrong? Alex Proskurin Altai state technical university

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Some Newbie Questions about Nektar++
by İlteber Özdemir 04 Sep '22

04 Sep '22

******************* 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 beginner in Nektar++ and have compiled some of my questions below. I would be glad if you can help. 1. Does IncNavierStokesSolver or any other solver support adaptive time marching? It seems to me that TimeStep, NumSteps, IO_CheckSteps, IO_InfoSteps, IO_CFLSteps are required by the solver. I was wondering if it would be possible to control the time step with e.g. a CFL number constraint? Then all IO_* (most importantly CheckSteps) can be expressed in terms of simulation time (not time step). 2. Is it possible to calculate the gradient of only one specific variable? The gradient module calculates the gradients of all variables which produces unnecessary data, slowing down post-processing and increasing the size of the files. Is there a better way than calculating the gradient and removing the unnecessary fields using removefield module? 3. Where can I find a use of the isocontours module of FieldConvert? I couldn't figure out what kind of output it gives, and what it expects as input. 4. Is it possible to map the results of a case to another where the meshes are neither at same refinement level nor at the same order? 5. Is there a way to control solver tolerance? The standard residual level allowed seems to be 1e-09, and how can I change it? 6. When visualising with ParaView (and also if you write a python script), the best way I know is to convert the chk files into vtu files. In each of those vtu files, the mesh is included, which increases its size. Is there a way to use one mesh file (e.g. mesh.vtu or mesh.xml) and only convert the variables to some other format? This would reduce the storage space needed for a case. I would also appreciate it if you can suggest a totally new and a better way of visualising the results. 7. In the mesh.xml file created by NekMesh, the NUMMODES of the expansions are always 4, irrespective of the value of the ORDER parameter. Are those just placeholders, or should I change them after meshing? In the session file I set the NUMMODES as 1 + "the value of ORDER (in the mesh file)". Is this the correct way? 8. When using AeroForces filter, can you change the formatting of the output file? For example I want the time and the forces in scientific format with 10 digits precision, how can I make this happen? Thank you in advance for your help! Best regards, Ilteber -- İlteber R. Özdemir

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Nektar++ Workshop 2022
by Chris Cantwell 01 Sep '22

01 Sep '22

Dear all, We are planning to hold the next Nektar++ workshop on the 13th-15th September 2022 at Imperial College London. So please save the date! We are finalising the exact timing of the event, but will put more information online soon, including how to register. The event is planned to be primarily an in-person meeting. However, we are, at a minimum, aiming to accommodate viewing of the talks by remote attendees for those unable to travel. We look forward to seeing you in London in September. Kind regards, Chris -- Chris Cantwell Senior Lecturer in Aeronautics Department of Aeronautics Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0)20 759 45050 Email: c.cantwell(a)imperial.ac.uk www.imperial.ac.uk/people/c.cantwell

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