January 2023 - Nektar-users

Spurious results using composites with different discretization orders
by Guillermo Suarez 13 Feb '23

13 Feb '23

******************* 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 want to solve the incompressible flow around the naca0012 with nektar++. I have attached the input file that I am using for such a case. For nektar++ versions v5.1.0, v5.2.0 and 5.3.0 (master) some spurious results, two checkerboard patterns, around half and one chord length right above the trailing edge show up. Such a checkerboard pattern does not appear when using nektar++ v5.0.1 and v5.0.2. I have enclosed a screenshot showing the comparison between the different versions. The checkerboard pattern seems to first appear in the horizontal velocity, u. It develops right at the boundary between two composites with different discretization orders. This is not the only boundary between composites with different nummodes. The pattern does not belong to a transitory state, once it shows up it will not fade or get shed outside of the domain. It will eventually appear in the pressure and vertical velocity fields as well, but their magnitudes are considerably smaller compared to one present in the horizontal velocity. I have tried different approaches to mitigate it: - Increase and decrease nummodes. - SVV - Diferent precodnitiones for velocity and pressure - Different Reynolds number - Differnt operators for SmoothAdvection - Differnt operators for GlobalSysSoln The pattern only does not show up when using the same discretization order for all the composites. Any help would be welcome. Cheers, Guillermo

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Help with using DIRK Time Integration Methods
by Andrew Barnes 31 Jan '23

31 Jan '23

******************* 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'm trying to use the DIRK Time Integration methods in the CompressibleFlowSolver but keep getting an error when trying to specify the order and variant. If I specify only <I PROPERTY="TimeIntegrationMethod" VALUE="DIRK" /> in SolverInfo it will work perfectly, however I am unsure which order this is using. When I try to define VALUE="DIRKOrder3" or in a separate TIMEINTEGRATIONSCHEME section as below instead, it will produce the error bad_function_call. <TIMEINTEGRATIONSCHEME> <METHOD> DIRK </METHOD> <ORDER> 3 </ORDER> </TIMEINTEGRATIONSCHEME> Could anyone clarify: 1. Which order is used for the default "DIRK" model? 2. What would be the correct way to specify the order of DIRK model? Thank you in advance, Andrew

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Help with spatially-varying sourcing function.
by Edward Threlfall 28 Jan '23

28 Jan '23

******************* 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 community, I've set up a convection problem in the incompressible Navier-Stokes solver. I have an equation for the time-evolution of the temperature to which I would like to add a right-hand-side describing sources of local heating. Can I do this in Nektar++? I have tried implementing it via the bodyforce, however this seems to apply a spatially-uniform source and I want something like the Gaussian profile below. I am trying: <FUNCTION NAME="BodyForce"> <E VAR="u" VALUE="Gr*T" EVARS="u v T p" /> <E VAR="v" VALUE="0" EVARS="u v T p" /> <E VAR="T" VALUE="(1e10)*exp(-((x+0.25)^2+y^2)/(0.05^2))" EVARS="u v T p x y" /> </FUNCTION> then <FORCING> <FORCE TYPE="Body"> <BODYFORCE> BodyForce </BODYFORCE> </FORCE> </FORCING> Can anyone help, please? Thanks! Ed.

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Nektar++ Workshop 2023: 13-15th June, London
by David Moxey 23 Jan '23

23 Jan '23

******************* 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, I hope you are all well! This is a brief email to say that we are planning to hold the next Nektar++ workshop for 2023 on 13th-15th June 2023 at King's College London. Please do therefore put the date in your diaries! We are finalising timings for the event, and will be back in touch with more details on registration over the next few weeks. We look forward to seeing you in London in June. Many thanks, Dave -- Dr David Moxey, PhD MMath FHEA Reader in Engineering david.moxey(a)kcl.ac.uk | web: davidmoxey.uk Department of Engineering, King's College London, Strand, London, WC2R 2LS.

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FIeldConvert homogeneous expansions
by Guillermo Suárez 18 Jan '23

18 Jan '23

******************* 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 have a 2.5D solution (2D in the x-y plane with Fourier expansion in the z direction) run with the incompressible Navier-Stokes solver and I need to replicate it N times in the homogeneous direction. If the solution has HomModesZ for an extension LZ, I need the new solution to fit N replica in an extension N*LZ with a resolution N*HomModesZ. I have tried several modules of FieldConvert, but rather than N replicas of the original solution, the result I get is a stretched version of it. In principle this should be a very simple thing to do, as the coefficients of mode k of the original solution should be copied to mode k*N of the new solution, leaving all modes that are not multiples of N empty (zeroes). The trouble is that implementing this requires an understanding of how modes are labeled and I don't manage to get the hold of it. For a simple 1D-periodic solution whose Fourier expansion modes are saved in a sequential complex array, replicating three times would be as simple as: A_original = {a0, a1, a2, a3, ..., an} A_new = {a0, 0, 0, a1, 0, 0, a2, 0, 0, a3, ..., 0, 0, an} Could someone please give me some hints as to how to implement this? Perhaps an existing module that I can take as a reference and the sort of changes that could get the intended result? I believe this would not take more than a few minutes for someone that is familiar with the code. Perhaps someone acquainted with the working can help me implement such a replication module for FieldConvert? Thank you. Cheers, Guillermo

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About Modified Arnoldi Driver
by 王舟阳 12 Jan '23

12 Jan '23

******************* 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 Wang Zhouyang, and I am sorry to present some questions about the Modified Arnoldi Driver in linear stability analysis: 1. When I was doing parallel computation, I was prompted that Arpack algorithm could not implement parallel in Nektar++. Although this is true based on other user communications here, I still want this issue to be confirmed. Thank you very much. 2. As described in the user documentation, the Arpack package can specify properties such as LargestMag or LargestReal etc to output eigenvalues. For the Modified Arnoldi algorithm, what is the property of the eigenvalues utilized to write the result? (For example, nvec=4, do the four eigenvectors output after iteration have the largest four magnitudes or the top four growth rates or other criteria?) 3. In solving, is it reasonable to have a mode with a frequency of 0? I understand it as a flow phenomenon of pure exponential growth (or decay).In my humble opinion, the frequency may suggest a flow structure with oscillation, and it would be unstable (or attenuated) regarding to the growth rate. Thank you very much for your help, and I sincerely hope to get your answers. Thanks to the Nektar++ project team. Best Regards, Wang Zhouyang

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Time series data
by Chengeng Qian 04 Jan '23

04 Jan '23

******************* 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, Could some please give me some hints as how to output time series data (for example, pressure evolution at some given point) using Nektar++? Thanks Chengeng

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