December 2024 - Nektar-users

Adding a passive scalar transport with a Coordinate Transformation
by ANTONIO MAZZARA 27 Dec '24

27 Dec '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, When I run a 2.5D simulation with a coordinate transformation and an extra passive scalar transport, I get the following error: CG iterations made = 5001 using tolerance of 1e-09 (error = -nan, rhs_mag = 1) Fatal : Level 0 assertion violation Exceeded maximum number of iterations However, if I repeat the simulation without the passive scalar transport, it proceeds correctly. Has anyone else encountered the same problem? If so, would you be able to assist me in resolving it? Thank you in advance for youe help, Antonio.

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TKE dissipation rate estimation
by Alexander Schukmann 18 Dec '24

18 Dec '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 would like to follow up on a post from Fri Apr 7 14:41:21 BST 2023 titled “Compute velocity gradient during runtime” that was made by another user. I am using the incompressible solver in Nektar++ 5.5.0 and need to calculate the Kolmogorov length scale for DNS analysis. For this, I rely on an estimation of the TKE dissipation rate which is defined using the fluctuation strain-rate tensor. In the post mentioned above, Ilteber suggested using the FieldConvert Checkpoints filter including the "gradient" module in order to extract field gradients. These could then be used to derive the fluctuation strain-rates and hence the dissipation in a post-processing step. However, in order to get a good estimate of the time-averaged dissipation, a sufficient amount of sampling points is needed. At this point, writing the whole domain seems quite excessive with regard to disk space. For this reason, I wonder whether there is maybe a clever way of combining the FieldConvert Checkpoints filter with e.g. the HistoryPoints filter in order to write only field gradients at specific points during runtime. I've seen some Nektar papers where the authors estimated the Kolmogorov length scale. Could anybody maybe comment on this? Thanks in advance! All the best Alex Sicher versendet mit [Proton Mail](https://proton.me/mail/home).

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Re: [Nektar-users] Noise forcing
by Daniel Garcia 18 Dec '24

18 Dec '24

In the case of a body force, you have to create the body force inside the "forcing" flag outside "conditions", then make a function for it inside "conditions". Have you tried to put the "noise forcing" flag outside the "conditions"? I think that the place is there. If that doesn't work, I can share with you how to set the body force with a random number to trigger turbulence, that would work for your case, I guess. Anyway, check if there is an example/tutorial using the noise forcing method and check its xml file. Em qua., 18 de dez. de 2024 às 10:46, Alexander Schukmann < alexander.schukmann(a)protonmail.com> escreveu: > Hello Daniel, > > thank you for your suggestions and sorry for the late reply. The user > guide doesn't mention any additional flag to be set for the noise forcing, > but I am not sure whether it is implemented for the incompressible solver. > How would I look that up? > > Thanks again and all the best > Alex > > Sicher versendet mit Proton Mail <https://proton.me/mail/home>. > > Daniel Garcia <ribeiro.danielg(a)gmail.com> schrieb am Montag, 16. Dezember > 2024 um 19:10: > > Hello Alexander. > > I was not aware of this forcing method. However, towards triggering > transition, I've successfully used the random number generator before. To > do so, you would use the body force as the forcing type and then create the > function based on your desired body force. Perhaps they work in a similar > way. In any case, check if that "Noise" forcing type does not require > another flag on the XML file or if it's implemented using your adopted > solver/set up. > > Cheers, > > Daniel. > > Em seg., 16 de dez. de 2024 às 16:35, Alexander Schukmann < > alexander.schukmann(a)protonmail.com> escreveu: > >> This email from alexander.schukmann(a)protonmail.com 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 would like to follow up on a post from Wed Oct 13 02:46:37 BST 2021 >> titled “Noise Force Specification” that was made by another user. I am >> using the incompressible solver in Nektar++ 5.5.0 and trying to trigger the >> transition of a flow between two parallel plates (2.5D case) using noise >> forcing. However, it seems that the forcing is not activated at all, since >> the velocity component along the homogeneous spatial direction is zero up >> to machine epsilon. Therefore, no superposed disturbance is recognizable. >> >> I use the following lines within the CONDITIONS section of my session >> file: >>  >> <FORCING> >> <FORCE TYPE="Noise"> >> <WHITENOISE> 0.005 </WHITENOISE> >> <UPDATEFREQ> 10 </UPDATEFREQ> >> <NSTEPS> 5000 </NSTEPS> >> </FORCE> >> </FORCING> >> >> The value for the WHITENOISE parameter was also used by Stan back then. I >> tried varying it, with no effect. Does anyone know whether this is this the >> variance or the amplitude? >> >> Back then, the user wrote: *I tried your suggestions, but came up with >> the same results (a laminar flow profile without any "noise").* >> >> However, there doesn't seem to be a reply to that. It looks like the >> problem still exists. >> >> All the best, >> Alex >> >> >> >> _______________________________________________ >> Nektar-users mailing list >> Nektar-users(a)imperial.ac.uk >> https://mailman.ic.ac.uk/mailman/listinfo/nektar-users >> > >

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Questions about Nektar++
by Gao 18 Dec '24

18 Dec '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 two questions about using Nektar++. First, When I change the initial value to the std file of the previous time step, then the instantaneous result (5.chk, 6.chk...) can come out, but the averge field result didn't appear. Is this normal? And the average field file is output only when the calculation is complete, is the mean field file at this point the result of a continuation run? Second, I am trying to monitor aerodynamic forces in the CompressibleFlowSolver. But it seems that the FilterAeroForces supports only the incompressible solver. Is there any other way to get the aerodynamic force over time? Thanks a lot. With best regards

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Noise forcing
by Alexander Schukmann 16 Dec '24

16 Dec '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 would like to follow up on a post from Wed Oct 13 02:46:37 BST 2021 titled “Noise Force Specification” that was made by another user. I am using the incompressible solver in Nektar++ 5.5.0 and trying to trigger the transition of a flow between two parallel plates (2.5D case) using noise forcing. However, it seems that the forcing is not activated at all, since the velocity component along the homogeneous spatial direction is zero up to machine epsilon. Therefore, no superposed disturbance is recognizable. I use the following lines within the CONDITIONS section of my session file:  <FORCING> <FORCE TYPE="Noise"> <WHITENOISE> 0.005 </WHITENOISE> <UPDATEFREQ> 10 </UPDATEFREQ> <NSTEPS> 5000 </NSTEPS> </FORCE> </FORCING> The value for the WHITENOISE parameter was also used by Stan back then. I tried varying it, with no effect. Does anyone know whether this is this the variance or the amplitude? Back then, the user wrote: I tried your suggestions, but came up with the same results (a laminar flow profile without any "noise"). However, theredoesn't seem to be a reply to that. It looks like the problem still exists. All the best, Alex

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