September 2020 - Nektar-users

Moving body
by Mahdi Erfanian Nakhchi 05 Oct '20

05 Oct '20

******************* 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 found an issue in moving cylinder problem in NEKTAR tests. I want to perform quasi 3D simulations over an oscillating cylinder by using mapping function. However, the velocity in the span direction (w) disappears after around 20,000 time-steps. In fact, the problem becomes full-2D after some time steps! I've tested various initial conditions for w, such as awgn(1) or awgn(1)*cos(2*PI*z/LZ), etc., and different mapping types, but I could not resolve it. I would be grateful if you could help me how to resolve this issue. The xml file and a screenshot are attached. Best regards, Mahdi This message is intended solely for the addressee and may contain confidential and/or legally privileged information. Any use, disclosure or reproduction without the sender's explicit consent is unauthorised and may be unlawful. If you have received this message in error, please notify Northumbria University immediately and permanently delete it. Any views or opinions expressed in this message are solely those of the author and do not necessarily represent those of the University. Northumbria University email is provided by Microsoft Office365 and is hosted within the EEA, although some information may be replicated globally for backup purposes. The University cannot guarantee that this message or any attachment is virus free or has not been intercepted and/or amended.

2 1

Issue with 3D convection.
by Edward Threlfall 24 Sep '20

24 Sep '20

******************* 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 users, I have been running simulations of 3D convection in a box with the incompressible Navier-Stokes solver. I find that there is always an anomaly at one of the points, where the pressure field is zero (it is obvious that this zero value is wrong - see attached image). It might be worth noting that in the image, there are 12 elements with 4 modes per direction each, so 12*4^3 (=768) degrees of freedom, and the anomalous point seems to be number 767 i.e. the final one, so perhaps the last pressure variable is not being updated. The session file used to generate the result shown in the image is attached (takes about 1min to run on my laptop). Also note it is correct that u, v, w, and T are zero at the sample point - just not p! I have found this issue on a variety of cuboidal and also tetrahedral meshes. The command to run I used is mpiexec -np 4 incnavierstokessolver nektar_3d_convection.xml Can anyone help resolve this? Many thanks, Dr Ed Threlfall, UKAEA.

3 9

About BaseFlow in Floquet stability analysis
by shan xiangjun 21 Sep '20

21 Sep '20

******************* 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++, I am learning to use Nektar++ and am very interested in the content related to Floquet stability analysis. But I encountered a problem: I found an example of ‘BiGlobal Floquet analysis of flow past a cylinder’ in section 7.5.12 of user-guide-4.0.0, but I don’t know how to set the BasicFlow function. It says that ’ In order to reconstruct the temporal behaviour of the flow, 32 time slices were considered over one period.’, I don’t know how to implement this operation. <FUNCTION NAME="BaseFlow"> <F VAR="u,v,p" FILE="cyinder_floq" /> </FUNCTION> I attempted to find the ‘cylinder_floq’ file mentioned in the above example but failed. In addition, I find this in 7.4.2 Parameters: ‘N_slices : sets the number of temporal slices for Floquet stability analysis.’ but I don't know how to use it. In addition, I tried to put several .chk files from basic flow calculations in a folder as snapshots for stability analysis, but it didn't work. Could you please provide me with this complete example? Or any other useful information will be appreciated. Looking for some help, please! Regards, Xiangjun x_j_shan(a)outlook.com<mailto:x_j_shan@outlook.com> 发送自 Windows 10 版邮件<https://go.microsoft.com/fwlink/?LinkId=550986>应用

2 1

(no subject)
by Robert Holmes 04 Sep '20

04 Sep '20

******************* 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 tried to run AcousticSolver in parallel, but it doesn't work as expected. So I looked through the user-guide and found a way to process each parallel partition in serial , but it seems only to work with ' FieldConvert '. I just want to run the solver faster through a multi-core computer. Could anyone give me some suggestions? Thank you! Best regards, Guangjian Liu

2 1