February 2022 - Nektar-users

monitor the torsional force of a 2-D cylinder in the new version code nektar ++ 5.10
by hongfu2233 15 Mar '22

15 Mar '22

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2D Incns solver(tutorial) restart simulation raises error
by 董智康 25 Feb '22

25 Feb '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 all, I am new to Nektar++, I was running tutorial: Incompressible Flow Simulation. When I tried to restart simulation by running code in 6.5 Optional additional tasks (Exercise1), it raised error Initial Conditions: - Field u: from file cyl2DMesh.fld - Field v: from file cyl2DMesh.fld - Field p: from file cyl2DMesh.fld Fatal : Level 0 assertion violation m_timestep < 0 I followed all instructions before, I’m not sure where I was wrong. It’s really confusing. Could you please help me with that? Thank you so much and have a good day. Best, Zhikang Dong

2 4

Restarting and post-processing multi-threaded jobs
by Paul Liu 23 Feb '22

23 Feb '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 Everyone, Upon running a nektar++ AcousticSolver job across multiple CPUS, i noticed that the outputs for each check point are partitioned into separate .fld files (each corresponds to a single node). Stored under say "problemName_100.chk" folder. My question is how might I restart a simulation given the partitioned mesh data at each checkpoint and how to post-process the results into a single .dat file using FieldConvert. I have only noticed the instructions for single outputs. Is there some kind of concatenation required? Thank you. *YiLin Liu * *403-397-3457* *liuyilin.liu(a)gmail.com <liuyilin.liu(a)gmail.com>* MASc Student at CML <https://cml.mech.ubc.ca/> UBC

2 1

pressure time history
by Alessandro Alberto de Lima 23 Feb '22

23 Feb '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, Creating a list of points on the surface of a bluff body is the best way to monitor pressure points? Is there a method to directly specify the entire boundary? Thanks.

2 1

Compiling for multi-threaded applications
by Paul Liu 22 Feb '22

22 Feb '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 Everyone, I was just wondering if there are specific flags or other instructions that need to be set to compile nektar++ for multi-core processing. The main reason is that I am trying to run a 16 core job and I am often encountering a "c group out of memory" exception and I think it might be due to me not compiling things properly for mullti-core processing. Thank you *YiLin Liu * *403-397-3457* *liuyilin.liu(a)gmail.com <liuyilin.liu(a)gmail.com>* MASc Student at CML <https://cml.mech.ubc.ca/> UBC

3 3

2D mesh generation
by Alessandro Alberto de Lima 21 Feb '22

21 Feb '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 Guys. At the moment, I have generated my quadrilateral meshes with gmesh. Are there other options? Is it possible to convert the quadrilateral meshes generated by ICEM CFD for example? I am trying to better control the quadrilateral mesh generation. Gmesh is starting to turn into an annoying experience. Thank you very much. Alessandro

4 4

2D direct stability analysis
by shan xiangjun 20 Feb '22

20 Feb '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 Everyone, For 2D direct stability analysis of Nektar + +, when raising the NumSteps, I get different eigenvectors and I'm not sure which is correct (as shown in the figure). TimeStep = 0.004 TimeStep = 0.004 NumSteps = 4250 NumSteps = 8250 [cid:image002.png@01D824E8.40318770] [cid:image006.png@01D824E8.40318770] Why does NumSteps affect the results and how do I set its value? Looking forward to your reply! Best regards, Xiangjun Shan 从 Windows 版邮件<https://go.microsoft.com/fwlink/?LinkId=550986>发送

3 7

Acoustic Solver Question
by Paul Liu 17 Feb '22

17 Feb '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 Everyone, One thing I am noticing with NEKTAR++ is that you specify the base flow function in the configuration/xml file. However, both LEE and APE equations require the estimation of the spatial gradients of the base flow. I was wondering what method of approximation is used within NEKTAR++ as the configuration files does not ask for an analytical expression of the spatial gradients. Thank you so much *YiLin Liu * *403-397-3457* *liuyilin.liu(a)gmail.com <liuyilin.liu(a)gmail.com>* MASc Student at CML <https://cml.mech.ubc.ca/> UBC

2 1

C0 problem
by mohammadreza rouhanian 15 Feb '22

15 Feb '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 all, When I solve the equation that has the gradient the C0 doesn't satisfy. I want to know the function name that imposes C0. Is it MultiplyByInvMassMatrix? Best Regards, Mohammad Reza

2 1

Nektar - adjoint stability analysis issue
by Matt Duran 12 Feb '22

12 Feb '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 Nektar++ community, I recently have been having issues using the stability analysis adjoint module. When running direct and adjoint stability analysis I would expect similar eigenvalues to converge. This is seen in the tutorial for ‘Global Stability Analysis: Cylinder Flow’. [image: image.png][image: image.png] Where the magnitude, frequency, and growth rate results are quite similar in value for the adjoint and direct Evolution Operators. However, from my own mesh and simulation of flow past a cylinder I get a discrepancy in the modes between direct and adjoint stability. Direct: [image: image.png] Adjoint: [image: image.png] My direct stability analysis simulation gives reasonable results; agreeing with the results in the Nektar++ tutorial on direct stability of a cylinder. But the adjoint stability modes are fairly different and don't yield values close to the tutorial. I have attached my case files for direct and adjoint stability. I would appreciate some insight if anyone has an idea why I have this discrepancy between direct and adjoint stability results. Thank you, Matt Duran PhD student University of Central Florida

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