July 2022 - Nektar-users - imperial.ac.uk

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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Mapped boundaries
by Marc Goldbach 11 Aug '22

11 Aug '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 would like to sample data from a plane within my domain (turbulent channel), and use those values as the inlet boundary. The plane at which data is sampled is in the middle of the domain, so a periodic boundary is not suitable. Is this possible, and if so how can I do this? So far I have looked at using the "HistoryPoints" filter to extract data from the simulation along a plane, but I cannot quite figure out how to read the time dependent boundary data from file: 88 <BOUNDARYCONDITIONS> 95 <REGION REF="0"> 96 <D VAR="u" FILE="periodicInlet_"/> 97 <D VAR="v" VALUE="0" /> 98 <D VAR="w" VALUE="0" /> 99 <N VAR="p" USERDEFINEDTYPE="H" VALUE="0" /> 100 </REGION> ... 185 </BOUNDARYCONDITIONS> ... 256 <FILTER TYPE="HistoryPoints"> 257 <PARAM NAME="OutputFile">periodicInlet</PARAM> 258 <PARAM NAME="OutputFrequency">1</PARAM> 259 <PARAM NAME="OutputOneFile">false</PARAM> 260 <PARAM NAME="plane"> 261 100, 100, 262 0, 0, 0, 263 0, 7, 0, 264 0, 0, 2, 265 0, 7, 2 266 </PARAM> 267 </FILTER> When using <PARAM NAME="OutputOneFile">false</PARAM>, the history point data is saved in files based on index (e.g. periodicInlet_0, periodicInlet_1, periodicInlet_2, etc.) Any suggestions are appreciated. Regards, *Marc Goldbach* PhD Student, Department of Mechanical Engineering University of North Carolina at Charlotte

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Reading Parameters from One File
by İlteber Özdemir 29 Jul '22

29 Jul '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 everybody, I am quite new to Nektar++ and trying to get used to it. I want to define some parameters in a separate file and want to use them both in my mesh.mcf and session.mcf files. By doing so I can define the problem parameters in one file and let all the other files read from it. How can I do this? Cheers, Ilteber

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About the LBB condition
by shan xiangjun 13 Jul '22

13 Jul '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 the continuous or discontinuous Galerkin method is used to solve the incompressible N-S equation, can the “checkerboarding” of the pressure field be avoided if the LBB (or inf-sup) condition is satisfied? Can anyone help me? Thank you very much. Best regards, Shan 从 Windows 版邮件<https://go.microsoft.com/fwlink/?LinkId=550986>发送

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Basic questions as a beginner
by Marc 11 Jul '22

11 Jul '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 came across Nektar++ and was very interested in it. As very new to it, I have tons of questions about Nektar++ of which I concerned the most: - The tutorials using Jupyter notebook on the website seem in completed. The mesh files and .xml configuration file are not available in most cases. Any suggestions how to fetch them somewhere else? - I basically play with Incompressible NS flow. Compared with finite volume method, e.g., OPENFOAM and ANSYS FLUENT, how is the efficiency of Nektar++? - Any suggestions how to begin with Nektar++? Marc Ph.D. student

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Re: [Nektar-users] Defining complex initial conditions in session files
by Vidhi Zala 07 Jul '22

07 Jul '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 Mike, Yes, min() seems to be the culprit. If you point me to where can I implement it, that would be great. I can find a workaround to not use min () in initial condition but the function is complicated enough already. V On Thu, 7 Jul 2022 at 05:30, Mike Kirby <kirby(a)cs.utah.edu> wrote: > > Hi - > > Did you try the expression without min(.) to verify that min is the > problem? Min may not exist in the set of functions implemented > (currently), but could be added. > > Cheers > Mike > > > > On Jul 7, 2022, at 3:33 AM, Vidhi Zala <vidhi.zala(a)utah.edu> wrote: > > Hi everyone, > > I am looking for a way to define initial conditions which contain min() > function. Can someone point to an example/syntax for the same? I am > currently getting an error saying > > Message : Equation::Equation() fails on expression > [(0.25*(1+cos(PI*min(sqrt(pow(x-bell_x0,2) + pow(y-bell_y0,2))/bell_r0, > 1.0))))] > > Thanks > V > -- > > ,-~~-.___._. / | ' \ | |--------. Vidhi Zala > ( ) 0 | | | Intel Corp. > \_/-, ,----' | | | School of Computing > ==== !_!-v---v--. Scientific Computing and Imaging Institute > / \-'~; .--------. University of Utah > / __/~| ._-""|| | vidhi.zala(a)utah.edu =( _____|_|____||________| http://sci.utah.edu/people/vidhi.html > > > > ---- > R.M. Kirby > Professor, School of Computing > and Scientific Computing and Imaging Institute > University of Utah > > -- ,-~~-.___._. / | ' \ | |--------. Vidhi Zala ( ) 0 | | | Intel Corp. \_/-, ,----' | | | School of Computing ==== !_!-v---v--. Scientific Computing and Imaging Institute / \-'~; .--------. University of Utah / __/~| ._-""|| | vidhi.zala(a)utah.edu =( _____|_|____||________| http://sci.utah.edu/people/vidhi.html

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Defining complex initial conditions in session files
by Vidhi Zala 07 Jul '22

07 Jul '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 am looking for a way to define initial conditions which contain min() function. Can someone point to an example/syntax for the same? I am currently getting an error saying Message : Equation::Equation() fails on expression [(0.25*(1+cos(PI*min(sqrt(pow(x-bell_x0,2) + pow(y-bell_y0,2))/bell_r0, 1.0))))] Thanks V -- ,-~~-.___._. / | ' \ | |--------. Vidhi Zala ( ) 0 | | | Intel Corp. \_/-, ,----' | | | School of Computing ==== !_!-v---v--. Scientific Computing and Imaging Institute / \-'~; .--------. University of Utah / __/~| ._-""|| | vidhi.zala(a)utah.edu =( _____|_|____||________| http://sci.utah.edu/people/vidhi.html

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Correct approach to add fluid Blowing and/or suction at a Plane Poiseuille Flow wall
by Debbahi Saad 07 Jul '22

07 Jul '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, I use Nektar++ mainly to study time dependent 3D plane Poiseuille flow, using the Incompressible Navier-Stokes Solver (using a fully 3D configuration), I'm wondering what would be the best approach to add Blowin and/or Suction at the wall ? Looking into the user-guide version 5.1.0 section 3.5.1- XML-Session-File>Forcing>Absorption seems to be a usable feature in this context Is there an efficient and suitable approach to add these perturbations to the flow ? Any general guidelines to achieve this are really appreciated, Thanks in advance, Kind regards, Saad

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2D Navier Stokes mesh generation
by 董智康 06 Jul '22

06 Jul '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 learning 2D Navier Stokes equations by using Nektar++, it is a really nice tool! However, I met a problem. I’m not sure how to customize my own 2D mesh, say change the flow domain, radius and position of cylinder. I have read though your tutorials. It seems like I need a CAD .step file to achieve my goal. But I also noticed that Nektar++ can generate meshes of NACA wings. So I’m wondering if I can do the similar things to generate meshes of a cylinder. Best, Zhikang

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