- Nektar-users - imperial.ac.uk

How to monitor the divergence of flow field during iteration
by ztdepyahoo＠163.com 16 Dec '16

16 Dec '16

Dear friends； I want to monitor the divergence of flow field during each time step. how to obtain this. ReGards

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Kinetic energy spectra
by Manuel F. Mejía De Alba 14 Dec '16

14 Dec '16

Dear Nektar users and team, I'm working on the correct "guess" to parameters SVVCutoffRatio and SVVDiffCoeff of the model SVV LES (SpectralVanishingViscosity). I trying to determine the influence of that values on the Kinetic energy spectra. So, I need to get the values of the Kinetic energy as a function of the k (where k = 1:NUMMODES). Using the filter "Modal energy" (user-guide 3.4.9) it is possible to obtain the integral over all the velocity not with of the modes k. It is possible but just with one-dimensional homogeneous expansion and I wanna plot the data on a general model. May anyone gives me a hand with this, any help is appreciated. Thanks in advance, --- Manuel Felipe Mejía De Alba.

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Re: [Nektar-users] Nektar++ questions
by Sherwin, Spencer J 11 Dec '16

11 Dec '16

Dear Hans, Sorry for being so slow in getting back to you. Things are just been a bit busy recently. I am new to Nektar++ and I would like to ask you some questions which I couldn't find in the documentation. - Plotting streamlines: I have been trying to plot streamlines with Paraview; any additional output option must be set in the .xml file? I do not believe so since if yo have the velocity field then the plotting package should be able to work this out. - Adding tracers: is there the possibility to add tracers to the simulations? That is, a way to track particles or groups of them throughout the simulation You should be able to add a passive scalar to the incompressible Navier-Stokes solver. I believe Douglas added this feature recently and am cc’ing him to confirm it is now in the master release (note this is different to the release on the web page which is slightly older). - Probes: is there a way to put probes? i.e. to output the change of certain variables at a particular computational domain's point. Yep we call these history points. Details of this should be in the user-guide. - Iteration curves: is there a way to plot the residuals (velocity's, for example) vs iterations? How to output this? Not quite sure what you require here but if you run with the -v option you can see the number of iterations per time step. - SFD: I would need to have a look at the source where this method is defined but the search option of the doxygen-generated documentation does not work. Which file should I have a look at? You should have a look at the Driver files. There are in the library library/SolverUtils/DriverSteadyState.cpp Also it would be good if you can send these request to the nektar-user list since you may then get more helpful responses from others. Cheers, Spencer. Spencer Sherwin McLaren Racing/Royal Academy of Engineering Research Chair, Professor of Computational Fluid Mechanics, Department of Aeronautics, Imperial College London South Kensington Campus London SW7 2AZ s.sherwin(a)imperial.ac.uk<mailto:s.sherwin@imperial.ac.uk> +44 (0) 20 759 45052

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FieldConvert output fields on GLL points
by F Mellibovsky 08 Dec '16

08 Dec '16

Dear all, Is there some easy way in FieldConvert to write a vtu file with all fields computed on the GLL points instead of on equispaced element sub-meshes? For wall-y+ calculation it is the first GLL point away from the surface that should be checked, rather than the element height, which I think is given. Or when assessing if near-wall gradients are well resolved, it would be better to have fields plotted on a mesh that is representative of the modal resolution used. Thanks.

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Using Nektar for solving compressible flow case
by devabratasahoo＠campus.technion.ac.il 05 Dec '16

05 Dec '16

Hi All, I am trying using Nektar for solving the compressible flow over a cavity at Re - 10^7 per meter. I tried to set the parameters as per the user guide but the solution terminates saying "NaN error found during time integration". Initially, I used structured grid with fine mesh near the walls, but it didn't work. And when I use a coarse structured grid it runs for a while and then terminates saying the same issue. When I tried with a lesser Reynolds no. (0.3x10^7) and a coarse unstructured grid, I worked but had a very bad residual. The tutorials provided by Nektar are all cases of incompressible flow, which works fine. I can't find any examples of using compressible flow solver in the tutorials. Can anyone please give me an example of how to set the parameters and solver info for using compressible flow solver. And what changes in the parameters and solverinfo should be done to solve steady cases of compressible flow in Nektar. Thanking you. Regards, Dev

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Using OpenMP on Nektar Libraries.
by ashok jallepalli 05 Dec '16

05 Dec '16

Hi, I have the following snippet of code and would like to know what I am doing wrong below. Without parallelizing, if this loop look takes 0.01 seconds. When I use k threads, this function is taking k*0.01 seconds. (1) Is there a faster way to evaluate a local expansion at a bunch of points. Or i must assess them 1by1 (2) I tried num threads from k=2 to k=10. This behavior is consistent. always takes (k*0.01). Is this behavior consistent? #pragma omp parallel num_threads(k) for (int i =0 ; i < values.num_elements(); i++) { values[i] = lexp->PhysEvaluate(glCoords.at(i),el_Phys); } // Info lexp is localExpansionShPtr; // num_elements ~21 // In the program, I am replacing k with 2 .. 10 number Ashok.

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Nektar++ 4.3.5 Released
by Chris Cantwell 03 Dec '16

03 Dec '16

Dear all, We are pleased to announce the release of Nektar++ v4.3.5. This release includes a number of further bug fixes and minor enhancements to the 4.3 release: **Library:** - Fix issue with parallel output (!699) - Fix performance issue with iterative full solver (!693) - Fix bug in DG with hybrid meshes (!694) - Enforced precision on history point output (!706) **Documentation** - Update build instructions in user guide for Windows (!692) **Tester** - Fix bug in tester when no parameters specified for test executable (!701) As always, if you encounter any problems please feel free to contact us on the mailing list nektar-users(a)imperial.ac.uk. Cheers, Chris -- Chris Cantwell Imperial College London South Kensington Campus London SW7 2AZ Email: c.cantwell(a)imperial.ac.uk www.imperial.ac.uk/people/c.cantwell

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merging partitions
by Asım Önder 29 Nov '16

29 Nov '16

Dear all, Due to memory limitations, often I have to partition large data files using something like FieldConvert --part-only=100 config.xml fields/field_1.chk , and postprocess them piece by piece: FieldConvert -v -m meanstats config_xml/P000000"$p".xml fields/field_1.chk meanFields/meanField_1_p"$p".fld In the case of meanmode module for example, the output is a collection of many small files associated with partitions, which can be analyzed piece by piece. I was wondering if there is a way to merge the outputs back into one piece again like one piece fld file. Any feedback is appreciated. Thanks, Asim

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Wall bounded incompressible flows: how to set pressure origin?
by F Mellibovsky 28 Nov '16

28 Nov '16

Dear all, I was trying to run a simple lid-driven cavity flow benchmark and I get rather strange results. The drag force on the lid is strongly mesh dependent, there are some numerical issues at the top right corner, the shear stress on the lid has a non-zero wall normal component and the pressure takes awfully large values across the domain. Before bothering you with setup or mesh files I was wandering if not setting a pressure origin somewhere may be causing some kind of trouble. Is it possible to set the pressure to a given value at a point of choice (e.g. p=0 on bottom left corner)? Cheers, Fer Mellibovsky

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Question on mesh partitions for post processing.
by ashok jallepalli 28 Nov '16

28 Nov '16

Hi Everyone, Does any know a smart way to partition to mesh(Nektar XML) file to contain all element in a bounding box? Example: If i have 10x10 element structure mesh on domain of [0,1]x[0,1]. I need to partition the mesh such that, the new partition file has all elements in the region (a,b) to (c,d). Assuming a,b,c,d are in [0,1]. - If there is no command line option for the above scenario, How can I accomplish it using the API? I have tried using the part-only and part-only-overlapping. I am unable to accomplish what I want. Thanks in advance, Ashok.

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