July 2019 - Nektar-users - imperial.ac.uk

Element with max CFL
by Vishal Saini 02 Apr '20

02 Apr '20

Hi all, Quick question: Has anyone tried to check the location of a particular element in the mesh? A log file reports the maximum (?) CFL and the corresponding element as: "CFL: 0.0337915 (in elmt 94488)"? Is there a quick way to locate "elmt 94488"? Cheers, Vishal

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Coordinate transformations
by 蒋树杰 15 Sep '19

15 Sep '19

Hi All, I am using the Coordinate transformations for generating the wavy wing.  <FUNCTION NAME="Mapping"> <E VAR="x" VALUE="x - wavyAmplitude/2 * cos(2*PI*z/wavyLambda)" /> </FUNCTION> <MAPPING TYPE="XofZ"> <COORDS>Mapping</COORDS> </MAPPING> When the computation is finished, I use FieldConvert -m mapping wavyWing-aoa12.xml wavyWing-aoa12.fld wavyWing-aoa12.plt to get the result. But in tecplot, I can not see the deformed geometry. The first picture is the slices on y=0. If someone is familiar with this, please no hesitate to contact me. Many thanks for your guys! Shujie University of Southampton

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3DH1D interppoints module
by Guillermo 15 Sep '19

15 Sep '19

Dear all, I have performed a quasi 3D simulation, being the z-axis the homogeneous direction, with an homogeneous length equal to 0.1 (LZ=0.1) and up to 3 Fourier modes (HomModesZ = 4). In that sense, my planes are located at: 0, 0.025, 0.05 and 0.075. I want to interpolate the solution to a series of points, thus I am using the interppoints module. These points are located along the z direction and between the Fourier planes, e.g., z=0.033, 0.066 etc. The output file from the FieldConvert -m interppoints command is quite strange, since each variable is constant along the z direction, and of course, it is not the actual case. I have also tested it for another set of points. In this second test I have changed the z-coordinates and fixed it to the Fourier planes. However, the result is the same as before, constant measure for each variable and with exactly the same value as for the first set of points. So, is the interppoints module implemented for the 3DH1D simulations? I would like to mention that on the user guide, the commands shown for the usage of the interppoints module, except for the first example, they are missing the output "file2.dat". Thank you. Regards, Guillermo

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Homoplane module wavespace output
by Guillermo 01 Aug '19

01 Aug '19

Dear all, I am using the homplane FieldConvert module with the wavespace option , but I do not completely understand the output (fld) result. I have performed a quasi 3D simulation, with up to 3 Fourier modes (HomModesZ = 4). Then, I use the FieldConvert -m homplane:wavespace:planeid=<value> ... command to obtain the Fourier coefficients. I have extracted 4 different planes, i.e. value={0,1,2,3}. I would like to know what is the information contained in the fld output files. Does planeid=0 and planeid=1 correspond to the real and the imaginary parts, respectively, of the Fourier coefficient for the mode 0, and planeid=2 and planeid=3 correspond to the real and the imaginary parts, respectively, of the Fourier coefficient for the mode +-1? Thank you in advance. Regards, Guillermo

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Generating Gaussian random process for velocity boundary conditions
by Akhavan Safaei, Ali 01 Aug '19

01 Aug '19

Hello everyone, I need to generate a velocity boundary condition for IncNavierStokesSolver as a Gaussian random process (in time) in the session file. I know we can use "awgn(sigma)", for example, to generate Gaussain random I.C.; but, I haven't been able to fine a way to extend it to random process B.C. . I would greatly appreciate it if anyone can help me with that. Best, Ali Akhavan-Safaei ---------------------------------------------------------------------------------- Ali Akhavan Safaei, PhD student, Graduate Research Assistant Michigan State University Department of Mechanical Engineering 428 S. Shaw Lane Engineering Bldg., Rm. #4110 East Lansing, MI 48824 Email: akhavans(a)msu.edu akhavans(a)egr.msu.edu ----------------------------------------------------------------------------------

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p adaption for compressible flow solver
by 蒋树杰 23 Jul '19

23 Jul '19

Hi All, I am using Nektar++ compressible flow solver. I noticed the p-adaptive algorithm can be used to optimize the computational cost. I have read the user guide but I still do not know how to perform it. I just add the AdaptiveModes and AdaptiveMinModes in the parameters. The SolverInfo like this: <SOLVERINFO> </SOLVERINFO> I use FieldConver -m nummodes to see the polynomial order distributions. But it seems the polynomial order is not changed in the fields. Does anyone familiar with it? I found a paper in 2013 about an inviscid transonic flow past a NACA0012 airfoil. I think this approach can be done by compressible flow solver. Many thanks for your help! Shujie University of Southampton

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Time-average field can not be used in a quasi 3d simualtion by the compressible solver
by 蒋树杰 18 Jul '19

18 Jul '19

Hi All, I found the time-average field can not be used in a quasi 3d simulation by the compressible solver. it comes with the error: [ubuntu:10117] *** Process received signal *** [ubuntu:10117] Signal: Segmentation fault (11) [ubuntu:10117] Signal code: Address not mapped (1) [ubuntu:10117] Failing at address: 0x208 [ubuntu:10117] [ 0] /lib/x86_64-linux-gnu/libc.so.6(+0x354b0)[0x7f5bcb64d4b0] [ubuntu:10117] [ 1] /home/shujie/nektar++/build/dist/lib64/libSolverUtils.so.5.0.0b(_ZN6Nektar10FieldUtils5Field13AppendExpListEiNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEb+0x74)[0x7f5bce1ac454] [ubuntu:10117] [ 2] /home/shujie/nektar++/build/dist/lib64/libSolverUtils.so.5.0.0b(_ZN6Nektar11SolverUtils18FilterFieldConvert12CreateFieldsERKNS_5ArrayINS_4OneDEKSt10shared_ptrINS_12MultiRegions7ExpListEEEE+0x334)[0x7f5bce1a6254] [ubuntu:10117] [ 3] /home/shujie/nektar++/build/dist/lib64/libSolverUtils.so.5.0.0b(_ZN6Nektar11SolverUtils18FilterFieldConvert11OutputFieldERKNS_5ArrayINS_4OneDEKSt10shared_ptrINS_12MultiRegions7ExpListEEEEi+0xd1)[0x7f5bce1a8641] [ubuntu:10117] [ 4] /home/shujie/nektar++/build/dist/lib64/libSolverUtils.so.5.0.0b(_ZN6Nektar11SolverUtils18FilterFieldConvert8v_UpdateERKNS_5ArrayINS_4OneDEKSt10shared_ptrINS_12MultiRegions7ExpListEEEERKd+0x417)[0x7f5bce1a9337] [ubuntu:10117] [ 5] /home/shujie/nektar++/build/dist/lib64/libSolverUtils.so.5.0.0b(_ZN6Nektar11SolverUtils14UnsteadySystem9v_DoSolveEv+0xddf)[0x7f5bce1bbc2f] [ubuntu:10117] [ 6] /home/shujie/nektar++/build/dist/lib64/libSolverUtils.so.5.0.0b(_ZN6Nektar11SolverUtils14DriverStandard9v_ExecuteERSo+0x8e)[0x7f5bce1724ee] [ubuntu:10117] [ 7] CompressibleFlowSolver(main+0x27d)[0x4798cd] [ubuntu:10117] [ 8] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7f5bcb638830] [ubuntu:10117] [ 9] CompressibleFlowSolver(_start+0x29)[0x4909a9] [ubuntu:10117] *** End of error message *** I put the test file on the attachment. I have tested it in Incompressible flow solver. It is fine. So I think maybe there is a bug in the compressible flow solver. But I am not looking deep into the code. So I can not find the problem. If someone has a solution, please let me. Kind regards, Shujie University of Southampton

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Regarding in FieldConvert
by Abhishek Kumar 16 Jul '19

16 Jul '19

Hi, Is it possible to delete a field from .fld file using FieldCovert? With regards Abhishek -- --------------------------------------------------------------------------------------- Abhishek Kumar Research Associate Centre for Fluid and Complex Systems Coventry University, Coventry CV15FB United Kingdom Webpage: https://abhishekkir.wixsite.com/website Email # ac7600(a)coventry.ac.uk, abhishek.kir(a)gmail.com Phone: +44 24 7765 9150 Mobile: +44 7464026494 ---------------------------------------------------------------------------------------

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y plus
by Vishal Saini 16 Jul '19

16 Jul '19

Hi all, Please, could anyone suggest an easy way to calculate y+ from an *AverageTurbStatsFile.fld* within Nektar++? Would it take into account the true distribution of expansion point locations? BR, Vishal --- *Vishal SAINI*

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Re: [Nektar-users] 答复: About the periodic boundary condition on quasi-3D simulation
by Yan, Zhenguo 09 Jul '19

09 Jul '19

Hi Shujie, I am not very familiar with the usage of NekMesh, but one reason that may lead to negative Jacobian is that the mesh near the wall is too coarse. This means one element cut across large radian and easily leads to negative Jacobian. I believe Joaquim has developed some techniques to tackle with this problem. But the easy solution is to use finer mesh where the curvature is large. I think this is also Gicomo's first suggestion. Best wishes, Zhenguo On 08/07/2019 11:34, Jiang S. wrote: > > Dear Giacomo, > > > I tried to use NekMesh to generate the mesh, there are two problems: > > > 1. 3D deformed Jacobian not positive in some elements; > 2. Periodic composites have a different number of elements; > > > Is there any way to let the periodic surface have the same element number? > > Thanks! > Shujie > ------------------------------------------------------------------------ > *发件人:* Castiglioni, Giacomo <g.castiglioni(a)imperial.ac.uk> > *发送时间:* 2019年7月8日 10:30 > *收件人:* Jiang S.; nektar-users; d.moxey(a)exeter.ac.uk; Yan, Zhenguo > *抄送:* Sherwin, Spencer J > *主题:* Re: About the periodic boundary condition on quasi-3D simulation > > Dear Shujie, > > I have used the peralign module many times with success, so I wonder > if the problem comes from somewhere else. > > > A couple of suggestions: > - I tried to generate the mesh from your .geo file and I think the > mesh is too coarse to get the wavy features resolved (I get several > warnings of this sort "Warning: degenerate tetrahedron") > - with the step file you can generate the mesh directly with NekMesh > without having to use Gmsh. > > Cheers, > > Giacomo > > ------------------------------------------------------------------------ > *From:* Jiang S. <Shujie.Jiang(a)soton.ac.uk> > *Sent:* Monday, July 8, 2019 10:05:24 AM > *To:* Castiglioni, Giacomo; nektar-users; d.moxey(a)exeter.ac.uk; Yan, > Zhenguo > *Cc:* Sherwin, Spencer J > *Subject:* About the periodic boundary condition on quasi-3D simulation > > Hi All, > > > I use Gmsh to generate a mesh for quasi-3D simulation. I want to use > periodic boundary conditions in the 'left' and 'right' side. > > > But the Nektar++ comes with the error: > > Fatal : Level 0 assertion violation > Unable to determine triangle orientation > > So I tried to change the mesh normal direction in Gmsh. Then the same > error comes again. > At last, I tried to use peralign in NekMesh, it generated a new mesh, > but the same error comes again. > > Actually, I tried to change the periodic boundary condition to wall > boundary condition. It runs successfully. > > Is there something wrong with my mesh? > > > Many thanks for your help! > Have a nice day! > Shujie

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