August 2019 - Nektar-users

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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Invitation to International Symposium on High-Fidelity Computational Methods & Applications 2019
by Xu, Hui 30 Aug '19

30 Aug '19

Dear Colleagues, We are very pleased to invite you to attend “International Symposium on High-Fidelity Computational Methods & Applications 2019 (ISHFCMA 2019)”, which will take place on 14-16 Dec. 2019 in Shanghai. Honorary Chairs: Jialing Le (Member of CAE), Wenquan Tao (Member of CAS) Chairs: Shiyi Chen (Member of CAS), Spencer J Sherwin (Fellow of the Royal Academy of Engineering) The symposium (International Symposium on High-Fidelity Computational Methods & Applications 2019, ISHFCMA 2019), which will be held in Shanghai, is to enhance deployment and applications of the high-fidelity methods in complex industrial fluid flows. Due to the increasingly stringent precision requirements for industrial designs, these methods have recently attracted great attention. The objective of this symposium is to bring together experts in computational science and experts in engineering application to exchange new ideas and discuss development perspectives of high-fidelity methods. It also offers a platform to show the exciting scientific and engineering study undertaken in this area. The symposium will also end with a Nektar++ workshop to provide a more opportunity to understand how to apply high order spectral/hp element software. The selected papers are recommended to be published in Advances in Aerodynamics, Journal of Hydrodynamics or Acta Aerodynamica Sinica. You can find the exact dates and further information at the webpage https://www.ishfcma.org Your attendance will be greatly appreciated, and your presence will do us great honour. Please let us know as soon as possible but no later than Sept 30 (extended) if you will be able to come to Shanghai. If you need further help for your trip, please feel free to contact us. Sincerely, Hui Xu, Secretary of ISHFCMA 2019 On behalf of ISHFCMA 2019 Committee Email: ishfcma(a)hotmail.com<mailto:ishfcma@hotmail.com> ---------------------------------------------------------------------------- School of Aeronautics and Astronautics Shanghai Jiao Tong University, Shanghai, China

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NekMesh compilation error
by Oliviu Sugar 15 Aug '19

15 Aug '19

Dear all, I get the following error when compiling://usr/lib/x86_64-linux-gnu/libpng16.so.16: undefined reference to `inflateValidate(a)ZLIB_1.2.9' collect2: error: ld returned 1 exit status utilities/NekMesh/CMakeFiles/NekMesh.dir/build.make:1083: recipe for target 'utilities/NekMesh/NekMesh' failed make[2]: *** [utilities/NekMesh/NekMesh] Error 1 CMakeFiles/Makefile2:618: recipe for target 'utilities/NekMesh/CMakeFiles/NekMesh.dir/all' failed make[1]: *** [utilities/NekMesh/CMakeFiles/NekMesh.dir/all] Error 2 Can anyone point me in the right direction about what could be causing this issue? Many thanks, Oliviu

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Mesh Generation
by 蒋树杰 12 Aug '19

12 Aug '19

Hi All, May I ask which software can generate high order quadrilateral mesh for Nektar++ easily? Now I want to use Quasi-3D approach. It seems that only quadrilateral mesh can be used in Quasi-3D approach. I tried to use Gmsh to generate mesh for NACA0002 airfoil. I have an example mesh. But I do not know which software can generate mesh like that. I used to use Gmsh for mesh generation. But for NACA0002 airfoil, it seems it is difficult to generate a good quality quadrilateral mesh. If someone has good ideas, please let me know! Many thanks! Kind regards, Shujie

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Implementation of New User-Defined BC -- CFS
by Eron Tiago V. Dauricio 12 Aug '19

12 Aug '19

Hello everyone, I'm using Nektar for Compressible, Implicit LES simulations (uDNS), and right now I'm studying the code in order to implement Wall Models so I can use it for the WMLES approach (Wall-Modeled LES, opposed to Wall-Resolved). I'll be using only the "Wall-Stress Model" approach, in which the ILES (uDNS) equations are solved in the entire domain and all we need to do to implement the modelling is to feed the LES simulation with a boundary condition on the wall, the wall stress \tau_w -- diffusion portion of the eq., that comes from our model (I'll start with algebraic models). Right now, I intend to use *AdvectionType* as a *3DHomogeneous1D* (FRDG and/or WeakDG), and *DiffustionType* as *LDGNS3DHomogeneous1D*. However, I'm having some trouble in actually finding where to implement the needed boundary condition. I'm following code already implemented, such as the WallViscousBC. As far as I could see, the *CFSBndCond::Apply* function (which calls *v_Apply*) is called only when *DoProjection* method is called on *TimeIntegrationSchemeOperator* object (which, in turn, calls the functor defined previously, in this case *CompressibleFlowSystem::DoOdeProjection* that calls *SetBoundaryConditions*, later calling the *Apply* function.) during *TimeIntegrate* function execution. There, in WallViscousBC case, all that is done is to Negate the velocity in the wall boundary region (pretty much equations 44 & 45 of Mengaldo et al. DOI: 10.2514/6.2014-2923). Then, the diffusion portion of the BC is applied inside the *Diffuse* function call on m_planeDiff obj., which, in this case (of a 3DHomogeneous1D), is of *DiffusionLDGNS* dynamic type. Hence, calling *Diffuse* on m_planeDiff will actually call *DiffusionLDGNS::v_Diffuse*. There, we have a lot of stuff going on, one of which is a call to *v_NumericalFluxO2* which, in turn, calls *v_WeakPenaltyO2*. Inside it, I can see some control flow statements for boundary conditions imposition on 2nd order derivative terms (i.e. the diffusive ones). *The real question is:* Is it in *this* function (v_WeakPenaltyO2) that I need to add my "if-statement" to check whether GetUserDefined() returns the name I've given to my model (say, WallModelLES), and then do the appropriate math? Or should I do it entirely inside *v_Apply* function of my new class (inherited from CFSBndCond, just like WallViscousBC) ? (Just as a reminder: I want to pass a calculated wall stress tensor as BC). I've successfully created an object for my boundary condition already, inheriting from CFSBndCond, and as of my debugging I'm able to instance the appropriate object (checked through std::cout in it's Constructor) when I set USERDEFINEDTYPE="WallModelLES" in the session file. If someone can help me, I'd be really grateful. Also, if is there anyone that has experience with Wall-Modeled LES that can give me any insight or hint about implementing it, I'd be glad to hear. P.S.: In the comments section of both functions that return the flux vector for the NavierStokesCFE Equation System (i.e. v_GetViscousFluxVector and v_GetViscousFluxVectorDeAlias) there is a TODO stating "Complete the viscous flux vector". Should I be concerned about it? I'm sorry for the long post, and I thank you in advance. Best regards, Eron Dauricio Ph.D. Candidate Instituto Tecnológico de Aeronáutica -- ITA, Brazil.

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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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