June 2017 - Nektar-users - imperial.ac.uk

Nektar++ transition to C++11
by Chris Cantwell 09 Sep '17

09 Sep '17

Dear all, As part of our ongoing efforts to modernise our codebase, we are planning to transition to the C++11 standard in the near future. A consequence of this is that you will in future require a compiler which supports the C++11 standard (either as an option, such as --std=c++11, or by default). Current versions of popular compilers all fully support the standard, but older compilers may only have partial support. We recommend the following compiler versions to minimise the likelihood of problems going forward: - GCC: 4.8 or later - Clang: 3.3 or later - MSVC: 19.0 or later - Intel: 15.0 or later - PGI: 2015 or later We encourage users to test out support for basic C++11 by compiling the branch 'feature/libutils-c++11' from the code repository and updating build scripts and configuration as necessary. Please let us know if you have any problems or concerns. We will be making the transition after the Nektar++ Workshop in mid-June. Cheers, Nektar++ Development Team

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Calculation on vorticity and other derivative quantities
by BF MA 03 Jul '17

03 Jul '17

Hello everyone, I am using the incompressible solver in Nektar++ for simulating vortex flows around bluff bodies or slender bodies. The results obtained look fine, and the velocity and pressure fields are smooth, but as I exported the results into post-process software, like Tecplot, for calculating vorticity, the vorticity obtained is not smooth. I looked into the reason and found that the vorticity inside each element was calculated separately, so the vorticty values at the boundary between elements are discontinuous. I guess that this should be a special issue existing in spectral element grids, and no this kind of problem exists in finite volume grids. This is also applicable to calculating other derivative quantities, like in Q or lambda2 methods for vortex identification. I'd like to know if there is some approaches to deal with this problem. Otherwise, it is difficult to visualize vortex structures. Many thanks. Baofeng Baofeng Ma, PH.D Associate Professor Institute of Fluid Mechanics School of Aeronautical Science and Engineering Beihang University Email: bf-ma(a)buaa.edu.cn Tel: 0086 (0)10 82338344

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Mesh interpolation issue
by Ismael El Houas Ghouddana 03 Jul '17

03 Jul '17

Dear Nektar development team, I am writing to you in order to communicate some issues which I have experimented,while performing a mesh interpolation with FieldConvert module. I am originally working with a specific mesh, Mesh1, with which I have obtained some results, chk1. Now, I want to redefine this mesh and make it more detailed, so I generated a new mesh, Mesh2, which has the same dimensions and geometry as mesh1, but it is better meshed (more elements). Then, the problem appears when I want to interpolate the solution chk1 to the new mesh, Mesh2. In order to perform this interpolation, I have used the "interpfield" module from FieldConvert. The output file from this operation, file2.fld, is not correct at all, as some incoherent velocities have appeared. Specifically, it appeared extremely high velocities which have no reason to be. In more detail, those velocities are located at some nodes along the boundary of the domain of the solution file2.fld. These high speeds have propagated and blurred a few elements into the domain. The geometry of this boundary is a circumference arc, and its boundary conditions are HOutflow. I also have tried to smooth the file2.fld by using the C0Projection module, file2_C0.fld, but has blurred the velocities only a few. I have attatched some photos from file2_C0.fld showing some of those high velocities on the boundary. Must be noted that file2.fld is quite similar to file2_C0.fld, but less blurred. I remain at your disposal for any doubt or clarification, Ismael El Houas

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Combustion using Nektar++
by Shervin Sammak 30 Jun '17

30 Jun '17

Is there any tutorial (with input files) on combustion simulation using Nektar++? Either with incompressible or compressible solver with simple A+B-->2P? I would appreciate if anyone can help me with this. Thanks, Shervin ----------------------------------------------------------- Shervin Sammak Research Assistant Professor Center for Research Computing University of Pittsburgh 1144 Benedum Hall Pittsburgh, PA 15261, USA E-mail: shervin.sammak(a)pitt.edu ~ You chase quality and quantity will chase you.

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Additional documentation for Nektar
by Guillermo 30 Jun '17

30 Jun '17

Dear Nektar development team, This is a support email request. I have recently learned that Nektar has available some options which are not specified on the user guide. For example, on the "Aerodynamic forces" filter, by using the XML parameters: "Direction1" and "Direction2" one can specify the projection axis direction instead of projecting the forces along the predefined Cartesian axes, but those parameters are not mentioned on the user guide. Thus, I would like to ask you if you could please provide me some resources or references where I can find all this information about special parameters and features. Many thanks in advance. Regards, Guillermo Suarez

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Import flow field from external solver
by wkrusz 30 Jun '17

30 Jun '17

Hello, I'm planning to use Nektar IncNavierStokesSolver for stability analysis of flow around airfoil. I have flow data obtained from Ansys Fluent solver and I'm looking for possibility to transfer it into Nektar flow file. For import mesh data Nektar has NekMesh functionality but for importing flow field data i can't find similar option. Is there is any script or method to prepare .fld file with data obtained from different solvers? Best regards, Witold Krusz

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stability analysis of compressible flows
by juan angel martin 28 Jun '17

28 Jun '17

Dear all, I would like to know if it is possible to use Nektar++ to analyze the stability of a compressible flow. All examples and studies I have found are related to incompressible flows, so I wonder if there is a way of compute the stability of a compressible flow with Nektar++. I have thought if the matrix operators could be extracted from the compressible solver to calculate the eigenvalues, is this possible? Thank you very much for your help. Best regards, Juan.

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Robin bcs with value dependent on other fields
by Vidhi Zala 16 Jun '17

16 Jun '17

Hello all, I have questions about a very specific boundary condition which I am trying to implement. For UnsteadyAdvectionDiffusion case, consider 3 fields - u1,u2 and u3. For u1, I have Robin bc with "Value" dependent on values of u2 and u3. I tried the following: I made the robin bc time dependent in order to force it to evaluate at each timestep. Then to enforce the "Value" part, I have to write solutions for u2 and u3 in a file ".bc" and load it up at each evaluate call for u1's robin bc. I was looking into examples to do this but could only find information about how to make the bcs load from file. The *.bc files in test folder of ADRSolver are compressed versions. It would be helpful if you could point me out to: 1. How to expand the *.bc file from given test examples 2. How to write out solutions for u2 and u3 at each timestep to a .bc file which u1 will utilize in next timestep 3. Is there a better way to do this? Thanks ! -- ,-~~-.___. ._. / | ' \ | |--------. Vidhi Zala ( ) 0 | | | School of Computing \_/-, ,----' | | | Scientific Computing and Imaging Institute ==== !_!-v---v--. University of Utah / \-'~; .--------. / __/~| ._-""|| | vidhi.zala(a)utah.edu =( _____|_|____||________| http://sci.utah.edu/people/vidhi.html

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No convergence in a Compressible Flow Simulation
by Ismael El Houas Ghouddana 15 Jun '17

15 Jun '17

Dear nektar developers, I am working on a supersonic intake for my bachelor degree project. The problem is that the simulation is not able to converge. I want to ask you some advice in order to fix this problem. First of all, your teamate Daniele De Grazia has helped me before, in order to improve the session file. However, the simulation continues being not able to converge. Some data of the session file: -I am studying the problem through the Euler equations. -As boundary conditions, I use far field at the inlet, upper, lower and outlet regions. -I use a non collocated base with a number of points which are the double of the number of modes. Finally, I attach the session file and the last .chk before the simulation blows up,so you can understand better the problem and the conditions that I am using. Kind Regard, Ismael

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GitLab maintenance
by David Moxey 13 Jun '17

13 Jun '17

Hi all, Apologies for the short notice but there are a number of performance and security updates I need to apply to GitLab before tomorrow's workshop. I'm taking it offline briefly to perform an upgrade -- it will be back up in around 30 minutes. Many thanks, Dave

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