- Nektar-users - imperial.ac.uk

FieldIO changes
by Julia Docampo (MTH) 10 Jul '17

10 Jul '17

Hello: I noticed some changes in the newest nektar version in the FieldIO class (?). This class had the constructor option: LIB_UTILITIES_EXPORT FieldIO(LibUtilities::CommSharedPtr pComm, bool sharedFilesystem = false); However, it is not there in the new one... I have a solver that uses this constructor like this LiibUtilities::FieldIO fIO(vSession->GetComm)) ie, with the default argument false. With the new version, there is no default argument but if I try to force the condition: fIO(vSession->GetComm,false)) I get errors $: cannot declare variable ‘fIO’ to be of abstract type ‘Nektar::LibUtilities::FieldIO’ How can I use this constructor like for the previous version? Thanks - Julia

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a bug in ProcessInterpPointDataToFld
by Ankang Gao 10 Jul '17

10 Jul '17

Hello, ProcessInterpPointDataToFld assigns the coordinates values instead of values of physical quantities when I using it to interpolate a fld from given points set in version 4.4.0 I find it is because line 131 in void Nektar::FieldUtils::ProcessInterpPointDataToFld::Process(po::variables_map & vm) is not right. 131 m_f->m_exp[j]->SetPhys(i, outPts->GetPointVal(j, i)); It should use an offset=outPts->GetDim() when assigning value to m_exp, like the follows m_f->m_exp[j]->SetPhys(i, outPts->GetPointVal(outPts->GetDim()+j, i)); Best wishes Ankang

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Bug during running with Larger Homogeneous Modes
by wasim sarwar 09 Jul '17

09 Jul '17

Hi, I am trying to run 3D simulations in parallel with 1D homogeneous in the span-wise direction. For a certain number of Fourier Modes the simulation runs smoothly, but increasing them beyond some critical value causes an error to pop up, and this error is not related to memory shortage. The cluster in which simulation is being run has the capacity of running 192 processors with 2GB Ram/core in parallel environment. Just to give you an idea, in my case with homogeneous modes 64 things are perfect and increasing them causes simulation to crash giving errors like: Fatal : Level 0 assertion violation Exceeded maximum number of iterations srun: error: s02r2b71: tasks 0-47: Exited with exit code 1 CG iterations made = 5001 using tolerance of 1e-09 (error = -nan, rhs_mag = 1) I would appreciate if someone could suggest something. Best Regards

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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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