September 2017 - Nektar-users

how to use HOBC?
by Kurt Sansom 25 Mar '18

25 Mar '18

Hi, I am trying to use the higher order outlet boundary conditions. I know that is formulated for truncated open domains, but am curious if I can use in the following way, where I want to specify the outlet pressure to some value to create back pressure in the system. I realize that for in-compressible flow it doesn't matter that much, but I am interested in implementing a time varying pressure condition at the outlet. I have tried the following boundary condition for a tube and it doesn't appear to apply the VALUE tag? I want to make sure before I file a bug. <REGION REF="2">  <N VAR="u" USERDEFINEDTYPE="HOutflow" VALUE="0" /> <N VAR="v" USERDEFINEDTYPE="HOutflow" VALUE="0" /> <N VAR="w" USERDEFINEDTYPE="HOutflow" VALUE="0" /> <D VAR="p" USERDEFINEDTYPE="HOutflow" VALUE="10665" /></REGION> Regards, ~Kurt -- Kurt Sansom

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where to download the "development guid"
by ztdepyahoo 01 Oct '17

01 Oct '17

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Mixed boundary condition
by Daiane Iglesia Dolci 29 Sep '17

29 Sep '17

Dear all, I need apply a mixed boundary condition of the Robin type. It is possible employ this boundary condition using the Nektar++? Best regards, Daiane I. Dolci

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Mesh interpolation issue
by Guillermo 22 Sep '17

22 Sep '17

Dear Dave, I am writing to you in behalf of Ismael El Houas. I apologize for the delay in the response, but I have been quite busy. I would like to send you the meshes and the resulting chks. However, I prefer to send you only the conflicting regions. My mesh is composed by two composites and fortunately the region where those incoherent velocities have appeared is located in only one of those composites. So I have been trying to extract the mesh for this region using the "4.4.3 Extract surfaces from a mesh" command (from 4.4.0 version): NekMesh -m extract:surf=2,3-5 Mesh.xml output.xml Unfortunately I was unable to extract it. The output.xml file is empty. /:(/ So, is there any option to extract the composite mesh? Thanks, Guillermo S. // / /

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Nektar++ apply in earth EM fields simulation
by 李建凯 22 Sep '17

22 Sep '17

to whom it may concern: sorry to trouble you. I am a PhD student in Ocean University of China. My major is geophysics and research topic is controlled-source marine electromagnetic (CSEM) modeling and inversion. my research interests focus on the electromagnetic numerical simulations. I try to apply the DG method to my research based on your software Nnetar++ platform. The DG method is usually used to time-domain electromagnetic in the papers published. Does the DG method suitable to the frequency-domain electromagnetic problem and is there perfect theory about the DG method in electromagnetic simulation until now ? And does this method suitable to the low frequency electromagnetic (0.01Hz~10Hz) simulation ? Looking forward to your reply. Thank your so much for your time and have a nice day. Best wishes, Jiankai Li

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stabilisation/dealiasing in Compressible solver
by Vishal Saini 18 Sep '17

18 Sep '17

Dear all, I've just started using high-order CFD (using Nektar++). To begin with, I've just been running the Isentropic vortex advection case in a 50x20 domain using the IsentropicVortex test case provided. The issue is that I've continually been observing spurious oscillations (a figure is attached) in velocity field. Increasing the resolution improves the situation a little, but I could not completely get rid of the oscillations. Next, I wanted to use dealiasing. However, the simulations do not even start when I use SVV and SPECTRALHPDEALIASING. Plus, I could not find any stabilization technique implementation in "nektar++-4.4.0/solvers/CompressibleFlowSolver/Utilities" folder (which is the case in Incompressible solver). Can anyone clarify if any dealiasing technique is implemented in Compressible Solver and if there are any future plans on that? Cheers and regards, Vishal --- *Vishal SAINI* Master of Research, University of Cambridge. Master in Turbulence EC Lille, ENSIP and ENSMA France. Contact: vs434(a)cam.ac.uk, vishal.saini.nitj(a)gmail.com <vishal.saini.nitj(a)gmail.com> (+44) 7 459 186 139 (UK) (+33) 7 58 24 84 02 <+33%207%2058%2024%2084%2002> (France)

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Nektar - Mapping
by Guillermo 10 Sep '17

10 Sep '17

Dear all, I am interested about studying the rotational cylinder in free flow (for incompressible flow). Looking around the Nektar's manual I realized that there is an option which, I think, allows to compute it, the MovingBody along with the Mapping (10.6.3 - 10.6.5) from Nektar++'s manual v4.4.0. I am using the example: the CylFlow_Mov_mapping as a reference one. However, I can not completely understand how it works. (I took the example from the 4.3.5 version) First of all, that example is for a rotational cylinder or is it for a cylinder moving up and down on a periodic motion? Tanking into account the first option, The mapping function computes the new coordinates for the specified boundary, However, I do not understand why the function is specified in that way: <FUNCTION NAME="Mapping"> <E VAR="x" VALUE="x" /> <E VAR="y" VALUE="y+A*cos(omega*t)" /> </FUNCTION> The value of the parameter A is not the radius of the cylinder, so it is not deifying a rotation over its center. Also, the new /x/ coordinate is the same as before, so the cylinder just moved upwards or downwards. Secondly, what is the MappingVel functions used for? I think it is used for specify the velocity on the new coordinates. However, the way it is defined, I think, it does not define a new velocity coordinates. What I am misleading? A part from that, I would also compute the aerodynamic forces on the moving surface, so I inserted the following: <FORCE TYPE="MovingBody"> <PARAM NAME="OutputFile">DragLift.frc</PARAM> <PARAM NAME="OutputFrequency">10</PARAM> <PARAM NAME="Boundary"> B[0] </PARAM> </FORCE> and also: <MAPPING TYPE="Translation"> <COORDS>MovingBody</COORDS> <VEL>MappingVel</VEL> </MAPPING> However, the file DragLift.frc is not generated. Hope I have well explained and clarified all my inquiries. Thank you very much, Guillermo Suarez.

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simulation on wall-mounted squared cylinder
by BF MA 10 Sep '17

10 Sep '17

Hi everyone, I am simulating the vortex flow around a squared cylinder mounted a surface using Nektar++ incompressible solver. For this layout (see attached 1), the vortex wakes will become unstable and be shedding as Re >150. However, the current problem is that the computation cannot get the unsteady vortex shedding, it always converges to steady solutions even at Re=500. I even tried giving an incoming disturbance, but the flow fields still cannot converge to vortex shedding. The steady drag coefficients at various Re agree well with the time-averaged results in previous publications, but no vortex shedding occurs. I have simulated the vortex flow past a 2D cylinder, and vortex shedding can be obtained. But for the 3D case, the results are strange. I attached the layout and grid file, and anyone can give some suggestions. 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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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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ADRSolver epsilon value defaults to 1.0
by ashok jallepalli 07 Sep '17

07 Sep '17

Hi All, I am trying to use ADR solver to run unsteady-advection diffusion reaction with epsilon value set to 0.01. But the simulation always defaults to 1.0. I changed epsilon value to 1.0,0.5 0.01. The end result is always the same (as if epsilon=1.0). Please let me know if anyone has encountered this issue or knows how to fix this bug. I have added the script files to reproduce this issue. Cheers, Ashok.

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