May 2014 - Nek5000-users - mailman3.cels.anl.gov

Re: [Nek5000-users] Object definition for surface integrals
by nek5000-users＠lists.mcs.anl.gov 27 May '14

27 May '14

Dear Prof. Fischer Thanks for the detailed reply. I will use your description and understand the relevant subroutines of navier5.f routine in detail. Regards, Ravi On Mon, May 26, 2014 at 5:39 PM, Ravi Tumkur <ravi.tumkur(a)gmail.com> wrote: > Dean NEK Users, > > I am looking for some sort of help or documentation explaining the object > definitions for evaluating surface integrals. > > My eventual application will be to evaluate the drag and lift forces for > the case of a 2D flow past a cylinder, supported on elastic foundation, > i.e., vortex-induced vibration simulations using NEK5000. > > So far, the examples available in the repository and the NEK mailing list > have enabled me to simulate the motionless cylinder and the case of > cylinder moving with a prescribed motion. > > However, I have hard time decoding the surface integral evaluation in > subroutine "set_obj" available in the "ext_cyl.usr". Overall, I understand > that there is a conditional statement to find all the elements (or element > edges) with "W" boundary condition and then an object is created for each > of those elements. It would be very helpful is someone could point me to a > documentation/help, which gives an explanation for the following functions > or variables which have been used in the "set_obj" subroutine. > > 1. variable "hcode" > 2. variable "lochis" > 3. variable "nhis" > 4. function or variable "cbc" > 5. variable "nmember" > 6. function or variable "object" > > Any hints to understand this subroutine "set_obj" of the example model > "ext_cyl" would be of great help for me to understand and develop the model > for vortex-induced vibration. > > In addition, if there is already an example model to perform > vortex-induced vibration, please let me know. > > Thanks in advance. Any hints and tips are much appreciated. > > Regards, > Ravi > > > -- > Ravi Kumar T R > > University of Illinois at Urbana-Champaign > ph : +1 217 778 7538 > http://lndvl.mechse.illinois.edu/ > -- Ravi Kumar T R University of Illinois at Urbana-Champaign ph : +1 217 778 7538 http://lndvl.mechse.illinois.edu/

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Outflow bc and pressure
by nek5000-users＠lists.mcs.anl.gov 27 May '14

27 May '14

Dear neks When we specify a boundary as outflow "O", I thought we take the normal stress to be zero -p*n + mu*(grad(u) + grad(u)^T)*n = 0 which is a natural boundary condition and where n = normal vector. But it seems that nek sets p=0 on the outflow boundary. So does this mean we on outflow boundary we take both normal stress to be zero and pressure to be zero ? Is it possible to use the normal stress condition without specifying a pressure ? Thanks praveen

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Object definition for surface integrals
by nek5000-users＠lists.mcs.anl.gov 26 May '14

26 May '14

Dean NEK Users, I am looking for some sort of help or documentation explaining the object definitions for evaluating surface integrals. My eventual application will be to evaluate the drag and lift forces for the case of a 2D flow past a cylinder, supported on elastic foundation, i.e., vortex-induced vibration simulations using NEK5000. So far, the examples available in the repository and the NEK mailing list have enabled me to simulate the motionless cylinder and the case of cylinder moving with a prescribed motion. However, I have hard time decoding the surface integral evaluation in subroutine "set_obj" available in the "ext_cyl.usr". Overall, I understand that there is a conditional statement to find all the elements (or element edges) with "W" boundary condition and then an object is created for each of those elements. It would be very helpful is someone could point me to a documentation/help, which gives an explanation for the following functions or variables which have been used in the "set_obj" subroutine. 1. variable "hcode" 2. variable "lochis" 3. variable "nhis" 4. function or variable "cbc" 5. variable "nmember" 6. function or variable "object" Any hints to understand this subroutine "set_obj" of the example model "ext_cyl" would be of great help for me to understand and develop the model for vortex-induced vibration. In addition, if there is already an example model to perform vortex-induced vibration, please let me know. Thanks in advance. Any hints and tips are much appreciated. Regards, Ravi -- Ravi Kumar T R University of Illinois at Urbana-Champaign ph : +1 217 778 7538 http://lndvl.mechse.illinois.edu/

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Solving linearized Navier-Stokes
by nek5000-users＠lists.mcs.anl.gov 24 May '14

24 May '14

Dear neks I want to solve linearized NS about a stationary base flow. Is there an example I can learn from to setup such a simulation ? Thanks praveen

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CVODE and IOFS
by nek5000-users＠lists.mcs.anl.gov 22 May '14

22 May '14

Dear nek5000 team, I have set-up a test case that consist of a free convection of a 2D vortex in a periodic domain. In the initial condition, I have put a line of passive scalars superimposed onto the vortex. If I use the standard solver for temperature and PS (p16 = 0 or 1), everything works fine. My vortex is convected and the line of passive scalars is distorted by the vortex and diffused progressivly. It works well even with IFCHAR= T or F. Perfect. However when I switch to the CVODE solver (p16 = 3) for time integration of temperature and PS, it works only with IFCHAR=F. When IFCHAR is T, my line of passive scalars is not convected by the flow and doesn’t interact with the vortex. Only the progressive diffusion is taken into account. A quick look at the routine makeq.f confirms this behaviour. If IFCHAR is F, the routine convab is called to compute the convective operator, and then the diffusion operator is computed with the call of the routine wlapacian. If IFCHAR is T, only this latter diffusion part is computed. In that case I didn’t find where the convection part is computed. It seems that it is missing. My question is just: is this normal? Why only the diffusion operator is computed when CVODE and IOFS are used together? Is it a bug? Am I missing something in the theory? Than you in advance for your explanations ! Best regards, Emmanuel

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Natural convection, parameters BETAG, GTHETA
by nek5000-users＠lists.mcs.anl.gov 21 May '14

21 May '14

Dear all, we would like to simulate natural convection using the Boussinesq approximation. In the example rayleigh the buoyancy force is implemented in userf, however there are the parameters BETAG and GTHETA, which appear not to be used. Is there any reason for that? Regards, clio

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Nek5000 Users Meeting, Aug. 21-22, Thessaloniki, Greece
by nek5000-users＠lists.mcs.anl.gov 21 May '14

21 May '14

We are pleased to invite you to attend the third Nek5000 User and Development Meeting, to be hosted by the University of Western Macedonia at the Aristotle University Conference Center in Thessaloniki, Greece, August 21-22, 2014. The registration site is now up on the meeting homepage: http://nek5000meeting.web.uowm.gr/ Registration is open until June 30 but please register as soon as possible; there are several optional events that we hope will be of interest to all. Description: The objective of the meeting is to bring developers and users of Nek5000 together to promote collaborative activities, exchange information, and share experiences in using Nek5000 in areas of common interest. The schedule is under development, but we are planning to have technical sessions on Thursday, August. 21 and Friday, August 22, including hands-on sessions in the use of Nek5000 and VisIt. One objective of the meeting is to assist users in defining their simulation problems and to address technical issues that they may face. Attendees are invited to contribute short (15 min.) presentations on their applications of Nek5000. Contributions should consist of an abstract (1-2 pages) and presentation slides. We look forward to your attendance! Sincerely, Nek5000 Development Team

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Regarding Resolution
by nek5000-users＠lists.mcs.anl.gov 21 May '14

21 May '14

Hello Neks, I am running simulation on expansion pipe with perturbation at inlet. with normal mesh of 14000 elements I find turbulence that stays forever inside the pipe at Re = 2000 and it quiet matches with previous articles and numerical study. When I tried to increase the resolution by 25000 elements for the same parameter the turbulence decayed completely and the flow became steady. Even when I increase the polynomial order from N=5 to N=7 the turbulence decays down completely. Could some tell me why I couldn't reproduce the result on a higher mesh resolution ?? Thanks in advance. Best, Kamal

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merging two meshes
by nek5000-users＠lists.mcs.anl.gov 20 May '14

20 May '14

Dear neks I am trying to merge two meshes as in ext_cyl example. Do the two meshes have to have matching grid lines for the merge to work ? Thanks praveen

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Initial condition problem
by nek5000-users＠lists.mcs.anl.gov 16 May '14

16 May '14

Hi, Neks I want to start Nek5000 from an initial condition in Cartesian coordinate which is from other software so it is not fld format. What I need to do to transform my initial condition to fld format. Mu Xu

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