June 2017 - Nek5000-users - mailman3.cels.anl.gov

Re: [Nek5000-users] Contents of Nek5000-users digest Corner elements giving large values
by nek5000-users＠lists.mcs.anl.gov 06 Jun '17

06 Jun '17

Swarandeep, Another issue that can arise in RBC simulations is poor numerical conditioning due to the non-dimensionalization. The non-dimensional form of the equations used in the Nek5000 examples is based off the conduction scales which result in a very small time-step and large velocities at larger Ra. I don't think you're case is high enough for it to be a problem, but you might try using the "freefall" scales if you aren't already. I suggest consulting the Scheel, Emran and Schumacher paper for some details on running an RBC simulation with Nek5000. Scheel, Janet D., Mohammad S. Emran, and Jörg Schumacher. "Resolving the fine-scale structure in turbulent Rayleigh–Bénard convection." *New Journal of Physics* 15.11 (2013): 113063. Kind Regards, Phil S. On Mon, Jun 5, 2017 at 10:00 AM, <nek5000-users-request(a)lists.mcs.anl.gov> wrote: > Send Nek5000-users mailing list submissions to > nek5000-users(a)lists.mcs.anl.gov > > To subscribe or unsubscribe via the World Wide Web, visit > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > or, via email, send a message with subject or body 'help' to > nek5000-users-request(a)lists.mcs.anl.gov > > You can reach the person managing the list at > nek5000-users-owner(a)lists.mcs.anl.gov > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Nek5000-users digest..." > > > Today's Topics: > > 1. Re: Corner elements giving large values > (nek5000-users(a)lists.mcs.anl.gov) > 2. Re: Corner elements giving large values > (nek5000-users(a)lists.mcs.anl.gov) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Mon, 5 Jun 2017 01:12:39 +0530 > From: nek5000-users(a)lists.mcs.anl.gov > To: nek5000-users(a)lists.mcs.anl.gov > Subject: Re: [Nek5000-users] Corner elements giving large values > Message-ID: > <mailman.7988.1496605362.2967.nek5000-users(a)lists.mcs.anl.gov> > Content-Type: text/plain; charset="UTF-8" > > Hi Nek Forum, Paul > > Thanks for the suggestions. I implemented them. Waiting for the > simulation to be over. > > Another issue I have is that the BC for T at the inner cylinder wall > does not stay at 0 as I have given in userbc. It becomes 0.2 over some > time. > > Thank you > Swarandeep > > > > > > On Fri, Jun 2, 2017 at 10:28 PM, <nek5000-users(a)lists.mcs.anl.gov> wrote: > > > > Hi Swarandeep, > > > > Set p26 in the .rea file to be 0.1 and make certain IFCHAR is F (a few > lines below); > > > > Make certain your dt is positive (param 12) > > > > Paul > > > > ________________________________________ > > From: nek5000-users-bounces(a)lists.mcs.anl.gov [ > nek5000-users-bounces(a)lists.mcs.anl.gov] on behalf of > nek5000-users(a)lists.mcs.anl.gov [nek5000-users(a)lists.mcs.anl.gov] > > Sent: Friday, June 02, 2017 10:31 AM > > To: nek5000-users(a)lists.mcs.anl.gov > > Subject: Re: [Nek5000-users] Corner elements giving large values > > > > Dear Nek Forum, Paul > > > > Yes, I have user defined grid such that the locations of the > > elements are distributed to lie on the chebyshev grid at the top and > > bottom and near the side walls. > > Also please tell which param sets the CFL. > > > > Thank you > > Swarandeep > > > > > > On Fri, Jun 2, 2017 at 8:00 PM, <nek5000-users(a)lists.mcs.anl.gov> > wrote: > >> > >> Dear Swarandeep, > >> > >> Did you refine your element size at the top and bottom and near the > side walls? > >> > >> Please set your CFL to 0.05 in order to get the flow started. > >> > >> Best, > >> > >> > >> Paul > >> > >> ________________________________________ > >> From: nek5000-users-bounces(a)lists.mcs.anl.gov [ > nek5000-users-bounces(a)lists.mcs.anl.gov] on behalf of > nek5000-users(a)lists.mcs.anl.gov [nek5000-users(a)lists.mcs.anl.gov] > >> Sent: Friday, June 02, 2017 1:04 AM > >> To: nek5000-users(a)lists.mcs.anl.gov > >> Subject: Re: [Nek5000-users] Corner elements giving large values > >> > >> Hi Nek Forum, Paul > >> > >> The top and bottom BC are zero heat flux. Please let me n=know > >> how to control the CFL. It is 0.5 in the logfile. I am having no > >> particular difficulty except these corner elements at the junction of > >> inner cylinder and the top/bottom planes. Is there a better way to > >> treat edge boundary elements. Also is it possible to have different > >> order of elements at different locations. > >> > >> Thank you > >> Swarandeep > >> > >> On Fri, Jun 2, 2017 at 12:50 AM, <nek5000-users(a)lists.mcs.anl.gov> > wrote: > >>> > >>> Hi Swarandeep, > >>> > >>> Sorry - I misunderstood. I guess my question was more about the > >>> temperature bcs at the bottom and top of the domain? > >>> > >>> In general, however, there should be no difficulty. What happens > >>> when you reduce your dt ? > >>> > >>> You need to keep the CFL < ~0.5 in general. CFL is printed in the > logfile, > >>> > >>> grep tep logfile > >>> > >>> and you'll see it "C= ....." > >>> > >>> Paul > >>> > >>> > >>> > >>> > >>> ________________________________________ > >>> From: nek5000-users-bounces(a)lists.mcs.anl.gov [ > nek5000-users-bounces(a)lists.mcs.anl.gov] on behalf of > nek5000-users(a)lists.mcs.anl.gov [nek5000-users(a)lists.mcs.anl.gov] > >>> Sent: Thursday, June 01, 2017 1:57 PM > >>> To: nek5000-users(a)lists.mcs.anl.gov > >>> Subject: Re: [Nek5000-users] Corner elements giving large values > >>> > >>> Hi NekForum, Paul > >>> > >>> I intent to have isothermal conditions at the inner and outer > >>> cylinders. The differential heating is achieved by imposing a > >>> temperature difference across the two cylinders. I have used T = 1 and > >>> 0 values for non-dimensional temperature. I think it should be fine. > >>> Do you see any problem here. > >>> > >>> Thank you > >>> Swarandeep > >>> > >>> On Thu, Jun 1, 2017 at 11:28 PM, <nek5000-users(a)lists.mcs.anl.gov> > wrote: > >>>> > >>>> Hi Swarandeep, > >>>> > >>>> Is 0/1 a realistic BC for T ? > >>>> > >>>> Best, > >>>> > >>>> Paul > >>>> > >>>> ________________________________________ > >>>> From: nek5000-users-bounces(a)lists.mcs.anl.gov [ > nek5000-users-bounces(a)lists.mcs.anl.gov] on behalf of > nek5000-users(a)lists.mcs.anl.gov [nek5000-users(a)lists.mcs.anl.gov] > >>>> Sent: Thursday, June 01, 2017 12:53 PM > >>>> To: nek5000-users(a)lists.mcs.anl.gov > >>>> Subject: Re: [Nek5000-users] Corner elements giving large values > >>>> > >>>> Hi Nek Forum, Paul > >>>> > >>>> I am having temp = 1 and temp = 0 at the inner and outer > >>>> boundaries. Gravity is pointing in the -ve z-direction along the axis > >>>> of the > >>>> annulus. The top and bottom planes have zero heat flux > conditions. > >>>> I have Coriolis force added as a body force. > >>>> The Rayleigh number is around 10000. The resolution is 8, 25, > >>>> 24 elements in the r, phi and z directions respectively with order 9. > >>>> My initial condition is very low arbitrary velocity > >>>> perturbation (~10^(-8)). The time resolution is set to 10^(-5) for > >>>> param12. The CFL is > >>>> set to 0.5. Please indicate how to control it. > >>>> > >>>> As you have rightly mentioned, I start the simulation with a > >>>> very low value of the Rayleigh number and gradually increase it. Yet, > >>>> the corner values only get large. Other regions of the domain are > >>>> fine. > >>>> > >>>> Thank you > >>>> Swarandeep > >>>> > >>>> On Thu, Jun 1, 2017 at 7:38 PM, <nek5000-users(a)lists.mcs.anl.gov> > wrote: > >>>>> > >>>>> Hi Swarandeep, > >>>>> > >>>>> How large is your Rayleigh number and what is your resolution? > >>>>> What are your thermal bcs? What are your ICs? > >>>>> > >>>>> There should be no particular issue with your configuration - but > you do need to > >>>>> control spatial and temporal resolution. > >>>>> > >>>>> > >>>>> For RB, you often have to start at low Ra and/or small dt because > the nonlinear > >>>>> response can often drive the velocities to be quite high very > rapidly before the > >>>>> CFL constraint kicks in. RB flows are one of the rare instances > where I use > >>>>> variable time step size (param 12 > 0), but even then you have to > keep the target > >>>>> CFL quite small until the flow is established. > >>>>> > >>>>> hth, > >>>>> > >>>>> Paul > >>>>> > >>>>> ________________________________________ > >>>>> From: nek5000-users-bounces(a)lists.mcs.anl.gov [ > nek5000-users-bounces(a)lists.mcs.anl.gov] on behalf of > nek5000-users(a)lists.mcs.anl.gov [nek5000-users(a)lists.mcs.anl.gov] > >>>>> Sent: Thursday, June 01, 2017 7:27 AM > >>>>> To: nek5000-users(a)lists.mcs.anl.gov > >>>>> Subject: [Nek5000-users] Corner elements giving large values > >>>>> > >>>>> Dear Nek forum, > >>>>> > >>>>> I am simulating Rayleigh Benard flow in a 3D finite > cylindrical annulus. > >>>>> I am getting spurious large values of velocity at the corner > regions > >>>>> of the annulus i.e. the edges where the inner cylinder joins > the > >>>>> top and bottom > >>>>> planes. The boundary condition is no-slip and no penetration > for velocity > >>>>> at these edges. Can someone point out a plausible reason. > >>>>> > >>>>> Thank you > >>>>> Swarandeep > >>>>> _______________________________________________ > >>>>> Nek5000-users mailing list > >>>>> Nek5000-users(a)lists.mcs.anl.gov > >>>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >>>>> _______________________________________________ > >>>>> Nek5000-users mailing list > >>>>> Nek5000-users(a)lists.mcs.anl.gov > >>>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >>>> _______________________________________________ > >>>> Nek5000-users mailing list > >>>> Nek5000-users(a)lists.mcs.anl.gov > >>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >>>> _______________________________________________ > >>>> Nek5000-users mailing list > >>>> Nek5000-users(a)lists.mcs.anl.gov > >>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >>> _______________________________________________ > >>> Nek5000-users mailing list > >>> Nek5000-users(a)lists.mcs.anl.gov > >>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >>> _______________________________________________ > >>> Nek5000-users mailing list > >>> Nek5000-users(a)lists.mcs.anl.gov > >>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >> _______________________________________________ > >> Nek5000-users mailing list > >> Nek5000-users(a)lists.mcs.anl.gov > >> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >> _______________________________________________ > >> Nek5000-users mailing list > >> Nek5000-users(a)lists.mcs.anl.gov > >> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > > _______________________________________________ > > Nek5000-users mailing list > > Nek5000-users(a)lists.mcs.anl.gov > > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > > _______________________________________________ > > Nek5000-users mailing list > > Nek5000-users(a)lists.mcs.anl.gov > > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > > > ------------------------------ > > Message: 2 > Date: Mon, 5 Jun 2017 01:20:04 +0000 > From: nek5000-users(a)lists.mcs.anl.gov > To: "nek5000-users(a)lists.mcs.anl.gov" > <nek5000-users(a)lists.mcs.anl.gov> > Subject: Re: [Nek5000-users] Corner elements giving large values > Message-ID: > <mailman.7989.1496625605.2967.nek5000-users(a)lists.mcs.anl.gov> > Content-Type: text/plain; charset="us-ascii" > > > Swarandeep, > > if you send me your .rea/.usr/SIZE file off-list, I'll take a look. > > Paul > ________________________________________ > From: nek5000-users-bounces(a)lists.mcs.anl.gov [ > nek5000-users-bounces(a)lists.mcs.anl.gov] on behalf of > nek5000-users(a)lists.mcs.anl.gov [nek5000-users(a)lists.mcs.anl.gov] > Sent: Sunday, June 04, 2017 2:42 PM > To: nek5000-users(a)lists.mcs.anl.gov > Subject: Re: [Nek5000-users] Corner elements giving large values > > Hi Nek Forum, Paul > > Thanks for the suggestions. I implemented them. Waiting for the > simulation to be over. > > Another issue I have is that the BC for T at the inner cylinder wall > does not stay at 0 as I have given in userbc. It becomes 0.2 over some > time. > > Thank you > Swarandeep > > > > > > On Fri, Jun 2, 2017 at 10:28 PM, <nek5000-users(a)lists.mcs.anl.gov> wrote: > > > > Hi Swarandeep, > > > > Set p26 in the .rea file to be 0.1 and make certain IFCHAR is F (a few > lines below); > > > > Make certain your dt is positive (param 12) > > > > Paul > > > > ________________________________________ > > From: nek5000-users-bounces(a)lists.mcs.anl.gov [ > nek5000-users-bounces(a)lists.mcs.anl.gov] on behalf of > nek5000-users(a)lists.mcs.anl.gov [nek5000-users(a)lists.mcs.anl.gov] > > Sent: Friday, June 02, 2017 10:31 AM > > To: nek5000-users(a)lists.mcs.anl.gov > > Subject: Re: [Nek5000-users] Corner elements giving large values > > > > Dear Nek Forum, Paul > > > > Yes, I have user defined grid such that the locations of the > > elements are distributed to lie on the chebyshev grid at the top and > > bottom and near the side walls. > > Also please tell which param sets the CFL. > > > > Thank you > > Swarandeep > > > > > > On Fri, Jun 2, 2017 at 8:00 PM, <nek5000-users(a)lists.mcs.anl.gov> > wrote: > >> > >> Dear Swarandeep, > >> > >> Did you refine your element size at the top and bottom and near the > side walls? > >> > >> Please set your CFL to 0.05 in order to get the flow started. > >> > >> Best, > >> > >> > >> Paul > >> > >> ________________________________________ > >> From: nek5000-users-bounces(a)lists.mcs.anl.gov [ > nek5000-users-bounces(a)lists.mcs.anl.gov] on behalf of > nek5000-users(a)lists.mcs.anl.gov [nek5000-users(a)lists.mcs.anl.gov] > >> Sent: Friday, June 02, 2017 1:04 AM > >> To: nek5000-users(a)lists.mcs.anl.gov > >> Subject: Re: [Nek5000-users] Corner elements giving large values > >> > >> Hi Nek Forum, Paul > >> > >> The top and bottom BC are zero heat flux. Please let me n=know > >> how to control the CFL. It is 0.5 in the logfile. I am having no > >> particular difficulty except these corner elements at the junction of > >> inner cylinder and the top/bottom planes. Is there a better way to > >> treat edge boundary elements. Also is it possible to have different > >> order of elements at different locations. > >> > >> Thank you > >> Swarandeep > >> > >> On Fri, Jun 2, 2017 at 12:50 AM, <nek5000-users(a)lists.mcs.anl.gov> > wrote: > >>> > >>> Hi Swarandeep, > >>> > >>> Sorry - I misunderstood. I guess my question was more about the > >>> temperature bcs at the bottom and top of the domain? > >>> > >>> In general, however, there should be no difficulty. What happens > >>> when you reduce your dt ? > >>> > >>> You need to keep the CFL < ~0.5 in general. CFL is printed in the > logfile, > >>> > >>> grep tep logfile > >>> > >>> and you'll see it "C= ....." > >>> > >>> Paul > >>> > >>> > >>> > >>> > >>> ________________________________________ > >>> From: nek5000-users-bounces(a)lists.mcs.anl.gov [ > nek5000-users-bounces(a)lists.mcs.anl.gov] on behalf of > nek5000-users(a)lists.mcs.anl.gov [nek5000-users(a)lists.mcs.anl.gov] > >>> Sent: Thursday, June 01, 2017 1:57 PM > >>> To: nek5000-users(a)lists.mcs.anl.gov > >>> Subject: Re: [Nek5000-users] Corner elements giving large values > >>> > >>> Hi NekForum, Paul > >>> > >>> I intent to have isothermal conditions at the inner and outer > >>> cylinders. The differential heating is achieved by imposing a > >>> temperature difference across the two cylinders. I have used T = 1 and > >>> 0 values for non-dimensional temperature. I think it should be fine. > >>> Do you see any problem here. > >>> > >>> Thank you > >>> Swarandeep > >>> > >>> On Thu, Jun 1, 2017 at 11:28 PM, <nek5000-users(a)lists.mcs.anl.gov> > wrote: > >>>> > >>>> Hi Swarandeep, > >>>> > >>>> Is 0/1 a realistic BC for T ? > >>>> > >>>> Best, > >>>> > >>>> Paul > >>>> > >>>> ________________________________________ > >>>> From: nek5000-users-bounces(a)lists.mcs.anl.gov [ > nek5000-users-bounces(a)lists.mcs.anl.gov] on behalf of > nek5000-users(a)lists.mcs.anl.gov [nek5000-users(a)lists.mcs.anl.gov] > >>>> Sent: Thursday, June 01, 2017 12:53 PM > >>>> To: nek5000-users(a)lists.mcs.anl.gov > >>>> Subject: Re: [Nek5000-users] Corner elements giving large values > >>>> > >>>> Hi Nek Forum, Paul > >>>> > >>>> I am having temp = 1 and temp = 0 at the inner and outer > >>>> boundaries. Gravity is pointing in the -ve z-direction along the axis > >>>> of the > >>>> annulus. The top and bottom planes have zero heat flux > conditions. > >>>> I have Coriolis force added as a body force. > >>>> The Rayleigh number is around 10000. The resolution is 8, 25, > >>>> 24 elements in the r, phi and z directions respectively with order 9. > >>>> My initial condition is very low arbitrary velocity > >>>> perturbation (~10^(-8)). The time resolution is set to 10^(-5) for > >>>> param12. The CFL is > >>>> set to 0.5. Please indicate how to control it. > >>>> > >>>> As you have rightly mentioned, I start the simulation with a > >>>> very low value of the Rayleigh number and gradually increase it. Yet, > >>>> the corner values only get large. Other regions of the domain are > >>>> fine. > >>>> > >>>> Thank you > >>>> Swarandeep > >>>> > >>>> On Thu, Jun 1, 2017 at 7:38 PM, <nek5000-users(a)lists.mcs.anl.gov> > wrote: > >>>>> > >>>>> Hi Swarandeep, > >>>>> > >>>>> How large is your Rayleigh number and what is your resolution? > >>>>> What are your thermal bcs? What are your ICs? > >>>>> > >>>>> There should be no particular issue with your configuration - but > you do need to > >>>>> control spatial and temporal resolution. > >>>>> > >>>>> > >>>>> For RB, you often have to start at low Ra and/or small dt because > the nonlinear > >>>>> response can often drive the velocities to be quite high very > rapidly before the > >>>>> CFL constraint kicks in. RB flows are one of the rare instances > where I use > >>>>> variable time step size (param 12 > 0), but even then you have to > keep the target > >>>>> CFL quite small until the flow is established. > >>>>> > >>>>> hth, > >>>>> > >>>>> Paul > >>>>> > >>>>> ________________________________________ > >>>>> From: nek5000-users-bounces(a)lists.mcs.anl.gov [ > nek5000-users-bounces(a)lists.mcs.anl.gov] on behalf of > nek5000-users(a)lists.mcs.anl.gov [nek5000-users(a)lists.mcs.anl.gov] > >>>>> Sent: Thursday, June 01, 2017 7:27 AM > >>>>> To: nek5000-users(a)lists.mcs.anl.gov > >>>>> Subject: [Nek5000-users] Corner elements giving large values > >>>>> > >>>>> Dear Nek forum, > >>>>> > >>>>> I am simulating Rayleigh Benard flow in a 3D finite > cylindrical annulus. > >>>>> I am getting spurious large values of velocity at the corner > regions > >>>>> of the annulus i.e. the edges where the inner cylinder joins > the > >>>>> top and bottom > >>>>> planes. The boundary condition is no-slip and no penetration > for velocity > >>>>> at these edges. Can someone point out a plausible reason. > >>>>> > >>>>> Thank you > >>>>> Swarandeep > >>>>> _______________________________________________ > >>>>> Nek5000-users mailing list > >>>>> Nek5000-users(a)lists.mcs.anl.gov > >>>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >>>>> _______________________________________________ > >>>>> Nek5000-users mailing list > >>>>> Nek5000-users(a)lists.mcs.anl.gov > >>>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >>>> _______________________________________________ > >>>> Nek5000-users mailing list > >>>> Nek5000-users(a)lists.mcs.anl.gov > >>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >>>> _______________________________________________ > >>>> Nek5000-users mailing list > >>>> Nek5000-users(a)lists.mcs.anl.gov > >>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >>> _______________________________________________ > >>> Nek5000-users mailing list > >>> Nek5000-users(a)lists.mcs.anl.gov > >>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >>> _______________________________________________ > >>> Nek5000-users mailing list > >>> Nek5000-users(a)lists.mcs.anl.gov > >>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >> _______________________________________________ > >> Nek5000-users mailing list > >> Nek5000-users(a)lists.mcs.anl.gov > >> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > >> _______________________________________________ > >> Nek5000-users mailing list > >> Nek5000-users(a)lists.mcs.anl.gov > >> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > > _______________________________________________ > > Nek5000-users mailing list > > Nek5000-users(a)lists.mcs.anl.gov > > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > > _______________________________________________ > > Nek5000-users mailing list > > Nek5000-users(a)lists.mcs.anl.gov > > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > _______________________________________________ > Nek5000-users mailing list > Nek5000-users(a)lists.mcs.anl.gov > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > > > ------------------------------ > > _______________________________________________ > Nek5000-users mailing list > Nek5000-users(a)lists.mcs.anl.gov > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > > > End of Nek5000-users Digest, Vol 100, Issue 4 > ********************************************* > -- Phil Sakievich Post Doctoral Research Associate - Mechanical and Aerospace Engineering Arizona State University - Ira A. Fulton School for Engineering of Matter Transport and Energy Tempe, Arizona

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Corner elements giving large values
by nek5000-users＠lists.mcs.anl.gov 04 Jun '17

04 Jun '17

Dear Nek forum, I am simulating Rayleigh Benard flow in a 3D finite cylindrical annulus. I am getting spurious large values of velocity at the corner regions of the annulus i.e. the edges where the inner cylinder joins the top and bottom planes. The boundary condition is no-slip and no penetration for velocity at these edges. Can someone point out a plausible reason. Thank you Swarandeep

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Read file without using load_fld nor mfi subroutines
by nek5000-users＠lists.mcs.anl.gov 01 Jun '17

01 Jun '17

Hi Neks, I may have a problem when I'm trying to read velocity field (only velocity field, I don't need pressure.) so I can assign specific boundary conditions using userbc(). My questions are : 1) Is it possible to read velocity fields in nek that are contained in .f000* files without modifying the pressure "pr" nor the velocity fields "vx,vy,vz" ? 2) Is there any subroutine (besides load_fld or mfi) that would allow me to read .f000* files? When I use the mfi (in ic.f) subroutine, it looks like the pressure field is modified and hence I'm quickly running into errors like the following: 100 **ERROR**: Failed in HMHOLTZ: VELX NaN NaN 1.0000E-12. If I use load_fld() I seem to me going back to the initial conditions. Thank you for your help, Arnold

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