December 2012 - Nek5000-users - mailman3.cels.anl.gov

Probability Density Function
by nek5000-users＠lists.mcs.anl.gov 17 Dec '12

17 Dec '12

Dear Neks, I want to calculate the probability density function of a scalar field ff in the attached subroutine. Since the element mesh is nonuniform I have to assign a weight "wght" with each grid point of ff. The weight is given by the volume of the associated grid cell. Coordinates of x,y,z of all vertices (primary and secondary nodes) are stored in xm1,ym1,zm1 as far as I know. This weight turns out to have in parts negative values which is unphysical. What went wrong? subroutine pdf_calc(ff,step,i_offset,i_name) include 'SIZE' include 'TOTAL' parameter(npdf=501) real ff(lx1,ly1,lz1,lelt) real pdf(npdf) real work(npdf) real val, vol, offset, wght integer e,eg,ex,ey,ez,f !-----Set arrays to zero call rzero(pdf,npdf) call rzero(work,npdf) !-----Offset if(i_offset==0) offset=0.0 if(i_offset==1) offset=int(npdf/2)*step !-----Pick face 5 f = 5 vol=atan(1.0) do e=1,nelv do k=1,nz1 do j=1,ny1 do i=1,nx1 wght= (zm1(i,j,k+1,e)-zm1(i,j,k,e)) * area(i,j,f,e) mpi_allreduce) call gop(pdf,work,'+ ',npdf) !------------------------------------------------------------ if(nid.eq.0)then if(i_name.eq.1)OPEN(10,file="pdf_uzte.dat",position="append") if(i_name.eq.2)OPEN(10,file="pdf_epst.dat",position="append") if(i_name.eq.3)OPEN(10,file="pdf_epsv.dat",position="append") if(i_name.eq.4)OPEN(10,file="pdf_temp.dat",position="append") if(i_name.eq.5)OPEN(10,file="pdf_dtdz.dat",position="append") do ipdf=1,npdf write(10,*) (ipdf-1)*step-offset, pdf(ipdf) enddo CLOSE(10) endif return end Thanks in advance and best wishes, Joerg. ---------------------------------------------------- Joerg Schumacher Heisenberg Professor for Theoretical Fluid Mechanics Institute of Thermodynamics and Fluid Mechanics Department of Mechanical Engineering Ilmenau University of Technology P.O. Box 100565 D-98684 Ilmenau Germany E-mail: joerg.schumacher(a)tu-ilmenau.de http://www.tu-ilmenau.de/tsm Phone: +49-3677-69-2428 Fax: +49-3677-69-2411

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3-D Taylor-Green problem
by nek5000-users＠lists.mcs.anl.gov 12 Dec '12

12 Dec '12

Hi I made the 28^3 computation without filter and all results are plotted together. The KE is well predicted even on the coarse mesh. The dissipation rate did not seem to change much with/without filtering on 28^3 mesh. I will try with more elements to see if the results improve and compare with Brachet et al. Thanks praveen On Sun, Dec 9, 2012 at 9:45 PM, <nek5000-users(a)lists.mcs.anl.gov> wrote: > Hi Praveen > > Filtering removes energy at the small scales (small length scales/high > frequency components) > If you estimate the turbulent kinetic energy removed by the filtering and > compare it to the resolved kinetic energy or the total (resolved+subgrid > scale) > then your simulation : > > (1) May be considered DNS ; if the above ratio is small > (2) LES if it is relatively big > > in (2) the hope is that subgrid scale motion does not affect the scales of > interest in a given problem. > > Filtering stabilizes simulations since it provides a way for removing > energy at the small unresolved scales. I ran turbulent wake simulations in > the past > where filtering was absolutely necessary and the argument was that it did > not affect the scales of interest. > > So the bottomline is you need to at least be aware of what scales are > impacted by filtering and if indeed you are interested in such scales. That > is why > you see some comparisons in the paper for a given case with different > values of the filtering parameter. > > so let me know what happens when 32^3 is run with f=0 and also the > comparison to Brachet et al. > > Ammar >

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3-D Taylor-Green problem
by nek5000-users＠lists.mcs.anl.gov 09 Dec '12

09 Dec '12

Hello I am solving the 3-D Taylor-Green problem as described here http://www.dlr.de/as/desktopdefault.aspx/tabid-8170/13999_read-35550/ C3.5 Direct Numerical Simulation of the Taylor-Green Vortex at Re = 1600<http://www.as.dlr.de/hiocfd/case_c3.5.pdf> using NEK. I use lx1 = 10 lx2 = lx1-2 ldx = 15 No of elements = 14^3 or 28^3 The evolution of dissipation rate with time is shown in attached pdf. f=0.0 indicates no filtering and f=0.05 means filter parameter P103. Use of filter seems to capture peak dissipation rate better but still some difference is seen. The DG results with similar number of dofs in the problem description give good estimate of peak rate. So I expect NEK results to improve further and would like to ask for any advice. Should I try with larger amount of filtering ? I have attached my SIZE and rea files. Thanks praveen

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Re: [Nek5000-users] Traveling gravity waves
by nek5000-users＠lists.mcs.anl.gov 07 Dec '12

07 Dec '12

I am not an expert on surface waves but just wondering if you are initializing with one wave component such as this? [image: \eta\, =\, a\, \cos\, ( k x\, -\, \omega t ).]My understanding is you should have multiple components to see something interesting. This can be simply achieved by modulating the above form by a spatial localization function such as exp(-(x-x0)2) or add other components such as a1 cos(kx...)+ a2 cos(2kx...)+...etc Ammar On Thu, Dec 6, 2012 at 6:38 AM, <nek5000-users(a)lists.mcs.anl.gov> wrote: > Hi Neks, > > I am trying to set up a traveling gravity wave and started from the > std.wv example. > > - In the useric I prescribed the the Initial velocity by using linear > wave theory (Airy) > > > http://en.wikipedia.org/wiki/Airy_wave_theory#Solution_for_a_progressive_mo… > wave amplitude > - the initial mesh was generate with genbox with periodic sides, bottom > wall and a free surface > - the surface tension was excluded by setting sigma & We = 0 > - reverted density & viscosity to dimensional variables (SI Units) in > the .rea to get correct velocities > - set the gravitational force in userf ffy = -9.81*param(1) > > But instead of a traveling wave the system reverts to a sort of standing > wave immediately > > Do I have set the initial velocity of the moving mesh as well? And if so > are wx,wy the correct variables to do so? > Did I apply the dimensions correctly? > > I attached the .rea & .usr, any help with my Problem would be greatly > appreciated. > > Thanks > Arne > > _______________________________________________ > Nek5000-users mailing list > Nek5000-users(a)lists.mcs.anl.gov > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > > -- http://aelghany.googlepages.com/home

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Traveling gravity waves
by nek5000-users＠lists.mcs.anl.gov 06 Dec '12

06 Dec '12

Hi Neks, I am trying to set up a traveling gravity wave and started from the std.wv example. - In the useric I prescribed the the Initial velocity by using linear wave theory (Airy) http://en.wikipedia.org/wiki/Airy_wave_theory#Solution_for_a_progressive_mo… wave amplitude - the initial mesh was generate with genbox with periodic sides, bottom wall and a free surface - the surface tension was excluded by setting sigma & We = 0 - reverted density & viscosity to dimensional variables (SI Units) in the .rea to get correct velocities - set the gravitational force in userf ffy = -9.81*param(1) But instead of a traveling wave the system reverts to a sort of standing wave immediately Do I have set the initial velocity of the moving mesh as well? And if so are wx,wy the correct variables to do so? Did I apply the dimensions correctly? I attached the .rea & .usr, any help with my Problem would be greatly appreciated. Thanks Arne

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How to use the linearised solver with a base flow
by nek5000-users＠lists.mcs.anl.gov 05 Dec '12

05 Dec '12

Dear All How to use the linearised NS solver with a base flow? Could someone can give me an example? Thanks very much. Hui

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Computing total kinetic energy
by nek5000-users＠lists.mcs.anl.gov 04 Dec '12

04 Dec '12

Hello I use following code to compute total kinetic energy in the domain inside userchk c Compute total kinetic energy if(mod(istep,10).eq.0)then n = nx1*ny1*nz1*nelv xke = glsc3(vx, vx, bm1, n) yke = glsc3(vy, vy, bm1, n) zke = glsc3(vz, vz, bm1, n) total_ke = 0.5*(xke + yke + zke) if(nid.eq.0) write(6,1) istep, time, total_ke 1 format(i6,1p2e14.6,' Totalke') endif Is this correct ? Does this account for the parallel computation or do I need to do something extra to gather from other processes ? Thanks praveen

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