[MITgcm-support] periodic boundary conditions in X, walls in Y

Wed Sep 29 13:01:22 EDT 2004

Jeff/Jane,

 Jeff - how big are the overshoots/undershoots and which advection
scheme are you using? With the default centered second order scheme
there can be numerical extrema. These are controlled by using numerical
diffusion with that scheme. There are other advection scheme options
where extrema do not occur, however, these have less well defined
implied diffusion.

 We have a couple of more experienced users doing channel runs. I have
mailed them to see if they would be willing to do a modest amount of
mentoring for you guys. 

Chris

On Tue, 2004-09-28 at 18:01, jeff polton wrote:
> Hi Jane,
> 
> I have been trying similar simulations; zonal periodic channel flow  
> with no slip bcs, zonal wind stress and meridional heating. I guess  
> when you say that you have  "dissipating T" you mean that the  
> temperature field is evolving to values outside the initial field and  
> forcing range. If so then I have also found this problem and supposed  
> it to be a symptom of the 2nd order Adams Bashforth  advection scheme  
> (http://mitgcm.org/sealion/online_documents/node80.html).
> 
> The bad news is that I haven't resolved the problem, so I was hoping  
> that someone with more experience than me would also respond to your  
> email...
> 
> Jeff
> 
> 
> On Sep 24, 2004, at 11:21 AM, Jane Jimeian wrote:
> 
> > i'm resending this message because the first message didn't get posted.
> > i've combined the two:
> >
> > i'm trying to set up a channel where there are perodic boundary  
> > conditions
> > in X and walls in Y.  i doesn't seem to work.  i try running the model  
> > without
> > the using bathyFile='topog.channel' and the results look ok.  when
> > i uses topog.channel then T starts to dissipate.  any suggestions  
> > would be
> > helpful.
> > ----------------------------------------------------------------------- 
> > ----
> > data.pkg
> > ----------------------------------------------------------------------- 
> > ----
> > # Packages
> >  &PACKAGES
> >  useOBCS=.FALSE.,
> >  &
> > ----------------------------------------------------------------------- 
> > ----
> > data
> > ----------------------------------------------------------------------- 
> > ----
> > # ====================
> > # | Model parameters |
> > # ====================
> > #
> > # Continuous equation parameters
> >  &PARM01
> >  tRef= 50*0,
> >  sRef= 50*35.,
> >  viscAz=1.E-4,
> >  viscAh=2.E1,
> >  no_slip_sides=.FALSE.,
> >  no_slip_bottom=.FALSE.,
> >
> >  viscA4=0.E12,
> >  diffKhT=2.E1,
> >  diffKzT=1.E-5,
> >  diffKhS=2.E1,
> >  diffKzS=1.E-5,
> >  f0=1.e-4,
> >  beta=0.E-11,
> >  tAlpha=2.E-4,
> >  sBeta =0.E-4,
> >  gravity=9.81,
> >  gBaro=9.81,
> >  rigidLid=.FALSE.,
> >  implicitFreeSurface=.TRUE.,
> >  eosType='LINEAR',
> >  hFacMin=0.2,
> >  nonHydrostatic=.FALSE.,
> >  readBinaryPrec=64,
> >  globalFiles=.TRUE.,
> >  &
> >
> > # Elliptic solver parameters
> >  &PARM02
> >  cg2dMaxIters=1000,
> >  cg2dTargetResidual=1.E-13,
> >  cg3dMaxIters=400,
> >  cg3dTargetResidual=1.E-13,
> >  &
> >
> > # Time stepping parameters
> >  &PARM03
> >  niter0=0,
> >  nTimeSteps=6048,
> >  deltaT=200.0,
> >  abEps=0.1,
> >  pChkptFreq=604800.0,
> >  chkptFreq=0.0,
> >  dumpFreq=86400.,
> >  monitorFreq=86400.,
> >  &
> >
> > # Gridding parameters
> >  &PARM04
> >  usingCartesianGrid=.TRUE.,
> >  usingSphericalPolarGrid=.FALSE.,
> >  delX=200*5.e3,
> >  delY=50*5.e3,
> >  delZ=50*30,
> >  &
> >
> > # Input datasets
> >  &PARM05
> >  bathyFile='topog.channel',
> >  hydrogThetaFile='theta.bin',
> >  &
> >
> > ----------------------------------------------------------------------- 
> > ----
> > gendata.m
> > ----------------------------------------------------------------------- 
> > ----
> >
> > % This is a matlab script that generates the input data
> >
> > % Dimensions of grid
> > nx=200;
> > ny=50;
> > nz=50;
> > % Nominal depth of model (meters)
> > H=1500;
> > % Scale of bump (m)
> > L=25e3;
> > % Height of bump (m)
> > %dh=0.90*H;
> > % Horizontal resolution (m)
> > dx=5e3;
> > % Rotation
> > f=1e-4;
> > % Stratification
> > N=1.5 * f*L/H;
> >
> > % Gravity
> > g=9.81;
> > % E.O.S.
> > alpha=2.e-4;
> >
> > z=[15:30:1500];
> > dz=30;
> > % dz=H/nz;
> > sprintf('delZ = %d * %7.6g',nz,dz)
> >
> > x=(1:nx)*dx;x=x-mean(x);x=x+nx/3*dx;
> > y=(1:ny)*dx;y=y-mean(y);
> > [Y,X]=meshgrid(y,x);
> > % z=-dz/2:-dz:-H;
> > %z=-(cumsum(dz)-dz/2);
> >
> > % Temperature profile
> > %Tz=N^2/(g*alpha)
> > %phi=sprintf(' %8.6g',Tz*z+sum(Tz*dz)/2);
> > %Tref=str2num(phi);
> > %[sprintf('Tref =') sprintf(' %8.6g,',Tz*z+sum(Tz*dz)/2)]
> >
> > ieee='b';
> > accuracy='real*8';
> >
> > % Create three dimensional temperature profile
> > t3d=zeros(nx,ny,nz);
> > r0=20e3;
> > r2=X.^2 + Y.^2;
> > z0=300;
> > for k=1:nz
> >  t3d(:,:,k)=10-10*z(k)/H;
> >  for i=1:nx
> >  for j=1:ny
> >   if Y(i,j) >= 0
> >    if z(k) >=240
> >      zp=z(k)-240;
> >      fz=(abs(zp)*exp(-abs(zp)/z0))/z0;
> >    else
> >      fz=0;
> >    end
> >   else
> >    if z(k) < 1260
> >      zp=z(k)-1260;
> >      fz=(abs(zp)*exp(-abs(zp)/z0))/z0;
> >    else
> >      fz=0;
> >    end
> >   end
> > %  Tp=fz.*(r0.*Y(i,j)./r0^2).*exp(-r2(i,j)./r0^2).*4.*2.7*2.7;
> >   zp=z(k)-750;
> >   Tp=3.*exp(-zp*zp/300^2);
> >   if r2(i,j) > 2*r0^2
> >     rp=r2(i,j)-2*r0^2;
> >     Tp=Tp*exp(-rp^2/r0^2);
> >   end
> >   t3d(i,j,k)=t3d(i,j,k)+Tp;
> > % t3d(i,j,k)=Tp;
> >  end
> >  end
> > end
> > fid=fopen('theta.bin','w',ieee); fwrite(fid,t3d,accuracy); fclose(fid);
> >
> > % Simple channel
> > h=zeros(nx,ny);
> > %h(:,1)=0;
> > h(:,2:ny-1)=-H;
> > %h(:,ny)=0;
> > fid=fopen('topog.channel','w',ieee); fwrite(fid,h,accuracy);  
> > fclose(fid);
> >
> > -- 
> > _______________________________________________
> > MITgcm-support mailing list
> > MITgcm-support at mitgcm.org
> > http://dev.mitgcm.org/mailman/listinfo/mitgcm-support
> >
> 
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