Getting started

$ \renewcommand{\vec}[1]{ {\bf #1} } \newcommand{\bnabla}{ \vec{\nabla} } \newcommand{\Rey}{Re} \def\vechat#1{ \hat{ \vec{#1} } } \def\mat#1{#1} $

Overview of files

• Makefile is likely to require modification for your compiler and libraries (see #Libraries). It has been set up for gfortran, but compile flags for several compilers (g95, gfortran, ifort, pathf90, pgf90) can be found at the top of the file.
• parallel.h Ensure _Nr and _Ns are both set to 1 if you do not have MPI. This file contains macros for parallelisation that are only invoked if the number of processes _Np=_Nr*_Ns is greater than 1. Unless you need many cores, it is easier to vary _Nr only, keep _Ns=1 .
• program/parameters.f90. Reynolds number, resolution, timestep, etc. See #Parameters
• utils/ contains a number of utilities. Almost anything can be done in a util, both post-processing and analysing data at runtime. There should be no need to alter the core code. See #Making_utils
• matlab/, a few scripts. See matlab/Readme.txt .

Libraries

The code uses freely availably libraries LAPACK, netCDF and FFTW3.

Take a look at Makefile. The compiler and flags will probably need editing first. There are suggested flags for several compilers at the top of this file.

In the openpipeflow directory, try make and look for errors indicating missing libraries

> make
...
Fatal Error: Can't open module file 'netcdf.mod'
/usr/bin/ld: cannot find -llapack
/usr/bin/ld: cannot find -lfftw3

Precompiled binaries

If using a linux environment, try installing the LAPACK, FFTW3 and netCDF packages with your package manager or 'software center'.

For netCDF, find the location of netcdf.mod

:~> cd /
:/> ls */netcdf.mod 
:/> ls */*/netcdf.mod
/usr/include/netcdf.mod 

and that it is in the include path in Makefile, e.g. -I/usr/include

Often the package manager supplies several versions of a package, distinguished by extra extensions. If a library has been installed but is not found, then search for the library, e.g.

:/> ls  */*/liblapack*  */*/*/libfftw3*
etc/alternatives/liblapack.so.3
etc/alternatives/liblapack.so.3gf
usr/lib/i386-linux-gnu/libfftw3_omp.so.3
usr/lib/i386-linux-gnu/libfftw3_omp.so.3.3.2
usr/lib/i386-linux-gnu/libfftw3.so.3
usr/lib/i386-linux-gnu/libfftw3.so.3.3.2

Next create symbolic links to one of the versions,

:~> mkdir /home/ash/lib 
:~> ln -s /etc/alternatives/liblapack.so.3 /home/ash/lib/liblapack.so
:~> ln -s /usr/lib/i386-linux-gnu/libfftw3.so.3 /home/ash/lib/libfftw3.so

and ensure that they are in the link path, e.g. -L/home/ash/lib

Note: Some extra libraries might be needed, depending on compiler/distribution. Try simply omitting the link flags -lblas and/or -lcurl at first, for example.

Compiling libraries

If it is not possible to link with precompiled libraries, or if special flags are necessary, e.g. for a very large memory model, then it may be necessary to build LAPACK and NetCDF with the compiler and compile flags that will be used for the main simulation code.

The default procedure for building a package (applicable to FFTW3 and netCDF) is

tar -xvvzf package.tar.gz
cd package/
[set environment variables if necessary]
./configure --prefix=<path>
make
make install

– FFTW3. This usually requires no special treatment. Install with your package manager or build with the default settings.

– LAPACK. If using gfortran you might be able to use the binary version supplied for your linux distribution. Otherwise, edit the file make.inc that comes with LAPACK, setting the fortran compiler and flags to those you plan to use. Type ‘make’. Once finished, copy the following binaries into your library path (see Makefile LIBS -L$<$path$>$/lib/)
cp lapack.a <path>/lib/liblapack.a
cp blas.a <path>/lib/libblas.a

– netCDF. If using gfortran you might be able to use the supplied binary version for your linux distribution. Several versions can be found at http://www.unidata.ucar.edu/downloads/netcdf/current/index.jsp. Version 4.1.3 is relatively straight forward to install, the following typical environment variables required to build netCDF should be sufficient:
CXX=""
FC=/opt/intel/fc/10.1.018/bin/ifort
FFLAGS="-O3 -mcmodel=medium"
export CXX FC FFLAGS
After building, ensure that files netcdf.mod and typesizes.mod appear in your include path (see Makefile COMPFLAGS -I$<$path$>$/include/).

netCDF installation is slightly trickier for more recent versions, currently netcdf-4.3.0.tar.gz [2015-07-20]. First
./configure --disable-netcdf-4 --prefix-<path>
which disables HDF5 support (not currently required, see comment on Parallel_i/o). Also, Fortran is no longer bundled, so get netcdf-fortran-4.2.2.tar.gz or a more recent version from here
http://www.unidata.ucar.edu/downloads/netcdf/index.jsp
Build with the environment variables above, and in addition
CPPFLAGS=-I<path>/include
export CPPFLAGS
Finally, add the link flag -lnetcdff immediately before -lnetcdf in your Makefile.

Parameters

./parallel.h:
_Nr split in radius
_Ns split axially
Number of processors is _Np=_Nr*_Ns.

Set both _Nr and _Nr to 1 for serial use. MPI not required in that case.

Unless a large number of cores is required, it is recommended to vary only _Nr and to keep _Ns=1, i.e. split radially only. Prior to openpipeflow-1.10, only _Np was available, equivalent to the current _Nr.

_Nr is 'optimal' if it is a divisor of i_N or only slightly larger than a divisor. To keep code simple, _Ns must divide both i_Z and i_M parameters below (easier to leave _Ns=1 if not needed).

./program/parameters.f90:

i_N	Number of radial points $n\in[1,N]$
i_K	Maximum k (axial), $k\in(-K,\,K)$
i_M	Maximum m (azimuthal), $m\in[0,\,M)$
i_Mp	Azimuthal periodicity, i.e. $m=0,M_p,2M_p,\dots,(M-1)M_p$
	(set =1 for no symmetry assumption)
d_Re	Reynolds number $Re$ or $Rm_m$
d_alpha	Axial wavenumber $\alpha=2\pi/L_z$
b_const_flux	Enforce constant flux $U_b=\frac1{2}$.
i_save_rate1	Save frequency for snapshot data files
i_save_rate2	Save frequency for time-series data
i_maxtstep	Maximum number of timesteps (no limit if set =-1)
d_cpuhours	Maximum number of cpu hours
d_time	Start time (taken from state.cdf.in if set =-1d0)
d_timestep	Fixed timestep (typically =0.01d0 or dynamically controlled if set =-1d0)
d_dterr	Maximum corrector norm, $\|f_{corr}\|$ (typically =1d-5 or set =1d1 to avoid extra corrector iterations)
d_courant	Courant number $\mathrm{C}$ (unlikely to need changing)
d_implicit	Implicitness $c$ (unlikely to need changing)

Note the default cases, usually if the parameter is set to -1.

Input files

State files are stored in the NetCDF data format are binary yet can be transferred across different architectures safely. The program main.out runs with the compiled parameters (see main.info) but will load states of other truncations. For example, an output state file state0018.cdf.dat can be copied to an input state.cdf.in, and when loaded it will be interpolated if necessary.

Sample initial conditions are available in the Database.

state.cdf.in:
$t$ – Start time. Overridden by d_time if d_time$\ge$0
$\Delta t$ – Timestep. Ignored, see parameter d_timestep.
$N, M_p, r_n$ – Number of radial points, azimuthal periodicity, radial values of the input state.
– If the input radial points differ from the runtime points, then the fields are interpolated onto the new points automatically.
$u_r,\,u_\theta,\, u_z$ – Field vectors.
– If $K\ne\,$i_K or $M\ne\,$i_M, then Fourier modes are truncated or zeros appended.

Output

Snapshot data

Data saved every i_save_rate1 timesteps:

   state????.cdf.dat
   vel_spec????.dat

All output is sent to the current directory, and ???? indicates numbers 0000, 0001, 0002,…. Each state file can be copied to a state.cdf.in should a restart be necessary. To list times $t$ for each saved state file,
> grep state OUT
The spectrum files are overwritten each save as they are retrievable from the state data. To verify sufficient truncation, a quick profile of the energy spectrum can be plotted with
gnuplot> set log
gnuplot> plot 'vel_spec0002.dat' w lp

Time-series data

Data saved every i_save_rate2 timesteps:

tim_step.dat	$t$, $\Delta t$, $\Delta t_{\|f\|}$, $\Delta t_{CFL}$	current and limiting step sizes
vel_energy.dat	$t$, $E$, $E_{k=0}$, $E_{m=0}$	energies. $E-E_{k=0}=$streamwise-dependent component
vel_friction.dat	$t$, $U_b$ or $\beta$, $\langle u_z(r=0)\rangle_z$, $u_\tau$	bulk speed or pressure measure $1+\beta=Re/Re_m$, mean centreline speed, friction vel.

Typical usage

See expanded examples in the Tutorial.

Setting parameters

• The files of importance are parallel.h and program/parameters.f90. Edit with your favourite

text editor e.g.

> nano program/parameters.f90   [OR]
> gedit program/parameters.f90

• Almost all parameters are found in program/parameters.f90.

• For serial use set both _Nr and _Ns to 1 in parallel.h. MPI is required if, and only if, _Np=_Nr*_Ns is greater than 1. The compiler in Makefile might need altering if switching between parallel and serial use, or is is possible to call mpirun -np 1 ....

Starting a job

• To compile

> make
> make install

The second command creates the directory install/ and a text file main.info, which is a record of settings at compile time. Try ('q' to quit)

> less install/main.info 

• Next an initial condition state.cdf.in is needed. NOTE: Any output state, e.g. state0012.cdf.dat can be copied to state.cdf.in to be used as an initial condition. If resolutions do not match, they are automatically interpolated or truncated.

> mv install ~/runs/job0001
> cd ~/runs/job0001/
> cp .../state0012.cdf.dat state.cdf.in

• To start the run (good to first double-check in main.info that the executable was compiled with correct parameters)

> nohup ./main.out > OUT 2> OUT.err &

After a few moments, press enter again to see if main.out stopped prematurely. If it has stopped there will be a message e.g. '[1]+ Done nohup...'; check OUT.err or OUT for clues why.

• To end the run

> rm RUNNING

This will terminate the job cleanly.

• NOTE: I generate almost all initial conditions by taking a state from a run with similar parameters. If there is a mismatch in i_Mp, use the utility changeMp.f90.

Monitoring a run

Immediately after starting a job, it’s a good idea to check for any warnings

> less OUT

To find out number of timesteps completed, or for possible diagnosis of an early exit,

> tail OUT

The code outputs timeseries data and snapshot data, the latter has a 4-digit number e.g. state0012.cdf.dat.

To see when the in the run each state was saved,

> grep state OUT | less   [OR]
> head -n 1 vel_spec* | less

I often monitor progress with tail vel_energy.dat or

> gnuplot
> plot 'vel_energy.dat' w l

Use rm RUNNING to end the job.

Making utils

The core code in program/ rarely needs to be changed. Almost anything can be done by creating a utility instead.

There are many examples in utils/. Further information can be found on the Utilities page.