- Well, my head's full of questions
- My temp'rature's risin' fast
- Bob Dylan (Mixed Up Confusion)
Questions that have been asked more than once.
The structure of this page is still evolving. Once enough questions are inserted it will be clear which structure is the best.
Contents
1 General
Questions concerning the history of OpenFOAM, the license etc
1.1 What is OpenFOAM ?
TODO
1.2 Can I use OpenFOAM?
Yes. OpenFOAM has been released by OpenCFD under the terms of the GNU GPL 2 license.
According to this licence, you can freely download, install and use OpenFOAM. Moreover, you have full access to the source code of OpenFOAM and you can modify it to customize it on your needs.
1.3 How can I properly reference OpenFOAM?
You can cite the www.openfoam.org website, if web-referencing is allowed, otherwise, cite the OpenFOAM documentation.
(Source: [1])
2 Installation and Running
Problems with the installation and running of applications
2.1 Which platforms are supported by OpenFOAM ?
Currently binaries exist for two platforms:
- Linux
- i386-Architecture
- AMD Opteron (probably also Intel Xeons with 64 Bit extension)
- Solaris
Ports to other operating systems that have been discussed on the message board are
- SGI Irix 6.5: Status unknown
- True 64: Status unknown
- Mac OS X: Compiles and beta-binaries are available (see thread)
- SGI Itanium (Linux): Should not be a problem according to this thread
2.2 Why isn't there a Windows port of OpenFOAM ?
The only feasible way to port OpenFOAM to Windows is by using Cygwin, an application that implements the most common UNIX APIs on Windows.
The problem is that the file-sytem NTFS, that is used by most modern Windows Versions, is case-insensitive (hello.c and Hello.C are the same file). The OpenFOAM-sources need a case-sensitive file-system and can't even be unpacked properly on a Windows sytem (see [2]).
Currently a way to compile OpenFOAM on cygwin is described on the Message-Board. This port does not include FoamX and paraFoam (but postprocessing can be done witn ParaView by using foamToVTK). This port is not part of the official distribution (yet).
2.3 How do I port OpenFOAM to an unsupported platform ?
If your platform is not some kind of UNIX-flavour you're probably going to have a hard time.
For a starter see Porting to a new platform.
2.4 Why doesn't FoamX allow me to enter numbers?
FoamX is set up to run on a system where the default language is English. If you want to run it on a system which uses another language, you have to manually modify the /OpenFOAM/OpenFOAM-1.1/bin/runFoamX script by adding the line:
export LANG=en_EN
at the beginning of the runFoamX script, and the line:
export LANG=your_LANGUAGE_CODE
at the end of the same file, replacing your_LANGUAGE_CODE with the corresponding code of the language in use in your system (for example, it_IT for italian).
(Source [3])
2.5 How can I make a solver stop if the solution contains NaNs ?
Usually OpenFOAM keeps calculating even if the solution contains NaNs (Not a number) and therefore is of no use. To avoid this set the environment variable FOAM_SIGFPE to a non-zero value. In tcsh:
setenv FOAM_SIGFPE 1
or in bash:
export FOAM_SIGFPE=1
3 Physical
Questions about the physics implemented (boundary conditions and similar)
3.1 General
3.1.1 What is the meaning of the Field X
A table of the fields most commonly written by OpenFOAM-solvers can be found here.
3.1.2 Where do I enter the fluid-density for icoFoam, turbFoam and other incompressible solvers?
You don't. Instead of the dynamic viscosity 
the kinematic viscosity 
is used by the OpenFOAM-solvers.
Note: the pressure has to be normalized with the density, too.
3.2 Boundary Conditions
3.2.1 What's the difference between the symmetryPlane and the zeroGradient boundary conditions?
The zeroGradient boundary condition sets the boundary value to the near-wall cell value.
A symmetryPlane boundary condition is a symmetry-plane which is equivalent to a zeroGradient for scalars, but not for vectors or tensors.
(Source: [4])
3.2.2 What does the lInf parameter mean in pressureTransmissive boundary condition?
lInf is the relaxation length-scale (in m) for outgoing pressure waves to return to pInf. This stops the pressure in the domain floating about it the inlet pressure is not specified. (source: [5])
3.3 Turbulence modeling
3.3.1 How is wall-functions for RANS disabled and enabled?
All high-Re RANS turbulence models include wall-functions because it is inappropriate to use them without. Only the low-Re models operate without wall-functions as they include model-specific wall treatments.
(Source: [6])
3.4 Additional models
Has OpenFOAM been used to calculate this type of problems?
3.4.1 Eulerian two fluid model and granular flow
It has been done and will be released. See here.
3.4.2 Viscoelastic flows?
Have been done. Will be released. For details see this thread on the Message Board.
4 Solution procedure
Manipulating the solution procedure by non-programming means
4.1 How does one turn off the dimensional checking?
Dimensional checking is one of the cool features in OpenFOAM that helps to develop solvers that do something physicaly meaningfull. Therefore: don't do this if not absolutely necessary.
To switch it off at run-time set
dimensionSet 0;
in OpenFOAM-1.1/.OpenFOAM-1.1/controlDict.
A more controlled way is to use the dimensions()-method to set the dimension of the volXXXField in question to the desired dimension.
(source: [7])
4.2 Is there a way to switch between single and double precision?
For Version 1.2 and older: Only by editing src/OpenFOAM/primitives/scalar/scalar.H and recompiling OpenFOAM. But why would you want to do that (except for memory issues)? (source: [8])
For Version 1.3: Recompile OpenFOAM with single-precision enabled (for details see Howto_compile_OpenFOAM)
5 Preprocessing
Preparing the simulations
5.1 How to quickly change the mesh with blockMesh
A description how to achieve this with m4 can be found here: How to quickly change the mesh with blockMesh
5.2 FoamX doesn't know my new solver
Look here: Howto_adding_a_new_solver_to_foamX
6 Postprocessing
Working with the results
6.1 Postprocessing of Lagrangian particles
This is not possible with paraFoam according to this thread. Use foamToVTK instead. Read the lagrangian data and 'Glyph' it.
7 Programming
Questions about writting applications and solvers
7.1 Compiling
7.1.1 Where does wmake get the values for the environmental variables from?
All wmake variables come from (in this order)
- $WM_DIR/rules/General/general
- $WM_DIR/rules/${WM_ARCH}${WM_COMPILER}/general
- $WM_DIR/rules/${WM_ARCH}/c++
(Source: [9]
7.2 Working with fields
7.2.1 How to calculate the field value of an arbitrary point?
See Calculating the field value at an arbitrary point.
7.3 Adding new features
7.3.1 How do I add a new wall-function?
See the How-To: Adding a new wall-function.
7.3.2 How do I add a new boundary condition?
See the How-To: Adding a new boundary condition.
8 Troubleshooting
8.1 An application ends with a segmentation fault. What is wrong?
A segmentation fault usually occurs when a program trys to access memory outside its bounds (see Segmentation Fault on Wikipedia). In OpenFOAM this usually occurs when a List<> or similar is accessed with an index outside of the allocated domain. To find out where this occurs make a separate copy of the OF-sources, recompile them with the swich WM_COMPILE_OPTION set to Debug (just uncomment the right lines in the bashrc/cshrc files). This makes OF run slower, but accesses to List<> etc are checked for ranges and the program aborts if you access outside of a range (plus you get a stack trace). This won't solve your problem, but it will help you find out where it occurs.
For recompiling OpenFOAM look at Howto_compile_OpenFOAM
If you want stack traces with line-numbers and source-files try to apply the patch described in the Message Board
8.2 FoamX is unable to contact name server
These problems are almost always one of the following:
- the hostname is not set ('localhost' is not acceptable to Corba)
- the hostname is not (or twice) in /etc/hosts
- only the truncated name is present in /etc/hosts
- some port opening problem due to security
(see the Messag Board)
