This serves as an example of the creation of a private method. It no
longer needs to convert the Function1 argument to user time, following
the addition of generalised unit conversion.
The majority of input parameters now support automatic unit conversion.
Units are specified within square brackets, either before or after the
value. Primitive parameters (e.g., scalars, vectors, tensors, ...),
dimensioned types, fields, Function1-s and Function2-s all support unit
conversion in this way.
Unit conversion occurs on input only. OpenFOAM writes out all fields and
parameters in standard units. It is recommended to use '.orig' files in
the 0 directory to preserve user-readable input if those files are being
modified by pre-processing applications (e.g., setFields).
For example, to specify a volumetric flow rate inlet boundary in litres
per second [l/s], rather than metres-cubed per second [m^3/s], in 0/U:
boundaryField
{
inlet
{
type flowRateInletVelocity;
volumetricFlowRate 0.1 [l/s];
value $internalField;
}
...
}
Or, to specify the pressure field in bar, in 0/p:
internalField uniform 1 [bar];
Or, to convert the parameters of an Arrhenius reaction rate from a
cm-mol-kcal unit system, in constant/chemistryProperties:
reactions
{
methaneReaction
{
type irreversibleArrhenius;
reaction "CH4^0.2 + 2O2^1.3 = CO2 + 2H2O";
A 6.7e12 [(mol/cm^3)^-0.5/s];
beta 0;
Ea 48.4 [kcal/mol];
}
}
Or, to define a time-varying outlet pressure using a CSV file in which
the pressure column is in mega-pascals [MPa], in 0/p:
boundaryField
{
outlet
{
type uniformFixedValue;
value
{
type table;
format csv;
nHeaderLine 1;
units ([s] [MPa]); // <-- new units entry
columns (0 1);
mergeSeparators no;
file "data/pressure.csv";
outOfBounds clamp;
interpolationScheme linear;
}
}
...
}
(Note also that a new 'columns' entry replaces the old 'refColumn' and
'componentColumns'. This is is considered to be more intuitive, and has
a consistent syntax with the new 'units' entry. 'columns' and
'componentColumns' have been retained for backwards compatibility and
will continue to work for the time being.)
Unit definitions can be added in the global or case controlDict files.
See UnitConversions in $WM_PROJECT_DIR/etc/controlDict for examples.
Currently available units include:
Standard: kg m s K kmol A Cd
Derived: Hz N Pa J W g um mm cm km l ml us ms min hr mol
rpm bar atm kPa MPa cal kcal cSt cP % rad rot deg
A user-time unit is also provided if user-time is in operation. This
allows it to be specified locally whether a parameter relates to
real-time or to user-time. For example, to define a mass source that
ramps up from a given engine-time (in crank-angle-degrees [CAD]) over a
duration in real-time, in constant/fvModels:
massSource1
{
type massSource;
points ((1 2 3));
massFlowRate
{
type scale;
scale linearRamp;
start 20 [CAD];
duration 50 [ms];
value 0.1 [g/s];
}
}
Specified units will be checked against the parameter's dimensions where
possible, and an error generated if they are not consistent. For the
dimensions to be available for this check, the code requires
modification, and work propagating this change across OpenFOAM is
ongoing. Unit conversions are still possible without these changes, but
the validity of such conversions will not be checked.
Units are no longer permitted in 'dimensions' entries in field files.
These 'dimensions' entries can now, instead, take the names of
dimensions. The names of the available dimensions are:
Standard: mass length time temperature
moles current luminousIntensity
Derived: area volume rate velocity momentum acceleration density
force energy power pressure kinematicPressure
compressibility gasConstant specificHeatCapacity
kinematicViscosity dynamicViscosity thermalConductivity
volumetricFlux massFlux
So, for example, a 0/epsilon file might specify the dimensions as
follows:
dimensions [energy/mass/time];
And a 0/alphat file might have:
dimensions [thermalConductivity/specificHeatCapacity];
*** Development Notes ***
A unit conversion can construct trivially from a dimension set,
resulting in a "standard" unit with a conversion factor of one. This
means the functions which perform unit conversion on read can be
provided dimension sets or unit conversion objects interchangeably.
A basic `dict.lookup<vector>("Umean")` call will do unit conversion, but
it does not know the parameter's dimensions, so it cannot check the
validity of the supplied units. A corresponding lookup function has been
added in which the dimensions or units can be provided; in this case the
corresponding call would be `dict.lookup<vector>("Umean", dimVelocity)`.
This function enables additional checking and should be used wherever
possible.
Function1-s and Function2-s have had their constructors and selectors
changed so that dimensions/units must be specified by calling code. In
the case of Function1, two unit arguments must be given; one for the
x-axis and one for the value-axis. For Function2-s, three must be
provided.
In some cases, it is desirable (or at least established practice), that
a given non-standard unit be used in the absence of specific
user-defined units. Commonly this includes reading angles in degrees
(rather than radians) and reading times in user-time (rather than
real-time). The primitive lookup functions and Function1 and Function2
selectors both support specifying a non-standard default unit. For
example, `theta_ = dict.lookup<scalar>("theta", unitDegrees)` will read
an angle in degrees by default. If this is done within a model which
also supports writing then the write call must be modified accordingly
so that the data is also written out in degrees. Overloads of writeEntry
have been created for this purpose. In this case, the angle theta should
be written out with `writeEntry(os, "theta", unitDegrees, theta_)`.
Function1-s and Function2-s behave similarly, but with greater numbers
of dimensions/units arguments as before.
The non-standard user-time unit can be accessed by a `userUnits()`
method that has been added to Time. Use of this user-time unit in the
construction of Function1-s should prevent the need for explicit
user-time conversion in boundary conditions and sub-models and similar.
Some models might contain non-typed stream-based lookups of the form
`dict.lookup("p0") >> p0_` (e.g., in a re-read method), or
`Umean_(dict.lookup("Umean"))` (e.g., in an initialiser list). These
calls cannot facilitate unit conversion and are therefore discouraged.
They should be replaced with
`p0_ = dict.lookup<scalar>("p0", dimPressure)` and
`Umean_(dict.lookup<vector>("Umean", dimVelocity))` and similar whenever
they are found.
The patch-specific mapper interfaces, fvPatchFieldMapper and
pointPatchFieldMapper, have been removed as they did not do anything.
Patch mapping constructors and functions now take a basic fieldMapper
reference.
An fvPatchFieldMapper.H header has been provided to aid backwards
compatability so that existing custom boundary conditions continue to
compile.
The patch field 'autoMap' and 'rmap' functions have been replaced with a
single 'map' function that can used to do any form of in-place
patch-to-patch mapping. The exact form of mapping is now controlled
entirely by the mapper object.
An example 'map' function is shown below:
void nutkRoughWallFunctionFvPatchScalarField::map
(
const fvPatchScalarField& ptf,
const fvPatchFieldMapper& mapper
)
{
nutkWallFunctionFvPatchScalarField::map(ptf, mapper);
const nutkRoughWallFunctionFvPatchScalarField& nrwfpsf =
refCast<const nutkRoughWallFunctionFvPatchScalarField>(ptf);
mapper(Ks_, nrwfpsf.Ks_);
mapper(Cs_, nrwfpsf.Cs_);
}
This single function replaces these two previous functions:
void nutkRoughWallFunctionFvPatchScalarField::autoMap
(
const fvPatchFieldMapper& m
)
{
nutkWallFunctionFvPatchScalarField::autoMap(m);
m(Ks_, Ks_);
m(Cs_, Cs_);
}
void nutkRoughWallFunctionFvPatchScalarField::rmap
(
const fvPatchScalarField& ptf,
const labelList& addr
)
{
nutkWallFunctionFvPatchScalarField::rmap(ptf, addr);
const nutkRoughWallFunctionFvPatchScalarField& nrwfpsf =
refCast<const nutkRoughWallFunctionFvPatchScalarField>(ptf);
Ks_.rmap(nrwfpsf.Ks_, addr);
Cs_.rmap(nrwfpsf.Cs_, addr);
}
Calls to 'autoMap' should be replaced with calls to 'map' with the same
mapper object and the patch field itself provided as the source. Calls
to 'rmap' should be replaced with calls to 'map' by wrapping the
addressing in a 'reverseFvPatchFieldMapper' (or
'reversePointPatchFieldMapper') object.
This change simplifies the creation of new patch fields and hence
improves extensibility. It also provides more options regarding general
mapping strategies between patches. Previously, general abstracted
mapping was only possible in 'autoMap'; i.e., from a patch to itself.
Now, general mapping is possible between different patches.
If the sequence of meshes are decomposed independently the number, order and
potentially type of processor patches is likely to change. Thus the processor
patches and patch fields must be replaced with those of the new mesh.
replacing the virtual functions overridden in engineTime.
Now the userTime conversion function in Time is specified in system/controlDict
such that the solver as well as all pre- and post-processing tools also operate
correctly with the chosen user-time.
For example the user-time and rpm in the tutorials/combustion/XiEngineFoam/kivaTest case are
now specified in system/controlDict:
userTime
{
type engine;
rpm 1500;
}
The default specification is real-time:
userTime
{
type real;
}
but this entry can be omitted as the real-time class is instantiated
automatically if the userTime entry is not present in system/controlDict.
The writeEntry form is now defined and used consistently throughout OpenFOAM
making it easier to use and extend, particularly to support binary IO of complex
dictionary entries.
"pos" now returns 1 if the argument is greater than 0, otherwise it returns 0.
This is consistent with the common mathematical definition of the "pos" function:
https://en.wikipedia.org/wiki/Sign_(mathematics)
However the previous implementation in which 1 was also returned for a 0
argument is useful in many situations so the "pos0" has been added which returns
1 if the argument is greater or equal to 0. Additionally the "neg0" has been
added which returns 1 if if the argument is less than or equal to 0.
Function1 is an abstract base-class of run-time selectable unary
functions which may be composed of other Function1's allowing the user
to specify complex functions of a single scalar variable, e.g. time.
The implementations need not be a simple or continuous functions;
interpolated tables and polynomials are also supported. In fact form of
mapping between a single scalar input and a single primitive type output
is supportable.
The primary application of Function1 is in time-varying boundary
conditions, it also used for other functions of time, e.g. injected mass
is spray simulations but is not limited to functions of time.
