ddt2

Description

The ddt2 function object computes the magnitude or magnitude squared of the Eulerian time derivative of an input volume field for time-variant simulations (not appropriate to steady-state simulations).

The result can be further used for determining e.g. variance or RMS values.

Operands

Operand	Type	Location
input	vol<Type>Field	$FOAM_CASE/<time>/<inpField>
output file	-	-
output field	vol<Type>Field	$FOAM_CASE/<time>/<outField>

where <Type>=Scalar/Vector/SphericalTensor/SymmTensor/Tensor.

Usage

Example of the ddt2 function object by using functions sub-dictionary in system/controlDict file:

ddt21
{
    // Mandatory entries (unmodifiable)
    type            ddt2;
    libs            (fieldFunctionObjects);

    // Mandatory entries (runtime modifiable)
    fields          (<field1> <field2> ... <fieldN>);

    // Optional entries (unmodifiable)
    mag             false;

    // Optional entries (runtime modifiable)
    result          d@@dt2;

    // Optional (inherited) entries
    region          region0;
    enabled         true;
    log             true;
    timeStart       0;
    timeEnd         1000;
    executeControl  timeStep;
    executeInterval 1;
    writeControl    timeStep;
    writeInterval   1;
}

where the entries mean:

Property	Description	Type	Required	Default
type	Type name: ddt2	word	yes	-
libs	Library name: fieldFunctionObjects	word	yes	-
fields	Names of the operand fields	wordList	yes	-
mag	Compute 'mag' instead of 'magSqr'	bool	no	false
result	Name of results	word	no	magSqr(ddt2(@@))

The inherited entries are elaborated in:

• functionObject

Usage by the postProcess utility is not available.

Notes on entries

A list of fields can contain exact names or regular expressions. The token \@\@ in the result name is replaced by the name of the source field. In the special case of a single source field (specified as a non-regex), the \@\@ token checking is suppressed.

The function object will skip over fields that appear to have already been processed (ie, their names are similar to the output names).

Further information

Tutorial:

• cavity

Source code:

• ddt2

API:

• Foam::functionObjects::ddt2

History: Introduced in version v1612+