log

Description

The log function object computes the natural logarithm of an input volScalarField.

$$f = s \ln(\max(f_0, a)) + t$$

where:

$f$ : Output volScalarField

$f_0$ : Input volScalarField

$\ln$ : Natural logarithm operator

$a$ : Clip scalar

$s$ : Scaling factor

$t$ : Offset factor

Operands

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

Usage

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

log1
{
    // Mandatory entries (unmodifiable)
    type            log;
    libs            (fieldFunctionObjects);

    // Mandatory (inherited) entry (runtime modifiable)
    field           <inpField>;

    // Optional entries (runtime modifiable)
    clip            1e-3;
    checkDimensions false;
    scale           1.0;
    offset          0.0;

    // Optional (inherited) entries
    result          <fieldResult>;
    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: log	word	yes	-
libs	Library name: fieldFunctionObjects	word	yes	-
field	Name of the operand field	word	yes	-
clip	Value to clip the operand field values to prevent zero or negative input	scalar	no	SMALL
checkDimensions	Flag to check dimensions of the operand field	bool	no	true
scale	Scaling factor - s above	scalar	no	1.0
offset	Offset factor - t above	scalar	no	0.0

The inherited entries are elaborated in:

• functionObject.H
• fieldExpression

Example by using the postProcess utility:

postProcess -func "log(<inpField>)" -scale 1.0 -offset 0.0

Further information

Tutorial:

• cavity

Source code:

• log

API:

• Foam::functionObjects::log

History: Introduced in version v2006