Curle

Description

The Curle function object computes the acoustic pressure based on Curle's analogy.

Curle's analogy is implemented as:

$$p' = \frac{1}{4 \pi} \frac{\vec{r}}{| \vec{r} | ^2} \cdot \left( \frac{\vec{F}}{| \vec{r} |} + \frac{1}{c_0}\frac{d\vec{F}}{dt} \right)$$

where:

$p'$ : Curle's acoustic pressure [Pa] or [Pa (m3/kg)]

$c_0$ : Reference speed of sound [m/s]

$\vec{r}$ : Distance vector to observer locations [m]

$\vec{F}$ : Force [N] or [N (m3/kg)]

$t$ : Time [s]

Operands

Operand	Type	Location
input	-	-
output file 1	dat	$FOAM_CASE/postProcessing/<FO>/<time>/<file>
output file 2	surface file	$FOAM_CASE/<outputDir>/<time>/<surfaceName>
output field	-	-

Usage

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

Curle1
{
    // Mandatory entries (unmodifiable)
    type            Curle;
    libs            (fieldFunctionObjects);
    input           <point|surface>;
    output          <point|surface>;
    patches         (<patch1> <patch2> ... <patchN>);
    c0              343;

    // Conditional mandatory entries (runtime modifiable)
    // if input=point
    observerPositions    (<point1> <point2> ... <pointN>);

    // if input=surface
    surface              <surfaceFileName>;    // "inputSurface.obj";

    // if output=surface
    surfaceType          <surfaceType>;        // ensight;
    formatOptions
    {
        vtk
        {
            format  ascii;
        }
    }

    // Optional entries (runtime modifiable)
    p               p;

    // Optional (inherited) entries
    writePrecision  8;
    writeToFile     true;
    useUserTime     true;
    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: Curle	word	yes	-
libs	Library name: fieldFunctionObjects	word	yes	-
patches	Sound generation patch names	wordList	yes	-
c0	Reference speed of sound	scalar	yes	-
input	Input type	word	yes	-
output	Output type	word	yes	-
p	Pressure field name	word	no	p
observerPositions	List of observer positions (x y z)	pointList	conditional	-
surface	Input surface file name	word	conditional	-
surfaceType	Output surface type	word	conditional	-
formatOptions	Dictionary of surface format options	dictionary	conditional	-

The inherited entries are elaborated in:

• functionObject
• writeFile

Options for the input and output entries:

point   | Operand is a set of points
surface | Operand is a surface

Usage by the postProcess utility is not available.

Notes on entries

• Only the normal-pressure force is included in the force calculation.

Further information

Tutorial:

• vortexShed

Source code:

• Curle

API:

• Foam::functionObjects::Curle

History: Introduced in version v1706