# PAABSF

Bulk Data Entry Defines the properties of the fluid acoustic absorber element.

## Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PAABSF PID TZREID TSIMID S A B K RHOC

## Example

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PAABSF 4 3 4 1.0 0.5

## Definitions

Field Contents SI Unit Example
PID Property identification number.

(Integer > 0)

TZREID TABLEDi entry identification number that defines the resistance as a function of frequency. The real part of the impedance.

(Integer > 0 or Blank)

TZIMID TABLEDi entry identification number that defines the reactance as a function of frequency. The imaginary part of impedance.

(Integer > 0 or Blank)

S Impedance scale factor.

Default = 1.0 (Real)

A Area factor when 1 or 2 grid points are specified in the CAABSF entry.

Default = 1.0 (Real > 0.0)

B Equivalent damping coefficient.

Default = 0.0 (Real)

K Equivalent stiffness coefficient.

Default = 0.0 (Real)

RHOC Constant used in data recovery for calculating an absorption coefficient.
RHO
Media density
C
Speed of sound in the media

Default = 1.0; current unused (Real)

1. PAABSF is referenced by a CAABSF entry only.
2. If only one grid point is specified on the CAABSF entry, the impedance $Z\left(f\right)={Z}_{R}+i{Z}_{i}$ is the total impedance at the point. If two grids are specified, then the impedance is the impedance per unit length. If three or four points are specified, then the impedance is the impedance per unit area. ${Z}_{R}\left(f\right)=TZREID\left(f\right)+B$ and $Zi\left(f\right)=TZIMID\left(f\right)=K/\left(\omega \right)$ .
3. The resistance represents a damper quantity B. The reactance represents a quantity of the type $\left(\omega M-K/\omega \right)$ . The impedance is defined as:
(1)
$Z=p/u$
Where,
$p$
Pressure
$u$
Velocity
4. The impedance scale factor S is used in computing element stiffness and damping terms as:(2)
$\begin{array}{l}k=\frac{A}{S}\frac{2\pi f{Z}_{i}\left(f\right)}{{S}_{R}^{2}+{Z}_{i}^{2}}\int \left(\mathit{of} \mathit{shape} \mathit{functions}\right)\\ b=\frac{A}{S}\frac{2\pi f{Z}_{R}\left(f\right)}{{Z}_{R}^{2}+{Z}_{i}^{2}}\int \left(\mathit{of} \mathit{shape} \mathit{functions}\right)\end{array}$
5. To create a non-reflecting boundary, set the values of the TABLEDi entry referenced by the TZREID field (Resistance-real part of Impedance) to be equal to ( $\left({\rho }_{fluid}\right)*\left({c}_{fluid}\right)$ for all frequencies. This will allow the acoustic wave to propagate normally through the boundary, without reflection. This condition is called the Sommerfeld boundary condition.
Where,
${\rho }_{fluid}$
Density of the fluid
${c}_{fluid}$
Speed of sound in the fluid
6. This card is represented as a property in HyperMesh.