To specify element type numbers and key options for acoustic elements, issue the ET command.
The key options (KEYOPTs) shown in the following two tables define the acoustic element properties:
Table 4.1: Key Options for FLUID30, FLUID220, FLUID221, FLUID243, and FLUID244
| KEYOPT | Options | Element Definitions |
| KEYOPT(1) | 0 | No specification |
| 2 | Symmetric harmonic formulation | |
| 3 | Deactivate the diagonalization of the damping matrix in an energy diffusion solution | |
| 4 | Activate the velocity potential formulation for a transient analysis | |
| KEYOPT(2) | 0 | Coupled element |
| 1 | Uncoupled element | |
| 4 | Element for room acoustics | |
| 5 | Coupled viscous-thermal acoustic element (FLUID220, FLUID221, and FLUID244) | |
| 6 | Uncoupled viscous-thermal acoustic element (FLUID220, FLUID221, and FLUID244) | |
| 7 | Poroelastic acoustic element (FLUID220, FLUID221, and FLUID244) | |
| KEYOPT(3) | 0 | 2D planar element (FLUID243 and FLUID244) |
| 1 | 2D axisymmetric element (FLUID243 and FLUID244) | |
| KEYOPT(4) | 0 | Normal element |
| 1 | Perfectly matched layers (PML) element for modal or harmonic analysis | |
| 2 | Irregular perfectly matched layers (IPML) element for modal or harmonic analysis | |
| 3 | Perfectly matched layers (PML) element for transient analysis | |
| 4 | Irregular perfectly matched layers (IPML) element for transient analysis | |
| KEYOPT(5) | 0 | Normal element |
| 1 | Non-morphed element during the static structural solution | |
| KEYOPT(6) | 0 | Compressible fluid |
| 1 | Incompressible fluid |
Table 4.2: Key Options for FLUID129
| KEYOPT | Options | Element Definitions |
| KEYOPT(1) | 0 | 2-node line element |
| 2 | 3-node line element |
Table 4.3: Key Options for FLUID130
| KEYOPT | Options | Element Definitions |
| KEYOPT(1) | 0 | 4-node surface element |
| 2 | 8-node surface element |
The following figure shows an example of coupled acoustic-structural interaction:
Example 4.1: Defining Element Types
The following example input defines second-order coupled, uncoupled, and PML elements:
et,1,220,,0,,0 ! coupled brick element with DOF: UX,UY,UX,PRES et,1,220,,1,,0 ! uncoupled brick element with DOF: PRES et,1,220,,1,,1 ! uncoupled PML brick element with DOF: PRES