These elements are available for acoustic analysis:
Element properties are as follows:
Table 2.1: Acoustic Element Properties
| Element | Attribute | Degrees of Freedom per Node |
| FLUID129 | 2D 2- or 3-node line |
PRES |
| FLUID243 | 2D 4-node quadrilateral with triangle degeneracy |
UX, UY, PRES (coupled element) PRES (uncoupled element) ENKE (room acoustics) PRES (auxiliary VX, VY, ENKE for transient perfectly matched layers) |
| FLUID244 | 2D 8-node quadrilateral with triangle degeneracy |
UX, UY, PRES (coupled element) PRES (uncoupled element) ENKE (room acoustics) UX, UY, VX, VY, TEMP, PRES (coupled viscous-thermal element) VX, VY, TEMP, PRES (uncoupled viscous-thermal element) UX, UY, PRES (poroelastic element) PRES (auxiliary VX, VY, ENKE for transient perfectly matched layers) |
| FLUID30 | 3D 8-node hexagonal with prism with tetrahedral and pyramid degeneracy |
UX, UY, UZ, PRES (coupled element) PRES (uncoupled element) ENKE (room acoustics) PRES (auxiliary VX, VY, VZ, ENKE for transient perfectly matched layers) |
| FLUID130 | 3D 4- or 8-node quadrilateral surface with triangle degeneracy |
PRES |
| FLUID220 | 3D 20-node hexagonal with pyramid and prism degeneracy |
UX, UY, UZ, PRES (coupled element) PRES (uncoupled element) ENKE (room acoustics) UX, UY, UZ, VX, VY, VZ, TEMP, PRES (coupled viscous-thermal element) VX, VY, VZ, TEMP, PRES (uncoupled viscous-thermal element) UX, UY, UZ, PRES (poroelastic element) PRES (auxiliary VX, VY, VZ, ENKE for transient perfectly matched layers) |
| FLUID221 | 3D 10-node tetrahedral |
UX, UY, UZ, PRES (coupled element) PRES (uncoupled element) ENKE (room acoustics) UX, UY, UZ, VX, VY, VZ, TEMP, PRES (coupled viscous-thermal element) VX, VY, VZ, TEMP, PRES (uncoupled viscous-thermal element) UX, UY, UZ, PRES (poroelastic element) PRES (auxiliary VX, VY, VZ, ENKE for transient perfectly matched layers) |
One element shape (hexahedral, wedge, or tetrahedral), or any combination of shapes, can be used in a 3D acoustic model. The pyramid elements are transitional elements between the hexahedral and tetrahedral elements.
Example 2.1: Creating Mixed Hexahedral and Wedge Elements
/prep7 et,1,220 ! define hexahedral element et,11,200,5 ! define 2D 6-node triangle mesh element et,12,200,7 ! define 2D 8-node quadrilateral mesh element rect,0,1,0,1 ! create area 1 rect,1,2,0,1 ! create area 2 aglue,all ! glue areas together esize,0.25 ! define the element size asel,s,loc,x,0,1 ! select area 1 type,11 ! select triangle element type mshape,1 ! define the triangle element shape amesh,all ! mesh area 1 with triangle mesh element asel,s,loc,x,1,2 ! select area 2 type,12 ! select quadrilateral mesh element type mshape,0 ! define the element quadrilateral shape amesh,all ! mesh area 2 with quadrilateral mesh element alls esize,,4 ! define element operation type,1 ! select hexahedral element asel,s,loc,z,0 ! select 2D element vext,all,,,0,0,1 ! create 3D elements by extruding 2D elements fini
Example 2.2: Creating Mixed Hexahedral, Pyramid, and Tetrahedral Elements
/prep7 ch=10.16e-3 cw=22.86e-3 cl=2.e-2 h=2.e-3 et,1,220,1 ! define hexahedral element et,2,221,1 ! define tet element block,-cw/2,0,-ch/2,ch/2,0,cl/2 ! create volume 1 block,-cw/2,0,-ch/2,ch/2,cl/2,cl ! create volume 2 vglue,all ! glue volumes together esize,h ! define element size type,1 ! select hexahedral element type mshape,0,3d ! define hexahedral mesh mshkey,1 ! use mapped mesh vmesh,1 ! mesh first volume mshape,1,3d ! define tetrahedral element mshkey,0 ! use free meshing vmesh,3 ! mesh second mesh tchg,220,221,2 ! convert degenerated brick into tet fini
Although a geometrically complex structure can be meshed with tetrahedral elements, it may require many elements and lead to a more computationally expensive simulation. Even a regularly shaped volume may require many tetrahedral elements if it has a very large aspect ratio. In such a case, hexahedral or wedge elements are a better choice.