Fluid Elements

  Fluid elements are modelled in FEMGEN in the same way as the other 'standard' elements. It is thus possible to generate F2D2, FAX2, F3D3, and F3D4 elements by selecting the relevant element variant via the MESHING TYPES command.

Fluid elements are generated from lines or surfaces which are overlayed onto the existing model geometry. The 'MESHING MERGE part1 part2' command should be used to ensure that the nodes of the fluid elements are coincident with the actual model geometry with which they are associated.

Fluid elements must be associated with a cavity reference node (FEMGEN point element variant 9). This is achieved by placing all geometric entities associated with the fluid into a set whose name begins with the characters 'FLUID'. The remaining three characters of the set name can be any printable character.

The user must ensure that the normals for all elements in a fluid definition point in the same direction. The commands 'LABEL GEOMETRY NORMAL' and VIEW HIDDEN FILL NORMAL' are useful to check this, and the 'GEOMETRY FLIP' command can be used to change the direction in which a surface faces.

It is also possible to define fluid link elements by using a single beam element on a line. The ends of the fluid link should be connected either to a dummy node element (see section 2.16 ) or a cavity reference node.

  

Figure 2.8: Example Fluid Element Definition