Use the TB,FLUID command to define a material model for compressible hydrostatic fluid elements. All elements sharing a pressure node must share the same material. There are three ways to define material data for compressible fluids: liquid, gas, or pressure-volume data. See Fluids in the Material Reference for a complete description of these material models.
Use the TB,FLUID command with TBOPT
= LIQUID to define material behavior for a liquid, and specify the following
material constants using the TBDATA command:
| Constant | Symbol | Meaning |
|---|---|---|
| C1 | K | Bulk modulus |
| C2 | α | Coefficient of thermal expansion |
| C3 | ρ0f | Initial density |
Use the TB,FLUID command with TBOPT
= GAS to define material behavior for a gas, and specify the following material
constant using the TBDATA command:
| Constant | Symbol | Meaning |
|---|---|---|
| C1 | ρ0f | Initial density |
Since the compressible gas is modeled using the Ideal Gas Law, you must specify a reference pressure (use real constant PREF on the hydrostatic fluid element) and you must specify a reference temperature (use the TREF or MP,REFT command) with temperature offset (use the TOFFST command).
Use the TB,FLUID command with TBOPT
= PVDATA to define compressible fluid behavior in terms of a pressure-volume curve.
Use the TBPT command to enter the data points
(X, Y) for the curve:
| Constant | Meaning |
|---|---|
X
| Pressure value |
Y
| Corresponding volume value |
Use the MP,DENS command to define initial density for a fluid with pressure-volume data.
Use the TBTEMP command to define temperature dependent material constants for all of the above material options.
Use the MP,DENS and MP,ALPX commands to specify density and coefficient of thermal expansion, respectively, for an incompressible fluid that accommodates thermal expansion.
The following loads and boundary conditions can be applied to hydrostatic fluid elements:
| Load | Command | Comments |
|---|---|---|
| Initial fluid pressure | IC | Apply initial fluid pressure at pressure node with HDSP degree of freedom. |
| Initial fluid temperature | TREF or MP,REFT | |
| Temperature offset (from absolute zero) | TOFFST | |
| Temperature loads | BF | By default, the temperature is set to TUNIF. |
| Hydrostatic pressure degree-of-freedom constraint | D | Apply this constraint type to the pressure node. This constraint is equivalent to applying a surface load on the underlying solid surface, as far as the effect of fluid pressure on the underlying solid is concerned. The change in hydrostatic pressure value is assumed to occur as a result of the addition or removal of fluid mass to or from the containing vessel. |
| Fluid mass flow rate | F | Apply fluid mass flow rate at the pressure node. A positive value adds fluid mass to the containing vessel, and a negative value results in removal of fluid mass. |