# Monitored Volume (/MONVOL)

A monitored volume is defined with one or more shell (3-node or 4-node) parts.

The defined surface must be closed (Radioss Starter checks it and outputs an error message, if the surface is not closed). The shells normal must be oriented outside the volume. It is possible to reverse the shells normal for a given part, set by entering a negative part number (or by using an appropriate pre-processor to reverse them).

- AIRBAG1: uniform pressure classical airbag
- AREA: a closed surface to output its volume and area of post-processing
- COMMU1: uniform pressure chambers with communication
- FVMBAG1: non-uniform pressure airbag solved by Finite Volume Method
- GAS: used to model tire pressure or a simple fuel tank
- LFLUID: linear fluid monitored volume to model an incompressible fluid
- PRES: a simple uniform pressure monitored volume

- /MAT/LAW19 + /PROP/SH_ORTH - Used to model a fabric with a linear elastic behavior.
- /MAT/LAW58 + /PROP/SH_FABR - Used to model the behavior of a nonlinear elastic fabric.

- Fabric materials behave as a membrane and therefore, one integration point through the thickness is recommended, N=1.
- The fabric may be modeled with 3-nodes shell element, using the default Standard
triangle (C0) element formulation which does not hourglass or with 4-nodes shell
using the QBAT element,
`I`_{shell}=12 with`I`_{smstr}=11. - Although no longer recommended, if
`I`_{shell}=4 is used, then to avoid hourglass, define the shell membrane hourglass coefficient`hm`and the shell out of plane hourglass`hf`to be 10%. - To define the communicating surface for the COMMU1 type monitored volume, void materials and properties should be used /MAT/VOID and /PROP/VOID).
- The FVMBAG1 type may be used to model gas flow effects which is necessary with curtain airbags and Out Of Position (OOP) simulations.
- Generally, to define an interface self-impact contact, you may define one
auto-impacting interface TYPE7 and one edge-to-edge interface contact TYPE11. If
there are some initial penetrations, then set
`Inacti`=6. These two contacts can also be replaced by one TYPE19 contact.