/MONVOL/GAS: Monitor volume for tire, tank or air bag, Simple example model.

altair_fukuoka

Overview:

/MONVOL/GAS is a monitor volume which uses ideal gas EOS. This is easy to use.

I will explain how /MONVOL/GAS works with a simple cube crash simulation.

Exanple 01: No /MONVOL/GAS

To understand diffarence caused by /MONVOL/GAS, I show a simulation without it.

In the simulation, the cube is crashed by the heavy rigidwall (/RWALL) on the top.

In this case, the air inside the cube does not prevent compressed.

Download this model:

01_without_monvol.7z

Example02: add basic /MONVOL/GAS setting to consider air pressure.

https://help.altair.com/hwsolvers/rad/topics/solvers/rad/monvol_gas_starter_r.htm

The minimal required fields are the green ones below,

surf_IDex: a surface /SURF id. This surface make a closed volume. Only shell element is available. The normal vector should go out from the volume.

γ: Ratio of specific heat

ρi: Density

Pext: External pressure

Pini: Initial pressure

Trelax: Time to increase pressure from Pext to Pini

I apply the following setting. The gas is air. The pressure is increased from 0.1MPa to 0.2MPa for 0.01sec,

/TH/MONV is used to output the history of the volume and the pressure,

Here is the result,

The air regists to the rigid wall and push it back.

We can check the history of the volume and the pressure. Even though Pini set to 0.2MPa, the presure does not reach 0.2MPa at T=Trelax=0.01s.

This is the reason:

• /MONVOL/GAS calculate adding mass to reach Pini with the initial volume of the cube.
• However, during adding mass (=increasing pressure), the cube itself becomes bigger.
• Thus, the resultant pressure is less than Pini.

Download the model:

02_basic_monvol-gas.7z

Example03: Surely increase Pressure to Pini

For this purpose, we can use Iequi=1. In Example02, the adding mass is limited. On the other hand, in this case, the adding mass is not limited. Until the pressure reaches Pini, this monitor volume keeps to add mass without any limitation.

Here is the result. The pressure surely reaches 0.2MPa as expected.

Download:

Example03.7z

Example04: Vent by material failure (=element deletion)

I apply maximum plastic strain in /MAT/LAW2. When the plastic strain reaches 0.11, the element is deleted.

Vent hole setting in /MONVOL/GAS,

The real input for this example is,

Here is the result. In the earlier stage, the cube regists, but it loses the registance later,

Here is the history plot. The pressure drops to the external pressure=Pext,

Download:

Example04.7z