IB_CONTROL
Solution control and techniques
Beta command
This command is in the beta stage and the format may change over time.
"Optional title"
coid, csysid, $w$, $\varepsilon_W$
Parameter definition
Description
This command is used in interior ballistics (IB) models to compensate for numerical discretization errors originating in the CFD-FE coupling interface (interaction between solid propellant and combustion products).
Anti-sticking
When using this command an anti-sticking algorithm is automatically activated. It applies an artificial pressure on propellant grain surfaces in narrow gaps, where there is no gas pressure (empty CFD cells). The artificial pressure prevents non-physical sticking effects where grains can't separate from each other. However, the algorithm comes with a negative side effect. If applied to grains in direct contact with the projectile, the force balance can be violated, resulting in an incorrect acceleration. Turning off the (automatically applied) anti-sticking near the projectile can be crucial for reliable results. For this purpose, a coordinate system can be attached to the back face of the projectile, with its local $x$-axis pointing in the axial direction of the gun barrel. $w$ then defines the width of a region where the propellant grain anti-sticking algorithm is deactivated.
Energy balancing
The CFD-FE coupling algorithm detects CFD cells that are overlapped by Finite Elements. Overapped cells are emptied and their masses and energies are transferred to neighbouring cells. This process disturbs the time integration scheme and creates small, but sometimes significant, energy balance errors. The energy errors are monitored and can be compensated for by depositing or removing small amounts of thermal energy for the neighbouring cells. $\varepsilon_W$ is a parameter that specifies the maximum adjustment of the transferred energy (default is $10\%$).
