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PARTICLE_SPH_JET

Particle

Beta command

This command is in the beta stage and the format may change over time.

*PARTICLE_SPH_JET
sid
$x_1$, $y_1$, $z_1$, $x_2$, $y_2$, $z_2$, $R$, $\xi$
$v_{min}$, $m_{min}$, no_ecc

Parameter definition

Variable
Description
sid
Particle subdomain ID
$x_1$, $y_1$, $z_1$
Cylinder face center coordinate 1
$x_2$, $y_2$, $z_2$
Cylinder face center coordinate 2
$R$
Cylinder radius
$\xi$
Dimensionless jet correction parameter
default: 0.1
$v_{min}$
Cut-off velocity in jet length calculation
default: 0
$m_{min}$
Threshold fragment mass
default: 0
no_ecc
Flag to deactivate eccentricity correction
options:
0 $\rightarrow$ jet eccentricity correction is active
1 $\rightarrow$ jet eccentricity correction is inactive

Description

This command is exclusively used when modelling the formation of shaped charge jets. Its purpose is to collect and output jet data and to enhance the accuracy of the simulated jet formation process.

The enhancement is based on the assumption that physical variations in the jet diameter have a significantly larger wave length than the distance between individual SPH particles. High frequency surface variations (spatially) are smoothed with a mild surface pressure. The pressure (positive or negative) is applied locally where non-physical surface variations are detected. This prevents a premature jet fragmentation.

The artificial surface pressure also compensates for geometrical discretization errors caused by an initially Cartesian distribution of SPH particles. The compensation results in a jet with a more circular cross section. Note that the need for an artificial pressure is reduced with a finer discretization and it will approach zero in the limit.

Shaped charge jet, with and without correction
Shaped charge jet, with and without correction
The domain where the correction is active is defined as a cylinder in space
The domain where the correction is active is defined as a cylinder in space

The resulting artificially applied impulse is (together with jet tip velocity and displacement) reported to the file particle_sph_jet.out. The jet tip displacement is calculated from the initial location of the cone base.

Definition of artificially applied impulse (reported in particle_sph_jet.out)
Definition of artificially applied impulse (reported in particle_sph_jet.out)

The parameter $\xi$ is dimensionless and controls the strength of the applied jet correction pressure. Parts of the slug travelling at a velocity smaller than $v_{min}$ (in the jet direction) are omitted from the jet length calculation. Jet tip fragments with a mass smaller than $m_{min}$ are also excluded from the jet length and velocity calculations.