## LS Dyna

#### Momentum of Sphere not equal to mass of sphere times velocity of sphere in X direction?

• Conorryan98
Subscriber

Hi there,

When I run an example hypervelocity impact simulation with SPH and output a text file with the X-Momentum values I get results as follows. Al 2024-T4 is the target plate and Al 2024 is the spherical projectile.

• Ram Gopisetti
Ansys Employee
what is the mass of the SPH particles, you can yield it by using an MASSALL scoped to the SPH bodies.
In SPH, velocities are carried to SPH nodes so any variation in velocities or change of mass will shown an significant effect.
Packing of the particles will not show any effect on the mass.
Is the Velocity specified is an applied or the velocity from AUTODYN, Usually, Autodyn will give out the Average Velocities.
Calculate the Momentum via MASSALL*VSUM or Componential velocities (VX,VY,VZ) and verify it with the Histories.
Cheers, Ram
• Conorryan98
Subscriber
I couldn't find a solution to the above problem. Furthermore I've realised that the mass of and hence kinetic energy of the projectile is a factor of 10 off where it should be theoretically.
Mass of 1mm Al2024-T4 sphere projectile theoretically = 1.166578072033E-5 kg
Mass in Autodyn = 1.38066E-6 kg
KE of projectile theoretically = 52.496 Joules
KE of projectile in Autodyn = 6.21297 Joules
It seems like there is a problem with Autodyn calculating the actual values associated with the projectile. Is it something to do with how packed the particle is? When I make it more packed the values in Autodyn get closer to theoretical but the simulation time suffers greatly.
Thanks.