Simulation fails due to SPH instability

Antonio_pol

Hi,

I am trying to model a bullet impacting on a composite panel. The projectile is made of two different materials and is meshed with SPH particles (all the same size and network). The panel on which the projectile impacts is made of an upper layer (meshed with solid tetra elements) and a lower one made of thin-walled cells (meshed shell). The simulation ends abruptly due to an excessive Total_Energy error (-50%, I set this). In the time of just one cycle, the energy collapses and the total mass of the SPH particles goes to zero. This is what you see in the 0001.out file:

     CYCLE    TIME      TIME-STEP  ELEMENT          ERROR  I-ENERGY    K-ENERGY T  K-ENERGY R  EXT-WORK     MAS.ERR     TOTAL MASS  MASS ADDED

    4100  0.3782E-04  0.9411E-08 SOLID     307062 -17.8%  0.2079E+06  0.1968E+06   63.08       0.000      0.9465E-04  0.9983E-04  0.9448E-08

 

CYCLE    TIME      TIME-STEP  ELEMENT          ERROR  I-ENERGY    K-ENERGY T  K-ENERGY R  EXT-WORK     MAS.ERR     TOTAL MASS  MASS ADDED

    4125  0.3805E-04  0.9412E-08 SOLID     307062 -17.9%  0.2093E+06  0.1950E+06   61.86       0.000      0.9465E-04  0.9983E-04  0.9448E-08

MESSAGE ID :        206

 

 ** RUN STOPPED: ENERGY ERROR LIMIT REACHED

CYCLE    TIME      TIME-STEP  ELEMENT          ERROR  I-ENERGY    K-ENERGY T  K-ENERGY R  EXT-WORK     MAS.ERR     TOTAL MASS  MASS ADDED

    4126  0.3806E-04  0.8186E-08 NODE      395436 -50.0%  0.5115E+05  0.1949E+06   62.02       0.000      0.9465E-04  0.9983E-04  0.9448E-08

 

For contacts between SPH particles and solid or shell elements I used TYPE 7 interface. What could be the error?

HM file attached.

PaulAltair

I had a look at this, couldn't see anything definitively wrong (maybe particle masses?), but I'm not that familiar with the material laws you are using.

I was able to get it to run much further by adding a timestep scale factor 0.7 and increasing h value on prop sph by 0.5, if I remove the failure criteria on the brass, then it runs to termination. 

The particle masses look like they may not be correct? The brass particle masses are higher than the lead ones, that shouldn't be the case I don't think.

Antonio_pol

Paul Sharp_21301 said:

I had a look at this, couldn't see anything definitively wrong (maybe particle masses?), but I'm not that familiar with the material laws you are using.

I was able to get it to run much further by adding a timestep scale factor 0.7 and increasing h value on prop sph by 0.5, if I remove the failure criteria on the brass, then it runs to termination. 

The particle masses look like they may not be correct? The brass particle masses are higher than the lead ones, that shouldn't be the case I don't think.

Thank you for your reply, Sir.

The mass of the SPH particles is obtained from the mass of the component divided by the number of particles created. The number of brass particles is much lower than that of lead particles and therefore brass particles are heavier.
​