Mass error with AMS in RADIOSS

Rahul Rajan_21763

Dear Experts,

 

I am implementing Adavanced Mass Scaling for one of my crash simulations. If I implement it on a small component (12k elements). There is no mass error % (DM/M) recorded in the .OUT file. However if I implement the same on a big model (1,5Million elements). There is a mass error % (DM/M) record in .OUT file. But theoritically with AMS there will be no added mass. So the mass change should be zero.  Is it a bug with RADIOSS solver ?  or Is there any theory supporting the result ? . Pl reply to me on this matter.

 

I have also checked in tutorials of AMS given in the users guide . Also I saw the appendix given for AMS. Even in the appendix there is a mass error recorded in .OUT file.

 

Using 13.0 version & got same result in 12.0 aswell.

 

Thanks in advance.

Altair Forum User

When you impose /AMS (Advanced Mass Scaling) in the model a non physical mass is added to a structure in order to achieve a larger explicit time step. And so. no mass is actually added to the system while solving.

In normal time step control the mass of small or stiff elements is increased to prevent a very small time step. Thus, artificial inertia forces are added which influence all eigen frequencies including rigid body modes. Whereas in Advanced Mass Scaling method only the high frequencies are affected, whereas the low frequencies (rigid body modes) are not influenced. Thereby, non structural mass can be added to the system without affecting the global solution.

There was a paper published on this: Selective mass scaling for explicit finite element analyses:::Authors -Lars Olovsson, Kjell Simonsson,Mattias Unosson