mass addition RADIOSS

Altair Forum User
Altair Forum User
Altair Employee
edited October 2020 in Community Q&A

Hello,

I m working with RADIOSS and trying to understand the mass addition it makes.
I know if the time step > critcal time step, radioss adds mass. But why ?

I don t understand how the mass is added? where (element,node)? And how can that  make calculation continue and not crash.

Thanks in advance for your help.

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Answers

  • Nachiket Kadu_22143
    Nachiket Kadu_22143 Altair Community Member
    edited June 2018

    Hi @Bakr Amine

    If you could go through the theory of explicit analysis you will find that nodal time step is equal to Sqrt(2M/K). Using this relation if you want the solution to complete faster you would increase the time step, so to counter this increase in time step system adds up mass so as to balance the equation. The amount of added mass should me minimum, in general 2% of mass error is acceptable, the more the increase in mass more will be your solution diverging from real time.

  • Simon Križnik
    Simon Križnik Altair Community Member
    edited June 2018

    Hi Bakr Amine,

     

    /DT/NODA/CST and /DT/INTER/CST will add some mass to the model. Increasing the mass will also increase kinetic energy. You have to check to see if these mass and energy increases are small enough and that they do not affect the solution. With /ANIM/DMASS and /ANIM/MASS,  relative mass and total mass increase respectively can be visualized in Hyperview with contour plot. With time history (/TH) energy and mass can also be plotted.

     

    Alternatively you could try with advanced mass scaling (AMS) which does not add mass.

     

    You can find more information from Introduction to Explicit Analysis using RADIOSS – A Study Guide in Time Step Control chapter. Also recommended is 2017 Radioss user guide starting from page 30.

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