Time Step

Altair Forum User

Hi, 

 

I'm a little confused with the time-steps: 

My simulation runs at a timestep of 2.4402E-05 (This is what I can see in the Radioss GUI). However, in my .out-file the smallest nodal time step is 6.6367471595250E-05 and the smallest solid time step is 2.7111706125757E-05. I was wondering how this is realated to the real time step? Furthermore I wonder why my solid time step is smaller than my nodal... what is the reason for this? Is this normal?  And third, why do I have a slight mass error even I don't use mass scaling. 

 

Thanks, Best

J

Altair Forum User

Hi J,

The time step, is the time required for a shock wave to propagate across the smallest distance in an element. In explicit simulations the solution is considered unstable if information passes across more than one element per time step. And so in order to ensure stability the smallest time step from the out file is chosen and it is multiplied with a scale factor of 0.9 ( In this case 2.7111706125757E-05 * 0.9 = 2.44e-5). This is how the time step for the run is selected.

Time step for elements is calculated in a different way rather than the nodal one.  The equation is as below for both the cases:

                                          

 

Do you have any Type 2 interface in your model?. If option Spotflag =1 is used in the Interface TYPE2, then there are added mass on master nodes during the run, which you can ignore.

 

 

Altair Forum User

Hi George, 

 

Thanks for the good answer! This is clear for me now. 

I didn't completely understand what you said about type 2 contact and I am very interested in this. I have type 2 interface, and my solution looks very bad if I use it without setting spotflag=1 . However, I never completely have understood what spotflag = 1 actually changes and I also don't understand what you mean with: 'then there are added mass on master nodes during the run, which you can ignore' related to the time-step -> are this added masses chancing the time-step?

 

Thanks a lot, Best

J

Altair Forum User

Hi,

Please go to Help Menu>>RADIOSS>>Frequently Asked Questions>>Kinematic Conditions (file:///C:/Program%20Files/Altair/2017/help/rad/topics/solvers/faq_rad_kinematic_conditions_r.htm) where this concept of mass addition for Type 2 interface is explained.

Altair Forum User

Hi George, 

 

I don't have this folder. Is there somewhere I can find the information online?

 

Best, J

Altair Forum User

Hi,

The information is a s below:

 

 

<?xml version="1.0" encoding="UTF-8"?>