Reverse Mass Scaling

Subhu_21017
Subhu_21017 Altair Community Member
edited October 2020 in Community Q&A

HI all,

 

As like mass addition, Is it possible to remove mass uniformly??

 

I am Increasing  the time step, which results in mass addition.

 

and thus kinetic energy is increased. It reulted in larger intrusion.

 

Since I need some very approx result immediately , I need to reduce the actual structural mass and have to run it again. 

 

Is it possible remove or reduce the structural mass uniformly???

 

 

Thanks in ADvance

 

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Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited January 2018

    Hi,

    Running the model with high imposed time step value will add more mass to the model which will change the physics of the simulation. The other possibility is using Advanced Mass Scaling (/AMS) which will not add structural mass to the model. But we don't recommend to use /AMS for crash and high velocity impact simulations.

    There are no options to remove the mass uniformly from a model. User may have to try it manually.

    But I strongly recommend you to run with a lower imposed time step value so that the mass error will not be more than 5% (.05).

     

    Also check what is causing for lower time step.  Check the model for any penetrations/intersections which could result in time step drop.

     From the engine out (_0001.out) file check which object is responsible for the low  time step. It can be an element, a node or an interface.

    • For an element, check the related material.There must not be an error in the units system that this data is given in. check the element size also
    • For a node, check the characteristics of connected elements. If the node is on the master side or the slave side of an interface, this interface must be verified.
    • For an interface, the gap of the interface must be verified if some failure happens on the master or the slave side of the interface

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  • Subhu_21017
    Subhu_21017 Altair Community Member
    edited January 2018

    Thank You George,

     

    The shell, solid and spring elements are corrected for 1e-7 time step.

     

    Type 7 contact is appended with dt min of 2e-6

     

    And my on running .out is...

    7540  0.7837E-02  0.9164E-06 INTER       3189  -0.1%  0.5093E+07  0.3628E+09  0.1387E+05 -0.3399E+05   4.611

     

    What is maximum type step we can impose??

     

    Regards,

    Subhu

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited January 2018

    Hi Subhu,

    Please check the interfaces in your model. Check for any penetrations/intersections.

    Use these recommended parameters for Type 7 interfaces:

    Istf=4

    Igap=2

    Fscale_Gap=0.8

    INACTI=6

    Gap_min=

    Fric = 0.1

    Iform=2.

     

    User has to select an ideal time step as Tmin for /DT/NODA/CST. From the starter out file user can review the current time step of the model and slightly higher value can be used. The mass error, which you can review in the engine out file, should be less than 5% (.05). In such a way user has to find the ideal time step for the run.

    Please go through https://altairuniversity.com/learning-library/considerations-about-time-step/ which is a webinar on time step control in RADIOSS.

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