time step calculation

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

Hello 

 

I have two geometry rectangular and hexagonal.  I used same material and same mesh size for both.   

why  their time step is different.

 

 

<?xml version="1.0" encoding="UTF-8"?>OCTAGONAL TİME STEP.JPG

<?xml version="1.0" encoding="UTF-8"?>Rectangular time step.JPG

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Answers

  • Simon Križnik
    Simon Križnik Altair Community Member
    edited January 2019

    Hi,

     

    the difference is because the characteristic element length is computed differently for shell and hexahedral elements:

    -Quad Shell: The square root of the shell area

    The critical length can vary with: • Shell formulation • Hourglass control parameters • Numerical damping • Membrane damping

    -8-node Hexahedral: Volume / largest face area

     

    I think the characteristic element length should be the same if element shape is close to ideal (square and cube), but could be different for distorted shapes.

     

  • Pranav Hari
    Pranav Hari Altair Community Member
    edited January 2019

    Hi beytut

     

    I recommend you to go through the RADIOSS ebook, Explicit analysis using Radioss  (https://altairuniversity.com/free-ebooks-2/free-ebook-crash-analysis-with-radioss-a-study-guide/) where all the basics for explicit analysis including time step calculations are covered.

     

    Thanks

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