SRCHDIS in Combination with CLEARANCE

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

Hi all,

 

i’ve got a problem regarding understanding contact modelling in optistruct:

I’s clear for me what the clearance is (overwriting the behavior that the contact is closed if the distance is greater than the initial distance).

In my case I’ve the case that one surface is allowed to move towards another surface by 2mm. So my clearance is 2 (close the contact after 2mm of movement). The point I don’t get in this case is the SRCHDIS: If I define the contact, the master and the slave surfaces are already defined, for what reason I would need a SRCDIS in this case? I’m reading that this is the distance in which the opposite gap-node is searched. But if I chose SRCHDIS as f.e. 2mm than it would find other surfaces at every step as the contact surfaces move to each other. Whats my mistake?

Can you give me maybe an example where the SRCHDIS is needed?

 

Thanks in advance!!

Peter

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Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited September 2018

    Hi @Peter_TRH

     

    Here is an example file. The geometric distance between the two plates is 3 units and the thickness of each plate is 1 unit. 

     

    If you provide a search distance of anything less than 2 units, you will see that contact is not established. 

    Unable to find an attachment - read this blog

  • Mario_21478
    Mario_21478 Altair Community Member
    edited September 2018

    Hi,

     

    The SRCHDIS  parameter is only used when generating the contact. This happens once at the beginning of the calculation.

     

    'The SRCHDIS field on the CONTACT and TIE entries is the search distance criterion for creating the contact interface. When specified, only slave nodes that are within the SRCHDIS distance from the master surface will have the contact condition checked. The default value is equal to twice the average edge length of the master surface. For FREEZE contact, it is equal to half the average edge length.'

     

    It has nothing to do with clearance.

     

    Best Regards,

    Mario

     

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited September 2018

    You can leave the SRCHDIS blank if you are not sure and let solver calculate the same. 

     

    Note that this may not work or the contact may behave weirdly in complex cases. 

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited September 2018

    FYI,

     

    For shell elements, the contact and tie search considers the shell thicknesses. Which implies that the defined search distance is expected to be the true distance between the shell surfaces facing each other. For example, in the case of shells without offset, if the geometric distance between the two shell surfaces facing each other is 5.0, and the shell thicknesses are 2.0 each, then the actual distance between the shell surfaces facing each other is 3.0. If the Search distance field is now set to 3.0, then the contact is generated as expected (in this scenario, if SRCHDIS is set lower than 3.0, then there is no contact generated).

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