Soil Spring

Casper Kruger
Casper Kruger Altair Community Member
edited March 2022 in Community Q&A

Hi,

 

I am trying to model a tunnel section buried in soil. I tried using the connector spot tool but it created 21000 spots with no real effect. How can I create spring normal to the outer surface nodes with a set stiffness in X and Y direction? 

The faces are constraint with a symmetry face, shown in red.

The load will be applied to the same surface as the springs, will this be an issue?

Will the free ends of the springs require a fixed SPC constraint or will HW know this is fixed in space? 

 

I did try and search the Altair One site, but did not see much on this topic. 

 image

image

 

 

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Best Answer

  • Adriano A. Koga
    Adriano A. Koga
    Altair Employee
    edited March 2022 Answer ✓

    There is a special type o spring, under 1D>>masses panel >> choose CBUSH

     

    This special CBUSH is a bushing element that by default is SPC'ed on the free end, thus resulting in a single noded CBUSH element. Might be useful for you.

    image

Answers

  • Adriano A. Koga
    Adriano A. Koga
    Altair Employee
    edited March 2022 Answer ✓

    There is a special type o spring, under 1D>>masses panel >> choose CBUSH

     

    This special CBUSH is a bushing element that by default is SPC'ed on the free end, thus resulting in a single noded CBUSH element. Might be useful for you.

    image

  • Casper Kruger
    Casper Kruger Altair Community Member
    edited March 2022

    Thank you Adriano. Should this be used with PELAS or HM_ELAS property? 

     

     

  • Casper Kruger
    Casper Kruger Altair Community Member
    edited March 2022

    or PBUSH with below setting?

     

    16 N/mm stiffness

    image

  • Adriano A. Koga
    Adriano A. Koga
    Altair Employee
    edited March 2022
    Casper Kruger said:

    or PBUSH with below setting?

     

    16 N/mm stiffness

    image

    PBUSH with stiffness for K1, K2, ...

     

    Make sure also that your CBUSH, even single-noded, has an apropriated coordinate system associated to it, to define what are the base directions of it.

    you can control that by using the 'card edit' option in each of your elements.

  • Casper Kruger
    Casper Kruger Altair Community Member
    edited March 2022

    Can the stiffness be set to act in compression only and be zero stiffness in tension? The soil will not have a tension stiffness and it looks like the cbush currently acts in both tension and compression. 

    Shall the remain DOF be zero or rigid?

     

    Thank you for the information. 

  • Adriano A. Koga
    Adriano A. Koga
    Altair Employee
    edited March 2022
    Casper Kruger said:

    Can the stiffness be set to act in compression only and be zero stiffness in tension? The soil will not have a tension stiffness and it looks like the cbush currently acts in both tension and compression. 

    Shall the remain DOF be zero or rigid?

     

    Thank you for the information. 

    CBUSH in linear analysis works the same in tension and compression, using the stiffness defined by the user in both directions.

     

    If you want different stiffness in each direction you need to run a NL analysis.

    You could use CGAP/PGAP elements (they have bilinear stiffness values), depending on the deflection.

    Or you can add a PBUSHT extension to you PBUSH property and assign a force x deflection table to it, creating a non-linear stiffness behavior.

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