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Interaction

Interaction

*Interaction, Name=<name>, Mechanical=<>, [noseparation], [user], [stiffness_factor=<>], [non constant]
<Normal contact model properties>
*Friction, model=<friction model name>, [stiffness_factor=<>]
<Properties of the friction model>

This option defines an interaction for contact analyses. The command is followed by two mandatory keywords and several optional keywords:

  • Name=<name> Set this parameter equal to the name of the interaction (can be chosen freely). This parameter is mandatory.

  • Mechanical=<>
    Set this parameter equal to the mechanical model to describe the normal contact constraint enforcement. The following normal contact models are available:

Model Contact tension possible Over-closure relation
Penalty no/yes with [no separation] linear
Augmented_Lagrange no/yes with [no separation] non-linear

  • The optional [no separation] allows for inseparable contact conditions. Therefore, tension contact conditions are possible. Note that the contact points have to come into contact once before the no separation conditions comes into effect.

  • The optional [user] allows for user defined frictional contact properties (in case *Friction is used) which can vary with respect to coordinates, node label or time. No properties for the frictional contact model have to be defined in the input file in this case, but a user defined file for the contact properties have to given in accordance to the routine described here.

  • The optional [stiffness_factor=<>] allows for a user defined stiffness factor used in the evaluation of the penalty factor. The penalty factor is calculated based on the trace of the stiffness matrix of the adjacent continuum element and multiplied with the given stiffness factor. This option only applies if no user defined penalty factor is given (see the following description of the <Normal contact model properties>). The default value of the stiffness factor is 20.

  • The optional [non constant] allows the penalty factor to change during the analysis based on the change of stiffness of the adjacent material. This is beneficial if the material stiffness changes considerably during the analysis, e.g. by spinning-up of a centrifuge.

The *Interaction command can be followed by the definition of properties of the normal contact:

  • Normal penalty contact. The following parameter can be defined:

    Parameter Unit Mandatory
    Penalty factor \(\varepsilon\) F/A no

  • Normal augmented Lagrange method. The following parameter can be defined:

    Parameter Unit Mandatory
    Initial penalty factor \(\varepsilon_0\) F/A no

In order to define a frictional contact, the *Friction statement has to follow the *Interaction statement (or following the given penalty factor, if applied). The following models are available:

Model
MC
Hypoplasticity_numgeo

The following properties have to be defined using the frictional models:

  • Coulomb friction. The following parameters are needed:

    Parameter Unit Mandatory
    Penalty factor tangential \(\varepsilon_T\) F/A no
    Wall friction angle \(\tan\delta\) - yes
    Dilatancy angle \(\tan\vartheta\) - yes
    Adhesion \(c\) F/A yes

    Note that the tangential penalty factor is not mandatory to be given. It is estimated based on the material stiffness if not given (see Section Coulomb friction in the Theory Manual).

  • Hypoplastic friction. The following parameters are needed:

    Parameter Unit
    Shear band thickness \(d_s\) Length
    Surface roughness \(\kappa\) -
    Friction angle \(\varphi\) rad
    Poisson's ratio \(\nu\) -
    Granular hardness \(h_s\) F/A
    Exponent \(n\) -
    Minimum void ratio \(e_{d0}\) -
    Maximum void ratio \(e_{c0}\) -
    Factor \(f_{ei0}\) (\(e_{i0}=f_{ei0}\cdot e_{c0}\)) \(f_{ei0}\) -
    Exponent \(\alpha\) -
    Exponent \(\beta\) -
    Intergranular strain multiplier \(m_T\) -
    Intergranular strain multiplier \(m_R\) -
    Intergranular strain radius \(R\) -
    Intergranular strain interpolation \(\beta_R\) -
    Intergranular strain interpolation \(\chi\) -

Fluid interaction

This option defines a fluid interaction for contact analyses with elements having a water displacement degree of freedom, e.g. U8U8 elements. The command is followed by two mandatory keywords and one optional keyword:

  • Name of the (solid) interaction to which this fluid interaction belongs. The interaction has to be defined beforehand. This parameter is mandatory. Currently, a surface interaction for the fluid alone is not allowed.

  • Set this parameter equal to the mechanical model chose to describe the contact behaviour of the fluid. The following mechanical models are available:

    Model Contact tension possible Over-closure relation
    Penalty no, yes with [no separation] linear

    The same properties as for the solid interaction given in Section *Interaction have to be defined. The definition of the penalty factor in case the penalty contact model is chosen, however, is not mandatory. If no value is given, the penalty factor will be calculated based on the bulk modulus of the fluid automatically.

  • The optional [no separation] allows for inseparable contact conditions for the fluid phase. Therefore, tension contact conditions are possible. Note that the contact points have to come into contact once before the no separation conditions comes into effect.