Modeling A
==============


Characteristics of modeling
-----------------------------------

A DIS_T element on a POI1 mesh is used to model the system.

The calculation is done on a modal basis. We block movements in :math:`Y` and :math:`Z`, so the modal base only contains one mode.

We use the dynamic calculation functionality based on the modal basis of the operator DYNA_VIBRA, with the keyword CHOC to model local nonlinearity.

An obstacle of type PLAN_Z (two parallel planes separated by a game) is used to simulate the sliding plane. We choose to use NORM_OBST: :math:`(0.,1.,0.)` as the generator of this plan :math:`\mathit{Oy}`. The origin of the obstacle is ORIG_OBST: :math:`(0.\mathrm{,0}\mathrm{.}\mathrm{,1}\mathrm{.})`, his game that gives the half-distance between planes is :math:`0.5`.

We place ourselves in the relative coordinate system (single-support loading) and we apply an accelerated loading with CALC_CHAR_SEISME.

A time step of :math:`{3.10}^{\mathrm{-}5}s` is used for time integration to limit the calculation time. This time step is much less than

.. image:: images/Object_137.svg
    :width: 255
    :height: 29


.. _RefImage_Object_137.svg:

.

The tangential friction stiffness is taken as high as possible to ensure the stability of the diagram, i.e. :math:`{K}_{T}\mathrm{=}900000N\mathrm{/}m`. The value :math:`{K}_{T}\mathrm{=}1000000N\mathrm{/}m` leads to numerical instability.

The normal stiffness :math:`{K}_{N}` should be taken equal to :math:`20N\mathrm{/}m` to exactly compensate for the weight of the mass. (the value of the game is :math:`\mathrm{0,50}m`). Any other value leads to outlier results.


Characteristics of the mesh
----------------------------

Number of knots: 1

Number of meshes and types: 1 POI1