Discrete Soil-Pipe Interaction

Soil-Pipe interaction concern mainly two non linear aspect::

1. non linear laws connecting pipe-soil relative displacements with soil reaction to the pipe
2. unilateral contact

The first aspect is modelled using the class of discrete element whose documentation is HERE

• DIS_T one or two node element with only translational DOFs
• DIS_TR one or two node element with translational and rotational DOFs

The use of the element it has to be defined in the MODELE analysis starting command, different element type can lay on different "group mesh"

mo = AFFE_MODELE ( MAILLAGE =ma,
                   VERIF =( 'MAILLE', 'NOEUD'),
                    AFFE = ( _F ( GROUP_MA= gma,
                    PHENOMENE= 'MECANIQUE',
                    MODELISATION = '3D'),
                    _F ( GROUP_NO = gno,
                    PHENOMENE= 'MECANIQUE',
                    MODELISATION = 'DIS_T'),
                         )
                         )

Linear

Each node has THREE or SIX DOFs and the element characteristics are its constant (not considering the available parametrization by FUNCTION) stiffness, mass and damping matrices that can be diagonal or full. They are defined using AFFE_CARA_ELEM with keyword DISCRET and DISCRET_2D below a atrip of code as an example. The default reference system is the GLOBAL. while in the figure is showed the LOCAL one

DISCRET=(_F(REPERE='LOCAL',
           CARA='K_T_D_N',
           GROUP_MA='SOIL',
           VALE=(100000.0,10000.0,1000.0,),),
           _F(REPERE='LOCAL',
           CARA='K_T_D_L',
           GROUP_MA='CONT',
           VALE=(10000.0,10000.0,10000.0,),),),

Non-Linear Behaviour

Soil deformation

In the following post http://www.code-aster.org/forum2/viewtopic.php?id=12150 some hints are done on the material model to be used to take account of material plasticity in the spring modeling the soil reaction.

Soil-Pipe Contact and Friction

Contact and friction have to be modelled using a different element respect to the one used to model the energy absorbed by the soil deformation. In the figure the local reference system

The non linearities involved in friction and contact have to be modelled using material model as defined in the operator DEFI_MATERIAU The "mot-cle" DIS_CONTACT defines the parameters associated to the non linear behavior DIS_CHOC that can be set up in non linear solution for condition of impact with friction. Here a strip of code

SoilCont=DEFI_MATERIAU(DIS_CONTACT=_F(RIGI_NOR=1.00E10,
                                      RIGI_TAN=1.00E7,
                                      AMOR_NOR=1.0E3,
                                      AMOR_TAN=1.0E3,
                                      COULOMB=0.25,
                                      DIST_1=0.00,
                                      DIST_2=0.00,),);

It is worthwhile to highlight that it is necessari to use the keyword ORIENTATION to define the normal direction of the contact. and that the node sequence should not be anything,
see post http://www.code-aster.org/forum2/viewtopic.php?pid=24663#p24663 The solution strategy, associated to keyword DIS_CHOC, is defined in the STAT_NON_LINE where the keyword COMP_INCR is build defining the material relationship of type DIS_CHOC using the operand RELATION (See Non Linear behaviour French manual )

-- RobertoBernetti - 16 Feb 2011