Hey there,
I am simulating a plate loaded at its centroid resting on an elastic foundation implemented with RIGI_PARASOL (scheme attached).
Although the model is very simple, I am encountering a persistent problem I cannot resolve. Before writing this I went through the SSNL130 case study and analysed its settings; I am attaching the .comm file for reference.
The issue appears when the applied force pushes the plate downward: some springs in the RIGI_PARASOL foundation stop providing reaction, and the structure acquires uncontrolled displacements so the simulation does not converge.
My only workaround so far has been to add a set of DISCRETE elements above the plate to prevent rigid-body motion when RIGI_PARASOL ceases to react. However, this creates a new problem: choosing a suitable stiffness for those DISCRETE elements. As I reduce their stiffness the displacements grow very large (the simulation still converges), which suggests the appearance of near-rigid-body motion. For relatively high stiffness values the displacement field shape looks reasonable, but the magnitudes do not seem correct — I have attached a screenshot illustrating this.
I have been working on this for weeks without success and would appreciate any advice.
Thanks in advance for your help.
Cheers
mesh = LIRE_MAILLAGE(FORMAT='MED',
UNITE=20)
mesh = DEFI_GROUP(reuse=mesh,
CREA_GROUP_NO=_F(TOUT_GROUP_MA='OUI'),
MAILLAGE=mesh)
mesh = MODI_MAILLAGE(reuse=mesh,
MAILLAGE=mesh,
ORIE_PEAU=_F(GROUP_MA_PEAU=('plate', )))
model = AFFE_MODELE(AFFE=(_F(GROUP_MA=('plate', ),
MODELISATION='DKT',
PHENOMENE='MECANIQUE'),
_F(GROUP_MA=('plate_node_extruded', ),
MODELISATION='DIS_T',
PHENOMENE='MECANIQUE'),
_F(GROUP_MA=('plate_node_extruded_1', ),
MODELISATION='DIS_T',
PHENOMENE='MECANIQUE')),
MAILLAGE=mesh)
elempro0 = AFFE_CARA_ELEM(COQUE=_F(COQUE_NCOU=1,
EPAIS=0.25,
GROUP_MA=('plate', )),
DISCRET=_F(CARA='K_T_D_L',
GROUP_MA=('plate_node_extruded_1', ),
REPERE='LOCAL',
SYME='OUI',
VALE=(100.0, 100.0, 100.0)),
MODELE=model,
ORIENTATION=_F(CARA='ANGL_VRIL',
GROUP_MA=('plate_node_extruded', ),
VALE=0.0),
RIGI_PARASOL=_F(CARA=('K_T_D_L', ),
COEF_GROUP=(1.0, ),
GROUP_MA=('plate', ),
GROUP_MA_SEG2=('plate_node_extruded', ),
GROUP_NO_CENTRE=('force', ),
REPERE='LOCAL',
VALE=(67500000.0, 67500000.0, 67500000.0)))
conc = DEFI_MATERIAU(ELAS=_F(E=15866700000.0,
NU=0.3))
dis = DEFI_MATERIAU(DIS_CONTACT=_F(DIST_1=0.05),
ELAS=_F(E=15866700000.0,
NU=0.3))
fieldma1 = AFFE_MATERIAU(AFFE=(_F(GROUP_MA=('plate_node_extruded_1', 'plate'),
MATER=(conc, )),
_F(GROUP_MA=('plate_node_extruded', ),
MATER=(dis, ))),
MODELE=model)
inst = DEFI_LIST_REEL(DEBUT=0.0,
INTERVALLE=_F(JUSQU_A=1.0,
NOMBRE=15))
mult = DEFI_FONCTION(NOM_PARA='INST',
PROL_DROITE='LINEAIRE',
PROL_GAUCHE='LINEAIRE',
VALE=(0.0, 0.0, 1.0, 1.0))
load = AFFE_CHAR_MECA(FORCE_NODALE=_F(FZ=-51750.0,
GROUP_NO=('force', )),
MODELE=model)
fix = AFFE_CHAR_MECA(DDL_IMPO=(_F(DX=0.0,
GROUP_MA=('sym_x', )),
_F(DY=0.0,
GROUP_MA=('sym_y', )),
_F(DX=0.0,
DY=0.0,
DZ=0.0,
GROUP_NO=('plate_node_top', 'plate_node_top_1'))),
MODELE=model)
reslin = MECA_STATIQUE(CARA_ELEM=elempro0,
CHAM_MATER=fieldma1,
EXCIT=(_F(CHARGE=load),
_F(CHARGE=fix)),
MODELE=model,
OPTION='SANS')
resnonl = STAT_NON_LINE(CARA_ELEM=elempro0,
CHAM_MATER=fieldma1,
COMPORTEMENT=(_F(RELATION='ELAS',
TOUT='OUI'),
_F(GROUP_MA=('plate_node_extruded', ),
RELATION='DIS_CHOC')),
CONVERGENCE=_F(ITER_GLOB_MAXI=50),
EXCIT=(_F(CHARGE=fix),
_F(CHARGE=load,
FONC_MULT=mult,
TYPE_CHARGE='FIXE_CSTE')),
INCREMENT=_F(LIST_INST=inst),
MODELE=model,
NEWTON=_F(MATRICE='ELASTIQUE',
PREDICTION='ELASTIQUE'),
SOLVEUR=_F(NPREC=-1))
IMPR_RESU(FORMAT='MED',
RESU=_F(NOM_CHAM=('DEPL', ),
RESULTAT=reslin),
UNITE=80,
VERSION_MED='4.0.0')
IMPR_RESU(FORMAT='MED',
RESU=_F(NOM_CHAM=('DEPL', ),
RESULTAT=resnonl),
UNITE=2,
VERSION_MED='4.0.0')
FIN()
