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## #1 2018-07-05 08:32:10

jeanpierreaubry
Guru
From: nantes (france)
Registered: 2009-03-12
Posts: 3,616

### trouble with FORCE_POUTRE and keyword VENT

hello

i am struggling with the use of FORCE_POUTRE with keyword VENT

the field read in sdnl102a.comm with VVENT=LIRE_RESU
looks like a speed field i.e. m/s

U4.44.01 in FORCE_POUTRE states the values introduced should be lineic force i.e. N/m

as far as i know we have Pressure=0.5*RHO*V^2

where is translation from speed to force is done in sdnl102?
how is the RHO value introduced?

what happens if we change the unit system from kg, m, s to t, mm, s?

i do not consider any dynamic behavior in a first analysis

jean pierre aubry

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## #2 2018-07-06 07:40:41

jlf
Member
Registered: 2007-11-22
Posts: 236

### Re: trouble with FORCE_POUTRE and keyword VENT

Hello,

First, in code_aster there are no units. The user must assume the coherence.

For sdnl102 :
- vvent = LIRE_RESU : read a time dependent, field of wind speed.
- FVENTCX = AFFE_CHAR_MECA : define the wind load

The relation between the field wind and the force is in AFFE_CARA_ELEM by the definition of FCX on the beams elements where FCX is a function of the relative speed. In the definition of FCX you find 0.5*rho*(Vrela^2)*Dimension

The unit for FCX, LIRE_RESU, your mesh must be coherent.

JLF

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## #3 2018-07-10 07:42:13

jeanpierreaubry
Guru
From: nantes (france)
Registered: 2009-03-12
Posts: 3,616

### Re: trouble with FORCE_POUTRE and keyword VENT

hello jlf

First, in code_aster there are no units. The user must assume the coherence.

yes i know that

let me present a simple example
one single tube l=100, r=5, wind linear force 10,
total reaction should be  Reac=100*10*10=10000
but result is 1000, 10 times as less
whatever i do to FCXV nothing changes

what is wrong

``````DEBUT();

mesh0=LIRE_MAILLAGE(UNITE=20,FORMAT='MED',);

mesh0=DEFI_GROUP(
reuse =mesh0,MAILLAGE=mesh0,
CREA_GROUP_NO=_F(TOUT_GROUP_MA='OUI',),
);

model=AFFE_MODELE(
MAILLAGE=mesh0,
AFFE=(
_F(GROUP_MA='tube',PHENOMENE='MECANIQUE',MODELISATION='POU_D_E',),
),
);

steel=DEFI_MATERIAU(ELAS=_F(E=210000.,NU=0.3,RHO=8.0e-9,),);

material=AFFE_MATERIAU(MAILLAGE=mesh0,AFFE=_F(GROUP_MA=('tube'), MATER=steel,),);

FCXV=DEFI_FONCTION(
NOM_PARA='VITE',
VALE=(  0.0 ,   0.0,
1.0 ,  1000.0 ),
PROL_GAUCHE='LINEAIRE',
PROL_DROITE='LINEAIRE',
)

elemcar=AFFE_CARA_ELEM(
MODELE=model,
POUTRE=_F(
GROUP_MA=('tube',),SECTION='CERCLE',CARA=('R','EP'),VALE=(5,5,),
FCX = FCXV,
),
);

ground=AFFE_CHAR_MECA(
MODELE=model,
DDL_IMPO=_F(GROUP_NO=('fix'),DX=0,DY=0,DZ=0,DRX=0,DRY=0,DRZ=0,),
);

vent=10.0*1;
fxf=DEFI_FONCTION(
NOM_PARA='INST',
VALE=(0,0, 1,1*vent),
PROL_DROITE='CONSTANT',
);
fyf=DEFI_FONCTION(
NOM_PARA='INST',
VALE=(0,0, 1,1*vent,),
PROL_DROITE='CONSTANT',
);

cvent=AFFE_CHAR_MECA_F(
MODELE=model,
FORCE_POUTRE=_F(
GROUP_MA=('tube'),
FX=fxf,FY=fyf,
TYPE_CHARGE='VENT',
),
);

liste=DEFI_LIST_REEL(
DEBUT=0.0,
INTERVALLE=(
_F(JUSQU_A=1.0,PAS=1.0,),
),
);

stat=STAT_NON_LINE(
MODELE=model,
CHAM_MATER=material,
CARA_ELEM=elemcar,
EXCIT=(
_F(CHARGE=ground,),
_F(CHARGE=cvent,TYPE_CHARGE='FIXE_CSTE',),
),
COMPORTEMENT=_F(RELATION='ELAS',DEFORMATION='PETIT',GROUP_MA=('tube',),),
INCREMENT=_F(LIST_INST=liste,),
NEWTON=_F(PREDICTION='TANGENTE',MATRICE='TANGENTE',REAC_ITER=1,),
RECH_LINEAIRE=_F(),
CONVERGENCE=_F(RESI_GLOB_RELA=1e-4,ITER_GLOB_MAXI=100,),
);

stat=CALC_CHAMP(
reuse =stat,RESULTAT=stat,
FORCE=('REAC_NODA',),
);

sreac=POST_RELEVE_T(
ACTION=_F(
INTITULE='sum reactions',
GROUP_NO=('tube',),
RESULTAT=stat,
NOM_CHAM='REAC_NODA',
TOUT_ORDRE='OUI',
RESULTANTE=('DX','DY','DZ',),
MOMENT=('DRX','DRY','DRZ',),
POINT=(0,0,0,),
OPERATION='EXTRACTION',
),
);
IMPR_TABLE (TABLE=sreac,FORMAT_R='1PE12.3',)

FIN();``````
``````##ASTER 13.04.00 CONCEPT sreac CALCULE LE 10/07/2018 A 06:37:54 DE TYPE
#TABLE_SDASTER
INTITULE         RESU     NOM_CHAM          NUME_ORDRE    INST          RESULT_X      RESULT_Y      RESULT_Z      MOMENT_X      MOMENT_Y      MOMENT_Z
sum reactions    stat     REAC_NODA                    0     0.000E+00     0.000E+00     0.000E+00     0.000E+00     0.000E+00     0.000E+00     0.000E+00
sum reactions    stat     REAC_NODA                    1     1.000E+00    -1.000E+03    -1.000E+03     1.578E-30    -5.000E+04     5.000E+04    -3.062E-12``````

PS
this investigation  comes from your remarks at last Pronet meeting

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## #4 2018-07-17 15:09:07

jlf
Member
Registered: 2007-11-22
Posts: 236

### Re: trouble with FORCE_POUTRE and keyword VENT

hello, Jean-pierre

If you want to take into account a wind field, there is only ONE method :
* You must define a time dependent field of wind on a mesh which represent the space around your structure.
* You read this file with LIRE_RESU command, TYPE_RESU='EVOL_CHAR' and NOM_CHAM= 'VITE_VENT' see "sdnl102".
* You define an FCX. A function of the relative speed of the structure vs the field wind.
* You define a load with AFFE_CHAR_MECA/EVOL_CHAR = VVENT (field you have read with LIRE_RESU).
Now code_aster have all the datas.

In your example the fxf and fyf are time dependent, and you don't have wind field. Code_aster detect you don't have a load define with EVOL_CHAR and NOM_CHAM='VITE_VENT'  (wind field), that why FCX is not take into account.

I don't understand Reac=100*10*10. Why 10*10
For me : Reac= Long*Load = 100[m]*10[N]/[m] = 1000[N]

JLF

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