Hi,
I am trying out simulations with large rotations and deformations GROT_GDEP. I have a horizontal beam fixed at the left end and at the right end loaded by a vertical surface pressure. The beam bends downwards in the negative z-direction. See attached figure.  The pressure load is of type SUIV/follower load. The beam is 1000mm long and the maximum displacement is ~170mm in the negative z-direction.

With DEFORMATION=‘GROT_GDEP’  I get the following displacement at the right end:
                             DX                                  DY                                       DZ
Right end        -9.49071988320817E-02 -1.93657103389098E+01 -1.72476505187015E+02

And the following forces:
                      RESULT_X      RESULT_Y     RESULT_Z      MOMENT_X     MOMENT_Y     MOMENT_Z
Beam            1.52710E-10 -2.29193E-10 -4.86864E-09   4.54745E+07  1.31263E+05 -3.13190E+04
Left end       -1.44293E+02  2.79228E+05  9.60747E+05   9.78294E+08 -4.79202E+07  1.40746E+07
Right end       1.44293E+02 -2.79228E+05 -9.60747E+05  -9.32819E+08  4.80515E+07 -1.41059E+07

‘Beam’ is the sum of all FORC_NODA of the nodes of the beam volume elements (TETRA10). ‘Right end’ is the force applied at the right end. ‘Left end’ is the reaction at the left end.  The MOMENT_X for all the beam nodes is 4.54745E+07  which is 4.54745E+07/9.32819E+08 =5% of the applied MOMENT_X= 9.32819E+08 at the right end. I find this result difficult to understand. That the beam is not in equilibrium regarding moment about X does not make sense.

With DEFORMATION=‘PETIT’  I get the following displacement at the right end:
                             DX                                  DY                                       DZ
N8        -9.78444452002913E-02 -1.24114888251096E-01 -1.70929183101883E+02
And the following forces:
                      RESULT_X      RESULT_Y     RESULT_Z      MOMENT_X     MOMENT_Y     MOMENT_Z
Beam            7.18131E-10  1.03910E-10  1.33582E-09  -4.32727E-07  1.48014E-07  1.75791E-07
Left end       -1.30319E+02  2.75596E+05  1.00028E+06   9.72714E+08 -5.00266E+07  1.39103E+07
Right end       1.30319E+02 -2.75596E+05 -1.00028E+06  -9.72714E+08  5.00266E+07 -1.39103E+07

The MOMENT_X for all the Beam nodes is zero and the moment applied at the right end MOMENT_X = 9.72714E+08 is the same as the moment supported at the left end. This result is what I would expect.

See attached files . Is the GROT_GDEP FORCE_NODA calculated correct? –is there some option that need the be specified in CALC_CHAMP for the calculation of FORC_NODA? –or what does it mean that the MOMENT_X  is non zero? The beam stress is high in this case ~5000MPa, still I think the equilibrium should be possible to understand.

Here is something similar where it is found that for GROT_GDEP with C_PLAN elements you have to use RELATION='VMIS_ISOT_LINE’: /forum2/viewtopic.php?id=21492 . But I have not found similar information for my case.

Any inputs are appreciated. -How can non zero MOMENT_X for the beam be understood or corrected?

BR/Micke

Hi, A Question about CREA_MAILLAGE HEXA20_27, PENTA15_18 and the conformity of the mesh.

HEXA27 is recommended for contact analysis(u4.44.11, u2.04.04, u4.23.02) and my experience is that for contact with friction it is a huge difference in converges compared to other elements. At least for FORMULATION='CONTINUE’.

But there is extra effort building the mesh. Building a combined mesh with HEXA20 and PENTA15 can often be easier. However it may then become complicated to convert the mesh into a HEXA27 mesh since CREA_MAILLAGE with keyword HEXA20_27 only modifies QUAD8  and HEXA20 elements (into QUAD 9 and HEXA27).

If you convert a combined HEXA20+PENTA15 mesh using HEXA20_27=_F(TOUT='OUI’) , then on the QUAD sides of the PENTA15 you will get QUAD9 elements that do not conform with the underlying PENTA15. The problem is not solved by sequentially adding the PENTA15_18 operation. QUAD9 elements will then exist on the quad sides of the PENTA18 but the elements will not be joined at the mid side node. The end result is a mesh where you can not use the quad side elements of the pentas.

Questions:
1 -If converting a combined mesh HEXA20+PENTA15 mesh using HEXA20_27=_F(TOUT='OUI’) and then only using the quad sides of the HEXA27 and the triangular sides of the PENTA15 elements: -Will this be ok? –Or will the nonconformity between then voluminal HEXA27(with mid side node) and the PENTA15(without midside node) reduce the accuracy of the stresses and the deformations?

2 -For a HEXA20_27=_F(TOUT='OUI’) + PENTA15_18=_F(TOUT='OUI’) mesh a way to attach the QUAD9 side to the PENTA18 could be to merge the mid side nodes manually (for example by importing them into Salome + merge + export). –Would this be good way to solve this issue if you want to be able to use also the quad sides of the pentas? –Or is there another way? (The documentation says not “At present, mixed grids made up at the same time ofHEXA20 and of PENTA15 are not transformable by CREA_MAILLAGE”) –Still Would the presented “manual merge” idea work?

3 –For a mesh with only PENTA18 (created with the PENTA15_18 =_F(TOUT='OUI’) operation) will the QUAD9 sides perform as good in contact as if the underlying element was a HEXA27?

4 -Anyone want to recommend an automatic hex-mesher?   -Are the Salome plugins DISTENE "MG-" algorithms good?

Thank you for your inputs!
BR/Micke