SPC sets in modal transient analysis

Altair Forum User

Hi,

 

I'm a bit lost with the SPC sets.

I have to apply a time dependent displacement on a node (802 035 in my model). As I understand, the HM has to create a constraint on the same node  to make the solver work. So in my model I have the general boundary conditions (embedded nodes including the excitation node) and this specific constraint due to the displacement excitation on the excitation node. My model .fem file thus contains :

 

SPC            1    7948  123456     0.0    $BC
SPC            1    7949  123456     0.0    $BC
SPC            1    7950  123456     0.0    $BC
SPC            1    7951  123456     0.0    $BC
SPC            1    7952  123456     0.0    $BC
SPC            1    7953  123456     0.0    $BC
SPC            1    7954  123456     0.0    $BC
SPC            1  802035  123456     0.0   $excitation node  

 

I have another fem file tu run the study :

$$------------------------------------------------------------------------------$
$$                            I/O Option
$$------------------------------------------------------------------------------$
TITLE=p21-pdb-slush_MTR_S2_11
METHOD(STRUCTURE)=1
SDISP(SORT2,PUNCH)=1
SPC=7
CPU=6
SCREEN OUT
output,HM,NONE
$$------------------------------------------------------------------------------$
$$                      Case Control Cards                                      $
$$------------------------------------------------------------------------------$
SUBCASE       1
  LABEL NM_200hz
ANALYSIS MODES
  DISPLACEMENT(H3D,MODAL,,,) =1
$$
$$
SUBCASE       2
  LABEL MTR_S2
ANALYSIS MTRAN
  RESVEC(APPLOAD)=YES
  DLOAD=9
  TSTEP=11
  SDAMPING(STRUCTURE)=999
  DISPLACEMENT(PUNCH,,,)=1
$$------------------------------------------------------------------------------$
$$                      Bulk Data                                      
$$------------------------------------------------------------------------------$
$$
$$
BEGIN BULK  
PARAM,AUTOSPC,YES     
PARAM,CHECKEL,NO      
$PARAM,G,0.08     
$$
$$
$-------2-------3-------4-------5-------6-------7-------8-------9------X
SPCADD,7,1
DLOAD,9,1.0,1.0,23,1.0,24,1.0,25
EIGRL,1,0.0,200.0,,,,,MASS
TSTEP,11,10000,0.001,2
TABDMP1,999,G
+,1.0,0.03,500.0,0.03,ENDT
$$
$$
$$
$-------2-------3-------4-------5-------6-------7-------8-------9------X
SPCD,20,802035,1,1.0
TLOAD1,23,20,,DISP,904043  
$$
$$
$$
$-------2-------3-------4-------5-------6-------7-------8-------9------X
SPCD,21,802035,2,1.0
TLOAD1,24,21,,DISP,904044
$$
$$
$$
$-------2-------3-------4-------5-------6-------7-------8-------9------X
SPCD,22,802035,3,1.0
TLOAD1,25,22,,DISP,904045
$$
$$  
INCLUDE 'signal_S2.dat'           $excitation signal
INCLUDE 'mesh_Squeak.fem'  $model file
ENDDATA

 

Do you think it's correct? Or I have to create 2 SPC sets in my model : general boundary conditions and constraint due to the excitation?

I hope I was clear,

Thank you

Altair Forum User

Hi @Alina

Did you constraint the node where excitation is load applied with SPCD/DAREA?

 

The excitation node needs a spcd/darea. Please check and update.

 

If you look into the .fem file data there is an SPCD present in it.

Altair Forum User

Hi @Alina,

the excitation node needs a SPCD to define the forced displacement, which then will be referenced in the TLOAD. The DOF in the SPCD additionally needs a SPC constraint.

The TLOAD (or DLOAD when there is more than one TLOAD) will be referenced as DLOAD in the subcase, the SPC will be referenced as SPC in the subcase.

Note: A dynamic force needs a DAREA entry, instead of SPCD. Attached a small example with one transient force.

Thanks, Christian

Unable to find an attachment - read this blog

Altair Forum User

Ok I see. Thank you !