General Mechanical

General Mechanical

why does 2 link manipulator with fixed and joint support has the same results in modal analysis?

    • Amirmkr
      Subscriber

      I have defined a 2 link manipulator using mpc184 between the 2 beams. In one problem I have defined fixed support in the following code:



      /PREP7  

      ET,1,BEAM188

      ET,2,MPC184 

      KEYOPT,2,1,6

      KEYOPT,2,4,1

      MPTEMP,1,0  

      MPDATA,DENS,1,,7830 


      SECTYPE,1,BEAM,RECT,Beam01,0

      SECDATA,0.01,0.01,2,2,0,0,0,0,0,0,0,0  


      MPDATA,EX,1,,2.068e11  

      MPDATA,PRXY,1,,0.3  


      LOCAL,11,0,1,0,0,0,0,0,1,1, 

      SECTYPE,2,JOINT,REVO,Joint1 

      SECJOINT,,11


      CSYS,0  



      N,2,0,0 

      N,3,0.5,0  

      N,4,1,0 

      N,5,1,0 

      N,6,1.5,0  

      N,7,2,0 


      TYPE,1  

      SECNUM,1


      E,2,3

      E,3,4

      E,5,6

      E,6,7


      TYPE,2  

      SECNUM,2

      E,4,5


      D,2,All,0  


      ANTYPE,2

      MODOPT,LANB,10  

      EQSLV,SPAR  

      MXPAND,10, , ,0 

      LUMPM,0 

      PSTRES,0

      MODOPT,LANB,10,0,0, ,OFF

      FINISH  

      /POST1  

      SET,LIST


       In the other problem I have defined a joint support in the following code:



      /PREP7  

      ET,1,BEAM188

      ET,2,MPC184 

      KEYOPT,2,1,6

      KEYOPT,2,4,1

      MPTEMP,1,0  

      MPDATA,DENS,1,,7830 


      SECTYPE,1,BEAM,RECT,Beam01,0

      SECDATA,0.01,0.01,2,2,0,0,0,0,0,0,0,0  


      MPDATA,EX,1,,2.068e11  

      MPDATA,PRXY,1,,0.3  


      LOCAL,11,0,0,0,0,0,0,0,1,1, 

      SECTYPE,2,JOINT,REVO,Joint1 

      SECJOINT,,11


      LOCAL,12,0,1,0,0,0,0,0,1,1, 

      SECTYPE,3,JOINT,REVO,Joint2 

      SECJOINT,,12


      CSYS,0  


      N,1,0,0

      N,2,0,0 

      N,3,0.5,0  

      N,4,1,0 

      N,5,1,0 

      N,6,1.5,0  

      N,7,2,0 


      TYPE,1  

      SECNUM,1


      E,2,3

      E,3,4

      E,5,6

      E,6,7


      TYPE,2  

      SECNUM,2

      E,1,2


      TYPE,2  

      SECNUM,3 

      E,4,5


      D,1,All,0  


      ANTYPE,2

      MODOPT,LANB,10  

      EQSLV,SPAR  

      MXPAND,10, , ,0 

      LUMPM,0 

      PSTRES,0

      MODOPT,LANB,10,0,0, ,OFF

      FINISH  

      /POST1  

      SET,LIST


      Why do both problems give the same natural frequencies?

    • Amirmkr
      Subscriber
      Even if you put

      D,2,ux,0
      D,2,uy,0
      D,2,uz,0
      D,2,rotx,0
      D,2,roty,0

      to the first case you will get the same results.
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