HyperWorks Solvers

Rotating Bar Example

Rotating Bar Example

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Rotating Bar Example

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This is an introductory example of the optimization of a multi-body dynamics system. The object of the rotating bar problem is to minimize the maximum stress of the bar. The structure consists of 5 bar elements. The driving motion has a velocity of sin(2t), which is applied to the left end of the structure. Sections of the bar elements are solid circles. Design variables are the radii of the sections. The mass of the structure should be less than 10kg.

bar_1

Rotating bar

A portion of the input file:

DESGLB   = 4

MINMAX   = 14

STRESS   = ALL

SUBCASE    1

 MBSIM  =   1

 MOTION =   1

 SPC    =   10

   :

   :

$

DESVAR  1       RAD1    10.00   0.05   100.0              

DESVAR  2       RAD2    10.00   0.05   100.0              

DESVAR  3       RAD3    10.00   0.05   100.0              

DESVAR  4       RAD4    10.00   0.05   100.0              

DESVAR  5       RAD5    10.00   0.05   100.0              

$

DVPREL1 10      PBARL   1       DIM1            0.0    

+   1   1.0    

DVPREL1 11      PBARL   2       DIM1            0.0    

+   2   1.0    

DVPREL1 12      PBARL   3       DIM1            0.0    

+   3   1.0    

DVPREL1 13      PBARL   4       DIM1            0.0    

+   4   1.0    

DVPREL1 14      PBARL   5       DIM1            0.0    

+   5   1.0    

$

DRESP1  33      STRESS  STRESS  PBARL           SNMAX             1

+   2   3       4       5

DRESP1  100     MASS    MASS

$

DOBJREF 14      33      1       -1.0    1.0

$

DCONSTR 4       100             2.5

 

     :

     :

 

SPC1    10      123456  1

       

     :

     :

 

ENDDATA

The input file is just like one for an ordinary min-max problem. The maximum normal stress of the flexible body of the subcase 1 is to be minimized by using DOBJREF and MINMAX.

Notable points include:

•Because the stress in multi-body dynamics systems is a time variant quantity, the minimization of stress in multi-body dynamics analysis subcases should be a min-max problem.
•The SPC1 card fixes only 6 dof of node 1 of the flexible body in order to remove 6 rigid body motions. If you fix more than 6 dof of the flexible body, the additional fixed dof become constraints of the flexible body.
•Stress output request is placed above the first subcase. If you place output request inside subcase, your output request will be ignored.

The input file can be found in <install_directory>/demos/hwsolvers/optistruct/rotating_bar_design.fem.