# Previous (OS3.5) Input Format

OptiStruct will continue to support the old input format from version 3.5. The new optimization capabilities will not be available if the old format is used for the set up of the optimization problem, that is, if matfrac, mini, maxi, ubcon or lbcon are present. This section is intended to be used for the purpose of debugging or re-running older decks.

## OptiStruct Version 3.5 Parameters

Checkerboard |
0,1,2, or blank (default =
0, if card not in deck) Default = 1, if blank |
Controls checkerboarding.
Use 0 for no checkerboard control. Use 1 or blank for global
averaging over the entire design domain. This option generally
yields a large number of semi-dense elements around fully dense
elements. To reduce the number of semi-dense elements in the
solution, restart the final iteration with checkerboard control off
and run for 10-20 iterations. This may reintroduce some local
checkerboarding. This method is used with plate/shell and solid
design elements and is highly recommended for tetra elements. Nodal
densities are output to the .res file if this
option is used. Use 2 for averaging at local areas identified as
checkerboarded. Since averaging is only applied locally, a much
smaller number of semi-dense elements are found in the final
iteration compared to the global averaging method. This method
applies only to plate/shell design elements. If used in models with
solid design elements, checkerboard control is not applied to solid elements. OptiStruct errors out if this parameter is repeated on DOPTPRM in the Bulk Data section. |

Discrete |
<real> Default = 1.0 |
Discreteness parameter.
Influences the tendency for elements to converge to a material
density of 0 or 1. Higher values decrease the number of elements
that remain between 0 and 1. Recommended bounds are 0.0 and 2.0. OptiStruct errors out if this parameter is repeated on DOPTPRM in the Bulk Data section. |

Dcomp |
<integer> | Shell elements with
PCOMP
PID given on this card will be placed in the
topology design domain. This card overrides declarations in the Bulk
Data section. |

Dshell |
<integer> No default <real> Default = 0.0 |
Shell elements with
PSHELL
PID given in first field of
DSHELL card will be placed into the topology
design domain with T0 given in the second field. This card overrides
declarations in the Bulk Data section. |

Dsolid |
<integer> | Solid elements with
PSOLID
PID given on this card will be placed into the
topology design domain. This card overrides declarations in Bulk
Data section. |

Matinit |
<real> Default = 0.9 or constraint val. |
This card declares the
initial material fraction. For runs with mass as the objective,
default is 0.9. For runs with constrained mass, default is reset to
constraint value. OptiStruct errors out if this parameter is repeated on DOPTPRM in the Bulk Data section. |

Maxiter |
<integer> Default = 30 |
Maximum number of
iterations. Sets an upper limit on the number of iterations OptiStruct can perform before completion. If
Maxiter = 0, baseline analysis is conducted
after initializing material fractions of all design elements at the
matfrac value. If check is present, it overrides
Maxiter = 0. If analysis is present, it
overrides Maxiter = 0.OptiStruct errors out if this parameter is repeated on DOPTPRM in the Bulk Data section. |

Mindens |
<real> Default = 0.01 |
Minimum element material
density. Sets a lower limit on the amount of material that can be
assigned to any design element. Extremely low values for this
parameter can result in an ill-conditioned stiffness
matrix. OptiStruct errors out if this parameter is repeated on DOPTPRM in the Bulk Data section. |

Minmember |
<real> No default <method> Default = 2 |
Specifies the minimum
diameter of members formed by OptiStruct. This also eliminates checkerboard results. This command is used
to eliminate small members. Method is either 1 or 2. Method 2 is set
as default since it achieves more discrete solutions for most
examples. OptiStruct errors out if this parameter is repeated on DOPTPRM in the Bulk Data section. |

Mmcheck |
No input | The use of this card will
ensure a checkerboard free solution, although with the undesired
side effect of achieving a solution that involves a large number of
semi-dense elements, similar to the result of using
CHECKER=1. Therefore, use this card only when
it is necessary.OptiStruct errors out if this parameter is repeated on DOPTPRM in the Bulk Data section. |

Objtol |
<real> Default = 0.005 |
Tolerance in objective
function. If the fractional change in objective function is below
this quantity for two consecutive iterations, the optimization is
considered converged and is stopped. OptiStruct errors out if this parameter is repeated on DOPTPRM in the Bulk Data section. |

Smooth |
<real> Default = 0.7071 |
Solution smoothness. Influences the step size of the optimization iterations if the optimality criteria method is used for topology optimization. Changing this parameter generally results in changes in the solution topology. Larger values of this parameter create smoother topologies for shell element models. Leave this parameter at the default value, unless a different solution topology is desired. Recommended bounds are 0.5 and 0.9. |

## OptiStruct Version 3.5 Subcase Information

lbcon |
<real> <string> no defaults | <integer*> <integer*> | Sets a lower bound constraint of value given in the first field of this card for the response given in the second field of the card. Supported responses are: volume, mass, disp, comp, freq, wcomp, wfreq, and comb. Global responses (volume, mass, wcomp, wfreq, and comb) must be located outside of all subcase declarations. Local responses (comp, freq, and disp) must be located within a subcase declaration. The third field is used for mode number declarations for freq responses or grid number declarations for disp responses. The fourth field is used for grid component declarations for disp responses. |

Mass |
<real> No default |
Mass of total model. If present, the matfrac parameter is not used. Input the total target mass for the part and OptiStruct calculates the material fraction automatically. If the computed material fraction is below 0.0 or above 1.0, OptiStruct returns an error. Not available if using multiple material types in the design domain. | |

Matfrac |
<real>
Default = 0.30 range = 0.0-1.0 |
Material fraction. Defines the amount of material to be distributed within the design domain as a fraction of the design domain. For shell elements, design volume is equal to (T - T0) * area. For solid elements, design volume is equal to the sum of the volume of the elements designated as design space. The design volume multiplied by the material fraction is the total amount of design material available. Material fractions for all design elements in the design space are initialized to matfrac value. | |

maxi |
<string> No default |
<integer*> <integer*> | Sets objective function to maximize a response. Supported responses are: volume, mass, disp, comp, freq, wcomp, wfreq, and comb. Global responses (volume, mass, wcomp, wfreq, and comb) must be located outside of all subcase declarations. Local responses (comp, freq, and disp) must be located within a subcase declaration. The second field is used for mode number declarations for freq responses or grid number declarations for disp responses. The fourth field is used for grid component declarations for disp responses. |

mini |
<string> No default |
<integer*> <integer*> | Sets objective function to minimize a response. Supported responses are: volume, mass, disp, comp, freq, wcomp, wfreq, and comb. Global responses (volume, mass, wcomp, wfreq, and comb) must be located outside of all subcase declarations. Local responses (comp, freq, and disp) must be located within a subcase declaration. The second field is used for mode number declarations for freq responses or grid number declarations for disp responses. The fourth field is used for grid component declarations for disp responses. |

Primary |
<integer or blank> default= lowest mode with highest weight if eigen. Subcase no default if static. | This card sets which mode of eigenvalue solution is used to set material orientation angles. Primary mode declaration only applies to runs without static analyses and must be placed in the subcase declaration. If the card is placed in a static subcase, only that subcase is used to determine material orientation angle - no fields are necessary. | |

ubcon |
<real> <string> no defaults | <integer*> <integer*> | Sets an upper bound constraint of value given in the first field of this card for the response given in the second field of the card. Supported responses are: volume, mass, disp, comp, freq, wcomp, wfreq, and comb. Global responses (volume, mass, wcomp, wfreq, and comb) must be located outside of all subcase declarations. Local responses (comp, freq, and disp) must be located within a subcase declaration. The third field is used for mode number declarations for freq responses or grid number declarations for disp responses. The fourth field is used for grid component declarations for disp responses. |