# Implementation

The optimization functionality in Radioss requires an extra input file apart from the usual Starter and Engine input files.

The extra file is an optimization input file termed <name>.radopt (the Starter and Engine files are usually named as <name>_0000.rad and <name>_0001.rad, respectively). The optimization input file (<name>.radopt) defines optimization entities such as the optimization objective, optimization constraints, design variables, optimization responses and so on. The typical set of input data required to optimize a model is listed as follows. The various optimization entries in Radioss that can be chosen to define the corresponding input data are also described.

## Optimization Objective

The optimization objective defines the overall objective of the optimization run. It is driven by the application requirements for the model in the real world. For example, the overall objective of an optimized automobile vehicle design can be to minimize the mass of the vehicle. The optimization objective can be defined in Radioss by selecting an optimization response and specifying whether the response is minimized or maximized. The /DESOBJ data entry is used to define the optimization objective.

## Optimization Constraint

The optimization constraint defines the upper and/or lower bound of a specific optimization response. The model is therefore optimized such that the value of the selected response lies within the defined bounds or constraints. For example, for a structure with a minimum mass objective, the stress response at a region of interest can be defined as an optimization constraint. The stress in the selected region can be constrained not to exceed a specific value (upper bound). The /DCONSTR data entry is used to define the optimization constraints in Radioss.

## Design Variables

Design variables typically correlate the properties of a model to the optimization run. They can be linked to the physical properties (for example, shell thickness) of a system via /DVPREL1 entries. The design variables vary (within their defined bounds) based on the optimization objective and the optimization constraints. Design variables are defined by /DESVAR (for size optimization), /DTPL (for topology optimization), /DSIZE (for free-size optimization), /DSHAPE (for free-shape optimization), and /DTPG (for topography optimization).

Refer to the respective data entry documentation for further information regarding their usage in Radioss. If you are an OptiStruct user, you will find that the Radioss optimization input entries are very similar to the OptiStruct optimization entries of the same name (for example, /DTPL is similar to the DTPL Bulk Data Entry in OptiStruct).

## Pass Bulk Data to OptiStruct Input File

Information can be passed from an RADOPT run to the intermediate OptiStruct input file. The /BULK, /BULKFMT, /BULKMAT, and /BULKPROP Block Format Entries are available.