Page 187 - Using ANSYS for Finite Element Analysis Dynamic, Probabilistic, Design and Heat Transfer Analysis
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174  •   using ansys for finite eLement anaLysis
                    Objective Function: The dependent variable that you are attempting
                to minimize. It should be a function of the DVs (i.e., changing the values
                of the DVs should change the value of the objective function). In the beam
                example, the total weight of the beam could be the objective function (to
                be minimized). You may define only one objective function in an ANSYS
                design optimization problem.
                    Optimization  Variables: Collectively, the design variables, state
                variables, and the objective function. In an ANSYS optimization, these
                variables are represented by user-named variables called parameters. You
                must identify which parameters in the model are DVs, which are SVs, and
                which is the objective function.
                    Design Set or Design: A unique set of parameter values representing
                a given model configuration. Typically, a design set is characterized by the
                optimization variable values; however, all model parameters (including
                those not identified as optimization variables) are included in the set.
                    Feasible  Design:  A  design  that  satisfies  all  specified  constraints
                (those on the SVs as well as on the DVs). If any one of the constraints is
                not satisfied, the design is considered infeasible. The best design is the one
                that satisfies all constraints and produces the minimum objective function
                value. (If all design sets are infeasible, the best design set is the one closest
                to being feasible, irrespective of its objective function value.)
                    Analysis File: An ANSYS input file containing a complete analy-
                sis sequence (preprocessing, solution, and postprocessing). The file must
                contain a parametrically defined model, using parameters to represent all
                inputs and outputs to be used as DVs, SVs, and the objective function.
                    Loop  File: An  optimization  file  (named  Jobname.LOOP),  created
                automatically via the analysis file. The design optimizer uses the loop file
                to perform analysis loops.
                    Loop: A single pass through the analysis file. Output for the last loop
                performed is saved in file Jobname.OPO. An optimization iteration (or
                simply iteration) is one or more analysis loops that result in a new design
                set. Typically, an iteration equates to one loop; however, for the first order
                method, one iteration represents more than one loop.
                    Optimization Database: This contains the current optimization envi-
                ronment, which includes optimization variable definitions, parameters, all
                optimization, specifications, and accumulated design sets. This database
                can be saved (to Jobname.OPT) or resumed at any time in the optimizer.
                    The following Figure 5.2 illustrates the flow of information during an
                optimization analysis.
                    The  analysis  file  must  exist  as  a  separate  entity. The  optimization
                database is not part of the ANSYS model database.
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