Users:Structural Optimization/Response Functions/Mass

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General Description

Short Info

This response function controls the mass of a finite element system. The value of this response function represents the overall system mass M of all elements computed by summation of all element masses mi.

M = ∑i mi

Input Parameters

Block headline
Parameter Values, Default(*) Description
OPT-RESPONSE_FCT int : MASS Function ID and type mechanical problem.
Common compulsory parameters
ETA real Finite difference disturbance for sensitivity analysis
GRAD DIRECT, ADJOINT Method of gradient computation
SA GLOBAL_FD, SEMI_ANALYTIC, EXACT_SEMI_ANALYTIC, ANALYTIC Method of derivative computations inside sensitivity analysis
FDA FOREWARD, CENTRAL, BACKWARD Method of finite difference approximation (if neccessary for the chosen sensitivity analysis method)
DESVAR OPT-VAR vector of integers Design variables that are considered in the sensitivity analysis of this response function
Common optional parameters
WEIGHT real, 1.0* The weighting factor for this response function in multi-objective optimization
ANALYSIS PC-ANALYSIS int ID of the underlying analysis
Specific parameters
DOMAIN EL-DOMAIN int ID of system domain
Common Compulsory Parameters for Constraints
Parameter Values, Default(*) Description
REL_LIMIT real Relative limit for constraint, depending on the actual value.
ABS_LIMIT real Absolute limit for constraint. Only one limit can be defined for a constraint.
CONSTRAINT_TYPE INEQUALITY_LT, INEQUALITY_GT, EQUALITY Type of constraint
Common Optional Parameters for Constraints
REL_TOLERANCE real, 0* Upper relative limit until which an inactive constraint is concidered as an active one
LAMBDA_ABS_MAX real, 1/cepsilon* Upper limit for lagrangian multiplier

Example of a Complete Input Block

OPT-RESPONSE_FCT 1 : MASS

  ! -- basic stuff
  WEIGHT=1.0  ETA=1e-06
  GRAD=ADJOINT SA=SEMI_ANALYTIC FDA=FOREWARD
  DESVAR=OPT-VAR 1,2,3,4,5,6

  ! -- response function dependant parameters
  DOMAIN = EL-DOMAIN 1

  ! -- constraint parameters
  ABS_LIMIT = 1-e3
  REL_TOLERANCE = 0.1
  CONSTRAINT_TYPE = INEQUALITY_LT
  LAMBDA_ABS_MAX = 20

Examples

Catenoid

This example considers the mass minimization of a simple catenoid structure. A catenoid can be designed by rotation of the catenary curve[1]. Due to the constant density and thickness it is equivalent to the pure mathematical minimal surface problem. The catenoid as a minimal surface was found by Leonard Euler [2] in 1744. Another principle to compute minimal surfaces is the Formfinding with isotropic pre-stress fields.

Scherkian Minimal Surface

A second example shows another famous minimal surface, namely the so called Scherkian minimal surface[3]. It was found by Heinrich Ferdinand Scherk[4] in 1835.

References

  1. http://en.wikipedia.org/wiki/Catenary
  2. http://de.wikipedia.org/wiki/Leonhard_Euler
  3. http://de.wikipedia.org/wiki/Minimalfl%C3%A4che#Die_Minimalfl.C3.A4che_von_H._F._Scherk
  4. http://de.wikipedia.org/wiki/Heinrich_Ferdinand_Scherk




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