بهينه سازي چند هدفه جاذب انرژي هرمي شكل جدار نازك با مقطع هشت گوشه اي با استفاده از الگوريتم هاي تكاملي

چكيده انگليسي :

Pareto Crashworthiness Optimization of Tapered Octagonal Thin walled Tubes Using Multi objective Genetic Algorithms Sayed Amir Masoud Salehizadeh sa salehizadeh@me iut ac ir Date of Submission 2012 03 03 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Mahmoud Salimi salimi@cc iut ac irAbstract Thin walled columns play an important role on passenger safety in vehicular collisions for their progressivedeformation patterns and large energy absorptions A thin walled column is often desirable to the automotiveindustry because such designs could enhance safety and reduce manufacturing cost Due to the complexity ofcrash mechanism obtaining such designs has been a challenge to the trial and error approach using physicalprototype testing To this end combining finite element simulations with optimization methodologies hasbecome the viable means to meet the challenge In this thesis a numerical study of crushing of tapered octagonaltubes was carried out to investigate their behaviors under axial impact loading To simulate this behavior thesoftware code ABAQUS Explicit 6 9 was used and FE models were constructed to study the characteristics ofthe tubes The crash performances of the tubes are evaluated by three criterions The mean crushing force thecrush force efficiency CFE the ratio of the average crushing load to the peak load and the specific energyabsorption SEA absorbed energy per unit mass Parametric studies were conducted to determine the effect ofgeometrical parameters such as the axial length of tube the side length the taper angle and the tube thickness oncrushing behavior of the tapered tubes The FE results are then compared with the existing solution as well asthe available experimental data which are shown to be in good agreement Then theoretical models forpredicting the mean loads in the plastic post buckling range were developed on the basis of inextensible andextensible folding mechanism based on the stationary and travelling plastic hinges The analytical results werecompared with simulation ones and is shown to be in good agreements In addition the optimum values of geometrical parameters are sought for maximum CFE and maximum SEAusing surrogate based optimization Multi objective genetic algorithms GAs are used for Pareto approachoptimization of the energy absorption of the tubes The design of experiments DoE of the factorial design isemployed to construct surrogate models for the objective of specific energy absorption SEA and the crushforce efficiency CFE Response surface artificial neural network and GMDH are the different surrogatemodels used in this study and The Non dominated Sorting Genetic Algorithm II NSGAII is applied to obtainthe Pareto optimal solutions and as a result a set of Pareto optimal solutions for every method are visualized Itis noted from the Pareto optima that these two objectives strongly compete with each other and different criteriaare emphasized along the Pareto frontier Based on this optimization procedure the optimum tube size forcrashworthiness in the impact loading condition has been presented in the three aims These aims covered inobjective functions with different weighting factors It is detected that the maximum CFE requires relativelylarge thickness and large taper angle while the maximum SEA requires large thickness and small taper angle Although ANN was found to be the most accurate surrogate model for SEA and CFE prediction but it was alsodetected that the globally most accurate surrogate model does not necessarily lead to the optimum KeywordsTapered tubes Axial Crushing Crush force efficiency Specific energy absorption Multi objective geneticalgorithms Pareto approach optimization Response surface Artificial Neural network

صالحي زاده، امير مسعود

بهينه سازي چند هدفه جاذب انرژي هرمي شكل جدار نازك با مقطع هشت گوشه اي با استفاده از الگوريتم هاي تكاملي

جبهه پارتو , فرايند مچالگي , الگوريتم مرتب سازي نامغلوب , مد فروريزش