Limit state design using exact sensitivity analysis and shape optimization

Abstract

Keywords

Data

Language:	English
Year of publishing:	2008
Source:	Ljubljana
Typology:	2.08 - Doctoral Dissertation
Organization:	UL FGG - Faculty of Civil and Geodetic Engineering
Publisher:	[N. Kristanič]
UDC:	624.04(043.3)
COBISS:	4132961
Views:	2265
Downloads:	574
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	Slovenian
Secondary title:	Sinteza konstrukcij z uporabo točne občutljivostne analize in optimizacije oblike v nelinearnem področju
Secondary abstract:	Optimization has become an important tool in engineering activities because it represents a systematic method to improve design with respect to certain criteria. Within the thesis a numeric-symbolic approach to limit load shape optimization is studied which enables the use of an optimization algorithm as an ultimate state design tool. Shape is parameterized symbolically using a general computer algebra system. Therefore the design velocity filed can be computed analytically and an exact sensitivity analysis can be carried out. Accurate sensitivity information is of crucial importance for proper gradient shape optimization. When analyzing imperfection sensitive structures it turns out that the choice of the shape and size of initial imperfections has a major influence on the response of the structure and its ultimate state. Further on, shape optimization applied on the perfect mathematical model can lead to non-optimal results, e.g. a very light structure but very sensitive to buckling. While imperfections are not known in advance, a method for direct determination of the most unfavorable imperfection of structures by means of ultimate limit states was developed. The method is implemented as an internal and separate optimization algorithm within the global shape optimization process. Full geometrical and material nonlinearity is considered throughout the global optimization process consistently, resulting in efficient and robust, ultimate limit load structure design algorithm. The numerical examples indicate that the use of a symbolic-numeric system for gradient shape optimization combined with the use of the most unfavorable imperfections can represent a superior alternative to conventional ultimate limit state design.
Secondary keywords:	gradbeništvo;disertacije;oblika konstrukcij;optimizacija oblike;nosilnost konstrukcij;mejna obtežba;najbolj neugodne začetne nepopolnosti;vpliv na stabilnost;simbolni pristop;
URN:	http://www.dlib.si/?urn=URN:NBN:SI:doc-RU420DHY
File type:	application/pdf
Type (COBISS):	Dissertation
Thesis comment:	Univ. v Ljubljani, Fak. za gradbeništvo in geodezijo
Pages:	XIX, 148 str.
Type (ePrints):	thesis
Title (ePrints):	Limit State Design Using Exact Sensitivity Analysis and Shape Optimization.
Keywords (ePrints):	shape optimization;limit load;worst initial imperfection;symbolic approach.
Keywords (ePrints, secondary language):	oblika konstrukcij;optimizacija oblike;nosilnost konstrukcij;mejna obtežba;najbolj neugodne začetne nepopolnosti;vpliv na stabilnost;simbolni pristop.
Abstract (ePrints):	Optimization has become an important tool in engineering activities because it represents a systematic method to improve design with respect to certain criteria. Within the thesis a numeric-symbolic approach to limit load shape optimization is studied which enables the use of an optimization algorithm as an ultimate state design tool. Shape is parameterized symbolically using a general computer algebra system. Therefore the design velocity filed can be computed analytically and an exact sensitivity analysis can be carried out. Accurate sensitivity information is of crucial importance for proper gradient shape optimization. When analyzing imperfection sensitive structures it turns out that the choice of the shape and size of initial imperfections has a major influence on the response of the structure and its ultimate state. Further on, shape optimization applied on the perfect mathematical model can lead to non-optimal results, e.g. a very light structure but very sensitive to buckling. While imperfections are not known in advance, a method for direct determination of the most unfavorable imperfection of structures by means of ultimate limit states was developed. The method is implemented as an internal and separate optimization algorithm within the global shape optimization process. Full geometrical and material nonlinearity is considered throughout the global optimization process consistently, resulting in efficient and robust, ultimate limit load structure design algorithm. The numerical examples indicate that the use of a symbolic-numeric system for gradient shape optimization combined with the use of the most unfavorable imperfections can represent a superior alternative to conventional ultimate limit state design.
Abstract (ePrints, secondary language):	Optimizacija postaja vedno bolj pomembno orodje v inženirski praksi saj predstavlja sistematično metodo izboljšanja izdelkov glede na dane kriterije. V okviru disertacije je predstavljen simbolno-numerični pristop k optimizaciji oblike konstrukcij v mejnem stanju nosilnosti. Pristop omogoča uporabo optimizacijskega algoritma kot orodje za projektiranje konstrukcij. Oblika konstrukcije je parametrizirana simbolno s pomočjo sistema za splošno računalniško algebro, ki s pomočjo neposrednega odvajanja omogoča analitičen izračun polja začetnih občutljivosti. Posledično je možno izvesti natančen izračun občutljivosti odziva, kar je ključnega pomena, saj so točne občutljivosti pogoj za uspešno uporabo gradientnih metod optimizacije oblike. Kadar obravnavamo konstrukcije, občutljive na spremembo začetne geometrije, se izkaže, da ima izbira oblike in velikosti začetnih nepopolnosti velik vpliv na odziv konstrukcije in njeno mejno stanje. Poleg tega uporaba idealne oblike konstrukcije lahko privede do nestabilnosti optimizacijskih algoritmov ali do neoptimalnih rezultatov, na primer izjemno lahkih konstrukcij, ki so močno občutljive na nepopolnosti. Začetne nepopolnosti niso znane v naprej, zato je v okviru disertacije bila razvita metoda za določitev najbolj neugodne začetne nepopolnosti v smislu mejnega stanja konstrukcij. Metoda je implementirana kot ugnezden optimizacijski algoritem v okviru globalne optimizacije oblike. Skozi celoten proces optimizacije oblike je uporabljen polno nelinearen pristop, ki omogoča učinkovito in robustno sintezo konstrukcij. Prikazani primeri prikazujejo uporabnost metode in nakazujejo, da uporaba simbolno numeričnega okolja za gradientno optimizacijo oblike v povezavi z metodo določitve najbolj neugodnih začetnih nepopolnosti predstavlja napredno alternativo klasičnemu projektiranju konstrukcij.
Keywords (ePrints, secondary language):	oblika konstrukcij;optimizacija oblike;nosilnost konstrukcij;mejna obtežba;najbolj neugodne začetne nepopolnosti;vpliv na stabilnost;simbolni pristop.
ID:	8311040