Limit state design using exact sensitivity analysis and shape optimization

Povzetek

Ključne besede

Podatki

Jezik:	Angleški jezik
Leto izida:	2008
Izvor:	Ljubljana
Tipologija:	2.08 - Doktorska disertacija
Organizacija:	UL FGG - Fakulteta za gradbeništvo in geodezijo
Založnik:	[N. Kristanič]
UDK:	624.04(043.3)
COBISS:	4132961
Št. ogledov:	2265
Št. prenosov:	574
Ocena:	0 (0 glasov)
Metapodatki:

Ostali podatki

Sekundarni jezik:	Slovenski jezik
Sekundarni naslov:	Sinteza konstrukcij z uporabo točne občutljivostne analize in optimizacije oblike v nelinearnem področju
Sekundarni povzetek:	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.
Sekundarne ključne besede:	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
Vrsta datoteke:	application/pdf
Vrsta dela (COBISS):	Doktorska disertacija
Komentar na gradivo:	Univ. v Ljubljani, Fak. za gradbeništvo in geodezijo
Strani:	XIX, 148 str.
Vrsta dela (ePrints):	thesis
Naslov (ePrints):	Limit State Design Using Exact Sensitivity Analysis and Shape Optimization.
Ključne besede (ePrints):	shape optimization;limit load;worst initial imperfection;symbolic approach.
Ključne besede (ePrints, sekundarni jezik):	oblika konstrukcij;optimizacija oblike;nosilnost konstrukcij;mejna obtežba;najbolj neugodne začetne nepopolnosti;vpliv na stabilnost;simbolni pristop.
Povzetek (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.
Povzetek (ePrints, sekundarni jezik):	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.
Ključne besede (ePrints, sekundarni jezik):	oblika konstrukcij;optimizacija oblike;nosilnost konstrukcij;mejna obtežba;najbolj neugodne začetne nepopolnosti;vpliv na stabilnost;simbolni pristop.
ID:	8311040