Automotive companies are exposed to tough competition and therefore strive to design better products in a cheaper and faster manner. This challenge requires continuous improvements of methods and tools, and simulation models are therefore used to evaluate every possible aspect of the product. Optimization has become increasingly popular, but its full potential is not yet utilized. The increased demand for accurate simulation results has led to detailed simulation models that often are computationally expensive to evaluate. Metamodel-based design optimization (MBDO) is an attractive approach to relieve the computational burden during optimization studies. Metamodels are approximations of the detailed simulation models that take little time to evaluate and they are therefore especially attractive when many evaluations are needed, as e.g. in multidisciplinary design optimization (MDO). In this thesis, state-of-the-art methods for metamodel-based design optimization are covered and different multidisciplinary design optimization methods are presented. An efficient MDO process for large-scale automotive structural applications is developed where aspects related to its implementation is considered. The process is described and demonstrated in a simple application example. It is found that the process is efficient, flexible, and suitable for common structural MDO applications within the automotive industry. Furthermore, it fits easily into an existing organization and product development process and improved designs can be obtained even when using metamodels with limited accuracy. It is therefore concluded that by incorporating the described metamodel-based MDO process into the product development, there is a potential for designing better products in a shorter time.

In the early design stage of automotive joints, fuzziness is omnipresent because designers reason in non quantitative terms and deal with imprecise data. Consequently, they need a design methodology that accounts for vagueness. Fuzzy sets and utility theory are appropriate tools because they link the vagueness in a problem formulation and the precise nature of mathematical models. Fuzzy multiobjective optimizations are performed on an automotive joint to maximize the overall designer's satisfaction. Several methods that account for all the attributes and the fuzziness in the goals are used. Three multiobjective fuzzy approaches, namely, the conservative, the aggressive and the moderate methods are investigated. Utility theory is also considered to optimize the joint. One of the performance attributes of the joint, the stiffness, is evaluated rapidly using approximate tools (neural networks and response surface polynomials) to overcome the high computational cost of PEA, which is traditionally used to calculate the stiffness. This research compares fuzzy set methods and utility theory in design of automotive components. These methods are applied on two examples where the same B-pillar to rocker joint of an actual car is optimized. Fuzzy set based methods and utility theory appear to be suitable for optimizing automotive joints because they allow for trading conflicting objectives. Fuzzy set based methods avoid trading objectives to the point of having a level of satisfaction equal to zero. When using the fuzzy set based methods investigated in this research, the trade-offs among the attributes are not explicitly defined by the user. Utility theory requires the user to quantify precisely the trade-offs among the attributes. When using utility theory, the overall satisfaction of a design can be non zero even if one or more attributes has a level of satisfaction equal to zero. The approximate tools enable us to perform the optimization efficiently by reducing considerably the computational cost. / Master of Science

Disertacijoje nagrinėjamos santvarų globalaus optimizavimo problemos. Pagrindinis darbo tikslas – sukurti technologiją ir ją aprašančius algoritmus santvarų topologijos optimizavimui ir sinchroniniam topologijos ir formos optimizavimui. Optimizavimui naudojami genetiniai algoritmai. Topologijai optimizuoti pasirinkta perdėtai sujungtos struktūros strategija (angl. ground structure approach). / The dissertation deals with the topology optimization problems of the truss systems. The main aim of the work is to create a technology and implementing algorithms for topology optimization and for simultaneous topology and shape optimization of truss systems. The genetic algorithms are used as the main tool for optimization. The topology optimization problems are formulated using the so-called ground structure approach.

The dissertation deals with the topology optimization problems of the truss systems. The main aim of the work is to create a technology and implementing algorithms for topology optimization and for simultaneous topology and shape optimization of truss systems. The genetic algorithms are used as the main tool for optimization. The topology optimization problems are formulated using the so-called ground structure approach. / Disertacijoje nagrinėjamos santvarų globalaus optimizavimo problemos. Pagrindinis darbo tikslas – sukurti technologiją ir ją aprašančius algoritmus santvarų topologijos optimizavimui ir sinchroniniam topologijos ir formos optimizavimui. Optimizavimui naudojami genetiniai algoritmai. Topologijai optimizuoti pasirinkta perdėtai sujungtos struktūros strategija (angl. ground structure approach).

Disertaciniame darbe išplėtota vieninga tamprių-plastinių prisitaikančių sistemų optimizavimo su stiprumo, standumo ir klumpamosios galios sąlygomis, taikant ekstreminius energinius principus, matematinio programavimo teoriją, šiuolaikines kompiuterines technologijas ir sąsajas su projektavimo standartais, metodika. Darbe parodyta, kad prisitaikomumo teorija yra bendriausias metodinis įrankis skirtas statybinių konstrukcijų skaičiavimui nuo įvairių apkrovų, įgalinantis išvengti detalios apkrovimo istorijos nagrinėjimo. Disertaciją sudaro įvadas, penkeri skyriai, rezultatų apibendrinimas, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai ir keturi priedai. Įvadiniame skyriuje aptariama tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas bei uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų praktinė reikšmė, ginamieji teiginiai. Įvado pabaigoje pristatomos disertacijos tema autoriaus paskelbtos publikacijos ir pranešimų konferencijose sąrašas bei disertacijos struktūra. Pirmasis skyrius skirtas literatūros apžvalgai. Jame atlikta prisitaikančių konstrukcijų optimizavimo metodų apžvalga, išryškinta būtinybė pasitelkti sąsajas tarp teorinių optimizavimo metodų ir projektavimo standartų. Antrajame skyriuje aptariama konstrukcijų diskretizacija, sudaryti patobulinti projektinio ir patikrinamojo uždavinių matematiniai modeliai. Trečiajame skyriuje parodyta sąsaja tarp statybos inžinerijoje... [toliau žr. visą tekstą] / The optimization methodology of shakedow structures evaluating strength, stiffness and stability constraints and unifying extremum energy principles, mathematical programming theory, stat-of-the-art computer technologies and design standards was developed in the dissertation. There are shown in the work that shakedown theory is a generalized tool for calculation of civil engineering structures under different loading conditions that avoid detailed investigation of loading history. The dissertation consists of six parts including Introduction, 5 chapters, Conclusions, References and 4 Annexes. The introduction reveals the investigated problem, importance of the thesis and the object of research and describes the purpose and tasks of the paper, research methodology, scientific novelty, the practical significance of results examined in the paper and defended statements. The introduction ends in presenting the author’s publications on the subject of the defended dissertation, offering the material of made presentations in conferences and defining the structure of the dissertation. Chapter 1 revises used literature. The optimization methods of shakedown structures are reviewed and a demand of linkage between theoretical optimization methods and standards is highlighted. Chapter 2 describes the discretization of structures, the mathematical models for improved design and check problems was created. In the Chapter 3 the equivalence between load combinations of civil engineering... [to full text]

Multidisciplinary design optimization (MDO) can be used as an effective tool to improve the design of automotive structures. Large-scale MDO problems typically involve several groups who must work concurrently and autonomously for reasons of efficiency. When performing MDO, a large number of designs need to be rated. Detailed simulation models used to assess automotive design proposals are often computationally expensive to evaluate. A useful MDO process must distribute work to the groups involved and be computationally efficient. In this thesis, MDO methods are assessed in relation to the characteristics of automotive structural applications. Single-level optimization methods have a single optimizer, while multi-level optimization methods have a distributed optimization process. Collaborative optimization and analytical target cascading are possible choices of multi-level optimization methods for automotive structures. They distribute the design process, but are complex. One approach to handle the computationally demanding simulation models involves metamodel-based design optimization (MBDO), where metamodels are used as approximations of the detailed models during optimization studies. Metamodels can be created by individual groups prior to the optimization process, and therefore also offer a way of distributing work. A single-level optimization method in combination with metamodels is concluded to be the most straightforward way of implementing MDO into the development of automotive structures.

Ce travail de thèse est une recherche sur l'interaction entre des états atomiques excités électroniquement et un environnement non réactif. Nous avons étudié théoriquement et expérimentalement des situations où un atome métallique (K et Ba) est placé dans un environnement de taille finie (agrégat d’argon). La présence de l'environnement affecte les niveaux électroniques de l'atome. En retour, l'excitation de l'atome induit une dynamique de relaxation de l'énergie électronique via les déformations du système atome-agrégat. La partie expérimentale du travail porte sur les deux aspects : spectroscopie et dynamique. Dans les deux cas un premier laser porte l'atome métallique dans un état électronique excité et un second l'ionise. L'observable est le spectre de photoélectrons enregistré après photo ionisation éventuellement complétée par des informations sur les photo-ions qui sont également produits. Cette technique à deux lasers conduit à des mesures de dynamique selon la technique pompe-sonde quand les lasers utilisés sont à impulsion ultracourte (60 fs). L'utilisation de lasers nanosecondes, conduit à des mesures de résonance non résolues temporellement qui donnent des informations spectroscopiques sur la position des niveaux d'énergie du système étudié. D’un point de vue théorique, les états excités du système M-Ar_n ont été calculés ab-initio en utilisant des pseudo-potentiels à grand cœur pour limiter les électrons actifs aux seuls électrons de valence du métal. L’étude d’un métal alcalin (potassium) rend cette méthode particulièrement attractive car un seul électron est actif. Le calcul ab-initio et une simulation Monte-Carlo ont été couplés pour optimiser la géométrie d'agrégats KAr_n (n=1-10) quand K est dans l'état fondamental, excité dans les états 4p ou 5s ou ionisé vers l'état fondamental de l'ion. Des calculs ont également été conduits en collaboration avec B. Gervais (CIMAP, Caen) sur des agrégats KAr_n comportant plusieurs dizaines d'atomes Ar. Des spectres d'absorption ont également été calculés. D’un point de vue expérimental, nous avons pu caractériser les niveaux électroniques excités du potassium et du baryum perturbés par l’agrégat. Dans les deux cas une bande ∏, liante, et une bande ∑, anti-liante, ont été observées. Dans le cas du potassium, nous avons montré que l’excitation dans la bande ∑ conduisait à une éjection de l’agrégat en 1-2 ps alors que pour le baryum, l’état électronique relaxe majoritairement sur l’état ∏ en ≈ 6 ps et ne conduit pas à une éjection. L’interprétation fait appel aux structures et aux potentiels calculés. Une étude équivalente a été conduite sur la molécule de DABCO déposée sur agrégat. Au contraire de K et Ba, le premier état excité de cette molécule a un fort caractère isotrope et diffus, ce qui confère un caractère particulier à la dynamique photoinduite. / This thesis is a study on the interaction between electronically excited atomic states and a non-reactive environment. We have theoretically and experimentally studied situations where a metal atom (Ba or K) is placed in a finite size environment (argon cluster). The presence of the medium affects the electronic levels of the atom. On the other side, the excitation of the atom induces a relaxation dynamics of the electronic energy through the deformation of the cluster. The experimental part of this work focuses on two aspects : the spectroscopy and the dynamics. In both cases a first laser electronically excites the metal atom and the second ionizes the excited system. The observable is the photoelectron spectrum recorded after photoionization and possibly information on the photoion which are also produced. This pump/probe technique, with also two lasers, provide the ultrafast dynamic when the lasers pulses used are of ultrashort (60 fs ). The use of nanosecond lasers leads to resonance spectroscopic measurement, unresolved temporally, which give information on the position of the energy levels of the studied system. From a theoretical point-of-view, the excited states of M-Ar_n were calculated at the ab initio level, using large core pseudo-potential to limit the active electrons of the metal to valence electrons. The study of alkali metals (potassium) is especially well adapted to this method since only one electron is active. The ab-initio calculation and a Monte-Carlo simulation where coupled to optimize the geometry of the KAr_n (n = 1-10) cluster when K is in the ground state of the neutral and the ion, or excited in the 4p or 5s state. Calculations were also conducted in collaboration with B. Gervais (CIMAP, Caen) on KAr_n clusters having several tens of argon atoms. Absorption spectra were also calculated. From an experimental point-of-view, we were able to characterize the excited states of potassium and barium perturbed by the clusters. In both cases a binding ∏-state, and an anti-binding ∑ -state were observed. In the case of potassium, we observered that the excitation on the ∑ -state leads to the ejection of the metal within 1-2 ps while for barium, the excited state relaxes mainly on the ∏-state within 6 ps and does not followed by an ejection. The interpretation of these results uses the structures and potential calculated. A similar study was conducted on the DABCO molecule deposited argon cluster. Instead of K and Ba, the first excited state of this molecule is a diffuse isotropic state, which gives a specific relaxation to the photoinduced dynamics.

This thesis describes the development and setup of hybrid index structures. They are access methods for retrieval techniques in hybrid data spaces which are formed by one or more relational or normalised columns in conjunction with one non-relational or non-normalised column. Examples for these hybrid data spaces are, among others, textual data combined with geographical ones or data from enterprise content management systems. However, all non-relational data types may be stored as well as image feature vectors or comparable types. Hybrid index structures are known to function efficiently regarding retrieval operations. Unfortunately, little information is available about reorganisation operations which insert or update the row tuples. The fundamental research is mainly executed in simulation based environments. This work is written ensuing from a previous thesis that implements hybrid access structures in realistic database surroundings. During this implementation it has become obvious that retrieval works efficiently. Yet, the restructuring approaches require too much effort to be set up, e.g., in web search engine environments where several thousands of documents are inserted or modified every day. These search engines rely on relational database systems as storage backends. Hence, the setup of these access methods for hybrid data spaces is required in real world database management systems. This thesis tries to apply a systematic approach for the optimisation of the rearrangement algorithms inside realistic scenarios. Thus, a measurement and evaluation scheme is created which is repeatedly deployed to an evolving state and a model of hybrid index structures in order to optimise the regrouping algorithms to make a setup of hybrid index structures in real world information systems possible. Thus, a set of input corpora is selected which is applied to the test suite as well as an evaluation scheme. To sum up, it can be said that this thesis describes input sets, a test suite including an evaluation scheme as well as optimisation iterations on reorganisation algorithms reflecting a theoretical model framework to provide efficient reorganisations of hybrid index structures supporting multimedia search criteria.