O presente trabalho trata da análise numérica de cascas abatidas com o uso do método dos elementos de contorno (MEC). A formulação é desenvolvida a partir do acoplamento entre as equações integrais para flexão de placas delgadas e para estado plano de tensão. No esquema implementado, os termos sobre o contorno são avaliados a partir de processos analíticos e numéricos de integração. No caso das integrais de domínio, aplica-se um procedimento semi-analítico de cálculo sobre células discretas. A validação do modelo computacional desenvolvido é feita com base em resultados da literatura, obtidos com uso do método dos elementos finitos e dos elementos de contorno, além de soluções analíticas. / The present work deals with the numerical analysis of shallow shells using boundary element method (BEM). The formulation is developed by coupling integral equations of plate bending and plane stress elasticity. In the implemented scheme, the boundary terms are evaluated with analytical and numerical processes of integration. In the case of domain integrals, a semi-analytical calculation procedure is applied on discrete cells. The validation of developed computational model is made with results from other works, obtained by use of BEM or finite element method, besides analytical solutions.

Les panneaux en bois lamellé croisé (en anglais CLT - Cross Laminated Timber) sont des éléments de structure composés de couches en bois collées entre eleese et empilées de façon croisée. Chaque couche est composée de planches en bois juxtaposées et généralement non collées sur leur chants. Dans cette thèse, nous étudions l'influence sur le comportement mécanique des espacements entre planches des panneaux avec une approche par modélisation et expérimentation. Les panneaux CLT standard sont considérés comme des panneaux avec des espacements de très faible dimension par opposition aux panneaux avec espacements importants que nous appelons panneaux innovants. Nous modélisons dans un premier temps le comportement en flexion de panneaux standard à l'aide d'un modèle de couche homogène équivalente basée sur des hypothèses simplifiées de la mécanique d'une couche avec chants collés ou non collés. Nous observons un bon accord entre les résultats de notre modélisation et des résultats expérimentaux issus de la littérature. Des études paramétriques sont ensuite réalisés portant sur certaines propriétés des panneaux.Nous avons ensuite réalisé des essais de flexion 4-points sur des panneaux CLT standard et innovants pour quantifier l'influence des espacements sur la réponse mécanique des panneaux. Il se trouve que l'influence des effets de cisaillement transverse sur le comportement élastique et à la rupture augmente avec l'augmentation des vides dans le panneau.Afin de prendre correctement en compte les effets du cisaillement, les CLT espacés sont modélisés comme des plaques épaisses périodiques à l'aide d'un modèle de plaque d'ordre supérieur. Ce modèle a été appliqué à la géométrie des panneaux CLT espacés avec un schéma d'homogénéisation périodique. Des méthodes simplifiées existantes ont également été comparées avec les résultats des essais et le modèle de plaque. De plus, des résultats d'essais de cisaillement dans le plan des panneaux CLT standard issus de la littérature ont été comparés avec nos résultats. La raideur de flexion des CLT espacés peut être prédite avec des méthodes simples existantes, alors que seule la modélisation que nous proposons permet de prédire le comportement en cisaillement transverse et dans le plan. Finalement, des formules analytiques ont été obtenues pour prédire le comportement élastique des CLT espacés. Ces formules donnent une bonne approximation u comportement des CLT espacés et peuvent être utilisées dans le cadre d'une démarche pratique de dimensionnement.Enfin, une étude concernant l'analyse du comportement au feu des panneaux CLT standard est présentée. La comparaison entre des résultats d'essais au feu et une modélisations avancée et simplifiée a permis de proposer une possible amélioration de la méthode de dimensionnement au feu standard / Cross Laminated Timber (CLT, or crosslam) panels are engineered timber products composed of layers made of wooden lamellas placed side by side, glued on their upperand lower faces and stacked crosswise. In the present thesis, the influence of lateral spaces between lamellas of each layer on the panel’s mechanical response is investigated with modeling and tests. Both configurations of standard panels having short spaces and innovative CLT panels with large spaces are analyzed.As a first approach, the bending behavior of standard crosslam was modeled by means of an equivalent-layer model based on simplified hypotheses on mechanical properties of laterally glued or unglued layers. The good agreement of the predicted behavior with an experiment of the literature finally allowed an investigation on several CLT properties by means of parameter studies.Then, 4-points bending tests on standard and innovative CLT floors were performed in order to quantify the influence of periodic spaces on the panels' mechanical response. It appears that the influence of transverse shear effects on the elastic and failure behavior of spaced CLT increases with the increasing spaces between boards.In order to take into account transverse shear effects, spaced CLT have been modeled as periodic thick plates by means of a higher-order plate theory for laminated plates. This model has been applied to the geometry of spaced CLT with a periodic homogenization scheme. Existing simplified methods for spaced crosslam were compared as well with refined modeling and test results. Moreover, available in-plane shear tests of the literature have been compared to the modeling results. It appears that the bending behavior of spaced CLT can be predicted with simplified existing approaches, while only the more refined modeling can predict the in-plane and transverse shear behavior. Then, closed-form solutions for predicting spaced CLT elastic behavior were derived in order to encourage the application of spaced CLT panels in modern timber construction.One further study within this thesis concerns the analysis of fire-exposed standard CLT floors. The comparison between test results and both advanced and simplified modeling led to a suggestion for a possible improvement the standard fire design model

The outstanding properties of carbon nanotubes (CNTs) keep attracting the attention of researchers from different fields. CNTs are promising candidates for applications e.g. in lightweight construction but also in electronics, medicine and many more. The basis for the realization of the manifold applications is a detailed knowledge of the material properties of the carbon nanotubes. In particular for applications in lightweight constructions or in composites, the knowledge of the mechanical behavior of the CNTs is of vital interest. Hence, a lot of effort is put into the experimental and theoretical determination of the mechanical material properties of CNTs. Due to their small size, special techniques have to be applied. In this research, a modified molecular structural mechanics model for the numerical determination of the mechanical behavior of carbon nanotubes is presented. It uses an advanced approach for the geometrical representation of the CNT structure while the covalent bonds in the CNTs are represented by beam elements. Furthermore, the model is specifically designed to overcome major drawbacks in existing molecular structural mechanics models. This includes energetic consistency with the underlying chemical force field. The model is developed further to enable the application of a more advanced chemical force field representation. The developed model is able to predict, inter alia, the lateral and radial stiffness properties of the CNTs. The results for the lateral stiffness are given and discussed in order to emphasize the progress made with the presented approach.

Asymmetric bending is explored as a means of inducing bend-twist coupling in an isotropic, fixed-wing airfoil. An analytical model describing the bend-twist coupling behavior of a constant-section airfoil undergoing steady wind loading is derived from Euler-Bernoulli beam theory, and evaluated over a range of structural and material stiffness. Finite element analysis is carried out in the ANSYS Parametric Design Language environment for an asymmetric, two-dimensional beam. Three-dimensional finite element analysis is carried out for two candidate blade models created in Pro/Engineer based on the NACA 64618 airfoil. Deformation results for the two- and three-dimensional finite element models are compared with analytical solutions. Results of this investigation highlight the dependency between the cross-sectional properties of a spar support and its tendency to exhibit twist-coupling under transverse loading.

Le projet consacré à la statique graphique étudie un aspect jusqu'ici peu exploré de l'histoire technique tchèque de la seconde moitié du XIXème au début du XXe siècle, lorsque les pays tchèques ont joué un rôle de premier plan en matière de technologie dans l'ancienne monarchie autrichienne. Une part du projet a permis de révéler le transfert de cette méthode de calcul en pratique d'ingénierie depuis son lieu d'origine, France et Suisse, vers les pays tchèques, et la contribution originale du milieu tchèque dans ce domaine. Le transfert de la statique graphique vers les pays tchèques fut effectué après sa formation dans la seconde moitié des années 1860. Le transfert culturel a prospéré grâce à la diffusion de la presse et des livres publiés principalement en allemand et, bien sûr, grâce aux contacts personnels étroits entre les conférenciers des écoles polytechniques européennes, en particulier des langues allemandes. La thèse contient également des exemples d'importants bâtiments historiques tchèques, pour lesquels la statique graphique a été utilisée pour calculer la structure. Ces calculs sont illustrés par la documentation archivistique, qui n'a pas encore été publiée. Une part de la thèse est également consacrée à la comparaison de deux méthodes de calcul de déformation des treillis (système triangulés). La première est la méthode du français V.-J. Williot, qui a été publiée en août 1878. La seconde est la méthode du professeur tchèque V. Bukovsky de janvier 1879. Comme il n'existe à l'heure actuelle aucune étude détaillée portant sur Victor-Joseph Williott ( 1843-1907), certains documents d'archives jamais publiés ont été recherchés pour illustrer sa vie. / The project of graphic statics is studying a heretofore little explored part of the Czech technical history of the second half of the 19th, and beginning of the 20th centuries, when the Czech lands held a leading role in technology in the former Austrian Monarchy. A part of the project is to reveal the transfer of this computational method in engineering practice from the place of its origin, France and Switzerland, to the Czech lands, as well as original contribution of the Czech millieu to this field. The transfer of graphic statics to the Czech lands came very soon after its formation in the second half of the 1860' s. Cultural transfer prospered thanks to the distribution of press and books published mainly in German, and, of course, thanks to the close persona) contacts among lecturers at European, especially German-speaking, polytechnic high school! The thesis also contains examples of significant Czech historical buildings, for which graphic statics was used to calculate the structure. These calculations are illustrated by archival documentation, which has not yet been published. A special part of the thesis is a comparison of two calculation methods of deformation of trusses. The first one is the method of French V.-J. Williot, which was published in August 1878. The second one is the Czech professor V. Bukovsky's method of January 1879. As no more detailed information was known about Victor-Joseph Williott ( 1843- 1907), some never published archival documents were searched to illustrate his life.

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simulationsunterstützte Weiterentwicklung eines Produktes mit dem Ziel der Material- sowie Energieeinsparung während des Herstellungsprozesses; konstruktive und simulative Optimierung des Kunststoff-Spritzgieß-Bauteils (Gewichtsreduktion, Einsparung von Zykluszeit) bei gleichzeitigem Erhalt der Funktion und mechanischen Eigenschaften; durch gekoppelte Simulation des Herstellungsprozesses und der Strukturmechanik konnten Herstellungskosten, Materialkosten sowie der Energieaufwand im Herstellungsprozess deutlich reduziert werden. / Simulation-supported further development of a product with the aim of saving material and energy during the manufacturing process; constructive and simulative optimisation of the plastic injection moulding component (weight reduction, saving of cycle time) while at the same time maintaining the function and mechanical properties; through coupled simulation of the manufacturing process and the structural mechanics, manufacturing costs, material costs and the energy input in the manufacturing process could be significantly reduced.

Monte Carlo simulation techniques have emerged as widely accepted computing tools in tackling many problems in modern structural mechanics. Apart from developments in computational hardware, which have undoubtedly made simulation strategies practically feasible, the success of Monte Carlo simulations has also resulted equally significantly from the methodological developments aimed at controlling sampling variance of the Monte Carlo estimates. The study reported in the present thesis is aimed at developing and validating Monte Carlo simulation based approaches with inbuilt variance reduction capabilities to deal with problems of time variant reliability modeling, random vibration testing, and updating reliability models for statically/dynamically loaded instrumented structures. The relevant literature has been reviewed in Chapter 1. Time variant reliability analysis of randomly parametered and randomly driven non-linear vibrating systems has been tackled by combining two Monte Carlo variance reduction strategies into a single framework (Chapter 2). The first of these strategies is based on the application of the Girsanov transformation to account for the randomness in dynamic excitations and, the second approach is fashioned after the subset simulation method to deal with randomness in system parameters. A novel experimental test procedure to estimate the reliability of structural dynamical systems under excitations specified via random process models has been proposed (Chapter 3). The samples of random excitations to be used in the test are modified by the addition of an artificial control force. An unbiased estimator for the reliability is derived based on measured ensemble of responses under these modified inputs based on the tenets of Girsanov’s transformation. The study observes that an acceptable choice for the control force (that can reduce the sampling variance of the estimator) can be made solely based on experimental techniques. This permits the proposed procedure to be applied in the experimental study of time variant reliability of complex structural systems which are difficult to model mathematically. Illustrative example consists of a multi-axes shake table study on bending-torsion coupled, geometrically non-linear, five-storey frame under uni/bi-axial, non-stationary, random base excitation. The first order reliability method (FORM) and inverse FORM have been extended to handle the problem of updating reliability models for existing, statically loaded structures based on measured responses (Chapter 4). The proposed procedures are implemented by combining Matlab based reliability modules with finite element models residing on the Abaqus software. Numerical illustrations on linear and non-linear frames are presented. A solution strategy within the framework of Monte Carlo simulation based dynamic state estimation method and Girsanov’s transformation for variance reduction has been developed to tackle the problem of updating the reliability of instrumented structures based on measured response under random dynamic loading (Chapter 5). For linear Gaussian state space models, the solution is developed based on continuous version of the Kalman filter, while, for non-linear and (or) non-Gaussian state space models, bootstrap particle filters are adopted. Results from laboratory testing of an archetypal five storey bending-torsion coupled frame under seismic base motions form the basis of one of the illustrative examples. A set of three annexures contain details of numerical methods for discretizing Ito’s differential equations (Annexure 1), working of the Girsanov transformation through Kolmogorov’s equations (Annexure 2) and tools for interfacing Matlab and Abaqus codes (Annexure 3).

Analytical and semi-analytical physical models for MEMS are derived from nonlinear mechanics. By taking into account system characteristics and assumptions, system identification enables the derivation of a mathematical model that is tailored to the effect and the MEMS under analysis. Such an adapted model can successfully emulate and explain the nonlinear dynamics of individual MEMS, including resonant actuation of parasitic modes. The performed analyses also confirm that small deviations in the mode spectrum between devices influence the occurrence of nonlinear effects.:1 Introduction 2 MEMS: Design, Devices & Modelling 3 Nonlinear Mechanics of Dynamical Systems 4 Modelling Approach 5 System Identification & Characterization 6 Conclusion / Analytische und semi-analytische physikalische Modelle für MEMS werden aus der nichtlinearen Mechanik abgeleitet. Durch die Berücksichtigung systemspezifischer Merkmale und Annahmen, ermöglicht die Systemidentifikation das Ableiten eines mathematischen Modells, das auf den analysierten Effekt und das MEMS zugeschnitten ist. Ein solches Modell kann für die Erklärung der nichtlinearen Dynamik einzelner MEMS herangezogen werden und bildet erfolgreich nichtlineare Effekte nach, einschließlich des resonanten Aufschwingens von Parasitärmoden. Die durchgeführten Analysen bestätigen auch, dass geringe Abweichungen im Modenspektrum zwischen Bauteilen das Auftreten nichtlinearer Effekte beeinflussen.:1 Introduction 2 MEMS: Design, Devices & Modelling 3 Nonlinear Mechanics of Dynamical Systems 4 Modelling Approach 5 System Identification & Characterization 6 Conclusion