Materiais compósitos avançados, que consistem basicamente de fibras de alta resistência e rigidez embebidas em um material matriz, têm revolucionado projetos de aeronaves, pois permitem significante economia de peso e conseqüente ganho de performance. Esses materiais são geralmente empregados na forma de placas laminadas, produzidas pela junção de várias camadas de material compósito, variando-se a orientação das fibras. Desta forma ée possível obter-se um componente estrutural com resistência e rigidez adequadas em cada direção, atendendo mais eficientemente às solicitações de serviço. Neste trabalho são estudadas soluções analíticas para flambagem de placas laminadas retangulares simplesmente apoiadas, submetidas a carregamento biaxial. São apresentados estudos paramétricos e comparações entre cargas de flambagem obtidas com a teoria clássica e a teoria de primeira ordem. A teoria clássica superestima cargas de flambagem e os erros resultantes são significativos em placas espessas. Os maiores erros encontrados aproximam-se de 100% para placas com a razão largura / espessura igual a 10 e baixos módulos de cisalhamento transversal, considerados infinitos pela teoria clássica.

Improvements to isogeometric blended shells are introduced which blend traditional Reissner-Mindlin shells, and Kirchhoff-Love shells, with an exact interpolation of the shell director increment. A gradient extraction operator is introduced which allows derivatives of basis functions to be exactly expressed as a linear combination of the basis functions themselves. Several benchmarks are investigated and the new blended shell is compared with different shell elements in ABAQUS and NASTRAN. In addition, the effect of different quadrature schemes is included in the comparisons. The new isogeometric blended shell performs comparably in some benchmarks, and even outperforms commercial shell finite elements in some benchmarks. Future improvements to the formulation are discussed.

Tese de mestrado integrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 2012

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnologico / Made available in DSpace on 2016-01-08T19:17:06Z (GMT). No. of bitstreams: 1 99944.pdf: 1541003 bytes, checksum: 1ce956e07d2631dcb9abbc0ea25132e0 (MD5) Previous issue date: 1994 / Formulação e análise de problemas de contato em placas utilizando o Método dos Elementos Finitos. A teoria de placas semi-espessas ou teoria de Mindlin-Reissner é utilizada, e a versão lagrangiana atualizada do princípio dos trabalhos virtuais é adotada para o tratamento da não-linearidade advinda do fato da estrutura poder sofrer grandes deflexões. A desigualdade variacional, característica do problema de contato, é resolvida fazendo-se uso do método da penalidade.

Submitted by Pedro Barros (pedro.silvabarros@ufpe.br) on 2018-07-25T20:33:05Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) DISSERTAÇÃO Adelma Ferreira de Araújo.pdf: 2128658 bytes, checksum: 515e628879fd7ecf2ee9317ce342b6b3 (MD5) / Approved for entry into archive by Alice Araujo (alice.caraujo@ufpe.br) on 2018-07-27T21:26:21Z (GMT) No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) DISSERTAÇÃO Adelma Ferreira de Araújo.pdf: 2128658 bytes, checksum: 515e628879fd7ecf2ee9317ce342b6b3 (MD5) / Made available in DSpace on 2018-07-27T21:26:21Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) DISSERTAÇÃO Adelma Ferreira de Araújo.pdf: 2128658 bytes, checksum: 515e628879fd7ecf2ee9317ce342b6b3 (MD5) Previous issue date: 2017-02-13 / Apresenta um estudo sobre bibliofilia a partir das memórias de Rubens Borba de Moraes e José Mindlin, destacando a importância de ambos para a preservação da memória escrita, a partir da formação das bibliotecas de coleções de livros raros, em especial à coleção Brasiliana. O posicionamento de disponibilizar para o público os acervos desenvolvidos durante anos pelos bibliófilos em destaque, traz uma nova proposta de pensar a bibliofilia como patrimônio informacional, idealizando um sentido utilitário à coleção com a criação da Brasiliana USP, em oposição a práticas correntes de fragmentação ou desuso das coleções. Quanto à metodologia foram utilizados materiais bibliográficos, tratando-se de uma pesquisa exploratória. Foram explanados assuntos sobre a história do livro, tipografia, colecionismo, livros raros, hábito de leitura e digitalização de acervos. A biografia dos bibliófilos auxiliou na contextualização da trajetória da formação das bibliotecas de livros raros. Houve também a aplicação dos pressupostos teóricos da biblioteconomia que tratam da seleção e aquisição de materiais bibliográficos; formação e desenvolvimento de coleções; organização, disponibilização e recuperação da informação e preservação da memória organizacional para assim haver uma interlocução da Ciência da Informação com a bibliofilia. / This research aims at analyzing bibliophily based upon the memories of Rubens Borba de Moraes and José Mindlin, thus pinpointing the importance of both theorists towards written memory preservation by the formation of rare book collection libraries, especially “Brasiliana” collection. The perspective of making the developed repository available to the public throughout the years present a new proposal of redefining bibliophily as informational heritage, thus idealizing an utilitarian sense to the collection with the USP Brasiliana creation, in opposition to the current practices of fragmentation and misuse of collections. As for the methodology, bibliographic materials were used due to the descriptive aspect of the research. Subjects concerning the history of the book, typography, collectionism, rare books, reading habits and collection digitalization were explained through. The bibliophile biografies helped in the formation path contextualization of rare book libraries. Informational theory corollaries towards selection and acquisition of bibliographic materials, collection formation and development, organization, availability, information recovery and organizational memory preservation so as to provide a crossroad between Information Science and bibliophily.

Es werden die vorgestellten Fehlerindikatoren in Bezug auf die Netzsteuerung anhand von drei Beispielen analysiert. Im weiteren werden auch die einzelen MITC-Elemente und ihre Besonderheiten bei dieser Analyse der Netzsteuerung mit berücksichtigt. Als Abschluss werden einige spezielle Fehlerindikatoren vorgestellt, die für die weitere Entwicklung einige interessante Eigenschaften aufzeigen. Im zweiten Teil geht es um die Auswertung mit dem speziellen Ziel der Findung einer optimalen Netzsteuerung. Dabei wird auf die Besonderheiten der Elemente eingegangen sowie auf die Plattendicke und auf ihre Wirkung bei den Fehlerindikatoren. Mit diesen Erkenntnissen wird ein spezieller Fehlerindikator vorgestellt, der die Vorteile aller Fehlerindikatoren aus Teil I vereint.

Within this thesis, thin walled shell structures are discussed with modern element formulationsin the context of the Isogeometric Analysis (IGA). IGA was designed to achieve a directinterface from CAD to analysis. According to the concept of IGA, Non-Uniform RationalB-Splines (NURBS) are used as shape functions in the design and the analysis. Dependingon the polynomial order, NURBS can come along with a high order continuity. Therefore,the curvature of a shell surface can be described directly by the shape function derivativeswhich is not possible within the classical Finite Element Analysis (FEA) using linear meshes.This description of the curvature gives rise to the application of the Kirchho-Love shellformulation, which describes the curvature stiness with the dierentiation of the spatialdegrees of freedom. Based upon this, the formulation can be enhanced with further kinematicalexpressions as the shear dierence vector, which leads to a 5-parameter Reissner-Mindlinformulation. This kinematic formulation is intrinsically free from transverse shear lockingdue to the split into Kirchho-Love and additional shear contributions. The formulation canbe further extended to a 7-parameter three-dimensional shell element, which considers volumetriceects in the thickness direction. Two additional parameters are engaged to describethe related thickness changes under load and to enable the use of three-dimensional materiallaws. In general, three-dimensional shell elements suer from curvature thickness and Poisson'sthickness locking. However, these locking phenomena are intrinsically avoided by thehierarchic application of the shear dierence vector and the 7th parameter respectively. The3-parameter Kirchho-Love, the 5-parameter Reissner-Mindlin and the 7-parameter 3D shellelement build a hierarchic family of model-adaptive shells.This hierarchic family of shell elements is presented and discussed in the scope of this thesis.The concept and the properties of the single elements are elaborated and the dierences arediscussed. Geometrically linear and non-linear benchmark examples are simulated. Convergencestudies are performed and the results are validated against analytical solutionsand solutions from literature, taking into account deections and internal forces. Furthermore,the dierent locking phenomena which occur in analyses with shell formulations areexamined. Several test cases are designed to ensure a validated implementation of the hierarchicshell elements. The element formulations and further pre- and postprocessing featuresare implemented and validated within the open-source software environment Kratos Multi-physics.

No description available.

Submitted by ANA KARLA PEREIRA RODRIGUES (anakarla_@hotmail.com) on 2017-08-23T16:00:02Z No. of bitstreams: 1 arquivototal.pdf: 9090532 bytes, checksum: d4fefb1d97e9c6d585d5d18a33abf752 (MD5) / Made available in DSpace on 2017-08-23T16:00:02Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 9090532 bytes, checksum: d4fefb1d97e9c6d585d5d18a33abf752 (MD5) Previous issue date: 2016-11-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this thesis we study controllability results, asymptotic behavior and inverse problem related to some problems of the theory of partial di erential equations. Two particular systems are the focus of the study: the Mindin-Timoshenko system, describing the vibrational motion of a plate or a beam, and the phase eld system describing the temperature and phase of a medium having two distinct physical states. The rst chapter is devoted to the study of the 1-D Mindlin-Timoshenko system with discontinuous coe cient. A Carleman inequality is obtained under the assumption of monotonicity on the beam speed. Subsequently, two applications are provided: the controllability of the control system acting on the boundary and Lipschitzian stability of the inverse problem of recovering a potential from a single measurement of the solution. In the second chapter we consider a contact problem characterized by the behavior of a two-dimensional plate whose board makes contact with a rigid obstacle. The formulation of this problem is presented by the 2-D Mindlin-Timoshenko system with boundary conditions and suitable damping terms. Concerning such system, is proved via penalty techniques, the existence of solution and that the system energy has exponential decay when the time approaches in nity. In the third chapter, the study is aimed at a nonlinear phase- eld system de ned in a real open interval. Here we present some controllability results when a single control acts, by means of Dirichlet conditions, on the temperature equation of the system on one of the endpoints of the interval. To prove the results is used the method of moments, plus a spectral study of operators associated to the system and xed point theory to deal with the nonlinearity. / Nesta tese estudamos resultados de controlabilidade, comportamento assintótico e problema inverso relacionados a alguns problemas da teoria de equações diferenciais parciais. Dois sistemas particulares são foco do estudo: o sistema de Mindin-Timoshenko, que descreve o movimento vibratório de uma placa ou viga, e o sistema de campo de fases que descreve a temperatura e a fase de um meio onde ocorrem dois estados físicos distintos. O primeiro capítulo é dedicado ao estudo do sistema de Mindlin-Timoshenko 1-D com coe ciente descontínuos. Uma desigualdade de Carleman é obtida sob a hipótese de monotonicidade sobre velocidade da viga. Posteriormente, são fornecidas duas aplicações: a controlabilidade do sistema com controles agindo na fronteira e a estabilidade Lipschitziana do problema inverso de recuperar um potencial através de uma única informação obtida sobre a solução. No segundo capítulo consideramos um problema de contato caracterizado pelo comportamento de uma placa bidimensional cujo bordo faz contato com um obstáculo rígido. A formulação deste problema é apresentada pelo sistema de Mindlin-Timoshenko 2-D com condi ções de fronteira e termos de amortecimento (damping) adequados. Sobre tal sistema, é provada, através de técnicas de penalização, a existência de solução e, posteriormente, que sua energia possui decaimento exponencial quando o tempo tende ao in nito. No terceiro capítulo o estudo é voltado a um sistema de campo de fases não-linear de nido em um intervalo aberto real. Neste espaço apresentamos alguns resultados de controlabilidade quando um único controle age, sob condições de Dirichlet, na equação da temperatura em um dos bordos do intervalo. Para provar os resultados é utilizado o método dos momentos, além de uma estudo espectral de operadores associados ao sistema e teoria de ponto xo para lidar com a não-linearidade.

Cette thèse présente des travaux effectués dans le cadre de l'optimisation de forme de pièces mécaniques, sous critère dynamique, par approche isogéométrique. Pour réaliser une telle optimisation nous mettons en place dans un premier temps les éléments coque au travers des formulations Kirchhoff-Love puis Reissner-Minlin. Nous présentons une méthode permettant d'atteindre les vecteurs normaux aux fibres dans ces formulations au travers de l'utilisation d'une grille mixte de fonctions de base interpolantes, traditionnellement utilisées en éléments finis, et de fonction non interpolantes issues de la description isogéométrique des coques. Par la suite, nous détaillons une méthode pour le couplage de patch puis nous mettons en place la méthode de synthèse modale classique dans le cadre de structures en dynamique décrites par des éléments isogéometriques. Ce travail établit une base pour l'optimisation de forme sous critères dynamique de telles structures. Enfin, nous développons une méthode d'optimisation de forme basée sur le calcul du gradient de la fonction objectif envisagée. La sensibilité de conception est extraite de l'analyse de sensibilité au niveau même du maillage du modèle, qui est obtenue par l'analyse discrète de sensibilité. Des exemples d'application permettent de montrer la pertinence et l'exactitude des approches proposées. / Isogeometric method is a promising method in bridging the gap between the computer aided design and computer aided analysis. No information is lost when transferring the design model to the analysis model. It is a great advantage over the traditional finite element method, where the analysis model is only an approximation of the design model. It is advantageous for structural optimization, the optimal structure obtained will be a design model. In this thesis, the research is focused on the fast three dimensional free shape optimization with isogeometric shell elements. The related research, the development of isogeometric shell elements, the patch coupling in isogeometric analysis, the modal synthesis with isogeometric elements are also studied. We proposed a series of mixed grid Reissner-Minlin shell formulations. It adopts both the interpolatory basis functions, which are from the traditional FEM, and the non-interpolatory basis functions, which are from IGA, to approximate the unknown elds. It gives a natural way to define the fiber vectors in IGA Reissner-Mindlin shell formulations, where the non-interpolatory nature of IGA basis functions causes complexity. It is also advantageous for applying the rotational boundary conditions. A modified reduce quadrature scheme was also proposed to improve the quadrature eficiency, at the same time, relieve the locking in the shell formulations. We gave a method for patch coupling in isogeometric analysis. It is used to connect the adjacent patches. The classical modal synthesis method, the fixed interface Craig-Bampton method, is also used as well as the isogeometric Kirchhoff-Love shell elements. The key problem is also the connection between adjacent patches. The modal synthesis method can largely reduce the time costs in analysis concerning structural dynamics. This part of work lays a foundation for the fast shape optimization of built-up structures, where the design variables are only relevant to certain substructures. We developed a fast shape optimization framework for three dimensional thin wall structure design. The thin wall structure is modelled with isogeometric Kirchhoff-Love shell elements. The analytical sensitivity analysis is the key focus, since the gradient base optimization is normally more fast. There are two models in most optimization problem, the design model and the analysis model. The design variables are defined in the design model, however the analytical sensitivity is normally obtained from the analysis model. Although it is possible to use the same model in analysis and design under isogeomeric framework, it might give either a highly distorted optimum structure or a unreliable structural response. We developed a sensitivity mapping scheme to resolve this problem. The design sensitivity is extracted from the analysis model mesh level sensitivity, which is obtained by the discrete analytical sensitivity analysis. It provides exibility for the design variable definition. The correctness of structure response is also ensured. The modal synthesis method is also used to further improve the optimization eficiency for the built-up structure optimization concerning structural dynamics criteria.