Problèmes d'interactions entre une structure déformable et un fluide visqueux et incompressible

Dans cette thèse, nous étudions un système fluide-solide qui modélise les interactions entre une struc- ture déformable, et un fluide visqueux et incompressible qui l'entoure. Il couple les équations de Navier- Stokes incompressibles (pour l'état du fluide) avec les lois de Newton (pour la dynamique du solide). L'existence de solutions fortes est étudiée dans les deux premiers chapitres, pour des déformations du solide limitées ou non en régularité. Puis nous prouvons la stabilisation à zéro de ce système couplé, pour des perturbations extérieures petites, par des déformations du solide soumises à des contraintes physiques qui lui garantissent en particulier d'être autopropulsé. Ensuite nous décrivons des moyens pratiques de générer de telles déformations. Enfin nous développons une méthode numérique pour un problème de Stokes avec conditions de Dirichlet non homogènes. Elle nous permet d'obtenir une bonne approximation de la trace normale du tenseur des contraintes de Cauchy, pour des frontières qui ne dépendent pas du maillage. Cette méthode combine une approche de type domaines fictifs basée sur les idées de Xfem, et une méthode de Lagrangien augmenté. Du point de vue des interactions fluide-structure, l'intérêt de cette méthode réside dans l'importance du rôle joué par les forces du fluide à l'interface fluide-solide.In this thesis, we study a fluid-solid system which is a model for the interactions between a deformable structure, and a viscous incompressible fluid surrounding it. It couples the incompressible Navier-Stokes equations (for the fluid flow) with the Newton's laws (for the solid's dynamics). The existence of strong solutions is studied in the first two chapters, for solid's deformations which are limited or not in regularity. Then we prove the stabilization to zero of this coupled system, for small external perturbations, by solid's deformations submitted to physical constraints which guarantee its self-propel led nature. After that we describe practical means of generating such deformations. Finally we develop a numerical method for a Stokes problem with nonhomogeneous Dirichlet conditions. It enables us to get a good approximation of the normal trace of the Cauchy stress tensor, for boundaries which does not depend on the mesh. This method combines a fictitious domain type approach based on the ideas of Xfem, and an augmented Lagrangian method. In a fluid-structure interaction perspective, the interest of this method lies in the importance of the role played by the fluid's forces at the fluid-solid interface

Architecture and the creation of worlds

This thesis is an enquiry by creative practice into the academic and aesthetic (avant-garde) practice of architecture. It explores the notion of the virtual as pure potentiality following an event, and defines architecture as the site of such potentiality. (Alain Badiou names event as the moment /encounter which initiates a radical break from a given situation /state of affairs. There are four types of event: artistic, political, scientific and amorous).The thesis follows two parallel strands of enquiry. One, into the material production of the architectural object and topological space, this is titled the actual; and the other, an investigation into the philosophical and antagonistic nature of the virtual, this is titled the virtual. The actual deals with the literature review, methodology, context of study and proposal for (the site of) actual engagement with theory, including a design element (House of the Chinese Mantis); while the virtual explores (through a series of five international and interdisciplinary conference papers) the philosophical problems of emergence. The 'context of study' in the actual centres around the move from the fetish of commodities to seduction and concludes with eroticism, while the body of work in the virtual concentrates on the notions of sovereignty, becoming, and concrete subjectivity.Following the technological practices of the avant-garde between hypersurface theory and catalytic formations in architecture, the thesis rejects the claims of virtual space as the digital space of computer -based design, and of emergence as mimetic and /or algorithm based design. It argues that the virtual is the intangible space of creative unfolding following Bergson and Deleuze, but resists the claim in Deleuze that event is a chance occurring. Also, it resists the claim in Baudrillard that seduction and /or enchanted simulation are event and abandons them to focus on the amorous (one of the four events in Badiou). This creates an inflection in the enquiry, moving the thesis towards Plato and the Renaissance, and a contemporary resurrection in architecture, of the tragic, as concrete manifestation of the amorous encounter.The method of inquiry is structured after the nomadic logic of the War Machine in the philosophy of Deleuze and Guattari, and of the revolutionary nature of fidelity to the scientific event in Badiou, which argues that new knowledge is created by 'revolutions' and from the anomalies and collaborations which arise as a result of such 'detours'; it is a strategy justified by the science historians Feyerabend, Kuhn and Lakatos.The thesis takes the form of two books (the actual and the virtual), and concludes that the avant-garde practice of architecture, with its infinite potentialities is distinct from the bureaucratic or State apparatus of building, and that the commonplace appropriation of the avant-garde by the State, as seen in the institutional recourse to parametrics, appears unproductive and uncreative with regard to knowledge

Consider the robot - Abstraction of bioinspired leg coordination and its application to a hexapod robot under consideration of technical constraints

Paskarbeit J. Consider the robot - Abstraction of bioinspired leg coordination and its application to a hexapod robot under consideration of technical constraints. Bielefeld: Universität Bielefeld; 2017.To emulate the movement agility and adaptiveness of stick insects in technical systems such as piezo actuators (Szufnarowski et al. 2014) or hexapod robots (Schneider, Cruse et al. 2006), a direct adaptation of bioinspired walking controllers like WALKNET has often been suggested. However, stick insects have very specific features such as adhesive foot pads that allow them to cling to the ground. Typically, robots do not possess such features. Besides, robots tend to be bigger and heavier than their biological models, usually possessing a different mass distribution as well. This leads to different mechanical and functional properties that need to be addressed in control. Based on the model of the stick insect *Carausius morosus*, the six-legged robot HECTOR was developed in this work to test and evaluate bioinspired controllers. The robot's geometrical layout corresponds to that of the stick insect, scaled up by a factor of 20. Moreover, like the stick insect, the robot features an inherent compliance in its joints. This compliance facilitates walking in uneven terrain since small irregularities can be compensated passively without controller intervention. However, the robot differs from the biological model, e.g., in terms of its size, mass, and mass distribution. Also, it does not possess any means to cling to the ground and therefore must maintain static stability to avoid tilting. To evaluate the ability of stick insects to maintain static stability, experimental data (published by Theunissen et al. (2014)) was examined. It can be shown that stick insects do not maintain static stability at all times. Still, due to their adhesive foot pads, they do not tumble. Therefore, a direct replication of the biological walking controller would not be suitable for the control of HECTOR. In a next step, the bioinspired walking controller WALKNET (Cruse, Kindermann, et al. 1998) was evaluated regarding its applicability for the control of HECTOR. For this purpose, different parametrizations of WALKNET were tested in a simulation environment. For forward walking, parameter sets were found that achieve a high, although not permanent stability. Thus, for the control of HECTOR, which requires continuous stability, a more abstract adaption of the bioinspired coordination had to be found. Based on the original coordination concepts of WALKNET, new coordination mechanisms were developed that incorporate the technical requirements (static stability, angular joint limits, torque constraints, etc.). The ability of the resulting controller to generate insect-like gaits is demonstrated for different walking scenarios in simulation. Moreover, locomotion that is unlikely for insects such as backwards and sidewards walking is shown to be feasible using the novel control approach. At the end of this work the applicability of the approach for the control of the real robot is proved in experiments on visual collision avoidance and basic climbing ability

The Transmission of Western Science Into China 1840-1900.

This thesis examines the process, practice and issues surrounding the transmission of Western science into China 1840-1900. It opens with a discussion of the previous (Jesuit) transmission of Western science, and the nature of the Chinese paradigms which the Jesuits tried to displace. The nineteenth-century Western chemical paradigms which were to be transmitted are then considered, together with the rapidly changing nature of the subject and the consequent problems for the translators and their readers. The context of the transmission in China is discussed, especially the nature of the kaozheng [evidential research] scholarly community in the Jiangnan region of China which, I hope to show, played an important role in the reception of science. The special problems of translation from Western languages into Chinese are then dealt with, including the transliteration of terms and the creation of new characters. Parallels are drawn with the methods of the Buddhist translators and of the early nineteenth-century Chinese geographers. There follow studies of the translation of chemical terminology, of a selection of important science textbooks, and of two Western agents of transmission, John Fryer and Calvin Mateer. The lives of Chinese scientists Li Shanlan, Xu Shou, Xu Jianyin and Hua Hengfang are studied, followed by a chapter on the new institutions which they and the Westerners created. The remarkably rich popular science literature such as Gezhi Huibian is then analysed, and conclusions drawn about the nature of 3 popular interest in science in this period. The intellectual impact of Western science in the last decade of the century is considered, especially the effects on the thinking of Tan Sitong and Kang Youwei. Finally, general conclusions are elaborated and the significance of the transmission is assessed