La conception de systèmes de perception autonomes, tels que des robots capables d’accomplir un ensemble de tâches de manière sûre et sans assistance humaine, est l’un des grands défis de notre siècle. Pour ce faire, la robotique développementale propose de concevoir des robots qui, comme des enfants, auraient la faculté d’apprendre directement par interaction avec leur environnement. Nous avons dans cette thèse exploré de telles possibilités en se limitant à l’apprentissage de la localisation des objets d’intérêt (ou objets saillants) dans l’environnement du robot.Pour ce faire, nous présentons dans ces travaux un mécanisme capable d’apprendre la saillance visuelle directement sur un robot, puis d’utiliser le modèle appris de la sorte pour localiser des objets saillants dans son environnement. Cette méthode a l’avantage de permettre la création de modèles spécialisés pour l’environnement du robot et les tâches qu’il doit accomplir, tout en restant flexible à d’éventuelles nouveautés ou modifications de l’environnement.De plus, afin de permettre un apprentissage efficace et de qualité, nous avons développé des stratégies d’explorations basées sur les motivations intrinsèques, très utilisées en robotique développementale. Nous avons notamment adapté l’algorithme IAC à l’apprentissage de la saillance visuelle, et en avons conçu une extension, RL-IAC, pour permettre une exploration efficace sur un robot mobile. Afin de vérifier et d’analyser les performances de nos algorithmes, nous avons réalisé des évaluations sur plusieurs plateformes robotiques dont une plateforme fovéale et un robot mobile, ainsi que sur des bases de données publiques. / Conceiving autonomous perceptual systems, such as robots able to accomplish a set of tasks in a safe way, without any human assistance, is one of the biggest challenge of the century. To this end, the developmental robotics suggests to conceive robots able to learn by interacting directly with their environment, just like children would. This thesis is exploring such possibility while restricting the problem to the one of localizing objects of interest (or salient objects) within the robot’s environment.For that, we present in this work a mechanism able to learn visual saliency directly on a robot, then to use the learned model so as to localize salient objects within their environment. The advantage of this method is the creation of models dedicated to the robot’s environment and tasks it should be asked to accomplish, while remaining flexible to any change or novelty in the environment.Furthermore, we have developed exploration strategies based on intrinsic motivations, widely used in developmental robotics, to enable efficient learning of good quality. In particular, we adapted the IAC algorithm to visual saliency leanring, and proposed an extension, RL-IAC to allow an efficient exploration on mobile robots.In order to verify and analyze the performance of our algorithms, we have carried out various experiments on several robotics platforms, including a foveated system and a mobile robot, as well as publicly available datasets.

Many highly-evolved bio-photonic structures, which tailor the propagation of light by coherent optical scattering, have been investigated. These natural designs, which have many diverse ecological functions, are becoming increasingly studied as sources of innovation and inspiration for a range of scientific, technological, and commercial applications. The brilliant blue colour reflected from the scales of the Morpho butterfly is just one example of nature’s ability to manipulate light and colour strongly. In this thesis, the photonic structure present in the scales of the Morpho butterfly is investigated as a source of bio-inspiration in the pursuit of high- performance photonic vapour sensors. The intention of this is to outperform classical sensor approaches which traditionally suffer from poor selectivity between chemical species. By measuring the change in reflectance from the iridescent scales of the Morpho butterfly, both a sensitive and, critically, a selective response to chemical vapours can be obtained. Here, the origin of this unique multivariable vapour-induced optical response is investigated, and this biological template is further explored as a source of innovation for the mature field of chemical sensing. By using synergy between experimental and theoretical techniques, a mechanism for the sensitive and selective response of the Morpho butterfly’s scales to different chemical vapour environments is elucidated. This mechanism arises from combined chemical and physical effects within the photonic nanostructure. Following this, demonstrations of this biological template’s vapour response attributes, which have large and desirable diversity in the optical responses, are made. These response attributes are visualised in the spectral changes associated with optical excitation conditions, such as from different angles and polarisation states, and also in the temporal response profiles. Finally, theoretical sensor designs that outperform the Morpho scales are described. Simple principles that might improve the currently unacceptable levels of selectivity in contemporary sensor implementations are outlined and the vapour response of a Morpho-inspired photonic structure is presented.

De nos jours, l'engouement pour la robotique autonome ne cesse d'augmenter en particulier pour les microdrones. En effet, ces aéronefs de petite taille font l'objet de nombreuses recherches afin de les miniaturiser et de rendre leur navigation plus autonome. Ainsi, cette thèse explore un système de vision parcimonieux dédié à la navigation courte portée au moyen de capteurs visuels auto-adaptatifs innovants composés de seulement 12 pixels aux propriétés optiques inspirées de celles de l'abeille. Deux algorithmes de mesure de flux optique sont ensuite comparés en conditions idéales sur 5 décades d'irradiance et 3 décades de vitesses optiques, puis testés en conditions réelles de vol. L'algorithme le plus robuste et le plus efficace, de par ses très faibles besoins calculatoires, a été embarqué à bord d'un micro quadrirotor pesant environ 400 g et équipé d'un système visuel parcimonieux de 96 pixels stabilisé via une nacelle articulée en roulis et tangage pour compenser les rotations du quadrirotor. Les stratégies de navigation observées chez l'abeille ont ensuite été simulées dans des environnements virtuels (tunnel de longueur 6 m ou 12 m pour une section minimale de 25 ou 50 cm) et la preuve de faisabilité de la détection du flux optique à bord d'un microdrone a été démontrée en conditions réelles de vol en salle expérimentale (vol de 4 m de long à une distance minimale de 50 cm). Couplé à des stratégies de navigation inspirées de l’abeille, ce système visuel innovant dédié à la perception du mouvement permettra dans un futur proche de naviguer dans des environnements encombrés ou exigus. / The interest in autonomous robotics is continually expanding, especially in the domain of micro air vehicles. Indeed, much research focuses on these small-size aircraft in order to miniaturize them and to make their navigation more autonomous. This PhD thesis explores a parsimonious vision system dedicated to short range navigation using innovative self-adaptive visual sensors composed of only 12 pixels with optical properties inspired by those of honeybees. Two optic flow measurement algorithms are first compared under ideal conditions over 5 decades of irradiance and 3 decades of optical velocity, then tested under real flight conditions. The most robust and efficient algorithm, due to its very low computing requirements, was embedded on board a micro quadrotor weighing about 400 g and equipped with a parsimonious visual system of 96 pixels stabilized via an articulated gimbal in roll and pitch to compensate the quadrotor rotations. The navigation strategies observed in honeybees were simulated in virtual environments (6 m or 12 m long tunnel for a minimum section of 25 or 50 cm) and the feasibility of the detection of the optic flow on board a micro quadrotor was demonstrated in real flight conditions in experimental room (flight of 4 m long at a minimum distance of 50 cm). Coupled with navigation strategies inspired by the honeybee, this innovative visual system dedicated to the perception of movement will in the near future allow to navigate in cluttered or cramped environments.

Les ailes iridescentes du papillon Morpho rhetenor sont couvertes d'écailles profondément striées comme des réseaux de diffraction. Chaque strie est un empilement de couches minces d'air et de chitine. La recherche d'inspiration pour de nouveaux composants motive l'étude des propriétés optiques de cette structure photonique. Sa géométrie est caractérisée à différentes échelles. Les spectres de réflexion confirment les interférences. La diffraction par les stries explique la répartition spatiale de l'intensité réfléchie. Nous avons exploré les propriétés optiques des écailles en microspectrophotométrie et en micropolarimétrie. Nous simulons le champ électromagnétique dans la structure avec la méthode Rigorous Coupled-Wave Analysis. L'introduction de désordre dans la structure photonique et entre écailles permet de mieux comprendre les résultats des mesures. Des simulations avec la méthode des éléments finis et la première approximation de Born montrent l'intérêt de ces outils.

La bio-inspiration applique des principes et des stratégies issus de systèmes biologiques afin de faciliter la conception technologique. Doté d’un fort potentiel pour l’Innovation, la biomimétique, son pendant méthodologique, est en passe d’évoluer vers un processus clé pour les entreprises. Un certain nombre de freins demeurent cependant à lever afin que la conception bio-inspirée s’apparente à une démarche robuste et répétable. Les travaux réalisés abordent cette diffusion de la conception bio-inspirée selon deux axes distincts. Ils s’efforcent tout d’abord d’harmoniser champs conceptuels relatifs à la bio-inspiration et modèles de processus biomimétiques, en vue de rendre possible l’évaluation des outils supportant cette démarche de conception. Cette évaluation méthodologique, couverte selon l’angle objectif et subjectif, aboutit à la formalisation d’un modèle structurant, un arbre de classification, à même de guider les concepteurs biomimétiques à travers le processus biomimétique. En parallèle de l’établissement de ce cadre de référence méthodologique, les travaux s’évertuent à explorer un autre verrou inhérent à la démarche : l’interaction entre biologie et ingénierie. Les travaux tendent ainsi, par le développement d’un outil, à réduire l’une des barrières d’entrée de ce type d’approche, en proposant un modèle décrivant fonctionnellement les systèmes biologiques sans prérequis d’expertise biologique. La concaténation de ces réalisations aborde directement l’enjeu principal de ce champs disciplinaire : son essor par la dissémination de son application à l’innovation industrielle, en vue de favoriser l’émergence de « produits biomimétiques » au détriment des « accidents bio-inspirées ». / Biomimetics applies principles and strategies which stem from biological systems in order to facilitate technological design. Providing a high innovation potential, biomimetics could become a key process for various business. However, there are still a few challenges to overcome in order for the bioinspired design to become a sustainable approach. The work which has been carried out addresses this bioinspired design diffusion with two distinct focuses. First of all, they tend to standardize conceptual fields for bio-inspiration and biomimetic process models to enable the evaluation of tools supporting said design process. This methodological assessment, addressed from an objective and subjective point of view, results in the formalization of a structuring model, a classification tree which guides designers through the biomimetic process. Alongside the development of this methodological reference framework establishment, the work tends to overcome another obstacle of the bioinspired design implementation which is the interaction between biology and engineering. By developing a specific tool, the research studies offer a model which functionally describes biological systems without biological expertise prerequisites. The concatenation of these accomplishments addresses the main issue of these disciplinary fields: its development through the dissemination of its application to industrial innovation, in order to encourage the emergence of “biomimetic products” at the expense of “bio-inspired accidents”.

Cette thèse a visé à comprendre et à recréer artificiellement un mécanisme d'auto-assemblage présent dans la soie d'araignée. Les gouttes de glue microniques qui existent sur la soie d'araignée dîte de capture servent à fournir à la toile ses propriétés adhésives. Ces gouttes jouent pourtant un autre rôle : elles améliorent grandement les propriétés mécaniques de la soie, et permettent de préserver l'intégrité structurelle de la toile. La localisation de l'instabilité de flambage au sein des gouttes de glue, site de surcompression par les ménisques capillaire, implique que ce système de gouttes sur fibre se comporte sous compression comme un liquide, alors que sous tension il possède un régime solide. Les araignées ont donc trouvé un moyen de créer des hybrides mécaniques liquide-solide.La première partie de ma thèse fut dédiée à la caractérisation d'échantillons naturels, qui a permis dans la seconde partie de construire un système entièrement artificiel qui reproduit la soie d'araignée de capture, grâce à des microfibres flexibles longues de plusieurs centimètres. Une simple goutte de liquide mouillant permet la création efficace d'un système semblable aux échantillons naturels. La caractérisation fine de ces systèmes de gouttes sur fibre enroulables a mené à un très bon accord entre les résultats expérimentaux, les simulations numériques et une analogie avec les transitions de phase, notamment pour des propriétés telles que le seuil d'activation, l'existence d'une hystérésis ou encore la morphologie de l'enroulement. Ces résultats ont permis la conception de techniques non conventionnelles dans des domaines tels que les méta-matériaux et la micro-fabrication. / This PhD work aimed to understand and recreate artificially a self-assembling mechanism involving capillarity and elasticity present in spider silk. The primary function of the micronic glue droplets that exist on spider capture silk is to provide the spider web with adhesive properties. These droplets play yet another role: the dramatic enhancement of silk mechanical properties, as well as the preservation of the integrity of the web structure. The localization of the buckling instability within the glue droplets, site of over-compression due to the capillary meniscii implies that under compression this special drop-on-fibre system behaves like a liquid, whereas under tension it has a classical elastic spring regime. Spiders have thus found a way to create liquid-solid mechanical hybrids.The first part of my thesis aimed to the characterization of natural samples, which allowed in the second part to build a completely artificial system that mimics the natural samples, through fabrication of centimeter-long micronic soft fibres. The simple addition of a wetting liquid droplet made for an effective system with mechanical properties quantitatively close to that of spider capture silk.Fine characterization of the created drop-on-coilable-fibre systems yielded very good agreement between experimental results and predictions from numerical simulations and a analogy with phase transition, especially for properties such as the threshold for activation, the existence of an hysteresis and the coiling morphology. All those results added up to the design of unconventional techniques in field such as metamaterials and micro-fabrication.

Jellyfish have inhabited this planet for millions of years and are the oldest known metazoans that swim using muscles. They are found in freshwater sources and in oceans all over the world. Over millions of years of evolution, they have adapted to survive in a given environment. They are considered as one of the most energy efficient swimmers. Owing to these characteristics, jellyfish has attracted a lot of attention for developing energy efficient unmanned undersea vehicles (UUVs). The goal of this thesis is to provide understanding of the different physical mechanisms that jellyfish employs to achieve efficient swimming by using analytical and computational models. The models were validated by using the experimental data from literature. Based upon these models refinements and changes to engineering vehicles was proposed that could lead to significant enhancement in propulsion efficiency. In addition to the propulsion, the thesis addresses the practical aspects of deploying a jellyfish-inspired robotic vehicle by providing insights into buoyancy control and energy generation. The thesis is structured in a manner such that propulsive and structural models inspired from the natural animal were systematically combined with the practical aspects related to ionic diffusion driven buoyancy control system and thermal -- magnetic energy harvesting system. Jellyfish morphology, swimming mechanism and muscle architecture were critically reviewed to accurately describe the natural behavior and material properties. We provide full understanding of mesoglea, which plays most significant role towards swimming performance, in terms of composition, mechanical properties and nonlinear dynamics. Different jellyfish species exhibit different microstructure of mesoglea and thus there is a wide variety of soft materials. Mechanical properties of collagen fibers that form the main constituent toward imparting elasticity to mesoglea were reviewed and analyzed. The thesis discusses the theoretical models describing the role of structure of mesoglea towards its mechanical properties and explains the variation occurring in stiffness under given experimental environment. Muscle architecture found in jellyfish, nerve nets and its interconnection with the muscles were investigated to develop comprehensive understanding of jellyfish propulsion and its reaction to external stimuli. Different muscle arrangements were studied including radial, coronal muscle, and coronal-muscles-with-breaks in-between them as observed in Cyanea capillata. We modeled these muscle arrangements through finite element modeling (FEM) to determine their deformation and stroke characteristics and their overall role in bell contraction. We found that location and arrangement of coronal muscle rings plays an important role in determining their efficient utilization. Once the understanding of natural jellyfish was achieved, we translated the findings onto artificial jellyfish vehicle designed using Bio-inspired Shape Memory Alloy Composite (BISMAC) actuators. Detailed structural modeling was conducted to demonstrate deformation similar to that of jellyfish bell. FEM model incorporated hyperelastic behavior of artificial mesoglea (Ecoflex-0010 RTV, room temperature vulcanizing silicone with shore hardness (0010)), experimentally measured SMA temperature transformation, gravity and buoyancy forces. The model uses the actual control cycle that was optimized for driving the artificial jellyfish vehicle "robojelly". Using a comparative analysis approach, fundamental understanding of the jellyfish bell deformation, thrust generation, and mechanical efficiency were provided. Meeting energy needs of artificial vehicle is of prime importance for the UUVs. Some jellyfish species are known to use photosynthesis process indirectly by growing algae on their exumbrella and thereby utilizing the sunlight to generate energy. Inspired by this concept, an extensive model was developed for harvesting solar energy in underwater environment from the jellyfish bell structure. Three different species were modeled for solar energy harvesting, namely A.aurita, C.capillata and Mastigia sp., using the amorphous silicon solar cell and taking into account effect of fineness ratio, bell diameter, turbidity, depth in water and incidence angle. The models shows that in shallow water with low turbidity a large diameter vehicle may actually generate enough energy as required for meeting the demand of low duty cycle propulsion. In future, when the solar energy harvesting technology based upon artificial photosynthesis, referred to as "dye-sensitized solar cells", matures the model presented here can be easily extended to determine its performance in underwater conditions. In order to supplement the energy demand, a novel concept of thermal -- magnetic energy harvesting was developed and extensively modeled. The proposed harvester design allows capturing of even small temperature differences which are difficult for the thermoelectrics.  A systematic step-by-step model of thermo-magnetic energy harvester was presented and validated against the experimental data available in literature. The multi-physics model incorporates heat transfer, magnetostatic forces, mechanical vibrations, interface contact behavior, and piezoelectric based energy converter. We estimated natural frequency of the harvester, operating temperature regimes, and electromechanical efficiency as a function of dimensional and physical variables. The model provided limit cycle operation regimes which can be tuned using physical variables to meet the specific environment. Buoyancy control is used in aquatic animals in order to maintain their vertical trajectory and travel in water column with minimum energy expense. Some crustaceans employ selective ion replacement of heavy or lighter ions in their dorsal carapace. A model of a buoyancy chamber was developed to achieve similar buoyancy control using electro-osmosis. The model captures all the essential ionic transport and electrochemistry to provide practical operating cycle for the buoyancy engine in the ocean environment. / Ph. D.

Biomineralized lattice materials with have high mineral contents (~ 99 wt%), usually "conceal" multiscale structural arrangements for unique mechanical or functional performance, such as the remarkable damage tolerance despite of the brittle nature of the constituents (e.g., biogenic silica and calcite). However, the quantitative explorations of the structure-mechanics relationships in multiscale of biomineralized lattices remain insufficient and hence hinder the leverage of the functional benefits to design architected cellular materials. In this dissertation, I selected two groups of marine animals (i.e., Hexactinellid sponges and Echinoderms) for systematic structural-mechanical study. Their biomineralized lattice skeletons exhibit three representative types of multiscale structures: 1) multiscale hierarchical structure: skeleton of Hexactinellid sponge such as Euplectella aspergillum; 2) multiscale functionally graded structure: spine of sea urchin Heterocentrotus mammillatus; and 3) dual-scale (atomic and microlattice scales) periodic structure: ossicle of starfish Protoreaster nodosus. This dissertation develops quantitatively the structural-mechanical/functional correlations in biomineralized cellular materials for bio-inspired material design. Four different species of Hexactinellid sponges have been studied with particular focus on the species E. aspergillum. As an example of the multiscale hierarchical biomineralized lattice, the extremely lightweight skeleton (~99% porosity) of E. aspergillum exhibits 1) amorphous nanoparticular biogenic silica; 2) micron-sized fibrous spicule with cylindrically laminated silica layers separated by organic interfaces; 3) spicule bundles where the individual spicules merged by secondary silica deposition; 4) a centimeter-sized Voronoi-like cellular dome known as sieve plate; and 5) a centimeter-sized cylindrically arranged rectangular lattice with double-diagonal reinforcement and external helical ridge. Here, we discovered a series of mechanical or functional properties or formation process of structures in different length scales: 1) for the biogenic silica in three different species of Hexactinellid sponge, consistent modulus and hardness of the biogenic silica throughout the cross section of the spicule are found via substantial correlation between the measured values and locations; 2) for the sieve plate, the Voronoi-like cellular dome constructed by porous branch with increased height achieves balance between improved mechanical stiffness and large pore opening for sponge's current pumping mechanism; 3) via microstructural study, the formation process of the sieve plate is proposed; and 4) for the cylindrical skeletal body, the double-diagonal configuration and the ridge structure are found to provide tendency to optimize torsional rigidity, and enhanced radial stiffening and improved permeability, respectively. The cellular structure in the spine of the H. mammillatus (i.e., stereom) made of ~99wt% of single-crystalline calcite shows a multiscale functionally graded structure. We developed and optimized a cellular network analysis workflow on the large-volume 3D lattice structure obtained from the synchrotron-based micro-Computed Tomography scan. The analysis provides quantitative descriptions of the branch, ring structure, and septum which reveals a functionally graded structure in multiscale from the center region to the edge region of the spine: 1) in microscale, the branch thickness and length increases, resulting in a significantly decreased porosity; and 2) in macroscale, the center region of the spine with galleried stereom of highly aligned branches transits to the edge region with laminar stereom of radially arranged septa and interconnecting branches. The multiscale structural variations lead to the mechanical variations the increased elastic modulus and mechanical isotropy from the center to the edge of the spine. This provides a biological pathway for designing the lightweight, strong, and tough beam with multiscale structural gradient. In previous work, we discovered that ossicle in starfish P. nodosus possesses a unique dual-scale periodic lattice structure, which means periodic single crystal calcite in nanoscale and diamond triply periodic minimal surface (diamond-TPMS) lattice in microscale. It has three unique structural features: 1) microlattice dislocations in ossicles similar to those found in crystals with diamond cubic lattice; 2) a diamond-TPMS microlattice with ca. 50% relative density; and 3) dual-scale crystallographic coalignment between c-axis of the single-crystalline constituent calcite and the [111] direction of the diamond-TPMS microlattice. Based on this work, this dissertation mainly reveals: 1) unique type and core structures of the dislocations in the ossicle for stiffness, strength, and toughness; 2) the 3D property compensation of dual-scale crystallographic coalignment for improved mechanical isotropy; and 3) mechanical benefits (improved mechanical isotropy and effective fragment jamming) and morphological benefits (minimal surface and highest surface area to volume ratio) for 50% relative density. / Doctor of Philosophy / Architected lattice materials, featured by their tailorable 3D multiscale architectures, achieve unique mechanical properties such as breaking the trade-off between strength and toughness, and mechanical isotropy reaching theoretical limit. In nature, as a result of evolutionary driving force, the biomineralized skeletons of the animals such as sea sponge, sea urchin, and starfish usually delicately control the architectural arrangements in different length scales and provide excellent templates for the design of architected lattices with desirable properties. Quantitative understanding of the 3D multiscale structures and mechanics of these natural biomineralized lattices allows the development of bio-inspired materials that are, for example, simultaneously stiff, strong, and tough. This dissertation establishes the quantitative structural-mechanical/functional relationships in multiscale of three biomineralized lattices with high mineral contents (~99 wt%) and a wide range of porosity (50~99 vol%) in Hexactinellid sponges with main emphasis on species (Euplectella aspergillum), sea urchin Heterocentrotus mammillatus, and starfish Protoreaster nodosus. They are selected for their representative multiscale structures, i.e., multiscale hierarchical structure, multiscale functionally graded structure, and dual-scale (i.e., atomic and microlattice scales) periodic structure, respectively. Study of these biomineralized lattices significantly improve our understanding of the biological strategies in structural arrangement and pave the way towards bio-inspired modeling to leverage the mechanical benefits.

<p dir="ltr">The natural honeycomb made from beeswax is an engineering marvel. Modern-day engineering has taken several inspirations from it in the form of hexagonal panels and cells made of various materials such as polymers, ceramics, and metals for light-weighting without compromising on its mechanical properties. Previously, characterizing this structure has relied on two-dimensional (2D) surface observations on the macroscale which have an inherently limited scope in understanding complex three-dimensional (3D) structures. As a result, several seminal features of the honeycomb that would have shed light on how it is constructed and what makes it so mechanically robust are left out of reach and overlooked. X-ray microscopy (XRM) is a powerful tool to characterize these complex structures non-destructively, yielding insights that are not possible without three-dimensional (3D) datasets. Further, when a time-resolved approach is adopted, where an external stimulus is interrupted for an XRM scan, one can obtain four-dimensional (4D) datasets. This provides unrivaled information on how complex 3D structures evolve over time when a stimulus is applied.</p><p dir="ltr">In this work, a time-resolved approach towards understanding how bees build out their hexagonal cells, both under normal and abnormal conditions was developed. Several previously unreported, but seminal features of the honeycomb such as the “coping” and porosity at well-defined locations yielded insights into how the comb is constructed. The corrugated spine is seen to be the foundation on which all hexagonal cells are built on. Additionally, this work also explores how bees accommodate distortions within the ordered lattice during the merger of two combs. Behaviorally they are seen to reduce the distortion within cells to minimize the wastage of wax and to keep the cells usable. A 3D parameter using automated image processing was developed to quantify how distortions are accommodated in an ordered lattice.</p><p dir="ltr">This work will further shed light on the mechanical behavior of the natural honeycomb arising from the corrugated nature of the spine and the gradient in its wall thickness which plays a role in crack deflection when the honeycomb is loaded under tension. When loaded under compression, the honeycomb lattice crumples in a manner to limit the damage to very local regions thereby forming a damage-tolerant crumple zone.</p>

Cities occupy 2% of the earth's surface, and yet consume 75% of the world's resources. As a major contributor to rapidly growing global energy expenditures, urban buildings are often designed and operated inefficiently despite their significant contributions to carbon emissions, triggering environmental deterioration locally and worldwide. Moreover, ongoing industrialization and urbanization pose challenges for achieving a more sustained and resilient built environment. The goal of this PhD research is to advance our understanding of urban building networks' thermal-energy dynamics in order to achieve sustainable energy conservation in the built environment. Considering buildings as networks rather than as stand-alone entities highlights the inextricably linked and interwoven relationship between urban micro-climates and buildings. With this approach, I strive to explore, mitigate, and optimize the mutual influences of the Inter-Building Effect (IBE) in dense urban settings through numerical and empirical analyses. My research also draws inspiration for investigating solutions to complex engineering problems from nature, as I seek to understand synergies between building and biological systems to discover innovative connections and integrate biology to transform buildings through sustainable building network designs. This dissertation contains three interdependent projects to explore, mitigate and optimize the IBE, respectively. I first developed a systematic approach to separately assess the complex interactions that constitute the IBE in dense urban settings and conducted cross-regional analyses in a dynamic simulation environment. Having disaggregated, quantified and understood the effects of mutual shading and mutual reflection within a network of buildings, I then, in the second project, examined different measures to mitigate the negative IBE impact under certain circumstances (e.g. directional reflective optical properties of building facades and thermal storage technologies). These two projects extended prior work that examined the potential for a biological system retroreflective surface to reduce IBE in urban building networks. Therefore, in my third project, I introduced a broad framework that draws parallels between natural and built environment systems through a levels-of-organization perspective leading to the search for an optimal status of the IBE. Inspired from a self-regulating phenomenon of plant density, I presented and discussed an approach to determine optimal urban building network density as an example for how this framework can support cross-level assessment. The findings expand and deepen our understanding of the IBE and provide insights on the strategies to mitigate the negative mutual impact within dense urban building networks. This research contributes a unique and holistic perspective on the interdependencies in the urban building network system. To design density-optimal building networks will become increasingly important to sustainable urban development and smart growth as clusters of dense urban settings continue to grow due to rapid urbanization and population migration in the next few decades. / Ph. D.