Thesis (doctoral)--Delft University of Technology, 2007. / "Proefschrift ter verkrijging van de graad van doctor aan de Technische Universiteit Delft." Includes bibliographical references (p.120-128) and index.

Thesis (doctoral)--Delft University of Technology, 2007. / "Proefschrift ter verkrijging van de graad van doctor aan de Technische Universiteit Delft." Includes bibliographical references (p.120-128) and index.

This dissertation reported an experimental answer to the long-standing question of how three-dimensionality appears in wall-bounded magnetohydrodynamic flows and presented also an experimental study on the transition to turbulence in a confined, mostly quasi two-dimensional flow. Accordingly, it was shown the analysis of a vortex array with susceptibility to three-dimensionality, enclosed in a cubic container and a mostly, quasi two-dimensional vortex pair confined by the walls of a shallow, cylindrical container. Both containers were hermetically filled by a liquid metal fluid and subject to a constant, homogeneous magnetic field. The flow forcing was made by injecting constant electric current from one wall that intersects magnetic field lines (Hartmann wall). Flow characteristics and the presence of three-dimensionality were monitored by measuring electric potentials on either Hartmann walls that confined the liquid metal. A form of three-dimensionality termed as weak appeared through differential rotation along the axis of individual vortices, while a strong form manifested itself in vortices that do not extend from one to the other Hartmann wall. In the cubic container, this resulted into an array of novel, spectacular flow structures that were both steady and strongly three-dimensional, and, yielded to a frequency-selective breakdown of quasi two-dimensionality in chaotic and turbulent flow regimes. The mostly quasi two-dimensional flow in the shallow, cylindrical container was shown to undergo a sequence of supercritical bifurcations to turbulence triggered by boundary layer separations from the circular wall. For very high forcing, the flow reached a turbulent regime where the dissipation increased drastically. This was related to a possible transition from a laminar to a turbulent Hartmann layer.

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Garments serve a number of purposes, from protection and physiological comfort to social and cultural expressions. With the recent developments of active textiles, sensors and actuators with shapes and sizes similar to textiles, the real multifunctional garments have been realized. The functions of such garments can be regulating heat by changing the spacing between the strands of yarn, giving massage or assisting lifting movement by expanding and contracting one or more actuators.   This project is a part of a main project targeting on reconfigurable hybrid wearables. The main started from studying possible actuators that could have textile-like properties, where pneumatic actuators were chosen. A model of different forces, strains and braiding angles of a pneumatic actuator sometimes called a McKibben muscle was made. It should be noted that such garments with pneumatic actuators to be functional and applicable each segment needed an external pump. For local actuation, miniaturized servo valves were needed. Hence, study on super coiled actuators (SCAs) was initiated to investigate their potential of controlling the valves for constricting the flow when needed. In this project different SCAs were developed and their performances were recorded. To assist with heating of the SCAs Galinstan and Gallium were used as electric resistors to provide for Joule heating.  A contraction of over 19% and an efficiency of 0.29% were achieved but could most likely be improved by optimizing the fabrication and testing process.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18778号 / 理博第4036号 / 新制||理||1581(附属図書館) / 31729 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 松田 和博, 教授 八尾 誠, 教授 田中 耕一郎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

<p>Room-temperature liquid metal, such as eutectic gallium indium (EGaIn), has attracted significant attention for the fabrication of high-density electronics, functional composites, and two-dimensional nanomaterials due to the high electrical conductivity, high thermal conductivity, low toxicity, and its naturally formed oxide skin. Pulsed laser beams are proved to be promising to process liquid metal due to laser induced high temperature and high pressure. Although extraordinary progresses are made, limitations that remain in advanced manufacturing and material performance are crucial to overcome before liquid metal can be more practically used. The goal of this dissertation is to utilize the unique interaction between laser and liquid metal to design and fabricate nanomaterials with scalable functionalities towards potential device applications. </p> <p>This dissertation is composed of a general review of related background and experimental methods, followed by three chapters of detailed research and one chapter of conclusion. In the first research chapter, liquid metal is used, due to its high electrical conductivity and high fluidity, to create self-packaged, high-resolution liquid metal patterns by the advanced pulsed laser lithography (PLL) technology. The PLL method here, for the first time, can directly generate self-packaged liquid metal nano-patterns with high resolution without being limited by laser beam size. The electrically self-packaged material is an intriguing candidate to serve in demanding applications with high integration densities. In the second research chapter, liquid metal is utilized to boost the thermal conductivity of porous metal-organic frameworks (MOFs) to realize a high energy-harvesting efficiency. In this work, a facile and straightforward manufacturing method, laser shock-induced evaporation, is devised to deposit liquid metal nanoparticle (LMNP) thin layers to the surface of MOFs, resulting in the MOF@LMNP nanocomposites with a boosted thermal conductivity. In the last research chapter, liquid metal is employed to create large-scale metal oxide thin film patterns by an advanced confined laser transfer printing (CLTP) technique. This technology can generate metal oxide thin films patterns with tunable thickness and electrical property in nano-second scale that were previously inaccessible with conventional methods. This room temperature confined laser transfer printing method is promising to provide the possibility to pattern metal oxide thin films into advanced electronic components. As a summary, these studies present different laser manufacturing approaches in addressing liquid metal fabrication challenges from fundamental materials perspective. </p>