A Shell Bonded to an Elastic Foundation

In our analysis, we derive a mathematical model for a shell bonded to an elastic foundation, by modifying Koiter's linear shell equations. We prove the existence and the uniqueness of the solutions, and we explicitly derive the governing equations and the boundary conditions for the general case. Finally, with numerical modelling and asymptotic analyses, we show that there exist optimal values of the Young's modulus, the Poisson's ratio and the thickness of the shell (with respect to the elastic foundation), and the curvature of the contact region such that the planar solution derived by the shell model (where stretching effects are dominant) is a good approximation. It is often regarded in the field of stretchable and flexible electronics that the planar solution is mostly accurate when the stiffness of the thinner body (e.g. the shell) increases indefinitely. The significance of our work is that, as far as we are aware, this is the first analysis showing that indefinitely increasing the stiffness of the shell may not guarantee a more accurate solution.Comment: https://discovery.ucl.ac.uk/id/eprint/1532145

Nanoporous Carbon Scaffolds for Energy Storage Applications

Nanoporous carbons (NCs) have become increasingly popular in various fields of research due to their unique properties including tunable pore sizes, higher pore volumes and higher surface areas, as well as being able to produce controlled nanostructures. The work presented here uses NC scaffolds with as active hosts for (1) Li-ion battery electrodes and (2) confined metal hydrides (MH) for hydrogen storage applications. In (1) we investigate the Li diffusion characteristics in hard carbons (HCs) that are important for electrochemical applications. We develop a novel method named Voltage-Relaxation Galvanostatic Intermittent Titration Technique (VR-GITT). Parameters derived from the fitting of electrochemical data provide both the diffusion constants as well as morphological information about the diffusion geometry. The VR-GITT method also allows determination of the diffusion constant in the two-phase region of many materials, where the standard GITT method fails. In (2) it is already known that confining MHs in NCs. can alter the kinetics of de/re-hydriding reactions. We investigate the effects of changing the surface electron density in these HCs by the addition of nitrogen (N). The various chemical environments for the surface nitrogens include pyridinic and pyrrolic. The pyridinic N contains a lone pair of electrons that should be available to form Lewis-acid/base complexes that interact with confined MHs, and provide a favorable (wetting) surface energy for incorporation of AlH3, LiBH4, and other hydrides into the carbons. Our results indicate that both B and Al interact with these pyridinic Ns upon introduction to the HCs. The infiltration of LiBH4 is straightforward, while the infiltration of AlH3 requires oxygen reduction techniques during the carbon scaffold synthesis

Wireless sensor system for infrastructure health monitoring

In this thesis, radio frequency identification (RFID)-based wireless sensor system for infrastructure health monitoring (IHM) is designed and developed. It includes mountable semi-passive tag antenna integrated sensors capable of measuring critical responses of infrastructure such as dynamic acceleration and strain. Furthermore, the system is capable of measuring structural displacement. One of the most important parts of this system is the relatively small, tunable, construction material mountable RFID tag antenna. The tag antenna is electronically integrated with the sensors. Leading to the process of developing tag antenna integrated sensors having satisfactory wireless performance (sensitivity and read range) when mounted on concrete and metal structural members, the electromagnetic performance of the tag antenna is analyzed and optimized using both numerical and experimental procedures. Subsequently, it is shown that both the simulation and the experimental measurement results are in good agreement. The semi-passive RFID-based system is implemented in a wireless IHM system with multiple sensor points to measure dynamic acceleration and strain. The developed system can determine the natural frequencies of infrastructure and identify any state changes of infrastructure by measuring natural frequency shifts. Enhancement of the spectral bandwidth of the system has been performed under the constraints of the RFID hardware. The influence of the orientation and shape of the structural members on wireless power flow in the vicinity of those members is also investigated with the RFID reader-tag antenna system in both simulation and experiments. The antenna system simulations with a full-scale structural member have shown that both the orientation and the shape of the structural member influence the wireless power flow towards and in the vicinity of the member, respectively. The measurement results of the conducted laboratory experiments using the RFID antenna system in passive mode have shown good agreement with simulation results. Furthermore, the system’s ability to measure structural displacement is also investigated by conducting phase angle of arrival measurements. It is shown that the system in its passive mode is capable of measuring small structural displacements within a short wireless distance. The benchmarking of the developed system with independent, commercial, wired and wireless measurement systems has confirmed the ability of the RFID-based system to measure dynamic acceleration and strain. Furthermore, it has confirmed the system’s ability to determine the natural frequency of an infrastructure accurately. Therefore, the developed system with wireless sensors that do not consume battery power in data transmission and with the capability of dynamic response measurement is highly applicable in IHM

Capstan Equation Generalised for Noncircular Geometries

In our analysis, we extend the capstan equation to noncircular geometries. We derive a closed from solution for a membrane with a zero-Poisson's ratio (or a string with an arbitrary Poisson's ratio) supported by a rigid prism, and then a rigid cone, at limiting-equilibrium. As a comparison, we extend Kikuchi and Oden's model for Coulomb's law of static friction to curvilinear coordinates. We also conduct numerical experiments to see how close Coulomb's law of static friction is to the ordinary friction law implied by our generalised capstan equation, in curvilinear coordinates. Our numerical results indicate that increasing the curvature, the Poisson's ratio and the thickness of the elastic body increases the frictional force, for a constant coefficient of friction, and incompressible materials such as rubber can have a high frictional forces, even under low coefficients of friction. Our analysis implies that the coefficient of friction is model dependent.Comment: https://discovery.ucl.ac.uk/id/eprint/1532145

Nanoporous carbon scaffolds for energy storage applications

Nanoporous carbons (NCs) have become increasingly popular in various fields of research due to their unique properties including tunable pore sizes, higher pore volumes and higher surface areas, as well as being able to produce controlled nanostructures. The work presented here uses NC scaffolds with as active hosts for (1) Li-ion battery electrodes and (2) confined metal hydrides (MH) for hydrogen storage applications. In (1) we investigate the Li diffusion characteristics in hard carbons (HCs) that are important for electrochemical applications. We develop a novel method named Voltage-Relaxation Galvanostatic Intermittent Titration Technique (VR-GITT). Parameters derived from the fitting of electrochemical data provide both the diffusion constants as well as morphological information about the diffusion geometry. The VR-GITT method also allows determination of the diffusion constant in the two-phase region of many materials, where the standard GITT method fails. In (2) it is already known that confining MHs in NCs. can alter the kinetics of de/re-hydriding reactions. We investigate the effects of changing the surface electron density in these HCs by the addition of nitrogen (N). The various chemical environments for the surface nitrogens include pyridinic and pyrrolic. The pyridinic N contains a lone pair of electrons that should be available to form Lewis-acid/base complexes that interact with confined MHs, and provide a favorable (wetting) surface energy for incorporation of AlH3, LiBH4, and other hydrides into the carbons. Our results indicate that both B and Al interact with these pyridinic Ns upon introduction to the HCs. The infiltration of LiBH4 is straightforward, while the infiltration of AlH3 requires oxygen reduction techniques during the carbon scaffold synthesis --Abstract, page iv

A Shell Frictionally Coupled to an Elastic Foundation

In our analysis, we derive a model for a shell that is frictionally coupled to an elastic foundation. We use Kikuchi and Oden's model for Coulomb's law of static friction to derive a displacement-based static-friction condition for our shell model, and we prove the existence and the uniqueness of solutions with the aid of the works of Kinderlehrer and Stampacchia. As far as we are aware, this is the first derivation of a displacement-based friction condition, as only force or stress based friction conditions currently exist in the literature. For numerical analysis, we extend Kikuchi and Oden's model for Coulomb's law of static-friction to model a full two-body contact problem in curvilinear coordinates. Our numerical results indicate that if the shell has a relatively high Young's modulus or has a relatively high Poisson's ratio, and the contact region has a very high coefficient of friction or less curved, then the displacement field of the foundation predicted by both models are in better agreement.Comment: https://discovery.ucl.ac.uk/id/eprint/1532145/. arXiv admin note: substantial text overlap with arXiv:2012.1218

Introducing a Real-Time Advanced Eye Movements Analysis Pipeline

Real-Time Advanced Eye Movements Analysis Pipeline (RAEMAP) is an advanced pipeline to analyze traditional positional gaze measurements as well as advanced eye gaze measurements. The proposed implementation of RAEMAP includes real-time analysis of fixations, saccades, gaze transition entropy, and low/high index of pupillary activity. RAEMAP will also provide visualizations of fixations, fixations on AOIs, heatmaps, and dynamic AOI generation in real-time. This paper outlines the proposed architecture of RAEMAP