No description available.

Over the previous summer I studied mixing of a passive tracer by flow in a straight cylindrical pipe, under the supervision of prof. Bernoff. The mixing process can be thought of as the successive action of advection by the fluid flow and diffusion modeled by random walks. With this method we were able to distinguish three different regimes. For short times, diffusion is more relevant than advection and we observed a Gaussian longitudinal distribution of the concentration. In an intermediate regime, advection by the shear is dominant over longitudinal diffusion and we observed a distinctively asymmetric distribution which spread much faster than would be expected by the action of diffusion alone. Finally when the tracer had completely mixed across the pipe’s cross- section, we recovered the classical Taylor regime with a longitudinal Gaussian distribution. In each regime we have analytical prediction of tracer distribution, confirmed by numerical calculation. The object of this thesis is to extend our results to curved pipes; we will start by considering curved planar pipes and helical pipes. We will try to determine if mixing in these geometries displays the same three distinctive regimes of mixing. The pipe’s curvature introduces a secondary flow in the form of a transverse recirculation with a dipolar form, discovered by Dean (1928). We believe this transverse flow should enhance mixing, which explains why curved pipes are used in cooling systems and other situations where heat exchange is relevant. Our object is to first understand existing analytical approximations to the flow in a curved pipe due to Dean and others and then to study analytically and numerically the spread of a passive scalar in these flows.

No description available.

No description available.

Typically wire antenna structures are modeled by approximating curved structures with straight wire segments. The straight wire approximation yields accurate results, but often requires a large number of segments to adequately approximate the antenna geometry. The large number of straight wire segments or unknowns requires a large amount of memory and time to solve for the currents on the antenna. By using curved segments which exactly describe the contour of the antenna geometry the number of unknowns can be reduced, thus allowing for bigger problems to be solved accurately. This thesis focuses on the analysis of a helix antenna. The Method of Moments is used to solve for the currents on the antenna, and both the triangle basis and pulse testing functions exactly follow the contour of the helix antenna. The thin wire approximation is used throughout the analysis. The helix is assumed to be oriented along the z-axis with an optional perfect electric conductor (PEC) ground plane in the x-y plane. For simplicity, a delta gap source model is used. Straight feed wires may also be added to the helix, and are modeled similarly to the helix by the Method of Moments with triangular basis and pulse testing functions. The primary validation of the curved wire approach is through a comparison with MININEC and NEC of the convergence properties of the input impedance of the antenna versus the number of unknowns. The convergence tests show that significantly fewer unknowns are needed to accurately predict the input impedance of the helix, particularly for the normal mode helix. This approach is also useful in the analysis of the axial mode helix where the current changes significantly around one turn. Because of the varying current distribution, the improvement of impedance convergence with curved segments is not as significant for the axial mode helix. However, radiation pattern convergence improvement is found. Multiple feed structures for the axial mode helix are also investigated. In general, the many straight wire segments, and thus unknowns, that are needed to accurately approximate the current around one turn can be greatly reduced by the using the curved segment method. / Master of Science

Published Article / Current fused deposition modelling (FDM) technologies deposit material as flat layers. The result is a "stair-case" effect on non-vertical or horizontal surfaces, and compromised part strength because of weakness between the laminations. This paper describes an FDM method through which layers of build material are deposited as curved layers following the shape of the part, thus removing the stair-case effect and creating parts that have an even strength distribution over their entire surface. Support material is first deposited as conventional flat layers, and build material is then deposited over the support structure following the curves of the part. The paper discusses a proof of concept of the system, the algorithms used to generate the curve paths for the deposition head, and examines the challenges and possibilities of this technology, including the capability of including composite materials.

In most flat bimetallic strip applications, the bending is employed in the transverse direction, that is, upon the application of uniform heating to the entire strip, the initially straight strip bends transversely up from the flat plane. This study is concerned with a pre-curved bimetallic strip that upon heating up from the ambient, straightens up along the chord line tending to become flatter. The initial ambient radius of curvature of the strip is smaller, and upon heating, the radius of curvature becomes larger. By mounting the curved bimetallic strip with a rotational degree of freedom at each end, and fixing one end against displacement, a chord line displacement of the free end of the strip occurs when the strip is uniformly heated. It is this chord line case that this work investigates and characterises. This work provides a way of evaluating the net combined axial loading case whereby an external load is applied to the free end of the strip as it uniformly heated. The main application of this work is for the characterisation of a curved bimetallic blade within a thermal motor. This is a novel device for converting renewable heat energy into mechanical energy and power as part of a larger energy harvesting network. The curved bimetallic strip with minor modifications, functions as a curved bimetallic blade within the thermal motor. The application of this work has a wider impact, in that it can be used in any other temperature induced force and displacement applications. Thus as a result of this investigation, a new form of linear actuator has been created that can utilise an input heat differential, and produce an output axial force and displacement. The displacements and forces generated by the axial case can be quite large, and as a result of this work, relatively easy to calculate, when designing a thermally driven linear actuator. The thermal motor, which possesses the curved bimetallic strip at the heart of its mechanism, can also be powered by other secondary heating sources such exhaust, or waste heat, that would otherwise be lost to the surroundings.

No description available.

Thesis advisor: Lawrence T. Scott / Chapter 1. The impact and growth of carbon nanotubes within the framework of nanotechnology is presented. Methods to produce single chirality nanotubes from template-mediated sources are evaluated. The concept of a nanotube endcap is introduced as a potential synthetic target toward the selective synthesis and growth of a single chirality carbon nanotube. Chapter 2. A modified synthesis of corannulene is presented, highlighting a selective imine based reaction protocol for the fuctionalization 4,7-dimethylacenaphthenequinone. Also reviewed is a cascade coupling approach toward the synthesis of corannulene, followed by an analysis of the thermochemistry of the two-component disconnection. Chapter 3. The synthesis of 6 different indenoannulated corannulene congeners derived from a single flash vacuum pyrolysis (FVP) is described. X-ray crystal structures for each indenoannulated corannulene are presented along with computational modeling. Spectroscopic comparison between observed and theoretical 1H NMR provides one of the largest complete and comparative data sets for a collection of PAHs. Chapter 4. The application of a palladium based indenoannulation reaction is presented as an alternative synthetic method to FVP. Heteroatom based derivatives of both tetraindenocorannulene and pentaindenocorannulene were both developed as potential solubilizing factors. The thermochemistry for each successive indenoannulation of 1,3,5,7,9-pentaphenylcorannulene leading to pentaindenocorannnulene has been calculated, providing an approximated energy landscape for the total transformation. Chapter 5. Several routes for the synthesis of 1,3,5,7,9-pentakis(2,6-dichlorophenyl)-corannulene are presented. The yield for this reaction has been improved through the use of a palladium based precatalyst. During this time we studied a five-fold palladium catalyzed borylation of corannulene using B2pin2. Finally development of a cascade coupling reaction towards a [5,5] SWNT endcap is highlighted by a 12 bond coupling reaction. Chapter 6. A nickel-promoted homo-coupling between the proximally situated aryl halides of 1,2,5,6-tetrakis(2-chlorophenyl)corannulene is used to complete the synthesis of diphenanthro[9,10-a:9′,10′-g]corannulene. X-ray quality crystal were grown of diphenanthro[9,10-a:9′,10′-g]corannulene, and the structure was solved. The crystals forms highly ordered arrays in a columnar fashion with each phenanthro segment aligned through a series of π - π stacking interactions. / Thesis (PhD) — Boston College, 2009. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

This work investigates how curved-crease origami and the developable surfaces which compose it can be transitioned to engineering design. Methods for creating flexible, tailorable-property surfaces that function as thick panels in place of paper are presented. Concepts from curved-crease origami and developable surfaces that can describe and extend engineering applications are discussed and demonstrated. These concepts are particularly beneficial to applications where curved surfaces are integral to the function, deployability is desired, and planar manufacturing could be beneficial.The first part of this work uses arrays of compliant elements to create flexible-tailorable property surfaces. The key feature to these arrays is the alignment of the most flexible bending axis of the individual elements to the ruling line arrangement of a developable surface. This alignment can enable bending of thick panels while maintaining lower stresses, a quality necessary for the transitioning of curved-crease origami into thick materials. The stiffness and stress of these arrays is modeled and physical prototypes are demonstrated. Additionally, shape factors are developed for these compliant arrays (CAs) to facilitate material selection for the panels and understand how the geometry of the array changes the effective properties of the panel. The second part of this work describes and demonstrates several concepts of curved-crease origami and developable surfaces that can benefit mechanism and structure design, particularly in the context of rolling-contact mechanisms. The design of a rolling-contact joint connected by flexible bands similar to a Jacob's Ladder toy is extended through incorporating curved creases into the design. The resulting design is deployable from a compact state to a functional state and can be manufactured from a single plane and folded into shape. Mathematical formulations are presented to describe the classes of developable surfaces in terms of properties which are frequently important in mechanism design. These natural equations for a single class of developable surface are conducive to modeling the folding motion of rigid-ruling developables, developables whose ruling lines do change location in a surface during folding. These formulations are used to generalize the design of rolling-contact joints to a family of joints capable of single degree of freedom spatial motions, being manufactured from a plane, and exhibiting a tailorable force response. Finally practical design suggestions for the implementation of rolling-contact joints is given. These include methodology to create sunken flexures which serve to increase the normal force between rolling bodies to prevent slip.