Two-dimensionally (2D) braided tubular composites have been utilized in a wide range of applications including medical equipment such as braided stents and catheters. Catheters are long flexible tubes used in catheterization procedures, such as angiography and ablations. In this thesis, angiographic catheters were specifically targeted; which are referred as catheters for the remaining of the document. Catheters are typically used with guidewires which provide structural support to the often low rigidity catheters. In some catheterization procedures, it may be beneficial to use a 2D braided catheter for increased control and maneuverability in the body. The 2D braided catheter, if designed properly, may provide all the required rigidities for a successful procedure and decrease the dependency to the guidewire compared to conventional catheters. Hence, use of 2D braided catheters may decrease the procedure time, may provide superior control of the device due to its design, and may also decrease the inherent patient discomfort. A thorough understanding of 2D braided composites is of absolute necessity considering the delicate use of medical equipment, such as catheters, in the human body. The aim of this PhD thesis is to address the shortcomings of the available models in the literature by developing an analytical model geometrically consistent with small braided tubular structures and provide all the necessary tools possible to design a target specific braided catheter. An analytical model that accounts for the effect of diameter of a braided tubular product on the elastic properties, needed for catheter design, was developed. Parametric studies were conducted to highlight the effects of the change in radius on elastic properties of braided composites. Case studies that underline the important geometrical parameters that affect predictions were conducted and findings discussed. Effect of increased undulation length on elastic properties of braided composites was also investigated. The findings were compared to experimental work using three different fiber/matrix system composites. As predicted by the model, a decrease in the properties was observed experimentally; however, this decrease was found to be more important than predicted. Possible reasons for this behavior are discussed in the view of composite materials and geometrical factors. The experimental findings of the open-mesh composites were also used to further validate a regression based model available in the literature. Lower linearity limit values for the regression based model were calculated for longitudinal elastic and shear moduli predictions.

No description available.

A morphing aircraft can be defined as an aircraft that changes configuration to maximize its performance at radically different flight conditions. Morphing structures require a large aspect ratio and area change during flight in order to optimise operational performance. Morphing wings are being developed to mimic bird’s wing movements. Birds have different wing profiles at different points in their flight, where swept wings reduce the drag at higher speeds at flight lift-off and long straight wing profile is better for performance at low loitering speed. Hyper-extensible braided cords have been developed to be used within morphing ‘skin’ materials. The cords use a low-modulus elastomeric core braided around with high-modulus yarns. These cords can be produced with various braid angles, which influence the extensibility of the cords. The higher the braid angle, the greater the extension The braid angle is controlled by the precision pre-tension of the elastomeric component. A computational model for predicting the load-strain behaviour of these hyper-extensible cords has been developed. Opposite to hyper-extensible cords are inextensible cord reinforcement composites, such as toothed timing belts used in car engines, which utilise a combination of reinforcement techniques to guarantee a high quality high strength product. Braiding is an alternate technology for producing cords with potentially superior performance in terms of improved ability to resist unravelling as well as superior interface due to ‘Chinese finger-trap effect.’ Carbon core with varying glass fibre braid have been developed. This led to various braid patterns being formed. A system for mapping braid pattern/topology has been developed. Aswel as the braid pattern, the braid colour patterns can also be produced. This mathematical model involves basic matrix manipulations, which have been proved using the MatLab program. The predicted braid patterns have been compared with actual samples. Being able to model braid patterns is a time and cost effective compared to previous trial and error methods.

No description available.

Chute channel formation is a key process in the transition from a single-thread meandering to a braided channel pattern, but the physical mechanisms driving the process remain unclear. This research combines GIS and spatial statistical analyses, field survey, Delft3D hydrodynamic and morphodynamic modelling, and Pb-210 alpha-geochronology, to investigate controls on chute initiation and stability, and the role of chute channels in the planform dynamics of large, sand-bed meandering rivers. Sand-bed reaches of four large, tropical rivers form the focus of detailed investigations; the Strickland and Ok Tedi in Papua New Guinea, the Beni in Bolivia, and the lower Paraguay on the Paraguay/Argentina border. Binary logistic regression analysis identifies bend migration style as a key control on chute channel initiation, with most chute channels forming at bends that are subject to a rapid rate of extension (elongation in a direction perpendicular to the valley axis). Bend extension rates are shown to track variation in potential specific stream power, such that reaches and sub-reaches of the rivers studied fit within a planform continuum expressed though increasing bend extension rates and chute initiation frequency, and driven by increasing stream power relative to bedload calibre. Field observations of point bar geomorphology and vegetation dynamics illustrate the importance of rapid bend extension in forming wide sloughs between scroll bars that are aligned with the direction of over-bar flow, and in breaking the continuity of vegetation encroachment on point bars. Bathymetric surveys and Delft3D simulations for the Strickland River provide insight into flow and sediment division at bifurcate meander bends. Coupled with GIS analyses, these simulations show that stable chute channels have higher gradient advantages than chute channels subject to infill, but that upstream and downstream changes in bend orientation can also influence chute stability. The process of bend extension is typically associated with an increase in the chute gradient advantage, further elucidating the role of bend migration style in chute stability. At the reach scale, rivers with higher sediment loads (Qs/Q) are characterised by higher rates of chute infill. Strickland River floodplain sedimentation rates derived through Pb-210 alpha-geochronology are substantially higher adjacent to single-thread bends than adjacent to bifurcate bends, potentially due to an observed increase in channel capacity (and reduction in floodplain inundation frequency) associated with bend bifurcation. Further research is needed to determine whether this observation is significant in light of high uncertainty in the spatial variability of sedimentation rate estimates, but the data presented highlight a need for carefully considered stratified sampling approaches in floodplain coring campaigns, and illustrate the complexity of possible sediment dispersal mechanisms, and associated ecological responses. GIS analysis of the response of the Ok Tedi in Papua New Guinea to direct addition of mine tailings elucidates interplay between channel steepening due to the propagation of a tailings sediment slug, and mid-channel bar formation induced by the increased sediment load, with associated topographic forcing of bend and chute development. A temporal pattern of increased chute initiation frequency on the Ok Tedi mirrors the inter- and intra-reach spatial pattern of chute initiation frequency on the Paraguay, Strickland and Beni Rivers, where increased stream power is associated with increased bend extension and chute initiation rates. The process of chute formation is shown to be rate-dependent, and the threshold value of bend extension for chute initiation is shown to scale with reach-scale stream power, reminiscent of slope-ratio thresholds in river avulsion. However, Delft3D simulations suggest that chute formation can exert negative feedback on shear stress and bank erosion in the adjacent mainstem bifurcate, such that the process of chute formation is also rate-limiting. Chute formation is activated iteratively in space and time in response to changes in river energy, selectively targeting sites of greatest change, and thereby mediating the river response.

Die Vorteile des Systems „Horn“ gegenüber dem Gangbahn-Flügelrad System liegen in der faserschonenden und lageparallelen Flechtfadenverlegung sowie in der gesteigerten Flechtgeschwindigkeit. Die Herausforderung um das Potential des Systems „Horn“ zur Herstellung von Preforms durch Überflechten zu erschließen, bestand in der Integration eines dritten Fadensystems in eine antriebstechnisch umsetzbare Verlegetechnik zur Fertigung einer triaxialen Flechtstruktur. Für die Synthese dieser Antriebstechnik zur kinematisch optimalen Verlegung der Flechtfäden wurde eine prozessorientierte Synthesemethodik, auf Basis einer Technologiesynthese, erarbeitet. / Advantages of the system “Horn” versus the horn gear motion system lie in a gentle and parallel processing of the braiding materials as well as in an increased speed of braiding. The challenge in extrapolating the potential of the system “Horn” for the production of preforms by over-braiding was to integrate a third yarn system into a laying technique that is technically feasible for processing a triaxial braided structure. For the synthesis of this drive technology and to guarantee an optimal kinematic transfer of threads, a process-oriented synthesizing method, based on a technology synthesis, was elaborated.

In this project the objective is to understand how to design a braiding machine capable of automated production of Omnifibre in a research environment. Automated production of Omnifibre is the key issue for the researchers as they want to increase the weaveabilty of the fibers and make it more suitable for use in active textiles. To achieve the necessary knowledge when designing a braiding machine, an extensive literature study was performed which focused on braids, braiding machines, and CNC manufacturing. An Interview with a researcher and with a manufacturing expert was conducted. Simulations of different braiding machine configurations were performed in TexMind braiding machine configurator. Solidworks was used to estimate the size of the braiding machine. A large amount of the machine’s parts were manufactured on a CNC mill and lathe to test manufacturability and to aid in designing optimal subsystems. The result is a proposed design for a braiding machine in the form of a 3-D model and a partially completed prototype used for testing and design evaluation. The conclusion is that Omnifibre is much like other ultra-fine braided threads, and the research on its applicability has a big impact on the braiding machine’s design, especially on flexibility in thread material and braiding patterns.

Die Vorteile des Systems „Horn“ gegenüber dem Gangbahn-Flügelrad System liegen in der faserschonenden und lageparallelen Flechtfadenverlegung sowie in der gesteigerten Flechtgeschwindigkeit. Die Herausforderung um das Potential des Systems „Horn“ zur Herstellung von Preforms durch Überflechten zu erschließen, bestand in der Integration eines dritten Fadensystems in eine antriebstechnisch umsetzbare Verlegetechnik zur Fertigung einer triaxialen Flechtstruktur. Für die Synthese dieser Antriebstechnik zur kinematisch optimalen Verlegung der Flechtfäden wurde eine prozessorientierte Synthesemethodik, auf Basis einer Technologiesynthese, erarbeitet. / Advantages of the system “Horn” versus the horn gear motion system lie in a gentle and parallel processing of the braiding materials as well as in an increased speed of braiding. The challenge in extrapolating the potential of the system “Horn” for the production of preforms by over-braiding was to integrate a third yarn system into a laying technique that is technically feasible for processing a triaxial braided structure. For the synthesis of this drive technology and to guarantee an optimal kinematic transfer of threads, a process-oriented synthesizing method, based on a technology synthesis, was elaborated.

Recent research and development has resulted in a working prototype of an automated process for manufacturing IsoTruss® and other innovative open lattice composite structures which yields faster, and more predictable and consistent parts, while automatically consolidating individual members. This machine is sufficiently versatile to manufacture any type of open lattice structure fabricated from filamentary composite materials. The objectives of the research in this thesis were two-fold: (1) to validate this new process for making IsoTruss structures; and (2) to measure the compression strength and stiffness of specimens produced on the machine. In order to accomplish the first purpose, various parts were manufactured on this prototype machine, including: a six-node IsoTruss structure with single outer longitudinal members, a three-longitudinal member section of an inner longitudinal IsoTruss structure with consolidated members, and a two-bay IsoTruss panel structure. By creating and running patterns to make these parts, the hypothesis that the machine will make any geometry of IsoTruss structure was validated. The second objective of this research was accomplished by testing the compression strength and stiffness of specimens manufactured with this automated process. Buckling versus compression failure of members was examined by varying member aspect ratios. The effect of intersecting helical members was also explored, as was the effect of changing the number of braiding bobbins used to consolidate members. Testing showed that increasing the number of braiders increases consistency of the braided sleeves and reduces scatter in the results. The ratio of helical to longitudinal tows at a joint is directly related to the percent decrease in member strength at the joint. Compression failure of individual members is the preferred method of failure, because this type of failure absorbs significantly more energy. This research proves that the manufacturing process will produce even the most complex IsoTruss geometries, with the necessary consolidation of individual members. Findings also indicate that a few modifications -- such as improved bobbins, more reliable switches, more accurate pulling system, etc. -- will enable this automated process to produce composite lattice structures with superior mechanical properties.

Gravel bed braided rivers are distinctive natural environments that provide a wide range of key environmental, economic and recreational services. There is, however, a growing concern that over the twentieth century, an increasing number of braided rivers have metamorphosed into wandering or single thread channels, representing a loss of key habitats, geodiversity and amenity. While in some situations, shifts in channel pattern may be unambiguously linked to abrupt changes in flow or sediment supply, the lack of a theoretical basis underpinning the development and maintenance of braiding makes identification of the cause and effect of channel metamorphosis hazardous. A growing body of research has suggested that the transition between channel patterns may depend on the poorly understood interaction between the flow regime, sediment supply and vegetation colonisation. Such interactions are governed by critical thresholds, due to changes in flow resistance and bank strength associated with the distribution, form and intensity of vegetation colonisation. Subtle changes in flow or sediment supply that promote vegetation growth or indeed remove it through inundation or attrition. This can lead to complex non-linear shifts in the balance of forces that govern sediment transport and bedform morphodynamics, ultimately resulting in one-way changes in channel morphology. There is, therefore, a critical need to develop a quantitative understanding of these feedbacks in order to design sustainable river management programmes that seek to optimize the ecological and socio-economic benefits these rivers offer. During the last three decades, significant advances in the understanding of the morphodynamics of braided rivers have been made through a combination of field and physical experimentation. More recently, the emerging field of numerical modelling has created a new avenue to investigate the processes that govern channel dynamics. While this methodology offers significant promise through the construction of virtual experiments that examine the spectrum of drivers and responses of river systems, such models require careful and critical evaluation before they can be used to guide management practice. The wider goal of this research is to explore the application of a numerical modelling to investigate the feedbacks associated with the development and maintenance of braiding. Specifically, the state-of-the-art numerical model, BASEMENT, was used to examine channel responses to steady, and unsteady flow regimes, with and without the representation of vegetation. The research focuses on four main contributions: 1. The development of a systematic framework to quantify the evolving form and processes of braided rivers that can be used as part of a comprehensive approach to model validation. 2. Simulation of braiding development and maintenance using BASEMENT under steady flow conditions. Model simulations based on the natural prototype of the braided River Feshie were used to examine the sensitivity of emergent channel morphologies to the model parameterisation, focusing in particular on the representation of bank erosion and gravity-driven sediment transport. A novel multi6metric framework for model validation is presented and the results demonstrate the critical importance of lateral bank migration processes in order to maintain braided morphologies under steady flow. 3. A critical evaluation of the simulation of braiding under different form of steady and unsteady flow regimes is presented. These experiments investigate how the morphodynamics of braiding vary under energetically-normalised flow regimes characterized by differences in hydrograph form (peak discharge and duration). This experiment provides a novel insight into the role of flow variation in the maintenance of braiding. 4. Finally, the feedback between flow regimes, sediment transport and vegetation growth are examined using a novel model of vegetation colonisation and die- back. Four scenarios are presented, a no-vegetation model, one based on low growth rate, one based on an intermediate growth rate, and finally a high growth rate parameterisation. These simulations provide a clear insight into the non-linear processes driving channel evolution and demonstrate how subtle changes in the balance between flow frequency and vegetation growth can lead to divergent channel patterns. In summary, this thesis aims to advance our understanding of the morphodynamics of braided rivers and the role numerical models may have in helping to interrogate their behaviour and governing controls. It is hoped that this work may contribute, albeit in a small way, to advancing the science that promotes the sustainability of these fascinating and valuable environments.