Polymeric systems become increasingly complicated and multifunctional if they involve a larger level of structural complexity. In the last couple of decades the level of interest has gradually shifted from the μm-scale to the nm-scale region, for instance, systems having at least one structural size below 100nm, e.g. nanocomposites. The physical properties of polymers such as crystallisation, tensile modulus, impact strength and viscosity are strongly influenced by the presence of additives in the polymer matrix. Semicrystalline polymers comprise nearly two-thirds of all synthetic polymers. These are processed to form films, fibers, and moulded articles using operations such as extrusion, moulding, fiber spinning, film blowing etc. During these processes, the polymer melt is subjected to complex and intense flow fields (shear or elongational) after which the polymer crystallises. The morphology of the semicrystalline polymer in the final product and subsequently its properties and quality, depend on the manner in which the polymer crystallises from the flowing melt. The subject is continuously driven by the quest to understand the molecular mechanism of flow induced crystallisation; nevertheless, the flow induced crystallisation in presence of nanofillers has received little attention. The thesis deals with the crystallisation studies of polymer molecules during shear in presence of nanofillers (viz. single walled carbon nanotube (SWCNT) and zirconia particle) having different aspect ratio. For this purpose, the polyethylene (PE) consisting of desired molar mass and molar mass distribution within the processing range is utilised. The morphology of semicrystalline polymer is revealed using time resolved X-ray scattering (SAXS/WAXS) techniques. The rheological aspects of polymer melt in presence of nanoparticles are manifested. In chapter 2, the effect of SWCNTs on the crystallisation kinetics of polymers has been studied with and without application of shear rate. The shear rate effect on the formation of shish-kebab structures in the polymer containing SWCNTs is investigated. The effect of shear rates on the stretching of long chains of PE is verified using the approach involving the use of Deborah number. The study reveals the significance of SWCNTs on crystallisation of PE. In chapter 3, the influence of zirconia nanoparticles on crystal orientation of polymers is studied. Enhanced crystallisation kinetics is observed due to presence of zirconia nanoparticles. Overall crystal orientation is improved as a result of zirconia nanoparticles in the polymer matrix. In chapter 4 of the thesis, the role of broad molecular weight distribution of PE in formation of oriented (shish-kebab) structures is demonstrated. The presence of nanoparticles of different aspect ratios and binding efficiency with polymer on the formation of highly oriented structures in the early stage crystallisation is verified. The study reveals the significant role of SWCNTs in shish-kebab structure formation as compared to zirconia nanoparticles. Further, the insight on the selective adsorption of polymer chains to the nanoparticles is provided. In chapter 5 of the thesis, the molecular interaction between polymer and nanoparticles under shear above the equilibrium point (T = 141.2°C) is investigated. The study reveals the major role of SWCNTs with high aspect ratio, in the stability of flow induced precursor (FIP) and formation of extended chain crystals, as a result of strong interaction with PE molecules. On contrary, the poor interaction of Zirconia particles having low aspect ratio, with PE molecules prohibits molecular chain extension.

A low-order, dynamical systems approach is applied to the modeling of flow induced vibrations of flexible cables. By combining a coupled map lattice wake model with a linear wave equation cable model, both the free response of the cable as well as the resulting wake structures are examined. This represents an extension of earlier coupled map lattice models that only modeled the wake of forced cable vibration. The validity of the model is assessed through comparisons with both Computational Fluid Dynamics models (NEKTAR spectral element code) and wake experiments. The experimental wake data was collected through the use of hot-film anemometry techniques. Eight hot-film probes were placed along the span of a flexible cable mounted in the test section of a water tunnel. Through the use of frequency domain correlation algorithms, the phase of vortex shedding was calculated along the cable span from the hot-film velocity data. Results for an elastically mounted rigid cylinder showed that the freely vibrating CML model predicted behavior characteristic of a self-induced oscillator; the maximum amplitude of vibration was found to occur at a cylinder natural frequency that did not coincide identically with the natural shedding frequency of the cylinder. Furthermore, the variation of the frequency of cylinder vibration with its natural frequency was seen to be linear. For standing wave cable responses, the freely vibrating CML model predicted lace-like wake structures. This result is qualitatively consistent with both the NEKTAR simulations and experimental results. Little difference was found between the wakes of forced and freely vibrating cables at the Reynolds number of the study $Re=100$. Finally, it was found that the freely vibrating CML could match numerical predictions of cross-flow amplitude as the cable mass-damping parameter was varied over an order of magnitude (once the CML was tuned to match results at a specific mass-damping level). In addition to providing wake patterns for comparisons with the freely vibrating CML, experimental data was supplied to a self-learning CML scheme. This self-learning CML was able to estimate the experimental wake data with good accuracy. The self-learning CML is seen as the next extension of the freely-vibrating CML model, capable of estimating unmodeled wake dynamics through the use of experimental data.

There are two main goals of this thesis: to investigate the flow-induced crystallization behaviour of Polybutene-1 (PB-1 samples, and to study the effects of molecular parameters on the crystallization behaviour While flow-induced crystallization is not a new area in polymer research, well-defined experimental methods that allow access to high flow rate range comparable to that encountered in real processing are still lacking. Two types of flow are considered: shear and uniaxial elongational. Regarding the second aim, several molecular parameters considered are: molecular weight, molecular weight distribution, isotacticity, presence of nucleating agents, and copolymer content. For this purpose an array of PB-1 samples were used. It is found that each of these parameters can have significant effect on the crystallization behaviour. Mainly rheological methods were utilized to conduct the flow-induced crystallization experiments. Crystallization onset time is define d from the change in viscosity or other related parameters. The experiments begin with low shear rate range, to ensure that the results are comparable with literature data. In this range we encounter the quasi-quiescent onset time at very small. shear rates, which draws an interesting comparison with another physical parameter, the gel time. Beyond a critical flow rate a decrease in the onset time is seen, and a plateau-and-slope trend is evident for a curve of onset time vs. shear rate. Using a combination of three experimental methods, shear rates ranging from Q0001 - 500 s-1 are successfully achieved, and a good agreement between these methods is observed. Furthermore, a normalization procedure is introduced, which yields temperature-invariant curves for the mentioned range of shear rate. For the uniaxial elongation flow, the Elongational Viscosity Fixture (EVF) is employed, with the strain rate ranging from 0.0001 - 10 s'. A greater reduction in onset time as compared to shear (at the same shear/strain r ate) is observed, and the difference in the onset times for shear and elongation already reaches more than one decade for a flow rate of 10 5. This quantitative comparison is particularly important; since not so many data on elongation-induced crystallization are available in the literature. Finally, the thesis compares several flow induced crystallization models that can be useful as prediction tools and selects one of these models to be compared with the experimental data. A qualitative agreement is found, however, for better quantitative prediction the model still needs to be.

No description available.

The present study aims to explore dynamical behavior of the fluid-elastic instability of a circular cylinder in shear flow by numerical simulations. The theoretical model comprises two groups of transient conservation equations of mass and momentum and the governing equations are solved numerically with Fluent software to determine the flow property. The analysis presented that there exist both vortex-induced vibration and flow-elastic vibration for single cylinder in sear flow. The numerical results with a Harmonic Model built from Gambit indicate that there is a transverse force acting from high velocity side toward the low velocity side in shear flow. The transverse force make cylinder move periodically and thus go to a vibration. Furthermore, this study appraises the amplitude and orbit of fluid elastic vibration of a circular cylinder in shear flow and shows the effects of the shear velocity slope and damping factor on fluid elastic vibration of the cylinder. Here in the thesis, as the function applied with Fluent of displaying dynamic mesh on-time, the movement and re-mesh of cylinder could be observed. A vibration expansion diagram was presented and the pictures of flow velocity and flow pressure were retrieved from Fluent.

Large structures exposed to the environment such as the collinear omni and large panel communication antennas in this research suffer damage from cyclic wind, rain, hail, ice load and impacts from birds and stones. Stresses from self-weight, ice loading and wind gusts will produce deformations of the structure that will lead to performance deterioration of the antenna. In order to avoid such a case, it is important to understand the static, dynamic and aerodynamic behavior of these structures and thus optimization can be achieved. In this research the current fluid-structure interaction methods are used to model, simulate and analyze these communication antennas in order to assess whether failure would occur under service loads. The FEA models developed are verified against analytical models and/or experiments. Different antenna configurations are compared based on their capacity to minimize vibration effects, stress-induced deformations and aerodynamic loading effects.

Large structures exposed to the environment such as the collinear omni and large panel communication antennas in this research suffer damage from cyclic wind, rain, hail, ice load and impacts from birds and stones. Stresses from self-weight, ice loading and wind gusts will produce deformations of the structure that will lead to performance deterioration of the antenna. In order to avoid such a case, it is important to understand the static, dynamic and aerodynamic behavior of these structures and thus optimization can be achieved. In this research the current fluid-structure interaction methods are used to model, simulate and analyze these communication antennas in order to assess whether failure would occur under service loads. The FEA models developed are verified against analytical models and/or experiments. Different antenna configurations are compared based on their capacity to minimize vibration effects, stress-induced deformations and aerodynamic loading effects.

No description available.

No description available.

A filament stretching extensional rheometer was used to investigate the effect of uniaxial flow on the crystallization of polypropylene. Samples were heated to a temperature above the melt temperature to erase their thermal and mechanical histories. The Janeschitz-Kriegl protocol was applied and samples were stretched at various extension rates to a final strain of e = 3.0. Differential scanning calorimetry was applied to crystallized samples to measure the degree of crystallinity. The results showed that a minimum extension rate, corresponding to a Weissenberg number of approximately Wi = 1, is required for an increase in percent crystallization to occur. Below this Weissenberg number, the flow is not strong enough to align the tubes of constrained polymer chains and as a result there is no change in the final percent crystallization. An extension rate was also found for which percent crystallization is maximized. The increase in crystallinity is likely due to flow-induced orientation and alignment of tubes of constrained polymer chains. Polarized-light microscopy verified an increase in number and decrease in size of spherulites with increasing extension rate. Small angle X-ray scattering showed a 7% decrease in inter-lamellar spacing at the transition to flow-induced increase in crystallization. Crystallization kinetics were examined by observing the time required for melts to crystallize under uniaxial flow. The crystallization time decreased with increasing extension rate, even for extension rates where no increase in percent crystallization was observed. These results demonstrate that the speed of crystallization kinetics is greatly enhanced by the application of extensional flow.