In a counter-current two-phase flow system, flooding can be defined as the onset of flow reversal of the liquid component which results in an upward co-current flow. Flooding in the surge line of pressurized water reactors poses a significant technical challenge in the analysis of several postulated nuclear reactor accident scenarios. Despite the importance of flooding in these analyses, previous work does not identify a universally accepted rigorous physics-based model of flooding, even for the simple case of flooding in adiabatic, vertical tubes. This can be attributed to a lack of conclusive understanding of the physics of two-phase counter-current flow, specifically the mechanism of flooding, and the large amount of uncertainty among data from various flooding experiments. This deficiency in phenomenological and experimental knowledge has led to the use of many empirical and semi-empirical correlations for specific system conditions and geometries. The goal of this work is the development of a model for flooding in vertical, adiabatic tubes from first principles. To address a source of uncertainty in the analysis of flooding, a model for the prediction of average film thickness in annular co- and counter-current flows has been developed by considering the conservation of momentum of the liquid and gas flows. This model is shown to be a quantitative improvement over the most commonly used models, those of Nusselt and Belkin, Macleod, Monrad, and Rothfus. The new model better considers the effects of interfacial shear and tube curvature by using closure relations known to represent forces appropriately in co- and counter-current flow. Previous work based on semi-empirical flooding models has been analyzed to develop a new theory on the hydrodynamic mechanism which causes flooding. It is postulated that the growth of an interfacial wave due to interfacial instability results in a flow reversal to ensure that momentum is conserved in the counter-current flow system by causing a partial or complete co-current flow. A model for the stability of interfacial waves in a counter-current flow system is proposed and has been developed herein. This model accurately represents the geometric and flow conditions in vertical adiabatic tubes and has been shown to have limits that are consistent with the physical basis of the system. The theory of waves of finite amplitude was employed to provide closure to an unknown parameter in the new model, the wave number of the wave that generates the interfacial instabil- ity. While this model underpredicts the flooding superficial gas velocity, the result is a conservative estimate of what conditions will generate flooding for a system. In the context of the analysis of a nuclear reactor, specifically a pressurized water reactor, conservatism means that the gas flow rate predicted to cause flooding for a fixed liquid flow rate will be less than the flow rate found experimentally, mean- ing that liquid delivery to the core would be safely underestimated. Future work includes the improvement of the closure relation for the limiting wave number that will cause unstable interfacial waves, as well as an assessment of the applicability of the stability-based model to flooding in the presence of phase change and flooding in complex geometries.

The hydraulic fracturing treatment is an essential tight sand gas reservoir stimulation that employs viscous fluid to break the formation rock to create a fracture and transport the propping agent to support the fracture from naturally healing. Despite proven economic benefit, the hydraulic fracture fluid damages the producing formation and the propped fracture. To analyze the gel damage effect quantitatively, the filter cake thickness is used as a parameter that has not been measured before. This project was divided into two stages. The first stage built up a filter cake and measured the filter cake thickness by a laser profilometer. A correlation between leakoff volume and filter cake thickness was produced. The second stage eroded the filter cake by flowing original fracturing fluid through the core sample to study the fracturing fluid shear clean up effect on filter cake thickness. The filter cake was built up in the lab and the thickness was measured with different methods. The profilometer has been tested as an effective tool to measure the filter cake thickness. A correlation for crosslinked guar fracture fluid filter cake thickness was produced. An experiment setup used to shear erode the filter cake was built and tested. The results showed the filter cake was not eroded at 200 s-1 shear rate.

It is a widely accepted fact that tourism has become a prominent part of local economic development regarding to global economic restructuring and over the last two decades many regions have achieved tourism-led local economic development. The concept of &amp / #8216 / Institutional Thickness&amp / #8217 / which has been introduced within the context of institutional turn in economic geography and discussed intensively in local economic development context has important implications for tourism-led local economic development. The concept describes how institutional arrangements influence the capacity of localities to compete globally and emphasizes the importance of strong local institutional base and inter-institutional collaboration in local economic development. This thesis discusses tourism-led local economic development and the concept of institutional thickness and investigates how the concept relates to tourism-led local economic development. It aims to make an empirical assessment of institutional thickness. Using case study as a research method, the research focuses on Beypazari district that achieved domestic tourism development involving day excursions from the major metropolitan areas and trying to improve its local economy through tourism. In this locally initiated project, the local government collaborated with many institutions. The thesis assesses institutional thickness of Beypazari within its local economic development process. Keywords: Tourism, local economic development, institutional thickness

The pipeline is playing an important role in industry nowadays. However, the inner wall of pipeline may suffer corrosion after a long service time. When excessive corrosion occurred, not only the transported material inside the pipe will let out but also serious accident may be induced. So, it¡¦s necessary to monitor pipeline thickness regularly. Conventionally, since most piping systems were subjected to high-temperature working environments, hence if an operator intend to examine the thickness of a pipeline, the whole piping system need to be shutdown and resulted in financial losses. Therefore, to develop on-line thickness measurement technique for pipelines subjected to high-temperature working environment is indispensable. ¡@¡@In this study, low-cost PZT sensors (Pb(ZrxTi1-x)O3), which can sustain high-temperature working environment, were used to execute the thickness measurements. A single PZT, which was bonded on the surface of a pipe as an actuator and a receiver simultaneously. Then, by utilizing the GUI(Graphic User Interface) system, which was designed in this study, the echo signal can be analyzed and the thickness of the pipe can be determined on-line and automatically. It is noted that the wave speed changed as environmental temperature increased. So, in this study, by using A36 steel plates and steel tubes as a specimens, a modified temperature versus wave velocity curve was proposed.. The experimental results showed that non-conservative thickness measurements will be obtained if modified wave speed was not adopted when working temperature increased. keywords¡GThickness measurement, PZT sensor, GUI system, Modified wave velocity curve.

¡@¡@An electrical discharge coating method, which an isolated sleeve is used to form a closed space between the end surface of electrode and the workpiece so that the particles, the ions, and the pressure during the discharge process are concentrated on this space, is employed to increase the coating speed and the quality of the coating. The electrode for the cathode is made of brass, and the workpiece for the anode SKD11. They are immersed in kerosene containing W/C powder with the concentration of 50g/L. The time for the pulse-on is 25£gs and that for the pulse-off times 500£gs. The growing thickness and the quality of coating layer are investigated under the supply voltage of 50-400V, discharge coating time of 34-284s, and the gap distance of 50-300£gm. ¡@¡@Experimental results show that when the supply voltage is larger than 100V, the gap distance less than 150£gm and discharge coating time 142s, the area covered by the coating can achieve more than 90 percent of the total surface area. Moreover, the coating thickness increases with increasing gap distance and discharge coating time, but as the gap distance is larger than 150£gm, the coating thickness decreases with increasing gap distance. ¡@¡@For a special case, under the supply voltage of 200V, the gap distance of 100£gm and the discharge coating time of 142s, the coating thickness can achieve about 17£gm with little pore in the coating layer. The hardness of the coating layer can almost achieve the level of W/C hardness.

This dissertation investigates the crustal structure of the eastern Basin and Range Province in the western United States and its relationship with the present-day extensional regime governing this region. The use of combined results from different geophysical methods provide a better understanding of the subsurface crustal structure and the processes involved in this extensional deformation. Teleseismic receiver functions were used to create a uniformly sampled map of the crustal thickness variations and stacked images of the crust beneath the majority of the state of Utah, which provide additional constraints on the seismic characteristics of the crust and upper mantle. These results reveal crustal variations characterized by a distinct change in crustal thickness that closely follows the surface trace of the Wasatch fault, with differences in depth of up to 10 km across a distance of less than 55 km. Analysis of seismic reflection profiles, horizontal and vertical crustal velocities from continuous GPS, and surface geology provide new constraints on the relationships between interseismic strain accumulation, subsurface fault geometry, and geologic slip rates on seismogenic faults. Seismic reflection data show recent activity along high-angle normal faults that become listric with depth, sole into preexisting décollements, reactivating them, and appear to be connected at depth with a regionally extensive detachment horizon. GPS data reveal present-day crustal extension of ~3 mm/yr and no net vertical motion between the Colorado Plateau and eastern Basin and Range. Inverse modeling results of the crustal deformation data include a low-angle dislocation (~8-20°) at a locking depth of ~7-10 km, consistent with the interpreted seismic data, and slipping at 3.2±0.2 mm/yr, suggesting an active regionally extensive sub-horizontal surface beneath the eastern Basin and Range. A test of this hypothesis using seismic data interpretation as the basis for a forward strain accumulation model shows that displacement across a deep low-angle detachment imaged seismically is also consistent with geodetic velocities. Seismic and geodetic data support a model for eastern Basin and Range mechanics wherein diffuse permanent strain of the upper crust by multiple discrete faults is facilitated by displacement along a single low-angle detachment at midcrustal depth.

Tube bending is a widely used manufacturing process in the aerospace, automotive, and other industries. During tube bending, considerable in-plane distortion and thickness variation occurs. The thickness increases at the intrados (surface of tube in contact with the die) and it reduces at the extrados (outer surface of the tube). In some cases, when the bend die radius is small, wrinkling occurs at the intrados. In industry a mandrel is used to eliminate wrinkling and reduce distortion. However, in the case of a close bend die radius, use of a mandrel should be avoided as bending with the mandrel increases the thinning of the wall at the extrados, which is undesirable in the manufacturing operation. The present research focuses on additional loadings such as axial force and internal pressure which can be used to achieve better shape control and thickness distribution of the tube. Based on plasticity theories, an analytical model is developed to predict cross section distortion and thickness change of tubes under various loading conditions. Results from both the FEA and analytical model indicated that at the intrados the increase in thickness for bending with internal pressure and bending with combined axial pull and internal pressure was nearly the same. But in the case of bending with the combination of axial pull and internal pressure there was a significant reduction of thickness at the extrados. A parametric study was conducted for the case of bending with combined internal pressure and axial pull and it was seen that with proper selection of the pressure and axial pull wrinkling can be eliminated, thickness distribution around the tube can be optimized, and cross section distortion of the tube can be reduced. Predictions of the analytical model are in good agreement with finite element simulations and published experimental results. The model can be used to evaluate tooling and process design in tube bending.

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One major way that running style varies between individuals is how their foot strikes the ground (forefoot strike or rearfoot strike). Running generates a torque about the ankle that depends on the individual’s foot strike pattern, length of their plantar flexor moment arm, and force generated from the plantar flexor muscles. The foot strike pattern during running, gastrocnemii muscle thickness, and heel length (used as an approximation for plantar flexor moment arm) were determined in 41 runners. Forefoot and rearfoot strike runners had the same thickness of the gastrocnemii muscles. However, in comparison with sedentary walkers, the runners had thicker calf muscles. These results imply a “peak” muscle thickness seems to be attained by running. Runners with longer heels were more likely to use a forefoot strike running style, possibly due to a mechanical advantage in the generation of torque.

No description available.