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A numerical study of natural convection across a window cavity with an insect screen was performed in order to investigate the effects of changing several variables on the heat transfer through the system. A two-dimensional, laminar model was created using the Computational Fluid Dynamics software FLUENT. The system was approximated by three rectangular zones, the largest representing the open room, a smaller area with an isothermal wall representing the window cavity and a thin area representing the insect screen, which connected the two other zones. The insect screen was assumed to be a porous media with a known pressure drop taken from experimentation and the Darcy-Forchheimer equation was applied to this zone. The factors that were changed in order to examine the effects were two window cavity heights and two widths, five different screen porosities and a variety of window, screen and ambient temperature combinations. The model was compared to analytical solutions for a vertical flat plate, as well as a qualitative analysis done through a simple flow visualization experiment for a midrange porosity of 0.5. It was found that the model matched the analytical solution very well and exhibited the same flow patterns as in the experiment. First a non-heated screen was used, simulating nighttime conditions. Velocity vector and temperature plots were created in order to see the changes in flow patterns as the porosity of the screen was decreased for the various geometries and as the temperature between the window and screen increased. Several flow patterns were observed. For small screen/window spacing, 0.0127m, the flow is fairly uniform for all porosities and follows the entire length of the cavity, slowing in velocity for decreasing porosities. For larger spacing, 0.0254m, there are recirculation zones present, one back up the screen, and one in the bottom corner which causes the flow to exit the cavity before it reaches the bottom. The results were then non-dimensionalized and the heat transfer rates were examined by comparing the local and average Nusselt and Rayleigh number for each model. The results showed the effects of the flow patterns on the heat transfer, with end effects jumping the Nusselt number as the flow navigates the bottom corner. These effects are lessened with decreasing porosity. The average Nusselt number also followed the same trend as flat plate correlations, but with less heat transfer. Finally, a methodology was proposed to approximate the heat transfer as resistor network in order to simplify the heat transfer calculations into a 1-D transfer analysis for building sciences applications. Each element of the system, the window, insect screen and open room, was reduced to an isothermal layer in order to describe the system solely by temperature differences in order to find the heat transfer rates. This final step was done in conjunction with ongoing research at the University of Waterloo Solar Thermal Research Lab.

Partially Recursive Acceptance Rejection (PRAR) and bounding chains used in conjunction with coupling from the past (CFTP) are two perfect simulation protocols which can be used to sample from a variety of unnormalized target distributions. This paper first examines and then implements these two protocols to sample from the hardcore gas process. We empirically determine the subset of the hardcore process's parameters for which these two algorithms run in polynomial time. Comparing the efficiency of these two algorithms, we find that PRAR runs much faster for small values of the hardcore process's parameter whereas the bounding chain approach is vastly superior for large values of the process's parameter.

In this work CFD was used to simulate the flow through a novel valve design for internal combustion engines. CFD is numerical method for simulating the behaviour of systems involving flow processes. A FEM was used for solving the equations. Literature on the topic was studied to gain an understanding of the performance limiters on the Internal combustion engine. This understanding was used to set up models that better would mimic physical phenomena compared to previous studies. The models gave plausible results as to fluid velocities and in-cylinder flow patterns. Comsol Multiphysics 4.1 was used for the computations.

A numerical study of natural convection across a window cavity with an insect screen was performed in order to investigate the effects of changing several variables on the heat transfer through the system. A two-dimensional, laminar model was created using the Computational Fluid Dynamics software FLUENT. The system was approximated by three rectangular zones, the largest representing the open room, a smaller area with an isothermal wall representing the window cavity and a thin area representing the insect screen, which connected the two other zones. The insect screen was assumed to be a porous media with a known pressure drop taken from experimentation and the Darcy-Forchheimer equation was applied to this zone. The factors that were changed in order to examine the effects were two window cavity heights and two widths, five different screen porosities and a variety of window, screen and ambient temperature combinations. The model was compared to analytical solutions for a vertical flat plate, as well as a qualitative analysis done through a simple flow visualization experiment for a midrange porosity of 0.5. It was found that the model matched the analytical solution very well and exhibited the same flow patterns as in the experiment. First a non-heated screen was used, simulating nighttime conditions. Velocity vector and temperature plots were created in order to see the changes in flow patterns as the porosity of the screen was decreased for the various geometries and as the temperature between the window and screen increased. Several flow patterns were observed. For small screen/window spacing, 0.0127m, the flow is fairly uniform for all porosities and follows the entire length of the cavity, slowing in velocity for decreasing porosities. For larger spacing, 0.0254m, there are recirculation zones present, one back up the screen, and one in the bottom corner which causes the flow to exit the cavity before it reaches the bottom. The results were then non-dimensionalized and the heat transfer rates were examined by comparing the local and average Nusselt and Rayleigh number for each model. The results showed the effects of the flow patterns on the heat transfer, with end effects jumping the Nusselt number as the flow navigates the bottom corner. These effects are lessened with decreasing porosity. The average Nusselt number also followed the same trend as flat plate correlations, but with less heat transfer. Finally, a methodology was proposed to approximate the heat transfer as resistor network in order to simplify the heat transfer calculations into a 1-D transfer analysis for building sciences applications. Each element of the system, the window, insect screen and open room, was reduced to an isothermal layer in order to describe the system solely by temperature differences in order to find the heat transfer rates. This final step was done in conjunction with ongoing research at the University of Waterloo Solar Thermal Research Lab.

The aggregate base layer is a vital part of the flexible pavement system. Unlike rigid pavements, the base layer provides a substantial contribution to the load bearing capacity in flexible pavements, and this contribution is complex: stress dependent, moisture dependent, particle size dependent, and is anisotropic in nature. Furthermore, the response of the aggregate layer in the pavement structure is defined not only by resilient properties of the base layer but also by permanent deformation properties of the aggregate layer. Before the benefits of revolutionary changes in the typical pavement structures, such as deep unbound aggregate base (UAB) layers under thin hot mix asphalt surfaces and inverted pavement systems can be justified, an accurate assessment of the UAB is required. Several researchers identified that in order to properly assess the contribution of the UAB in the pavement structure, it is necessary to consider not only the vertical modulus but also the horizontal modulus as this substantially impacts the distribution of stresses within the pavement structure. Anisotropy, which is defined as the directional dependency of the material properties in unbound granular bases, is inherent even before the aggregate layer is subjected to traffic loads due to random arrangement of particles upon compaction. Distribution of particle contacts is dominated by the geometry of the aggregates as well as the compaction effort at the time of construction. Critical pavement responses and therefore performance of flexible pavements are significantly influenced by the level of anisotropy of aggregate layers. There are several ways to characterize the level of anisotropy in unbound aggregate systems. Previous research at Texas A&M University suggests functions of fitting parameters in material models (kvalues) as characterizers of the level of anisotropy. In the realm of geotechnical engineering, the ratio of the horizontal modulus to vertical modulus is commonly referred to as the level of anisotropy. When the vertical and horizontal moduli are equal, the system is isotropic, but when they differ, the system is anisotropic. This research showed that the level of anisotropy can vary considerably depending on aggregate mix properties such as gradation, saturation level, and the geometry of the aggregate particles. Cross anisotropic material properties for several unbound and stabilized aggregate systems were determined. A comprehensive aggregate database was developed to identify the contribution level of aggregate features to the directional dependency of material properties. Finally a new mechanistic performance protocol based on plasticity theory was developed to ensure the stability of the pavement foundations under traffic loads.

With electronic packaging towards the development of lead free process, the research on the portable electronic devices subject to impact load is emphasized gradually. At present, for drop test and cyclic bending test, most of the failure modes lie on the modes of "fracturing in IMC layer" or "fracturing on IMC/solder boundary". The purpose of this work is to use 3D numerical analysis software ANSYS/LS_DYNA, that were found out a proper numerical model, to further analyze the impact fracture of lead-free solder. From the numerical results, the strain rate of solder joint ranges from 103 s-1 to 104 s-1 under an impact velocity of 2 m/s. At this strain rate, the mechanical properties of solder joint could be effectively investigated. When IMC strength is smaller than 300MPa, the main failure mode is fracturing of IMC; whilst, IMC strength is greater than 300MPa, the failure mode becomes fracturing of bulk solder, but the failure mode of fracturing of IMC and a partial solder requires a model with more fine meshes to simulate. Different velocities did not affect the numerical results significantly, because the material parameters of a solder ball is strongly dependent on strain rate. Also, we found that the impact test in reality does not present a shear-dominant mode alone even when the impact angle is 0¢X. While using simulation to carry out the dynamic experiment, it can be observed that the course of solder joint suffering the damage provides a good reference and contrast for the experimental work in the future.

With the electronic packaging towards the rapid development of lead free process, the related research on the portable electronic devices subject to impact load is emphasized urgently. At present, the failure modes of fracturing in IMC layer and fracturing on IMC/solder boundary are mostly encountered due to drop test and cyclic bending test respectively. The purpose of this work is to use 3D numerical analysis software ANSYS/LS_DYNA, that were found to be a suitable numerical model for further analyzing the impact fracture of lead-free solder. The relationship between simulation and ball impact test system was compared and the effects of variable parameters on solder balls subjected to impact loading was investigated. Also, the transient deformation and fracturing of solder joints subjected to the impact load were studied numerically and experimentally. Then, the transient response and the failure modes of the solder joint due to impact load were predicted by varied strain rate tests. From the numerical results, the strain rate mechanical properties of solder joint due to high can be effectively obtained. The difference of IMC strength caused three kinds of failure modes of the solder ball, however the failure mode of fracturing in IMC and a party of solder requires a model to simulate with more refined meshes. Different velocities affected the numerical results significantly. The higher the velocity of impact test applied, the lower the impact loading received. That is mainly attributed to the material parameters adopted of a solder ball is strongly dependent on the strain rate considered. Also, it is found that the impact test in reality does not result in a shear-dominant failure mode. While using dynamic simulation instead of the experiment, the damage process of solder joint can be observed. That provides a good reference and contrast for the experimental work in the future.

The influence of the surface excavation and loading on the existing tunnels has been investigated using a Finite Element Method program, Plaxis 3D Tunnel. A parametric study has been carried out where the parameters were the depth of the surface excavation, the eccentricity of the excavation with respect to the tunnel axis, the height of the embankment fill and the stiffness of the soil. It is found that, excavations over the existing tunnels have a negative effect on the tunnel lining capacity since the unloading due the excavation reduces the normal forces and increases the bending moments. On the other hand, it is found that surface loading within the limits considered in this study is not critical in terms of the tunnel stability due to the increase in normal forces and decrease in bending moments.

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