published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Statistics and Actuarial Science / Doctoral / Doctor of Philosophy

published_or_final_version / Mathematics / Doctoral / Doctor of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Economics and Finance / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / Statistics and Actuarial Science / Doctoral / Doctor of Philosophy

In view of the worsening air quality in the world, more concerns are focused on the environment. This thesis uses the technique of CFD and develops the computer model to investigate the wind and pollutant transport, as well as the chemistry of reactive pollutants in idealized two-dimensional (2D) street canyons. Three scientific questions are raised in this thesis. The first task is to find out the po- sition with the most favorable pollutant removal along the ground level over 2D idealized street canyon of different building-height-to-street-width (aspect) ratios (ARs). The di- mensionless parameter, C, represents the pollutant removal performance. In the isolated roughness regime, the two local maximum C locate at the reattachment point and the windward corner. In the wake interference regime, C is peaked on the windward side. The number of vertically aligned recirculations depends on the street depth in the skimming flow regime. The sizes of the secondary recirculation upstream and downstream deter- mine how the maximum C shifts from the street centre. After identifying the position of peaked pollutant removal rate at the ground level, the emission source should be placed with the highest constant C in order to remove the pollutants upward more quickly to safeguard the street-level air quality. After understanding the best pollutant removal in the street canyon of different ARs, the second task is to find out what AR is the most favorable for the ventilation and pollutant removal across the roof level. The three parameters, namely friction factor, air exchange rate (ACH) and pollutant exchange rate (PCH), are introduced to quantify the pressure difference to sustain the mean flow, the ventilation and pollutant removal, respectively. The turbulence contributes more than 70% to the total ACH and PCH in all the three flow regimes. By increasing the atmospheric turbulence in building geometry as well as the surface roughness, the ventilation and pollutant removal performance can be improved. The linear relation between the friction factor and ACH demonstrates the larger resistance that in turn promotes the air exchange over the roof level. The physical dispersion is studied; however atmospheric pollutants are seldom in- ert but chemically reactive instead. The last task is to include the three common air pollutants, NO, NO2 and O3, in the simple NOx ?O3 mechanism in terms of the photo- stationary state and reaction rates. The Damkohler numbers of NO and O3, DaNO and DaO3, are parameterized by the concentrations of the sources NO and O3. The normalized mean and fluctuation NO, NO2 and O3 are separately considered. The integrated pho- tostationary state (PSS) in the first canyon increases with DaO3 under the same DaNO. The integrated PSS of the second to the twelveth street canyons are compared with each case, the monotonic increase in the PSS from the second to twelveth canyon is perceived in DaNO/DaO3 1, 0.03, 0.02, 0.001 and 0.000333. Further decreases the DaNO/DaO3 to 0.000143, 0.000125, 0.000118, 0.000111 and 0.0001, the PSS is found to be non-linear and the trough appears in the fourth and fifth canyons. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

Modeling of the mechanical behavior of geomaterials is a fundamental yet very difficult problem in geotechnical engineering. The difficulty lies in that the engineering behavior of geomaterials is strongly nonlinear and anisotropic, depending on confining pressure, void ratio, stress history, and drainage conditions. A traditional approach to the modeling of geomaterials is to formulate empirical equations to fit experimental data. Generally, this approach is not able to provide physical insights into the diverse responses observed in the soil mechanics laboratories. Another conventional approach is to make use of the classical plasticity theory, established mainly for metals, to develop constitutive models for geomaterials. While this approach is capable of shedding light on the mechanisms involved, it has been recognized that such models may violate the basic laws of physics. The objective of this thesis is to apply a new approach to constructing constitutive models for geomaterials, by making use of thermomechanical principles. The essence of the new approach is that the constitutive behavior of geomaterials can be completely determined once two thermomechanical potentials, i.e. the free energy and dissipation rate functions, are specified. The yield function and flow rule in the classical plasticity theory can be established from the two potentials, and the models so derived satisfy the basic laws of physics automatically. In this thesis, the theoretical framework for constructing thermomechanical models is introduced. Several concepts in relation to plastic work, dissipated and stored energy are discussed. Both the isotropic and anisotropic models are formulated and realized in this framework and the generated predictions are compared with the test data of a series of triaxial compression tests on sand. To address the important density- and pressure-dependent behaviors of sand in the framework, a state-dependent thermomechanical model is developed, by introducing the state parameter into the dissipation rate function such that a unique set of model parameters is able to predict the behaviors of sand for a wide variation of densities and pressures. Finally, a thermomechanical model for predicting the complex unloading and reloading behaviors of sand is developed by modifying the hardening laws, and the performance of this model is investigated. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

In recent years, lots of research effort was spent on the integration of process planning and job-shop scheduling. Various integrated process planning and scheduling (IPPS) models and solution approaches have been proposed. The previous and existing research approaches are able to demonstrate the feasibility of implementing IPPS. However, most of them assumed that setup time is negligible or only part of the processing time. For machined parts, the setup for each operation includes workpiece loading and unloading, tool change, etc. For setup that depends only on the operation to be processed (sequence-independent), it is applicable to adopt the assumption of not considering setup in IPPS. For setup that depends on both the operation to be processed and the immediately preceding operation (sequence-dependent), it is an oversimplification to adopt such assumption. In such cases, the setup time varies with the sequence of the operations. The process plans and schedules constructed under such assumption are not realistic or not even feasible. In actual practice, therefore, the setup time should be separated from the process time in performing the IPPS functions. In this thesis, a new approach is proposed for IPPS problems with setup time consideration for machined parts. Inseparable and sequence-dependent setup requirements are added into the IPPS problems. The setup times are separated from the process times and they vary with the sequence of the operations. IPPS is regarded as NP-hard problem. With the separated consideration of setup times, it becomes even more complicated. An Ant Colony Optimization (ACO) approach is proposed to handle this complicated problem. The system is constructed under a multi-agent system (MAS). AND/OR graph is used to record the set of feasible production procedures and sequences. The ACO algorithm computes results by an autocatalytic process with the objective to minimize the makespan. Software agents called “artificial ants” traverse through the feasible routes in the graph and finally construct a schedule. A setup time parameter is added into the algorithm to influence the ants to select the process with less setup time. The approach is able to construct a feasible solution with less setup time. Experimental studies have been performed to evaluate the performance of MAS-ACO approach in solving IPPS problems with separated consideration of setup times. The experimental results show that the MAS-ACO approach can effectively handle the problem. / published_or_final_version / Industrial and Manufacturing Systems Engineering / Master / Master of Philosophy