It is well established that the temperature gradients in the interiors of internally-heated mantle convection models are subadiabatic (e.g. Parmentier et al., 1994; Bunge et al., 1997, 2001). The subadiabatic gradients have been explained to arise due to a balance between vertical advection and internal heating, however, a detailed analysis of the energy balance in the subadiabatic regions has not been undertaken. In this research, I examine in detail the energy balance in a suite of two-dimensional convection calculations with mixed internal and basal heating, depth-dependent viscosity and continents. I find that there are three causes of subadiabatic gradients. One is the above-mentioned balance, which becomes significant when the ratio of internal heating to surface heat flux is large. The second mechanism involves the growth of the overshoot (maximum and minimum Temperatures along a geotherm) of the geotherm near the lower boundary where the dominant balance is between vertical and horizontal advection. The latter mechanism is significant even in relatively weakly internally heated calculations. For time-dependent calculations, I find that local secular cooling can be a dominant term in the energy equation and can lead to subadiabaticity. However, it does not show its signature on the shape of the time-averaged geotherm. I also compare the basal heat flux with parameterized calculations based on the temperature drop at the core-mantle boundary, calculated both with and without taking the subadiabatic gradient into account and I find a significantly improved fit with its inclusion.<p> I also explore a wide range of parameter space to investigate the dynamical interaction between effects due to surface boundary conditions representing continental and oceanic lithosphere and the endothermic phase boundary at 660 km-depth in two-dimensional Cartesian coordinate convection calculations. I find that phase boundary induced mantle layering is strongly affected by the wavelength of convective flows and mixed surface boundary conditions strongly increase the horizontal wavelength of convection. My study shows that for mixed cases the effects of the surface boundary conditions dominate the effects of the phase boundary. I show that the calculations with complete continental coverage have the most significantly decoupled lower and upper mantle flows and substantial thermal and mechanical layering. Unlike the free-slip case where the surface heat flux decreases substantially with increasing magnitude of the Clapeyron slope, surface heat flux is shown to be almost independent of the Clapeyron slope for mixed boundary condition cases. Although very different when not layered, models with free and mixed surfaces have very similar planforms with very large aspect ratio flows when run with large magnitudes of the Clapeyron slope. I also calculate the critical boundary layer Rayleigh number as a measure of the thermal resistance of the surface boundary layer. My results show that the thermal resistance in the oceanic and the continental regions of the mixed cases are similar to fully free and no-slip cases, respectively. I find that, even for purely basally heated models, the mantle becomes significantly subadiabatic in the presence of partial continental coverage. This is due to the significant horizontal advection of heat that occurs with very large aspect ratio convection cells.

While shoaling from deepwater in a stratified ocean, an interfacial solitary wave (ISW) may experience waveform inversion on a continental margin. Although many oceanographers have believed that the inversion from depression to elevation may commence at the turning point where the upper and bottom layers are equal in depth, this phenomenon has not been fully verified in field observations nor in a laboratory. In this study, a series of laboratory experiments and numerical modeling were conducted on the evolution of an ISW of depression across uniform slope joining a horizontal plateau which resembles pseudo slope-shelf topography, in order to clarify this fascinating phenomenon and the variations of wave properties associated with the process. In the laboratory experiments, a depression ISW was produced by a collapse mechanism in a stratified two-layer fluid system within a steel-framed wave flume (12 m long, 0.7 m high by 0.5 m wide) at the National Sun Yat-sen University in Taiwan. The fluid density in the upper (fresh) and bottom (brine) layers was 996 and 1030 kg/m3, respectively. A series of experiments were conducted upon varying the magnitude of the most important physical factors (i.e., nominal thickness of pycnocline, depth ratio between upper and bottom layer, front gradient and shape of pseudo slope-shelf), from which the results are now discussed in four separate chapters in this thesis. Present laboratory results indicate that the process of waveform inversion took place after an ISW had experienced internal run-down, hydraulic jump, vortex motion and surge-up on the front slope, prior to its propagation onto the plateau. Moreover, the fundamental wave period of leading wave on the plateau was significantly smaller than that in the preceding sections on the front slope and the incident stage earlier, thus representing frequency downshift. Amongst the factors involved, the depth ratio between the upper and bottom layer was the most significant one for waveform inversion. Only when the upper layer was thicker than the bottom layer on the plateau of pseudo slope-shelf, waveform inversion could occur, besides the length of the plateau. On the other hand, the front gradient and shape of pseudo slope-shelf also affected the magnitude of the transmitted wave over the plateau as the wave across this specific topography. In the case of a steeper front gradient, waveform inversion became insignificant due to stronger wave reflection and intense energy dissipation caused by turbulent mixing while a depression ISW propagated over a slope-shelf; particularly against a submerged vertical cliff. As a depression ISW across pseudo slope-shelf with short plateau, intense wave breaking might occur again with vortex motion at its rear end as the newly inversed waveform reentering deep water. In this region, the upper layer was smaller than the bottom layer, hence it could not support the continuous existence of an ISW in elevation. Again, energy dissipation occurred due to turbulent mixing beyond the rear end of a short plateau. Finally, a different mode of ISW appeared within pycnocline, while its nominal thickness was larger than the amplitude of the incident wave. In addition to the laboratory investigations, numerical model was also adopted to study the variations in the flow field as an ISW propagated over a pseudo slope-shelf, in order to complement the experimental results. The results of numerical modeling revealed that the horizontal velocity in the bottom layer increased when the wave encountered the front slope, even if the depth of upper layer was thinner than that of the bottom layer on the plateau. Consequently, the velocity in the upper layer became less than that in the bottom layer when the former was thicker than that of the latter on the plateau. On the other hand, the vertical velocity within the self-generated vortex switched direction as waveform inversion commenced after the wave across the shoulder of pseudo slope-shelf where the local depth of the upper layer was larger than that of bottom part. Overall, the significance of the four pertinent factors (i.e., nominal thickness of pycnocline, water depth ratio, front slope, and plateau length) that affected a depression ISW across pseudo slope-shelf is discussed in detail in this thesis, as well as the variation of flow field calculated by the numerical mode presented.

The sediment resuspension and turbidity created during dredging operations is both an economical and environmental issue. The movement of sediment plumes created from dredging operations has been predicted with numerical modeling, however, these far-field models need a “source term” or near-field model as input. Although data from field tests have been used to create near-field models that predict the amount of material suspended in the water column, these results are skewed due to limitations such as non-uniform sediment distributions, water currents, and water quality issues. Laboratory investigations have obtained data for turbidity during dredging operations, but these results do not take advantage of the most contemporary testing methods. The purpose of this dissertation is to provide an estimation of turbidity created during a cutter suction dredging operation. This estimation was facilited by the development of resuspension measurement and data acquisition techniques in a laboratory setting. Near-field turbidity measurements around the cutter head were measured in the Haynes Coastal Engineering Laboratory at Texas A&M University. The laboratory contains a dredge/tow tank that is ideal for conducting dredging research. A dredge carriage is located in the dredge/tow tank and is composed of a carriage, cradle, and ladder. Acoustic Doppler Velocimetry (ADV) and Optical Backscatter Sensor (OBS) measurements were taken at specific points around the cutter head. The variables of suction flow rate, cutter speed, and the thickness of cut were investigated to understand their specific effect on turbidity generation and turbulence production around the cutter head. A near-field advection diffusion model was created to predict resuspension of sediment from a cutter suction dredge. The model incorporates the laboratory data to determine the velocity field as well as the turbulent diffusion. The model is validated with laboratory testing as well as field data. Conclusions from this research demonstrate undercutting consistently produced larger point specific turbidity maximum than overcutting in the laboratory testing. An increase in suction flow rate was shown to increase production and decrease turbidity around the cutter head. In general, an increase in cutter speed led to an increase in turbidity. The thickness of cut produced less resuspension for a full cut versus a partial cut. Data for a “shallow cut” also produced less turbidity generation than partial cuts. The numerical model was compared to all laboratory testing cases as well as the Calumet Harbor and New Bedford cutter resuspension data and produced suitable MRA values for all tests. The numerical model produced higher point specific regions of turbidity for undercutting but produced larger mean values of turbidity for overcutting.

ABSTRACT Three-dimensional modeling on the aerodynamics of airflow and diffusion of air pollutants in a longitudinal-ventilated traffic tunnel was carried out. The model takes ventilation fans, traffic flow rate, speed, emission factor and piston effect of moving vehicles into consideration. Turbulent flow and dispersion of gaseous pollutants in road tunnels were solved numerically using the finite volume method. Traffic emissions were accordingly modeled as banded line sources along the tunnel floor. The effects of fan ventilation, roughness and piston effect of moving vehicles on the air flow and pollutant dilution are examined. Concentrations of gaseous pollutants CO, NOX, SO2 and THC (total hydrocarbons) at three axial locations in the tunnel, together with traffic flow rate, traffic speed and types of vehicle were measured. Case study was conducted on the Cross-Harbor Tunnel and the Chungcheng Tunnel in which on-site measurements of traffic flow were also conducted concurrently to provide traffic emission data to the tunnel environment for numerical simulation and comparisons. The aim of this study was to understand the spatial variation of air pollutants generated by traffic emissions and evaluation of ventilation performance and piston effect of moving vehicles on dilution of air pollutants in these tunnels. The results show that the major emission sources of CO are passenger cars and motorcycles, while major emission sources of NOx are trucks. Pollutants convect downstream with the wind generated either by longitudinal ventilation fans and/or moving vehicles, thus causing increasing pollutants concentrations with increasing downstream distance. The piston effect of moving vehicle alone can provide 64% ~ 85% increase of wind speed in Chungchen Tunnel and 13% ~ 20% in Cross-Harbor Tunnel. When all fans are on, showing 185% ~ 328% and 120% ~ 182% increases in Chungchen Tunnel and Cross-Harbor Tunnel, respectively. The piston effect of moving vehicle alone can provide 14% ~ 32% dilution of air pollutants in the Chungcheng Tunnel. The piston effect of moving vehicles is compounded with ventilation fans, showing a 47% ~ 66% dilution effect when all fans are on. For the Cross-Harbor Tunnel, the piston effect of moving vehicle alone can provide 9% ~ 23% dilution of air pollutants and 36% ~ 74% dilution effect when all fans are on. The results reveal that cross-sectional concentrations are non-uniformly distributed and that concentrations rise with downstream distance. When all fans were turned off, wind speed in tunnels would be considered as constant, and gaseous pollutants concentration agree with linearly alone the tunnel.

Impact hammer is the current modal testing way in Dynapac testing department. Due to highly damped characteristic of big construction machines, there are a few weaknesses for modal testing when using hammer, such as short response time, limited frequency resolution, poor quality of frequency response functions. Therefore, a more advanced excitation equipment is needed to improve the measurement quality. The object for this study is to compare two different measuring methods. The thesis will show a comparison between the hammer testing and the shaker MIMO testing compared with analytical model in a highly damped system. It will also give a reference for further highly damped modal analysis and budgetary assessment to decide the budget expenditure. Result from shaker testing shows a little better correlation than hammer testing compared with FEM model. While the correlation between FEM model and measurement is bad due to many reasons, such as many local modes that can not excited, lack of excitation points, unexpected noise and error from the measurement. While considering the compared results obtained from this machine for now, a simpler structure experiment is suggested to be carried on in the future. Shorter length of stinger can be used to enable higher amplitude of force to excite the property on this machine.

The Earth's magnetic field is generated in its fluid outer core through dynamo action. In this process, convection and differential rotation of an electrically conducting fluid maintain the magnetic field against its ohmic decay. Using numerical models, we can investigate planetary dynamo processes and the importance of various core properties on the dynamo. In this thesis, I use numerical dynamo models in Earth-like geometry in order to understand the influence of inner core electrical conductivity and the choice of thermal and velocity boundary conditions on the resulting magnetic field. I demonstrate how an electrically conducting inner core can reduce the frequency of reversals and produce axial-dipolar dominated fields in our models. I also demonstrate that a strong planetary magnetic field intensity does not imply that the dynamo operates in the strong field regime as is usually presumed. Through a scaling law analysis, I find that irrespective of the choice of thermal or velocity boundary conditions, the available power determines the magnetic and velocity field characteristics like the field strength, polarity and morphology. Also, whether a dynamo model is in a dipolar, transitional or multipolar regime is dependent on the force balance in the model. I demonstrate that the Lorentz force is balanced by the Coriolis force in the dipolar dynamo regime models resulting in magnetostrophically balanced dynamos whereas the Lorentz force is balanced by the Inertial force (and not the Coriolis force) in the multipolar dynamo regime models resulting in a non-magnetostrophically balanced dynamo. The generation mechanism differs between the regimes and depends on the velocity boundary conditions. The zonal flows of the stress-free models are stronger than in the no-slip models, and bistability is more prominent when stress-free boundary conditions are used. A single scaling law may be feasible for all the models, but there does appear to be some variation for models with different thermal and velocity boundary conditions. The results presented in this thesis are not only applicable to the geodynamo, but will also aid in understanding the dynamos of other planets and exoplanets.

The Earth's magnetic field is generated in its fluid outer core through dynamo action. In this process, convection and differential rotation of an electrically conducting fluid maintain the magnetic field against its ohmic decay. Using numerical models, we can investigate planetary dynamo processes and the importance of various core properties on the dynamo. In this thesis, I use numerical dynamo models in Earth-like geometry in order to understand the influence of inner core electrical conductivity and the choice of thermal and velocity boundary conditions on the resulting magnetic field. I demonstrate how an electrically conducting inner core can reduce the frequency of reversals and produce axial-dipolar dominated fields in our models. I also demonstrate that a strong planetary magnetic field intensity does not imply that the dynamo operates in the strong field regime as is usually presumed. Through a scaling law analysis, I find that irrespective of the choice of thermal or velocity boundary conditions, the available power determines the magnetic and velocity field characteristics like the field strength, polarity and morphology. Also, whether a dynamo model is in a dipolar, transitional or multipolar regime is dependent on the force balance in the model. I demonstrate that the Lorentz force is balanced by the Coriolis force in the dipolar dynamo regime models resulting in magnetostrophically balanced dynamos whereas the Lorentz force is balanced by the Inertial force (and not the Coriolis force) in the multipolar dynamo regime models resulting in a non-magnetostrophically balanced dynamo. The generation mechanism differs between the regimes and depends on the velocity boundary conditions. The zonal flows of the stress-free models are stronger than in the no-slip models, and bistability is more prominent when stress-free boundary conditions are used. A single scaling law may be feasible for all the models, but there does appear to be some variation for models with different thermal and velocity boundary conditions. The results presented in this thesis are not only applicable to the geodynamo, but will also aid in understanding the dynamos of other planets and exoplanets.

The significant generation of municipal solid waste (MSW) has become a controversial global issue. Pyrolysis and gasification technologies for treating rejects from solid waste disposal sites (SWDSs), for which over 50 % of MSW is attributed to combustible species, have attracted considerable attention. MSW is an alternative energy source that can partly replace fossil resources; there is an increasing awareness that global warming caused by the utilization of fossil resources is occurring. The goal of this thesis is to realize the efficient and rational utilization of MSW and decrease the harmful impact of pollutants, such as dioxin, HCl, and CO2, on the environment. To achieve this goal, some fundamental studies have been experimentally and numerically conducted to enhance the understanding of the properties of municipal solid waste thermal conversion. In this thesis, the pyrolysis behaviors of single pelletized recovered fuel were tested. A detailed comparison of the pyrolysis behaviors of typical recovered solid waste and biomass particles was conducted. A swelling phenomenon with a swelling ratio of approximately 1.6 was observed on the surface of pelletized recovered fuels. Subsequently, a particle model was constructed to describe the thermal conversion process for large recovered fuel particles that are composed of a high fraction of polyethylene (PE) and a comparable low fraction of cardboard. The results indicate that an understanding of the heat transfer mechanism in highly porous and molten structures and the selection of a heat transfer model are crucial for accurate prediction of the conversion process. MSW pyrolysis is a promising method for producing liquid products. With the exception of lignocellulosic materials, such as printing paper and cardboard, PE, polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) are the six main polymers in domestic waste in Europe. Characterization studies of the products obtained from these individual components, such as PE, PET, PVC, printing paper, and cardboard, have been conducted on a pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) system and a fixed-bed reactor. The possible pathways for the formation of the main primary/secondary products in rapid and conventional pyrolysis were also discussed. MSW steam gasification with CaO was performed in a batch-type fixed-bed gasifier to examine the effect of CaO addition on the heat transfer properties, pollutant removal, and devolatilization and char gasification behaviors in the presence of steam. A new carbon capture and recycle (CCR) system combined with an integrated municipal solid waste system was proposed. The foundation of the system is the development of a novel method to remediate CO2 using a high-temperature process of reforming CH4 and/or O2 and/or H2O without catalysts. Thermodynamic and experimental studies were performed. High temperatures significantly promoted the multi-reforming process while preventing the problem of catalyst deactivation. Potential improvements in the efficiency of the novel technology can be achieved by optimizing the reforming reactants. Landfill gas (LFG) and fuel gas from bio-waste treatment contain a considerable fraction of CH4, which may be a source of CH4 for this process. / <p>QC20141028</p>

Closed-loop ground source heat pumps (GSHPs) are used to transfer thermal energy between the subsurface and conditioned spaces for heating and cooling applications. A basic GSHP is composed of a ground heat exchanger (GHX), which is a closed loop of pipe buried in the shallow subsurface circulating a heat exchange fluid, connected to a heat pump. These systems offer an energy efficient alternative to conventional heating and cooling systems; however, installation costs are higher due to the additional cost associated with the GHX. By further developing our understanding of how these ground loops interact with the subsurface, it may possible to design them more intelligently, efficiently, and economically. To gain insight into the physical processes occurring between the GHX and the subsurface and to identify efficiencies and inefficiencies in GSHP design and operation, two main research goals were defined: comprehensive monitoring of a fully functioning GSHP and intensive simulation of these systems using computer models. A 6-ton GSHP was installed at a residence in Elora, ON. An array of 64 temperature sensors was installed on and surrounding the GHX and power consumption and temperature sensors were installed on the system inside the residence. The data collected were used to help characterize and understand the function of the system, provide motivation for further investigations, and assess the impact of the time of use billing scheme on GSHP operation costs. To simulate GSHPs, two computer models were utilized. A 3D finite element model was employed to analyse the effects of pipe configuration and pipe spacing on system performance. A unique, transient 1D finite difference heat conduction model was developed to simulate a single pipe in a U-tube shape with inter-pipe interactions and was benchmarked against a tested analytical solution. The model was used to compare quasi-steady state and transient simulation of GSHPs, identify system performance efficiencies through pump schedule optimization, and investigate the effect of pipe length on system performance. A comprehensive comparison of steady state and pulsed simulation concludes that it is possible to simulate transient operation using a steady state assumption for some cases. Optimal pipe configurations are identified for a range of soil thermal properties. Optimized pump schedules are identified and analysed for a specific heat pump and fluid circulation pump. Finally, the effect of pipe spacing and length on system performance is characterized. It was found that there are few design inefficiencies that could be easily addressed to improve general design practice.

In this thesis, the theory of three dimensional numerical modeling of transport and re-suspension of fine sediments is studied and a computer program is develped for simulation of the three dimensional suspended sediment transport. The computer program solves the three dimensional advection-diffusion equation simultaneously with a computer program prepared earlier for the simulation of three dimensional current systems. This computer program computes the velocity vectors, eddy viscosities and water surface elavations which are used as inputs by the program of fine sediment transport. The model is applied to Bay of Izmir for different wind conditions.