Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / The successful operation of a pulsed monostatic borehole radar system requires that cur- rent on the antenna due to transmitter pulses subsides quickly. Deterioration of the radar antenna feed-point current settling times when deployed in water-¯lled boreholes showed that the radar system's performance is highly environmentally sensitive. Electromagnetic models are used to investigate this e®ect, since measuring the feed-point and radiative characteristics of an insulated antenna deployed in a borehole is practically impossible at present. A transmission line model for insulated antennas is utilized to model the borehole radar antenna in electrically dense media. Predicted input impedance values however do not correspond well to those from numerical ¯eld simulation software and the model is shown to be inadequate for modelling insulated antennas in environments of low conductivity. Radiated ¯eld results are however found to be accurate. A study of the feed-point and radiative characteristics of the borehole radar antenna in a range of di®erent borehole environment is performed using electromagnetic ¯eld simulation software. Results con¯rm that the borehole radar antenna has longer feed- point current settling times and degraded radiated pulse waveforms when deployed in water-¯lled boreholes. Simple lumped element networks with driving-port impedances approximately equal to antenna input impedances are synthesized from simulated input impedance results for a range of borehole environments. This allows diagnostics on the radar system to be performed in the laboratory, with the antenna load appearing as if the system were deployed in a borehole. The use of an antenna with distributed resistive and capacitive loading is proposed as a modi¯cation that would result in improved feed-point characteristics in water-¯lled boreholes. Results from simulations and experiments are presented that con¯rm that the new antenna design substantially reduces feed-point current settling times after the transmitter ¯res.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2000. / South Africa has an immensely rich reserve of minerals which still has to be exploited. The problem with these reserves is that they exist in reefs where the mining environment is extremely hazardous, and where mining is very expensive. These are only two of the reasons why borehole radar has recently become a very important field of research in the South African mining industry. These radars have to operate in rock, which has a number of electromagnetically problematic characteristics, which greatly complicate modelling and design of suitable radars. The goal of this project is to demonstrate how the Finite Difference Time Domain (FDTD) method may be used to electromagnetically model and simulate borehole radars and subterranean environments.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Accurate and detailed costs for individual municipal waste collection, treatment and landfill methods are not readily available. Neither is there a reliable means of comparing between two or more alternative options. However, before improvements to the management and planning of solid waste disposal can be achieved both are required. Currently, comparisons and planning in this field are highly ambiguous, often misleading, with individual operators using widely different accounting conventions and operating standards. The purpose of this work has been to establish accurate comparisons. Initially, detailed financial and technical information \'las collected from numerous operators, and then a standard basis for comparison (the "base case") was derived onto which the costs obtained were adjusted. Cost functions were also generated to interpret component costs fora range of sizes of operation. The economics of five collection methods, four transfer methods, seven bulk transport vehicle types and several landfill disposal variations are considered. For each a detailed appraisal of the component capital and operating costs has been made so as to identify the largest expenditures. The effect of uncertainty on cost estimates was also emphasised and explicitly considered by sensitivity analyses on selected economic and physical parameters. These analyses have indicated those component costs which exert the most significant influence on the total costs, and as such should be the most closely monitored by a waste manager. One notable example is the sensitivity of total landfill costs to leachate treatment. Six case studies are also presented. These are designed to demonstrate the versatility of the cost models derived and also the method developed for unambiguous economic comparison. This research provides a large financial data base on all of the collection, transfer and landfill methods in common use in Britain. Use of this information and the principles for comparison put forward would enable waste managers to incorporate sound financial appraisals into both their operational and forward planning decisions. This should subsequently improve not only the quality of their decisions but ultimately the standard of service they offer too.

In 2012, the fatal shooting of Trayvon Martin brought national attention to Florida’s Stand Your Ground (SYG) law. As of 2012, more than 20 states have enacted SYG laws. Previous studies suggest that these laws increase homicide, particularly justifiable homicide. However, these studies ignore race and/or gender. This study seeks to fill this gap in the literature by examining the effect of SYG laws on the number of homicide and justifiable homicide victims and offenders of a given race or gender. Using data from the Federal Bureau of Investigation’s Supplementary Homicide Reports between 2000 and 2012, we create a generalized least squares model with random and fixed effects and controls for time-varying state effects and year fixed effects to empirically examine this impact. We find that while SYG laws have no effect on the number of homicide victims or offenders of any race or gender, they significantly increase the number of black and male justifiable homicide victims by 32 percent and 26 percent respectively and the number of white and female justifiable homicide offenders by 34 and 25 percent respectively. These findings suggest that, in terms of justifiable homicide, SYG laws differentially affect racial and gender groups.

Seismic slope stability is often evaluated via permanent displacement analyses, which quantify the cumulative, downslope displacement of a sliding mass subjected to earthquake loading. Seismic sliding block displacements provide a useful index as to the seismic performance of a slope. Seismic sliding block displacements can be computed for a suite of acceleration-time histories selected to fit a design event. This thesis explores the effect of ground motion selection on computed seismic sliding block displacements through two approaches. First, rigid sliding block displacements were computed for ground motion suites developed to fit uniform hazard spectra (UHS), conditional mean spectra (CMS), and conditional probability distributions for peak ground velocity (PGV) and Arias Intensity (Ia). Evaluation of the suites in terms of their PGV and Ia distributions provided useful insight into the relative displacements computed for the suites. The PGV and Ia distributions of the suite selected to fit the UHS exceed the theoretical distributions of these ground motion parameters. In fact, the scaled Ia values of motions in the UHS suite are greater than the largest Ia values in the Next Generation Attenuation (NGA) ground motion database. As such, the displacements computed for the UHS suite exceed the displacements computed for any other suite. If only two ground motion parameters are to be considered in ground motion selection we recommend those parameters be PGA and PGV. However, it is important to consider PGA, PGV, and Ia when developing ground motion suites for permanent displacement analyses. Next, the use of simulated ground motions for permanent displacement analyses was addressed by comparing displacements computed for simulated ground motions to displacements computed for the corresponding recorded ground motion. Simulated ground motions generated via four seismological models were considered: the deterministic Composite Source Model (CSM), the stochastic model EXSIM, the deterministic-stochastic hybrid model by Graves and Pitarka (GP), and the deterministic-stochastic hybrid model developed at San Deigo State University (SDSU). The displacements computed for the SDSU simulations were the most similar to those computed using the recorded motions, with the average displacement of the SDSU simulations exceeding that of the corresponding recorded ground motion by about 6%. Additionally, the displacements from the SDSU simulations provided the smallest variability about the displacements computed for the recorded motions. / text

Ground source heat pumps (GSHPs) offer an efficient method for cooling and heating buildings, reducing energy usage and operating cost. In hot, arid regions such as Texas and the southwest United States, building load imbalance towards cooling causes design and performance challenges to GSHP systems in residential and commercial building applications. An integrated building load and GSHP model is developed in this thesis to test approaches to reduce GSHP cost, to properly size ground heat exchanger (GHEX) installations and to offer methods to improve GSHP performance in commercial buildings. The integrated model is comprised of a three-story office building, heat pumps, air handling system and a GHEX. These component models were integrated in the Matlab® Simulink® modeling environment, which allows for easy model modification and expansion. The building-load model was developed in HAMBASE, which simulates the thermal and hygric response of each zone in the building to external weather and internal loads. The building-load model was validated using the ASHRAE 140-2007 Standard Method of Test and with results from EnergyPlus. The heat pump model was developed as a performance map, based on data commonly provided by heat pump manufacturers. This approach allows for easy expansion of the number and type of heat pump models supported. The GHEX model was developed at Oklahoma State University and is based on Eskilson’s g-function model of vertical borehole operation. The GHEX model accurately represents the interaction between boreholes and the ground temperature response over short and long time-intervals. The GHEX model uses GLHEPRO files for parameter inputs. Long time-interval simulations of the integrated model are provided to assess the sensitivity of the GSHP system to various model parameters. These studies show that: small changes in the total GHEX length reduce system cost with minimal impact on performance; increased borehole spacing improves system performance with no additional cost; supplemental heat rejection reduces installation costs and improves system performance; industry-recommended design cutoff temperatures properly size the GHEX system; and, while cooling is the greatest contributor to operating cost in the southwest and southcentral United States, heating is the limiting design case for GHEX sizing. / text

<p>Polythermal glaciers, i.e. glaciers with a combination of ice at and below the freezing point, are widespread in arctic and subarctic environments. The polythermal structure has major implications for glacier hydrology, ice flow and glacial erosion. However, the interplay of factors governing its spatial and temporal variations such as net mass balance, ice advection and water content in the ice is poorly investigated and as yet not fully understood. This study deals with a thorough investigation of the polythermal regime on Storglaciären, northern Sweden, a small valley glacier with a cold surface layer in the ablation area. Extensive field work was performed including mapping of the cold surface layer using ground-penetrating radar, ice temperature measurements, mass balance and ice velocity measurements. Analyses of these data combined with numerical modelling were used specifically to investigate the spatial and temporal variability of the cold surface layer, the spatial distribution of the water content just below the cold surface layer transition, the effect of radar frequency on the detection of the surface layer, and the sensitivity of the cold surface layer to changes in forcing.</p><p>A comparison between direct temperature measurements in boreholes and ground-penetrating surveys shows that the radar-inferred cold-temperate transition depth is within ±1 m from the melting point of ice at frequencies above ~300 MHz. At frequencies below ~155 MHz, the accuracy degrades because of reduced scattering efficiency that occurs when the scatterers become much smaller compared to the wavelength. The mapped spatial pattern of the englacial cold-temperate transition boundary is complex. This pattern reflects the observed spatial variation in net loss of ice at the surface by ablation and vertical advection of ice, which is suggested to provide the predominant forcing of the cold surface layer thickness pattern. This is further supported by thermomechanical modeling of the cold surface layer, which indicates high sensitivity of the cold surface layer thickness to changes in vertical advection rates.</p><p>The water content is the least investigated quantity that is relevant for the thermal regime of glaciers, but also the most difficult to assess. Spatial variability of absolute water content in the temperate ice immediately below the cold surface layer on Storglaciären was determined by combining relative estimates of water content from ground-penetrating radar data with absolute determination from temperature measurements and the thermal boundary condition at the freezing front. These measurements indicate large-scale spatial variability in the water content, which seems to arise from variations in entrapment of water at the firn-ice transition. However, this variability cannot alone explain the spatial pattern in the thermal regime on Storglaciären.</p><p>Repeated surveys of the cold surface layer show a 22% average thinning of the cold surface layer on Storglaciären between 1989 and 2001. Transient thermomechanical modeling results suggest that the cold surface layer adapts to new equilibrium conditions in only a few decades after a perturbation in the forcing is introduced. An increased winter air temperature since mid-1980s seems to be the cause of the observed thinning of the cold surface layer. Over the last decades, mass balance measurements indicate that the glacier has been close to a steady state. The quasi-steady state situation is also reflected in the vertical advection, which shows no significant changes during the last decades. Increased winter temperatures at the ice surface would result in a slow-down of the formation of cold ice at the base of the cold surface layer and lead to a larger imbalance between net loss of ice at the surface and freezing of temperate ice at the cold-temperate transition.</p>

Mr Wayne Tobeck, Director of Southrim Group (SRG), sponsored this 2013 MEM Project titled; A Technical and Economic Feasibility Study for the Integration of GSHP Technology in the Christchurch Rebuild. Following the recent Christchurch earthquakes, a significant amount of land has become too unstable to support traditional building foundations. This creates an opportunity to implement new and unique foundation designs previously unconsidered due to high costs compared to traditional methods. One such design proposes that an Injection Micro-Piling technique could be used. This can also be coupled with HVAC technology to create a Ground Source Heat Pump (GSHP) arrangement in both new buildings and as retrofits for building requiring foundation repair. The purpose of this study was to complete a feasibility study on the merits of SRG pursuing this proposed product. A significant market for such a product was found to exist, while the product was also found to be technically and legally feasible. However, the proposed product was found to not be economically feasible with respect to Air Source Heat Pumps due to the significantly higher capital and installation costs required. Further analysis suggests GSHPs may become more economically attractive in operating temperatures lower than -9oC, though the existence of markets with this climate in NZ has not been studied. It is therefore suggested that SRG do not proceed with plans to develop a GSHP coupled foundation solution for the Christchurch rebuild.

This research employs a deterministic seismic risk assessment methodology to assess the potential damage and loss at meshblock level in the Christchurch CBD and Mount Pleasant primarily due to building damage caused by earthquake ground shaking. Expected losses in terms of dollar value and casualties are calculated for two earthquake scenarios. Findings are based on: (1) data describing the earthquake ground shaking and microzonation effects; (2) an inventory of buildings by value, floor area, replacement value, occupancy and age; (3) damage ratios defining the performance of buildings as a function of earthquake intensity; (4) daytime and night-time population distribution data and (5) casualty functions defining casualty risk as a function of building damage. A GIS serves as a platform for collecting, storing and analyzing the original and the derived data. It also allows for easy display of input and output data, providing a critical functionality for communication of outcomes. The results of this study suggest that economic losses due to building damage in the Christchurch CBD and Mount Pleasant will possibly be in the order of $5.6 and $35.3 million in a magnitude 8.0 Alpine fault earthquake and a magnitude 7.0 Ashley fault earthquake respectively. Damage to non-residential buildings constitutes the vast majority of the economic loss. Casualty numbers are expected to be between 0 and 10.