Infrastructure Engineering - Research Publications
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ItemToward capturing hydrologically significant connectivity in spatial patterns(AMER GEOPHYSICAL UNION, 2001-01)Many spatial fields exhibit connectivity features that have an important influence on hydrologic behavior. Examples include high‐conductivity preferred flow paths in aquifers and saturated source areas in drainage lines. Connected features can be considered as arbitrarily shaped bands or pathways of connected pixels having similar (e.g., high) values. Connectivity is a property that is not captured by standard geostatistical approaches, which assume that spatial variation occurs in the most random possible way that is consistent with the spatial correlation, nor is it captured by indicator geostatistics. An alternative approach is to use connectivity functions. In this paper we apply connectivity functions to 13 observed soil moisture patterns from the Tarrawarra catchment and two synthetic aquifer conductivity patterns. It is shown that the connectivity functions are able to distinguish between connected and disconnected patterns. The importance of the connectivity in determining hydrologic behavior is explored using rainfall‐runoff simulations and groundwater transport simulations. We propose the integral connectivity scale as a measure of the presence of hydrologic connectivity. Links between the connectivity functions and integral connectivity scale and simulated hydrologic behavior are demonstrated and explained from a hydrologic process perspective. Connectivity functions and the integral connectivity scale provide promising means for characterizing features that exist in observed spatial fields and that have an important influence on hydrologic behavior. Previously, this has not been possible within a statistical framework.
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ItemOn the computation of the quasi-dynamic wetness index with multiple-flow-direction algorithms(AMER GEOPHYSICAL UNION, 2003-05-06)The quasi‐dynamic wetness index, in its original development, was computed by calculating the travel time along all the possible upslope flow paths on a contour‐based terrain network. In more recent applications the same approach has been extended to gridded digital elevation models with single‐flow‐direction algorithms. Multiple‐flow‐direction algorithms, although more effective in representing flow paths, have not been used because they are not practicable with the established methodology. We propose an alternative method for computing the quasi‐dynamic wetness index based on the numerical integration of the linear‐kinematic wave equation. This method can be applied to any of the terrain‐based flow‐direction algorithms currently published. The method is robust and efficient.
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ItemCharacteristic space scales and timescales in hydrology -: art. no. 1304(AMER GEOPHYSICAL UNION, 2003-10-30)We analyzed spatial and temporal variograms of precipitation, runoff, and groundwater levels in Austria to examine whether characteristic scales exist and, if so, how big they are. In time, precipitation and runoff are stationary with characteristic scales on the order of a day and a month, respectively, while groundwater levels are nonstationary. In space, precipitation is almost fractal, so no characteristic scales exist. Runoff is nonstationary but not a fractal as it exhibits a break in the variograms. An analysis of the variograms of catchment precipitation indicates that this break is due to aggregation effects imposed by the catchment area. A spatial variogram of hypothetical point runoff back calculated from runoff variograms of three catchment size classes using aggregation statistics (regularization) is almost stationary and exhibits shorter characteristic space scales than catchment runoff. Groundwater levels are nonstationary in space, exhibiting shorter‐scale variability than precipitation and runoff, but are also not fractal as there is a break in the variogram. We suggest that the decrease of spatial characteristic scales from catchment precipitation to runoff and to groundwater is the result of a superposition of small‐scale variability of catchment and aquifer properties on the rainfall forcing. For comparison, TDR soil moisture data from a comprehensive Australian data set were examined. These data suggest that in time, soil moisture is close to stationary with characteristic scales of the order of 2 weeks while in space soil moisture is nonstationary and close to fractal over the extent sampled. Space‐time traces of characteristic scales fit well into a conceptual diagram of Blöschl and Sivapalan [1995]. The scaling exponents z in T ∼ Lz (where T is time and L is space) are of the order of 0.5 for precipitation, 0.8 for runoff from small catchments, 1.2 for runoff from large catchments, 0.8 for groundwater levels, and 0.5 for soil moisture.
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ItemModal analysis of steel-framed residential structures for application to seismic design(SAGE PUBLICATIONS INC, 2001-01)There has been a significant worldwide increase in the use of cold-formed steel in low-rise resi dential structures as an alternative to timber. A major research project to assess the performance under lateral loading of cold-formed steel frames commenced more than 7 years ago at The University of Melbourne, Australia, in collaboration with industry and other research organizations. This paper reports key findings from an extensive experimental program. It details a particular aspect of the program that uses nondestruc tive dynamic testing to identify the basic dynamic properties of such structures. Laboratory tests, employing a shaking table, have been conducted on unclad wall panels and a model test house to study the influence of different framing connection types and to assess the influence of nonstructural components, namely, plas terboard interior lining and brick-veneer exterior cladding. The findings from these tests were verified and further extended by testing a full-scale prototype house at various stages of construction. This paper presents information concerning typical natural frequencies and mode shapes for such structures. It also details the contribution of nonstructural components to the lateral stiffness, which was found to be significant. The re sults have important implications for seismic design and performance of such structures, even in regions of low to moderate seismicity.
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ItemAn ice thermal storage computer model(Elsevier, 2001-12-01)In hot humid countries such as Thailand, air conditioning plant is installed in most commercial and industrial buildings. A conventional air conditioning system, which is normally operated when cooling is required, is the most favored option. Ice thermal storage on a large scale, used to provide a cool reservoir for use in peak periods, is however an attractive financial option for large buildings to supply coolness. There are two means of operating ice thermal storage systems, namely full storage and partial storage. In this paper, a computer model has been developed in order to compare energy use in conventional air cooling systems and ice thermal storage systems. Under Thailand electricity tariff rates, the results from the simulations show that the full ice thermal storage can save up to 55% of the electricity cost required for cooling per month when compared with the conventional system. It is also found that using full storage option can reduce the total energy consumption by 5% for the selected building.
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ItemNo Preview AvailableThe potential of wood gasifiers for tea drying in Sri Lanka(RERIC, 2001-12-01)One of the reasons for the higher production cost of tea in Sri Lanka compared to other countries is the high specific energy consumption. In Sri Lanka, 38% more energy is used to produce one kilogram of tea compared to India, largely because of the use of inefficient wood-fired air heaters. Gasifiers have been proposed as an alternative method of providing the hot air used for drying. A locally built gasifier has been tested and found to have a conversation efficiency of 80%, which is comparable to that of an imported unit. The heat loss of local gasifier was found to be between 11.5-14% of the input energy. An analysis shows that the life cycle cost of energy produced by the gasifier is US$ 3.00 per GJ, which is 8% less than the cost of energy from a conventional wood heater. Wood consumption is also reduced by 12%. Some transfer of gasifier technology to the crematoria industry in Sri Lanka has already occurred and this enhances the prospect of the successful introduction of this technology to the tea industry.
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ItemBenefits of cool thermal storage in Thailand(RERIC, 2001-06-01)The use of thermal storage on a large to provide a cool reservoir for use in peak periods is an attractive financial option for large hotels, hospitals or office blocks. This enables the refrigeration plant to operate more effectively and to be completely or partially shut down during peak periods when the demand can be met in full or in part from the cool store. In this paper an overview is given of the power generation capacity and costing structure in Thailand and a typical load profile is presented to illustrate the advantages to be gained by shifting plant operation to off-peak periods. Specific load calculations have been utilized to demonstrate the cost savings possible by incorporation of such a cool thermal storage system into a traditional refrigeration and air conditioning plant for a major hotel complex.
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ItemComputer simulation of a downdraft wood gasifier for tea drying(Elsevier, 2003-10-01)A gasifier has been fabricated in Sri Lanka for the tea industry, but there is a lack of knowledge of the effect of certain key operating parameters and design features on its performance. Experimental testing of the design under various conditions has produced data that has then been used to calibrate a computer program, developed to investigate the impact of those parameters and features on conversion efficiency. The program consists of two sub-models of the pyrolysis and gasification zones, respectively. The pyrolysis sub-model has been used to determine the maximum temperature and the composition of the gas entering the gasification zone. The gasification zone sub-model has been calibrated using data gathered from the experiments. It was found that a wood chip size of 3–5 cm with a moisture content below 15% (d.b.) should be used in this gasifier. Feed material with a fixed carbon content of higher than 30% and heat losses of more than 15% should be avoided. For the above parameters, the gasification zone should be 33 cm long to achieve an acceptable conversion efficiency.
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ItemElectrical and engine driven heat pumps for effective utilisation of renew-able energy resources(PERGAMON-ELSEVIER SCIENCE LTD, 2003-07)
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ItemA review of a two-phase population study of multiple chemical sensitives(National Institute of Environmental Health Sciences, 2003)In this review we summarize the findings of a two-phase study of the prevalence, symptomatology, and etiology of multiple chemical sensitivities (MCS). We also explore possible triggers, the potential linkage between MCS and other disorders, and the lifestyle alterations produced by MCS. The first phase of the study consisted of a random sampling of 1,582 individuals from the Atlanta, Georgia, metropolitan area to determine the reported prevalence of a hypersensitivity to common chemicals. In this phase, 12.6% of the sample reported a hypersensitivity. Further questioning of individuals with a hypersensitivity indicated that 13.5% (1.8% of the entire sample) reported losing their jobs because of their hypersensitivity. The second phase was a follow-up questioning of the respondents who initially reported hypersensitivity. In this phase, we found that individuals with hypersensitivity experience a variety of symptoms and triggers. A significant percentage (27.5%) reported that their hypersensitivity was initiated by an exposure to pesticides, whereas an equal percentage (27.5%) attributed it to solvents. Only 1.4% had a history of prior emotional problems, but 37.7% developed these problems after the physical symptoms emerged. This suggests that MCS has a physiologic and not a psychologic etiology.