56 research outputs found
Accounting for seasonal land use dynamics to improve estimation of agricultural irrigation water withdrawals
No full textThe assessment of water withdrawals for irrigation is essential for managing water resources in cultivated tropical catchments. These water withdrawals vary seasonally, driven by wet and dry seasons. A land use map is one of the required inputs of hydrological models used to estimate water withdrawals in a catchment. However, land use maps provide typically static information and do not represent the hydrological seasons and related cropping seasons and practices throughout the year. Therefore, this study assesses the value of seasonal land use maps in the quantification of water withdrawals for a tropical cultivated catchment. We developed land use maps for the main seasons (long rains, dry, and short rains) for the semi-arid Kikuletwa catchment, Tanzania. Three Landsat 8 images from 2016 were used to develop seasonal land use land cover (LULC) maps: March (long rains), August (dry season), and October (short rains). Quantitative and qualitative observation data on cropping systems (reference points and questionnaires/surveys) were collected and used for the supervised classification algorithm. Land use classifications were done using 20 land use and land cover classes for the wet season image and 19 classes for the dry and short rain season images. Water withdrawals for irrigated agriculture were calculated using (1) the static land use map or (2) the three seasonal land use maps. Clear differences in land use can be seen between the dry and the other seasons and between rain-fed and irrigated areas. A difference in water withdrawals was observed when seasonal and static land use maps were used. The highest differences were obtained for irrigated mixed crops, with an estimation of 572 million m3/year when seasonal dynamic maps were used and only 90 million m3/year when a static map was used. This study concludes that detailed seasonal land use maps are essential for quantifying annual irrigation water use of catchment areas with distinct dry and wet seasonal dynamics.Water Resource
Efficient and Robust Sensitivity Analysis of Complex Environmental Models: An Application for Water Productivity simulations using SWAT Model
No full textComplex agro-environmental models have a large number of parameters which are problematic during calibration. A sensitivity analysis can help identify the most sensitive parameters which should be included in the calibration process. Depending on the number of parameters being analysed and the method used, the required number of simulations varies from moderate to very large. Consequently, the number of simulations, number of years run and size of the model affect the computation power and thus, computer time required. This often limits the number of parameters and/or number of simulations, hence the robustness of the analysis. A possible solution is to conduct an initial screening of parameters using a method that requires fewer simulations and therefore can include more parameters. Subsequently, a more robust method can be performed on the obtained fewer sensitive parameters using substantially more simulation runs. Additionally, cloud computing and parallelisation can be used to reduce the computation time taken. SWAT, a complex hydrological model, has a large number of parameters that influence Water Productivity (WP) estimations, defined as the ratio of production (calculated as biomass increment or agricultural crop yield) over water consumption (calculated as evapotranspiration). To aid the calibration process, a sensitivity analyses for WP variables at the basin scale was conducted investigating the possible benefits of using: a two-step method with an initial screening (LH-OAT) prior to running a more advanced quantitative method (SOBOL); parallelisation and cloud computing. Initial results indicate substantial time benefits using the two-step method including parallelisation and cloud computing
Fire performance of concrete flat slabs
No full text© 2020 Pasindu Laknath Weerasinghe Thalpe GurugeConcrete flat slabs are widely used, especially in multi-storey buildings, because of their resource efficiency and fast construction. The requirements for fire safety critically affect the overall design of these slabs. Fire design guidelines which are based on research carried out a few decades ago hinder the effective use of concrete flat slabs as they impose strict thickness and cover requirements. Since then, material properties of concrete have significantly changed, and construction methods have evolved considerably. Therefore, new research is needed to assess the fire performance of concrete flat slabs and provide a research base to improve the current fire safety design guidelines for concrete flat slabs.
Among the limited number of fire tests performed on concrete flat slabs, most of them were simply supported isolated specimens which did not take into account the continuity of the slab. Therefore, the author conducted a large-scale fire test on a laterally restrained flat slab specimen simulating the effect of adjacent slab panels in case of a fire. Recent studies emphasise the importance of capturing the behaviour during the cooling phase as there is a risk of failure also during that phase. Hence, the experiment was extended to measure the thermal and structural response during the cooling phase. Results indicate that the fire resistance level (FRL) of the restrained flat slab has been improved compared to the FRLs predicted by the design standards. The use of restrained support conditions which allows the development of membrane actions could be the reason for improved FRL.
Although fire tests provide vital information on the behaviour of flat slabs in fire, they are very expensive and time-consuming. As an alternative, numerical methods can be utilized to capture the effects of elevated temperatures on concrete flat slabs. Building upon the existing material models for concrete and steel at elevated temperatures, the author introduced the use of explicit coupled-temperature analysis technique in finite element software ABAQUS to determine the thermal and structural response of concrete flat slabs in fire. The models also account for the transient thermal creep of concrete when heated and change of material properties during the cooling phase. The developed models were validated with the experimental results from the fire test carried out by the author, along with two more independent fire tests.
A validated numerical modelling technique was then employed in a parametric study to evaluate the influence of the thickness, the span between columns and the reinforcement arrangement on the FRL of concrete flat slabs. The aim of the study was to further understand the new design rules imposed by the latest Australian concrete design code. Outcomes of the analysis further validate some amendments incorporated in the design code while suggesting improvements to the critical distance rule.
The current construction industry prefers performance-based fire design over prescription-based fire design as it yields more optimized solutions on a case by case basis. In order to apply such methods to concrete flat slab fire design, a case study was conducted to model an actual fire scenario within a compartment in a multi-storey building and its effects on the flat slab. Fire Dynamics Simulator (FDS), a computational fluid dynamics based fire simulation software was implemented to capture the growth and decay of a compartment fire incorporating the combustible material characteristics of the furniture inside. Different fire scenarios were simulated, taking into account the different ventilation conditions. Critical temperature fields generated from the fire simulation were then applied to a FE model to assess the structural response. The predicted structural response for the actual fire scenario is significantly different from the response when the flat slab was subjected to standard design fire. This observation further highlights the importance of performance-based fire design approach, which takes building-specific parameters into account rather than generalized fire curves
Improving Citation Network Scoring by Incorporating Author and Program Committee Reputation
No full textPublication venues play an important role in the
scholarly communication process. The number of publication
venues has been increasing yearly, making it difficult for
researchers to determine the most suitable venue for their
publication. Most existing methods use citation count as the metric
to measure the reputation of publication venues. However, this
does not take into account the quality of citations. Therefore, it is
vital to have a publication venue quality estimation mechanism.
The ultimate goal of this research project is to develop a novel
approach for ranking publication venues by considering
publication history. The main aim of this research work is to
propose a mechanism to identify the key Computer Science
journals and conferences from various fields of research. Our
approach is completely based on the citation network represented
by publications. A modified version of the PageRank algorithm is
used to compute the ranking scores for each publication. In our
publication ranking method, there are many aspects that
contribute to the importance of a publication, including the
number of citations, the rating of the citing publications, the time
metric and the authors’ reputation. Known publication venue
scores have been formulated by using the scores of the
publications. New publication venue ranking is taken care by the
scores of Program Committee members which derive from their
ranking scores as authors. Experimental results show that our
publication ranking method reduces the bias against more recent
publications, while also providing a more accurate way to
determine publication quality
Improving citation network scoring by incorporating author and program committee reputation
No full textWetSpa-Urban: An Adapted Version of WetSpa-Python, A Suitable Tool for Detailed Runoff Calculation in Urban Areas
No full textA tool called WetSpa-Urban was developed to respond to the need for precise runoff estimations in an increasingly urbanized world. WetSpa-Urban links the catchment model WetSpa-Python to the urban drainage model Storm Water Management Model (SWMM). WetSpa-Python is an open-source, fully distributed, process-based model that accurately represents surface hydrological processes but does not simulate hydraulic structures. SWMM is a well-known open-source hydrodynamic tool that calculates pipe flow processes in an accurate manner while runoff is calculated conceptually. Merging these tools along with certain modifications, such as improving the efficiency of surface runoff calculation and simulating flow at the sub-catchment level, makes WetSpa-Urban suitable for event-based and continuous rainfall–runoff modeling for urban areas. WetSpa-Urban was applied to the Watermaelbeek catchment in Brussels, Belgium, which recently experienced rapid urbanization. The model efficiency was evaluated using different statistical methods, such as Nash–Sutcliffe efficiency and model bias. In addition, a statistical investigation, independent of time, was performed by applying the box-cox transformation to the observed and simulated values of the flow peaks. By speeding up the simulation of the hydrological processes, the performance of the surface runoff calculation increased by almost 130%. The evaluation of the simulated 10 minute flow versus the observed flow at the outlet of the catchment for 2015 reached a Nash–Sutcliffe efficiency of 0.86 and a bias equal to 0.06
Chromium oxide loaded silica aerogels: novel visible light photocatalytic materials for environmental remediation
No full textVarious photocatalytic systems have been reported for degradation of harmful air pollutants. Most of the reported catalysts are based on well-known semiconducting material, Titanium Dioxide (TiO[subscript 2]), while some are based on other materials such as Silicon Dioxide (SiO[subscript 2]), various Zeolites. However, titania based systems are very popular in this regard and the most of the photocatalytic processes that involve titania are considered non-localized. Thus, to study the photocatalytic ability of a localized system, novel aerogel based samples were studied using silica and chromium and tested for photocatalytic activities. The new photocatalytic systems were prepared to obtain aerogel silica as the matrix material by cohydrolyzing silica precursor with chromium(III) ions to obtain chromium loaded silica materials. Later, these prepared samples were compared to chromium loaded titania and mixed silica-titania systems. All the prepared systems have high surface areas compared to the systems that have been reported in literature. Samples were characterized by X-ray diffraction, Diffusive reflectance UV spectroscopy, and BET surface analysis methods. The kinetics of photocatalytic degradation of a model pollutant, acetaldehyde, was performed using a Shimadzu GCMS-QP 5000 instrument and a glass reactor with a quartz window. Change in photocatalytic activity was found with various molar ratios of SiO[subscript 2] to TiO[subscript 2]. From all the systems, chromium loaded pure SiO[subscript 2] showed the highest activity towards acetaldehyde degradation compared to mixed systems and TiO[subscript 2] based systems. The interesting photocatalytic activity of silica based materials occurs due to the efficient insertion of chromium ions into silica matrix to generate reactive sites. The photo excitation is believed to occur at molecular orbital level at localized chromium sites
The Economics of Agricultural Water Productivity in the Blue Nile
No full textAgricultural Water Productivity (AWP) is often simplified as the ‘crop per drop’, described as the output in terms of yield or biomass per unit of water input. This purely physical measure of Water Productivity (WP) using only a single factor input (water) does not consider: (1) the level of other inputs used in conjunction with water, (2) the opportunity cost of water as an input, (3) the value of the output and (4) the costs of production for different crops. This study presents a justification and methodology for incorporating these factors into WP indicators. The application of these extensions to WP in a data poor region is demonstrated for the Blue Nile using the new Water Accounting Plus (WA+) framework. Particular attention is made to the use of globally applicable, remotely sensed data sources for estimation of physical and socioeconomic variables. An advantage of using the WA+ framework in calculating WP is that it provides basin water information partitioned into ‘blue’ and ‘green’ water, land use categories, consumptive and non-consumptive and beneficial and non-beneficial water as well as information on return flows. Extending single factor measures of WP should result in more theoretically justified yet practical WP results, making this a more comparable measure from basin to basin and sub-basin to sub-basin
Particle Swarm Optimization Simulation via Optimal Halton Sequences
No full textAbstractInspired by the social behavior of the bird flocking or fish schooling, the particle swarm optimization (PSO) is a population based stochastic optimization method developed by Eberhart and Kennedy in 1995. It has been used across a wide range of applications. Faure, Halton and Vander Corput sequences have been used for initializing the swarm in PSO. Quasirandom(or low-discrepancy) sequences such as Faure, Halton, Vander Corput etc are deterministic and suffers from correlations between radical inverse functions with different bases used for different dimensions. In this paper, we investigate the effect of initializing the swarm with scrambled optimal Halton sequence, which is a randomized quasirandom sequence. This ensures that we still have the uniformity properties of quasirandom sequences while preserving the stochastic behavior for particles in the swarm. Numerical experiments are conducted with benchmark objective functions with high dimensions to verify the convergence and effectiveness of the proposed initialization of PSO
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