Engineering & Technology

Permanent URI for this community

https://repository.must.ac.tz/handle/123456789/54

Browse

Now showing 1 - 20 of 56

Developing a Surface Water - Groundwater Interaction Model for Letaba River System in South Africa
(KATAMBARA, 2006) Katambara, Z.; Ndiritua, J.G.
There is a constant increase in water demand and a pressing need to conserve the environment in the Letaba River system. This is leading to a situation where the demand for water may have outstripped the capacity of the existing resources to sustainably meet them. In the past dams were constructed and boreholes drilled as a strategy of reconciling demand and supply and this is evidenced by the numerous dams and boreholes in the Letaba River system. There are five major dams; three of which have a capacity exceeding 60 million cubic meters and also more than 3000 boreholes in the river basin. Currently, all the dams are stressed and the releases from Tzaneen Dam, intended to meet the water requirements of downstream users including Kruger National Park fail to meet these requirements substantially. Although these demands are high and probably exceed the system’s capacity, it is likely that the reliability of supply can be improved significantly if the surface water - groundwater (sw/gw) interactions within the basin are modelled comprehensively and then incorporated into system operation. This paper reports on an ongoing development of a sw/gw model of the Letaba River System. The model development intends to maximize the use of the relevant available information and data and recognizes the existence of an interaction zone which forms a major link of many of the processes that will be included in the model. It has been found that the scale of monitoring processes in the river system is inadequate and is a significant constraint to the development of the model that is expected to impact on the level of confidence in model implementation and application. Incorporation of uncertainties will therefore be an integral part of the modelling.
Developing a Surface Water - Groundwater Interaction Model for Letaba River System in South Africa.
(University of the Witwatersrand., 2006) Katambara, Z; Ndiritu, J.G.
There is a constant increase in water demand and a pressing need to conserve the environment in the Letaba River system. This is leading to a situation where the demand for water may have outstripped the capacity of the existing resources to sustainably meet them. In the past dams were constructed and boreholes drilled as a strategy of reconciling demand and supply and this is evidenced by the numerous dams and boreholes in the Letaba River system. There are five major dams; three of which have a capacity exceeding 60 million cubic meters and also more than 3000 boreholes in the river basin. Currently, all the dams are stressed and the releases from Tzaneen Dam, intended to meet the water requirements of downstream users including Kruger National Park fail to meet these requirements substantially. Although these demands are high and probably exceed the system’s capacity, it is likely that the reliability of supply can be improved significantly if the surface water - groundwater (sw/gw) interactions within the basin are modeled comprehensively and then incorporated into system operation. This paper reports on an ongoing development of a sw/gw model of the Letaba River System. The model development intends to maximize the use of the relevant available information and data and recognizes the existence of an interaction zone which forms a major link of many of the processes that will be included in the model. It has been found that the scale of monitoring processes in the river system is inadequate and is a significant constraint to the development of the model that is expected to impact on the level of confidence in model implementation and application. Incorporation of uncertainties will therefore be an integral part of the modeling.
A Fuzzy Inference System for Modelling Streamflow: Case of Letaba River, South Africa.
(Elsevier, 2008-07-10) Katambara, Zacharia; Ndiritu, John
Stream flow modeling of Letaba River in South Africa is complicated by several factors including the existence of dams and other storage structures whose releases are intermittent and based on rules of thumb depending on the irrigation demands and the need to maintain the flow required in the Kruger National park (KNP). The KNP is located about a hundred kilometers downstream of the main storage and water flows through an alluvial aquifer where complex surface–groundwater interactions occur. Farmers abstract water intermittently along the route directly from the river or indirectly from the alluvial aquifer complicating the flow patterns even more. Consequently, the stream flow series in the river shows very little similarity to what would be considered as natural. The actual abstractions are not measured and only monthly estimates of the abstractions currently exist. Like in many other basins in South Africa, stream flow, groundwater level, rainfall and evaporation data in Letaba is sparse and not very reliable. The Takagi–Sugeno fuzzy inference system using subtractive clustering, an approach which is capable of dealing with vague and inadequate information and data has therefore been used to develop a daily stream flow model for Letaba River. In order to take into account the spatial variability and to maximize the use of the available data, the model is applied in a semi-distributed manner consisting of three river reaches. The shuffled complex evolution (SCE-UA) optimizer has been used to calibrate the model. Six years of data from March 2002 to April 2008 has been used for model calibration and verification. To maximize the Nash-Sutcliffe efficiency, the minimum number of clusters required was found to be 10 for 1000 data points in calibration. An analysis of the location of the cluster centers, the coefficients relating the inputs with the simulated stream flow, and the degrees of membership indicates that no single cluster can be associated to the simulation of a specific hydrologic process or component of the stream flow hydrograph (e.g. high flows or low flows). The fuzzy model does not therefore provide any evidence that it is not a pure black box. The Nash–Sutcliffe efficiency results obtained in calibration and verification showed average values of 0.658 and 0.535 with poor values on the first river reach. Very low percent bias values averaging to _0.4% and _2.7% in calibration and verification are obtained highlighting the model’s potential for applications where mass balance considerations are most important.
An Artificial Neural Network Model of the Crocodile River System for Low Flow Periods.
(Wits, 2009-01-21) Sebusang, Nako M.
With increasing demands on limited water resources and unavailability of suitable dam sites, it is essential that available storage works be carefully planned and efficiently operated to meet the present and future water needs.This research report presents an attempt to: i) use Artificial Neural Networks (ANN) for the simulation of the Crocodile water resource system located in the Mpumalanga province of South Africa and ii) use the model to assess to what extent Kwena dam, the only major dam in the system could meet the required 0.9m3/s cross border flow to Mozambique. The modelling was confined to the low flow periods when the Kwena dam releases are significant. The form of ANN model developed in this study is the standard error backpropagation run on a daily time scale. It is comprised of 32 inputs being four irrigation abstractions at Montrose, Tenbosch, Riverside and Karino; current and average daily rainfall totals for the previous 4 days at the respective rainfall stations; average daily temperature at Karino and Nelspruit; daily releases from Kwena dam; daily streamflow from the tributaries of Kaap, Elands and Sand rivers and the previous day’s flow at Tenbosch. The single output was the current day’s flow at Tenbosch. To investigate the extent to which the 0.9m3/s flow requirement into Mozambique could be met, data from a representative dry year and four release scenarios were used. The scenarios assumed that Kwena dam was 100%, 75%, 50% and 25% full at the beginning of the year. It was found as expected that increasing Kwena releases improved the cross border flows but the improvement in providing the 0.9m3/s cross border flow was minimal. For the scenario when the dam is initially full, the requirement was met with an improvement of 11% over the observed flows.
A TIME-DEPENDENT GREEN ELEMENT FORMULATION FOR SOLUTION OF POTENTIAL FLOW PROBLEMS IN 3 DIMENSIONAL DOMAINS
(University of the Witwatersrand, Johannesburg, 2010) Nyirenda, Edwin
In this work we develop a generalised methodology for the solution of the time dependent second order parabolic differential equation of potential flow in heterogeneous media using the Green element method. Parabolic differential equations are one class of differential equations, the others being elliptic partial differential equations and hyperbolic differential equations. Since elliptic differential equations generally arise from a diffusion process that has reached equilibrium, they can also be solved using the methodology developed, and represent a simplification because of the steady state situation. Potential flow problems are of great interest in many engineering applications such as flow in aquifers, heat transfer processes, electro-magnetic field problems, etc. Traditionally, the finite difference method and the finite element method have proved to be powerful techniques to solve such potential flow problems, but each has limitations and challenges which have led to continued research in numerical methods. The finite difference method is more applicable to domains with regular boundary, and the finite element method, though extremely versatile, exhibits unacceptable inaccuracies with coarse meshes, thus requiring fine meshes with the associated high computation costs. In view of some of the limitations with these earlier methods, several numerical schemes are now being developed as viable alternatives to these conventional methods. Among such methods are the boundary element method, the finite volume method, and the analytic element method. The boundary element method has been particularly promising because of its domain-reduction feature and the second order accuracy that can generally be achieved. The domain-reduction feature of the boundary element method, though achieved for restricted class of problems, lends it to efficient grid generation algorithm, while its second-order accuracy ensures reliability and consistency of the numerical solutions.-iv _________________________________________________________________ The boundary element method in its original formulation is unable to deal with heterogeneities in the domain. For physical problems, especially in groundwater flow, heterogeneities and anisotropy are a natural and frequent occurrence, and this has fuelled research into boundary element techniques that are capable of accommodating these features. The Green element method is one technique which is based on the boundary element theory and which has been proven to be very effective in handling heterogeneities and anisotropy in 1D and 2D domains. However, development of techniques to implement the Green element method in 3D domains has remained largely unexplored. This work represents an effort in this direction. We have investigated the adoption of the general tetrahedral and hexahedra elements for use with the Green element method, and found that the large number of degrees of freedom generated precludes retention of the internal normal direction as in 1D and 2D formulations. Furthermore, some of the complicated surface and domain integrations with these elements can only be addressed with quadrature methods. The compatibility issues that arise between element faces, which present considerable challenges to multi-domain boundary element techniques, are innovatively addressed in the computer code that has been developed in this work. The Green element method is implemented for steady and time-dependent problems using regular hexahedra elements, and the results show that the performance is slightly better than the results obtained using FEMWATER. FEMWATER is an established finite element method software. No attempt is made to compare the computation efficiencies of the 3D GEM code and FEMWATER because the two codes were not developed on a common platform.
Estimation of Extreme Flows in Nkana River to Verify the Adequacy of Naming’ongo Bridge Waterway.
(ScientificResearch, 2012-12-26) Katambara, Zacharia; Msambichaka, Joseph J.; Mkisi, Joseph
The response by the government of Tanzania to food security and poverty alleviation in the Naming’ongo area in Mbozi District has been to develop Naming’ongo irrigation scheme as well as construct a bridge across River Nkana to con- nect the farms and other parts of the district to facilitate a reliable transportation of the produce to the market. The Aus- tralian Water Balance Model was calibrated by using 10 years data from a nearby sub-catchment of Mbarali. The Nam- ing’ongo Sub-catchment was delineated form a 30 m digital elevation model. The observed rainfall was obtained from Mbozi Meteorological station. The study approximated the peak flows in River Nkana for a return period of 50 years to be slight above 560 m3/s. This was considered to be adequate for the proposed structure. The study recommends that when undertaking human activities such as deforestation and cultivation an account for soil and environmental conser- vation should be considered. While it is necessary to establish a monitoring system within the catchment, the designs of future hydraulic structures should incorporate stream flow measuring facilities.
Mapping the Distribution of Digitate and Tabulate Acropora Corals in Selected Reefs of Zanzibar
(Mbeya University of Science and Technology, 2013) Mwakalapa, Eliezer. Brown
Mapping the boundaries and distribution of reef corals, especially at growth form level, is an important coastal zone management step. Digitate and tabulate Acropora are growth forms of stone corals associated with abundance of reef fishes and are important in building reef framework. In this study boundaries of coral reefs and the distribution of digitate and tabulate Acropora around Bawe and Mnemba Islets, Zanzibar Island were mapped and results compared with environmental parameters. Data were collected by manta tow technique, line intercept transect, belt intersect transect, GPS unit and an underwater camera. Geo-referenced data was processed using ArcMap 9.3 software. The border line was set where live coral cover was above 5%. At the boundaries reef corals are intermixed with seagrasses, sand, rock and algal mats. The estimated area of coral reef was 1.9 km2 at Bawe Island and 20 km2 at Mnemba Island. Tabulate Acropora were aggregated on Bawe and Mnemba coral reefs, while digitate Acropora were aggregated on the reef flats, randomly distributed on Bawe and dispersed on Mnemba reef slopes. Small sized colonies of 11 to 40 cm and 21 to 60 cm diameters dominated the distributions of digitate and tabulate Acropora respectively. Higher contribution of digitate Acropora (2.07 cm) were observed in terms of coral cover as compared to tabulate Acropora (0.03 cm). The study also revealed that the distribution of tabulate and digitate Acropora is influenced by depth, turbidity and habitat type. This study provides useful information on the location and distribution of digitate and tabulate Acropora and provides recommendations for management and future studies on ecosystem changes and vulnerability.
Estimation of Extreme Flows in Nkana River to Verify the Adequacy of Naming’ongo Bridge Waterway
(Mbeya University of Science and Technology Journal of Research and Development (MJRD), 2013-02-05) Katambara, Z; Msambichaka, J & Mkisi, J
The response by the government of Tanzania to food security and poverty alleviation in the Naming’ongo area in Mbozi District has been to develop Naming’ongo irrigation scheme as well as construct a bridge across River Nkana to con- nect the farms and other parts of the district to facilitate a reliable transportation of the produce to the market. The Aus- tralian Water Balance Model was calibrated by using 10 years data from a nearby sub-catchment of Mbarali. The Nam- ing’ongo Sub-catchment was delineated form a 30 m digital elevation model. The observed rainfall was obtained from Mbozi Meteorological station. The study approximated the peak flows in River Nkana for a return period of 50 years to be slight above 560 m3/s. This was considered to be adequate for the proposed structure. The study recommends that when undertaking human activities such as deforestation and cultivation an account for soil and environmental conser- vation should be considered. While it is necessary to establish a monitoring system within the catchment, the designs of future hydraulic structures should incorporate stream flow measuring facilities.
Estimation of Extreme Flows in Nkana River to Verify the Adequacy of Naming’ongo Bridge Waterway.
(Scientific Research, 2013-02-05) Katambara, Zacharia; Msambichaka, Joseph J.; Mkisi, Joseph
The response by the government of Tanzania to food security and poverty alleviation in the Naming’ongo area in Mbozi District has been to develop Naming’ongo irrigation scheme as well as construct a bridge across River Nkana to connect the farms and other parts of the district to facilitate a reliable transportation of the produce to the market. The Australian Water Balance Model was calibrated by using 10 years data from a nearby sub-catchment of Mbarali. The Naming’ongo Sub-catchment was delineated form a 30 m digital elevation model. The observed rainfall was obtained from Mbozi Meteorological station. The study approximated the peak flows in River Nkana for a return period of 50 years to be slight above 560 m3 /s. This was considered to be adequate for the proposed structure. The study recommends that when undertaking human activities such as deforestation and cultivation an account for soil and environmental conservation should be considered. While it is necessary to establish a monitoring system within the catchment, the designs of future hydraulic structures should incorporate stream flow measuring facilities.
Developing a Surface Water - Groundwater Interaction Model for Letaba River System in South Africa
(Mbeya University of Science and Technology Journal of Research and Development (MJRD), 2013-02-06) Katambara, Z; Ndiritua,G. J
There is a constant increase in water demand and a pressing need to conserve the environment in the Letaba River system. This is leading to a situation where the demand for water may have outstripped the capacity of the existing resources to sustainably meet them. In the past dams were constructed and boreholes drilled as a strategy of reconciling demand and supply and this is evidenced by the numerous dams and boreholes in the Letaba River system. There are five major dams; three of which have a capacity exceeding 60 million cubic meters and also more than 3000 boreholes in the river basin. Currently, all the dams are stressed and the releases from Tzaneen Dam, intended to meet the water requirements of downstream users including Kruger National Park fail to meet these requirements substantially. Although these demands are high and probably exceed the system’s capacity, it is likely that the reliability of supply can be improved significantly if the surface water - groundwater (sw/gw) interactions within the basin are modelled comprehensively and then incorporated into system operation. This paper reports on an ongoing development of a sw/gw model of the Letaba River System. The model development intends to maximize the use of the relevant available information and data and recognizes the existence of an interaction zone which forms a major link of many of the processes that will be included in the model. It has been found that the scale of monitoring processes in the river system is inadequate and is a significant constraint to the development of the model that is expected to impact on the level of confidence in model implementation and application. Incorporation of uncertainties will therefore be an integral part of the modelling.
Adopting the System of Rice Intensification (SRI) In Tanzania: A Review
(SciRes., 2013-06-02) Katambara,Zacharia; Kahimba, Frederick C.; Mahoo, Henry F.; Mbungu, Winfred B.; Mhenga, Fikiri; Reuben,Paul; Maugo, Muyenjwa; Nyarubamba, Anthony
The demand of water for irrigation purposes in Tanzania outstrips the amount of water available for irrigation and other demands. On the other hand, the demand for more food to feed the growing population is increasing, calling for the need to have technologies and farming practices that ensure more food production while minimizing water uses. Rice is among cereal crops grown in Tanzania, and it can assist in meeting the food demand for the nation. Majority of rice producers in Tanzania and Sub-Saharan Africa (SSA) are subsistence farmers and they practice continuous flooding, a technique that requires much water. In addition to using large amounts of water, the conventional practices of growing paddy using local varieties transplanting process are implemented when seedlings are more than 21 days old, and 3 - 4 seedlings are transplanted in one hole. This practice results in low yields, and low water productivity and water use efficiency. The system of rice intensification (SRI) on the other hand, is a promising new practice of growing paddy rice that has proven to be very effective in saving water and increasing rice yields in many parts of the world. SRI practice is spreading fast and it has been adopted in many countries. The SRI practice has been introduced in Tanzania during the last 3 years as such it is not widely practiced. This paper reviews SRI practice at global, regional and country (Tanzania) level, and evaluates the challenges, opportunities and implications for its adoption in Tanzania. Knowledge gaps at each level have been identified and discussed as well as suggestions for researchable areas.
Adopting the system of rice intensification (SRI) in Tanzania: A review
(Mbeya University of Science and Technology Journal of Research and Development (MJRD), 2013-07-02) Katambara, Z
The demand of water for irrigation purposes in Tanzania outstrips the amount of water available for irrigation and other demands. On the other hand, the demand for more food to feed the growing population is increasing, calling for the need to have technologies and farming prac- tices that ensure more food production while minimizing water uses. Rice is among cereal crops grown in Tanzania, and it can assist in meeting the food demand for the nation. Majority of rice producers in Tanzania and Sub-Saharan Africa (SSA) are subsistence farmers and they practice continuous flooding, a technique that requires much water. In addition to using large amounts of water, the conventional practices of growing paddy using local varieties transplant- ing process are implemented when seedlings are more than 21 days old, and 3 - 4 seedlings are transplanted in one hole. This practice re- sults in low yields, and low water productivity and water use efficiency. The system of rice in- tensification (SRI) on the other hand, is a prom- ising new practice of growing paddy rice that has proven to be very effective in saving water and increasing rice yields in many parts of the world. SRI practice is spreading fast and it has been adopted in many countries. The SRI prac- tice has been introduced in Tanzania during the last 3 years as such it is not widely practiced. This paper reviews SRI practice at global, re- gional and country (Tanzania) level, and evalu- ates the challenges, opportunities and implica- tions for its adoption in Tanzania. Knowledge gaps at each level have been identified and dis- Copyright © 2013 SciRes. cussed as well as suggestions for researchable areas.
Positioning Mbeya University of Science and Technology in Tanzania in the Systems of Innovation Perspective.
(Scienetific Research, 2013-10-06) Katambara, Zacharia
The chronological development of universities ranges from the state at which universities are considered to be knowledge accumulators followed by knowledge factories and finally the knowledge hubs. The various national systems of innovations are aligned with the knowledge hubs and it involves a substantial amount of research activities. The newly established Mbeya University of Science and Technology is recognized as a knowledge hub in some particular niches. However, there are a limited number of research activities conducted at the university and this study is an attempt to identify the reasons that limit research activities. Well-structured research questionnaires were designed and distributed to academic staff members and thereafter the respondents were analyzed by using SPSS software package. The lack of knowledge, skills and funds as well as equipment was earmarked as the reason that hindered the research activities. Therefore, resources are required to improve the capabilities of the staff members and the study recommends on the need for deliberate efforts to improve the knowledge of the staff members with respect to research activities.
Positioning Mbeya University of Science and Technology in Tanzania in the Systems of Innovation Perspective
(Mbeya University of Science and Technology Journal of Research and Development (MJRD), 2013-11-13) Katambara, Z
The chronological development of universities ranges from the state at which universities are considered to be knowledge accumulators followed by knowledge factories and finally the knowledge hubs. The various national systems of innovations are aligned with the knowledge hubs and it involves a substantial amount of research activities. The newly established Mbeya University of Science and Technology is recognized as a knowledge hub in some particular niches. However, there are a limited number of research ac activities conducted at the university and this study is an attempt to identify the reasons that limit research activities. Well-structured research questionnaires were designed and distributed to academic staff members and thereafter the respondents were analyzed by using SPSS software package. The lack of knowledge, skills and funds as well as equipment was earmarked as the reason that hindered the research activities. Therefore, resources are required to improve the capabilities of the staff members and the study recommends on the need for deliberate efforts to improve the knowledge of the staff members with respect to research activities.
Evaluation of Local Ceramic Materials for High Voltage Insulation Application
(Nelson Mandela African Institution of Science and Technology, 2014) Moyo, Moses George
This study investigated the Tanzanian local ceramic material for their potential as raw materials for production of high voltage insulators based on the mix proportion of raw materials and firing temperatures. The raw materials used were: Pugu kaolin, quartz supplied by the Kilimanjaro Industrial Development Trust (KIDT), and Kilimanjaro feldspar. The study characterised both individual raw materials and the blends produced from these raw materials. A total of six batches were prepared by varying the proportion of raw materials. Cylindrical samples of 10 and 60 mm diameter were produced by slip casting method and fired at the maximum temperature of 1100, 1200 and 1300 ºC. Fired samples were tested for insulation resistance, bending strength, and bulk properties. The X-ray diffraction (XRD) analysis showed that on heating Pugu kaolin produces mullite phase which is very important for mechanical and dielectric properties. Furthermore, the highest trend in insulation resistance and bending strength is revealed to samples fired at 1200 ºC with lower values for those fired at 1100 and 1300 ºC. The optimum mix proportion and firing temperature, which compromise both insulation resistance and bending strength is with 33 wt% Pugu kaolin, 11 wt% Kilimanjaro quartz, and 56 wt% Kilimanjaro feldspar at the firing temperature of 1200 ºC. With this mix proportion and firing temperature at maximum insulation resistance of 205800 MΩ at the injection of 1000 V is achieved. The bending strength and water absorption for this mix proportion and firing temperature is 65.358 MPa and 0.01 %, respectively. These results correspond to the standard specifications for ceramic insulators.
An Investigation for Energy Sustainability in Cement Industries in Tanzania: The Case of Mbeya Cement
(Technische Universität Berlin Institut für Energietechnik, 2017) John, John Pius
Cement production processes are facing crucial sustainability issues such as inefficient en‐ ergy and raw material use, product supply, production cost and environmental pollution. High energy and material use dominated by inefficient characteristics of cement production processes, in turn, lead into depletion of non‐renewable resources, increased production costs as well as environmental degradation due to emissions. The main objective of the study was to investigate performance of cement industry in Tanza‐ nia relative to sustainable energy utilization. Most of past researches have evaluated the per‐ formance of cement production processes using first law of thermodynamics alone (mass and energy balances) with the objective of improving energy efficiency. Although this ap‐ proach sheds light on the question of improvement of energy use in the processes, it has some limitations. The limitations are imposed by the internal irreversibility due to combustion and other physico‐chemical nature of reactions dominating the whole processes. The current emerging approach, which overcomes limitations imposed to the first law approach is ex‐ ergy‐based method, relatively new in evaluation of performance of cement production pro‐ cesses. However, owing to complexity of cement production processes, applying an exergy‐ based method manually is very difficult and complex. The current study proposes combined approach of exergy based method and modeling as well as simulation. The model was successfully developed, validated using real plant data and was used to predict the performance of the cement dry rotary kiln system of Mbeya Cement production processes. Data obtained from modeling and simulation were further used to evaluate the performance of processes, individual components, sub‐systems and overall kiln system at large using exergy based method. The approach not only simplifies the analyses but also gives detailed insight of real processes, source and type of real imperfections, its magnitudes and how imperfections can be minimized. Major findings indicated that the rotary kiln sub‐systems and the overall kiln system have poor exergetic performance, suggesting that potential for improvement exists. The overall exergy efficiency of the kiln system is around 33 %. Also results indicated that the rotary kilns have the lowest exergetic efficiency of about 14 % followed by the clinker cooler with exergetic efficiency of about 41.11 %. The highest source of irreversibility encompassed chemical reactions, especially calcination and clinker burning processes with exergy destruc‐ tion of 2,813.75 kJ⋅kgcl−1 and 1,148.17 kJ⋅kgcl−1. Results from parametric analysis suggested that if measures for improvements of processes, components and sub‐systems are taken, a significant amount of fuel and specific energy could be saved. Furthermore, it was confirmed that if the avoidable exergy destruction is minimized, processes, system components and sub‐systems performance could be improved from exergetic point of view.
Optimizing the Conjunctive Use of Surface Water and Groundwater in Water Stressed River Basins: Case of Olifants River Basin, South Africa
(Tshwane University Of Technology, 2017) Kifanyi, Gislar Edgar
One of the new techniques currently used to address water shortage problems in the developed countries is the optimum conjunctive water use. Optimum conjunctive water use demands that the surface and subsurface reservoirs are fully characterized if deterministic methods are to give reliable results. However, in real world phenomena, full characterization of surface – groundwater reservoirs is neither practically nor economically feasible. This research, therefore, aimed at developing a combined simulation-optimization quantitative conjunctive water use management model which can sustainably manage water resources taking into account input parameter uncertainty. Response matrix technique was used to combine simulation model with optimization model (procedure). The novelty of this research work is that determination of optimum conjunctive water use was determined under scanty data and uncertain condition. Surface water and groundwater conceptual models were developed, and integrated to form a conjunctive water use conceptual model which was converted into numerical simulation model for both deterministic and stochastic simulations. MODFLOW 2000 and RIVER Package (RIV) (together referred to as conjunctive water use simulation model) supported in Visual MODFLOW 2014.2 Classical Interface was used to determine aquifer system responses (drawdowns). These drawdowns were assembled as response matrices and then incorporated into an optimization management model as drawdowns constraints coefficients. The simulation optimization problems were solved and analysed through “Active-Set” (Sequential Quadratic Programming (SQP) optimizer (algorithm)) implemented under the MATLAB 2014a environment. The Retrospective Optimization Approximation (ROA) method was used for solving the stochastic optimization problem and to v investigate the impact of uncertainty on optimal management strategies. ROA procedure solves and evaluates a sequence of optimization sub-problems in an increasing number of realizations. Results indicated that the study area aquifer has potential groundwater resource which is undeveloped. Deterministic approach underestimates the water withdrawal rates. The optimal withdrawal rates designed based on ROA approach were relatively higher than those designed based on deterministic approach. Moreover, the overall percentages of contribution of surface water and groundwater sources to the total water demand obtained through ROA approach was about 58% and 42%, respectively while the overall percentages contribution obtained through deterministic approach was about 85% and 15%, respectively. This is about ±27 % variation (i.e., Differences between the approaches realized) of percentages of contribution of the two water sources to the total water demand. Furthermore, findings indicated that ROA conjunctive water use management technique has potential to ensure sustainability of limited water resources of river basins. Through ROA approach the expected total optimal objective function value converged to its maximum value within a relatively few iterations (6 to 8 iterations) in about 2.30 Hrs computational time. In conclusion, results demonstrated that the ROA approach is a promising technique for use in managing conjunctive water use under uncertainty conditions. It is recommended that guidelines for determination of the sequence of sample sizes for use in ROA method framework should be established. The use of parallel computer processors to enhance computational time efficiency for large optimization problems should be explored. Quantitative methods for determination of weights for estimating values of objective functions should be investigated. The application of the ROA approach to multi-objectives optimization problems should be explored.
Effect of Ipomoea Hildebrandtii and I. Kituiensis on Loss of Native Herbages of Maasai Steppe Rangelands in Simanjiro District
(The University Of Dodoma, 2018) Ndaki, Manyanza
Sustainability of many rangelands including Simanjiro Maasai steppe rangelands is limited in part by invasive plant species. A study was conducted among two selected village rangelands (Terrat and Sukuro) of the Simanjiro district aimed to (1) determine the effect of Ipomoea hildebrandtii and I. kituiensis on herbage species composition, richness, and basal cover; and (2) determine the effect of Ipomoea hildebrandtii and I. kituiensis on herbage biomass productivity. Other objectives were to (3) assess the distribution of Ipomoea hildebrandtii and I. kituiensis across grassland and woodland habitats, and (4) evaluate the available mitigation measures among the Maasai pastoralists on the effects of Ipomoea hildebrandtii and I. kituiensis on their rangelands. A total of 10 plots of 70 m2 each with 9 quadrats of 1 m2 each in the invaded and non-invaded grazing-lands coupled with point sampling technique. Purposeful sampling involved 10 key informants’ interviewees; 24 participants for focus group discussions. Simple random sampling involved 30 hamlets representatives for questionnaire surveys. Data on herbage species composition, richness, basal cover, biomass productivity; distribution of invasive Ipomoea spp; and mitigation measures for effects of invasive Ipomoea spp. were analysed using STATA, Microsoft Excel and SPSS, respectively. Non-invaded grazing-lands had a higher basal cover (54.71%±1.95% for grasses, 45.29%±1.95% for forb) than invaded grazing-lands (29.38%±1.34% for grasses, 24.70%±1.20% for forb), (P0.05). Non-invaded grazing-lands had higher biomass productivity (0.289±0.03 t DM/ha) than invaded grazing-lands (0.202±0.02 t DM/ha), (P
Potential of Scoria, Pumice, and RHA as Supplementary Cementitious Materials for Reducing Setting Time and Improving Early Strength of Pozzolan Blended Composite Cement
(NMAIST, 2019) Mboya, Hieronimi Alphonce
Tanzania has huge deposits of scoria (S-N) and pumice (P-N) minerals that can be used as supplementary cementing materials (SCMs) in cement factories to cut down the cost of cement and its pollution effect to the environment. Besides this, agricultural wastes such as rice husk produce rice husk ash (RHA) having high silica content that can be used with cement to reduce the cost of cement and its impact to environment. Performance indicators of mortar and concrete such as slump, flow, permeability, shrinkage, modulus of rupture, compressive and tensile splitting strength were tested with different proportions of SCMs. It was found out that in addition to cutting the CO2 emissions, SCMs reduce energy bills and that they confer extra strength and resistance to mortar and concrete. This work only examined the properties of scoria (S-N) and pumice (P-N) and rice husk ash (RHA) as supplementary cementing materials (SCMs) for Portland cement. The investigation considered these materials in binary and ternary module. X-ray fluorescence, X-ray diffraction, and pozzolanic activity index (PAI) tests confirmed the suitability of these materials as potential SCMs. Initial and final mean setting times observed for a binary composite cement were 166 and 285 min respectively. The setting times were longer than those of Ordinary Portland cement (OPC) but shorter when compared to Portland pozzolana cement. Characteristic and target mean strengths of 30 and 38.2 MPa were considered. The ultimate mean compressive strengths achieved at 28 days of curing were 42.5, 44.8, and 43.0 MPa for S-N, P-N, and RHA respectively indicating the potentials of these materials as SCMs. Further observation show that, the 28-days maximum compressive strength achieved by the blended cement concrete (with 10% replacement of SCMs) were 44.2 and 43.1 MPa for S-N 10 and P-N 10, respectively. The modulus of rupture decreased with an increase in the amount of S-N. On the other hand with P-N, a maximum of 8.0 MPa at 20% replacement was observed iii but then dropped to a minimum value of 6.4 MPa at 40% replacement level. This indicated potentially a superior ability of the P-N concrete to endure more sustained stress such as those caused by tremors and earthquakes and impact-related stresses. The residual compressive strength of P-N blended cement concrete samples, after subjection to a high temperatures of 600 ºC, was higher compared to S-N blended cement indicating the superior resistance of P-N to higher temperatures. S-N 10, S-N 20 and S-N 30 gave coefficients of permeability, (K), of 5.2526E-08, 5.20833E-08, and 4.9741E-08 m/s, in that order. This low permeability was attested by their dense microstructure, with implied reduced chemical attack, less carbonation, improved steel protection against corrosion, and enhanced durability of the reinforced concrete. The maximum compressive strength of ternary materials of 53.8 MPa was attained at 10/20% P-N/RHA replacement level. The 28 days Strength Activity Index (SAI) of S-N/RHA blended cement at 30/0, 10/20, 5/25 and 0/30% S-N/RHA were above 75% recommended by ASTM. On the other hand the SAI of P-N/RHA blended cement were higher than the ASTM recommended value at all replacement levels. Therefore, 10% of S-N, P-N or RHA is recommended as the optimum replacement for Portland cement in binary materials and 10/20% P-N/RHA for ternary materials to enhance performance of cement.
Optimization of Incineration Process
(Nelson Mandela African Institution of Science and Technology, 2019) Omari, Arthur Mngoma
Municipal solid waste management has become a challenge in many cities in the developing countries due to the poor methods of waste disposal, which increase the risk of the spread of diseases, leach and increase the demand of land for waste disposal. Characterization study of waste samples from Arusha shows that the combustible fraction is about 87% and biodegradable is 80%. The Thermal gravimetric analyser and Bomb calorimeter show the energy value of about 12.5 MJ/kg and the degradation of about 85%. The study shows that the municipal solid waste disposal method can be thermal, biological or physical. However, thermal method by incineration process is the most preferred and convenient because it destroys pathogens and reduces waste volume in the fastest way. The waste flow analysis of Arusha city shows that the waste has the annual recoverable potential of 128GWh. The case study used an existing incinerator as showed the variation of effluents with operating conditions. The design optimization using computational fluid dynamic techniques to predict the performance of incinerator showed the deviation of input air by 14%, the mass flow rate by 26.5%, the mass fraction of carbon dioxide by 10.4% and slight deviation of nitrogen dioxide and carbon monoxide. The research suggested removing the ash during the incineration process by using a moving grate mechanism to minimize the possibility of formation of NOX. To feed the incinerator by using mechanical means without direct opening the door, it suggested to incorporating moving grate mechanism. The operating conditions of the incinerator designed should have the optimum values for input air one A1-1 as 0.036 39 kg/s, the input air two A2-1 as 0.030 46 kg/s, the input air three A3-1 as 0.034 09 kg/s, the input fuel value as 19.6 kg/h and the maximum capacity of incinerator as 68 kg/h

Browse

Browsing Engineering & Technology by Issue Date

Results Per Page

Sort Options