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Item Modelling the leaching behaviour of selected Heavy Metals in Solidified/Stabilised Gold Mine Tailings(University of Dar es salaam, 2019) Paul, RestitutaThis study aimed at modelling the leaching behaviour of selected heavy metals, namely Cu2+, , Cd2+ , Cr3+, Zn2+, and Pb2+ in stabilized/ solidified (S/S) gold mine tailings intended for utilization works. The modelling focused on factors such as pH, tailings particle size, cements content and liquid to solid ratio (L/S) interface conditions, which could potentially influence the leaching behaviour of the heavy metals in S/S tailings.t the leaching behaviour test protocols. Chemical speciation of the heavy metals in leachant was modelled using visual MINTEQ3.1 (R) software. The major tailing constituents were found to be quartz (SiO2) and muscovite. The tailings had average concentrations of Cr3+, Cu2+,Pb2+, Zn2+ and Cd2+ ranging from (14.1-79.9),(42.3-45.9),(122.3-135.9). (31.4-43.9) and (21.1-37.4) mg/kg. respectively. The PH-dependent leaching tests revealed a strongly Ph dependent leaching behaviour of selected metals. The lowest leaching rates were observed in alkaline conditions(i.e>pH 10), regardless of initial concentrations. Using visual Minteq 3.1 (® ) it was established that the immobilization of heavy metals at high PH was due to their precipitation as insoluble hydroxides in the stabilized matrix. Immobilization of Zn in the tailings was through substitution on cement ettringite and formation of insoluble complex compound (Zn6Al2 (OH)16CO3-4H2O) at pH values> 9.5. Pb exhibited amphoteric leaching behaviour with minimum leaching between pH 10.5-11.5. the immobilization of Cu and Cd at high pH was due to its precipitation as Cu(OH) and Cd(OH)2 respectively, while the immobilization of Cr in alkaline conditions was associated with a reduction of the more soluble Cr+6 salts less soluble Cr(OH)3. Results of speciation modelling with MINTEQ3.1® indicate that the dissolution of alkaline metals and oxyanions (such as (SO42- ,HCO32- ) raised both the PH and EC of leachant which in –turn affected leaching behaviour of heavy metals. It was revealed that under acidic conditions, the leaching solution was dominated by metal chlorides. Under alkaline conditions, mostly metal hydrozxides were leached into the solution. Adsorption simulation reveals that only <1% of each metal is immobilized on either HFO or Gibbsite, with a pH-dependent sorption process. It has further been observed that the major leaching mechanism for the soluble fraction of the metals in S/S was surface washout. Multi-linear regression models were developed for Cu2+, Cd2+, Cr3+, Zn2+ and Pb2+ . the models and laboratory experiment showed that metal leaching was controlled by pH of leachant and cement content. It is concluded that S/S is an effective method for reducing leaching of heavy metals in the tailings. However, since risk levels are dependent on the composition of the tailings, it is recommended that a risk assessment must precede S/S tailing utilization in construction works.Item Modelling the leaching behaviour of selected heavy metals in solidified/stabilised gold mine tailings(University of Dar es Salaam, 2020) Paul, RestitutaThis study aimed at modelling the leaching behaviour of selected heavy metals, namely Cu2+,Cd2+,Cr3+, Zn2+ and Pb2+ in stabilized/solidified (S/S) gold mine tailings intended for utilization in construction works. The modelling focused on factors such as Ph, tailings particle size, cements content and liquid to solid ratio (L/S ) interface conditions, which could potentially influence the leaching behaviour of the heavy metals in S/S tailings. The leaching behaviour of heavy metals in S/S tailings was investigated following standard leaching test protocols. Chemical speciation of the heavy metals in leachant was modelled using Visual MINTEQ 3.1 R Software. The major tailing constituents were found to be quartz (SiO2) and muscovite. The tailings had average concentrations of Cr3+ ,Cu2+ ,Pb2+,Zn2+ and Cd2+ ranging from (14.1 -79.9) ,(42.3 -45.9), (122.3 -135.9, (31.4 -43.9) and (21.1-37.4) mg/kg, respectively. The Ph –dependent leaching tests revealed a strong ph-dependent leaching behaviour of the selected metals. The lowest leaching rates were observed in alkaline conditions (i.e. –ph 10), regardless of initial concentrations. Using visual minteq 3.1 it was established that the immobilization of heavy metals at high ph was due to the precipitation as insoluble hydroxides in the stabilized matrix. Immobilization of Zn in the tailings was through substitution on cement ettringite and formation of insoluble complex compound (Zn6A12 (OH)16CO3. 4H20) AT PH Values 9.5 Pb exhibited amphoteric leaching behaviour with minimum leaching between Ph 10.5 -11.5. The immobilization of Cu and Cd at high Ph was due to its precipitation as Cu (OH)2 and Cd(OH)2 respectively, while the immobilization of Cr in alkaline conditions was associated with a reduction of the more soluble Cr +6 salts less soluble Cr (OH)3.results of speciation modelling with visual MINTEQ 3.1 indicate that the dissolution of alkaline metals and oxyanions (such as SO42-, HCO32-) raised both the PH and EC of leachant which in-turn affected leaching behaviour of heavy metals. It was revealed that under acidic conditions, the leaching solution was dominated by metal chlorides. Under alkaline conditions; mostly metal hydroxides were leached into the solution. Adsorption simulation reveals that only 1% of each metal is immobilized on either HFO or Gibbsite with a PH –dependent sorption process.it has further been observed that the major leaching mechanism for the soluble fraction of the metals in S/S was surface washout.Multi-linear regression models were developed for Cu2+,Cd2+ ,Cr3+ ,Zn2+ and Pb 2+ .The models and laboratory experiment showed that metal leaching was controlled by PH of leachant and cement content . It is concluded that S/S is an effective method for reducing leaching of heavy metals in the tailings. However, since risk levels are dependent on the composition of the tailings, it is recommended that a risk assessment must precede S/S tailing utilization in construction Chemical technology.Item A model for indertaking business process re-engineering (BPR) to improve construction project performance in Tanzania(University of Dar es Salaam, 2019) Mwishwa, Yazidi Hassan BakariThe performance of construction projects in Tanzania is commonly plagued with time overrum, cost overrun and poor quality. These problems are deeply rooted in weaknesses of project processes. This thesis improve the project processes and project performance through BPR philosophy. The BPR model was developed based on the concepts of process performance measurement and BPR philosophy. Data used to develop the model was obtained through interviews and questionnaire surveys from 33 selected organizations. Data from a case study of a road construction project together with the critical comparative analysis of a BPR model against other models were used to validate the model. The dimensions of the developed model include: BPR foundation; Understand Current Process; Weaknesses of Current Processes; Desired (To-Be) Processes and Continuous Improvement. The model considers design, procurement and construction management as core project processes. The Model also analysed indicators for identifying weaknesses and for driving improvement. The thesis has established forty (40) indicators to identify process weaknesses and fourteen measures to identify desired project process. With regard to strategies to enable continuous improvement, the study proposes continuous learning, benchmarking, use of IT technology, plan resources and adopt Capability Maturity Model. Model was validated to identify weaknesses, identify desired (To-Be) process, enable improved project processes, identified weaknesses of traditional processes and compared with the other models. The study concludes that forty established indicators are appropriate to identify process weaknesses; fourteen measures are useful to design To-Be process. They can be deployed through using of the proposed strategies for improvement. Suggestion is made for each contracting party in the country to use the model to undertake BPR to improve performance of core project processes.Item Development of a model for optimising the variations on the forecasted constructed construction cashflows: a case of building projects in Dar es salaam-Tanzania(University of Dar es Salaam, 2019) Malekela, Kimata NewmanThe contingency sum is provided as the ceiling amount for absorbing variations that may occur on planned budget during execution of construction projects. However, there have been significant variations on forecasted construction cash flows which exceed the contingency sum provided. This study is therefore aimed to develop a model for optimizing the total variations in overall forecasted construction cash flows within the contingency sum provided during execution of building projects in Tanzania. Specifically, this model is used to minimize those variations within the contingency sum provided in building projects. Data were collected through questionnaire from 284 building contractors in Dar es salaam. In addition, documentary review of historical data from contract documents of 40 recently completed building projects was conducted and supported by interviews to project participants and self-auditing to contact documents. Eight major risk factors were identified but the leading four risk factors with their overall (0.246); errors in project documents (Bills of Quantities) (0.187); consultants’ lack of experience and technical skills (0.131); and poor /incomplete design (0.130). The study concludes that the model of this study can minimize more than 60% of the total variations planned to occur in execution of building projects. It is therefore recommended that model solutions should be used in establishing the proactive risk measure for controlling variations causes by risk factors on forecasted construction cash flows of building projects.Item Hydraulic modeling of Mara natural wetland using remote sensed data(University of Dar es Salaam, 2019) Mtamba, Joseph OchiengIn the last ten years climate change has increased concerns in natural wetlands and floodplains. Floods disaster has negative impacts on the infrastructure, livelihoods and environment. Sustainable planning and management for flood disaster management can be achieved through application of hydraulic models. In remote data scarce areas remote sensed data for topography and roughness may be used as an alternative source of data, hence evaluation of its suitability is necessary. Vegetation resistance influences water flow in floodplains. Characterization of vegetation for hydraulic modeling includes the description of the spatial variability of vegetation type, height and density. In this research, the application of dual polarized Radarsat-2 wide swath mode backscatter coefficients (o°) and Landsat imagery to derive spatial hydraulic roughness was explored. Simulations were performed using the FLO-2D hydraulic model to evaluate model performance under three Manning’s coefficient parameterizations which include derived optimum floodplain roughness, constant floodplain roughness referred to as scenario 1, 2 and 3 respectively. The model was used to derive spatial hydraulic indices and flood hazard maps for the floodplain wetland system. The model performance was evaluated using Nash-Sutcliffe model efficiency coefficient (E) and coefficient of determination (R^2), based on water levels measurements and simulated water levels at a gauging station within the wetland. The overall performance of scenario 2 to E = 0.95 and R^2 = 0.95, which was improved in scenario 2 to E = 0.95 and R^2= 0.99. When spatially distributed Manning values derived from SAR relative surface values were parameterized in the model, the model also performed well and yielding E = 0.97 and R^2 = 98. Improved model performance using spatial roughness shows that spatial roughness parameterization can support flood modeling and provide good flood wave simulation over the inundated riparian areas equality as calibrated model. Further, the results can be improved by more accurate elevation data.Item Modeling processes governing transformations and transport of nitrogen compounds and heavy metals in Geita Wetland: The case of Mtakuja and Mabubi rivers(University of Dar es salaam, 2019) Maswe, Ezrael JosephatGeita wetland suffers heavy metals pollution loads due to mining activities in the upstream and nitrogen nutrient loads due to agricultural practices in the area. In this research the processes governing transformations and transport of nitrogen compounds (NO3-N and NH4-N) and heavy metals (Hg, Ni and Cu) through Geita wetland were studied. The Mtakuja and Mabubi rivers which pass through the wetland were used as case studies. The hydrologic and water quality models SWAT and DUFLOW were applied to model transport of the nitrogen compounds and heavy metals, respectively. The results of modelling and the measured water quality data from the monitoring stations in the Mabubi and Mtakuja Rivers document higher concentration levels of the studied pollutants above the WHO recommended surface water quality standards for aquatic life. The results of study showed that the main processes governing transformations of nitrogen compound are mineralization, nitrification and denitrification. It was also revealed that adsorption and accumulation in the sediment are the major processes that determine the fate and transport of heavy metals. The models results and field measurements demonstrated that about 40% of the studied annual heavy metals and 70% of the studied nitrogen compounds loadings which would otherwise reach the lake Victoria is retained in the wetland. Therefore, the study results advocate for retention, conservation and rehabilitation of wetland ecosystem especially around areas where agricultural and mining activities take place. The models can therefore be used to hlp future water quality monitoring efforts in the Geita wetland and other wetlands with similar problems around the world.Item Improvement of performance prediction methods for selecting pump as turbine in micro hydropower systems(University of Dar es Salaam, 2019) Mdee, Ombeni JohnEven though pumprunning in a reverse direction as a turbine to generate mechanical rotational energy is a more than 50-year-old concept, the technology development is still growing and more pumps are being installed on the micro hydropower scales. This study assessed four technological developments, which included pump component modification, internal flow characteristics, control mechanism, and conversion methods. The constructed open-circuit test rig indicated the first pump of specific 57.7 rpmhas a head of 5.9 m and flow rate of 34.14 l/s with the maximum efficiency of 60%. The second pump of specific speed of 27.6 rpm indicated the performance characteristic ratios in turbine mode over pump mode in terms of head, flow rate and efficiency are 2.106, 1.448 and 0.941; respectively. Both the experimental result and literature data indicated the pump designed point is easier to change when running in turbine mode that makes the difficulties during off-the-shelf pump selection. However, the use of conversion methods to select the off-the-shelf pumps contains numerous inaccuracies and do not provide an acceptable prediction coefficient of head and flow rate. This study used the velocity relations of pump geometrical shape and site conditions related to head and flow rate to develop the Analytical Model Equation (AME). The improvement of performance prediction method was obtained by applying differential calculus technique to AME and it resulted inanalytical head ratio and flow rate ratio equations. The derivative results of AME indicated the coefficient of determination (R2) of greater than 0.9 when compared together conversion method sat the 95% confidence level. Also, the prediction coefficient equation was developed when combined with the derivative results of AME and tested with pumps of specific speed ranging from 9.08 to 94.4 rpm. The AME coefficient is equal to 1 when deduced from the minimum head ratio and flow rate ratio of one and extended between -4 and +4 as varying the head ratio and flow rate ratio. Therefore, the prediction coefficient equation would be used to define the acceptable prediction range of head and flow rate that has been predicted by conversion methods.Item Hydraulic modeling of Mara natural wetland using remote sensed data(University of Dar es Salaam, 2019) Mtamba, Joseph OchiengIn the last ten years, climate change has increased concerns in natural wetlands and floodplains. Foods disaster has negative impacts on the infrastructure, Livelihoods and environment. Sustainable planning and management for flood disaster management can be achieved through application of hydraulic models. In remote data scarce areas remote sensed data for topography and roughness may be used as an alternative source of data, hence evaluation of its suitability is necessary. Vegetation resistance influences water flow in floodplains. Characterization of vegetation for hydraulic modeling includes the description of the spatial variability of vegetation type, height and density. In this research, the application of dual polarized Radarsat-2 Wide swath mode backscatter coefficients (00) and Landsat imagery to derive spatial hydraulic roughness was explored. Simulations were performed using the FLO-2D hydraulic model to evaluate model to evaluate model performance under three Manning’s coefficient parameterizations which include derived optimum floodplain roughness, constant floodplain roughness and spatial Manning’s coefficients derived with aid of relative surface roughness referred to as scenario 1, 2 and 3 respectively. The model was used to derive spatial hydraulic indices and flood hazard maps for the floodplain wetland system. The model performance was evaluated using Nash-Sutcliffe model efficiency coefficient (E) and coefficient of determination (R2), based on water levels measurements and simulated water levels at a gauging station within the wetland. The overall performance of section 1 was characterized with E=0.75 and R2=0.95, which was improved in scenario 2 to E=0.95 and R2=0.99. When spatially distributed Manning values derived from SAR relative surface values were parameterized in the model, the model also performed well and yielding E=0.97 and R2=0.97 and R2=0.98. Improved model performance using spatial roughness shows that spatial roughness parameterization can support flood areas equally as calibrated model. Further, the results can be improved by more accurate elevation data.Item A Framework for assessing innovation capability of incubator-based enterprises: case of business and technology incubators(University of Dar es salaam, 2019) Machuve, Juliana ZawadiInnovation is globally recognised for its contribution towards productivity, competitiveness and social development. Several efforts to promote innovation have included the establishment of Business and Technology Incubators. However, the contribution of the incubators to the incubated-enterprises has been reported more in terms of number of graduating firms, employment creation, sales growth, than in terms of innovation performances. There is limited clarity on the role at which incubators promote innovation of the start-up enterprises. Therefore, this research work focused on investigating it from the perspective of innovation capability of the incubatees / start-up enterprises operating under incubation within the context of a least developed country, Tanzania in Sub-Saharan Africa. Seventy three incubatees were surveyed; six incubator managers were interviewed and focus group discussions with twenty nine incubatees were conducted. The results revealed significant relationship among manufacturing, marketing, networking and managerial capability. In addition, the results showed no statistically significant relationship between incubatees’ innovation capability and their start-ups performance. In overall, the incubatees had high opinion with regards to the incubation value added services, namely infrastructure; business assistance; technical assistance; network access; business incubation policies and business incubator management. However, the results showed no significant relationship between the incubation services and incubatees’ innovation capability. Furthermore, the study developed a tool for assisting the incubator managers to record and track progress of the innovation capability of their incubatees. In order for incubators to contribute towards the promotion of innovation, they need to provide an integrated package of services that align with the capabilities required by the respective incubatees for carrying out their innovation activities. The study further recommends for creation and raising public awareness on the concepts of innovation, business and technology incubation, and their assessment frameworks to be realistic to the local context.Item Enhancement of heat tranfer by corona wind(University of Dar es Salaam, 1987) Kadete, HenryThe mechanism of heat transfer enhancement across solid gaseous interfaces by corona wind directed towards the heat transfer surface is investigated. Basic principles of heat transfer, negative dc corona and the nature of corona wind are studied. Voltage-current characteristics of negative dc corona in geometries which create corona wind are measured. The velocity distribution and velocity characteristics of corona wind are measured by Pitot-tube and by hot-wire constant-temperature anemometer. Corona wind is visualized by Toeplers children measurements. Corona wind is also visualized by the injection of carbon dioxide generated mist into the flow. Heat transfer measurements with and without corona wind reaching an upward facing heat transfer surface are made. Voltage-current characteristics of a corona triode are measured. The corona triode is used to generate corona wind and to control the magnitude of current which reaches the heat transfer surface. Heat transfer measurements in this corona triode geometry are made. Conclusions are that corona wind may adequately be described by the Navier-Stokes equations of motion. The Coulombion drag forces transferred to the neutral gas background create corona wind. The corona current is a function of the applied voltage and the electrode gap geometry. The average corona wind turns out to be proportional to the square root of the corona current. The corona wind velocity distribution is bell shaped with a maximum of about 5 m/s.The electro kinetic conversion efficiency is of the order of one percent. The enhancement of heat transfer by corona wind insignificant. Heat convection enhancement by up to 90 percent is measured. The enhancement of convective heat transfer by corona wind blowing on a heat transfer surface turns out to be proportional to the 0,3Power of the corona current. It turns out that the enhancement of convective heat transfer is only due to the augmentation of the hydrodynamic flow of the air. The corona wind is laminar, less turbulent than a mechanically created jet, has a small spread with a cross-section area of about 2x4 on-1i and has a long reach of up to 25cm which makes it superior to mechanically created jets for enhancement of heat convection by blowing towards heat transfer surfaces. The Langmuir-Child equation for space charge limited Current [SCLC] in vacuum is expressed in a general form in a gaseous media.Item Development of a model for assessing organizational innovation on research and development institutions in Tanzania(University of Dar es Salaam, 2016) Kerefu, Lawrence J‘Innovate or die’ a slogan which indicates the growing significance of innovation in business. In developing countries such as Tanzania, R&D institutions are the main reliable formal sources of innovation. There are various types of innovation including product, process, marketing and organizational innovation (OI). Few researchers for R&D activities in developing countries focused on products and processes only while the influence of OI to the innovate performance of R&D institutions is enclosed in a black box. Furthermore, as R&D activities lie at the heart of business development, strategies and innovation, it is important to have an ability to a33c33 R&D’s organizational capability to innovate in a diverse way. Literature reviewed show that the available tools have limitations in assessing OI in R&D institutions particularly in the least developed countries. Therefore the main objective of this research was to develop a model for assessing OI in R&D institutions in Tanzania. The research was divided into research design, data collection, analysis and conclusion. A model, with four hypotheses which were highly statistically significant at 1% significance level, was developed. Employing survey methodology and a sample of 56 R&D institutions in Tanzania, and using the Model, it was established that OI has a significant positive impact on the Innovative performance of R&D Institutions. The Model was tested in selected R&D institutions and the obtained results showed to be consistent with the established organizational innovation factors from the developed hypotheses. It was thus concluded that the model can be used to assess OI in R&D institutions in Tanzania and increase research research results uptake by industries. Also it can be replicated to other sectors.Item Performance Prediction of Electronic Energy Converters in Connection with Intermittent Energy source: With Special Attention to Wind and Insolation Energies(University of Dar es Salaam, 1991) Nzali, Aggrey Hezron Stephen JifikeTo encounter the problems accompanying the use of insolation energy and wind energy separately. In this thesis a new method which involves harnessing the two types of energies simultaneously in a combined manner is proposed. Since separately the two types of energies are unreliable, irregular and stochastic in nature, in the thesis. Performance prediction of electronic energy converters when operated in intermittent energy sources of wind and insolation combined has been done by simulations. To prepare the work of simulating. Simulation models for the wind energy conversion system. Insolation energy conversion system and storage batteries system were first developed. The simulation results, which involved four types of wind turbine system, one type of solar cells modules and one type of storage batteries showed that in some months when the two energy source are to a high degreed complementary, the resulting demand on storage batteries and the number of solar cells modules was reduced while in the months when the two were not, the performance prediction results were poor. To examine whether the newly proposed method was economically superior to the existing methods, a systems life-cycle counting method was used. The results showed that of the four alternative methods namely wind only, isolation only. Wind and diesel system, and a combined wind and insolation energy conversion systems taking into account the life –cycle costs of the systems for a period of twenty years, the method that of the systems for a period of twenty year, the method that used a combined wind and insolation energy conversion system was the cheapest and more reliable alternative compared to the others. Additionally in the thesis it is shown that a part from the cloudy activity, the available insolation energy throughout the year is constantly high for most places in Tanzania and that because of the technological advances. Made in the field of power electronics, solar cells and wind turbines, engineering, the energy problems in the rural areas of developing nations can eventually be weakened by employing these technologies to harness efficiently the alternative energy sources of wind and insolation simultaneously.Item Factors influencing the quality of maintenance and their impact on product and services offered by Tanzanian industries(University of Dar es Salaam, 2011) Mkilania, Joseph NeligwaThe research on quality of maintenance has been carried out for the purpose of investigation of factors influencing the quality of maintenance, which in turn affect the production output in terms of quality and capacity for Tanzania industries. There is limited literature that addresses the quality of maintenance. The approach used to attain the study objectives are synthesis of literature; statistical data analysis in identification of factors and finally formation of the model by use of multiple regression and statistical software SPSS version 15. The model is validated by using data collected from 21st Century Textile Ltd of Morogoro. Eventually, the stepwise regression was done by comparing the control and treatment data in order to test the reliability and validity of the model. By use of Durbin Wetson test, R2, and p- value test, the model were found to be valid, reliable and significance. The main result achieved was the developed quantitative model that integrates the refined factors. These factors are wages and salaries; experience of maintenance personnel; quality of spare parts; allocation of maintenance resources; correctness of maintenance action; duration for maintenance action; age of facilities and equipment; maintainability as well as reliability of services rendered. In summary, a regression equation model for predicting and explaining the quality of maintenance has been developed. The model main components are factors related to spare parts, human resources, maintenance strategies, facilities and equipment and functional quality.Item Development of a decision support system for the rufiji river basin - Tanzania(University of Dar es Salaam, 2003) Yawson, Daniel KwesiThree stand-alone Decision Support System (DSS) models have been developed at three critical locations within the Rufiji River Basin in Tanzania. The models are the Usangu Basin Model (UsaBaMod) for the headwaters of the Great Ruaha River, which is the main contributor to the Mtera-Kidatu Reservoir System, the Mtera- Kidatu Simulation Model (MteKid) for the optimal operational procedure of the reservoir system, and the Rufiji River Basin Flood Warning System (RBFWS) for the Rufiji floodplain and the Delta. For the UsaBaMod, dry season irrigation was found to be the main cause of the drying up of the Great Ruaha River among the numerous possibilities considered, and that if the dry season irrigation abstractions are restricted to crop water requirements, for example, instead of the constant abstraction methods being employed, then the river would be able to sustain flows during the dry season. Investigations about the possible cause of the failure of the reservoir system have shown that the actual amount of water that was being released from the Mtera Reservoir as spill must have been much higher than what had been recorded. It was also evident from the investigation that while Mtera Reservoir was “struggling” to get refilled in certain years the Kidatu Reservoir recorded large amounts of spill more enough to bring the Mtera Reservoir to its full condition. RBFWS in a form of a user-friendly computer package to generate flood forecasts within the Rufiji River at Stiegler’s Gorge and at Mloka as well as showing the extent of flood inundation in the floodplain with the corresponding flow magnitude had also been developed.Item Effect of plastification on the buckling behaviour of non-linear structural two-dimensional reinforced concrete frames(University of Dar es Salaam, 2005) Salim, Wanjala RamadhanThis Thesis deals with non-linear finite element analysis of structural 2-D reinforced concrete frames. It explores the effect of progressive material failure due to flexural actions on axial load carrying capacity of the frame. A plane stress field is assumed to describe the behaviour of frame members. The thesis proposes a new finite beam-column element that takes into consideration non-linear geometrical and material response. The non-linear incremental formulation is based on the Principle of Virtual Work. The equilibrium equations are derived using the Updated Lagrange Formulation. The material behaviour of concrete is described by failure surface described by Kupfer/Tusuji et al. The modified model of Hognestad is used for the concrete stress- strain relation. The material behaviour of rebar is described by Von Mises yield criterion while the stress-strain relation is modelled as bilinear elastic work hardening plastic material. Typical structures have been analyzed and results presented. The results show that consideration of plastification in a 2-D reinforced concrete frame, when the effect of cracking is taken into account, leads to a lower axial load carrying capacity of the structure. Thus the study results show that the effects of plastification on axial load carrying capacity of structures are important and should always be included in finite element models for predicting response of reinforced concrete members.Item Performance of constructed wetland coupled with dynamic roughing filter in the treatment of mixed wastewaters: a case of two Macrophytes planted in Series(University of Dar es Salaam, 2007) Nzabuheraheza, Francois DominicusA study of BOD5 removal from wastewater in coupled Dynamic Roughing Filter (DRF) and Horizontal Subsurface Flow Constructed Wetland (HSSFCW) system was carried out at the University of Dar es Salaam, which is located at latitude 6° 48' S and longitude 39° 13' E. The overall objective was to assess the performance of the DRF-HSSFCW treating mixed wastewaters using two macrophytes planted in series (Cyperus papyrus and Phragmites maurif ianus). The mixture re was made of domestic waste from the University of Dar es Salaam main campus (80 %), Kimara abattoir wastewater (10 %), and Mwenge soft drinks wastewater (I0 %). The overall BODs removal in DRF¬ HSSFCW system was 92%. The BOD5 concentration in CW effluent was about 28 mg/l, Which is within the recommended effluent standards (TBS, 1989; FAO, 1997; WHO 1998). This high performance was attributed to a number of factors, namely the removal of mainly suspended solids (removal efficiency of about 64 %) in the DRF and C. papyrus and P. mauritianus roots, which were weaved together in CW and hence provided a good filter mat and a better bacterial attachment. Optimum parameters for design of DRF system were found to be: (i) low flow rate (Q, = 0.50 m3/m2 .day), (ii) small gravel size (Gs) of 12-18 mm (gravel diameter), and (iii) big filter media thickness (Gt) of 25 cm. In the HSSFCW, the optimum removal efficiency of BOD5 (80 %) was obtained with a flow rate of 0.060 m3/m2 .day. Mathematical model estimated removal efficiency of about 92 % BODs. Thus the model was considered to be an appropriate tool for system design and prediction of BOD, removal in the above treating mixed wastewater in tropical condition.Item Investigation of broadband access over power-line network for communications services provision in developing countries(University of Dar es Salaam, 2007) Anatory, JustinianThe provision of the various broadband communications services in developed countries is usually not a very big problem since a number of options are available ranging from wireless technology, wire line networks. Recently many authors have studied the technology viable for communication in developing countries environment such as non- urban areas, municipality and low density in different environment, by reflecting the already available wireless technology adopted in some of urban areas and developed countries. Technologies, which have realized to be the candidates for communications in such areas, are VSAT/Satellite systems which at least can provide broadband services in different remote areas and municipality. But the indications in various developing countries like Tanzania show that the implementation of such technologies for a true broadband accessibility and at affordable price is still a problem. It has been proposed that to be able to have connections different initiatives are needed. There is one technology which could be applicable to developing countries due to its penetrations and might provide the affordability for broadband services in most of developing countries. The technology is power-line networks. The applicability of Broadband Power-line Communication (BPLC) for communication has been reported in different areas of developed countries. Moreover, a lot of problems still impede the utilization of such infrastructure. This thesis is attempted to solve various problems whereby new Transfer function (TF) channel model and new model for current/voltage distribution are developed. In addition, by using the developed TF the channel capacity, the effects of channel load impedances, line length and branches, including ground to the stochastic channel attenuation for indoor, medium voltage, and low voltage are investigated. It has been observed that the channel capacity of broadband power-line network is minimum when the channel is terminated in characteristics impedances. In addition the position of notches are branched line lengths and load impedances dependant. Finally the ground return causes the high attenuation in the BPLC systems.Item Development of low flow prediction models for southern Africa(University of Dar es Salaam, 2002) Mngodo, Raymond JuliusHydrological Network does not cover all catchments in the Southern Africa region. There are many ungauged catchments that could have the potential for water resources development. A database was established for 638 river flow stations from 11 Southern Africa countries, covering an area of 6,929,826 km2. Spatial database consisting of river basins, gauged catchments, national boundaries; river; rainfall; potential evaporation; wetlands; and geology was established using ARC-INFO. The objective of this study was to develop low flow prediction models. The low flow index Q70 from flow duration curve was used to describe flow regime and map spatial variability of mean annual runoff, temporal variability of annual runoff, temporal variability of annual runoff and base flow contributions to river flow. About 25% of the rivers are ephemeral, 30% are intermittent and the remaining 45% are perennial rivers. Linear regression models were developed to predict Q70 for ungauged catchments in the nine primary basins of Southern Africa using catchment area, MAR, AAR, BFI and their GIS coverage’s. The BFI has a strong influence in estimation of Q70. For Tanzania, a non-linear regression equation was obtained by including geology indices. Eight homogeneous regions of 10-day annual minimum flows for Tanzania were delineated using a simple test based on the variability of at-site values of Cv: The L-moment ratio diagrams and the goodness of fit test of Hosking and Wallis are used to assess the suitability of selected distributions as regional parent distributions. The LLG distribution provides a good fit to low flows in one region while the LN distribution fits well in seven regions. The GEV-4 and non-parametric kernel estimation models were explored as other possible methods of low flow analysis. The GEV-4 models and the NKE when compared with Weibull models for its predictive and descriptive ability tests showed better results.Item Development of a model for optimising the variations on forecasted construction cash flows: the case of building projects in Dar es Salaam – Tanzania(University of Dar es Salaam, 2018) Malekela, Kimata NewmanThe contingency sum is provided as the ceiling amount for absorbing variations that may occur on planned budget during execution of construction projects. However, there have been significant variations on forecasted construction cash flows which exceed the contingency sum provided. This study is therefore aimed to develop a model for optimising the total variations on overall forecasted construction cash flows within the contingency sum provided during execution of building projects in Tanzania. Specifically, this model is used to minimise those variations within the contingency sum provided in building projects. Data were collected through questionnaire from 284 building contractors in Dar es Salaam. In addition, documentary review of historical data from contract documents of 40 recently completed building projects was conducted and supported by interviews to project participants and self-auditing to contract documents. Eight major risk factors were identified, but the leading four risk factors with their overall relative contributions in causing variations are unclarity of clients’ requirements (0.249); errors in project documents (Bills of Quantities) (0.187); consultants’ lack of experience and technical skills (0.131); and poor/incomplete design (0.130). The study concludes that the model of this study can minimise more than 60% of total variations planned to occur in execution of building projects. It is therefore recommended that the model solutions should be used in establishing the proactive risk measures for controlling variations caused by risk factors on forecasted construction cash flows of building projects.Item Investigation of performance characteristics of multi-phase thermal pump(University of Dar es Salaam, 2004) Chami, Francis AugustineA multi-phase thermal pump has been investigated. Basically the pump is a metal tube, which on one end has separate water and steam inlets and a water outlet on the other end. Non-return valves are employed on all inlets and outlet. Experimental methods coupled with mathematical modeling were done. The results indicated that the discharge head of the pump increased linearly with steam pressure. The temperature of the inlet water influenced significantly the volumetric discharge rate. The discharge rate increased with steam pressure to a maxima and decreased thereafter, for a given inlet water temperature. Except for very low steam pressures, the discharge volume per stroke of the pump was found to be higher than the volume of the smaller cylinder, an observation that did not support the sudden expansion theory of operation of the pump with two cylinders. Further investigations of the pump to establish operating characteristics for steam gauge pressure between 0.05 and 0.5 bar indicated the existence of substantial suction head and a maximum developed head was measured. Entry and exit losses accounts were made of the developed head. The process of pumping was found to be a sensitive one and highly dependent on heat transfer from the steam. Both heat loss through the pump walls and to the water being pumped contributed in creating conditions for condensation and this in turn initiated the filling of the pump with water ready for another pumping stroke. Experiments were conducted to find the influence of operating parameters on the performance of the pump, with the focus on the optimum parameters for a given condition. Observation of the results revealed that pump diameter did not have significant influence on the flow rate. It was also observed that each pump has at least one common cycle time where different discharge heads produced the same flow rate. Modeling of the pump has revealed the existence of dimensionless parameters that influence the operation of the pump. These are Reynold’s, Prandtl’s dimensionless numbers and length to diameter ratio of the pump. Conditions necessary for the reversal of the pump caused by the involved forces have been established. A novel idea has been worked out on the application of the multi-phase thermal pump in refrigeration system. This idea has introduced a new refrigeration system to the refrigeration industry, which involved a principle different from that of conventional refrigeration systems. A coefficient of performance (COP) of 8.3 and the overall heat energy balance of the system has been calculated and a working model has been produced. Recommendations are made for more efforts to be directed in the application of the pump in the refrigeration industry using different environmentally friendly refrigerants and improving the system.