Browse
Recent Submissions
Now showing 1 - 5 of 49
- ItemConvergence Analysis of Massive MIMO Antenna Arrays Using a Geometry-Based Stochastic Channel Model(KNUST, 2019-10) Patrick DanourIn order to reap the full benefits of massive MIMO, the Base Station (BS) antennas must be significantly large to converge to favorable propagation condition or attain convergence (the state where the effect of noise and fast fading vanishes). However, increasing BS antennas results in closely spaced antenna elements which inadvertently leads to the detrimental effects of Spatial Correlation (SC) and that can affect the convergence of Massive MIMO System. So far, research works on Convergence have been investigated using Correlation-based Stochastic (CBSCM) channel models, which does not reflect accurate massive MIMO channel. This channel model does not take into consideration channel parameters such as the Pathloss, power delay profile as well as the characteristics of the antenna array needed for the practical massive MIMO system implementation. Therefore analysis of massive MIMO convergence regarding the Geometry-Based Stochastic Channel model (GBSCM), which reflects real practical massive MIMO channel and the effects of SC is needed. In this thesis, the convergence of massive MIMO based on GBSCM is studied. The effect of 3D SC of uniform rectangular and cylindrical array (URA and CA) based on the Maximum Power of Arrival (MPA) is incorporated. In the analysis, the Diagonal Dominance and Mean Absolute Deviation convergence metrics, were considered to study the effects of the SC on the asymptotic behavior of the channel matrix. The results support existing development that, increase in azimuth and elevation spreads of the angular distributions of arrival and antenna element spacing reduces the SC and thereby increases convergence rate of massive MIMO. Results also show poor performance for the Laplacian and Von Misses distributions in GBSCM, even for higher AS and ES, and angular spreads. Further it was realized that, in GBSCM, the convergence of massive MIMO was sensitive to antenna array topology regarding Gaussian and Student’s t-distributions. This contradicts previously established results that convergence is insensitive to antenna topology in CBSCM.
- ItemImpact Of Mining On Vegetation Cover: A Case Study Of Prestea Huni-Valley Municipality(KNUST, 2019-11) Nathaniel BineyABSTRACT Land use and land cover (LULC) change, also known as land cover change is a general term for the human and physical modification of the earth’s terrestrial surface. LULC changes are the direct and indirect consequences of human actions to secure essential resources for a successful livelihood. It has therefore become very necessary to analyze such changes for the effective management of natural resources and the protection of our environment to ensure its continuous existence and usage. Anthropogenic factors such as urbanization, mining and population increase in the Prestea Huni-Valley Municipality are causing rapid changes to LULC. These factors and others are putting a lot of pressure on the forest vegetation and this has dire consequences on the availability and protection of the vegetative cover. In view of this, the study focused on assessing the impact of mining on vegetation cover with particular focus on Prestea Huni-Valley Municipality. Multi-spectral satellite images of the study area from 1986 to 2016 were spatially analyzed to identify the LULC change patterns. Modelling and analysis of these images were performed using Erdas Imagine Software and R. Six LULC classes were identified including: forest, open vegetation, cultivated areas, bare lands, built-up and mine sites. The results showed that during the period under study (1986-2016) there have been losses in forest, cultivated land and open vegetation while bare lands, built-up and mine sites have seen substantial increases. Also, an annual rate of change of 5% was realized within the 30-year period under study.
- ItemEvaluation Of The Thermal Performance Of Walls Using Time Lag And Decrement Factor(KNUST, 2019-04) Kojo Adom QuagraineABSTRACT This study dealt with the evaluation of the thermal performance of walls in the climatic area of Kumasi using the parameters time lag and decrement factor. A numerical model was developed using the finite volume method with implicit formulation for four different wall configurations used in building constructions in Kumasi. The wall configurations had the same thickness and consisted of the mass concrete block wall, hollow concrete wall, mud brick wall and sandrete block wall. The simulation was carried in the month of March and August which respectively have the highest and lowest global solar radiation and dry bulb air temperature using mathcad software tool. The results showed that the heat gain by the walls through irradiation and ambient temperature in the area had some impact on the time lag and the decrement factor of the wall. The time lag values for the hollow concrete wall, mud wall and sandcrete had high values in March when the level of global solar radiation and outside dry bub temperature was high and reduced by an hour in August when the levels were low. The highest time lag was achieved by the mud brick wall which had five hours in the month of March. This was followed by the mass concrete wall which had time lag value of four hours for both months. The lowest decrement factor value was also given by the mud brick wall in the month of March whiles the lowest decrement factor in the month of August was given by the sandcrete block wall which also followed the mud brick wall closely in March. The numerical model was verified with analytical solution. The study is important in determining heat storage capabilities and temperature fluctuation reduction in wall configurations used in the West African tropical savannah climatic area.
- ItemPerformance Evaluation Of A Crossflow Column Drying System With A Biomass Burner Heat Source(KNUST, 2019-06) George Obeng,AkrofiGrain drying is an important unit operation due to the vital role it plays in reducing grain loss and improving storability of grains. It is therefore, necessary to provide drying options which can easily be adopted by small-scale farmers in Ghana and other parts of sub-Saharan Africa. In view of that, this study assessed the technical and economic performance of a 500 kg capacity crossflow column dryer with a biomass burner heat source. The study applied the method of Analytical Hierarchy Process in the selection of an appropriate biomass burner which was incorporated into the drying system. System Thinking Approach was adopted in the development of a mathematical model to simulate the performance of the biomass burner. The model was validated with experimental results, which revealed an under prediction of burner efficiency by 4.06 %. 250 kg of maize at an initial moisture content of 22.30 % was used to assess the complete drying system and, its economic viability was appraised using Net Present Value (NPV), Internal Rate of Return (IRR), Payback Period (PBP) and Benefit Cost Ratio (BCR). The results of the study showed that per every 0.1 m increase in the length of heat exchanger, burner efficiency would have the capability to be increased by 20.4 % ± 1.34. Per the operating conditions presented in the study, drying rate and drying efficiency of 1.81 % and 64.65 % were achieved, respectively. The economic performance of the drying system also showed that for an operation period of 10 years, which represents the lifespan of the column dryer, NPV, IRR, PBP and BCR of GH¢ 8,094, 67 %, 1.48 yrs and 2.55 are anticipated to be achieved, respectively. From the results of the study, it can be inferred that the drying system could be adopted as a viable drying option by smallholder maize farmers in farming communities in Ghana.
- ItemAssessment Of Risk Priority Number Of 2.5 Mw Polycrystalline Silicon Photovoltaic Power Plant At Navrongo, Ghana In Sub-Sahara Africa.(KNUST, 2019-04) ALHASSAN SULLAIMANUnderstanding failures of photovoltaic (PV) modules is one key factor in enhancing the reliability and service lifetime of PV modules; and hence reducing the cost of PV systems and financial implications on investment. This study seeks to identify the field failures associated with installed PV modules in the Ghanaian climatic condition, which minimize the performance of modules, and pose reliability issues to the solar plants as well as financial implications to manufacturers and investors in the PV sector. Physical examination of the modules using visual inspection checklist and their corresponding electrical performance parameters (I-V characteristics) measurement using multimeter and I-V tracer were performed on two models of the five (5) year old 2.5 MW PV power plant at Navrongo. A MatLab program was used to evaluate the failures and degradation modes of 144 Polycrystalline silicon (Poly-Si) framed modules under the hot dry climate of Navrongo. The program is a statistical reliability tool that uses Risk Priority Number (RPN) to determine the dominant failures by means of ranking and prioritizing the failure modes. The visual inspection revealed front glass slightly soiled, junction box lid fell off, cell interconnect discoloration and backsheet crack between cells as the peculiar failure issues either affecting the performance of the modules and/ or posing safety concern to personnel and properties on site. Mean degradation rates of 1.11%/year and 1.23%/year were respectively computed for Model A (Jinko solar) and Model B (Suntech technologies) types of modules for the power plant studied. These degradation rates values are beyond the standard warranty limit of 1.0%/year reported in literature. In addition, short circuit current (Isc) and fill factor (FF) were determined as the dominant I-V parameters affecting the power degradation rates of the Model A and Model B modules respectively. The study also determined the total Global RPN value of 606 for the Model A type of modules for this plant, whereas that for Model B is 583. These RPN values fall within the reported values ranging from 500 to 755 in literature. With this information, investors can have an insight on the worth of a PV Plant and viability of their investment before making a decision. From this study, it can be concluded that, the five years old PV plant in operation is not performing very well and needs urgent attention to avoid loss based on the degradation rates of the fielded modules.