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VOLTAGE CONTROL OF A DC-DC BUCK CONVERTER FOR ELECTROLYSIS USING FRACTIONAL ORDER SLIDING MODE CONTROL
(Hawassa University, 2020-10-22) DEMOZ LISANEWORK WELDETSADIK
Switching DC-DC converters are non-linear and the most widely used circuits in power
electronics. Generally, they are used in all conditions where there is need of stabilizing a
given DC voltage to a desired value. DC-DC buck converters are used in voltage step down applications. A DC solar energy is converted to the desired voltage level using the a
buck converter, for hydrogen generation with electrolysis process have been investigated.
The electrolysis load for hydrogen production especially needs low voltage and high
currents. To have these conditions the converter must be designed and controlled
sensitively. For this aim, the fractional order sliding mode (FOSM) controller is used as a
solution in this paper.
Simulation results showed that, FOSM controller improved the rise time and settling time
by 2% and 15.3% respectively compared the values using PID controller. Similarly, FOSM
controller shows comparatively best performance improvement over SOSM in terms of
high reduction of unwanted oscillation in addition to the rise time, settling time
improvements. The overshoot is reduced from 46.3% to 5.208% using PID controller while
it is totally removed when SOSM and FOSM controllers are applied. Both SOSM and
FOSM controllers overcome the effect of electrolysis load variations. The actual output
voltage is not deviated from desired value even for large input voltage variation using
FOSM controller. Furthermore, the performance of controller was tested by increasing
and decreasing 58.52% electrolysis load from operating point while desired output voltage
is decreased by 50% and increased up to 20% from operating point. Generally, from the
above analysis results it is evident enough that FOSM is better and preferable controller
than the SOSM and PID controller
IMPROVING COMPETITIVENESS OF SMALL AND MEDIUM MANUFACTURING ENTERPRISES THROUGH SUPPLY CHAIN MANAGEMENT: A CASE OF LEATHER PRODUCTS MANUFACTURING ENTERPRISE IN HAWASSA CITY
(Hawassa University, 2021-10-22) TAMIRAT YOHANNES GONDALO
Small and medium leather products manufacturing enterprises are one of the enterprises
provides expectation for the government to achieve target as one of the competitive sector in
current market for economic growth, employment generation and building an industrial
economy. In the different the enterprises has recorded very stagnant level of competitiveness
with dynamic current market cause of gap on practicing supply chain managements. In order
to conduct this research, questionnaire was developed and distributed for 132 respondents in
eleven leather products manufacturing enterprises those work on different department and
level. All the questionnaires were collected by using schedule data collection method; beside
the questioner interview and detail observation also conducted with experts to supports the
findings from the questionnaire. Then the collected data was analyzed using IBM SPSS 26; in
both descriptive and inferential statics. Regarding the descriptive statistic and inferential
statistics results the finding shows; the current supply chain management practice level of the
leather products manufacturing enterprise is medium, this indicate its influence on their
competitiveness. Regarding the correlation, all the independent variables are positively and
significantly correlated with dependent variable with a significant level of less than 1%. As
per the regression analysis output result the coefficients of four predictor variables are
statistically significant at less than one percent (P<.001). Therefore, the purpose of this study
is to propose ways to improve the competitiveness of small and medium leather products
manufacturing enterprises through Supply Chain management and applying competitive
priority on operation. Finally the study proposed adoptable SCM framework and
recommended the manufacturing enterprises are using supply chain management practices
and applying competitive priority to customer value and need with the proper support and
guidance of governments in order to improve their competitiveness
APPLICATION OF HYBRID APPROACH FOR WOLAITA LANGUAGE PART OF SPEECH TAGGING
(Hawassa University, 2020-03-24) BIRHANESH FIKRE SHIRKO
The aim of this research is to develop part-of-speech tagger for Wolaita Language using hybrid
approach. Part of speech tagger is one of the subtasks in natural language processing (NLP)
applications which is vital for other NLP tasks, like parser, machine translator, speech recognizer
and search engines. It is a process of labeling a corresponding part of speech (PoS) tag for a
word that defines how the word is used in a sentence. The PoS tagging for Wolaita language is
not sufficient yet to be used as one important component in other natural language processing
(NLP) applications. In this thesis, the development of part of speech tagger using hybrid
approach that combines HMM and transformation based learning approaches is conducted for
Wolaita language. In general, HMM model needs large data to increase the performance and the
transformation based learning model learn rule based on the language features. The HMM
model tags the words based on the optimal path for a given sequence of words and
transformation based learning is a rule based model that tag the words based on rules; it learns
rule directly from the training corpus without expert knowledge. The developed hybrid approach
of Wolaita language PoS tagger uses HMM tagger as initial annotators and the rule based tagger
as a corrector based on fixed threshold values. For implementation and experiment, the author
used python programming and NLTK. For training and testing the model, 14,358 untagged
Wolaita language words are collected from three different categories (Bible, Social media in
Wolaita language (Wogetta FM 96.6) and Wolaita language department). The annotation of
corpus performed manually by two language experts. For tagging purpose 26 PoS tag are
identified based on the work of Berhanu H., work of wakasa (2008) and with help of language
experts. From the entire corpus, 90% is used for training and the remaining 10% is used for
testing purpose. The performance of the three taggers is tested by using different experiments.
After experiment the researcher found that the performance of HMM, rule based and hybrid
taggers shows 88.14%, 92.96% and 94.82% respectively. Generally, hybrid approach showed
the better performance to assigning part of speech tag for Wolaita language sentences
EVALUATING THE PERFORMANCE OF HEC-HMS AND SWAT HYDROLOGICAL MODELS IN SIMULATING THE RAINFALL RUNOFF PROCESS FOR DATA SCARCE REGION OF ETHIOPIAN RIFT VALLEY LAKE BASIN
(Hawassa University, 2020-10-23) MOHAMMEDRESHID ABDALA ALIYE
Several physically-based and distributed watershed models have been developed to model the
hydrology of the watershed. For a specific watershed, selecting the most suitable hydrological
model is necessary to obtain good simulated results. In this study, two hydrologic models, Soil
and Water Assessment Tool (SWAT) and Hydrological Engineering Centre–Hydrologic
Modeling System (HEC-HMS), were applied to simulate streamflow in the Katar river basin,
Ethiopia. The performances of these two models were compared to select the right model for the
study basin. Both models were calibrated and validated with streamflow data of 11 years (1990-
2000) and 7years (2001-2007) respectively. Nash-Sutcliffe Error (NSE) and Coefficient of
Determination (R2
) were used to evaluate the efficiency of the models. The results of calibration
and validation indicated that, for river basin Katar, both models could simulate fairly well the
streamflow. SWAT gave the model performance with the R2 > 0.78 and NSE > 0.67; and the
HEC-HMS model provided the model performance with the R2
> 0.87 and NSE > 0.73. Hence,
the simulated streamflow given by the HEC-HMS model is more satisfactory than that provided
by the SWAT model
PERFORMANCE OF HOLLOW CONCRETE BLOCKS WITH CRUSHED WASTE GLASS AS PARTIAL REPLACEMENT OF FINE AGGREGATE
(Hawassa University, 2020-10-23) YOSEF KUMA AYANA
Construction is booming in developing countries like Ethiopia. As construction is increasing,
demand and price of the construction materials are increasing. Among building construction
components hollow concrete block is being widely used. From concrete block making
materials fine aggregate is higher constituent. The uses of river sand as fine aggregate leads
to exploitation of natural resources and also environmental concerns related to the disposal
of various waste materials have escalated to a worrying level, among those: crushed wastes
glass is one of them. Therefore, to make the construction industry sustainable, the use of
waste materials in place of natural resources is one of the recommended. The main objectives
of this study was to investigate the performance of class C hollow concrete blocks with
crushed waste glass as partial replacement of fine aggregate and to determine the
replacement percentages at which crushed waste glass can be effectively put into service and
also compare the cost of crushed waste glass partially replaced in hollow concrete block
with the conventional ones. The method used was experimental study. The crushed waste
glass partial replaced fine aggregate with 10%, 20% and 30% by volume and the control
mix was prepared. The compressive strength test was carried out at the 7th, 14th and 28th
days, whereas the density and water absorption tests were carried out on the 28th day. As
per the finding, the control mix compared with the replacement specimen, the density is
decreased as the proportion of crushed waste glass increases and decreases by 5.6% at a
30% replacement, the water absorption decreases as crushed waste glass content increases
and it decreased by 2.5% at a 30% replacement, the compressive strength with up to 20%
replacement increases by 59.72%, but after that, it starts decreasing for 30% replacement
by 10.64%, results showed that replacement of 20% fine aggregate by crushed waste glass
was found to have optimal compressive strength, and also the production of block using 20%
crushed waste glass saves cost compared to the conventional once by 2.06% in 1m2
area.