African
Journals On-line
Botswana Journal of Technology
Volume
12, Number 1, 2003
ABSTRACTS
Steady magnetohydrodynamic radiating flow
past a vertical porous plate
A
Ogulu and G Tay
Fluid
motion generated by a vertical porous hot plate in the presence of a transverse
magnetic field is studied when the viscous and ohmic dissipations are
significant. Approximate solutions to the coupled non-linear equations
governing the steady velocity, temperature, skin friction and rate of heat
transfer are obtained invoking a perturbative series expansion in terms of the
Eckert number Ec, since the Eckert, number Ec for all
incompressible flows is small. We notice that the rate of heat transfer between
the plate and the fluid is constant irrespective of the value of the magnetic
parameter, Bo, but increases with decreasing values of the Prandtl
number Pr. Our results show that the shear stress distribution is
higher for strongly Newtonian fluids such as Mercury with Pr =
0.025, than it is for a non-Newtonian fluid such as air with Pr =
0.71. The study confirms that for this type of flow the temperature
distribution decreases with increase in the radiation parameter. It is further
shown in this study that increased heating of the plate results in an increase
in the shear stress and vice versa.
Computation of loss allocation in electric power
networks using loss vector
Andrew Obok Opok
This paper presents the
computation of loss allocation that can be applied to sellers and buyers
participating in electric power trade in a deregulated power market. The
approach is based on the Jacobian and Hessian matrices of the power flow
equations. The losses to be allocated are derived from load flow of a specified
power network and operating conditions. Loss vectors associated with demand and
generation buses of the network are defined and derived and how they are
applied in allocating losses to the nodes are demonstrated using an example
three node network. An algorithm for the loss allocation associated with the
example network is implemented using matlab programming platform. The proposed
method is suitable for a application in a deregulated power market where market
participants can arrange to cover for the cost of losses. The method contrasts
with approach used in the underegulated electric power system where losses are
accounted for by penalizing the generators using penalty factor approach.
Effect of firing on colour of clayey
materials applied to traditional ceramics
G.E.
Ekosse, A.Mulaba-Bafibiandi, J.S. Nkoma
Increasing demand for use of clayey material in the
traditional ceramic industry whereby clayey materials are fired at < 1300 oC,
motivated this work, which focused on understanding the effect of firing on
colour of clayey materials from Botswana, Mozambique, Pakistan, Senegal and the
United States of America (USA). The colours of raw, fired, chemically bleached
and magnetically separated clay samples were observed as one of the determining
criterion for their suitability for use in the ceramics industry. Except for
one sample obtained from South Africa, all the other samples of clayey
materials were found to be suitable for the fabrication of fine and coarse
ceramic products. However, other indicative tests such as particle size
determination, mineralogical and chemical compositions, clay shrinkage as well
as clay plasticity should be performed before a final decision on the use of
the clayey material is reached at.
Groundwater
management by using mathematical modeling: case of the Makutupora groundwater
basin in dodoma Tanzania
J. J. Kashaigili, D. A. Mashauri, G. Abdo
The
ever-growing dependency on groundwater sources for both agriculture and
domestic water uses has called for studies to ensure aquifer sustainability.
The computer code Visual MODFLOW was employed in the study. The study intended
at developing a groundwater management model for Makutupora groundwater basin
through mathematical modeling. The model was calibrated using a set of observed
dynamic water levels, aquifer parameters until the best fit between the
observed and simulated heads was obtained. The model was then verified using
parameters that gave the least Root Mean Square Error (RMSE). The developed
model was then used to simulate the dynamic water table elevations for the next
twenty years under the different management scenarios and pumping policies from
the year 2000 to 2020. The model revealed that a pumping scenario that
considers a 10 % of rainfall as recharge could ensure aquifer sustainability
for the planned period.
A multiple buckling curve formulation for
design of aluminium alloy elements
M.A.Gizejowski,
A.M. Barszcz and K.M. Nikonowicz
The paper refers to the overall stability design of
aluminium structural elements. Buckling curves for members subjected to
compression and members subjected to bending are dealt with. The formulation is
based on probabilistic considerations of two random events, namely the elastic
buckling of a perfect member and the inelastic buckling load of a perfect
member initially stressed to the level s0 and then subjected to strain hardening with the hardening
modulus EH. This allowed for accounting the effect of gradual
yielding and hardening of the aluminium alloy material. For compression members
two curves d (n-h-t) and d (h-t) are proposed for flexural buckling mode and
another two c and b for buckling modes involving torsion. The buckling curves
of aluminium alloy columns conform the recent proposal of Rasmussen-Rondal
based on available experimental data. For members in bending two buckling
curves are proposed, namely a and a0. The model of present study is
compared with that of ENV 1999-1-1. The design buckling strengths from the
present study are found to be generally slightly more conservative than those
from ENV 1999-1-1, except in the range corresponding to stocky elements.
Improved design format for doubly symmetric
thin-walled structural steel beam-columns
J.O. Afolayan
An existing design format for doubly symmetric
cold-formed structural steel beam-columns was probabilistically assessed and
modified to offer a consistent reliability level. Using the First-Order
Reliability Method (FORM) and Value Analysis (VA) a target reliability level
for the current design format was established to be 4.265. The proposed format
is built on reduced load factors for imposed and dead loads as well as a
sectional resistance factor which is related to the slenderness parameter of
the structural element in place of the conventional single value.
Towards a systems approach to sustainable
developments
S.
Kutua, J. Mothibi
“Sustainable development”
as a concept was popularised by a 1987 report of the United Nations World
Commission on Environment and Development. The report defined sustainable
development as “development that meets the needs of the present without
compromising the ability of future generations to meet their own needs”.
However, from this definition, we cannot ascertain the central intuition of the
notion of sustainable development. Failure to do this makes it difficult to
derive methods that can be used to formulate effective intervention policies
that can enable nations to attain sustainable development. This paper briefly
reviews various schools of thought in popular literature on the notion of
sustainable development, exposes their weaknesses and develops a holistic
notion of sustainable development based on the systems approach.
Assessment of the natural radioactivity in
the coastal areas of Lagos, Nigeria
O. O.
Kuforiji, I. A. Babalola, I. R. Ajayi
The concentrations of natural radionuclides, namely 40K,
238U and 232Th, in the surface soils around the coastal
lands of Lagos, were measured using a highly sensitive γ-ray spectrometric
system coupled to a computerized ACCUSPEC multichannel analyzer system. 146
samples from 22 different locations were analyzed and the mean radioactivity
concentrations obtained were (0.2293 ± 0.0277), (0.0200 ± 0.0054) and (0.0524 ±
0.0042) KBqkg-1 for 40K, 238U and 232Th
respectively. The mean absorbed dose rate, the mean annual effective dose
equivalent and the collective effective dose equivalent for these coastal areas
were assessed to be (52.23 ± 0.124) nGyh-1, 64.055 µSvy-I
and 1.8468 x 102 man.Sv.y-1 respectively. Exposure to
these low doses, over a long period of time, can constitute health hazard,
especially inside dwellings where sand taken from these areas are used as
building materials.
Clients satisfaction with local design
consultancy practices in Gaza Strip
A.
Enshassi and Y. Al-Ghuraiz
The aim
of this paper is to investigate the degree of public clients satisfaction with
local consultancy practices in the Gaza strip. The paper deals with three types
of clients: Local Ministries, Municipalities and other organizations such as
Palestinian Water Authority, United Nation Development Program, and the
Palestinian Economic Council for Development and Reconstruction. Interviews
were conducted with twenty-one professionals who are working with public
clients and involved directly with local consultancy firms. The result shows
the average clients' satisfaction with local consultancy practices was 65.7
percent. This study reveals the reasons for satisfaction and dissatisfaction
for some issues related to clients' satisfaction with consultants' performance.
The study concludes with recommendations to improve the local design
consultancy firms efficiency and consequently to increase the level of clients'
satisfaction with consultancy practices.
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