scholarly works
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Item Forced convection on isothermal plates and channels using diffusion velocity(2010-06) Petinrin, M. O.; Dare, A. A.; Oke, S. A.In many industrial applications, such as electronic systems, performance failure and breakdown usually occur due to poor thermal management, which could be adequately controlled through a proper understanding and management of the forced convection system and use of the vortex element method. The main contribution of this paper is that it shows how the vortex element method is capable of producing results similar to those reported in literature. The paper utilised vortex element method to model familiar problems in heat transfer, which is laminar flow over isothermal flat plate and isothermal two parallel-plate channels. Numerical models were developed using diffusion velocity method, a version of vortex element method, from vorticity transport equation and the energy equation for each of the cases. The velocity and temperature distributions, obtained for both plates and channels, were utilised to calculate Nusselt numbers with Reynolds numbers in the range of 20 to 120. The logarithmic plot of Nusselt number versus Reynolds number for forced convection on single horizontal plates yielded a slope of 0.46 and an intercept of -0.29 while that for forced convection in horizontal channels had a slope of 0.87 and an intercept of -0.88. The results obtained in this work show the diffusion velocity method to be a viable numerical tool for modelling fluid flow problems and also heat transfer problems.Item The application of fractal box dimensions in predicting the emission characteristics of colliding sawdust particles for sustainable sawmilling(CSIRO Publishing, 2012) Salau, T. A. O.; Oke, S. A."The prediction of emission characteristics of sawdust particles immediately after the cutting operation from the interaction of band saw's blade and plank is a growing research area. Still, a wide gap exists with respect to understanding the behaviour of sawdust particles as they collide with one another. Previous efforts have focused on non-collision states of sawdust particles. However, in real life, collision of particles must occur. With several particles colliding after the cutting operation. This paper establishes a new perspective of the fractal properties of sawdust particles in motion as a motivation to understanding how to control its toxicitv of effects on sawmill workers and maintain sustainable sawmilling activities. In particular, the possibility of predicting the fractal dimension of the randomly moving sawdust particles in sawmills that is generated as fractal curves using the combination of probabilities and theoretical fractal dimensions is investigated for the first time. Cases were established on the possible representations of the theory and practice. As an example, four cases were designed around varied number of fractal pattern combinations drawn out of five and fifty different probabilities combinations, ten different random number generating seed values and maximum of four fractal curves generation iterations as driven parameters. Preliminary study of the differences between theoretical fractal box dimension recorded a maximum absolute percentage error of 7.24% for fractal curve associated with fractal pattern five (i.e. Koch 5). In all the cases studied, average absolute percentage error decreases between 3.52 ± 1.18 and 1.51 ± 1.14 while the correlation coefficient (R2) decreases between 0.9315 and 0.7365 from case 1 to case 4, respectively. It is concluded that the model is a good predictor of sawdust particle emission at colliding states from cutting operation. This is reflected in the fact that the higher the number of fractal patterns (generators) in a study case, the smaller the correlation coefficient between average estimated fractal box dimension and predicted fractal dimension of the sawdust particles in motion in the sawmill. "Item The application of duffing's equation in predicting the emission characteristics of sawdust particles(2010-09) Salau, T. A. O.; Oke, S. A."Sawdust particles soon after emission from the cutting machine usually move dynamically with transformation in some dimensions. This paper models the sawdust particle motion as a two dimensional transformation system of continuous time series. Cost could be saved using this approach instead of utilizing dynamic systems that depend on time history Two dimensional graphical representation of continuous time series of Duffing's dynamic system for sawdust particles was investigated with emphasis placed on application to sawdust particle motion and the saw machines. Pr~liminary studies were made using the harmonic functions, F(t) = Cos(wt) and F(t) = Sin(wt), for their familiarity in both science and technology communities. The solution to Duffing's model equation for the sawdust particles was sought from displacement and velocity perspectives, using the Runge-Kutta Algorithm. Linear transformation that guarantees non-negative values of time series was implemented. This was followed by the respective computation of the x- and y-components of the resulting time series values of the sawdust movement using a 21tmodulated time measured in radians. The graphical representations of the x- and y-components compared well quantitatively and qualitatively with the corresponding phase plots. The feasibility of modelling sawdust dynamics as emission from band saws was therefore demonstrated here, in approaches that thus advance knowledge of sawdust emission studies. "Item Estimation of thermal contact resistance in metal-plastic interface of semiconducting electronic devices(2009) Oke, S. A.; Oyekunle, A. A.; Salau, T. A. O.; Adegbemile, A. A.; Lawal, K. O.For decade, thermal contact resistance (TCR) has been measured experimentally. Unfortunately, the database, which should regularly support decision-making on TCR coefficients, seems not to exist. Thus, companies result to using outdated or irrelevant data that limits lifespan of electronics devices, their performance and reliability. This paper mathematically models the problem of TCR between two media (plastic-metal interface) in semi conductors with reference to resistance and the flow of heat across or interface of two surfaces that are in contact, particularly in engineering applications. In this paper, a semiconductor/ heat sink assembly is used to model the behaviour of thermal contact resistance. A cylindrical shaped semi-conductor was conceptualised, with the governing differential equations derived and the boundary conditions for the problem stated. The effect of parameters such as surface roughness, contact pressure, density of interstitial gas, heat capacity, thermal and mechanical properties on the temperature at the center of the semiconductor was studied. From the analysis, it can be inferred that by effectively lowering thermal contact resistance, efficient heat transfer results, which helps to prolong the life and reliability of the semi-conductor. The current work is motivated to fill an important gap that may be beneficial to practitioners in the semi-conductor industry.Item Mathematical modelling of the traffic congestion problem at a University campus(2008-04) Oke, S. A.; Lofinmakin, O. O.; Salau, T. A. O.; Akanbi, O. G.; Ofiabulu, C. E."The traffic situation at many university campuses in developing countries has been a source of concern to both the school authority and the campus populace. This may be largely due to the increasing enrolment level for university admissions since most employers are certificate-biased instead of skill rewarding. The roads are often congested during the day thereby causing inconveniences to everyone. During the ""peak period"" when vehicular traffic is beyond what the road can contain conveniently, traffic jams occur, which accounts for a great amount of time wastage by commuters. This paper deals with the traffic congestion problem in a university in a developing country. The approach employs mathematical modeling to solve the problem. The principles of flow in fluid mechanics are interpreted at a macro level to the flow of traffic. The model describes the traffic situation, explains the causes and periods of congestion, and proffers a solution to the problem. "Item Fractal dynamics of a bouncing ball on a accelerating lift tabletop with both constrained to vertical motion(2008) Alabi, B.; Salau, T. A. O.; Oke, S. A."The bouncing ball problem has proved to be an important phenomenon in engineering applications involving vibro-transportation and vibratory feeder systems. In this paper, the dynamics of a bouncing ball falling consecutively on an accelerating lift tabletop is studied. Using simulation, it is established that the dynamic interaction of accelerating lift tabletop constrained to one-dimensional motion on which the ball is bouncing is fractal. The acceleration of the lift table top was varied gradually as a percentage of acceleration due to gravity over one thousand steps while the number of bounces-off made by the bouncing ball before the lift table top covered a fall distance of 10.000 m was recorded graphically. Similarly, every lift tabletop acceleration has the set of bounce-off height of the bouncing ball recorded graphically, and taken to be one third of height of fall. The number of bounce off drastically dropped to about zero when the acceleration of the lift tabletop was 40% of acceleration due to gravity. The graphical presentation of the ball bounce off height has normal distribution shape with fractal detail. This study showed that two objects, initially at different heights, falling under gravity, maintain separating heights for the period of their fall. The equation governing the dynamics of the bouncing ball and the lift tabletop are of quadratic type but the ball bounce off height graphical results contain fractal details. "Item Quantitative characterisation of an engineering write-up using random walk analysis(2008) Alabi', B.; Salau, T. A. O.; Oke, S. A."This contribution reports on the investigation of correlation properties in an English scientific text (engineering write-up) by means of a random walk. Though the idea to use a random walk to characterise correlations is not new (it was used e.g. in the genome analysis and in the analysis of texts), a random walk approach to the analysis of an English scientific text is still far from being exploited in its full strength as demonstrated in this paper. A method of high-dimensional embedding is proposed. Case examples were drawn arbitrarily from four engineering write-ups (Ph.D. synopsis) of three engineering departments in the Faculty of Technology, University of Ibadan, Nigeria. Thirteen additional analyses of non-engineering English texts were made and the results compared to the engineering English texts. Thus, a total of seventeen write-ups of eight Faculties and sixteen Departments of the University of Ibadan were considered. The characterising exponents which relate the average distance of random walkers away from a known starting position to the elapsed time steps were estimated for the seventeen cases according to the power law and in three different dimensional spaces. The average characteristic exponent obtained for the seventeen cases and over three different dimensional spaces studied was 1.42 to 2-decimal with a minimum and a maximum coefficient of determination (R2) of 0.9495 and 0.9994 respectively. This is found to be 284% of the average characterising exponent value (0.5), as supported by the literature for random walkers based on the pseudo-random number generator. The average characteristic exponent obtained for the four cases that were engineering-based and over the three different dimensional studied spaces was 1.41 to 2-decimal (closer by 99.3% to 1.42) with a muumum and a maximum coefficient of determination (R2) of 0.9507 and 0.9974 respectively. This is found to be 282% of the average characterising exponent value (0.5), as supported by the literature for random walkers based on the pseudo-random number generator. In .view of the range of the average characterising exponent across Faculties and the closeness of the average characterising exponent in the engineering-based cases in particular, it can be concluded that the engineering writing is strongly correlated. This study recommends that a very high characterising exponent value (e.g 1.42) is a mark of a very good engineering write-up. "Item Analysis of traffic inflow to a university campus in a developing country:a rescale range approach(2007-10) Alabi, B.; Salau, T. A. O.; Oke, S. A."All over the world, there is an increasing enrolment level for university admissions in view of the ever-increasing benefits of earning university degrees. Thus, the high population of students in many universities, coupled with a high number of vehicles has made traffic control a challenge to University traffic managers. In this paper, the method of Resca1e Range Analysis (RRA) was used to estimate the Hurst Exponent Value (HEV) for the traffic inflow through the main entrance gate of a university as a control measure. Data from a university in the developing countries was collected and analysed. The number of vehicles that entered consecutively per five minutes was observed between 07:00 and 19:00 over a 144 count and 17 independent cases constructed between adjacent cases. Rescale Range Algorithm platform is then used for the data, and coded in FORTRAN Language. With a case made up of 128 consecutive five-minute dependent traffic inflow records, a total of 3348 vehicles entered the university community within the studied period while the average number of vehicles inflow per hour was 279. Average number of vehicles that entered per five minutes was 24. No vehicle entered between 13:25 and 13:30. For all cases, the estimated HEV range between 0.5742 and 0.6955. The computed average HEV was 0.6303, the coefficient of fitness (R2) for all cases range between 0.9552 and 0.9787, while the computed average value was 0.9680. The HEV greater than 0.5 estimated for all cases is an indication of positive con-elation called Persistent. It expresses the fact that there are extended periods in which the traffic inflow to the university community deviated from the long term mean. This information is useful for vehicle garage design. For reliable estimates of the average HEV for design purposes, the study period should be extended to a whole week or an academic session. "Item Application of neurofuzzy in the develoment of road bump designs(2007-05) Oke, S. A.; Johnson, A. O,; Salau, T. A. O.; Adeyefa, A. O."This contribution is on the development of a neurofuzzy model that aids in capturing imprecision and uncertainty in the. various road bump parameters. Road bumps are structures built on roads to act as obstructions to vehicles plying these roads. The neurofuzzy methodology is used to check the vehicle speeds to acceptable standards. Particular use is made of neurofuzzy since it is an improvement on the traditional model proposed earlier in the literature. The work is motivated by the need for a more reliable and easily understandable methodology that guides decision makers in making correct decisions in a timely manner The results obtained demonstrate that it is feasible to apply the model in practice. The paper is new in that it proposes a novel approach to quantifying the results of road bump design in order to achieve worthy and reliable result. "Item Surface finish quality characterisation of machined workpieces using fractal analysis(2007) Alabi, B.; Salau, T. A. O.; Oke, S. A."A new method on machined surface finish quality characterization using fractal analysis is proposed. This seems to be an improvement on Olaosebikan's spectral analysis index method for surface finish assessment. Mathematical model based on disk count-Monte Carlo approach is developed' and tested with simulated results from computer programme written in Fortran. Test cases Involve five-finished machine surfaces (work pieces) that are ranked based on fractal dimensions obtained for the respective machined surface spectral trace. The work pieces, made using different machining operations (milling, grinding, etc.), have their quality of finishing described as a function of the machine operation that! each work piece passes through. The respective spectral fractal dimensions of six fractal images (A, B, C, D, E and F) were then obtained. The conjecture is that the ranked results will agree with ranking obtained by both CLA and spectral index methods. Contrarily, the ranked results disagreed with both CLA and spectral trace results. The new method seems superior to both CLA and spectral trace approaches since a higher accuracy and much less computation time is observed. The maximum percentage relative absolute difference is 13.1 %, and the computation time is as short as 3 minutes. "