Browsing by Author "Kra, E.Y."
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Item Mathematical modeling of open-channel velocity profiles for float method calibration(Agricultural Water Management, 2004-12) Kra, E.Y.; Merkley, G.P.A computational method based on mathematical modeling of steady-state hydraulics is described for improving the accuracy of the float method for estimating open-channel discharge. Both two-dimensional (2-D) and three-dimensional (3-D) velocity distribution model versions were developed for steady-state uniform flow in open channels with rectangular cross-sections. The normal depth of flow was obtained by solving the Chézy equation for uniform flow conditions. Cross-sectional velocity distributions were calculated by solving the Reynolds-averaged Navier-Stokes (RANS) equations and an algebraic model for turbulent stresses, without the use of wall proximity corrections to the pressure strain term. The calculated 3-D velocity coefficients were found to be in the same range as previously published United States Bureau of Reclamation (USBR) coefficients, but the results also indicate that the USBR coefficients, which are based solely on average water depth, can be improved by taking into account other hydraulic parameters such as longitudinal bed slope, channel base width, and wall roughness. The mathematical model exhibited considerable sensitivity to initial conditions, boundary condition parameters, and numerical convergence criteria, also manifesting spikes in the calculated surface velocity coefficients for discrete changes in hydraulic parameters. Finally, it was found that the 2-D version of the model is not appropriate for calculating surface velocity coefficients because it does not account for secondary flow in the channel cross-section, and the calculated surface velocity in the center of the cross-section is overestimated. © 2004 Elsevier B.V. All rights reserved.Item Postharvest losses of tomatoes in transit(AMA, Agricultural Mechanization in Asia, Africa and Latin America, 2006-03) Bani, R.J.; Josiah, M.N.; Kra, E.Y.Tomatoes are highly perishable and very susceptible to mechanical damage with poor handling and transportation. This study was conducted with the primary objective of establishing the current practices of handling and transportation of tomatoes from a main producing area, Bolgatanga, in the Upper East Region of Ghana, to a main marketing center, Accra, 815 kilometers away. The primary method was to interview the producers, tomato merchants and sellers in the market with the help of a prepared questionnaire. Observations were made on the journey from Bolgatanga to Accra. An assessment of losses along the route was found to be 20%.Item Prediction of surface area of garden egg (Solanum Aethiopicum L) from weight measurements(AMA, Agricultural Mechanization in Asia, Africa and Latin America, 2009-09) Bani, R.J.; Kra, E.Y.; Amoah, J.; Aggey, M.Estimation of surface area of various agricultural produce can have a wide range of applications for both producers and processors. The methods available are tedious and in certain cases destructives Studies have been conducted with respect to predicting the surface area of some fruits and vegetables such as apples and tomatoes. Very few, if any, similar attempts have been made to estimate the surface area of indigenous African crops. The objective of this study was to develop a model that will predict the surface area of the garden egg (Solanum aethiopicum L) from weight measurements. It is easier to measure the weight of the garden egg than to measure its surface area. Weight and surface area measurements of each garden egg were used to develop equations to predict fruit surface area (cm2) from the raw weight. The linearregression model developed showed strong correlation between surface area and weight measurement and can be used to estimate the surface area of garden egg. For a garden egg weighting 47.4 gm, the model predicts its surface area between 96.3 and 118.5 mm2 with 95 % confidence.