Abstract: A new analytical solution for soil water two-dimensional movement to an orthogonal mesh of parallel drains is presented, as an extended case of the one-dimensional flow problem of the same nature. An equation is provided, that gives the profile of the water surface as well as the volume that has passed through the drains at a given time moment. Non-dimensional profiles of the piezometric surface are given for various values of time and space parameters. The water volume versus time derived from the respective equation is in very good accordance with the volume derived from surface profile integration. We also explore the possibility to solve this problem by using the fuzzy set approach, to cope with the uncertainties of the hydraulic parameters. Triangular fuzzy numbers are used to represent the hydraulic conductivity of the soil as well as the storativity of the aquifer. The drained water volume derived from the fuzzy set after defuzification, approaches the one calculated by the analytical solution, included in the interval of presumption level α = 0.8.
Abstract: In this research, the possibility of predicting potential evapotranspiration using fuzzy logic theory with temperature as input is studied. The fuzzy logic model is being trained using a series of temperature and evapotranspiration values. The results are being compared to measured values and with the ones obtained using the Blaney-Criddle method. The results show a high efficiency in calculating and predicting the potential evapotranspiration values.
Abstract: In the present paper, a statistical analysis of the experimental results of the hydrostatic force versus water depth is provided. The experiments were executed on a model setup in the Laboratory of Hydraulics in the Department of Civil Engineering of the Technical Educational Institute of Serres, Greece. The results of a total of 79 identical experiments are presented. Each experiment has concluded in a certain linear relation between depth and force. A statistical analysis was carried out, testing the hypothesis that the residuals of the experimental values from the respective theoretical parameter values are normally distributed. This hypothesis was found to be true at a level of significance of 0.1, leading to the conclusion that only random errors have occurred, thus excluding the systematic ones.
Abstract: Orifice flow is studied experimentally for solutions of flexible polymers. In the present second part, the elastic stresses are explored, of fluids that were well - characterized in shear in the first part of the article and after having clearly distinguished the concentration ranges with regard to the overlapping of the chains. Results are presented for solutions of polyethylene oxide (concentrations from 10 ppm to 10%) and for two international workshop fluids based on polyisobutylene in organic solvents, the M1 (2440 ppm polymer) and Al (2% polymer) fluids.
The flow regimes observed for the dilute solutions are the ones observed by Cartalos and Piau and predicted by their model where each regime is interpreted in terms of distinct molecular effects governing tensile stress growth. For semi-dilute non-entangled solutions (1000ppm<c<1% for polyethylene oxide and the M1 fluid), a further scaling is observed here, which is also predicted by the same model. In the intermediate regime pressure drop varies as the fourth power of the flow rate, due to hydrodynamic interaction stresses that become dominant over elastic stresses as molecules unravel.
For entangled solutions (4% and 10% of PEO and the A1), a single smoother scaling is observed at stable flow. Extensional effects become less pronounced. This is attributed to the fact that entanglements limit both the rate and the extent of molecular deformation. For the pure PEO polymer, the flow curve has the form already found with other polymer melts.
The stability of the flow is also examined. The onset of small scale instabilities is observed at relatively low flow regimes for concentrated solutions. 3D unstable flow characterizes the high flow regimes. A non-dimensional representation where pressure drop is reduced by the one for an inelastic fluid and plotted as a function of the ratio of extensional to shear stress on the orifice plane, makes data collapse on a single curve for concentrated solutions.
Abstract: The orifice flow of scleroglucan solutions is studied. Under given conditions, this molecule behaves as a semi-rigid rod in solutions. Solutions in glucose-water syrups were examined, which show considerable vortex growth in orifice flow depending on flow regime and concentration. The vortex reattachment length is studied as a function of regime and concentration. The flow curves in orifice flow are characterized by a linear pressure drop â flow rate relation. The extensional viscosity is derived from the orifice flow data by the Binding analysis. Comparison with the Batchelor analysis for closely spaced fibers is satisfactory if molecular extension as well as alignment along the streamlines is considered.
Abstract: The present article is concerned with the mechanical properties of aqueous and organic-solvent flexible polymer solutions. In this first part, the steady shear viscosity is of main interest, as well as its evolution with concentration and the exploration of rheological means of distinguishing the different concentration regimes. The second part that will follow, is concerned with the orifice flow of the same solutions, as a way to explore their behavior in flows with a high extensional component.
Results are presented for solutions of polyethylene oxide (PEO) in a sugar/ water mixture (concentrations from 10 ppm to 10%) for which concentration regimes were determined by shear rheometry, as well as for two international workshop fluids based on polyisobutylene in organic solvents, the M1 (2440 ppm polymer) and Al (2% polymer) fluids.
The shear viscosity was measured with rotative rheometers using both coaxial cylindersâ and cone-plate geometries. A master curve of the shear viscosity was found for solutions in the entanglement range, using the Graessley relaxation time. The sugar/water mixture was proven to be a good solvent for PEO as opposed to pure water. The examination of zero-shear viscosity versus reduced concentration allowed the definition of various concentration regimes. It was proven that the concentration covers the dilute and semi-dilute regimes. In the semi-dilute regime we defined the sub-regime where chain entanglements exist. For plain water solutions (from 1% to 5% polymer), entanglements were proven to exist in all examined concentrations.
Abstract: The present work is about the evaluation of the application of the optimization method called âtabu searchâ, to the optimization of an irrigation network, that is, to its cost of installation and functioning. Initially the most popular optimization methods were selected and classified. The tabu search method was selected to apply to an irrigation network. An algorithm was produced that seeks the best solution for a six-pipe network. The objective function was considered to be the sum of the cost of the yearly functioning of the network, plus the cost of the purchase and the positioning of the pipes reduced to an annual basis. The best solution was known beforehand, following an exhaustive search.
The results were very encouraging. After 50 runs, the best solution was found in a very large percentage of them, the rest resulting to a solution very close to the best one. Thus, the results suggest further application of the method to bigger networks.
Abstract: In this paper a new analytical solution for soil-water two-dimensional movement to an orthogonal mesh of parallel drains is presented, as an extended case of the one-dimensional flow problem of the same nature. An equation is provided, that gives the profile of the water surface as well as the volume that has passed through the drains at a given time. A simplified form of the equation is presented, which provides very good results, for time values higher than a certain level. Non-dimensional profiles of the piezometric surface are given for various values of time and space parameters. The water volume versus time derived from the respective equation accords well with the volume derived from surface profile integration.
