Characterization of aerodynamic performance of wind-lens turbine using high-fidelity CFD simulations

Wind-lens turbines (WLTs) exhibit the prospect of a higher output power and more suitability for urban areas in comparison to bare wind turbines. The wind-lens typically comprises a diffuser shroud coupled with a flange appended to the exit periphery of the shroud. Wind-lenses can boost the velocity of the incoming wind through the turbine rotor owing to the creation of a low-pressure zone downstream the flanged diffuser. In this paper, the aerodynamic performance of the wind-lens is computationally assessed using high-fidelity transient CFD simulations for shrouds with different profiles, aiming to assess the effect of change of some design parameters such as length, area ratio and flange height of the diffuser shroud on the power augmentation. The power coefficient (C_p) is calculated by solving the URANS equations with the aid of the SST k–ω model. Furthermore, comparisons with experimental data for validation are accomplished to prove that the proposed methodology could be able to precisely predict the aerodynamic behavior of the wind-lens turbine. The results affirm that wind-lens with cycloidal profile yield an augmentation of about 58% increase in power coefficient compared to bare wind turbine of the same rotor swept-area. It is also emphasized that diffusers (cycloid type) of small length could achieve a twice increase in power coefficient while maintaining large flange heights.     

A computational method for optimal control problems with a free final time using the modified quasilinearization and the gradient method†

This paper presents a computational method for the solution of a class of optimal control problems with a free final time. The method is based on the combination of the modified quasilinearization and the gradient method. A numerical example is included for illustration.     

Survey of the microbiological quality of the raw cow milk in the Tadla area of Morocco

Cow milk samples were collected during three periods and from four milk collection centres located in four different geographical zones. Samples were analysed for their standard plate count, enterococci, total coliform and feacal coliform, lactic acid bacteria, spoilage bacteria and some of the pathogenic bacteria. The most contaminated cooperatives were those located essentially in the irrigated zones. The less contaminated ones belong to semipublic farms. It seems that transportation, milking and pre‐storage conditions constitute the main basic relevant factors for heavy bacterial contamination. This is the first survey of the microbiological characteristics of raw milk produced in the Tadla area of Morocco.     

Non-linearity detection of weakly non-linear dynamic systems using cumulants

Non-linearity detection in dynamic systems is a fundamental issue in non-linear system identification. This problem is treated with the aid of the perturbation technique. A criterion for the detection of even non-linearities is developed in terms of the third-order cumulants of vector stochastic processes.     

Learning rates in the digital iterative learning control of linear multivariable plants

The learning rates achievable in the digital iterative learning control of linear multi-variable plants are investigated. It is shown that the irregularity and stability characteristics of the plants under control impose severe constraints on the achievable learning rates. These results are not only significant in their own right but also strongly motivate the introduction of compensators to increase the learning rates achievable in irregular plants. These general results are illustrated by the presentation of numerical results for the iterative learning digital control of an uncompensated fourth-order completely irregular plant with two inputs and two outputs     

ELECTROMAGNETIC TRANSIENTS ON COMPENSATED LINES UNDER CORONA

ABSTRACT

The purpose of this paper is to present a digital computational method for the determination of the fast electromagnetic transients propagating on compensated overhead power lines, evoked by internal or external over voltages, as effected by corona discharges. The approach enables the consideration of series capacitor and shunt reactor compensation. The line model is based on time-domain solution using the Runge-Kutta-Verner numerical technique to solve a set of simultaneous differential equations, whose number depends on the assumed number of line sections, as derived from the line equivalent circuit. The increase of the location-dependent conductor effective radius due to corona is considered as one of variable sets, using an iterative solution procedure. To avoid the parasitic Gibbs-oscillations due to the finite number of line sections (which are superimposed on the actual solutions, a set of properly chosen damping resistors is added to the line model, yielding a frequency-dependent damping. The simulation of the corona discharge uses a model derived from an experimentally measurable voltage-charge hysteresis loop relationship of a line test length. As far the input voltage stimuli are concerned, so the model can consider any voltage-time function (step, ramp, double-exponential, sine waves...etc), or even be in the form of tabulated numerical data. The validity of the model is checked by comparing its results to corresponding measurements.     

Storage stability of traditional Tunisian butter oil produced from spontaneous fermentation of cow's milk

Physicochemical characteristics of traditional Tunisian butter (TTB) and thermal stability of the butter oil were studied. Thermal stability of samples was estimated by using the accelerated shelf life testing method. Effect of heating on some quality characteristics of traditional Tunisian butter oil (TTBO) was investigated and compared at different temperatures (60°C, 100°C and 130°C). Induction period of sample heated at 60°C was important compared to that at 100°C and 130°C. This result may indicate the sensitivity of TTBO to elevated temperature. Absorption at 232 and 270 nm, acidity and PV increased rapidly after reaching the oxidation induction time. The temperature had a significant effect on the formation of oxidation products in traditional butter oil (TTBO). Fatty acid composition of TTBO was also changed after heating. This may explain the observed modification on some quality characteristics of TTBO such as viscosity, hardness, cohesiveness and colour. As a consequence, heat treatment produced alterations in the oxidative status of the butter oil that could affect the shelf life.