Current Issue : October - December Volume : 2014 Issue Number : 4 Articles : 5 Articles
This work focuses on a particular type of vertical-axis wind turbine, in which a number of inclined arms with airfoil-shaped\ncross-sections are mounted to connect the principal blades to their hub. While the majority of the known studies on verticalaxis\nturbines is devoted to the role of principal blades, in most of the cases without taking into account other parts of the wind\nturbine, the objective of this work is to investigate the effect of uncommon arm geometries, such as the inclined arms.The inclined\narms are known to have a potentially beneficial role in the power extraction from the wind current but, due to the complexity of\nthe phenomena, the investigation on aerodynamics of this type of turbine is often impossible through analytical models, such as\nblade-element momentum theory. It turns out that adequate studies can only be carried out by wind tunnel experiments or CFD\nsimulations. Thiswork presents a methodical CFD study on howinclined arms can be used on a selectedwind turbine configuration\nto harvest additional power fromthe wind. The turbine configuration, geometry, and some fundamental definitions are introduced\nfirst. Then an in-depth CFD analysis is presented and discussed...
GPS is a satellite-based navigation system that is able to determine the exact position of objects on the Earth, sky, or space. By\nincreasing the velocity of a moving object, the accuracy of positioning decreases; meanwhile, the calculation of the exact position\nin the movement by high velocities like airplane movement or very high velocities like satellite movement is so important. In this\npaper, seven methods for solving navigation equations in very high velocities using least squares method and its combination with\nthe variance estimation methods for weighting observations based on their qualities are studied. Simulations on different data with\ndifferent velocities from 100 m/s to 7000 m/s show that proposed method can improve the accuracy of positioning more than 50%....
This paper investigates the mechanical response of a coated Ti-6Al-4V alloy surface under different sliding contact stress conditions.\nThe surface was coated with an oxide ceramic material created through the use of a recently developed technique known as plasma\nelectrolytic oxidation (PEO). During the PEO procedure, a composition of silicate and phosphate was used as the electrolyte.\nIn order to evaluate the coating, pin-on-disk (POD) tribology tests and cyclic inclined sliding tests were used under dry room\nconditions. Furthermore, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were utilized to examine\nthe morphology and composition of the coating surfaces. The results of the POD tests revealed that the PEO coating could have a\nlow coefficient of friction and suggested that high silicon concentrations in the PEO coatings take away oxygen fromstoichiometric\nTi oxides to create lubricating oxides. In addition, cyclic inclined sliding tests showed that smaller pores on the surface of the coating\ncould permit a higher coating cohesive strength and allow the coated Ti alloy surface to perform better under high inclined sliding\nforces....
We developed a GlobalModel for N2O plasmas valid for applications in various power, gas flow rate, and pressure regimes. Besides\nenergy losses from electron collisions with N2O, it takes into consideration those due to molecular N2 and O2 and to atomic N and\nO species. Positive atomic N+ and O+ and molecular N2O+, N2\n+, andO2\n+ have been treated as separate species and also negative\nO? ions.The latter confer an electronegative character to the discharge, calling for modified plasma sheath and plasma potential\nformulas. Electron density and temperature and all species densities have been evaluated, hence the ionization and dissociation\npercentages of N2O, N2, and O2 molecules and the plasma electronegativity.The model is extended to deal with N2/O2 mixtures\nfeedings, notably with air. Rate coefficients andmodel results are discussed and compared with those fromavailable theoretical and\nexperimental work on ICP and glow discharge devices....
Wind tunnel tests to measure unsteady cavity flow pressure measurements can be expensive, lengthy, and tedious. In this work, the\nfeasibility of an active machine learning technique to design wind tunnel runs using proxy data is tested. The proposed active\nlearning scheme used scattered data approximation in conjunction with uncertainty sampling (US). We applied the proposed\nintelligent sampling strategy in characterizing cavity flowclasses at subsonic and transonic speeds and demonstrated that the scheme\nhas better classification accuracies, using fewer training points, than a passive Latin Hypercube Sampling (LHS) strategy....
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