Real-Time Attitude Stabilization of a Mini-UAV Quad-rotor Using Motor Speed Feedback

A real-time attitude stabilization control scheme is proposed for the efficient performance of a mini-UAV Quad-Rotor. Brushless DC (BLDC) motor speed sensing is performed by reflective sensors in order to obtain a robust stabilization of the vehicle in hovering mode both indoor and outdoor. The speed measurement has the advantage of introducing this state information directly in the closed loop control which should be very useful for achieving robust stabilization of the mini-UAV. Furthermore a stabilizing control strategy based on Control Lyapunov Function (CLF) is proposed. The control scheme contains two control loops. The inner loop is devoted to control the motors speed while the outer loop is devoted to control the attitude stabilization of a mini-UAV. Assuming that the motors can be considered as a disturbance of the system, then by the standard singular perturbation theory, we may conclude that the system is asymptotically stable. Finally, to verify the satisfactory performance of proposed embedded controller, simulations and experimental results of speed sensing feedback in BLDC motors of the Quad-rotor aircraft in the presence of disturbances are presented.     

Real-time Stabilization of a Quadrotor UAV: Nonlinear Optimal and Suboptimal Control

In this paper a nonlinear suboptimal stabilizing control strategy based on Control Lyapunov Functions (CLF) is synthesized and applied to a quadrotor helicopter. Sufficient conditions are obtained for this control law to ensure the asymptotic stability of the closed loop system. Furthermore, a particular methodology to find a CLF candidate for nonlinear affine system is also presented, which is highly relevant because the dynamical model representing the VTOL aerial vehicles have this affine structure. Using this CLF candidate, we are able to synthesize a nonlinear stabilizing optimal control law which allows energy saving. Numerical simulations were developed for both control strategies and real time experiments have been performed using the nonlinear stabilizing control algorithm. The numerical simulations have shown a successful performance of the autonomous aerial vehicle.     

Data-Based Models for the Prediction of Dam Behaviour: A Review and Some Methodological Considerations

Predictive models are an important element in dam safety analysis. They provide an estimate of the dam response faced with a given load combination, which can be compared with the actual measurements to draw conclusions about dam safety. In addition to numerical finite element models, statistical models based on monitoring data have been used for decades for this purpose. In particular, the hydrostatic-season-time method is fully implemented in engineering practice, although some limitations have been pointed out. In other fields of science, powerful tools such as neural networks and support vector machines have been developed, which make use of observed data for interpreting complex systems. This paper contains a review of statistical and machine-learning data-based predictive models, which have been applied to dam safety analysis. Some aspects to take into account when developing analysis of this kind, such as the selection of the input variables, its division into training and validation sets, and the error analysis, are discussed. Most of the papers reviewed deal with one specific output variable of a given dam typology and the majority also lack enough validation data. As a consequence, although results are promising, there is a need for further validation and assessment of generalisation capability. Future research should also focus on the development of criteria for data pre-processing and model application.     

Optimization of freezing parameters for freeze-drying mango (Mangifera indica L.) slices

Today, there is an increasing trend toward consuming healthful food products, and dried fruits are one option for obtaining desirable nutrition in dehydrated products. Proper drying method selection is important for minimizing quality losses. Lyophilization (freeze-drying), a technique that removes water by sublimation at low temperature, can produce excellent dried products. Fast vacuum induction during freezing has been proposed as a way to control ice nucleation and to obtain enhanced lyophilized pharmaceutical products. However, this technique has not yet been applied to food freeze-drying. The aim of this work was to evaluate the effects of the freezing rate (0.4, 0.25, and 0.1°C/min), the minimum chamber pressure during vacuum-induced surface freezing (900, 700, and 500?mTorr) and the sample temperature at which the induced vacuum was applied (0, ?2, and ?4°C) on the total process time, final moisture content, rehydration capacity, total color difference, and total polyphenol content during the lyophilization of mango (Mangifera indica L.) slices. A Box–Behnken design with three factors at three levels was used to design the experiments, to generate the polynomial equations relating the dependent and independent variables, and to determine the optimal operational conditions. The results highlight the reduction of total process time (30%) at high freezing rates and the influence of the tested operating conditions on freeze-drying optimization. It was found that the optimal conditions that satisfy commercial quality goals were pressure between 500 and 650?mTorr, temperature between ?2 and 0°C, and freezing rate values close to 0.4°C/min.     

Fracture behaviour of controlled‐rheology ethylene–propylene block copolymers

The evolution of the molecular weight distribution and the thermal, mechanical and fracture behaviour of controlled‐rheology ethylene‐propylene block copolymers (ca 8 wt% ethylene content) has been analysed. Various concentrations of di‐tert‐butylperoxide were utilized. The melt flow index increased with the peroxide content due to the reduction of the molecular weight and the narrowing of the molecular weight distribution. However, the thermal behaviour and degree of crystallinity were not improved and some mechanical properties, such as the tensile strength and elongation at break, presented an anomalous behaviour. This trend can be explained by the presence of the elastomeric phase. The addition of peroxide influenced strongly the J–R curves obtained via the elastic–plastic fracture mechanics approach. The slope of these curves was markedly reduced with addition of peroxide to almost being flat for the highest concentration. This loss of ductility and the sudden decrease of the fracture toughness values with an increasing amount of peroxide were mainly due to the reduction in the molecular weight. Copyright © 2011 Society of Chemical Industry     

Behavior of asphaltene and asphaltene fractions films on a Langmuir–Blodgett trough and its relationship with proposed molecular structures

Abstract

Asphaltenes were precipitated from a Venezuelan Ayacucho crude oil and separated into two fractions (A1 and A2) by the p-nitrophenol method. The asphaltenes and the fractions A1 and A2, as well as mixtures of the two fractions were tested in a Langmuir–Bodgett trough. It was found that the asphaltenes and the fraction A2 had similar behavior and higher compressibility than the fraction A1. This is because the molecules of A2 are more flexible than the molecules of A1 as they have aliphatic chains that bond aromatic structures while the A1 has an aromatic nucleus.     

Molecular structure and properties of ethylene‐co‐styrene polymers obtained from [norbornane‐7,7‐bis(1‐indenyl)]titanium dichloride catalyst system

Ethylene‐co‐styrene polymers have been synthesized using the new catalyst system [norbornane‐7,7‐bis(1‐indenyl)]titanium dichloride, and characterized by SEC, ¹³C‐NMR, DSC, and dynamic‐mechanical analysis. The copolymers have higher average molecular weights compared with those produced in our group with other single‐site catalysts systems in the same conditions. More specifically, the homopolymers are ultra high molecular weight polyethylenes (molecular weight higher than 10⁶ g mol^?1) and with a narrow molecular weight distribution. All samples have shown an unprecedented homogeneous chemical composition with a random incorporation of the comonomer during the polymerization. The expected relationship between thermal properties and the amount of comomoner related to the exclusion of the phenyl units from the crystalline structure has been found, but the correlation is slightly different from those found in other copolymers. This is likely due to the different molecular features of the copolymers. In addition, intense and narrow mechanical relaxations have been found in the samples tested, pointing towards an extremely homogeneous microstructure. The materials obtained show a conspicuous strain hardening during tensile deformation at high strains, not only related to the constrain imposed by the bulky phenyl group in the amorphous region, but additionally to the extremely high number of entanglements in this region as a consequence of the high molecular mass of the samples. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007