Parametric and non parametric characterization of a shear mode magnetorheological damper

MR (magnetorheological) dampers are versatile devices whose design is aimed to take the best of magnetorheological fluids: high yield strength, low power requirements, insensitivity to contaminants and hence, low cost. MR dampers have proven to be a good option for the mitigation of uncomfortable and hazardous vibrations in systems such as vehicles, buildings, bridges, etc. However, MR dampers are highly nonlinear devices that exhibit a hysteretic force-velocity loop. Their extensive applications in vibration control systems demand an accurate mathematical model. In this paper, two models for an MR damper operated in shear mode are presented: a parametric approach (Bouc-Wen model) and a non parametric one (neural network model

Feedback vibration control of a base-isolated building with delayed measurements using h∞ techniques

n this paper we address the problem of vibration reduction of buildings with delayed measurements, where the delays are time-varying and bounded. We focus on a convex optimization approach to the problem of state-feedback H ∞ control design. An appropriate Lyapunov-Krasovskii functional and some free weighting matrices are used to establish some delay-range-dependent sufficient conditions for the design of desired controllers in terms of linear matrix inequalities (LMIs). The controller, which guarantees asymptotic stability and an H ∞ performance, simultaneously, for the closed-loop system of the structure, is then developed. The performance of the controller is evaluated through the simulation of an n-story base-isolated building

Feedback vibration control of a base-isolated building with delayed measurements using h∞ techniques

Published version of a paper presented at the American Control Conference (ACC), 2010. (c) 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other worksn this paper we address the problem of vibration reduction of buildings with delayed measurements, where the delays are time-varying and bounded. We focus on a convex optimization approach to the problem of state-feedback H ∞ control design. An appropriate Lyapunov-Krasovskii functional and some free weighting matrices are used to establish some delay-range-dependent sufficient conditions for the design of desired controllers in terms of linear matrix inequalities (LMIs). The controller, which guarantees asymptotic stability and an H ∞ performance, simultaneously, for the closed-loop system of the structure, is then developed. The performance of the controller is evaluated through the simulation of an n-story base-isolated building

Caracterización química, térmica y viscosa de oleínas ácidas de girasol alto oleico y orujo de oliva y estólidos derivados

This work deals with the chemical, thermal and viscous characterization of a variety of estolides, prepared from higholeic sunflower and olive pomace acid oils, using different acid-catalyzed synthesis protocols and reaction times. Estolides with weight-average molecular weights between 1.7 and 3.4 times higher than the original acid oils were obtained. The molecular weight of the estolides was higher when using the sulphuric acid-catalyzed method and a reaction time of 3-6 h. Estolides presented higher freezing temperatures than acid oils. In general, viscosity values are related to estolide molecular weight. Significant increments in viscosities were found in comparison with acid oils. Maximum viscosity values were obtained for estolides prepared using the sulphuric acidcatalyzed method. The largest viscosity increments in olive pomace acid oil-derived estolides were observed during the first 6 hours of reaction, due to an increase in the molecular weight; longer reaction times yielded adverse results. The temperature dependence of viscosity for all estolides studied is significantly larger than for the original acid oils.Este trabajo presenta la caracterización química, térmica y viscosa de estólidos preparados a partir de oleínas ácidas de girasol alto-oleico y de orujo de oliva, utilizando diferentes métodos catalizados por ácidos y diferentes tiempos de reacción. Se obtuvieron estólidos con pesos moleculares promedios en peso entre 1,7 y 3,4 veces más altos que las oleínas de origen. El peso molecular de los estólidos aumenta cuando se utiliza el método catalizado por ácido sulfúrico y un tiempo de reacción de 3-6 h. Los estólidos obtenidos presentan temperaturas de congelación más altas que las oleínas. En general, los valores de viscosidad están relacionados con el peso molecular del estólido. Se encontraron incrementos significativos de viscosidad en comparación con las oleínas. Los valores máximos de viscosidad se obtuvieron para los estólidos preparados con el método catalizado por ácido sulfúrico. En los estólidos derivados de oleína de orujo de oliva se observaron los mayores incrementos de viscosidad durante las 6 primeras horas de reacción, debido al mayor aumento en el peso molecular. Tiempos más largos de reacción dan lugar a resultados desfavorables. La dependencia de la viscosidad con la temperatura de todos los estólidos es más importante que en las oleínas de partida

Biopolymer-based structuring of liquid oil into soft solids and oleogels using water-continuous emulsions as templates

Physical trapping of a hydrophobic liquid oil in a matrix of water-soluble biopolymers was achieved using a facile two-step process by first formulating a surfactant-free oil-in-water emulsion stabilized by biopolymers (a protein and a polysaccharide) followed by complete removal of the water phase (by either high- or low-temperature drying of the emulsion) resulting in structured solid systems containing a high concentration of liquid oil (above 97 wt %). The microstructure of these systems was revealed by confocal and cryo-scanning electron microscopy, and the effect of biopolymer concentrations on the consistency of emulsions as well as the dried product was evaluated using a combination of small-amplitude oscillatory shear rheometry and large deformation fracture studies. The oleogel prepared by shearing the dried product showed a high gel strength as well as a certain degree of thixotropic recovery even at high temperatures. Moreover, the reversibility of the process was demonstrated by shearing the dried product in the presence of water to obtain reconstituted emulsions with rheological properties comparable to those of the fresh emulsion

Chemical, thermal and viscous characterization of high-oleic sunflower and olive pomace acid oils and derived estolides

This work deals with the chemical, thermal and viscous characterization of a variety of estolides, prepared from higholeic sunflower and olive pomace acid oils, using different acid-catalyzed synthesis protocols and reaction times. Estolides with weight-average molecular weights between 1.7 and 3.4 times higher than the original acid oils were obtained. The molecular weight of the estolides was higher when using the sulphuric acid-catalyzed method and a reaction time of 3-6 h. Estolides presented higher freezing temperatures than acid oils. In general, viscosity values are related to estolide molecular weight. Significant increments in viscosities were found in comparison with acid oils. Maximum viscosity values were obtained for estolides prepared using the sulphuric acidcatalyzed method. The largest viscosity increments in olive pomace acid oil-derived estolides were observed during the first 6 hours of reaction, due to an increase in the molecular weight; longer reaction times yielded adverse results. The temperature dependence of viscosity for all estolides studied is significantly larger than for the original acid oils.Este trabajo presenta la caracterización química, térmica y viscosa de estólidos preparados a partir de oleínas ácidas de girasol alto-oleico y de orujo de oliva, utilizando diferentes métodos catalizados por ácidos y diferentes tiempos de reacción. Se obtuvieron estólidos con pesos moleculares promedios en peso entre 1,7 y 3,4 veces más altos que las oleínas de origen. El peso molecular de los estólidos aumenta cuando se utiliza el método catalizado por ácido sulfúrico y un tiempo de reacción de 3-6 h. Los estólidos obtenidos presentan temperaturas de congelación más altas que las oleínas. En general, los valores de viscosidad están relacionados con el peso molecular del estólido. Se encontraron incrementos significativos de viscosidad en comparación con las oleínas. Los valores máximos de viscosidad se obtuvieron para los estólidos preparados con el método catalizado por ácido sulfúrico. En los estólidos derivados de oleína de orujo de oliva se observaron los mayores incrementos de viscosidad durante las 6 primeras horas de reacción, debido al mayor aumento en el peso molecular. Tiempos más largos de reacción dan lugar a resultados desfavorables. La dependencia de la viscosidad con la temperatura de todos los estólidos es más importante que en las oleínas de partida.This work is part of a research project (CTQ2010-15338) sponsored by a MINECO-FEDER programme (70% European cofunding rate). The authors gratefully acknowledge its financial support

Landing gear suspension control through adaptive backstepping techniques with H∞ performance

Landing gear suspension systems fulfill the tasks of absorbing the vertical energy of the touch-down as well as providing passenger and crew comfort with a smooth ground ride before take-off and after landing. They are also designed to have optimal performance in the case of a hard landing. In general, the tasks of aircraft landing gears are complex and sometimes lead to a number of contradictory requirements. Although there are existing modifications of aircraft shock absorbers to reduce the problem, the basic design conflict between the requirements for landing and for rolling cannot be fully overcome by a passive suspension layout. Active and semiactive suspension techniques are a solution to this problem and are capable of reducing fuselage vibrations effectively. In order to get satisfactory damping performance with active and semiactive devices, appropriate control laws must be employed. In this paper, we study the use of an adaptive backstepping control with H∞ performance to cope with disturbances, uncertainties and nonlinearities, typical of suspension systems and damping devices. A comparison between active and semiactive strategies is provided through the analysis of simulation results

Stability analysis of neutral systems with mixed time-varying delays and nonlinear perturbations

In this paper, the problem of stability analysis for a class of neutral systems with mixed time-varying neutral, discrete and distributed delays and nonlinear perturbations are addressed. By introducing a novel Lyapunov-Krasovskii functional and combining the descriptor model transformation, the Leibniz-Newton formula, some free weighting matrices and a suitable change of variables, new sufficient conditions are established for the stability of the considered system, which are neutral-delay-dependent, discrete-delay-range-dependent and distributed-delay-dependent. The conditions are presented in terms of linear matrix inequalities (LMIs) and can be easily solved by existing convex optimization techniques. A numerical example is given to demonstrate the less conservatism of the proposed results over some existence results in the literature