7 research outputs found
SHS powders for thermal spray applications
No full textSelf-propagating high temperature synthesis (SHS) is defined as a combustion process in which reagents, when ignited, spontaneously transform, to complete conversion, into products, due to the exothermic heat of reaction. This process has been recently recognised as a very promising technique for materials processing: ceramics, intermetallics and cermets with good physico-chemical properties have been produced at low costs. The use of SHS products for thermal spray applications represents a natural evolution of the technique. Demanded characteristics for thermal spray feedstock powders can be very different, depending on the spraying process, the operating conditions, the desired properties of the final coating, etc. However, technical requirements can also be extremely rigid and detailed. As a consequence, the production process must be reliable and flexible, while remaining possibly inexpensive. SHS is investigated as a promising candidate technique for the production of different powders to be used for thermal spray coatings with different applications: metallic mixtures are considered, as well as ceramic and composite powders. The chemical and morphological features of different SHS powders are described, and their technical characteristics of flowability and sprayability are outlined. Wear performance and hardness tests results for some of the coatings obtained by both air and vacuum plasma spraying of SHS powders are also reported. (C) 1996 Elsevier Science Limited and Techna S.r.l
Constant volume explosions of aerosols of metallic mechanical alloys and powder blends
No full textHigh-energy ball milling was used to prepare sets of mechanical alloys in the systems Al-Mg, Al-Mg-H, B-Mg, and Ti-B, X-ray diffraction, electron microscopy, and low-angle laser diffraction were used to characterize structures, morphology, and sizes of the alloys, respectively. The produced materials were metastable and nanocrystalline; the particle sizes were in the range of 1-50 μm. A constant volume explosion technique was used to evaluate performance of the mechanical alloys and to compare it to the performance of blends of elemental powders of the same bulk composition. For reference, samples of mechanical alloys were annealed to produce stable intermetallic phases and tested in the same explosion experiments. Pressure traces recorded in real time served as the main piece of experimental information. After selected experiments, combustion products were collected and analyzed. The results have shown that the combustion rates of mechanical alloys are appreciably higher than those of the respective powder blends, thermodynamically stable intermetallics, and pure metals. The analyses of the combustion products also showed that combustion was more complete for mechanical alloys. It was found that combustion parameters of mechanical alloys compared to other metallic fuels were significantly improved even though their particle sizes were identical or greater than those of the reference metals. The use of mechanical alloy powders with relatively large particle sizes is expected to be advantageous in many practical applications requiring mixing and handling of energetic formulations
Enhanced Continuous Higher Order Sliding Mode Control with Adaptation
No full textThis is the author accepted manuscript. The final version is availabel from Elsevier via the DOI in this recordThis paper proposes a new Continuous Adaptive HOSM control algorithm. The key
advantage of the adaption scheme is that it does not require knowledge of the bounds on
the matched uncertainty, and the gains themselves are not conservatively overestimated
by the adaption scheme – which helps mitigate the problem of chattering. Compared
with earlier work, two variable parameters are allowed to adapt and this facilitates
much better self-tuning capabilities and improved closed-loop performance
Adaptive Dual Layer Super-Twisting Control and Observation
No full textThis is the author accepted manuscript. The final version is available from Taylor & Francis via the DOI in this record.In this paper a super-twisting-like structure with adaptive gains is proposed. The structure is parameterized by two scalar gains, both of which adapt, and by an additional time-varying term. The magnitudes of the adaptive terms are allowed to both increase and decrease as appropriate so that they are as small as possible, in the sense that they do not unnecessarily over-bound the uncertainty, and yet are large enough to sustain a sliding motion. In the paper, a new time varying gain is incorporated into the traditional super-twisting architecture. The proposed adaption law has a dual-layer structure which is formally analyzed using Lyapunov techniques. The additional term has the effect of simplifying the stability analysis whilst guaranteeing the second order sliding mode properties of the traditional super-twisting schem
Cyber-attacks and faults reconstruction using finite time convergent observation algorithms: Electric power network application
No full textThis is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordIn this work, linear (linearized) cyber-physical systems with output feedback control,
whose sensors are experiencing faults or are under cyber-attack, are studied. Two
different cases are investigated. First, when all sensors are attacked, then, when some
sensors are protected from the attacks. Finite time convergent observers, specifically
the sliding mode ones, including the observers with gain adaptation, are employed for
on-line reconstruction of the cyber-attacks. The corrupted measured outputs are
“cleaned” from cyber-attacks, and feedback control that uses the “cleaned” outputs is
shown to provide elevated cyber-physical system performance close to the one
without attack. Finally, the proposed methodology is applied to an electric power
system under cyber-attack. Simulation results illustrate the efficacy of the proposed
observers
Modeling and control strategy to obtain maximum electrical energy production in a generation system from organic solid waste
No full textEl detrimento medioambiental y la necesidad de fuentes alternativas de energía hoy y a futuro, hacen que las energías renovables empiecen a ser parte fundamental de la matriz energética a nivel mundial, por ello, la generación de energía eléctrica a partir de residuos sólidos orgánicos se está posicionando como una de las principales alternativas en el panorama energético mundial. El desarrollo de estrategias de control que lleven al mejoramiento de la eficiencia de la producción de energía a partir de residuos sólidos orgánicos juega un papel importante en el avance hacia la implementación de esta tecnología. Este proceso se desarrolla mediante dos grandes etapas, digestión anaerobia y generación de energía a partir de biogás. Esta Tesis se desarrolla con el objetivo de mejorar los índices de producción de energía eléctrica generada desde Residuos Sólidos Orgánicos (RSO); inicia con la determinación del modelo de la Digestión Anaerobia sobre la base del modelo Anaerobic Model 2 (AM2), posteriormente se plantea el modelo de generación de energía eléctrica a partir de metano, se diseña e implementa el reactor para pruebas de validación y se establecen las condiciones requeridas para la producción máxima de energía. Posteriormente, se diseña y valida una estrategia de control para la variable tasa de dilución, que permite mantener estable el proceso mediante control lineal. El compensador diseñado se valida comparando las respuestas del modelo linealizado con las respuestas del modelo teórico no lineal en torno a su punto de operación, mediante simulación en MATLAB. Finalmente, se diseña e implementa una estrategia de control PI-difuso y otra estrategia de control LQR para la concentración estequiométrica de metano, la cual se valida mediante simulación en MATLAB y mediante implementación en los componentes a nivel de laboratorio.
Dentro de los resultados más relevantes de esta Tesis se encuentran, método para determinación de los parámetros del modelo del proceso de Digestión Anaerobia (DA) AM2, observador para la tasa de dilución, D, método para calcular D*, estrategia de control lineal de la tasa de dilución para mantener estable el proceso de biodigestión y estrategia que mejora la producción de energía eléctrica mediante el control de concentración estequiométrica de metano.
Estos resultados permiten mejorar la eficiencia de producción de energía eléctrica a partir de residuos sólidos orgánicos y pueden ser implementados en sistemas que ya estén funcionando, Planta de Tratamiento de Aguas Residuales (PTAR) Salitre, al igual que en sistemas que se diseñan con la solución incorporada.The environmental detriment and the need for alternative sources of energy today and in the future mean that renewable energies are beginning to be a fundamental part of the energy matrix worldwide, therefore, the generation of electrical energy from organic solid waste is positioning itself as one of the main alternatives in the global energy panorama. The development of control strategies that lead to the improvement of the efficiency of energy production from organic solid waste plays an important role in the progress towards the implementation of this technology. This process is developed through two major stages, anaerobic digestion and the generation of energy from biogas. This Thesis is developed with the objective of improving the production rates of electrical energy generated from RSO; It begins with the determination of the Anaerobic Digestion model based on the AM2 model, subsequently the model for generating electrical energy from methane is proposed, the reactor is designed and implemented for validation tests and the conditions required for the maximum energy production. Subsequently, a control strategy for the variable dilution rate is designed and validated, which allows the process to be kept stable through linear control. The designed compensator is validated by comparing the responses of the linearized model with the responses of the nonlinear theoretical model around its operating point, through simulation in MATLAB. Finally, a PID-fuzzy control strategy for the stoichiometric concentration of methane is designed and implemented, which is validated through simulation in MATLAB and through implementation in the components at the laboratory level.
Among the most relevant results of this Thesis are:
• A method for determining the parameters of the DA AM2 process model,
• A method for to calculate an observer for the dilution rate, D.
• A method for to design a linear control strategy for the dilution rate to keep the biodigestion process stable, and
• A method for to design a strategy that improves the production of electrical energy by controlling the stoichiometric concentration of methane.
These results allow improving the efficiency of electrical energy production from organic solid waste and can be implemented in systems that are already operating, Salitre PTAR, as well as in systems that are designed with the solution incorporated.Sistema General de Regalias (SGR), con gestión de MINCIENCIAS a través de prestamo condonable
