FIME

Every system is vulnerable to faults due to the physical nature of its components. These faults could cause severe damage. A way to reduce the effect of faults consist basically in two steps: first, in detect if they are present in a system as soon as they occur and second: to take a corrective action. This work offers a panoramic view about the fault detection methods based on analytical redundancy. The last part of this work contains a description of some applications in different areas.

Robust and early detection of oscillatory failures in the electrical flight control system of an aircraft is a crucial issue. Oscillatory failures, if not detected and passivated in time, can lead to strong interactions with loads and aeroelasticity and may potentially lead to structural damages. A nonlinear observer-based solution to detect such failures with small amplitude at a very early stage is presented. The stability and convergence proofs are given and experimental results with real A380 flight data are presented.

En este trabajo se considera el desarrollo de un esquema para el diagnóstico de fallas en los componentes de una Unidad Separadora con Fluido Catalítico (Fluid Catalytic Cracking Unit (FCC)). El algoritmo considerado está basado en una linealización de la unidad FCC no lineal y en un procedimiento que utiliza observadores para el diagnóstico. Se modelan y simulan cuatro fallas en los componentes. El diseño resultante es verifi cado usando simulación no lineal de la unidad FCC. El desempeño del algoritmo utilizado para el diagnóstico es mostrado mediante simulaciones en los diferentes escenarios de falla. Se muestra que el método lineal basado en observadores es adecuado para la detección y localización de fallas en la unidad FCC, esto a pesar de la característica no lineal del proceso.

This paper presents the development of a process control interface system (PCIS) for a distillation pilot plant that is based on the communication protocol called MODBUS. MODBUS communicates the computer (used as a control unit) with the process because it allows an efficient, flexible, and reliable system. The interface system is presented in an operator-friendly application, which has the capability to monitor the variables, manipulate actuators, and tune the controllers in the distillation process.

This paper considers a general approach to fault diagnosis using a generalized Hamiltonian system representation. It can be considered that, in general, nonlinear systems still represent a problem in fault diagnosis because there are results only for a specific class of them. Therefore, fault diagnosis remains a challenging research area despite the maturity of some of the available results. In this work, a type of nonlinear system that admits a generalized Hamiltonian representation is considered; in practice, there are many systems that have this kind of representation. Thereupon, an approach for fault detection and isolation based on the Hamiltonian representation is proposed. First, following the classic approach, the original system is decoupled in different subsystems so that each subsystem is sensitive to one particular fault. Then, taking advantage of the structure, a simple way to design the residuals is presented. Finally, the proposed scheme is validated at the two-degree...

La representación Hamiltoniana generalizada de sistemas brinda una estructura que puede ser utilizada con ventaja en muchas ´areas, entre las cuales se puede mencionar el diseño de observadores y el diagnóstico de fallas basado en modelos. Muchos de los trabajos en estos temas tienen como punto de partida al sistema en forma Hamiltoniana generalizada y, en general, se omite la explicación de como llegar a esta representación, por ejemplo, a partir de un modelo no lineal basado en las ecuaciones de Euler-Lagrange. En este trabajo se presenta un análisis detallado de como es que se obtiene la representación Hamiltoniana generalizada de un sistema a partir de las n ecuaciones diferenciales de segundo orden obtenidas con el formalismo Euler-Lagrange. Con la finalidad de mostrar en lo particular, después del caso general, cómo se obtiene la representación Hamiltoniana generalizada, se presentan algunos casos de estudio.

We present results of experimental and theoretical studies of polarization-resolved light transmission through optical fiber with disorder generated in its germanium-doped core via UV radiation transmitted through a diffuser. In samples longer than a certain characteristic length, the power transmitted with preserved polarization is observed to be distributed over all forward-propagating modes, as evidenced by the Rayleigh negative exponential distribution of the near-field intensity at the output surface of the fiber. Furthermore, the transmitted power becomes also equally distributed over both polarizations. To describe the optical properties of the fibers with the experimentally induced disorder, a theoretical model based on coupled-mode theory is developed. The obtained analytical expression for the correlation function describing spatial properties of the disorder shows that it is highly anisotropic. Our calculations demonstrate that this experimentally controllable anisotropy can lead to suppression of the radiative leakage of the propagating modes, so that intermode coupling becomes the dominant scattering process. The obtained theoretical expressions for the polarization-resolved transmission fit very well with the experimental data, and the information extracted from the fit shows that radiative leakage is indeed small. The reported technique provides an easy way to fabricate different configurations of controlled disorder in optical fibers suitable for such applications as random fiber lasers.

We present results of experimental and theoretical studies of polarization-resolved light transmission through optical fiber with disorder generated in its germanium-doped core via UV radiation transmitted through a diffuser. In samples longer than a certain characteristic length, the power transmitted with preserved polarization is observed to be distributed over all forward-propagating modes, as evidenced by the Rayleigh negative exponential distribution of the near-field intensity at the output surface of the fiber. Furthermore, the transmitted power becomes also equally distributed over both polarizations. To describe the optical properties of the fibers with the experimentally induced disorder, a theoretical model based on coupled-mode theory is developed. The obtained analytical expression for the correlation function describing spatial properties of the disorder shows that it is highly anisotropic. Our calculations demonstrate that this experimentally controllable anisotropy can lead to suppression of the radiative leakage of the propagating modes, so that intermode coupling becomes the dominant scattering process. The obtained theoretical expressions for the polarization-resolved transmission fit very well with the experimental data, and the information extracted from the fit shows that radiative leakage is indeed small. The reported technique provides an easy way to fabricate different configurations of controlled disorder in optical fibers suitable for such applications as random fiber lasers.

Impressed current cathodic protection (ICCP) is a widely used method to protect steel reinforcements against corrosion. Bond degradation between concrete and steel at protection and overprotection levels was studied. Two types of materials were tested: an ordinary Portland cement (OPC) and a mixture of 85% OPC and 15% fly ash (OPC/FA). Concrete specimens were immersed in a 3.5% sodium chloride (NaCl) solution. Chemical analysis of sodium, potassium and hydrogen ions was performed using atomic absorption spectrophotometry (AAS). Hydrogen ion content was monitored using electrochemical impedance spectroscopy (EIS). Mechanical behaviour was analysed by means of pullout tests, and microstructure characterisation was carried out using scanning electron microscopy (SEM). Sodium, potassium and hydrogen ions were found at the concrete-steel interface. The mechanical properties of the specimens were poorer at overprotection level than at protection level.

OPEN ACCESS / Free download: http://dx.doi.org/10.20964/2022.10.07

The present research objective is to evaluate microstructure's influence on corrosion behavior of a new series of Zn-Al-Sr alloys with possible coating applications. Conventional casting procedures prepared four Zn-Al-Sr alloys. The alloys were Zn-1Al-0.05Sr, Zn-2.5-Al-0.1Sr, Zn-4.5-Al-0.5Sr, and Zn 10Al 1Sr. Microstructural characterization was performed by scanning electron microscopy. Corrosion behavior was evaluated employing electrochemical techniques such as potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS). The alloys were exposed to 3.5 wt. % NaCl. Results indicated that all samples presented the η-Zn, α-Al, and SrZn13 phases in different arrangements depending on the alloy composition. Electrochemical tests revealed that Al increased alloy corrosion resistance by forming insoluble oxides, whereas Sr improved corrosion product layer compactness and homogeneity of the corrosion product layer. However, the large grain size of the SrZn13 compound favored the corrosion process by galvanic coupling. Compositions between 2.5 and 4.5 wt.% Al and 0.05 and 0.5 wt.% Sr exhibited the highest corrosion resistance of the Zn-Al-Sr alloys in 3.5 wt.% NaCl solution, lower Sr content promoted both homogenous corrosion and a compacted corrosion products layer. A high density of intermetallic particles adversely affects Zn-Al-Sr alloys corrosion resistance, and Sr content must not exceed 0.5 wt.%.

A simplified kinetic model, coupled with the bed hydrodynamics and a volatile evolution region within the bed, was formulated to predict the extent of gas-phase combustion in a laboratory-scale fluidized bed coal combustor (FBC). A close examination has also been made to highlight the relevance of the reducing/oxidizing environment (computed with the present theoretical model) in relation to FBC materials exposed to fireside corrosion at high temperature, under various operating conditions. The model results revealed that, for high-volatile coals with particle diameters (d c) of 1±3 mm and sand particle size (d s) of 0.674 mm, over one third of the original coal volatiles may burn in the freeboard region at bed temperature (T b) £ 850 C and excess air (XSA) £ 10 %. These values, together with the computed equilibrium conversion of alkali chlorides to sulfates, may suggest that sodium and potassium salts present in the vapor phase are likely to accelerate hot corrosion of heat exchange tubes above the bed when an FBC operates at T b £ 840 C, XSA £ 20 %, d c < 5 mm, d s < 1 mm, H s £ 0.2 m and U o < 1 m/s. Conversely, at T b > 890 C and XSA > 30 %, high oxidation rates may be present for the in-bed tubes. At these higher T b values and XSA < 10 %, a sulfidation mechanism presumably influences the extent of corrosion on the metallic components within the bed.