Ricardo Aguilar-López

Chaotic Synchronization and Its Applications in Secure Communications

Ricardo Aguilar-López et al. — Tue, 08 Nov 2011 10:50:38 PST

Observability and Observers for Nonlinear Dynamical Systems: Nonlinear Systems Analysis

Ricardo Aguilar-López et al. — Tue, 08 Nov 2011 10:46:55 PST

A chaotic system in synchronization and secure communications

Ricardo Aguilar-López et al. — Tue, 08 Nov 2011 10:43:14 PST

Chaotic systems synchronization via high order observer design

Ricardo Aguilar-López et al. — Tue, 08 Nov 2011 10:38:30 PST

Modelling Catalyst Deactivation by External Coke Deposition during Fluid Catalytic Cracking

Ricardo Aguilar-López et al. — Tue, 08 Feb 2011 09:10:52 PST

Although the Fluid Catalytic Cracking (FCC) is an economic important process, simulation of its kinetics is rather empirical-mainly it is a consequence of the complex interactions among operating variables and the complex kinetics that take place. A crucial issue is the inevitable catalyst reversible deactivation, consequence of both, coke (by-product) deposition on the catalyst surface (external) and inside the catalytic zeolite (internal). In order to tackle this problem, two main proposals to evaluate deactivation rate by coking have been extensively applied, both use a probability distribution function called "the negative exponential function"-one of them uses the time that catalyst has been in the reacting stream (named Time-on-Stream), and the other is related to the coke amount on/inside the catalyst (denoted as Coke-on-Catalyst). These two deactivation models can be unified by tracking catalyst activity as function of the decrease on effective diffusivity due to pore occlusion (external) by coke-this situation leads to an increase of Thiele modules and consequently a decrease of the effectiveness factor of each reaction. This tracking of catalyst activity incorporates, implicitly, rates of reaction and transport phenomena taking place in the catalyst pores and is therefore phenomenological rather than statistical. In this work, the activity profiles predicted previously are reproduced at MAT laboratory reactor. The same approach is used to model an industrial riser and the results are in agreement with previous reports.

OBSERVER BASED ADAPTIVE MODEL FOR A CLASS OF AEROBIC BATCH BIOREACTOR

Ricardo Aguilar-López et al. — Tue, 08 Feb 2011 09:04:50 PST

The main issue of this work is to design a nonlinear observer (soft sensor) with finite convergence time for a class of batch bioreacting systems. Considering the necessity to fast response for monitoring and control issues for batch processes a finite time high order sliding-mode observer is considered. It is presented a theoretical analysis to provide a sketch of proof to demonstrate the convergence properties of the proposed observer and the finite time of convergence is calculated from the same analysis. A simple model for a batch aerobic wastewater bioreactor, experimentally corroborated, is proposed as application example and numerical experiments show the adequate observer performance compared to a standard nonlinear Luenberger observer.

Control of a Class of Sulfate Reducing Chemostat Via Feedback Polynomial Injection

Ricardo Aguilar-López et al. — Tue, 08 Feb 2011 09:02:09 PST

The main goal of this work is to present a new class of feedback controller which contains on its structure a polynomial form of the named control error, the proposed controller is applied to a class of sulfate-reducing chemostat in order to control the sulfate concentration, which would be useful for several biotechnological issues, as heavy metal removal in wastewater. The closed-loop behavior of the chemostat is theoretically analyzed and a practical convergence to the selected optimum trajectory is proved. The proposed methodology is applied to an experimentally corroborated kinetic model of a sulfate-reducing bacterium and further numerical experiments show the satisfactory closed-loop performance of the process in comparison with other controllers.

Simulation factors of steel continuous casting

Ricardo Aguilar-López et al. — Tue, 08 Feb 2011 08:44:45 PST

The factors involved in simulating the continuous casting process of steel and the effects of the factors on the thermal behavior were investigated. The numerical methods and the influence of some assumptions were also analyzed, such as nodes used to discretize the steel in array size and computing time to obtain good approaches. The results show that some of these factors are related with the design of the continuous casting plant (CCP), such as geometrical configuration, and the operating conditions, such as water flow rate, heat removal coefficient in the mold, casting times, and casting speed in the strand, which affect the heat removal conditions over the temperature and solidification profiles.

Simulation of heat transfer in steel billets during continuous casting

Ricardo Aguilar-López et al. — Tue, 08 Feb 2011 08:41:36 PST

This work is focused on the development of computational algorithms to create a simulator for solving the heat transfer during the continuous casting process of steel. The temperatures and the solid shell thickness profiles were calculated and displayed on the screen for a billet through a defined continuous casting plant (CCP). The algorithms developed to calculate billet temperatures, involve the solutions of the corresponding equations for the heat removal conditions such as radiation, forced convection, and conduction according to the billet position through the CCP. This is done by a simultaneous comparison with the kinematics model previously developed. A finite difference method known as Crank-Nicholson is applied to solve the two-dimensional computational array (2D model). Enthalpy (H-I,H-J) and temperature (T-I,T-J) in every node are updated at each step time. The routines to display the results have been developed using a graphical user interface (GUI) in the programming language C++. Finally, the results obtained are compared with those of industrial trials for the surface temperature of three steel casters with different plant configurations in different casting conditions.

Computational algorithms to simulate the steel continuous casting

Ricardo Aguilar-López et al. — Tue, 08 Feb 2011 08:39:07 PST

Computational simulation is a very powerful tool to analyze industrial processes to reduce operating risks and improve profits from equipment. The present work describes the development of some computational algorithms based on the numerical method to create a simulator for the continuous casting process, which is the most popular method to produce steel products for metallurgical industries. The kinematics of industrial processing was computationally reproduced using subroutines logically programmed. The cast steel by each strand was calculated using an iterative method nested in the main loop. The process was repeated at each time step (Delta t) to calculate the casting time, simultaneously, the steel billets produced were counted and stored. The subroutines were used for creating a computational representation of a continuous casting plant (CCP) and displaying the simulation of the steel displacement through the CCP. These algorithms have been developed to create a simulator using the programming language C++. Algorithms for computer animation of the continuous casting process were created using a graphical user interface (GUI). Finally, the simulator functionality was shown and validated by comparing with the industrial information of the steel production of three casters.

Importance of Chaos Synchronization on Technology and Science

Ricardo Aguilar-López — Thu, 03 Feb 2011 11:51:14 PST

High order sliding-mode dynamic control for chaotic intracellular calcium oscillations

Ricardo Aguilar-López et al. — Thu, 03 Feb 2011 11:48:18 PST

In this article the closed-loop stability conditions and the control design of a class of biological system that exhibit chaotic oscillations are addressed. It is proved that the biological system is minimum phase. A class of nonlinear dynamic feedback control is designed using sliding-mode control ideas, which can be used for regulation, tracking and synchronization tasks. Numerical experiments illustrate the satisfactory performance of the proposed control methodology

On the observability for a class of nonlinear (bio) chemical systems

Ricardo Aguilar-López et al. — Thu, 03 Feb 2011 11:45:34 PST

In this work the observability properties for a class of nonlinear systems is presented, by considering linear, geometric and algebraic approaches. The observability conditions for state variables, unstructured uncertainties and detectable states are considered for a class of nonlinear systems related with several (bio)-chemical reacting processes. The considered examples are related with (bio)-chemical continuous reactors and a metabolic model, where their observability properties are analyzed. A comparison of the corresponding results is done, showing the suitability of each approach.

Monitoring in a predator-prey systems via a class of high order observer design

Ricardo Aguilar-López et al. — Thu, 03 Feb 2011 11:43:55 PST

The goal of this work is the monitoring of the corresponding species in a class of predator-prey systems, this issue is important from the ecology point of view to analyze the population dynamics. The above is done via a nonlinear observer design which contains on its structure a high order polynomial form of the estimation error. A theoretical frame is provided in order to show the convergence characteristics of the proposed observer, where it can be concluded that the performance of the observer is improved as the order of the polynomial is high. The proposed methodology is applied to a class of Lotka-Volterra systems with two and three species. Finally, numerical simulations present the performance of the proposed observer.

An exponential polynomial observer for synchronization of chaotic systems

Ricardo Aguilar-López et al. — Thu, 03 Feb 2011 11:42:06 PST

In this paper, we consider the synchronization problem via nonlinear observer design. A new exponential polynomial observer for a class of nonlinear oscillators is proposed, which is robust against output noises. A sufficient condition for synchronization is derived analytically with the help of Lyapunov stability theory. The proposed technique has been applied to synchronize chaotic systems (Rikitake and Rossler systems) by means of numerical simulation.

Synchronization and parameter estimations of an uncertain Rikitake system

Ricardo Aguilar-López et al. — Thu, 03 Feb 2011 11:38:48 PST

In this Letter we address the synchronization and parameter estimation of the uncertain Rikitake system, under the assumption the state is partially known. To this end we use the master/slave scheme in conjunction with the adaptive control technique. Our control approach consists of proposing a slave system which has to follow asymptotically the uncertain Rikitake system, refereed as the master system. The gains of the slave system are adjusted continually according to a convenient adaptation control law, until the measurable output errors converge to zero. The convergence analysis is carried out by using the Barbalat's Lemma. Under this context, uncertainty means that although the system structure is known, only a partial knowledge of the corresponding parameter values is available.

Towards modelling production of clean fuels: Sour gas formation in catalytic cracking

Eduardo Villafuerte-Macías et al. — Tue, 14 Jul 2009 08:38:25 PDT

Although one important by-product of fluidised-bed catalytic cracking of hydrocarbons is the sour gas (mainly hydrogen sulfide), there are no kinetic models to predict its generation. Moreover, if feedstock sulfur is not directed to sour gas, it will be present in gasoline, cycle oils and coke. These products are used as fuels, which could emit sulfur oxides during their combustion. In order to be able to model production of clean fuels, a kinetic scheme that considers sour gas as unmatched product was developed; meanwhile, the sulfur distribution in cracking products is predicted. Model parameters are validated using industrial operating data. This kinetic scheme is employed tomodel steady state operation of an industrial catalytic cracking riser and to find operating conditions that diminish the sulfur content in fuels.

Temperature Regulation via PI High-Order Sliding-Mode Controller Design: Application to a Class of Chemical Reactor

Ricardo Aguilar-López et al. — Tue, 14 Jul 2009 08:38:24 PDT

The main issue of this paper is the synthesis of a robust control law for regulation purposes, which is applied to a class of chemical reactor which exhibits highly nonlinear and oscillatory behavior. The considered methodology employs the typical structure of Proportional-Integral controllers, where the corresponding integral term is now proposed as an integral high order sliding-mode compensator, which deals with the intrinsic nonlinearities of the system to be regulated. A theoretical frame is provided to demonstrate that the proposed controller produces semi-global practical stability; performance of the proposed methodology is assessed via comparison with other controllers.

Input-Output Linearizing Control based on Robust Observers: Application to a Class of Reacting Systems

Ricardo Aguilar-López et al. — Tue, 14 Jul 2009 08:38:22 PDT

The aim of this paper is the synthesis of a robust control law for regulation control of a class of relative-degree one non-linear systems. The control design is based on sliding-mode uncertainty estimator, developed under the framework of algebraic-differential concepts. The closed-loop stability for the underlying closed-loop system is done via averaging techniques. Robustness of the proposed control scheme is proved in the face of noise measurements, model uncertainties and sustained disturbances. The performance of the proposed control law is illustrated with numerical simulations

Tracking Catalyst Activity during Fluidized-bed Catalytic Cracking

Rafael Maya-Yescas et al. — Tue, 14 Jul 2009 08:38:21 PDT

Fluidized- bed Catalytic Cracking (FCC) of vacuum gas oils, which produces aggregated value liquid fuels such as gasoline and liquid petroleum gas, is an important process in petroleum refining. Cracking reactions take place in risers, which are transported solid bed devices. In order to model risers it is necessary to develop kinetic schemes; however complex catalyst deactivation, reaction paths and non-isothermal behaviour of these adiabatic units make difficult to propose accurate schemes. The main mechanism of catalyst deactivation has been under research for more than 60 years, being related to coke formation during FCC reactions and the consequent active sites coverage and catalyst’s pore blockage. Although it is usual to model these phenomena as function of “time-on-stream”, it is possible to explain it in terms of effectiveness factors. If pore blockage is noticeable, then different activity related to each reactant is reflected by the relative magnitude of individual effective diffusion coefficients; unfortunately, these transport parameters are difficult to measure. In this work, a theoretical methodology based on the comparison of yield to products from different feed stocks is proposed to track catalyst activity dynamics; estimation functions are based on fundamental transport parameters, mainly effective diffusion, inside the catalyst particle. Experimental results obtained in MAT and industrial reactors are used to adjust values of catalytic activity and probe the approach proposed; simulation results for an industrial riser reactor confirm the satisfactory description of the activity profiles.