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Search Results: 1 - 10 of 13553 matches for " Marcelo Kaminski Lenzi "
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Fractional control of an industrial furnace = Controle fracionário de um forno industrial
Luis Antonio Duarte Isfer,Ervin Kaminski Lenzi,Giovani Marcelo Teixeira,Marcelo Kaminski Lenzi
Acta Scientiarum : Technology , 2010,
Abstract: The requirements of high production allied with product quality, process safety and environmental regulation, lead control systems to play a key role in the operation of chemical and biochemical plants. In petrochemical plants, furnaces are essential equipments for process operation and due to energy costs, adequate operation and control are of extreme importance for process economics. The search for new and more efficient control laws led to the development of fractional PID control algorithm, which is based on the use of fractional differential equations. In this work, a previously identified mathematical model of an actual industrial furnace is used for fractional PID control studies. Feedback loop in servo control was analyzed, focusing on the study of the influence of the controller parameters over control loop performance. Particularly, P, fractional PI and fractional PD controller were considered in this study. Simulations were carried out showing that the fractional controllers were able to perform set-point transitions. The control loop performance was evaluated by ITAE and ISE criteria, showing that, in this study, fractional PI is the best algorithm. A necessidade da elevada produtividade aliada à qualidade dos produtos, seguran a dos processos e a legisla es ambientais levaram sistemas de controle a possuírem papel fundamental na opera o deplantas químicas e petroquímicas. Em plantas petroquímicas, fornos s o equipamentos fundamentais para a opera o do processo e, pelo custo da energia, a opera o e o controle adequados s o de essencial importancia para a economia do processo. A procura de novas e mais eficientes leis de controle levou ao desenvolvimento do algoritmo de controle PID fracionário, o qual é baseado no uso de equa es diferenciais de ordem fracionária. Neste trabalho, um modelo matemático previamente identificado para um forno real é utilizadopara estudos de controle fracionário. Foi analisado o problema de controle servo em malha retroalimentada (feedback), focando o estudo da influência dos parametros do controlador sobre o comportamento da malha de controle. Especificamente, controladores tipo P, PI fracionário e PD fracionário foram considerados neste estudo. Simula es foram realizadas mostrando que controladores foram capazes de fazer a transi o de setpoint. O desempenho das malhas de controle foi avaliado com os critérios ITAE e ISE, mostrando que, neste estudo, o controlador PI fracionário foi o melhor algoritmo.
Equa o da difus o fracionária n o-linear: solu o exata = Nonlinear fractional diffusion equation: exact solutions
Giane Gon?alves,Marcelo Kaminski Lenzi,Ervin Kaminski Lenzi,Fernando José Antonio
Acta Scientiarum : Technology , 2006,
Abstract: Neste trabalho investigaremos as solu es de uma equa o da difus ogeneralizada que contém derivadas fracionárias aplicadas a variável espacial e termos n olineares. Nesta equa o também consideraremos a presen a de for as externas e termos absorventes. As solu es encontradas aqui poder o ter um comportamento de cauda curtaou longa. Em particular, no último caso que é caracterizado pelas distribui es de cauda longa será relacionado com as distribui es de Lévy. Além disso, a partir dos resultados encontrados aqui, poderemos obter uma rica classe de processos difusivos incluindo normais e an malos. We devote this work to investigate the solutions of a generalized diffusion equation which contains spatial fractional derivatives and nonlinear terms. The presence of external forces and absorbent terms is also considered. The solutions found here can have a compact or long tail behavior. Particularly in the last case in the asymptotic limit, we relate these solutions to the Lévy or Tsallis distributions. In addition, from the results presented here, a rich class of diffusive processes, including normal and anomalous ones, can be obtained.
Difus o an mala e equa es fracionárias de difus o = Anomalous diffusion and fractional diffusion equations
Giane Gon?alves,Marcelo Kaminski Lenzi,Luciana de Souza Moraes,Ervin Kaminski Lenzi
Acta Scientiarum : Technology , 2005,
Abstract: Neste trabalho investigaremos as equa es de difus o, usualmente aplicadas na descri o da difus o an mala, que empregam derivadas fracionárias tanto na variável temporal quanto na variável espacial. Em particular, para essas equa es obteremos solu es exatas levando em conta uma condi o inicial genérica e formularemos uma teoria deperturba o para o estudo de situa es mais complexas. Também verificaremos que as derivadas fracionárias, quando aplicadas na parte temporal, possibilitam-nos o estudo de um processo de difus o an mala com o segundo momento finito, i.e., x 2 μ t a ( 0 < a < 1 , e a > 1 , correspondendo aos casos, sub e superdifusivo, respectivamente). Em contraste, com a derivada fracionária aplicada na variável espacial que resulta em uma difus o an mala cujo segundo momento n o é finito. Complementando o cenário acima, empregaremos o formalismo de caminhantes aleatórios para explorar as implica es obtidas por usar derivadas fracionárias na equa o de difus o. In this work we investigate the anomalous diffusion equations, usually applied to describe the anomalous diffusion, which employ fractional derivatives for the time or the spatial variables. Inparticular, we obtain exact solutions by taking a generic initial condition into account and developing a perturbation theory to investigate complex situations. We also verify that the fractional derivatives, when applied to the time variable, lead us to a anomalous diffusion with second moment finite, i.e., x 2 μ t a ( 0 < a < 1 and a > 1 , corresponding to sub and superdifusive behavior, respectively). By way of contrast, the fractional derivative applied to the spatial variable results in a anomalous diffusion where the second moment is not finite. These equations generalize the usual diffusion equation in order to incorporate several situations. We also employ the continuous time random walking formalism to investigate the implications obtained by using fractional derivatives in the diffusion equation.
Solu es para a equa o de difus o com um termo n o-local = Solutions for diffusion equation with a nonlocal term
Ervin Kaminski Lenzi,Marcelo Kaminski Lenzi,Roberto Rossato,Luiz Carlos Martins Filho
Acta Scientiarum : Technology , 2009,
Abstract: Neste trabalho, foram obtidas solu es para a equa o da difus o na presen a de um termo n o-local dependente de variáveis espaciais e temporais utilizando a técnica de fun o de Green. O termo n o-local incorporado na equa o da difus o pode ser relacionado a várioscontextos de interesse físico, como, por exemplo, derivadas de ordem fracionárias espaciais ou temporais, e introduz diferentes regimes de dispers o para a solu o. Os resultados encontrados aqui também permitem a descri o de uma extensa classe de processos difusivos, em particular das situa es caracterizadas pela difus o an mala. This work is devoted to investigating solutions for the diffusion equation with a nonlocal spatial and time-dependent term by using the Green function approach. This nonlocal term incorporated in the diffusion equation may be related to several physical contexts – inparticular with the fractional spatial and time derivatives and reaction processes. It also introduces different regimes for the diffusion process and may be connected to a rich class of anomalous diffusive processes.
Equa o de difus o n o linear, solu es e difus o an mala = Nonlinear diffusion equation, solutions and anomalous diffusion
Renata Ferreira Colli Badini,Giane Gon?alves,Marcelo Kaminski Lenzi,Onélia Aparecida Andreo dos Santos
Acta Scientiarum : Technology , 2007,
Abstract: Neste trabalho, investigaremos uma equa o de difus o n o linearconsiderando a presen a de termos convectivos, absorventes e um coeficiente de difus o dependente do tempo. Os termos n o lineares presentes na equa o ser o uma conseqüência do emprego de uma generaliza o n o linear da Lei de Darcy ( (r, t) = - (t)r-q r(r, t) r [r(r, t)]u ) n J D r ou da presen a de um termo absorvente n o linear (- a(t)[r(r, t)]m ) que pode, por exemplo, representar um processo de difus o com rea o. Em particular, para esta equa o de difus o obteremos uma nova classe de solu es e analisaremos os efeitos produzidos por tais termos, assim como rela o com processosdifusivos an malos. This work aimed to investigate a nonlinear diffusion equation by considering the presence of a time dependent diffusion coefficient, convective and absorbent terms. The nonlinear terms present in the diffusion equation are consequence of employing a nonlineargeneralization of Darcy’s law ( [ ] ) = - -q r r ) u (r, t) (t)r (r, t) r (r, t n J D r or a nonlinear absorbent term(- a(t)[r(r, t)]m ), which may be related to a reaction diffusion process. Particularly, we will obtain new classes of solutions, analyze the effects produced by these terms and the relation of the results presented here with anomalous diffusion.
The Kramers-Kronig relations for usual and anomalous Poisson-Nernst-Planck models
Luiz Roberto Evangelista,Ervin Kaminski Lenzi,Giovanni Barbero
Physics , 2013, DOI: 10.1088/0953-8984/25/46/465104
Abstract: The consistency of the frequency response predicted by a class of electrochemical impedance expressions is analytically checked by invoking the Kramers-Kronig (KK) relations. These expressions are obtained in the context of Poisson-Nernst-Planck usual (PNP) or anomalous (PNPA) diffusional models that satisfy Poisson's equation in a finite-length situation. The theoretical results, besides being successful in interpreting experimental data, are also shown to obey the KK relations when these relations are modified accordingly
Modelagem de um reator integral aplicado na rea o de reforma a vapor de metano = Modeling of integral reactor applied methane steam reforming
Giane Gon?alves,Daniel Russo,Ervin Kaminski Lenzi,Onélia Aparecida Andreo dos Santos
Acta Scientiarum : Technology , 2007,
Abstract: Freqüentemente, a valida o de modelos matemáticos aplicados a reatores industriais esbarra na dificuldade de obten o de medidas experimentais confiáveis. Uma maneira de contornar esta limita o corresponde à implanta o de uma unidade em escala de bancada devidamente instrumentada, na qual s o obtidos dados experimentais emcondi es controladas. Neste contexto, foram efetuados ensaios em um reator integral de reforma a vapor de metano em escala de bancada, em diversas condi es experimentais. As medidas de temperatura no leito foram efetuadas por meio de um termopar multiponto em seis posi es axiais distintas, enquanto a composi o do efluente do reator foi determinada por cromatografia gasosa. Estes dados experimentais foram comparados com as previs es de um modelo pseudo-homogêneo, unidimensional e dinamico. Os resultados indicam que o modelo é adequado, sendo que tanto a atividade catalítica como a convers o s o sensíveis à temperatura operacional, enquanto a temperatura do leito é praticamente insensível à vaz o nas condi es experimentais exploradas. Frequently, the validation of applied mathematical models of industrial reactors dash into the difficulty of obtaining reliable experimental data. A way to overcome this limitation is the proper use and operation or a in bench scale, experimental setup from whichexperimental data can be obtained in controlled conditions. In this context, experiments were carried out in an integral reactor of steam reform, in different experimental conditions. Thermocouples were placed along the catalyst bed to allow for temperature monitoring in six equally spaced and distinct positions of the reactor, the composition of the effluent of the reactor was determined by gas chromatography. These experimental data were compared with the theoretical results of a pseudo-homogeneous one-dimensional,dynamic mathematical model. The results indicate that the model can successfully describe the experimental data set and the catalytic activity and the conversion are sensitive to variations of the operational temperature, while the temperature of the bed is practically constant to the flow variations in the explored experimental conditions.
Immittance response of an electrolytic cell in the presence of adsorption, generation, and recombination of ions
Jamile Lorena de Paula,José Adauto da Cruz,Ervin Kaminski Lenzi,Luiz Roberto Evangelista
Physics , 2012,
Abstract: Effects of the adsorption-desorption process on the immittance response of an electrolytic cell are theoretically investigated in the framework of the diffusional Poisson-Nernst-Planck (PNP) continuum model, when the generation and recombination of ions is taken into account. The analysis is carried out by searching solutions for the drift-diffusion equation coupled to the Poisson's equation relating the effective electric field to the net charge density. The effect of different ion mobilities on the immittance, i.e., situations with equal and different diffusion coefficients for positive and negative ions, are considered. A general exact expression for the admittance in the context of the linear approximation is obtained.
A connection between anomalous Poisson-Nernst-Planck models and equivalent circuits with constant--phase elements
Ervin Kaminski Lenzi,Jamile Lorena de Paula,Fernanda R. G. B. Silva,Luiz Roberto Evangelista
Physics , 2013,
Abstract: A connection between the impedance spectroscopy response of anomalous Poisson-Nernst-Planck (PNPA) diffusional models and of equivalent circuits containing constant phase elements (CPE) is established for a typical electrolytic cell. The analysis is carried out in the limit of low frequency in order to highlight the surface effects and to explore how they can be connected to the presence of CPE in the circuit. It is shown that, depending on the choice of the equivalent circuit, the action of these elements can be the same as the one obtained by using integro-differential boundary conditions to describe anomalous diffusive processes in the framework of PNPA models. The predictions are also compared with an experimental data obtained from an electrolytic solution.
Modelagem da polimeriza??o simultanea de estireno em suspens?o e emuls?o
Lenzi, Marcelo K.;Lima, Enrique L.;Pinto, José Carlos;
Polímeros , 2004, DOI: 10.1590/S0104-14282004000200015
Abstract: although both emulsion and suspension polymerization processes are performed in heterogeneous media, each process presents its own typical characteristics, such as the particle size distribution, molecular weight distribution, polymer particle nucleation rates, rates of polymerization, and so on. in this work styrene polymerizations are carried out in suspension and emulsion processes simultaneously. the initial reactor charge resembles the recipe of standard styrene suspension polymerizations, while emulsion polymerization constituents are added during the batch. the influence of the moment when emulsion feed is started on the course of the polymerization and the effects on the polymer properties are analyzed. a mathematical model is developed to describe the behavior of the system. simulation data obtained with the proposed model are in good agreement with experimental conversion, average molecular weight and molecular weight distribution data. it was observed that the polymer particle morphology and the average molecular weight change very significantly with the emulsion feed time and that such changes can lead to bimodal molecular weight distributions. core-shell polymer particles were obtained, with the core being formed by polymer particles from the suspension polymerization process and the shell formed by polymer particles from the emulsion one.
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