Romuel F. Machado

A methodology for the teaching of dynamical systems using analogous electronic circuits

The behaviour of dynamical systems can be reproduced from analogous electronic circuits, which allows the study of many interesting phenomena associated with them using inexpensive and versatile electronic components easily found on the market. This paper proposes a methodology to develop didactic platforms for the study of dynamical systems based on analogous electronic circuits. Presented here are the design and implementation of three electronic circuits that mimic natural chaotic systems: the forced Duffing system, the Lorenz system and the Rössler system.

Numerical simulation of solute trapping phenomena using phase-field solidification model for dilute binary alloys

Numerical simulation of solute trapping during solidification, using two phase-field model for dilute binary alloys developed by Kim et al. [Phys. Rev. E, 60, 7186 (1999)] and Ramirez et al. [Phys. Rev. E, 69, 05167 (2004)] is presented here. The simulations on dilute Cu-Ni alloy are in good agreement with one dimensional analytic solution of sharp interface model. Simulation conducted under small solidification velocity using solid-liquid interface thickness (2λ) of 8 nanometers reproduced the solute (Cu) equilibrium partition coefficient. The spurious numerical solute trapping in solid phase, due to the interface thickness was negligible. A parameter used in analytical solute trapping model was determined by isothermal phase-field simulation of Ni-Cu alloy. Its application to Si-As and Si-Bi alloys reproduced results that agree reasonably well with experimental data. A comparison between the three models of solute trapping (Aziz, Sobolev and Galenko [Phys. Rev. E, 76, 031606 (2007)]) was performed. It resulted in large differences in predicting the solidification velocity for partition-less solidification, indicating the necessity for new and more acute experimental data.

The effect of adding boron in solidification microstructure of dilute iron-carbon alloy as assessed by phase-field modeling

Alloying element like boron, even in small addition, is well known to improve hardenability of steels. Its application can improve mechanical properties of steels and reduce alloying costs. Despite these benefits is not easy to cast boron steels, mainly in dynamical solidification process like continuous casting, due to their crack susceptibility1,2. The strategy of using Phase-Field simulation of the solidification process is based on its proved capacity of predicting realistic microstructure that emerge during solidification under conditions even far from equilibrium3-5. Base on this, some comparative simulations were performed using a three component dilute alloy in a two dimensional domain under unconstrained (isothermal) and constrained (directional) solidification. Simulation results suggested two fragile mechanisms: one related to a deep dendritic primary arms space and other due to the remelting of this region at low temperature. Both resulted mainly from the high boron segregation in interdendritic regions.

Granulometric analysis based on the energy of Wavelet Transform coefficients

Esse artigo apresenta uma metodologia para analise de granulometria por imagem, baseada na modelagem de energia no espaco das frequencias, utilizando a transformada Wavelet. Apresenta uma breve revisao da ferramenta da transformada Wavelet, e detalha a metodologia proposta. Os resultados apresentados foram obtidos utilizando imagens simuladas numericamente e imagens experimentais. Esses resultados mostram uma correlacao importante entre a energia dos coeficientes das Wavelets e a distribuicao das dimensoes dos objetos analisados.

Análise numérica bidimensional da morfologia dendrítica do níquel e do ferro utilizando o método de campo de fase.

Nesse trabalho, sao apresentados os resultados de simulacoes bidimensionais da formacao de dendritas durante a solidificacao do niquel e do ferro puros, utilizando um modelo de campo de fase. A morfologia obtida mostrou-se qualitativamente semelhante a forma dendritica, com bracos primarios e secundarios bem desenvolvidos. Alem disso, as velocidades de crescimento em regime permanente, calculadas no presente trabalho, apresentaram boa conformidade com os dados experimentais em uma grande faixa de super-resfriamentos. Foi observado que a espessura da interface apresenta um forte efeito sobre a morfologia e a velocidade de solidificacao. Interfaces espessas reduzem o tempo computacional; entretanto podem gerar resultados inconsistentes. A espessura que apresentou os melhores resultados sem aumento acentuado do tempo de processamento foi 4x10-8m.

Analogia eletrônica no ensino de física

This work introduces a procedure for analogue electronic circuits design that emulate the dynamic behavior of physical and mathematical systems. Such circuits can be applied as a practical approach for didactic experiments, and easily settled at any laboratory. As instance, electronic version of Duffing and Rossler chaotic systems are designed and implemented, resulting in simple, low cost, robust and functional prototypes.