Elmer M. Gennaro

Influences of Damping Resistances on Transient Simulations in Transmission Lines

Simulations of electromagnetic transients in transmission lines can be carried out using simple circuit model. In the case of applications of simple circuit models based on π circuits, there are problems mainly caused by numeric oscillations. The lumped-parameter π equivalent model can be used with some advantages. The numeric integration method applied to the simulations of electromagnetic transients is the trapezoidal rule. If this numeric method is associated with the π equivalent model, results obtained from the simulations are distorted by Gibbs’ oscillations or numeric ones. The introduction of damping resistance parallel to the series RL branch of the π equivalent model can mitigate Gibbs’ oscillations in obtained results. Voltage peaks caused by these oscillations can also be decreased. So, in this paper, the combined influences of the introduction of damping resistance, the number of π circuits and the time step are investigated searching for minimizing Gibbs’ oscillations and the voltage peaks in electromagnetic transient simulations. For this, transient simulations are exhaustively carried out for determining the highest voltage peaks, ranges of damping resistances and other parameters of the model, which minimize these voltage peaks caused by Gibbs’ oscillations.

Transmission Lines Model with Different Basic Structures Applied to Transient Electromagnetic Simulations

Models based on lumped elements are simple ones to represent systems composed by distributed parameters when models with lumped elements use a lot of these elements. However, such mentioned models usually present numerical problems because it is subject to the influence of numerical oscillations. When introducing new elements, such as damping resistors, in the mentioned models, the numerical oscillations can be minimized. The introduction of new elements increases the computational time for the analysis and simulations with the modified model. Thus, by applying π circuit cascades, simulations with abrupt changes in voltage or current are carried out using two different structures of π circuits with the purpose to achieve a similar accuracy and less computational time than those obtained with application damping resistor in every π circuit units.

Aeroacústica de emparelhamento de vórtices em esteiras assimétricas

O objetivo deste estudo e analisar a aeroacustica de esteiras assimetricas. Tal escoamento pode ser encontrados a jusante de perfis aerodinamicos que geram sustentacao, dispositivos hipersustentadores de aeronaves ou de tubos proximos a paredes, por exemplo. A evolucao do escoamento e calculada por simulacao numerica direta, na qual sao induzidas perturbacoes controladas, podendo-se obter o comportamento aeroacustico para diferentes frequencias. Sao formados vortices assimetricos que se emparelham. Tanto a formacao quanto o emparelhamento geram som. Devido a assimetria, este som se propaga de maneira distinta em diferentes direcoes. Estudando-se os fatores que influenciam nesta distribuicao pode-se entender melhor a aeroacustica de corpos de formas mais complexas. Futuramente tal conhecimento pode ser aplicado na concepcao de aeronaves mais silenciosas, cumprindo requisitos ambientais mais rigidos