System Engineering Paper

The Iowa State University team, Team LunaCY, is composed of the following sub-teams: the main student organization, the Lunabotics Club; a senior mechanical engineering design course, ME 415; a senior multidisciplinary design course, ENGR 466; and a senior design course from Wartburg College in Waverly, Iowa. Team LunaCY designed and fabricated ART-E III, Astra Robotic Tractor- Excavator the Third, for the team's third appearance in the NASA Lunabotic Mining competition. While designing ART-E III, the team had four main goals for this year's competition:to reduce the total weight of the robot, to increase the amount of regolith simulant mined, to reduce dust, and to make ART-E III autonomous. After many designs and research, a final robot design was chosen that obtained all four goals of Team LunaCY. A few changes Team LunaCY made this year was to go to the electrical, computer, and software engineering club fest at Iowa State University to recruit engineering students to accomplish the task of making ART-E III autonomous. Team LunaCY chose to use LabView to program the robot and various sensors were installed to measure the distance between the robot and the surroundings to allow ART-E III to maneuver autonomously. Team LunaCY also built a testing arena to test prototypes and ART-E III in. To best replicate the competition arena at the Kennedy Space Center, a regolith simulant was made from sand, QuickCrete, and fly ash to cover the floor of the arena. Team LunaCY also installed fans to allow ventilation in the arena and used proper safety attire when working in the arena . With the additional practice in the testing arena and innovative robot design, Team LunaCY expects to make a strong appearance at the 2012 NASA Lunabotic Mining Competition.

Analysis methodology for wind-induced vibrations on chimneys

No presente trabalho é realizado um estudo sobre uma chaminé da Refinaria Alberto Pasqualini (REFAP) da Petrobras que apresentou vibração com grande amplitude de oscilação e trincas de fadiga. O estudo apresenta um caso clássico de vibração induzida pelo vento, em que os vórtices formados em uma chaminé atingem a chaminé à frente e induzem oscilações severas, principalmente quando está apoiada sobre uma base flexível. O trabalho tem como objetivo apresentar uma metodologia para análise desse tipo de caso. Conhecido em inglês como vortex shedding, o fenômeno é bastante popular na literatura, porém devido à sua complexidade se torna bastante complicado o cálculo dos esforços atuantes sobre as estruturas e consequentemente ele é muito pouco explorado. A fim de analisar fielmente o fenômeno observado em campo, três configurações da estrutura são estudadas: original, na qual foi observada vibração excessiva; chaminé com a base reforçada com vigas, na qual se buscou aumentar a rigidez total da estrutura; e chaminé com reforço na base e na região onde apresentou trincas. Para tal, são realizadas análises modais para obter as frequências naturais das diferentes configurações da chaminé, análises harmônicas para obtenção das tensões nas estruturas sob vibração, e simulações em CFD para prever o fenômeno de formação e propagação de vórtices e obter uma comparação com os valores fornecidos na literatura. De modo a obter frequências e probabilidades de indução de vórtices sobre a chaminé, uma análise estatística é realizada sobre os ventos predominantes para a região de Canoas-RS, onde a refinaria se encontra. Finalmente, é estimada a vida em fadiga da chaminé com e sem reforço na região onde foram identificadas as trincas.A study is performed on a chimney that is located at Petrobras Alberto Pasqualini refinery (REFAP) in which high oscillatory amplitude vibration and fatigue cracks were observed. The study presents a classic case of wind-induced vibration, where the vortices originated in one chimney strike the following one and induce severe oscillations, specially when it is supported by a flexible base. The objective of this study is to present a methodology for analyzing this type of case. Known as vortex shedding, it is a very popular phenomenon in literature, however because of its complexity becomes quite complicated to calculate the loads acting on the structures and therefore it is very little explored. In order to accurately analyze the phenomenon observed in the field, three structure configurations are studied: original, which was observed excessive vibration; chimney with reinforced base, where its total stiffness was increased; and chimney with reinforced both base and zone where the cracks were observed. To achieve that, modal analysis are performed in order to obtain the natural frequencies of different chimneys’ configurations, harmonic analysis to obtain stress in the structures due to vibration, and CFD simulations to forecast vortex shedding formation and propagation and compare to the values provided from literature. In order to obtain the frequencies and probabilities of vortex shedding, a statistics analysis of predominant winds in Canoas-RS, where the refinery is located, is performed. Finally, fatigue life is estimated for the chimneys both with and without reinforcement where the cracks were identified