Transactions of the Canadian Society for Mechanical Engineering
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Volume 36 (2012), Issue 4
Direct adaptive fuzzy sliding observation and control
Alireza Gholami, Amir H.D. Markazi
In this paper, a new direct adaptive fuzzy sliding observation and control (AFSOC) method is proposed. The method can be applied to a class of unknown nonlinear systems. The proposed observer estimates the closed-loop state tracking error asymptotically, provided that the output gain matrix includes Hurwitz coefficients. The chattering phenomenon is overcome by using a boundary layer around the sliding surface. The stability of the AFSOC method is proved using the Lyapunov stability theory. Numerical simulation on a benchmark chaotic system depicts the effectiveness of the proposed algorithm.
Design and optimization of an eight-bar legged walking mechanism imitating a kinetic sculpture, "Wind Beast"
Daniel Giesbrecht, Christine Q. Wu, Nariman Sepehri
Legged off-road vehicles exhibit better mobility while moving on rough terrain. Development of legged mechanisms represents a challenging problem and has attracted significant attention from both artists and engineers. In this paper, we present the design of a single-degree-of-freedom legged walking mechanism using the mechanism design theory and optimization to imitate a well-known kinetic sculpture, a Wind Beast. The optimization is set up to: i) minimize the energy input and ii) maximize the stride length. The optimization is based on the dynamic force analysis. A prototype of the optimized walking mechanism with 6 legs was built to demonstrate its smooth motion. The success in designing a legged mechanism capable of imitating the well-known kinetic sculpture using the engineering design theories is a small step bridging the gap between art and engineering.
Heat transfer from two discrete flush-mounted heaters subjected to laminar pulsating air flow in a channel
In this article, a numerical study on heat transfer in laminar pulsating air flow in a channel around two discrete flush-mounted heat sources is reported. Simulations are conducted for five different frequencies and three different amplitudes while the Reynolds number (Re = 125) and Prandtl number (Pr = 0.71) remain constant for all cases. In addition, limited geometric parameters such as spacing between the two discrete heaters are investigated. Numerical simulations are performed by using the commercial CFD code Fluent. The optimum heat transfer parameters are analyzed. The time-mean Nusselt number is obtained for a cycle and given as dimensionless parameters. The heat transfer enhancements are found for low frequencies and high amplitudes.
Multi-beam laser heating of steel: temperature and thermal stress analysis
Shahzada Zaman Shuja, Bekir Sami Yilbas
Laser multi-beam heating of steel sheet surface is considered. The irradiated laser spots are located along an arc to increase heated surface area during laser scanning at a constant speed. Temperature and stress fields are predicted for various number of spots along the arc. It is found that temperature and stress fields in the irradiated substrate can be controlled through proper selection of the number of irradiated spots along the arc. Increasing number of irradiated spots results in development of almost uniform high temperature and high stress fields around the arc; however, local heating and discontinuous stress field giving rise to large differences in von Mises stress occurring for reduced number of spots in the arc.
Improving crashworthiness in railcar against rollover
Sarmad Riazi, Mohammad Mahdi Feizi, Parisa Hosseini-Tehrani
Roof strength is critical to survival in rollover accidents in railcars. In this task using LS-DYNA software different scenarios are examined in order to strengthen railcar roof and to improve the crashworthiness features against rollover. The performance of each scenario is investigated through presenting the results of crushing behavior and energy absorption versus displacement response. Eventually, the best solution providing the highest ratio of "Energy absorption per Mass" among the studied model is presented.
Investigation of hybrid and different cross-section composite disc springs using finite element method
In this study the effectiveness of composite disc springs with different cross-section and hybrid type are determined by taking into account load capacities, masses, hybridization characteristics and costs of composite disc springs. The disc springs are analyzed with ABAQUS finite elements program by compressing between two rigid plates. The load-deflection characteristics obtained as a result of the analysis are compared with the analytic and experimental studies. Then different cross-section and hybrid composite disc springs were modeled. The trapeze A disc spring were confirmed to be more advantageous in terms of load capacity and mass by investigating the modeled disc springs. The effect of hybridization on hybrid disc springs with standard cross-section was investigated and optimum hybrid disc spring was determined according to cost and maximum loading capacity. Consequently, it is determined that carbon/epoxy plies used for outer layers are more advantageous. But the outer ply subjected to force was damaged thus this layer should be particularly reinforced.
Determination of the convective heat transfer coefficient of hot air rising through terracotta flues
Taylor A. Oetelaar, Clifton R. Johnston
We experimentally studied natural convection processes inside terracotta flues as a part of a larger numerical study of ancient Roman baths. The air, heated in a plenum below the wall, rose through the tubes. Two clusters of thermocouples, equally spaced in the flues, measured temperatures throughout the thickness of the wall. The data from the two clusters proved to be measurably different. The resulting convective heat transfer coefficients determined using the bottom cluster, showed no dependence on the plenum temperature. The measured convective heat transfer coefficient was between 6.2 and 7.6 W/m2ˇ°C, with an average of 7.0 W/m2ˇ°C.
Studies on effects of combustion chamber geometry and injection pressure on biodiesel combustion
Chandrashekharapua Ramachandraiah Rajashekhar, Tumkur Krishnamurthy Chandrashekar, Chebbiyyan Umashankar, Rajagopal Harish Kumar
Combustion of biodiesels has inherent problems due to their high viscosity and low volatility. This paper relates the modification of engine combustion chamber design, for inducing turbulence to improve the combustibility of combustible mixture. A survey of literature shows that experimental studies have not been done on a tri-chambered piston for evaluating influence on the performance and emission characteristics using diesel blends as well. The objective of this work is to study the effect of combustion chamber geometry and injection pressure on performance and emissions of a biodiesel (Jatropha) fuelled multi-chambered piston diesel engine. The performance and emission characteristics were studied and it has been noticed that for the engine under consideration 200 bar injection pressure gives optimum performance.
Full journal title: Transactions of the Canadian Society for Mechanical Engineering
Abreviated journal title: Trans. Can. Soc. Mech. Eng.
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