In this article, the piezoelectric coverage area of a shear deformable cantilever beam is optimized for maximum modal electromechanical coupling coefficient. A discrete layer finite element model with piezoelectric capability is implemented to solve the free vibration problem under open-circuit and short-circuit electric boundary conditions. A binary-coded genetic algorithm was used to carry out the optimization. The piezoelectric coverage locations are found to be dependent upon the mode of vibration, which is primarily due to charge cancelation at higher modes. Optimal distribution tends to cover part of the beam experiencing maximum bending. It is shown that the type of base beam material has negligible effect on the optimum locations of the piezoelectric material. Furthermore, an optimum ratio of piezoelectric-to-beam thickness exists for the first three modes.
SUMMARYEvolutionary algorithms mimic the process of natural evolution governed by the 'survival of the ÿttest' principle. In this work, a genetic algorithm (GA) is successfully used to solve problems in potential ow in a gradual contraction, viscous ow over a backward facing step, and non-Newtonian ow using the power law model. Speciÿcally, the GA heuristically searches the domain for potential solutions, precluding many convergence di culties associated with the sti ness of a problem. The GA was able to solve problems that the gradient-based method could not mainly because of its relative indi erence to regions of high gradients when performing the search and that systems of discretized equations are never actually solved. The GA exhibited excellent scalability properties for solving problems with a large number of nodes. These results show evolutionary techniques to be of great utility in solving sti problems in uid ow.
A hybrid algorithm that combines genetic programming (GP) and genetic algorithms (GAs) that deduce a closed-form correlation of building energy use is presented. Throughout the evolution, the terms, functions, and form of the correlation are evolved via the genetic program. Whenever the fitness of the best correlation stagnates for a specific number of GP generations, the GA optimizes the real-valued coefficients of each correlation in the population. When the GA, in turn, stagnates, correlations with optimized coefficients and powers are passed back to the GP for further search. The hybrid algorithm is applied to the problem of predicting energy use of a U-shape building. More than 800 buildings with various foot-print areas, relative compactness (RC), window-to-wall ratio (WWR), and projection factor (PF) values were simulated using the VisualDOETM energy simulation engine. The algorithm tries to minimize the difference between simulated and predicted values by maximizing the R2 value. The algorithm was able to arrive at a closed-form correlation that combines the four building parameters, accurate to within 4%. The methodology can be easily used to model any type of data behavior in any engineering or nonengineering application.
Abstract-Over a wide range of Reynolds numbers, the phenomenon of vortex shedding and the associated fluctuations in drag and lift, and the possible vibration in the structure, can be a formidable problem in many applications. Attempts have been made to control, reduce, or altogether eliminate these vortex-induced fluctuations in flow properties. In this study, unsteady laminar flow around a circular cylinder is numerically simulated using the finite volume method. The passive technique of introducing simple slits at specified locations around the cylinder for the purpose of modulating the effect of vortex shedding is investigated. It was found that at a Reynolds number of 1000 the reduction in the coefficient of drag is over 14%, which decreases in Nusselt number, and thus the total heat transfer from the cylinder, of 15.5% and 4.44%, respectively. Physical insight is given to explain the source of the phenomenon, and the advantages of applying such passive techniques to control free flows are discussed.
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