•An alternative Active Contour Model solution for medical images is introduced.•A multi-population Cuckoo Search Strategy (MCSS) is implemented to boost ACM.•Proposed method was applied on Magnetic ...Resonance Imaging (MRI) data.•MCSS outperforms traditional ACM and ACM driven by multi-population PSO.
In this paper, an alternative Active Contour Model (ACM) driven by Multi-population Cuckoo Search (CS) algorithm is introduced. This strategy assists the converging of control points towards the global minimum of the energy function, unlike the traditional ACM version which is often trapped in a local minimum. In the proposed methodology, each control point is constrained in a local search window, and its energy minimisation is performed through a Cuckoo Search via Lévy flights paradigm. With respect to local search window, two shape approaches have been considered: rectangular shape and polar coordinates. Results showed that the CS method using polar coordinates is generally preferable to CS performed in rectangular shapes. Real medical and synthetic images were used to validate the proposed strategy, through three performance metrics as the Jaccard index, the Dice index and the Hausdorff distance. Applied specifically to Magnetic Resonance Imaging (MRI) images, the proposed method enables to reach better accuracy performance than the traditional ACM formulation, also known as Snakes and the use of Multi-population Particle Swarm Optimisation (PSO) algorithm.
Fault monitoring systems in Induction Motors (IMs) are in high demand since many production environments require yielding detection tools independent of their power supply. When IMs are inverter-fed, ...they become more complicated to diagnose via spectral techniques because those are susceptible to produce false positives. This paper proposes an innovative and reliable methodology to ease the monitoring and fault diagnosis of IMs. It employs fractional Gaussian windows determined from Caputo operators to stand out from spectral harmonic trajectories. This methodology was implemented and simulated to process real signals from an induction motor, in both healthy and faulty conditions. Results show that the proposed technique outperforms several traditional approaches by getting the clearest and most useful patterns for feature extraction purposes.
From the beginning of ferro-hydrodynamics, several authors have proposed analytical models to describe the movement of ferrofluids in the presence of rotating external magnetic fields. To this effect ...they have made valid simplifications in certain and very restricted physical situations. In this work we analyze the effects of these approaches against numerical solutions that do not make use of them. A sample of ferrofluid immersed in containers with three types of geometries was considered: one of flat and parallel plates, one cylindrical and another coaxial cylindrical. Velocity profiles were obtained by these two strategies. The analytical solution leads to a linear model with several simplifications, while the second, numerical in nature, generates a non-linear model, but without approximations. The simulation results showed that the implifications made in the analytical strategy generate profiles that are valid only for magnetic field intensities lower than the respective ferrofluid saturation values. Additionally, and given the level of development of analytical modeling, it was found that the numerical solution is currently the most appropriate to evaluate the ferro-hydrodynamic model, since it does not have restrictions related to the intensity of the magnetic field. In the same way, it allows to evidence the phenomenon of saturation in the velocity profiles by increasing the intensity of the magnetic field, a situation observed experimentally, and unpredictable by means of these currently available pseudo-analytical solutions.
Este artículo describe el diseño de un microcanal rectangular óptimo, construido con grafi to de alta conductividad térmica (HTCG). Para simular el disipador de microcanales propuesto se utilizó el ...modelo de resistencia térmica total y el criterio de minimización de la generación de entropía. Para solucionar el problema de optimización, se utilizó el algoritmo de enjambre de partículas unifi cado (UPSO). Los resultados mostraron un efecto marcado al utilizar este conductor térmico, en comparación con materiales tradicionales (tales como aluminio), y utilizando aire y amoniaco gaseoso como fl uidos de trabajo. También se reporta el efecto relativo de las resistencias térmicas de constricción, de convección y del fl uido, sobre la resistencia térmica equivalente total. Como un ejemplo demostrativo del efecto causado al cambiar la naturaleza del refrigerante, se seleccionó un nanofl uido de dióxido de titanio. Se encontró que el número de Nusselt es perceptiblemente menor, cuando se utiliza un nanofl uido como refrigerante y cuando el material con que está construido el microcanal es HTCG.
Models of series-parallel (SP) photovoltaic (PV) arrays focus on the system of nonlinear equations that represents the array’s electrical behavior. The solution of the system of nonlinear equations ...can be posed as an optimization problem and solved with different methods; however, the models do not formulate the optimization problem and do not evaluate different optimization algorithms for its solution. This paper proposes a solution, using global optimization algorithms, of the mathematical model that describes the electrical behavior of a SP generator, operating under uniform and partial shading conditions. Such a model is constructed by dividing the generator into strings and representing each module in the string with the single-diode model. Consequently, for each string a system of nonlinear equations is build applying the Kirchhoff’s laws, where the unknowns are the modules’ voltages. The solution of the resulting nonlinear equation system is posed as an optimization problem, where the objective function is defined as the sum of the squared of each nonlinear equation. Minimum and maximum values of each voltage are defined from the datasheet information of the modules and bypass diodes. As a demonstrative example, we arbitrarily select two well-known algorithms to solve this problem: Genetic Algorithms and Particle Swarm Optimization. Simulation results show that both algorithms solve the optimization problem and allow the reproduction of the generator’s characteristic curves. Moreover, the results also indicate that the optimization problem is correctly defined, which opens the possibility explore other optimization algorithms to reduce the computation time.
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This article describes one way to solve the mathematical model of a system is made up of a mass-spring-dashpot (MSD), using the virtual firefly metaheuristic algorithm. Using this strategy, the MSD ...problems are transformed into a problem of minimization of the system’s maximum frequency for all its natural frequencies, in such a way, that the value found corresponds to the global minimum. The viability of this strategy solving some typical MSD systems was demonstrated, as shown. It was concluded that this algorithm is very helpful, because it allows to the user to dedicate more time to the analysis of the system itself, instead to the solution methods of the model. It was also helpful as a no conventional way to solve this kind of problems numerically.
En el presente artículo se propone una metodología para resolver el modelo matemático de un sistema compuesto de Masa-Resorte-Amortiguador (MRA), mediante el uso de un método de optimización global que, como ejemplo ilustrativo, se utilizó el Algoritmo de la Luciérnaga Virtual (ALV). Con esta estrategia, los problemas MRA se transforman en problemas de optimización (minimización de la frecuencia máxima del sistema para todas sus frecuencias naturales), de tal forma que, el valor encontrado es el mínimo global. Se demostró la viabilidad de esta estrategia mediante la solución de algunos ejemplos demostrativos de sistemas MRA descritos en el artículo. Se concluye que esta estrategia resultó de gran ayuda, pues permite concentrar al usuario en el análisis del mecanismo propiamente, en lugar de la metodología de solución del modelo. Resultó igualmente útil como una forma no convencional, de resolver este tipo de problemas numéricamente.
This article describes the design of an optimal rectangular microchannel made of a high thermal conductive graphite (HTCG). For simulating the proposed microchannel heat sink, the total resistance ...model and the entropy generation minimization criterion were used. For solving the optimization problem, the unifi ed particle swarm optimization algorithm (UPSO), was used. Results showed a marked effect of using this high thermal conductor when compared to traditional materials, such as aluminum, and while using air and ammonia gas as the working fl uids. It is also reported the relative effect of the constriction, convective and fl uid thermal resistances on the overall equivalent thermal resistance. As a demonstrative example when changing the nature of the coolant, a titanium dioxide nanofl uid was selected. It was found that the Nusselt number is perceptibly lower, when the coolant is a nanofl uid and the material for the making of the microchannel is an HTCG.
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