The Experts below are selected from a list of 5244 Experts worldwide ranked by ideXlab platform
Farhat Fnaiech - One of the best experts on this subject based on the ideXlab platform.
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a suitable Initialization Procedure for speeding a neural network job shop scheduling
IEEE Transactions on Industrial Electronics, 2011Co-Authors: A Yahyaoui, N Fnaiech, Farhat FnaiechAbstract:Artificial neural network models have been successfully applied to solve a job-shop scheduling problem (JSSP) known as a Nonpolynomial (NP-complete) constraint satisfaction problem. Our main contribution is an improvement of the algorithm proposed in the literature. It consists in using a Procedure optimizing the initial value of the starting time. The aim is to speed a Hopfield Neural Network (HNN) and therefore reduce the number of searching cycles. This new heuristic provides several advantages; mainly to improve the searching speed of an optimal or near optimal solution of a deterministic JSSP using HNN and reduce the makespan. Simulation results of the proposed method have been performed on various benchmarks and compared with current algorithms such as genetic algorithm, constraint satisfaction adaptive neural networks, simulated annealing, threshold accepting, flood method, and priority rules such as shortest processing time (SPT) to mention a few. As the simulation results show, and Brandts algorithm, combined with the proposed heuristic method, is efficient with respect to the resolution speed, quality of the solution, and the reduction of the computation time.
Grigorios N Beligiannis - One of the best experts on this subject based on the ideXlab platform.
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solving the urban transit routing problem using a particle swarm optimization based algorithm
Applied Soft Computing, 2014Co-Authors: Panagiotis N Kechagiopoulos, Grigorios N BeligiannisAbstract:Abstract The Urban Transit Routing Problem (UTRP) comprises an NP-hard problem that deals with the construction of route networks for public transit networks. It is a highly complex and multiply constrained problem, in which the assessment of candidate route networks can be both time consuming and challenging. Except for that, a multitude of potential solutions are usually rejected due to infeasibility. Because of this difficulty, soft computing algorithms can be very effective for its efficient solution. The success of these methods, however, depends mainly on the quality of the representation of candidate solutions, on the efficiency of the Initialization Procedure and on the suitability of the modification operators used. An optimization algorithm, based on particle swarm optimization, is designed and presented in the current contribution, aiming at the efficient solution of UTRP. Apart from the development of the optimization algorithm, emphasis is also given on appropriate representation of candidate solutions, the route networks in other words, and the respective evaluation Procedure. The latter Procedure considers not only the quality of service offered to each passenger, but also the costs of the operator. Results are compared on the basis of Mandl's benchmark problem of a Swiss bus network, which is probably the only widely investigated and accepted benchmark problem in the relevant literature. Comparison of the obtained results with other results published in the literature shows that the performance of the proposed soft computing algorithm is quite competitive compared to existing techniques.
Vladimir Zeitlin - One of the best experts on this subject based on the ideXlab platform.
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nonlinear geostrophic adjustment of long wave disturbances in the shallow water model on the equatorial beta plane
Journal of Fluid Mechanics, 2004Co-Authors: Le J Sommer, G M Reznik, Vladimir ZeitlinAbstract:We study the nonlinear response of the equatorial shallow-water system at rest to a localized long-wave perturbation with small meridional to zonal aspect ratio. An asymptotic theory of such a response (adjustment) for small Rossby numbers is constructed. Possible scenarios of nonlinear adjustment are classified depending on the relation between the Rossby number and the aspect ratio. The calculations show that slow, geostrophically balanced Rossby and Kelvin waves and the fast inertia–gravity waves are dynamically split off. The fast component of motion exerts no drag on the slow one, which is proved by direct computation. Evolution equations are derived for both components confirming earlier results which were obtained by ad hoc filtering of one of the components of motion. A well-defined Initialization Procedure is developed for each component. Due to the breaking of non-dispersive Kelvin waves, the asymptotic theory has obvious limits of validity. In order to go beyond these limits and to study strongly nonlinear effects during the adjustment process we undertook high-resolution shock-capturing numerical simulations based on recent progress in finite-volume numerical methods. The simulations confirm theoretical results but also reveal new effects such as fission of a strongly nonlinear Rossby-wave packet into a sequence of equatorial modons or jet formation in the wake of a breaking Kelvin wave.
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nonlinear geostrophic adjustment of long wave disturbances in the shallow water model on the equatorial beta plane
Journal of Fluid Mechanics, 2004Co-Authors: Le J Sommer, G M Reznik, Vladimir ZeitlinAbstract:We study the nonlinear response of the equatorial shallow-water system at rest to a localized long-wave perturbation with small meridional to zonal aspect ratio. An asymptotic theory of such a response (adjustment) for small Rossby numbers is constructed. Possible scenarios of nonlinear adjustment are classified depending on the relation between the Rossby number and the aspect ratio. The calculations show that slow, geostrophically balanced Rossby and Kelvin waves and the fast inertia–gravity waves are dynamically split off. The fast component of motion exerts no drag on the slow one, which is proved by direct computation. Evolution equations are derived for both components confirming earlier results which were obtained by ad hoc filtering of one of the components of motion. A well-defined Initialization Procedure is developed for each component. Due to the breaking of non-dispersive Kelvin waves, the asymptotic theory has obvious limits of validity. In order to go beyond these limits and to study strongly nonlinear effects during the adjustment process we undertook high-resolution shock-capturing numerical simulations based on recent progress in finite-volume numerical methods. The simulations confirm theoretical results but also reveal new effects such as fission of a strongly nonlinear Rossby-wave packet into a sequence of equatorial modons or jet formation in the wake of a breaking Kelvin wave.
A Yahyaoui - One of the best experts on this subject based on the ideXlab platform.
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a suitable Initialization Procedure for speeding a neural network job shop scheduling
IEEE Transactions on Industrial Electronics, 2011Co-Authors: A Yahyaoui, N Fnaiech, Farhat FnaiechAbstract:Artificial neural network models have been successfully applied to solve a job-shop scheduling problem (JSSP) known as a Nonpolynomial (NP-complete) constraint satisfaction problem. Our main contribution is an improvement of the algorithm proposed in the literature. It consists in using a Procedure optimizing the initial value of the starting time. The aim is to speed a Hopfield Neural Network (HNN) and therefore reduce the number of searching cycles. This new heuristic provides several advantages; mainly to improve the searching speed of an optimal or near optimal solution of a deterministic JSSP using HNN and reduce the makespan. Simulation results of the proposed method have been performed on various benchmarks and compared with current algorithms such as genetic algorithm, constraint satisfaction adaptive neural networks, simulated annealing, threshold accepting, flood method, and priority rules such as shortest processing time (SPT) to mention a few. As the simulation results show, and Brandts algorithm, combined with the proposed heuristic method, is efficient with respect to the resolution speed, quality of the solution, and the reduction of the computation time.
Shengyin Wang - One of the best experts on this subject based on the ideXlab platform.
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shape and topology optimization of compliant mechanisms using a parameterization level set method
Journal of Computational Physics, 2007Co-Authors: Liyong Tong, Michael Yu Wang, Shengyin WangAbstract:In this paper, a parameterization level set method is presented to simultaneously perform shape and topology optimization of compliant mechanisms. The structural shape boundary is implicitly embedded into a higher-dimensional scalar function as its zero level set, resultantly, establishing the level set model. By applying the compactly supported radial basis function with favorable smoothness and accuracy to interpolate the level set function, the temporal and spatial Hamilton-Jacobi equation from the conventional level set method is then discretized into a series of algebraic equations. Accordingly, the original shape and topology optimization is now fully transformed into a parameterization problem, namely, size optimization with the expansion coefficients of interpolants as a limited number of design variables. Design of compliant mechanisms is mathematically formulated as a general optimization problem with a nonconvex objective function and two additionally specified constraints. The structural shape boundary is then advanced as a process of renewing the level set function by iteratively finding the expansion coefficients of the size optimization with a sequential convex programming method. It is highlighted that the present method can not only inherit the merits of the implicit boundary representation, but also avoid some unfavorable features of the conventional discrete level set method, such as the CFL condition restriction, the re-Initialization Procedure and the velocity extension algorithm. Finally, an extensively investigated example is presented to demonstrate the benefits and advantages of the present method, especially, its capability of creating new holes inside the design domain.