Design of code division multiple access filters based on sampled fiber Bragg grating by using global optimization algorithms

Ivorra, Benjamín; Mohammadi, Bijan; Ramos, Ángel

doi:10.1007/s11081-013-9212-z

Cited by 7 publications

(14 citation statements)

References 35 publications

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“…This algorithm, called Hybrid GA Multi-layer line search Algorithm (HGMA), has been reported and validated on various industrial problems in 11,14,15,16,17 .…”

Section: Hybrid Ga Secant Methodsmentioning

confidence: 99%

Modeling the Optimal Trajectory of a Skimmer Ship to Clean Oil Spills in the Open Sea

et al. 2015

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Oil spill contamination in the open sea has been at the origin of some of the worst environmental disasters. One of the major cleaning techniques is the use of skimmer ships that contain various pumps distributed along its waterline to suck the oil from the surface of the water directly into storage units. We want to improve this process. We developed a model to simulate the effect of the skimmer ship on the evolution of the oil spill. This model, based on a finite volume approximation of an advection-diffusion-reaction equation, considers: the motion of oil spots resulting from the movement of the source of contamination; the diffusion and transport by wind and sea currents; and the phenomena associated with the action of the skimmer ship, assuming that it follows a pre-assigned trajectory. We introduce a nonlinear diffusion term to obtain finite speed diffusion. Also, we use an absorbing boundary condition, to account for the oil exiting the computational domain. To reduce numerical artificial diffusion, we use second order numerical schemes to discretize the advection terms. We also apply splitting schemes to decrease the computational complexity. To improve the whole process, we optimize the trajectory of a skimmer ship to maximize the amount of recovered oil during a fixed period of time, using an optimization method. The novel approach we advocate here is validated by comparing our numerical results with real life measurements from the Prestige spill, which took place in Spain in 2002. We were able to reproduce the satellite image of the spot after 4 days of pollution. We also prove that the optimal trajectory we get cleans the area near the coast up to 55 percent before the Prestige ship broke up. This percentage was improved to 88 percent by using a second ship on the entire area.

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“…This algorithm, called Hybrid GA Multi-layer line search Algorithm (HGMA), has been reported and validated on various industrial problems in 11,14,15,16,17 .…”

Section: Hybrid Ga Secant Methodsmentioning

confidence: 99%

Modeling the Optimal Trajectory of a Skimmer Ship to Clean Oil Spills in the Open Sea

et al. 2015

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“…The stopping criteria is based on a target minimum value for the functional to be reached within given maximum number of iterations. Global optimization is necessary since we have no information on the convexity of the cost function and several local minima may be present.We apply a multi-criteria global optimization algorithm (Ivorra et al, 2013) which aims at improving the initial condition for classical gradient-based methods (Mohammadi & Pironneau, 2009).…”

Section: Global Optimizationmentioning

confidence: 99%

Joint estimation of tiltmeter drift and volume variation during reservoir monitoring

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Chéry

Mohammadi

et al. 2019

J Geod

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Borehole tiltmeters are widely used to continuously record small surface deformation of reservoirs and volcanoes. Because these instruments display unknown long-term drift, only short-term tilt signal can be used for monitoring purpose. We propose a method to invert long-term time series of tilt data induced by strain variations at depth. The assumption that tiltmeter drift is linear over time is on its own insufficient to remove the drift and uniquely determine the deformation source parameters. To overcome this problem, we first invert the data with no constrain on the drift to obtain one particular solution among all admissible. Then, using the linearity of the forward model, we use the statistical properties of the drift distributions to restore the uniqueness of the solution. We illustrate our approach with four synthetic cases simulating volume changes of a reservoir. We demonstrate the efficiency of our method and show that the accuracy of estimated volume variation dramatically improves if low drift tiltmeters are used.

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“…In this work, we set this maximum value to 50,000 for each performance because, according to the literature [12,13,16,17], it is a high enough value. If such an algorithm consumes all the 50,000 evaluations and its solution does not satisfy the first stopping criterion (7), we consider that the algorithm has failed solving numerically the problem at hand.…”

Section: Validation Of the Gmamentioning

confidence: 99%

“…Initialization is also of vital importance for meta-heuristic methods such as Genetics Algorithms (GA) [7,8], for which a lack of heterogeneity in the individuals of the initial population may yield to a early convergence to a local minimum of T [9]. From a general point of view, choosing suitable initial conditions can improve the efficiency of existing optimization algorithms by reducing the number of evaluations of the cost function, which is particularly worthy when dealing with expensive functional calculations, as it is the case in many industrial design problems [10][11][12][13][14][15][16][17][18]. There already exists several optimization algorithms which have been improved by choosing appropriate initialization techniques.…”

Section: Introductionmentioning

confidence: 99%

Modelling and optimization applied to the design of fast hydrodynamic focusing microfluidic mixer for protein folding

et al. 2018

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In this work, we consider a microfluidic mixer that uses hydrodynamic diffusion stream to induce the beginning of the folding process of a certain protein. To perform these molecular changes, the concentration of the denaturant, which is introduced into the mixer together with the protein, has to be diminished until a given value in a short period of time, known as mixing time. In this context, this article is devoted to optimize the design of the mixer, focusing on its shape and its flow parameters with the aim of minimizing its mixing time. First, we describe the involved physical phenomena through a mathematical model that allows us to obtain the mixing time for a considered device. Then, we formulate an optimization problem considering the mixing time as the objective function and detailing the design parameters related to the shape and the flow of the mixer. For dealing with this problem, we propose an enhanced optimization algorithm based on the hybridization of two techniques: a genetic algorithm as a core method and a multi-layer line search methodology based on the secant, which aims to improve the initialization of the core method. More precisely, in our hybrid approach, the core optimization is implemented as a sub-problem to be solved at each iteration of the multi-layer algorithm starting from the initial conditions that it provides. Before applying it to the mixer design problem, we validate this methodology by considering a set of benchmark problems and, then, compare its results to those obtained with other classical global optimization methods. As shown in the comparison, for the majority of those problems, our methodology needs fewer evaluations of the objective function, has higher success rates and is more accurate than the other considered algorithms. For those reasons, it has been selected for solving the computationally expensive problem of optimizing the mixer design. The obtained optimized device shows a great reduction in its mixing time with respect to the state-of-the-art mixers.

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Design of code division multiple access filters based on sampled fiber Bragg grating by using global optimization algorithms

Cited by 7 publications

References 35 publications

Modeling the Optimal Trajectory of a Skimmer Ship to Clean Oil Spills in the Open Sea

Modeling the Optimal Trajectory of a Skimmer Ship to Clean Oil Spills in the Open Sea

Joint estimation of tiltmeter drift and volume variation during reservoir monitoring

Modelling and optimization applied to the design of fast hydrodynamic focusing microfluidic mixer for protein folding

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