Acoustic cloak based on Bézier scatterers

[EN] Among the different approaches proposed to design acoustic cloaks, the one consisting on the use of an optimum distribution of discrete scatters surrounding the concealing object has been successfully tested. The feasibility of acoustic cloaks mainly depends on the number and shape of the scatterers surrounding the object to be cloaked. This work presents a method allowing the reduction of the number of discrete scatterers by optimizing their external shape, which is here defined by a combination of cubic Bézier curves. Based on scattering cancellation, a two-dimensional directional cloak consisting of just 20 Bézier scatters has been designed, fabricated and experimentally characterized. The method of fundamental solutions has been implemented to calculate the interaction of an incident plane wave with scatterers of arbitrary shape. The acoustic cloak here proposed shows a performance, in terms of averaged visibility, similar to that consisting of 120 scatterers with equal circular cross sections. The operational frequency of the proposed cloak is 5940 Hz with a bandwidth of about 110 Hz.J. Sanchez-Dehesa acknowledges the financial support by the Spanish Ministerio de Economia y Competitividad and the European Union Fondo Europeo para el Desarrollo Regional (FEDER) under Grant with Ref. TEC2014-53088-C3-1-R. Lu Zhimiao acknowledges the financial support from the program of China Scholarships Council (No. 201503170282), Wen Jihong, Cai Li and Lu Zhimiao acknowledge the support by National Natural Science Foundation of China (Grant Nos 51275519 and 11372346)Lu, Z.; Sanchis Martínez, L.; Wen, J.; Cai, L.; Bi, Y.; Sánchez-Dehesa Moreno-Cid, J. (2018). Acoustic cloak based on Bézier scatterers. Scientific Reports. 8. https://doi.org/10.1038/s41598-018-30888-7S8Cummer, S. A. & Schurig, D. One path to acoustic cloaking. 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Optimization of Low Reynolds Number Airfoils for Martian Rotor Applications Using an Evolutionary Algorithm

The Mars Helicopter (MH) will be flying on the NASA Mars 2020 rover mission scheduled to launch in July of 2020. Research is being performed at the Jet Propulsion Laboratory (JPL) and NASA Ames Research Center to extend the current capabilities and develop the Mars Science Helicopter (MSH) as the next possible step for Martian rotorcraft. The low atmospheric density and the relatively small-scale rotors result in very low chord-based Reynolds number flows over the rotor airfoils. The low Reynolds number regime results in rapid performance degradation for conventional airfoils due to laminar separation without reattachment. Unconventional airfoil shapes with sharp leading edges are explored and optimized for aerodynamic performance at representative Reynolds-Mach combinations for a concept rotor. Sharp leading edges initiate immediate flow separation, and the occurrence of large-scale vortex shedding is found to contribute to the relative performance increase of the optimized airfoils, compared to conventional airfoil shapes. The oscillations are shown to occur independent from laminar-turbulent transition and therefore result in sustainable performance at lower Reynolds numbers. Comparisons are presented to conventional airfoil shapes and peak lift-to-drag ratio increases between 17% and 41% are observed for similar section lift

Aerodynamic Optimization of High-Speed Trains Nose using a Genetic Algorithm and Artificial Neural Network

An aerodynamic optimization of the train aerodynamic characteristics in term of front wind action sensitivity is carried out in this paper. In particular, a genetic algorithm (GA) is used to perform a shape optimization study of a high-speed train nose. The nose is parametrically defined via Bézier Curves, including a wider range of geometries in the design space as possible optimal solutions. Using a GA, the main disadvantage to deal with is the large number of evaluations need before finding such optimal. Here it is proposed the use of metamodels to replace Navier-Stokes solver. Among all the posibilities, Rsponse Surface Models and Artificial Neural Networks (ANN) are considered. Best results of prediction and generalization are obtained with ANN and those are applied in GA code. The paper shows the feasibility of using GA in combination with ANN for this problem, and solutions achieved are included

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Metamaterials are artificial composites with micro-structures that are systematically designed such that the macroscopic behavior can accommodate particular functionalities or exhibit extraordinary properties, which are not commonly found in natural materials. Topology and geometry of micro-structures play an important role in characterizing the properties of the metamaterials. Inverse design of metamaterials via topology optimization methods offer new topological features and helps in achieving novel physical mechanism or high-performance functionalities. Inverse design is an iterative process, that involves numerical analysis and requires much computational resources. This dissertation proposes the methodology for designing metamaterials using topology optimization with level set functions and model order reduction methods. Level set method enables design with smooth boundaries, while the computational effort required in solving large linear system of equations is eliminated with reduced basis approximations. An example of the inverse design method from the dissertation is to find a unit cell structure that results in macroscopic properties with intended elastic modulus for instance, with negative Poisson's ratio. The other example is to enhance hydrophone performance in 1-3 piezoelectric composites. Numerical examples demonstrate that the methodology is computationally efficient and robust for designing metamaterials. Taking advantage of inverse design as a powerful tool in designing metamaterials, it is adopted in this dissertation for the waveguides design. The second part of this thesis aims to design phononic crystals that offer robust transport of mechanical waves on the interfaces. The propagating wave modes in plate-like structures are topologically protected edge states and are analogous to quantum valley hall effect and quantum spin hall effect in the electronic systems. The computational inverse design methodology adopted is through topology optimization using genetic algorithm to find optimized unit cell geometries resulting from objective functions based on band structures and wave modes. The optimized phononic crystals support wave propagation against backscattering inspite of the presence of defects.Metamaterialien sind künstliche Verbundwerkstoffe mit Mikrostrukturen, die systematisch so gestaltet sind, dass das makroskopische Verhalten besondere Funktionen oder außergewöhnliche Eigenschaften aufweist, die in natürlichen Materialien nicht üblich sind. Topologie und Geometrie der Mikrostrukturen spielen eine wichtige Rolle bei der Charakterisierung der Eigenschaften der Metamaterialien. Das inverse Design von Metamaterialien mittels Topologie-Optimierungsmethoden bietet neue topologische Eigenschaften und hilft bei der Erreichung neuartiger physikalischer Mechanismen oder Hochleistungsfunktionen. Inverses Design ist ein iterativer Prozess, der numerische Analysen beinhaltet und viel Rechenleistung erfordert. In dieser Dissertation wird eine Methodik für den Entwurf von Metamaterialien unter Verwendung von Topologieoptimierung mit Level-Set-Funktionen und Methoden zur Reduzierung der Modellordnung vorgeschlagen. Die Level-Set-Methode ermöglicht ein Design mit glatten Grenzen, während der Rechenaufwand, der für die Lösung großer linearer Gleichungssysteme erforderlich ist, durch reduzierte Basisapproximationen entfällt. Ein Beispiel für die inverse Entwurfsmethode aus der Dissertation ist die Suche nach einer Einheitszellenstruktur, die zu makroskopischen Eigenschaften mit beabsichtigtem Elastizitätsmodul führt, beispielsweise mit negativer Poissonzahl. Ein anderes Beispiel ist die Verbesserung der Leistung von Hydrophonen in 1-3 piezoelektrischen Verbundwerkstoffen. Numerische Beispiele zeigen, dass die Methodik für die Entwicklung von Metamaterialien rechnerisch effizient und robust ist. Die Vorteile des inversen Designs als leistungsfähiges Werkzeug bei der Entwicklung von Metamaterialien werden in dieser Dissertation für die Entwicklung von Wellenleitern genutzt. Der zweite Teil dieser Arbeit zielt darauf ab, phononische Kristalle zu entwerfen, die einen robusten Transport von mechanischen Wellen an den Grenzflächen ermöglichen. Die sich ausbreitenden Wellenmoden in plattenförmigen Strukturen sind topologisch geschützte Randzustände und entsprechen dem Quanten-Tal-Hall-Effekt und dem Quanten-Spin-Hall-Effekt in elektronischen Systemen. Die angewandte rechnerische inverse Entwurfsmethodik besteht in der Topologieoptimierung mit Hilfe eines genetischen Algorithmus, um optimierte Einheitszellengeometrien zu finden, die sich aus Zielfunktionen auf der Grundlage von Bandstrukturen und Wellenmoden ergeben. Die optimierten phononischen Kristalle unterstützen die Wellenausbreitung trotz des Vorhandenseins von Defekten gegen Rückstreuung

Multi-Objective Optimization of Motor Vessel Route

International audienceThis paper presents an original method that allows computation of the optimal route of a motor vessel by minimizing its fuel consumption. The proposed method is based on a new and efficient meshing procedure that is used to define a set of possible routes. A consumption prediction tool has been developed in order to estimate the fuel consumption along a given trajectory. The consumption model involves the effects of the meteorological conditions, the shape of the hull and the power train characteristics. Pareto-optimization with a Multi-Objective Genetic Algorithm (MOGA) is taken as a framework for the definition and the solution of the multi-objective optimization problem addressed. The final goal of this study is to provide a decision helping tool giving the route that minimizes the fuel consumption in a limited or optimum time

Isogeometric Boundary Elements in Electromagnetism: Rigorous Analysis, Fast Methods, and Examples

We present a new approach to three-dimensional electromagnetic scattering problems via fast isogeometric boundary element methods. Starting with an investigation of the theoretical setting around the electric field integral equation within the isogeometric framework, we show existence, uniqueness, and quasi-optimality of the isogeometric approach. For a fast and efficient computation, we then introduce and analyze an interpolation-based fast multipole method tailored to the isogeometric setting, which admits competitive algorithmic and complexity properties. This is followed by a series of numerical examples of industrial scope, together with a detailed presentation and interpretation of the results

Métodos de reconstrucción en dominio temporal para tomografía por transmisión de ultrasonidos

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física Atómica, Molecular y Nuclear, leída el 06-06-2017Breast cancer (BC) is the leading cause of cancer-related death for women in Europe, and the second one after lung cancer in the US [World Cancer Report, 2008]. Early detection is very important for the survival rate of BC, because the smaller the local extension of the neoplasia, the better the output of the surgical treatments employed. Besides, early detection increases the possibility of preserving the breast and decreases the probability of needing more invasive treatments [Secretaría de Salud, 2007, Alteri et al., 2011]. Mammography is currently the standard procedure employed for breast screening programs around the world. Nevertheless, its efficiency has been questioned lately because: (i) it generates many abnormal findings not related to cancer, (ii) it requires irradiating the patient and (iii) it has low specificity with dense breasts [Santen and Mansel, 2005]. Consequently, complementary techniques to mammography are being proposed to improve the detection and characterization of BC. Among these techniques, is the Ultrasound Computed Tomography (USCT), in reflection mode (which provides qualitative maps with the concentration of scatterers in the tissue), and transmission mode (which provides quantitative maps of the sound speed (SS) and the acoustic attenuation (AA) of the tissues). The images provided by the transmission modality have been proposed for BC detection as they can improve the detectability of malignancies in the breast [Mast, 2000, Duric et al., 2009]...El cáncer de mama (CM) es el cáncer más mortal entre las mujeres europeas, y el segundo más común en Estados Unidos [World Cancer Report, 2008]. La detección temprana es un factor que condiciona en gran medida la tasa de supervivencia a esta enfermedad, ya que a menor tamaño de la neoplasia detectada, mejores resultados pueden esperarse para los tratamientos quirúrgicos que se realicen. Además, la detección temprana aumenta la posibilidad de conservar la mama después de la cirugía y disminuye la necesidad de emplear otros tratamientos más invasivos[Secretaría de Salud, 2007, Alteri et al., 2011]. La mamografía es actualmente el procedimiento estándar que se emplea para el cribado del CM. Sin embargo, en los últimas años su eficiencia está siendo muy cuestionada por varios factores: (i) alta tasa de falsos positivos, (ii) requiere la irradiación del paciente y (iii) baja especificidad en mamas densas 2. Debido a lo anterior, para mejorar la detección y caracterización del CM se han propuesto varias técnicas complementarias. Entre ellas está la tomografía ultrasónica (TU), que es una técnica en desarrollo que presenta dos modalidades principales: la reflexión (proporciona mapas cualitativos de la concentración de dispersores en el tejido) y la transmisión (proporciona mapas cuantitativos de la velocidad y atenuación del sonido en el tejido). Los mapas del modo transmisión han sido propuestos como una eficiente alternativa, libre de radiación, para la detección del CM, ya que proporcionan alto contraste y especificidad [Mast, 2000, Duric et al., 2009]...Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEunpu

Convergence in non‐associated plasticity and fracture propagation for standard, rate‐dependent, and Cosserat continua

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