Application of the CUDA technology to the solution of fluid dynamics problems

Este trabajo explora el uso de la tecnología CUDA en la solución de problemas relacionados con la dinámica de fluidos. Tres problemas clásicos de diferente nivel de complejidad: convección-difusión en un canal, la cavidad movida por pared y la cavidad movida por diferencia de temperatura, fueron solucionados por el método de las diferencias finitas, usando la CPU (procesador) y la GPU (tarjeta de vídeo) para comparar el desempeño. Algunos aspectos importantes vinculados con la implementación numérica en la GPU son discutidos. Así mismo, los resultados mostraron un importante aumento de la velocidad cuando se usó la GPU

Optimización topológica aplicada al diseño de componentes estructurales mecánicos de peso reducido

En este trabajo se presenta una implementación de la técnica de optimización topológica (OT) aplicada al diseño de elementos estructurales mecánicos de peso reducido. La OT es un método numérico que ha captado el interés de ingenieros y científicos en los últimos años, pues permite la síntesis de estructuras con valores óptimos de uno o varios de sus parámetros físicos. El problema de máxima rigidez con restricción de volumen consiste en encontrar la distribución de material en un dominio donde se tenga dicha máxima rigidez, para determinada carga aplicada, restringiendo el volumen final del material usado en la estructura. Fue implementado un algoritmo de solución usando elementos finitos planos de cuatro nodos e interpolación lineal para la discretización del dominio y programación lineal secuencial para la solución del problema de optimización no lineal y multivariado. La validez de los resultados fue comprobada solucionando algunos casos test bien conocidos. Finalmente, el algoritmo se usó para rediseñar una pieza mecánica existente, donde la OT permitió una reducción de peso del 24 % manteniendo un factor de seguridad comparable. La reducción de peso en estructuras mecánicas es importante por su impacto en el ahorro de energía al reducir la inercia en máquinas y vehículos, además de la posible reducción de costos de fabricación

Ultrasonic measurement of the viscoelastic properties of liquids.

A medição das propriedades viscoelásticas de líquidos por ultrassom tem sido um tema de pesquisa importante desde meados do século XX, principalmente, pela possibilidade de realizar medições em tempo real da viscosidade. O método de medição baseia-se na determinação do coeficiente de reflexão complexo (magnitude e fase) de ondas de cisalhamento refletidas da interface definida entre um sólido e uma amostra líquida. Enquanto a medição da magnitude é relativamente simples e precisa, a medição da fase é muito difícil devido à forte dependência da temperatura, que gera uma incerteza muito grande. No entanto, na medição da viscosidade em regime newtoniano somente a magnitude é requerida. Ocorre que os resultados experimentais reportados até o momento na literatura não coincidem quantitativamente com a teoria. Neste trabalho, uma nova técnica que permite determinar com boa precisão a magnitude do coeficiente de reflexão e, por conseguinte, a viscosidade de líquidos em regime newtoniano foi desenvolvida. Foi mostrado que a maioria dos líquidos testados apresentam comportamento newtoniano à frequência de trabalho de 1MHz, com exceção de alguns óleos automotivos de alta viscosidade, que possuem claramente comportamento viscoelástico. Desvios menores que 12,5% nas medições da viscosidade dinâmica de substâncias com moléculas relativamente simples, como glicerina e glicose, mostram a viabilidade da técnica. Também é proposto um novo método que permite calibrar o dispositivo de medição para monitorar a viscosidade de um líquido ou grupo de líquidos. Além disso, uma aplicação na monitoração da contaminação da água por substâncias oleosas é apresentada.The ultrasonic measurement of viscoelastic properties of liquids has been an important research topic since the mid-twentieth century mainly due to the possibility of real-time viscosity measurements. The measurement technique is based on the determination of the complex reflection coefficient (magnitude and phase) of shear waves reflected from the solid-liquid interface. While magnitude measurement is relatively simple and precise, phase measurement is a difficult task due to strong temperature dependence that induces large errors. However, when the measurement is carried out under Newtonian regimen only the magnitude is required. Nonetheless, experimental results reported in literature until now do not agree quantitatively with the theory. In this work, it was developed a novel technique that accurately and precisely determines the reflection coefficient magnitude and, consequently, the Newtonian viscosity. Most tested liquids showed Newtonian behavior at the working frequency of 1 MHz except for some automotive oils of high viscosity, which showed an evident viscoelastic behavior. Deviations up to 12.5% in the dynamic viscosity measurement of substances with relatively simple molecules, such as glycerin and corn syrup, show the technique suitability. A calibration method of the measurement cell allowing the indirect viscosity measurement of a liquid or group of liquids is proposed. Moreover, a new application to oil-in-water contamination monitoring is presented

Sensor ultrasónico para la presencia de contaminantes oleosos en agua

La determinación del coeficiente de reflexión de ondas transversales ultrasónicas en la interfaz sólido-líquido es una técnica que ha sido usada para la medición de las propiedades viscoelásticas de líquidos. Una característica interesante de la técnica es la pequeña distancia recorrida por las ondas transversales dentro del fluido, antes de ser completamente atenuadas, permitiendo la medición con una película muy delgada de líquido, del orden de algunos micrómetros. Esta característica, además de la conocida tendencia de las sustancias oleosas a adherirse a superficies, puede ser usada para la detección de contaminantes oleosos en agua. Este trabajo propone el uso de la técnica de reflexión de ondas transversales en el rango ultrasónico para la detección de contaminantes oleosos en agua y discute las bases teóricas y experimentales relacionadas. Resultados experimentales preliminares muestran que es posible la detección de la presencia de aceite automotriz SAE 40 en agua en proporciones menores a 0,5% en volumenThe determination of the complex reflection coefficient of ultrasonic shear-waves at the solid-liquid interface is a technique employed for the measurement of the viscoelastic properties of liquids. An interesting property of the measurement technique is the very small penetration depth of the shear-waves into the liquid sample, which permits measurements with liquid films of some micrometers thick. This property, along with the adhesion of oily substances to surfaces, can be used for the detection of oily contaminants in water. In this work, the employment of the ultrasonic shear-wave reflection technique to the detection of oily contaminants in water is proposed and the theoretical and experimental concepts involved are discussed. Preliminary experimental results show the measurement technique can detect SAE 40 automotive oil in water in volume proportions less than 0.5

Implementación de la técnica de la transmisión ultrasónica para la caracterización de compuestos laminados reforzados con fibras

Los compuestos laminados son usados en aplicaciones donde una alta relación resistencia/peso es requerida. Las industrias aeronáutica, naval y automotriz usan estos materiales para reducir el peso de sus vehículos y ahorrar combustible. Sin embargo, los materiales compuestos laminados son anisotrópicos y sus propiedades varían ampliamente debido a procesos de manufactura no estandarizados. La caracterización elástica de estos materiales usando ensayos mecánicos no es fácil, por lo general las pruebas son destructivas y, en la mayoría de los casos, no es posible obtener todas las constantes elásticas. Por tanto, técnicas de caracterización alternativas son requeridas para asegurar la calidad de las piezas fabricadas y el estudio de nuevos materiales. En este trabajo se reporta la implementación de la técnica de la transmisión ultrasónica y la caracterización de algunos materiales de ingeniería. Muestras de materiales isotrópicos y compuestos laminados de fibra de carbono y vidrio en matriz polimérica fueron caracterizados por ultrasonido y ensayos mecánicos. Se reporta una metodología alternativa para el cálculo de los atrasosLaminated composites are widely used in applications when a high strength-to-weight ratio is required. Aeronautic, naval and automotive industries use these materials to reduce the weight of the vehicles and, consequently, fuel consumption. However, the fiber-reinforced laminated materials are anisotropic and the elastic properties can vary widely due to non-standardized manufacturing processes. The elastic characterization using mechanical tests is not easy, destructive and, in most cases, not all the elastic constants can be obtained. Therefore, alternative techniques are required to assure the quality of the mechanical parts and the evaluation of new materials. In this work, the implementation of the ultrasonic through-transmission technique and the characterization of some engineering materials is reported. Isotropic materials and laminated composites of carbon fiber and glass fiber in a polymer matrix were characterized by ultrasound and mechanical tests. An improved methodology for the transit time delay calculation is reporte

Characterization of phased array-steered acoustic vortex beams

Acoustic vortex (AV) beams generation is a subject of current interest. Even though different applications have been proposed using AV, their potential of use is still to be explored. Recent research works on particle manipulation use phased array systems for AV generation because it allows a flexible beam configuration, i.e., the beam can be easily focalized and modified in its shape. However, little attention has been paid to the fact that the AV can also be electronically steered. In view of this, this work presents an study of the steering capability of an AV. In particular, we analyze the effect of the applied delay law on the structure of AV beams steered at different angles using an array transducer of 32 equidistant elements, deployed on a triangular lattice, operating at 40 kHz. Special attention is paid to the appearance of grating vortices and their characteristics. The effect of the individual element directivity on the resultant beam is also studied. Experimental measurements were carried out in order to validate numerical estimations. Obtained results paves the way for the use of electronically steered vortices in different applications. Also, the potential of use of acoustic grating vortices is discusse

Shear-wave corner retroreflector device for ultrasonic measurement of viscosity

This work shows a novel ultrasonic viscosity measurement device with increased sensitivity. The measuring principle is based on the determination of the complex reflection coefficient of shear-waves at the solid–liquid interface. But the proposed approach is the replacement of the flat surface at the measurement interface with a grooved surface, which works in a similar way to an optical retroreflector. The complete reflection of the waves involves a double reflection with oblique incidence, where both phenomena increase sensitivity, in comparison with a plane surface. It is shown that a set of orthogonal flat interfaces reflects a well-defined ultrasonic pulse. The sensitivity is enough to measure the change in the magnitude and phase of the reflection coefficient even for the small portion of the energy transmitted to water. A model for calculating the viscosity and a calibration approach for the measurement were proposed. Results with samples of corn syrup–water mixture are reporte

Ultrasonic monitoring of the water content in concentrated water–petroleum emulsions using the slope of the phase spectrum

This work proposes the slope of the phase spectrum as a signal processing parameter for the ultrasonic monitoring of the water content of water-in-crude oil emulsions. Experimental measurements, with water volume fractions from 0 to 0.48 and test temperatures of 20 ◦C, 25 ◦C, and 30 ◦C, were carried out using ultrasonic measurement devices operating in transmission–reception and backscattering modes. The results show the phase slope depends on the water volume fraction and, to a lesser extent, on the size of the emulsion droplets, leading to a stable behavior over time. Conversely, the behavior of the phase slope as a function of the volume fraction is monotonic with low dispersion. Fitting a power function to the experimental data provides calibration curves that can be used to determine the water content with percentage relative error up to 70% for a water volume fraction of 0.06, but less than 10% for water volume fractions greater than 0.06. Furthermore, the methodology works over a wide range of volume fractions

Subwavelength twin ultrasound focused (STUF) beam generated by shear-to-longitudinal mode conversion in a triangular prism

Focusing ultrasound fields in regions below the incident wavelength using elementary objects (such as spherical and cylindrical) as acoustic lenses have been successfully demonstrated over the last five years. This unique way to tightly concentrate the energy of acoustic fields is interesting for the development of new high resolution ultrasound systems. Usually, an incident longitudinal beam interacts with these lenses to produce a subwavelength beams at its shadow region. However, no shear-wave beam has been reported to produce subwavelength beams using objects as acoustic lenses. In this work, we numerically and experimentally report the generation of a subwavelength twin ultrasound focusing (STUF) beam using a 1 MHz shear transducer coupled to a Rexolite triangular prism. Numerical simulations were performed in order to study the generated field as a function of the apical angle of the prism and to find the mechanical configuration for the experimental validation. The results show that by changing the apical angle of the triangular prism, the main features of the STUF beams can be changed. To validate the numerical model, a prism with apical angle of 90o was built and the acoustic field distribution was measured by a needle hydrophone. A STUF beam with width of 0.8λ and depth of focus (DOF) 3λ was generated. A good agreement between numerical and experimental results was reported. The proposed system open new possibilities to design and built a simple and low cost acoustic system for microparticle trapping applications

Ultrasonic determination of the elastic constants of epoxy-natural fiber composites

This paper shows the applications ultrasonic through–transmission technique to determine the elastic constants of two polymer-natural fiber composite materials with potential industrial application and economic and environmental advantages. The transversely isotropic coconut-epoxy and fique-epoxy samples were analyzed using an experimental setup which allows the sample to be rotated with respect to transducers faces and measures the time-of-flight at different angles of incidence. Then, the elastic properties of the material were obtained by fitting the experimental data to the Christoffel equation. Results show a good agreement between the measured elastic constants and the values predicted by an analytical model. The velocities as a function of the incidence angle are reported and the effect of the natural fiber on the stiffness of the composite is discusse