Estudio del comportamiento mecánico de morteros modificados con fibras de aserrín bajo esfuerzos de compresión

In this paper, a study about the mechanical behavior of mortar modified with sawdust fibers under compression load was performed. Density, compressive strength and dynamic elastic modulus of mortar modified with 0, 0,5, 1 and 3% of sawdust were estimated. Composites were evaluated after 7, 30 and 90 days of curing. In addition, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used ton chracterize the morphology and to find elemental composition for both, fibers and cement matrix. The results show that compressive strentgth, elastic modulus and density decreases as sawdust percentage increases. It is suggested to use 1% of sawdust fiber mortars in order to avoid an important reduction of the mortar mechanical properties. En este artículo, se presenta un estudio sobre el comportamiento mecánico de morteros modificados con fibras de aserrín bajo cargas de compresión. Se estimó la densidad, resistencia a la compresión, y el módulo de elasticidad dinámico de morteros modificados con 0, 0,5, 1 y 3% en peso de fibra de aserrín. Los compuestos fueron evaluados luego de 7, 30 y 90 días de curado. Además, se utilizó microscopia electrónica de barrido (SEM) y espectroscopía de rayos X de energía dispersa (EDX) para caracterizar la morfología y encontrar la composición elemental tanto de las fibras como de la matriz de cemento. Los resultados muestran que a mayor porcentaje de aserrín, la resistencia, el módulo de elasticidad y la densidad disminuyen. Se sugiere utilizar hasta 1% de fibra de aserrín en morteros para evitar una reducción importante en las propiedades mecánicas de los morteros.

Energy harvesting from transverse galloping

Some elastic bluff bodies under the action of a fluid flow can experience transverse galloping and lose stability if the flow velocity exceeds a critical value. For flow velocities higher than this critical value, there is an energy transfer from the flow to the body and the body develops an oscillatory motion. Usually, it is considered as an undesirable effect for civil or marine structures but here we will show that if the vibration is substantial, it can be used to extract useful energy from the surrounding flow. This paper explores analytically the potential use of transverse galloping in order to obtain energy. To this end, transverse galloping is described by a one-degree-of-freedom model where fluid forces obey the quasi-steady hypothesis. The influence of cross-section geometry and mechanical properties in the energy conversion factor is investigated

Improvements in CO2 Booster Architectures with Different Economizer Arrangements.

CO2 transcritical booster architectures are widely analyzed to be applied in centralized commercial refrigeration plants in consonance with the irrevocable phase-out of HFCs. Most of these analyses show the limitations of CO2 cycles in terms of energy e ciency, especially in warm countries. From the literature, several improvements have been proposed to raise the booster e ciency in high ambient temperatures. The use of economizers is an interesting technique to reduce the temperature after the gas cooler and to improve the energy e ciency of transcritical CO2 cycles. The economizer cools down the high pressure’s line of CO2 by evaporating the same refrigerant extracted from another point of the facility. Depending on the extraction point, some configurations are possible. In this work, di erent booster architectures with economizers have been analyzed and compared. From the results, the combination of the economizer with the additional compressor allows obtaining energy savings of up to 8.5% in warm countries and up to 4% in cold countries with regard to the flash-by-pass arrangement and reduce the volumetric displacement required of the MT compressors by up to 37%

Experimental determination of the optimum working conditions of a transcritical CO2 refrigeration plant with integrated mechanical subcooling

Subcooling methods for transcritical CO2 plants are being studied in order to improve their behavior. Among them, the Integrated Mechanical Subcooling system is one of the most promising owing that performs with high efficiency and it is a total-CO2 system. This work presents the experimental determination of the optimum working conditions of a transcritical CO2 plant working with an integrated mechanical subcooling system. The plant was tested at different pressure and subcooling conditions in order to optimize the COP of the plant and determine the optimal conditions for three ambient temperatures 25.0 °C, 30.4 °C and 35.1 °C and evaporation levels between −15.6 °C and −4.1 °C. Optimum operating conditions were determined and two correlations are proposed to determine the optimal pressure and subcooling as function the gas-cooler outlet temperature and the evaporation level

Hysteresis in transverse galloping: the role of the inflection points

Transverse galloping is here considered as a one-degree-of-freedom oscillator subjected to aerodynamic forces, which are described by using the quasi-steady hypothesis. The hysteresis of transverse galloping is also analyzed. Approximate solutions of the model are obtained by assuming that the aerodynamic and damping forces are much smaller than the inertial and stiffness ones. The analysis of the approximate solution, which is obtained by means of the method of Krylov–Bogoliubov, reveals the existing link between the hysteresis phenomenon and the number of inflection points at the aerodynamic force coefficient curve, Cy(α)Cy(α); CyCy and αα being, respectively, the force coefficient normal to the incident flow and the angle of attack. The influence of the position of these inflection points on the range of flow velocities in which hysteresis takes place is also analyzed

Sistema de toma de decisiones basado en modelo para cambios de carril en vehículos autónomos

En las últimas décadas se ha presentado un gran incremento en la congestión de tráfico urbano tanto en grandes ciudades en países desarrollados, como en aquellos en vías de desarrollo, generando también un incremento en la tasa de accidentalidad. Con el rápido crecimiento de las tecnologías de la información, y las comunicaciones y la electrónica, los avances investigativos en la caracterización del tráfico vehicular y mejoras en la capacidad de cómputo y simulación computacional, una de las soluciones más prometedoras para enfrentar estos problemas consiste en el mejoramiento de la infraestructura de movilidad basado en el modelado matemático y la simulación de la dinámica vehicular. Por otro lado, los vehículos poseen niveles de autonomía cada vez mayores y capacidad de comunicarse con otros vehículos (comunicaciones vehículo a vehículo, V2V) y con la infraestructura de gestión de tráfico (comunicaciones vehículo a infraestructura, V2I), de manera que estas tecnologías también aportan no solo a la reducción de la congestión sino a la disminución de las tasas de accidentalidad. Los sistemas de toma de decisiones para la gestión de tráfico, los sistemas de asistencia al conductor y los vehículos autónomos permiten mejorar los tiempos de viaje, la confiabilidad y robustez para mejorar la experiencia de conducción y la seguridad. Una de las principales características de estos sistemas es que se basan en un modelo de predicción que les permite anticipar el estado de los vehículos y su entorno con el fin de reducir la congestión y prevenir accidentes, entre otros. El modelado de la dinámica de vehículos se puede dividir en modelos longitudinales, que describen el comportamiento de aceleración y frenado, y modelos laterales, los cuales describen los cambios de dirección del vehículo. Estos modelos han sido aplicados en sistemas de control enfocados en la seguridad activa, sistemas avanzados de asistencia al conductor (ADAS) y vehículos autónomos. Algunas aplicaciones incluyen el control de crucero, sistemas de alerta de desvío de carril y sistemas de evasión de obstáculos. En la actualidad también se han desarrollado diferentes aplicaciones para cambios de carril autónomos y semi-autónomos. Sin embargo, existen aún desafíos en cuanto a la inclusión de diferentes tipos de vehículos y criterios de confort para la ejecución de la maniobra en relación con características como la relación peso-potencia. En este trabajo se presenta un sistema de toma de decisiones basado en modelo para cambios de carril en venículos autónomos que considera diferentes tipos de vehículos y modos de conducción, con el cual es posible caracterizar la trayectoria de la maniobra. Este sistema se compone de dos partes, las cuales conforman un sólo sistema de toma de decisiones: un sistema para la generación de trayectorias de cambio de carril utilizando optimización basada en un modelo de predicción y una red neuronal que utiliza estas trayectorias en un esquema de aprendizaje supervisado.Abstract: In the last decades, urban traffic congestion has increased not only in big cities of developed countries, but in those of developing ones, which leads also to an increased accident rate. With the fast growing of information and communication technologies and electronics, research advances on road traffic characterization and improvements in computing capacity and simulation, one of the most promising solutions to face the congestion problem consists on the improvement of the mobility infrastructure based on mathematical modeling and simulation of vehicle dynamics. On the other hand, vehicles have increasing levels of autonomy and the capacity of communicating with others (Vehicle to Vehicle, V2V) and with the infrastructure (Vehicle to Infrastructure, V2I), so that these technologies improve not only the congestion reduction but also the rates of accidents. The decision-making systems for traffic management, driving assistance systems and autonomous vehicles allow to improve travel times and reliability, allowing a better driving experience and security. One of the main features of these systems relies in the fact that they are based on prediction models that permits to anticipate the state of vehicles and their environment with the aim of reducing congestion and prevent accidents, among others. Vehicle dynamics modeling can be divided into longitudinal models, which describe the behavior of acceleration and braking, and lateral models, which describe the direction changes of the vehicle. These models have been applied in control systems focused on active safety, advanced driving assistance systems (ADAS) and autonomous vehicles. Currently, different applications for autonomous and semi-autonomous lane changes have also been developed. However, some challenges remain in regards to the inclusion of different vehicle types and comfort criteria for the execution of the maneuver based on characteristics such as the power-to-weight ratio. In this work, a lane changing model-based decision-making system for autonomous vehicles is presented, which considers different types of vehicles and driving modes and adequately characterized the trajectory of the maneuver. This system is composed of two parts, which conform a single decision-making system: one system for generating lane changing trajectories using a prediction model-based optimization and a neural network that utilizes these trajectories in a supervised learning scheme.Maestrí