Claudia del Carmen Gutiérrez-Torres

Data Transmission Strategies for Event Reporting and Continuous Monitoring Applications in Wireless Sensor Networks

Wireless Sensor Networks (WSNs) can be typically used to achieve Continuous Monitoring (CM) or Event-Detection inside the supervised area. In CM applications each sensor node transmits periodically its sensed data to the sink node while in Event-Detection Driven (EDD) applications, once an event occurs, it is reported to the sink node by the sensors within the event area. Applications using both continuous monitoring and event driven reporting can also be considered. In this paper, we investigate such hybrid WSNs. Specifically, we propose two different strategies that explicitly assign a time period for the event reporting data by means of the NP-CSMA random access protocol. Both strategies take advantage of the clustered based architecture which assign a TDMA schedule for the continuous monitoring data transmission. By doing so, the continuous monitoring clusters are also used for the event reporting. Hence, no extra energy is consumed for separate event clusters. The performance of these strategies is analyzed for low and high event rate occurrence. These strategies are compared to both continuous monitoring protocols (such as LEACH) and event driven reporting protocols (such as TEEN).

Computational Fluid Dynamics in Turbulent Flow Applications

This chapter is intended to present to readers a general scope of the technical, theoretical, and numerical applications of computational fluid dynamics using the finite volume method, restricted to incompressible turbulent flows (Ma < 0.3). The main objective of this chapter was to provide readers of a starting point to select an adequate numerical model for the flow regime of interest. Such knowledge could be a key at the moment of extending the analysis to more complex problems, for example, the ones found in heat transfer and fluid flows, multiphase flows, and compressible flows.

Comportamiento Hidrodinámico y Térmico del Flujo Gas- Sólido en un Reactor de Tubo Vertical (Riser) del Proceso de Craqueo Catalítico (FCC) con dos Salidas Laterales Asimétricas

Resumen En este trabajo se realiza la simulacion numerica en 2D del comportamiento hidrodinamico y termico del flujo gas-solido en un reactor industrial (riser) con dos salidas colocadas asimetricamente, utilizando un modelo de la Dinamica de Fluidos Computacional. El sistema se considera adiabatico y el modelo del sistema se resuelve por una aproximacion Euleriana transitoria y la Teoria Cinetica del Flujo Granular (KTGF, Kinetic Theory for Granular Flow). Como modelo de arrastre se utiliza la minimizacion multiescala de la energia (EMMS, Energy Minimization Multi-Scale). Las variables que se analizan son la distribucion de densidad, la distribucion de velocidades, la distribucion del flujo masico, y los perfiles de temperatura de la fase solida, a varias alturas del riser. Los resultados de este trabajo se comparan con los obtenidos anteriormente para una configuracion de salidas simetricas. El modelo predice adecuadamente la presencia de tres zonas de concentracion y velocidad de solidos, asi como la formacion del patron de flujo anular esperado en el riser.

Numerical Simulation of the Subcritical Flow Over a Circular Cylinder With “U” and “V” Grooves

In this paper the comparative results of three numerical simulations of the subcritical turbulent flow over a circular cylinder (Re = 140,000) for the cases of a “U” grooved cylinder, a smooth cylinder, and a “V” grooved cylinder are presented. Due to the high resolution capabilities of the LES model, it was preferred over the RANS or URANS turbulence models. The simulation was carried out using the commercial CFD code ANSYS FLUENT V.12.0. The grid sizes were: 2.6 million cells for the smooth cylinder, and 14.5 and 13 million for the “U” grooved and “V” grooved cylinders respectively. In order to improve the quality of the solutions, the grids were structured and composed of hexahedral cells. Due to the requirements of the LES technique, the lower y+ values obtained were below 5. With the aim of capture the non-steady characteristics of this kind of flows, the simulations were performed over 8 vortex shedding cycles. Although the cross sections of the V and U grooves have almost the same shape, the resulting flow structures and calculated quantities such as the separation point, turbulent intensity in the normal and streamwise direction and recirculating bubble length were different for both cases. Apparently, the flow configuration resulted from the V grooves is similar to the smooth cylinder flow, being the U grooved cylinder flow different from both of them. This could be related to the drag reduction of about 27% obtained for the U grooved cylinder flow For the V grooved cylinder flow, the obtained drag presented an increase of about 7%.© 2013 ASME

Turbulent Flow Over a Facing Step at Several Reynolds Numbers

An experimental study was performed over forward facing step (FFS). It was located within a transparent rectangular acrylic channel (1.4 m in length, 0.1 m in width and 0.02 m in height). The step is 0.01 m in height and 0.1 m in width, and was located 0.7 m downstream (fully developed region); a spanwise aspect ratio, w/h = 10 was used. The experiments were carried out using particle image velocimetry (PIV), which is a non intrusive experimental technique. The experimental water flow conditions include three Reynolds numbers based on the step height, Reh = 1124, 1404 and 1685. These flow conditions correspond to turbulent flow. Measurements were carried out in two zones; zone A begins at x = 8 cm (measured from the step base), and zone B starts at x = 0, y = 0, the visualization region corresponds to an area of 22.76 mm × 16.89 mm. 100 instantaneous velocity fields were obtained for each Reh . A temporal and spatial average was performed to obtain a velocity profile in zone A; likewise, the corresponding turbulence intensity and shear stress distribution were evaluated. The average velocity profile was evaluated for each Reh . Regarding the vortex center location, it was observed that as Reh increases, the y-direction coordinate moves towards bottom of wall channel. For zone B, it was also observed a reduction of the shear stress as Reh increases.Copyright

Análisis Numérico de la Convección Mixta en un Conducto Horizontal de Sección Rectangular Tridimensional que Encierra un Escalón

Laminar mixed convection over a backward-facing step is studied and presented in this work. A finite volume discretization technique is used to solve the momentum and energy equations. The SIMPLE algorithm is used to link the pressure distribution and velocity field inside the computational domain. The buoyancy forces affecting the velocity and temperature distributions are simulated for constant air flow and constant Reynolds number (Re=200) for a mixed convective flow (Ri=3) and the results are compared with those of pure force convective flow (Ri=0). The results indicate that the re-circulation zones at the vicinity of the back step are reduced if the buoyancy effects are considered. It is concluded that the flow is highly tridimensional.