Numerical Simulations And Laboratory Measurements In Hydraulic Jumps

Hydraulic jump is one of the most extended and effective mechanism for hydraulic energy dissipation. Usually, hydraulic jump characteristics have been studied through physical models. Nowadays, computational fluid dynamics (CFD) are an important tool that can help to analyze and to understand complex phenomena that involve high turbulence and air entrainment cases. Free and submerged hydraulic jumps with Froude numbers from 2.9 to 5.5 are studied in a rectangular channel downstream a sluice gate. Velocity measurements with different flow rates are carried out by using Acoustic Doppler Velocimeter (ADV) and Particle Image Velocimeter (PIV) instrumentations. In this paper, laboratory measurements are used to calibrate and to validate open source and commercial CFD programs. Air-water two-phase flows are considered in the simulations. The closure problem is solved by using different turbulence models. Water depths, hydraulic jumps lengths, velocity profiles and energy dissipation rates are compared with laboratory measurements and other referenced results

Lens-based Ka-band antenna system using planar feed

This paper presents a simple, low-cost and compact mobile ground terminal antenna for Ka-band satellite communications that operates in the downlink band (19.7-20.2 GHz). The antenna is composed of a shaped dielectric lens which tilts in front of a planar feed to direct the beam. The planar feed is a circularly polarized patch antenna placed inside a cavity. The lens allows a mechanical beam steering from 0° to 57° in relation to zenith with a scan loss of 4.5 dB. In order to show the potential of a planar antenna as a feeder for this application, the proposed system is compared with a previous solution composed of the same dielectric lens and a horn antenna as feeder.info:eu-repo/semantics/publishedVersio

Multivariate linear regression versus symbolic regression from genetic programming. Application to the spectroscopic characterisation of urban wastewater

[EN] Characterising urban wastewater in real time is key to ensure the proper management of water resources and environmental protection. From indirect measurements, such as the molecular spectroscopy which provides information on the physicochemical properties of the water, it is possible to determine the pollutant load of wastewater from mathematical correlation models. The research compares multivariate linear regression models and symbolic regression models based on genetic programming to establish a correlation with the pollutant load of the wastewater. The study has focused on the comparison of models for the characterisation of total nitrogen, total phosphorus and nitrogen in the form of nitrate of 90 urban wastewater samples. It is observed that the symbolic regression based on genetic programming provides an improvement in goodness of fit (R2) of between 72.76% and 146.39% with respect to multivariate linear regression.[ES] Caracterizar en tiempo real las aguas residuales urbanas es clave para poder garantizar una correcta gestión de los recursos hídricos y la protección del medioambiente. A partir de mediciones indirectas, como la espectroscopía molecular que proporciona información sobre las propiedades físico-químicas del agua, es posible determinar la carga contaminante de las aguas residuales empleando modelos matemáticos de correlación. El presente trabajo compara la regresión lineal multivariable y los modelos de regresión simbólica basados en programación genética, para establecer una correlación con la carga contaminante de las aguas residuales. El estudio se ha centrado en la comparativa de modelos para la caracterización de nitrógeno total, fósforo total y nitrógeno en forma de nitrato, considerando 90 muestras de aguas residuales urbanas. Se observa que la regresión simbólica basada en programación genética proporciona una mejora en el ajuste (R2) de entre el 72.76% y 146.39% respecto a la regresión lineal multivariable.El primer autor agradece la financiación recibida de la Fundación Séneca-Agencia de Ciencia y Tecnología de la Región de Murcia (España), a través del programa de capacitación para nuevos investigadores en áreas específicas de interés para la industria y alta capacidad de transferencia de los resultados de investigación generados, titulado: “Subprograma Regional de Contratos de Formación de Personal Investigador en Universidades y OPIs” (Mod. B, Ref. 20320/FPI/17)”. El presente trabajo de investigación ha sido financiado mediante el proyecto MONITOCOES: New intelligent monitoring system for microorganisms and emerging contaminants in sewage networks. Referencia: RTC2019-007115-5, otorgado por el Ministerio de Ciencia e Innovación – Agencia Estatal de Investigación, dentro de la convocatoria RETOS COLABORACIÓN 2019. El equipo desarrollado también ha recibido financiación para su industrialización a través del programa “Proof of Concept” de la Fundación Séneca, en el marco del proyecto “ Equipo de MONITORIZACIÓN en Tiempo REAl de Contaminantes en Aguas Residuales (MONITOREA).” (21662/PDC/21.).Carreres-Prieto, D.; García, JT.; Castillo, LG.; Carrillo, JM.; Vigueras-Rodriguez, A. (2022). Regresión lineal multivariable versus regresión simbólica a partir de programación genética. Aplicación a la caracterización espectroscópica de aguas residuales urbanas. Ingeniería del Agua. 26(4):261-277. https://doi.org/10.4995/ia.2022.1807326127726

Matching and gain enhancement of leaky-wave dielectric horn antenna

International audienceBy flaring a dielectric waveguide in the H-plane, an H-plane dielectric horn is formed, which could be directly excited by an SIW feed. However, matching and radiation performances are poor due to the thinness of the substrate. To improve these performances, some periodic parallel strips are printed both on the top and bottom planes of the dielectric horn. These strips guide and leak the electromagnetic waves gradually along the horn, finally enhancing the end-fire radiation both in H-plane and E-plane. Moreover, they increase the impedance bandwidth up to 40% in Ka-band, and improve the realized gain by more than 2 dB. Indeed, a gain of 14.9 dBi is achieved at the center frequency, with a front-to-back ratio of 33.8 dB, and a side-lobe level of -22.9 dB in the H-plane. With these quite impressive performances, the proposed leaky-wave dielectric horn antenna is very compact, low cost, and easily integrated. © 2016 European Association of Antennas and Propagation

Design of Full-Metal Polarizing Screen Based on Circuit Modeling

International audienceA polarizing sheet based on a fully metallic structure is here reported for the first time. The polarizer consists of a doubly-periodic arrangement of squared-waveguide sections enclosed by two perforated screens. Though the waveguide sections are highly reactive (operating below cutoff), the perforations placed at both sides of the unit-cell allow for total transmission at a certain frequency band. Within this band, the unit-cell allows additionally to tune its anisotropy in order to transform the linear polarization of an impinging 45° -slant plane wave into circular. An equivalent circuit model of this structure is proposed that reproduces its full-wave scattering properties and explains its principle of operation. A design is performed operating around 20 GHz showing good performance. © 2018 IEEE

All-metal 3-D Frequency Selective Surface with Versatile Dual-Band Polarization Conversion

International audienceA dual-band periodic structure is here proposed, which allows for versatile frequency selectivity and polarization conversion functionality. The structure is a monolithic full-metal piece, and it is built from the arrangement of unit-cells consisting of waveguide sections at cutoff loaded with compound perforations. The topology of such unit-cells enables the efficient and independent interaction with vertical and horizontal electric field components illuminating the periodic structure. A circuit model is proposed to characterize the cells and understand their behaviour. Three different examples of cells are designed to illustrate the structure versatile functionality. One of these examples is manufactured, consisting of a dual-band structure that converts linear polarization into circular with orthogonal senses of rotation at each band. The experimental results are in good agreement with the theoretical predictions, thus validating the underlying operation mechanism and its practical feasibility

Combined plasmon-resonance and photonic-jet effect in the THz wave scattering by dielectric rod decorated with graphene strip

International audienceWe consider the scattering of an H-polarized plane wave by an infinite dielectric rod with a conformal graphene strip of arbitrary angular width, placed at the rod rear side. Our analysis is based on the hypersingular integral equation for the current induced on the strip. Discretization of this equation is carried out by the Nystrom-type method, which has a guaranteed convergence. This meshless trusted computational instrument enables us to plot the dependences of the absorption cross-section (ACS) and the total scattering cross-section (TSCS) on the strip angular width and the frequency, in wide range from 1 GHz to 6 THz. We concentrate our analysis on studying the interplay between the broadband photonic-jet effect of dielectric rod and the reasonably high-Q resonances on the plasmon modes of graphene strip. It is found that as the photonic jet becomes brighter with higher frequencies, the plasmon-mode resonances become more intensive as well

Metal-Only Reflectarray Generating Two Independent Beams with Orthogonal Linear Polarizations

International audienceThis paper presents a Metal-Only reflectarray antenna generating two independent beams with orthogonal linear polarizations. Such reflecctarray is based on a dual polarized cell that allows to control the reflection phase of incident waves independently in both polarizations. The simulated gains of the two beams at 25 GHz are 30.77 dBi and 30.14 dBi respectively

Near-field focusing employing sinusoidally modulated reactance surfaces

International audienceThis work aims at showing the feasibility of performing 2D near-field focusing using a Leaky-Wave Lens (LWL) based on Sinusoidally Modulated Reactance Surfaces (SMRS). The polarization of the field at the focus is perpendicular to the antenna aperture, due to the geometry of the structure. Electrically small focal distances are achieved, combined with very small spot diameters. The limitations of this approach are discussed, which are mainly related to the prediction of the focal point. The concept is proven by simulations and experimental testing is in progress. © 2016 European Association of Antennas and Propagation

Terahertz Range Elementary Dipole Excitation of a Thin Dielectric Disk Sandwiched between Two Graphene Covers Integral Equation Analysis

International audienceWe study, using the integral equation technique, the scattering of the field radiated by an elementary dipole, by a thin dielectric disk sandwiched between two conformal graphene covers, on the top and bottom faces. To build a mathematical model of such scatterer, we use the generalized boundary condition in the form first obtained by Mitzner and Bleszynski et al. and generalized by Karlsson. This enables us to derive dual integral equations in the disk plane for the Hankel transforms of the tangential electric and magnetic field components, and cast it to a set of two coupled Fredholm second-kind integral equations. The latter equations are discretized and solved numerically with the guaranteed convergence. We compute and plot the power radiated by an elementary magnetic dipole placed above such a composite disk, in the THz range. This reveals that the studied scatterer is a complicated open resonator supporting the low-frequency plasmon modes and the high-frequency dielectric-disk modes. © 2019 IEEE