1,720,972 research outputs found
Interaction between incident and reflected mechanical waves in the presence of an opposing wind
Get PDFThe interaction between wind and waves largely determines exchanges of mass, momentum, energy, and substances which take place at the air-sea interface. Usually, the parameterization of such interaction considers only the case of progressive waves. However, reflection is practically ubiquitous in the field, especially in coastal areas, and in the lab. Recent experimental studies have extensively treated this subject, showing that even a small amount of wave reflection can significantly modify the free surface elevation and the velocity field on the water side. Nonetheless, a theoretical framework for an exhaustive description of the wave reflection role is still lacking. In this work, an analytical model is developed to emphasize the role of reflection in terms of incident-reflected waves interaction in the 2D momentum equations. A non-null interaction between the incident and the reflected waves is predicted for partially-reflected monochromatic waves, and it is represented by a reflection-induced stress tensor. A phase shift is found among the total wave height, the velocity and the shear stress, with implications on the partition of the wave velocity and stresses. Then, the incident, reflected, and total components of the velocity and of the stresses along the regular wave phase are compared with a set of laboratory experiments, where monochromatic waves in condition of partial reflection are ruffled by an opposing wind. The overlap between experiments and theory is remarkably good, thus validating the entire procedure and assumptions. From the experiments, the fluctuating shear stress and kinetic energy are also extracted for different reflection conditions of the mechanical wave, showing a peak of both quantities near the wave trough (close to the surface). Overall, the experimental analysis gives insights into the velocity, momentum and energy fluxes along the wave phase, based on velocity measurements at one fetch length
Gravity currents in a linearly stratified ambient fluid created by lock release and influx in semi-circular and rectangular channels
No full textWe present an experimental investigation, supported by a theoretical model, of the
motion of lock-release, constant inflow, and time varying inflow gravity currents
(GCs) into a linearly stratified ambient fluid at large Reynolds number. The aim is the
experimental validation of a simple model able to predict the slumping phase front
speed and the asymptotic self-similar front speed for rectangular and circular cross
section channels. The first investigated system is of Boussinesq type with the dense
current (salt water dyed with aniline) released in a circular channel of 19 cm diameter
and 400 cm long (605 cm in the inflow experiments), half-filled of linearly stratified
ambient fluid (salt water with varying salt concentration). The second system has the
same components but with a channel of rectangular cross section of 14 cm width,
11 cm ambient fluid depth, and 504 cm length. The density stratification of the
ambient fluid was obtained with a computer controlled set of pumps and of mixing
tanks. For the experiments with inflow, a multi-pipes drainage system was set at the
opposite end with respect to the inflow section, computer controlled to avoid the
selective withdrawal. The numerous experiments (28 for circular cross section, lock
release; 26 for circular and 14 for rectangular cross section, constant inflow (fluid
volume ∝ tα, with α = 1); 6 for circular cross section, linearly increasing inflow (α =
2)), with several combination of the stratification parameter (0 < S < 1) confirm the
theory within ≈30% (≈40% for a single series of experiments), which is considered
a good result in view of the various underlying simplifications and approximations.
The results on the front speed of the GCs are discussed in the presence of the internal
waves, which have a celerity given by a theoretical and experimentally tested model
for the rectangular but not for the circular cross section. The theoretical analysis
of internal waves in circular cross sections has been extended and experimentally validate
Estudio experimental del transporte de cantidad de movimiento bajo la influencia de viento
Get PDFEn este trabajo se presentan los resultados preliminares de una serie de ensayos realizados en el Canal de Interacción Atmósfera-Océano (CIAO) del Instituto Interuniversitario de Investigación del Sistema Tierra en Andalucía. Se realizaron ensayos para analizar la influencia del viento en el transporte de cantidad de movimiento y en las componentes del tensor de Reynolds bajo una combinación de oleaje generado mediante palas y oleaje generado por viento. Se pone en evidencia las incosistencias respecto a orden de magnitud y signo de la componente turbulenta en estudios previos y se estudia el coeficiente de reflexión y la fase como parámetros fundamentales en la caracterización del estudio y la necesidad de profundizar en éstos en trabajos futuros
GRAVITY CURRENTS IN LINEARLY STRATIFIED AMBIENT FLUID
No full textThe present work aims to study the behavior of a dense fluid current in a rectangular (or in a circular) cross-section
channel. The denser fluid propagates into a less dense ambient fluid, with linear stratification of density in the
vertical
A simplified model was used to compute the front speed of the gravity current. The theoretical speed was obtained
by: a) imposing the continuity between the injected and the propagating fluid; b) by considering the jump condition
and the energetic balance at the head of the current.
Seventy-six experiments were performed. The results show a systematic overestimation of the experimental front
speed. The discrepancy decreases significantly for increasing value of the parameter S (representative of the
relation between the density stratification of the ambient fluid and the density of the intruding current) and is at a
minimum for S 1 (i.e., density of the intruding current equal to the bottom density of the ambient fluid)
Numerical Simulation of Turbulent Fountains with Negative Buoyancy
Get PDFFountains take place when a source fluid is driven by its momentum into a surrounding ambient fluid, and it is counterbalanced by buoyancy. These phenomena are largely encountered in nature and human activities. Despite the numerous studies on the subject, few experimental data are available about the internal structure of turbulent fountains. Here, we present a set of laboratory experiments with the aim to (i) get direct velocity and density measurements of fountains in a controlled environment and (ii) obtain insights into the basic physics of the phenomenon. The present paper also aims to study the flow physics of the phenomenon using a Computational Fluid Dynamics (CFD) model developed in OpenFOAM
Gravity currents in a linearly stratified ambient fluid created by lock release and influx in semi-circular and rectangular channels
No full textWe present an experimental investigation, supported by a theoretical model, of the motion of lock-release, constant inflow, and time varying inflow gravity currents (GCs) into a linearly stratified ambient fluid at large Reynolds number. The aim is the experimental validation of a simple model able to predict the slumping phase front speed and the asymptotic self-similar front speed for rectangular and circular cross section channels. The first investigated system is of Boussinesq type with the dense current (salt water dyed with aniline) released in a circular channel of 19 cm diameter and 400 cm long (605 cm in the inflow experiments), half-filled of linearly stratified ambient fluid (salt water with varying salt concentration). The second system has the same components but with a channel of rectangular cross section of 14 cm width, 11 cm ambient fluid depth, and 504 cm length. The density stratification of the ambient fluid was obtained with a computer controlled set of pumps and of mixing tanks. For the experiments with inflow, a multi-pipes drainage system was set at the opposite end with respect to the inflow section, computer controlled to avoid the selective withdrawal. The numerous experiments (28 for circular cross section, lock release; 26 for circular and 14 for rectangular cross section, constant inflow (fluid volume ∞ tα, with α = 1); 6 for circular cross section, linearly increasing inflow (α = 2), with several combination of the stratification parameter (0 < S < 1) confirm the theory within ≈30% (≈40% for a single series of experiments), which is considered a good result in view of the various underlying simplifications and approximations. The results on the front speed of the GCs are discussed in the presence of the internal waves, which have a celerity given by a theoretical and experimentally tested model for the rectangular but not for the circular cross section. The theoretical analysis of internal waves in circular cross sections has been extended and experimentally validated
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
An Interactive WebGIS Framework for Coastal Erosion Risk Management
Get PDFThe Italian coastline stretches over about 8350 km, with 3600 km of beaches, representing a significant resource for the country. Natural processes and anthropic interventions keep threatening its morphology, moulding its shape and triggering soil erosion phenomena. Thus, many scholars have been focusing their work on investigating and monitoring shoreline instability. Outcomes of such activities can be largely widespread and shared with expert and non-expert users through Web mapping. This paper describes the performances of a WebGIS prototype designed to disseminate the results of the Italian project Innovative Strategies for the Monitoring and Analysis of Erosion Risk, known as the STIMARE project. While aiming to include the entire national coastline, three study areas along the regional coasts of Puglia and Emilia Romagna have already been implemented as pilot cases. This WebGIS was generated using Free and Open-Source Software for Geographic information systems (FOSS4G). The platform was designed by combining Apache http server, Geoserver, as open-source server and PostgreSQL (with PostGIS extension) as database. Pure javascript libraries OpenLayers and Cesium were implemented to obtain a hybrid 2D and 3D visualization. A user-friendly interactive interface was programmed to help users visualize and download geospatial data in several formats (pdf, kml and shp), in accordance with the European INSPIRE directives, satisfying both multi-temporal and multi-scale perspectives. © 2021 by the authors. Licensee MDPI, Basel, Switzerlan
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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