8,269 research outputs found
Formation of corner waves in the wake of a partially submerged bluff body
We study theoretically and numerically the downstream flow near the corner of a bluff body partially submerged at a deadrise depth Δh into a uniform stream of velocity U, in the presence of gravity, g. When the Froude number, Fr=U/√gΔh, is large, a three-dimensional steady plunging wave, which is referred to as a corner wave, forms near the corner, developing downstream in a similar way to a two-dimensional plunging wave evolving in time. We have performed an asymptotic analysis of the flow near this corner to describe the wave's initial evolution and to clarify the physical mechanism that leads to its formation. Using the two-dimensions-plus-time approximation, the problem reduces to one similar to dam-break flow with a wet bed in front of the dam. The analysis shows that, at leading order, the problem admits a self-similar formulation when the size of the wave is small compared with the height difference Δh. The essential feature of the self-similar solution is the formation of a mushroom-shaped jet from which two smaller lateral jets stem. However, numerical simulations show that this self-similar solution is questionable from the physical point of view, as the two lateral jets plunge onto the free surface, leading to a self-intersecting flow. The physical mechanism leading to the formation of the mushroom-shaped structure is discussed
Hydroelastic effects during the fast lifting of a disc from a water surface
Here we report the results of an experimental study where we measure the hydrodynamic force acting on a plate which is lifted from a water surface, suddenly starting to move upwards with an acceleration much larger than gravity. Our work focuses on the early stage of the plate motion, when the hydrodynamic suction forces due to the liquid inertia are the most relevant ones. Besides the force, we measure as well the acceleration at the centre of the plate and the time evolution of the wetted area. The results of this study show that, at very early stages, the hydrodynamic force can be estimated by a simple extension of the linear exit theory by Korobkin (J. Fluid Mech., vol. 737, 2013, pp. 368–386), which incorporates an added mass to the body dynamics. However, at longer times, the measured acceleration decays even though the applied external force continues to increase. Moreover, high-speed recordings of the disc displacement and the radius of the wetted area reveal that the latter does not change before the disc acceleration reaches its maximum value. We show in this paper that these phenomena are caused by the elastic deflection of the disc during the initial transient stage of water exit. We present a linearised model of water exit that accounts for the elastic behaviour of the lifted body. The results obtained with this new model agree fairly well with the experimental results
Campos de urnas en Navarra
Traemos a la memoria la "historia" de los Campos de Urnas navarros
excavados a mediados del siglo XX y los nuevos hallazgos que se han producido en fechas
recientes. El emplazamiento de todos ellos, a corta distancia del Ebro, pone de manifiesto que esta
fue, probablemente, la única vÃa de penetración de las novedades culturales, que se producen a lo
largo de la protohistoria. La vÃa de los Pirineos no conserva, de momento, vestigio alguno que
permita hacer tal consideración
Análisis diferencial del proteoma de dos cepas de Aspergillus carbonarius con diferente nivel de producción de ocratoxina a mediante electroforesis bidimensional
GRB 051221A and Tests of Lorentz Symmetry
Various approaches to quantum gravity suggest the possibility of violation of
Lorentz symmetry at very high energies. In these cases we expect a modification
at low energies of the dispersion relation of photons that contains extra
powers of the momentum suppressed by a high energy scale. These terms break
boost invariance and can be tested even at relatively low energies. We use the
light curves of the very bright short Gamma-Ray Burst GRB 051221A and compare
the arrival times of photons at different energies with the expected time delay
due to a modified dispersion relation. As no time delay was observed, we set a
lower bound of 0.0066 E_{pl} \sim 0.66 10^{17} GeV on the scale of Lorentz
invariance violation.Comment: 9 pages, 2 figure
Influencia biomecánica de la artroplastia total de rodilla en el apoyo metatarsal
Las articulaciones de la extremidad inferior forman una cadena cinemática y tanto desde
el punto de vista normal como patológico se influyen mutuamente. El objetivo de nuestro
trabajo es analizar las caracterÃsticas del apoyo plantar en 100 pacientes subsidiarios de
prótesis total de rodilla que presentan trastornos en la alineación del miembro antes y
después de la corrección del eje de la extremidad que supone la cirugÃa. Además se compara
el patrón de apoyo metatarsal con sujetos sanos de caracterÃsticas antropométricas similares
(grupo control).El genu varo preoperatorio se relaciona con un hiperapoyo de la paleta
externa y un hipoapoyo de las paletas central e interna del antepié. En cambio el valgo
fisiológico conseguido en el postoperatorio se corresponde con un patrón de apoyo
metatarsal al año y a los dos años similar al del grupo control con pequeñas variaciones.Peer Reviewe
- …