Inestabilidades en un lecho granular móvil: análisis matemático de formas de fondo

[ES] Se presenta un análisis teórico de las condiciones para las cuales se generan ondas sedimentarias en un flujo turbulento sobre lecho móvil. Se revisa una metodología general para el análisis de estabilidad lineal de las ecuaciones que gobiernan el flujo y el movimiento del sedimento del lecho. Esta metodología se aplica al análisis de la formación de barras, y de dunas y antidunas. El análisis predice que la formación de barras depende fundamentalmente de la razón entre el ancho del canal y la altura de escurrimiento. A menor altura de escurrimiento el sistema selecciona estructuras más complejas, formándose sucesivamente barras alternadas, dobles, triples, etc., las cuales poseen longitudes de onda respectivamente más pequeñas. En todos estos casos las barras migran hacia aguas abajo. Del análisis también se concluye que la formación de dunas y antidunas depende fundamentalmente del número de Froude del flujo. Las dunas se forman en condiciones de flujo subcrítico y siempre migran hacia aguas abajo. Las antidunas se forman en condiciones de flujo supercrítico y pueden migrar tanto hacia aguas arriba como hacia aguas abajo. En las cercanías del flujo crítico el análisis predice la desaparición de formas de fondo.El presente trabajo se desarrolló con financiamiento otorgado por FONDECYT, a través del Proyecto No 1950592-95, y por el Departamento de Ingeniería Civil de la Universidad de Chile.Niño, Y. (1996). Inestabilidades en un lecho granular móvil: análisis matemático de formas de fondo. Ingeniería del Agua. 3(4):25-36. https://doi.org/10.4995/ia.1996.2706SWORD253634Blondeaux, P. y Seminara, G. (1985) A unified bar-bend theory of river meanders. J. Fluid Mech. vol 157, pp 449-470.Casti, J. L. (1994) Complexification.Harper-Perennial.Colombina, M., Seminara, G. y Tubino, M. (1987) Finite-amplitude alternate bars. J. Fluid Mech., vol 181, pp 213-232.Drazin, P.G., y Reid, W.H. (1981) Hydrodynamic stability. Cambridge Monographs on Mechanics and Applied Mathematica. Cambridge University Press.Engelund, F., y Fredsøe, J. (1982) Sediment ripples and dunes. Ann. Rev. Fluid Mech. vol 1, pp 13-37Engelund, F. (1970) Instability of erodible beds. J. Fluid Mech., vol 42, part 2, pp 225-244.Engelund, F. y Hansen, E. (1967) A monograph on sediment transport in alluvial streams. Teknisk Forlag, Copenhagen.Engelund, F. (1964) A practical approach to self-preserving turbulent flows. Acta Polytechnica Scandinavica, pp 6.Fredsøe, J. (1974) On the development of dunes in erodible channels. J. Fluid Mech., vol 64, part 1, pp 1-16.García, M., y Niño, Y. (1993) Dynamics of sediment bars in straight and meandering channels: experiments on the resonance phenomenon. J. Hydr. Research, vol 31, No 6, pp 739-761.Hinze, I. O. (1959) Turbulence. McGraw-Hill Series in Mechanical Enrgr.Jackson, E. A. (1991). Perspectives of nonlinear dynamics. Cambridge University Press.Jaeggi, M. N. R. (1984) Formation and effects of alternate bars. J. Hydr. Engrg., vol 110, No 2, pp 142-156.Kuroki, M. y Kishi, T. (1985) Regime criteria on bars and braids. Hydraulic Papers, The Res. Lab. of Civil and Env. Engrg., Hokkaido University. Sapporo, Japan.Meyer-Peter, E. y Muller, R. (1948) Formulas for bedload transport. 2nd IAHR Congress, Stockholm.Parker, G. (1984) Lateral bedload transport on side slopes. J. Hydr. Engrg., vol 110, pp 197-199.Stuart, J. T. (1958) n the nonlinear mechanics of hydrodynamic stability. J. Fluid Mech., vol 4, pp 1-21.Vanoni, V. A. (1974) Factors determining bed forms of alluvial streams. J. Hydr. Div., vol 100, NOHY3, pp 363-377

On the Application of the Fourier Series Solution to the Hydromagnetic Buoyant Two-Dimensional Laminar Vertical Jet

The problem of a hydromagnetic hot two-dimensional laminar jet issuing vertically into an otherwise quiescent fluid of a lower temperature is studied. We propose solutions to the boundary layer equations using the classical Fourier series. The method is essentiall to transform the boundary layer equations to a coupled set of nonlinear first-order ordinary differential equations through the Fourier series. The accuracy of the results has been tested by the comparison of the velocity distributions obtained by the Fourier series with those calculated by finite difference method. The results show that the present method, based on the Fourier series, is an efficient method, suitable to solve boundary layer equations applied to plane jet flows with high accuracy

Dynamic pore-pressure variations induce substrate erosion by pyroclastic flows

International audienceField evidence shows that pyroclastic flows can entrain blocks from underlying substrates formed by earlier geological events, yet, counterintuitively, they are less likely to erode unconsolidated layers of fine particles. Here we report laboratory experiments that reproduce these seemingly contradictory observations and also offer a means to infer pyroclastic flow velocity. Experiments demonstrate that the sliding head of a granular flow generates a dynamic upward pore-pressure gradient at the flow-substrate interface. Associated upward air flux is enough to fluidize a substrate of fines, so that particles are not entrained individually but the substrate instead is subject to small shear instabilities. In contrast, coarse particles forming a non-fluidized substrate are lifted at a critical upward force due to the pore-pressure gradient, according to their individual masses, which provides a basis for a model to calculate the flow velocity. Application to the 18 May 1980 pyroclastic flow deposits at Mount St. Helens (Washington State, USA) gives velocities of ∼9-13 m s-1 at ∼6-7 km from the vent on gentle slopes (<4°-6°), in agreement with field observations at this volcano and at others

Estudio experimental de la presencia de barreras en flujos detríticos

[ES] En este artículo se presentan resultados experimentales sobre la interacción de flujos detríticos con barreras transversales, permeables e impermeables. Las primeras bloquean completamente el cauce y las segundas sólo de manera parcial. Las barreras fueron ubicadas en serie dentro de una canal rectangular por donde fluían mezclas de agua y sedimento. Los sólidos incorporados a la mezcla aguasedimentos están constituidos por arena, grava y bentonita en distintas concentraciones volumétricas según el experimento. Los resultados muestran que tanto las barreras permeables como impermeables se comportan adecuadamente como medidas de control aluvional. La elección del tipo de barrera dependerá de la estrategia de control aluvional utilizada. Se determinaron las características de los depósitos generados: volumen de retención, segregación del material depositado y, en el caso de barreras impermeables, pendiente de los depósitos. Las variables más relevantes que definen estas características son la concentración de finos y el espaciamiento entre barreras. La presencia de finos en la mezcla altera la reología del fluido intersticial, lo que incide directamente en el comportamiento del flujo y capacidad de los sólidos en depositarse. En cuanto al espaciamiento entre barreras, éste controla los efectos de la socavación al pie de ellas, lo que puede disminuir la capacidad de retención. Debido a que son varios los parámetros adimensionales que representan distintos aspectos de la dinámica del flujo, todos ellos deben ser considerados en la modelación ya que, en general, no existe un dominio de un aspecto sobre otro. Por esto, se concluye que es muy difícil escalar, a dimensiones de prototipo, resultados obtenidos en estudios a escala reducida. Esta conclusión, sin embargo, no invalida los estudios experimentales, ya que estos permiten orientar el diseño de barreras dentro del régimen de flujo estudiado.Se agradece el financiamiento parcial dado por el Centro del Agua para Zonas Áridas y Semiáridas de América Latina y El Caribe, CAZALAC, a través de una beca otorgada al primer autor de este artículo.Montserrat M., S.; Tamburrino T., A.; Niño C., Y. (2005). Estudio experimental de la presencia de barreras en flujos detríticos. Ingeniería del agua. 12(3):1-13. https://doi.org/10.4995/ia.2005.2562OJS113123ARMANINI, A. Control Measures for Debris Flows, En: Recent Developments on Debris Flows. Armanini and Michieu (Eds.), Springer-Verlag, Berlin. 1997.ARMANINI, A. DELLAGIACOMA and F. FERRARI, L. From the check dam to the development of functional check dams. Fluvial Hydraulics of Mountain Regions. Lecture notes in earth sciences, n.37, Springer-Verlag, pp. 331-344, 1991AYALA, L. Hidráulica de los Fenómenos de Remoción en Masa: Corrientes de Detritos y Flujos de Barro. Curso Pre- XVII Congreso Latinoamericano de Hidráulica, Guayaquil, Ecuador,1996.FIEBIGER, G. Structures of Debris Flow Countermeasures, En: Debris -Flow Hazards Mitigation: Mechanics, Prediction and Assessment, First International Conference, August 7-9, San Francisco, California. 1997. pp 596-605IVERSON, R. The Physics of Debris Flows, Review of Geophysics, (35)3: 245-296. August 1997.LIN, P. CHANG, W. LIU, K. Retaining Function of Open-Type Sabo Dams, En: Debris -Flow Hazards Mitigation: Mechanics, Prediction and Assessment, First International Conference, August 7-9, San Francisco, California. 1997. pp 636-645MIZUYAMA, T. KOBASHI, S. and MIZUNO, H. Development and Improvement of Open Dams. Proc. Int. Symp. Interpraevent, 1996, Garmisch-Partenkirchen, Alemania, Vol. 5, pp. 59-65MONTSERRAT, S. TAMBURRINO y A. NIÑO, Y. Relaciones Friccionales de Mezclas de Agua y Sedimentos. XXI Congreso Latinoamericano de Hidráulica, São Pedro, Brasil, 2004.OKUBO, S. IKEYA, H., ISHIKAWA, Y. and YAMADA T. Development of New Methods for Countermeasures against Debris Flows, En: Recent Developments on Debris Flows. Armanini and Michieu (Eds.), Springer-Verlag, Berlin. 1997. pp 166-185SEMINARA, G. and TUBINO, M. Debris Flows: Meccanica, Contollo e Previsione. Monografia delle Unità Operativa del Guppo Nazionale per la Difesa dalle Catastrofi Idrogeologiche, Instituto di Idraulica, Universidad de Genova. Giugno 1993SENOO, K. and MIZUYAMA, T. Function of Structures against Debris Flow. Proc. Int. Symp. Interpraevent, 1984, Villach, Austria, Vol. 3, pp 113-120.VANDINE, D. Debris Flow Control Structures for Forest Engineering. British Columbia. 1996

Experimental study of the free evolution of the internal gravitational waves affect by Coriolis in a stratified flow

Abstract Laboratory experiments are presented to analyze the free evolution of large-scale internal gravitational waves in a stratified water body affected by Coriolis. This investigation was made in a rotating table, where a two-layer stratification was created into a circular basin, using a fresh water layer on top of a dyed salty water layer on the bottom. The control parameters used to characterize the experiments were the dimensionless Burger number, Wedderburn number and aspect ratio of the stratified water column. The free evolution of the internal waves field was measured by tracking the vertical displacements of the pycnocline using an optical method based on digital image analysis. Three sets of experiments were developed for capturing the internal gravity waves behavior as a function of the dimensionless numbers. The results show that the dynamics of the density interface is mainly modulated by the Kelvin-Poincaré interaction and the nonlinear response of solitary type waves, observed in the experiments for specific conditions. Finally, the results show that Earth rotation and nonlinear interactions are important aspects to understand the energy dissipation of internal gravitational basin scale waves

3D numerical modeling to support the design of contractions in supercritical flow channels

This article compares the usual methods in the design of contractions in supercritical open channel flows with the capabilities of Computational Fluid Dynamics (CFD). Contractions in supercritical flow channels generate cross waves in the flow, which can greatly increase the runoff height at the point they are generated and downstream, due to the propagation of these waves. The usual analytical methods to determine the runoff height in contractions in supercritical flow underestimate the height for Froude numbers greater than 6, according to previous experiments, because these methods do not consider the conservation of momentum in the vertical direction, but only in the horizontal directions. Numerical modeling in three dimensions is presented as a support to the design of contractions in supercritical flow channels, since there are no limitations to the usual methods. The modeling is done using the ANSYS-CFX software of several scenarios, which were tested in previous experiments, obtaining results consistent with the observations made. The values obtained for the numerical simulations compared with experimental data, present a maximum error of 5.3%, delivering a better approximation than the analytical methods analyzed. For Froude numbers greater than 6, the flow is strongly governed by vertical accelerations, which makes the approximations made by the analytical methods studied ineffective. Therefore, the numerical simulation delivers results closer to the experimental ones when considering momentum conservation in the three directions. Thus, it is convenient to use numerical modeling for the design effects of contractions in supercritical flow channels with Froude numbers greater than 6

Towards management and regulation of gravel mining in urban areas: application of an optimization/morphological model to Maipo river

River engineeringFlow management and contro

Infiltration Depth of Mineral Particles in Gravel-Bed Rivers

This article discusses the results of an experimental study of a spill of mineral particles in gravel-bed rivers due to mining accidents. The purpose of this research is to characterize the dynamics of the fine mining particles spilled on a bed of immobilized gravel as a hyper-concentrated mixture and to experimentally characterize the infiltration phenomenon. We analyzed the type of infiltration considering the dimensionless coarse to fine particle size relationship, the dimensionless weight of the fine particles, the relative density of the particles, and the relationship between the subsurface and surface velocities, in addition to the densimetric Froude and Reynolds numbers of the fine particles. We found that the dimensionless infiltration depth is not associated with hydraulic parameters or the weight of the fine sediment spilled; however, fine sediment deposition decreases with depth, and infiltration depth may increase if subsurface flow decreases over time. Finally, a relationship of the dimensionless maximum infiltration depth with the relative density of the mining particles, the ratio of the bed sediment and the mining particles sizes, and the ratio between the subsurface and surface velocities is established

Numerical Study of the Hydrodynamics of Waves and Currents and Their Effects in Pier Scouring

The scour around cylindrical piles due to codirectional and opposite waves and currents is studied with Reynolds Averaged Navier&ndash;Stokes (RANS) equations via REEF3D numeric modeling. First, a calibration process was made through a comparison with the experimental data available in the literature. Subsequently, not only the hydrodynamics, but also the expected scour for a set of scenarios, which were defined by the relative velocity of the current ( U C W ), were studied numerically. The results obtained show that the hydrodynamics around the pile for codirectional or opposite waves and currents not have significant differences when analyzed in terms of their velocities, vorticities and mean shear stresses, since the currents proved to be more relevant compared to the net flow. The equilibrium scour, estimated by the extrapolation of the numerical data with the equation by Sheppard, enabled us to estimate values close to those described in the literature. From this extrapolation, it was verified that the dimensionless scour would be less when the waves and currents are from opposite directions. The U C W parameter is an indicator used to adequately measure the interactions between the currents and waves under conditions of codirectional flow. Nevertheless, it is recommended to modify this parameter for currents and waves in opposite directions, and an equation is proposed for this case