Scour Caused by Rectangular Impinging Jets in Cohesionless Beds

Se desarrolló un programa experimental para encontrar expresiones que permitan predecir la profundidad de socavación generada por chorros de agua sobre lechos no cohesivos. Se demostró que la profundidad de socavación depende del caudal unitario, del ángulo de incidencia; del tamaño del material del lecho, su gravedad específica sumergida y su velocidad de caída; el espesor del chorro en el punto de impacto y la profundidad del agua en la zona de impacto. Esta última variable influye en la disipación de energía, reduciendo el potencial de socavación del chorro cuando aumenta su valor. Además, de los datos del programa experimental, en que los chorros fueron "hiperventilados" (con contenido de aire entre 90 a 98%), se emplearon datos de otros autores en los que los chorros tenían un contenido muy bajo de aire, a los que se denominaron "compactos". Se concluyó que los chorros hiperventilados se disipan con mayor facilidad que los chorros compactos, disminuyendo su potencial de erosión en lechos no cohesivos. La investigación demostró que se requieren al menos dos expresiones diferentes para calcular la profundidad de erosión causada por chorros de agua: una para chorros con alto contenido de aire y otra para chorros con bajo contenido de aire.Trabajo de investigació

Vibration test of a multistory building

Vibration tests were performed on a 9 story reinforced concrete building with basement, in order to investigate its dynamical characteristics, by exciting the building with 2 vibration generators installed on its 9th floor. The natural periods of vibration, the value of the damping, and the mode shapes, in the N-S and E-W directions and in torsion, were determined by measurement. Before the main part of the testing was carried out, some preliminary tests were made to check the correctness of some assumptions which would simplify the main test procedure. It was possible to investigate in detail only the first mode of each type of motion, because of the relatively high rigidity of the building and a limitation on the maximum frequency at which the shakers could be driven. The periods measured were quite short for a 9 story building, 0. 505 sec in the N-S direction, 0. 662 sec in the E- W direction, and 0.346 sec in torsion, and their values increased by about 3 per cent when the tests were performed at the highest force levels. The damping, which consistently increased as the exciting force increased, varied between 0. 70 and 2. 00 per cent of the critical viscous damping. The periods and damping values were also deter- mined at very low force levels by exciting the building with a rhythmical movement of the operator's body. The periods measured in this way were slightly smaller than those found using the shakers, and the damping varied between 0.6 and 0.9 per cent of the critical viscous damping. The mode shape did not seem to be well defined for the lower force levels, but after the force level reached a certain minimum value, the normalized mode shape remained unchanged, both with further increases in the forces, and with changes in the frequency of excitation. However, in both the N-S direction and in torsion, the horizontal displacements of the first and basement floors consistently increased, on the order of 3 per cent with respect to the displacements of the upper floors as the exciting force increased. Some aspects of the dynamical behavior of buildings, which have not been studied by other investigators in previous tests , were examined. It is a common practice in the seismic analysis of structures to assume that the floor systems act as rigid diaphragms when the building is acted upon by horizontal forces, and also to assume that the structure is fixed at the ground level. It was found that the first assumption was correct, but instead of the second it is more accurate to assume that the building is fixed at the foundation, and not at ground level. The vibration of the ground in the vicinity of the building was also measured, together with the vibrations of the basement and first floor. It was also possible to measure the acceleration at the top of one of the units of the air conditioning equipment located on the roof. The acceleration at the top of this unit was about 8.5 times that of the roof

Time-dependent scour processes on granular beds at large scale

AbstractA theoretical framework, based on the phenomenological theory of turbulence applied to scour-related processes due to plunging jets on cohesionless beds, is considered in this paper. More specifically, its predictive capability is assessed herein for large-scale domains, after it was developed for small scales elsewhere. The analysis focuses on both the time-evolution process and the equilibrium configuration for a wide range of hydraulic structures. After revisiting the theory for the temporal evolution of the scour processes, the scour for large-scale tests is investigated using unpublished experiments performed at Colorado State University by the last author. These tests confirm the existence of two stages in the scour hole development, namely the developing and developed phases. Thus, the scour dynamics at large scales is shown to be consistent with that at smaller scales. Then, the theory recently introduced by the first three authors is used to predict the time evolution of scour, corroborating that the very same equations, together with the same coefficients, provide successful predictions, regardless of scale and granulometric distribution. Finally, the theory is again verified against laboratory data on PK weirs obtained at the University of Pisa. Overall, the work described in the paper offers a tool with general validity

Water and agriculture

This chapter shows the strong links between water, agriculture and the economy in Latin America and Caribbean (LAC). Both green and blue water are vital for LAC's economies and for its food security. Awareness of LAC's virtual water trade volumes and water footprints alone will not solve the local or global water problems. However, the awareness gained increases the likelihood that optimized water allocation decisions, which consider the hydrological and economical aspects of water resources, are made. • Agriculture is a significant economic sector for many LAC countries with some being major world players in the agricultural commodities world markets, such is the case for Brazil and Argentina who contribute to 13% of the global green water export. At the micro level, agriculture still plays a significant role for the food security of the population. • The consumptive water use of agricultural production was on average 1,057Gm 3 / yr for the period 1996–2005; of which, 95% corresponds to the green water footprint, whereas 5% refers to the blue component. This indicates that LAC relies heavily on green water for agricultural production, i.e. rain-fed agriculture. • Maize is a fundamental crop in Argentina, Brazil, Chile, Mexico and Peru, representing 15% of the total agricultural blue and green water footprint (773,408hm 3 /yr) and contributing to 35% of the agricultural nitrogen pollution, estimated as grey water footprint, in Argentina, Brazil, Chile, Colombia, Mexico and Peru. Only in Mexico, maize contributes 60% of the agricultural grey water footprint. • Grazing represents 24% of the total green water footprint of agriculture in these countries. The blue water consumption by the animal water supply is very significant in Argentina, Brazil, Chile, Mexico and Peru, which amounts to 13% (38,825hm 3 /yr) of the total consumption

Vibration tests of a multistory building

Vibration tests were performed on a 9 story reinforced concrete building with basement, in order to investigate its dynamical characteristics, by exciting the building with 2 vibration generators installed on its 9th floor. The natural periods of vibration, the value of the damping, and the mode shapes, in the N-S and E-W directions and in torsion, were determined by measurement. Before the main part of the testing was carried out, some preliminary tests were made to check the correctness of some assumptions which would simplify the main test procedure. It was possible to investigate in detail only the first mode of each type of motion, because of the relatively high rigidity of the building and a limitation on the maximum frequency at which the shakers could be driven. The periods measured were quite short for a 9 story building, 0.505 sec in the N-S direction, 0.662 sec in the E-W direction, and 0.346 sec in torsion, and their values increased by about 3 per cent when the tests were performed at the highest force levels. The damping, which consistently increased as the exciting force increased, varied between 0.70 and 2.00 per cent of the critical viscous damping. The periods and damping values were also determined at very low force levels by exciting the building with a rhythmical movement of the operator's body. The periods measured in this way were slightly smaller than those found using the shakers, and the damping varied between 0.6 and 0.9 per cent of the critical viscous damping. The mode shape did not seem to be well defined for the lower force levels, but after the force level reached a certain minimum value, the normalized mode shape remained unchanged, both with further increases in the forces, and with changes in the frequency of excitation. However, in both the N-S direction and in torsion, the horizontal displacements of the first and basement floors consistently increased, on the order of 3 per cent with respect to the displacements of the upper floors as the exciting force increased. Some aspects of the dynamical behavior of buildings, which have not been studied by other investigators in previous tests, were examined. It is a common practice in the seismic analysis of structures to assume that the floor systems act as rigid diaphragms when the building is acted upon by horizontal forces, and also to assume that the structure is fixed at the ground level. It was found that the first assumption was correct, but instead of the second it is more accurate to assume that the building is fixed at the foundation, and not at ground level. The vibration of the ground in the vicinity of the building was also measured, together with the vibrations of the basement and first floor. It was also possible to measure the acceleration at the top of one of the units of the air conditioning equipment located on the roof. The acceleration at the top of this unit was about 8.5 times that of the roof.</p

Influencia de la geometría de entrada en tomas sumergidas sobre la sumersión crítica para la formación de vórtices que arrastran aire

RESUMENSe realizó un estudio experimental para estudiar la influencia de la geometría de una toma horizontal sumergida en la formación de vórtices de superficie libre que arrastran aire. Se ensayaron dos tipos de perfiles de ingreso a la toma: perfil acampanado y de arista viva. En un gráfico adimensional, en el que la sumersión relativa se expresa en función del número de Froude, se delinearon para cada caso las regiones en las que no se formaron vórtices con arrastre de aire. Se determinó el tipo de vórtice para cada punto y se delinearon las regiones donde no se forma ningún vórtice. Se comprobó que, a medida que aumenta el número de Froude, es necesaria una mayor sumersión relativa para evitar el ingreso de aire hacia la toma sumergida. Además, la toma de arista viva requirió una mayor sumersión relativa que la toma de perfil acampanado, en el rango de número de Froude ensayado, para evitar la formación de vórtices que atrapen aire. Se comprobó, en los vórtices de tipo B, que los periodos de ingreso de aire eran más prolongados cuando se instalaba una toma de arista viva para las mismas condiciones hidráulicas que para la toma de perfil acampanado