Aeronautical engineering: A continuing bibliography with indexes (supplement 260)

This bibliography lists 405 reports, articles, and other documents introduced into the NASA scientific and technical information system in December, 1990. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Biomediation of Turbulence and Suspended Sediment Characteristics in Marsh Surface Flows - The Influence of Spartina anglica

Laboratory experimentation in a large aimular flume (radius 3 m, channel width and water depth 0.4 m) has been conducted using a geometrically and dynamically similar Spariina anglica mimic (canopy height 0.21 m, stem density 1000 stems m~^) to investigate the influence of submerged Spartina on hydrodynamics under unidirectional currents {Uh = 0.2 m s~*) and the impact upon the dynamics of suspended cohesive sediments near the bed within the canopy. The vertical distribution of canopy biomass strongly influences vertical profiles of time-averaged velocity and turbulent quantities. An inflected velocity profile is observed in the region 0.79 < z/h < 0.9 which generates shear, T K E and Reynolds Stress peaks within vicinity of the canopy top. In this region T K E peaks at 15 times the levels observed in un-vegetated experiments. Flows at the canopy top are strongly intermittent with extremely efficient downward momentum transfer, uf] and ufz (stream-wise and vertical zero-mean fluctuating velocity) skewness are 0.5 and -0.5 indicating the presence of intermittent downward penetrating gusts. Near the bed (0 < z/h < 0.3) mean flow velocities are reduced by 88 - 90% in comparison to un-vegetated flows but turbulence intensities are strongly augmented by wake shedding from vegetative elements. TKE in this region is approximately equal to that in un-vegetated flows. Novel field observations in a low energ>', estuarine fringing marsh site on the Tavy Estuary, UK, with a vertical array of synchronous velocimeters and optical backscatter sensors exhibit low velocities (<0.6 ra s"*) and suspension concentrations (<100 mg L"*) in agreement with laboratory simulations. While field observations of near bed flows exhibit similarity to those measured in the laboratory, magnitudes of time-averaged flow throughout the water column are so small that the velocity profile appears constant over depth. Superimposed upon the low field velocities are small wind generated waves ( < 0.05 m in height and with periods < 3 s) which have a considerable impact on flow energy and stress estimates, but crucially, cannot be replicated in the laboratory experiments. Dissipation rates within the laboratory canopy are 70-200x10"'* m~^s"^ giving reduced Kohnogorov length scales of 0.04 - 0.14 mm. Field values for dissipation are generally of similar magnitude but peak at up to 600 X10"** m~^s~^. Kolmogorov length scales are consequently 0.06 - 2.6 mm. Using natural intertidal mud, suspension concentrations of 100-200 mg L~* have been sheared through the mimic canopy. Observations from a vertical array of miniaturised OBS sensors suggests sediments are maintained in suspension twice as long, under constant unidirectional currents, compared to un-vegetated flows. In the field initial concentrations of 100 mg L~* quickly decay to background levels of <20 mg L"* indicating the rapid setthng of material from suspension. Use of a novel digital in-line holographic particle iinaging system and the development of a particle tracking methodology has enabled the high resolution observation of both sample size and settling velocities of suspended cohesive particles. Laboratory observations of sample averaged size (74.5 - 111.7 mm) and settling rates (0.35 - 1 mm s~*) are in agreement with published estimates and the limited observational data that exists for settling rates in marsh systems. Settling velocities estimated in the field at 0.1 - 0.8 mm s~^. Significantly larger and fast settling aggregates have been observed than previously recorded. In the narrow range of experimental suspension concentrations and shear stresses utilised in the present experiments, significant diff^erences in particle size and settling velocity between vegetated and un-vegetated flows cannot be identified. Contrasting flux estimates using sample averaged settling rates and concentrations with full spectral estimates derived from the holographic particle imager indicate an error in the former fluxes of, on average, 62%. The range of settling rates observed during the pr^ent study raises questions regarding the accurate representation of marsh surface settling fluxes in numerical simulations. Large magnitude flux errors may have significant implications for accurate accretion rates in numerical models of marsh sedimentation

Proceedings of the 8th International Junior Researcher and Engineer Workshop on Hydraulic Structures

Full proceedings for the 8th International Junior Researcher and Engineer Workshop on Hydraulic Structures

A numerical and experimental study on cavitation in positive displacement pumps and its application in valve design optimization

Appendix of "Technical sheets and drawings" appears in the online version only.This thesis was previously held under moratorium from 26/11/2015 to 15/06/2021.A comprehensive and transient Computational Fluid Dynamic model of a Positive Displacement reciprocating pump in cavitating condition was developed in order to study the main features and the causes of cavitation in this kind of device. Several sensitivity analyses were also carried out in order to identify the most influential parameters on cavitation; the design of the inlet valve as well as the operating conditions were found to be the main parameters playing an important role in cavitation. To complete the numerical study, a sensitivity analysis on the air content in the water was carried out.;This highlighted the importance of the physical properties of the working liquid in influencing the vapour generation during cavitation. The second part of the project was dedicated to the experimental analysis; a test rig replicating the numerical model was designed and built. The experimental tests were carried out and the results were compared to the numerical data obtained in the previous part. The comparison revealed a reasonable accuracy as well as good consistency although numerical problems were found in the way the cavitation model accounted for the influence of the air dissolved in the water which was overestimated. The validated numerical model was utilised to modify the design of the inlet valve.;A new model of the valve was presented and described, it was demonstrated capable of minimising the vapour generation under the same operating condition with respect to the initial valve design. The modification proposed was implemented in the design of new valves which are already being manufactured and tested in the field, they will be introduced into the market afterwards. The project is the demonstration that numerical tools based on CFD are nowadays ready to effectively support designers and industries in bringing down the cost of the engineering process of new and more efficient products.A comprehensive and transient Computational Fluid Dynamic model of a Positive Displacement reciprocating pump in cavitating condition was developed in order to study the main features and the causes of cavitation in this kind of device. Several sensitivity analyses were also carried out in order to identify the most influential parameters on cavitation; the design of the inlet valve as well as the operating conditions were found to be the main parameters playing an important role in cavitation. To complete the numerical study, a sensitivity analysis on the air content in the water was carried out.;This highlighted the importance of the physical properties of the working liquid in influencing the vapour generation during cavitation. The second part of the project was dedicated to the experimental analysis; a test rig replicating the numerical model was designed and built. The experimental tests were carried out and the results were compared to the numerical data obtained in the previous part. The comparison revealed a reasonable accuracy as well as good consistency although numerical problems were found in the way the cavitation model accounted for the influence of the air dissolved in the water which was overestimated. The validated numerical model was utilised to modify the design of the inlet valve.;A new model of the valve was presented and described, it was demonstrated capable of minimising the vapour generation under the same operating condition with respect to the initial valve design. The modification proposed was implemented in the design of new valves which are already being manufactured and tested in the field, they will be introduced into the market afterwards. The project is the demonstration that numerical tools based on CFD are nowadays ready to effectively support designers and industries in bringing down the cost of the engineering process of new and more efficient products

Calibrating saturated conductivity and soil cohesion in rainfall-triggered landslides in the Langhe area (1994)

In this work we have analyzed a “cold case”, i.e., the prolonged rainfall and flood event occurred in the Piedmont region (Northern Italy) in November 1994, causing several hundred of shallow landslides. The research aim is to put some focus on the possibility to calibrate soil parameters by means of the combined use of a simple hydrological model (Rosso et al. 2006) and post-event geotechnical surveys. For this purpose, a database of geometries and soil characteristics for 238 observed landslides has been used. To address the calibration of the cohesion and hydraulic conductivity parameters, the safety factor expression from the Limit Equilibrium Analysis has been targeted to assume a maximum value of 1 for all the slopes made unstable by the actual (measured) rainfall. Significant reduction of the cohesion parameter was observed after calibration, suggesting caution in the use of literature values, typically obtained on mechanically undisturbed soil sample

Environmental Hydraulics Research

This book aims to provide research and engineering applications related to water and hydraulic problems. It is comprised of scientific papers in all topics of hydraulics, in particular, on sustainable water management, environmental hydraulics, ecohydraulics, water–energy nexus, and systems protection and efficiency. Safety and innovation issues, interdisciplinary problems, and linkage of theory to experimental and field applications can also be found within. Solutions of water problems in the form of prediction models, flow simulations, engineering systems, monitoring, management strategies covering scientific investigations and/or experimental or field studies of flow behaviour, hydrodynamics, and climate changes effects and adaptation, new design solutions, innovative approaches in the field of environment, hydraulics, techniques, methods, and analyses to address the new challenges in environmental hydraulics are alo presented and explored. This topic is studied both from a technical and environmental point of view, with the objective of protecting and enhancing the quality of the environment. In a cross-disciplinary field of study, this book comprises open channel/river flows and pressurised systems, combining, among others, new technological, social, and environmental hydraulic challenges, working in water-related fields with available information, new concepts and tools, new design solutions, eco-friendly technologies, and the advanced materials necessary to address the increasing challenges of ensuring a sustainable water environment by promoting the adaptation, flexibility, integration, and sustainability of recognised environmental solutions