Mechanical & Aerospace Engineering Research
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Item Data from: Evolution of turbulent boundary conditions on the surface of large barchan dunes: anomalies in aerodynamic roughness and shear velocity, aeolian thresholds and the role of dune skewnessLouge, Michel Y.; Valance, Alexandre; Porté-Agel, Fernando; Fang, Jiannong; Harnett, Stephen; Chasle, Patrick (2023-12-12)This collection contains supporting information for M. Y. Louge, A. Valance, J. Fang, S. Harnett, F. Porte-Agel, P. Chasle, Evolution of turbulent boundary conditions on the surface of large barchan dunes: anomalies in aerodynamic roughness and shear velocity, aeolian thresholds and the role of dune skewness, J. Geophys. Res. Earth Surface (2023). It consists of one .xlsx Excel workbook and six .csv worksheets, with contents summarized in the readme.txt file. Wind friction is the engine that erodes sand dunes, relentlessly pushing them over roads, houses and infrastructure. Our records of wind speed on crescent-shaped mobile dunes challenge conventional understanding of this process. Using field measurements and models, we show that the highest friction occurs where the gentle upward dune surface abruptly gives way to a steeper avalanching downward slope. Our data also reveals that the `aerodynamic roughness', a measure of wind friction on sand, contradicts existing models based on historical data for turbulent pipe flow. Because numerical simulations are used to predict flow over landforms that are inaccessible to detailed measurements, we validate them against data on a large dune. Our observations imply that, to achieve greater fidelity, simulations should subdivide the fluid neighborhood of the dune more finely, and revisit how they treat aerodynamic friction on its surface. Although our work involved large desert dunes, we expect these suggestions to apply more broadly to atmospheric, fluvial or submarine landforms that are surrounded by rougher terrain or that feature sudden changes in slope.Item Data from: Water vapor transport across an arid sand surface - non-linear thermal coupling, wind-driven pore advection, subsurface waves, and exchange with the atmospheric boundary layerLouge, Michel Yves; Valance, Alexandre; Xu, Jin; Ould el-Moctar, Ahmed; Chasle, Patrick (2022-03-01)These files contain data and other outputs supporting all results reported in Louge et al. Water vapor transport across an arid sand surface - non-linear thermal coupling, wind-driven pore advection, subsurface waves, and exchange with the atmospheric boundary layer. In Louge et al., we found: Deserts inhale and exhale water vapor through their surface. Although this process affects the water balance over vast sand seas, it is poorly understood for want of sensitive instruments. We discover how it operates using a new probe that detects tiny amounts of moisture on sand grains. Our analysis reveals that vapor infiltration is considerably slower in dry sand, and that wind flowing over a dune creates weak internal air currents contributing to the transport of moisture. Their strength depends on dune location, wind speed and direction. When wind is strong enough to let dry sand meander over a dune, the resulting rapid variation in surface moisture sends evanescent waves of humidity downward. An analysis of these waves implies that water evaporation from individual sand grains behaves like a slow chemical reaction. The exchange of moisture with the atmosphere is not always driven by the difference between humidity at the dune surface and in the ambient, as current models assume, and it is weaker than they predict. In future, the new probe can be used as ground truth to calibrate satellite observations over deserts, explore extra-terrestrial environments holding scant water, and detect moisture contamination in pharmaceutical products.Item Crane Runway Girder ProjectIngraffea, Anthony; McGuire, W.; Pekoz, Teoman; Gerstle, W.; Mettam, K.; Wawrzynek, P.; Hellier, A.K. (Cornell Univesity, 1986-06-23)Item BEST PRACTICE FOR MEASURING WIND SPEEDS AND TURBULENCE OFFSHORE THROUGH IN-SITU AND REMOTE SENSING TECHNOLOGIESBarthelmie, Rebecca J; Wang, H; Doubrawa, P; Pryor, S.C. (2016-07-07)The motivation for making offshore wind measurements for the wind energy industry is summarized including identifying the key parameters of interest, and providing a limited summary of available best practice recommendations for the offshore wind energy industry. A précis of in situ measurement technologies, installation guidance and uncertainty analyses, and best practice recommendations is provided. Next wind measurement devices are reviewed that are based on optical remote sensing (ground-based, airborne, and satellite-based techniques and applications) are relevant to the demands of the wind energy industry. Emphasis is placed on a review of lidar measurement techniques and use of lidar. For both ground-based and satellite-borne instrumentation, a précis of the technologies, uncertainty analyses, and best practice recommendations are given. Finally, the report concludes by providing a number of recommendations for future work.Item A direct method for the determination of the mean orientation-dependent elasticBernier, Joel V.; Miller, Matthew P. (International Union of Crystallography, 2006)A salient manifestation of anisotropy in the mechanical response of polycrystal- line materials is the inhomogeneous partitioning of elastic strains over the aggregate. For bulk samples, the distributions of these intergranular strains are expected to have a strong functional dependence on grain orientations. It is then useful to formulate a mean lattice strain distribution function (LSDF) over the orientation space, which serves to characterize the micromechanical state of the aggregate. Orientation-dependent intergranular stresses may be recovered from the LSDF via a constitutive assumption, such as anisotropic linear elasticity. While the LSDF may be determined directly from simulation data, its experimental determination relies on solving an inverse problem that is similar in character to the fundamental problem of texture analysis. In this paper, a versatile and robust direct method for determining an LSDF from strain pole figures is presented. The effectiveness of this method is demonstrated using synthetic strain pole figures from a model LSDF obtained from the simulated uniaxial deformation of a 1000-crystal aggregate.