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  • 2015-2019  (4)
  • Physics  (4)
  • 1
    Online Resource
    Online Resource
    A Numerical Study on the Attitudes and Aerodynamics of Freely Falling Hexagonal Ice Plates
    American Meteorological Society ; 2015
    In:  Journal of the Atmospheric Sciences Vol. 72, No. 9 ( 2015-09-01), p. 3685-3698
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 72, No. 9 ( 2015-09-01), p. 3685-3698
    Abstract: The fall attitudes and the flow fields of falling hexagonal ice plates are studied by numerically solving the transient incompressible Navier–Stokes equation for flow past ice plates and the body dynamics equations representing the 6-degrees-of-freedom motion that determine the position and orientation of the ice plates in response to the hydrodynamic force of the flow fields. The ice plates investigated are from 1 to 10 mm in diameter, and the corresponding Reynolds number ranges from 46 to 974. The results indicate that the 1-mm plate generates a steady flow field and exhibits a steady motion, whereas the rest of the ice plates generate unsteady flow fields and exhibit unsteady motions, including horizontal translation, rotation, and axial oscillation. The horizontal translation is primarily determined by the inclination due to oscillation. The pressure distributions around the falling plates are examined and discussed in association with the oscillation. The vortex structure in the wake of the plate is examined. Empirical formulas for fall speed, oscillation frequency, and drag coefficient are given. Potential impacts of the fall attitudes and flow characteristics on the microphysics of ice plates are discussed.
    Type of Medium: Online Resource
    ISSN: 0022-4928 , 1520-0469
    URL: Article
    DOI: 10.1175/JAS-D-15-0059.1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2015
    detail.hit.zdb_id: 218351-1
    detail.hit.zdb_id: 2025890-2
    SSG: 16,13
    Location Call Number Limitation Availability
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    Online Resource
  • 2
    Online Resource
    Online Resource
    Numerical Study of Motion and Stability of Falling Columnar Crystals
    American Meteorological Society ; 2016
    In:  Journal of the Atmospheric Sciences Vol. 73, No. 5 ( 2016-05-01), p. 1923-1942
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 73, No. 5 ( 2016-05-01), p. 1923-1942
    Abstract: Understanding of the flow field and falling patterns of ice crystals is fundamental to cloud physics and radiative transfer, and yet the complex shape hampers a comprehensive understanding. In order to create better understanding of falling patterns of columnar crystals, this study utilizes a computational fluid dynamics package and explicitly simulates the motion as well as the flow fields. Three modes of patterns (i.e., strong damping, fluttering, and unstable modes) were identified in the space of inverse aspect ratio (q) and Reynolds number (Re). The boundary of stability depicts the “L” shape as found in a previous experimental study. This study newly found that the range of Re for stable motion increases with a decrease in q. Decomposition of hydrodynamic torques indicates that, for stable mode, the pressure and viscous torques acting on the lower prism faces counteract the rotation when the inclination angle becomes 0°. The unstable motion was attributed to the pressure torque acting on the upper prism faces, which is associated with eddies that lag behind the oscillating boundary. Observed Re–q relationships of columns suggest that the strong damping mode is most likely to occur in the atmosphere, but the fluttering mode is also possible. Furthermore, the time scales of oscillation and damping were parameterized as a function of q and Re. The impact of the fluttering on the riming process is limited at the beginning, which supports the current formulation in numerical weather and climate models.
    Type of Medium: Online Resource
    ISSN: 0022-4928 , 1520-0469
    URL: Article
    DOI: 10.1175/JAS-D-15-0219.1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2016
    detail.hit.zdb_id: 218351-1
    detail.hit.zdb_id: 2025890-2
    SSG: 16,13
    Location Call Number Limitation Availability
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    Online Resource
  • 3
    Online Resource
    Online Resource
    A Numerical Study on the Aerodynamics of Freely Falling Planar Ice Crystals
    American Meteorological Society ; 2018
    In:  Journal of the Atmospheric Sciences Vol. 75, No. 9 ( 2018-09-01), p. 2849-2865
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 75, No. 9 ( 2018-09-01), p. 2849-2865
    Abstract: Fluid flow fields and fall patterns of falling planar ice crystals are studied by numerically solving the unsteady, incompressible Navier–Stokes equations using a commercially available computational fluid dynamics package. The ice crystal movement and orientation are explicitly simulated based on hydrodynamic forces and torques representing the 6 degrees of freedom. This study extends the current framework by investigating four planar-type ice crystals: crystals with sector-like branches, crystals with broad branches, stellar crystals, and ordinary dendritic crystals. The crystals range from 0.2 to 5 mm in maximum dimension, corresponding to Reynolds number ranges from 0.2 to 384. The results indicate that steady flow fields are generated for flows with Reynolds numbers less than 100; larger plates generate unsteady flow fields and exhibit horizontal translation, rotation, and oscillation. Empirical formulas for the drag coefficient, 900-hPa terminal velocity, and ventilation effect are given. Fall trajectory, pressure distribution, wake structure, vapor field, and vorticity field are examined.
    Type of Medium: Online Resource
    ISSN: 0022-4928 , 1520-0469
    URL: Article
    DOI: 10.1175/JAS-D-18-0041.1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2018
    detail.hit.zdb_id: 218351-1
    detail.hit.zdb_id: 2025890-2
    SSG: 16,13
    Location Call Number Limitation Availability
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    Online Resource
  • 4
    Online Resource
    Online Resource
    Dry-wet digital etching of Ge1− x Sn x
    AIP Publishing ; 2016
    In:  Applied Physics Letters Vol. 108, No. 6 ( 2016-02-08)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 108, No. 6 ( 2016-02-08)
    Abstract: The development of a precise micromachining process for Ge1–xSnx has the potential to enable both the fabrication and optimization of Ge1−xSnx-based devices in photonics and microelectromechanical systems. We demonstrate a digital etching scheme for Ge0.922Sn0.078 based on a two-stage, highly selective CF4 plasma dry etch and HCl wet etch. Using X-Ray Reflectivity, we show consistent etch control as low as 1.5 nm per cycle, which is defined as one dry etch step followed by one wet etch step. The etch rate increases to 3.2 nm per cycle for a longer dry etch time due to physical sputtering contributions, accompanied by an increase in RMS surface roughness. By operating within a regime with minimal sputtering, we demonstrate that good digital etch depth control and surface quality can be achieved using this technique.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/1.4941800
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2016
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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