Comparison of Speed-Up Over Hills Derived from Wind-Tunnel Experiments,Wind-Loading Standards,and Numerical Modelling     

Amir A. Safaei Pirooz  Richard G. J. Flay 《Boundary-Layer Meteorology》2018,168(2):213-246

We evaluate the accuracy of the speed-up provided in several wind-loading standards by comparison with wind-tunnel measurements and numerical predictions, which are carried out at a nominal scale of 1:500 and full-scale, respectively. Airflow over two- and three-dimensional bell-shaped hills is numerically modelled using the Reynolds-averaged Navier–Stokes method with a pressure-driven atmospheric boundary layer and three different turbulence models. Investigated in detail are the effects of grid size on the speed-up and flow separation, as well as the resulting uncertainties in the numerical simulations. Good agreement is obtained between the numerical prediction of speed-up, as well as the wake region size and location, with that according to large-eddy simulations and the wind-tunnel results. The numerical results demonstrate the ability to predict the airflow over a hill with good accuracy with considerably less computational time than for large-eddy simulation. Numerical simulations for a three-dimensional hill show that the speed-up and the wake region decrease significantly when compared with the flow over two-dimensional hills due to the secondary flow around three-dimensional hills. Different hill slopes and shapes are simulated numerically to investigate the effect of hill profile on the speed-up. In comparison with more peaked hill crests, flat-topped hills have a lower speed-up at the crest up to heights of about half the hill height, for which none of the standards gives entirely satisfactory values of speed-up. Overall, the latest versions of the National Building Code of Canada and the Australian and New Zealand Standard give the best predictions of wind speed over isolated hills.  相似文献   

The Quadrennial Ozone Symposium 2016     

Sophie GODIN-BEEKMANN  Irina PETROPAVLOSKIKH  Stefan REIS  Paul NEWMAN  Wolfgang STEINBRECHT  Markus REX  Michelle L. SANTEE  Richard S. ECKMAN  Xiangdong ZHENG  Matthew B. TULLY  David S. STEVENSON  Paul YOUNG  John PYLE  Mark WEBER  Johanna TAMMINEN  Gina MILLS  Alkis F. BAIS  Clare HEAVISIDE  Christos ZEREFOS 《大气科学进展》2017,34(3):283-288

<正>1.Overview The 2016 Quadrennial Ozone Symposium(QOS-2016)was held on 4–9 September 2016 in Edinburgh,UK.The Symposium was organized by the International Ozone Commission(IO3C),the NERC Centre for EcologyHydrology and the University of Edinburgh,and was co-sponsored by the International Union of Geodesy and Geophysics,the International Association of Meteorology and Atmospheric  相似文献   

In Memoriam: Herbert Edgar Wright,Jr.     

Daniel R. Engstrom  Hilary H. Birks  Richard W. Battarbee 《Journal of Paleolimnology》2016,56(1):73-78

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Quantifying system disturbance and recovery from historical mining-derived metal contamination at Brotherswater,northwest England     

Daniel N. Schillereff  Richard C. Chiverrell  Neil Macdonald  Janet M. Hooke  Katharine E. Welsh 《Journal of Paleolimnology》2016,56(2-3):205-221

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An inconvenient dispatch from the San Francisco AAG: of conferences and contradictions     

Richard Shearmur 《Urban geography》2016,37(4):483-484

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Li Be B Energetics and Cosmic Ray Origin     

Reuven Ramaty  Richard E. Lingenfelter 《Astrophysics and Space Science》1999,265(1-4):71-76

Three different models have been proposed for LiBeB production bycosmic rays: the CRI model in which the cosmic rays areaccelerated out of an ISM of solar composition scaled withmetallicity; the CRS model in which cosmic rays with compositionsimilar to that of the current epoch cosmic rays are acceleratedout of fresh supernova ejecta; and the LECR model in which adistinct low energy component coexists with the postulated cosmicrays of the CRI model. These models are usually distinguished bytheir predictions concerning the evolution of the Be and Babundances. Here we emphasize the energetics which favor the CRSmodel. This model is also favored by observations showing that thebulk (80 to 90%) of all supernovae occur in hot, low densitysuperbubbles, where supernova shocks can accelerate the cosmicrays from supernova ejecta enriched matter. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Taking Stock: New Zealand Population Geography at the End of the Millennium     

Richard Bedford 《New Zealand geographer》1999,55(2):1-3

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The colour–magnitude relation of early-type galaxies in the Hubble Deep Field     

Tadayuki Kodama  Richard G. Bower  Eric F. Bell 《Monthly notices of the Royal Astronomical Society》1999,306(3):561-566

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Hydrodynamic simulations of propagating warps and bending waves in accretion discs     

Richard P. Nelson  John C. B. Papaloizou 《Monthly notices of the Royal Astronomical Society》1999,309(4):929-940

We present the results of a study of propagating warp or bending waves in accretion discs. Three-dimensional hydrodynamic simulations were performed using smoothed particle hydrodynamics (SPH), and the results are compared with calculations based on the linear theory of warped discs.
We examine the response of a gaseous disc to an initially imposed warping disturbance under a variety of physical conditions. We consider primarily the physical regime in which the dimensionless viscosity parameter α < H r , where H r is the disc aspect ratio, so that bending waves are expected to propagate. We also performed calculations for disc models in which α > H r , where the warps are expected to evolve diffusively. Small-amplitude (linear) perturbations are studied in both Keplerian and slightly non-Keplerian discs, and we find that the results of the SPH calculations can be reasonably well fitted by those of the linear theory. The main results of these calculations are: (i) the warp in Keplerian discs when α < H r propagates with little dispersion, and damps at a rate expected from estimates of the code viscosity; (ii) warps evolve diffusively when α > H r ; (iii) the slightly non-Keplerian discs lead to a substantially more dispersive behaviour of the warps, which damp at a similar rate to the Keplerian case, when α < H r .
Initially imposed higher amplitude, non-linear warping disturbances were studied in Keplerian discs. The results indicate that non-linear warps can lead to the formation of shocks, and that the evolution of the warp becomes less wave-like and more diffusive in character.
This work is relevant to the study of the warped accretion discs that may occur around Kerr black holes or in misaligned binary systems, and is mainly concerned with discs in which α < H r . The results indicate that SPH can model the hydrodynamics of warped discs, even when using rather modest numbers of particles.  相似文献   

Space weathering on the Moon: Patina on Apollo 17 samples 75075 and 76015     

Susan J. WENTWORTH  Lindsay P. KELLER  David S. McKAY  Richard V. MORRIS 《Meteoritics & planetary science》1999,34(4):593-603

Abstract— We studied patinas on lunar rocks 75075 and 76015 from the Apollo collection using a multi-disciplinary approach, including scanning electron microscopy (SEM), energy dispersive x-ray spectrometry (EDS), transmission electron microscopy (TEM), wavelength-dispersive x-ray (WDS) mapping, Mössbauer spectroscopy, spectral reflectance, and microspectrophotometry. Based on SEM petrography, we have defined three textural types of patina: glazed, fragmental, and classic (cratered). The presence of classic patina is diagnostic of lunar samples that have been exposed directly to the space weathering environment. It is characterized by the presence of microcraters and glass pancakes and is the patina type studied by earlier workers. Classic patina is found on 76015 but not on 75075. Glazed patina is found on both 76015 and 75075, whereas fragmental patina is found only on 75075. The glazed and fragmental patinas on 75075 were probably formed as a result of relatively large nearby impacts; and although these two types of patina are not strictly the result of direct exposure to the space weathering environment, they are important because they affect the optical properties of the rocks. Field emission gun SEM (FE-SEM) of classic patina on 76015 shows evidence of possible solar wind sputtering erosion. Transmission electron microscope studies of 76015 reveal the presence of impact-generated deposits and solar flare particle tracks which, like microcraters and pancakes, are diagnostic of direct exposure to space weathering processes. The outermost surface of the 76015 patina consists of an amorphous rim very much like the rims found on individual lunar soil grains; this amorphous patina rim probably formed by similar processes of impact-generated vapor condensation and possible sputter deposition. Wavelength-dispersive x-ray element maps of polished thin sections of 75075 and 76015 indicate that patina compositions are poor indicators of the compositions and mineralogies of the rocks underlying them. On average, the reflectance spectra of patinas on both samples are slightly darker than those of their unweathered equivalents. Microreflectance measurements show that a thick patina can dramatically alter the optical properties of the rock on which it forms. The backscatter Mössbauer (BaMS) spectrum of a patina-covered surface of 76015 is very similar to that of an unweathered surface, indicating that the Mössbauer signal is generated from beneath the patina. Because BaMS “sees” through surface space-weathering effects to the underlying rock, this technique has great potential for use in robotic missions to other planetary bodies.  相似文献