Validation of a finite difference method for the simulation of vortex-induced vibrations on a circular cylinder     

J. B. V. Wanderley  C. A. Levi 《Ocean Engineering》2002,29(4):445-460

The Karman Vortex Street generated by a circular cylinder is investigated by the numerical solution of the compressible Navier–Stokes equations in the incompressible Mach number range (Mach<0.3) using the Beam and Warming implicit scheme. The agreement with the fully incompressible projection method (Chorin, 1968) is fairly good while convergence time is very much better. The investigation suggests that the compressible Navier–Stokes equations may be used as an efficient alternative to study incompressible flows as well. Mach numbers just below 0.3 are enough to simulate incompressible flow behavior and at the same time do not cause numerical ill-conditioning in the solution. In addition, some relevant features of the vortices generated and carried by the wake of the cylinder could be fairly well captured.  相似文献   

Study of an unexpected convective storm     

Maria E. Saluzzi  Laura Levi  Luisa Lubart  Gustavo Carri 《Atmospheric Research》1997,44(3-4)

The occurrence of a severe storm in the Argentine littoral has been analyzed. Although general atmospheric conditions were not favorable to the development of deep convection, this storm produced strong winds and hail of considerable intensity. Its occurrence was associated with the entrance of a pulse of humid air at low levels and could be related to the development of two vorticity centers in the region. Atmospheric conditions existing above a low-level inversion are used to simulate two possible clouds, with base altitudes at 2200 and 3000 m and updraft speeds reaching maximum values of 27 and 29 m s⁻¹ respectively. It is noted that the base temperature of about 13°C, found for the first cloud, can be correlated with the prevalence of frozen drop embryos, observed in an analyzed hailstone sample. Hailstone vertical trajectories are simulated in both modeled clouds, assuming spheroidal and spherical particles and assigning different values to the drag coefficient C_d.  相似文献   

Metamorphic gradients in burial metamorphosed vesicular lavas: Comparison of basalt and spilite in Cretaceous basic flows from central Chile     

Beatriz Levi  Luis Aguirre  Jan Olov Nyström 《Contributions to Mineralogy and Petrology》1982,80(1):49-58

Partial spilitization of a 9 km thick pile of flood basalts with highly vesicular flow tops gave rise to patterns of secondary mineralogy at different scales: (a) a local pattern of mineralogical variation from the almost unaltered bottom towards the altered top of each flow, and (b) an overall pattern, comparing flow tops throughout the pile, with changes in mineralogical composition within a sequence of metamorphic zones and facies. The local patterns mimic the trend of the overall pattern, but are of opposite direction and telescoped. Thus, a gradual ordering and Andepletion of the secondary albite and increases in the Fe^*/Al ratio of epidote and pumpellyite upwards within individual flows are comparable in range to corresponding overall changes downwards throughout several kilometres. The mineralogical changes within the flows diminish in range towards the more altered deeper part of the pile.The local and overall patterns cannot be interpreted in terms of grade. They represent trends from metastable towards stable equilibrium, this latter only approached in the flow tops of the lower part of the pile. The patterns of secondary mineralogy were formed by an interplay of metamorphic gradients at different scales at any given time, and as burial proceeded. The overall pattern was caused by depth-controlled gradients: increasing P _fluid, temperature and temperature-induced increase of reaction rates, and decreasing fO₂ (downwards in the pile). The local patterns resulted from permeability-controlled gradients: increasing reaction rates, fO₂ and contrast in chemical activity between different domains, and decreasing P _fluid (upwards in each flow). The mineralogical observations reported in this paper fall into line if the overall temperature-induced increase of reaction rates and the local permeability-controlled rate factors played the leading role during burial metamorphism of the pile.  相似文献   

Burial metamorphism of a Cretaceous volcanic sequence west from Santiago,Chile     

B. Levi 《Contributions to Mineralogy and Petrology》1969,24(1):30-49

This report is a petrographic study of alteration phenomena in an area of 100 km² in the Coastal Range west of Santiago. The stratified sequence of the area is of Cretaceous age and belongs to the western monoclinal limb of the Andean Geosyncline. Two structural units are present, separated by an angular unconformity. The older is about 9,000 m thick, and the younger 300 m thick. The rock types are mostly altered andesitic flows and flow breccias, and keratophyric ignimbrites and lavas, with alternating marine, brackish-water and terrestrial interbeds. Stratified rocks are cut locally by acid and basic apophyses and dikes, probably feeders of their volcanic host rocks. Discordant Cretaceous granitic plutons intrude the older unit. Throughout the whole stratigraphic section there are alteration minerals, which selectively replace the primary minerals, or fill amygdules and open fractures, or form a cement in flows, dikes and sedimentary interbeds. Patterns of alteration are regular and persistent; they correlate on a large scale with stratigraphic level and on a smaller scale with position within each individual flow and situation within amygdules. The stratigraphically controlled pattern is as follows: $$\begin{gathered} 1.{\text{ Younger unit}}{\text{.}} \hfill \\ {\text{ }}\left. \begin{gathered} {\text{Lower portion: 30m: albite}}---{\text{pistacite}}---{\text{actinolite}}---{\text{chlorite}}---{\text{ }} \hfill \\ {\text{calcite}}---{\text{sphene}}---{\text{quartz}} \hfill \\ \end{gathered} \right\}{\text{greenschist facies}} \hfill \\ {\text{2}}{\text{. Older unit}}{\text{.}} \hfill \\ {\text{ }}\left. \begin{gathered} {\text{a) 0}}---{\text{1,280 m : albite}}---{\text{pumpellyite}}---{\text{prehnite}}---{\text{calcite}}---{\text{chlorite}}---{\text{ }} \hfill \\ {\text{ laumontite}} \hfill \\ {\text{b) 1,280}}---{\text{4,850 m: albite}}---{\text{adularia}}---{\text{calcite}}---{\text{prehnite}}---{\text{pumpellyite}}--- \hfill \\ {\text{pistacite}}---{\text{white mica}}---{\text{quartz}} \hfill \\ {\text{c) 4,850}}---{\text{8,110 m: albite}}---{\text{pistacite}}---{\text{quartz}}---{\text{chlorite}}---{\text{calcite}}--- \hfill \\ {\text{white mica}}---{\text{sphene}}---{\text{adularia prehnite}}---{\text{pumpellyite}} \hfill \\ \end{gathered} \right\}{\text{prehnite}}---{\text{pumpellyite facies}} \hfill \\ {\text{ d) 8,110}}---{\text{9,060 m: albite}}---{\text{pistacite}}---{\text{actinolite}}---{\text{sphene}}---{\text{calcite \} greenschist facies}} \hfill \\ \end{gathered} $$ The pattern of alteration in the older unit is comparable to that described for burial metamorphosed sequences in New Zealand and Australia. Reappearence of the greenschist facies at a higher level in the younger unit poses a problem for which several explanations are possible. The smaller scale pattern of alteration shows a persistent tendency —not without exception — for the “grade” of the alteration assemblage (as correlated with depth on the large scale) to increase: from the base of the flow (non-amygdaloidal part) upward (amygdaloidal part), and from the rim of each amygdule inward. Also recognizable on the scale of a single flow is a tendency for upward increase in: a) extent of alteration (the basal zone may be fresh andesite), and b) weight percent of Na₂O, K₂O (with complementary depletion in CaO), and of Fe₂O₃/FeO. Preliminary observations indicate that this alteration pattern persists for at least 400 km north of the area here described in rocks of similar lithology and age. It is unrelated to local granitic plutons.  相似文献   

THERMAL FATIGUE: A POSSIBLE SOURCE OF STRUCTURAL MODIFICATIONS IN METEORITES     

F. A. Levi 《Meteoritics & planetary science》1973,8(3):209-221

Periodic thermal excursions, even in a low-temperature range, may cause internal stresses and give origin to some of the observed plastic and clastic deformations in stony meteorites. An experimental test confirms our hypothesis: lattice distortions, cleavage and cracking were artificially induced in specimens of two H-chondrites (Mills and Bur-Gheluai) by low-temperature “thermal fatigue.” The observed effects appear to be increasing with increasing number of cycles.  相似文献   

A comparison of ARM and TRM in magnetite     

Shaul Levi  Ronald T. Merrill 《Earth and Planetary Science Letters》1976,32(2):171-184

Experiments comparing anhysteretic remanence (ARM) and thermoremanence (TRM) in samples containing natural and synthetic magnetite, whose mean particle sizes range from single domain to multidomain, show that ARM and TRM are very similar (but not identical) in their stabilities with respect to alternating field (AF) demagnetization, temperature cycles in zero field to below magnetite's isotropic temperature near 130°K, and stability with respect to spontaneous decay in zero field. Therefore, for magnetites, ARM can be used to model (with reasonable success) these stability properties of TRM. The field dependence of the acquisition of ARM and TRM shows that the low field susceptibility ratio, χ_ARM/χ_TRM, has a particle size dependence, increasing from 0.1 for certain submicron particles to 2.0 for large multidomain crystals. Even for samples whose remanence is predominantly carried by submicron particles χ_ARM/χ_TRM is highly variable, 0.11 ≤ χ_ARM/χ_TRM ≤ 0.50. Therefore, ARM paleointensity methods which do not take into account the large variability in and the particle size dependence of χ_ARM/χ_TRM are subject to order-of-magnitude uncertainties.  相似文献   

Major-element petrochemistry of some extrusive rocks from the volcanically active Mariana Islands     

E. E. Larson  R. L. Reynolds  R. Merrill  S. Levi  M. Ozima  Y. Aoki  H. Kinoshita  S. Zasshu  N. Kawai  T. Nakajima  K. Hirooka 《Bulletin of Volcanology》1974,38(1):361-377

Volcanic rocks from six of the currently or recently active volcances of the Mariana Island are show little variation in major element abundances. SiO₂ content averages 51.5 wt.%. The flows are high in Al₂O (mean 17.7 wt.%) and Fe oxides (mean 10.1 wt.% calculated as FeO only), and moderate in MgO content (mean 4.7 wt.%), Na₂O (mean 2.7 wt.%), and K₂O (mean 0.7 wt.%). Only the rocks from Farallon de Pajaros, the northernmost of the Mariana Islands, deviate slightly from the average of the analyses. Three analyses from this island are slightly higher in SiO₂ (about 54 wt.%) and Al₂O₃, and are lower in total Fe oxides and MgO. According to preferred classification, the lavas of the Mariana Islands can be termed mela-andesites, high-alumina basalts, or calc-alkaline (orogenic) basalts. The K₂O values (mean 0.7 wt.%) obtained from lavas of the Mariana Islands are significantly higher than the K₂O values (about 0.33 wt.%) from volcanics of the Izu chain to the north. Inasmuch as the substantial scatter in location of earthquake foci beneath both arcs prevents accurate delineation of the upper boundary of the Benioff zone, it presently cannot be determined whether this discrepancy in K₂O values reflects a difference in depth from the volcanic are to the dipping seismic zone or relates to other phenomena. The older volcanic islands within the Mariana-Bonin island chain apparently defined an island arc system during Eocene to Miocene time. This indicates that the present plane of convergence between the Pacific plate and the Philippine Sea plate has defined the convergence between these plates since Eocene time.  相似文献   

GEOGRAPHY IN MEXICO     

Jerry P. Schofer  Silvana Levi  Efrain Pena Villada  Andrzej M. Zeronski 《The Professional geographer》1990,42(3):380-382

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Estimating the density of intermediate size KBOs from considerations of volatile retention     

Amit Levi 《Icarus》2011,214(1):308-315

By using a hydrodynamic atmospheric escape mechanism (Levi, A., Podolak, M. [2009]. Icarus 202, 681-693) we show how the unusually high mass density of Quaoar could have been predicted (constrained), without any knowledge of a binary companion. We suggest an explanation of the recent spectroscopic observations of Orcus and Charon [Delsanti, A., Merlin, F., Guilbert, A., Bauer, J., Yang, B., Meech, K.J., 2010. Astron. Astrophys. 520, A40; Cook, J.C., Desch, S.J., Roush, T.L., Trujillo, C.A., Geballe, T.R., 2007. Astrophys. J. 663, 1406-1419]. We present a simple relation between the detection of certain volatile ices and the body mass density and diameter. As a test case we implement the relations on the KBO 2003 AZ₈₄ and give constraints on its mass density. We also present a method of relating the latitude-dependence of hydrodynamic gas escape to the internal structure of a rapidly rotating body and apply it to Haumea.  相似文献   

A scoping review on the multiplicity of scale in spatial analysis     

Oshan  Taylor M.  Wolf  Levi J.  Sachdeva  Mehak  Bardin  Sarah  Fotheringham  A. Stewart 《Journal of Geographical Systems》2022,24(3):293-324

Journal of Geographical Systems - Scale is a central concept in the geographical sciences and is an intrinsic property of many spatial systems. It also serves as an essential thread in the fabric...  相似文献