Large Eddy Simulation on Interaction Between in-Line and Cross-Flow Oscillation of A Circular Cylinder

This paper discusses numerical results from three-dimensional large eddy simulations of an oscillating cylinder under prescribed movements in uniform flow. Six cases,namely pure in-line,pure cross-flow and two groups of 'Figure of Eight' oscillation patterns are under investigation at Reynolds number Re=24000. The 'Figure of Eight' pattern in each group is with identical shape but opposite orbital directions. The numerical results on hydrodynamic forces,higher order force components,and vortex shedding mode...     

http://www.sciencedirect.com/science/article/pii/S167498711600030X

Proterozoic(pre-Ediacaran) glaciations occurred under strongly seasonal climates near sea level in low palaeolatitudes.Metre-scale primary sand wedges in Cryogenian periglacial deposits are identical to those actively forming,through the infilling of seasonal(winter) thermal contraction-cracks in permafrost by windblown sand,in present-day polar regions with a mean monthly air temperature range of40 ℃ and mean annual air temperatures of-20 ℃ or lower.Varve-like rhythmites with dropstones in Proterozoic glacial successions are consistent with an active seasonal freeze-thaw cycle.The seasonal(annual) oscillation of sea level recorded by tidal rhythmites in Cryogenian glacial successions indicates a significant seasonal cycle and extensive open seas.Palaeomagnetic data determined directly for Proterozoic glacial deposits and closely associated rocks indicate low palaeolatitudes:Cryogenian deposits in South Australia accumulated at 10°,most other Cryogenian deposits at 20° and Palaeoproterozoic deposits at 15° palaeolatitude.Palaeomagnetic data imply that the Proterozoic geomagnetic field approximated a geocentric axial dipole,hence palaeolatitudes represent geographic latitudes.The Cryogenian glacial environment included glacier-free,continental permafrost regions with ground frozen on a kyr time-scale,aeolian sand-sheets,extensive and long-lived open seas,and an active hydrological cycle.This palaeoenvironment conflicts with the 'snowball Earth' and 'slushball Earth' hypotheses,which cannot accommodate large seasonal changes of temperature near the equator.Consequently,their proponents have attempted to refute the evidence for strong seasonality by introducing Popperian'auxiliary assumptions'.However,non-actualistic arguments that the Cryogenian sand wedges indicate diurnal or weakly seasonal temperature changes are based on misunderstandings of periglacial processes.Modelling of a strongly seasonal climate for a frozen-over Earth is invalidated by the evidence for persistent open seas and glacier-free continental regions during Cryogenian glaciations,and gives a mean monthly air temperature range of only 10 ℃ for 10° latitude.By contrast,a strongly seasonal climate in low palaeolatitudes,based on the actualistic interpretation of cryogenic sand wedges and other structures,is consistent with a high obliquity of the ecliptic(54°) during Proterozoic low-latitude glaciations,whereby the equator would be cooler than the poles,on average,and global seasonality would be greatly amplified.     

The Mesoproterozoic to early Neoproterozoic passive margin Lajeado Group and Apiaí Gabbro,Southeastern Brazil

The Lajeado Group in the Ribeira Belt,southeastern Brazil,corresponds to an open-sea carbonate platform,comprised of seven overlapping siliciclastic and carbonatic formations,intruded in its upper portion by the Apiai Gabbro.These rocks have a Neoproterozoic tectonometamorphic overprint related to arc magmatism and the Brasiliano collisional orogeny.Geochronological constraints are given by new UPb SHRIMP and LA-ICP-MS data for Lajeado Group detrital zircons and for magmatic zircons from the Apiai Gabbro.The youngest detrital zircons in the Lajeado Group are 1400-1200 Ma,and constrain its maximum age of deposition to be 1200 Ma,whereas the 877 ± 8 Ma age for magmatic zircons in the Apiai Gabbro give the minimum age.Detritus source areas are mainly Paleoproterozoic(2200-1800 Ma)with some Archean and Mesoproterozoic contribution(1500-1200 Ma),with distal or tectonic stable cratonic character.The Lajeado Group should be a Stenian-Tonian carbonate platform passive margin of a continent at this time,namely the Columbia/Nuna or the Rodinia.The Apiai Gabbro displays similar age to other intrusive basic rocks in the Lajeado and Itaiacoca groups and represents tholeiitic MORB-like magmatism that we relate to the initial break-up of a Mesoproterozoic continent and the formation of the Brasiliano oceans.     

http://www.sciencedirect.com/science/article/pii/S1674987115001516

The Semail ophiolite of Oman and the United Arab Emirates(UAE) provides the best preserved large slice of oceanic lithosphere exposed on the continental crust,and offers unique opportunities to study processes of ocean crust formation,subduction initiation and obduction.Metamorphic rocks exposed in the eastern UAE have traditionally been interpreted as a metamorphic sole to the Semail ophiolite.However,there has been some debate over the possibility that the exposures contain components of older Arabian continental crust.To help answer this question,presented here are new zircon and rutile U-Pb geochronological data from various units of the metamorphic rocks.Zircon was absent in most samples.Those that yielded zircon and rutile provide dominant single age populations that are 95-93 Ma,partially overlapping with the known age of oceanic crust formation(96.5-94.5 Ma),and partially overlapping with cooling ages of the metamorphic rocks(95-90 Ma).The data are interpreted as dating high-grade metamorphism during subduction burial of the sediments into hot mantle lithosphere,and rapid cooling during their subsequent exhumation.A few discordant zircon ages,interpreted as late Neoproterozoic and younger,represent minor detrital input from the continent.No evidence is found in favour of the existence of older Arabian continental crust within the metamorphic rocks of the UAE.