Numerical simulation of a short flexible pipe subject to forced motion and vortex-induced vibration

A series of numerical simulations about a small scale(aspect ratio:63.2) flexible pipe undergoing forced harmonious oscillation and vortex-induced vibration(VIV) have been taken into account.The wake hydrodynamics and pipe deformation were accomplished by ANSYS MFX solution strategy designed for fluid-structure interaction(FSI) problem with well-performed LES model.The configuration of structured mesh,multi-domain design,different mesh stiffness admeasured by User Fortran ensured that the numerical task was competent to deal with large deformation related to this case.The introduction of instantaneous amplitude definition and modeless component decomposition method(Chen and Kim,2008) was helpful to reveal much more information from modal analysis.Most results from numerical simulation are generally consistent with those from model test(Choi and Hong,2000) via the comparison between them.As supplementary to model test,visualization of the vortex wake was also provided.It has been proved that the forced oscillation doesn't only excite a complicated dumbbell-like wake pattern around the outer thimble,but also results in inner flow inside the PVC pipe.The velocity of the inner flow increases with the frequency of forced oscillation.     

Anthropogenic and biogenic winter sources of Arctic CO2—a model study

Long‐range transport of anthropogenic and biogenic CO₂ to a remote site in the Arctic is studied. A limited area, off‐line, Eulerian atmospheric transport model is used, and the results are compared to the observed CO₂ concentration at the "Ny‐Alesund International Arctic Research and Monitoring Facility". Inventories of anthropogenic CO₂ emissions and estimates of biogenic CO₂ emissions are used to investigate the respective impact of these emissions on Arctic CO₂ variations during 4 winter months. A direct comparison of the modelled and observed concentrations reveals remarkably good timing in the modelled variations as compared to the observed variations for most of the time. The correlation of observed versus modelled CO₂ concentration is significant at the 95% confidence level. The biogenic and the anthropogenic CO₂ emissions are shown to have approximately equal influence on Arctic CO₂ variations during winter. Europe is found to be the dominant source of anthropogenic CO₂ at the monitoring station, while Siberia and Northern America have little influence on Arctic CO₂, during the months studied. These results contradict Engardt and Holmén whose results indicate that the lower‐Ob region in western Siberia has a large impact on Arctic CO₂.     

基于遗传算法局部方向梯度的古墓葬圆形土壤标志检测

中国新疆北部古墓葬目标在Google Earth上显示为两大类:一类是斑点型,另一类是圆环型,两类的边界都比较模糊。自动提取这些古墓葬目标比较困难,针对这一问题,提出了一种基于遗传算法局部方向梯度的圆形检测算法。该方法采用局部方向梯度,并且基于计算边缘方向梯度的主分量实现,因此该方法能适用各种边缘特征,遗传算法的加入能够提高在圆形不连贯、多圆相交等情况下圆形自动检测的鲁棒性。本文选取新疆北部作为试验区域,结果表明本文方法与传统的基于霍夫变换的圆形检测算法相比,能适应多特征的圆形边缘,而且不用设定自动检测中的阈值,更加智能化,自动化。     

Observational Diagnosis of Cloud Phase in the Winter Antarctic Atmosphere for Parameterizations in Climate Models

The cloud phase composition of cold clouds in the Antarcticatmosphere is explored using data from the Moderate Resolution ImagingSpectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization(CALIOP) instruments for the period 2000--2006. We used the averaged fractionof liquid-phase clouds out of the total cloud amount at the cloud tops sincethe value is comparable in the two measurements. MODIS data for the wintermonths (June, July, and August) reveal liquid cloud fraction out of the totalcloud amount significantly decreases with decreasing cloud-top temperaturebelow 0oC. In addition, the CALIOP vertical profiles show that below theice clouds, low-lying liquid clouds are distributed over ～20% of thearea. With increasing latitude, the liquid cloud fraction decreases as afunction of the local temperature. The MODIS-observed relation between thecloud-top liquid fraction and cloud-top temperature is then applied to evaluatethe cloud phase parameterization in climate models, in which condensed cloudwater is repartitioned between liquid water and ice on the basis of the gridpoint temperature. It is found that models assuming overly high cut-offs(》-40oC) for the separation of ice clouds from mixed-phase clouds maysignificantly underestimate the liquid cloud fraction in the winter Antarcticatmosphere. Correction of the bias in the liquid cloud fraction would serve toreduce the large uncertainty in cloud radiative effects.     

Effects of Street-Bottom and Building-Roof Heating on Flow in Three-Dimensional Street Canyons

Using a computational fluid dynamics(CFD)model,the effects of street-bottom and building-roof heating on flow in three-dimensional street canyons are investigated.The building and street-canyon aspect ratios are one.In the presence of street-bottom heating,as the street-bottom heating intensity increases,the mean kinetic energy increases in the spanwise street canyon formed by the upwind and downwind buildings but decreases in the lower region of the streamwise street canyon.The increase in momentum due to buoyancy force intensifies mechanically induced flow in the spanwise street canyon.The vorticity in the spanwise street canyon strengthens.The temperature increase is not large because relatively cold above-roof-level air comes into the spanwise street canyon.In the presence of both street-bottom and building-roof heating,the mean kinetic energy rather decreases in the spanwise street canyon.This is caused by the decrease in horizontal flow speed at the roof level,which results in the weakening of the mean flow circulation in the spanwise street canyon.It is found that the vorticity in the spanwise street canyon weakens.The temperature increase is relatively large compared with that in the street-bottom heating case,because relatively warm above-roof-level air comes into the spanwise street canyon.     

Petrogenesis of anhydrous clinopyroxenite xenoliths and clinopyroxene megacrysts in alkali basalts from the Ganseong area of South Korea

Late Cenozoic alkali basalts in the Ganseong area of South Korea contain abundant ultramafic xenoliths and clinopyroxene megacrysts. Anhydrous clinopyroxene‐rich wehrlite–clinopyroxenites make up the majority of the xenolith population and range from wehrlite through olivine clinopyroxenite to clinopyroxenite. This study investigates the petrogenesis of wehrlite–clinopyroxenite xenoliths and clinopyroxene megacrysts on the basis of petrography and mineral and whole‐rock chemistry. Observations such as an absence of carbonate or apatite, high Ti/Eu ratio, and clinopyroxene‐dominated mineralogy lead us to rule out peridotite–melt reactions as the origin of the Ganseong wehrlites– olivine clinopyroxenites. The whole‐rock compositions (e.g. high abundance of CaO at a given MgO content and low abundance of incompatible elements, such as U, K, P, and Ti compared with mafic melts) indicate that the pyroxenites do not represent crystallized magma itself, but are rather cumulates with a small amount of residual liquid. Anhydrous and orthopyroxene‐free mineral assemblages, crystallization sequence of olivine→clinopyroxene→plagioclase, and mineral chemistries (e.g. low Cr# and high TiO₂ abundances in spinels and high TiO₂ and Na₂O abundances in clinopyroxenes at a given Mg#) suggest that relatively anhydrous intraplate alkaline basalt is the most likely candidate for the parent magma. Texture and compositions of the clinopyroxene megacrysts preclude a cognate origin via high‐pressure crystallization of the host magma. The clinopyroxene megacrysts occupy the Fe‐rich end of the compositional trends defined by wehrlite–pyroxenite clinopyroxenes. Progressive decreases in Mg# and an absence of significant compositional gaps between pyroxenite xenoliths and clinopyroxene megacrysts indicate fractionation and differentiation of a similar parental magma. We suggest that the clinopyroxene megacrysts represent fragments of pegmatitic clinopyroxenites crystallized from more advanced fractionation stages of the evolution of a series of magmatic liquids formed Ganseong wehrlite–clinopyroxenites.     

An englacial image and water pathways of the Fourcade glacier on King George Island, Antarctic Peninsula, inferred from ground-penetrating radar

The distribution of small fractures and water content of the Fourcade glacier on King George Island, Antarctica, was investigated in November 2006 and December 2007 by two ground-based (470-and 490-m-long profiles) and one helicopter-borne (470-m-long profile) ground-penetrating radar (GPR) surveys using 50-, 100-, and 500-MHz antennas. Radar images in the pre-migrated GPR sections are characterized by a smooth ice surface and irregular bed topography, numerous diffraction hyperbolas in the ice and at the g...