湍流热对流系统中粗糙壁面对流动结构的影响

自然界中存在的热对流现象大部分都具有粗糙边界, 研究粗糙壁面 Rayleigh-Bénard(RB)湍流热对流对理解湍流传热和流动结构具有重要的理论价值和实际意义. 采用数值模拟的方法研究二维粗糙壁面对 RB 湍流热对流流动结构的影响, 主要参数 Rayleigh 数(Ra)和 Prandtl 数(Pr)分别为 10$^{7}\le $Ra$\le $10$^{9}$和 $Pr = 0.7$. 计算中采用的粗糙元形状为等腰直角三角形. 结果表明:粗糙元对大尺度环流的抑制作用与粗糙元对羽流的生成和二次涡的促进作用相互竞争, 导致 Reynolds 数(Re)变化复杂, Ra 数与 Re 数的标度律关系异常.     

地幔柱的发生机制研究——以Ferrar为例

利用三维数值模拟方法,根据地幔对流控制方程,以180 Ma喷发的Ferrar大火成岩省(LIP)为例,在模型中引入Pangea超大陆、大型横波低速带(LLSVPs)和Pangea超大陆边缘的俯冲带,模拟地幔对流过程,研究其对应地幔热柱从地球内部热边界层(例如核幔边界)的生成过程,并讨论导致该地幔柱产生的相关因素.结果表...     

固定汽泡周围的温度场分布

为估计M arangon i对流和自然对流对汽泡周围流场的影响,对加热面朝上和朝下的不同大小和过冷度的汽泡周围温度场进行了测量。通过比较测量所得温度场和带N av ier-S tokes方程的数值模拟结果可知,在完全没有浮升力时,M arangon i流会使得流场呈现一个向下的类似于射流的形状,但有了浮升力,向下的流动会立刻转向上,在加热表面附近形成涡流。即使加热面朝下,这种浮升力引起的自然对流依然影响整个流场,以至于这个系统不能很好地表现在微重力条件下的汽泡周围的流场。     

Formation of current coils in geodynamo simulations

Computer simulations have been playing an important role in the development of our understanding of the geodynamo, but direct numerical simulation of the geodynamo with a realistic parameter regime is still beyond the power of today's supercomputers. Difficulties in simulating the geodynamo arise from the extreme conditions of the core, which are characterized by very large or very small values of the non-dimensional parameters of the system. Among them, the Ekman number, E, has been adopted as a barometer of the distance of simulations from real core conditions, in which E is of the order of 10(-15). Following the initial computer simulations of the geodynamo, the Ekman number achieved has been steadily decreasing, with recent geodynamo simulations performed with E of the order of 10(-6). Here we present a geodynamo simulation with an Ekman number of the order of 10(-7)-the highest-resolution simulation yet achieved, making use of 4,096 processors of the Earth Simulator. We have found that both the convection flow and magnetic field structures are qualitatively different from those found in larger-Ekman-number dynamos. The convection takes the form of sheet plumes or radial sheet jets, rather than the columnar cell structures that are usually found. We have found that this sheet plume convection is an effective dynamo and the generated current is organized as a set of coils in the shape of helical springs or at times as a torus.     

煤粉加压气化炉膜式螺旋管和蛇形管对流传热特性研究

对煤粉加压气化炉对流段的不同换热结构进行了换热特性的实验研究,其中换热结构包括膜式螺旋管环形通道换热器和膜式蛇形管平行通道换热器,实验气体为单质气体N2、He及其混合气,实验压力为0.5～3.5MPa.为此,针对不同冲刷形式、不同气体和压力提出了换热器换热系数及其扩展的计算方法,同时给出了典型冲刷形式的对流换热的关联式和适用条件.实验研究表明:冲刷形式对换热系数有很大影响,单通道和多通道换热系数与换热面积之间呈加权平均的关系;在相同换热条件下,膜式螺旋管环形通道换热器的换热系数高于膜式蛇形管平行通道换热器.     

Mantle plumes： Why the current skepticism？

The present reappraisal of the mantle plume hypothesis is perhaps the most exciting current debate in Earth science. Nevertheless, the fundamental reasons for why it has arisen are often not well understood. They are that 1） many observations do not agree with the predictions of the original model, 2） it is possible that convection of the sort required to generate thermal plumes in the Earth＇s mantle does not occur, 3） so many variants of the original model have been invoked to accommodate conflicting data that the plume hypthesis is in practice no longer testable, and 4） alternative models are viable, though these have been largely neglected by researchers. Regardless of the final outcome, the present vigorous debate is to be welcomed since it is likely to stimulate new discoveries in a way that unquestioning acceptance of the conventional plume model will not.     

基于PHOENICS螺旋翅片管的数值研究

运用PHOENICS对自然对流条件下螺旋翅片管的速度场、温度场及压力场进行了数值计算，并绘出了计算结果图，得出了与实验结果相符的结论，为螺旋翅片管的研究提供了一种经济、省力的快捷方法．     

水电站垫层蜗壳结构应力及配筋分析

以某大型水电站为实例,采用接触非线性间隙元法模拟了蜗壳、混凝土及垫层之间的接触摩擦效应,并以分段线性模型的方式近似模拟了垫层的非线性本构关系,对不同垫层厚度下的水电站垫层蜗壳结构进行了计算分析,给出了垫层厚度与蜗壳应力、混凝土应力、承载比例及截面配筋量的关系,供工程设计参考．     

底吹氩气和旋转磁场复合作用对两相流动行为影响

提出利用旋转磁场作用于底吹氩气钢包冶金反应器的方法,建立了底吹氩气和旋转磁场作用下钢包冶金反应器内两相流动行为的数学模型,分析了改变吹气位置和磁场强度等参数对气泡运动行为的影响.结果表明:无旋流时,不断上升的气泡形成"倒锥形"的气柱.在旋转磁场和底吹气共同作用时,上升的气泡形成了"螺旋状气柱",这和试验结果相吻合.当吹气位置离中心的距离和磁场强度增大时,气泡在反应器内运动的路程分别呈线性和指数形式增加.     

三峡工程建筑物设计关键技术问题研究与实践

针对三峡水利枢纽拦河大坝泄洪流量大、孔口多、泄洪消能结构复杂,岸坡厂房坝段基岩长大缓倾角结构面因坝后厂房深挖临空危及坝基稳定,坝体混凝土耐久性要求高且温控防裂困难;茅坪溪防护土石坝沥青混凝土心墙设计施工尚缺乏实践经验;电站运行水头高、变幅大,引水压力管道及进水口选型和蜗壳埋设方式技术复杂,地下电站采用变顶高尾水洞替代常规的尾水调压室;双线五级船闸运行水头高、输水水力条件复杂,且在山体深挖岩槽中修建,全衬砌船闸结构、高水头输水系统和大型人字闸门及启闭机设计难度大等关键技术问题,文章重点介绍了各建筑物设计研究解决问题的途径、采用的优选方案及技术措施和通过实践检验的创新成果。     

烟道气的冷凝传热与脱硫的实验研究

实验研究了锅炉烟气在轴流式塑料螺旋板空气预热器中的传热特性．与圆管内和圆形套管内层流单相对流换热进行了比较．具有烟气冷凝的对流换热研究反映冷凝换热与单相对流换热具有同等重要性,与纯蒸气冷凝换热有明显不同,也不同于湿空气去湿过程．采用修正后的古典膜模型对烟气冷凝的计算与实验结果有较好的一致性．伴随烟气冷凝,烟道气中所含SO2和NO2被冷凝液吸收,降低了有害气体浓度．     

超临界混合流体自然对流的三维数值模拟

针对三维矩形腔体中超临界氮氩混合流体的Rayleigh-Bénard对流进行了数值模拟,研究了活塞效应、Soret效应和Dufour效应在自然对流发生发展过程中所产生的影响.结果显示:3种效应作用下自然对流可分为稳定边界层、对流产生和发展、稳定对流3个阶段.活塞效应在稳定热边界层时期发挥主导作用并促进对流发生,形成双热边界层结构.受温度梯度驱动Soret效应引起组分定向迁移,产生Dufour效应促进能量输运.与拟纯流体对比后发现,自然对流发展阶段混合流体中Soret和Dufour效应具有促进流动增强换热的效果.     

Rayleigh-Bénard湍流热对流中主动和被动标量场Cliff结构统计特性的实验研究

实验研究了Rayleigh-Bénard湍流热对流中主动和被动标量场Cliff结构的统计特性,实验参数Rayleigh数为Ra=1.2×10¹⁰,Prandtl数为Pr=5.3.在充满对流介质水的长方体对流槽边壁附近实验测量了局域浓度场（被动标量场）和局域温度场（主动标量场）的时间序列,从测得的时间序列中提取出Cliff结构,提取参数为β,并分析了Cliff结构的宽度、振幅和尺寸的数量分布图.研究发现,浓度和温度场Cliff结构宽度的数量分布图形状并不随β而改变,而Cliff结构的最可几振幅却随着β的增大而增大.此外,Cliff结构的尺寸满足对数正态分布,这表明湍流热对流中被动标量场的扩散和混合是由羽流等浮力相干结构所驱动的.     

A salt-water reservoir as the source of a compositionally stratified plume on Enceladus

The discovery of a plume of water vapour and ice particles emerging from warm fractures ('tiger stripes') in Saturn's small, icy moon Enceladus raised the question of whether the plume emerges from a subsurface liquid source or from the decomposition of ice. Previous compositional analyses of particles injected by the plume into Saturn's diffuse E ring have already indicated the presence of liquid water, but the mechanisms driving the plume emission are still debated. Here we report an analysis of the composition of freshly ejected particles close to the sources. Salt-rich ice particles are found to dominate the total mass flux of ejected solids (more than 99 per cent) but they are depleted in the population escaping into Saturn's E ring. Ice grains containing organic compounds are found to be more abundant in dense parts of the plume. Whereas previous Cassini observations were compatible with a variety of plume formation mechanisms, these data eliminate or severely constrain non-liquid models and strongly imply that a salt-water reservoir with a large evaporating surface provides nearly all of the matter in the plume.     

大空间中庭及周边房间烟气运动和消防设计

采用数值模拟的方法,对大空间中庭结构内火灾及周边房间火灾的烟气运动情况进行了分析。着重分析了周边房间发生火灾后烟气及热羽流对上层房间的影响和烟气在中庭顶部的积聚和沉降情况。分析结果表明,在大空间内合理设置排烟系统对保证其消防安全至关重要;在大空间中庭内部排烟充分的情况下,可将大空间中庭作为与之相通的建筑结构的蓄烟空间和排烟途径,在其消防设计中可对中庭设置普通开口而不设置机械排烟系统。分析结果为大空间中庭及其周边房间的消防安全设计与评估提供参考。     

Design of Magnetic RF Inductor in CMOS

Traditional planar inductors in Radio Frequency (RF) Integrated Circuits (ICs) are plagued by large areas, low quality, and low frequencies. This paper describes a magnetic-based CMOS-compatible RF in-ductor. Magnetic-core inductors with various ferrite-filled structures, spiral structures, and magnetic material permeabilities were simulated to show that this inductor greatly improves the inductance by up to 97% and quality factor by 18.6% over a multi-GHz frequency range. The results indicate that the inductor is a very promising and viable solution to realize miniature, high quality, and high frequency on-chip inductors for high-end RF ICs.     

Structural Research on Embedment of a Bare Deflated Spiral Case

Complete bearing spiral case has not been applied to large power stations in China so far. The proposal of applying complete bearing spiral case necessitates an analysis of the reliability of the spiral case structure and the security of units under various working conditions. In combination with practice of a project, this paper presents a three-dimensional nonlinear finite element static analysis of the concrete using a concrete smeared crack model by means of the well-known finite element method （FEM） software ABAQUS. The stress distribution of the spiral case and reinforcing bars, the range of damages in surrounding concrete, and the displacement of structure are quantified. The computational results indicate that the embedment method ensures the structure＇s safety in strength. At the same time, the result shows that this embedment is a kind of preponderant method for embedment in aspects of economy and technique of construction, and the application of this embedment method to the hydropower station is feasible provided that some proper engineering measures are taken to constrain the width of the concrete in accord with the code＇s requirements. The paper proves the security and reliability of the structural design of spiral case in hydropower station accordingly.     

Multiple volcanic episodes of flood basalts caused by thermochemical mantle plumes

The hypothesis that a single mushroom-like mantle plume head can generate a large igneous province within a few million years has been widely accepted. The Siberian Traps at the Permian-Triassic boundary and the Deccan Traps at the Cretaceous-Tertiary boundary were probably erupted within one million years. These large eruptions have been linked to mass extinctions. But recent geochronological data reveal more than one pulse of major eruptions with diverse magma flux within several flood basalts extending over tens of million years. This observation indicates that the processes leading to large igneous provinces are more complicated than the purely thermal, single-stage plume model suggests. Here we present numerical experiments to demonstrate that the entrainment of a dense eclogite-derived material at the base of the mantle by thermal plumes can develop secondary instabilities due to the interaction between thermal and compositional buoyancy forces. The characteristic timescales of the development of the secondary instabilities and the variation of the plume strength are compatible with the observations. Such a process may contribute to multiple episodes of large igneous provinces.     

大功率LED封装散热关键问题的仿真

基于ANSYS有限元软件对目前3种典型LED封装结构的温度场进行模拟分析.通过比较得出,优化封装结构可以有效地提高LED散热性能,途径最佳的是减少热沉数量,次之为降低热沉热阻;经与热对流方式对LED散热效果比较,发现优化封装结构降低结温的效果并不明显.而在可实现的光转换效率下,经过必要的选材优化后,强制对流是最有效解决散热的方法.     

High velocity dispersion in a rare grand-design spiral galaxy at redshift z = 2.18

Although grand-design spiral galaxies are relatively common in the local Universe, only one has been spectroscopically confirmed to lie at redshift z?>?2 (HDFX 28; z = 2.011); and it may prove to be a major merger that simply resembles a spiral in projection. The rarity of spirals has been explained as a result of disks being dynamically 'hot' at z?>?2 (refs 2-5), which may instead favour the formation of commonly observed clumpy structures. Alternatively, current instrumentation may simply not be sensitive enough to detect spiral structures comparable to those in the modern Universe. At z?相似文献