L形和U形三维钝体结构绕流的数值模拟研究

采用大涡模型对L形和U形三维钝体建筑物的绕流特性和风压分布特性进行数值研究。考虑平均和脉动速度入口边界,在雷诺数为1.5×10~5～7×10~5条件下,对2种钝体的9种分析工况进行瞬态动力分析,并将计算结果与已有研究进行对比。研究表明,钝体绕流对周围流场影响的强弱程度依次为尾流区、屋顶区、来流区,影响大小随着流场与钝体之间距离、钝体建筑高宽比、离地高度的增大而减小,且对来流区0.25H、屋顶上部0.4H、左右两侧0.5H、尾流区2.0H范围内流场的影响最大;钝体迎风面风压分布比较均匀,而侧面、背面和顶面受绕流涡旋的影响较大,平均风压分布较为复杂,并与脉动风压分布具有类似的变化趋势。研究结果对结构抗风设计与建筑风环境设计具有一定的参考价值。     

A Review of the Nonlinear Dynamics of Intraseasonal Oscillations

In recent years,significant progress has been made regarding theories of intraseasonal oscillations (ISOs) (also known as the Madden-Julian oscillation (MJO) in the tropics).This short review introduces the latest advances in ISO theories with an emphasis particularly on theoretical paradigms involving nonlinear dynamics in the following aspects:(1) the basic ideas and limitations of the previous and current theories and hypotheses regarding the MJO,(2) the new multi-scale theory of the MJO based on the intraseasonal planetary equatorial synoptic dynamics (IPESD) framework,and (3) nonlinear dynamics of ISOs in the extratropics based on the resonant triads of Rossby-Haurwitz waves.     

Geometric characteristics and evolution of a tidal channel network in experimental setting

This paper reports on a laboratory study that aims to reproduce a tidal channel network, in order to enhance the understanding of the morphodynamic evolution of the channel characteristics as the network expands and finally reaches equilibrium. A high‐resolution laser system scanned the bed topography at different time steps creating multiple digital elevation models of the channel network. Two hundred and seventy individual channel segments are analyzed and cross‐correlated in terms of their width, depth and length. The laboratory results show positive linear correlations between depth and width as well as between length and width of channel segments of the network configuration at final equilibrium. In a downstream direction, channels appear to widen more than they deepen, indirectly a sign that discharge has a stronger control on channel width than on depth. In contrast to fluvial drainage networks that commonly display fractal and scale‐invariant behavior, the geometric properties of the experimental tidal creek network shows scale dependence. Channel attributes exhibit consistent patterns of exponentially decreasing abundance, with increasing creek length, depth and width. The nature of the observed exponential distributions within creek attributes (width, depth, length) allows for statistical predictability of relative creek attribute dimensions downstream and through time. Copyright © 2010 John Wiley & Sons, Ltd.     

四川省青川县碾子村清岭沟泥石流特征及防灾对策

清岭沟位于四川省青川县碾子村五社,该区工程地质条件复杂。＂5.12＂地震后沟内出现大量崩塌落石和松散堆积物,为泥石流的爆发提供了充足的物源,2008年8月清岭沟地区发生连续强降雨,8月25日清岭沟爆发了泥石流。目前沟源及沟道两侧发育一处规模较大的潜在不稳定斜坡、三处规模较大的危岩体、一处形成于＂5.12＂地震期间的崩塌堆积物,一旦遭遇暴雨等不良地质作用这些潜在物源极易失稳,成为清岭沟泥石流的物源,使清岭沟再次发生泥石流灾害,威胁清岭沟下游村落及公路。通过野外对清岭沟进行地质调查、室内试验和动力学特征分析提出了UX—150型泥石流栅栏、拦砂坝、排导槽和桥涵改造的综合治理措施。     

浅析松原市地下水水位动态及环境问题

随着松原市社会经济的发展,地下水开采量逐年增大,由此引发的环境地质问题逐渐加剧,如地下水水位下降、地下水降落漏斗、水质污染、土壤沙漠化、饮水型地方病问题等等.利用水位动态观测资料,对松原市地下水动态分析,总结了近几年地下水开发利用现状,并针对人类活动所引起的地下水环境问题,提出自己的建议.     

Application of a BEM time stepping algorithm in understanding complex unsteady propulsion hydrodynamic phenomena

We solve the problem of unsteady potential flow around a system of arbitrarily moving rigid or flexible, lifting or non-lifting bodies, in an infinite fluid free of distributed vorticity. For the solution we use a time stepping algorithm and a potential based formulation of the corresponding free BVP. Nonlinear free shear layer dynamics are included in our modeling. This is a major innovation in treating complex unsteady propulsion problems since no simplifying assumptions (like that of a helicoidal wake) are used regarding the wake model. Bilinear quadrilateral elements are used to describe body and shear layer geometry at each time t. Three types of Kutta conditions can be alternatively applied for the determination of the shed vorticity from lifting bodies. The theoretical and numerical aspects of the method are presented followed by a number of applications, elucidating the qualitative and quantitative physical characteristics of a number of complex unsteady propulsion problems.     

Dynamic factor analysis considering elastic boom effects in heavy lifting operations

The dynamic factor is the ratio of the maximum dynamic load to the static load acting on the wire ropes between the boom of a floating crane and a cargo. In this paper, the dynamic factor is analyzed based on dynamic simulations of a floating crane and a cargo, considering an elastic boom. For the simulation, we designed a multibody system that consists of a floating crane barge, an elastic boom, and a cargo connected to the boom through wire ropes. The dynamic equations of motion of the system are based on flexible multibody system dynamics. Six-degree-of-freedom motions are considered for the floating crane and for the cargo, and three-dimensional deformations for the elastic boom. The hydrostatic force, the hydrodynamic force, the gravitational force, and the wire rope forces are considered as external forces. The dynamic factor is obtained by numerically solving the equation. The effects of the elastic boom on heavy cargo lifting are discussed by comparing the simulation results of an elastic boom and a rigid boom.     

Effect of UV-B radiation on the population dynamics of the rotifer Brachionus urceus

The effect of UV-B radiation enhancement at experimental doses of 0.00,0.24,0.48,0.72,0.96,and 1.20 kJ/m 2 on the population dynamics of the rotifer Brachionus urceus feeding on the alga Chlorella sp.was studied under controlled laboratory conditions using clonal culture and life-table techniques.The results show that UV-B radiation treatment significantly shortened the survival time of the rotifer (P <0.05): The longest survival time (336 h) occurred in the control (0.00 kJ/m 2 ) while the shortest (222 h) occurred when exposed to the highest UV-B radiation treatment (1.20 kJ/m 2 ).The fecundity of the rotifer B.urceus was enhanced by the lower UV-B radiation treatment (0.24 and 0.48 kJ/m 2 ) but inhibited by the higher treatments (0.96 and 1.20 kJ/m 2 ).Life expectancy also was obviously affected by UV-B radiation (P <0.05).The highest life expectancy occurred in the control (0.00 kJ/m 2 ),and it became shorter with increasing doses of UV-B radiation.The resutls in the present study indicate that the life expectancy of the rotifer B.urceus can be used as an indicator for UV-B radiation enhancement.     

吉林省双辽市氟中毒病区与非病区水文地球化学特征

双辽市氟中毒病区与非病区地下水水化学类型均处于重碳酸型水带内。病区水文地球化学作用处于元素迁移—富集的过渡阶段或元素富集阶段的初期,其水化学类型呈现由HCO3→HCO3.Cl→Cl.HCO3型水的分带性展布,地下水溶解固体浓度为0.5～2.0 mg/L;非病区则处于元素迁移阶段,其水化学类型则为单一的HCO3.Ca型水,地下水溶解固体浓度一般均低于0.5 mg/L。地方性氟中毒的分布与区域水文地球化学特征之间存在着一定的联系,此种关系虽然不可作为病因看待,但仍可当作一种环境标志加以考虑。     

Anthropogenic impacts on the water and salt budgets of St Lucia estuarine lake in South Africa

Lake St Lucia in South Africa is part of a UNESCO World Heritage site and a Ramsar wetland of international importance. Like many coastal wetlands worldwide, anthropogenic activities including catchment land-use changes, water diversions/abstractions, and manipulation of the mouth state have significantly affected its functioning over the past century. Questions concerning its sustainability have motivated a re-evaluation of management decisions made in the past and of options for the future. A model for the water and salt budgets has therefore been used to investigate “what if” scenarios in terms of past anthropogenic interventions. In particular, simulations allow us to evaluate the effects of diverting the Mfolozi river from St Lucia on the functioning of the system and on the occurrence of various water level/salinity states that drive the biological functioning of the ecosystem. In the past, when the St Lucia estuary and the Mfolozi river had a combined inlet, the mouth was predominantly open. The lake had relatively stable water levels but variable salinities that increased during dry conditions due to evaporative losses and saltwater inflows from the sea. If the mouth closed, the Mfolozi flow was diverted into the lake which reduced salinities and maintained or increased water levels. Simulations indicate that without a link to the Mfolozi the lake system would naturally have a mainly closed inlet with lower average salinities but more variable water levels. During dry conditions water levels would reduce and result in desiccation of large areas of the lake as has recently occurred. We conclude that the artificial separation of the St Lucia and Mfolozi inlets underpins the most significant impacts on the water & salt budget of the lake and that its reversal is key to the sustainability of the system.