Characterization of experimental dynamos     

Nicholas L. Peffley  Alexei G. Goumilevski  A. B. Cawthrone  & Daniel P. Lathrop 《Geophysical Journal International》2000,142(1):52-58

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不同高度潜堤减淤效果水槽实验研究   总被引：1，自引：0，他引：1  

庞启秀  张瑞波  杨华 《海洋工程》2012,30(2):66-71

潜堤高程是淤泥质海岸潜堤设计的关键要素之一。为了确定潜堤高程,首先根据已建潜堤工程的经验分析得出潜堤减淤的主要机理,即主要是阻挡了浮泥或底部高含沙水体直接进入航道和缩短了含沙水体进入航道的时间,进而在长水槽中开展了一系列比对实验,主要研究不同堤顶高程时的水流紊动、堤前浮泥起动、浮泥层厚度变化、堤后航道泥沙落淤情况等,并以此作为比选堤顶高度的基本依据。实验结果表明当相对高度即潜堤高度与堤前水深之比为0.2～0.5时,便有较好的减淤效果。  相似文献   

模拟增温对生态系统碳循环影响研究进展   总被引：1，自引：1，他引：0  

彭飞  薛娴  尤全刚 《中国沙漠》2014,34(5):1285-1292

气候变暖影响着生态系统碳循环,碳循环的变化反馈于气候变化。这两者的相互作用影响着未来气候变化的方向和强度。野外增温试验有助于了解生态系统碳循环对气候变化的响应及其机制,因此成为近年来的研究热点。生态系统所处的地理位置及相应的气候背景影响着碳循环对增温的响应。增温后不同生态系统的碳释放和碳固定均可表现为增加、减小或者无显著变化,因而生态系统净碳收支对气候变化响应多样。增温后土壤氮矿化速率、物候、生态系统物种组成和结构的变化间接影响着生态系统净碳收支。多年冻土区储存了大量的土壤有机碳,冻土融化后冻土有机碳分解将释放大量的CO₂到大气中,正反馈于气候变暖,因而是目前野外增温试验对碳循环影响研究的焦点。  相似文献   

The stability of dipolar gyres on a beta-plane     

Steven Herbette  Antoine Hochet  Thierry Huck  Alain Colin de Verdière  Jérémy Collin  Frank Shillington 《地球物理与天体物理流体动力学》2014,108(5):479-502

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不耦合装药下爆炸应力波传播规律的试验研究   总被引：2，自引：0，他引：2  

王伟  李小春 《岩土力学》2010,31(6):1723-1728

通过室外爆破试验,利用预埋研制的PVDF压力传感器对耦合及水不耦合延长药包装药爆破时爆炸应力波的中远场压力进行测量,拟合实测结果,得到4种不耦合系数下爆炸应力波峰值随传播距离衰减的指数关系式。分析试验结果可知： ①在试验所涉及的范围内,不耦合装药时爆破应力波峰值衰减幅度小于耦合装药（即K =1）时爆破应力波峰值衰减幅度,验证了水介质作为炸药爆轰产物与岩体间的弹性缓冲层作用,减少了粉碎孔壁岩体造成的能量耗散,增加了能量传递,加大了爆炸的作用范围;②当不耦合系数K = 3.29时,应力波峰值衰减指数表现出大于K =1.79及大于K =2.57时应力波峰值衰减指数的趋势,表明过大的不耦合系数造成了不耦合介质--水过多的能量耗散（在高温高压下水并不完全是弹性的）,削弱了不耦合装药爆破的优势;③在不耦合装药爆破中,存在最佳的不耦合系数,此时爆炸应力波峰值衰减最慢,爆炸能得到充分利用,达到最优的爆破效果。研究结果对不耦合装药爆破的设计及工程应用有一定的指导意义。  相似文献   

Experimentation at the interface of fluvial geomorphology,stream ecology and hydraulic engineering and the development of an effective,interdisciplinary river science     

Stephen P. Rice  Jill Lancaster  Paul Kemp 《地球表面变化过程与地形》2010,35(1):64-77

One ‘2020 vision’ for fluvial geomorphology is that it sits alongside stream ecology and hydraulic engineering as a key element of an integrated, interdisciplinary river science. A challenge to this vision is that scientists from these three communities may approach problems from different perspectives with different questions and have different methodological outlooks. Refining interdisciplinary methodology is important in this context, but raises a number of issues for geomorphologists, ecologists and engineers alike. In particular, we believe that it is important that there is greater dialogue about the nature of mutually‐valued questions and the adoption of mutually‐acceptable methods. As a contribution to this dialogue we examine the benefits and challenges of using physical experimentation in flume laboratories to ask interdisciplinary questions. Working in this arena presents the same challenges that experimental geomorphologists and engineers are familiar with (scaling up results, technical difficulties, realism) and some new ones including recognizing the importance of biological processes, identifying hydraulically meaningful biological groups, accommodating the singular behaviour of individuals and species, understanding biological as well as physical stimuli, and the husbandry and welfare of live organisms. These issues are illustrated using two examples from flume experiments designed (1) to understand how the movement behaviours of aquatic insects through the near‐bed flow field of gravelly river beds may allow them to survive flood events, and (2) how an understanding of the way in which fish behaviours and swimming capability are affected by flow conditions around artificial structures can lead to the design of effective fish passages. In each case, an interdisciplinary approach has been of substantial mutual benefit and led to greater insights than discipline‐specific work would have produced. Looking forward to 2020, several key challenges for experimentalists working on the interface of fluvial geomorphology, stream ecology and hydraulic engineering are identified. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Formative conditions and sedimentary structures of sandy 3D antidunes: an application of the gravel step‐pool model to fine‐grained sand in an experimental flume     

Miwa Yokokawa  Kazuyoshi Hasegawa  Satoru Kanbayashi  Noritaka Endo 《地球表面变化过程与地形》2010,35(14):1720-1729

Antidunes and their sedimentary structures can be useful in reconstructing paleo‐hydraulic conditions, especially for large discharge events. However, three‐dimensional (3D) antidunes in sand‐sized sediments have not yet been studied extensively, as compared to either two‐dimensional (2D) antidunes or antidunes in gravel‐sized sediments. In this study, we estimated formative conditions of gravel step‐pool morphologies and applied them to the formation of 3D antidunes over a sand bed. Formative conditions are expressed in terms of a relationship between the water discharge per unit width and the bed slope. Flume experiments demonstrated that 3D mound‐like antidune configurations and their associated internal sedimentary structures could be preserved. Internal sedimentary structures were characterized by shallow lens‐like structures whose bases were erosional. Although gently‐dipping concave‐upward lamination was dominant, convex‐upward lamination was occasionally observed. The dimensions of lenticular lamina‐sets can be used to estimate antidune geometry. Thus if 3D antidunes can be interpreted in the stratigraphic record, it is possible to estimate the paleo‐hydraulic parameters such as water discharge and bed slope more precisely than previously. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Experimental study on transient and steady‐state dynamics of bedforms in supply limited configuration     

Julie Dreano  Alexandre Valance  Dimitri Lague  Cyril Cassar 《地球表面变化过程与地形》2010,35(14):1730-1743

The purpose of the present study is to investigate experimentally the development of bedforms in a configuration where the sediment supply is limited. The experimental setup is a rectangular closed duct combining an innovative system to control the rate of sediment supply Q_in , and a digitizing system to measure in real time the 3D bedform topography. We carried out different sets of experiments with two sediment sizes (100 µm and 500 µm) varying both the sediment supply and the water flow rate to obtain a total of 46 different configurations. After a transient phase, steady sub‐centimeter bedforms of various shapes have been observed: barchans dunes, straight transverse dune, linguoid transverse dunes and bedload sheets. Height, spacing, migration speed, and mean bed elevation of the equilibrium bedforms were measured. For a given flow rate, two regimes were identified with fine sediment: (i) a monotonic increasing regime where the equilibrium bedform height and velocity increase with the sediment supply rate Q_in and (ii) an invariant regime for which both parameters are almost independent of Q_in. For coarse sediment, only the first regime is observed. We interpret the saturation of height and velocity for fine sediment bedforms as the transition from a supply‐limited regime to a transport‐limited regime in which the bedload flux has reached its maximum value under the prevailing flow conditions. We also demonstrate that all experiments can be rescaled if the migration speed and height of the bedforms are, respectively, divided and multiplied by the cube of the shear velocity. This normalization is independent of grain size and of bedform morphology. These experimental results provide a new quantification of the factors controlling equilibrium height and migration speed of bedforms in supply‐limited conditions against which theoretical and numerical models can be tested.  相似文献   

Patterns of surface downwearing on shore platforms in eastern Canada     

Neil J. Porter  Alan S. Trenhaile  Kyle Prestanski  Jacob I. Kanyaya 《地球表面变化过程与地形》2010,35(15):1793-1810

Downwearing rates were measured on shore platforms at about 200 transverse micro‐erosion meter (TMEM) stations, over periods ranging from 2 to 6 years. There were seven study areas in eastern Canada. The platforms were surveyed and a Schmidt Rock Test Hammer was used to measure rock hardness. More than 1200 rock samples from three of the study areas were also subjected each day, over a 3 year period, to two tidal cycles of immersion and exposure, which simulated the central intertidal zone. A further 840 samples were subjected to longer periods of exposure and immersion, over a 1 year period, which represented different elevations within the upper and lower intertidal zone, respectively. These experiments suggested that tidally generated weathering and debris removal is an effective erosional mechanism, particularly at the elevation of the lowest high tides. In the field, mean rates of downwearing for each study area ranged from 0·24 mm yr^?1 to more than 1·5 mm yr^?1. Rates tended to increase with elevation in the field, with maxima in the upper intertidal zone. This trend in the field cannot be attributed entirely to the tidally induced weathering processes that were simulated in the laboratory, and must reflect, in part, the effect of waves, frost, ice, and other mechanisms. It is concluded that there are no strong spatial downwearing patterns on shore platforms, and that downwearing rates in the intertidal zone are the result of a number of erosional mechanisms with different elevation‐efficacy characteristics. Furthermore, even if only one or two mechanisms were dominant in an area, any resulting relationship between downwearing rates and elevation would be obscured or eliminated by the effect of variations in the chemical and physical characteristics of the rocks. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Effects of vegetation on channel morphodynamics: results and insights from laboratory experiments   总被引：1，自引：0，他引：1  

Michal Tal  Chris Paola 《地球表面变化过程与地形》2010,35(9):1014-1028

A series of laboratory experiments demonstrates that riparian vegetation can cause a braided channel to self‐organize to, and maintain, a dynamic, single‐thread channel. The initial condition for the experiments was steady‐state braiding in non‐cohesive sand under uniform discharge. From here, an experiment consisted of repeated cycles alternating a short duration high flow with a long duration low flow, and uniform dispersal of alfalfa seeds over the bed at the end of each high flow. Plants established on freshly deposited bars and areas of braidplain that were unoccupied during low flow. The presence of the plants had the effect of progressively focusing the high flow so that a single dominant channel developed. The single‐thread channel self‐adjusted to carry the high flow. Vegetation also slowed the rate of bank erosion. Matching of deposition along the point bar with erosion along the outer bend enabled the channel to develop sinuosity and migrate laterally while suppressing channel splitting and the creation of new channel width. The experimental channels spontaneously reproduced many of the mechanisms by which natural meandering channels migrate and maintain a single dominant channel, in particular bend growth and channel cutoff. In contrast with the braided system, where channel switching is a nearly continuous process, vegetation maintained a coherent channel until wholesale diversion of flow via cutoff and/or avulsion occurred, by which point the previous channel tended to be highly unfavorable for flow. Thus vegetation discouraged the coexistence of multiple channels. Varying discharge was key to allowing expression of feedbacks between the plants and the flow and promoting the transition from braiding to a single‐thread channel that was then dynamically maintained. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献