PREDICTION OF THE GRAIN SIZE OF SUSPENDED SEDIMENT： IMPLICATIONS FOR CALCULATING SUSPENDED SEDIMENT CONCENTRATIONS USING SINGLE FREQUENCY ACOUSTIC BACKSCATTER     

R. A. KUHNLE D. G. WREN J. P. CHAMBERS 《国际泥沙研究》2007,22(1):1-15

Collection of samples of suspended sediment transported by streams and rivers is difficult and expensive. Emerging technologies, such as acoustic backscatter, have promise to decrease costs and allow more thorough sampling of transported sediment in streams and rivers. Acoustic backscatter information may be used to calculate the concentration of suspended sand-sized sediment given the vertical distribution of sediment size. Therefore, procedures to accurately compute suspended sediment size distributions from easily obtained river data are badly needed. In this study, techniques to predict the size of suspended sand are examined and their application to measuring concentrations using acoustic backscatter data are explored. Three methods to predict the size of sediment in suspension using bed sediment, flow criteria, and a modified form of the Rouse equation yielded mean suspended sediment sizes that differed from means of measured data by 7 to 50 percent. When one sample near the bed was used as a reference, mean error was reduced to about 5 percent. These errors in size determination translate into errors of 7 to 156 percent in the prediction of sediment concentration using backscatter data from 1 MHz single frequency acoustics.  相似文献   

Field measurements of three-dimensional hydraulics in a step-pool channel   总被引：4，自引：0，他引：4  

Andrew C. Wilcox  Ellen E. Wohl 《Geomorphology》2007,83(3-4):215-231

We investigated the effects of morphologic position and discharge on flow structure in a steep (0.10 m/m) mountain channel by collecting three-dimensional measurements of time-averaged and turbulent velocity components with a SonTek FlowTracker Handheld ADV (acoustic Doppler velocimeter) on a 30-m reach of a step-pool channel in the Colorado Rockies. Velocity profiles were measured at morphologic positions characteristic of steep channels (above steps, step lips, base of steps, pools, cascades, runs), and at five different discharges. A marked three-dimensionality of flow structure was documented in East St. Louis Creek. Velocities in the streamwise component were the largest contributors to overall velocity vector magnitudes; cross-stream and vertical components contributed averages of 20% and 15%, respectively, to overall vector magnitudes. Turbulence intensities were especially multi-dimensional, however, with large contributions to turbulent kinetic energy from the vertical component of velocity. Analysis of variance indicated that discharge and morphologic position significantly affected mean streamwise velocities, with substantially higher velocities upstream from steps than in pools. Discharge and morphology effects on cross-stream and vertical velocity components, however, were not significant. Discharge and morphologic position also significantly affected turbulence intensities for all flow components, with the greatest turbulence intensities occurring in pools and at high discharges. These results illustrate the strong discharge-dependence of hydraulics in step-pool channels, where relative submergence of bedforms changes rapidly with discharge, and the substantial spatial variation in hydraulics created by step-pool sequences.  相似文献   

Analysis of Low-Frequency Turbulence Above Tall Vegetation Using a Doppler Sodar     

Christoph Thomas  Jens-Christopher Mayer  Franz X. Meixner  Thomas Foken 《Boundary-Layer Meteorology》2006,119(3):563-587

This study applies acoustic sounding to observe coherent structures in the roughness sublayer (RSL) above tall vegetated surfaces. Data were collected on 22 days during two separate field experiments in summer 2003. A quality control scheme was developed to ensure high data quality of the collected time series. The data analysis was done using both discrete and continuous wavelet transform. The flow in the RSL was found to be a superposition of dynamic Kelvin–Helmholtz instabilities and convective mixing. The characteristic time scales for coherent structures resulting from the dynamic instabilities were observed to be approximately 20–30 s while thermal eddies have much larger time scales of 190–210 s. The degree of vertical coherency in the RSL increases with the flow evolving from neutral to near-convective conditions. This increase in the degree of organisation is attributed to the evolution of attached thermal eddies. The coherent structures resulting from instabilities were found to be present throughout the RSL but do not contribute to the increased vertical coherency. An alternative conceptual approach for the definition of the RSL is proposed, which yields its maximum vertical extent to five times the canopy height.  相似文献   

含弱层岩石破裂前兆规律的数值模拟分析   总被引：3，自引：0，他引：3  

梁正召  唐春安  杨天鸿  焦明若 《地震》2003,23(3):65-70

利用数值模拟软件RFPA^2D模拟了含断层带岩体的破裂过程及其应力、位移和声发射前兆的复杂性和规律性。模拟结果表明。应力和位移在同一点的变化情况不同。不同点在同一时刻的位移和应力也不同。应力、位移和声发射在时间和空间上的分布呈现出一系列复杂图像。但是这些复杂变化并不是随机的。都遵循相同的物理过程和一定的演化规律。应力和位移的变化量比应力和位移本身更重要。同时这些变化的大小和断层结构紧密相关。而单一物理量的异常并不一定预示着必然的破裂。  相似文献   

Reverse modelling for seismic event characterization   总被引：5，自引：0，他引：5  

Dirk Gajewski  Ekkehart Tessmer 《Geophysical Journal International》2005,163(1):276-284

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Interactions between serpentinite devolatilization, metasomatism and strike-slip strain localization during deep-crustal shearing in the Eastern Alps   总被引：4，自引：0，他引：4  

J. D. Barnes  J. Selverstone  Z. D. Sharp 《Journal of Metamorphic Geology》2004,22(4):283-300

The Greiner shear zone in the Tauern Window, Eastern Alps, changes from a zone of distributed (dominantly sinistral) shear in supracrustal rocks to a series of narrow, gully forming dextral splays where it enters basement gneisses. Within these splays, granodiorite is transformed into quartz‐poor biotite and/or chlorite schists, reflecting hydration, removal of Si, Ca and Na, and concentration of Fe, Mg and Al. Stable isotope analyses show a prominent increase in δD and a decrease in δ¹⁸O from granodiorite into the shear zones. These changes indicate significant channelized flow of an externally derived, low‐δ¹⁸O, high‐δD fluid through the shear zones. The shear zone schists are chemically similar to blackwall zones developed around serpentinite bodies elsewhere in the Greiner zone and the stable isotope data support alteration via serpentinite‐derived fluid. Monazite in schist from one shear zone yields spot dates of 29–20 Ma, indicating that the fluid influx and switch from sinistral to dextral shear occurred at or shortly after the thermal peak of the Alpine orogeny (c. 30 Ma). We suggest that Alpine metamorphism of serpentinites released large amounts of high‐δD, low‐δ¹⁸O, Si‐undersaturated, Fe + Mg‐saturated fluids that became channelized along prior zones of weakness in the granodiorite. Infiltration of this fluid facilitated growth of chlorite and biotite, which in turn localized later dextral strain in the narrow splays via cleavage‐parallel slip. This dextral strain event can be linked to other structures that accommodated tectonic escape of major crustal blocks during dextral transpression in the Eastern Alps. This study shows that serpentinite devolatilization can play an important role in modifying both the chemistry and rheology of surrounding rocks during orogenesis.  相似文献   

Seismic strain rates and distributed continental deformation in the northern Andes and three-dimensional seismotectonics of northwestern South America   总被引：1，自引：0，他引：1  

Freddy Corredor 《Tectonophysics》2003,372(3-4):147-166

Remote sensing and field studies of several extensional basins along the northern margin of the Gulf of Aden in Yemen show that Oligocene–Miocene syn-rift extension trends N20°E on average, in agreement with the E–W to N120°E strike of main rift-related normal faults, but oblique to the main trend of the Gulf (N70°E). These faults show a systematic reactivation under a 160°E extensional stress that we interpret also as syn-rift. The occurrence of these two successive phases of extension over more than 1000 km along the continental margin suggests a common origin linked to the rifting process. After discussing other possible mechanisms such as a change in plate motion, far-field effects of Arabia–Eurasia collision, and stress rotations in transfer zones, we present a working hypothesis that relates the 160°E extension to the westward propagation since about 20 Ma of the N70°E-trending, obliquely spreading, Gulf of Aden oceanic rift. The late 160°E extension, perpendicular to the direction of rift propagation, could result from crack-induced extension associated with the strain localization that characterises the rift-to-drift transition.  相似文献   

热红外震兆成因的模拟实验研究   总被引：43，自引：3，他引：40  

耿乃光  于萍 《地震》1998,18(1):83-88

对完整岩石破裂前和既存断层粘滑失稳前的红外辐射温度场进行了遥感观测研究,发现岩石破裂前出未来断层处出现条带状的红外热像,粘滑失稳前断层闭锁点出现升温现象,声发射测量表明,岩石破裂前已有大量微破裂产生,地壳中的既存断层和大震前的微小破裂均可能为震前地壳中的热能转移提供通道,从而导致地面热外震兆的出现。  相似文献   

基于Rough Set理论的油层识别方法   总被引：1，自引：0，他引：1  

陈遵德 《地球物理学进展》1998,13(4):52-59

本文简介了智能信息处理中新出现的Ｒｏｕｇｈ Ｓｅｔ（ＲＳ）理论,讨论了ＲＳ理论进行决策分析的方法,提出了将连续属性离用化的最优化思想,并探讨了ＲＳ理论用于测井数据判别油水层的问题。判别结果表明;本方法具有速度快,易实现,可优选属性等特点,且判别符合油水层的问题,判别结果表明：本方法具有速度快,易实现,可优选属性等特点,且判别符合率优于手工方法与ＢＰ网络方法,具有实用价值。  相似文献   

态矢量方法的实验研究   总被引：5，自引：1，他引：5  

余怀忠  尹祥础  张永仙  夏蒙棼  梁乃刚  李敏  许昭永  彭克银  颜玉定  Wu Zhishen  Qi Li 《地震》2004,24(3):1-7

在地震等灾变的发生之前，会出现一定的前兆现象。中通过实验方法对这些前兆现象之一的态矢量的异常变化进行了研究。实验使用声发射技术(Acoustic Emission)，对三轴应力条件下岩石试件内部微裂纹的产生和扩展进行了记录。实验结果表明在岩石试件最终破坏之前，表征态矢量的相关参量都发生了异常明显的变化，这表明态矢量的异常变化可以被用作为岩石等脆性材料灾变的前兆，使用态矢量方法可以对脆性材料的破坏乃至地震作出预测。  相似文献