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21.
A parametrization method used to account for the effects of flow separation and wall roughness on the lower boundary condition
for turbulent boundary layers is investigated against direct numerical simulation and laser Doppler anemometry data. The numerical
simulation represents flow over a smooth, flat surface with a prescribed external adverse pressure gradient. The water-channel
experiments cover flow over smooth and rough hills for two specified Reynolds numbers. Global optimization algorithms based
on four different direct search methods are used to assess the parametrization function, C, in terms of local mean velocity profiles and the parametrization parameters u
* (friction velocity), ∂
x
p (local pressure gradient), z
0 (effective roughness) and d (zero-plane displacement). The study investigates regions of attached and reversed flows, and forty-two velocity profiles
are compared with the proposed expression for the function C, including two profiles that satisfy the solution of Stratford. 相似文献
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海水与空气间的强波阻抗界面使得海洋地震数据普遍发育自由表面相关多次波,多次波信息的利用是提高海洋地震资料成像品质的新突破点.近年来发展了一系列多次波成像方法,干涉假象是制约其应用推广的关键问题之一.为了避免假象影响,本文提出了不同阶次自由表面相关多次波预测与成像方法,首先,修改了传统SRME(表面相关多次波衰减)方法中的边界条件,通过多次波升阶次与匹配相减的方法预测出不同阶次自由表面相关多次波;其次,基于单程波偏移算子和"面炮"偏移策略,以一次反射波或第(N-1)阶自由表面相关多次波为下行波场正向延拓,以第1阶多次或第N阶多次波为上行波场逆向延拓,并在每一层互相关成像得到第1阶或N阶多次波单独成像.本方法避免了低阶多次波和高阶多次波产生的相关假象,且相对于全波算子的偏移方法具有较高的计算效率,增强了多次波成像方法的实用性.单层模型和三层模型测试验证了本方法的正确性,并在我国某深海探区实际资料处理中得到了成功应用.相对于传统一次波成像,分阶次多次波成像具有更高的照明均衡度、垂向分辨率和信噪比.本研究表明,海洋多次波成像是一次波成像的有力补充,对于稳定海底沉积的深海地区,具有一定的应用前景. 相似文献
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26.
The present work are extract cesium (Cs+) and rubidium (Rb+) from the salt lake brine containing the potassium (K+) and magnesium (Mg2+) after concentrated through evaporation. It has excellent effect of extraction that 4-sec-butyl-2-(α-methylbenzyl) phenol (t-BAMBP) was diluted in the Sulfonated Kerosene (SK). The infrared spectrum studies indicate that polymerize to form the dimer in the t-BAMBP when Cs+ or Rb+ were extracted. The effect of K+ and Mg2+, t-BAMBP concentration, the volume ratio of organic phase to aqueous phase (O/A) and the alkalinity(pH) of aqueous phase were investigated. The K+ and Mg2+ should be eliminated through precipitation before extraction and separation Cs+ and Rb+. The experimental brine was extracted of optimum conditions were using 0.8 mol/L t-BAMBP in SK, the pH exceed 13, and O/A of 1:1 for 2 min contact time under room temperature. The optimal extraction yields of Cs+ and Rb+ up to 100% and 85.8%, and 8.76% K+ was co-extracted. Further work target to increase theSextractionSyield and selectivity ofSRb+, and realize the efficient seperation of Cs+ and Rb+ products . 相似文献
27.
可可西里北缘火山活动带为可可西里中新世火山活动区数条火山活动带之一,其特征十分典型。本文以火山地质、同位素、岩石化学以及稀土元素地球化学为基础对其岩浆来源、演化、火山活动规律进行了研究。该火山带粗安岩-粗面岩-亚碱性流纹岩组合与世界高原溢流玄武岩类似,同时反映大陆伸展的构造环境。 相似文献
28.
The horizontal distribution of the Tsushima Current in the Tsushima/Korea Strait is assessed by a fine-resolution numerical experiment. The comparison of the model results with the observations along a section crossing the strait shows that the model represents relatively well, the general tendency of what was observed, such as the separation of the Tsushima Current into the western and eastern streams by the Tsushima Island. In summer, strong and relatively uniformly distributed surface currents enhance the formation of the wake downstream of the Tsushima Island. The axis of the countercurrent, embedded in the wake, is closer to the western stream. Anti-cyclonic eddies are shed near the downstream tip of the Tsushima Island and propagate along the boundary between the western stream and the wake. The exchange of water between the western stream and the wake takes place through the intermediation of these eddies. There is a net water supply from the western stream to the wake, which is then carried to the eastern stream by the countercurrent via the eastern coast of the Tsushima Island. In winter, currents, strongly barotropic, tend to have banded structures, especially in the region downstream of the western channel where isobaths converge in the downstream direction. The eddies found in this region in winter appear to be fundamentally different from those associated with the Tsushima Island wake. The necessary condition for barotropic instability is satisfied for the monthly mean currents in this region, suggesting that the currents are barotropically unstable in this region in winter. 相似文献
29.
J. B. R. Loureiro D. V. Soares J. L. A. Fontoura Rodrigues F. T. Pinho A. P. Silva Freire 《Boundary-Layer Meteorology》2007,122(2):343-365
The present work investigates the role of different treatments of the lower boundary condition on the numerical prediction
of flows over two-dimensional, smooth, steep hills. Four different law of the wall formulations are tested when a large recirculating
region is formed on the lee side of the hill. Numerical implementation of the near-wall functions was made through a finite
elements code. The standard κ–ε model was used to close the averaged Navier–Stokes equations. Results are validated through
original data obtained in a water tank. Measurements resorted to laser Doppler anemometry. The experiment provide detailed
data for the characterization of the reverse flow in the region between the separation and the reattachment points, with emphasis
on the near wall region. The experimental wall shear stress distribution is compared with the results provided by the different
laws of the wall showing good agreement. The numerical predictions are shown to vary markedly between different formulations. 相似文献
30.
In jigging, amplitude and frequency of pulsation, and feed characteristics are the most important process parameters. Effects of these parameters on particle segregation during jigging are studied and explained through experimental as well as numerical means by drawing parallel to liquid/solid fluidization process. This is permissible because jigging could also be viewed as a repetitive process of fluidization and defluidization. Unlike a normal fluidization process, in jigging, particle segregation takes place under rapid rate of change of water velocity. The rate of change of water velocity is decided by the maximum water velocity of the jig cycle, which in turn is controlled primarily by the amplitude. Experimental evidence of the role of maximum water velocity on jigging is given. Next, the feed to the jig that varies in both size and density is conceived as a mixture of many density variant binary systems. This way, the effect of feed characteristic is conveniently analyzed through several indicators of the binary feed namely size ratio, volume fraction, and particle size. Finally, the effect of frequency is studied by considering the particles in the jig bed analogous to tuned mass dampers. This concept is used to explain the preferential segregation of particles at certain jig frequency. 相似文献