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A trigger-tube tracer dilution technique for determining Darcy and apparent velocities of groundwater in dug wells: A case study on phreatic aquiferous formation in Bamenda -Cameroon 预览
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作者 Akoanung Ayaba ABENDONG ENDENE Emmanuel +2 位作者 Enoh Jeanot FONGOH AKOACHERE Richard Ayuk II NJENG Napoleon Ngenge 《地下水科学与工程:英文版》 2019年第2期182-194,共13页
The need to understand flow within aquiferous formations for a complete evaluation of groundwater resource and quality control prompts the determination of groundwater velocities through well dilution technique. Well ... The need to understand flow within aquiferous formations for a complete evaluation of groundwater resource and quality control prompts the determination of groundwater velocities through well dilution technique. Well dilution techniques utilize tracer solutions after establishing an initial homogenous condition to monitor the flow rate of ambient groundwater into the wells. Application of dilution techniques in wells makes it feasible to determine the velocities of groundwater in the aquiferous formation surrounding the well. In this study, a simple trigger-tube tracer dilution technique was employed to determine the Darcy and apparent velocities of groundwater in the phreatic aquiferous formation in Bamenda, Cameroon. Eighteen (18) hand dug-wells at different locations within Bamenda were sampled by utilizing sodium chloride (NaCl) as the conservative tracer. Field estimates of groundwater flow velocities in the phreatic aquiferous formation in Bamenda reveal Darcy's groundwater velocity in the range of 0.39 m/d at Nacho to 130.64 m/d at Foncha Street and apparent velocity in the range of 0.78 m/d at Nacho to 277.86 m/d at Foncha Street. The immense variations in the velocities of groundwater indicate that the groundwater flows at different rates and directions within the aquiferous formation in Bamenda, possibly due to variations in their hydraulic conductivities. Moreover, the spatial variations in the formation types, facies changes, thickness, and layering of the aquiferous formation also contribute to the variation of velocities. Areas with low groundwater velocities are associated with a lower contaminant transport rate when compared to areas with high groundwater velocities. The findings of this study are important for assessing the rates of pollutant movement in the subsurface, as well as the effectiveness and efficacy of the trigger-tube technique in evaluating the hydraulic properties of aquiferous formations. 展开更多
关键词 Trigger-tube GROUNDWATER DARCY VELOCITY APPARENT VELOCITY Bamenda- Cameroon
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A nonlinear model for aerodynamic configuration of wake behind horizontal-axis wind turbine 预览
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作者 Deshun LI Tao GUO +4 位作者 Rennian LI Congxin YANG Zhaoxue CHENG Ye LI Wenrui HU 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第9期1313-1326,共14页
Determination of the aerodynamic configuration of wake is the key to analysis and evaluation of the rotor aerodynamic characteristics of a horizontal-axis wind turbine. According to the aerodynamic configuration, the ... Determination of the aerodynamic configuration of wake is the key to analysis and evaluation of the rotor aerodynamic characteristics of a horizontal-axis wind turbine. According to the aerodynamic configuration, the real magnitude and direction of the onflow velocity at the rotor blade can be determined, and subsequently, the aerodynamic force on the rotor can be determined. The commonly employed wake aerodynamic models are of the cylindrical form instead of the actual expanding one. This is because the influence of the radial component of the induced velocity on the wake configuration is neglected. Therefore, this model should be called a "linear model". Using this model means that the induced velocities at the rotor blades and aerodynamic loads on them would be inexact. An approximately accurate approach is proposed in this paper to determine the so-called "nonlinear" wake aerodynamic configuration by means of the potential theory, where the influence of all three coordinate components of the induced velocity on wake aerodynamic configuration is taken into account to obtain a kind of expanding wake that approximately looks like an actual one. First, the rotor aerodynamic model composed of axial (central), bound, and trailing vortexes is established with the help of the finite aspect wing theory. Then, the Biot-Savart formula for the potential flow theory is used to derive a set of integral equations to evaluate the three components of the induced velocity at any point within the wake. The numerical solution to the integral equations is found, and the loci of all elementary trailing vortex filaments behind the rotor are determined thereafter. Finally, to formulate an actual wind turbine rotor, using the nonlinear wake model, the induced velocity everywhere in the wake, especially that at the rotor blade, is obtained in the case of various tip speed ratios and compared with the wake boundary in a neutral atmospheric boundary layer. Hereby, some useful and referential conclusions are offered for the aerodynamic c 展开更多
关键词 nonlinear WAKE aerodynamic model vortex-induced VELOCITY INTEGRAL equation of vortex-induced VELOCITY horizontal-axis WIND TURBINE
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Analysis on the velocity relationship and deceleration of long-rod penetration 预览
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作者 W.J.Jiao X.W. Chen 《力学学报:英文版》 SCIE EI CAS CSCD 2019年第4期852-865,共14页
The relationship between the average penetration velocity,UˉUˉ,and the initial impact velocity, V0V0,in long-rod penetration has been studied recently. Experimental and simulation results all show the linear relatio... The relationship between the average penetration velocity,UˉUˉ,and the initial impact velocity, V0V0,in long-rod penetration has been studied recently. Experimental and simulation results all show the linear relationship between UˉUˉ and V0V0 over a wide range of V0V0 for different combinations of rod and target materials. However, the physical essence has not been fully revealed.In this paper, the Uˉ?V0Uˉ?V0relationship is profoundly analyzed using hydrodynamic model and Alekseevskii-Tate model. Especially, the explicitUˉ?V0Uˉ?V0 relationships are derived fromapproximate solutions of Alekseevskii-Tate model. Besides, the decelerationin long-rod penetration is discussed. The decelerationdegree is quantified by adeceleration index,α=2μˉ/(KΦJp)≈Ypρ?1/2p(ρ?1/2p+ρ?1/2t)V?20α=2μˉ/(KΦJp)≈Ypρp?1/2(ρp?1/2+ρt?1/2)V0?2, which is mostly related to the impact velocity, rod strength and rod/target densities. Thus, the state of penetration process can be identified and designed in experiments. 展开更多
关键词 Long-rod PENETRATION Average PENETRATION VELOCITY Initial impact VELOCITY Alekseevskii-Tate model DECELERATION
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一种时变分布式单位线计算方法 预览
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作者 孔凡哲 郭良 《水科学进展》 EI CAS CSCD 北大核心 2019年第4期477-484,共8页
为了解决由降雨强度引起的径流汇流的非线性问题,提出一种基于SCS(United States Department of Agriculture-Soil Conservation Service)流速公式的时变分布式单位线计算方法。引入参考雨强表征SCS公式中流速系数对应的水力条件。由降... 为了解决由降雨强度引起的径流汇流的非线性问题,提出一种基于SCS(United States Department of Agriculture-Soil Conservation Service)流速公式的时变分布式单位线计算方法。引入参考雨强表征SCS公式中流速系数对应的水力条件。由降雨过程的时段雨强与参考雨强的比值构成一个量纲一因子,将该因子加入SCS公式后使其能够考虑降雨对流速的影响。改进后的流速公式用于计算一次降雨过程中不同降雨时段对应的时变分布式单位线,时变分布式单位线与新安江模型的产流模块构成降雨径流模型,将模型用于裴河流域率定参考雨强。率定后的模型用于谭家河流域进行应用检验,结果显示,确定性系数大于等于0.9的洪水场次,由时不变单位线的42%增大为83%。提出的方法能够显著提高流域水文模型的降雨径流模拟能力。 展开更多
关键词 分布式单位线 流速 流速场 时变 SCS流速公式
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基于惯性权重的蝙蝠算法 预览
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作者 杨晓琴 《太原科技大学学报》 2019年第2期123-128,共6页
蝙蝠算法是一种有效地求解单目标优化问题的启发式算法。然而,标准蝙蝠算法的速度更新方式偏向于搜索当前全局最优个体周围潜在较优个体,导致算法过早收敛。针对此缺陷,提出了基于惯性权重的蝙蝠算法,即在速度更新时添加惯性权重以改进... 蝙蝠算法是一种有效地求解单目标优化问题的启发式算法。然而,标准蝙蝠算法的速度更新方式偏向于搜索当前全局最优个体周围潜在较优个体,导致算法过早收敛。针对此缺陷,提出了基于惯性权重的蝙蝠算法,即在速度更新时添加惯性权重以改进速度更新的方向,使得种群中个体可以有效地跳出局部最优点。为验证所提算法的性能,采用了CEC2013作为测试集,PSO和标准蝙蝠算法作为对比算法。实验结果显示,所提改进算法可以有效地提升标准蝙蝠算法性能。 展开更多
关键词 蝙蝠算法 速度 过早收敛 惯性权重
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城市道路坡度和车速对机动车排放的影响 预览
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作者 郑春燕 张海 +2 位作者 郭栋 王娟 赵金宝 《河南科技大学学报:自然科学版》 CAS 北大核心 2019年第2期35-39,44,107共7页
为了分析城市道路坡度变化对机动车排放的影响,基于车载排放测试平台获取实际道路排放数据,并通过比功率反推完善数据。分析了在4个坡度区间的城市道路下,轻型车3种排放污染物(CO、HC、NOX)在不同速度区间的排放特性。研究结果表明:当... 为了分析城市道路坡度变化对机动车排放的影响,基于车载排放测试平台获取实际道路排放数据,并通过比功率反推完善数据。分析了在4个坡度区间的城市道路下,轻型车3种排放污染物(CO、HC、NOX)在不同速度区间的排放特性。研究结果表明:当车速处于20~50km/h时,每升高一个坡度区间,3种污染物的质量排放率分别提升约22.8%、23.6%、24.4%。在坡度一定的路面上,当车速处于20~40km/h时,3种污染物处于高排放状态,其质量排放率比低排放状态分别提升约64.3%、80.0%、95.0%。 展开更多
关键词 车载排放测试 城市道路坡度 速度 排放特性
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浓香型白酒乳酸乙酯蒸馏规律及提取影响因素的研究 预览
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作者 黄永军 谢旭 +2 位作者 洪胜 王亚庆 陈敏 《酿酒》 CAS 2019年第3期28-30,共3页
跟踪浓香生产过程,分析乳酸乙酯在不同流酒时段及不同工序时段中含量,研究其提取与润料水分、流酒温度及速度的关系,结果表明,乳酸乙酯主要存在于酒醅蒸馏的后段,且在酒样酒度接近于零时含量较高;增加润料水分对乳酸乙酯提取影响不大;... 跟踪浓香生产过程,分析乳酸乙酯在不同流酒时段及不同工序时段中含量,研究其提取与润料水分、流酒温度及速度的关系,结果表明,乳酸乙酯主要存在于酒醅蒸馏的后段,且在酒样酒度接近于零时含量较高;增加润料水分对乳酸乙酯提取影响不大;增大流速,乳酸乙酯提取含量增加;乳酸乙酯提取量随着流酒温度的增加而加大。 展开更多
关键词 乳酸乙酯 水分 温度 流速
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Complex Semblance and Its Application
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作者 Taikun Shi Shoudong Huo 《地球科学学刊:英文版》 SCIE CAS CSCD 2019年第4期849-852,共4页
Semblance,a measure of multi-trace coherence,has been used extensively in seismic data processing and interpretation such as velocity analysis and fault detection. The traditional algorithm has a difficulty at zero-cr... Semblance,a measure of multi-trace coherence,has been used extensively in seismic data processing and interpretation such as velocity analysis and fault detection. The traditional algorithm has a difficulty at zero-crossings of seismic recordings. This problem is alleviated by applying a smoothing window at the cost of losing vertical resolutions. In this paper,we improve the algorithm by computing semblance from complex traces. Our initial results show that the complex semblance is smooth at zero-crossings. Because the smoothing time window becomes unnecessary,the higher vertical resolution can be achieved by using small windows or none. Some geological features,like faults and unconformities,appear clearer and easier to identify with the complex semblance. As the advantages are obvious and the implementation is straight-forward with the Hilbert transform,this new algorithm may replace the traditional one in future applications. 展开更多
关键词 semblance COMPLEX TRACE HILBERT TRANSFORM VELOCITY analysis FAULT detection
Weak Seismic Signal Extraction Based on the Curvelet Transform 预览
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作者 TAN Junqing YANG Runhai +1 位作者 WANG Bin XIANG Ya 《中国地震研究:英文版》 CSCD 2019年第2期220-234,共15页
Seismic signal denoising is a key step in seismic data processing.Airgun signals are easy to be interfered with by noise when it travels a long distance due to the weak energy of active source signal of the airgun.Aim... Seismic signal denoising is a key step in seismic data processing.Airgun signals are easy to be interfered with by noise when it travels a long distance due to the weak energy of active source signal of the airgun.Aiming to solve this problem,and considering that the conventional Curvelet transform threshold processing method does not use the seismic spectrum information,we independently process the Curvelet scale layer corresponding to valid data based on the characteristics of the Curvelet transform of multi-scale,multi-direction and capable of expressing the sparse seismic signals in order to fully excavate the information features.Combined with the Curvelet adaptive threshold denoising the algorithm,we apply the Curvelet transform to denoising seismic signals while retaining the weak information in the signal as much as possible.The simulation experiments show that the improved threshold denoising method based on Curvelet transform is superior to the frequency domain filtering,wavelet denoising and traditional Curvelet denoising method in detailed information extraction and signal denoising of low SNR signals.The calculation accuracy of the relative wave velocity variation of underground medium is improved. 展开更多
关键词 Seismic SIGNAL DENOISING Airgun active source SIGNAL CURVELET TRANSFORM The velocity of the UNDERGROUND medium
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Experiments on Exploration of Shallow Fine Structures and the Construction of the 1-D Velocity Model in the Pingtan Island,Fujian 预览
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作者 GUO Yang XU Jiajun +4 位作者 LIN Chen JIN Xing YAO Huajian YANG Hongfeng CAI Huiteng 《中国地震研究:英文版》 CSCD 2019年第2期265-275,共11页
112 short-period seismographs were set up in the 400 km^2 area of Pingtan Island and its surrounding areas in Fujian.The combined observations of the airgun source and ambient noise source were carried out using a den... 112 short-period seismographs were set up in the 400 km^2 area of Pingtan Island and its surrounding areas in Fujian.The combined observations of the airgun source and ambient noise source were carried out using a dense array to receive the 387 airgun signals excited around the island and one month of continuous ambient noise recording.The 1-D P-wave and S-wave shallow velocity model of Pingtan Island is obtained by the inversion of the airgun body wave’s first arrival time data,and the reliability of the velocity model is verified by using the surface wave phase velocity dispersion curve,which can provide initial model for subsequent 3-D imaging.The experimental results show that this experiment is a successful demonstration of local scale green non-destructive detection,which can provide basic data for shallow surface structure research and strong vibration simulation of the Pingtan Island. 展开更多
关键词 PINGTAN ISLAND Fujian DENSE array Airgun AMBIENT noise 1-D velocity model
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The vP Velocity Structures of Sub-blocks in the North China Craton from Active Source Waveform Modeling and Tectonic Implications 预览
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作者 LIU Hanqi TIAN Xiaofeng +1 位作者 LIU Baofeng WANG Honglei 《中国地震研究:英文版》 CSCD 2019年第2期276-287,共12页
We present the 1-D crustal velocity structure of the major tectonic blocks of the North China Craton(NCC)along 36°N based on synthetic seismogram modeling of long-range wide-angle reflection/refraction data.This ... We present the 1-D crustal velocity structure of the major tectonic blocks of the North China Craton(NCC)along 36°N based on synthetic seismogram modeling of long-range wide-angle reflection/refraction data.This profile extends from southwest Yan’an of central Shaanxi Province of China(109.47°E),across the southern Trans-North China Orogen(TNCO),the southwestern part of the North China Plain(NCP),the Luxi Uplift(LU)and the Sulu Orogen(SLO),ending at Qingdao City of Shandong Province,the eastern margin of China(120.12°E)along 36°N.We utilized reflectivity synthetic seismogram modeling of the active source data to develop 1-D velocity structures of the sub-blocks of the NCC.Our final model shows that the NCC crust varies remarkably among the tectonic units with different velocity structure features.Higher lower crustal velocity and Moho depth~42 km is a major feature of the crust beneath southern Ordos Blockt.The TNCO which is composed of Lyuliangshan Mountains(LM),Shanxi Graben(SXG)and Taihangshan Mountains(TM)shows dominant trans-orogenic features.The NCP shows a dominant thickening of sediments,sharp crust thinning with Moho depth~32 km and significant lower average velocity.The SLO and the LU shows a stratified crust,higher average velocity and crust thinning with Moho depth of~35 km.Our model shows the coincidence between the deep structure and the surface geology among all the tectonic sub-blocks of the NCC. 展开更多
关键词 The North China CRATON CRUSTAL velocity structure CRATON destructure WIDE-ANGLE reflection/refraction
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Study of flow characteristics within randomly distributed submerged rigid vegetation 预览
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作者 Paromita Chakraborty Arindam Sarkar 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第2期358-367,共10页
Flow through submerged rigid vegetation has been studied both analytically and experimentally.The Reynolds stress,present in the governing equation,has been modeled using one of the turbulent stress equations,adopted ... Flow through submerged rigid vegetation has been studied both analytically and experimentally.The Reynolds stress,present in the governing equation,has been modeled using one of the turbulent stress equations,adopted in numerous cases.The adva ntage of this turbulent stress model is to replace the mixing length non linear term of the stress with a linear relatio n between stress and the velocity gradient.The velocity field and shear stress are obtained by solving the governing force balance equation numerically.A correlation,validated with the experimental results,has been developed for the relevant non-dimensional numbers. 展开更多
关键词 SUBMERGED VEGETATION REYNOLDS stress drag force STREAM WISE velocity
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Study of the Change in Wave Velocity Ratio before and after Two Strong Earthquakes Using Airgun Source Data 预览
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作者 LIU Zifeng YE Beng +4 位作者 CHEN Jia ZHOU Qingyun WANG Guangming PENG Guanling LI Yongli 《中国地震研究:英文版》 CSCD 2019年第2期305-319,共15页
Using the signals excited by the large-volume airgun source at the Binchuan transmitting seismic station from January to June,2016,arrival-time data was acquired at four stations near the epicenter of the Eryuan MS4.5... Using the signals excited by the large-volume airgun source at the Binchuan transmitting seismic station from January to June,2016,arrival-time data was acquired at four stations near the epicenter of the Eryuan MS4.5 and MS4.0 earthquakes on February 8,2016,as well as the epicenter of the Yunlong MS5.0 and Eryuan MS4.6 earthquakes on May 18,2016 through the waveform cross-correlation technique.The wave velocity ratio of the four stations was calculated using the single-station method.At the same time,the b-value and the focal mechanism consistency parameters of the study area were also calculated.The results show that:(1)the wave velocity ratio of each station experienced a process of decline-recovery-fast rise before the two strong earthquakes,and a significant quasi-synchronous rapid rise occurred within 3-12 days before the earthquake;(2)the timing of the rapid rise of the wave velocity ratio of the four stations before the Yunlong MS5.0 and Eryuan MS4.6 earthquakes were related to the epicentral distance.The station which observed the earliest increase in rapid rise is the farthest one from the epicenter,and the station where the rapid rise appeared in the latest is closest to the epicenter;(3)the form of change of the wave velocity ratio before the earthquake was different between stations located at different directions in the epicenter area;(4)the b-value and the focal mechanism consistency parameter which is commonly used to characterize the stress level both showed a downward trend before the two strong earthquakes,and were consistent with the change in the wave velocity ratio.According to the preliminary analysis,the wave velocity ratio obtained by using airgun source can better reflect the change in the stress state of the underground medium. 展开更多
关键词 Airgun source Wave VELOCITY RATIO B-VALUE FOCAL mechanism CONSISTENCY
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Earthquake hazard on Iraqi soil: Halabjah earthquake as a case study
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作者 Abbas J.Al-Taie Bushra S.Albusoda 《大地测量与地球动力学:英文版》 2019年第3期196-204,共9页
Iraq is not secure from seismic hazards. Earthquakes are likely to happen and may cause substantial damage. Actually, such hazards were happened and recorded after the last earthquake in November 2017(Halabjah earthqu... Iraq is not secure from seismic hazards. Earthquakes are likely to happen and may cause substantial damage. Actually, such hazards were happened and recorded after the last earthquake in November 2017(Halabjah earthquake). Unfortunately, there is a lack of studies concerns the assessment of the earthquake hazard on the soil in Iraq. The available research efforts directed toward the earthquakes and their effects on bridge piers, and traditional commercial buildings of Iraq. A historical view of earthquakes that struck Iraq was presented in this paper. Evaluation of liquefaction susceptibility of poorly graded sand at the southwest of Baghdad, Iraq was studied considering the last earthquake. The NCEER, 1997 workshop procedure using shear wave velocity was used to evaluate liquefaction susceptibility of soil. The variation of safety factor with depth had been investigated at different earthquake magnitudes and accelerations.The study revealed that the soil had a high tendency to liquefaction if subjected to earthquake magnitudes within the ranges that hit Iraq in November 2017. Large attention should be given to the effect of the earthquake on soil foundation in the future for all engineering project that constructed in Iraq. 展开更多
关键词 EARTHQUAKE Halabjah EARTHQUAKE LIQUEFACTION SHEAR wave VELOCITY SAND
坡面水流流速对贴地植被的响应特性试验研究 预览
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作者 孙一 田勇 +1 位作者 刘晓燕 王协康 《工程科学与技术》 EI CAS CSCD 北大核心 2019年第2期85-89,共5页
坡面上植被对坡面流流速有着显著影响,进而对坡面的输沙特性起着重要作用,而覆盖度是植被影响坡面粗糙度的一个重要因素。以往研究多集中在植被覆盖度相对较小的范围。为进一步探明植被覆盖度与坡面流流速间的相关关系,基于坡面流系列... 坡面上植被对坡面流流速有着显著影响,进而对坡面的输沙特性起着重要作用,而覆盖度是植被影响坡面粗糙度的一个重要因素。以往研究多集中在植被覆盖度相对较小的范围。为进一步探明植被覆盖度与坡面流流速间的相关关系,基于坡面流系列概化变坡水槽试验,采用人工塑料草模拟贴地植被,设置了在0~80%范围之间的9种不同的贴地植被覆盖度、3种不同的坡度(10°、20°、25°)以及6个不同的流量级(0.286~1.058 L/s)条件下的共计162组清水径流试验,对坡面流流速特性进行了定量研究。试验结果表明:随着贴地植被覆盖度的增大,流速沿坡长由增大变为减小;当覆盖度小于30%时,流速受流量的影响较大;当覆盖度大于30%后,流速受流量的影响较小。将植被覆盖度引入坡面流流速计算公式,采用生长模型中常见的e^-x表达形式反映植被对坡面粗糙度的影响,对公式中的k进行修正,应用非线性回归的方法对试验数据进行回归分析,确定参数k、a、b、c分别为10.06、–1.71、0.22、0.4,所得公式的计算效果良好(R^2=0.96)。将公式应用于其他文献中提及的实验室水槽试验条件,所得的计算值与文献中的实测值符合较好(R^2=0.73)。公式对实验室试验具有良好的适应性,而其对野外条件的适用性仍有待于进一步检验。 展开更多
关键词 坡面水流 贴地植被 覆盖度 流速
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On the stabil让y of Wiirster fluid bed of pharmaceutical pellets
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作者 Mohammad Foroughi-Dahr Rahmat Sotudeh-Gharebagh Navid Mostoufi 《颗粒学报:英文版》 SCIE EI CAS CSCD 2019年第4期81-90,共10页
The flow of pharmaceutical pellets in a Wiirster fluid bed (WFB) was characterized by a frequency domain analysis of pressure fluctuations. Pellets with a diameter of 0.780 mm and density of 1.225 kg/m^3 were used in ... The flow of pharmaceutical pellets in a Wiirster fluid bed (WFB) was characterized by a frequency domain analysis of pressure fluctuations. Pellets with a diameter of 0.780 mm and density of 1.225 kg/m^3 were used in the experiments. Different flow structures were identified in the bed, including bulk movement of pellets in the annulus (f<5Hz), bulk movement of pellets inside the draft tube and bulk horizontal movement of pellets through the entrainment zone (5 </<15 Hz), and clustering (15<f< 145 Hz). The minimum spouting velocity was also measured experimentally. Effects of bed height, distanee of the entrainment zone, and distributor hole pitch on minimum spouting velocity were investigated. It was Found that the minimum spouting velocity increased with increasing bed height and distance of the entrainment zone while it decreased w ith in creasing distributor hole pitch. A correlation was developed for estimating the minimum spouting velocity in WFBs containing pharmaceutical pellets. The correlation fit the experimental data satisfactorily. Studying the WFB hydrodynamics and determining the minimum spouting velocity provides information that can be used to properly design, operate, and scale up such systems. 展开更多
关键词 PHARMACEUTICAL PELLETS Wiirster FLUID BED Draft tube Minimum SPOUTING VELOCITY
Configuration of propagator method for calculation of electron velocity distribution function in gas under crossed electric and magnetic fields
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作者 Hirotake SUGAWARA 《等离子体科学与技术:英文版》 SCIE EI CAS CSCD 2019年第9期1-18,共18页
This paper presents a self-contained description on the configuration of propagator method(PM)to calculate the electron velocity distribution function(EVDF) of electron swarms in gases under DC electric and magnetic f... This paper presents a self-contained description on the configuration of propagator method(PM)to calculate the electron velocity distribution function(EVDF) of electron swarms in gases under DC electric and magnetic fields crossed at a right angle. Velocity space is divided into cells with respect to three polar coordinates v,θ and f. The number of electrons in each cell is stored in three-dimensional arrays. The changes of electron velocity due to acceleration by the electric and magnetic fields and scattering by gas molecules are treated as intercellular electron transfers on the basis of the Boltzmann equation and are represented using operators called the propagators or Green’s functions. The collision propagator, assuming isotropic scattering, is basically unchanged from conventional PMs performed under electric fields without magnetic fields. On the other hand, the acceleration propagator is customized for rotational acceleration under the action of the Lorentz force. The acceleration propagator specific to the present cell configuration is analytically derived. The mean electron energy and average electron velocity vector in a model gas and SF6 were derived from the EVDF as a demonstration of the PM under the Hall deflection and they were in a fine agreement with those obtained by Monte Carlo simulations. A strategy for fast relaxation is discussed, and extension of the PM for the EVDF under AC electric and DC/AC magnetic fields is outlined as well. 展开更多
关键词 PROPAGATOR method ELECTRON velocity distribution function ELECTRON transport COEFFICIENTS CROSSED electric and magnetic fields MAGNETIZED plasma BOLTZMANN equation
Flow characteristics of supersonic gas passing through a circular micro-channel under different inflow conditions
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作者 郭广明 罗琴 +1 位作者 朱林 边义祥 《中国物理B:英文版》 SCIE EI CAS CSCD 2019年第6期270-283,共14页
Gas flow in a micro-channel usually has a high Knudsen number. The predominant predictive tool for such a microflow is the direct simulation Monte Carlo(DSMC) method, which is used in this paper to investigate primary... Gas flow in a micro-channel usually has a high Knudsen number. The predominant predictive tool for such a microflow is the direct simulation Monte Carlo(DSMC) method, which is used in this paper to investigate primary flow properties of supersonic gas in a circular micro-channel for different inflow conditions, such as free stream at different altitudes, with different incoming Mach numbers, and with different angles of attack. Simulation results indicate that the altitude and free stream incoming Mach number have a significant effect on the whole micro-channel flow field, whereas the angle of attack mainly affects the entrance part of micro-channel flow field. The fundamental mechanism behind the simulation results is also presented. With the increase of altitude, thr free stream would be partly prevented from entering into micro-channel.Meanwhile, the gas flow in micro-channel is decelerated, and the increase in the angle of attack also decelerates the gas flow. In contrast, gas flow in micro-channel is accelerated as free stream incoming Mach number increases. A noteworthy finding is that the rarefaction effects can become very dominant when the free stream incoming Mach number is low. In other words, a free stream with a larger incoming velocity is able to reduce the influence of the rarefaction effects on gas flow in the micro-channel. 展开更多
关键词 rarefied FLOW MICRO-CHANNEL MASS FLOW VELOCITY temperature distribution
Traction rheological properties of simulative soil for deepsea sediment 预览
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作者 QI Cailing RAO Qiuhua +1 位作者 LIU Qi MA Wenbo 《海洋湖沼学报(英文)》 SCIE CAS CSCD 2019年第1期62-71,共10页
The traction capacity of the mining machine is greatly infl uenced by the traction rheological properties of the deep-sea sediments.The best simulative soil was prepared for substituting the deep-sea sediment based on... The traction capacity of the mining machine is greatly infl uenced by the traction rheological properties of the deep-sea sediments.The best simulative soil was prepared for substituting the deep-sea sediment based on the deep-sea sediment collected from the Pacifi c C-C mining area.Traction rheological properties of the simulative soil were studied by a home-made test apparatus.In order to accurately describe the traction rheological properties and determine traction rheological parameters,the Newtonian dashpot in Maxwell body of Burgers model was replaced by a self-similarity spring-dashpot fractance and a new rheological constitutive model was deduced by fractional derivative theory.The results show the simulative soil has obvious non-attenuate rheological properties.The transient creep and stable creep rate increase with the traction,but they decrease with ground pressure.The fractional derivative Burgers model are better in describing non-attenuate rheological properties of the simulative soil than the classical Burgers model.For the new traction rheological constitutive equation of the simulative soil,the traction rheological parameters can be obtained by fi tting the tested traction creep data with the traction creep constitutive equation.The ground contact length of track and walking velocity of the mining machine predicted by the traction rheological constitutive equation can be used to take full advantages of the maximum traction provided by the soil and safely improve mining effi ciency. 展开更多
关键词 simulative SOIL TRACTION RHEOLOGICAL properties CONSTITUTIVE model RHEOLOGICAL parameters ground contact length of track WALKING VELOCITY
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Electron-Electron Collision Term Describing the Reflections Induced Scattering in a Magnetized Plasma
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作者 董超 李定 姜畅 《中国物理快报:英文版》 SCIE CAS CSCD 2019年第7期56-60,共5页
For an electron-electron collision with characteristic scale length larger than the relative gyro-radius of the two colliding electrons, when the initial relative parallel kinetic energy cannot surmount the Coulomb re... For an electron-electron collision with characteristic scale length larger than the relative gyro-radius of the two colliding electrons, when the initial relative parallel kinetic energy cannot surmount the Coulomb repulsive potential, reflection will occur with interchange of the parallel velocities of the two electrons after the collision. The Fokker–Planck approach is employed to derive the electron collision term C_R describing parallel velocity scattering due to the reflections for a magnetized plasma where the average electron gyro-radius is much smaller than the Debye length but much larger than the Landau length. The electron parallel velocity friction and diffusion coefficients due to the reflections are evaluated, which are found not to depend on the electron perpendicular velocity. By studying the temporal evolution of the H quantity due to CR, it is found that C_R eventually makes the system relax to a state in which the electron parallel velocity distribution is decoupled from the perpendicular velocity distribution. 展开更多
关键词 For an electron-electron scale LENGTH larger VELOCITY distribution
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