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Transient simulation of a pump-turbine with misaligned guide vanes during turbine model start-up

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Acta Mechanica Sinica 2014年第5期30卷 646-655页

作者： Ye-xiang xiao Ruo-Fu xiao State Key Laboratory of Hydroscience and Engineering & Department of Thermal Engineering Tsinghua University College of Water Resources and Civil Engineering China Agricultural University

Experimental studies of a model pump-turbine S-curve characteristics and its improvement by misaligned guide vanes （MGV） were extended to prototype pump turbine through 3-D transient flow simulations. The unsteady Reynolds-averaged Navier-Stokes equations with the SST turbulence model were used to model the transient flow within the entire flow passage of a reversible pump-turbine with and without misaligned guide vanes during turbine model start-up. The unstable S-curve and its improvement by using misaligned guide vane were verified by model test and simulation. The transient flow calculations were used to clarify the variations of pressure pulse and internal flow behavior in the entire flow passage. The use of misaligned guide vanes can eliminate the S-curve characteristics of a pump-turbine, and can significantly increase the pressure pulse amplitude in the entire flow passage and the runner radial forces during start-up. The MGV only decreased the pulse amplitude on the guide vane suction side when the rotating speed was less than 50% rated speed. The hydraulic reason is that the MGV dramatically changed the flow patterns inside the entire flow passage, and destroyed the symmetry of the flow distribution inside the guide vane and runner.

关键词： Transient flow. Pump turbine. Misaligned guide vane Model test Pressure pulse

On Pseudo-Holomorphic Curves from Two-Spheres into a Complex Grassmannian G(2, 5)

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Acta Mathematica Sinica,English Series 2010年第4期26卷 759-762页

作者： xiao xiang JIAO Department of Mathematics Graduate University of Chinese Academy of Sciences Beijing 100049 P. R. China

Let s ： S2 → G（2, 5） be a linearly full totally unramified pseudo-holomorphic curve with constant Gaussian curvature K in a complex Grassmann manifold G（2, 5）. It is prove that K is either 1 4 1 or 4/5 if s is non-±holomorphic. Furthermore, K = 1/3 if and only if s is totally real. We also prove that the Gaussian curvature K is either 1 or -4/3 if s is a non-degenerate holomorphic curve under some conditions.

关键词： pseudo-holomorphic curves Gaussian curvature harmonic seouence. Kaihler angle

Improved delayed detached-eddy simulation of massive separation around triple cylinders

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Acta Mechanica Sinica 2015年第6期31卷 799-816页

作者： Zhi-xiang xiao Kun-Yu Luo School of Aerospace Engineering Tsinghua University

The massively separated flow past triple cylin- ders （TriC） in tandem arrangement is simulated using the improved delayed detached-eddy simulation （IDDES） method based on the shear stress transport （SST） model, coupled with the high order adaptive dissipation scheme. The spacing between adjacent cylinders is sub-critical （1.435D）. IDDES prediction of two cylinders （TC） with the same spacing is compared to experimental data for validation, and the numerical results agree well with the available measurements, except for the asymmetry in the gap region. The flow past TriC is investigated using the same method. Generally, the mean flow quantities past TriC, such as the velocity, pressure, and vorticity, are similar to the corresponding components of TC. However, the pressure fluctuations on the TriC surface are uniformly larger than those on TC. Meanwhile, the instantaneous flows past TriC are much more complex. The periodical blockage in the first gap region is found in the TriC case and leads to the up-and-down movement of shear layer in the second gap region.

关键词： Triple cylinders - Massive separation. IDDES ·Hybrid RANS/LES methods

Fe、Ir掺杂MoS_(2)表面对N_(2)气敏吸附与解离反应性能提升的第一性原理研究

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原子与分子物理学报 2025年第1期42卷 13-19页

作者：肖香珍胡林峰张建伟河南科技学院新乡453003

基于第一性原理方法,采用周期性平板模型,研究了N_(2)分子在掺杂体系TM-MoS_(2)(TM=Fe、Ir)表面的吸附和解离行为.研究表明:N_(2)分子在TM-MoS_(2)(TM=Fe、Ir)表面吸附能依次为0.62和0.47 eV,而完整MoS_(2)表面的吸附能只有0.08 eV,说... 详细信息

基于第一性原理方法,采用周期性平板模型,研究了N_(2)分子在掺杂体系TM-MoS_(2)(TM=Fe、Ir)表面的吸附和解离行为.研究表明:N_(2)分子在TM-MoS_(2)(TM=Fe、Ir)表面吸附能依次为0.62和0.47 eV,而完整MoS_(2)表面的吸附能只有0.08 eV,说明掺杂之后对N_(2)表现出略好的吸附性能.差分电荷密度分析表明,N_(2)吸附后,掺杂Fe、Ir原子与两个N原子之间电荷有所增加,N-N键之间的区域电荷密度减少,N-N键的强度减弱.态密度计算结果发现,N_(2)在吸附过程中,主要是N原子的2p_(y)、2p_(z)轨道与Ir的5d_(xy)和5d_(z^(2))以及Fe的3d_(xy)和3d_(z^(2))发生杂化作用.通过分析解离活化能,N_(2)在掺杂体系TM-MoS_(2)(TM=Fe、Ir)表面解离需要活化能均较高,且远大于在相应掺杂表面的吸附能,说明N_(2)在掺杂体系TM-MoS_(2)(TM=Fe、Ir)表面解离应该表现为分子吸附或脱附.

关键词： Fe、Ir 掺杂单层MoS_(2) N_(2) 吸附与解离活化能密度泛函理论

Preparation and properties of C/C-SiC brake composites fabricated by warm compacted-in situ reaction

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International Journal of Minerals,Metallurgy and Materials 2010年第4期17卷 500-505页

作者： Zhuan Li Peng xiao xiang Xiong State Key Laboratory of Powder Metallurgy Central South University Changsha 410083 China

Carbon fibre reinforced carbon and silicon carbide dual matrix composites（C/C-SiC） were fabricated by the warm compacted-in situ *** microstructure,mechanical properties,tribological properties,and wear mechanism of C/C-SiC composites at different brake speeds were *** results indicate that the composites are composed of 58wt%C,37wt%SiC,and 5wt%*** density and open porosity are 2.0 ***^（-3） and 10%,*** C/C-SiC brake composites exhibit good mechanical *** flexural strength can reach up to 160 MPa,and the impact strength can reach 2.5 kJ.m^（-2）.The C/C-SiC brake composites show excellent tribological *** friction coefficient is between 0.57 and 0.67 at the brake speeds from 8 to 24 m·s^（-1）.The brake is stable,and the wear rate is less than 2.02×10^（-6） cm^3·J^（-1）.These results show that the C/C-SiC brake composites are the promising candidates for advanced brake and clutch systems.

关键词： C/C-SiC ceramic matrix composites tribological properties microstructure

Interaction effect of micro-and macro-organic on the biogeochemical function of the sediment and aquatic interface

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Journal of Environmental Sciences 2006年第3期18卷 468-474页

作者： xiao xiang LIAO Ling ZHANG Xin-hua Guangzhou Environment Protection Bureau Guangzhou 510032 China Guangzhou Research Institute of Environmental Protection Guangzhou 510620 China South China Botanical Garden Chinese Academy of Sciences Guangzhou 510650 China

Constructed stormwater infiltration basins have been broad applied in urban areas in terms of stormwater disposal and compensation of reduced groundwater recharge. However, stormwater derived from sediments accumulating in infiltration beds may act as a source of dissolved contaminants for groundwater. Concentrations of DO, NO3-N, NO2^--N, NH4^＋-N and PO4^3--P were monitored at multiple depth with time. The results showed that the occurrence of denitrificarion was restrained by sediments in term of no invertebrates. Under the conditions of invertebrates inoculated, the concentrations of DO, NO^3--N, NO2^＋-N, NH4^＋-N and PO4^3＋-P varied respectively with time and the occurrence of nitrification and mobilizing nitrate in the sediment. It is concluded that there exist the invertebrate activities such as building tubes and galleries and excreting faecal pellet which may increase water dispersion and enhance accessibility of nutrient, and stimulate microbial process effected in the sediment. Besides, the natural death and rot of worms were also found to be important factors of the invertebrate activities.

关键词： infiltration basins urban stormwater polluted sediments invertebrates effects

Distortion-aware beamforming design for multi-beam satellite communications with nonlinear power amplifiers

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Science China(Information Sciences) 2024年第6期67卷 359-369页

作者： xiang xiao Li YOU Kezhi WANG Xiqi GAO National Mobile Communications Research Laboratory Southeast University Purple Mountain Laboratories Department of Computer Science Brunel University London

Hardware components can cause different impairments, including power amplifier(PA) nonlinearities, which inevitably impact the system performance of satellite communications(SATCOM). In this work, we consider a multi-beam SATCOM downlink system and investigate the distortion-aware beamforming scheme with the characteristics of PA non-linearities. Notably, we aim to maximize the resource efficiency(RE), defined as the weighted sum of energy efficiency(EE) with spectral efficiency(SE), to obtain a flexible EE-SE tradeoff while accounting for the characteristics of PA distortion and the total power *** that the optimization objective is a sum of ratios and the high non-convexity involved in constraints,we propose an efficient approach that exploits the quadratic transformation, the Lagrange multiplier method,and the gradient ascent approach to handle this issue. Simulation results demonstrate the effectiveness of the distortion-aware beamforming approach in achieving the EE-SE tradeoff and exhibit a substantial RE performance gain over the conventional approach with ideal linear PAs assumed at the satellite transmitters.

关键词： multi-beam satellite communications nonlinear power amplifier energy and spectral efficiency tradeoff resource efficiency robust beamforming

Outage analysis of opportunistic multi-antenna relay selection in decode-and-forward relay networks

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The Journal of China Universities of Posts and Telecommunications 2010年第4期17卷 6-12页

作者： WANG xiao-xiang ZHENG Zi-yun Key Laboratory of Universal Wireless Communications Ministry of Education Beijing University of Posts and Telecommunications Beijing 100876 China

This article studies the closed-form expressions of outage performance for opportunistic relay under aggregate power constraint in decode-and-forward （DF） relay networks over Rayleigh fading channels, assuming that multiple antennas are available at the relay node. According to whether instantaneous signal-to-noise ratio （SNR） or average SNR can be utilized for relay selection, two opportunistic relay schemes, opportunistic multi-antenna relay selection （OMRS） and average best relay selection （ABRS） are proposed. The performances of both two schemes are evaluated by means of theoretical analysis and simulation, it is observed that OMRS is outage-optimal among multi-antenna relay selection schemes and closely approaches the beamforming （BF） scheme known as theoretical outage-optimal. Compared with previous single-antenna opportunistic relaying （OR） scheme, OMRS brings remarkable performance improvement, which is obtained from maximum ratio combining （MRC） and beamforming techniques. It is also shown that the performance of ABRS in asymmetric channels is close to OMRS in the low and median SNR range.

关键词： relay selection multiple antennas multiple relays decode and forward cooperative networks

Curve Shortening Flow in Arbitrary Dimensional Euclidian Space

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Acta Mathematica Sinica,English Series 2005年第4期21卷 715-722页

作者： Yun Yan YANG xiao xiang JIAO School of Mathematical Sciences Peking University Beijing 100871 P. R. China Graduate School Chinese Academy of Sciences P. R. China

In this paper, curve shortening flow in Euclidian space R^n（n≥3） is studied, and S. Altschuler＇s results about flow for space curves are generalized. We prove that the curve shortening flow converges to a straight line in infinite time if the initial curve is a ramp. We also prove the planar phenomenon when the curve shortening flow blows up.

关键词： Curve shortening flow Singularity formation Blow up