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Experimental Study of the Influence of Flow Passage Subtle Variation on Mixed-flow Pump Performance

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Chinese Journal of Mechanical engineering 2014年第3期27卷 615-621页

作者： BING Hao CAO Shuliang State Key Laboratory of hydroscience and engineering Tsinghua University

In the mixed-flow pump design, the shape of the flow passage can directly affect the flow capacity and the internal flow, thus influencing hydraulic performance, cavitation performance and operation stability of the mixed-flow pump. However, there is currently a lack of experimental research on the influence mechanism. Therefore, in order to analyze the effects of subtle variations of the flow passage on the mixed-flow pump performance, the frustum cone surface of the end part of inlet contraction flow passage of the mixed-flow pump is processed into a cylindrical surface and a test rig is built to carry out the hydraulic performance experiment. In this experiment, parameters, such as the head, the efficiency, and the shaft power, are measured, and the pressure fluctuation and the noise signal are also collected. The research results suggest that after processing the inlet flow passage, the head of the mixed-flow pump significantly goes down; the best efficiency of the mixed-flow pump drops by approximately 1.5%, the efficiency decreases more significantly under the large flow rate; the shaft power slightly increases under the large flow rate, slightly decreases under the small flow rate. In addition, the pressure fluctuation amplitudes on both the impeller inlet and the diffuser outlet increase significantly with more drastic pressure fluctuations and significantly lower stability of the internal flow of the mixed-flow pump. At the same time, the noise dramatically increases. Overall speaking, the subtle variation of the inlet flow passage leads to a significant change of the mixed-flow pump performance, thus suggesting a special attention to the optimization of flow passage. This paper investigates the influence of the flow passage variation on the mixed-flow pump performance by experiment, which will benefit the optimal design of the flow passage of the mixed-flow pump.

关键词： mixed-flow pumps flow passage hydraulic performance pressure fluctuation model test

Simulation of large-scale numerical substructure in real-time dynamic hybrid testing

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Earthquake engineering and engineering Vibration 2014年第4期13卷 599-609页

作者： Zhu Fei Wang Jinting Jin Feng Zhou Mengxia Gui Yao State Key Laboratory of hydroscience and engineering Tsinghua University

A solution scheme is proposed in this paper for an existing RTDHT system to simulate large-scale finite element （FE） numerical substructures. The analysis of the FE numerical substructure is split into response analysis and signal generation tasks, and executed in two different target computers in real-time. One target computer implements the response analysis task, wherein a large time-step is used to solve the FE substructure, and another target computer implements the signal generation task, wherein an interpolation program is used to generate control signals in a small time-step to meet the input demand of the controller. By using this strategy, the scale of the FE numerical substructure simulation may be increased significantly. The proposed scheme is initially verified by two FE numerical substructure models with 98 and 1240 degrees of freedom （DOFs）. Thereafter, RTDHTs of a single frame-foundation structure are implemented where the foundation, considered as the numerical substructure, is simulated by the FE model with 1240 DOFs. Good agreements between the results of the RTDHT and those from the FE analysis in ABAQUS are obtained.

关键词： real-time dynamic hybrid testing large-scale numerical substructure control signal generation finite element simulation

Seasonal compensation implied no weakening of the land carbon sink in the Northern Hemisphere under the 2015/2016 El Niño

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Science China Earth Sciences 2024年第1期67卷 281-294页

作者： Fangzhong SHI Xiuchen WU Xiaoyan LI Philippe CIAIS Hongyan LIU Chao YUE Yuting YANG Shulei ZHANG Shushi PENG Yi YIN Benjamin POULTER Deliang CHEN State Key Laboratory of Earth Surface Processes and Resource Ecology Beijing Normal UniversityBeijing 100875China Faculty of Geographical Science Beijing Normal UniversityBeijing 100875China Key Laboratory of Tibetan Plateau Land Surface Processes and Ecological Conservation Qinghai Normal UniversityXining 810016China Research and Development Center for Watershed Environmental Eco-engineering Beijing Normal University(Zhuhai)Zhuhai 519085China Laboratoire des Sciences du Climat et de l’Environnement(LSCE) CEA-CNRS-UVSQUMR821291191Gif-sur-YvetteFrance College of Urban and Environmental Science MOE Laboratory for Earth Surface ProcessesPeking UniversityBeijing 100871China State Key Laboratory of hydroscience and engineering Department of Hydraulic EngineeringTsinghua UniversityBeijing 100084China Southern Marine Science and engineering Guangdong Laboratory(Zhuhai) School of Atmospheric SciencesSun Yat-sen UniversityGuangzhou 510275China California Institute of Technology PasadenaCA 91125USA Biospheric Sciences Laboratory NASA Goddard Space Flight CenterGreenbeltMaryland 20771USA Regional Climate Group Department of Earth SciencesUniversity of GothenburgGothenburg SE-40530Sweden

The recurrent extreme El Niño events are commonly linked to reduced vegetation growth and the land carbon sink over many but discrete regions of the Northern Hemisphere(NH).However,we reported here a pervasive and continuous vegetation greening and no weakened land carbon sink in the maturation phase of the 2015/2016 El Niño event over the NH(mainly in the extra-tropics),based on multiple evidences from remote sensing observations,global ecosystem model simulations and atmospheric CO_(2)*** discovered a significant compensation effect of the enhanced vegetation growth in spring on subsequent summer/autumn vegetation growth that sustained vegetation greening and led to a slight increase in the land carbon sink over the spring and summer of 2015(average increases of 23.34%and 0.63%in net ecosystem exchange from two independent datasets relative to a 5-years average before the El Niño event,respectively)and spring of 2016(6.82%),especially in the extra-tropics of the NH,where the water supply during the pre-growing-season(November of the previous year to March of the current year)had a positive *** seasonal compensation effect was much stronger than that in 1997 and 1998 and significantly alleviated the adverse impacts of the 2015/2016 El Niño event on vegetation growth during its maturation *** legacy effect of water supply during the pre-growing-season on subsequent vegetation growth lasted up to approximately six *** findings highlight the role of seasonal compensation effects on mediating the land carbon sink in response to episodic extreme El Niño events.

关键词： El Niño Seasonal compensation effect Vegetation greening Land carbon sink Net ecosystem exchange Legacy effect

Accuracy of the half-power bandwidth method with a third-order correction for estimating damping in multi-DOF systems

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Earthquake engineering and engineering Vibration 2013年第1期12卷 33-38页

作者： Wang Jinting Lü Dandan Jin Feng Zhang Chuhan State Key Laboratory of hydroscience and engineering Tsinghua University

A third-order correction was recently suggested to improve the accuracy of the half-power bandwidth method in estimating the damping of single DOF *** paper analyzes the accuracy of the half-power bandwidth method with the third-order correction in damping estimation for multi-DOF linear *** ratios in a two-DOF linear system are estimated using its displacement and acceleration frequency response curves,respectively.A wide range of important parameters that characterize the shape of these response curves are taken into *** show that the third-order correction may greatly improve the accuracy of the half-power bandwidth method in estimating damping in a two-DOF *** spite of this,the half-power bandwidth method may significantly overestimate the damping ratios of two-DOF systems in some cases.

关键词： half-power bandwidth method third-order correction damping ratio estimation error two-DOF system

Lake surface area method to define minimum ecological lake level from level-area-storage curves

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Journal of Arid Land 2013年第2期5卷 133-142页

作者： SongHao SHANG State Key Laboratory of hydroscience and engineering Tsinghua University

Lake level assessment is essential for the protection of ecosystem in shrunk or shrinking lakes. Minimum ecological lake level is the critical lake level below which there should be no human activities to further decrease the lake level, and this level can provide a certain protection for the lake ecosystem. Lake surface area method was proposed to define the minimum ecological lake storage as the breakpoint of the lake surface area-storage curve, where the curve slope equals to the ratio of maximum lake surface area to maximum lake storage. If the curve can be expressed as a simple analytical function, the minimum ecological lake storage can be calculated analytically. Otherwise, it can be calculated numerically using the ideal point method for an equivalent multi-objective optimization model that balances ecosystem protection and water use. Then the minimum ecological lake level can be estimated from the lake level-storage curve. Compared with available lake morphology analysis methods, the lake surface area method is superior in its definition of minimum ecological lake level, applicable range of lake morphology, and calculation complexity. The proposed method was applied to two representative lakes in China, including one freshwater lake (the Dongting Lake in Hunan province in Central China) and one saltwater lake (the Ebinur Lake in Xinjiang Uygur autonomous region in Northwest China). The estimated minimum ecological lake level for the Dongting Lake is 26.7 m, at which 31% of the maximum lake storage provides 87% of the maximum lake surface area. The result for the Ebinur Lake is 191.2 m, at which 24% of the maximum lake storage provides 54% of the maximum lake surface area. The estimated minimum ecological lake level balances the conflict between economical and ecological water uses, and can provide a relatively larger habitat for the lake ecosystem with relatively smaller lake storage. These results are rational compared with the results of other methods. Th

关键词： lake level assessment minimum ecological lake level lake surface area lake storage multi-objective optimization model

Numerical predictions of pressure pulses in a Francis pump turbine with misaligned guide vanes

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Journal of Hydrodynamics 2014年第2期26卷 250-256页

作者：肖业祥王正伟张瑾罗永要 State Key Laboratory of hydroscience and engineering and Deparment of Thermal engineering Tsinghua University

Previous experimental and numerical analyses of the pressure pulse characteristics in a Francis turbine are extended here by using the unsteady Reynolds-averaged Navier-Stokes equations with the shear stress transport （SST） turbulence model to model the unsteady flow within the entire flow passage of a large Francis pump turbine with misaligned guide vanes at the rated rotational speed. The S-curve characteristics are analyzed by a combined use of the model test and the steady state simulation with the aligned guide vane firstly. Four misaligned guide vanes with two different openings are chosen to analyze the influence of pressure pulses in the turbine. The characteristics of the dominant unsteady flow frequencies in different parts of the pump turbine for various misaligned guide vane openings are investigated in detail. The predicted hydraulic performance and the pressure fluctuations show that the misaligned guide vanes reduce the relative pressure fluctuation amplitudes in the stationary part of the flow passage, but not the runner blades. The misaligned guide vanes have changed the low frequencies in the entire flow passage with the change of the pulse amplitudes mainly due to changes in the rotor-stator interaction and the low frequency vortex rope flow behavior.

关键词： pump turbine misaligned guide vanes pressure pulsation rotor stator interaction numerical simulation

Sediment yield computation of the sandy and gritty area based on the digital watershed model

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Science China(Technological Sciences) 2006年第6期49卷 752-763页

作者： LIU Jiahong WANG Guangqian LI Tiejian XUE Hai HE Li State Key Laboratory of hydroscience and engineering Tsinghua University Beijing 100084 China State Key Laboratory of Hydroscience and Engineering Tsinghua University Beijing 100084 China State Key Laboratory of Hydroscience and Engineering Tsinghua University Beijing 100084 China State Key Laboratory of Hydroscience and Engineering Tsinghua University Beijing 100084 China State Key Laboratory of Hydroscience and Engineering Tsinghua University Beijing 100084 China

The Yellow River is well known as a sediment-laden river, which is the main reason that it cannot be controlled as easily as other rivers. Many researchers, such as Qian Ning et al., have found that the sediment load of the Yellow River comes mainly from the sandy and gritty area of the Loess Plateau. Therefore, it is very important to simulate the sediment yield in this area. This paper proposes a method to compute the sediment production in the sandy and gritty area based on the digital watershed model. The suggested model is calibrated and validated in the Chabagou basin, which is a small catchment in the study area. Finally, the model simulates the sediment yield of the sandy and gritty area in 1967, 1978, 1983, 1994 and 1997, which represents a high water and high sediment year, a mean water and mean sediment year, a high water and low sediment year, a low water and high sediment year, and a low water and low sediment year separately. The simulation results, including the runoff depth and erosion modulus, can well explain the "low water and high sediment" phenomena in the Yellow River basin. The total amount of the sediment production and its distribution generated by the model is very useful for water and soil conservation in the sandy and gritty area of the Loess Plateau.

关键词： the digital watershed model, the sandy and gritty area, sediment yield.

Spatio-temporal variation of net anthropogenic nitrogen inputs in the upper Yangtze River basin from 1990 to 2012

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Science China Earth Sciences 2016年第11期59卷 2189-2201页

作者： WANG Ai TANG LiHua YANG DaWen LEI HuiMin State Key Laboratory of hydroscience and engineering Department of Hydraulic Engineering Tsinghua University

The net anthropogenic nitrogen input(NANI) is an important nutrient source that causes eutrophication in water bodies. Understanding the spatio-temporal variation of NANI is important for regional environment assessment and *** paper calculated NANI in the upper Yangtze River basin(YRB), upstream of the Three Gorges Dam(TGD), from1990 to 2012, and analyzed its spatio-temporal characteristics. Over the past 23 years of the study, the average annual NANI increased from 3200 kg N km^(-2) to 4931 kg N km^(-2). The major components were fertilizer N application, atmospheric N deposition,and net food and feed N import. In the northwest high mountainous region with a sparse population, the main component was atmospheric N deposition. Fertilizer N application and net food and feed N import were concentrated in the Chengdu Plain because of the high population density and large areas of farmland. This research found that NANI increased with rapid urbanization and increasing population. The Pearson correlation results illustrated that the spatial distributions of NANI and its major components were affected by land cover/use, agricultural GDP and total population. Increasing NANI has been the major cause of the degrading stream water quality over the past 20 years and is becoming a major threat to the water quality of the TGD reservoir.

关键词： Net anthropogenic nitrogen input Yangtze River basin Land use Urbanization Water quality

Evaluating the safety of high arch dams with fractures based on numerical simulation and geomechanical model testing

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Science China(Technological Sciences) 2015年第10期58卷 1648-1659页

作者： HE Zhu LIU YaoRu PAN YuanWei YANG Qiang State Key Laboratory of hydroscience and Hydraulic engineering Tsinghua University

It is important to estimate the probability of fracture extension and its impact on the safety of arch dams with fractures. Numerical simulation and geomechanical model test were combined to evaluate the overall stability and the extension probability of fractures. Numerical simulation forecasted the dam displacement and the operating behavior based on the parameters obtained from the back analysis. Geomechanical model test was based on small block masonry and the models with or without fractures were both tested. The results show that the deformation of dams is in line with general rules at a normal water load and the extension probability of the existing fractures is very small, which has no significant impact on the global stability of dams. Moreover, the failure process of arch dams with the existing fractures in dams at overload scenarios is similar to the one without the embedded fractures, i.e., the failure crack which is not caused by the existing fractures inside comes into being on the surface of dams itself.

关键词： numerical simulation geomechanical model test safety evaluation arch dams fractures