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01 September 2022, Volume 39 Issue 9
    

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    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 0-0.
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    • SPECIAL CONTRIBUTION
  • Evaluating Winter Temperature Grade for the Middle Route Project of South-to-North Water Diversion Based on Air Temperature Chain
    DUAN Wen-gang, HAO Ze-jia
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 1-8. https://doi.org/10.11988/ckyyb.20220187
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    The freezing of water-conveying open channel in winter is a common natural phenomenon in cold regions. Once ice carapace appears in the middle route of the South-to-North Water Transfer Project, the safe flow reduces to only 30%-50% of the design flow. As temperature is the main factor driving the formation of ice carapace, the evaluation of air temperature level in winter became a key problem for water conveyance in freezing period. The interannual variations of air temperature along the main canal is revealed according to the daily average temperature and daily minimum temperature data of eight meteorological stations along the line of the Project in winter from 1951 to 2021. A concept of air temperature chain is proposed and the general mathematical expression is given based on the Lagrange particle tracking method in line with the physical process of air temperature affecting water temperature and then further producing ice carapace along the line. The National Standard Method, January’s Average Temperature Method, and the proposed Air Temperature Chain Method are used to evaluate the winter temperature level and construct the temperature order in 71 years. Results manifest that: 1) The air temperature along the main canal decreased gradually from south to north at a rate of 0.48 ℃/(100 km), and in particular, Baoding station displayed an accelerated downward trend, which made the greatest contribution to the formation of ice carapace. 2) The temperature in winter was fluctuating upwardly in general at a rate of 0.37 ℃/10 a. Severe warm winter appeared in the recent three decades and severe cold winter in the first three decades. The rising of air temperature is conducive to alleviating the formation of large-scale ice carappace. 3) The proposed Air Temperature Chain Method is superior to the January’s Average Temperature Method and the National Standard Method in predicting the formation of ice carapace. Better prediction result can be achieved by combining different time scales. Under the background of continuous global warming, the joint evaluation by January’s Average Temperature Method and Air Temperature Chain Method with 6-day data at two north stations can be adopted. 4) The thresholds of winter temperature grade obtained by the Air Temperature Chain Method with 6-day data at two north stations are given as follows. Strong warm winter: TC≥-4.0 ℃; weak warm winter: -5.7 ℃≤TC＜-4.0 ℃; normal winter: -7.4 ℃＜TC＜-5.7 ℃; weak cold winter: -9.1 ℃＜TC≤-7.4 ℃; strong cold winter: TC≤-9.1 ℃. The average value of long series TC is -6.5 ℃. The research finding is expected to offer a new reference for predicting the formation of ice carapace in the main canal.
    • COMPREHENSIVE MANAGEMENT OF RIVER BASIN
  • Basic Situation and Coupling Relationship of the Yangtze River Water Problems
    ZHANG Xiang, LIU Hao-yuan, WU Zhi-guang, ZHANG Peng, OUYANG Shuo, LI Jian, WANG Jun
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 9-14. https://doi.org/10.11988/ckyyb.20210562
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    The old and new water problems of Yangtze River intertwined as disturbed by intensifying human activities and increasingly frequent climate change. In line with the new requirements posed by the 14th Five-Year Plan and the Great Protection of the Yangtze River, we analyzed the basic situation of Yangtze River’s four water problems from a macroscopic view: water resources problem involving local water shortage, insufficient management performance and others, water environment problem including excessive total phosphorus emission and unclear characteristics of persistent organic pollutants, water ecology problem such as sharp decline in ecological capacity and biological resources, as well as water-related disaster problem like frequent extreme floods and droughts. We further revealed the external driving influences of climate change factors such as temperature increase and human factors such as hydropower development, shipping, agricultural activities, and urbanization on the development and change of the four water problems. We also expounded the internal connection and feedback mechanism among the four water problems in expectation of enhancing people’s understanding of the coupling relationship among the four water problems and improving the ability of managing the Yangtze River.
    • RIVER-LAKE PROTECTION AND REGULATION
  • Research Advances in Morphological Evolution of Lakes Connecting the Yangtze River and Its Influences
    YAO Shi-ming, HU Cheng-wei, QU Geng, CHAI Zhao-hui, LUAN Hua-long
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 15-23. https://doi.org/10.11988/ckyyb.20220304
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    On the basis of extensive review of relevant literatures in China and abroad, we summarize and analyse the research progresses on three hot issues concerning two river-connecting lakes in the middle and lower reaches of the Yangtze River, namely, the Dongting Lake and the Poyang Lake. Such issues include: water and sediment transport law, erosion and deposition evolution law, and their impacts on flood/dry regulation function. We also put forward such aspects to be strengthened corresponding to the shortcomings of current research as follows: 1) the quantitative evolution mechanism of the two lakes under natural and human influences, including the evolution of the two lakes in the period of scarce data, identification of the impact of natural factors on the erosion/deposition of the two lakes, and the natural erosion/deposition of the two lakes in the period of intensified human activities, etc; 2) forecasting the trend of long-term and wide-range erosion and deposition of the two lakes, transforming from total sediment deposition forecast of the two lakes to prediction of spatio-temporal distribution pattern of sediment deposition; 3) indicative assessment of the impact of the evolution of the two lakes on flood/dry regulation function, including indicators characterizing the flood/dry regulation function of the lakes and their responses to different scouring and silting scenarios in the future.
  • Water-Sediment Asynchrony and Transport Time of Sand Peak in Flood Season of Three Gorges Reservoir
    WANG Yu-xuan, JIN Zhong-wu, CHEN Peng, XU Quan-xi, REN Shi
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 24-29. https://doi.org/10.11988/ckyyb.20210510
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    The basic laws of water-sediment asynchrony in the reservoir area at sediment incoming moment were statistically analyzed based on the water-sediment data from main monitoring stations of the Three Gorges Reservoir in 2003-2018. The duration of sand peak transport affected by various factors during typical floods under different water levels was discussed. The regression formula for the transport time of sand peak with a good degree of fitting was also obtained via regression analysis. Results revealed that among 40 typical flood processes with peak discharge greater than 30,000 m3/s, the floods with sand peak arriving earlier than flood peak, sand peak arriving synchronously with flood peak, and sand peak lagging behind flood peak accounted for 42.5%, 42.5%, and 15%, respectively. After the operation of Xiangjiaba and other cascade reservoirs on the lower reaches of the Jinsha River, the propagation of sand peaks in the reservoir area elongated apparently. In view of the different ranges of water level fluctuation in front of dam during flood season, the rating and grouping of water level was considered to analyze the correlation between sand peak transport time and different influencing factors; furthermore, stepwise regression was adopted to establish the formula of sand peak propagation time with good fitting effect. The research results offer technical support for the sand peak dispatching of reservoirs.
    • WATER RESOURCES
  • Modeling and Application of Joint Optimal Scheduling of Cascade Reservoirs on Yalong River and the Middle and Downstream of Jinsha River Ⅰ: Potential Analysis
    ZHANG Hai-rong, YAO Hua-ming, BAO Zheng-feng, TANG Zheng-yang, HUA Xiao-jun, ZHANG Dong-jie
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 30-37. https://doi.org/10.11988/ckyyb.20210532
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    The optimal scheduling of cascade reservoir groups involves joint modeling, efficient solution, rule extraction, benefit evaluation and other aspects. With the joint optimal scheduling of cascade power stations on the Yalong River and the middle and downstream of Jinsha River as the main goal, the large-scale system decomposition coordination and discrete differential dynamic programming method are introduced for optimal solution on the basis of joint scheduling modeling, and a variety of schemes are designed for benefit analysis. Results reveal that the power generation by joint optimal scheduling of cascades is much larger than those by separate scheduling, up by 2.8% on average. Especially in high flow year, joint optimal scheduling has a significant effect on the growth of power generation. The increase in power generation in downstream Jinsha River shares more than 70% of the total increase on average. In low flow year, the increase in power generation of downstream Jinsha River is basically equal to the total increase of the three basins, reflecting the great advantage of cascade reservoirs in downstream Jinsha River in terms of large storage capacity and high water head. In the mean time, the joint optimal power generation of the middle and downstream Jinsha River is larger than that of Yalong River and downstream Jinsha River. It would be of great significance to explore the joint optimal scheduling of cascade power station groups in the middle and downstream of Jinsha River through investment mergers and acquisitions, dispatching compensation and other forms.
  • Modeling and Application of Joint Optimal Scheduling of Cascade Reservoirs on Yalong River and the Middle and Downstream of Jinsha River Ⅱ: Joint Optimal Dispatch Rules
    ZHANG Hai-rong, YAO Hua-ming, TANG Zheng-yang, WU Bi-qiong, XIN Tian-qi
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 38-42. https://doi.org/10.11988/ckyyb.20210533
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    On the basis of our previous potential analysis, we further probed into the operation rules between different reservoirs and different cascades, gave the joint optimal scheduling diagram, and analyzed the sequences of water impoundment and discharging of involved power stations to improve the utilization efficiency of water resources. Results demonstrate that the release sequence of the reservoirs before flood season should be: Lianghekou-Longpan-Jinping I-Ertan-Xiangjiaba-Baihetan-Xiluodu-Wudongde. The overall water releasing idea is to give priority to the upstream reservoirs and keep the downstream power stations such as Xiluodu and Wudongde operating at high water level as far as possible to improve the overall power generation efficiency of the basin. The order of water storage in the reservoirs at the end of flood season should be: Jinping I-Longpan/Ertan-Lianghekou-Wudongde-Baihetan/Xiluodu-Xiangjiaba. The overall water storage idea is to release the flood control capacity of the upstream reservoirs to start storage on a priority basis so as to alleviate the flood control pressure in the downstream, and the storage in wet years should be delayed accordingly.
    • WATER ENVIRONMENT AND WATER ECOLOGY
  • Estimating Ecological Water Demand of Polders in Dongting Lake Area Based on Environmental Dilution Method
    AN Qiu-xiang, LI Hong-xiang, HUANG Bing, LI Xi-chun
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 43-48. https://doi.org/10.11988/ckyyb.20210578
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    The ecological water demand in the plenty polders of the Dongting Lake are difficult to calculate due to the lack of observation data and inadequate water circulation caused by severe eutrophication. To achieve the goal of reaching grade III water quality in 25 polders in the northern part of Dongting Lake in three years, we arranged 88 surface water sampling points and monitored the concentration of ammonia nitrogen pollutants based on field survey and investigation. By using the environmental dilution method, we established a calculation model for the ecological water demand of polders and obtained the ecological water demand of polders in north Dongting Lake in the presence of water supplement as 3.216 billion m3 in comparison with the result of water exchange cycle method. The research finding is of reference value for improving the ecological environment in polders of the Dongting Lake area.
    • SOIL AND WATER CONSERVATION AND ECOLOGICAL RESTORATION
  • Spatio-temporal Evolution Characteristics of Vegetation in Water Source Area of the Middle Route Project of South-to-North Water Diversion
    LI Peng-ao, JIANG Yong-tao, QI Peng-cheng, WANG Li-mei
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 49-55. https://doi.org/10.11988/ckyyb.20210505
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    The spatio-temporal evolution of vegetation in the water source area of the middle route project of South-to-North Water Diversion is researched via data processing and analysis using ArcMap software and Unary Linear Regression Model based on the Moderate-resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) data in 2010—2019.The causes of vegetation change are also discussed in association with the data of surface temperature,precipitation and soil humidity in the water source area.Results manifest that (1) the distribution of NDVI in the source area is strongly correlated with terrain.From 2010 to 2019,the mean value of NDVI displayed a steady upward trend.(2) From 2013 to 2015,NDVI showed a notable decrease-recovery trend,which is possibly related to the extreme drought due to land surface temperature and precipitation anomalies in 2014,the restoration of precipitation and the increase in the water level of Danjiangkou Reservoir in 2015.(3) From 2010 to 2019,the areas with significant changes in NDVI mainly concentrated in low-altitude densely populated areas,indicating that the vegetation in these areas is more susceptible to climate change,urban expansion and the policy of “farm land returning to woodland and planting trees”.In addition,the rising of the water level of Danjiangkou Reservoir after the running of middle route project led to the reduction of NDVI in the reservoir area.The research findings offer scientific basis for the restoration and protection of natural vegetation in the water source area of the Middle Route Project of South-to-North water diversion.
    • ENGINEERING SAFETY AND DISASTER PREVENTION
  • A Displacement Prediction Model for Dahua Landslide
    WANG Wei, ZOU Li-fang, ZHOU Qian-yao, JIANG Yu-hang, CHEN Hong-jie, XU Wei-ya
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 56-64. https://doi.org/10.11988/ckyyb.20210462
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    A method of landslide displacement prediction based on least squares support vector machine (LSSVM) is proposed to overcome the shortcomings of traditional prediction for Dahua landslide in Lancang River basin as a case study. The original sequence is decomposed and reconstructed into trend item and fluctuation item based on time series analysis and ensembled empirical mode decomposition (EEMD). The displacement of trend item is affected by internal factors of landslide,and the least square method and polynomial equation are used for fitting prediction. The displacement of fluctuation item is affected by periodic factors such as reservoir water level,rainfall and groundwater level. The grey correlation degree method and kernel principal component analysis (KPCA) are combined to screen and reduce the dimension of input factors,and then PSO-LSSVM coupling model is used for predicting the fluctuation item. Finally,the cumulative predicted displacement is obtained by adding the predicted displacement of trend item and fluctuation item,and the model prediction accuracy is quantitatively analyzed. Results demonstrate that the EEMD-KPCA-PSO-LSSVM combined model has a sound prediction performance with higher prediction accuracy than traditional BP neural network,LSSVM and other single models.
  • Analysis of Highly Risky Rockfall Movement and Comprehensive Design of Slope Protection
    LI Yuan-liang, GUO A-long
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 65-70. https://doi.org/10.11988/ckyyb.20210557
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    A highway on the border between China and Vietnam is faced with severe risk of rockfall from high mountain, and conventional protection scheme is hardly effective.To solve this problem, the movement law of rockfall is analyzed via numerical simulation and protection design scheme is put forward.The conclusions are as follows:1) When the impact energy of rockfall far exceeds the protection capacity of engineering measures, great attention should be paid to slope design to guide the rockfall to move along controllable trajectory and reduce the energy by collision. In this research, the energy attenuation rate of rockfall after collision could reach over 80% by wide platform and rockfall trough. 2) The smaller the angle between the excavation line at the top of the slope and the tangent line of the natural slope, the more conducive it is to guide the falling rock to fall along the slope. 3) Due to complex rockfall movement track, the inward sloping platform can be used together with higher low-energy passive protection net despite its excellent rockfall retention and energy attenuation effect. Wide platform could generate regular rockfall trajectory and low bounce, hence can be used with lower high-energy level passive protection net. 4) Using waste soil as cushion could remarkably improve the effect of rockfall protection and alleviate environmental pollution, and also could beautify the landscape after planting. The research ideas and results provide reference for rockfall protection.
    • HYDRAULICS
  • Surface Tension Effects on Cavitation Bubble Collapse with Lattice Boltzmann Pseudo-potential Model
    ZOU Jian-feng, HE Xiao-long, YUAN Hao, WANG Kai-di, ZHOU Xi-dong
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 71-76. https://doi.org/10.11988/ckyyb.20210450
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    The process of near-wall cavitation bubble collapse was simulated by using Lattice Boltzmann pseudo-potential cavitation model with tunable surface tension and large density and viscosity coefficient ratio.Furthermore,the influence of surface tension and the initial pressure difference between inside and outside the bubble on the flow field distribution was analyzed,and the relationship between surface tension and maximum micro-jet and collapse pressure was investigated.The results indicate that,with the decrease of surface tension,the range of high-pressure region above the cavitation bubble increases,while the range of low-pressure region between bubble and wall decreases in the final collapse stage.The smaller surface tension intensifies the deformation of the gas-liquid interface,resulting in a more concentrated micro-jet.In addition,more surface energy accumulated during cavitation bubble collapse strengthens the collapse intensity,leading to the increase of the maximum micro-jet velocity and collapse pressure.However,with the increase of pressure difference between inside and outside the cavitation bubble,the effect of surface tension is reduced.Besides,the smaller surface tension leads to the shorter lifetime of cavitation bubble,which increases the Bjerknes force and aggravates the trend of cavitation bubbles collapse towards the wall.
  • Preliminary Research on Characteristics of Very-large-scale Turbulence Motions in Decelerating Open Channel Flow
    ZHANG Peng, DUAN Yan-chong, WANG Yong-qiang, HU Jiang, YANG Sheng-fa, LI Wen-jie
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 77-83. https://doi.org/10.11988/ckyyb.20210617
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    This study experimentally examined the very-large-scale motions (VLSMs) characteristics in decelerating open-channel flow based on acoustic Doppler current profiler (ADCP) and acoustic Doppler velocimeter (ADV) measurements. Meanwhile, the turbulence intensity, VLSMs’ wavelength and turbulent kinetic energy ratio were analyzed. Statistical evidence of the presence of VLSMs in decelerating open channel flow was presented. Moreover, its streamwise scale increased first and then decreased along with the water depth. The VLSMs still exist in the water surface area of the decelerating open channel flow and occupy about 46% of the turbulent kinetic energy.
    • ROCK-SOIL ENGINEERING
  • Dynamic Failure Mechanism and Damage Constitutive Relation of Frozen Sandstone with Initial Damage
    WANG Lei, WANG Yuan-peng, QIN Yue, SU Hong-ming
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 84-89. https://doi.org/10.11988/ckyyb.20210485
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    Uniaxial impact tests with different strain rates were carried out on -30 ℃ water-saturated sandstone with the help of split Hopkinson pressure bar to investigate the dynamic compression failure mechanism of Cretaceous frozen sandstone.Results reveal that the frozen sandstone experienced four stages of dynamic damage: linear elastic deformation,microcrack evolution,unstable crack propagation,and strain softening.The damage comes from the interactive evolution of initial macro- and micro-defects and new cracks.The change of dynamic growth factor demonstrates significant strain rate strengthening effect of sandstone’s strength and deformation.The initial damage is composed of the accumulation of macro- and micro-defects,and the dynamic total damage is formed by the coupling of damage and defects of different scales.The damage evolution of rock under uniaxial impact compression is orthotropic.The dynamic damage constitutive relationship of sandstone is modified based on the isotropic equation.Critical damage is a comprehensive quantity involving initial damage,dynamic elastic modulus,dynamic compressive strength and peak strain.The theoretical results are in good agreement with the experimental curves,with a decisive coefficients over 0.910.The present constitutive relation well reflects the strength characteristics of frozen sandstone before reaching peak.
  • Numerical Study on 3D Water-Air Two-phase Seepage Characteristics of Undisturbed Soil Based on Level Set Method
    CAI Pei-chen, QUE Yun
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 90-95. https://doi.org/10.11988/ckyyb.20210436
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    The 3D water-air two-phase seepage characteristics of undisturbed granite residual soil at REV (representative elementary volume) scale are examined by using the Level Set method based on computer tomography (CT) and AVIZO-COMSOL interactive docking technology. Results reveal that the residual air in pores mainly distributes in blocks on the pore edges, dead corners and abrupt changes of pore throats. A few main seepage channels, generally wide and straight, exist in the pores of the REV model. The two-phase seepage velocity is controlled by the tortuosity of the pores, yet with obvious advantage channels. The average flow velocity of the main seepage channel is 47.26% higher than the model as a whole. The maximum displacement resistance appears at the pore wall; the narrower the pore, the greater the resistance. The research finding offers an approach and a theoretical basis for further understanding the pore seepage law in undisturbed soil.
  • Distribution Characteristics of Two Kinds of Plant Roots and Their Effects on Surface Reinforcement of Open-Pit Mine Slope
    IU Xiang-feng, HAO Guo-liang, YU Bing
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 96-101. https://doi.org/10.11988/ckyyb.20210402
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    An ideal slope model of open-pit mine dump was established to investigate the influence of two plant roots,i.e.,Periploca sepium Bunge (shrub plant) and Conyza canadensis L. Cronq. (herb plant),on the stability of shallow slope. The west dump of Haizhou open-pit mine was selected as the research site. The distributions of root area ratio (RAR) on soil profiles at different depths (2,4,6,8,10,12 and 14 cm) were determined by using image processing technology;the tensile properties of the roots of the two plants were measured by a tension meter. Furthermore,the additional cohesion of roots on soil profiles at different depths was quantified by using the fiber bundle model. Results showed that the average RAR of the two plant roots decreased with the increase of soil profile depth,and the RAR of each individual plant root varied significantly at different soil profile depths. The relationship between tensile force and diameter of the two plant roots showed a power law function,and the tensile force of Conyza canadensis L. Cronq. root was higher than that of Periploca sepium Bunge root given the same diameter. Moreover,the additional cohesion of the roots of the two plants decreased with the increase of depth,displaying significant differences at various depths. The data dispersion of RAR and additional cohesion attenuated with the increase of root depth. In conclusion,the root systems of the two plants have obvious reinforcement effects on the slope. The safety factors of slopes reinforced by Periploca sepium Bunge and Conyza canadensis L. Cronq. increased by 5.4% and 9%,respectively.
  • Numerical Analysis of Slope Protection Effect of Root System of Different Plants Considering Hydrological Effect
    LIAO Tian-ting, JIANG Guan-lu, ZHANG Chong-lei, SHAN Yuan-chun, YE Xiong-wei
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 102-108. https://doi.org/10.11988/ckyyb.20210439
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    The aim of this research is to compare the influence of root systems of different vegetation types on water transport in slope and shallow soil-stabilizing effect under rainfall condition.The slope reinforced with three different plants’ root system and the unreinforced slope were numerically simulated under intermittent rainfall and heavy rain conditions using a secondary development of FISH programming module of FLAC3D,and the simulation results were compared with the that of centrifugal model test.The results demonstrated that root system could solidify the soil by preventing from water infiltration.Heart-root-reinforced slope has a entirely different water transport law from plain slope (unreinforced slope) which has a larger water permeation rate of the near-slope surface than that of the far-slope surface.Heart-root system has an optimum transpiration,while plate-root system better resists shallow rainfall erosion and penetration due to its wide wings. In general,heart-root system could reduce the moisture inside the slope body best.The maximum horizontal displacement of taproot,plate-root and heart-root reinforced slope reduce by 52.22%,73.68% and 70.24%,respectively.In conclusion,heart-root system has the best soil-stabilizing effect.In addition,the numerical simulation results are in agreement with centrifugal model test results,which verifies the correctness and effectiveness of the developed program,and lays a foundation for the simulation of more working conditions and more complex root types.
  • A Reliability-based Method of Borehole Pre-immersion Treatment for Self-weighted Collapsible Loess Foundation
    WANG Xiao-chan, ZHI Bin, LIU En-long, XIONG Kai-cheng, WANG Pan
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 109-117. https://doi.org/10.11988/ckyyb.20210504
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    Traditional pre-immersion method requires long immersion time with the scope of immersion treatment difficult to determine. In view of this, a borehole pre-immersion method to eliminate the collapsibility of loess is proposed in line with the law of water movement in soil based on the reliability theory, the limit state design method and the compound Poisson process principle. The deterministic model of the horizontal and vertical immersion influence range is given. On this basis, the method of determining the parameters of water immersion holes such as hole depth, hole spacing and the number of holes is given in association with Darcy’s law. Combined with a project in Tongchuan, the rationality of the proposed method is verified by borehole pre-immersion test on site at Tongchuan, and the treatment effect of the method is further evaluated through on-site drilling, on-site exploration, and indoor collapsibility test. The proposed immersion method is proved to be of short immersion time, controllable range of immersion influence via the layout of immersion holes, and sound treatment effect, which fully meets construction requirements.
  • A Model of the Relationship between Elastic Modulus and Saturation of Unsaturated Loess
    ZHENG Jie, ZHENG Hong-wei, WANG Jing-e
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 118-123. https://doi.org/10.11988/ckyyb.20210410
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    In the aim of investigating the relationship between elastic modulus and saturation of unsaturated loess,a testing method based on the suction stress theory and particle image velocimetry technique is employed to test the variation of elastic modulus with saturation of typical remolded Malan loess.The high-resolution digital images and moisture content data of flat cylindrical soil samples subjected to dessication from saturation to dry condition are obtained by this method using a self-made multi-function photogrammetric device.Meanwhile,the soil-water characteristic curve and Poisson’s ratio of the samples are measured by pressure plate instrument and uniaxial compression instrument,respectively.Furthermore,the elastic modulus of unsaturated soil with different water content are calculated based on the suction stress theory and the stress-strain relations in polar coordinates.The test data of samples with different dry densities during air drying process indicates that the elastic modulus of Malan loess samples increase exponentially with the decrease of saturation.A mathematical model for the relationship between the elastic modulus and saturation degree is proposed.
    • HYDRAULIC STRUCTURE AND MATERIAL
  • Influence of K2O/Na2O on Early-age Shrinkage and Cracking of Different Cement-based Materials
    LI Yang, ZHANG Hui, JIANG Ke, YUAN Jun, YIN Hai-bo
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 124-130. https://doi.org/10.11988/ckyyb.20210585
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    The total alkali content of low heat Portland cement, medium heat Portland cement and ordinary Portland cement were adjusted to 1.2% by adding Na2SO4 and K2SO4 respectively, in which the K2O/Na2O (by weight) were in the range of 0.4-13.7. The influence of alkali of different K2O/Na2O on shrinkage properties and cracking properties of cement-based materials were explored. Besides, with the help of microcalorimetry, scanning electron microscopy and energy dispersive spectroscopy, the influence mechanism of alkali of different K2O/Na2O on shrinkage properties and cracking properties of cement-based materials was revealed. The results show that with the increase of K2O/Na2O, the autogenous shrinkage and drying shrinkage of low-heat and ordinary Portland cement intensified, while those of medium-heat cemet first decreased and then increased, and the cracking sensitivity of different cement-based materials always increased. The difference in shrinkage properties caused by K2O/Na2O was related to the hydration process of cement-based materials. The difference in cracking sensitivity was not only related to shrinkage properties, but also affected by the morphology of hydrated calcium silicate (C-S-H), calcium hydroxide (CH) and the enrichment of elements in the interfacial transition zone (ITZ).
  • Plastic Damage Performance of Recycled Concrete Based on ABAQUSY
    AO Ze-liang, CUI Ting-ting, DANG Fa-ning, WEN Shuo, LINGHU Tian-jing, QI Ya-lun
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 131-136. https://doi.org/10.11988/ckyyb.20210496
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    In line with the principle of Sidoroff energy equivalence,the key parameters of CDP model such as plastic damage factor,inelastic strain,and cracking strain were studied. A meso-structure model of recycled concrete was designed based on random polygonal aggregate,old mortar,new mortar,aggregate-old mortar interface,old-new mortar interface and aggregate-new mortar interface. Some crucial compression and tension properties of recycled concrete were studied,including damage development process,stress level in all directions,failure forms,and damage values. The calculation results were compared and analyzed with test results. Research shows that the damage factors based on the principle of energy equivalence is suitable for ABAQUS modeling,and this modeling method is concise and of good convergence. The cloud diagram of compression damage of recycled concrete displays V-shape,while tension damage I-shape,and the tensile and compression damage values both reached 0.956. The simulation calculation results are in good agreement with the test results,indicating that the mesoscopic model of recycled concrete based on random polygonal aggregates is rational.
    • INFORMATION TECHNOLOGY APPLICATION
  • Research Hotspots and Trends of Water Eco-environmental Governance in China Based on Bibliometric and Visual Analysis
    WANG Yue-han, HUANG Yu-lu, XIA Yu, ZHENG Jia-xi
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 137-143. https://doi.org/10.11988/ckyyb.20220218
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    To understand the research trend of China’s water eco-environmental governance, the relavant research papers indexed by the Web of Science database from 2004 to 2022 are examined via visualization approach using bibliometric tool Citespace. The core researchers, research hotspots and research trends in China are analyzed in emphasis. Results reveal that researches on the following aspects will be deepened: the evolution of water ecological environment, the eco-environmental impact of water projects, the water pollution control in river basins, the simulation of water environment,the protection and restoration of water ecology, the green sustainable science and technology and the biodiversity protection. Core researchers mainly come from universities and research institutes whose cooperation is conducive to the coordinated governance among water resources, water ecology, and water environment. Core topics of the researches lie in how to deal with the impacts of pollution, climate change and vegetation dynamics on waters. The construction of water pollution control evaluation system in plateau and arid areas, the predicaments of water eco-environmental governance posed by climate change, and the innovations and deficiencies of management and policy are the research fronts. In addition, logistic regression analysis, classification tree and other calculation models and empirical methods are current trends.
    • NUMERICAL MANIFOLD METHOD BASED ON INDEPENDENT COVERS
  • Analysis of Thin Curved Beam and Curved Shell with Exact Geometry Using Piecewise-defined Series Solutions
    SU Hai-dong, HAN Lu-chao, XIE Zhi-qiang
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 144-151. https://doi.org/10.11988/ckyyb.20210697
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The numerical calculation of thin beam, plate and shell involves the fourth-order differential equation about deflection whose difficulty lies in constructing approximation functions with C1 continuity. In the meantime, due to the complexity of the governing equation, the thin curved beam and curved shell are usually simulated approximately by using straight beam or flat plate elements, which is prone to generate geometric errors and then brings errors in mechanical analysis. In our previous study, manifold method based on independent covers is used to analyze curved beam and shell with exact geometry based on the assumption of thick beam and shell. On this basis, the C1 continuity of the piecewise-defined series solutions of the new manifold method is discussed. The thin curved beam and shell with exact geometry is analyzed based on Euler-Bernoulli beam theory and Kirchhoff-Love shell theory, and the complexity of derivation of geometric formula is overcome. The calculation formula of thin curved beam is given in detail, and the process of thin curved shell is briefly described. The examples in previous study are recalculated under the assumption of thin beam, plate and shell, which verifies the effectiveness of the proposed method. Compared with the assumption of thick beam, plate and shell, the method saves about 30% of the degree of freedom. Meanwhile, the research demonstrates the potential of solving the fourth-order differential equations by applying manifold method based on independent covers.
  • Rigid Connection Between Plate Shell Elements and Solid Elements in the Manifold Method Based on Independent Covers
    SU Hai-dong, WEI Yu-xia, HAN Lu-chao, XIE Zhi-qiang
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 152-158. https://doi.org/10.11988/ckyyb.20220404
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    In Finite Element Method, the connection between plate shell elements and solid elements needs special treatment, and their meshes at the connection must be matched, which brings some inconveniences. In our previous research, the piecewise-defined series solutions for the numerical analysis of beam, plate and shell are proposed by using manifold method based on independent covers. On this basis, the rigid connection between plate shell elements and solid elements is studied in this paper. The solid calculation mode is also adopted in the analysis of plate and shell which are naturally connected with the solid element through the overlapping area of the covers. In view of the characteristic of arbitrary connection of independent covers, the plate or the shell is inserted into the solid to form the overlapping area of the covers. The solid and the shell can be meshed separately in no need of mesh matching at the connection, which is very conducive to the preprocessing work. Highly precise results can be obtained when the mesh division reaches a certain density. The effectiveness of the method is verified by examples of a cantilever beam with variable sections, and a spherical shell with a solid base. The accurate geometry of the intersection curve between the curved shell and the solid is also preliminarily demonstrated. The three-dimensional elastic matrix of the new method is also modified.
  • Solving Geometric Nonlinear Problems in Fixed Meshes of Independent Covers
    SU Hai-dong, DONG Peng, XIE Zhi-qiang
    Journal of Changjiang River Scientific Research Institute. 2022, 39(9): 159-166. https://doi.org/10.11988/ckyyb.20201111
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Using Manifold Method based on independent covers, or piecewise-defined series solutions based on manifold idea, a novel method of solving geometric nonlinear problems in fixed meshes is proposed. In the current configuration, the material point passing through each space point is paid attention to. Through the series solutions, the position of the material point in the previous step is traced backwards, and its stress, velocity and other physical quantities are obtained. A new series is formed as the initial values of the current time step using the least square method, hence the Lagrangian governing equation can be solved in fixed meshes. After each step, the material configuration is updated, that is, the integral region in the fixed meshes (independent covers) is updated so as to obtain the accurate material boundaries. The “small block” in the boundary meshes is processed by cover merging, and the information to the new mesh is transmitted through the “small block”. Some examples such as the large deformation of elastic body and the rotation of rigid body are given to verify the effectiveness of the method. The proposed method combines the advantages of Lagrangian method in tracking material points, simplicity of the governing equation, accurate boundary description, and of Eulerian method of undistorted meshes, and in the meantime avoids the defects of the two methods. The research finding lays a foundation for the next step adaptive analysis of solving geometric nonlinearity in fixed meshes.
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Founded: 1984
Publication Frequency: Monthly
Governing Body: Changjiang Water Resources Commission, Ministry of Water Resources
Sponsor: Changjiang River Scientific Research Institute, Changjiang Water Resources Commission
ISSN 1001-5485
CN 42-1171/TV
Postal Distribution Code: 38-147
Subscription: Available at post offices nationwide
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