Abstract:The torrential rain on July 20, 2021 in Zhengzhou was one of the heaviest disasters in history. By using the observation and re-analysis data, the characteristics and main causes of the torrential rain are analyzed via statistical methods, such as the composite analysis and anomaly analysis. The results show that this torrential rain event was characterized by the extremely strong sudden, short-time and heavy rainfall, and prominent extreme.For the atmospheric pressure of 200.hPa, there are abnormally strong and stable high-altitude troughs and high-altitude cold vortices, which make the upper layers above the rainstorm area have a strong divergence condition. Moreover, the western Pacific subtropical high was significantly strong and shifted northward. Under the joint effect of the Typhoon “In-Fa” and “Cempaka”, the moisture transport and its convergence were extremely strong over Zhengzhou. The echoes over Zhengzhou are developing vigorously, and convective echoes are continuously converging, showing an obvious “train effect”. Additionally, the topography of the Fu-niu Mountain and the Tai-hang Mountain also contributed to the low-level convergence and ascending motion over Zhengzhou, and played an important role in the increase of precipitation. Therefore, the general circulation and extremely strong water vapor conditions in high, medium and low airs as well as the amplification of local topography were all beneficial to the development of the heavy rain, leading to the occurrence of extreme flood-causing torrential rain event in Zhengzhou on July 20, 2021.

Abstract:Accurate short-term precipitation forecasts are an important basis for improving the capacities for the forecasting of urban rainstorms, urban floods, and small and medium-sized river floods, and disaster risk prevention and control. In order to improve the accuracy of short-term quantitative precipitation forecasts (QPF), a short-term (0-12.h) QPF model based on the optimization fusion method of multi-model forecasts is developed. The developed model system mainly includes four modules: a single model-based quantile mapping correction module, a real-time optimization module based on model forecasts correction, a real-time fusion module of optimized forecasts and quantile mapping correction module of fused forecasts. By taking the Henan Province as a test region, the developed model is applied and tested for the short-term quantitative precipitation forecasting. The results show that the developed model performs well, and the distribution and intensity of the precipitation forecasts using the new approach are much closer to the observations than the traditional methods; the developed model forecast is able to forecast the precipitation intensity and its cover area of the “7·20” rainstorm in Zhengzhou for 6 hours in advance; the forecasting accuracy of the developed model is much higher than the other traditional models through the intercomparing of rainfall predictions from January to September, 2021, and the forecasting accuracy increases gradually as the forecasting lead-time approaches the rainfall event.

Abstract:Based on the multi-source observation and reanalysis data, the characteristics and main causes of the flood-causing rainstorm in May, 2019 in the middle-lower reaches of the Yangtze River were studied by using the synoptic diagnostic analysis method. The results indicated that the extreme rainstorm with the characteristics of mesoscale and stage was formed by the accumulation of continuously short-time heavy precipitation under the stable "low in the west and high in the east" weather background. The mesoscale convective system directly causing the extreme rainstorm was constantly regenerated and moved eastward in the front of the low-level jet with obvious "train effect" and quasi-static features. Continuously favorable water vapor and convective instability were provided by theextremely strong low-level jet and ultra-low-level jet. In particular, the high humidity of the whole layer, low lifting condensation height and large warm cloud thickness were conducive to improving theprecipitation efficiency and producing the short-term heavy precipitation with high rain intensity. The high- and low-level jet coupling was an important dynamic mechanism for the occurrence and development of heavy rainfall, and the strong vertical wind shear area has a good correspondence with the heavy rainfall area.

Abstract:Taking the upper and middle reaches of the Huaihe River (above Bengbu Station) as the study area, seven flow indicators including the high flow, average flow and low flow are adopted to characterize the features of runoff changes and investigate the influences of climate change and human activities on the runoff characteristics at different time scales. Firstly, the Mann-Kendall trend test and the sliding Ttest are used to identify the mutation year of each flow index. Secondly, the derived differential equation of flow indicators change is used to improve the original method based on the Budyko hypothesis, so as to quantitatively identify the contribution rate of climate change and human activities to the change of runoff. Finally, the driving mechanism of human activities on changes of runoff characteristics is analyzed by constructing a land-use transfer matrix. The results show that most of the flow indicators in the upper and middle reaches of the Huaihe River show a downward trend after mutation years. Among them, the average flow indicators declined most significantly, ranging from 2.25% to 44.25%. High flow indicators, floodseason runoff depth and climate indicators have the highest correlation, with a correlation coefficient of 0.859~0.987, while low flow indicators and non-flood season runoff depth have a low correlation. Climate change and human activities make most of the flow indicators show a downward trend, among which human activities are the dominant factor, and their contribution rates at Xixian, Wangjiaba, Lutaizi, and Bengbu stations are from 87.55% to 98.46%, 80.91% to 88.50%, 80.42% to 92.42% and 83.23% to 99.99%, respectively.

Abstract:To provide substantial information of extreme water level fluctuations (EWLF) on thermal stratification at Lake Qiandao, the DYRESM model was used to simulate water levels at different scenarios with lack of observed water temperature. This study set up two scenarios including one with EWLF (scenario 1) and the other one with normal hydrological condition (scenario 2) to compare their vertical structure of water temperatures. Based on Lake Analyzer, the depths of top and bottom of thermocline, thermocline thickness and Schmidt stability were calculated for both two scenarios. The results show that the water was mixed during November 20th 2013 to March 23th 2014 in scenario 1 and was mixed during December 5th 2013 to March 16th 2014 in scenario 2. The vertical water temperature structure followed a pattern of “mixed layer-thermocline-hypolimnion (30-40 m)-thermocline-hypolimnion” from top to bottom in scenario 1 and it followed a pattern of “mixed layer-thermocline-hypolimnion” from top to bottom in scenario 2 with the same meteorological conditions. The average water level in scenario1 was less than that in scenario 2 by 2.24 m. Schmidt stability in scenario 1 was also less than that in scenario 2 by 119.19 J/m2, showing that the extreme low water level will significantly reduce the water stability.

Abstract:Aiming at the serious problem of confluence overflow pollution in Beijing sub-center section of the North Canal, this paper calculated the river pollution carrying capacity of the overflow event by means of monitoring and simulation and selected the non-deterioration of the water quality of the receiving water body in the outlet cross section as the management goal. The frequency of exceeding standard was taken as the CSO control index and the results were compared with those taking the overflow frequency as the CSO control index. The results show that the average annual overflow frequency of each outlet from 2013 to 2017 is 7 to 9, and the average overflow volume is 0.142.7 million m3. There were 19 rains, of which 10 overflowed in 2017. All overflow events exceeded the receiving capacity of the river water body. Taking the overflow frequency and exceeding standard frequency as CSO control indexes, the input-output ratio was the best when the valued of frequency was set as 3 times. The corresponding regulation and storage volumes were 18.116 m3 and 13.899 m3 respectively, the control rate of annual overflow volume can reach 52% and 44%, and the load control rate of overflow pollution can reach 59% and 51%. Using the exceeding standard frequency as the control index can make full use of the water environment capacity, reduce the scale of CSO treatment project, and enrich the engineering measures.

Abstract:This study conducted a three-year monthly survey of zooplankton and environmental factors in typical Dazong Lake from January 2017 to December 2019, in order to explore the succession characteristics and driving factors of zooplankton community in Dazong Lake and comprehensively evaluate its water quality after the stable operation of water delivery project. The results show that 49 species of zooplankton were identified in Dazong lake during the survey, including 33, 9 and 7 species of rotifers, cladocerans and copepods respectively. The interspecific connectivity statistics show that the dominant species in Dazong Lake showed a significant positive correlation overall, and the correlation increased year by year, which meant the zooplankton population structure tended to be stable. Average density was 623.17 per liter, showing a downward trend, and the average biomass was 1.63 mg/L, showing an upward trend. Compared with rotifers, the proportion of cladocerans and stilts gradually increased. The results of RDA redundancy analysis show that chlorophyll a, total nitrogen and water temperature were important factors affecting the succession of zooplankton species in Dazong Lake. The organic pollution of Dazong Lake was evaluated by Shannon-Wiener diversity index, Margalef richness index and Pielou evenness index. The results were low pollution and the B/Tindex was consistent with the results of TLI eutrophication evaluation, thus Dazong Lake was in a medium eutrophic state. Zooplanktons have a good response to the changes of environmental factors in Dazhong Lake, which can be applied to the evaluation of water ecological status in the lake area.

Abstract:To evaluate the differences of tidal bore generation by existing methods and propose the solution strategies such as mesh size and turbulent model, a series of numerical tests were carried out with the CFD method. The tide bores were generated by discharge method and boundary method, respectively, and by comparing the hydrodynamic characteristics, the influences of mesh size and turbulent model on the tide simulation precision were investigated. The results show that under the condition of the same boundary flow discharge, the tidal bores generated respectively by discharge method and boundary method have almost the same water surface variations, velocity distributions and velocities of bore propagation. Besides, the influence of mesh size on simulation results is weak when the mesh size is not larger than 0.100H(tidal bore height). Compared with the standard k-εmodel, RNG k-εmodel is more suitable for modelling the tidal bore.

Abstract:A scaled 4-pile jacket wind turbine model was used to study the impact of scour holes on the jacket stiffness. The scouring process was simulated by controlling the occurrence sequence of scour holes and different scour depths of jacket foundation and this paper investigated the influence of local scour holes on the distribution of internal forces and stiffness of jacket foundation under static load. The results show that: when the load is small, the influence of local hole within 1.5D (Dis the pile diameter) on the static stiffness of jacket is small; But the impact of scour hole on the static stiffness increases gradually with the increase of load, because with the increase of load, the axial force of the back-row pile gradually shifts from compression to tension, which leads to the stiffness decreaseof the pile. For the resonance frequency of jacket, the study shows that when the depth of the scour hole is greater than 1D, jacket resonance frequency started to decrease; At this time, any pile with a deeper hole will cause the resonance frequency to drop; When the local scour depth is 1.5D, the first-order resonance frequency of the wind turbine decreases about 3.2%, while the resonance frequency of the wind turbine decreases by about 6.3% when the scour depth is 2D. When the shape of scour hole is conical and the depth of local scour is kept unchanged, the change of the scour hole slope will cause a small change in the resonance frequency of jacket wind turbine.

Abstract:In order to promote the intelligent and automatic development of optimal design of U-shaped aqueduct, a structural optimal design system for the U-shaped aqueduct was proposed, which combines the parametric finite element program and the intelligent optimization algorithm. Firstly, based on the large-scaled finite element program HSNAP, a parametric modelling module was developed for establishing 3D parametric model of aqueduct. Then, the paralleled whale optimization algorithm was implemented with the multi-core parallelization technology for the optimization. Taking a U-shaped aqueduct project as an example, under the condition that the strength and geometric constraints of aqueduct were satisfied, the geometric parameters of aqueduct were optimized with the minimum amount of concrete as the optimization objective. The results show that the optimized scheme can meet the safety requirements of the structure and has significant economic benefits compared with the original design scheme.

Abstract:In order to study the movement and migration of fine particles in piping of embankment foundation due to the flood transit, the sinusoidal water head was used to simulate the flood condition in the laboratory piping test of gap-graded non-cohesive soil. The piping rule under constant water head was used as the control group and the migration of fine particles during piping was tracked by the colored sand. The variation law of permeability coefficient, hydraulic gradient and the step-change of fine particle loss in samples with different content of fine particle and different pore ratio were analyzed according to the test results. The results show that under the variable water head, there is countercurrent motion in the descending section. The loss of fine particles is mainly concentrated downstream. Compared with the constant water head, variable head loses more fine particles and the migration channel runs through a larger area under the same test conditions. In addition, the larger the content of fine particles is, the smaller the pore ratio is, the larger the maximum hydraulic gradient difference is, and the more the loss of fine particles is.

Abstract:In view of the lack of considering the temperature component in the statistical analysis of the horizontal displacement of the concrete faced rockfill dam (CFRD), the water pressure component is derived from the Boussinesq solution and it has been proved that the horizontal displacement in the typical section of the dam is directly proportional to the reservoir water level. The expression of the aging component is derived based on the Merchant rheological model, the aging relationship of the periodic non-monotonic increase of rock fill is established and the temperature component is added by the form of measured temperature. Thereafter, a modified hydrostatic thermal time (MHTT) model is proposed as the statistical model of internal horizontal displacement of CFRDs. The results of a case study show that the MHTT model has not only a better data interpretation ability than the HTT model and HT-JU model, but also a strong ability to interpret the physical mechanism of horizontal displacement of CFRDs.

Abstract:Through the large-scale model test of cemented earth dam, the velocity distribution and the dam erosion process of cemented earth dam under the flood overtopping were analyzed to verify the feasibility of non-failure overtopping of cemented earth dam. The test results show that the unconfined compressive strength of cemented soil within the model is more than 4.MPa after 28 days. When the maximum water head at the crest of cemented earth dam is 55.cm, the downstream slope ratio is 1∶2 and the maximum velocity reaches 5.6.m/s, there is no collapse failure after the overtopping scouring for 44.h. After the overtopping scouring, the maximum erosion depth of downstream dam slope is 10.cm and the average erosion depth is only 1.07.cm, thus the cemented earth dam can effectively prevent the collapse caused by the overtopping scouring of flood.

Abstract:This paper focus on the mechanical properties of the surrounding rock (sandstone) in the chamber of Chongqing Panlong Pumped-Storage Power Station. Conventional triaxial compression instantaneous tests under different confining pressures were first performed using a servo-controlled triaxial testing machine for rocks, based on which a macroscopic elastoplastic constitutive model was developed and validated. The testing results show that with the increase of confining pressure, the compaction stage caused by the progressive closure of initial voids and microcracks becomes less and less obvious, and the nonlinearity disappears gradually.In addition, the peak strengths of rock specimen increase with the confining pressure, ranging from 84.8 MPa under uniaxial compression to 168.5 MPa under the confining pressure of 10 MPa. There presents a satisfactory linear relationship between peak strengths and confining pressures, from which we derive the material cohesion 15.2 MPa and the friction angle 52 degrees. Numerical results show that the proposed model containing a unified hardening/softening function can describe quite well the fundamental mechanical behaviors of the investigated sandstone, which demonstrates the feasibility of the proposed constitutive model.

Abstract:In order to evaluate the safety of the repository (disposal container, buffer material and surrounding rock), an unsaturated Thermo-Hydro-Mechanical (THM) fully coupled numerical model was built to conduct the unsaturated multifield-coupled numerical simulation. Based on the Comsol Multiphysics platform, the high-level radioactive waste repository was simulated for 500 years, with the basis of experimental data from the candidate area of the Beishan high-level radioactive waste repository in China and the Gaomiaozi bentonite. Results of the coupled simulations were compared with those of uncoupled simulations, and the parametric sensitivities of permeability, heat transfer coefficient and underground water depth were analyzed. The results show that temperature in coupled simulation is 13 degrees Celsius higher than that in uncoupled simulation. When the water table rises from 0 m to 1,000 m, the time it takes to fully saturate the buffer material will fall from 703 to 28 years. The saturation time of the buffer material will increase from 28 years to 250 years when the permeability of the surrounding rock decreases by five orders of magnitude. Each physical field is coupled to each other, which affects the long-term stability of the repository.

Abstract:In order to investigate the strength and deformation characteristics of soilbags filled with expansive soil, a series of unconfined compression strength tests were conducted. The evolution of the stress-strain relationship during the loading process of soilbags was subsequently analyzed. In addition, the feasibility of falling weight deflectometer used on the construction quality inspection of soilbags filled with expansive soil was verified, and the influence of the compaction duration of small-sized plate vibration rollerand the number of compactionof small-sized drum vibration rolleron the resilient modulus of soilbags filled with expansive soil was further investigated. The test results show that the initial stage with relatively low deformation modulus from the stress-strain curve can be successfully eliminated through simple compaction when soilbags are used for treating expansive soil channel slope. In addition, the falling weight deflectometer can be used to inspect the construction quality of soilbags filled with expansive soil. Furthermore, it is suggested that the soilbag filled with expansive soil should be compacted by use of a small-sized drum vibration roller during the construction on the expansive soil channel slope, with the number of compactionno less than 4 times.

Abstract:In order to study the influence of joint inclination and penetration rate on the mechanical properties of rock-like material, by selecting the prefabricated joint rock-like materials as the research object, a series of uniaxial compression tests on two sets of mortar samples considering different joint inclined angles and penetration rates were conducted. The results show that when the joint inclination angle is0°, the peak strength, peak strain and elastic modulus of the specimens decrease with the increase of the joint penetration rate and the specimens with different penetration rates all show the overall tensile failure. When the joint penetration rate is the same, with the increase of the joint inclination angle, the peak strength of the sample shows a V-shaped change trend. The peak strain of the sample first decreases, then increases and then decreases, while the elastic modulus first increases, then decreases and then increases. The two deformation properties show a good corresponding relationship. Furthermore, the results show that the joint penetration rate plays a major role in the strength, deformationand failure of the specimen compared with the joint inclination angle.

Abstract:The current monitoring system of dam rolling quality relies on the two-dimensional visual interface, which has the disadvantages of poor visual interaction level, and the C/S (client/server) architecture cannot realize the cross-platform query and sharing of rolling construction information, resulting in the shortcomings of low feedback-control level. In this study, a three-dimensional intelligent monitoring system of construction quality for the earth-rock dam is constructed under the B/S architecture by coupling the hierarchical loading mechanism based on the level of detail(LOD) technology and augmented reality technology. The application results in the Lianghekou Hydropower Project show that the system established in this study can realize the intelligent monitoring of the rolling process, the efficient and smooth cross-platform interactive query, the immersive visual display of construction information, and the intelligent evaluation of rolling quality, which effectively improves the intelligent level of the construction process.

Abstract:Aiming at the problems that the existing dynamic equivalent modeling based on component mechanism may lead to the complex model structure and the difficult parameter identification, by introducing a feature modeling method with simple model structure and easy engineering implementation, this paper models the dynamic equivalence of the lower-level grid (or regional grid) online and realizes the hierarchical and zonal modelling of modern power grids. Firstly, the input and output variables of the characteristic model are determined by theoretical analysis and simulation comparison. Voltage is selected as the input variable, while the real part and imaginary part of current are selected as output variables. Then, to address the problem that the operating conditions of actual grid change at any time, the recursive least squares algorithm is used to identify the slowly-time-varying parameters of the characteristic model, when the component mechanism model undergoes slow time-varying. The results show that the fitting error of this kind of characteristic model is small, and the parameters have high stability.