Abstract:To define the inner outline of a tunnel cross-section, a novel Wu’s two-parametric curve(heteromorphic ellipse)was proposed in this study, based on the iso-concentration curve equation of a conservative substance under the condition of steady point source from river center. The heteromorphic ellipse is a completely continuous and derivative-smooth curve, represented by the maximum height(H)and the maximum width(W)of the tunnel cross-section. Taking the compressibility factor θ=W/H as the criterion, the shape classification of H-type, Standard-type and W-type for the heteromorphic ellipse were given. The cross section, the theoretical calculation formula of water surface width, flow area, wetted perimeter, hydraulic radius and other hydraulic elements were deduced for the free-flow tunnel. The theoretical calculation formulas and curves for the velocity and the flow rates were found to be applicable to different specifications of the cross-section size, compressibility, roughness and gradient. Case studies show that the characteristic values of hydraulic elements have a high degree of anastomosis for the equivalent heteromorphic ellipse and the Ⅱ-type horseshoe(with chamfer)cross-section in a free-flow tunnel. Therefore, the proposed heteromorphic ellipse cross-section can be a novel application in water-conveyance tunnels with great academic research value.

Abstract:Through the integral model test of the Rumei Hydropower Station, characteristics of flow pattern, water cushion depth, hydrodynamic pressure and velocity distribution at the downstream channel were studied. Optimization schemes of adding a subsidiary dam and lowering the bottom elevation of the plunge pool were compared. The results show that the effect of adding a subsidiary dam downstream the plunge pool is closely related to the height of the subsidiary dam, the discharge and the width of the valley, and can worsen the joint of the outflow and the downstream channel. Lowering the bottom elevation of the plunge pool has little influence on the downstream connection, and it can effectively increase the depth of the water cushion and reduce the near-bottom hydraulic indexes of the plunge pool.

Abstract:Aiming at the influence of high sediment-laden flow on the uplift characteristics of a plunge pool slab, the distribution, magnitude and spectrum characteristics of the uplift force under different sediment concentrations was studied by model test. The results show that the distribution of the uplift force on the plunge pool in sediment-laden flow is similar with that in clean water. For each flow rate, the mean value of the uplift force increases with the increase of the sediment concentration, and basically shows a linear function with a slope between 0. 17 and 0. 22. The standard deviation of the uplift force increases first and then decreases with the increase of sediment concentration, and the standard deviation of the uplift peaks at the critical sediment concentration of 183 kg/m³. The pulsation of the uplift force is in the low frequency range of 0~3 Hz, but compared with the clean water, the frequency band width of the power spectrum increases and the power spectral density in the high frequency domain increases when sediment is added to water. The time integral scale of the flow increases first and then decreases with the increase of sediment concentration.

Abstract:The LBM pseudo-potential model was used to simulate the cavitation bubble collapse process in the near-wall region. The effects of different vapor and liquid phase viscosity coefficients on the maximum micro-jet flow velocity, collapse pressure and collapse time during the cavitation bubble collapse process were analyzed. The results show that under the same liquid phase viscosity coefficient, when the viscosity coefficient of the vapor phase is changed, the maximum micro-jet flow velocity, collapse pressure and collapse time remain unchanged. When the vapor viscosity coefficient remains unchanged, the maximum collapse pressure and the maximum micro-jet flow velocity decrease with the increase of the liquid phase viscosity coefficient, while the maximum collapse time increases with the increase of the liquid phase viscosity coefficient.

Abstract:The Songzi River is one of the main channels connecting the middle Yangtze River(Jingjiang)and the Dongting Lake. Since 1950s, hydraulic projects such as artificial cutoffs in the lower Jingjiang River, the Gezhouba Dam, and the Three Gorges Reservoir have been implemented successively, leading to periodic decrease of water and sediment diversion of the Songzi River. Hydrological data, channel topography, and remote sensing imagery were used to analyze the temporal change of runoff and sediment load, channel morphology at the inlet and tail zone from 1951 to 2016. Both grid and cross-section topographical methods were applied to calculate the temporal change of the local erosion and deposition amount from 2003 to 2011 and from 2006 to 2009, respectively. The results show that from 1951 to 1980, the inter-annual changes in runoff and sediment load were relatively stable. After the impoundment of the Gezhouba project in 1981, the amount of sediment load in the Songzi River decreased rapidly, from 50. 98×10⁶ t to 36. 11×10⁶ t, about 29. 1% from 1981-1990 to 1991-2000. After the impoundment of the Three Gorges Reservoir in 2003, the amount of sediment load was continuously reduced, but the runoff reduction was delayed due to riverbed erosion and increased water level in non-flood seasons. From 1987 to 2018, the area of the Yanggezhou Island at the inlet zone of the Songzi River decreased by 0. 4 km² with a reduction rate of 4. 2%, but the variation of the channel morphology of the inlet zone was little.

Abstract:To quantitatively analyze the variation of river network structure and water system connectivity caused by urbanization, the river network density, water surface rate, river network complexity, river network structural stability, river network connectivity, and hydrological connectivity of the Qinhuai River Basin in 1990, 2000, 2010 and 2015 were calculated. The evolution process of the water system structure and connectivity in the Qinhuai River Basin were obtained. The statistical method is used to obtain the relationship between the water system structure index and the water system connectivity. The results show that the river network density and water surface rate in the Qinhuai River Basin have been decreasing continuously in the past 25 years. The river channel is characterized by main trunking. The overall scale of the river network in the basin is shrinking. The water system connectivity variation is consistent with the overall trend of river network structure variation, both showing a decreasing tendency. The change is significantly correlated with the water surface rate, river network density and river network complexity.

Abstract:Based on abundant and detailed basic data, a hydrological and hydrodynamic model was established. The influence of the urban drainage of Suzhou, Wuxi and Changzhou on the water level of the Jiangnan Canal under the current scheduling scheme, optimal scheduling scheme and no scheduling scheme was analyzed. The characteristics of urban flood and regional drainage were also analyzed. The results show that the current scheduling scheme can reduce the urban flood peak water level of Changzhou, Wuxi and Suzhou by 0. 28-1. 10m compared with the no scheduling scheme, revealing that the large surrounding of the urban area can effectively reduce the flood water level and ensure the safety of the urban area. However, the water level of the Jiangnan Canal increases with the rainfall and the drainage in Suzhou, Wuxi, and Changzhou. If the optimal scheduling scheme of which the beginning pumping stage rises by 0. 17-0. 30m appropriately is adopted, the water level of the canal will decrease by 0. 00-0. 12m. It shows that on the premise of not greatly increasing the urban flood risk, the amount of urban drainage can be appropriately reduced to decrease the water level of the Jiangnan Canal and the relationship between urban and regional flood control can be coordinated.

Abstract:In order to explore the applicability of the quantile regression model in non-stationary frequency analysis, the quantile regression model and the GAMLSS model were used to analyze the non-stationary frequency of the annual maximum flood series at five stations in the Weihe River Basin and the Pearl River Basin. Qualitative analysis of the probability coverage shows that the goodness of the fitting effect for the quantile regression model is better than that of the GAMLSS model. Quantitative analysis of the Filliben correlation coefficient shows that the GAMLSS model has a better fitting effect but the advantages are not obvious. Comprehensive analysis shows that the overall fitting goodness of the quantile regression model is better than the GAMLSS model.

Abstract:Through the combination method of physical model and numerical model, the hydrodynamic load, structural dynamic characteristics and flow-induced vibration characteristics of a large-span upwelling arch gate were studied systematically. The strong resonance phenomenon and causes of flow-induced vibration of the gate structure are revealed. Aiming at the problem of strong vibration, structural optimization was carried out by reducing the size of the projected area of the inclined plane downstream of the gate and the small cross beam at the bottom of the gate. The results of the optimized field prototype measurement show that the proposed scheme can effectively control the harmful vibration of the gate, which makes the gate run stably, safely and reliably, and the correctness of the physical model test is verified.

Abstract:Aiming at the annually measured continuous growth phenomenon of the dam body deformation towards the downstream direction for Jinping-I Arch Dam when the reservoir keeps stable at the normal water level elevation of 1 880 m, back analysis was conducted for the viscoelastic working behavior of the dam based on the measured displacement data and the concrete creep data. The results show that the dam body is in a working state of viscoelastic at present, and the measured short-term trend deformation is jointly caused by the hysteretic hydraulic deformation and the ambient temperature drop effect. Good linear relationships exist between the viscoelastic mechanical parameters of the dam concrete. The elastic modulus of the dam concrete through back analysis according to the elastic hydraulic component is actually an equivalent value of the instantaneous and delayed elastic modulus. For Jinping-I Arch Dam, this inversion value is 35. 5 GPa, which is close to the earlier back-analysis value and experimental value. The instantaneous elastic modulus, two delayed elastic moduli and two viscosity coefficients in the generalized Kelvin model are 47. 3 GPa, 189. 4 GPa, 132. 3 GPa, 383. 8 GPa·d and 20 574. 6 GPa·d, respectively. To establish deformation monitoring models for Jinping-I Arch Dam, it is recommended that a new viscoelastic hysteretic hydraulic component should be added to the traditional hydraulic, seasonal and time(HST)model.

Abstract:Aiming at the aging problem of the Nangudong masonry aqueduct in the Hongqi Canal, a three-dimensional finite element mesh was generated based on the Hypermesh software, and a three-dimensional finite element model for the aqueduct was established. The ABAQUS software was used to calculate the structural stress and deformation of the aqueduct. The structure stability of the aqueduct was checked by the material mechanics method. The results show that the maximum settlement of the pier foundation is 3. 05 mm. The maximum settlement difference of adjacent pier foundation is 0. 43 mm. The maximum compressive stress of the aqueduct is 4. 56 MPa and the maximum tensile stress is 1. 93 MPa, which appear in the local area at the side wall of the aqueduct. The minimum safety coefficients of anti-sliding stability and anti-capsizing stability of the groove pier are 10. 1 and 2. 4, respectively, both larger than the allowable values. Comprehensive analysis shows that the aqueduct is safe.

Abstract:To investigate the crack resistance effect of low-heat cement concrete in the Baihetan Dam, the thermodynamic performances of low-heat cement concrete and regular medium hot cement were compared, and the temperature control scheme was designed on a typical dam section. The temperature and stress were calculated by finite element simulation, and their effects on temperature, stress and surface crack resistance were analyzed and compared in the critical periods of early cooling, primary cooling, secondary cooling and arch sealing. The results show that the stress process trend of concrete is consistent in different seasons. Compared with medium hot concrete, low-heat cement concrete has higher safety factor of crack resistance, but the key point of temperature control and crack prevention is still at the end of the secondary cooling. In addition, for the case of large temperature difference between day and night, the low-heat cement needs better insulation measures at the early age to achieve the surface anti-cracking effect.

Abstract:In order to study the applicability of oblique photography in the field of damming hazard, the model construction principles of oblique photography were introduced, and the key steps of UAV oblique photography were expounded. Based on the POS data and image data collected by the UAV, image screening, air triangulation calculation, point cloud dense reconstruction and point cloud triangulation were carried out to complete the 3D digital model reconstruction, and the terrain of the Baige damming area is displayed in the form of digital elevation model, digital surface model and orthoimage. The morphology of the Baige dam is also measured. The results show that UAV oblique photography can well adapt to the complex environment of the damming site, and has the ability to access the target area quickly and complete the mapping task efficiently.

Abstract:In order to reduce the wind speed to satisfy code requirement for the core wall construction area under strong wind, the method of wind-proof structure formed by height difference between dam body and core wall was proposed to reduce the wind velocity near the surface of the core wall. The effects of wind-proof structure with different arrangements were studied by field test and numerical simulation. The results show that increasing the height difference of the wind-proof structure and decreasing the setting distance are propitious to reduce the wind speed near the core wall. When the distance of wind-proof structure is set to be 9. 08 m and the height difference is between 10 m and 12 m, the wind level 8(wind speed 20. 7 m/s)can be reduced to less than level 4(wind speed 5. 5 m/s)near the core wall ground. There is a linear relationship between the distance of the wind-proof structure and the minimum height difference to meet the wind-proof requirement. The fitting between the wind speed and the minimum height difference to meet the wind-proof requirement has a quadratic polynomial relationship.