Abstract:To examine the damage causes of warping dams and their impacts on sediment delivery into the Yellow River, the characteristics of the rainstorm process at August 17 and the inflow of water-sediment into the Yellow River were obtained based on the field investigation results of 19 warping dam breaches and the data of hydrological stations and rainfall stations in Xiliugou and Hantaichuan watersheds. According to the structure and operation characteristics of the warping dams, combined with the detailed investigation of the flood-induced damage situation, especially the erosion form at the break sites, the causes of flood-induced damage were analyzed from the aspects of rainfall, planning, design, construction and operation management of the warping dams. The break modes and sand-blocking effects of the warping dams were qualitatively presented. Suggestions are proposed, including optimizing dam-system layout and construction standard, improving the structure of drainage structures, strengthening construction quality management, and paying attention to non-engineering measures such as early warning and prediction.

Abstract:Two small adjacent typical karst peak cluster-depression watersheds(Chenqi and Changchong)were chosen as the research objects, and then 26 flood processes with different magnitudes of flow were selected. The characteristics of the lag time and similarity of the surface and subsurface runoff in Chenqi watershed were compared and analyzed with those in Changchong watershed. The results show that due to the soluble rock of the depression and the threshold effect of the impervious or weakly permeable transition at the Chenqi watershed, the characteristics of the lag time and similarity between the surface and underground runoff show obvious differences. The surface runoff fluctuates more rapidly but its peak time lags behind that of the underground runoff. The flood fluctuation shape of the watershed is controlled by the surface river and it has high similarity with the flood process of the surface river. The flood process in the Changchong watershed is similar to the surface river flood process, and as the rainfall decreases, the flood shape tends to change the characteristics of the underground river runoff. The distribution of impervious rocks in the watershed reduces the aquifer's ability to regulate storage. The flood lag time in the watershed is short and the runoff responds quickly to the rainfall.

Abstract:As one of the largest cities in the world, London faces multiple flood pressures. With the development of the times, the concept of flood control in London has gradually shifted from the traditional flood control-oriented defense to the comprehensive flood risk management focused on flood prevention and recovery, which has achieved satisfactory effects. This study started from the types and characteristics of floods in London and then the current flood risk management organization system in the UK was acquainted. Risk management measures in London were analyzed and summarized from five aspects, including preventive measures, resilience measures, mitigation measures, preparatory measures and recovery measures. Among them, the city planning, the Thames estuary flood control project system which is capable of resisting the millennium storm surge, the underground drainage system with ecological drainage measures, the accurate flood warning and forecasting system, and the perfect flood insurance and rescue systems can provide reference for urban flood management in China.

Abstract:In order to reveal the effects of polyacrylamide(PAM)on pipeline spiral flows, an experimental facility of pipeline system and a revolving device consisted of a multi-guide vane were built. The hydrostatic pressure near the pipe wall and the dynamic pressure inside the probes in the pipeline spiral flow containing PAM were measured by a 5-hole spherical head probe and a piezometer tube, respectively. The velocity distribution, the capacity of mass transport, and the pressure characteristics of the pipeline spiral flow were analyzed. The experimental results show that the velocity distribution of the pipeline spiral flow is slightly different from that of clear water after the addition of a small quantity of PAM(100 mg/L), and the generation-development process of the pipeline spiral flow is extended by 67%. Besides, the mass transport capacity of the pipeline spiral flow is increased by 79. 1%~91. 5%, and the loss of pipeline drag force is reduced by 18. 0%~23. 8%.

Abstract:The primary objective of this study is to explore the wave attenuation effects of single and patchy arrays of rigid vegetation under both regular and irregular wave conditions by multi-group physical model tests. The experimental results show that for vegetation belts of a single-rectangular distribution with the same distribution density, wave dissipation is higher with an increasing space between adjacent plants along the flow direction. For vegetation belts of a single-staggered distribution, drag coefficients increase with an increasing space between plants and submergence ratio. For the patchy vegetation belts, transmission coefficients decrease with the increasing number of plants within a single patch and the decreasing space between adjacent patches. Fitting relationships between wave attenuation and hydrodynamic factors as well as vegetation factors are obtained under the experimental conditions, revealing the effects of distribution densities and arrangement structures of vegetation belts on wave attenuation.

Abstract:The decision-making of dams for long-term service needs to strictly meet the engineering and technical requirements, as well as considering a series of complex social, economic, environmental and ecological issues. This paper presents the general idea of the decision-making method for dams and reservoirs of long-term service, and discusses the optional life promotion measures, including reinforcement, degradation, retirement by demolition and reconstruction near the dam site. The life quality index(LQI)is introduced to evaluate the comprehensive improvements of the dam life promotion measures caused by social life quality improvements based on the calculation of dam service reliability. The decision-making criteria of dam performance promotion measures are then proposed based on LQI and the social willingness to pay. Finally, a concrete gravity dam with stability risks was taken as an example and the optimal engineering measures of performance promotion were recommended. It is suggested to operate with a 10 m reduction of the reservoir water level or with suitable dam reinforcement measures to promote the long-term service performance, consistent with engineering practice.

Abstract:Five standard test functions were used to verify the multi-group teaching optimization(MGTLO)algorithm, and the simulation results were compared with those of the basic teaching optimization(TLBO)algorithm, shuffled frog leaping algorithm(SFLA), differential evolution(DE)algorithm and particle swarm optimization(PSO)algorithm. MGTLO was used to search for the optimum model parameters and the weight coefficients of the combined model based on the generalized regression neural network(GRNN), the radial basis function neural network(RBF)and the support vector machine(SVM)model elements. Four combined prediction models, including MGTLO-GRNN-RBF, MGTLO-GRNN-SVM, MGTLO-RBF-SVM, and MGTLO-GRNN-RBF-SVM were proposed and case studies of the runoff prediction were performed at the Yamadu Hydrological Station of the Yili River in Xinjiang and a hydrological station in Yunnan Province. The predicted results were compared with the following six single models, MGTLO-GRNN, MGTLO-RBF, MGTLO-SVM, GRNN, RBF and SVM. The results show that the optimization accuracy of MGTLO algorithm is better than that of TLBO, SFLA, DE and PSO, with good convergence speed and global optimization ability. The combined model merges the advantages of MGTLO algorithm, GRNN, RBF, and SVM model elements. It is superior to single models in terms of prediction accuracy and generalization ability. MGTLO algorithm can effectively optimize the parameters and weight coefficients of the combined models and the MGTLO-GRNN-RBF-SVM model has the highest prediction accuracy.

Abstract:To study the cavitation effect of an axial flow pump on its internal flow characteristics and energy conversion, constant cavitation calculation was performed using the SST k-ω turbulence model and the homogenous multiphase flow model for an axial pump. The results show that the cavitation volume fraction of the axial pump gradually increases as the effective net positive suction head a decreases, which can induce undesirable flow states like jet-flow or vortex on the surface of the pump blade and can lead to an adverse impact on the homogeneity of the outlet flow field. From the pump blade inlet to the outlet, the relative velocity of the liquid in the cavitation region is higher than that before cavitation while the absolute velocity and the static pressure are lower than those before cavitation. In the axial direction, under the operation condition of no cavitation and the early-stage of cavitation, the static and dynamic lift remain constant. As the inlet pressure of the pump gradually decreases, the static lift doesn’t change but the dynamic lift rises slightly, which results in a small increase in the hydraulic performance of the pump for a=5. 33 m. For a= 4. 71 m, the static lift decreases with a drop range larger than that of the dynamic lift rise, resulting in a significant decline in lift efficiency. As the cavitation degree increases, the static and dynamic lift continue to decline, and the hydraulic performance of the axial pump drops sharply.

Abstract:Ambient excitation modal tests of one-way SIMO(single input multiple output)method and two-way MIMO(multiple input multiple output)method were carried out to obtain the dynamic characteristics of aqueduct bent structures. Longitudinal, transverse and bidirectional modal parameters were identified by enhanced frequency domain decomposition. The results show that most spectrum peaks of longitudinal modes are obvious with better identification results, and the longitudinal modes are more abundant than transverse ones by SIMO method. Most spectrum peaks of longitudinal or mainly longitudinal modes are also obvious by MIMO method. However, spectrum peaks of transverse modes or mainly transverse modes, bidirectional modes are small and some are difficult to be identified except for the second bidirectional order mode, i. e. the first transverse order mode. The column is identified with bending vibration. The beam is identified with rigid body vibration of translation or rotation for longitudinal low-order modal shapes, while it is characterized with bending vibration for high-order modes. For transverse modal shapes, the beam is identified with rigid body vibration of translation or immovability. The error of modal frequency identified by SIMO and MIMO methods is small. The results by SIMO method are more reliable, especially for low-order modes. Therefore, in the aspects of low-order modes identification accuracy, test workload and operation convenience, one-way SIMO method is better than two-way MIMO method for bent structure modal test.

Abstract:In order to reflect the stochastic and time-varying characteristics of seepage failure for earth-rock dams more truthfully, the dynamic seepage failure probability of earth-rock dams is characterized by means of geotechnical dry-wet cycle tests and permeability coefficient inversion. The fusion of RBF neural network and LHS method is used to improve the random sampling method, and the shortcomings of the traditional Monte Carlo random sampling method with heavy calculation burden are overcome. The accuracy and efficiency of the improved method are proved by comparison. The improved method is applied to the dynamic analysis of the seepage failure probability of an earth-rock dam, and the conclusion shows that the risk of seepage failure of the earth-rock dam is high and it increases year by year, indicating the need to be reinforced.

Abstract:With reviewing and summarizing the evolution of the reinforcement methods for massive concrete structures in Design Specification for Hydraulic Concrete Structures(SDJ 20-78), the regulations of the minimum reinforcement ratio of massive concrete in currently domestic and oversea codes of various industries are compared and analyzed, and the principles of relevant provisions are investigated. A new method to determine the minimum reinforcement ratio is presented and the recommendations on relevant provisions are made. The advantages of DL/T 5057-2009 and Building Code Requirements for Structural Concrete(ACI 318-14)are combined skillfully in the suggested method, which guarantes that the amount of reinforcement is fixed when ρ<ρ_min, ensures that the less reinforcement failure will not occur when γ_dM is less than and close to the cracking moment M_cr. In addition, the limit that the minimum reinforcement ratio for massive concrete structures in DL/T 5057-2009 is only applicable to the bottom plate mounted on foundation and mainly subjected to vertical load with more than 2. 5m thickness is eliminated.

Abstract:Coastal storm has important impacts on morphological evolution of mud tidal flat-creek system, and related research is of great practical value to the safety of coastal engineering and to the development and protection of coastal zone resources. The research progress of coastal storm impacts on morphological evolution of mud tidal flat-creek system was reviewed in terms of research methods, evolution characteristics and dynamic mechanisms. The storm profile for the accretional mudflats is generally eroding in the middle and depositing at both ends, but the study on its dynamic mechanism is not systematic enough. Salt marshes can effectively weaken storm and stabilize sand, but their lateral evolution deserves more attention. Under the impact of storm, the activity of tidal creeks is greatly enhanced, among which the mechanism of tidal creek shift and the bank erosion is a scientific problem urgently to be solved. In the future, it is necessary to further strengthen the acquisition of field data and strengthen the study on the morphological evolution mechanism of the tidal flat-creek system under the impact of storm by means of numerical simulations and physical experiments.

Abstract:Due to the complex interaction between vegetation and hydrodynamics, research progress in the characteristics of flows with vegetation from both home and abroad were reviewed in three aspects, including flow resistance, vegetation-induced turbulence and wave attenuation. The quantitative relationship between Manning coefficient and vegetation features, and the relationship between drag factors and vegetation features under different hydrodynamic conditions were summarized. The vertical distribution of stream-wise velocity and turbulence caused by vegetation as well as the wave attenuation effects by vegetation in costal zones were also discussed. Aiming at the shortcomings in the current research of vegetated flow hydrodynamics, the future research direction in this field were proposed, including the drag factors, the turbulent characteristics of vegetated flows and the coupling mechanisms of vegetation-flow-wave.