Abstract:Improving the spatial resolution and forecasting accuracy of rainfall-runoff model is one of the hotspots and difficulties in flood forecasting and hydrological research. To address this problem, a high-resolution rainfall-runoff model, Grid-XAJ-SATIN, considering the spatial combination of infiltration-excess and saturation-excess runoff is proposed in this paper, which is based on the existing study of the grid-based rainfall-runoff models. Several aspects of this model are discussed including its principle and structure, processing of the geographical information, spatial distribution of parameters, model forcing data and assimilation of basin states. The model is then applied to both humid and semi-humid catchments for flood simulation. The simulation results show that the accuracy of the flood forecasting is well realized in both conditions. Moreover, this model is demonstrated to be able to forecast not only the hydrograph at the catchment outlet but also the streamflow at any interior grid cells.

Abstract:To explore the relationship between EI Nino event and the summer precipitation, the variation trend and mutation of Nino index are firstly examined to identify the types and intensity characteristics of El Nino events during 1961-2016. The spatial distribution and inter-annual variation pattern of precipitation are then examined by analyzing the monthly precipitation anomaly using EOF method. Emphasis is placed on the analysis of the characteristics of El Nino events during 2014-2016, and their impacts on the temporal-spatial distribution of the summer precipitation in 2016. The study shows that both Nino index and the precipitation variability fluctuate significantly during the period of EI Nino event, and the spatial and temporal distribution of precipitation in the next summer is largely influenced by the event. Specifically, the summer precipitation appears to increase in Yangtze River basin and decrease across most northern Huai River Basin and the southeast coastal areas after Eastern EI Nino’s heyday. For Central EI Nino, the summer precipitation appears to decrease in Yangtze River Basin and increase in Yellow River Basin and Southern China. For Mixed EI Nino, the increase in summer precipitation is detected across the Yellow River Basin.

Abstract:Bioturbation is one of the important influence factors in the sediment-water interface reaction. To identify the influence mechanism of bioturbation on redox characteristics in the sediment-water interface, Chironomus plumosus is selected to examine its effect on the vertical distribution characteristics of O₂, pH and Eh using the high resolution microelectrode system. The result shows that the concentration of dissolved oxygen at the sediment-water interface is significantly increased, and the pH value of the overlying water is reduced together with increased pH value in the sediments. Moreover, due to the bioturbation of the Chironomus plumosus, the temporal and spatial variation of pH value in the overlying water becomes large, which is however less significant in the sediments. The Eh value appears to be significantly increased due to the increment of the Oxygen content in the corridor, which is low instead in the places without bioturbation. In general, the sediment-water micro interface is influenced by changing its redox conditions due to the oxygen, the latter is introduced into the corridor through breathing and ingestion of the Chironomus plumosus.

Abstract:Case study is performed on the arable land soil in the southeast of Huzhou in this paper, the spatial distribution characteristics of soil heavy metals are studied using the Geostatistical method, in which soil pollution conditions are evaluated using single pollution index, Nemerow complex pollution index, index of geoaccumulation and potential ecological risk index. The results show that the average content of Cd in this area is higher than that of national soil environmental standard(Ⅱ), and the contents of heavy metals(Cr、Ni、Cu、Zn、Cd、Pb、Hg)are higher than the background values. It is also found that the soil pollution degree of the research area is not high, Hg pollution degree appears to increase from the west area to the east area, and Cd pollution is concentrated in the southeast of Nanxun and the middle of Lianshi. The geoaccumulation indices of Hg and Cd are 0. 50 and 0. 11, respectively, which belonged to light-moderate pollution. The single pollution index of each heavy metal in soil is as follow: Cd(1. 47)>Hg(0. 69)>Ni(0. 66)>Zn(0. 41)>Cu(0. 31)>Cr(0. 27)>As(0. 25)>Pb(0. 11). The Nemerow complex pollution index suggests that the pollution condition of the arable soil is insignificant, only the soil in the middle of Nanxun, the south of Shanlian, and the junction area between Jiuguan and Shuanglin is lightly polluted. The potential pollution risk of Cd appears to be moderate and the comprehensive ecological pollution risk shows to be in a light level. The soil pollutions are supposed to be mainly from agricultural activities and industrial wastes.

Abstract:To study the effects of different collection methods on hydrogen and oxygen isotope values of soil water, a laboratory experiment is designed to model the rainfall infiltration behavior, and the water outflow from the bottom of the soil column is collected. In this experiment, soil waters at depths of 10 cm, 40 cm, 70 cm and 100 cm are collected and this collection method is termed as in-situ collection method. On the other hand, soil samples at the same depths are taken out with the soil waters being collected using vacuum distillation extraction method. The comparison results between D and ¹⁸O values show that during the process of rainfall infiltration in the dry soil sample, the light isotopes are preferentially adsorbed by soil particles, and the outflow water collected first has the most positive hydrogen and oxygen isotope values. The soil water extracted by the vacuum distillation method is composed of moisture-absorbing water of the air-dried soil and the water infiltrated into the unsaturated zone. The soil water collected by the in-situ soil solution sampler represents the water flowing in the soil and could be effectively used.

Abstract:To identify the effect of contraction joint state on the anti-knock performance of concrete gravity dam, numerical simulations based on fluid-solid interaction(FSI)method are conducted, which simulates the formation and propagation of shock wave due to shallow underwater explosion, and its interaction with free surface and dam structure. Considering that the shock wave propagation is influenced by the opening states of the contraction joints in the dam, the impact of the latter on the anti-knock performance of the dam is hence investigated in three aspects, including dynamic response, gradual damage failure process and the accumulation of damage dissipation energy. The numerical results show that the anti-knock performance of the dam is significantly influenced by the opening area of the contraction joint, a larger opening area appears to yield enhanced dynamic response, wider damage area and larger accumulation of damage dissipation energy in the dam, thereby weakening the anti-knock performance of the dam.

Abstract:In this paper, the SPH method is modified by incorporating a new coupled dynamic solid boundary with high calculation accuracy, in which non-penetrating condition is maintained within the particles and the free surface conditions are applied by using the sum of the support regions of corresponding particles. This method is expected to provide an accurate estimation of the rolling and broken effects of the water flow. A simplified flooding flow model is thus established to examine the effect of bulwark against the flood, in which various characteristics of the 3D flooding flow are well predicted. The collapse behavior of the cylindrical body of water is simulated using a 3D SPH model. The finding shows that the numerical results agree well with the experimental results, which demonstrates the effectiveness of the modified SPH method in modelling the free surface with violent flow behavior.

Abstract:It is recognized that air expansion of geomembrane is essentially a three-phase coupled problem, which is water-air-solid in unsaturated soil, and is influenced by the rise of ground water level, storage of the reservoir and the rapid draw down of the water level in the reservoir. In this respect, a special laboratory equipment for the air expansion test of geomembrane is developed. Air expansion tests are then conducted to explore the variations of the displacement, gas pressure, suction, pore water pressure and vertical earth pressure under different working conditions. The test results show that the pore air pressure and pore water pressure are increased with the rise of the ground water level and the magnitude of the air pressure is dependent on the rising amplitude of groundwater level. It is found that the pore pressure of the soil under the geomembrane is significantly increased due to the increased water pressure during storage in the reservoir, and air expansion failure in the geomembrane is more likely to be induced at the initial storage period, especially when the unsaturated zone between the ground water level and geomembrane is small. It is therefore suggested that a certain amount of preloading could be applied over the geomembrane to prevent its expansion behaviour. As the pore pressure response below the geomembrane is usually later than the preloading above the geomembrane, pore pressure would become larger than the preloading applied during the rapid draw down of water level in the reservoir, which will lead to the air expansion failure on the geomembrane.

Abstract:The main objective of this paper is to examine the feasibility of the hybrid bridge column. To address this problem, quasi-static tests are conducted to explore the differences of seismic behaviors between hybrid bridge column and reinforced concrete(RC)bridge column and STRC bridge column, each column with shear span ratio of 3. 0. The test results show that flexural-ductile failures are observed for all three columns, and much more cracks with wider distribution area are found to be created in the hybrid bridge column. This demonstrates that the hybrid bridge column yields a much better seismic behavior over the RC bridge column. In addition, the ductility and self-centering capability of hybrid bridge column are superior to those of the STRC bridge column. In general, the hybrid bridge column has the advantage of both economical efficiency and favorable seismic behavior, thus can be considered as a highly competitive bridge column scheme in seismic active regions.

Abstract:By adopting gradually tetrahedral meshing technique for random distributed aggregates and embedding scheme of cohesive element, a high efficiency 3D aggregate-mortar-interface meso finite element model is established, in which the uniaxial tension and uniaxial compression experiments of concrete cube samples are carried out in single computer. The numerical result shows that the whole process from weak connection to separation between aggregates and mortar is readily captured, which reproduces the failure mode of concrete specimens. The inner mechanism of the macro-mechanical properties of concrete is thus revealed by comparing the computed stress-strain curves from uniaxial tension and compression experiments, which is supposed to provide a technical support to explore the inner mechanism of concrete like composite materials.

Abstract:This paper is aimed to quickly and accurately solve the parameters of photovoltaic(PV)cell model, in which the reference value at the maximum power point of the local shaded PV array is calculated. To address this issue, Gauss Seidel method is used. Based on the local shading conditions in practical engineering, the PV array model is split into a number of new PV array models under uniform light, the latter are supposed to be solved using the data manual of PV cell. The simulation results show that the reference value at the maximum power point of the split PV array model can be solved quickly and accurately by using the Gauss Seidel method. This would demonstrate that the method is suitable to model the output characteristics of PV array under local shading condition and solve its maximum power point value of each peak point.

Abstract:One of the important problems in the development of micro grid is related with its operation optimization including multiple distributed generators(DG). To improve the operation level of the micro grid, the modified particle swarm optimization(PSO)algorithm based on chaos theory and simulated annealing algorithm is proposed in the paper. The mathematical model regarding optimal operation of micro grid is established incorporating different operation indexes of the distributed generators, in which the optimized object function is assumed to be correlated with operation indexes such as operation cost and environmental benefit. The modified PSO algorithm is used to solve the multi-objective problem, with the optimized operation of the mirco-grid with DGs being obtained. A case study regarding 24 hours operation of one mico-grid shows that, the modified PSO algorithm appears to have enhanced optimization ability and convergence rate.

Abstract:Power mismatches of zero injection nodes have significant impact on the security estimation of the power system. In this paper, a novel state estimation method for the power system is proposed to reduce the power mismatches of zero injection nodes, in which zero injection constraints are added in the form of equality constraints in the bilinear WLAV(Weighted Least Absolute Value). Based on the IEEE standard system, a case study on a provincial system is performed using this method. The results demonstrate that this method can not only ensure the existing high computational efficiency of bilinear WLAV based on interior point method, but also reduce the power mismatches of zero injection nodes. Meanwhile, its robustness is improved to a certain degree.