Abstract:To improve the accuracy of flood forecasting, 13 flood events between 2000 and 2017 were selected from the sections of Lutaizi and Lubeng, and the Xin’anjiang three-source model(XAJ model)was used to simulate the flood events. The Lutaizi basin can be divided into 9 natural sub-basins and the Lubeng basin can be divided into 4 natural sub-basins. Then, the XAJ model was calibrated for these basins. The node generalizability was carried out in the mainstream section of the Huaihe River with flood diversion and flood retarding areas. Combined with the diversion ratio method and the Muskingen method, the simulation method of flood diversion was established, and fairly good forecasting results were obtained. The research results show that: for the relative error of flood volume, the qualified rates of Lutaizi and Lubeng region are both up to 100%, and the Lutaizi reached a qualified rate of 100% in the flood peak, while the Lubeng region reached 92. 3%. In two floods in 2003 and 2007, the relative error and the certainty coefficient of flood peak have been significantly improved.

Abstract:In order to make full use of the continues pumping test data to estimate the hydraulic conductivity(K), the transmissivity(T)and the storage coefficient(μ^*)of different head depression cones in a confined aquifer, a dimensionless analytical solution of drawdown transients with variable pumping rates was derived based on the Theis formula and the principle of superposition. Furthermore, a new type curve method was proposed. The in-situ pumping test was conducted to obtain the drawdown record perturbed by stepwise rates. Then, the drawdown curve was used to match the corresponding type curve. After that, this method selects one match point and records its coordinate values on both the type curve and the real drawdown curve. By substituting these recorded values into related formulas, the hydraulic parameters of the confined aquifer can be determined. This method was applied to a field pumping test conducted at a southern highway in Wuxi, Jiangsu Province, China. The type curve matching process is implemented in stages. Field test results reveal that the hydraulic conductivity of the confined aquifer with the 2-3 silt layer are 5. 12×10^-4 cm/s, 2. 54×10^-3 cm/s and 2. 83×10^-3 cm/s respectively, which are corresponding to three-stage stepwise pumping rates.

Abstract:Quantitative evaluation of the ecological vulnerability for the Tarim River Basin(TRB)in Xinjiang from 2005 to 2015 was achieved through the combination of the Pressure-State-Response(PSR)model and the fuzzy analytical hierarchy process(FAHP). The distribution and dynamics of ecological vulnerability over the decade were analyzed after the establishment of evaluation system. The results show that the ecological vulnerability in the TRB during the time of 2005-2015 is at Heavy level Ⅲ with the average value of 0. 538, and shows a continuously rising trend. The ecological vulnerability synthetic index(EVSI), based on the different levels of ecological vulnerability over the time, has a minimum of 1. 14 in 2005 as well as a maximum of 3. 69 in 2015, and increases significantly with a fluctuation after reaching a peak of 3. 07 in 2009. In addition, the ecological vulnerability in this basin displays a noticeable spatial distribution, which are strongly vulnerable areas mainly in the east with significantly increasing vulnerability and lightly vulnerable areas in the west at the transition stage of increase.

Abstract:A new comprehensive evaluating system of water quality has been proposed based on the variable weight, which includes a single-factor evaluating method based on percentile system, a determination method for the dynamic factor of weight based on water quality data, and an integrated evaluating method of water quality. This evaluation system is used to carry out the single-factor evaluation, the factor weight calculation and the comprehensive evaluation on the water quality of some stations in Jiangsu province. After that, the correlation analysis on the evaluated results has also been conducted. The results show that the evaluating system of water quality based on variable weight is very suitable for the evaluation of high-frequent monitoring data for the water quality, which not only highlights the direct influence of dramatically changing factor on the evaluated results but also comprehensively reflects the integrated water quality condition.

Abstract:This paper firstly explores and applies the newly low-altitude airborne LiDAR technology to solve the mapping problem of the middle-lower Yangtze River Riparian zone covered with multi-layer and high-density vegetation. A vegetation filtering algorithm is proposed for the low-attitude airborne LiDAR point clouds collected in the complex area with multi level and dense vegetation coverage. After the coarse filtering of point clouds by multi-echo analysis, this algorithm extracts the ground seed points by morphological calculation, fits the trend surface of the local terrain, then eliminates the vegetation points and preserves the ground points using the Random Sample Consensus, thereby acquiring the DEM of measured area. The experimental results show that the proposed algorithm can intelligently remove the vegetation point clouds in the middle-lower Yangtze River riparian zone, where topographic relief is large and vegetation cover is dense. This research also shows that by designing a special filtering approach, it is possible to classify laser points into terrain and vegetation automatically even for thoroughly mixed vegetation and terrain points with low penetration rate of below 15%.

Abstract:The single-factor perturbation analysis method was used for the sensibility analysis of soil hydraulic parameters, including the residual water content θ_r, the saturated water content θ_s, the saturated hydraulic conductivity K_s, the empirical parameters α and n. With the help of HYDRUS-1D model, the process of water infiltration in the soil was simulated for the two-year-once storm in Nanjing and the sensitivity of soil hydraulic parameter was evaluated for the varying-head infiltration, which can quantitatively describe the effects of soil hydraulic parameters on two output variables of HYDRUS-1D(soil water potential and cumulative infiltration), simplify the model calibration and improve the accuracy of model simulation. The results show that under the condition of varying-head infiltration, the parameter’s influence degree on both soil water potential and cumulative infiltration are in this order: n>K_s>θ_s>α>θ_r. Empirical parameters α and n have a great influence on the soil water potential with a depth of 0~10 cm beneath the surface, and the influence are similar when changing parameters K_s, θ_r or θ_s and α on the soil water potential. In the case of ±25% disturbance, the influence degree of θ_s, K_s and n on the cumulative infiltration are more than 10%. Therefore, the accuracy of K_s, θ_s, α and n should be ensured during the simulation of varying-head infiltration.

Abstract:In order to solve the safety evaluation problem of existing prestressed cable truss structures considering the corrosion degree of cables, an objective evaluation system is established based on the characteristics of the structure and the corrosion degree of the cables. Firstly, the dynamic response analysis method of cable-strut system under the instantaneous break is established, and the rationality and feasibility of proposed method are verified by three cable structures. According to the construction theory of judgment matrix and the result of the cable breaking analysis, the method for determining the weight coefficient of each cable in the cable-strut system is established considering the corrosion degree of the cable. On this basis, the membership function of the corrosion degree of the cable is established, and the safety evaluation set of the cable system is built. At last, based on the weight coefficient and the corrosion degree of the cable, the fuzzy comprehensive evaluation system is established for the safety of existing prestressed spatial cable system. Furthermore, the weight coefficient determination method, the membership function and the fuzzy comprehensive evaluation model are applied and verified by a practical spatial cable-strut structure.

Abstract:Through the isothermal adsorption of chloride ion, the adsorption kinetics and the adsorption thermodynamics, the influence of polycarboxylate superplasticizer on the chloride binding in cement paste has been investigated. Besides, the influencing mechanism was examined by the X-ray powder diffractometer(XRD). It has been found that the polycarboxylate superplasticizer reduces the chloride binding, and the smaller the water-cement ratio is, the greater the effect is. Chloride binding onto cement paste with polycarboxylate superplasticizer in a short time conforms to pseudo-first-order kinetic equation, indicating the physical adsorption of chloride ions. In a long time, it conforms to pseudo-second-order kinetic equation, indicating the chemical adsorption of chloride ions. With the increase of content of polycarboxylate superplasticizer, the adsorption rate decreases. The free energy, enthalpy and entropy of chloride binding are decreased with the increase of polycarboxylate superplasticizer, and this process is spontaneous and exothermic. The influence of polycarboxylate superplasticizer on the chloride binding is mainly attributed to the physical adsorption, not chemical combination of chloride ions.

Abstract:Ocean thermal energy conversion(OTEC)is a hot research topic in the field of ocean renewable energy. The developments of OTEC resource assessment, resource distribution, and cycle mode as well as the OTEC demonstration project were reviewed and analyzed. Then, the key technologies of OTEC from the stability of power generation platform, the comprehensive utilization of cold water, the efficiency improving, the multi ocean renewable energy complementary and the environment effect of OTEC plant have been discussed. Although the development of OTEC is feasible and necessary, there are still many challenges and difficulties to solve.

Abstract:Experiments on the interaction forces between waves and seawalls on reefs were conducted in the large wave flume of Tianjin Research Institute of Water Transport Engineering. Wave forces, including the horizontal and uplift pressure on seawalls, were measured at different water levels and wave conditions. The forces values were compared with those obtained by formulas in Hydrographic code for ports and waterways. The experimental results show that wave forces on seawalls were controlled by wave setup, wave height and wave induced flow after breaking. Horizontal pressure had a rectangular distribution while uplift pressure had a triangular distribution. The experimental values were less than those obtained by formulas using wave conditions in deep water. Correction coefficients based on the relative distance of seawalls and reef edge as well we the relative water depth on reefs were proposed. It has been demonstrated that values of the correction formula were in good agreement with the experimental results.

Abstract:The near-field velocity and concentration fields of vertical multiple jets in wavy cross-flow were measured by using the PIV and PLIF techniques. The characteristics of multiple jets, including the trajectory, velocity field, concentration field and vorticity field, were analyzed, focusing on the differences between the jet in wavy cross-flow and that in cross-flow as well as the wave effect on the development of multiple jets. The results show that the time averaged trajectories of jets in wavy cross-flow are distorted with “effluent cloud” existing on the jet body. Further, wave has a significant influence on the movement of multiple jets in wavy cross-flow, including increasing the interaction area between jets and surrounding waters, accelerating the decay of the vertical momentum of jets, enhancing the shielding effect of leading jet on the rear jets, and reducing the height of the confluent point of the jets, etc. In present cases, waves lead to the decreasing of the peak concentration of contaminant at all sections, and thus have a positive effect on the dilution of multiple jets in wavy cross-flow.

Abstract:To solve the problem that the PSASP built-in generator model can’t express the actual operating characteristics of direct-driven permanent magnet wind turbine(D-PMSG)in large-scale wind farm system, a simplified D-PMSG based on PSASP user custom model(PSASP/UD)has been built. The influences of generator and machine side converter are ignored by the transient simplified model of permanent magnet direct-drive fan. Considering the characteristics of the dynamic short circuit current during low voltage ride-through, the voltage frequency protection control and the active recovery rate setting, the transient simplified model is taken as a controlled current source with low-voltage protection characteristics and important parameters are optimized based on genetic algorithm. By comparing the D-PMSG transient simplified model with the detailed model, increasing the active recovery rate setting, and comparing the measured operating data of the single-machine test system under three-phase short-circuit fault condition, the correctness of transient simplified method for the permanent magnet direct-drive fan has been verified, and the parameter optimization method is also validated.

Abstract:In this paper, a new dynamic clustering method for the DDPMSG-based wind farm is proposed based on the action time of current limiting component in the grid-side controller. Firstly, the affecting factors on the action time of current limiting component in grid-side controller are analyzed, and it is pointed out that the action time of limiting component dominates the dynamics of DDPMSG-based wind turbines. Secondly, the estimating method of limiting component action time is proposed based on the steady active power and the terminal voltage sag. Finally, the DDPMSG-based wind turbines are grouped based on the limiting component action time with K-means method. The 10-machine 39-node system integrated with a wind farm is used as the test system, and the dynamic responses of the wind farm based on its detailed model and the equivalent one are compared. Meanwhile, the small-signal stability and transient stability of the overall system are analyzed with detailed wind farm model and equivalent wind farm model. Compared result validates the clustering method proposed in this study.