Abstract:Based on the principle of minimum action and taking time as the minimum action quantity, the functional of two-dimensional Richards equation was established. The variational solution of soil slope water infiltration under ponding was proposed. Brooks-Corey model was used to calculate the hydraulic slope of soil mass and the shape of the infiltration curve was discussed. Hydrus 2D software was used to analyze the water content distribution in the slope under the first type of boundary conditions. The results show that the variational solution of the 2-D infiltration has the same form as that of the 1-D horizontal infiltration and vertical infiltration. The infiltration path is convex shape. The infiltration capacity is linearly related to the depth of the wetting front, which is consistent with the results obtained by variational solution. Therefore, the depth of wet front and the distribution of water content obtained by the variational solution are feasible to analyze the macro-engineering problems such as slope stability.

Abstract:The RNG k-ε turbulence model was used to simulate and analyze the open channel flow with patchy distributed double-layer rigid vegetation. The flow velocity and turbulence parameters of the open channel flow with vegetation were statistically analyzed based on the double-average method of time and space. The results show that the open channel flow with patchy distributed vegetation can be divided into vegetation zone, gap zone, and mainstream zone, and the magnitude and distribution of time-averaged flow velocity vary in different zones. In the open channel flow with double-layer vegetation, the vertical distribution of time-averaged flow velocity exhibits inflection points near the bed surface, near the top of the low plants, and near the top of the high plants, and the maximum values of fluctuation intensity and turbulence kinetic energy occur near the top of the high plants.

Abstract:The connotation of urban vulnerability to heavy rain and flood disasters is expounded based on the concept of vulnerability. A comprehensive evaluation index system and an evaluation model for urban vulnerability to heavy rain and flood disasters are constructed from three aspects: exposure, sensitivity, and adaptability, including 11 indicators. The criteria for dividing vulnerability levels are determined. Taking Qinhuai District of Nanjing City as an example, for a 100-year return period design rainstorm scenario, quantitative analysis of the indicator values is conducted using the MIKE coupled one- and two-dimensional model. The index of urban vulnerability to heavy rain and flood disasters is evaluated using the constructed evaluation model. A spatial distribution map of vulnerability in the research area is drawn, and the characteristics and causes of vulnerability distribution are analyzed. The results show that the MIKE coupled one- and two-dimensional model can be used to obtain the maximum inundation depth and end-of-period inundation depth in the exposure index. Areas along rivers with relatively flat terrain, low-lying areas in the transportation network, areas prone to water accumulation under overpasses, densely populated areas, high GDP value areas, and areas with high exposure levels such as residential areas and business centers exhibit higher vulnerability.

Abstract:In order to analyze the contribution rate of runoff variability from climate change and human activities in the Nam Ngum River Basin in Laos since the 1960s, the daily precipitation data from two widely used satellite precipitation products in the Mekong River Basin, APHRODITE and MSWEP, were bias-corrected based on the measured precipitation data from ground stations in the basin. The Xin’anjiang model was constructed using corrected satellite daily precipitation and measured daily runoff data from Pakkanhoung and Hinheup stations during reference period, and the natural daily runoff process in the basin during reservoir influence periods was simulated. The contribution rate of climate change and human activities to runoff variability was quantified. The results show that there is a general downward trend in annual runoff in the Nam Ngum River Basin. The contribution rates of climate change to the runoff variability during the two reservoir influence periods were -429% and -399% at the Pakkanhoung station, respectively, and the contribution rate was -380% at the Hinheup station. The corresponding anthropogenic contribution rates were 529%, 499% and 480%, respectively. Anthropogenic activities are the main cause of runoff variability in the basin. Anthropogenic activities mainly based on reservoir operation, have a significant imp.

Abstract:A typical peatland watershed in the upper reaches of the Black River in the Zoige Basin in the Source Region of the Yellow River is taken as the research object. The groundwater level monitoring data, meteorological data, and unmanned aerial vehicle aerial survey topographic data in 2018-2022 were used to statistically analyze the spatiotemporal changes of the groundwater level in the peatland watershed, and the section depth and discharge process of the channel outlet in the watershed were calculated. The results show that precipitation is the dominant factor of groundwater level change in the peatland watershed, and the changing trend of groundwater level is consistent with that of precipitation, which increases with the increase of the ratio of precipitation to evaporation. The groundwater level in the middle reaches of the small basin fluctuates more violently than that in the upper reaches. The average groundwater level in the upper reaches is higher than that in the middle reaches, and the water storage capacity of the peat wetland in the middle portion is decreasing. Based on the hydraulic method and the monitoring data of groundwater level, the empirical relationship formula between water depth and discharge in the channel sections of the peatland watershed is obtained, which can be used to calculate the daily discharge process line.

Abstract:Four different scaling methods, including scalping method, equal-weight replacement method, similar grading method and mixing method were used to obtain the maximum dry density in laboratory according to the original average design gradation curve of rockfill in the Shuangjiangkou core-wall rockfill dam. Based on the test results and gradation equation of soil, a quantitative index of gradation composed of grading area and the content of grains smaller than 5 mm ( P 5) was adopted. The relationship of dry density versus grading area before tests, P 5 and maximum particle size was fitted. According to the relationship, the maximum dry density of the real gradation can be determined. The fitting formula between the quantified index of gradation before and after the test was obtained, and the relative change B w of the quantified index of gradation before and after the test was used as the quantitative index of particle breakage to discuss the influence of scaling method on the particle breakage of coarse particles during the compaction process. The results show that B w decreases with the increase of particle size for equal-weight replacement method, but B w increases with the increase of particle size for scalping method, similar grading method and mixing method.

Abstract:To investigate the effects of different sand rates and aggregate sizes on the fracture toughness of plastic concrete, mechanical property tests and three-point bending notched beam fracture tests were conducted to analyze the physical and mechanical properties and apparent morphology of plastic concrete with different mix ratios. The evolution of fracture toughness of plastic concrete with different sand rates and aggregate sizes was revealed. The results show that the strength and fracture toughness of plastic concrete with different sand rates and aggregate sizes vary significantly. With an increase in the sand content from 45% to 85%, the strength and fracture toughness of plastic concrete exhibit a noticeable decline and an upward trend for aggregate particle sizes in the range of 0 to 5 mm and 5 to 10 mm, respectively, but the variation in fracture toughness is comparatively lower. For aggregate particle sizes ranging from 10 to 20 mm, the specimen strength variation law is comparable to that observed for particle sizes between 5 and 10 mm, with a general upward tendency. With an increase in the sand content from 45% to 85%, the fracture toughness first decreases and then increases. The changes in strength, characteristic load, and fracture toughness of plastic concrete under the same mix ratio conditions are relatively consistent with the variation of aggregate particle size.

Abstract:The drift distance, offset distance, and landing range of sandbags thrown by bottom-opening barges and flipper boats in the presence of riverbank slopes are analyzed through generalized flume experiment. The influence of different throwing methods is also investigated. The experimental results show that the existence of the riverbank slope will cause the sandbags to slide or roll, increasing their drift and offset distance. Moreover, as the slope gradient increases, the landing points of the sandbags become more scattered in the downstream direction. The average drift distance of sandbags increases with the flow velocity. When the flow velocity is high, the variation in slope gradient has a relatively small impact on the drift distance of the sandbags. However, when the flow velocity is low, the average drift distance of the sandbags thrown by the bottom-opening barges increases with increasing slope gradient, while the landing points of the sandbags thrown by the flipper boats become more concentrated in the downstream direction. The throwing method of bottom-opening barges results in more dispersed landing points compared to flipper boats, although the difference in landing range between the two throwing methods is insignificant.

Abstract:To study the hydraulic characteristics and applicability of the free-surface-pressure flow tailwater system in the water conveyance and hydropower system, an analysis model for the transition process of the water conveyance and hydropower system was established based on the method of characteristics and the characteristic implicit format. The hydraulic characteristics of two types of tailwater systems, namely, the free-surface-pressure flow and the full-pressure flow, were compared and analyzed. Furthermore, the influence of the transition process of the free-surface-pressure flow tailwater system on the transient parameters of the water conveyance and hydropower system and the regulating quality of the units was further investigated. The results show that, under the conditions of full-pressure flow and free-surface-pressure flow in the tailwater tunnel, the regulating quality of the units ensures that the controlled value deviation of the calculated parameters is small, and the minimum internal water pressure at the inlet of the tailwater pipe corresponding to the free-surface-pressure flow tailwater system is relatively large. The regulating quality of the units of the free-surface-pressure flow tailwater system is better than that of the full-pressure flow tailwater system, and there is no obvious high-frequency oscillation superposition phenomenon.

Abstract:In order to discuss the characteristics of asymmetric inlet flow in a seawater pumping station, a numerical model of inlet flow passage in a liquefied natural gas receiving station was established using OpenFOAM. Based on the measured data, the distribution characteristics of flow velocity and turbulent energy in the inlet flow channel were simulated and analyzed. The simulation results show that when the seawater pumping station is asymmetric, the flow velocity entering the forebay is high, and the flow cannot be fully diffused at a low water level. The flow is biased at the entrance of the flow channel, and is basically uniform in front of the seawater pump. In the asymmetric water diversion condition, the average uniformity index of each section is higher than that of the symmetrical condition, and the average turbulent energy of each water pump is also lower than that of the symmetrical condition. From the perspective of flow velocity uniformity and turbulence magnitude, the asymmetric water diversion is more beneficial to the operation of the pump.

Abstract:To clarify the influence of key shape parameters on the characteristics of water and sediment in the channel and sediment transport pipe, numerical simulations of the water and sediment two-phase flow in the desilting channel with swirling flow were conducted based on the model experimental test. The results show that the height of the swirling flow generator significantly affects the sediment trapping efficiency, with a maximum difference of 5.41%. The diameter and inclination angle of the sediment transport pipe, and the outlet width of the swirling flow generator have significant influences on the split ratio, with a maximum difference of 8.13%. Increasing the inclination angle improves the sediment accumulation caused by wall conditions at the closed end of the sediment transport pipe. The outlet width of the swirling flow generator has no evident effect on the characteristics of water and sediment in the channel. The desilting channel with swirling flow can discharge sediment efficiently and continuously in all types of desilting channels, with sediment trapping efficiency greater than 90%. After passing through the swirling flow generator, the water with high sediment content flows out of the sediment transport pipe, and the sediment content in the downstream channel decreases sharply.

Abstract:Based on the data of 12 representative cross-sections in the Lower Yellow River from October 2006 to November 2018, the adjustment process and characteristics of downstream riverbeds during the continuously scouring period is investigated by analyzing the variation rates of the morphology characteristic parameters of the main channel and the migration intensity of the thalweg and the centerline. The results show that the morphological adjustment of the Lower Yellow River has exhibited a diversity with both lateral widening and vertical scouring or depositing in recent years.The riverbed migration has promoted the adjustment of the cross-sectional morphology of the main channel. The rate of change in cross-sectional geomorphic coefficient was positively correlated with the migration intensity of the thalweg and the main channel centerline. Furthermore, water-sediment condition is the main contributor to the changes in the main channel morphology, causing an increase in the migration intensity of the thalweg in local reach. Hence, a stable medium-size river channel of the Lower Yellow River will be further shaped and maintained when the operation mode of the Xiaolangdi Reservoir is adjusted and the reasonable river control work is established.

Abstract:Taking Ganlu and Dangbei polders in the western polder area of the Wangyu River as the study area, a hydrodynamic and water quality coupling model was constructed, and appropriate parameters of hydrodynamic, water quality, and economic costs were selected to construct a multi-objective evaluation indicator system for flowing water dispatch. The weights of the indicators are determined through a combination of the analytic hierarchy process (AHP) and entropy weight method. The optimal flowing water dispatch scheme for each individual polder is determined, and the effectiveness of these schemes are compared with the jointly coordinated flowing water dispatch scheme for the polder area. The results show that the multi-objective evaluation index system effectively determines the optimal flowing water dispatch scheme. For Ganlu Polder, the optimal scheme involves jointly diverting water from the Chenjiajiao Sluice and Ganlugang Sluice, with the Xujiabang Sluice discharging at a flow rate of 6 m³/s. For Dangbei Polder, the optimal scheme involves diverting water from the Huangtang River Sluice and Wuxing River North Sluice, with the Zhuqiao River Sluice and Wuxing River Sluice jointly discharging at a flow rate of 9 m³/s. Compared with individual flowing water dispatch schemes, the jointly coordinated flowing water dispatch for both polders exhibits superior effectiveness in ensuring smooth water flow.

Abstract:Combined with saturated-unsaturated seepage and consolidation theories, a three-dimensional seepage analysis model of a soil slope in the main stream of the Irrawaddy River was established to investigate the change rule of slope stability under different water level reduction magnitude and reduction speed conditions, and to evaluate the reinforcement effect of the micro wood piles on the slope. The results show that the faster the river water level decreases and the higher the water level is during the flood season, the greater the permeation slope drop near the slope surface is during the water level decrease process, and the lower the safety coefficient is. By installing a group of micro wood piles, the slope stability safety coefficient increased by 4.50%, 9.00%, and 39.60%, respectively, when the height of the wood pile group was 2, 4, and 6 m compared with the case of no reinforcement, indicating that the reinforcement effect of micro wood pile group is good and has some popularization value.

Abstract:Traditional prediction models are difficult to consider the uncertainty of causality of arch dam deformation, leading to the lack of causality mechanism in the established static displacement confidence interval.To solve the difficulty, a prediction method which considers the influence of cognitive uncertainty of temperature deformation effects, was proposed for the confidence interval of high arch dams’ displacement.The dynamic time warping method was used to calculate the similarity between the measured time series of multiple temperature monitoring points on the dam body, and a criterion was established to select the measured temperature deformation factors with the minimum similarity. Multiple support vector machine models were then established,in which the orthogonal experimental sampling of selected temperature factor was used as inputs. The distribution of multi-model predicted displacements was analyzed and used to establish a dynamic changed confidence interval.Research results of the Jinping I Arch Dam indicate that the proposed methods and criteria can effectively optimize the most representative dam temperature monitoring points. The minimum similarity temperature factor-based orthogonal experiment design has small error and high modeling efficiency.The confidence interval of displacement prediction is more consistent with the causal mechanism and the optimal measured temperature factor combination of the high arch dam is dynamic.

Abstract:In order to fully extract the nonlinear and non-stationary characteristics of the dam deformation monitoring data, deeply mine the topological relationship between the preceding and following information, effectively improve the prediction accuracy, a bidirectional long short-term memory (LSTM) neural network dam deformation prediction model based on quadratic modal decomposition and dung beetle optimization algorithm is proposed. The model introduces a quadratic modal decomposition that combines adaptive noise-complete integrated empirical modal decomposition and variational modal decomposition to preprocess the data, which effectively reduces the negative influence of high-frequency non-stationary components on the prediction accuracy, and utilizes dung-beetle optimization algorithm to search for the optimal hyper-parameters of bidirectional LSTM neural networks to deeply explore the effective information of the deformation data of the dams. Taking a hydropower dam as an example, the prediction results of the model are compared with those of several commonly used models, and the experimental results show that the model can effectively exploit the complex nonlinear features of dam deformation data, and its prediction accuracy is significantly better than its counterparts, and the feasibility and superiority of the model in the prediction of dam deformation is verified.