Abstract:From the perspective of physical mechanism of rainfall-runoff behaviour, three small watersheds in different hydrometeorological regions were selected and the design storms were calculated based on the attenuation formula of rainstorm in this study. According to the characteristics of the underlying surface of the basin, the model parameters were deduced, and the hydrological model was constructed to realize the design flood calculation. The results of using the hydrological model to estimate design floods were compared with those of the reasoning formula method. The results show: the design flood obtained by the hydrological model method is similar to that obtained by the inference formula method, with relative errors of flood peak and flood volume not exceeding 30%; the hydrological model method takes into account the variation of soil infiltration capacity during rainfall processes and the uncertainty of the catchment process at various points within the watershed; the uneven spatiotemporal distribution of hydrological model parameters is more in line with the actual runoff generation and concentration laws of the basin, improving the reliability of design flood calculation in the complex situation.

Abstract:To explore the prediction accuracy and physical properties of the grid water drop confluence method, and verify its applicability in areas lacking of or without data, based on the grid model of Xin’anjiang model, the flow yield calculation is carried out, and the confluence model based on the grid water drops is constructed. Tunxi and its nested basin in the humid area and Dongwan and its nested basin in the semi-arid area are taken as the study basins, and the nested sub-basin is assumed to be the area lacking of data. The simulation validation of Tunxi and the inner sub-basin of Dongwan is carried out without re-setting parameters, and the results indicate that in the same watershed, the comprehensive simulation accuracy of the grid water drop confluence model decreases with the decrease of the subwatershed area. The simulation accuracy of the model in Tunxi River basin reaches grade A and the simulation accuracy in its sub-basins basically meets the requirements, while the simulation accuracy of Dongwan reaches Class B and the accuracy of its sub-basins reaches Class C except for the pass rate of flood peak. This study validates the applicability of the grid-water-drop based confluence method in the area lacking of or without data.

Abstract:Based on the supply chain of water resources for the South to North Water Diversion Project, a diversified ecological compensation mechanism that combined the government compensation and the market-oriented compensation was established. By assuming that each member of the water supply chain has the altruistic preference, this paper compared and analyzed the effects of the compensation mechanism of cross-section water quality and the compensation mechanism of water resources protection cost by the central government under altruistic preference. The results show that the water quality, water price and consumer surplus in the water supply chain of water transfer project are positively related to the altruistic preference level of water distributors. The vertical compensation of the central government and the horizontal compensation of the local government can promote the improvement of water quality, and the utility of water receiving areas will increase with the improvement of water quality under altruistic preference. The transfer contract can alleviate the double marginal utility of supply chain members’decision-making under the market-oriented compensation mechanism, alleviate the “hitchhiking” behavior of water distributors, and promote the total utility of supply chain and the welfare of consumers.

Abstract:In order to control the effluent discharge of the Shaying River more effectively and to ensure the normal operation on the water diversion project on the Xifei River line, a one-dimensional hydrodynamic-water quality coupling model was established from MIKE11, and the degradation and dilution characteristics of pollutants in the process of sewage effluent discharge were analyzed in terms of the mechanism of the influence on the water quality of the water-intake of Xifei River, using ammonia nitrogen as the water quality index. The results show that before flood, with the increase in the ratio of feeder flow, the pollution mass transitions from being mainly subject to degradation to dilution and the effluent discharged at the beginning of the flood mainly relies on the dilution effect of the main stream to reduce the concentration. When the sewage flow of the Shaying River before and at the beginning of the flood is greater than that of the main stream by 10% and 7%, respectively, the water quality at the water intake is at risk of exceeding Class III of surface water standard. There is a power function relationship between the concentration of ammonia nitrogen at the intake and the branch to trunk flow ratio, and the fitting effect of the two is related to the degree of dilution of the polluted mass by the main stream.

Abstract:This study tested the contaminant removal effect under the conditions of substrate combination, packing arrangement, and hydraulic loading under four substrates (gravel, zeolite, ceramsite and vermiculite) as part of an attempt to improve the purification capacity of ecological filter dams. The results showed that the gravel and ceramsite group had the superior COD removal efficiency, whereas the best removal efficiencies of NH+4-N and TP were achieved by the gravel and zeolite group. It was also found that uniform mixing mode could most effectively improve the removal of COD, but the best removal efficiencies of NH+4-N and TP were found in the gravel in former and zeolite in behind mode. With the increase of hydraulic loading, the removal rates of COD and TP in three mixing modes were gradually decreased, and NH+4-N removal behaved decrease in uniform mixing mode, but increased first and then decreased in two-layer mixing modes.

Abstract:To improve the prediction accuracy on the deformation of dam structure, the complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) algorithm was adopted in this work to decouple the measured sequence into a series of intrinsic mode functions with different time-frequency characteristics, and then the wavelet threshold denoising was used to stabilize the high frequency component for the reconstruction. Afterwards, a dual-stage attention-based long short-term memory network (DA-LSTM) model was introduced to predict the reconstructed deformation sequence. The results show that the denoising processing method combining CEEMDAN algorithm and wavelet threshold denoising can effectively identify and deal with the outliers in the measured data to improve the representation capacity on the dam performance. Moreover, the established model can exploit the hysteresis of dam deformation and enhance the interpretability of the DA-LSTM network, indicating the strong robustness.

Abstract:To study the influence of the convex terrain in the left bank and excavation schemes on the stress-deformation characteristics of concrete slab and joints displacement of concrete face rockfill dams (CFRD), a three-dimensional nonlinear FEM analysis was conducted on a CRFD built on the foundation with local convex terrain. The distribution law of tensile stress on the concrete face was explained according to the deflection curves of concrete slab along the dam axis and the slope direction. Besides, the risk index of the concrete face cracking was proposed, which was used to evaluate the effect of excavation schemes. The results show that the convex terrain in the left side of dam has a great influence on the stress deformation of concrete slab and joints displacement. Compared with the completely excavated scheme, the convex terrain has the effect of constraint and support for rockfill materials and concrete slab in the left side of the dam, which leads to the decrease of the dam axial displacement and deflection of the concrete slab, increase of the tensile area of the concrete slab, and increase of the number of tension joints. However, the maximum tensile stress of the concrete slab, opening of the vertical joints, as well as the opening and dislocation of the peripheral joints are reduced. As the upstream side of the convex terrain excavated at the slope of 1∶1.5, the deformation coordination of the concrete can be improved. The tensile area and the number of tensile vertical joints are reduced, which can effectively reduce the risk of cracking of concrete slab.

Abstract:Based on the large-scale triaxial compression test and creep test of coarse aggregates under freezing and thawing environment, the deformation and creep characteristics of coarse aggregates under different freezing-thawing cycles, confining pressures and stress levels are studied. The test results show that the stress-strain relationship of unfrozen coarse-grained materials is a strain hardening curve, and the coarse-grained materials show dilatancy in the shear process within the confining pressure range of 100-600.kPa. Under the influence of freeze-thaw cycle, the initial elastic modulus and failure stress both show a downward trend. When the confining pressure is 200.kPa, the initial elastic modulus decreases by 20% and the failure stress decreases by 37%. When the confining pressure is 600.kPa, the initial elastic modulus decreases by 5% and the failure stress decreases by 25%. The deformation of coarse-grained materials under freeze-thaw cycles develops into a decay-type creep with time. Meanwhile, the axial creep strain gradually increases with the increase of the number of freeze-thaw cycles and the stress level. The axial creep strain obviously increases after 8 freeze-thaw cycles and the creep time curve of coarse aggregates under the influence of stress level can be expressed in the form of exponential function.

Abstract:To analyze the mutual influence of adjacent twin-bore tunnel’s construction, complex function and Schwarz alternation method were used to solve the analytical function of ground displacement based on the gravity effect of soil layers and the convergent deformation of tunnel chamber, and the ground displacement was corrected by setting displacement constraints, so that an analytical model of adjacent twin-bore tunnel under the gravity effect of soil layers was finally obtained. Based on the model mentioned above, this study analyzed the influence of iteration number, displacement binding, and horizontal chamber deformation on the strata displacement, and the results shows that the calculation meets the accuracy requirements with iteration number of 2. It should be noted that by comparing the results corrected by displacement with those without the displacement correction, setting the boundary condition of vertical displacement makes the relative displacement curve of ground surface shifted downward as a whole, and the left horizontal displacement boundary condition can make horizontal deformation shift leftward at a certain amount. With the increase of chamber’s horizontal deformation coefficient, the relative vertical deformation of strata will increase while the relative horizontal deformation will decrease, and the effects on them are different. Based on the criterion of ground displacement, the strong, weak and no influence zones of the twin-core tunnel with geometric proximity and buried depth ratio are obtained.

Abstract:In order to investigate the improvement effect of the basalt fiber reinforced polymer (BFRP) on the mechanical behavior of recycled concrete, the BFRP tube confined recycled concrete cylinders were tested under axial compression and the effect of the number of BFRP layers on the compressive behavior of cylinders was analyzed. Test results show that the failure mode of BFRP tube confined recycled concrete cylinders is characterized by the rupture of the BFRP followed by the compressive failure of cylinders. The confinement of BFRP tube can significantly increase the ultimate capacity and deformation ability of recycled concrete cylinders, and the axial compressive stress-strain curves exhibit an obvious hardening stage. With an increase in the BFRP layer, the axial compressive strength of confined recycled concrete increases by 78%-281%, and the ultimate axial compressive strain increases by 6.16-18.10 times, compared those of the unconfined recycled concrete. Both the axial compressive strength and ultimate axial compressive strain of the BFRP tube confined recycled concrete are much greater than those of the corresponded unconfined normal concrete. Finally, the applicability of the typical axial compressive strength and ultimate axial compressive strain models of fiber reinforced polymer (FRP) confined concrete cylinders in the BFRP confined recycled concrete was evaluated based on test data, and it is observed that the evaluated typical models cannot provide an accurate prediction in the axial compressive strength and ultimate axial compressive strain of specimens.

Abstract:To improve the control accuracy of the multiple-regression feedback model of intelligent compaction control technology based on compaction parameters and filler properties, this study constructed the multiple regression model considering only the compaction parameters, and then optimized the feedback model with the moisture content as the correction parameter on the basis of analyzing its influence law on the observation value of vibrations. The results of previous feedback model and optimized feedback model show that although the intelligent compaction construction control using these two feedback models meet the requirements of specification, the qualified rate of the optimized feedback model is greater than the previous feedback model and the control accuracy is improved by 54.1%, which proves the scientificity and feasibility of the optimized feedback model.

Abstract:In order to study the compressive properties, deformation rules and improvement mechanism of sand improved by the organic polymer composite fiber, through the unconfined compressive strength test and the numerical simulation, the laws of force chain change and microcrack development in the compressive deformation process of improved sand were analyzed, from which the destruction and improvement mechanism of improved sand were summarized. The results show that the organic polymer composite fiber can effectively improve the compressive strength of sand. With the increase of organic polymer content, the unconfined compressive strength of improved sand increases. In addition, with the increase of organic polymer content and strain, the force chain evolution and microcrack development of the improved sand change obviously. The force chain changes from a ring-column structure to an arch structure, and the total number of microcracks and tensile microcracks also increases, indicating that failure changes from single path to multiple paths. The improvement mechanism shows that the organic polymer composite fiber can effectively improve the compressive properties of sand by binding and wrapping the sand grains. When the load is too large, the organic polymer film breaks, the fibers break and slip gradually, and the network structure becomes unstable gradually. In such a condition, the sand is forced to displace and rotate, forming local micro-cracks that eventually develop and extend to form cracks resulting in damages.

Abstract:A physical model experiment was carried out in the laboratory flume to study the wave attenuation characteristics of tidal flat, vegetation and mangrove ecosystem, while the wave-height attenuation contribution of tidal flat to the mangrove ecosystem was quantitatively analyzed. The results show that with the increase of vegetation submergence, the wave height ratio of tidal flat and mangrove ecosystem increases gradually, namely the wave attenuation effect is getting weaker and weaker. The wave height ratio of vegetation first decreases and then increases, and the wave height ratio of vegetation is much higher than that of other vegetation parts when the water level is in the center of vegetation canopy. With the increase of relative wave height, the wave height ratio of tidal flat first stabilizes around 1.0 and then decreases, and the wave height ratio of mangrove ecosystem gradually decreases, while the wave height ratio of the vegetation first decreases and then increases. With the increase of relative width, the wave height ratio of tidal flat first decreases slightly and then increases, but most of them stabilize around 1.0, while the wave height ratio of vegetation and mangrove ecosystem first increases and then decreases slightly. The contribution of tidal flat to the wave height attenuation of mangrove ecosystem increases with the decreases of vegetation submergence, and the maximum contribution can reach 63%. Wave propagation in the mangrove ecosystem is characterized by the nonlinear attenuation and the attenuation rate of wave height per unit length is much larger in the first quarter width than that in the last three quarters width of the vegetation belt.

Abstract:To respond to the global climate change and to help achieve the “double carbon” goal in China, this paper proposed an idea of implementing the “Blue Carbon Project”offshore moored kelp farms. Based on this idea, the design and analysis procedures for the offshore moored kelp farms were described, and numerical simulations of core breeding facility in the kelp farm module were also conducted. The results show that tension values of mooring ropes, breeding boom ropes, connecting ropes and lifting ropes do not exceed the breaking limit values in extreme sea conditions. Besides, the heaving motion of buoys makes little impact on the regular sunlight exposure of seaweed and the breakage of seaweed’s holdfast is an event of low probability. The design and analysis method proposed in this paper will provide a reference for the mooring design of kelp farms with a water depth over 40 m.

Abstract:The southern Yellow Sea is selected as the research area, and the hindcast of significant wave heights simulated by SWAN model during 1979-2018 are used as the initial database. The independent non-tropical cyclone samples are extracted from the original data set by the automated method to calculate the extreme wave height. The N largest maxima method is selected to extract the extreme sample and the generalized extreme value model is matched for fitting. By analyzing the model fitting results and the uncertainty of extrapolated effective wave height, a reasonable range of N value was determined and validated by the stable threshold range of the threshold method. By using this method, the estimated extreme wave heights of 50, 100, 150 and 200 a return periods in the southern Yellow Sea are obtained, which can provide reference for the design and construction of marine and coastal projects in the southern Yellow Sea.

Abstract:Based on a open-source numerical software of wave, COBRAS, a two-dimensional numerical model is developed to study the wave propagation and evolution characteristics over a beach in Benin, in which the free surface is captured by the Volume-of-Fluid method and the Reynold stress is obtained by solving the k-epsilon equations. The numerical model is validated with the experimental data for the free surface of a solitary wave during the shoaling and breaking over a slope. The proposed model is then used to study the shoaling and breaking processes under ordinary and extreme wave conditions. The results show that the waves break near the sandbar under the ordinary wave condition. However, under the extreme wave condition, they start to break 200 m away from the sandbar, and during the interaction of the rundown water and the incident wave, vortexes shall be formed over the sandbar. In the breaking zone, the water velocity is relatively large, which can be 7.5 m/s under the ordinary wave condition and even reach 12.4 m/s under the extreme wave condition. With the increase of the nonlinearity of the incident wave, the runup height increases, and overtopping occurs under the extreme wave condition.

Abstract:Based on MIKE 21 model and Holland typhoon wind field model, the wind field and pressure field during No.1909 Typhoon Lekima and No.0509 Typhoon Matsa are constructed, and the corresponding storm surge process is simulated. The results show that the increase of water near the typhoon center changes significantly and the storm surge in the northeast of Zhejiang Province is greater during the typhoon landing. Affected by the typhoon intensity, the high value area of storm surge during Typhoon Lekima is larger, and the maximum difference of storm surge during two typhoons in some sea areas is close to 1.0 m. The large value of tidal Euler residual current is mainly distributed in the sea area within a depth of 100 m and a velocity of more than 20 cm/s. Meanwhile, the Euler residual circulation exists in the coastal sea areas of Jiangsu Province and the northeastern sea areas of Taiwan Province. The value of Stokes residual current in the offshore during Typhoon Lekima is generally lower than that during Typhoon Matsa. The Stokes residual current term plays a certain leading role in the short-term transport process of net material in the coastal shallow water areas such as the Yangtze River Estuary, Zhejiang Province and Fujian Province during the typhoon. The empirical mode decomposition (EMD) method and Hilbert transform are used to analyze the characteristics of storm tide level at typical stations. It is found that the IMF1 mode at stations is in good agreement with the astronomical tide level. The water depth and the maximum power spectral density of IMF3 mode show a high correlation, and with the increase of water depth, the maximum power spectral density of IMF3 mode gradually increases.