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Extracellular polymeric substances (EPS) have a great impact on the characteristics of sediment particles and their environmental effects in hydro-environmental systems, yet little effort has been made to study the considerable variability in the element adsorption process of sediment particles caused by EPS. Understanding the variability of the adsorption characteristics of sediment particles associated with EPS and quantifying the scale of the adsorption isotherm parameters are important for understanding how EPS mediate sediment properties and environmental factors. In this paper, isothermal equilibrium adsorption experiments are done on phosphorus to study the influence of EPS on the adsorption characteristics of sediment particles, and the Langmuir adsorption isotherm is applied to analyze the adsorption rule of sediment particles under the impact of EPS. The current research demonstrates that significant differences will take place in the adsorption characteristics of sediments coated with EPS at different development phases and the phosphorus adsorption capacity of sediment particles increases with the growth of EPS. The difference in the adsorption percentage between sediment particles coated with EPS of 0 and 6 weeks growth time is about 42%–60% for different initial aqueous phosphorus concentration. A formula describing the adsorption isotherm parameter of the maximum material (element) adsorption capacity of sediment particles change over time is further proposed based on the experimental data. The current study provides some evidence for the interaction of sediment particles, EPS, and adsorbed elements in the water environment.

Morphological evolution in tidally influenced estuarine channel networks has strong influence on the redistribution of fluvial discharge and tidal motion. Based on channel bathymetry and hydrological data observed in 2002 and 2016, this study investigated the influence of morphological evolution on subtidal flow division in the Yangtze River Delta. Experiments using a 2D hydrodynamic model revealed the subtidal discharge was allocated more equally to the downstream channels at the main bifurcation in 2016. The bathymetric variation results in reduction of the discharge asymmetry index by reducing the effect of tidal motion. The decreased channel volume and cross-sectional area of the North Branch has been responsible for the reduction of the tidal flow intrusion into this channel. Allocation of the subtidal discharge to the North Branch has increased because of the reduction of tidal motion in this channel, induced by accretion in this channel during 2002–2016.

In this work, we carried out bulge test for quantifying the viscoelastic properties of poly (vinyl alcohol) (PVA) thin films with custom-developed apparatus. A viscoelastic bulge deformation (VBD) model based on the elasticity–viscoelasticity correspondence principle and spherical cap equation is established to describe the bulge deformation of polymeric thin films. The VBD model can be used to determine the time-dependent modulus by bulge test for polymeric films. Uniaxial compressive relaxation test and PRONY series fitting method are used to define the constitutive parameters of the VBD equations. We presented two types of VBD models in frequency domain under linear loading and step loading conditions. Through inverse Laplace transformation, the proposed VBD model can effectively predict the bulge deformation of PVA hydrogel thin film. Numerical simulations are also conducted to validate the VBD model under step loading conditions. This work provides a methodology to characterize the viscoelastic properties of polymeric films by bulge test.

Qinzhou Bay consists of an inner bay, an outer bay and a connecting rocky inlet. A large-scale channel-shoal morphological system has been historically present in the outer bay. Qinzhou Harbor has utilized the east channel as access route and plans further dredging and expansion of its operational yard by land reclamation; meanwhile, a 6×1000 MW nuclear power plant is being constructed. The plant is to build long-range jetties to intake sea water as cooling water from the west channel and release thermal waste water into the same channel. To ascertain the combined influences of these large engineering projects upon the long-term evolution of the channel-shoal system this study uses FVCOM to investigate the tidal discharges, flow asymmetries and sediment discharges of three channels and perform one-hundred-year-long morphological simulation. It is found that the loss of wide intertidal flats and the cross-section of the inlet will not cause migration or merging of channels as long as tidal prism into the inner bay is not reduced significantly; meanwhile, the full-length dredging in the ebb-dominated east channel in terms of ‘bed-erodible tidal excursion’ can trigger long-term erosions in other ebb-dominated channels, and helps maintain the overall stability of channel-shoal system.

This study examines long-term channel-shoal stability in the Tieshan Bay, which is located on the southwest coast of China. A large-scale channel-shoal system has historically existed in the outer Tieshan Bay. A navigation waterway is initiated by cutting and dredging a mid-channel shoal to supply coal to a power plant on the middle coast of the Tieshan Bay. Dredging of the access channel to the Tieshan Port was conducted in two stages followed by land reclamation. It is thus of practical meaning to explore how the channel-shoal system will evolve in long term afterwards. This study uses the process-based finite-volume coastal ocean model (FVCOM) to investigate long-term (centennial) morphological evolution of the channel-shoal system. After well calibration of hydrodynamics and sediment transport, the model forecasts morphodynamic evolution in hundred years. The simulations show that continuous erosion in tidal channels and accretion over shoals and intertidal flats occur. However, the cutting and access channels will be subjected to long-term siltation. A secondary channel indicating the reorientation of the access channel will emerge, and a localized channel-ridge system at the junction of the major channels will be formed. The overall erosion/accretion pattern demonstrates the combined effect of bottom friction and advective sediment transport processes to be responsible for the channel-shoal formation. Dredging of the tidal channels will stimulate the stability of the channel-shoal pattern. It suggests that the navigation waterway should be set up following the long-term morphological evolution of the channel-shoal system at a design stage and maintenance dredging volume might thus be minimized.

Uniaxial tension, inter-laminar shear and bending behaviors of stitched sandwich panels (SSPs) are simulated using the finite-element method. The effects of stitching angle on the uniaxial tensile, bending and inter-laminar shear stiffness and the inter-laminar shear strength of the SSP are numerically analyzed by ABAQUS codes. The SSP consists of three components: upper and lower skins, heat insulation core and stitches, and it modeled as a discrete stitched three-layer structure. Representative volume element (RVE) with periodic mechanical boundary conditions is constructed. SSP specimens subjected to uniaxial tensile, bending and inter-laminar shear loadings to yield the mechanical response of the SSP. Sandwich panel specimens unstitched and the SSP specimens with six different stitching angles are numerically tested. The uniaxial tensile, bending and inter-laminar shear stiffness and inter-laminar shear strength of the SSP are then computed. The results of simulations showed that: stitches in SSP significantly improved the tensile and inter-laminar shear stiffness of the SSP, while the enhancement of bending stiffness by stitching is not much; except that, the tensile and inter-laminar shear stiffness are influenced by the stitching angle significantly and the value 45° is recommended.

The effects of aggregate shape and distribution on the strength and fracture behavior of Polyurethane Polymer Concrete (PPC) are analyzed through a numerical approach. A 2D FE model is constructed in which aggregates are modeled by random distributed polygon, and interfaces are the areas surrounding each aggregate. The mechanical parameters of the polyurethane (PU) matrix and the bonding properties between the PU matrix and aggregate are experimentally determined. Compressive testing of the PPC specimens is firstly carried out to provide experimental benchmark for calibration of the proposed numerical model. Numerical simulations of the model with static tension are then carried out using thirty generated specimens and the tensile stress–strain curves are obtained. It is found that the aggregate shape and distribution have significant effects on the failure behaviors of the PPC specimen under loading, i.e. the micro-cracks formation, growth and the failure strength. Based on numerical analysis, a threshold value of the aggregate polygon meso-statistical parameter is recommended, under which the PPC material presents the best mechanical properties.

Climate extremes, characterized by droughts and floods, have become one of the major constraints to sustainable improvement of rice productivity. Variety choice, considered as one of the main adaptation measures, could help farmers reduce yield loss resulting from these extremes. Based on a three-year panel survey of 1,080 Chinese rice farms in major rice producing provinces, we study the effect of adopting stress tolerant variety rice as a main adaptation measure against climate extremes. Taking into account the endogeneity of adoption behavior, we employ an endogenous switching regression to separately estimate the treatment effects of adoption for adopters and non-adopters. We find that farmers who adopted the new variety increased yield by 537 kg/ha (about 7%), compared with the counterfactual case of no-adoption. In contrast, the farmers who did not adopt, would increase rice yield by 272 kg/ha (about 4 %) if they adopted, much smaller than the adopters. However, adoption of new variety demands more knowledge, better education, more intensive management, and higher seed costs. As a policy implication, expansion of public extension services could help relax these restrictions., Updated version for AAEA full paper

Climate extremes, characterized by droughts and floods, have become one of the major constraints to sustainable improvement of rice productivity. Variety choice, considered as one of the main adaptation measures, could help farmers reduce yield loss resulting from these extremes. Based on a three-year panel survey of 1,080 Chinese rice farms in major rice producing provinces, we study the effect of adopting weather tolerant variety rice as a main adaptation measure against climate extremes. Taking into account the endogeneity of adoption behavior, we employ an endogenous switching regression to separately estimate the treatment effects of adoption for adopters and non-adopters. We find that farmers who adopted the new variety increased yield by 537 kg/ha (about 7%), compared with the counterfactual case of no-adoption. In contrast, the farmers who did not adopt, would increase rice yield by 272 kg/ha (about 4 %) if they adopted, much smaller than the adopters. However, adoption of new variety demands more knowledge, better education, more intensive management, and higher seed costs. As a policy implication, expansion of public extension services could help relax these restrictions.

The mathematical model of contaminant migration with the Langmuir isotherm equation to describe nonlinear equilibrium sorption in porous medium was developed in the present paper. The model was deduced based on the migration mechanism of pollutants in pore water of soil and the mass conservation. The two dimensional finite element models of the governing equations were discretized with the Full Upwind Petrov-Galerkin method (FUPG), and the nonlinear algebraic equations were received, and the program of the present finite element model was developed to solve the equations. Numerical simulations were carried out with the present model. The benchmark of 1D clay column was numerically analyzed, the influence of nonlinear equilibrium sorption on the transportation was studied. A two dimensional problem of the long term contamination transportation was analyzed. The numerical results show the stability of the current model and the ability of the program to analyze the contaminant transportation of nonlinear equilibrium sorption in clay, and the delay of absorption on the contamination transportation are exhibited.

PVA (Polyvinyl Alcohol) hydrogel is a kind of soft materials, with nontoxic and good biocompatibility. This kind of hydrogel shows strong nonlinearity in the static compression tests because of the high water content (~60‑90%), and the water is squeezed out when the PVA hydrogel is compressed. It means that the PVA hydrogel losts the mass during compression. Aiming at the changing mass mechanism and constitution in the compression of PVA hydrogel, we established a simplified microscopic model which is a single layer frame composite structure consisting of PVA fibers, water, and virtual membrane, in which the membrane wraps outside surfaces of the cubic cells and has no mass, but its membrane force has same properties with the surface tension of water. In the model, the deformation of PVA fibers and the compressive water sustains the external stress when the PVA hydrogel is compressed. In addition, by considering the limitation of the maximum membrane force induced by compressive water, the squeezed water will be calculated in each compressive step and the mechanism of the changing mass is determined quantitatively; in the meantime, the constitution of the PVA hydrogel may be deduced.

Metallic foam is a typical porous material whose yield surface is related to not only von Mises equivalent stress but also the hydrostatic pressure. It is essential to study the yield properties of closed-cell aluminum foam under complex loading conditions. However, because the current experimental technique may support only a few proportions of multiaxial loading, it is hard to learn the yield surface well especially for the tensile hydrostatic pressure. In this article, we explored a numerical method to learn the yield properties of aluminum foam, in which the meso structures of aluminum foam were simulated by 3D Voronoi method. In addition, the yield surface of aluminum foam was drawn successfully with the numerical method. The main works included: (1) In our numerical simulation, we tested the calculating parameters such as mass scaling, elements number, and loading velocity on simulation results and verified the homogeneity of the 3D Voronoi model firstly. Furthermore, the optimized calculating parameters were determined by considering both reliability and feasibility of the calculation. Homogeneity of 3D Voronoi model was checked by the compression behaviors of aluminum in different directions. (2) In order to overcome the difficulty to determine critical yield state of metallic foams under complex loads, we recommended criterion by setting a dimensionless plastic dissipation value to determine the onset yield state of the foam under multiaxial loads. The critical value of dimensionless plastic dissipation was deduced from the common criterion—0.2% plastic strain in uniaxial loading, and the effect of relative densities on critical values was analyzed. (3) Three normal stresses were applied on cubic aluminum foam proportionally to implement the proportional loading. The different loading proportional factors of the three normal stresses were set widely to insure the yield surface including enough data, such as the hydrostatic loads cover from minimum negative to maximum positive values; each proportion has three loading proportional factors. Further, effects of the relative density on yield surface were investigated.