•The decrease of structural densities of cohesive silt beds is captured.•Influences of Bond number and dispersity on structural density are investigated.•The decrease of characteristic line ...separation due to flocculation is reported.•Variation of the particle settling velocity during the settling process is captured.•The collision frequency functions of cohesive silt particles are presented.
The settling of cohesive sediment is ubiquitous in aquatic environments, and the study of the settling process is important for both engineering and environmental reasons. In the settling process, the silt particles show behaviors that are different from non-cohesive particles due to the influence of inter-particle cohesive force. For instance, the flocs formed in the settling process of cohesive silt can loosen the packing, and thus the structural densities of cohesive silt beds are much smaller than that of non-cohesive sand beds. While there is a consensus that cohesive behaviors depend on the characteristics of sediment particles (e.g., Bond number, particle size distribution), little is known about the exact influence of these characteristics on the cohesive behaviors. In addition, since the cohesive behaviors of the silt are caused by the inter-particle cohesive forces, the motions of and the contacts among silt particles should be resolved to study these cohesive behaviors in the settling process. However, studies of the cohesive behaviors of silt particles in the settling process based on particle-resolving approach are still lacking. In the present work, three-dimensional settling process is investigated numerically by using CFD–DEM (Computational Fluid Dynamics–Discrete Element Method). The inter-particle collision force, the van der Waals force, and the fluid–particle interaction forces are considered. The numerical model is used to simulate the hindered settling process of silt based on the experimental setup in the literature. The results obtained in the simulations, including the structural densities of the beds, the characteristic lines, and the particle terminal velocity, are in good agreement with the experimental observations in the literature. To the authors’ knowledge, this is the first time that the influences of non-dimensional Bond number and particle polydispersity on the structural densities of silt beds have been investigated separately. The results demonstrate that the cohesive behavior of silt in the settling process is attributed to both the cohesion among silt particles themselves and the particle polydispersity. To guide to the macro-scale modeling of cohesive silt sedimentation, the collision frequency functions obtained in the numerical simulations are also presented based on the micromechanics of particles. The results obtained by using CFD–DEM indicate that the binary collision theory over-estimated the particle collision frequency in the flocculation process at high solid volume fraction.
•A simple algorithm is proposed to discretize the common sediment-grain shapes.•The discretization algorithm is adequate to reproduce particle-shape properties.•The algorithm is capable of capturing ...integral sediment transport quantities.
Development of algorithms and growth of computational resources in the past decades have enabled simulations of sediment transport processes with unprecedented fidelities. The Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) is one of the high-fidelity approaches, where the motions of and collisions among the sediment grains as well as their interactions with surrounding fluids are resolved. In most DEM solvers the particles are modeled as soft spheres due to computational efficiency and implementation complexity considerations, although natural sediments are usually a mixture of non-spherical (e.g., disk-, blade-, and rod-shaped) particles. Previous attempts to extend sphere-based DEM to treat irregular particles neglected fluid-induced torques on particles, and the method lacked flexibility to handle sediments with an arbitrary mixture of particle shapes. In this contribution we proposed a simple, efficient approach to representing common sediment grain shapes with bonded spheres, where the fluid forces are computed and applied on each sphere. The proposed approach overcomes the aforementioned limitations of existing methods and has improved efficiency and flexibility over existing approaches. We use numerical simulations to demonstrate the merits and capability of the proposed method in predicting the falling characteristics, terminal velocity, threshold of incipient motion, and transport rate of natural sediments. The simulations show that the proposed method is a promising approach for faithful representation of natural sediment, which leads to accurate simulations of their transport dynamics. While this work focuses on non-cohesive sediments, the proposed method also opens the possibility for first-principle-based simulations of the flocculation and sedimentation dynamics of cohesive sediments. Elucidation of these physical mechanisms can provide much needed improvement on the prediction capability and physical understanding of muddy coast dynamics.
Subgrade soils of traffic infrastructures are subjected to large numbers of load applications at a stress level below their shear strength. It is therefore of great practical relevance to study the ...deformation behavior of soft clay under long-term cyclic loading. In this study, a series of monotonic triaxial tests and long-term cyclic (50,000 cycles) triaxial tests have been carried out to investigate the undrained deformation behavior of undisturbed soft clay from Wenzhou, China. The stress–strain hysteretic loop, resilient modulus and permanent strain of the tested samples were found significantly dependent on CSR and confining pressure. With an increase of CSR and confining pressure, the resilient modulus decreases more significantly with increasing number of cycles and the accumulation rate of permanent strain increases. Furthermore, the shape of the stress–strain hysteretic loop almost remains unchanged and the resilient modulus tends to a steady value after a large number of cycles. Based on the experimental results, two equations are established for the prediction of long-term resilient modulus and permanent strain. Finally, a new critical value of 0.65 is suggested for CSR. When CSR>0.65, the resilient modulus for large number of cycles is reduced to a so called “asymptotic stiffness” and the accumulation rate of permanent strain significantly increases.
► A series of long-term cyclic (50,000 cycles) triaxial tests are carried out. ► Deformation behavior is significantly dependent on CSR and confining pressure. ► After large number of cycles, the resilient modulus tends to be a steady value. ► Two equations are given for long-term resilient modulus and permanent strain. ► A new critical value of 0.65 is suggested for CSR.
Soil settlement is one of the most common and critical issues in geologic and geotechnical engineering. Due to various sources of uncertainties, it is hard to predict soil settlement accurately. An ...inverse analysis using the information provided by field measurements is desirable for prediction with higher confidence. In this study, an inverse framework based on ensemble Kalman filtering (EnKF) is proposed to evaluate the soil settlement with quantified uncertainty. The theoretical and practical effectiveness of this scheme is demonstrated through synthetic and realistic tests to predict soil settlement of embankment roads. Inferred results including quantified uncertainties are obtained based on Bayesian theory, which makes a distinction between this method and conventional settlement prediction methods. The results of two synthetic tests show the parameters inferred by the EnKF converge to true values, which verify the satisfactory performance of the proposed scheme. A realistic application of Saga airport road is investigated, and the simulated settlement results are consistent with the field measurements. Moreover, Sobol method is adopted to study the sensitivity of model parameters, and detailed parameter studies are conducted to estimate the influence of ensemble size, the value range of prior distribution and observation error.
•An EnKF-based framework is proposed for settlement in a statistical and inverse way•The model parameters are updated based on sequentially observed data•Sobol method is used to study the sensitivity of model parameters•Improved predictions of subsequent settlement can be obtained
The emergence of human infection with a novel H7N9 influenza virus in China raises a pandemic concern. Chicken H9N2 viruses provided all six of the novel reassortant’s internal genes. However, it is ...not fully understood how the prevalence and evolution of these H9N2 chicken viruses facilitated the genesis of the novel H7N9 viruses. Here we show that over more than 10 y of cocirculation of multiple H9N2 genotypes, a genotype (G57) emerged that had changed antigenicity and improved adaptability in chickens. It became predominant in vaccinated farm chickens in China, caused widespread outbreaks in 2010–2013 before the H7N9 viruses emerged in humans, and finally provided all of their internal genes to the novel H7N9 viruses. The prevalence and variation of H9N2 influenza virus in farmed poultry could provide an important early warning of the emergence of novel reassortants with pandemic potential.
In this paper, a mechanical model of axial and circumferential bidirectional deformation has been developed by considering two factors: roller shape and radial reduction. Since the calibration of the ...roundness and that of the straightness of pipes are currently separate processes, the established mechanical models are based on a single direction. However, the established bidirectional mechanical model can describe not only the stress-strain distribution of the pipe in deformation to determine the position of the stress concentration but also the deformation curve of the pipe in different directions. As a result, it can serve as a theoretical basis for setting process parameters and optimizing roller shape. A large thin-walled pipe of Al6063 is modeled and then numerically simulated with FEM software of ABAQUS, and the results are compared with the model. Then, the process is fabricated and tested experimentally. The results are compared with the mechanical and numerical models. The distribution of equivalent stress and equivalent strain obtained by the model has a good match with the simulation results, and the maximum relative error is not more than 25%. The axial and circumferential deformation curve calculated by the mechanical model coincides well with the simulation and experimental results, and the maximum error is not greater than 3.0 mm. Obviously, both the experiment and the simulation have verified a superior validity of the model.
Graphical abstract
A mechanical model of axial and circumferential bidirectional deformation has been developed by considering two factors: roller shape and radial reduction. The model can describe not only the stress-strain distribution of pipes in deformation to determine the position of the stress concentration but also the deformation curve of pipes in different directions. It provides a theoretical basis for the setting of process parameters and the optimization of roller shape.
Extrusion-based 3D printed concrete is a promising material and processing technique for use in the construction industry. In this study, 3D printed specimens were loaded dynamically and statically ...to investigate their anisotropic characteristics. The experimental results showed that the average static compressive strength of the 3D printed concrete specimens was 115% of that of the cast specimens. Meanwhile, the dynamic compressive strength of DX specimens was significantly larger than that of other 3D printed specimens and cast specimens under the same impact pressure. In particular, ultrasonic pulse velocity values were used to quantitatively represent the anisotropy of 3D printed specimens. In conclusion, the anisotropic characteristics of 3D printed concrete were studied. The results indicate that the performance of 3D printed concrete was best (especially in the
X
-direction). The results provide a reference for engineers looking to design 3D printed components for use in construction.
H5N6 highly pathogenic avian influenza virus (HPAIV) clade 2.3.4.4 not only exhibits unprecedented intercontinental spread in poultry, but can also cause serious infection in humans, posing a public ...health threat. Phylogenetic analyses show that 40% (8/20) of H5N6 viruses that infected humans carried H9N2 virus-derived internal genes. However, the precise contribution of H9N2 virus-derived internal genes to H5N6 virus infection in humans is unclear. Here, we report on the functional contribution of the H9N2 virus-derived matrix protein 1 (M1) to enhanced H5N6 virus replication capacity in mammalian cells. Unlike H5N1 virus-derived M1 protein, H9N2 virus-derived M1 protein showed high binding affinity for H5N6 hemagglutinin (HA) protein and increased viral progeny particle release in different mammalian cell lines. Human host factor, G protein subunit beta 1 (GNB1), exhibited strong binding to H9N2 virus-derived M1 protein to facilitate M1 transport to budding sites at the cell membrane. GNB1 knockdown inhibited the interaction between H9N2 virus-derived M1 and HA protein, and reduced influenza virus-like particles (VLPs) release. Our findings indicate that H9N2 virus-derived M1 protein promotes avian H5N6 influenza virus release from mammalian, in particular human cells, which could be a major viral factor for H5N6 virus cross-species infection.
Rock-embedded foundations with good uplift and bearing capacity are often used in mountains or hilly areas. However, there are soil layers with a certain thickness on the rocks in these mountainous ...areas, and the utilization of those soil layers is a problem worthy of attention in foundation construction. Considering construction- and cost-related factors, traditional single-form foundations built on such sites often cannot provide sufficient resistance against uplift. Therefore, an anchored pier foundation composed of anchors and belled piers, specifically constructed for such conditions, can be invaluable in practice. This paper introduces an experimental and analytical study to investigate the uplift capacity and the uplift mobilization coefficients (UMCs) of the anchored pier foundation. In this study, three in-situ monotonic pullout tests were carried out to analyze the load–displacement characteristics, axial force distribution, load transfer mechanism, and failure mechanism. A hyperbolic model is used to fit the load–displacement curves and to reveal the asynchrony of the ultimate limit states (ULSs) of the anchor group and the belled pier. Based on the results, the uplift capacity can be calculated by the UMCs and the anchor group and pier uplift capacities. Finally, combined with the estimation of the deformation modulus of the soil and rock, the verification calculation of the uplift capacity and UMC was carried out on the test results from different anchored pier foundations.
The influences of the tunnel settlement on vibrations of the saturated poroelastic ground and on the additional forces of the tunnel lining are investigated numerically in this paper. A ...three-dimensional finite element model incorporating the metro train, the tunnel lining and the saturated ground has been established. The ground settlement is introduced into the computational model by a specifically developed vehicle-rail interaction (VRI) element, through which the metro train can be dynamically coupled to the track. The ground is considered as a saturated poroelastic medium that is discretized by a self-developed saturated-soil element based on Biot's theory. Moreover, at truncation boundaries of the ground model, an absorbing boundary condition termed multi-transmitting formula (MTF) that is specially developed for the saturated soil element is applied to meet the far-filed radiation condition. With the inputs of ground settlement data from in-situ measurement, amplifications in the ground vibration and the lining forces have been quantitatively determined by comparing to the settlement-free case. It is found that the ground vibrational velocity and acceleration can reach 40–60 times the responses when there is no differential settlement of the tunnel; the dynamic internal forces including the axial force, the shear force and the bending moment of the tunnel lining can be 7–20 times higher than their static counterparts.
•The ground vibrational velocity and acceleration can be as high as 40–60 times the responses when there is no differential settlement of the tunnel.•The differential settlement of the tunnel has negligible influence on the vibration amplification zone at the ground surface.•The differential settlement of the tunnel not only induce static internal forces to the lining structure, but also prompt the wheel/rail interaction and considerably amplify the dynamic internal forces of the lining.
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