The Material Deformation and Internal Structure Development of Granular Materials under Different Cyclic Loadings

Common structures in engineering such as slopes,roadbeds,ballasts,etc.,are closely related to granular materials.They are usually subjected to long-term cyclic loads.This study mainly focused on the mechanical behaviors of randomly arranged granular materials before they reach a stable state under different cyclic loads.The variation of the maximum axial strain and the influence of CSR(cyclic stress ratio)were analyzed.The energy consumed in each cycle under constant confining stress loading condition is significantly greater than that of the fixed wall loading condition.The internal deformation evolution of granular materials is studied in detail.The deformation mode of granular material under cyclic loading at different positions inside the material is different according to the strain variation.In addition,the strain,force chain structure and contact force magnitude are combined to explore their effects on local deformation of granular materials under cyclic loading.From the perspective of the deformation form,the material sample can be divided into several regions,and the ability to adjust particle positions determines the deformation mode of different regions.The changes of local strain with the cyclic loading also reflect the contribution of particle displacements to the evolution ofmicrostructure.This research will provide insights into the understanding of granular materials behaviors under cyclic loading.

Statistical Analyses of Wave Height Distribution for Multidirectional Irregular Waves over A Sloping Bottom

The main objective of this paper is to examine the influences of both the principal wave direction and the directional spreading parameter of the wave energy on the wave height evolution of multidirectional irregular waves over an impermeable sloping bottom and to propose an improved wave height distribution model based on an existing classical formula.The numerical model FUNWAVE 2.0,based on a fully nonlinear Boussinesq equation,is employed to simulate the propagation of multidirectional irregular waves over the sloping bottom.Comparisons of wave heights derived from wave trains with various principal wave directions and different directional spreading parameters are conducted.Results show that both the principal wave direction and the wave directional spread have significant influences on the wave height evolution on a varying coastal topography.The shoaling effect for the wave height is obviously weakened with the increase of the principal wave direction and with the decrease of the directional spreading parameter.With the simulated data,the classical Klopman wave height distribution model is improved by considering the influences of both factors.It is found that the improved model performs better in describing the wave height distribution for the multidirectional irregular waves in shallow water.

An Improved Approach for Interaction of Wave with Floating Spheres and Its Applications

To develop and utilize marine resources in the deep sea, the higher requirements for floating structures, which are operated in marine environment for a long term, have been put forward. Reasonable structure type and accurate force analysis are favorable guarantees to improve the survival performance and working performance of the floating structures. Floating spheres fastened by mooring cable were widely used in floating structures. In this paper, the wave forces of the floating sphere are efficiently and accurately calculated by solving the geometric relationship between the non-submerged floating sphere and wave surface. Combined with the hydrodynamic calculation of mooring cables based on the lumped mass method, the coupled motion model of multi-floating spheres fastened by multi-mooring cable was established under wave action. Furthermore, according to the floating structures fastened by mooring cable in the actual ocean engineering, the topological method of multi-mooring cables fastening the multifloating spheres was expounded from simple to complex. Finally, the modeling method and preliminarily hydrodynamic characteristics of the fastened floating structures, including the mooring system of renewable energy devices, ocean buoy, and coral nursery, were presented and analyzed in detail. The obtained results showed that the method for calculating the wave force on the floating sphere developed in this paper can accurately describe the motion process of the floating mooring sphere and the force on the mooring cable. Also, the topological method of multiple buoys and multiple mooring cables could efficiently establish various numerical hydrodynamic models of fastened buoys in ocean engineering.

Exact solution and approximate solution of irregular wave radiation stress for non-breaking wave

Wave radiation stress is the main driving force of wave-induced near-shore currents. It is directly related to the hydrodynamic characteristics of near-shore current whether the calculation of wave radiation stress is accurate or not. Irregular waves are more capable of reacting wave motion in the ocean compared to regular waves. Therefore,the calculation of the radiation stress under irregular waves will be more able to reflect the wave driving force in the actual near-shore current. Exact solution and approximate solution of the irregular wave radiation stress are derived in this paper and the two kinds of calculation methods are compared. On the basis of this,the experimental results are used to further verify the calculation of wave energy in the approximate calculation method. The results show that the approximate calculation method of irregular wave radiation stress has a good accuracy under the condition of narrow-band spectrum,which can save a lot of computing time,and thus improve the efficiency of calculation. However,the exact calculation method can more accurately reflect the fluctuation of radiation stress at each moment and each location.

Effect of Nb doping on microstructure and magnetic properties of hot-deformed Nd-Fe-B magnets with Nd-Cu eutectic diffusion

To restrict grain growth in coarse grain regions caused by the diffusion of Nd-Cu eutectic alloys,the Nb element was introduced into the precursor alloy to regulate the microstructure of melt-spun powder and die-upset magnets.The magnetic properties and thermal stability of die-upset magnets were appreciably improved through the addition of Nb.For the Nb-doped diffusion die-upset magnet,the grains inside the ribbons were refined and the coarse non-oriented surface crystallite got suppressed on the interface of ribbons during the hot-deformation process to form the anisotropic magnet.Moreover,Nd gathers at the intergranular phases,which is considered to enforce domain wall pinning force.The Nb-modified microstructure is advantageous to thermal stability and coercivity enhancement.High-resolution transmission electron microscopy images revealed that the Nb element gathered on the grain boundary and triple grain boundary to form c-Nb and h-Nb Fe B to hinder the grain growth during the hot-deformation process,which led to direct enhancement in the coercivity.Furthermore,the c-Nb and h-Nb Fe B are nonmagnetic phases that strengthened the magnetic isolation.However,the h-Nb Fe B precipitated from the hard magnetic phase and formed crystal defects which led to remanence deterioration.

Sediment Dynamics Subject to Sea Level Rise in the Yangtze River Estuary

In this study,a two-dimensional hydrodynamic and sediment transport model is established to quantify the influences of sea level rise on sediment transport in the Yangtze River Estuary(YRE).After validation,the model was employed to investigate the sediment transport and seabed evolution under four different scenarios of sea level rise,specifically,0,0.5,1 and 1.5 m.The results reveal that there exists a‘transition point(TP)'of SSC in each main channel of YRE.Upstream of the transition point,the suspended sediment concentration(SSC)increases along with the rise in sea level,while downstream of the transition point,SSC decreases as sea level rises.Similarly,there are also transition points for topography evolution.The maximum scouring rate upstream of the transition points exceeds 4.32% for a 1.5 m rise in sea level,while the maximum deposition rate downstream of the transition points is 2.48%.The sediment fluxes from upstream to downstream in the branches of YRE are enhanced by the rise in sea level.The direction of sediment flux in the North Branch reverses downstream as sea level rises.The sediment flux from the North Channel towards downstream increases significantly,while there is no significant change in sediment flux for South Channel.Sediment deposition in the North Passage is also accelerated by sea level rise.In addition,the sediment flux from YRE to northern Jiangsu and Hangzhou Bay is also weakened by the rise in sea level.

Influence of Ship-based Vibration on Characteristics of Arc and Droplet and Morphology in Wire Arc Additive Manufacturing

To explore the feasibility of using wire arc additive manufacturing(WAAM)for forming and repairing marine components during ship navigation,this study conducted deposition experiments of ER50-6 steel and investigated the interference of ship-based vibrations on the WAAM equipment and influence of the characteristics of the arc droplets and sample morphology.The results revealed that the WAAM equipment vibrated with the external vibrations from the surrounding environment,and the welding gun and base plate produced dissimilar vibrations,which yielded unstable arc shapes resembling a bell,trumpet,fan,broom,and other irregular shapes.The mode of the droplet transfer ranged from the stable spray transfer mode to extensive amounts of large droplet transfer and short-circuit transfer.Although the morphology of the obtained sample deteriorated,the fully dense and defect-free interior demonstrated the applicability of ship-based WAAM.

Improving performance of ZnO Schottky photodetector by inserting MXenes modified-layer

The development of low-cost and high-performance ZnO Schottky photodetectors (PDs) has drawn intensive attention,but still a challenge due to their poor conductivity and low light utilization efficiency.Here,we introduce Ti_(3)C_(2)T_(X) into ZnO films to fabricate Schottky UV PDs via facile spin-coated method.The fabricated ZnO/Ti_(3)C_(2)T_(X)/ZnO compound film shows outstanding performance on photocurrent,responsivity,noise equivalent power (NEP),normalized detection rate (D~*),and linear dynamic region (LDR),compared with the original Zn O device.The photocurrent is significantly increased by 466%,and the responsivity is improved by one order of magnitude.In addition,it exhibits relatively low NEP (5.99×10^(-11)W),strong D~*(2.53×10~9 Jones),and high LDR (28 dB).The superior performance is ascribed to the enhanced conductivity and light absorption of ZnO film after introduction of Ti_(3)C_(2)T_(X) modification layer,leading to simultaneously faster electron transfer,lower the radiation recombination of electron and holes on the ZnO/Ti_(3)C_(2)T_(X)/ZnO compound film.This work provides a facile way to develop low-cost and highperformance ZnO Schottky PDs.