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Under the action of dynamic loadings such as earthquakes and volcanic activities, the mechanical properties of gas-hydrate-bearing sediments will deteriorate, leading to a decrease in the stability of hydrate reservoirs and even inducing geological disasters such as submarine landslides. In order to study the effect of dynamic loading on the mechanical properties of hydrate sediments, triaxial compression tests of numerical specimens were carried out by using particle flow code (PFC2D), and the macro-meso mechanical behaviors of specimens were investigated. The results show that the loading frequency has a small effect on the stiffness of the hydrate sediment, while it has a large effect on the peak strength. The peak strength increases and then decreases with the increase in loading frequency. Under the same loading frequency, the peak strength of the hydrate sediment increases with the increase in loading amplitude, and the stiffness of the specimen decreases with the increase in loading amplitude. The maximum shear expansion of the specimen changes with the movement of the phase change point and the rearrangement of the particles. The maximum shear expansion of the specimen changes with the movement of the phase change point and the change of the bearing capacity of the particles after the rearrangement, and the more forward the phase change point is, the stronger the bearing capacity of the specimen in the plastic stage. The shear dilatancy angle and the shear dilatancy amount both increase linearly with the increase in loading amplitude. The influence of loading frequency and amplitude on the contact force chain, displacement, crack expansion, and the number of cementation damage inside the sediment is mainly related to the average axial stress to which the specimen is subjected, and the number of cracks and cementation damage of the sediment specimen increases with the increase in the average axial stress to which the sediment specimen is subjected. As the rate of cementation damage increases, the distribution of shear zones becomes more obvious.

In order to study the macro-meso shear mechanical characteristics of natural gas hydrate-bearing sediments, the direct shear simulations of natural gas hydrate-bearing sediment specimens with different saturations under different normal stress boundary conditions were carried out using the discrete element simulation program of particle flow, and the macro-meso shear mechanical characteristics of the specimens and their evolution laws were obtained, and their shear damage mechanisms were revealed. The results show that the peak intensity of natural gas hydrate-bearing sediments increases with the increase in normal stress and hydrate saturation. Hydrate particles and sand particles jointly participate in the formation and evolution of the force chain, and sand particles account for the majority of the force chain particles and take the main shear resistance role. The number of cracks produced by shear increases with hydrate saturation and normal stress. The average porosity in the shear zone shows an evolutionary pattern of decreasing and then increasing during the shear process.

Discrete element method was used to study and analyze the interaction between rice straws and between rice straw and agricultural machinery parts, thereby providing a scientific basis for post-harvest paddy field processing. Calibrations of rice straw-rice straw, rice straw-agricultural machinery part contact parameters (collision recovery coefficient, static friction coefficient and rolling friction coefficient) constitute an important prerequisite for the discrete element research process. In this study, the collision recovery coefficients of rice straw-steel and rice straw-rice straw were 0.230 and 0.357, respectively, which were calibrated by the collision method. The static friction coefficient and rolling friction coefficient of rice straw-steel were 0.363 and 0.208 respectively, which were calibrated by the inclined plate method and the slope method. The static friction coefficient and rolling friction coefficient of rice straw-rice straw were 0.44 and 0.07, respectively, which were calibrated by the split cylinder method. The paired t-test showed insignificant differences between calibration parameter simulation results and the physical test values (p>0.05). Taking the angle of repose that reflecting rice straw flow and friction characteristics as the evaluation index, the verification tests of the above calibration values indicated that the simulated angle of repose has no significant difference from the physical test value (p>0.05). The side plate lifting test on rice straw of different lengths showed no significant difference between the simulated angle of repose and the physical test value (p>0.05). This study can provide a basis for contact parameters choice in discrete element simulation analysis with rice straw-rice straw and rice straw-agricultural machinery parts as the research object. The calibration method can provide a reference for the contact parameter calibration of other crop straws.

In order to investigate the motion characteristics of the abrasive media in the vibratory finishing, the RecurDyn and EDEM coupled simulation method is employed. The simulation results show that the trajectories of the abrasive media are annular spiral motions in general, including a circular motion about the central axis of the vibratory finishing machine and an elliptical motion around the center of the media flow. The reliability of the RecurDyn-EDEM coupled simulation for the vibratory surface finishing process is validated by X-ray real-time detection, which has significance in better understanding of the motion characteristics of abrasive media and the optimal design of the vibratory surface finishing processes.

With the mass implementation of rail transit engineering, the tunnel constructed by the shield method will inevitably pass through increasingly complex strata. Compared with single formation, studying the disturbance rule of shield tunneling in composite formation is more difficult. This paper takes the shield section of Jinan Metro Line R3 from Olympic Center West Station to Dingjiadong Station as an example, adopts EDEM simulation to simulate the shield tunneling process of clay-limestone composite formation, and studies the transverse and longitudinal settlement of composite formation under different stratification coefficients. Based on Peck’s empirical formula, an improved Peck formula suitable for the surface settlement prediction of composite formation is proposed. The disturbance law of clay-limestone composite stratum caused by shield tunneling is revealed. The results show that the horizontal and longitudinal settlement increases with the increase of the stratification coefficient. When the delamination coefficient increases from 0.2 to 0.8, the maximum lateral displacement increases by 1.03 times, and the maximum longitudinal displacement increases by 0.99 times. The maximum transverse settlement occurs at the central axis of the tunnel. The longitudinal settlement increases gradually with the arrival, passing, and departure processes of the shield machine. The calculation result of the modified Peck formula accords with the law of practical measurement and numerical simulation. The relevant research can provide theoretical support for similar shield construction and has important reference significance for shield tunnel construction under similar geological conditions in China.

The stability of excavation face in shield tunneling plays a key role for construction safety. The ignorance of soil anisotropy in most previous studies would induce inaccurate stability assessment. This paper studies the failure of shield tunnel face in cross-anisotropic granular media by physical model tests and discrete element simulation. Model tests were carried out on the tunnel face stability in anisotropic granular media, and initial anisotropy was generated by controlling the long axis of non-spherical particles. By conducting image analysis on the picture taken by HD camera, the failure mode of tunnel face was obtained. It consists of a sliding wedge and an overlying loosen area, and the inclination angle of sliding wedge varies with the bedding plane. The variation in limit support pressure with the intersection angle of the shield tunneling direction and the soil bedding plane was obtained. Discrete element simulation was further employed to study the tunnel face stability in cross-anisotropic granular media; the microscopic parameters were calibrated by fitting against the particle drop test and repose test. Clump particle consisted of three identical ball was used in the simulations, and its long and short axes were in accordance with rice particles. The obtained varying characteristic of limit support pressure with intersection angle from simulation is consistent with the test results, and the obtained failure mode is also similar to that of physical model test. The principal stress distribution at failure state was analyzed in the discrete element simulation, and the change of major principal stress direction from vertical to nearly horizontal in the loosen area clearly shows the formation of soil arches.

To improve the accuracy of discrete element simulation parameters of sugarcane tail-leaf (STL) feed during dust removal and crushing, this study used a combination of physical tests and EDEM software simulations to calibrate the discrete element simulation parameters of crumbs and dust in the feed. Taking the experimental physical stacking angle (SA) as the response value, the second-order regression models of SA and significant factors were established by Plackett-Burman test, steepest climb test, and Box-Behnken test. Variance analysis and interaction effect analysis were conducted. Taking the accumulation angle of 41.27° obtained by physical experiments as the target value, the significant parameters were optimized. The optimal combination of the following parameters was obtained: tail stem-dust static friction coefficient (SFC) of 0.46, tail leaf-dust coefficient of sliding friction (COSF) of 0.205, JKR surface energy of 0.26, and dust-steel collision recovery coefficient (CRC) of 0.338. Through software simulation verification, the average value was 40.81°, and the relative error of the SA with the physical experiment was 1.13%. The results showed that the calibrated parameters are real and reliable, which can provide a theoretical reference for the design optimization of the straw crushing device, feed processing device, and other related components.

Improved soil fertility to sustain crop productivity is important to enhance agroecosystem services. To address the low nutrient content, subsoil compaction, and poor root penetration in Planosol, a new machine was designed to improve these conditions. This machine integrates subsoil mixing and fertilizer application. The paper details the machine’s structure and working principle, focusing on optimizing the vertical mixing plow. Furthermore, discrete element method simulations were conducted, using tillage depth, forward speed, and plow height as factors, with soil mixing rate and tractive resistance serving as the evaluation indicators. Results showed optimal performance at 553 mm tillage depth, 1 m/s speed, and 227 mm plow height, with tractive resistance of 7460.5 N and a soil mixing rate of 72.1%. Field trials and soil improvement tests based on optimized parameters confirmed the accuracy and reliability of the simulation results. Compared to the Shallow plowing and subsoiling area, the subsoil mixing improvement area showed significant improvement, with a yield increase of 16.4–18.9% over two years.

To improve the accuracy of the discrete element research, physical and simulation experiments were used to calibrate the cotton stalk contact parameters. Based on the stalk-stalk and stalk-steel contact mechanics, the parameters were measured in physical experiments, and the discrete element simulation software was used to build the stalk model. In the simulation process, the Plackett-Burman experiment was used to screen three significant factors from six initial factors. The steepest Plackett-Burman experiment was used to determine the optimal interval of the significant factors. A second-order regression model of the significant factors and the angle of repose was established according to the Central Composite design experiment. The best parameter combination of the significant factors was then obtained: the coefficient of static friction on stalk-steel contact was 0.31, the coefficient of static friction on stalk-stalk contact was 0.62, and the coefficient of rolling friction on stalk-stalk contact was 0.02. The relative error between the physical angle of repose and the simulated angle was 3.27%, indicating that it is feasible to apply the simulation experiment instead of the physical one. It offers insights into cotton stalk contact parameter settings and film-stalk separation in the simulation.

Predicting the perforation limit of composite laminates is an important design aspect and is a complex task due to the multi-mode failure mechanism and complex material constitutive behaviour required. This requires high-fidelity numerical models for a better understanding of the physics of the perforation event. This work presents a numerical study on the perforation behaviour of a satin-weave S2-glass/epoxy composite subjected to low-velocity impact. A novel strain-rate-dependent finite-discrete element model (FDEM) is presented and validated by comparison with experimental data for impacts at several energies higher and lower than their perforation limit. The strain rate sensitivity was included in the model by developing a novel user-defined material model, which had a rate-dependent bilinear traction separation cohesive behaviour, implemented using a VUSDFLD subroutine in Abaqus/Explicit. The capability of the model in predicting the perforation limit of the composite was investigated by developing rate-sensitive and insensitive models. The results showed that taking the strain rate into account leads to more accurate predictions of the perforation limit and damage morphology of the laminate subjected to impacts at different energies. The experimental penetration threshold of 89 J was estimated as 79 J by the strain-rate-sensitive models, which was more accurate compared to 52 J predicted by the strain-rate-insensitive model. Additionally, the coupling between interlaminar and intralaminar failure modes in the models led to a more accurate prediction of the delamination area when considering the rate sensitivity.