Computational Particle Mechanics最新文献

In the combined finite-discrete element method, the crack element was an important bridge to realize the transition from continuous to discontinuous deformation. The crack element was assumed as a non-thickness cohesive element, which could not be tested directly. The fracture energy rate for the crack element was an essential parameter determining the deformation and fracture process during the FDEM simulation. However, the common parameter calibration method required experience and time. Thus, a new estimation method of fracture energy rate was derived based on the energy mechanism. The proposed estimation method was consistent with the Griffith fracture criterion but also can reflect the influence of mechanical and inherent properties. Then, the influence of fracture energy rate on rock strength and fracture characteristic was analysed. The results showed that both the tensile strength and uniaxial compressive strength were increased with the fracture energy rate. A smaller tensile fracture energy rate would lead to a larger ratio of tensile fracture and a decrease in shear fracture. It was opposite for the shear fracture energy rate. Based on the rock strength and fracture characteristics, the initial coefficient of fracture energy rate should be 1.0. The fracture energy rate determined by the proposed estimation method and initial coefficient was close to the optimal value, which was well verified by the laboratory test result and tunnel engineering. Finally, the improved calibration steps of fracture energy rate for the complex material were put forward, which was expected for the fast and accurate calibration of model parameters.

This study meticulously explores the deposition dynamics of aluminum oxide nanoparticles in a triangular tube heat exchanger to enhance heat transfer efficiency and gas dynamics, crucial for mitigating deposition risks. By investigating various parameters such as nanoparticle diameters (10–100 nm), heat flux (1000–3000 W/m²), Reynolds numbers (308–925), mass fractions (0.5–2%), and geometry lengths (50–90 mm), the research provides a comprehensive understanding. Employing Python programming, the methodology integrates machine learning algorithms (RF and DNN) with Eulerian and Lagrange methods, achieving an impressive model accuracy of 84% with low errors. Key findings include the correlation between heightened heat flux and increased nanoparticle deposition, particularly at a 100 nm diameter, and the direct relationship between mass fraction and deposition, peaking at 2% mass fraction and a 100 nm diameter. The Reynolds number significantly influences deposition, peaking with lower Reynolds numbers and larger nanoparticle diameters, shedding light on critical aspects of deposition behavior in heat exchangers. Furthermore, the research identifies tube geometry and nanoparticle size as critical factors affecting deposition patterns.

The mechanized water direct seeding technology of rice has the advantages of saving time and labor, saving cost and increasing yield. The existing wheeled tractor direct seeding operation in paddy field mainly has technical problems such as large wheel rut, floating stubble blockage, and high-speed operation backwater, resulting in the quality of seedbed is not up to standard and cannot meet the requirements of direct seeding operation in paddy field. In view of the above problems, a high-speed rice seedbed preparation machine which can be matched with a wheeled tractor was developed. The overall scheme of the machine was put forward, and the structure design of key devices such as rut coverage, stubble burying and ditching was carried out. The corresponding motion analysis and simulation were carried out. Finally, the bench test and field test were carried out. The test results show that the designed operating machine can complete the rutting coverage, stubble burying, ditching and other operations at one time. The coverage rate of wheel track is 98.52%. The stubble rate was 98.89%; the ditch type of the ditching operation is complete and the ditch is clean. The components of the designed machine meet the design requirements, and the operation effect can better meet the operation requirements of high-speed rice seedbed preparation.

The multiphase flows modelling, including computational fluid dynamics (CFD), is extremely difficult due to the complexity of the phenomena and the influence of a large number of factors. The main purpose of this work is to show how the available models can help to reproduce a simple two-phase flow. In the presented work, using one of the commercial CFD programs, a new flat centrifugal separator design was investigated. The separator consists of a circle with a diameter of 0.2 m and two tangential channels (inlet and outlet). An outlet channel was divided into two separate ones additionally. Simulations were carried out for solid mass flow rate from 0.001 to 0.5 kg/s and for two particle sizes—1 and 30 µm. The performed calculations showed that two-way coupling can correctly reflect the improvement of the particle separation efficiency with the increase in the mass loading. The calculated total separation efficiency increased by approximately four percentage points and resulted from better retention of finer particles.

In cemented paste backfill (CPB), the connection mode and spatial position arrangement of particles determine the deformation, structural strength and stability of the backfill. Based on the scanning electron microscope images of CPB, the representative elementary area (REA) of the pore structure of CPB is obtained. The actual microstructure of CPB in PFC^2D according to REA was modeled, and the microscopic parameters of the model based on the results of indoor uniaxial compression tests were calibrated. Finally, by studying the microstructure, mechanical properties, force chain, normal contact force, tangential contact force and coordination number of CPB with different curing time (3 days, 7 days, 28 days), the internal relationship between mesoscopic parameters and macroscopic mechanical properties during CPB development was analyzed. Exploring the changes of mesostructure during the development of CPB is of great significance to the study of heterogeneous structure and multi-scale mechanical theory system.

The grab bucket plays an important role in the construction process of dredging, and analyzing the excavation characteristics of the grab is helpful for the mechanical design of the grab bucket. In this investigation, the digging device and the digging mudstone are detailed as a system dynamic process, and a theoretical model for calculating digging resistance is established based on the Rankine theory. Furthermore, the particle shear test is performed to analyze the influence of changes in sand physical parameters on its shear characteristics. The DEM-MBD coupling simulation is adopted to calculate the particle distribution and the digging trajectory, and the influence of digging depth and particle cohesion strength is analyzed on the digging resistance. Moreover, an excavator digging experimental platform is established to validate the feasibility of the experimental results. The results show that the 10% moisture content is the inflection point of the sand particles physical and mechanical properties, and its shear strength decreases with the augment of moisture content; the variation law of the simulation results is consistent with the theoretical calculation, and the digging resistance reduction is proportional to the cohesion strength when the particles are completely sheared; the same key point parameter error of the digging curve obtained by the test and the simulation are consistent.

With the development of urbanization, a large number of foundation pits have been built. Water inrush is one of the most important causes of foundation pit accidents, and it is of great significance to understand the process and mechanism of water inrush. A laboratory small-scale water inrush test at foundation pit base was established by using discrete element method and numerical simulation was conducted on the water inrush failure of aquitard. The water inrush process of Shanghai clay ⑤₁ was divided into continuous deformation stage, equilibrium stage, and failure stage. The mechanism of water inrush failure was explained from a mesoscopic perspective, and the trend of the development and evolution of cracks was studied. The variation laws of monitoring variables such as porosity, coordination number, and the particle displacement of observation points were analyzed. The influences of vertical weak area in pit base and the thickness and properties of aquitard on water inrush were further discussed. The research work in this paper not only provides a new perspective for the analysis of water inrush failure in foundation pits, but also provides a reference for the simulation of fluid–solid coupling in other geotechnical engineering.

This research investigates the effect of various fibers on the strength and flexibility of concrete from an educational perspective. In this research, the use of additives including types of fibers (macrosynthetic fibers, polypropylene, and glass fibers) which make up 1% of the volume of hybrid concrete is taught. The combined addition of these fibers to create the hybrid reinforced concrete with high tensile strength and plasticity is discussed in this education. The tensile strength results obtained from direct and indirect methods have significant differences. In the concrete laboratory, multiple experiments were carried out to determine the best fiber composition using two different types of fibers. The experiments included direct tensile testing using the compressive-to-tensile force conversion (CTFC) method, which is a new approach, and indirect tensile testing using the Brazilian disk method. The loading rate for the tests was 1 kg/sec. The average tensile strength was 3.3 MPa, and the average compressive strength was 35 MPa. The Young’s modulus was measured to be 20 GPa. The results showed that macrosynthetic fibers were more effective in increasing the concrete’s tensile strength compared to other combinations. The tests performed on the effects of combining glass fibers with macrosynthetic fibers compared to combining macrosynthetic fibers with polypropylene show a more effective tensile strength. In this article, the direct tensile strength of concrete samples is evaluated by introducing an innovative tensile test device with a ring-shaped sample. The results obtained from this new device have been numerically compared with the uniaxial direct tension method proposed by ISRM. The educational measures of this new knowledge regarding concrete additives and performing innovative tensile strength tests and comparing them with each other provide a detailed understanding of concrete strength evaluation.

In recent years, geosynthetic-reinforced pile-supported (GRPS) embankments have gathered increasing attention in the scientific community for their effectiveness in improving soft ground. This study aims to investigate the load transfer of double-layer GRPS embankments using the discrete element method (DEM), with a focus on soil arching effects and membrane effects. A coefficient, denoted as η and defined as h/H, was introduced to study the influence of the distance between two geosynthetics on load transfer. The results indicated: (1) Double-layer GRPS embankments demonstrated uniform load transmission downwards, thereby reducing the large deformation zone within the embankment fill. (2) Maximum tension in geosynthetics occurred at the edges of pile caps in both single-layer and double-layer GRPS embankments. However, double-layer GRPS embankments effectively mitigated the maximum tension in geosynthetics. (3) Double-layer GRPS embankments minimized soil arching formation within the embankment while enhancing membrane effects. (4) With increasing η, soil arching gradually formed between the two layers of geosynthetics. (5) Above a η threshold of 0.1, the maximum tension in the lower layer of geosynthetics significantly exceeded that in the upper layer.

The behavior of road or perimeter protection barriers under vehicle impact are usually investigated based on crash tests and finite element (FE) numerical approaches, which are ether expensive or time-consuming. Several studies have proposed to reduce the computation time of the numerical analysis by substituting the complex FE models of vehicles using simplified mass–spring–damper system models. However, these models have drawbacks since consideration of different vehicle impact angles is difficult and they are unable to correctly simulate the risk of high-speed vehicle collision running over the barrier. In this paper, a new approach is proposed to simulate the collision of vehicles with barriers based on the discrete element method (DEM). Here, to save computation time only a handful of 3D non-spherical particles are used to represent the barrier and vehicle. These particles are generated based on the super-quadric function, which is capable of generating a variety of shapes needed for the model. The contact detection and evaluation are carried out based on discrete function representation of the particles with uniform sampling. The bond between two discrete elements is defined using a nonlinear cohesive beam model since the distance between the elements is relatively large. The simulation results obtained based on this approach are more accurate and complete than the simplified mass–spring models and computationally more efficient than the FE model.