A new erosion model, which is referred to as SIEM (shear impact energy model), is used to investigate elbow erosion under different working conditions using numerical simulations. The fluid motions ...are predicted by CFD (computational fluid dynamics), and the particle movements are calculated using DEM (discrete element method) in the simulations. Both a one-way coupling method and a two-way coupling method in CFD-DEM are adopted to calculate the gas-solid interaction. The prediction results of elbow erosion subject to a condition of dilute gas-particle flow are validated against corresponding experimental data. Because DEM and SIEM can be easily applied to dense gas-particle flows, the effect of the particle concentration on the erosion is also investigated. The simulation results show that the coupling methods have little influence on the erosion prediction when the particle concentration is low, whereas erosion in the elbow is significantly sensitive to the particle concentration. Finally, the effects of the friction coefficient, restitution coefficient and spring stiffness coefficient on elbow erosion are also investigated using simulations, and the effects were not as remarkable as the concentration.
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•The erosion in the elbow is studied by CFD-DEM simulation.•A new erosion model is employed and the simulation results are verified.•Effect of particle concentration on erosion in elbow is obtained.•Effects of coefficients of friction and restitution on erosion are also obtained.
The thermal and mechanical behaviors of powders are crucial for additive manufacturing. In powder bed fusion, capturing temperature profiles and packing structures before melting is challenging due ...to diverse heat transfer pathways and powder properties. This study tackles this challenge with a discrete element model simulating non-spherical particles with thermal properties during powder spreading. Thermal conduction and radiation are integrated into a multisphere particle formulation to model heat transfer among irregular-shaped powders with temperature-dependent elastic properties. The model is utilized to simulate the spreading of pre-heated PA12 powder over a hot substrate representing the part under manufacturing. Variances in temperature profiles are observed in the spreading cases based on particle shapes, spreading speed, and temperature-dependent elastic modulus. Particle temperature beneath the spreading blade is influenced by the kinematics of the particle heap and temperature-dependent properties.
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•We couple heat transfer with multisphere DEM to model complex particle shapes.•The coupled model is used to simulate powder spreading in additive manufacturing.•Varied spreading speeds yield diverse temperature profiles of the powder bed.•Thermal sensitivity of the elastic modulus also affects the temperature profiles.•Particle shapes significantly impact the bed temperature profiles.
Earthquake ruptures dynamically activate coseismic off‐fault damage around fault cores. Systematic field observation efforts have shown the distribution of off‐fault damage around main faults, while ...numerical modeling using elastic‐plastic off‐fault material models have demonstrated the evolution of coseismic off‐fault damage during earthquake ruptures. Laboratory‐scale microearthquake experiments have pointed out the enhanced high‐frequency radiation due to the coseismic off‐fault damage. However, the detailed off‐fault fracturing mechanisms, subsequent radiation, and its contribution to the overall energy budget remain to be fully understood because of limitations of current observational techniques and model formulations. Here, we constructed a new physics‐based dynamic earthquake rupture modeling framework, based on the combined finite‐discrete element method, to investigate the fundamental mechanisms of coseismic off‐fault damage, and its effect on the rupture dynamics, the radiation and the overall energy budget. We conducted a 2‐D systematic case study with depth and showed the mechanisms of dynamic activation of the coseismic off‐fault damage. We found the decrease in rupture velocity and the enhanced high‐frequency radiation in near field due to the coseismic off‐fault damage. We then evaluated the overall energy budget, which shows a significant contribution of the coseismic off‐fault damage to the overall energy budget even at depth, where the damage zone width becomes narrower. The present numerical framework for the dynamic earthquake rupture modeling thus provides new insights into earthquake rupture dynamics with the coseismic off‐fault damage.
Plain Language Summary
The medium surrounding fault cores can be damaged due to stress concentration caused by the dynamic earthquake ruptures propagating on the faults, which is called coseismic off‐fault damage. Systematic field observation efforts have shown the distribution of off‐fault damage around main faults, while numerical modeling has demonstrated the evolution of off‐fault damage during earthquake ruptures. Laboratory‐scale microearthquake experiments have pointed out the enhanced high‐frequency radiation due to the off‐fault damage. However, the detailed off‐fault fracturing mechanisms, subsequent seismic wave radiation and its contribution to the overall energy budget remain to be fully understood. Here, we constructed a new physics‐based dynamic earthquake rupture modeling framework to investigate the fundamental mechanisms of coseismic off‐fault damage and its effect on the rupture dynamics, the radiation, and the overall energy budget. We found the enhanced high‐frequency radiation in near field due to the coseismic off‐fault damage. We then evaluated the overall energy budget, which shows a significant contribution of the coseismic off‐fault damage to the overall energy budget even at depth. The present numerical framework for the dynamic earthquake rupture modeling thus provides the insight into the earthquake rupture dynamics with the coseismic off‐fault damage.
Key Points
Earthquake ruptures dynamically activate coseismic off‐fault damage, whose feedback plays an important role in rupture dynamics
We show the mechanism of dynamically activated off‐fault fractures and its effect on rupture velocity and enhanced high‐frequency radiation
The contribution of off‐fault damage to the overall energy budget associated with earthquakes is nonnegligible even at depth
•Structural response of dry-stone masonry structures is analysed by a 3D combined finite-discrete element method (FDEM).•Proposed approach includes modelling of discontinuities across dry joints and ...fracturing and fragmentation of the blocks, in order to correctly simulate the mechanical behaviour of dry-stone masonry.•Model is capable of predicting structural damage, failure mechanisms and collapse of these structures under static and seismic loads.•The influence of the numerical parameters, such as penalty terms and damping coefficient, on the accuracy of the solution was analysed through various examples.
The evaluation of damage mechanism and the failure of dry-stone masonry structures subjected to seismic load is one of the most important aspects of seismic assessment of existing masonry buildings. Discontinuities between the blocks, their mechanical interaction, large displacement and rotation are the main causes of degradation and collapse of these structures. This paper presents the application of the combined finite-discrete element method (FDEM) in the analysis of 3D dry-stone masonry structures which is able to capture such mechanisms and structural damage both at joint and at block level. Moreover, the proposed approach includes friction forces based on Coulomb-type of law accounting for friction effects across dry joints and open cracks, in order to correctly simulate the mechanical behaviour of dry-stone masonry. The capabilities of presented approach are demonstrated in a series of numerical tests, starting with sliding and rocking of single blocks, examination of dry joints shear behaviour, walls subjected to in-plane and out-of-plane load, and finally the simulation of the simple spatial stone masonry structure.
It is well known that kaolinite platelets readily aggregate into ‘stacks’, having face-to-face contact. The traditional view of kaolin has been that the platelet faces are negatively charged and the ...edges are positively charged in an acidic environment, but that some attraction between faces may exist at some close range of approach. Particle-scale simulations in this paper show that this is insufficient to explain aggregation during sedimentation. Recently it has been established that the silica and alumina faces of kaolinite platelets have opposite charges in acidic conditions, and taking these findings into account, discrete element simulations are presented which replicate and explain the face-to-face aggregation that occurs during sedimentation. The results demonstrate the importance of correctly modelling the interactions between the various surfaces of individual platelets in any particle-based model.
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•Using Discrete Element Method to model kaolinite platelets.•Each platelet has 3 distinct surfaces: silica face, alumina face, edge.•Different interactions used between different surfaces.•Using multifaceted interactions controls ability to aggregate/flocculate.
•A system is proposed to obtain heterogeneous rocks with irregular inclusions.•Realistic inclusion geometry is obtained and controlled by combining the circular parameterization and Fourier ...transformation.•An unique overlapping detection algorithm based on level-set function is developed to allocate inclusions.•Hydraulic fracturing are captured by integrating cohesive pore pressure elements into traditional finite element model.•A systematic hybrid finite-discrete approach for investigating hydraulic fracturing of heterogeneous rocks is proposed and validated.
A systematic hybrid approach for modelling the hydraulic fracturing process of heterogeneous rocks with irregular inclusions is developed. This approach is based on a series of computational algorithms, including Fourier series transformation, level-set-based overlapping detection, and the finite-discrete element method. Three major steps are included: (1) circular parameterization and Fourier transformation are employed to reproduce realistic inclusion contours with arbitrary irregular shapes; (2) a novel overlapping detection method based on a level-set function is employed to allocate irregular inclusions effectively and efficiently; and (3) the finite-discrete element model is established by integrating cohesive elements with pore pressure nodes into the solid mesh to simulate the progressive hydraulic fracture and interface crack of heterogeneous rocks. To validate the proposed hybrid approach, modelling results by the established model are compared with numerical simulations in the literature. In addition, the influences of injection speed and interface strength on the mechanical and fracturing responses of heterogeneous rocks are discussed. The results demonstrate that the proposed hybrid approach is capable of simulating the hydraulic fracturing process of heterogeneous rocks.
•A 2D fully coupled hydro-mechanical finite-discrete element model with real pore seepage is proposed.•The model can simulate the deformation and fracture of rock with an arbitrary complex fracture ...network driven by fluid pressure.•The proposed method can capture crack initiation and propagation, the interaction of hydraulic fractures and natural fractures, and the fluid pressure distribution in the rock mass.
Based on the finite-discrete element method (FDEM), a 2D fully coupled model with real pore seepage is proposed. This model can solve the problem of the deformation and fracture of porous medium driven by fluid. In this model, the fluid flow in the fracture is expressed by the cubic law, while the fluid flow in the rock matrix is characterized by Darcy's law and solved by the finite volume method. The interaction between pore seepage and fracture seepage is realized at the fracture. Three analytical solutions are presented to verify the correctness of the proposed model. The results show that the numerical solutions agree well with the analytical solutions. In addition, a hydraulic fracturing problem with a complex fracture network is studied using this model. The simulation results show that the model can capture the fracture initiation, propagation, and intersection, the interaction of natural fractures and newly generated fractures, and the evolution of fluid pressure during hydraulic fracturing. The model can be used not only to simulate hydraulic fracturing in shale gas and geothermal mining but also to solve a series of geomechanical problems related to the effect of fluid. Thus, this model has broad application prospects.
This study introduces GeoTaichi, an open-source high-performance numerical simulator designed for addressing multiscale geophysical problems. By leveraging the power of the Taichi parallel language, ...GeoTaichi maximizes the utilization of modern computer resources on multicore CPU and GPU architectures. It offers robust and reliable modules for the discrete element method (DEM), material point method (MPM), and coupled material point-discrete element method (MPDEM). These modules enable efficient solving of large-scale problems while being implemented in pure Python. The design philosophy of GeoTaichi focuses on creating a framework that is readable, extensible, and user-friendly. This paper highlights the coupling procedure of MPDEM, the code structures, and the most important features of GeoTaichi. Rigorous benchmark tests have been conducted to verify the validity and robustness of GeoTaichi. Additionally, the performance of GeoTaichi is compared with similar software tools in the field, underscoring a notable improvement in both computational efficiency and memory savings when compared to existing alternatives.
Program title: GeoTaichi
CPC Library link to program files:https://doi.org/10.17632/858bmcf7j6.1
Developer's repository link:https://github.com/Yihao-Shi/GeoTaichi
Licensing provisions: GNU General Public License v3.0
Programming language: Python
Nature of problem: The simulations of large-deformation geophysical flows and their interaction with structures play a crucial role in the field of geophysics. To address the complexities of these nonlinear problems, the discrete element method (DEM), material point method (MPM), and their coupling (MPDEM) have proven to be highly suitable numerical schemes. However, these schemes impose substantial computational demands, necessitating the development of an efficient framework that can harness modern computer resources on multicore CPU and GPU architectures.
Solution method: The open-source code GeoTaichi implements the DEM, MPM, and coupled MPDEM, encompassing a range of constitutive models and contact laws for different geologic materials. The clump particle model is also introduced in DEM to solve granular mechanics involving complex-shaped particles. One significant advantage of GeoTaichi is its utilization of the Taichi parallel language, which is designed to be user-friendly and easily extensible for customized applications.
This paper presents a new, fully-coupled, hydro-mechanical (HM) formulation for a finite-discrete element method computer code. In the newly-developed, hydraulic solver, fluid flow is assumed to ...occur through the same triangular mesh used for the mechanical calculations. The flow of a viscous, compressible fluid is explicitly solved based on a cubic law approximation. The implementation is verified against closed-form solutions for several flow problems. The approach is then applied to a field-scale simulation of fluid injection in a jointed, porous rock mass. Results show that the proposed method can be used to obtain unique geomechanical insights into coupled HM phenomena.
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•Bionic stirring device to enhance food waste composting was designed.•Design parameter of stirring device using discrete element method was optimized.•Failure risk analysis of ...stirring device undertaken using finite element method.•Conditions found for optimal stirred material fluffiness validated via test bench.•Insights can aid design of compost stirring and stirring devices.
Effective stirring devices are essential for horizontal composting to enhance food waste disintegration, but studies on flexible compost stirrers, their fracture risk, and prevention methods are limited. This study developed an innovative design for a bionic stirring device in a horizontal compost bin to enhance the food waste composting process by improving the dissolved oxygen levels. Three-dimensional models of primary particles from a standard food waste sample were utilised, and the design parameters of the stirring device were optimised using the discrete element method. A regression analysis of the test results was performed using the response surface method to investigate the effects of variables such as the stirring shaft speed, torsion spring diameter, and material filling volume on the fluffiness of the post-stirring material and to explore the mechanism of the bionic tumbling device on the fluffiness of the compost material. A failure risk analysis of the stirring device was also performed using the finite element method. The research findings indicate that optimal fluffiness of the stirred material can be achieved with a stirring shaft speed of 0.24 r/s, torsion spring diameter of 5.5 mm, and material filling volume of 70 %. Realistic validation experiments confirmed that the optimal biomimetic mixing structure improved material fluffiness by 18.69 % (measured as volume change in the upper layer of the pile) and reduced the risk of structure failure with a strain of 0.00038. This research provides a reliable design method for horizontal compost bin stirring devices, contributing to enhanced composting efficiency and serving as a valuable reference for the design of other compost stirring devices.
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