Computational Particle Mechanics最新文献

This paper presents a novel method for smoothed particle hydrodynamics (SPH) with thin-walled rigid structures. Inspired by the direct forcing immersed boundary method, this method employs a moving least square method for the velocity interpolation instead of the linear interpolation. It reduces oscillations due to changing relative positions between fluid grids and structures. It also simplifies thin-walled rigid structure simulations by eliminating the need for multiple layers of boundary particles, and improves computational accuracy and stability in three-dimensional scenarios. Results of the impulsively started plate test demonstrate that the proposed method obtains smooth velocity and pressure, as well as a good match to the references results of the vortex wake development. Results of the flow past cylinder test show that the proposed method avoids mutual interference on both side of the boundary, while accurately calculating the forces acting on structure. By comparing to linear least square direct forcing scheme and the diffusive direction scheme, advantages of lower oscillation and higher accuracy are proven. Results of flow past a sphere further indicate the stability of the proposed method for three-dimensional simulations.

Existing literature on true triaxial and torsional shear tests indicate that the mechanical response of a granular assembly is significantly influenced by the magnitude of the intermediate principal stress ratio. The present study aims to explore the mechanism behind such effects in reference to the particle-level interaction using 3D DEM simulations. In this regard, true triaxial numerical simulations have been carried out with constant minor principal stress and varying (b) values employing rolling resistance-type contact model to mimic particle shape. The numerical simulations have been validated against the true triaxial experiments reported in the literature for dense Santa Monica beach sand. The macro-level shearing response of the granular assembly has been examined in terms of the evolution of stress ratio and volumetric strain for different rolling resistance coefficients. Further, such macro-level response has been assessed in reference to the micro-scale attributes, e.g. average contact force, number of interparticle contacts, mechanical coordination number, contact normal orientation, and fabric tensor as well as meso-scale attribute like strong contact force network. Lade’s failure surface has been adopted to represent the stress and fabric at peak state in the octahedral plane, and mathematical expressions have been proposed relating the failure surface parameters to the rolling resistance coefficient.

Graphical abstract

Discrete element method (DEM) is a powerful tool for the dynamic simulation of irregular non-spherical particle systems. The efficient integration of the rotational motions of numerous particles in DEM poses a big challenge. This paper presents six explicit time integration algorithms, comprising three first-order algorithms and three second-order algorithms, for the rotational motions of non-spherical particles based on the theory of unit quaternion group S(3). The proposed algorithms based on Cayley map do not contain any transcendental function and have high efficiency. The numerical examples underscore the superiority of the first-order symplectic Euler Cayley algorithm (SECay) and the second-order central difference Cayley algorithm (CDCay) in terms of both efficiency and accuracy. In the testing cases of granular systems, SECay and CDCay demonstrate approximately 80% reduction in computational time for the time integration part, compared to the improved predictor–corrector direct multiplication method (IPCDM). Therefore, SECay and CDCay emerge as promising tools for non-spherical DEM simulations.

Motivated by the spatial variability observed in geological profiles, this study explored the feasibility of using discrete element method (DEM) to capture the effect of layered spatial variability into overall soil performance. The spatial variability of packing densities, particle Young’s modulus (E), and frictional properties (μ) within specimens was studied. It was observed that samples with similar overall void ratios exhibited comparable small-strain stiffness and shearing behaviors. In contrast, the coordination number and particle stress transmission demonstrated significant sensitivity to the layer-wise spatial variability in packing densities. Regarding the spatial variability effect of particle-scale E values, this study illustrates that spatial variability strongly affects the stiffness contributions of individual layers. Specifically, layers with higher E values are capable of transferring much stress and stiffness. For the spatial variability effect of frictional property, a degree of consistency in shearing behaviors was observed among specimens with similar average frictional characteristics, while layers with lower frictional property were identified as potential initial failure junctures. Overall, this study validates the utility of employing a DEM code for analyzing both the macroscopic behavior and localized vulnerabilities within complex granular systems, presenting profound implications for engineering practices.

Microstructure plays a significant role in the fracture behavior of the material. To analyze the microstructure effect on crack propagation, a peridynamic model named Cosserat bond-based correspondence model (CBBCM) is proposed based on the Cosserat continuum theory and bond-based correspondence model. In CBBCM, the peridynamic (PD) force and moment are obtained by Cosserat constitutive equations through the relation between PD forces/moment and the stress/couple stress. Such relation is derived according to the bond relation of the Cosserat peridynamic model. To validate the proposed CBBCM, three numerical examples are presented, and the comparison shows good agreement between the CBBCM and the experimental observation and numerical results. The numerical convergence studies of m-convergence and δ-convergence are made to demonstrate the proposed CBBCM. The microstructure effect of crack propagation is analyzed by applying different Cosserat shear modulus and internal length scales in the simulation. The results indicate that the Cosserat shear modulus has an impact on the crack propagation and the crack propagates slower with a greater Cosserat shear modulus. The internal length scale has little impact on the crack path and only influences the local damage distribution.

Experimental and discrete element methods were used to investigate the effects of joint number and joint angle on the failure behavior of rock pillars under the uniaxial compressive test. Gypsum samples with dimensions of 200 mm × 200 mm × 50 mm were prepared. The model material had a tensile strength of 1 MPa. Embedded notches with a length of 6 cm were utilized within the samples to determine its compressive strength. In constant notch length, the number of notches was one, two, and three. In the experimental test, the angle of the diagonal plane related to the horizontal axis was 0°, 30°, 60°, and 90°. In the numerical test, the angles of the diagonal plane related to the horizontal axis were 0°, 15°, 30°, 45°, 60°, 75°, and 90°. The axial load was applied to the model at a rate of 0.05 mm/min. The results show that the failure process was mostly governed by both the non-persistent notch angle and notch number. The compressive strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behavior of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the notch angle. The strength of samples increases by increasing both the notch angle and notch number. The failure pattern and failure strength are similar in both methods, i.e., the experimental testing and the numerical simulation methods.

In this paper, we present a coupled smoothed particle hydrodynamics and a constitutively informed particle dynamics model of a hyperelastic material. The proposed coupling strategy accurately transmits the forces between the fluid and solid, conserving momentum strictly. Using this model, we simulate the role of fluid impact on failure of a nonlinear elastic solid in the case of a canonical dam break problem. The location of the notch on the failure of the obstacle is found to be critical. Several modes of failure of the obstacle are observed, depending on the location of the notch and the height of the obstacle. Under some conditions, multiple failures of the obstacle occur simultaneously.

In this investigation, the influences of filling shapes on the failure mechanisms of rock masses under uniaxial compressive tests were analyzed using experimental and numerical simulation methods. For this purpose, a gypsum filling slab with three different shapes (isosceles trapezoid shape, triangle shape, and square shape) was inserted between the two granite specimens. In this regard, three different gypsum conditions were prepared; (1) gypsum containing a hole, (2) intact gypsum, and (3) gypsum containing the grout. Nine models were subjected to compression load with an axial load rate of 0.05 mm/min. Moreover, PFC2D was also employed to conduct numerical simulations of the models containing gypsum filling. In this matter, eight distinct types of soft gypsum filling were created; (1) concave shape, (2) semi-concave shape, (3) isosceles trapezoid shape, (4) triangle shape, (5) square shape, (6) bit shape, (7) lozenge shape, and (8) trapezoid. In addition, three different conditions were considered, i.e., gypsum containing a hole, intact gypsum, and gypsum containing the grout. The Brazilian tensile strength of gypsum and grout was 0.4 and 1 MPa, respectively. According to the results obtained, the failure process was predominantly controlled by the filling shape and filling conditions. With regard to the compressive strength, the fracture pattern and the failure mechanisms associated with the filling were found to play the main role. It was concluded that the compressive behavior of the filling is highly affected by the number of generated tensile cracks. As for hits of the acoustic emission (AE), a few AE hits were captured in the preliminary phase of loading, followed by a rapid growth in AE hits when the applied load reached its highest value. Furthermore, a large number of AE hits were observed during the stress drop.

To investigate the effect of particle shape on the dynamics of projectile impact into granular media, this study conducted discrete element method (DEM) numerical simulation using Particle Flow Code (PFC) software. Three particle shapes of granular materials were selected, where spherical particles represented by ball elements, ellipsoidal particles and irregular particles generated by clumps according to a certain template profile. The microscopic contact parameters were calibrated by laboratory tests and numerical simulations of standard direct shear tests. On this basis, the DEM model of a spherical projectile impact into the granular bed was established and laboratory tests were conducted. The test data matched well with the numerical results, verifying the reasonableness and accuracy of the numerical model. Analysing the results by varying the parameters shows that the impact process can be divided into three stages: impact, penetration and collapse. The particle shape does not affect the final penetration depth of the projectile as a power-law function of the initial velocity, and all follow the generalised Poncelet law. The difference in the peak impact force indicates that non-spherical particles have better cushioning capacity, and the analysis of the energy evolution during impact shows that there is significant variability in the effect of particle shape on the energy dissipation of the system. Finally, the internal response of the granular media during the impact process is elucidated by the results of porosity and coordination number. The force chains of granular materials undergo fracture and recombination during the impact process, and the particle shape significantly affects the structural distribution and evolution of the force chains.

The material point method (MPM) is computationally costly and highly parallelisable. With the plateauing of Moore’s law and recent advances in parallel computing, scientists without formal programming training might face challenges in developing fast scientific codes for their research. Parallel programming is intrinsically different to serial programming and may seem daunting to certain scientists, in particular for GPUs. However, recent developments in GPU application programming interfaces (APIs) have made it easier than ever to port codes to GPU. This paper explains how we ported our modular C++ MPM code Karamelo to GPU without using low-level hardware APIs like CUDA or OpenCL. We aimed to develop a code that has abstracted parallelism and is therefore hardware agnostic. We first present an investigation of a variety of GPU APIs, comparing ease of use, hardware support and performance in an MPM context. Then, the porting process of Karamelo to the Kokkos ecosystem is detailed, discussing key design patterns and challenges. Finally, our parallel C++ code running on GPU is shown to be up to 85 times faster than on CPU. Since Kokkos also supports Python and Fortran, the principles presented therein can also be applied to codes written in these languages.