Coupling of discrete-element method and smoothed particle hydrodynamics for liquid-solid flows

Particle based methods can be used for both the simulations of solid and fluid phases in multiphase medium, such as the discrete-element method for solid phase and the smoothed particle hydrodynamics for fluid phase. This paper presents a computational method combining these two methods for solid-liquid medium. The two phases are coupled by using an improved model from a reported Lagrangian-Eulerian method. The technique is verified by simulating liquid-solid flows in a two-dimensional lid-driven cavity.

Effects of model size and particle size on the response of sea-ice samples created with a hexagonal-close-packing pattern in discrete-element method simulations

We investigated the effects of model size and particle size on the simulated macroscopic mechanical properties, uniaxial compressive strength, Young＇s modulus, and flexural strength of sea-ice samples, using the discrete-element method （DEM） with a bonded-particle model. Many different samples with a hexagonal-close-packing pattern and a unique particle size were considered, and several ratios of particle size to sample dimension （D/L） were studied for each sample. The macroscopic mechanical properties simulated by the DEM decrease monotonously with an increase in D/L. For different samples with different particle sizes, the macroscopic mechanical properties will be identical when D/L is constant. The quanti- tative relationships between macroscopic mechanical properties and ratio of particle size to sample size are important aspects in engineering applications of the DEM method. The results provide guidance on the choice of a particle size in the DEM simulation for numerical samples with a hexagonal-close-packing pattern.

Three-dimensional discrete element numerical simulation of Paleogene salt structures in the western Kuqa foreland thrust belt

Taking the Paleogene salt strata in the west of Kuqa foreland thrust belt as study object, the deformation features of salt structure in the compression direction and perpendicular to the compression direction were examined to find out the control factors and formation mechanisms of the salt structures. By using the three-dimensional discrete element numerical simulation method, the formation mechanisms of typical salt structures of western Kuqa foreland thrust belt in Keshen and Dabei work areas were comprehensively analyzed. The simulation results show that the salt deformation in Keshen and Dabei work areas is of forward spread type, with deformation concentrated in the piedmont zone;the salt deformation is affected by the early uplift near the compression end, pre-existing basement faults, synsedimentary process and the initial salt depocenter;in the direction perpendicular to the compression direction, salt rocks near the compression end have strong lateral mobility with the velocity component moving towards the middle part, and the closer to the middle, the larger the velocity will be, so that salt rocks will aggregate towards the middle and deform intensely, forming complex folds and separation of salt structures from salt source, and local outcrop with thrust faults. Compared with 2 D simulation, 3 D simulation can analyze salt structures in the principal stress direction and direction perpendicular to the principal stress, give us a full view of the formation mechanisms of salt structures, and guide the exploration of oil and gas reservoirs related to salt structures.

Potential application of particle based simulations in reservoir security management

In order to model the movement progress in case of risks such as dam collapse and coastal inundation, particle-based simulation methods, including the discrete-element method and smoothed particle hydrodynamics, which have specific advantages in modeling complex three-dimensional environmental fluid and particulate flows, are adopted as an effective way to illustrate environmental applications possibly happening in the real world. The theory of these methods and their relative advantages compared with traditional methods are discussed. Examples of 3-D flows on realistic topography including the flooding of a river valley as a result of a dam collapse and coastal inundation by a tsunami are introduced. Issues related to validation and quality data availability are also discussed. The results show that the simulations provide a valuable insight in a given situation for the security management of reservoir dams. Validation can only be performed where both the initial and final states can be very well characterized.

Discrete and continuum modeling of granular flow in silo discharge

Granular material discharge from a flat-bottomed silo has been simulated by using continuum modeling and a three-dimensional discrete-element method （DEM）. The predictive abilities of three commonly used frictional viscosity models （Schaeffer, S-S, and μ（I）） were evaluated by comparing them with the DEM data. The funnel-flow pattern （type C） and the semi-mass-flow pattern （type B） that was predicted by DEM simulations can be represented when the Schaeffer orμ（I） model is used, whereas the S-S model gives a consistent type-B flow pattern. All three models over-estimate the discharge rate compared with the DEM. The profiles of the solids volume fraction and the vertical velocity above the outlet show that the larger discharge rates given by the Schaeffer and μ（I） model result from an over-estimation of volume fraction, whereas the deviation in the S-S model stems from the failure to predict a solid vertical velocity and a volume fraction.

Studying the particle size ratio effect on granular mixing in a vertically vibrated bed of two particle types

The uniform mixing of solids is important in many industries,such as the pharmaceutical,food,petrochemical and chemical industries.We numerically investigated the effect of particle size ratio on the mixing of bisized particles in a quasi-two-dimensional vibrationally fluidized bed.The granular bin ary mixtures comprised spherical particles with different size ratios.Three-dimensional discrete-element simulations agreed with previous experimental results.Convective and diffusive mechanisms occurred Keywords:Discrete-element modeling Fluidization Granular media Mixing Particle size ratio Vibration within the vibrated bed.The particle size had no significant influence on convective mixing,whereas the diffusive mechanism strengthened for large size ratios.The average particle velocity was larger in a mixture of large size ratios.The stronger diffusive motion and larger average particle velocity caused the particles to mix faster for large size ratios.The final mixing index decreased with size ratio because of the difference between the size and number of small and large particles.

Multi-scale investigation of active failure for various modes of wall movement

Retained backfill response to wall movement depends on factors that range from boundary conditions to the geometrical characteristic of individual particles.Hence,mechanical understanding of the problem warrants multi-scale analyses that investigate reciprocal relationships between macro and micro effects.Accordingly,this study attempts a multi-scale examination of failure evolution in cohesionless backfills.Therefore,the transition of retained backfills from at-rest condition to the active state is modeled using the discrete element method(DEM).DEM allows conducting virtual experiments,with which the variation of particle and boundary properties is straightforward.Hence,various modes of wall movement(translation and rotation)toward the active state are modeled using two different backfills with distinct particle shapes(spherical and nonspherical)under varying surcharge.For each model,cumulative rotations of single particles are tracked,and the results are used to analyze the evolution of shear bands and their geometric characteristics.Moreover,dependencies of lateral pressure coefficients and coordination numbers,as respective macro and micro behavior indicators,on particle shape,boundary conditions,and surcharge levels are investigated.Additionally,contact force networks are visually determined,and their influences on pressure distribution and deformation mechanisms are discussed with reference to the associated modes of wall movement and particle shapes.

Study on the mechanical properties of outwash deposits with random structure method

Outwash deposit is one of the major threats to the safety and stability of railway transit engineering in the Sichuan–Tibet area.In this paper,different samples of outwash deposits were prepared based on the random structure method,and a series of large-scale direct shear tests were carried out under different normal stresses.The influence of stone content and the spatial distribution of stone blocks on the physical and mechanical properties of outwash deposits were studied.The results show that with the increase of stone content,the shear stress-displacement curve changs from strain softening to strain hardening.The shear zone is larger,and its shape is more tortuous due to the movement and rotation of stone blocks.The internal frictional angle increases linearly while the cohesion diseases with the increase of stone content.The main influence of the spatial distribution of stone blocks on the mechanical properties of outwash deposits is the peak stress.The shear zone is mainly determined by the distribution of the stone blocks near the shear zone.