The solid–liquid two-phase flow with coarse particles is ubiquitous in natural phenomena and engineering practice, which is characterized by coarse particles, high particle concentration, and large particle size distribution. In this work, the numerical models describing two-phase flows are reviewed, which given that the Eulerian–Lagrangian method is applicable in this work. Then, some modified models are proposed for the situation where the conventional Eulerian–Lagrangian method is not applicable to deal with coarse particles. The continuous phase equations of liquid are solved based on the finite volume method. The pressure implicit with splitting of operators algorithm for solving the Navier–Stokes (N–S) equations of the pseudo-single-phase flow, considering phase fraction and momentum exchange source term, is proposed. The discrete coarse particle is tracked in the Lagrangian method. A virtual mass distribution function is proposed for calculating coarse particle volume fraction. A weighted function method relating to the particle size is given for the interpolation between the Eulerian and Lagrangian fields. The barycentric coordinates are introduced into the particle localization. All the modified models are algorithmically implanted in the open-source field operation and manipulation (OpenFOAM) as a new solver named coarse discrete particle method FOAM (CoarseDPMFoam). Subsequently, the applicability of the numerical simulation method is verified by some typical test cases. The proposed numerical simulation method provides new ideas and methods for the mechanism investigation and engineering application of the two-phase flow with coarse particles.

Solid–liquid two-phase flow with dense coarse particles in the pipeline exists widely in energy and resources engineering, especially in the prospective hydraulic lifting scenario of deep-sea mining. In this paper, the coarse particles' transportation behavior in a vertical pipe is investigated based on an optimized Eulerian–Lagrangian method proposed in our previous work. The coarse particle transportation in the vertical pipe is characterized as multi-processes and multi-physical effects and is not fully captured due to the limitations on experimental apparatus, experimental measurement techniques, and numerical simulation techniques. Little research has been done on the local characteristics of the flow and their effect on the hydraulic lifting performance. The characteristics of the internal flow field, particle retention, and hydraulic lifting efficiency are disturbed under the condition of the continuous supply with the constant inlet two-phase concentration and velocity. The simulation results illustrate that particle transportation process can be roughly divided into three stages, single phase flow stage, mixing stage, and stable transportation stage, and shows a dilute-dense non-continuous flow pattern due to particle retention. Based on parametric studies, the retention phenomenon is alleviated by the increase in the water inlet velocity and almost disappears at approximately 12 000 of the Reynolds number, where the flow pattern transition occurs. Finally, the hydraulic lifting performance, such as a critical lifting condition and the friction loss, is analyzed and the transition of flow pattern is discussed.

The occurrence of a shear band is often thought as the precursor of failure. To study the initiation of shear banding in gas hydrate-bearing sediments, two groups of triaxial compression tests combined with a CT (computer tomography) scan were conducted by triaxial CT-integrated equipment under two confining pressures and seven hydrate saturations. The macro stress–strain curves and the corresponding CT scanning images of the micro-structure and the distribution of the components were obtained. The geometric parameters of the shear bands were measured based on the CT images at four typical axial strains, respectively. The distribution characteristics of soil particles, water, hydrate and gas were also analyzed. It is shown that the existence of methane hydrate changes the mechanical property of hydrate-bearing sediment from plastic failure to brittle failure when the hydrate saturation is over 13%, which occurs in the range of the tests in this paper. The peak of the deviatoric stress increases with the hydrate saturation. The shear band is in either a single oblique line or inter-cross lines depending on the hydrate saturation, the effective confining pressure and the initial distribution of the gas hydrate. Most of the shear band surfaces are not straight, and the widths of the shear bands are almost non-uniformly distributed.

The solid–fluid two-phase flow with coarse particles is an important research object in the two-phase transportation field, such as deep-sea mining. This paper adopts the resolved computational fluid dynamics-discrete element method to investigate the motion and mechanical characteristics of the coarse particles during the hydraulic collection. First, the rising process of coarse particles by combining the particle trajectory with the qualitative force analysis is analyzed during the hydraulic collection. The spiral phenomenon of the particle is found through the particle trajectory in numerical results, and the centripetal force is the reason for the spiral phenomenon of the particle. Second, the variations of the normalized fluid drag force and the rise time of particles are investigated at different fluid velocities and particle sizes. The results show that the rise of particles during hydraulic collection results from the rising and settling effects characterized by the fluid drag force and the relative gravity, respectively. Finally, appropriate particle size is recommended to save energy and improve the efficiency of hydraulic collection. In addition, the influence of the horizontal distance between coarse particles and the inlet of the suction pipe on particle rise is discussed.

Computational fluid dynamics-discrete element method is frequently used for modeling particulate flows due to its high efficiency and satisfactory accuracy. The particle volume fraction is a crucial parameter that significantly affects the computation accuracy. It may be extremely large when the particulate flows contain coarse particles because it is determined by the ratio of particle volume to cell volume. In this paper, the performance of different methods, such as the divided particle volume method (DPVM), the big particle method, and the diffusion-based method, for computing the particle volume fraction is thoroughly reviewed, implemented, and investigated. It turns out that the DPVM must not be used when the particle size is larger than cell size due to significant fluctuation of the particle volume fraction field. The big particle method is optimized for simulation accuracy and code implementation. The optimized big particle method is similar to the diffusion-based method by diffusing the particle effects to the surrounding cells. It demonstrates greater consistency with experimental observations compared to the diffusion-based method, primarily attributed to its incorporation of polydisperse effects.