When transplanting the gas–solid fluidized bed technology to the offshore floating platform, the gas–solid flow characteristics in the bed will be affected by the rolling of the platform. In this paper, the flow field, especially the dynamic variation characteristics of the particles, in a two-dimensional rolling fluidized bed, is investigated using the numerical simulation method. The results show that when the bed is in an inclined position, the gas/particle phases gather in the upper/lower wall region of the inclined bed. During the rolling process of the bed, this behavior results in a periodic change in the gas–solid flow state near the wall region, forming an overall particle internal circulation flow mode of ‘upward flow rate in the upper wall region and downward flow rate in the lower wall region’. The solid holdup in the lower wall region fluctuates at a low amplitude around high values, with a corresponding downward solid flow rate. Meanwhile, the upper wall region has a high frequency and amplitude of solid holdup fluctuations and a corresponding upward solid flow rate. In addition, affected by the Coriolis force, a ‘lag phenomenon’ appears when the inclination angle decreases, compared with the instantaneous inclination angle increase stage. It is anticipated that this paper will provide theoretical guidance for the engineering application of the fluidized bed on the offshore floating platform. Full article

In an axial granular bed filter (GBF), a new mesoscale simulation approach is obtained by combining the macroscopic calculation models, i.e., the equations of the total pressure drop and dust-removal efficiency into the porous media model and the source term of the conservation equations. After grid-dependent tests and experimental validation, the effects of different conditions, i.e., granular bed height L, superficial gas velocity u_g, dust diameter d_p, dust concentration c_p, granular diameter d_g, initial bed voidage ε₀, and filtration time t, on the pressure drop and dust-removal efficiency are investigated. The results show that the pressure drop is related to the inertial and viscous resistance terms, which increase with increasing L, u_g, c_p and t and decreasing ε and d_g. The dust-removal efficiency is related to the Reynolds number, effective Stokes number, and equivalent granular diameter ratio. It increases with increasing L, u_g, d_p and t (small values), and decreasing c_p, ε, and d_g. Moreover, the influence of different conditions coincides well with dust-removal efficiency in relevant studies, which further demonstrates the accuracy of the mesoscale simulation approach. With the application of this method, the flow field can also be obtained easily and quickly, which is expected to provide a reference for the simulation study of GBF. Full article

The creep damage behavior of rocks is very important for evaluating the stability and safety of key rock engineering. Based on the Lianhua Tunnel Project in China, this paper aims to study the creep damage mechanics, the influencing factors and the creep constitutive models of sandy shale. In order to achieve these goals, a uniaxial compressive strength test and a creep test under different moisture contents and load levels were carried out. According to the test results, the creep parameters (elastic coefficients E₁ and E₂ and viscosity coefficients η₁ and η₂) of the Burgers Model were achieved, and the relationship between the creep parameters and moisture content, ω, was established accordingly (E₁ = f(ω), E₂ = f(ω), η₁ = f(ω), η₂ = f(ω)). A fully weathered sandy-shale creep constitutive model considering moisture content was finally obtained. Test results showed that creep deformation increases with any increase in load level or moisture content, and the influence of moisture content is more significant. For instance, creep deformation increased by 35% when the load increased by 50%, and creep deformation increased by 82% when the moisture content increased by 45%. In addition, the creep rate in the steady stage and the duration of the primary creep stage increased with any increase in moisture content or load level. The higher the moisture content, the greater the influence of creep deformation on the total deformation. The creep model of fully weathered sandy shale showed that the elastic coefficients (E₁, E₂) and the viscosity coefficients (η₁, η₂) are negatively correlated to moisture content; E₁ is negatively correlated to load level; and E₂, η₁ and η₂ are positively correlated to load level. Qualitative and quantitative analysis of fully weathered sandy shale can improve the existing research of creep properties and is expected to provide theoretical support for treatment of large deformation disasters in the fully weathered sandy-shale stratum. Full article

The heat and mass transfer to solid particles in one-dimensional oscillating flows are investigated in this work. A meta-correlation for the calculation of the Nusselt number (Sherwood number) is derived by comparing 33 correlations and data point sets from experiments and simulations. These models are all unified by their dependencies on the amplitude parameter ${10}^{-3}\le ϵ\le {10}^3$ and the Reynolds number ${10}^{-1}\le Re\le {10}^6$, while the $ϵ$-$Re$ plane is applied as a framework in order to graphically display the various models. This is the first study to consider this problem in the entire $ϵ$-$Re$ plane quantitatively while taking preexisting asymptotic models for various areas of the $ϵ$-$Re$ plane into account. Full article

The most common scale-up approach for gas–solids fluidized beds is based on matching the governing dimensionless parameters. In the literature, this approach has been validated only by means of measuring global parameters between different sizes of fluidized beds. However, such global measurements are not sufficient to depict all the interplaying hydrodynamic phenomena and hence verify the scale-up relationships. Therefore, to assess this approach, an advanced gas–solids optical probe and pressure transducer measurement techniques have been applied to quantify local hydrodynamic parameters in two different sized fluidized beds. Four different sets of experimental conditions were designed and conducted to examine the assessment of the scaling approach with matched and mismatched dimensionless groups between the two beds. The results indicated that the reported dimensionless groups are not adequate for achieving similarity between the two gas–solids fluidized beds in terms of solids holdup, gas holdup, particle velocity, mass flux, and pressure fluctuation. This finding demonstrates the importance of local measurements of the hydrodynamic parameters of fluidized beds in order to evaluate scale-up relationships. Finally, the results further advance the understanding of the gas–solids fluidized beds and present deeper insight into their solids dynamics. Full article

A cold-flow lab-scale cross-flow fluidized bed classifier was simulated using the CFD software Barracuda VR^®. The purpose of the study was to identify the most suitable drag model and make the model adjustments that provide the best representation of the flow situation in the classifier when comparing the results with the experimental data. Two particle types were used in the simulations and in the experiments: zirconia (median diameter 69 µm, skeletal density 3830 kg/m³) and steel (290 µm, 7790 kg/m³). Ten different cases, with different solids loading values, were investigated: three with pure zirconia particles, three with pure steel particles, and four with a mixture of zirconia (28%) and steel (72%). Several different drag models were tried out in the simulations. However, none of the available models were able to predict the classification efficiency observed in experiments with their default settings. Although most of the drag models correctly predicted the inversely proportional behavior of the classification efficiency vs. solids loading, the classification efficiency was overpredicted. It was observed that a combined WenYu/Ergun drag model gave a wide range of accuracy, by being able to capture the behavior of both dense and dilute particle systems. Even though the predictions of the classification efficiency for steel particles were acceptable, a larger deviation was observed with Geldart A zirconia particles. CFD simulations with the WenYu and Ergun combined drag model were used for further validation against the experimental observations. In this case, previously published experimental data for fluidization of pure Zirconia particles were used. The fluidization of zirconia was modelled in Barracuda VR^® with adjustment of the combined WenYu/Ergun drag model parameter (k₁), to obtain a suitable validation. Furthermore, the effect of adding the blended acceleration model (BAM) for the fluidization simulations is discussed. It was observed that the fixed bed pressure drop was very accurate compared to the experimental observation, but the pressure drop after the fluidization was slightly overpredicted. Full article

During the construction of tunnels in saturated water-bearing sand stratum, water and mud inrush disasters often occur. Grouting is the most convenient and effective method to improve the mechanical properties of the soil and prevent groundwater seepage. The reasonableness of the Discrete Element Method (DEM) contact parameters is verified by comparing the repose angle test with that obtained by simulations. The grouting model of saturated water-bearing sand stratum was established based on the Volume of Fluid-Discrete Element Method (VOF-DEM). Then, the effects of sand stratum porosity and grouting pressure on grouting were discussed. The results show that (1) in dense sands, the permeation diffusion of the slurry dominates, whereas in loose sands, the compaction zone is well developed. (2) Loose sand has a wider propagation of stress and dense sand has a larger increase in the stress state. (3) In loose sand the slurry diffusion is significantly affected by gravity, whereas in dense sand the slurry diffusion along the dominant path of the grouting pipe wall boundary is obvious. (4) The range of slurry diffusion and compaction zone is positively related to the porosity and grouting pressure. (5) In loose sand with grouting pressure below 200 kPa, no compaction diffusion occurs during the grouting process, whereas in dense sand, when the grouting pressure is below 500 kPa no compaction diffusion occurs during the grouting process. Full article

The relaxation of a rigid particle suspended in a one-dimensional oscillating flow is calculated according to different drag models and the results are compared. Conditions are derived under which relaxation can be neglected or drag models can be substituted by simpler ones. This investigation is conducted analytically and graphically via the plane defined by the Reynolds number and amplitude parameter. This work matches various, mostly analytic drag models together to consider simple particle relaxation with a few, broad range input parameters and cover large parts of the plane spanned by Reynolds number and amplitude parameter. Full article

In this paper, three types of air guide vanes are designed: direct-type, L-type, and logarithmic spiral type, respectively. ANSYS-FLUENT 20.0 is used to numerically simulate the internal flow field of turbo air classifier by novel different structures. The numerical results show that the guide vane structures have a good effect on the flow field stability of the annular function zone in the classifying chamber. The distribution of tangential velocity and radial velocity verified the logarithmic spiral guide vane, and makes the airflow flow along the rotor cage circumferentially uniformly. In addition, the turbulent dissipation rate and energy loss decreases in the rotor cage region, which also shows that the guide vane is beneficial to improve classification performance. The tromp curve of the numerical simulation shows that the logarithmic spiral guide vane reduced the cutting size by 6.3% and 23.7% at two different process parameters, and is obviously better than other guide vane structures in improving the classification sharpness index (K). Finally, the reliability of numerical simulation is verified by material experiment. The research results have certain theoretical significance and guidance for the structural design of the guide vanes of the turbo air classifier. Full article

Grouting is an effective method to reduce permeability and improve the mechanical performance of sand layers, preventing a disastrous inrush of sand and water. A scientific grouting design scheme is the premise for satisfying grouting reinforcement requirements. Due to a lack of theoretical basis for current grouting designs, grouting projects are conducted empirically and blindly. This paper presents a quantitative design method for grouting in sand layers. Based on this method, a quantitative design is realized for judgment of the grouting mode, determination of grouting range and calculation of grouting reinforcement effect. Moreover, for the fracture–compaction grouting mode, a theoretical model is proposed to calculate the grouting process, considering the coupling effect of grout flow and sand layer deformation. Meanwhile, a calculation method for reinforcement is put forward, which can connect macroscopic performance of the grouted body and individual performance of grout veins, compacted sand and undisturbed sand. In order to verify the efficiency of the grouting design method, it has been used in a sand grouting project in Qingdao Metro Line 2. In this project, judgment of the grouting mode, selection of grouting type and determination of grouting parameters have been completed based on the design method. Several inspection approaches have been performed to evaluate the effectiveness of the grouting design, showing that engineering stability was guaranteed after the grouting operation. Full article

Awareness of granulated soils’ internal instability is an important parameter when designing granulated filters, and the ability of a granulated soil’s internal stability can be verified using the soil PSD (Particle Size Distribution) curves’ secant slopes. The current work presents a new method to calculate the soil PSD curves’ secant slopes automatically, and a synthetic diagram is presented for the potential examination of the granulated soils’ internal stability. To verify the feasibility and accuracy of this synthetic diagram, 80 specimens of soil were investigated in this work and categorized into two groups: 50 sand–gravel soils and 30 (clay)–silt–sand–gravel soils. The obtained conclusions indicate that the internal stability and instability potentials of sand–gravel soils can be distinguished successfully with a synthetic chart and the Kenney and Lau criterion but cannot be assessed with the Kezdi and Sherard criteria. None of the criteria studied here can be used for the internal stability assessment of silt–sand–gravel and clay–silt–sand–gravel soils. Full article

Cement-sodium silicate grout (CSG) is now widely adopted in water plugging engineering to prevent water inrush disasters, and the gelation and consolidation characteristics of CSG in water environment significantly affect the grouting effect. To obtain an in-depth understanding of the performance of CSG in water, the CSGs with different water-cement ratios and volume ratios were tested, and the gelation properties, the deposition characteristics and the diffusion process of CSG within water were examined. The compressive strength and microstructure of CSG consolidation formed in air and water were also analyzed comparatively. The test results indicate that the CSG consolidation exhibits obvious stratification and segregation phenomena in water, which can be divided into three layers with different substance compositions. The compressive strength of CSG consolidation formed in water is much lower than that of the grout consolidation formed in air, indicating that the water environment has a significant weakening effect on the consolidation properties of CSG. The hydration products and microstructure of CSG consolidation in water change clearly due to the dilution effect of water. Full article

During methane extraction, the permeability of a coal seam is the vital factor affecting recovery. Although the permeability of a coal seam and its relationship with porosity have been studied in a few works, the calculation process of coal seam permeability is usually too simplistic or neglects the influence of microscopic fracture structures. Statistical research shows that the permeability of coal seams with the same porosity and different fracture structures is quite different. For the purpose of quantitatively investigating the contribution of fractures and pore structure in coal seams, a fractal permeability model considering the microstructure of coal seam fracture is established in this paper. The correctness of the model is verified by comparing with the previous research results. Then, the influence of the microscopic fracture structure on the equivalent permeability is analyzed. The simulation results show that the permeability of fractured coal is directly proportional to the fractal dimension of the fracture, the maximum fracture length and the azimuth. It is inversely proportional to the tortuous fractal dimension and the dip angle of the fracture surface. This conclusion provides the foundation for revealing the microstructure mechanisms of macroscopic seepage characteristics of coal seams, and implementing effective strategies to enhance gas recovery rates under different geological structures. Full article

Grouting is a reinforcing method commonly used in underground engineering. The grouting-reinforced body is in saturated groundwater, which is due to long-term seepage, resulting in reinforcing performance attenuation. This is a guarantee for the safe operation of the underground structure’s long life cycle that obtains the performance attenuation law of the grouting-reinforced body under the action of seepage. This paper uses primitive to describe the mechanical properties of grouting-reinforced body under seepage erosion, establishing the damage mechanics model of grouting-reinforced body under seepage, designing deterioration experimental of grouting-reinforced body under seepage, studying the mechanism of the permeation water pressure on the permeability of the grouting-reinforced body, and obtaining the variable of the grouting-reinforced body damage variable with the permeation water pressure. Studies have shown that seepage effects have a “sudden jump” phenomenon in the process of grouting-reinforced body erosion, and the limit damage of grouting-reinforced body is 0.15~0.19. The relationship between the permeability and damage variables of grouting-reinforced body under seepage are verified, and the quantitative relationship of grouting-reinforced body between permeation pressure, time and damage variables are obtained. This research is of great importance for improving the deterioration theory under seepage and ensuring the long-term safety of tunnel operations. Full article

The pores in rocks are multi-scale and highly complex. Based on complex network theory, the topological properties of a sandstone flow network are studied. The results show that the sandstone pore scale network is a small-world network with an average shortest path of 5.720, and 80% of the network node degree is less than 3. This network structure can improve the security of the network and ensure the permeability of the pores under the action of external forces. In addition, nodes with appropriate degree distribution have a significant influence on permeability. Nodes with a larger degree will significantly reduce the average shortest path of the network, while nodes with a smaller degree will expand the coverage of the seepage network. Full article

An experimental model of a corner-injected flow is built to investigate the turbulent flow behavior by employing the PIV technique. The influences of the ideal tangential circle, the additive particles and the initial gas mass flux on the corner-injected flow are analyzed systematically. To be specific, the flow deviation, the velocity profile, the vortex evolution and the turbulent flow development are discussed quantitatively. The influences of the increasing ideal tangential circle on the turbulent jet deviation are shortened gradually, and the impinging circles are obviously narrowed with the injection of particles. The gas-particle corner-injected flow can obtain a good rotation when the ideal tangential circle is 0.25 times the width of the impinging chamber. The momentum decay of the corner-injected flow diminishes with the increasing ideal tangential circle and the decreasing initial gas velocity. The rotation strength of the vortex is more affected by the injection of laden particles, while the angular distortion enhances when increasing the ideal tangential circle. The increasing initial gas mass flux plays a dominant role in the development of the corner-injected flow, secondly the increasing ideal tangential circle, and last the injection of particles. All these findings can provide theoretical support in the design of a corner-fired furnace. Full article