Irregular-shaped Particles Research Articles

A fully resolved SPH-DEM method for heterogeneous suspensions with arbitrary particle shape

The study on fluid-solid interaction in heterogeneous suspensions is essential for theoretical research and engineering practice. In this paper, a three-dimensional fully resolved SPH-DEM method is presented to model suspensions with non-Newtonian fluids and solid particles of arbitrary shape. The fluid phase is modelled using SPH with a regularized Bingham model, whereas aggregates with irregular shapes is modelled using a DEM method based on surface mesh representation. A simple unified hybrid contact method is proposed to model the SPH-boundary, SPH-DEM, DEM-DEM, and DEM-boundary interactions in a generalized fashion. Furthermore, GPU parallelization is employed to increase the numerical efficiency. The coupling method is validated using numerical examples including: (1) water-entry of a sphere, (2) Poiseuille flow of a Bingham material, (3) collapse of columns of irregular particles, and (4) gravity-driven heterogeneous flows with irregular particle shape. The simulation results indicate that the presented method is suitable for heterogeneous flows with irregular solid particles.

Long-term variation in aerosol lidar ratio in Shanghai based on Raman lidar measurements

Abstract. Accurate lidar ratio (LR) and better understanding of its variation characteristics can not only improve the retrieval accuracy of parameters from elastic lidar, but also play an important role in assessing the impacts of aerosols on climate. Using the observational data of a Raman lidar in Shanghai from 2017 to 2019, LRs at 355 nm were retrieved and their variations and influence factors were analyzed. Within the height range of 0.5–5 km, about 90 % of the LRs were distributed in 10–80 sr with an average value of 41.0 ± 22.5 sr, and the LR decreased with the increase in height. The volume depolarization ratio (δ) was positively correlated with LR, and it also decreased with the increase in height, indicating that the vertical distribution of particle shape was one of the influence factors of the variations in LR with height. LR had a strong dependence on the original source of air masses. Affected by the aerosols transported from the northwest, the average LR was the largest, 44.2 ± 24.7 sr, accompanied by the most irregular particle shape. The vertical distribution of LR was affected by atmospheric turbidity, with the greater gradient of LR under clean conditions. The LR above 1 km could be more than 80 sr, when Shanghai was affected by biomass burning aerosols.

Improved Hydrogenation Kinetics of TiMn1.52 Alloy Coated with Palladium through Electroless Deposition.

The deterioration of hydrogen charging performances resulting from the surface chemical action of electrophilic gases such as CO2 is one of the prevailing drawbacks of TiMn1.52 materials. In this study, we report the effect of autocatalytic Pd deposition on the morphology, structure, and hydrogenation kinetics of TiMn1.52 alloy. Both the uncoated and Pd-coated materials were characterized using scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD). XRD analyses indicated that TiMn1.52 alloy contains C14-type Laves phase without any second phase, while the SEM images, together with a particle size distribution histogram, showed a smooth non-porous surface with irregular-shaped particles ranging in size from 1 to 8 µm. The XRD pattern of Pd-coated alloy revealed that C14-type Laves phase was still maintained upon Pd deposition. This was further supported by calculated crystallite size of 29 nm for both materials. Furthermore, a Sieverts-type apparatus was used to study the kinetics of the alloys after pre-exposure to air and upon vacuum heating at 300 °C. The Pd-coated AB2 alloy exhibited good coating quality as confirmed by EDS with enhanced hydrogen absorption kinetics, even without activation. This is attributed to improved surface tolerance and a hydrogen spillover mechanism, facilitated by Pd nanoparticles. Vacuum heating at 300 °C resulted in removal of surface barriers and showed improved hydrogen absorption performances for both coated and uncoated alloys.

Geotechnical properties of unprocessed soil from abandoned Mamut mine in Sabah, Borneo

The issue related to the geotechnical stability of land mining area in Malaysia had become more critical after a strong earthquake struck Sabah, Borneo in 2015 centred in Ranau District where Mamut copper mine is located. As part of safety assessment and future planning, knowledge of soil characteristics in this risky area is necessary. This paper presents some findings on geotechnical properties of unprocessed soil obtained from the abandoned mine. Results found that Mamut soil can be classified as SW and has higher coarse-grained percentage (97.4%) compared to other copper mines elsewhere. The soil also has higher permeability (3.61 x 10−3 m/s), lower organic content (0.15%), lower pH (4.53), higher specific gravity (2.75) and higher maximum dry density (1780 kg/m3). Mamut soil is found to be cohesionless, while the angle of friction shows a variation with the relative compaction. Chemical analysis shows that SiO2 and C12H10MgO6S2 are the two predominant compounds of the soil. Morphologically, Mamut soil appears to be composed of powdered and hardened particles with dark brown colour. They contain higher amount of irregular-shaped particles but well-rounded and spherical shapes are also observed. Smooth surfaces with no agglomeration between particles indicates that the strength value of the soil is low due to the weak bonding between the loose grain structure. These findings suggest that Mamut soil is suitable for chemical stabilisation or remediation method such as microbiologically induced calcite precipitation (MICP).

Simulations of biomass pyrolysis using glued-sphere CFD-DEM with 3-D intra-particle models

The shape of biomass particles influences intra-particle heat transfer, particle-particle collisions, interphase momentum, heat transfer, and pyrolysis yield. In this research, the effects of these multi-scale phenomena are captured using a glued-sphere computational fluid dynamic discrete element method (CFD-DEM) with 3-D intra-particle models. The glued-spheres resolved the shapes of particles and intra-particle temperature and species distributions. The implementation was validated using the pyrolysis data of a spherical particle and a cylindrical particle. Then, the influences of biomass shapes and sizes on pyrolysis were investigated. The results revealed the significant influence of surface areas and mass distributions on interphase heat transfer and chemical reactions. The intra-particle heat transfer is neglectable for a Biot number smaller than 0.41. Finally, the pyrolysis of irregularly shaped biomass particles in a fixed bed, fluidized bed, and spouted bed was simulated. Analysis of conversion distributions showed the largest deviations in the fixed bed and the slowest conversion rate in the spouted bed. A good balance between uniform and fast conversion is achieved in the fluidized bed. The multi-scale method proposed in this research provides a tool for the evaluation of large irregular-shaped biomass particle pyrolysis in different types of reactors.

Evaluating the crushing characteristics of recycled construction and demolition waste for use in road bases

With the increasing production of construction and demolition waste (CDW), the use of CDW as a road base has become a sustainable and eco-friendly disposal approach. The aggregate crushing value is an essential index in the construction of road bases and is defined as the mass percentage of fine particles after a confined compression test of recycled CDW. In this study, experiments and numerical simulations were conducted to evaluate the crushing characteristics of the CDW, consisting of three main components, i.e., gravel, brick, and mortar. From the single-particle crushing tests, the gravel was strongest, and the mortar was weakest. Multi-particle confined compression tests showed that the load–displacement curves of the recycled aggregates exhibited an increasing trend. The fluctuations during loading were attributed to the particle breakage. A three-dimensional discrete element method (DEM) with a laser scanning and reconstruction technique was proposed to model irregular-shaped aggregate particles using a cluster of bonded particles. A comparison of the experimental and numerical results showed that the bond breakage ratio linearly increased with the aggregate crushing value, providing a quantitative linkage between the micro-scale numerical model and the macro-scale test. It was found that the volume proportion of the gravel significantly affected the mechanical behavior of the mixed aggregates, and 75% was the critical threshold of the gravel component. As gravel with a volume proportion from zero to 75% was added to the brick or mortar, the aggregate crushing value increased by only 10–15%. In the mixed aggregates with brick and gravel, more of the brick particles were crushed when gravel with a proportion of 50–75% was added due to inconsistent deformation and stress concentration. If the gravel proportion exceeded 75%, the aggregate crushing value was reduced by 30%. Based on the numerical and experimental investigations of the crushing characteristics of the recycled aggregates, a ternary diagram was proposed to design the proportion of the three components in recycled CDW for road bases.

SPH-DEM simulations of saturated granular soils liquefaction incorporating particles of irregular shape

A coupled smoothed particle hydrodynamics (SPH) and discrete element method (DEM) scheme is presented herein to investigate liquefaction of saturated granular deposits during strong seismic ground motions. Irregular-shaped solid particles in the form of polyhedral blocks are utilized to represent soil grains using DEM. In SPH, the fluid domain is discretized into distinct particles carrying local properties of the fluid. Therefore, the presented approach is a fully particle-based technique ideal for handling free-surface and moving boundary problems. The phase coupling is achieved through local averaging techniques and well-established semi-empirical relations quantifying fluid-particle interaction. Level and mildly sloped deposits were subjected to seismic ground motions introduced into the system through the base wall. The results of the performed simulations suggest that both deposits liquefied during strong base excitation due to the contraction of pore spaces leading to large increases in the excess pore fluid pressure that in turn results in significant loss of interparticle contacts and degradation of soil strength and stiffness. In addition, the sloping deposit experienced large lateral displacements, especially, at the shallow soil layers which completely liquefied during the seismic loading.

A polybézier-based particle model for the DEM modeling of granular media

The discrete element method (DEM) has become a prominent tool for modeling granular media, whereas the development of versatile and efficient particle models for the modeling of irregular-shaped particles remains a heated topic and challenge. In this work, a new particle model based on polybézier curves to describe particle shapes is proposed for the modeling of smooth and irregular-shaped particles. In particular, cubic bézier curves are adopted because they have a fairly high degree of freedom in modeling curved geometries as well as a closed-form support function. With the particle geometry and support function derived from cubic polybézier curves, the Gilbert-Johnson-Keerthi algorithm is adopted to detect contacts, and the expanding polytope algorithm is adopted to resolve contact geometric features. To generate polybézier-based particle templates from images of particle shapes, a particle swarm optimization-based geometric fitting procedure is also developed. The effectiveness of the proposed particle model for shape representation is validated using a chart of particle shapes with various roundness and sphericity characteristics. DEM simulations of random packing and biaxial compression tests on polydispersed irregular-shaped particles are also presented, and the results show that the proposed model has fairly good computational efficiency and numerical stability.

Particle shape influence on the deformation resistance of carbonate sands under drained condition

The carbonate sand has high porosity and irregular particle shape compared with the quartz sand. Under dynamic loads, the carbonate sand perhaps experiences drained or partial drained shear, and the contribution of particle shape to its deformation resistance was still unrevealed. In this paper, particle shapes of five samples were first quantitively evaluated. Then, monotonic and cyclic tests under drained condition were carried out based on the simple shear apparatus. The particle size and shape were quantitively measured after the tests, and the particle breakage degree and its breakage mode were discussed. It is found that before phase transformation points (PT points), the irregular particles mobilize greater shear resistance. The particle breakage reduces the deformation resistance after the PT point due to its depression effect on the volume shear dilation. In cyclic shear, irregular particles have larger volume contraction due to the particle breakage, and the surface grinding is the major breakage mode. Under the same cyclic stress ratio (CSR), the irregular particles show smaller shear strain amplitudes, indicating that the irregular particles have stronger resistance to deformation. It is also found that the particle shape mainly influences the deformation resistance when the overall regularity (OR) is less than 0.8.

Comparative study on cyclic behavior of marine calcareous sand and terrigenous siliceous sand for transportation infrastructure applications

Calcareous sand has been used as an emerging unbound granular filler to replace siliceous sand in the construction of marine transportation infrastructure. However, the critical feasibility of and differences between using calcareous sand as a filler instead of siliceous sand have yet to be suitably assessed. In light of this, this paper presented a comparative study on the cyclic behavior of calcareous sand and siliceous sand through a series of high-cycle drained triaxial tests. To facilitate comparison, the same grain-size distribution and relative density were used for calcareous sand and siliceous sand to investigate any underlying cyclic behavior divergence caused by their respective distinctive particle shapes and breakage. Owing to the irregular and rough properties of calcareous sand particles, results showed that it exhibited stronger shear strength and resistance to permanent deformation than siliceous sand. However, during the early and middle stages of cyclic loading, the accumulation rate of permanent strain in calcareous sand was found to exceed that of siliceous sand due to its violent particle breakage habit, whereas a more severe dilatancy of calcareous sand induced by irregular particle shape was observed during the subsequent loading stage. Moreover, particle shape and particle breakage were found to have different competitive contributions to the increase of resilient modulus during different loading stages. In this work, the allowable cyclic strength ratio capable of better determining the suitable load level for a practical design was suggested. Furthermore, to capture the particle breakage extent under long-term cyclic loads, a refined hyperbolic equation was projected to model the relationship between relative particle breakage index and plastic work.

A kinematics-based model for the settling of gravity-driven arbitrary-shaped particles on a surface.

A discrete model is proposed for settling of an arbitrary-shaped particle onto a flat surface under the gravitational field. In this method, the particle dynamics is calculated such that (a) the particle does not create an overlap with the wall and (b) reaches a realistic equilibrium state, which are not guaranteed in the conventional discrete element methods that add a repulsive force (torque) based on the amount of overlap between the particle and the wall. Instead, upon the detection of collision, the particle’s kinematics is modified depending on the type of contact, i.e., point, line, and surface types, by assuming the contact point/line as the instantaneous center/line of rotation for calculating the rigid body dynamics. Two different stability conditions are implemented by comparing the location of the projection of the center of mass on the wall along gravity direction against the contact points to identify the equilibrium (stable) state on the wall for particles with multiple contact points. A variety of simulations are presented, including smooth surface particles (ellipsoids), regular particles with sharp edges (cylinders and pyramids) and irregular-shaped particles, to show that the method can provide the analytically-known equilibrium state.

COMPARATIVE EXPERIMENTAL STUDY ON LIQUEFACTION CHARAC TERISTICS OF CARBONATE AND SILICA SANDS

Carbonate sand has the characteristics of irregular particle shape, high porosity and low particle strength, and thus exhibits more complicated liquefaction characteristics than silica sand. Physical property tests, undrained cyclic triaxial tests and light dynamic penetration tests are conducted to study the differences in physical properties, liquefaction resistance and penetration resistance between carbonate sand and silica sand. Carbonate sand is found to have larger void ratio and internal friction angle than silica sand, which is consistent with the characteristics of carbonate sand particles. The liquefaction resistance increases with increasing relative density for both sands, and it is found that under the same relative density, carbonate sand has higher liquefaction resistance than silica sand. The penetration resistance increases with increasing relative density for both sands, and it is also found that under the same relative density, carbonate sand has higher penetration resistance than silica sand. Combining the results of undrained cyclic triaxial tests and light dynamic penetration tests, it can be concluded preliminarily that the current liquefaction evaluation methods based on the empirical data on terrestrial silica sand foundations can be conservative for evaluating the liquefaction susceptibility of carbonate sand foundations.

Fabrication and transport properties of ternary thermoelectric composites 0.7 Ca3Co3.9Cu0.1O9/0.3 Bi2Ca2Co1.9Cu0.1Oy/x Ag

Ag inclusions were introduced into 0.7 Ca3Co3.9Cu0.1O9/0.3 Bi2Ca2Co1.9Cu0.1Oy composites. Characteristic diffraction peak (111) of Ag is detected. Ag inclusions are with irregular particle shape, and the largest particle is about 10 μm. As Ag content (≤ 9 wt%) increases, the electrical resistivity reduces; meanwhile, transformation from semiconductor transport to metallic transport happens. With the rise of Ag content, the Seebeck coefficient reduces in the temperature range 373 K to 773 K apparently. However, its divergence among samples gradually becomes narrow above 773 K. The highest ZT of composites reaches 0.29 at 973 K.

Crack Extraction for Polycrystalline Solar Panels

Crack extraction of solar panels has become a research focus in recent years. The cracks are small and hidden. In addition, there are particles of irregular shape and size on the surface of the polycrystalline solar panel, whose reflection position and direction are random. Therefore, there is a complex and uneven texture background on the solar panel image, which makes the crack extraction more difficult. In this paper, a crack extraction method combining image texture and morphological features is proposed. Firstly, the background texture and multi-scale details are suppressed by the linear filter and the Laplace pyramid decomposition method. Secondly, the edge can be extracted based on the modulus maximum method of the wavelet transform. Finally, cracks were extracted by using the improved Fuzzy C-means (FCM) clustering combining the morphological and texture features of the cracks. To make the extraction results more accurate and reasonable, an improved region growth algorithm is proposed to optimize the extraction results. All of the above research is closely centered on the accuracy and stability requirements of the solar cell crack detection, which is also the key point of this paper. The experimental results show that various improved or innovative algorithms proposed in this paper can accurately extract the position of cracks and obtain better extraction results. The detection results have good stability and can be faithful to the actual situation, which will promote the application of solar cells in more fields.

Exploration Testing on High-Performance Cement-Based Materials Using Granulated Blast Furnace Slag as Fine Aggregates

This study investigates the feasibility of using granulated blast furnace slag (GBFS) as fine aggregates for high-performance cement-based (HPCB) materials. The mixture ratio of HPCB materials using GBFS as fine aggregates is calculated based on the dense packing theory of aggregates and the minimum water requirement. A series of cement-based material mixes are prepared with three water binder ratios (0.16, 0.18, and 0.2) and three GBFS replacement ratios (0%, 50%, and 100%). Various properties of the cement-based materials, such as the compressive strength, flexural strength, splitting tensile strength, and elastic modulus, are studied. The research on the selected HPCB material compositions using scanning electronic microscopy (SEM), hardened concrete pore structure determination (HCPD), and mercury intrusion porosimetry (MIP) enables a further understanding of the relationship between the mechanical properties and microstructures. The test results show that it is feasible to produce HPCB materials using GBFS as fine aggregates. Despite its large crushing value index and irregular particle shape, GBFS has hydraulic properties that can make up for these disadvantages. GBFS and mixed fine aggregate cement-based materials with good properties can be prepared with a reasonable mix design. The strength of such cement-based materials is consistent with that of ordinary quartz sand (QS) fine aggregate cement-based materials. The compressive, flexural, and splitting tensile strengths of GBFS and mixed fine aggregate cement-based materials may be higher than those of ordinary QS fine aggregate HPCB materials. The relationship between the compressive strength and porosity is in agreement with the formulas proposed by Powers, Ryshkevitch, Schiller, and Hasselman.

Preparation of dimethylaminopropyl octadecanamide/stearic acid vesicles incorporating azobenzene and their UV-responsive release property

UV-responsive vesicle was prepared by incorporating azobenzene in the vesicular membrane composed of dimethylaminopropyl octadecanamide (DMAPODA) and stearic acid (SA). Azobenzene intercalated in the vesicular membrane underwent cis-to-trans isomerization under the UV irradiation, confirmed by UV spectroscopy. The phase transition temperature of vesicle was found to be around 51.2 °C by differential scanning calorimetry. Using a negative staining technique, the vesicles were found as circular and irregular-shaped particles on the TEM photo. The mean hydrodynamic diameter of vesicles increased from 199.4 to 1597.3 nm when the lipid/azobenzene ratio increased from 100/0 to 100/5. The zeta potential of DMAPODA/SA vesicle decreased from about + 60 mV to – 60 mV when the pH value of medium increased from 3.0 to 10.0, and the inclusion of azobenzene in the vesicular membrane had little effect on the zeta potential. UV irradiation markedly promoted the release of carboxylic fluorescein loaded in vesicle incorporating azobenzene, possibly because the cis-to-trans photoisomerization would disturb the well-ordered crystalline structure of the vesicular membrane.

Influence of Particle Shape on the Macroscopic and Mesolevel Mechanical Properties of Slip Zone Soil Based on 3D Scanning and 3D DEM

The macroscopic and mesolevel mechanical mechanisms of slip zone soil are a crucial subject for the research of landslide deformation evolution and slope control, but the effects of the shape and psephicity of coarse particles in a slip zone soil on the mechanical properties of the slip soil zone still need to be explored. Discrete element method (DEM) can effectively monitor and track the mesolevel mechanical parameters of geotechnical materials, such as displacement vector field, contact force chain, and particle coordination number. The rock blocks in the medium‐sized shear test undergo a sophisticated process by 3D scanning technology, and a database of the blocks is established and accurately modeled by combining 3D DEM to simulate the indoor medium‐sized shear test for numerical investigation in line with the test conditions. The numerical simulation results demonstrate that the psephicity and particle shape of the rock blocks significantly affect the dilatancy and mesolevel mechanical parameters of the slip zone soil specimens. In addition, the numerical models featured by poorer psephicity and more irregular particle shape display more evident dilatancy, larger particle coordination numbers, as well as better contact density inside the model. Some references for the study of the macroscopic and mesolevel mechanical mechanisms of slip zone soil are provided.

Hydraulic conductivity and calcium carbonate content of biocemented heavy-metal contaminated mine waste soil

It is not uncommon for mining activity to generate wastes associated with negative engineering impacts include susceptibility to runoff due to the absence of vegetation, erosion, and sinkhole. Due to their high degree of permeability, movement of heavy metal contaminants in waste soils and aquifers occurs actively along with the hydrogeological parameters, and research on using biocementation methods such as enzyme induced calcite precipitation (EICP) to reduce the hydraulic conductivity is therefore beneficial. Mine waste soil collected from a copper mine in Lohan Dam, Sabah is characterized physically, morphologically, and chemically then treated with EICP under different operational parameters include curing duration (1,3,7 days), curing temperatures (5, 10, and 25 oC ), and relative density (70 and 80 %). The hydraulic conductivity was then tested using a constant head permeability test and the calcium carbonate content (%) is determined using the HCL washing method. Properties of the Lohan Dam wastes are found to be predominantly coarse grain soil of low plasticity, high specific gravity, high permeability, acidic in nature, and low organic content. Morphologically, they are composed of powdered and hardened particles with dark brown color with high amount of irregular-shaped particles. Mineralogical, Lohan Dam soil wastes contain a high level of heavy metals beyond the safety level of the Department of Environmental Malaysia. EICP treatment had to change the degree of permeability from ‘high and medium’ to ‘low’ with a 94-97% reduction in hydraulic conductivity corresponding to the amount of calcium carbonate content produced ranging 6.94-9.63%. In conclusion, relative density shows the marginal effect, curing duration, and temperature shows a more significant impact on the treatment effectiveness.

Coprecipitation Temperature Effects of Morphology-Controlled Nickel Hexacyanoferrate on the Electrochemical Performance in Aqueous Sodium-Ion Batteries.

Coprecipitation effortlessly fabricated nickel hexacyanoferrate (NiHCF) with outstanding rate capability and stability for aqueous batteries. Citrate-aided coprecipitation decelerated the crystallization, assembling cubic-shaped powder based on separation between nucleation and growth. This study revealed that coprecipitation temperature determined the electrochemical performance. With lower temperatures, smaller particles with more water were formed by predominant nucleation, resulting in low crystallinity and capacity of 58 mAh g-1 . Expanded surface area reduced electrode/electrolyte interface charge-transfer resistance and showed excellent rate capability (79 % of initial capacity at 100 C-rate). However, poor cyclability was obtained. At elevated temperatures, nuclei growth and dehydration occurred, and thus highly crystalline large particles were formed. In turn, NiHCF delivered excellent capacity of 76 mAh g-1 at 1 C-rate but exhibited inferior rate performance because of longer diffusional path. Meanwhile, normal coprecipitation at 70 °C induced irregular-shaped tiny particles, presenting 93 % retention of initial capacity at 100 C-rate.

Study of the properties of nanoparticles of Ag and Zn citrates

The use of nanomaterials has become especially relevant as components of new drugs, adjuvants and new ingredients in feed additives. The very combination of inorganic components (metals) with natural minerals (сeolites, clenoptolites) made it possible to create fundamentally new chemical compounds that differ significantly in the mechanism of action and their physicochemical characteristics from traditionally used drugs for the treatment of bacterial diseases of poultry. The practical application of the composition involves the use of small sizes of nanoparticles that are in the “nanoscale” from 1 to 100 nm. Our article contains the results of studies of Ag and Zn nanomaterials in combination with citrate in the form of powder and dispersed solutions. As a result of scanning electron microscopy, it was found that the studied sample of Ag and Zn nanoparticles is a gray powder of monocrystalline particles of irregular shape, the size of which varies from 160 to 350 nm. Particles of three sizes were most often found among Ag and Zn citrates, namely: 160 nm – 45 %, 210 nm – 35 %, 350 nm – 20 %. Studying the bactericidal properties of dispersed solutions of Ag and Zn citrates on microbial suspensions of test cultures of Escherichia coli (ser.O2), Salmonella typhimurium, Pseudomonas aeruginosa, Staphylococcus epidermidis, we found that Ag citrate showed better bactericidal properties in relation to all experimental test cultures of Escherichia coli (ser.O2), Salmonella typhimurium, Pseudomonas aeruginosa, Staphylococcus epidermidis, in contrast to the citrate solution Zn, which was only effective against Escherichia coli (ser.O2), and Staphylococcus epidermidis.