Irregular Particles Research Articles

Optimising Mg-Ca/PLA Composite Filaments for Additive Manufacturing: An Analysis of Particle Content, Size, and Morphology.

Low-temperature additive manufacturing of magnesium (Mg) alloy implants is considered a promising technique for biomedical applications due to Mg's inherent biocompatibility and 3D printing's capability for patient-specific design. This study explores the influence of powder volume content, size, and morphology on the mechanical properties and viscosity of polylactic acid (PLA) matrix composite filaments containing in-house-produced magnesium-calcium (Mg-Ca) particles, with a focus on their application towards low-temperature additive manufacturing. We investigated the effects of varying the Mg-Ca particle content in a PLA matrix, revealing a direct correlation between volume content and bending strength. Particle size analysis demonstrated that smaller particles (D50: 57 μm) achieved a bending strength of 63.7 MPa, whereas larger particles (D50: 105 μm) exhibited 49.6 MPa at 20 vol.%. Morphologically, the filament containing spherical particles at 20 vol.% showed a bending strength that was 11.5 MPa higher than that of the filament with irregular particles. These findings highlight the critical role of particle content, size, and shape in determining the mechanical and rheological properties of Mg-Ca/PLA composite filaments for use in material extrusion additive manufacturing.

Experimental and numerical investigation of iron ore pellet firing using coupled CFD-DEM method

Iron ore pellets are the main feedstock in ironmaking processes. While extensive research has addressed numerical modeling of the iron ore pellet induration process, little effort has been made to describe the intricate thermochemical processes occurring within the reactor starting from the pellet and particularly at the intra-particle scale. In this regard, discrete-continuous methods like CFD-DEM can generate more realistic, irregular particle assemblies, which leads to significantly more accurate predictions of voidage variation, wall effects, temperature distribution, and associated mass transfer phenomena. This study presents a numerical model based on computational fluid dynamics (CFD) coupled with the discrete element method (DEM) to simulate the thermal induration process of iron ore pellets. The presented model solving heat, mass, and momentum conservation equations for both continuous and discrete phases, provides detailed information on the thermochemical aspects of the process. Pilot-scale induration experiment was conducted to validate model predictions in terms of thermal history and final conversion fraction. It was found that inlet charge specifications, such as particle and pellet size, significantly impact the productivity of pelletizing plants, highlighting the potential of the presented model to optimize the process and improve plant productivity.

Optimal development of the new type of ultra-fine fly ash semi flexible pavement grouting material: Rheological, mechanical, pore distribution, and hydration characteristics

In order to solve the problems that the fluidity of semi-flexible pavement grouting materials (SFPGM) is not up to standard, the early strength is not enough, or the fluidity meets the requirements but the early strength is not up to standard, the power plant by-Product -ultra-fine fly ash (UFA) was used to optimized the performance of grouting materials (GM) in this study. The microstructure of hardened slurry was analyzed by XRD, FTIR, MIP and SEM. The findings indicate that when the UFA content increases, the fluidity of the GM initially increases and then declines, whereas the compressive strength initially reduces and then increases. The sample exhibits optimal fluidity performance when the content of UFA is 9 %. The flow cone fluidity of the initial and 20 min is 12.33 % and 17.63 % lower than that of the reference sample. When the amount of UFA is 12 %, the compressive strength of sample is the highest at each age. Additionally, that the fluidity of sample S12 is sub-optimal in all samples, only worse than that of sample S9. In the early stage of GM hydration, UFA with slow hydration rate produces a significant ‘ball-bearings effect’ between irregular cement particles. This is beneficial to the relative sliding between the slurry particles, reduces the yield stress and plastic viscosity of the fresh slurry, and improves the flow performance of the GM. The pozzolanic effects of UFA in GM primarily manifests during the later stages of hydration. The primary hydration products of UFA modified GM include ettringite, C-S-H gel, C-A-S-H gel, calcium carbonate, and aluminium glue (AH3). During the progression of the hydration reaction, the quantity of ettringite (AFt) in the slurry steadily augments, causing the initial fine needle-like structure to evolve into a more fully formed needle-like structure. A complex three-dimensional network of interlocking spatial structures is formed by many hydration products that continually interlace and develop, improving strength. The higher the perfusion rate of the GM, the higher the compactness of the SFPGM, and the better the high temperature stability and low temperature crack resistance.

Microplastic pollution responses to spatial and seasonal variations and water level management in a polymictic tropical reservoir (São Paulo, Brazil).

We assessed microplastic (μP) pollution in water and sediment samples during the dry and rainy season (October/2018 and March/2019, respectively) from the Guarapiranga Reservoir in the Metropolitan Region of São Paulo, Brazil, which provides drinking water for up to 5.2 million people. The concentration of mPs varied spatially and seasonally, with the higher concentrations observed near the urbanized areas and during the dry season. Water column concentrations ranged from 150 to 3100 particles/m3 and 0.07-25.05 mm3 plastic/m3 water during the dry season, and 70-7900 particles/m3 and 0.06-4.57 mm3 plastic/m3 water during the rainy season. Sediment samples were collected only during the rainy season, with concentrations ranging from 210 to 22,999 particles/kg dry weight and 0.15-111.46 mm3/kg dry weight. The particle size distribution exhibited seasonal variation, with μPs >1 mm predominating during the dry season, constituting 60-75% of all particles. In terms of quantity, fibers accounted for the majority of microplastics, comprising 55-95% during the dry season and 70-92% during the rainy season. However, when considering particle volume, irregular particles dominated in some samples, accounting for up to 95%of the total amount. The predominant colors of microplastics were white/crystal, black, and blue, with the main compositions identified as polypropylene (PP) and polyethylene terephthalate (PET), suggesting the influence of untreated domesticsewage discharge. Additionally, some additives were detected, including the pigments Fast RED ITR and phthalocyanine blue. The management of reservoir water levels appears to influence the quantity of μPs in the water column. As the water level increases up to 90% of the reservoir capacity during the rainy season, the amount of μPs in the water decreases, despite the higher influx of particles resulting from surfacerunoffcaused by rainy conditions. This suggests a "dilution" effect combined to the polymictic mixing hydrodynamics. Our results may contribute to the creation and improvement of monitoring programs regarding mP pollution and to the adoption of specific public policies, which are still lacking in legislation.

Aerodynamic resuspension of irregular flat micro-particles

This study investigates the role of particle shape on the aerodynamic resuspension process of irregular flat micro-particles on a substrate. We propose that these particles resuspend at higher velocities than spherical ones of the same size under the same aerodynamic forces. Two sets of data are analyzed to test the argument, the first from experiments we conducted using crushed glass particles (ranging from 80 μm to 300 μm) and the second from published data on RDX explosive residue particles (sized between 10 μm and 25 μm) published previously.We particularly analyze the shape factors of the particles used in the experiments and introduce them into a Monte Carlo (MC) simulation model. The probabilities for the time evolution of the resuspension process are calculated through a Markov chain of states. The transition probabilities entail the balance between the forces and moments involved in the mechanisms for particle detachment from the surface.The particle resuspension rate as a function of the fluid velocity is evaluated both experimental and numerically. Additionally, we assess the removal efficiency for different particle size ranges whenever possible.Both experimental and numerical results demonstrate that the resuspension fraction of irregular flat particles is significantly lower than for equally sized glass microspheres under the same conditions. Simulations corroborate previous experimental findings, indicating that smaller irregular particles exhibit higher removal efficiency. According to the MC model results, irregular particles detach by sliding rather than rolling.

Improving preservation of bioactive compounds in mangosteen peel flour through pre-treatment with bleaching, ethanol, and vacuum pulse

One method of utilizing mangosteen peel involves subjecting it to the drying process. Applying different pre-treatments before drying is seen as an alternative to minimize the negative effects of temperature on obtaining flours. The study investigated various pre-treatment methods to enhance the production of mangosteen peel flour (MPF) while preserving its bioactive compounds. Pre-treatments with ethanol (E), blanching (B), and vacuum pulse (V) were used individually and in combination (EV, BE, BV and BEV), followed by convective drying at 80 °C. The obtained flours were evaluated for antioxidant capacity, profile of phenolic compounds and minerals, morphology of particles (SEM), and physical properties. The pre-treated samples showed higher levels of phenolic compounds than the control sample (C), with flavonoids standing out, especially in variants blanched. Samples EV and BEV exhibited high antioxidant capacity. All samples are sources of potassium, copper and zinc. The samples showed irregular particles, with varying sizes, with V, EV, and BEV being smaller and less agglomerated, and the results indicated cohesive properties in MPF. The porosity of the samples was consistent, limiting their flowability. The BEV approach stood out, preserving bioactive components, increasing antioxidant capacity, and proving to be effective in obtaining better MPF.

Modelling polarized pulsed LiDAR signals in scattering media: an approach for optimizing systems in real-world scenarios.

Adverse weather conditions present a primary challenge for ground-based LiDAR imaging systems in outdoor applications. The use of polarization has been proposed as an effective filtering mechanism. However, the number of potential situations is large, complex and difficult to parameterize with accuracy. In such conditions, advanced simulation methods enable the testing of different experimental configurations and the determination of the best possible setup. With this purpose, a Monte Carlo algorithm is presented for modeling polarized pulsed LiDAR signals in turbid media. This algorithm is designed for immediate applicability, incorporating realistic media characterization and accounting for the attributes of existing prototypes. It allows testing various experimental configurations, managing optical obstacles, adjusting polarization arrangements, and different geometries of particles within the medium. The developed algorithm accurately characterizes backscattering signals, revealing their dependence on medium properties. A relationship between visibility and backscattering energy is identified, offering insights for sensor optimization. Polarization analysis highlights the efficacy of circular polarization in mitigating scattering effects and establishes a connection with the polarimetric characteristics of imaged targets. The algorithm's application to irregular particles reveals also an unexpected behavior of polarized light, challenging established strategies. These diverse use cases exemplify the algorithm's capability to model real-world circumstances, emphasizing its significance in predicting cutting-edge situations when designing optical systems for complex and demanding outdoor scenarios.

Particle breakage of calcareous sand from low-high strain rates

The influence of strain rate on the mechanics of particles is well documented. However, a comprehensive understanding of the strain rate effect on calcareous particles, particularly in the transition from static to dynamic loading, is still lacking in current literature. This study conducted 720 quasi-static and impact tests on irregular calcareous particles to investigate the macroscopic strain rate effect, and performed numerical simulations on spherical particles to explore the underlying microscopic mechanisms. The strain rate effect on the characteristic particle strength was found to exhibit three regimes: in Regime 1, the particle strength gradually improves when the strain rate is lower than approximately 102 s−1; in Regime 2, the particle strength sharply enhances when the strain rate increases from 102 s−1 to 104 s−1; and in Regime 3, the particle strength remains almost constant when the strain rate is higher than 104 s−1. The three-regime strain rate effect is an inherent property of the material and independent of particle shape. The asynchrony between loading and deformation plays a dominant role in these behaviors, leading to a thermoactivation-dominated effect in Regime 1, a macroscopic viscosity-dominated effect in Regime 2, and a combined thermoactivation and macroscopic viscosity-dominated effect in Regime 3. These mechanisms induce a transition in the failure mode from splitting to exploding and then smashing, which increases the energy required to rupture a single bond and, consequently, enhances the particle strength.

Photocatalytic Performance of the BaSn-based Nanoscale Materials for the Organic Pollutants Enhanced by Sm (Er) Doping

Background: Sm (Er) doping is an effective strategy for enhancing the photocatalytic activity of the semiconductor photocatalysts for the degradation of organic pollutants. BaSnbased nanorods possess wide band gap energy, which limits the photocatalytic application. It is important to research the feasibility of the improved photocatalytic performance of the BaSnbased nanorods by doping with Sm (Er). Objective: The aim is to synthesize Sm (Er)-doped BaSn-based nanoscale materials through a simple hydrothermal process and research the photocatalytic performance of the Sm (Er)-doped BaSn-based nanoscale materials for the gentian violet degradation. Methods: Sm (Er)-doped BaSn-based nanoscale materials with a polycrystalline structure were synthesized through a simple hydrothermal process. The Sm (Er)-doped composites were analyzed by X-ray diffraction, electron microscopy, solid diffuse reflectance spectrum, X-ray photoelectron spectroscopy, photoluminescence, and electrochemical impedance spectroscopy. Results: Sm (Er) doping induces the morphological evolution of the BaSn-based nanoscale materials from the nanorods to irregular nanoscale particles. Sm (Er) in the doped BaSn-based nanoscale materials exists in the form of the cubic Sm2Sn2O7 and orthorhombic ErF3 phases. The band gap value is decreased with increasing the Sm (Er) dopant contents. Sm (Er)-doped BnSnbased nanoscale materials with the Sm (Er) content of 8wt.% have the lowest band gap and show the strongest light absorption ability. Compared with the un-doped BaSn-based nanoscale materials, the Sm (Er)-doped BnSn-based nanoscale materials exhibit higher photocatalytic activity for the gentian violet degradation. 8wt.% Sm-doped BnSn-based nanoscale materials show the highest photocatalytic activity for the degradation of the gentian violet. 20 mL gentian violet solution (concentration of 10 mg·L-1) can be totally degraded using 20 mg 8wt.% Sm-doped BnSnbased nanoscale materials under UV light illumination for 150 min. Conclusion: The enhanced photocatalytic activity of the Sm (Er)-doped BnSn-based nanoscale materials can be attributed to the decreased band gap, enhanced light absorption ability, and decreased recombination of the photo-generated electron-hole pairs.

Experimental Study on Surface Segregation Law of Three-Dimensional Accumulation Body of Sand and Stone Particles by Binary Mechanism

Sand and stone materials are one of the important raw materials for infrastructure construction. In recent years, natural sand resources have decreased rapidly. In order to protect rivers and DAMS and ecological balance, local governments have increased the control power of natural sand mining, and replacing natural sand with mechanically broken parent rock formation mechanism sand has become an inevitable trend of the industry development. During the crushing process of parent rock, sand particles of different particle size range are produced, and particle segregation occurs in the process of stacking in the yard, which brings great trouble to the calculation of particle grading and material sample detection, and hinders the large-scale application of machine-made sand. In this paper, three-dimensional stacking tests of irregular particles were carried out to identify the particle distribution on the surface of the stack by digital image technology, analyze the relationship between particle size composition of particle mixture and the particle distribution of the accumulation body, and study the distribution law and segregation characteristics of the accumulation body. The experimental results show that the mixture with different coarse particle content will produce the corresponding distribution on the surface of the accumulation body after the accumulation. On the surface of the accretion body, the content of coarse particles is vertically distributed along the height of the accretion body. The content of coarse particles in the lower part of the accretion body is greater than that in the upper part of the accretion body. The overall segregation coefficient on the surface of the pile decreases with the increase of coarse particle content, and the variation is the largest in the lower part of the pile surface with the initial coarse particle content. Based on the test results in this paper, it provides a basis for formulating the sampling and inspection method of machine-made sand, ensuring the quality of machine-made sand and improving the utilization rate of machine-made sand.

Sintering behaviour of liquid phase sintered 90Mo-10(Ni–Cu) alloys

Molybdenum (Mo), a refractory material, boasts an elevated melting point of 2610 °C and is predominantly synthesised through powder metallurgy at high temperatures reaching 2000 °C, necessitating the use of liquid phase sintering (LPS) technique. This study investigates the LPS of Mo with varying proportions of Ni–Cu binders, aiming to understand the mechanism of intermetallic formation and to manufacture low-cost, dense, intermetallic-free and near-net-shape Mo-base alloys. Employing the manufacturing design paradigm for 90W-10(Ni–Cu) tungsten heavy alloys (WHAs) and utilising conventional powder metallurgy techniques, Mo-based 90Mo10(Ni–Cu) alloys were synthesised. Initial findings indicate that the densification of Mo-compacts increases with increasing the Ni–Cu ratio in the binder phase. However, an excess of Ni results in the loss of structural rigidity and geometric distortion during sintering. In Ni-rich alloys, two distinct liquid phases, Ni-rich and Cu-rich, emerge at sintering temperatures. These phases exhibit different solubilities for Mo and solidify into a dual-phase matrix. Intriguingly, in contrast to WHAs, 90Mo-10(Ni–Cu) alloys with a Ni-rich composition manifested irregular Mo particles, a dual-phase matrix, and δ-MoNi intermetallic compound formation. The formation of the intermetallic compound can be avoided by reducing the solubility of Mo in the Ni-rich liquid during sintering. Microstructural evolution and distortion are analysed using stereological quantification of various microstructural parameters. It reveals that alloys with low Mo solubility, high connectivity and high dihedral angle maintain their structural rigidity and resist distortion. Both micro-hardness and bulk hardness increased with increasing Ni–Cu ratios in the binder phase. Based on the present results, a mechanism for liquid phase sintering in the 90Mo-10(Ni–Cu) system in the presence of two liquid phases is postulated.

Crop plants transport irregularly shaped mineral particles from root to shoot: Tracking and quantifying

Mineral particles, ubiquitous in soils, influence crop plant growth by carrying nutrients and pollutants. While the uptake of dissolved mineral nutrients is well-established, the direct incorporation of irregular mineral particles into plants remains unclear. This study investigated the uptake and transport of kaolin particles, representative of minerals, by wheat and lettuce seedlings using hydroponic and soil cultures. Covalent labeling and advanced microscopy revealed that kaolin enters root steles at lateral root emergence sites, followed by transport to shoots. Fluorescent dyes and lanthanum (La)-labeled kaolin particles demonstrated that wheat surpassed lettuce in kaolin uptake in hydroponics, but both plants showed similar levels of particles in the shoots. Translocation factors (TFs) for kaolin were significantly higher in soil (0.089 for wheat, 0.039 for lettuce) compared to hydroponics (0.001 for wheat, 0.003 for lettuce). These findings provide compelling evidence for the direct uptake and transport of kaolin particles in crop plants. This opens new avenues for research on the interactions between plant and mineral particles, including other colloidal particles, in terrestrial ecosystems.

Study on the formation of PM10 from high-sodium coal under gasification conditions in a flat-flame burner reactor

The deposition of fly ash is a key problem during utilization of high-sodium coal. A flat-flame burner reactor was used to investigate PM10 formation during high-sodium coal entrained flow gasification. The results showed that all particle size of PM10 at different gasification stages exhibits bimodal distributions. It transforms from irregular soot and char particles to square NaCl, spherical aluminosilicate and irregular char particles as gasification proceeds. As gasification time increases, Na and Cl in PM0.1 increases from 20.39 % to 57.61 %, Ca and Mg in PM0.1–1 increases from 22.51 % to 38.74 %, Si and Al in PM0.1–10 increases from 36.87 % to 71.60 %. Besides, a model is established to reveal the formation mechanism of PM10. It well-predicts the PM10 yields, and demonstrates that PM0.154, PM0.154–2.47, and PM2.47–10 come from the nucleation-collision-coagulation of vaporized Na and Cl etcetera, fragmentation of Ca, Mg-contained minerals, and fragmentation and gasification of char, respectively. The results provide valuable information for understanding of PM10 formation during high-sodium coal gasification.

Exploring the micro-to-macro response of granular soils with real particle shapes by way of μCT-aided DEM analyses

This contribution provides high-fidelity images of real granular materials with the aid of X-ray micro-computed tomography (μCT), and employs a multi-sphere representation to reconstruct non-spherical particles. Through discrete-element method (DEM) simulations of granular samples composed of these non-spherical clumps, the effect of particle shape on the macroscopic mechanical response and microscopic soil fabric evolution is examined for soil assemblies under triaxial compression. Simulation results indicate that materials with more irregular particles tend to show higher shear resistance in both peak and critical states, while exhibiting higher void ratio under isotropic loading conditions and in the critical state. The proposed critical state parameters for describing the sensitivity of the mean coordination number to confining pressures are larger as particles become more irregular. At a microscopic level of observation, directional and scalar parameters of particle contacts are sensitive to predefined particle shapes. More irregular materials appear to exhibit higher fabric anisotropy with respect to particle orientation in the critical state, while the branch vector is affected by both contact modes and particle shape. The critical stress ratio from the simulation results is validated by comparing with experimental results, and further found to be linearly linked to the shape-weighted fabric anisotropy indices.

Study on microstructure and mechanical properties of 3003 aluminum alloy joints brazed with Al–Si–Cu–Ni paste brazing materials

Paste-type brazing materials have advantages such as adjusting the complexity of the parts to be soldered, easy storage and production in certain quantities. They can be used for brazing heat exchangers, liquid tanks and corrosion resistant parts. In this work, the microstructures and thermal behaviors of Al–Si–Cu–Ni brazing materials with different contents were investigated, and the effect of brazing process on the microstructural evolution and mechanical properties of brazed joints produced under nitrogen-filled environment was examined. It was found that the melting temperature of brazing material Al–5Si–20.5Cu–2Ni were ranged from 512.86 to 549.37 °C. The microstructure of Al–5Si–20.5Cu–2Ni consisted of α-Al solid solution, CuAl2 intermetallic compounds, the Al–Si–Cu phase, and some fine irregular Si particles in a homogenous manner. The microstructure of the brazed joints was uniformly formed during the brazing condition of 580 °C for 20 min, and the shear strength of the joints reached 41.76 MPa.

Settling velocity of atmospheric particles in seawater: Based on hydrostatic sedimentation method using video imaging techniques

When atmospheric particles deposit to the ocean, their settling velocities and residence times associated are critical for their effects on oceanic ecosystems. We developed a hydrostatic sedimentation method using video imaging techniques to track particles of 5–20 μm in diameter falling into seawater and determine the particle settling velocities in relation to their diameter, shape, organic matter contained, and seawater salinity. The measured settling velocities varied from 0.025 to 0.41 mm/s. Irregular particle shape and organic matter contained in particles also, however, reduced the values. The settling velocities were decelerated by the dissolution process of particle in seawater. Combined with the experimental results, a formula for calculating the settling velocity formulae for atmospheric particles was estimated. Using this equation, the residence time of particles is estimated to be less than one month in continental shelf sea and more than 100 days in the oceans.

Solubility, (micro)structure, and in vitro digestion of pea protein dispersions as affected by high pressure homogenization and environmental conditions

In this work, dispersions were prepared with commercial pea protein isolate (PPI) and subjected to different (i) high pressure homogenization (HPH) intensities (0 – 200 MPa) (room temperature, pH 7) or (ii) environmental conditions (60 °C, pH 7 or pH 12) to generate dispersions with distinct protein molecular and microstructural characteristics, impacting protein solubility. Besides, protein digestion was analyzed following the static INFOGEST in vitro digestion protocol. Generally, increasing pressure of the homogenization treatment was linked with decreasing particle sizes and enhanced protein digestion. More specifically, the dispersion that did not undergo HPH (0 MPa) as well as the dispersion treated at 60 °C, pH 7, had highly similar microstructures, consisting of large irregular particles (10 – 500 µm) with shell-like structures, and exhibited low solubility (around 15 % and 28 %, respectively), which resulted in limited proteolysis (35 % and 42 %, respectively). In contrast, the dispersion subjected to HPH at 100 MPa and the dispersion treated at 60 °C, pH 12 also had similar microstructures with small and homogeneous particles (<1 µm), and exhibited relatively good solubility (54 % and 31 %, respectively), which led to enhanced protein digestion levels (87 % and 74 %, respectively). This study highlights the potential of food processing on macronutrient (micro)structure and further gastrointestinal stability and functionality.

Microstructure evolution and mechanical properties of large-size AZ31 magnesium alloy block fabricated by wire arc additive manufacturing

With the urgent demand for lightweight and integrated structural parts in the aerospace field, the use of cold metal transfer wire arc additive manufacturing (CMT-WAAM) to form large-size magnesium alloy structural parts has become a research hotspot. In this paper, a large AZ31 magnesium alloy multilayer block with a lower porosity was successfully prepared by CMT-WAAM. The AZ31 block exhibits a fully equiaxed grain morphology, the average grain diameters of the top, middle, and bottom are 16.1 µm, 12.4 µm, and 10.4 µm, respectively. The submicron spherical particles measuring 0.09 to 0.4 µm are Mg17Al12 phases, irregular particles are Al8Mn5 + Mg17Al12 composite phases and large particles measuring 5 to 10 µm are Al8Mn5 in AZ31 block. The UTS of CMT-WAAM AZ31 block from the bottom of 239.9 ± 5.0 MPa to the top of 237.3 ± 3.1 MPa, and the EL from the bottom of 22.7 ± 0.6 % to the top of 30.0 ± 1.1 %, exceeding the casting standards. In the CMT-WAAM processed AZ31 alloy, the pre-existing coarse second phase particles in the AZ31 filaments acted as nucleating agents, and the electromagnetic stirring effect in the WAAM process broke up the dendrites and increased the number density of nucleation sites to improve the rate of nucleation, and the complex thermal conditions in the WAAM process restricted the growth of the grains and the precipitated phases. The mechanical properties of AZ31 alloy were improved by effectively refining its grain size and precipitated phase size.

A modified drag coefficient model for calculating the terminal settling velocity and horizontal diffusion distance of irregular plume particles in deep-sea mining.

Deep-sea mining inevitably produces plumes, which will pose a serious threat to the marine environment with the continuous movement and diffusion of plumes along with ocean currents. The terminal settling velocity (wt) of irregular particles is one of the crucial factors for determining the plumes' diffusion range. It is generally calculated by drag coefficient (CD), while most existing CD models only consider single shape characteristic parameter or have a smaller range of Reynolds number (Re). In this study, a new shape factor (γ) of irregular particles is proposed by considering the thickness (one-dimension), the projected area (two-dimension), and the surface area (three-dimension) of irregular particles as well as their coupling effect to establish a modified CD model for calculating the wt. A modified Gaussian plume model is proposed to predict the horizontal diffusion distance of the plume particles by considering the settling velocity and diffusion effect of irregular particles. Research results show that the wt increases nearly linearly, with a gradually decreased slope and slightly then greatly with the increasing of γ, dp (diameter) and ρp (density), respectively. The modified CD model is verified to be more valid with a wider application range (Re < 3×105) than five existing CD models by the test results. The larger the ρp or dp, the larger the wt and thus the smaller the Sh. This study could provide a theoretical basis for calculating the plume diffusion range to further study the impact of deep-sea mining on the ocean environment.

Morphological analysis of ballast particles: Characterization and simplified analysis of particle morphology using imaging data

This paper introduces a novel algorithm for the rigorous characterization of three-dimensional (3D) particles, particularly for railway ballast. Degraded railway ballast must be replaced with fresh material for efficient functioning. This study examined the shape and form of degraded (used) ballast to guide future maintenance efforts. Laboratory-generated used ballast, obtained via the Los Angeles abrasion test, was compared to fresh ballast. Thirteen fundamental morphological parameters of fresh and used ballasts were investigated by utilizing the shape information obtained through 3D scanning. The algorithm efficiently processed datasets comprising multiple irregular particles and monitored the morphological characteristics of ballasts based on the shape of the particles. The trimesh library was imported for 3D processing, facilitating the mathematical calculation of diverse parameters using the developed algorithm. The algorithm also incorporated mechanisms for simultaneously storing parameters provided in various 3D configuration models. With the support of the trimesh library, a morphology analyzer was used to analyze various 3D model file formats, such as .stl, .obj, and csg. This method demonstrated its efficacy with reduced runtime and computation cost. Thus, the proposed algorithm has emerged as a valuable resource for researchers investigating the influence of ballast particle shape on the mechanical behavior of granular assemblies.