Particles In Space Research Articles

A nonlocal general particle dynamics method for modeling soil-structure interaction

Modeling the failure of structures induced by the movement of soils has consistently been one of the challenges that computational mechanics aims to address. In this study, an innovative nonlocal general particle dynamic method is established for soil-structure interaction problems. The pivotal advantage of the proposed method is its capability to achieve a comprehensive simulation from soil sliding to structural collapse. The treatments of the interaction force of particles near the soil-structure interface are introduced in detail in this paper. A particle shifting technology, which uses the condition number of the shape tensor to identify free surface particles, is proposed to improve the numerical stability. To enhance computational efficiency and accuracy, different particle spacings and time steps are employed to simulate soil and solid structures. A staggered solution scheme is developed to solve the movements of soil and solid. The framework proposed in this paper is verified by several benchmark examples, including a free oscillating cantilever beam and a soil column on an elastic plate. Then, the proposed method is further applied to investigate the fracture behavior of a structure subjected to the soil impact. The numerical results demonstrate that the proposed method has favorable convergence and the ability to simulate soil-structure interaction problems.

SPH simulations of non-isothermal viscoplastic free-surface flows incorporating Herschel-Bulkley-Papanastasiou model

In this paper, an improved smoothed particle hydrodynamics (SPH) method is employed to accurately simulate non-isothermal viscoplastic free surface flows, wherein the viscoplastic behavior of the fluid is precisely captured through the incorporation of the Herschel-Bulkley-Papanastasiou constitutive model. To suppress the non-physical oscillation arising from the weakly compressible hypothesis within the pressure field, the density dissipation term is incorporated into the mass conservation equation. To address the tensile instability arising from the uneven distribution of particles, the particle shifting technique is incorporated as a solution. To enhance the precision and ensure numerical stability of the gradient operator, a kernel gradient correction algorithm is implemented. The improved SPH method is employed for numerically simulating the non-isothermal viscoplastic mixed convection, dam-break flow and droplet impacting the solid wall. The effectiveness of the improved SPH method in tackling the complexities of non-isothermal viscoplastic fluid is validated through a rigorous comparison of its outcomes with those derived from alternative numerical methodologies. The assessment of the numerical convergence of the improved SPH method is undertaken through the utilization of varying initial particle spacings. The numerical outcomes demonstrate that the improved SPH method adeptly and precisely delineates the heat transfer mechanisms, intricate rheological properties, as well as the dynamic variation characteristics of the free surface in non-isothermal viscoplastic free surface flows.

Particle spacing and stability of initially staggered deformable particle trains migrating in a channel

Abstract We investigated the inertial migration of deformable particles in a two-dimensional channel flow. This study analyzes the effects of the channel Reynolds number ($Re$), channel blockage ratio ($k$), particle number ($N_p$) and reduced bending modulus ($E_b$) on the formation of staggered particle trains. The results show that the stable normalized distance $d_{p_{eq}} / H$ between two staggered particles is influenced by $Re$, $k$ and $E_b$, where $H$ is the channel width. As $k$ increases or $E_b$ decreases, $d_{p_{eq}} / H$ decreases. The value of $d_{p_{eq}} / H$ initially increases and then decreases with the increase of $Re$; when $E_b$ is large and $k$ is small, $d_{p_{eq}} / H$ continuously increases with increasing $Re$. With the increase of $N_p$, the closely arranged staggered particle trains evolve into five distinct migration Regimes. We explain the conditions for the formation of each Regime and explore the mechanisms of their interconversion. The findings of this study contribute to a better understanding of the self-organization process of deformable particles in channel flow.

Functionalisation of polyhydroxybutyrate for diagnostic uses

Polyhydroxybutyrate (PHB) is a biodegradable and biocompatible biopolyester, naturally produced and self-assembled as spherical inclusions inside bacteria. These PHB particles contain a hydrophobic PHB core covalently coated with PHB synthase (PhaC), which serves as an anchoring linker for foreign proteins of interest. Protein engineering of PhaC enables the display of biologically active protein functions on the surface of PHB particles suitable for different applications. Many biomolecules, such as e.g. antigens, enzymes, fluorescent proteins were immobilized to PHB particles and exhibited superior functionalities when compared to their respective soluble counterparts. Recently, PHB particles have been successfully applied for various diagnostics applications. This mini review provides an overview of the unique design space of PHB particles towards the development of safe and cost-effective diagnostic tools, and highlights the important research progresses of manufacturing PHB particles-based diagnostics.

Study of the residual stress distribution in SiCp/Al composites under thermal cycling conditions

In this study, a three-dimensional random representative volume element model was constructed using the finite element method combined with Python script to investigate the residual stress distribution in SiCp/Al composites with varying volume fractions, particle shapes, and particle size under thermal cycling conditions. The model has two different particle morphologies: spheres and irregular polygons. The results show that the irregular polygonal SiC particles exhibit higher residual stresses than spherical particles before and after thermal cycling due to their complex load transfer pathways and higher stress concentration at particle corners, which makes them more consistent with the characterization of SiCp/Al composites under practical application conditions. As the volume fraction of SiC particles increases, the particle spacing decreases, hindering the release of thermal stresses through plastic deformation. Notably, the relief rate of residual stress reached 53% in the 12 vol% SiCp/Al composites, with the stress decreasing from 698 MPa to 328 MPa after 50 thermal cycles. In contrast, the reduction rate for 18 vol% composites is only 13% after thermal cycling. Furthermore, compared to larger particles (7.3 µm, 8.9 µm), the smaller particles (4.3 µm, 5.9 µm) exhibit a more uniform stress distribution and lower thermal stresses before and after thermal cycling. Consequently, our work provides a significant theoretical basis for the design and application of SiCp/Al composites, especially for the application of materials under extreme temperature changes.

Nano-laminated clay-essential oil composite formulations: Key mechanistic antibacterial processes and in vitro antibiofilm activity

This study involves fabrication of nano-clay-essential oil hybrid nanostructures using acoustic cavitation-based probe ultrasonication for controlled release antibacterial effect. Both the pristine and composites were characterized and showed no structural (shape and size) changes in clay nanoparticles (NPs) after adsorption of essential oil as examined by Transmission electron microscope. Adsorption of essential oil in the interlayer space of nano-clay particles was confirmed by increase in d-spacing value for both nano-bentonite (3.31 to 3.44 nm) and nano-MMT (3.36 to 3.45 nm) composites. The FTIR (Fourier transform infrared) spectroscopy showed disappearance or weakening of bands at 3500-3600 cm-1 (hydroxyl group) wavenumber and appearance of new bands at 1700 cm-1 (C-H bending) suggesting interlayer adsorption of essential oil within the nano-clay. Thermogravimetric analysis (TGA) revealed three step mass loss in nano-clay-essential oil composites with the lowest mass loss (81 %) reported in Nano-bentonite-Basil essential oil composite. The GC-MS analysis confirmed the presence of similar components in both pure and composite formulations but with varied compositions. The developed nanocomposites (nano-clay-essential oil) exhibited enhanced antibacterial and anti-biofilm activity against Staphylococcus aureus and Escherichia coli as compared to pure EOs. This work is a first report for elucidating the antimicrobial mechanism of nano-clay-essential oil composite as identified by determining cell membrane damaging effect and level of reactive oxygen species (ROS). The present study provides insights on the potential role of nano-clay as adsorbent/nanocarrier and nano-clay-essential oil formulation for effective drug delivery.

Hilbert space of dyons

We revisit the construction of the Hilbert space of nonrelativistic particles moving in three spatial dimensions. This is given by the space of sections of a line bundle that can in general be topologically nontrivial. Such bundles are classified by a set of integers—one for each pair of particles—and arise physically when we describe the interactions of dyons, particles which carry both electric and magnetic charges. The choice of bundle fixes the representation of the Euclidean group carried by the Hilbert space. These representations are shown to recover the “pairwise helicity” formalism recently discussed in the literature. Published by the American Physical Society 2024

Manipulating three-dimensional magnetic particles motion in a rotating magnetic field

The application of rotating magnetic field can reduce the effect of agglomeration of fine-grained strong magnetic minerals in the sorting process. In this study, a three-dimensional finite element model of two spherical magnetic particles agglomerated in a rotating magnetic field is established, and a rotating magnetic field is constructed using a quadrupole magnet to verify the simulation results. The results show that the numerical simulation results can predict the experimental results more accurately, and the trajectories of the magnetic particles in the agglomeration process are centrosymmetric spiral curves. The utilization of the rotating magnetic field as well as increasing the rotating magnetic field speed, magnetic field strength, and the initial spacing of the magnetic particles will enhance the tendency of the magnetic particles to get rid of the agglomeration.

Impact of acid surface pretreatment on the hydrophobic agglomeration of micro-fine ilmenite and titanaugite in flotation

Acid surface pretreatment was employed to realize the selective hydrophobic agglomeration of micro-fine ilmenite in flotation. Microflotation and artificially mixed mineral experiments manifested that after acid surface pretreatment, the recovery of micro-fine ilmenite with the increase of NaOL concentration and the floatability difference of micro-fine ilmenite and titanaugite increased significantly. Zeta potential and contact angle analyses suggested that acid surface pretreatment intensified the adsorption of NaOL on ilmenite surfaces while reducing it on titanaugite surfaces. Turbidity, optical microscope, and EDLVO theory analyses attested that the hydrophobic attraction dominated in a short particle spacing in NaOL solution. Following acid surface pretreatment, the hydrophobic agglomeration between micro-fine ilmenite particles enhanced in NaOL solution due to increased hydrophobic attraction. In contrast, the hydrophobic attraction and agglomeration between micro-fine titanaugite particles as well as between micro-fine ilmenite and titanaugite particles weakened. Overall, acid surface pretreatment improved the selective adsorption of NaOL and the selective hydrophobic agglomeration of micro-fine ilmenite, resulting in enhanced separation efficiency and recovery of micro-fine ilmenite.

Maximum acceleration and quantum clock: on the existence of a new universal constant

In the pseudo-Euclidean Minkowski space, the four-dimensional volume element is invariant under Lorentz transformations. By hypothesising that in this space there is a minimum volume, it is possible to demonstrate the existence of a maximum acceleration. The volume element cannot be derived from the theory and must be obtained through direct measurement, thus it assumes the role of a bona fide universal constant. Two different estimates of the elementary volume are given, which differ by several orders of magnitude: the first is obtained in a pseudo-Euclidean space for particles with mass, and the second represents an absolute minimum volume, independent of the mass.

Numerical analysis of the ignition and gas-phase flame evolution of pulverized coal based on online experimental diagnostics

A transient ignition model employing a reduced chemical mechanism was developed to investigate the ignition characteristics and the gas-phase flame evolution of pulverized coal particles. The chemical percolation devolatilization (CPD) model was chosen to simulate the devolatilization process, and its accuracy was validated using a high-temperature entrained-flow reactor. Additionally, a novel method was introduced to cross-validate the single-particle simulation results with real-time OH-PLIF experimental measurements of particle streams, particularly at a large particle spacing ratio. The ignition mode was determined using the ignition delay time and volatile burnout time. Results show that as the oxygen volume fraction increases from 5% to 50% at a temperature of 1800 K, the ignition mode transitions from homogeneous ignition (GI) to heterogeneous ignition (HI). Notably, the same ignition mode was observed regardless of whether GI was defined using gas-phase temperature or OH levels. In the homo-heterogeneous ignition mode, the gas-phase flame intensity, characterized by OH levels, increases rapidly, then decreases, and re-increases slightly. The sequence of gas-phase reactions initiates with volatile combustion, followed by the co-combustion of residual volatiles and newly generated CO, and culminates in the combustion of CO itself. Online experimental findings confirmed that CO originates from char oxidation. Throughout this process, the gas-phase flame front extends outward until the volatiles are consumed.

Search for photons above 1018 eV by simultaneously measuring the atmospheric depth and the muon content of air showers at the Pierre Auger Observatory

The Pierre Auger Observatory is the most sensitive instrument to detect photons with energies above 1017 eV. It measures extensive air showers generated by ultrahigh energy cosmic rays using a hybrid technique that exploits the combination of a fluorescence detector with a ground array of particle detectors. The signatures of a photon-induced air shower are a larger atmospheric depth of the shower maximum (Xmax) and a steeper lateral distribution function, along with a lower number of muons with respect to the bulk of hadron-induced cascades. In this work, a new analysis technique in the energy interval between 1 and 30 EeV (1 EeV=1018 eV) has been developed by combining the fluorescence detector-based measurement of Xmax with the specific features of the surface detector signal through a parameter related to the air shower muon content, derived from the universality of the air shower development. No evidence of a statistically significant signal due to photon primaries was found using data collected in about 12 years of operation. Thus, upper bounds to the integral photon flux have been set using a detailed calculation of the detector exposure, in combination with a data-driven background estimation. The derived 95% confidence level upper limits are 0.0403, 0.01113, 0.0035, 0.0023, and 0.0021 km−2 sr−1 yr−1 above 1, 2, 3, 5, and 10 EeV, respectively, leading to the most stringent upper limits on the photon flux in the EeV range. Compared with past results, the upper limits were improved by about 40% for the lowest energy threshold and by a factor 3 above 3 EeV, where no candidates were found and the expected background is negligible. The presented limits can be used to probe the assumptions on chemical composition of ultrahigh energy cosmic rays and allow for the constraint of the mass and lifetime phase space of super-heavy dark matter particles. Published by the American Physical Society 2024

Mesh coated with microbially induced nanoscale vaterite for oil-in-water emulsion separation

Microbial-induced calcium carbonate precipitation (MICP), with its hydrophilic rough microstructures and as an environmentally friendly material modification method, has shown great potential for oil-water separation. However, its efficiency in separating oil-in-water emulsions remains challenging. This study advances the MICP method by producing microbially induced nanoscale calcium carbonate on a mesh using calcium acetate instead of traditional calcium chloride, successfully achieving efficient separation of oil-in-water emulsions. The stainless-steel mesh (SSM) after calcium acetate-MICP treatment obtained nano-elliptical flake-like vaterite (vaterite-SSM) and demonstrated superior superhydrophilicity and underwater superoleophobicity compared to the mesh coated with micro-cubic structured calcite (calcite-SSM) treated by calcium chloride-MICP. Notably, vaterite-SSM achieved a flux of up to 309 L·m−2·h−1 and an oil rejection rate of over 98.7 % in gravity-driven separation of oil-in-water emulsions, demonstrating significant reusability after 6 cycles. Conversely, calcite-SSM was ineffective in emulsion separation due to coating instability and large particle spacing. Additionally, vaterite-SSM effectively separated various oil-water mixtures, maintaining high performance across 30 separation cycles. This study underscores the important use of calcium acetate in MICP to obtain nano-elliptical flake-like vaterite for efficient oil-water emulsion separation, advancing the promise of MICP as an effective and sustainable method for environmental applications.

Research on the shear stress and microscopic deformation mechanism of deep sea sediments under the action of tracked miner

The traction force of the tracked miner is primarily determined by the shear characteristics of deep-sea sediments. The influence of different parameters on the shear characteristics of deep-sea sediments and the particles change law of the soil–track interface are discussed. By constructing the relationship between the particles horizontal displacement and residual shear strength, a novel shear rheological damage model of deep-sea sediments considering the influence of grounding pressure is proposed, and the microscopic mechanism of shear displacement of deep-sea sediments is explained. The results show that the peak shear strength and residual shear strength increase significantly with the increase of grounding pressure, track length, grouser height and shear speed. Moreover, the particles within the soil–track interface move along the lower right of the vehicle operating direction during the shearing process under different working conditions, the change of particle spacing shows a non-linear trend, and a quantitative equation for the horizontal deformation of soil–track interface under the experimental conditions is constructed. Additionally, the new shear model has a high level of accuracy in fitting with the experimental data, the internal particle migration changes on the soil–track interface can be divided into four characteristics: compaction, failure, deformation and translation.

A modified bond-based peridynamic approach for rigid projectile perforation on concrete slabs

Peridynamic (PD) has a unique advantage in describing the crack growth and fragmentation of brittle materials. Concerning the dynamic behaviors and failure patterns of concrete slabs under projectile perforations, a modified bond-based PD approach maintaining both the easy implementation and computational stability characteristics was firstly developed from the following three aspects, (i) a rate-dependent PD constitutive model was proposed for describing the dynamic behaviors of concrete; (ii) a progressive damage criterion considering the tension-compression anisotropy, softening behavior, and strain rate effect of concrete was incorporated to more accurately reproduce the damage and failure of concrete; (iii) an improved micro-modulus function related to bond length was introduced to reveal the internal length effect of bond force. Then, numerical simulations of projectile perforation on concrete slabs by utilizing the developed modified bond-based PD approach, as well as the corresponding sensitivity analyses of discretization parameters including horizon size and particle spacing were performed. Based on the recommended horizon size and particle spacing, the predicted residual velocity of projectile and failure patterns of concrete slabs exhibited an excellent agreement with the test data. Furthermore, by comparisons of the traditional bond-based PD and classical finite element methods, the superiority of developed approach in describing the perforation damage of concrete targets against projectile impact was demonstrated. Finally, the modified bond-based PD approach was employed to blind simulate the projectile normal and oblique perforating multi-layered spaced concrete target plates. It was found that the modified PD model reasonably predicted the terminal ballistic trajectory, deflection angle, and residual velocity of projectile, as well as the failure patterns of target plates. The present work provides a new way to predict the terminal ballistic effect of projectile and dynamic behaviors of concrete slabs.

Numerical study on the motion of two parallel spherical particles with different diameters in upward flow

The settling of particles is related to many industrial processes and research fields. However, due to the complex particle–particle and particle–fluid interactions, the settling mechanism of particles in flowing fluids is not fully understood. This article conducts numerical research on the settling process of two particles with different diameters in parallel in upward flow using the immersion boundary method. The numerical method was validated against experimental results including one particle settling, two parallel particles settling, and two series particles settling. The effects of large particle diameter, upward flow velocity, and initial particle spacing on the settling process were explored. The results indicate that the two particles with same diameter will repel each other when settling in upward flow. Moreover, when the diameters differ, the two particles can experience both attractive and repulsive interactions. The larger the diameter of the large particle, the stronger its attractive influence on the small particle. When the diameter of large particle d2 = 3.0d1, large particle only has an attractive effect on small particle. The wake of each particle forms a distinct velocity boundary with the upward fluid. As the upward flow velocity increases, the interactions between the two particles become increasingly intense. With increasing initial spacing between the particles, their mutual interactions gradually weaken.

Effect of particle space distribution on the magnetism and the high-frequency power loss

The effects of different particle space distributions on the magnetism and the high-frequency power loss are studied and analyzed. The parallel arrangement of the easy-plane FeSi3.5 particles along the x-y plane can make hysteresis loops of composite in the x-y plane obtain extremely large slopes, and make the composite more easily magnetize in the x-y plane. The composite can obtain an extremely small demagnetization factor in the x-y plane due to the parallel arrangement of the easy-plane FeSi3.5 particles with the x-y plane, leading to a significant increase of the real part of complex permeability. In addition, the parallel arrangement of the easy-plane FeSi3.5 particles along the x-y plane can effectively decrease the hysteresis loss and the excess loss. The parallel arrangement of the easy-plane FeSi3.5 particles with the x-y plane reduces the angle between the magnetic moment and the magnetic circuit, making the energy that magnetizes the magnetic moment to the direction of the magnetic circuit decrease. Meanwhile, this makes the composite obtain a more homogeneous arrangement of magnetic domains and a larger number of activated domain walls along the direction of the magnetic circuit. It is important for the study of the magnetism and power loss of composites in the MHz frequency band.

Quantitative dispersion characterization of cement particles in hardened cement matrix

Optimizing the cement particle distribution in hardened cement matrix is one of the effective means to utilize cement efficiently, and obtaining information about cement distribution is a prerequisite for this. In view of this, this paper investigates the quantitative dispersion of cement particles in hardened cement paste from an experimental perspective. Cement pastes with different water-binder (W/B) ratios were prepared as the objects. BSE images of these samples were acquired for further analysis, including Delaunay triangulation algorithm, nearest neighbor distance function G(r) and fractal theory. Results showed that when the W/B ratio increases from 0.36 to 0.42, the average cement particle spacing rises from 32.7 μm to 34.9 μm and the proportion of particles with spacing between particle centroids <20 μm decreases from 41.96 % to 25.98 %. Similarly, the increasing W/B ratio causes the nearest neighbor distance function G(r) to shift towards larger distances. When the W/B ratio is 0.34, the median distance between particles (R50) exhibits the most significant change. Additionally, the intricate details of cement particle spacing information can be accurately described by fractal theory. Parameters such as R50 and the proportion of particles with spacing between centroids <20 μm demonstrate strong fits with various fractal parameters. Notably, they exhibit optimal fitting with the spectral width of the generalized fractal spectrum, with an R2 value of 0.99.

Lattice Boltzmann simulation on particle suspensions containing porous particles in a narrow channel

The suspension of porous particles in fluids occurs widely in various natural and industrial processes. However, the sedimentation behavior of porous particles is not extensively understood as the solid impermeable counterparts. In this work, the drafting–kissing–tumbling (DKT) phenomenon in a narrow channel containing porous particles is investigated by the multi-relaxation-time (MRT) lattice Boltzmann method (LBM). The initial particle spacing Lp* (1.5∼6) and Darcy number Da (8×10−6∼6×10−2) are examined on the sedimentation process of two particles under three initial arrangements, i.e., the trailing particle is porous (case 1), the leading particle is porous (case 2), and both the particles are porous (case 3). The results show that the presence of porous particles can enhance the interactions between two particles, and increasing the penetrability reduces the particle drag force to accelerate sedimentation. The drafting time is insensitive to Da at small Lp*, and it decreases with Da at large Lp* in cases 1 and 3 while it changes to increase with Da in case 2. A phase diagram with respect to Da and Lp* is further extracted to identify three sedimentation modes of particle pairs. It is found that the transition between the one-off DKT and repeated DKT modes is not affected by Lp* in cases 2 and 3, while the critical condition for the non-DKT and one-off DKT modes depends strongly on Da and Lp* in case 2.

Mechanical Quantities Prediction of Metal Cutting by Machine Learning and Simulation Data

Metal cutting is an important process in industrial manufacturing. Using the mechanical quantities of metal cutting to optimize process design is helpful to improve productivity. However, it is expensive to obtain these quantities due to the complexity of the cutting process, including material nonlinearity, geometric nonlinearity, state nonlinearity and their interactions. In this paper, a prediction model is constructed by combining machine learning (ML) and simulation data to quickly acquire multi-difficult-to-obtain metal cutting mechanical quantities to solve this problem. First, Adaptive Smoothed Particle Hydrodynamics (ASPH) is used to generate a simulation dataset of 2000 metal cutting cases. Based on the simulation data, six machine learning (ML) methods are employed to establish two prediction models, single-task learning and multi-task learning, to predict the mechanical quantities of metal cutting. The experimental results demonstrate that the ML method can predict abundant reference data efficiently after understanding the relationship between simulation parameters and mechanical quantities from simulation data, which is expected to replace some similar and repetitive simulation work. The Multilayer Perceptron (MLP) model under the multi-task setting provides the best prediction performance, fastest prediction time efficiency, and stable model behavior. Additionally, input erasure experiments reveal that the prediction of maximum equivalent plastic strain is significantly affected by particle spacing, and cutting speed plays a vital role in predicting maximum velocity. This work highlights the promotion of the data-driven ML method in quickly obtaining abundant reference data for the metal cutting process, and provides an auxiliary means for process optimization.