Irregular Particle Distributions Research Articles

Synthesis and characterization of bacterial cellulose composite with graphite and TiO2-ZnO: structural and functional analysis

This research aims to synthesize and characterize a bacterial cellulose (BC)-based composite with graphite and TiO2-ZnO as reinforcement materials using ex-situ synthesis with CTAB as a surfactant. FTIR and SEM-EDS analysis revealed interactions between the matrix and the reinforcement materials, as well as irregular particle distribution in the BC/G-TiO2-ZnO composite. The addition of graphite to BC significantly increased the conductivity of the composite, while the addition of TiO2-ZnO had the opposite effect. The mechanical properties of the composite exhibited an inverse relationship with the conductivity parameter. Swelling tests indicated that pH and the addition of CTAB influenced the swelling behavior of the BC-based composite. The results of this study provide a strong foundation for the development of potential applications in the fields of electronics and pollutant filtration. The synthesis of this composite aims to harness the unique properties of BC, graphite, and TiO2-ZnO, creating a multifunctional material with potential uses in flexible electronics, sensors, biocompatible conductive materials, and advanced filtration systems.

A non-contact solid particle moisture sensor based on near-infrared spectroscopy technology

The detection of moisture content in solid particles has important applications in fields such as biological research, coal mine production, and medicine. This article develops a non-contact solid particle moisture sensor (NcSPMS). NcSPMS uses the multi-light source detection method based on the principle of diffuse reflection absorption to detect the moisture content of solid particles with different particle sizes, distributions and colors. Firstly, the stacked LED light source structure (SLED-LSS) was designed to achieve illumination of LED light source for measurement (M-LED) and the LED light source for reference (R-LED) at the same position and exit angle, eliminating the influence of irregular particle size and distribution on diffuse reflected light intensity. Secondly, the stacked LED array light source structure (SLEDA-LSS) was designed to improve the detection light intensity and enable NcSPMS to detect the moisture content of solid particles of different colors. Thirdly, modulated light technology is used for the transmission of moisture content information. Two modulation frequencies were set to modulate the measurement light source and reference light source, and different intensities of square wave currents were determined to drive the M-LED and R-LED to improve detection accuracy. Fourthly, the FFT-KF data processing method was designed to effectively extract the information of diffuse reflection measurement light intensity. Finally, the function expression of moisture content was obtained through cubic fitting, and the detection of moisture content by NcSPMS was achieved. In order to verify the effectiveness of NcSPMS, the NcSPMS control system was designed. The experimental results show that compared with SLED-LSS, SLEDA-LSS improves measurement accuracy; the different current pairs driving M-LED and R-LED affect the measurement accuracy of NcSPMS; NcSPMS can detect the moisture content of white, yellow, green, red, and black sand particles, with the detection range of 0.10–11.00 %. The relative uncertainty obtained by applying NcSPMS to the detection of nickel ore particles is 4.37 %.

A high-order fully Lagrangian particle level-set method for dynamic surfaces

We present a fully Lagrangian particle level-set method based on high-order polynomial regression. This enables meshfree simulations of dynamic surfaces, relaxing the need for particle-mesh interpolation. Instead, we perform level-set redistancing directly on irregularly distributed particles by polynomial regression in a Newton-Lagrange basis on a set of unisolvent nodes. We demonstrate that the resulting particle closest-point (PCP) redistancing achieves high-order accuracy for 2D and 3D geometries discretized on irregular particle distributions and has better robustness against particle distortion than regression in a monomial basis. Further, we show convergence in classic level-set benchmark cases involving ill-conditioned particle distributions, and we present an example application to multi-phase flow problems involving oscillating and dividing droplets.

A dual-horizon peridynamic model for Reissner–Mindlin plates with arbitrary horizon sizes and shapes

A dual-horizon peridynamic (DHPD) model with arbitrary horizon sizes and shapes is proposed for predicting structural responses of thin-walled structures subjected to out-of-plane loadings. The proposed DHPD method can diminish the influence arising from ghost forces in irregular particle distributions and lessen the computational consumption with optimal refinement discretizations. Meanwhile, the variable PD parameters of each discrete particle that derive based on its own current horizon domain are adopted to mitigate the PD surface effect. Several static and dynamic structural responses with different geometric and boundary conditions are compared between the reference and DHPD approaches. It is concluded that the proposed DHPD method can effectively reproduce structural behaviors in fracture mechanics problems with less computational effort.

Biosynthesis of ZnO Nanoparticles Using the Aqueous Extract of Mucuna pruriens (utilis): Structural Characterization, and the Anticancer and Antioxidant Activities

A simple, green, and cost-effective synthesis of ZnO nanoparticles particles (NPs) using an extract of Mucuna pruriens utilis is reported. The nanoparticles were characterized by X-ray diffraction, UV–vis spectroscopy, SEM, and TEM measurements. XRD results showed diffraction patterns that are consistent with the hexagonal phase of the wurtzite ZnO structure. Spherical morphology with irregular size and particle distribution was confirmed by the microscopic characterization. The antioxidant activity of the nanoparticles showed a concentration-dependent profile with an IC50 of 4.10 µg mL− 1, which was quite lower than that of the standard ascorbic acid (4.72 µg mL− 1), and indicated a significant free radical scavenging activity of the nanomaterials. The cytotoxicity properties of the nanoparticles were evaluated against human cancer cell lines HeLa and HEK 293 by the MTT assay, and the anticancer drug (5-Fluorouracil) was used as a control. The results showed selective toxicity of the nanoparticles towards cancerous cell lines and non-toxicity to normal cells. The study provides a simple and non-toxic protocol for biosynthesis of ZnO nanoparticles with potential biomedical applications as anticancer and antioxidant agents. However, further studies are necessary to ascertain the biochemical reactions and mechanisms responsible for the antioxidant and anticancer activities.

Energy balance in quasi-Lagrangian Riemann-based SPH schemes

The Smoothed Particle Hydrodynamics (SPH) method suffers from the presence of irregular particle distributions inherent in its Lagrangian nature. A way to circumvent this problem is to consider a quasi-Lagrangian SPH scheme and use a Particle Shifting Technique (PST). In this framework, we include an approximate Riemann solver to represent the particle interaction and obtain two different quasi-Lagrangian Riemann-based SPH schemes: one is a mass-constant SPH model whereas the other is derived from an ALE formalism. These schemes are examined and validated by focusing on their energy balance. In particular, the energy contribution provided by the terms associated to Riemann solver and PST is studied from both a theoretical and numerical point of view. The consistency and the diffusive properties of these energy terms are investigated on test cases involving confined and free-surface flows. Albeit the investigation is performed for a specific Riemann solver and PST, the proposed methodology can be easily extended to other formulations.

Soy-based yogurt-alternatives enriched with brewers’ spent grain flour and protein hydrolysates: Microstructural evaluation and physico-chemical properties during the storage

Current study evaluated the influence of brewers’ spent grain (BSG) flour and its three different protease-treated protein extracts (BSGPs) in the production of soybean based yogurt-alternatives (SYA). Confocal laser scanning microscopy showed that protease-treated protein extracts from BSG generated a softer, more regular and denser network distribution while BSG flour generated an irregular and less fat particle distribution. Rheological properties showed that BSG derivatives significantly (p < 0.05) increased the viscosity index of the yogurt from a range of 44–80 at the first day to a range of 91–150 at 14 days of storage showing a strengthening effect on the formed network of SYA. It also preserved the flow behavior and consistency during the storage shown by syneresis value which was stable during the 14 days storage at a range of 270–380 g/kg. BSG derivatives enhanced the amount of lactic acid on SYA which increased from 4 g/kg at control to 6–11 g/kg at SYA with BSG derivatives. In conclusion, BSG derivatives modified the microstructural properties of SYA, improved rheological behavior and acidity during the refrigerated storage.

A conservative particle splitting and merging technique with dynamic pattern and minimum density error

Splitting and merging technique is one of the effective refinement tools to increase the resolution in particle methods. However, it still has many challenges in stability, accuracy and conservation issues. In this research, a pair splitting technique with minimum density error, as well as with mass, momentum and energy conservations, is proposed. Instead of using a fixed splitting pattern adopted in previous researches, the splitting angle and distance in this research are dynamically obtained by achieving the total minimum density error of splitting particles and their surrounding particles. Regarding the merging algorithm, a triplet particle merging model with two small particles and one large particle is proposed to maintain angular momentum conservation. A minimum merging distance limitation is developed to ensure mass, momentum and energy conservations at the same time. A set of cases are investigated to validate the effectiveness, stability and conservation of the present splitting and merging model. The results show that the present model decreases large oscillations and avoids sudden disturb caused by irregular particle distribution due to splitting and merging.

Enhanced photocatalytic degradation of 4-nitrophenol using polyacrylamide assisted Ce-doped YMnO3 nanoparticles

This research article mainly reports on the precise structural, optical, and photocatalytic properties of cerium (Ce)-substituted yttrium manganite (YMnO3) nanoparticles synthesized by the polyacrylamide gel method. The characteristics of YMnO3 were investigated by the substitution of Ce into the Y site at various molar percentages. The Raman and X-ray diffraction (XRD) analyses confirmed the pure phase of hexagonal YMnO3, supported by the Rietveld refinement. The microstructural studies indicate inhomogeneous and irregular particle distribution. The X-ray photoelectron spectroscopy (XPS) results show the presence of two ionic states of Mn and Ce along with Y3+ state and oxygen vacancies. Extensive optical exploration using photoluminescence (PL) spectroscopy and UV–Vis–NIR analysis indicates that the intensity of absorption peak increases in the visible region, while the bandgap decreases from 1.42 to 1.30 eV with the Ce ion doping (5 mol%–15 mol%). Photocatalytic properties of the polycrystalline nanoparticles were investigated by degradation of the pollutant 4-nitrophenol. The process of amplified photocatalysis process was elucidated by the lowered bandgap and rate of charge carrier recombination. It can be conjugated from this study that the synthesized nanoparticles may be employed as highly efficient (92.8%) visible light-triggered photocatalysts in a variety of real-world applications.

SPH modeling of substance transport in flows with large deformation

The velocity field in coastal and oceanic currents is mostly non-uniform, which will result in irregular particle distribution when the fluid is represented by an amount of moving discrete particles as in smoothed particle hydrodynamics (SPH). When the non-uniformity of the flow is big, i.e., with large deformation, the conventional SPH method can hardly solve the associated advection-diffusion process (e.g., substance transport). To accurately simulate the substance transport in flows with large deformation, two types of particle shifting techniques (PSTs) are incorporated into the conventional SPH in this paper. One is based on current particle distance, and the other is based on Fick’s law. In the second type, the repulsive force (RF) term for suppressing the paring instability that occurs in particle shifting technique (PST) is studied and the effect of the kernel function is examined. By introducing a particle disorder measurement, the simulated results of SPH with the two types of PSTs and their modifications are evaluated and the influence of the shifting magnitude is analyzed. The suggestions for how to set reasonable parameters in PSTs are provided by a systematic parametric study. For further illustration, the simulation of the anisotropic diffusion is also examined. To give reliable reference solutions, the high-resolution modified total variation diminishing Lax Friedrichs scheme with Superbee limiter (MTVDLF-Superbee) with fine mesh is also implemented. The validated Lagrangian particle model with optimized PST is applied to a practical application.

Improvement and application of weakly compressible moving particle semi-implicit method with kernel-smoothing algorithm

The moving particle semi-implicit method (MPS) is a well-known Lagrange method that offers advantageous in addressing complex fluid problems, but particle distribution is an area that requires refinement. For this study, a particle smoothing algorithm was developed and incorporated into the weakly compressible MPS (sWC-MPS). From the definition and derivation of basic MPS operators, uniform particle distribution is critical to numerical accuracy. Within the framework of sWC-MPS, numerical operators were modified by implementing coordinate transformation and smoothing algorithm. Modifying numerical operators significantly improved particle clustering, smoothed pressure distributions, and reduced pressure oscillations. To validate the numerical feasibility of the method, several cases were numerically simulated to compare sWC-MPS to the weakly compressible MPS (WC-MPS): a pre-defined two-dimensional (2-D) analytical function, Poiseuille's flow, Taylor Green vortex, and dam break. The results showed a reduction of errors caused by irregular particle distribution with lower particle clustering and smaller pressure oscillation. In addition, a larger Courant number, which represents a larger time step, was tested. The results showed that the new sWC-MPS algorithm achieves numerical accuracy even using a larger Courant number, indicating improved computational efficiency.

A consistent peridynamic formulation for arbitrary particle distributions

The Peridynamic Petrov–Galerkin (PPG) method is a meshfree particle method based on the weak form of the peridynamic momentum equation. It can be applied to arbitrary constitutive laws from the classical continuum mechanics theory. With non-linear approximation functions the rank deficiency present in many nodally integrated discretization schemes is prevented. The consistency of trial functions is not sufficient for the convergence with irregular particle distributions. In this paper the consistency of the test space is examined and possible correction techniques are presented. The resulting variationally consistent PPG method is able to pass the patch test and to restore the optimal convergence rates. A correction of the test functions that preserves the linear trial function consistency allows the use of displacement–pressure–dilation formulations and exhibits stability and robustness for 3-D in the regime of non-linear elasticity. Besides, the direct nodal coupling with Finite Elements and the application of symmetry boundary conditions are enabled.

A local refinement purely meshless scheme for time fractional nonlinear Schrödinger equation in irregular geometry region* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11501495, 51779215, and 11672259), the Postdoctoral Science Foundation of China (Grant Nos. 2015M581869 and 2015T80589), and the Jiangsu Government Scholarship for Overseas Studies, China (Grant No. JS-2017-227).

A local refinement hybrid scheme (LRCSPH-FDM) is proposed to solve the two-dimensional (2D) time fractional nonlinear Schrödinger equation (TF-NLSE) in regularly or irregularly shaped domains, and extends the scheme to predict the quantum mechanical properties governed by the time fractional Gross–Pitaevskii equation (TF-GPE) with the rotating Bose–Einstein condensate. It is the first application of the purely meshless method to the TF-NLSE to the author’s knowledge. The proposed LRCSPH-FDM (which is based on a local refinement corrected SPH method combined with FDM) is derived by using the finite difference scheme (FDM) to discretize the Caputo TF term, followed by using a corrected smoothed particle hydrodynamics (CSPH) scheme continuously without using the kernel derivative to approximate the spatial derivatives. Meanwhile, the local refinement technique is adopted to reduce the numerical error. In numerical simulations, the complex irregular geometry is considered to show the flexibility of the purely meshless particle method and its advantages over the grid-based method. The numerical convergence rate and merits of the proposed LRCSPH-FDM are illustrated by solving several 1D/2D (where 1D stands for one-dimensional) analytical TF-NLSEs in a rectangular region (with regular or irregular particle distribution) or in a region with irregular geometry. The proposed method is then used to predict the complex nonlinear dynamic characters of 2D TF-NLSE/TF-GPE in a complex irregular domain, and the results from the posed method are compared with those from the FDM. All the numerical results show that the present method has a good accuracy and flexible application capacity for the TF-NLSE/GPE in regions of a complex shape.

Simulation of Nonlinear Heat Conduction in Perforated Material by Improved Moving Particle Semi-Implicit Method

Abstract An improved moving particle semi-implicit (MPS) method is presented to simulate heat conduction with temperature-dependent thermal conductivity. Based on Taylor expansion, a modified Laplacian operator is proposed, and its accuracy in irregular particle distributions is verified. Two problems are considered: (1) heat conduction in a one-dimensional (1D) slab and (2) heat conduction in a perforated sector with different boundary conditions. Consistent results with a mesh-based method are obtained, and the feasibility of the proposed method for heat conduction simulation with temperature-dependent conductivity is demonstrated.

A Study on Stable Regularized Moving Least-Squares Interpolation and Coupled with SPH Method

The smoothed particle hydrodynamics (SPH) method has been popularly applied in various fields, including astrodynamics, thermodynamics, aerodynamics, and hydrodynamics. Generally, a high-precision interpolation is required to calculate the particle physical attributes and their derivatives for the boundary treatment and postproceeding in the SPH simulation. However, as a result of the truncation of kernel function support domain and irregular particle distribution, the interpolation using conventional SPH interpolation experiences low accuracy for the particles near the boundary and free surface. To overcome this drawback, stable regularized moving least-squares (SRMLS) method was introduced for interpolation in SPH. The surface fitting studies were performed with a variety of polyline bases, spatial resolutions, particle distributions, kernel functions, and support domain sizes. Numerical solutions were compared with the results using moving least-squares (MLS) and three SPH methods, including CSPH, K2SPH, and KGFSPH, and it was found that SRMLS not only has nonsingular moment matrix, but also obtains high-accuracy result. Finally, the capability of the algorithm coupled with SRMLS and SPH was illustrated and assessed through several numerical tests.

Improvement of voidage prediction in liquid-solid fluidized beds by inclusion of the Froude number in effective drag relations

A novel effective drag relation for liquid-solid fluidisation is proposed, suitable for application in full-scale installations. This is achieved by presenting new insights related to the influence of the temporal-spatial heterogeneity on the effective hydrodynamic drag for large fluidised systems. While heterogeneous flow behaviour can be predicted increasingly accurately in CFD simulations that explicitly model the heterogeneous solids distribution, for the operation of many large-scale applications it is infeasible to perform such computationally intensive simulations. Therefore, there is a clear need for full-scale drag relations that effectively take into account the heterogeneous behaviour and irregular spatial particle distributions. Our new drag relation is based on a large set of experiments, which shows that the degree of overall expansion is not only dependent on the ratio of laminar-turbulent flow, but also on the amount of homogenous versus heterogeneous flow, which is not included in current full-scale drag relations. To include the effect of heterogeneity, the standard drag relation, based on the Reynolds number, is extended with a specific type of Froude number. Because fully turbulent flow regimes are rare in applications of liquid-solid fluidisation, our focus is not on the turbulent flow regime but instead on laminar and transitional flow regimes. In these regimes, three types of models are investigated. The first type is based on a theoretical similarity with terminal settling, the second is based on the semi-empirical Carman-Kozeny model, and the third is based on empirical equations using symbolic regression techniques. For all three types of models, coefficients are calibrated on experimental data with monodisperse and almost spherical glass beads. The models are validated with a series of calcium carbonate grains applied in drinking water treatment processes as well as data obtained from the literature. Using these models, we show that the voidage prediction average relative error decreases from approximately 5% (according to the best literature equations which use Reynolds number only) to 1–2% (using both Reynolds and Froude number). This implies that our new models are more suitable for operational control in full-scale fluidised bed applications, such as pellet softening in drinking water treatment processes.

Modified incompressible SPH method for simulating free surface problems using highly irregular multi-resolution particle configurations

In this study, the conventional incompressible smoothed particle hydrodynamics (I-SPH) formulations are modified to be applicable for highly irregular multi-resolution particle distributions for simulation of transient free surface flows. The modifications are based on distinguishing between particle density calculated by interpolation functions in SPH method and fluid density as a physical quantity. I-SPH is a fully Lagrangian method having great potential in dealing with large deformations of the free surface. Flow domain is discretized into a set of moving particles, and each particle carries mass, velocity and pressure during simulation time. Variations in these field parameters can be determined by temporal discretization of Navier–Stokes equation followed by a spatial discretization using I-SPH method. In addition to this, three pressure gradient models are employed for simulation of free surface flows to examine efficiency of the models coupled with the modifications. Furthermore, a simple and efficient method to find free surface particles which is compatible with highly irregular multi-resolution particle distributions is proposed. The modified approach is tested against different free surface problems using highly irregular particle configurations. The classic pressure gradient model employed in SPH method coupled with constant smoothing distance gives accurate results with lower computational times over highly irregular particle distributions. The method can be applied for adaptive refinement strategy to reduce computational times of transient free surface problems.

An approximately consistent SPH simulation approach with variable particle resolution for engineering applications

This paper focuses on consistency issues caused by truncated kernels and irregular particle distributions in Smoothed-Particle-Hydrodynamics (SPH). The analysis starts from the kernel-based approximations inherent to the SPH method. An explicit kernel correction is proposed, which approximately achieves first-order consistency. The suggested approach is additionally combined with a Eulerian variable resolution approach, which conserves the number of particles but changes the individual particle mass in a transit regime. Validation studies featuring fully wetted and free-surface flow configurations are employed to assess the benefits of the combined approach. Results indicate benefits of the kernel correction and display merits and drawbacks of the variable resolution approach.

A kernel gradient-free SPH method with iterative particle shifting technology for modeling low-Reynolds flows around airfoils

The conventional SPH method does not perform well for simulating flows around rigid bodies. Especially, it is difficult to get convergent and accurate results when simulating flows around a thin airfoil. The reason is its low accuracy especially for highly irregular particle distributions in the process of SPH simulation of flow around slender structures. In this paper, a kernel gradient-free (KGF) SPH method with iterative particle shifting technology (PST) is proposed for the simulation of flow around the airfoil. KGF-SPH can maintain high accuracy without using kernel gradients. Iterative PST can maintain uniform particle distribution even if the smoothing length is less than the average particle spacing. Lid-driven shear cavity flows, Taylor–Green flow, the stretching of a free-surface circular fluid patch and flows around a cylinder are simulated to test the numerical method. Numerical results are almost in consistent with the analytical or reference results. Finally, flows past an airfoil are simulated by using the proposed SPH method. The results show that the present SPH method effectively improves numerical stability and accuracy for simulating flows around an airfoil.

Improved Moving Particle Semi-implicit method for multiphase flow with discontinuity

The variation of physical properties across the interface and the inaccuracy of spatial derivative on discontinuity contribute to the numerical instability in multiphase flow with large density or viscosity ratio. With integral basic equation in Peridynamic theory under updated Lagrangian formulation and stress tensor calculation by Moving Particle Semi-implicit method(MPS), a new numerical approach on dealing with the abrupt physical quantities is introduced. Besides, a modified matrix inspired by the shape function in Peridynamics is added in the gradient and divergence operators to eliminate the error caused by irregular particle distribution. In addition, to decrease the calculation error caused by large properties difference, a decomposition process on the stress tensor and its divergence are proposed, the large acceleration difference by the discontinuity of density on the interface is smoothed after a mean density and the accuracy is validated by a simple example. Four benchmark cases, oscillating two-layer elliptical region, Rayleigh–Taylor instability, two-phase dam-break and bubble rising examples, are simulated to demonstrate the feasibility and accuracy of the proposed method in multiphase flow with both small and large physical quantity ratio.