Multiphase Particle Research Articles

Panchromatic spectral energy distributions of simulated galaxies: results at redshift z = 0

We present predictions of Spectral Energy Distributions (SEDs), from the UV to the FIR, of simulated galaxies at $z=0$. These were obtained by post-processing the results of an N-body+hydro simulation of a small cosmological volume, that uses the Multi-Phase Particle Integrator (MUPPI) for star formation and stellar feedback, with the GRASIL-3D radiative transfer code, that includes reprocessing of UV light by dust. Physical properties of galaxies resemble observed ones, though with some tension at small and large stellar masses. Comparing predicted SEDs of simulated galaxies with different samples of local galaxies, we find that these resemble observed ones, when normalised at 3.6 $\mu$m. A comparison with the Herschel Reference Survey shows that, when binning galaxies in Star Formation Rate (SFR), average SEDs are reproduced to within a factor of $\sim2$ even in normalization, while binning in stellar mass highlights the same tension that is present in the stellar mass -- SFR plane. We use our sample to investigate the correlation of IR luminosity in Spitzer and Herschel bands with several galaxy properties. SFR is the quantity that best correlates with IR light up to $160\ \mu$m, while at longer wavelengths better correlations are found with molecular mass and, at $500\ \mu$m, with dust mass. However, using the position of the FIR peak as a proxy for cold dust temperature, we assess that heating of cold dust is mostly determined by SFR, with stellar mass giving only a minor contribution. We finally show how our sample of simulated galaxies can be used as a guide to understand the physical properties and selection biases of observed samples.

A multiphase MPS solver for modeling multi-fluid interaction with free surface and its application in oil spill

Numerical simulation of free surface multi-fluid flow is a challenging problem owning to the interaction between deformed interface and free surface. In this paper, a multiphase particle solver (free surface multiphase moving particle semi-implicit method, FS-MMPS) is developed to predict the early spreading flow of spilled oil where exist the oil–water interface and air–oil/air–water free surface. First, a multiphase virtual particle model is proposed to substitute the inaccurate free surface boundary condition for multiphase flow in conventional MPS methods. Specifically, virtual particles of different liquid phases are compensated outside free surface so that the pressure of free surface particles can be solved from pressure Poisson equation, thereby improving the accuracy of multi-fluid interaction at free surface. Meanwhile, a pressure gradient model based on the coupling of Taylor series expansion and dynamic specification of particle stabilizing term (PST) is proposed to simultaneously enhance accuracy and depress instability caused by multiphase virtual particles. Experiments of early spreading of thick oil slicks and continuous oil spill from a damaged tank are conducted for validation and demonstration of the accuracy and stability enhancements in 2D. Finally, the effects of traveling wave and continuous spilling on oil spreading are investigated to show the capability of the proposed method. The spreading of thick oil slicks is accelerated when wave height increases or wave length decreases, and the largest increase of spreading rate accelerated by traveling wave is 14%.

Applying multi-phase particle swarm optimization to solve bulk cargo port scheduling problem

Applying multi-phase particle swarm optimization to solve bulk cargo port scheduling problem

A multi-phase particle shifting algorithm for SPH simulations of violent hydrodynamics with a large number of particles

ABSTRACTA numerical inconsistency has emerged for multi-phase smoothed particle hydrodynamics simulations when using very high resolution, made possible by graphical processing units. In violent flows unphysical voids and phase separation occur ultimately leading to numerical instability. New Fickian-based particle shifting algorithms with a selectively activated free-surface correction are developed for air–water simulations to prevent the creation of unnatural voids and maintain numerical stability through nearly uniform distributions. Using the shifting algorithm without surface correction in the air phase is recommended, with marginal improvements if the shifting algorithm is not applied in water. However, maintaining shifting in water would avoid possible void occurrence. The improvement is demonstrated using a dry-bed dam break and a sloshing tank case. A 3D case involving the impact of the water flow on an obstacle is compared with experimental data. The multi-phase SPH scheme gives closer agreement with experiment than a single-phase simulation.

Viscous stress distribution over a wavy gas–liquid interface

Viscous stress contributes to momentum transfer between two phases, which plays an important role in both industrial applications and environmental processes. Near a wavy interface, the flow is modulated and produces a spatially non-uniform normal and tangential viscous stress. This study presents measurements of these stresses at a liquid–gas interface populated with two-dimensional millimeter scale waves performed with multiphase particle image velocimetry. Large datasets enable conditional phase-averaging of the data based on wave steepness, which increases the precision of the results and allows statistical analysis. For the first time at this scale, the spatial distribution of normal and tangential viscous stress is obtained for a large range of wave steepness (ak = 0–1, with a the amplitude and k the wavenumber). As the steepness increases, the mean shear stress over a wavelength decreases in magnitude, while the normal viscous stress increases. These trends are linear for ak < 0.6, and correlations are proposed. At ak > 0.7, flow separation is observed in the gas phase near the troughs and drastically alters the viscous stress distribution.

A novel dynamic scheduling strategy for solving flexible job-shop problems

A simulation model was established, minimizing the makespan and stability value, to solve the dynamic scheduling of flexible job-shop problems, and an improved hybrid multi-phase quantum particle swarm algorithm is proposed. Firstly, a double chain structure coding method, including a machine allocation chain and a process chain, is proposed. Secondly, a dynamic periodic and event-driven scheduling strategy is proposed. Finally, the novel method is applied to the Brandimarte set and a dynamic simulation is performed. Comparing the results with the results of existing algorithms demonstrates the effectiveness of the proposed hybrid multi-phase quantum particle swarm optimization algorithm and strategy for solving the dynamic scheduling of flexible job-shop problems.

Improved 3D image segmentation for X-ray tomographic analysis of packed particle beds

Although High Resolution X-ray Micro Tomography (HRXMT) has been developed in the past years for the 3D analysis of multiphase mineral particles in packed particle beds, image analysis of fine and/or high-density/high atomic number particles has been limited by existing segmentation algorithms. In this regard, a feature-based segmentation algorithm has been developed and demonstrated to provide a more accurate image processing method for the analysis of such multiphase particle populations. Based on this improved segmentation algorithm, image analyses of packed particle bed samples were compared to segmentation by traditional 3D watershed segmentation. Also, calculation of particle number using optical microscopy, together with a digital camera, was accomplished to validate feature-based segmentation. Detailed procedures and results for sample preparation, image analysis and validation are presented and discussed.

Numerical analysis of mixing performance in sinusoidal microchannels based on particle motion in droplets

This numerical study was conducted to analyze and understand the parameters that affect the mixing per- formance of droplet-based flow in sinusoidal microfluidic channels. Finite element analysis was used for modeling fluid flow and droplet formation inside the microchannels via tracking interface between the two heterogeneous flu - ids along with multiple particle trajectories inside a droplet. The solutions of multiphase fluid flow and particle trajec - tories were coupled with each other so that drag on every single particle changed in every time step. To solve fluid motion in multiphase flow, level set method was used. Para - metric study was repeated for different channel dimensions and different sinusoidal channel profiles. These results were compared with mixing in droplets inside a straight microchannel. Additionally, tracking of multiple particles inside a droplet was performed to simulate the circulating flow profile inside the droplets. Based on the calculation of the dispersion length, particle trajectories, and velocities inside droplets, it is concluded that having smaller chan- nel geometries increases the mixing performance inside the droplet. This also shows that droplet-based fluid flow in microchannels is very suitable for performing chemical reactions inside droplets as it will occur faster. Moreover, narrower and sinusoidal microchannels showed better dis- persion length difference compared to straight and wider microchannels.

The attitude estimation of three-axis stabilized satellites using hybrid particle swarm optimization combined with radar cross section precise prediction

An attitude estimation approach based on the hybrid particle swarm optimization (HPSO) and radar cross section (RCS) precise prediction for the three-axis stabilized satellites in space is presented in this paper. The modified strategies with quantum behavior operator and cloud mutation based on the multi-phase particle swarm optimization are used to increase the diversity of particles, reduce the objective function evaluation times and improve the global searching ability. The simulated RCS sequences of three-axis stabilized satellites at the specified epoch are determined by the method combined the precise orbit and the RCS of satellites calculated by fast multipole method. The mean square error between measured RCS sequences and simulated RCS sequences is considered as the objective function. The attitude estimation problem is transferred to an optimization problem by minimizing the objective function with attitude angles, which is solved by HPSO. The operation procedure is shown clearly, and the set of measurement is analyzed. The numerical results of optimizing the test functions showing better behavior of the proposed algorithm method than standard particle swarm optimization in terms of accuracy are provided. Representative examples validate the accuracy and the anti-noise jamming ability of the proposed algorithm for attitude estimation of three-axis stabilized satellites.

Simulation of an internally circulating fluidized bed using a multiphase particle-in-cell method

This paper investigates the use of the multiphase particle in cell method (MP-PIC) in modelling the gas–solid flow in a laboratory-scale isothermal internally circulating fluidized bed (ICFB), and compares results with experimental observations previously published by Hadley et al. (“Experimental quantification of the solids flux in an internally circulating fluidised bed”, Fluidization XIII, 2010, pp. 885–892). Glass ballotini (140μm mean diameter) were fluidized with room temperature air, and fluidisation velocities in both the central reaction chamber and two heat exchange chambers were varied to provide nine different chamber velocity ratio conditions for investigation. The model reliably predicted the overall bed dynamics of both gas and solid flow. Predicted solid recirculation rates were generally within one standard deviation of the mean experimental values, although under-prediction tended to occur at lower fluidisation rates. It was concluded that the MP-PIC method was a reliable tool for modelling bubbling fluidized bed behaviour of non-cohesive particles.

Simulating gas–liquid multiphase flow using meshless Lagrangian method

SUMMARYA multiphase flow model has been established based on a moving particle semi‐implicit method. A surface tension model is introduced to the particle method to improve the numerical accuracy and stability. Several computational techniques are employed to simplify the numerical procedure and further improve the accuracy. A particle fraction multiphase flow model is developed and verified by a two‐phase Poiseuille flow. The multiphase surface tension model is discussed in detail, and an ethanol drop case is introduced to verify the surface tension model. A simple dam break is simulated to demonstrate the improvements with various modifications in particle method along with a new boundary condition. Finally, we simulate several bubble rising cases to show the capacity of this new model in simulating gas–liquid multiphase flow with large density ratio difference between phases. The comparisons among numerical results of mesh‐based model, experimental data, and the present model, indicate that the new multiphase particle method is acceptable in gas–liquid multiphase fluids simulation. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Heat Transfer Modeling and Analysis of Solar Thermo-chemical Reactor for Hydrogen Production from Water

A solar thermo-chemical reactor is modeled and analyzed for the solar thermal dissociation of zinc oxide into zinc and oxygen involved in the thermo-chemical cycle for hydrogen production. The reactor consists of a cavity surrounded by a rotating insulation layer made of alumina. The granular zinc oxide particles are fed into the cavity and are directly exposed to the solar radiation entering the cavity through a quartz window. A three dimensional numerical model coupling the multiphase particle dynamics in gravitational field, multiphase heat transfer, k-ɛ turbulence model, discrete ordinates radiation model, Arrhenius reaction rate model is developed. The cavity temperature and oxygen molar flow rate at the outlet of the reactor which is the indicator of the reaction rate has been validated with a 10kW reactor prototype. An energy balance study of thermal performance parameters including the various losses occurring from the reactor and efficiency is also done. The major losses were contributed by re-radiation (46%) and sensible heating of reactor components (35.5%), while the minor losses were contributed by convection by argon (1%) and conduction through insulation (2%).The thermal efficiency of the reactor is calculated to be 15.5%.

Discrete Models of Fluids: Spatial Averaging, Closure, and Model Reduction

We consider semidiscrete ODE models of single-phase fluids and two-fluid mixtures. In the presence of multiple fine-scale heterogeneities, the size of these ODE systems can be very large. Spatial averaging is then a useful tool for reducing computational complexity of the problem. The averages satisfy exact balance equations of mass, momentum, and energy. These equations do not form a satisfactory continuum model because evaluation of stress and heat flux requires solving the underlying ODEs. To produce continuum equations that can be simulated without resolving microscale dynamics, we recently proposed a closure method based on the use of regularized deconvolution. Here we continue the investigation of deconvolution closure with the long term objective of developing consistent computational upscaling for multiphase particle methods. The structure of the fine-scale particle solvers is reminiscent of molecular dynamics. For this reason we use nonlinear averaging introduced for atomistic systems by Noll, Hardy, and Murdoch-Bedeaux. We also consider a simpler linear averaging originally developed in large eddy simulation of turbulence. We present several simple but representative examples of spatially averaged ODEs, where the closure error can be analyzed. Based on this analysis we suggest a general strategy for reducing the relative error of approximate closure. For problems with periodic highly oscillatory material parameters we propose a spectral boosting technique that augments the standard deconvolution and helps to correctly account for dispersion effects. We also conduct several numerical experiments, one of which is a complete mesoscale simulation of a stratified two-fluid flow in a channel. In this simulation, the operation count per coarse time step scales sublinearly with the number of particles.

Influence of interfacial zone between asphalt mastic and aggregate on the elastic behavior of asphalt concrete

The interfacial zone between asphalt mastic and aggregate has a significant influence on the macro-mechanical properties and failure mechanisms of asphalt concrete (AC). To investigate the effect of interfacial zone, a 3D two layer built-in micromechanical model is established first, and the interface spring layer is considered to simulate the interfacial zone. Then, the effective elastic modulus and shear modulus of single-phase composite materials with the specific aggregate size are derived. A stepping-scheme is adopted to further obtain the effective elastic properties of multi-phase composite materials. The developed closed-form equations are used to predict the elastic behavior of asphalt concrete, and are able to take into account material characteristic of asphalt mastic and aggregate, the aggregate size and its volume fraction, the interface property, and air voids. Tests on four types of AC are conducted to verify the proposed approach. Finally, the influence of interfacial zone on the elastic behavior of AC is discussed. The developed method can also be used to research other multi-phase particle reinforced composites.

Application of Eulerian–Lagrangian Approach to Gas-Solid Flows in Interior Ballistics

In a gun system, polydisperse phenomenon may occur due to the local combustion by an igniter system during the firing process. The Eulerian–Eulerian approach still lacks the capability of describing particle mixing under given conditions. A detailed insight of the interior ballistics must be predicted for the better safety and the lower cost at the development stage. The multiphase particle in cell (MP-PIC) model based on the Eulerian–Lagrangian approach, known to be more efficient than the conventional Eulerian–Lagrangian approach, has been initially applied for the simulation of the interior ballistics. A good efficiency with the MP-PIC model has been obtained in terms of the computational cost. The axisymmetric numerical code with the MP-PIC model has been developed for two-dimensional analysis of the interior ballistics. As part of the verification process for the code, several test computations have been performed: sod shock tube, free piston motion problem, and virtual gun calculated by IBHVG2 code. The code has become reliable with well-agreed results with the comparison data. Additionally, a numerical model for the orifices to describe the vent holes of the igniter on the coarse grid has been developed with the lumped parameter method used in the IBHVG2. Based on the model, the pressure behavior in the gun chamber according to the igniter length has been investigated. The computational results have shown that the negative differential pressure occurs clearly when the igniter is sufficiently short.

Two-Phase Internal Flow: Toward a Theory of Everything

Two-phase flow and heat transfer is still an area of intense research and great uncertainty. Even severely restricting ourselves to just annular, internal two-phase flow does not significantly improve our chances of accurately predicting either pressure gradients or heat transfer coefficients for an arbitrary tube geometry or fluid. This article summarizes a series of investigations that aim to identify the fundamental governing physics of internal two-phase flow: a Theory of Everything. The techniques developed to do so have been varied, and novel approaches are presented here. At the macro scale, simultaneous visualization and measurement of pressure gradient have led to interesting observations about the relationship between flow regimes and these fundamental macroscale behaviors. Since the macroscale behaviors are governed, for the most part, by behaviors at the micro scale, a number of techniques have been developed to study this near-wall behavior in quantitative detail. In particular, dye-assisted planar laser induced fluorescence has provided the first accurate portrayals of the gas–liquid interface annular flow, and microscale multiphase particle image velocimetry has been used to obtain the velocity within the liquid film of annular flow from within micrometers of the wall to velocities within the waves 500 μm or more from the wall. Statistical analyses of these data point toward a general approach for modeling wall shear in two-phase concurrent internal flow.

Quantification of Grain, Pore, and Fluid Microstructure of Unsaturated Sand from X-Ray Computed Tomography Images

Abstract A comprehensive series of three-dimensional x-ray computed tomography (XCT) imaging experiments was conducted to quantitatively assess the multiphase particle- and pore-scale properties of fine Ottawa (F-75) sand. The specimens were prepared to saturations ranging from approximately 5 % to 80 %. Specimens were doped with 10 % CsCl pore fluid solution and imaged using a monochromatic synchrotron x-ray source at energies below and above the Cs x-ray absorption k-edge to allow for high contrast between the solid, liquid, and air phases. Multiphase properties quantified from the XCT images included individual particle sizes and areas, as well as grain size distribution, pore shape and size distribution, water menisci distribution, solid, liquid, and gas surface areas, and particle contact coordination number. At low saturations, pore water is distributed primarily in the form of pendular rings and liquid bridges located between individual grains and in the smallest pore throats and bodies. A highly discontinuous water phase is evident as a large number of separately identifiable water units having very small volume. As the water saturation increases, the number of individual water units decreases; as expected, the average volume of these units increases significantly as the pore water coalesces into larger and larger units. Results obtained using SEM imaging and conventional geotechnical testing methods for particle-size distribution and soil–water retention were compared with those derived from analysis of the XCT images. Results compare very well in each case, typically within a few %. It is shown that the XCT is a reliable and non-destructive method to quantify pore-scale information vital to advance understanding of the hydrologic and mechanical behavior of unsaturated soils at the macroscale.

MP-PIC simulation of CFB riser with EMMS-based drag model

MP-PIC (multi-phase particle in cell) method combined with the EMMS (energy minimization multi-scale) drag force model was implemented with the open source program MFIX to simulate the gas–solid flows in CFB (circulating fluidized bed) risers. Calculated solid flux by the EMMS drag agrees well with the experimental value; while the traditional homogeneous drag over-predicts this value. EMMS drag force model can also predict the macro- and meso-scale structures. Quantitative comparison of the results by the EMMS drag force model and the experimental measurements show high accuracy of the model. The effects of the number of particles per parcel and wall conditions on the simulation results have also been investigated in the paper. This work proved that MP-PIC combined with the EMMS drag model can successfully simulate the fluidized flows in CFB risers and it serves as a candidate to realize real-time simulation of industrial processes in the future.

Simulations of Multiphase Particle Deposition on a Showerhead With Staggered Film-Cooling Holes

The demand for cleaner, more efficient energy has driven the motivation for improving the performance standards for gas turbines. Increasing the combustion temperature is one way to get the best possible performance from a gas turbine. One problem associated with increased combustion temperatures is that particles ingested in the fuel and air become more prone to deposition with an increase in turbine inlet temperature. Deposition on aero-engine turbine components caused by sand particle ingestion can impair turbine cooling methods and lead to reduced component life. It is necessary to understand the extent to which particle deposition affects turbine cooling in the leading edge region of the nozzle guide vane where intricate showerhead cooling geometries are utilized. For the current study, wax was used to dynamically simulate multiphase particle deposition on a large scale showerhead cooling geometry. The effects of deposition development, coolant blowing ratio, and particle temperature were tested. Infrared thermography was used to quantify the effects of deposition on cooling effectiveness. Although deposition decreased with an increase in coolant blowing ratio, results showed that reductions in cooling effectiveness caused by deposition increased with an increase in blowing ratio. Results also showed that effectiveness reduction increased with an increase in particle temperature. Reductions in cooling effectiveness reached as high as 36% at M = 1.0.

Schmidt-Kennicutt relations in SPH simulations of disc galaxies with effective thermal feedback from supernovae

We study several versions of the Schmidt-Kennicutt (SK) relation obtained for isolated spiral galaxies in TreeSPH simulations run with the GADGET3 code including the novel MUlti-Phase Particle Integrator (MUPPI) algorithm for star formation and stellar feedback. [...] The standard SK relation between surface densities of cold (neutral+molecular) gas and star formation rate of simulated galaxies shows a steepening at low gas surface densities, starting from a knee whose position depends on disc gas fraction: for more gas-rich discs the steepening takes place at higher surface densities. Because gas fraction and metallicity are typically related, this environmental dependence mimics the predictions of models where the formation of H2 is modulated by metallicity. The cold gas surface density at which HI and molecular gas surface densities equate can range from ~10 up to 34 Msun/pc^2. As expected, the SK relation obtained using molecular gas shows much smaller variations among simulations. We find that disc pressure is not well represented by the classical external pressure of a disc in vertical hydrostatic equilibrium. Instead is well fit by the expression P_fit = Sigma_cold sigma_cold kappa / 6, where the three quantities on the right-hand side are cold gas surface density, vertical velocity dispersion and epicyclic frequency. When the "dynamical" SK relation, i.e. the relation that uses gas surface density divided by orbital time, is considered, we find that all of our simulations stay on the same relation. We interpret this as a manifestation of the equilibrium between energy injection and dissipation in stationary galaxy discs, when energetic feedback is effective and pressure is represented by the expression given above. These findings further support the idea that a realistic model of the structure of galaxy discs should take into account energy injection by SNe. [Abridged]