Motion Of Fluid Particles Research Articles

Improved SPH simulation of spilled oil contained by flexible floating boom under wave–current coupling condition

A multi-phase Smoothed Particle Hydrodynamics (SPH) method is developed to model the failure process of a flexible oil boom. An algorithm is proposed based on the dynamic boundary particles (DBPs) for preventing particle disorders of multi-phase fluid particle movement around solid boundary. The improved multi-phase SPH model is firstly validated by the experimental data of a wedge falling into a two-layer oil–water fluid. Then a numerical wave–current flume is established with a piston-type active absorbing wave generator and a circulating current system. The model reliability is validated against the measured vertical profiles of velocity. Simulation of the flexible floating boom movement is implemented by introducing a Rigid Module and Flexible Connector (RMFC) multi-body system. The model is finally applied to the simulation of movement of a flexible floating boom in containing industrial gear oil under the action of combined waves and currents. Good agreements are obtained between the SPH modeling results and the experimental data in terms of the ambient wave–current field, hydrodynamic responses of the floating body and evolution process of the oil slick for the flexible boom. The hydrodynamic responses and containment performances of the flexible floating boom are also compared with those of the rigid one. It is found from both the experimental and numerical results that two vortices of the water phase exist in the front and rear of the boom skirt and the size of the front vortex decreases with increase of the current velocity while the wake vortex is reversed. It is also found that the skirt of the flexible boom has a larger magnitude of swaying and rolling than the rigid one and the maximum quantity of escaped oil of a flexible boom within one wave cycle is about 5% more than a rigid one under the present test conditions.

Numerical simulation of scour around a submarine pipeline using computational fluid dynamics and discrete element method

• Numerical simulation of scour around a pipeline using a coupled CFD-DEM model. • Simulated scour evolution is in good agreement with published experimental results. • Detailed information, e.g., particle position, velocity, and force, is obtained to improve the understanding of scour mechanism. • Particle motion and particle–particle interactions are found to be most intense during tunnel erosion stage. • Both pressure gradient and drag forces are important at onset and early stages of scour, but drag is dominant at the last stage. Scour under a submarine pipeline can lead to structural failure; hence, a good understanding of the scour mechanism is paramount. Various numerical methods have been proposed to simulate scour, such as potential flow theory and single-phase and two-phase turbulent models. However, these numerical methods have limitations such as their reliance on calibrated empirical parameters and inability to provide detailed information. This paper investigates the use of a coupled computational fluid dynamics-discrete element method (CFD-DEM) model to simulate scour around a pipeline. The novelty of this work is to use CFD-DEM to extract detailed information, leading to new findings that enhance the current understanding of the underlying mechanisms of the scour process. The simulated scour evolution and bed profile are found to be in good agreement with published experimental results. Detailed results include the contours of the fluid velocity and fluid pressure, particle motion and velocity, fluid forces on the particles, and inter-particle forces. The sediment transport rate is calculated using the velocity of each single particle. The quantitative analysis of the bed load layer is also presented. The numerical results reveal three scour stages: onset of scour, tunnel erosion, and lee-wake erosion. Particle velocity and force distributions show that during the tunnel erosion stage, the particle motion and particle–particle interactive forces are particularly intense, suggesting that single-phase models, which are unable to account for inter-particle interactions, may be inadequate. The fluid pressure contours show a distinct pressure gradient. The pressure gradient force is calculated and found to be comparable with the drag force for the onset of scour and the tunnel erosion. However, for the lee-wake erosion, the drag force is shown to be the dominant mechanism for particle movements.

Force moments of an active particle in a complex fluid

A generalized reciprocal theorem is formulated for the motion and hydrodynamic force moments of an active particle in an arbitrary background flow of a (weakly nonlinear) complex fluid. This formalism includes as special cases a number of previous calculations of the motion of both passive and active particles in Newtonian and non-Newtonian fluids.

Ferrite nanoparticles Ni- ZnFe2O4 , Mn- ZnFe2O4 and Fe2O4 in the flow of ferromagnetic nanofluid

The performance of convective heat transfer is elevated in boundary layer flow regions via nanoparticles. A magnetic dipole in the presence of ferrite nanoparticles plays a vital role in controlling the thermal and momentum boundary layers. In view of this, the impacts of a magnetic dipole on the nano boundary layer, laminar, and steady flow of an incompressible ferromagnetic NiZnFe2O4-C2H6O2 (nickel zinc ferrite-ethylene glycol), MnZnFe2O4-C2H6O2 (manganese zinc ferrite-ethylene glycol), and Fe2O4-C2H6O2 (magnetite ferrite-ethylene glycol) nanofluids are characterized for the first time in the present analysis. Flow is caused by a linear stretching sheet. Fourier’s law of heat conduction is hired for the evaluation of heat flux. Impacts of emerging parameters on the magneto-thermomechanical coupling are analyzed numerically. It is seen that the characteristics of magneto-thermomechanical interaction decelerate the movements of fluid particles, thereby strengthen the skin friction coefficient and reduce the heat transfer rate at the surface. Further, it is evident that a solid volume fraction has increasing behaviour on the rate of heat transfer in the boundary layer. Comparisons with available results for specific cases are found in excellent agreement.

Chaotic behavior of modified stretch-twist-fold (STF) flow with fractal property

In this paper, a modified stretch-twist-fold (STF) flow is introduced, which is based on STF flow that is associated with fluid particle motion that naturally arises in the dynamo theory. Dynamo theory intends a some typical procedure which follows the celestial bodies, such as earth, sun and other stars; due to this mechanism, they can maintain and amplify the magnetic field continuously. Chaoticity of modified STF attractor is discussed for different values of chaotic parameter. With the help of fractal process based on the modified STF flow, a multi-wing modified STF flow is obtained that gives a 2n-wing modified STF flow system. The Hamiltonian energy function of modified STF flow concludes that the energy is decreased as the number of multi-wing increases. Moreover, with the help of Melnikov technique and Hamiltonian energy function, existence of periodic solutions for modified STF flow is derived analytically.

On the kinematics-wave motion of living particles in suspension.

This work presents theoretical and experimental analyses on the kinematics-wave motion of suspended active particles in a biological fluid. The fluid is an active suspension of nematodes immersed in a gel-like biological structure, moving at a low Reynolds number. The nematode chosen for the study is Caenorhabditis elegans. Its motion is subjected to the time reversibility of creeping flows. We investigate how this worm reacts to this reversibility condition in order to break the flow symmetry and move in the surrounding fluid. We show that the relationship between the length of an individual nematode and the wavelength of its motion is linear and can be fitted by a theoretical prediction proposed in this work. We provide a deep discussion regarding the propulsion mechanics based on a scaling analysis that identifies three major forces acting on an individual nematode. These forces are a viscous force, a yield stress force due to gelification of agar molecules in the gel-like medium, and a bending force associated with the muscular tension imposed by the nematodes in the medium. By the scalings, we identify the most relevant physical parameters of the nematode's motion. In order to examine and quantify the motion, dynamical system tools such as FFT are used in the present analysis. The motion characterization is performed by examining (or studying) two different populations: (i) in the absence of food with starving nematodes and (ii) with well-fed nematodes. In addition, several kinematic quantities of the head, center of mass, and tail for a sample of nematodes are also investigated: their slip velocities, wavelengths, trajectories, frequency spectra, and mean curvatures. The main findings of this work are the confirmation of a linear relationship between the nematode's physical length and its motion wavelength, the identification of secondary movements in high frequencies that helps breaking the time-reversibility in which the worms are bonded, and the observation and interpretation of a systematic difference between the individual motion of well-fed and starving nematodes.

DEM analysis of acoustic wake agglomeration for mono-sized microparticles in the presence of gravitational effects

The application of the discrete element method (DEM) to numerical simulation of the acoustic agglomeration of micron-sized mono-dispersed aerosol particles is demonstrated. The conventional DEM technique used in granular dynamics is modified for the simulation of the acoustically induced attractive motion of particles in incompressible fluid. The relationship between the acoustic wake and the gravity is investigated by simulating the binary interaction of two particles for a wide range of particles’ orientations to the sound direction. The main finding obtained by simulation results shows that agglomeration time is solely predefined by the acoustic wake effect independently of gravity. On the other hand, the gravitational motion is contributed by the sound, and an increase of settling velocity due to the sound of individual particles was found. Additionally, two particles surrounded by a system of other particles are illustrated by numerical results. It was also shown that isolated particles demonstrate an overestimated increase of the agglomeration time, which was essentially reduced by the contribution of other particles in the multi-particle system.

Bilge-Keel Influence on Free Decay of Roll Motion of a Realistic Hull1

The prediction of roll motion of a ship with bilge keels is particularly difficult because of the nonlinear characteristics of the viscous roll damping. Flow separation and vortex shedding caused by bilge keels significantly affect the roll damping and hence the magnitude of the roll response. To predict the ship motion, the Slender-Ship Free-Surface Random-Vortex Method (SSFSRVM) was employed. It is a fast discrete-vortex free-surface viscous-flow solver developed to run on a standard desktop computer. It features a quasi-three-dimensional formulation that allows the decomposition of the three-dimensional ship-hull problem into a series of two-dimensional computational planes, in which the two-dimensional free-surface Navier–Stokes solver Free-Surface Random-Vortex Method (FSRVM) can be applied. In this paper, the effectiveness of SSFSRVM modeling is examined by comparing the time histories of free roll-decay motion resulting from simulations and from experimental measurements. Furthermore, the detailed two-dimensional vorticity distribution near a bilge keel obtained from the numerical model will also be compared with the existing experimental Digital Particle Image Velocimetry (DPIV) images. Next, we will report, based on the time-domain simulation of the coupled hull and fluid motion, how the roll-decay coefficients and the flow field are altered by the span of the bilge keels. Plots of vorticity contour and vorticity isosurface along the three-dimensional hull will be presented to reveal the motion of fluid particles and vortex filaments near the keels.

Modelling and Simulation of Solid Particle Sedimentation in an Incompressible Newtonian Fluid

We present in this paper a method that simulates the motion of rigid particles in a Newtonian fluid. This method is based on a variational formulation throughout the fluid/solid domain, with constraints on the unknown and on the test functions. The rigid motion of the particle is enforced by penalizing the strain tensor on the rigid domain for canceling the deformation rate in the volume occupied by the particle. The time discretization is performed by using the characteristics method. We developed a code from FreeFem++ that simulates Stokes flows or Navier–Stokes flows (low Reynolds number). A simulation of an elliptical rigid particle sedimentation in a Newtonian fluid has shown the importance of this approach.

Yield limit analysis of particle motion in a yield-stress fluid

A theoretical and numerical study of yield-stress fluid creeping flow about a particle is presented. Yield-stress fluids can hold rigid particles statically buoyant if the yield stress is large enough. In addressing sedimentation of rigid particles in viscoplastic fluids, we should know this critical ‘yield number’ beyond which there is no motion. As we get close to this limit, the role of viscosity becomes negligible in comparison to the plastic contribution in the leading order, since we are approaching the zero-shear-rate limit. Admissible stress fields in this limit can be found by using the characteristics of the governing equations of perfect plasticity (i.e. the sliplines). This approach yields a lower bound of the critical plastic drag force or equivalently the critical yield number. Admissible velocity fields also can be postulated to calculate the upper bound. This analysis methodology is examined for three families of particle shapes (ellipse, rectangle and diamond) over a wide range of aspect ratios. Numerical experiments of either resistance or mobility problems in a viscoplastic fluid validate the predictions of slipline theory and reveal interesting aspects of the flow in the yield limit (e.g. viscoplastic boundary layers). We also investigate in detail the cases of high and low aspect ratio of the particles.

Pair mobility functions for rigid spheres in concentrated colloidal dispersions: Stresslet and straining motion couplings.

Accurate modeling of particle interactions arising from hydrodynamic, entropic, and other microscopic forces is essential to understanding and predicting particle motion and suspension behavior in complex and biological fluids. The long-range nature of hydrodynamic interactions can be particularly challenging to capture. In dilute dispersions, pair-level interactions are sufficient and can be modeled in detail by analytical relations derived by Jeffrey and Onishi [J. Fluid Mech. 139, 261-290 (1984)] and Jeffrey [Phys. Fluids A 4, 16-29 (1992)]. In more concentrated dispersions, analytical modeling of many-body hydrodynamic interactions quickly becomes intractable, leading to the development of simplified models. These include mean-field approaches that smear out particle-scale structure and essentially assume that long-range hydrodynamic interactions are screened by crowding, as particle mobility decays at high concentrations. Toward the development of an accurate and simplified model for the hydrodynamic interactions in concentrated suspensions, we recently computed a set of effective pair of hydrodynamic functions coupling particle motion to a hydrodynamic force and torque at volume fractions up to 50% utilizing accelerated Stokesian dynamics and a fast stochastic sampling technique [Zia et al., J. Chem. Phys. 143, 224901 (2015)]. We showed that the hydrodynamic mobility in suspensions of colloidal spheres is not screened, and the power law decay of the hydrodynamic functions persists at all concentrations studied. In the present work, we extend these mobility functions to include the couplings of particle motion and straining flow to the hydrodynamic stresslet. The couplings computed in these two articles constitute a set of orthogonal coupling functions that can be utilized to compute equilibrium properties in suspensions at arbitrary concentration and are readily applied to solve many-body hydrodynamic interactions analytically.

Unsteady particle motion in an acoustic standing wave field

The acoustic-based separation has attracted considerable attention in biomedical research, such as sorting of cells and particles. Current design principles used for acoustic systems are based on the steady Stokes theory, equating the Stokes drag with the primary radiation force. However, this approach is not valid for large cells/particles or in the presence of particle–particle interaction. In this work, we analytically examine unsteady inertial affects and particle–particle hydrodynamic interaction on the particle motion in a viscous fluid in the presence of an acoustic standing wave field. Comparing our results to the steady Stokes theory, we find that the unsteady inertial force decreases the particle’s velocity, while particle–particle interaction enhances it. For a particular acoustic-based separation approach ‘tilted-angle standing surface acoustic waves (taSSAW)’, we find that both effects of unsteady inertial force and particle–particle interaction are evident and should be considered for m) par...

A two-way couple of Eulerian-Lagrangian model for particle transport with different sizes in an obstructed channel

In this paper, a two-way couple of Eulerian-Lagrangian model is used to simulate and account the discrete nature of Al2O3 particles in a particulate channel flow with a built-in heated obstruction. The governing equations for fluid flow and particle motions are solved by using the finite volume and trajectory analysis approaches. The simulations are performed for different particle sizes and solid volume fractions of particles (φ) in the ranges of 30–500nm and 0–0.05, respectively and at fixed values of blockage ratio (S=1/8) and Reynolds number (Re=100). The effects of interaction forces acting between the fluid and particles containing the drag, gravity, Brownian, and thermophoresis forces on the particle transport and thermal behaviour of system are investigated. It was found that the nanometer particle does not follow the flow streamline and in fact diffuses across the streamlines. For larger sizes (i.e. 100 and 250nm), particles concentrate in the vorticity regions around the periphery of the vortices. Moreover, the particle deposition percentage increases with an increase in the particle size.

Dynamic motion analysis of magnetic particles in microfluidic systems under an external gradient magnetic field

To gain an insightful understanding of motion behavior of paramagnetic particles suspended in a nonmagnetic fluid under a gradient magnetic field, a coupled fluid–structure model based on a direct numerical scheme is developed in this work. The governing equations of magnetic field, fluid flow field and particle motion are simultaneously solved using an Arbitrary Lagrangian–Eulerian method, taking into account magnetic and hydrodynamic interactions between particles in a fully coupled manner. The accuracy of the proposed method is validated using the magnetic particulate flows of two particles under a uniform magnetic field as the test problem and is then applied to investigate effects of magnetic and hydrodynamic interactions between particles on the particle motion behavior. Results show that neighboring magnetic particles are easy to form chain-like clusters along field direction due to magnetic interactions between particles and then move together toward the surface of magnetic source under the action of gradient magnetic force. More importantly, it has been found that both magnetic and hydrodynamic interactions between particles are conducive to the acceleration of particles and the chain formation of particles. The present method and results could help in understanding the basic mechanism underlying the low-gradient magnetophoretic separation process and designing magnetic aggregate-based microfluidic devices.

Two-dimensional spin coating technology and the effect of artificial gravity on film’s air-bubbling

This article mathematically and experimentally investigates the effects of increased artificial gravity acceleration on a film's air-bubbling defect. The controllable artificial gravity is generated using a two-dimensional (2D) spin coating method. In order to conduct these studies a 2D spin coater was designed and manufactured. The mathematics of particle motion in fluids (Stokes' Law) is investigated in order to analyze the motion of air-bubbles along the thickness of the film. The mathematic of particle motion in fluids is simulated using MATLAB in a wide range of variation of related parameters. These simulations illustrate that increasing the artificial gravity acceleration increases the velocity of air-bubbles motion and decreases the decay time of the air-bubble release. Simulations also show that the fluid viscosity and size of air-bubbles are effective factors which can affect the decay time of air-bubble release and their velocity along the thickness of the film. To investigate the simulation results, a high viscous photoresist (SU8-3050) is used as the coating material. The mentioned photoresist is coated with the both conventional and 2D spin coating methods and their results are compared. The surface and cross section of coated substrates are imaged with an SEM device. The natural results of mathematic simulations are in agreement with our experimental comparisons.

Effect of homogeneous-heterogeneous reactions on ferrofluid in the presence of magnetic dipole along a stretching cylinder

This article characterizes the influence of magnetic dipole in a non-Newtonian ferrofluid. The flow is caused by an incompressible stretchable cylinder. The effects of homogeneous and heterogeneous reactions are taken into account. Heat flux is evaluated by the Fourier’s law of heat conduction. Characteristics of pertinent parameters on magneto-thermomechanical coupling and chemical reactions are explored numerically. It is depicted that the magneto-thermomechanical interaction slows down the motion of fluid particles, thereby increases skin friction and decreasing rate of heat transfer at the surface of a cylinder. Comparison with available results for some cases is found good agreements.

Comparative study of the two-fluid momentum equations for multi-dimensional bubbly flows: Modification of Reynolds stress

Two-fluid equations are widely used to obtain averaged behaviors of two-phase flows. This study addresses a problem that may arise when the two-fluid equations are used for multi-dimensional bubbly flows. If steady drag is the only accounted force for the interfacial momentum transfer, the disperse-phase velocity would be the same as the continuous-phase velocity when the flow is fully developed without gravity. However, existing momentum equations may show unphysical results in estimating the relative velocity of the dispersephase against the continuous-phase. First, we examine two types of existing momentum equations. One is the standard two-fluid momentum equation in which the disperse-phase is treated as a continuum. The other is the averaged momentum equation derived from a solid/ fluid particle motion. We show that the existing equations are not proper for multi-dimensional bubbly flows. To resolve the problem mentioned above, we modify the form of the Reynolds stress terms in the averaged momentum equation based on the solid/fluid particle motion. The proposed equation shows physically correct results for both multi-dimensional laminar and turbulent flows.

A level-set model for thermocapillary motion of deformable fluid particles

A new level-set model is proposed for simulating immiscible thermocapillary flows with variable fluid-property ratios at dynamically deformable interfaces. The Navier–Stokes equations coupled with the energy conservation equation are solved by means of a finite-volume/level-set approach, adapted to a multiple marker methodology in order to avoid the numerical coalescence of the fluid particles. The temperature field is coupled to the surface tension through an equation of state. Some numerical examples including thermocapillary driven convection in two superimposed fluid layers, and thermocapillary motion of single and multiple fluid particles are computed using the present method. These results are compared against analytical solutions and numerical results from the literature as validations of the proposed model.

Study of Heat Transfer with Nonlinear Thermal Radiation on Sinusoidal Motion of Magnetic Solid Particles in a Dusty Fluid

Abstract In this article, heat transfer with nonlinear thermal radiation on sinusoidal motion of magnetic solid particles in a dust Jeffrey fluid has been studied. The effects of Magnetohydrodynamic (MHD) and hall current are also taken under consideration. The governing equation of motion and energy equation are modelled with help of Ohms law for fluid and dust phases. The solutions of the resulting ordinary coupled partial differential equations are solved analytically. The impact of all the physical parameters of interest such as Hartmann number, slip parameter, Hall parameter, radiation parameter, Prandtl number, Eckert number and particle volume fraction are demonstrated mathematically and graphically. Trapping mechanism is also discussed in detail by drawing contour lines. The present analysis affirms many interesting behaviours, which permit further study on solid particles motion with heat and mass transfer.

A level-set method for thermal motion of bubbles and droplets

A conservative level-set model for direct simulation of two-phase flows with thermocapillary effects at dynamically deformable interface is presented. The Navier-Stokes equations coupled with the energy conservation equation are solved by means of a finite-volume/level-set method. Some numerical examples including thermocapillary motion of single and multiple fluid particles are computed by means of the present method. The results are compared with analytical solutions and numerical results from the literature as validations of the proposed model.