scholarly journals Dynamics of elastic dumbbells sedimenting in a viscous fluid: oscillations and hydrodynamic repulsion

2015 ◽  
Vol 767 ◽  
pp. 95-108 ◽  
Author(s):  
Marek Bukowicki ◽  
Marta Gruca ◽  
Maria L. Ekiel-Jeżewska
Keyword(s):  
Viscous Fluid ◽  
Point Particle ◽  
Spring Constant ◽  
Particle Model ◽  
Relaxation Phase ◽  
Mass Frame ◽  
Periodic Dynamics ◽  
Oscillating Motion ◽  
Elastic Particles ◽  
Time Dependent Solution

AbstractHydrodynamic interactions between two identical elastic dumbbells settling under gravity in a viscous fluid at low Reynolds number are investigated using the point-particle model. The evolution of a benchmark initial configuration is studied, in which the dumbbells are vertical and their centres are aligned horizontally. Rigid dumbbells and pairs of separate beads starting from the same positions tumble periodically while settling. We find that elasticity (which breaks the time-reversal symmetry of the motion) significantly affects the system dynamics. This is remarkable when taking into account that elastic forces are always much smaller than gravity. We observe oscillating motion of the elastic dumbbells, which tumble and change their length non-periodically. Independently of the value of the spring constant, a horizontal hydrodynamic repulsion appears between the dumbbells: their centres of mass move apart from each other horizontally. This motion is fast for moderate values of the spring constant $k$, and slows down when $k$ tends to zero or to infinity; in these limiting cases we recover the periodic dynamics reported in the literature. For moderate values of the spring constant, and different initial configurations, we observe the existence of a universal time-dependent solution to which the system converges after an initial relaxation phase. The tumbling time and the width of the trajectories in the centre-of-mass frame increase with time. In addition to its fundamental significance, the benchmark solution presented here is important to understanding general features of systems with a larger number of elastic particles, in regular and random configurations.

Monte Carlo Schemes for Radiative Transfer in Media Represented by Particle Fields

2005 ◽  
Author(s):  
Anquan Wang ◽  
Michael F. Modest
Keyword(s):  
Monte Carlo ◽  
Ray Tracing ◽  
Radiative Heat ◽  
Solid Angle ◽  
Scalar Fields ◽  
Point Particle ◽  
Particle Model ◽  
Test Problems ◽  
Combustion Modeling ◽  
Radiation Properties

Monte Carlo ray-tracing schemes are developed for the evaluation of radiative heat transfer for problems, in which the participating medium is represented by discrete point-masses, such as the flow field and scalar fields in PDF Monte Carlo methods frequently used in combustion modeling. Photon ray tracing in such cases requires that an optical thickness is assigned to each of the point-masses. Two approaches are discussed, the Point Particle Model (PPM), in which the shape of particle is not specified, and the Spherical Particle Model (SPM) in which particles are assumed to be spheres with constant radiation properties. Another issue for ray tracing in particle fields is the influence region of a ray. Two ways of modeling a ray are proposed. In the first, each ray is treated as a standard volume-less line. In the other approach, the ray is assigned a small solid angle, and is thus treated as a cone with a decaying influence function away from its center line. Based on these models, three different interaction schemes between rays and particles are proposed, i.e., Line-SPM, Cone-PPM and Cone-SPM methods, and are compared employing several test problems.

On the Predictive Capability of DNS-DEM Applied to Suspended Sediment-Turbulence Interactions

2017 ◽  
Author(s):  
Pedram Pakseresht ◽  
Sourabh V. Apte ◽  
Justin R. Finn
Keyword(s):  
Point Particle ◽  
Particle Model ◽  
Wall Region ◽  
Dynamical Interaction ◽  
Kolmogorov Length Scale ◽  
Large Particles ◽  
Wall Collision ◽  
Kolmogorov Scale ◽  
Particle Approach ◽  
Near Wall

DNS coupled with a Point-Particle based model (PP) is used to study and predict particle-turbulence interactions in an open channel flow at Reynolds number of 811 (based on the friction velocity) corresponding to the experimental observations of [Righetti & Romano, JFM 2004]. Large particles of diameter 200 microns (8.1 in wall units) with average volume loading on the order of 0.001 are simulated using four-way coupling with closure models for drag, added mass, lift, pressure, and inter-particle/particle-wall collision forces. The point-particle model is able to accurately capture the effect of particles on the fluid flow in the outer layer where particles are under resolved. However, the dynamical interaction of particle-turbulence is under predicted in the near wall region where particles size are much larger than Kolmogorov scale and grid resolution in wall-normal direction, but smaller in both stream and span wise directions. It is conjectured that due to the large size particles compared to the Kolmogorov length scale near the bed, the effect of disturbances and deflections in the flow due to presence of such large particles is not captured using Lagrangian Point-Particle approach. For this configuration, the point-particle model is not appropriate in the near wall region and a hybrid resolved particle approach may be necessary.

A point-particle model universe

1982 ◽  
Vol 14 (6) ◽  
pp. 591-608 ◽  
Author(s):  
R. P. A. C. Newman ◽  
G. C. McVittie
Keyword(s):  
Point Particle ◽  
Particle Model ◽  
Model Universe

Photon Monte Carlo Simulation for Radiative Transfer in Gaseous Media Represented by Discrete Particle Fields

2006 ◽  
Vol 128 (10) ◽  
pp. 1041-1049 ◽  
Author(s):  
Anquan Wang ◽  
Michael F. Modest
Keyword(s):  
Monte Carlo ◽  
Ray Tracing ◽  
Radiative Heat ◽  
Scalar Fields ◽  
Point Particle ◽  
Particle Model ◽  
Test Problems ◽  
Combustion Modeling ◽  
Radiation Properties ◽  
Gaseous Media

Monte Carlo ray-tracing schemes have been developed for the evaluation of radiative heat transfer for problems, in which the participating medium is represented by discrete point masses, such as the flow field and scalar fields in PDF Monte Carlo methods frequently used in combustion modeling. Photon ray tracing in such cases requires that an optical thickness is assigned to each of the point masses. Two approaches are discussed, the point particle model (PPM), in which the shape of particle is not specified, and the spherical particle model (SPM) in which particles are assumed to be spheres with specified radiation properties across their volumes. Another issue for ray tracing in particle fields is the influence region of a ray. Two ways of modeling a ray are proposed. In the first, each ray is treated as a standard volume-less line. In the other approach, the ray is assigned a small solid angle, and is thus treated as a cone with a decaying influence function away from its centerline. Based on these models, three different interaction schemes between rays and particles are proposed, i.e., line-SPM, cone-PPM and cone-SPM methods, and are compared employing several test problems.

scholarly journals A point particle model of lightly bound skyrmions

2017 ◽  
Vol 917 ◽  
pp. 286-316 ◽  
Author(s):  
Mike Gillard ◽  
Derek Harland ◽  
Elliot Kirk ◽  
Ben Maybee ◽  
Martin Speight
Keyword(s):  
Point Particle ◽  
Particle Model

A direct comparison of particle-resolved and point-particle methods in decaying turbulence

2018 ◽  
Vol 850 ◽  
pp. 336-369 ◽  
Author(s):  
M. Mehrabadi ◽  
J. A. K. Horwitz ◽  
S. Subramaniam ◽  
A. Mani
Keyword(s):  
Numerical Simulation ◽  
Particle Acceleration ◽  
Direct Numerical Simulation ◽  
Volume Fraction ◽  
Fluid Velocity ◽  
Point Particle ◽  
Particle Methods ◽  
Particle Model ◽  
Second Moment ◽  
Acceleration Model

We use particle-resolved direct numerical simulation (PR-DNS) as a model-free physics-based numerical approach to validate particle acceleration modelling in gas-solid suspensions. To isolate the effect of the particle acceleration model, we focus on point-particle direct numerical simulation (PP-DNS) of a collision-free dilute suspension with solid-phase volume fraction $\unicode[STIX]{x1D719}=0.001$ in a decaying isotropic turbulent particle-laden flow. The particle diameter $d_{p}$ in the suspension is chosen to be the same as the initial Kolmogorov length scale $\unicode[STIX]{x1D702}_{0}$ ($d_{p}/\unicode[STIX]{x1D702}_{0}=1$) in order to overlap with the regime where PP-DNS is valid. We assess the point-particle acceleration model for two different particle Stokes numbers, $St_{\unicode[STIX]{x1D702}}=1$ and 100. For the high Stokes number case, the Stokes drag model for particle acceleration under-predicts the true particle acceleration. In addition, second moment quantities which play key roles in the physical evolution of the gas–solid suspension are not correctly captured. Considering finite Reynolds number corrections to the acceleration model improves the prediction of the particle acceleration probability density function and second moment statistics of the point-particle model compared with the particle-resolved simulation. We also find that accounting for the undisturbed fluid velocity in the acceleration model can be of greater importance than using the most appropriate acceleration model for a given physical problem.

scholarly journals MASSIVE SPINNING PARTICLE ON ANTI-DE SITTER SPACE

1996 ◽  
Vol 11 (18) ◽  
pp. 3307-3329 ◽  
Author(s):  
S.M. KUZENKO ◽  
S.L. LYAKHOVICH ◽  
A. YU. SEGAL ◽  
A.A. SHARAPOV
Keyword(s):  
Configuration Space ◽  
Degrees Of Freedom ◽  
Massive Particle ◽  
De Sitter Space ◽  
Arbitrary Spin ◽  
Point Particle ◽  
Particle Model ◽  
De Sitter ◽  
Spinning Particle ◽  
Classical Counterpart

To describe a massive particle with fixed, but arbitrary, spin on d=4 anti-de Sitter space M4, we propose the point particle model with configuration space ℳ6=M4×S2, where the sphere S2 corresponds to the spin degrees of freedom. The model possesses two gauge symmetries expressing strong conservation of the phase space counterparts of the second and fourth order Casimir operators for so (3, 2). We prove that the requirement of energy to have a global positive minimum Eo over the configuration space is equivalent to the relation Eo>s, s being the particle’s spin, which presents the classical counterpart of the quantum massive condition. States with minimal energy are studied in detail. The model is shown to be exactly solvable. It can be straightforwardly generalized to describe a spinning particle on d-dimensional anti-de Sitter space Md, with ℳ2(d−1)=Md×S(d−2) the corresponding configuration space.

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