3,863 research outputs found
Numerical Simulation of Non-Homogeneous Viscous Debris-Flows Based on the Smoothed Particle Hydrodynamics (SPH) Method
Non-homogeneous viscous debris flows are characterized by high density, impact force and destructiveness, and the complexity of the materials they are made of. This has always made these flows challenging to simulate numerically, and to reproduce experimentally debris flow processes. In this study, the formation-movement process of non-homogeneous debris flow under three different soil configurations was simulated numerically by modifying the formulation of collision, friction, and yield stresses for the existing Smoothed Particle Hydrodynamics (SPH) method. The results obtained by applying this modification to the SPH model clearly demonstrated that the configuration where fine and coarse particles are fully mixed, with no specific layering, produces more fluctuations and instability of the debris flow. The kinetic and potential energies of the fluctuating particles calculated for each scenario have been shown to be affected by the water content by focusing on small local areas. Therefore, this study provides a better understanding and new insights regarding intermittent debris flows, and explains the impact of the water content on their formation and movement processes
Melting and Mixing States of the Earth's Mantle after the Moon-Forming Impact
The Earth's Moon is thought to have formed by an impact between the Earth and
an impactor around 4.5 billion years ago. This impact could have been so
energetic that it could have mixed and homogenized the Earth's mantle. However,
this view appears to be inconsistent with geochemical studies that suggest that
the Earth's mantle was not mixed by the impact. Another plausible outcome is
that this energetic impact melted the whole mantle, but the extent of mantle
melting is not well understood even though it must have had a significant
effect on the subsequent evolution of the Earth's interior and atmosphere. To
understand the initial state of the Earth's mantle, we perform giant impact
simulations using smoothed particle hydrodynamics (SPH) for three different
models: (a) standard: a Mars-sized impactor hits the proto-Earth, (b)
fast-spinning Earth: a small impactor hits a rapidly rotating proto-Earth, and
(c) sub-Earths: two half Earth-sized planets collide. We use two types of
equations of state (MgSiO3 liquid and forsterite) to describe the Earth's
mantle. We find that the mantle remains unmixed in (a), but it may be mixed in
(b) and (c). The extent of mixing is most extensive in (c). Therefore, (a) is
most consistent and (c) may be least consistent with the preservation of the
mantle heterogeneity, while (b) may fall between. We determine that the Earth's
mantle becomes mostly molten by the impact in all of the models. The choice of
the equations of state does not affect these outcomes. Additionally, our
results indicate that entropy gains of the mantle materials by a giant impact
cannot be predicted well by the Rankine-Hugoniot equations. Moreover, we show
that the mantle can remain unmixed on a Moon-forming timescale if it does not
become mixed by the impact.Comment: Accepted for publication in EPS
The origin of the Moon within a terrestrial synestia
The giant impact hypothesis remains the leading theory for lunar origin.
However, current models struggle to explain the Moon's composition and isotopic
similarity with Earth. Here we present a new lunar origin model. High-energy,
high-angular momentum giant impacts can create a post-impact structure that
exceeds the corotation limit (CoRoL), which defines the hottest thermal state
and angular momentum possible for a corotating body. In a typical super-CoRoL
body, traditional definitions of mantle, atmosphere and disk are not
appropriate, and the body forms a new type of planetary structure, named a
synestia. Using simulations of cooling synestias combined with dynamic,
thermodynamic and geochemical calculations, we show that satellite formation
from a synestia can produce the main features of our Moon. We find that cooling
drives mixing of the structure, and condensation generates moonlets that orbit
within the synestia, surrounded by tens of bars of bulk silicate Earth (BSE)
vapor. The moonlets and growing moon are heated by the vapor until the first
major element (Si) begins to vaporize and buffer the temperature. Moonlets
equilibrate with BSE vapor at the temperature of silicate vaporization and the
pressure of the structure, establishing the lunar isotopic composition and
pattern of moderately volatile elements. Eventually, the cooling synestia
recedes within the lunar orbit, terminating the main stage of lunar accretion.
Our model shifts the paradigm for lunar origin from specifying a certain impact
scenario to achieving a Moon-forming synestia. Giant impacts that produce
potential Moon-forming synestias were common at the end of terrestrial planet
formation.Comment: Accepted for publication in Journal of Geophysical Research: Planets.
Main text: 44 pages, 24 figures. Supplement: 16 pages, 5 figures, 3 table
Recent advances in the simulation of particle-laden flows
A substantial number of algorithms exists for the simulation of moving
particles suspended in fluids. However, finding the best method to address a
particular physical problem is often highly non-trivial and depends on the
properties of the particles and the involved fluid(s) together. In this report
we provide a short overview on a number of existing simulation methods and
provide two state of the art examples in more detail. In both cases, the
particles are described using a Discrete Element Method (DEM). The DEM solver
is usually coupled to a fluid-solver, which can be classified as grid-based or
mesh-free (one example for each is given). Fluid solvers feature different
resolutions relative to the particle size and separation. First, a
multicomponent lattice Boltzmann algorithm (mesh-based and with rather fine
resolution) is presented to study the behavior of particle stabilized fluid
interfaces and second, a Smoothed Particle Hydrodynamics implementation
(mesh-free, meso-scale resolution, similar to the particle size) is introduced
to highlight a new player in the field, which is expected to be particularly
suited for flows including free surfaces.Comment: 16 pages, 4 figure
Comparison of multiphase SPH and LBM approaches for the simulation of intermittent flows
Smoothed Particle Hydrodynamics (SPH) and Lattice Boltzmann Method (LBM) are
increasingly popular and attractive methods that propose efficient multiphase
formulations, each one with its own strengths and weaknesses. In this context,
when it comes to study a given multi-fluid problem, it is helpful to rely on a
quantitative comparison to decide which approach should be used and in which
context. In particular, the simulation of intermittent two-phase flows in pipes
such as slug flows is a complex problem involving moving and intersecting
interfaces for which both SPH and LBM could be considered. It is a problem of
interest in petroleum applications since the formation of slug flows that can
occur in submarine pipelines connecting the wells to the production facility
can cause undesired behaviors with hazardous consequences. In this work, we
compare SPH and LBM multiphase formulations where surface tension effects are
modeled respectively using the continuum surface force and the color gradient
approaches on a collection of standard test cases, and on the simulation of
intermittent flows in 2D. This paper aims to highlight the contributions and
limitations of SPH and LBM when applied to these problems. First, we compare
our implementations on static bubble problems with different density and
viscosity ratios. Then, we focus on gravity driven simulations of slug flows in
pipes for several Reynolds numbers. Finally, we conclude with simulations of
slug flows with inlet/outlet boundary conditions. According to the results
presented in this study, we confirm that the SPH approach is more robust and
versatile whereas the LBM formulation is more accurate and faster
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Particle Dynamics Simulation toward High-Shear Mixing Process in Many Particle Systems
Granular materials appear in a broad range of industrial processes, including mineral processing, plastics manufacturing, ceramic component, pharmaceutical tablets and food products. Engineers and scientists are always seeking efficient tools that can characterize, predict, or simulate the effective material properties in a timely manner and with acceptable accuracy, such that the cost for design and develop novel composite granular materials could be reduced.
The major scope of this dissertation covers the development, verification and validation of particle system simulations, including solid-liquid two-phase particle mixing process and foaming asphalt process. High shear mixing process is investigated in detail with different types of mixers. Besides particle mixing study, one liquid-gas two phase foaming asphalt simulation is studied to show the broad capacity of our particulate dynamics simulation scheme. Methodologies and numerical studies for different scenarios are presented, and acceleration plans to speed up the simulations are discussed in detail.
The dissertation starts with the problem statement, which briefly demonstrates the background of the problem and introduces the numerical models built from the physical world. In this work, liquid-solid two-phase particle mixing process is mainly studied. These mixing processes are conducted in a sealed mixer and different types of particles are mixed with the rotation of the mixer blades, to obtain a homogeneous particle mixture. In addition to the solid-liquid particle mixing problem, foaming asphalt problem, which is a liquid-gas two phase flow problem is also investigated. Foaming asphalt is generated by injecting a small amount of liquid additive (usually water) to asphalt at a high temperature. The volume change during this asphalt foaming process is studied.
Given the problem statement, detailed methodologies of particle dynamics simulation are illustrated. For solid-liquid particle mixing, Smoothed Particle Hydrodynamics (SPH) and Discrete Element Method (DEM) are introduced and implemented to simulate the dynamics of solid and liquid particles, respectively. Solid-liquid particle interactions are computed according to Darcy`s Law. Then the proposed SPH coupling DEM model is verified by three classical case studies.
For foaming asphalt problems, a SPH numerical model for foaming asphalt simulation is proposed, and simulations with different water contents, pressures and temperatures are conducted and the results agree with the experiments well. The coupled SPH-DEM method is applied to the particle mixing process, and several particle mixing numerical studies are conducted and these simulations are analyzed in multiple aspects. For the solid-liquid particle mixing problem, liquid plays an important role in the mixing performance. The effects of liquid content and liquid viscosity on mixing performance are studied. The mixing indexes of the mixture are applied to analyze the mixing quality, and the differences between three kinds of mixing indexes are discussed. Then mixers commonly used in industry such as Double Planetary Mixer (DPM) are modeled in mixing simulation and their results are compared with the experiments.
Similar to other numerical simulation problems, the scale of the model and the accuracy of the simulation results are constrained by the computational capacity. Our in-house software package Particle Dynamics Parallel Simulator(PDPS) has been used as a platform to implement the algorithms above and conduct the simulations. Two parallel computing methods of Message Passing Interface (MPI) parallel computing and Graphics Processing Unit (GPU) acceleration have been used to accelerate the simulations. Speedup results for both MPI parallel computing and GPU methods are illustrated in the case studies.
In summary, a comprehensive approach for particle simulation is proposed and applied to particle mixing process and asphalt foaming simulation. The simulation results are analyzed in various aspects to provide valuable insights to the problems studied in this work. Given the improvement of computational capacity, particle dynamics in higher resolution and simulations in more complex configurations can be obtained. This particle simulation platform is general and it can be straightforwardly extended to many-particle systems with more particle phases and solid-liquid-gas dynamics problems
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