Energy Dependent Streaming in Lattice Boltzmann Simulations

Czech Academy of Sciences Publication Activity Database

Pavlo, Pavol; Vahala, G.; Vahala, L.

2001-01-01

Roč. 46, č. 8 (2001), s. 241 ISSN 0003-0503. [Annual Meeting of the Division of Plasma Physics of the American Physical Society/43rd./. Long Beach, CA, 29.10.2001-02.11.2001] R&D Projects: GA ČR GA202/00/1216 Institutional research plan: CEZ:AV0Z2043910 Keywords : Lattice Boltzmann Simulations Subject RIV: BL - Plasma and Gas Discharge Physics

A multicomponent multiphase lattice Boltzmann model with large liquid–gas density ratios for simulations of wetting phenomena

International Nuclear Information System (INIS)

Zhang Qing-Yu; Zhu Ming-Fang; Sun Dong-Ke

2017-01-01

A multicomponent multiphase (MCMP) pseudopotential lattice Boltzmann (LB) model with large liquid–gas density ratios is proposed for simulating the wetting phenomena. In the proposed model, two layers of neighboring nodes are adopted to calculate the fluid–fluid cohesion force with higher isotropy order. In addition, the different-time-step method is employed to calculate the processes of particle propagation and collision for the two fluid components with a large pseudo-particle mass contrast. It is found that the spurious current is remarkably reduced by employing the higher isotropy order calculation of the fluid–fluid cohesion force. The maximum spurious current appearing at the phase interfaces is evidently influenced by the magnitudes of fluid–fluid and fluid–solid interaction strengths, but weakly affected by the time step ratio. The density ratio analyses show that the liquid–gas density ratio is dependent on both the fluid–fluid interaction strength and the time step ratio. For the liquid–gas flow simulations without solid phase, the maximum liquid–gas density ratio achieved by the present model is higher than 1000:1. However, the obtainable maximum liquid–gas density ratio in the solid–liquid–gas system is lower. Wetting phenomena of droplets contacting smooth/rough solid surfaces and the dynamic process of liquid movement in a capillary tube are simulated to validate the proposed model in different solid–liquid–gas coexisting systems. It is shown that the simulated intrinsic contact angles of droplets on smooth surfaces are in good agreement with those predicted by the constructed LB formula that is related to Young’s equation. The apparent contact angles of droplets on rough surfaces compare reasonably well with the predictions of Cassie’s law. For the simulation of liquid movement in a capillary tube, the linear relation between the liquid–gas interface position and simulation time is observed, which is identical to

Lattice gas methods for predicting intrinsic permeability of porous media

Energy Technology Data Exchange (ETDEWEB)

Santos, L.O.E.; Philippi, P.C. [Santa Catarina Univ., Florianopolis, SC (Brazil). Dept. de Engenharia Mecanica. Lab. de Propriedades Termofisicas e Meios Porosos)]. E-mail: emerich@lmpt.ufsc.br; philippi@lmpt.ufsc.br; Damiani, M.C. [Engineering Simulation and Scientific Software (ESSS), Florianopolis, SC (Brazil). Parque Tecnologico]. E-mail: damiani@lmpt.ufsc.br

2000-07-01

This paper presents a method for predicting intrinsic permeability of porous media based on Lattice Gas Cellular Automata methods. Two methods are presented. The first is based on a Boolean model (LGA). The second is Boltzmann method (LB) based on Boltzmann relaxation equation. LGA is a relatively recent method developed to perform hydrodynamic calculations. The method, in its simplest form, consists of a regular lattice populated with particles that hop from site to site in discrete time steps in a process, called propagation. After propagation, the particles in each site interact with each other in a process called collision, in which the number of particles and momentum are conserved. An exclusion principle is imposed in order to achieve better computational efficiency. In despite of its simplicity, this model evolves in agreement with Navier-Stokes equation for low Mach numbers. LB methods were recently developed for the numerical integration of the Navier-Stokes equation based on discrete Boltzmann transport equation. Derived from LGA, LB is a powerful alternative to the standard methods in computational fluid dynamics. In recent years, it has received much attention and has been used in several applications like simulations of flows through porous media, turbulent flows and multiphase flows. It is important to emphasize some aspects that make Lattice Gas Cellular Automata methods very attractive for simulating flows through porous media. In fact, boundary conditions in flows through complex geometry structures are very easy to describe in simulations using these methods. In LGA methods simulations are performed with integers needing less resident memory capability and boolean arithmetic reduces running time. The two methods are used to simulate flows through several Brazilian reservoir petroleum rocks leading to intrinsic permeability prediction. Simulation is compared with experimental results. (author)

Nuclear lattice simulations

Directory of Open Access Journals (Sweden)

Epelbaum E.

2010-04-01

Full Text Available We review recent progress on nuclear lattice simulations using chiral effective field theory. We discuss lattice results for dilute neutron matter at next-to-leading order, three-body forces at next-to-next-toleading order, isospin-breaking and Coulomb effects, and the binding energy of light nuclei.

Towards the simplest hydrodynamic lattice-gas model.

Science.gov (United States)

Boghosian, Bruce M; Love, Peter J; Meyer, David A

2002-03-15

It has been known since 1986 that it is possible to construct simple lattice-gas cellular automata whose hydrodynamics are governed by the Navier-Stokes equations in two dimensions. The simplest such model heretofore known has six bits of state per site on a triangular lattice. In this work, we demonstrate that it is possible to construct a model with only five bits of state per site on a Kagome lattice. Moreover, the model has a simple, deterministic set of collision rules and is easily implemented on a computer. In this work, we derive the equilibrium distribution function for this lattice-gas automaton and carry out the Chapman-Enskog analysis to determine the form of the Navier-Stokes equations.

Multisite Interactions in Lattice-Gas Models

Science.gov (United States)

Einstein, T. L.; Sathiyanarayanan, R.

For detailed applications of lattice-gas models to surface systems, multisite interactions often play at least as significant a role as interactions between pairs of adatoms that are separated by a few lattice spacings. We recall that trio (3-adatom, non-pairwise) interactions do not inevitably create phase boundary asymmetries about half coverage. We discuss a sophisticated application to an experimental system and describe refinements in extracting lattice-gas energies from calculations of total energies of several different ordered overlayers. We describe how lateral relaxations complicate matters when there is direct interaction between the adatoms, an issue that is important when examining the angular dependence of step line tensions. We discuss the connector model as an alternative viewpoint and close with a brief account of recent work on organic molecule overlayers.

Advancements in simulations of lattice quantum chromodynamics

International Nuclear Information System (INIS)

Lippert, T.

2008-01-01

An introduction to lattice QCD with emphasis on advanced fermion formulations and their simulation is given. In particular, overlap fermions will be presented, a quite novel fermionic discretization scheme that is able to exactly preserve chiral symmetry on the lattice. I will discuss efficiencies of state-of-the-art algorithms on highly scalable supercomputers and I will show that, due to many algorithmic improvements, overlap simulations will soon become feasible for realistic physical lattice sizes. Finally I am going to sketch the status of some current large scale lattice QCD simulations. (author)

Numerical simulation of vapor film collapse behavior on high-temperature droplet surface with three-dimensional lattice gas cellular automata

International Nuclear Information System (INIS)

Tochio, Daisuke; Abe, Yutaka; Matsukuma, Yosuke

2008-01-01

It is pointed out that a vapor film on a premixed high-temperature droplet surface is needed to be collapsed to trigger vapor explosion. Thus, it is important to clarify the micromechanism of vapor film collapse behavior for the occurrence of vapor explosion. In a previous study, it is suggested experimentally that vapor film collapse behavior is dominated by phase change phenomena rather than by the surrounding fluid motion. In the present study, vapor film collapse behavior is investigated to clarify the dominant factor of vapor film collapse behavior with lattice gas automata of three-dimensional immiscible lattice gas model (3-D ILG model). First, in order to represent the boiling and phase change phenomena, the thermal model of a heat wall model and a phase change model is newly constructed. Next, the numerical simulation of vapor film collapse behavior is performed with and without the phase change effect. As a result, the computational result with the phase change effect is observed to be almost same as the experimental result. It can be considered that vapor film collapse behavior is dominated by phase change phenomena. (author)

Lattice gas cellular automata and lattice Boltzmann models an introduction

CERN Document Server

Wolf-Gladrow, Dieter A

2000-01-01

Lattice-gas cellular automata (LGCA) and lattice Boltzmann models (LBM) are relatively new and promising methods for the numerical solution of nonlinear partial differential equations. The book provides an introduction for graduate students and researchers. Working knowledge of calculus is required and experience in PDEs and fluid dynamics is recommended. Some peculiarities of cellular automata are outlined in Chapter 2. The properties of various LGCA and special coding techniques are discussed in Chapter 3. Concepts from statistical mechanics (Chapter 4) provide the necessary theoretical background for LGCA and LBM. The properties of lattice Boltzmann models and a method for their construction are presented in Chapter 5.

Lattice Model for Production of Gas

KAUST Repository

Marder, M.; Eftekhari, Behzad; Patzek, Tadeusz

2017-01-01

We define a lattice model for rock, absorbers, and gas that makes it possible to examine the flow of gas to a complicated absorbing boundary over long periods of time. The motivation is to deduce the geometry of the boundary from the time history

Efficient LBM visual simulation on face-centered cubic lattices.

Science.gov (United States)

Petkov, Kaloian; Qiu, Feng; Fan, Zhe; Kaufman, Arie E; Mueller, Klaus

2009-01-01

The Lattice Boltzmann method (LBM) for visual simulation of fluid flow generally employs cubic Cartesian (CC) lattices such as the D3Q13 and D3Q19 lattices for the particle transport. However, the CC lattices lead to suboptimal representation of the simulation space. We introduce the face-centered cubic (FCC) lattice, fD3Q13, for LBM simulations. Compared to the CC lattices, the fD3Q13 lattice creates a more isotropic sampling of the simulation domain and its single lattice speed (i.e., link length) simplifies the computations and data storage. Furthermore, the fD3Q13 lattice can be decomposed into two independent interleaved lattices, one of which can be discarded, which doubles the simulation speed. The resulting LBM simulation can be efficiently mapped to the GPU, further increasing the computational performance. We show the numerical advantages of the FCC lattice on channeled flow in 2D and the flow-past-a-sphere benchmark in 3D. In both cases, the comparison is against the corresponding CC lattices using the analytical solutions for the systems as well as velocity field visualizations. We also demonstrate the performance advantages of the fD3Q13 lattice for interactive simulation and rendering of hot smoke in an urban environment using thermal LBM.

Layer features of the lattice gas model for self-organized criticality

International Nuclear Information System (INIS)

Pesheva, N.C.; Brankov, J.G.

1995-06-01

A layer-by-layer description of the asymmetric lattice gas model for 1/f-noise suggested by Jensen [Phys. Rev. Lett. 64, 3103 (1990)] is presented. The power spectra of the lattice layers in the direction perpendicular to the particle flux is studied in order to understand how the white noise at the input boundary evolves, on the average, into 1/f-noise for the system. The effects of high boundary drive and uniform driving force on the power spectrum of the total number of diffusing particles are considered. In the case of nearest-neighbor particle interactions, high statistics simulation results show that the power spectra of single lattice layers are characterized by different β x exponents such that β x → 1.9 as one approaches the outer boundary. (author). 10 refs, 6 figs

A lattice gas model on a tangled chain

International Nuclear Information System (INIS)

Mejdani, R.

1993-04-01

We have used a model of a lattice gas defined on a tangled chain to study the enzyme kinetics by a modified transfer matrix method. By using a simple iterative algorithm we have obtained different kinds of saturation curves for different configurations of the tangled chain and different types of the additional interactions. In some special cases of configurations and interactions we have found the same equations for the saturation curves, which we have obtained before studying the lattice gas model with nearest neighbor interactions or the lattice gas model with alternate nearest neighbor interactions, using different techniques as the correlated walks' theory, the partition point technique or the transfer matrix model. This more general model and the new results could be useful for the experimental investigations. (author). 20 refs, 6 figs

Lattice Model for Production of Gas

KAUST Repository

Marder, M.

2017-12-01

We define a lattice model for rock, absorbers, and gas that makes it possible to examine the flow of gas to a complicated absorbing boundary over long periods of time. The motivation is to deduce the geometry of the boundary from the time history of gas absorption. We find a solution to this model using Green\\'s function techniques, and apply the solution to three absorbing networks of increasing complexity.

Lattice Model for Production of Gas

OpenAIRE

Marder, M.; Eftekhari, Behzad; Patzek, Tadeusz W

2017-01-01

We define a lattice model for rock, absorbers, and gas that makes it possible to examine the flow of gas to a complicated absorbing boundary over long periods of time. The motivation is to deduce the geometry of the boundary from the time history of gas absorption. We find a solution to this model using Green's function techniques, and apply the solution to three absorbing networks of increasing complexity.

Temperature-dependent errors in nuclear lattice simulations

International Nuclear Information System (INIS)

Lee, Dean; Thomson, Richard

2007-01-01

We study the temperature dependence of discretization errors in nuclear lattice simulations. We find that for systems with strong attractive interactions the predominant error arises from the breaking of Galilean invariance. We propose a local 'well-tempered' lattice action which eliminates much of this error. The well-tempered action can be readily implemented in lattice simulations for nuclear systems as well as cold atomic Fermi systems

Multispeed models in off-lattice Boltzmann simulations

NARCIS (Netherlands)

Bardow, A.; Karlin, I.V.; Gusev, A.A.

2008-01-01

The lattice Boltzmann method is a highly promising approach to the simulation of complex flows. Here, we realize recently proposed multispeed lattice Boltzmann models [S. Chikatamarla et al., Phys. Rev. Lett. 97 190601 (2006)] by exploiting the flexibility offered by off-lattice Boltzmann methods.

Application of lattice-gas cellular automata to the Brownian motion of solids in suspension

International Nuclear Information System (INIS)

Ladd, A.J.C.; Colvin, M.E.; Frenkel, D.

1988-01-01

An adaptation of lattice-gas cellular automata to the simulation of solid-fluid suspensions is described. The method incorporates both dissipative hydrodynamic forces and thermal fluctuations. At low solid densities, theoretical results for the drag force on a single disk and the viscosity of a suspension of disks are reproduced. The zero--shear-rate viscosity has been obtained over a range of packing fractions and results indicate that simulations of three-dimensional suspensions are feasible

Lattice Boltzmann simulations of the contact angle in a liquid-gas system

International Nuclear Information System (INIS)

Ryu, Seung Yeob; Park, Cheon Tae; Kim, Keung Koo

2008-01-01

Recently, the lattice Boltzmann method (LBM) has gained much attention for its ability to simulate fluid flows, and for its potential advantages over a conventional CFD method. The key advantages of LBM are, (1) suitability for parallel computations, (2) absence of the need to solve the time-consuming Poisson equation for a pressure, and (3) an ease with multiphase flows, complex geometries and interfacial dynamics may be treated. The shape of a moving droplet is difficult to investigate analytically because the classical continuum hydrodynamic equations of motion with the usual no-slip condition at the surface predict a singularity in the stress at the contact line. Briant et al. have proposed a wetting boundary condition by using the wetting potential. In this study, we introduce the wetting boundary condition into the LBM proposed by Zheng et al. The static contact angle of a droplet onto a wall in order to validate the method is calculated. By adopting a finite difference gradient operator of a sufficient isotropy, the spurious currents can be made small in the wall surface. The main objective of the present work is to establish the lattice Boltzmann method as a viable tool for the simulation of multiphase or multi-component flows

Nuclear Lattice Simulations with Chiral Effective Field Theory

OpenAIRE

Lee, Dean

2008-01-01

We present recent results on lattice simulations using chiral effective field theory. In particular we discuss lattice simulations for dilute neutron matter at next-to-leading order and three-body forces in light nuclei at next-to-next-to-leading order.

Lattice BGK simulation of natural convection

International Nuclear Information System (INIS)

Chen, Yu; Ohashi, Hirotada; Akiyama, Mamoru

1995-01-01

Recently a new thermal lattice Bhatnagar-Gross-Krook fluid model was suggested by the authors. In this study, this new model was applied into the numerical simulation of natural convection, namely the Rayleigh Benard flow. The critical number for the onset of convective phenomenon was numerically measured and compared with that of theoretical prediction. A gravity dependent deviation was found in the numerical simulation, which is explained as an unavoidable consequence of the incorporation of gravity force in the lattice BGK system. (author)

Deflation acceleration of lattice QCD simulations

International Nuclear Information System (INIS)

Luescher, Martin

2007-01-01

Close to the chiral limit, many calculations in numerical lattice QCD can potentially be accelerated using low-mode deflation techniques. In this paper it is shown that the recently introduced domain-decomposed deflation subspaces can be propagated along the field trajectories generated by the Hybrid Monte Carlo (HMC) algorithm with a modest effort. The quark forces that drive the simulation may then be computed using a deflation-accelerated solver for the lattice Dirac equation. As a consequence, the computer time required for the simulations is significantly reduced and an improved scaling behaviour of the simulation algorithm with respect to the quark mass is achieved

Deflation acceleration of lattice QCD simulations

CERN Document Server

Lüscher, Martin

2007-01-01

Close to the chiral limit, many calculations in numerical lattice QCD can potentially be accelerated using low-mode deflation techniques. In this paper it is shown that the recently introduced domain-decomposed deflation subspaces can be propagated along the field trajectories generated by the Hybrid Monte Carlo (HMC) algorithm with a modest effort. The quark forces that drive the simulation may then be computed using a deflation-accelerated solver for the lattice Dirac equation. As a consequence, the computer time required for the simulations is significantly reduced and an improved scaling behaviour of the simulation algorithm with respect to the quark mass is achieved.

Multiscale Lattice Boltzmann method for flow simulations in highly heterogenous porous media

KAUST Repository

Li, Jun

2013-01-01

A lattice Boltzmann method (LBM) for flow simulations in highly heterogeneous porous media at both pore and Darcy scales is proposed in the paper. In the pore scale simulations, flow of two phases (e.g., oil and gas) or two immiscible fluids (e.g., water and oil) are modeled using cohesive or repulsive forces, respectively. The relative permeability can be computed using pore-scale simulations and seamlessly applied for intermediate and Darcy-scale simulations. A multiscale LBM that can reduce the computational complexity of existing LBM and transfer the information between different scales is implemented. The results of coarse-grid, reduced-order, simulations agree very well with the averaged results obtained using fine grid.

Lattice Boltzmann simulations of water transport in gas diffusion layer of a polymer electrolyte membrane fuel cell

Energy Technology Data Exchange (ETDEWEB)

Hao, Liang; Cheng, Ping [Ministry of Education Key Laboratory of Power Machinery and Engineering, School of Mechanical Engineering, Shanghai Jiaotong University, DongChuan Road 800, Shanghai 200240 (China)

2010-06-15

The effect of wettability on water transport dynamics in gas diffusion layer (GDL) is investigated by simulating water invasion in an initially gas-filled GDL using the multiphase free-energy lattice Boltzmann method (LBM). The results show that wettability plays a significant role on water saturation distribution in two-phase flow in the uniform wetting GDL. For highly hydrophobicity, the water transport falls in the regime of capillary fingering, while for neutral wettability, water transport exhibits the characteristic of stable displacement, although both processes are capillary force dominated flow with same capillary numbers. In addition, the introduction of hydrophilic paths in the GDL leads the water to flow through the hydrophilic pores preferentially. The resulting water saturation distributions show that the saturation in the GDL has little change after water breaks through the GDL, and further confirm that the selective introduction of hydrophilic passages in the GDL would facilitate the removal of liquid water more effectively, thus alleviating the flooding in catalyst layer (CL) and GDL. The LBM approach presented in this study provides an effective tool to investigate water transport phenomenon in the GDL at pore-scale level with wettability distribution taken into consideration. (author)

Lattice Boltzmann simulation of the gas-solid adsorption process in reconstructed random porous media

Science.gov (United States)

Zhou, L.; Qu, Z. G.; Ding, T.; Miao, J. Y.

2016-04-01

The gas-solid adsorption process in reconstructed random porous media is numerically studied with the lattice Boltzmann (LB) method at the pore scale with consideration of interparticle, interfacial, and intraparticle mass transfer performances. Adsorbent structures are reconstructed in two dimensions by employing the quartet structure generation set approach. To implement boundary conditions accurately, all the porous interfacial nodes are recognized and classified into 14 types using a proposed universal program called the boundary recognition and classification program. The multiple-relaxation-time LB model and single-relaxation-time LB model are adopted to simulate flow and mass transport, respectively. The interparticle, interfacial, and intraparticle mass transfer capacities are evaluated with the permeability factor and interparticle transfer coefficient, Langmuir adsorption kinetics, and the solid diffusion model, respectively. Adsorption processes are performed in two groups of adsorbent media with different porosities and particle sizes. External and internal mass transfer resistances govern the adsorption system. A large porosity leads to an early time for adsorption equilibrium because of the controlling factor of external resistance. External and internal resistances are dominant at small and large particle sizes, respectively. Particle size, under which the total resistance is minimum, ranges from 3 to 7 μm with the preset parameters. Pore-scale simulation clearly explains the effect of both external and internal mass transfer resistances. The present paper provides both theoretical and practical guidance for the design and optimization of adsorption systems.

Dynamical Behavior of Multi-Robot Systems Using Lattice Gas Automata

Energy Technology Data Exchange (ETDEWEB)

Cameron, S.M.; Robinett, R.; Stantz, K.M.; Trahan, M.W.; Wagner, J.S.

1999-03-11

Recent attention has been given to the deployment of an adaptable sensor array realized by multi-robotic systems. Our group has been studying the collective behavior of autonomous, multi-agent systems and their applications in the area of remote-sensing and emerging threats. To accomplish such tasks, an interdisciplinary research effort at Sandia National Laboratories are conducting tests in the fields of sensor technology, robotics, and multi-robotic and multi-agents architectures. Our goal is to coordinate a constellation of point sensors that optimizes spatial coverage and multivariate signal analysis using unmanned robotic vehicles (e.g., RATLERs, Robotic All-ten-sin Lunar Exploration Rover-class vehicles). Overall design methodology is to evolve complex collective behaviors realized through simple interaction (kinetic) physics and artificial intelligence to enable real-time operational responses to emerging threats. This paper focuses on our recent work understanding the dynamics of many-body systems using the physics-based hydrodynamic model of lattice gas automata. Three design features are investigated. One, for single-speed robots, a hexagonal nearest-neighbor interaction topology is necessary to preserve standard hydrodynamic flow. Two, adaptability, defined by the swarm's deformation rate, can be controlled through the hydrodynamic viscosity term, which, in turn, is defined by the local robotic interaction rules. Three, due to the inherent non-linearity of the dynamical equations describing large ensembles, development of stability criteria ensuring convergence to equilibrium states is developed by scaling information flow rates relative to a swarm's hydrodynamic flow rate. An initial test case simulates a swarm of twenty-five robots that maneuvers past an obstacle while following a moving target. A genetic algorithm optimizes applied nearest-neighbor forces in each of five spatial regions distributed over the simulation domain. Armed with

Comparing the results of lattice and off-lattice simulations for the melt of nonconcatenated rings

International Nuclear Information System (INIS)

Halverson, Jonathan D; Kremer, Kurt; Grosberg, Alexander Y

2013-01-01

To study the conformational properties of unknotted and nonconcatenated ring polymers in the melt, we present a detailed qualitative and quantitative comparison of simulation data obtained by molecular dynamics simulation using an off-lattice bead-spring model and by Monte Carlo simulation using a lattice model. We observe excellent, and sometimes even unexpectedly good, agreement between the off-lattice and lattice results for many quantities measured including the gyration radii of the ring polymers, gyration radii of their subchains, contact probabilities, surface characteristics, number of contacts between subchains, and the static structure factors of the rings and their subchains. These results are, in part, put in contrast to Moore curves, and the open, linear polymer counterparts. While our analysis is extensive, our understanding of the ring melt conformations is still rather preliminary. (paper)

Distribution for fermionic discrete lattice gas within the canonical ensemble

International Nuclear Information System (INIS)

Kutner, R.; Barszczak, T.

1991-01-01

The distinct deviations from the Fermi-Dirac statistics ascertained recently at low temperatures for a one-dimensional, spinless fermionic discrete lattice gas with conserved number of noninteracting particles hopping on the nondegenerated, well-separated single-particle energy levels are studied in numerical and theoretical terms. The generalized distribution is derived in the form n(h) = {Y h exp[(var-epsilon h -μ)β]+1} -1 valid even in the thermodynamic limit, when the discreteness of the energy levels is kept. This distribution demonstrates good agreement with the data obtained numerically both by the canonical partition-function technique and by Monte Carlo simulation

Study of deformation of droplet in external force field by using liquid-gas model of lattice-gas

International Nuclear Information System (INIS)

Ebihara, Ken-ichi; Watanabe, Tadashi

2000-10-01

The deformation of the droplet by the external force which is assumed to be gravity is studied by using the liquid-gas model of lattice-gas. Two types of liquid-gas models, one is the minimal model and the other is the maximal model, which are distinguished from each other by the added long-range interactions are used for the simulation of the droplet deformation. The difference of the droplet deformation between the maximal model and the minimal model was observed. While the droplet of the minimal model elongates in the direction of the external force, the droplet of the maximal model elongates in the perpendicular direction to the external force. Therefore the droplet deformation in the external force field of the maximal model is more similar to the droplet deformation which is observed in experiments than that of the minimal model. (author)

Simulation of diffusion in a two-dimensional lattice gas cellular automaton: a test of mode-coupling theory

NARCIS (Netherlands)

Frenkel, D.; Ernst, M.H.

1989-01-01

We compute the velocity autocorrelation function of a tagged particle in a two-dimensional lattice-gas cellular automaton using a method that is about a million times more efficient than existing techniques. A t-1 algebraic tail in the tagged-particle velocity autocorrelation function is clearly

Simulation of Cavity Flow by the Lattice Boltzmann Method using Multiple-Relaxation-Time scheme

International Nuclear Information System (INIS)

Ryu, Seung Yeob; Kang, Ha Nok; Seo, Jae Kwang; Yun, Ju Hyeon; Zee, Sung Quun

2006-01-01

Recently, the lattice Boltzmann method(LBM) has gained much attention for its ability to simulate fluid flows, and for its potential advantages over conventional CFD method. The key advantages of LBM are, (1) suitability for parallel computations, (2) absence of the need to solve the time-consuming Poisson equation for pressure, and (3) ease with multiphase flows, complex geometries and interfacial dynamics may be treated. The LBM using relaxation technique was introduced by Higuerea and Jimenez to overcome some drawbacks of lattice gas automata(LGA) such as large statistical noise, limited range of physical parameters, non- Galilean invariance, and implementation difficulty in three-dimensional problem. The simplest LBM is the lattice Bhatnager-Gross-Krook(LBGK) equation, which based on a single-relaxation-time(SRT) approximation. Due to its extreme simplicity, the lattice BGK(LBGK) equation has become the most popular lattice Boltzmann model in spite of its well-known deficiencies, for example, in simulating high-Reynolds numbers flow. The Multiple-Relaxation-Time(MRT) LBM was originally developed by D'Humieres. Lallemand and Luo suggests that the use of a Multiple-Relaxation-Time(MRT) models are much more stable than LBGK, because the different relaxation times can be individually tuned to achieve 'optimal' stability. A lid-driven cavity flow is selected as the test problem because it has geometrically singular points in the flow, but geometrically simple. Results are compared with those using SRT, MRT model in the LBGK method and previous simulation data using Navier-Stokes equations for the same flow conditions. In summary, LBM using MRT model introduces much less spatial oscillations near geometrical singular points, which is important for the successful simulation of higher Reynolds number flows

Canonical sampling of a lattice gas

International Nuclear Information System (INIS)

Mueller, W.F.

1997-01-01

It is shown that a sampling algorithm, recently proposed in conjunction with a lattice-gas model of nuclear fragmentation, samples the canonical ensemble only in an approximate fashion. A residual weight factor has to be taken into account to calculate correct thermodynamic averages. Then, however, the algorithm is numerically inefficient. copyright 1997 The American Physical Society

Topology in dynamical lattice QCD simulations

International Nuclear Information System (INIS)

Gruber, Florian

2012-01-01

Lattice simulations of Quantum Chromodynamics (QCD), the quantum field theory which describes the interaction between quarks and gluons, have reached a point were contact to experimental data can be made. The underlying mechanisms, like chiral symmetry breaking or the confinement of quarks, are however still not understood. This thesis focuses on topological structures in the QCD vacuum. Those are not only mathematically interesting but also closely related to chiral symmetry and confinement. We consider methods to identify these objects in lattice QCD simulations. Based on this, we explore the structures resulting from different discretizations and investigate the effect of a very strong electromagnetic field on the QCD vacuum.

Topology in dynamical lattice QCD simulations

Energy Technology Data Exchange (ETDEWEB)

Gruber, Florian

2012-08-20

Lattice simulations of Quantum Chromodynamics (QCD), the quantum field theory which describes the interaction between quarks and gluons, have reached a point were contact to experimental data can be made. The underlying mechanisms, like chiral symmetry breaking or the confinement of quarks, are however still not understood. This thesis focuses on topological structures in the QCD vacuum. Those are not only mathematically interesting but also closely related to chiral symmetry and confinement. We consider methods to identify these objects in lattice QCD simulations. Based on this, we explore the structures resulting from different discretizations and investigate the effect of a very strong electromagnetic field on the QCD vacuum.

A Unified Theory of Non-Ideal Gas Lattice Boltzmann Models

Science.gov (United States)

Luo, Li-Shi

1998-01-01

A non-ideal gas lattice Boltzmann model is directly derived, in an a priori fashion, from the Enskog equation for dense gases. The model is rigorously obtained by a systematic procedure to discretize the Enskog equation (in the presence of an external force) in both phase space and time. The lattice Boltzmann model derived here is thermodynamically consistent and is free of the defects which exist in previous lattice Boltzmann models for non-ideal gases. The existing lattice Boltzmann models for non-ideal gases are analyzed and compared with the model derived here.

Method of storing radioactive rare gas. [gas occupies spaces in the zeolite crystal lattice

Energy Technology Data Exchange (ETDEWEB)

Nagao, H; Miharada, H; Takiguchi, Y; Kanazawa, T; Soya, M

1975-05-15

A method is provided to prevent dispersion of radioactive rare gas atoms by sealing them in a pressurised state within zeolite and thereby confining them in position within the zeolite crystal lattice. Radioactive rare gas is separated from exhaust gas and concentrated by using a low temperature adsorption means or liquefaction distillation means and necessary accessory means, and then it is temporarily stored in a gas holder. When a predetermined quantity of storage is reached, the gas is led to a sealing tank containing zeolite heated to 300 to 400/sup 0/C and held at 3,000 to 4,000 atmospheres, and under this condition radioactive rare gas is brought to occupy the spaces in the zeolite crystal lattice. After equilibrium pressure is reached by the pressure in the tank at that temperature, the gas is cooled in the pressurised state down to room temperature. Subsequently, the rare gas remaining in the tank and duct is recovered by a withdrawal pump into the gas holder. Thereafter, the zeolite with radioactive rare gas sealed in it is taken out from the tank and sealed within a long period storage container, which is then housed in a predetermined place for storage.

Stability of mutualisms in a lattice gas system of two species

Directory of Open Access Journals (Sweden)

Yuanshi Wang

2015-01-01

Full Text Available This article considers mutualisms in a lattice gas system of two species. The species are mutualistic since each one can provide resources to the other. They are also competitive since they compete for empty sites on the same lattice. The mutualisms are assumed to have a saturated response, and the intraspecific competition is considered because of self-limitation. The mutualism system is characterized by differential equations, which are derived from reactions on lattice and are extension of a previous model. Global stability analysis demonstrates that (i When neither species can survive alone, they can coexist if mutualisms between them are strong and population densities are large, which exhibits the Allee effect in obligate mutualism; (ii When one species can survive alone but the other cannot, the latter one will survive if the mutualistic effect from the former is strong. Even if the effect is intermediate, the latter species can survive by strengthening its mutualistic effect on the former and enhancing its population density; (iii When either species can survive alone, a weak mutualism will lead to extinction of one species. When in coexistence, intermediate strength of mutualism is shown to be beneficial under certain parameter range, while over- or under- mutualism is not good. Furthermore, extremely strong/weak mutualism is exhibited to result in extinction of one/both species. While seven typical dynamics are displayed by numerical simulation in a previous work, they are proved in this work and the eighth one is exhibited. Numerical simul ations validate and extend our conclusions.

Lattice Boltzmann simulation of endothermal catalytic reaction in catalyst porous media

International Nuclear Information System (INIS)

Li Xunfeng; Cai Jun; Xin Fang; Huai Xiulan; Guo Jiangfeng

2013-01-01

Gas catalytic reaction in a fixed bed reactor is a general process in chemical industry. The chemical reaction process involves the complex multi-component flow, heat and mass transfer coupling chemical reaction in the catalyst porous structure. The lattice Boltzmann method is developed to simulate the complex process of the surface catalytic reaction in the catalyst porous media. The non-equilibrium extrapolation method is used to treat the boundaries. The porous media is structured by Sierpinski carpet fractal structure. The velocity correction is adopted on the reaction surface. The flow, temperature and concentration fields calculated by the lattice Boltzmann method are compared with those computed by the CFD software. The effects of the inlet velocity, porosity and inlet components ratio on the conversion are also studied. Highlights: ► LBM is developed to simulate the surface catalytic reaction. ► The Sierpinski carpet structure is used to construct the porous media. ► The LBM results are in agreement with the CFD predictions. ► Velocity, temperature and concentration fields are obtained. ► Effects of the velocity, porosity and concentration on conversion are analyzed.

Lattice-Boltzmann simulations of droplet evaporation

KAUST Repository

Ledesma-Aguilar, Rodrigo; Vella, Dominic; Yeomans, Julia M.

2014-01-01

© the Partner Organisations 2014. We study the utility and validity of lattice-Boltzmann (LB) simulations to explore droplet evaporation driven by a concentration gradient. Using a binary-fluid lattice-Boltzmann algorithm based on Cahn-Hilliard dynamics, we study the evaporation of planar films and 3D sessile droplets from smooth solid surfaces. Our results show that LB simulations accurately reproduce the classical regime of quasi-static dynamics. Beyond this limit, we show that the algorithm can be used to explore regimes where the evaporative and diffusive timescales are not widely separated, and to include the effect of boundaries of prescribed driving concentration. We illustrate the method by considering the evaporation of a droplet from a solid surface that is chemically patterned with hydrophilic and hydrophobic stripes. This journal is

Lattice-Boltzmann simulations of droplet evaporation

KAUST Repository

Ledesma-Aguilar, Rodrigo

2014-09-04

© the Partner Organisations 2014. We study the utility and validity of lattice-Boltzmann (LB) simulations to explore droplet evaporation driven by a concentration gradient. Using a binary-fluid lattice-Boltzmann algorithm based on Cahn-Hilliard dynamics, we study the evaporation of planar films and 3D sessile droplets from smooth solid surfaces. Our results show that LB simulations accurately reproduce the classical regime of quasi-static dynamics. Beyond this limit, we show that the algorithm can be used to explore regimes where the evaporative and diffusive timescales are not widely separated, and to include the effect of boundaries of prescribed driving concentration. We illustrate the method by considering the evaporation of a droplet from a solid surface that is chemically patterned with hydrophilic and hydrophobic stripes. This journal is

Long-time tails of the velocity autocorrelation function in 2D and 3D lattice gas cellular automata: a test of mode-coupling theory

NARCIS (Netherlands)

Hoef, M.A. van der; Frenkel, D.

1990-01-01

We report simulations of the velocity autocorrelation function (VACF) of a tagged particle in two- and three-dimensional lattice-gas cellular automata, using a new technique that is about a million times more efficient than the conventional techniques. The simulations clearly show the algebraic

Anisotropic ordering in a two-temperature lattice gas

DEFF Research Database (Denmark)

Szolnoki, Attila; Szabó, György; Mouritsen, Ole G.

1997-01-01

We consider a two-dimensional lattice gas model with repulsive nearest- and next-nearest-neighbor interactions that evolves in time according to anisotropic Kawasaki dynamics. The hopping of particles along the principal directions is governed by two heat baths at different temperatures T-x and T...

Monte Carlo simulations of lattice gauge theories

International Nuclear Information System (INIS)

Forcrand, P. de; Minnesota Univ., Minneapolis, MN

1989-01-01

Lattice gauge simulations are presented in layman's terms. The need for large computer resources is justified. The main aspects of implementations on vector and parallel machines are explained. An overview of state of the art simulations and dedicated hardware projects is presented. 8 refs.; 1 figure; 1 table

High-order dynamic lattice method for seismic simulation in anisotropic media

Science.gov (United States)

Hu, Xiaolin; Jia, Xiaofeng

2018-03-01

The discrete particle-based dynamic lattice method (DLM) offers an approach to simulate elastic wave propagation in anisotropic media by calculating the anisotropic micromechanical interactions between these particles based on the directions of the bonds that connect them in the lattice. To build such a lattice, the media are discretized into particles. This discretization inevitably leads to numerical dispersion. The basic lattice unit used in the original DLM only includes interactions between the central particle and its nearest neighbours; therefore, it represents the first-order form of a particle lattice. The first-order lattice suffers from numerical dispersion compared with other numerical methods, such as high-order finite-difference methods, in terms of seismic wave simulation. Due to its unique way of discretizing the media, the particle-based DLM no longer solves elastic wave equations; this means that one cannot build a high-order DLM by simply creating a high-order discrete operator to better approximate a partial derivative operator. To build a high-order DLM, we carry out a thorough dispersion analysis of the method and discover that by adding more neighbouring particles into the lattice unit, the DLM will yield different spatial accuracy. According to the dispersion analysis, the high-order DLM presented here can adapt the requirement of spatial accuracy for seismic wave simulations. For any given spatial accuracy, we can design a corresponding high-order lattice unit to satisfy the accuracy requirement. Numerical tests show that the high-order DLM improves the accuracy of elastic wave simulation in anisotropic media.

Degenerate Fermi gas in a combined harmonic-lattice potential

International Nuclear Information System (INIS)

Blakie, P. B.; Bezett, A.; Buonsante, P.

2007-01-01

In this paper we derive an analytic approximation to the density of states for atoms in a combined optical lattice and harmonic trap potential as used in current experiments with quantum degenerate gases. We compare this analytic density of states to numerical solutions and demonstrate its validity regime. Our work explicitly considers the role of higher bands and when they are important in quantitative analysis of this system. Applying our density of states to a degenerate Fermi gas, we consider how adiabatic loading from a harmonic trap into the combined harmonic-lattice potential affects the degeneracy temperature. Our results suggest that occupation of excited bands during loading should lead to more favorable conditions for realizing degenerate Fermi gases in optical lattices

Local lattice-gas model for immiscible fluids

International Nuclear Information System (INIS)

Chen, S.; Doolen, G.D.; Eggert, K.; Grunau, D.; Loh, E.Y.

1991-01-01

We present a lattice-gas model for two-dimensional immiscible fluid flows with surface tension that uses strictly local collision rules. Instead of using a local total color flux as Somers and Rem [Physica D 47, 39 (1991)], we use local colored holes to be the memory of particles of the same color. Interactions between walls and fluids are included that produce arbitrary contact angles

Anomalous diffusion in a lattice-gas wind-tree model

International Nuclear Information System (INIS)

Kong, X.P.; Cohen, E.G.D.

1989-01-01

Two new strictly deterministic lattice-gas automata derived from Ehrenfest's wind-tree model are studied. While in one model normal diffusion occurs, the other model exhibits abnormal diffusion in that the distribution function of the displacements of the wind particle is non-Gaussian, but its second moment, the mean-square displacement, is proportional to the time, so that a diffusion coefficient can be defined. A connection with the percolation problem and a self-avoiding random walk for the case in which the lattice is completely covered with trees is discussed

Large scale simulation of liquid water transport in a gas diffusion layer of polymer electrolyte membrane fuel cells using the lattice Boltzmann method

Science.gov (United States)

Sakaida, Satoshi; Tabe, Yutaka; Chikahisa, Takemi

2017-09-01

A method for the large-scale simulation with the lattice Boltzmann method (LBM) is proposed for liquid water movement in a gas diffusion layer (GDL) of polymer electrolyte membrane fuel cells. The LBM is able to analyze two-phase flows in complex structures, however the simulation domain is limited due to heavy computational loads. This study investigates a variety means to reduce computational loads and increase the simulation areas. One is applying an LBM treating two-phases as having the same density, together with keeping numerical stability with large time steps. The applicability of this approach is confirmed by comparing the results with rigorous simulations using actual density. The second is establishing the maximum limit of the Capillary number that maintains flow patterns similar to the precise simulation; this is attempted as the computational load is inversely proportional to the Capillary number. The results show that the Capillary number can be increased to 3.0 × 10-3, where the actual operation corresponds to Ca = 10-5∼10-8. The limit is also investigated experimentally using an enlarged scale model satisfying similarity conditions for the flow. Finally, a demonstration is made of the effects of pore uniformity in GDL as an example of a large-scale simulation covering a channel.

Preparing a highly degenerate Fermi gas in an optical lattice

International Nuclear Information System (INIS)

Williams, J. R.; Huckans, J. H.; Stites, R. W.; Hazlett, E. L.; O'Hara, K. M.

2010-01-01

We propose a method to prepare fermionic atoms in a three-dimensional optical lattice at unprecedentedly low temperatures and uniform filling factors. The process involves adiabatic loading of degenerate atoms into multiple energy bands of an optical lattice followed by a filtering stage whereby atoms from all but the lowest band are removed. Of critical importance is the use of a nonharmonic trapping potential to provide external confinement for the atoms. For realistic experimental parameters, this procedure will produce a Fermi gas in a lattice with a reduced temperature T/T F ∼0.003 and an entropy per particle of s∼0.02 k B .

Lattice Boltzmann simulation of flow across a staggered tube bundle array

Energy Technology Data Exchange (ETDEWEB)

Tiftikçi, A.; Kocar, C., E-mail: ckocar@hacettepe.edu.tr

2016-04-15

Highlights: • Large eddy simulation of the cross-flow in a staggered tube bundle array in 3D was made. • LBM and FVM are used separately as numerical solvers and the results of each method compared with experimental data. • Effect of lattice model is studied for tube bundle flow. • Filter size effects, mesh size effects are studied for VLES turbulence model. - Abstract: The decision on the magnitude of the grid size is a crucial problem in large eddy simulations. Finer mesh requires excessive memory and causes long simulation time. Large eddy simulation model becomes inefficient when the extent of the flow geometry to be simulated with the lattice-Boltzmann method is large. Thus, in this study, it is proposed to investigate the capabilities of three turbulence models, namely, very large eddy simulation, Van Driest and Smagorinsky–Lilly. As a test case, a staggered tube bundle flow experiment is used for the validation and comparison purposes. Sensitivity analyses (including mesh and filter size) have been made. Furthermore, the effect of lattice model is investigated and it is showed that the D3Q27 and D3Q19 models do not differ significantly in lattice-Boltzmann method for this type of flow. The results of turbulence model comparisons for staggered tube bundle flow showed that very large eddy simulation is superior at low resolution. This paper might be considered as a good validation of the lattice-Boltzmann method. In turbulent flow conditions, the code successfully captures the velocity and stress profiles even if the flow is quite complicated.

arXiv Stochastic locality and master-field simulations of very large lattices

CERN Document Server

Lüscher, Martin

2018-01-01

In lattice QCD and other field theories with a mass gap, the field variables in distant regions of a physically large lattice are only weakly correlated. Accurate stochastic estimates of the expectation values of local observables may therefore be obtained from a single representative field. Such master-field simulations potentially allow very large lattices to be simulated, but require various conceptual and technical issues to be addressed. In this talk, an introduction to the subject is provided and some encouraging results of master-field simulations of the SU(3) gauge theory are reported.

Aspects of confinement in QCD from lattice simulations

International Nuclear Information System (INIS)

Spielmann, Daniel

2011-01-01

We study confinement in quantum chromodynamics via numerical simulations in the framework of lattice gauge theory. In Landau gauge, the mechanism of confinement is related to the infrared behavior of the ghost and gluon propagators via the Gribov-Zwanziger and Kugo- Ojima scenarios. These scenarios entail a scaling behavior. Functional methods in the continuum allow both for this behavior and for decoupling solutions, while lattice simulations in three and four dimensions yield only the latter. A possible explanation for this mismatch is based on limitations of standard lattice gauge fixing methods. Hence, we investigate a number of alternative gauge fixing algorithms in pure SU(2) gauge theory in two, three and four dimensions. We find that stochastic quantization yields an infrared behavior of the propagators in agreement with the results of standard procedures, even though the Faddeev-Popov operator spectrum indicates some different properties. In the strong-coupling limit, our results challenge the standard picture. In particular, we find in a non-perturbative completion of Landau gauge an enormous effect of the Gribov ambiguity. It entails that no subset of infrared solutions can be excluded yet. Moreover, we study the gluon propagator with free boundary conditions. On large lattices, the results mostly show the standard behavior. We also examine non-periodic gauge transformations. Furthermore, we analyze two topics related to the phase diagram of QCD. First, we explore the sign problem for fermions on the lattice by simulating the three-dimensional Thirring model with a complex Langevin equation. The algorithm succeeds in yielding a 'Silver Blaze' behavior of observables, but it does not reliably describe the onset to a phase with non-zero density. Second, we determine properties of the deconfinement phase transition of pure SU(2) gauge theory in 2+1 dimensions, like the critical temperature, by means of the gluon propagator in Landau gauge. (orig.)

Aspects of confinement in QCD from lattice simulations

Energy Technology Data Exchange (ETDEWEB)

Spielmann, Daniel

2011-01-12

We study confinement in quantum chromodynamics via numerical simulations in the framework of lattice gauge theory. In Landau gauge, the mechanism of confinement is related to the infrared behavior of the ghost and gluon propagators via the Gribov-Zwanziger and Kugo- Ojima scenarios. These scenarios entail a scaling behavior. Functional methods in the continuum allow both for this behavior and for decoupling solutions, while lattice simulations in three and four dimensions yield only the latter. A possible explanation for this mismatch is based on limitations of standard lattice gauge fixing methods. Hence, we investigate a number of alternative gauge fixing algorithms in pure SU(2) gauge theory in two, three and four dimensions. We find that stochastic quantization yields an infrared behavior of the propagators in agreement with the results of standard procedures, even though the Faddeev-Popov operator spectrum indicates some different properties. In the strong-coupling limit, our results challenge the standard picture. In particular, we find in a non-perturbative completion of Landau gauge an enormous effect of the Gribov ambiguity. It entails that no subset of infrared solutions can be excluded yet. Moreover, we study the gluon propagator with free boundary conditions. On large lattices, the results mostly show the standard behavior. We also examine non-periodic gauge transformations. Furthermore, we analyze two topics related to the phase diagram of QCD. First, we explore the sign problem for fermions on the lattice by simulating the three-dimensional Thirring model with a complex Langevin equation. The algorithm succeeds in yielding a 'Silver Blaze' behavior of observables, but it does not reliably describe the onset to a phase with non-zero density. Second, we determine properties of the deconfinement phase transition of pure SU(2) gauge theory in 2+1 dimensions, like the critical temperature, by means of the gluon propagator in Landau gauge. (orig.)

Fermionic Collective Excitations in a Lattice Gas of Rydberg Atoms

International Nuclear Information System (INIS)

Olmos, B.; Gonzalez-Ferez, R.; Lesanovsky, I.

2009-01-01

We investigate the many-body quantum states of a laser-driven gas of Rydberg atoms confined to a large spacing ring lattice. If the laser driving is much stronger than the van der Waals interaction among the Rydberg atoms, these many-body states are collective fermionic excitations. The first excited state is a spin wave that extends over the entire lattice. We demonstrate that our system permits us to study fermions in the presence of disorder although no external atomic motion takes place. We analyze how this disorder influences the excitation properties of the fermionic states. Our work shows a route towards the creation of complex many-particle states with atoms in lattices.

Simulations to study the static polarization limit for RHIC lattice

Science.gov (United States)

Duan, Zhe; Qin, Qing

2016-01-01

A study of spin dynamics based on simulations with the Polymorphic Tracking Code (PTC) is reported, exploring the dependence of the static polarization limit on various beam parameters and lattice settings for a practical RHIC lattice. It is shown that the behavior of the static polarization limit is dominantly affected by the vertical motion, while the effect of beam-beam interaction is small. In addition, the “nonresonant beam polarization” observed and studied in the lattice-independent model is also observed in this lattice-dependent model. Therefore, this simulation study gives insights of polarization evolution at fixed beam energies, that are not available in simple spin tracking. Supported by the U.S. Department of Energy (DE-AC02-98CH10886), Hundred-Talent Program (Chinese Academy of Sciences), and National Natural Science Foundation of China (11105164)

Comparative study of the discrete velocity and lattice Boltzmann methods for rarefied gas flows through irregular channels.

Science.gov (United States)

Su, Wei; Lindsay, Scott; Liu, Haihu; Wu, Lei

2017-08-01

Rooted from the gas kinetics, the lattice Boltzmann method (LBM) is a powerful tool in modeling hydrodynamics. In the past decade, it has been extended to simulate rarefied gas flows beyond the Navier-Stokes level, either by using the high-order Gauss-Hermite quadrature, or by introducing the relaxation time that is a function of the gas-wall distance. While the former method, with a limited number of discrete velocities (e.g., D2Q36), is accurate up to the early transition flow regime, the latter method (especially the multiple relaxation time (MRT) LBM), with the same discrete velocities as those used in simulating hydrodynamics (i.e., D2Q9), is accurate up to the free-molecular flow regime in the planar Poiseuille flow. This is quite astonishing in the sense that less discrete velocities are more accurate. In this paper, by solving the Bhatnagar-Gross-Krook kinetic equation accurately via the discrete velocity method, we find that the high-order Gauss-Hermite quadrature cannot describe the large variation in the velocity distribution function when the rarefaction effect is strong, but the MRT-LBM can capture the flow velocity well because it is equivalent to solving the Navier-Stokes equations with an effective shear viscosity. Since the MRT-LBM has only been validated in simple channel flows, and for complex geometries it is difficult to find the effective viscosity, it is necessary to assess its performance for the simulation of rarefied gas flows. Our numerical simulations based on the accurate discrete velocity method suggest that the accuracy of the MRT-LBM is reduced significantly in the simulation of rarefied gas flows through the rough surface and porous media. Our simulation results could serve as benchmarking cases for future development of the LBM for modeling and simulation of rarefied gas flows in complex geometries.

Comparative study of the discrete velocity and lattice Boltzmann methods for rarefied gas flows through irregular channels

Science.gov (United States)

Su, Wei; Lindsay, Scott; Liu, Haihu; Wu, Lei

2017-08-01

Rooted from the gas kinetics, the lattice Boltzmann method (LBM) is a powerful tool in modeling hydrodynamics. In the past decade, it has been extended to simulate rarefied gas flows beyond the Navier-Stokes level, either by using the high-order Gauss-Hermite quadrature, or by introducing the relaxation time that is a function of the gas-wall distance. While the former method, with a limited number of discrete velocities (e.g., D2Q36), is accurate up to the early transition flow regime, the latter method (especially the multiple relaxation time (MRT) LBM), with the same discrete velocities as those used in simulating hydrodynamics (i.e., D2Q9), is accurate up to the free-molecular flow regime in the planar Poiseuille flow. This is quite astonishing in the sense that less discrete velocities are more accurate. In this paper, by solving the Bhatnagar-Gross-Krook kinetic equation accurately via the discrete velocity method, we find that the high-order Gauss-Hermite quadrature cannot describe the large variation in the velocity distribution function when the rarefaction effect is strong, but the MRT-LBM can capture the flow velocity well because it is equivalent to solving the Navier-Stokes equations with an effective shear viscosity. Since the MRT-LBM has only been validated in simple channel flows, and for complex geometries it is difficult to find the effective viscosity, it is necessary to assess its performance for the simulation of rarefied gas flows. Our numerical simulations based on the accurate discrete velocity method suggest that the accuracy of the MRT-LBM is reduced significantly in the simulation of rarefied gas flows through the rough surface and porous media. Our simulation results could serve as benchmarking cases for future development of the LBM for modeling and simulation of rarefied gas flows in complex geometries.

Numerical modeling of carrier gas flow in atomic layer deposition vacuum reactor: A comparative study of lattice Boltzmann models

International Nuclear Information System (INIS)

Pan, Dongqing; Chien Jen, Tien; Li, Tao; Yuan, Chris

2014-01-01

This paper characterizes the carrier gas flow in the atomic layer deposition (ALD) vacuum reactor by introducing Lattice Boltzmann Method (LBM) to the ALD simulation through a comparative study of two LBM models. Numerical models of gas flow are constructed and implemented in two-dimensional geometry based on lattice Bhatnagar–Gross–Krook (LBGK)-D2Q9 model and two-relaxation-time (TRT) model. Both incompressible and compressible scenarios are simulated and the two models are compared in the aspects of flow features, stability, and efficiency. Our simulation outcome reveals that, for our specific ALD vacuum reactor, TRT model generates better steady laminar flow features all over the domain with better stability and reliability than LBGK-D2Q9 model especially when considering the compressible effects of the gas flow. The LBM-TRT is verified indirectly by comparing the numerical result with conventional continuum-based computational fluid dynamics solvers, and it shows very good agreement with these conventional methods. The velocity field of carrier gas flow through ALD vacuum reactor was characterized by LBM-TRT model finally. The flow in ALD is in a laminar steady state with velocity concentrated at the corners and around the wafer. The effects of flow fields on precursor distributions, surface absorptions, and surface reactions are discussed in detail. Steady and evenly distributed velocity field contribute to higher precursor concentration near the wafer and relatively lower particle velocities help to achieve better surface adsorption and deposition. The ALD reactor geometry needs to be considered carefully if a steady and laminar flow field around the wafer and better surface deposition are desired

Numerical modeling of carrier gas flow in atomic layer deposition vacuum reactor: A comparative study of lattice Boltzmann models

Energy Technology Data Exchange (ETDEWEB)

Pan, Dongqing; Chien Jen, Tien [Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201 (United States); Li, Tao [School of Mechanical Engineering, Dalian University of Technology, Dalian 116024 (China); Yuan, Chris, E-mail: cyuan@uwm.edu [Department of Mechanical Engineering, University of Wisconsin-Milwaukee, 3200 North Cramer Street, Milwaukee, Wisconsin 53211 (United States)

2014-01-15

This paper characterizes the carrier gas flow in the atomic layer deposition (ALD) vacuum reactor by introducing Lattice Boltzmann Method (LBM) to the ALD simulation through a comparative study of two LBM models. Numerical models of gas flow are constructed and implemented in two-dimensional geometry based on lattice Bhatnagar–Gross–Krook (LBGK)-D2Q9 model and two-relaxation-time (TRT) model. Both incompressible and compressible scenarios are simulated and the two models are compared in the aspects of flow features, stability, and efficiency. Our simulation outcome reveals that, for our specific ALD vacuum reactor, TRT model generates better steady laminar flow features all over the domain with better stability and reliability than LBGK-D2Q9 model especially when considering the compressible effects of the gas flow. The LBM-TRT is verified indirectly by comparing the numerical result with conventional continuum-based computational fluid dynamics solvers, and it shows very good agreement with these conventional methods. The velocity field of carrier gas flow through ALD vacuum reactor was characterized by LBM-TRT model finally. The flow in ALD is in a laminar steady state with velocity concentrated at the corners and around the wafer. The effects of flow fields on precursor distributions, surface absorptions, and surface reactions are discussed in detail. Steady and evenly distributed velocity field contribute to higher precursor concentration near the wafer and relatively lower particle velocities help to achieve better surface adsorption and deposition. The ALD reactor geometry needs to be considered carefully if a steady and laminar flow field around the wafer and better surface deposition are desired.

Direct numerical simulation of turbulent pipe flow using the lattice Boltzmann method

Science.gov (United States)

Peng, Cheng; Geneva, Nicholas; Guo, Zhaoli; Wang, Lian-Ping

2018-03-01

In this paper, we present a first direct numerical simulation (DNS) of a turbulent pipe flow using the mesoscopic lattice Boltzmann method (LBM) on both a D3Q19 lattice grid and a D3Q27 lattice grid. DNS of turbulent pipe flows using LBM has never been reported previously, perhaps due to inaccuracy and numerical stability associated with the previous implementations of LBM in the presence of a curved solid surface. In fact, it was even speculated that the D3Q19 lattice might be inappropriate as a DNS tool for turbulent pipe flows. In this paper, we show, through careful implementation, accurate turbulent statistics can be obtained using both D3Q19 and D3Q27 lattice grids. In the simulation with D3Q19 lattice, a few problems related to the numerical stability of the simulation are exposed. Discussions and solutions for those problems are provided. The simulation with D3Q27 lattice, on the other hand, is found to be more stable than its D3Q19 counterpart. The resulting turbulent flow statistics at a friction Reynolds number of Reτ = 180 are compared systematically with both published experimental and other DNS results based on solving the Navier-Stokes equations. The comparisons cover the mean-flow profile, the r.m.s. velocity and vorticity profiles, the mean and r.m.s. pressure profiles, the velocity skewness and flatness, and spatial correlations and energy spectra of velocity and vorticity. Overall, we conclude that both D3Q19 and D3Q27 simulations yield accurate turbulent flow statistics. The use of the D3Q27 lattice is shown to suppress the weak secondary flow pattern in the mean flow due to numerical artifacts.

Exact results on the one-dimensional Potts lattice gas

International Nuclear Information System (INIS)

Riera, R.; Chaves, C.M.G.F.

1982-12-01

An exact calculation of the Potts Lattice Gas in one dimension is presented. Close to T=O 0 K, the uniform susceptibility presents an essencial singularity, when the excharge parameter is positive, and a power law behaviour with critical exponent γ=1, when this parameter is negative. (Author) [pt

Exact results on the one-dimensional Potts lattice gas

International Nuclear Information System (INIS)

Riera, R.; Chaves, C.M.G.F.

1983-01-01

An exact calculation of the Potts Lattice Gas in one dimension is presented. Close to T=O 0 K, the uniform susceptibility presents an essential singularity, when the exchange parameter is positive, and a power law behaviour with critical exponent γ=1, when this parameter is negative. (Author) [pt

From lattice gases to polymers

NARCIS (Netherlands)

Frenkel, D.

1990-01-01

The modification of a technique that was developed to study time correlations in lattice-gas cellular automata to facilitate the numerical simulation of chain molecules is described. As an example, the calculation of the excess chemical potential of an ideal polymer in a dense colloidal

Study of Drying Shrinkage Cracking by Lattice Gas Automaton and Environmental Scanning Electron Microscope

NARCIS (Netherlands)

Van Mier, J.G.M.; Jankovic, D.

2005-01-01

Numerical modeling of moisture flow, drying shrinkage and crack phenomena in cement microstructure, by coupling a Lattice Gas Automaton and a Lattice Fracture Model, highlighted the importance of a shrinkage coefficient (?sh) as the most significant parameter for achieving realistic numerical

Monte Carlo simulation of lattice bosons in three dimensions

International Nuclear Information System (INIS)

Blaer, A.; Han, J.

1992-01-01

We present an algorithm for calculating the thermodynamic properties of a system of nonrelativistic bosons on a three-dimensional spatial lattice. The method, which maps the three-dimensional quantum system onto a four-dimensional classical system, uses Monte Carlo sampling of configurations in either the canonical or the grand canonical ensemble. Our procedure is applicable to any system of lattice bosons with arbitrary short-range interactions. We test the algorithm by computing the temperature dependence of the energy, the heat capacity, and the condensate fraction of the free Bose gas

Critical slowing down and error analysis in lattice QCD simulations

Energy Technology Data Exchange (ETDEWEB)

Virotta, Francesco

2012-02-21

In this work we investigate the critical slowing down of lattice QCD simulations. We perform a preliminary study in the quenched approximation where we find that our estimate of the exponential auto-correlation time scales as {tau}{sub exp}(a){proportional_to}a{sup -5}, where a is the lattice spacing. In unquenched simulations with O(a) improved Wilson fermions we do not obtain a scaling law but find results compatible with the behavior that we find in the pure gauge theory. The discussion is supported by a large set of ensembles both in pure gauge and in the theory with two degenerate sea quarks. We have moreover investigated the effect of slow algorithmic modes in the error analysis of the expectation value of typical lattice QCD observables (hadronic matrix elements and masses). In the context of simulations affected by slow modes we propose and test a method to obtain reliable estimates of statistical errors. The method is supposed to help in the typical algorithmic setup of lattice QCD, namely when the total statistics collected is of O(10){tau}{sub exp}. This is the typical case when simulating close to the continuum limit where the computational costs for producing two independent data points can be extremely large. We finally discuss the scale setting in N{sub f}=2 simulations using the Kaon decay constant f{sub K} as physical input. The method is explained together with a thorough discussion of the error analysis employed. A description of the publicly available code used for the error analysis is included.

Critical slowing down and error analysis in lattice QCD simulations

International Nuclear Information System (INIS)

Virotta, Francesco

2012-01-01

In this work we investigate the critical slowing down of lattice QCD simulations. We perform a preliminary study in the quenched approximation where we find that our estimate of the exponential auto-correlation time scales as τ exp (a)∝a -5 , where a is the lattice spacing. In unquenched simulations with O(a) improved Wilson fermions we do not obtain a scaling law but find results compatible with the behavior that we find in the pure gauge theory. The discussion is supported by a large set of ensembles both in pure gauge and in the theory with two degenerate sea quarks. We have moreover investigated the effect of slow algorithmic modes in the error analysis of the expectation value of typical lattice QCD observables (hadronic matrix elements and masses). In the context of simulations affected by slow modes we propose and test a method to obtain reliable estimates of statistical errors. The method is supposed to help in the typical algorithmic setup of lattice QCD, namely when the total statistics collected is of O(10)τ exp . This is the typical case when simulating close to the continuum limit where the computational costs for producing two independent data points can be extremely large. We finally discuss the scale setting in N f =2 simulations using the Kaon decay constant f K as physical input. The method is explained together with a thorough discussion of the error analysis employed. A description of the publicly available code used for the error analysis is included.

Axion cosmology, lattice QCD and the dilute instanton gas

International Nuclear Information System (INIS)

Borsanyi, S.; Fodor, Z.; Mages, S.W.; Nogradi, D.; Szabo, K.K.

2015-08-01

Axions are one of the most attractive dark matter candidates. The evolution of their number density in the early universe can be determined by calculating the topological susceptibility χ(T) of QCD as a function of the temperature. Lattice QCD provides an ab initio technique to carry out such a calculation. A full result needs two ingredients: physical quark masses and a controlled continuum extrapolation from non-vanishing to zero lattice spacings. We determine χ(T) in the quenched framework (infinitely large quark masses) and extrapolate its values to the continuum limit. The results are compared with the prediction of the dilute instanton gas approximation (DIGA). A nice agreement is found for the temperature dependence, whereas the overall normalization of the DIGA result still differs from the non-perturbative continuum extrapolated lattice results by a factor of order ten. We discuss the consequences of our findings for the prediction of the amount of axion dark matter.

Application of the lattice Boltzmann method for simulation of the mold filling process in the casting industry

Science.gov (United States)

Szucki, Michal; Suchy, J. S.; Lelito, J.; Malinowski, P.; Sobczyk, J.

2017-12-01

The aim of this work is the development of the lattice Boltzmann model for simulation of the mold filling process. The authors present a simplified approach to the modeling of liquid metal-gas flows with particular emphasis on the interactions between these phases. The boundary condition for momentum transfer of the moving free surface to the gaseous phase is shown. Simultaneously, the method for modeling influence of gas back pressure on a position and shape of the interfacial boundary is explained in details. The problem of the lattice Boltzmann method (LBM) stability is also analyzed. Since large differences in viscosity of both fluids are a source of the model instability, the so-called fractional step (FS) method allowing to improve the computation stability is applied. The presented solution is verified on the bases of the available reference data and the results of experiments. It is shown that the model describes properly such effects as: gas bubbles formation and air back pressure, accompanying liquid-gas flows in the casting mold. At the same time the proposed approach is easy to be implemented and characterized by a lower demand of operating memory as compared to typical LBM models of two-phase flows.

Cluster evolution and critical cluster sizes for the square and triangular lattice Ising models using lattice animals and Monte Carlo simulations

NARCIS (Netherlands)

Eising, G.; Kooi, B. J.

2012-01-01

Growth and decay of clusters at temperatures below T-c have been studied for a two-dimensional Ising model for both square and triangular lattices using Monte Carlo (MC) simulations and the enumeration of lattice animals. For the lattice animals, all unique cluster configurations with their internal

Lattice-Boltzmann simulation of the sedimentation of charged disks

NARCIS (Netherlands)

Capuani, F.; Pagonabarraga, I.; Frenkel, D.

2006-01-01

We report a series of lattice-Boltzmann simulations of the sedimentation velocity of charged disks. In these simulations, we explicitly account for the hydrodynamic and electrostatic forces on disks and on their electrical double layer. By comparing our results with those for spheres with equal

Simulation of plume dynamics by the Lattice Boltzmann Method

Science.gov (United States)

Mora, Peter; Yuen, David A.

2017-09-01

The Lattice Boltzmann Method (LBM) is a semi-microscopic method to simulate fluid mechanics by modelling distributions of particles moving and colliding on a lattice. We present 2-D simulations using the LBM of a fluid in a rectangular box being heated from below, and cooled from above, with a Rayleigh of Ra = 108, similar to current estimates of the Earth's mantle, and a Prandtl number of 5000. At this Prandtl number, the flow is found to be in the non-inertial regime where the inertial terms denoted I ≪ 1. Hence, the simulations presented lie within the regime of relevance for geodynamical problems. We obtain narrow upwelling plumes with mushroom heads and chutes of downwelling fluid as expected of a flow in the non-inertial regime. The method developed demonstrates that the LBM has great potential for simulating thermal convection and plume dynamics relevant to geodynamics, albeit with some limitations.

Diffusion in heterogeneous lattices

Czech Academy of Sciences Publication Activity Database

Tarasenko, Alexander; Jastrabík, Lubomír

2010-01-01

Roč. 256, č. 17 (2010), s. 5137-5144 ISSN 0169-4332 R&D Projects: GA AV ČR KAN301370701; GA MŠk(CZ) 1M06002 Institutional research plan: CEZ:AV0Z10100522 Keywords : lattice- gas systems * diffusion * Monte Carlo simulations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.795, year: 2010

Numerical Analysis of Moisture Flow and Concrete Cracking by means of Lattice Type Models

NARCIS (Netherlands)

Jankovic, D.; Küntz, M.; Van Mier, J.G.M.

2001-01-01

Modelling of fluid-flow and the resulting effects on shrinkage and microcracking by means of a combination of two lattice models are presented. For the moisture transport, a Lattice Gas Automaton (LGA) is adopted since it can effectively model moisture loss, whereas for cracking simulation a Lattice

Hydraulic fracture conductivity: effects of rod-shaped proppant from lattice-Boltzmann simulations and lab tests

Science.gov (United States)

Osiptsov, Andrei A.

2017-06-01

The goal of this study is to evaluate the conductivity of random close packings of non-spherical, rod-shaped proppant particles under the closure stress using numerical simulation and lab tests, with application to the conductivity of hydraulic fractures created in subterranean formation to stimulate production from oil and gas reservoirs. Numerical simulations of a steady viscous flow through proppant packs are carried out using the lattice Boltzmann method for the Darcy flow regime. The particle packings were generated numerically using the sequential deposition method. The simulations are conducted for packings of spheres, ellipsoids, cylinders, and mixtures of spheres with cylinders at various volumetric concentrations. It is demonstrated that cylinders provide the highest permeability among the proppants studied. The dependence of the nondimensional permeability (scaled by the equivalent particle radius squared) on porosity obtained numerically is well approximated by the power-law function: K /Rv2 = 0.204ϕ4.58 in a wide range of porosity: 0.3 ≤ ϕ ≤ 0.7. Lattice-Boltzmann simulations are cross-verified against finite-volume simulations using Navier-Stokes equations for inertial flow regime. Correlations for the normalized beta-factor as a function of porosity and normalized permeability are presented as well. These formulae are in a good agreement with the experimental measurements (including packings of rod-shaped particles) and existing laboratory data, available in the porosity range 0.3 ≤ ϕ ≤ 0.5. Comparison with correlations by other authors is also given.

Ultracold atoms in one-dimensional optical lattices approaching the Tonks-Girardeau regime

International Nuclear Information System (INIS)

Pollet, L.; Rombouts, S.M.A.; Denteneer, P.J. H.

2004-01-01

Recent experiments on ultracold atomic alkali gases in a one-dimensional optical lattice have demonstrated the transition from a gas of soft-core bosons to a Tonks-Girardeau gas in the hard-core limit, where one-dimensional bosons behave like fermions in many respects. We have studied the underlying many-body physics through numerical simulations which accommodate both the soft-core and hard-core limits in one single framework. We find that the Tonks-Girardeau gas is reached only at the strongest optical lattice potentials. Results for slightly higher densities, where the gas develops a Mott-like phase already at weaker optical lattice potentials, show that these Mott-like short-range correlations do not enhance the convergence to the hard-core limit

Microcanonical and hybrid simulations of lattice quantum chromodynamics with dynamical fermions

International Nuclear Information System (INIS)

Sinclair, D.K.

1986-10-01

Lattice QCD is simulated using Microcanonical and Hybrid (Micro-canonical/Langevin) methods to facilitate the inclusion of dynamical fermions (quarks). We report on simulations with 4 flavors of light dynamical quarks on a 10 3 x 6 lattice to study the finite temperature deconfinement/chiral transition which should be observable in relativistic heavy ion collisions, as a function of quark mass. A first order transition is observed at large mass, weakens at intermediate mass and strengthens for very small quark mass

Cluster computing for lattice QCD simulations

International Nuclear Information System (INIS)

Coddington, P.D.; Williams, A.G.

2000-01-01

Full text: Simulations of lattice quantum chromodynamics (QCD) require enormous amounts of compute power. In the past, this has usually involved sharing time on large, expensive machines at supercomputing centres. Over the past few years, clusters of networked computers have become very popular as a low-cost alternative to traditional supercomputers. The dramatic improvements in performance (and more importantly, the ratio of price/performance) of commodity PCs, workstations, and networks have made clusters of off-the-shelf computers an attractive option for low-cost, high-performance computing. A major advantage of clusters is that since they can have any number of processors, they can be purchased using any sized budget, allowing research groups to install a cluster for their own dedicated use, and to scale up to more processors if additional funds become available. Clusters are now being built for high-energy physics simulations. Wuppertal has recently installed ALiCE, a cluster of 128 Alpha workstations running Linux, with a peak performance of 158 G flops. The Jefferson Laboratory in the US has a 16 node Alpha cluster and plans to upgrade to a 256 processor machine. In Australia, several large clusters have recently been installed. Swinburne University of Technology has a cluster of 64 Compaq Alpha workstations used for astrophysics simulations. Early this year our DHPC group constructed a cluster of 116 dual Pentium PCs (i.e. 232 processors) connected by a Fast Ethernet network, which is used by chemists at Adelaide University and Flinders University to run computational chemistry codes. The Australian National University has recently installed a similar PC cluster with 192 processors. The Centre for the Subatomic Structure of Matter (CSSM) undertakes large-scale high-energy physics calculations, mainly lattice QCD simulations. The choice of the computer and network hardware for a cluster depends on the particular applications to be run on the machine. Our

Lattice-enabled nuclear reactions in the nickel and hydrogen gas system

International Nuclear Information System (INIS)

Nagel, David J.

2015-01-01

Thousands of lattice-enabled nuclear reaction (LENR) experiments involving electrochemical loading of deuterium into palladium have been conducted and reported in hundreds of papers. But, it appears that the first commercial LENR power generators will employ gas loading of hydrogen onto nickel. This article reviews the scientific base for LENR in the gas-loaded Ni-H system, and some of the tests of pre-commercial prototype generators based on this combination. (author)

Second order bounce back boundary condition for the lattice Boltzmann fluid simulation

International Nuclear Information System (INIS)

Kim, In Chan

2000-01-01

A new bounce back boundary method of the second order in error is proposed for the lattice Boltzmann fluid simulation. This new method can be used for the arbitrarily irregular lattice geometry of a non-slip boundary. The traditional bounce back boundary condition for the lattice Boltzmann simulation is of the first order in error. Since the lattice Boltzmann method is the second order scheme by itself, a boundary technique of the second order has been desired to replace the first order bounce back method. This study shows that, contrary to the common belief that the bounce back boundary condition is unilaterally of the first order, the second order bounce back boundary condition can be realized. This study also shows that there exists a generalized bounce back technique that can be characterized by a single interpolation parameter. The second order bounce back method can be obtained by proper selection of this parameter in accordance with the detailed lattice geometry of the boundary. For an illustrative purpose, the transient Couette and the plane Poiseuille flows are solved by the lattice Boltzmann simulation with various boundary conditions. The results show that the generalized bounce back method yields the second order behavior in the error of the solution, provided that the interpolation parameter is properly selected. Coupled with its intuitive nature and the ease of implementation, the bounce back method can be as good as any second order boundary method

Lattice-Boltzmann Method with Dynamic Grid Refinement for Simulating Particle Deposition on a Single Fibre

Directory of Open Access Journals (Sweden)

Helmut Schomburg

2013-03-01

Full Text Available In this work a numerical approach to predict the deposition behaviour of nano-scale particles on the surface of a single fibre by resolving the resulting dendrite-like particle structures in detail is presented. The gas flow simulation is carried out by a two-dimensional Lattice-Boltzmann method, which is coupled with a Lagrangian approach for the particle motion. To decrease calculation time and system requirements the Lattice-Boltzmann model is extended to allow for local grid refinement. Because of the a priori unknown location of deposition, the simulation procedure starts on a coarse mesh which is then locally refined in a fully adaptive way in regions of accumulated particles. After each deposition the fluid flow is recalculated in order to resolve the coupling of the flow with the growing particle structures correctly. For the purpose of avoiding unphysical blocking of flow by growing particle dendrites the Lattice-Boltzmann method is extended to permeable cells in these regions using the Brinkmann equation. This extended deposition model is compared to simpler approaches, where the deposit has no retroaction on the flow or is treated as a solid structure. It is clear that the permeable model is most realistic and allows considering the particle deposition on a fibre as two-dimensional problem. Comprehensive simulations were conducted for analysing the importance of different parameters, i.e. free-stream velocity and particle diameter on the deposit structure. The results of this sensitivity analysis agree qualitatively well with former published numerical and experimental results. Finally the structure of the particle deposit was quantitatively characterised by using a modified fractal dimension.

A lattice-gas model of the ion current across the solid interface: fast-ion conductor - intercalate

International Nuclear Information System (INIS)

Nachev, I.; Balkanski, M.

1994-12-01

The transport of Lithium ions across the material interface: fast-ion conducting glass - intercalate is simulated by a non-trivial lattice-gas model. The model takes explicitly into account the influence of the Coulomb correlations, the site-blocking effect and the boundary conditions on the ion kinetics. Potential device applications of the model are pointed out by computing the current density of Lithium ions for material parameters of the real interface: doped ternary borate glass - Indium Selenide, which constitute the electrolyte and the cathode, respectively, of a thin-film microbattery with improved performance. (author). 10 refs, 4 figs

Numerical simulation of flow behavior in tight lattice rod bundle

International Nuclear Information System (INIS)

Yu Yiqi; Yang Yanhua; Gu Hanyang; Cheng Xu; Song Xiaoming; Wang Xiaojun

2009-01-01

The Numerical investigation is performed on the air turbulent flow in triangular rod bundle array. Based on the experimental data, the eddy viscosity turbulent model and the Reynold stress turbulent model are evaluated to simulate the flow behavior in the tight lattice. The results show that SSG Reynolds Stress Model has shown superior predictive performance than other Reynolds-stress models, which indicates that the simulation of the anisotropy of the turbulence is significant in the tight lattice. The result with different Reynolds number and geometry shows that the magnitude of the secondary flow is almost independent of the Reynolds number, but it increases with the decrease of the P/D. (authors)

History dependent quantum random walks as quantum lattice gas automata

Energy Technology Data Exchange (ETDEWEB)

Shakeel, Asif, E-mail: asif.shakeel@gmail.com, E-mail: dmeyer@math.ucsd.edu, E-mail: plove@haverford.edu; Love, Peter J., E-mail: asif.shakeel@gmail.com, E-mail: dmeyer@math.ucsd.edu, E-mail: plove@haverford.edu [Department of Physics, Haverford College, Haverford, Pennsylvania 19041 (United States); Meyer, David A., E-mail: asif.shakeel@gmail.com, E-mail: dmeyer@math.ucsd.edu, E-mail: plove@haverford.edu [Department of Mathematics, University of California/San Diego, La Jolla, California 92093-0112 (United States)

2014-12-15

Quantum Random Walks (QRW) were first defined as one-particle sectors of Quantum Lattice Gas Automata (QLGA). Recently, they have been generalized to include history dependence, either on previous coin (internal, i.e., spin or velocity) states or on previous position states. These models have the goal of studying the transition to classicality, or more generally, changes in the performance of quantum walks in algorithmic applications. We show that several history dependent QRW can be identified as one-particle sectors of QLGA. This provides a unifying conceptual framework for these models in which the extra degrees of freedom required to store the history information arise naturally as geometrical degrees of freedom on the lattice.

The nature of turbulence in a triangular lattice gas automaton

Science.gov (United States)

Duong-Van, Minh; Feit, M. D.; Keller, P.; Pound, M.

1986-12-01

Power spectra calculated from the coarse-graining of a simple lattice gas automaton, and those of time averaging other stochastic times series that we have investigated, have exponents in the range -1.6 to -2, consistent with observation of fully developed turbulence. This power spectrum is a natural consequence of coarse-graining; the exponent -2 represents the continuum limit.

Parallel-plate rheometer calibration using oil and lattice Boltzmann simulation

DEFF Research Database (Denmark)

Ferraris, Chiara F; Geiker, Mette Rica; Martys, Nicos S.

2007-01-01

compute the viscosity. This paper presents a modified parallel plate rheometer, and proposes means of calibration using standard oils and numerical simulation of the flow. A lattice Boltzmann method was used to simulate the flow in the modified rheometer, thus using an accurate numerical solution in place...

Digital Quantum Simulation of Z2 Lattice Gauge Theories with Dynamical Fermionic Matter

Science.gov (United States)

Zohar, Erez; Farace, Alessandro; Reznik, Benni; Cirac, J. Ignacio

2017-02-01

We propose a scheme for digital quantum simulation of lattice gauge theories with dynamical fermions. Using a layered optical lattice with ancilla atoms that can move and interact with the other atoms (simulating the physical degrees of freedom), we obtain a stroboscopic dynamics which yields the four-body plaquette interactions, arising in models with (2 +1 ) and higher dimensions, without the use of perturbation theory. As an example we show how to simulate a Z2 model in (2 +1 ) dimensions.

Digital Quantum Simulation of Z_{2} Lattice Gauge Theories with Dynamical Fermionic Matter.

Science.gov (United States)

Zohar, Erez; Farace, Alessandro; Reznik, Benni; Cirac, J Ignacio

2017-02-17

We propose a scheme for digital quantum simulation of lattice gauge theories with dynamical fermions. Using a layered optical lattice with ancilla atoms that can move and interact with the other atoms (simulating the physical degrees of freedom), we obtain a stroboscopic dynamics which yields the four-body plaquette interactions, arising in models with (2+1) and higher dimensions, without the use of perturbation theory. As an example we show how to simulate a Z_{2} model in (2+1) dimensions.

Lattice simulation of 2d Gross-Neveu-type models

International Nuclear Information System (INIS)

Limmer, M.; Gattringer, C.; Hermann, V.

2006-01-01

Full text: We discuss a Monte Carlo simulation of 2d Gross-Neveu-type models on the lattice. The four-Fermi interaction is written as a Gaussian integral with an auxiliary field and the fermion determinant is included by reweighting. We present results for bulk quantities and correlators and compare them to a simulation using a fermion-loop representation. (author)

First-principles lattice-gas Hamiltonian revisited: O-Pd(100)

OpenAIRE

Kappus, Wolfgang

2016-01-01

The methodology of deriving an adatom lattice-gas Hamiltonian (LGH) from first principles (FP) calculations is revisited. Such LGH cluster expansions compute a large set of lateral pair-, trio-, quarto interactions by solving a set of linear equations modelling regular adatom configurations and their FP energies. The basic assumption of truncating interaction terms beyond fifth nearest neighbors does not hold when adatoms show longer range interactions, e.g. substrate mediated elastic interac...

Quantum Monte Carlo Simulation of Frustrated Kondo Lattice Models

Science.gov (United States)

Sato, Toshihiro; Assaad, Fakher F.; Grover, Tarun

2018-03-01

The absence of the negative sign problem in quantum Monte Carlo simulations of spin and fermion systems has different origins. World-line based algorithms for spins require positivity of matrix elements whereas auxiliary field approaches for fermions depend on symmetries such as particle-hole symmetry. For negative-sign-free spin and fermionic systems, we show that one can formulate a negative-sign-free auxiliary field quantum Monte Carlo algorithm that allows Kondo coupling of fermions with the spins. Using this general approach, we study a half-filled Kondo lattice model on the honeycomb lattice with geometric frustration. In addition to the conventional Kondo insulator and antiferromagnetically ordered phases, we find a partial Kondo screened state where spins are selectively screened so as to alleviate frustration, and the lattice rotation symmetry is broken nematically.

U(1) Wilson lattice gauge theories in digital quantum simulators

Science.gov (United States)

Muschik, Christine; Heyl, Markus; Martinez, Esteban; Monz, Thomas; Schindler, Philipp; Vogell, Berit; Dalmonte, Marcello; Hauke, Philipp; Blatt, Rainer; Zoller, Peter

2017-10-01

Lattice gauge theories describe fundamental phenomena in nature, but calculating their real-time dynamics on classical computers is notoriously difficult. In a recent publication (Martinez et al 2016 Nature 534 516), we proposed and experimentally demonstrated a digital quantum simulation of the paradigmatic Schwinger model, a U(1)-Wilson lattice gauge theory describing the interplay between fermionic matter and gauge bosons. Here, we provide a detailed theoretical analysis of the performance and the potential of this protocol. Our strategy is based on analytically integrating out the gauge bosons, which preserves exact gauge invariance but results in complicated long-range interactions between the matter fields. Trapped-ion platforms are naturally suited to implementing these interactions, allowing for an efficient quantum simulation of the model, with a number of gate operations that scales polynomially with system size. Employing numerical simulations, we illustrate that relevant phenomena can be observed in larger experimental systems, using as an example the production of particle-antiparticle pairs after a quantum quench. We investigate theoretically the robustness of the scheme towards generic error sources, and show that near-future experiments can reach regimes where finite-size effects are insignificant. We also discuss the challenges in quantum simulating the continuum limit of the theory. Using our scheme, fundamental phenomena of lattice gauge theories can be probed using a broad set of experimentally accessible observables, including the entanglement entropy and the vacuum persistence amplitude.

Lattice Boltzmann simulations of liquid crystalline fluids: active gels and blue phases

OpenAIRE

Cates, M. E.; Henrich, O.; Marenduzzo, D.; Stratford, K.

2010-01-01

Lattice Boltzmann simulations have become a method of choice to solve the hydrodynamic equations of motion of a number of complex fluids. Here we review some recent applications of lattice Boltzmann to study the hydrodynamics of liquid crystalline materials. In particular, we focus on the study of (a) the exotic blue phases of cholesteric liquid crystals, and (b) active gels - a model system for actin plus myosin solutions or bacterial suspensions. In both cases lattice Boltzmann studies have...

Kinetics of diffuesion-controlled oxygen ordering in a lattic-gas model of YBa₂Cu₃O_7-δ

DEFF Research Database (Denmark)

Andersen, Jørgen Vitting; Bohr, Henrik; Mouritsen, Ole G.

1990-01-01

Nonequilibrium properties of oxygen ordering in high-Tc superconductors of the Y-Ba-Cu-O type are studied via computer simulation of an anisotropic two-dimensional lattice-gas model in which the ordering processes are controlled by diffusion across the sample edges. With a view to designing optimal...

Molecular dynamics simulation of thin film interfacial strength dependency on lattice mismatch

International Nuclear Information System (INIS)

Yang, Zhou; Lian, Jie; Wang, Junlan

2013-01-01

Laser-induced thin film spallation experiments have been previously developed to characterize the intrinsic interfacial strength of thin films. In order to gain insights of atomic level thin film debonding processes and the interfacial strength dependence on film/substrate lattice structures, in this study, molecular dynamics simulations of thin film interfacial failure under laser-induced stress waves were performed. Various loading amplitudes and pulse durations were employed to identify the optimum simulation condition. Stress propagation as a function of time was revealed in conjunction with the interface structures. Parametric studies confirmed that while the interfacial strength between a thin film and a substrate does not depend on the film thickness and the duration of the laser pulse, a thicker film and a shorter duration do provide advantage to effectively load the interface to failure. With the optimized simulation condition, further studies were focused on bulk Au/Au bi-crystals with mismatched orientations, and Ni/Al, Cu/Al, Cu/Ag and Cu/Au bi-crystals with mismatched lattices. The interfacial strength was found to decrease with increasing orientation mismatch and lattice mismatch but more significantly dominated by the bonding elements' atomic structure and valence electron occupancy. - Highlights: • Molecular dynamics simulation was done on stress wave induced thin film spallation. • Atomic structure was found to be a primary strength determining factor. • Lattice mismatch was found to be a secondary strength determining factor

Simulating colloid hydrodynamics with lattice Boltzmann methods

International Nuclear Information System (INIS)

Cates, M E; Stratford, K; Adhikari, R; Stansell, P; Desplat, J-C; Pagonabarraga, I; Wagner, A J

2004-01-01

We present a progress report on our work on lattice Boltzmann methods for colloidal suspensions. We focus on the treatment of colloidal particles in binary solvents and on the inclusion of thermal noise. For a benchmark problem of colloids sedimenting and becoming trapped by capillary forces at a horizontal interface between two fluids, we discuss the criteria for parameter selection, and address the inevitable compromise between computational resources and simulation accuracy

New one-flavor hybrid Monte Carlo simulation method for lattice fermions with γ5 hermiticity

International Nuclear Information System (INIS)

Ogawa, Kenji

2011-01-01

We propose a new method for Hybrid Monte Carlo (HMC) simulations with odd numbers of dynamical fermions on the lattice. It employs a different approach from polynomial or rational HMC. In this method, γ 5 hermiticity of the lattice Dirac operators is crucial and it can be applied to Wilson, domain-wall, and overlap fermions. We compare HMC simulations with two degenerate flavors and (1+1) degenerate flavors using optimal domain-wall fermions. The ratio of the efficiency, (number of accepted trajectories)/(simulation time), is about 3:2. The relation between pseudofermion action of chirally symmetric lattice fermions in four-dimensional (overlap) and five-dimensional (domain-wall) representation are also analyzed.

Lattice Boltzmann simulations of attenuation-driven acoustic streaming

International Nuclear Information System (INIS)

Haydock, David; Yeomans, J M

2003-01-01

We show that lattice Boltzmann simulations can be used to model the attenuation-driven acoustic streaming produced by a travelling wave. Comparisons are made to analytical results and to the streaming pattern produced by an imposed body force approximating the Reynolds stresses. We predict the streaming patterns around a porous material in an attenuating acoustic field

Lattice Boltzmann simulation of antiplane shear loading of a stationary crack

Science.gov (United States)

Schlüter, Alexander; Kuhn, Charlotte; Müller, Ralf

2018-01-01

In this work, the lattice Boltzmann method is applied to study the dynamic behaviour of linear elastic solids under antiplane shear deformation. In this case, the governing set of partial differential equations reduces to a scalar wave equation for the out of plane displacement in a two dimensional domain. The lattice Boltzmann approach developed by Guangwu (J Comput Phys 161(1):61-69, 2000) in 2006 is used to solve the problem numerically. Some aspects of the scheme are highlighted, including the treatment of the boundary conditions. Subsequently, the performance of the lattice Boltzmann scheme is tested for a stationary crack problem for which an analytic solution exists. The treatment of cracks is new compared to the examples that are discussed in Guangwu's work. Furthermore, the lattice Boltzmann simulations are compared to finite element computations. Finally, the influence of the lattice Boltzmann relaxation parameter on the stability of the scheme is illustrated.

Lattice Boltzmann simulation of flow and heat transfer in random porous media constructed by simulated annealing algorithm

International Nuclear Information System (INIS)

Liu, Minghua; Shi, Yong; Yan, Jiashu; Yan, Yuying

2017-01-01

Highlights: • A numerical capability combining the lattice Boltzmann method with simulated annealing algorithm is developed. • Digitized representations of random porous media are constructed using limited but meaningful statistical descriptors. • Pore-scale flow and heat transfer information in random porous media is obtained by the lattice Boltzmann simulation. • The effective properties at the representative elementary volume scale are well specified using appropriate upscale averaging. - Abstract: In this article, the lattice Boltzmann (LB) method for transport phenomena is combined with the simulated annealing (SA) algorithm for digitized porous-medium construction to study flow and heat transfer in random porous media. Importantly, in contrast to previous studies which simplify porous media as arrays of regularly shaped objects or effective pore networks, the LB + SA method in this article can model statistically meaningful random porous structures in irregular morphology, and simulate pore-scale transport processes inside them. Pore-scale isothermal flow and heat conduction in a set of constructed random porous media characterized by statistical descriptors were then simulated through use of the LB + SA method. The corresponding averages over the computational volumes and the related effective transport properties were also computed based on these pore scale numerical results. Good agreement between the numerical results and theoretical predictions or experimental data on the representative elementary volume scale was found. The numerical simulations in this article demonstrate combination of the LB method with the SA algorithm is a viable and powerful numerical strategy for simulating transport phenomena in random porous media in complex geometries.

Modeling and simulation of ocean wave propagation using lattice Boltzmann method

Science.gov (United States)

Nuraiman, Dian

2017-10-01

In this paper, we present on modeling and simulation of ocean wave propagation from the deep sea to the shoreline. This requires high computational cost for simulation with large domain. We propose to couple a 1D shallow water equations (SWE) model with a 2D incompressible Navier-Stokes equations (NSE) model in order to reduce the computational cost. The coupled model is solved using the lattice Boltzmann method (LBM) with the lattice Bhatnagar-Gross-Krook (BGK) scheme. Additionally, a special method is implemented to treat the complex behavior of free surface close to the shoreline. The result shows the coupled model can reduce computational cost significantly compared to the full NSE model.

Lattice Boltzmann simulation for temperature-sensitive magnetic fluids in a porous square cavity

International Nuclear Information System (INIS)

Jin Licong; Zhang Xinrong; Niu Xiaodong

2012-01-01

A lattice Boltzmann method is developed to simulate temperature-sensitive magnetic fluids in a porous cavity. In the simulation, the magnetic force, efficient gravity, viscous loss term and geometric loss term in porous medium are imported to the momentum equation. To test the reliability of the method, a validation with water in porous cavity is carried out. Good agreements with the previous results verify that the present lattice Boltzmann method is promising for simulation of magnetic fluids in porous medium. In this study, we investigate the change of magnetization with external magnetic field, and we present numerical results for the streamlines, isotherms, and magnetization at vertical or horizontal mid-profiles for different values of Ram. In addition, Nusselt numbers changing with magnetic Rayleigh numbers are also investigated. - Highlights: → Developed a lattice Boltzmann method for magnetic nano-fluids in porous cavity. → Clarified flow and heat transfer for different values of (magnetic) Rayleigh numbers. → Heat transfer enhancement for magnetic fluid in porous cavity.

A mass-conserving multiphase lattice Boltzmann model for simulation of multiphase flows

Science.gov (United States)

Niu, Xiao-Dong; Li, You; Ma, Yi-Ren; Chen, Mu-Feng; Li, Xiang; Li, Qiao-Zhong

2018-01-01

In this study, a mass-conserving multiphase lattice Boltzmann (LB) model is proposed for simulating the multiphase flows. The proposed model developed in the present study is to improve the model of Shao et al. ["Free-energy-based lattice Boltzmann model for simulation of multiphase flows with density contrast," Phys. Rev. E 89, 033309 (2014)] by introducing a mass correction term in the lattice Boltzmann model for the interface. The model of Shao et al. [(the improved Zheng-Shu-Chew (Z-S-C model)] correctly considers the effect of the local density variation in momentum equation and has an obvious improvement over the Zheng-Shu-Chew (Z-S-C) model ["A lattice Boltzmann model for multiphase flows with large density ratio," J. Comput. Phys. 218(1), 353-371 (2006)] in terms of solution accuracy. However, due to the physical diffusion and numerical dissipation, the total mass of each fluid phase cannot be conserved correctly. To solve this problem, a mass correction term, which is similar to the one proposed by Wang et al. ["A mass-conserved diffuse interface method and its application for incompressible multiphase flows with large density ratio," J. Comput. Phys. 290, 336-351 (2015)], is introduced into the lattice Boltzmann equation for the interface to compensate the mass losses or offset the mass increase. Meanwhile, to implement the wetting boundary condition and the contact angle, a geometric formulation and a local force are incorporated into the present mass-conserving LB model. The proposed model is validated by verifying the Laplace law, simulating both one and two aligned droplets splashing onto a liquid film, droplets standing on an ideal wall, droplets with different wettability splashing onto smooth wax, and bubbles rising under buoyancy. Numerical results show that the proposed model can correctly simulate multiphase flows. It was found that the mass is well-conserved in all cases considered by the model developed in the present study. The developed

A new simulation algorithm for lattice QCD with dynamical quarks

CERN Document Server

Bunk, B.; Jegerlehner, B.; Luscher, M.; Simma, H.; Sommer, R.; Bunk, B; Jansen, K; Jegerlehner, B; Luscher, M; Simma, H

1994-01-01

A previously introduced multi-boson technique for the simulation of QCD with dynamical quarks is described and some results of first test runs on a 6^3\\times12 lattice with Wilson quarks and gauge group SU(2) are reported.

Canonical simulations with worldlines: An exploratory study in ϕ24 lattice field theory

Science.gov (United States)

Orasch, Oliver; Gattringer, Christof

2018-01-01

In this paper, we explore the perspectives for canonical simulations in the worldline formulation of a lattice field theory. Using the charged ϕ4 field in two dimensions as an example, we present the details of the canonical formulation based on worldlines and outline the algorithmic strategies for canonical worldline simulations. We discuss the steps for converting the data from the canonical approach to the grand canonical picture which we use for cross-checking our results. The canonical approach presented here can easily be generalized to other lattice field theories with a worldline representation.

Monte Carlo simulations of lattice models for single polymer systems

Science.gov (United States)

Hsu, Hsiao-Ping

2014-10-01

Single linear polymer chains in dilute solutions under good solvent conditions are studied by Monte Carlo simulations with the pruned-enriched Rosenbluth method up to the chain length N ˜ O(10^4). Based on the standard simple cubic lattice model (SCLM) with fixed bond length and the bond fluctuation model (BFM) with bond lengths in a range between 2 and sqrt{10}, we investigate the conformations of polymer chains described by self-avoiding walks on the simple cubic lattice, and by random walks and non-reversible random walks in the absence of excluded volume interactions. In addition to flexible chains, we also extend our study to semiflexible chains for different stiffness controlled by a bending potential. The persistence lengths of chains extracted from the orientational correlations are estimated for all cases. We show that chains based on the BFM are more flexible than those based on the SCLM for a fixed bending energy. The microscopic differences between these two lattice models are discussed and the theoretical predictions of scaling laws given in the literature are checked and verified. Our simulations clarify that a different mapping ratio between the coarse-grained models and the atomistically realistic description of polymers is required in a coarse-graining approach due to the different crossovers to the asymptotic behavior.

Monte Carlo simulations of lattice models for single polymer systems

International Nuclear Information System (INIS)

Hsu, Hsiao-Ping

2014-01-01

Single linear polymer chains in dilute solutions under good solvent conditions are studied by Monte Carlo simulations with the pruned-enriched Rosenbluth method up to the chain length N∼O(10 4 ). Based on the standard simple cubic lattice model (SCLM) with fixed bond length and the bond fluctuation model (BFM) with bond lengths in a range between 2 and √(10), we investigate the conformations of polymer chains described by self-avoiding walks on the simple cubic lattice, and by random walks and non-reversible random walks in the absence of excluded volume interactions. In addition to flexible chains, we also extend our study to semiflexible chains for different stiffness controlled by a bending potential. The persistence lengths of chains extracted from the orientational correlations are estimated for all cases. We show that chains based on the BFM are more flexible than those based on the SCLM for a fixed bending energy. The microscopic differences between these two lattice models are discussed and the theoretical predictions of scaling laws given in the literature are checked and verified. Our simulations clarify that a different mapping ratio between the coarse-grained models and the atomistically realistic description of polymers is required in a coarse-graining approach due to the different crossovers to the asymptotic behavior

Chiral Extrapolations of the $\\boldsymbol{ρ(770)}$ Meson in $\\mathbf{N_f=2+1}$ Lattice QCD Simulations

Energy Technology Data Exchange (ETDEWEB)

Molina, Raquel [Univ. of Sao Paulo (Brazil); Hu, Bitao [George Washington Univ., Washington, DC (United States); Doering, Michael [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); George Washington Univ., Washington, DC (United States); Mai, Maxim [George Washington Univ., Washington, DC (United States); Alexandru, Andrei [George Washington Univ., Washington, DC (United States)

2018-04-01

Several lattice QCD simulations of meson-meson scattering in p-wave and Isospin = 1 in Nf = 2 + 1 flavours have been carried out recently. Unitarized Chiral Perturbation Theory is used to perform extrapolations to the physical point. In contrast to previous findings on the analyses of Nf = 2 lattice data, where most of the data seems to be in agreement, some discrepancies are detected in the Nf = 2 + 1 lattice data analyses, which could be due to different masses of the strange quark, meson decay constants, initial constraints in the simulation, or other lattice artifacts. In addition, the low-energy constants are compared to the ones from a recent analysis of Nf = 2 lattice data.

Effect of lattice-gas atoms on the adsorption behaviour of thioether molecules.

Science.gov (United States)

Pan, Yi; Yang, Bing; Hulot, Catherine; Blechert, Siegfried; Nilius, Niklas; Freund, Hans-Joachim

2012-08-21

Using STM topographic imaging and spectroscopy, we have investigated the adsorption of two thioether molecules, 1,2-bis(phenylthio)benzene and (bis(3-phenylthio)-phenyl)sulfane, on noble and transition metal surfaces. The two substrates show nearly antipodal behaviour. Whereas complexes with one or two protruding centres are observed on Au(111), only flat and uniform ad-structures are found on NiAl(110). The difference is ascribed to the possibility of the thioethers to form metal-organic complexes by coordinating lattice-gas atoms on the Au(111), while only the pristine molecules adsorb on the alloy surface. The metal coordination in the first case is driven by the formation of strong Au-S bonds and enables the formation of characteristic monomer, dimer and chain-like structures of the thioethers, using the Au atoms as linkers. A similar mechanism is not available on the NiAl, because no lattice gas develops at this surface at room temperature. Our work demonstrates how surface properties, i.e. the availability of mobile ad-species, determine the interaction of organic molecules with metallic substrates.

Electrostatic modulation of periodic potentials in a two-dimensional electron gas: From antidot lattice to quantum dot lattice

Energy Technology Data Exchange (ETDEWEB)

Goswami, Srijit; Aamir, Mohammed Ali; Shamim, Saquib; Ghosh, Arindam [Department of Physics, Indian Institute of Science, Bangalore 560 012 (India); Siegert, Christoph; Farrer, Ian; Ritchie, David A. [Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Pepper, Michael [Department of Electrical and Electronic Engineering, University College, London WC1E 7JE (United Kingdom)

2013-12-04

We use a dual gated device structure to introduce a gate-tuneable periodic potential in a GaAs/AlGaAs two dimensional electron gas (2DEG). Using only a suitable choice of gate voltages we can controllably alter the potential landscape of the bare 2DEG, inducing either a periodic array of antidots or quantum dots. Antidots are artificial scattering centers, and therefore allow for a study of electron dynamics. In particular, we show that the thermovoltage of an antidot lattice is particularly sensitive to the relative positions of the Fermi level and the antidot potential. A quantum dot lattice, on the other hand, provides the opportunity to study correlated electron physics. We find that its current-voltage characteristics display a voltage threshold, as well as a power law scaling, indicative of collective Coulomb blockade in a disordered background.

Electrostatic modulation of periodic potentials in a two-dimensional electron gas: From antidot lattice to quantum dot lattice

International Nuclear Information System (INIS)

Goswami, Srijit; Aamir, Mohammed Ali; Shamim, Saquib; Ghosh, Arindam; Siegert, Christoph; Farrer, Ian; Ritchie, David A.; Pepper, Michael

2013-01-01

We use a dual gated device structure to introduce a gate-tuneable periodic potential in a GaAs/AlGaAs two dimensional electron gas (2DEG). Using only a suitable choice of gate voltages we can controllably alter the potential landscape of the bare 2DEG, inducing either a periodic array of antidots or quantum dots. Antidots are artificial scattering centers, and therefore allow for a study of electron dynamics. In particular, we show that the thermovoltage of an antidot lattice is particularly sensitive to the relative positions of the Fermi level and the antidot potential. A quantum dot lattice, on the other hand, provides the opportunity to study correlated electron physics. We find that its current-voltage characteristics display a voltage threshold, as well as a power law scaling, indicative of collective Coulomb blockade in a disordered background

Static Q anti Q force from instanton gas and numerical lattice calculations

International Nuclear Information System (INIS)

Ilgenfrits, E.M.; Mueller-Preussker, M.

1982-01-01

Lattice Monte Carlo calculation predictions for the static strength between quarks are compared with the results obtained in the framework of instanton gas model and a typical instanton size is determined. Yang-Mills theory data for different ratios of Wilson loops in case of SU(3) for the string tension are presented. The instanton corrections to perturbation strength turn to be essential to reach an agreement with obtained by lattice calculations data inside the small-distance region up to approximately 0.3 fm. Arguments in favour of the statement that data difference in this region from the phenomenologically known value is connected with the notion of infinitely heavy quarks but not with neglect of virtual quark loops are presented

Lattice Boltzmann simulations of heat transfer in fully developed periodic incompressible flows

Science.gov (United States)

Wang, Zimeng; Shang, Helen; Zhang, Junfeng

2017-06-01

Flow and heat transfer in periodic structures are of great interest for many applications. In this paper, we carefully examine the periodic features of fully developed periodic incompressible thermal flows, and incorporate them in the lattice Boltzmann method (LBM) for flow and heat transfer simulations. Two numerical approaches, the distribution modification (DM) approach and the source term (ST) approach, are proposed; and they can both be used for periodic thermal flows with constant wall temperature (CWT) and surface heat flux boundary conditions. However, the DM approach might be more efficient, especially for CWT systems since the ST approach requires calculations of the streamwise temperature gradient at all lattice nodes. Several example simulations are conducted, including flows through flat and wavy channels and flows through a square array with circular cylinders. Results are compared to analytical solutions, previous studies, and our own LBM calculations using different simulation techniques (i.e., the one-module simulation vs. the two-module simulation, and the DM approach vs. the ST approach) with good agreement. These simple, however, representative simulations demonstrate the accuracy and usefulness of our proposed LBM methods for future thermal periodic flow simulations.

Lattice Boltzmann Simulation of Permeability and Tortuosity for Flow through Dense Porous Media

Directory of Open Access Journals (Sweden)

Ping Wang

2014-01-01

Full Text Available Discrete element method (DEM is used to produce dense and fixed porous media with rigid mono spheres. Lattice Boltzmann method (LBM is adopted to simulate the fluid flow in interval of dense spheres. To simulating the same physical problem, the permeability is obtained with different lattice number. We verify that the permeability is irrelevant to the body force and the media length along flow direction. The relationships between permeability, tortuosity and porosity, and sphere radius are researched, and the results are compared with those reported by other authors. The obtained results indicate that LBM is suited to fluid flow simulation of porous media due to its inherent theoretical advantages. The radius of sphere should have ten lattices at least and the media length along flow direction should be more than twenty radii. The force has no effect on the coefficient of permeability with the limitation of slow fluid flow. For mono spheres porous media sample, the relationship of permeability and porosity agrees well with the K-C equation, and the tortuosity decreases linearly with increasing porosity.

Simulation of turbulent flow over staggered tube bundles using multi-relaxation time lattice Boltzmann method

International Nuclear Information System (INIS)

Park, Jong Woon; Choi, Hyun Gyung

2014-01-01

A turbulent fluid flow over staggered tube bundles is of great interest in many engineering fields including nuclear fuel rods, heat exchangers and especially a gas cooled reactor lower plenum. Computational methods have evolved for the simulation of such flow for decades and lattice Boltzmann method (LBM) is one of the attractive methods due to its sound physical basis and ease of computerization including parallelization. In this study to find computational performance of the LBM in turbulent flows over staggered tubes, a fluid flow analysis code employing multi-relaxation time lattice Boltzmann method (MRT-LBM) is developed based on a 2-dimensional D2Q9 lattice model and classical sub-grid eddy viscosity model of Smagorinsky. As a first step, fundamental performance MRT-LBM is investigated against a standard problem of a flow past a cylinder at low Reynolds number in terms of drag forces. As a major step, benchmarking of the MRT-LBM is performed over a turbulent flow through staggered tube bundles at Reynolds number of 18,000. For a flow past a single cylinder, the accuracy is validated against existing experimental data and previous computations in terms of drag forces on the cylinder. Mainly, the MRT-LBM computation for a flow through staggered tube bundles is performed and compared with experimental data and general purpose computational fluid dynamic (CFD) analyses with standard k-ω turbulence and large eddy simulation (LES) equipped with turbulence closures of Smagrinsky-Lilly and wall-adapting local eddy-viscosity (WALE) model. The agreement between the experimental and the computational results from the present MRT-LBM is found to be reasonably acceptable and even comparable to the LES whereas the computational efficiency is superior. (orig.)

Simulation of turbulent flow over staggered tube bundles using multi-relaxation time lattice Boltzmann method

Energy Technology Data Exchange (ETDEWEB)

Park, Jong Woon; Choi, Hyun Gyung [Dongguk Univ., Gyeongju (Korea, Republic of). Nuclear and Energy Engineering Dept.

2014-02-15

A turbulent fluid flow over staggered tube bundles is of great interest in many engineering fields including nuclear fuel rods, heat exchangers and especially a gas cooled reactor lower plenum. Computational methods have evolved for the simulation of such flow for decades and lattice Boltzmann method (LBM) is one of the attractive methods due to its sound physical basis and ease of computerization including parallelization. In this study to find computational performance of the LBM in turbulent flows over staggered tubes, a fluid flow analysis code employing multi-relaxation time lattice Boltzmann method (MRT-LBM) is developed based on a 2-dimensional D2Q9 lattice model and classical sub-grid eddy viscosity model of Smagorinsky. As a first step, fundamental performance MRT-LBM is investigated against a standard problem of a flow past a cylinder at low Reynolds number in terms of drag forces. As a major step, benchmarking of the MRT-LBM is performed over a turbulent flow through staggered tube bundles at Reynolds number of 18,000. For a flow past a single cylinder, the accuracy is validated against existing experimental data and previous computations in terms of drag forces on the cylinder. Mainly, the MRT-LBM computation for a flow through staggered tube bundles is performed and compared with experimental data and general purpose computational fluid dynamic (CFD) analyses with standard k-ω turbulence and large eddy simulation (LES) equipped with turbulence closures of Smagrinsky-Lilly and wall-adapting local eddy-viscosity (WALE) model. The agreement between the experimental and the computational results from the present MRT-LBM is found to be reasonably acceptable and even comparable to the LES whereas the computational efficiency is superior. (orig.)

Large eddy simulation of rotating turbulent flows and heat transfer by the lattice Boltzmann method

Science.gov (United States)

Liou, Tong-Miin; Wang, Chun-Sheng

2018-01-01

Due to its advantage in parallel efficiency and wall treatment over conventional Navier-Stokes equation-based methods, the lattice Boltzmann method (LBM) has emerged as an efficient tool in simulating turbulent heat and fluid flows. To properly simulate the rotating turbulent flow and heat transfer, which plays a pivotal role in tremendous engineering devices such as gas turbines, wind turbines, centrifugal compressors, and rotary machines, the lattice Boltzmann equations must be reformulated in a rotating coordinate. In this study, a single-rotating reference frame (SRF) formulation of the Boltzmann equations is newly proposed combined with a subgrid scale model for the large eddy simulation of rotating turbulent flows and heat transfer. The subgrid scale closure is modeled by a shear-improved Smagorinsky model. Since the strain rates are also locally determined by the non-equilibrium part of the distribution function, the calculation process is entirely local. The pressure-driven turbulent channel flow with spanwise rotation and heat transfer is used for validating the approach. The Reynolds number characterized by the friction velocity and channel half height is fixed at 194, whereas the rotation number in terms of the friction velocity and channel height ranges from 0 to 3.0. A working fluid of air is chosen, which corresponds to a Prandtl number of 0.71. Calculated results are demonstrated in terms of mean velocity, Reynolds stress, root mean square (RMS) velocity fluctuations, mean temperature, RMS temperature fluctuations, and turbulent heat flux. Good agreement is found between the present LBM predictions and previous direct numerical simulation data obtained by solving the conventional Navier-Stokes equations, which confirms the capability of the proposed SRF LBM and subgrid scale relaxation time formulation for the computation of rotating turbulent flows and heat transfer.

Migration of particles on heterogeneous bivariate lattices: the universal analytical expressions for the diffusion coefficients

Czech Academy of Sciences Publication Activity Database

Tarasenko, Alexander; Boháč, Petr; Jastrabík, Lubomír

2015-01-01

Roč. 74, Nov (2015), s. 556-560 ISSN 1386-9477 R&D Projects: GA MŠk LO1409; GA TA ČR TA03010743 Institutional support: RVO:68378271 Keywords : surface diffusion * heterogeneous lattices * lattice-gas models * kinetic Monte Carlo simulation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.904, year: 2015

Simulating lattice fermions by microcanonically averaging out the nonlocal dependence of the fermionic action

International Nuclear Information System (INIS)

Azcoiti, V.; Cruz, A.; Di Carlo, G.; Grillo, A.F.; Vladikas, A.

1991-01-01

We attempt to increase the efficiency of simulations of dynamical fermions on the lattice by calculating the fermionic determinant just once for all the values of the theory's gauge coupling and flavor number. Our proposal is based on the determination of an effective fermionic action by the calculation of the fermionic determinant averaged over configurations at fixed gauge energy. The feasibility of our method is justified by the observed volume dependence of the fluctuations of the logarithm of the determinant. The algorithm we have used in order to calculate the fermionic determinant, based on the determination of all the eigenvalues of the fermionic matrix at zero mass, also enables us to obtain results at any fermion mass, with a single fermionic simulation. We test the method by simulating compact lattice QED, finding good agreement with other standard calculations. New results on the phase transition of compact QED with massless fermions on 6 4 and 8 4 lattices are also presented

Practical Implementation of Lattice QCD Simulation on Intel Xeon Phi Knights Landing

OpenAIRE

Kanamori, Issaku; Matsufuru, Hideo

2017-01-01

We investigate implementation of lattice Quantum Chromodynamics (QCD) code on the Intel Xeon Phi Knights Landing (KNL). The most time consuming part of the numerical simulations of lattice QCD is a solver of linear equation for a large sparse matrix that represents the strong interaction among quarks. To establish widely applicable prescriptions, we examine rather general methods for the SIMD architecture of KNL, such as using intrinsics and manual prefetching, to the matrix multiplication an...

Towards the petaflop for Lattice QCD simulations the PetaQCD project

International Nuclear Information System (INIS)

D'Auriac, Jean-Christian Angles; Carbonell, Jaume; Barthou, Denis

2010-01-01

The study and design of a very ambitious petaflop cluster exclusively dedicated to Lattice QCD simulations started in early '08 among a consortium of 7 laboratories (IN2P3, CNRS, INRIA, CEA) and 2 SMEs. This consortium received a grant from the French ANR agency in July '08, and the PetaQCD project kickoff took place in January '09. Building upon several years of fruitful collaborative studies in this area, the aim of this project is to demonstrate that the simulation of a 256 x 128 3 lattice can be achieved through the HMC/ETMC software, using a machine with efficient speed/cost/reliability/power consumption ratios. It is expected that this machine can be built out of a rather limited number of processors (e.g. between 1000 and 4000), although capable of a sustained petaflop CPU performance. The proof-of-concept should be a mock-up cluster built as much as possible with off-the-shelf components, and 2 particularly attractive axis will be mainly investigated, in addition to fast all-purpose multi-core processors: the use of the new brand of IBM-Cell processors (with on-chip accelerators) and the very recent Nvidia GP-GPUs (off-chip co-processors). This cluster will obviously be massively parallel, and heterogeneous. Communication issues between processors, implied by the Physics of the simulation and the lattice partitioning, will certainly be a major key to the project.

Lattice Boltzmann model for simulating immiscible two-phase flows

International Nuclear Information System (INIS)

Reis, T; Phillips, T N

2007-01-01

The lattice Boltzmann equation is often promoted as a numerical simulation tool that is particularly suitable for predicting the flow of complex fluids. This paper develops a two-dimensional 9-velocity (D2Q9) lattice Boltzmann model for immiscible binary fluids with variable viscosities and density ratio using a single relaxation time for each fluid. In the macroscopic limit, this model is shown to recover the Navier-Stokes equations for two-phase flows. This is achieved by constructing a two-phase component of the collision operator that induces the appropriate surface tension term in the macroscopic equations. A theoretical expression for surface tension is determined. The validity of this analysis is confirmed by comparing numerical and theoretical predictions of surface tension as a function of density. The model is also shown to predict Laplace's law for surface tension and Poiseuille flow of layered immiscible binary fluids. The spinodal decomposition of two fluids of equal density but different viscosity is then studied. At equilibrium, the system comprises one large low viscosity bubble enclosed by the more viscous fluid in agreement with theoretical arguments of Renardy and Joseph (1993 Fundamentals of Two-Fluid Dynamics (New York: Springer)). Two other simulations, namely the non-equilibrium rod rest and the coalescence of two bubbles, are performed to show that this model can be used to simulate two fluids with a large density ratio

Lattice models for large-scale simulations of coherent wave scattering

Science.gov (United States)

Wang, Shumin; Teixeira, Fernando L.

2004-01-01

Lattice approximations for partial differential equations describing physical phenomena are commonly used for the numerical simulation of many problems otherwise intractable by pure analytical approaches. The discretization inevitably leads to many of the original symmetries to be broken or modified. In the case of Maxwell’s equations for example, invariance and isotropy of the speed of light in vacuum is invariably lost because of the so-called grid dispersion. Since it is a cumulative effect, grid dispersion is particularly harmful for the accuracy of results of large-scale simulations of scattering problems. Grid dispersion is usually combated by either increasing the lattice resolution or by employing higher-order schemes with larger stencils for the space and time derivatives. Both alternatives lead to increased computational cost to simulate a problem of a given physical size. Here, we introduce a general approach to develop lattice approximations with reduced grid dispersion error for a given stencil (and hence at no additional computational cost). The present approach is based on first obtaining stencil coefficients in the Fourier domain that minimize the maximum grid dispersion error for wave propagation at all directions (minimax sense). The resulting coefficients are then expanded into a Taylor series in terms of the frequency variable and incorporated into time-domain (update) equations after an inverse Fourier transformation. Maximally flat (Butterworth) or Chebyshev filters are subsequently used to minimize the wave speed variations for a given frequency range of interest. The use of such filters also allows for the adjustment of the grid dispersion characteristics so as to minimize not only the local dispersion error but also the accumulated phase error in a frequency range of interest.

Thermal lattice Boltzmann simulation for multispecies fluid equilibration

International Nuclear Information System (INIS)

Vahala, Linda; Wah, Darren; Vahala, George; Carter, Jonathan; Pavlo, Pavol

2000-01-01

The equilibration rate for multispecies fluids is examined using thermal lattice Boltzmann simulations. Two-dimensional free-decay simulations are performed for effects of velocity shear layer turbulence on sharp temperature profiles. In particular, parameters are so chosen that the lighter species is turbulent while the heavier species is laminar--and so its vorticity layers would simply decay and diffuse in time. With species coupling, however, there is velocity equilibration followed by the final relaxation to one large co- and one large counter-rotating vortex. The temperature equilibration proceeds on a slower time scale and is in good agreement with the theoretical order of magnitude estimate of Morse [Phys. Fluids 6, 1420 (1963)]. (c) 2000 The American Physical Society

Thermal lattice Boltzmann simulation for multispecies fluid equilibration

Energy Technology Data Exchange (ETDEWEB)

Vahala, Linda [Department of Electrical and Computer Engineering, Old Dominion University, Norfolk, Virginia 23529 (United States); Wah, Darren [Department of Physics, William and Mary College, Williamsburg, Virginia 23187 (United States); Vahala, George [Department of Physics, William and Mary College, Williamsburg, Virginia 23187 (United States); Carter, Jonathan [NERSC, Lawrence Berkeley Laboratory, Berkeley, California 97320 (United States); Pavlo, Pavol [Institute of Plasma Physics, Czech Academy of Science, Praha 8, (Czech Republic)

2000-07-01

The equilibration rate for multispecies fluids is examined using thermal lattice Boltzmann simulations. Two-dimensional free-decay simulations are performed for effects of velocity shear layer turbulence on sharp temperature profiles. In particular, parameters are so chosen that the lighter species is turbulent while the heavier species is laminar--and so its vorticity layers would simply decay and diffuse in time. With species coupling, however, there is velocity equilibration followed by the final relaxation to one large co- and one large counter-rotating vortex. The temperature equilibration proceeds on a slower time scale and is in good agreement with the theoretical order of magnitude estimate of Morse [Phys. Fluids 6, 1420 (1963)]. (c) 2000 The American Physical Society.

Lattice-Boltzmann Simulation of Tablet Disintegration

Science.gov (United States)

Jiang, Jiaolong; Sun, Ning; Gersappe, Dilip

Using the lattice-Boltzmann method, we developed a 2D model to study the tablet disintegration involving the swelling and wicking mechanisms. The surface area and disintegration profile of each component were obtained by tracking the tablet structure in the simulation. Compared to pure wicking, the total surface area is larger for swelling and wicking, which indicates that the swelling force breaks the neighboring bonds. The disintegration profiles show that the tablet disintegrates faster than pure wicking, and there are more wetted active pharmaceutical ingredient particles distributed on smaller clusters. Our results indicate how the porosity would affect the disintegration process by changing the wetting area of the tablet as well as by changing the swelling force propagation.

Towards quantum simulation of the Kondo-Lattice-Model

Energy Technology Data Exchange (ETDEWEB)

Kochanke, Andre

2017-04-25

Ultracold quantum gases of alkaline-earth-like metals are a versatile tool to investigate interacting many-body physics by realizing clean and controllable experimental model systems. Their intriguing properties range from energetically low-lying clock transitions, which allow for high-resolution spectroscopy, over meta-stable states, which can be regarded as a second species with orbital degree of freedom, to SU(N) symmetry, allowing novel magnetic phases. These open up new possibilities for quantum simulators. Using them in combination with optical lattices dissipative Fermi-Hubbard models and the Kondo-lattice-model can be realized, two promising examples for probing strongly correlated systems. This thesis presents an experimental apparatus for producing ultracold samples of fermionic {sup 173}Yb (N≤6). A new bicolor dipole trap was implemented with a final, average trap frequency of anti ω=36 Hz. Using optical, resonant pumping and an Optical-Stern-Gerlach scheme, the spin mixture can arbitrarily be changed from a six- to a one-component gas. Typically the degenerate Fermi gases consist of 87000 atoms at 17.5% T{sub F} (N=6) and of 47000 atoms at 19.4% T{sub F} (N=1). The lowest lying meta-stable state {sup 3}P{sub 0} (578 nm) is coherently controlled using a clock-laser setup with a linewidth of FWHM=1 Hz by means of Rabi oscillations or rapid adiabatic passage. By conducting spectroscopic measurements in a 3D magic lattice (759 nm) we demonstrate inter band transitions and observe the {sup 1}S{sub 0}<=>{sup 3}P{sub 0} excitation with a resolution of FWHM=50(2) Hz. Applying these techniques to a two-component spin mixture reveals a shift of the clock-transition caused by spin-exchange interaction between the orbital symmetric vertical stroke eg right angle {sup +} vertical stroke ↑↓ right angle {sup -} and the orbital antisymmetric vertical stroke eg right angle {sup -} vertical stroke ↑↓ right angle {sup +} state. Using the inelastic properties of

First results from simulations of supersymmetric lattices

Science.gov (United States)

Catterall, Simon

2009-01-01

We conduct the first numerical simulations of lattice theories with exact supersymmetry arising from the orbifold constructions of \\cite{Cohen:2003xe,Cohen:2003qw,Kaplan:2005ta}. We consider the Script Q = 4 theory in D = 0,2 dimensions and the Script Q = 16 theory in D = 0,2,4 dimensions. We show that the U(N) theories do not possess vacua which are stable non-perturbatively, but that this problem can be circumvented after truncation to SU(N). We measure the distribution of scalar field eigenvalues, the spectrum of the fermion operator and the phase of the Pfaffian arising after integration over the fermions. We monitor supersymmetry breaking effects by measuring a simple Ward identity. Our results indicate that simulations of Script N = 4 super Yang-Mills may be achievable in the near future.

The observation of helium gas bubble lattices in copper, nickel and stainless steel

International Nuclear Information System (INIS)

Johnson, P.B.; Mazey, D.J.

1978-10-01

Transmission electron microscopy is used to investigate the spatial arrangement of the small gas bubbles produced in several fcc metals by 30 keV helium ion irradiation to high dose at 300K. In what is a new result for this important class of metals it is found that the helium gas bubbles lie on a superlattice having an fcc structure with principal axes aligned with those of the metal matrix. The bubble lattice constant, asub(l), is measured for a helium fluence just below the critical dose for radiation blistering of the metal surface. Implantation rates are typically approximately 10 14 He ions cm -2 sec -1 . The values of asub(l) obtained for copper, nickel and stainless steel are given. Above the critical dose the bubble lattice is seen to survive in some blister caps as well as in the region between blisters. Bubble alignment is also observed in the case of hydrogen bubbles produced in copper by low energy proton irradiation to high fluence at 300K. (author)

Lattice gas automaton scheme with stochastic particle movement for a rotated fluid flow

International Nuclear Information System (INIS)

Ishiguro, Misako

2002-01-01

Lattice gas automaton (LGA) models developed so far are just for Cartesian geometries, and no direct approach to rotated fluid flows is found. In this paper, LGA method is applied to model a two-dimensional rotated flow. Several problems specific to the rotated flow are to be solved: hexagonal lattice geometry to effectively identify the neighbors, boundary condition for irregular walls, multi-speed scheme to represent angular-oriented fluid velocity υ θ ≅γω, shape of macroscopic domain for statistics, formula to obtain macroscopic quantities such as density and mean fluid velocities, application method of Fermi-Dirac function to the initial particle arrangement. For this purpose, FHP-I type hexagonal lattice model is revised and a new LGA model with stochastic particle movement is proposed. The results of the trial calculation are shown. It is also investigated whether or not the underlying microscopic Boolean equations newly introduced leads to Navier-Stokes equation. (author)

Lattice Boltzmann flow simulations with applications of reduced order modeling techniques

KAUST Repository

Brown, Donald

2014-01-01

With the recent interest in shale gas, an understanding of the flow mechanisms at the pore scale and beyond is necessary, which has attracted a lot of interest from both industry and academia. One of the suggested algorithms to help understand flow in such reservoirs is the Lattice Boltzmann Method (LBM). The primary advantage of LBM is its ability to approximate complicated geometries with simple algorithmic modificatoins. In this work, we use LBM to simulate the flow in a porous medium. More specifically, we use LBM to simulate a Brinkman type flow. The Brinkman law allows us to integrate fast free-flow and slow-flow porous regions. However, due to the many scales involved and complex heterogeneities of the rock microstructure, the simulation times can be long, even with the speed advantage of using an explicit time stepping method. The problem is two-fold, the computational grid must be able to resolve all scales and the calculation requires a steady state solution implying a large number of timesteps. To help reduce the computational complexity and total simulation times, we use model reduction techniques to reduce the dimension of the system. In this approach, we are able to describe the dynamics of the flow by using a lower dimensional subspace. In this work, we utilize the Proper Orthogonal Decomposition (POD) technique, to compute the dominant modes of the flow and project the solution onto them (a lower dimensional subspace) to arrive at an approximation of the full system at a lowered computational cost. We present a few proof-of-concept examples of the flow field and the corresponding reduced model flow field.

Calibration of modified parallel-plate rheometer through calibrated oil and lattice Boltzmann simulation

DEFF Research Database (Denmark)

Ferraris, Chiara F; Geiker, Mette Rica; Martys, Nicos S

2007-01-01

inapplicable here. This paper presents the analysis of a modified parallel plate rheometer for measuring cement mortar and propose a methodology for calibration using standard oils and numerical simulation of the flow. A lattice Boltzmann method was used to simulate the flow in the modified rheometer, thus...

Magnon and phonon dispersion, lifetime, and thermal conductivity of iron from spin-lattice dynamics simulations

Science.gov (United States)

Wu, Xufei; Liu, Zeyu; Luo, Tengfei

2018-02-01

In recent years, the fundamental physics of spin-lattice (e.g., magnon-phonon) interaction has attracted significant experimental and theoretical interests given its potential paradigm-shifting impacts in areas like spin-thermoelectrics, spin-caloritronics, and spintronics. Modelling studies of the transport of magnons and phonons in magnetic crystals are very rare. In this paper, we use spin-lattice dynamics (SLD) simulations to model ferromagnetic crystalline iron, where the spin and lattice systems are coupled through the atomic position-dependent exchange function, and thus the interaction between magnons and phonons is naturally considered. We then present a method combining SLD simulations with spectral energy analysis to calculate the magnon and phonon harmonic (e.g., dispersion, specific heat, and group velocity) and anharmonic (e.g., scattering rate) properties, based on which their thermal conductivity values are calculated. This work represents an example of using SLD simulations to understand the transport properties involving coupled magnon and phonon dynamics.

Ultracold atoms in optical lattices simulating quantum many-body systems

CERN Document Server

Lewenstein, Maciej; Ahufinger, Verònica

2012-01-01

Quantum computers, though not yet available on the market, will revolutionize the future of information processing. Quantum computers for special purposes like quantum simulators are already within reach. The physics of ultracold atoms, ions and molecules offer unprecedented possibilities of control of quantum many body systems and novel possibilities of applications to quantum information processing and quantum metrology. Particularly fascinating is the possibility of usingultracold atoms in lattices to simulate condensed matter or even high energy physics.This book provides a complete and co

Lattice gauge theory using parallel processors

International Nuclear Information System (INIS)

Lee, T.D.; Chou, K.C.; Zichichi, A.

1987-01-01

The book's contents include: Lattice Gauge Theory Lectures: Introduction and Current Fermion Simulations; Monte Carlo Algorithms for Lattice Gauge Theory; Specialized Computers for Lattice Gauge Theory; Lattice Gauge Theory at Finite Temperature: A Monte Carlo Study; Computational Method - An Elementary Introduction to the Langevin Equation, Present Status of Numerical Quantum Chromodynamics; Random Lattice Field Theory; The GF11 Processor and Compiler; and The APE Computer and First Physics Results; Columbia Supercomputer Project: Parallel Supercomputer for Lattice QCD; Statistical and Systematic Errors in Numerical Simulations; Monte Carlo Simulation for LGT and Programming Techniques on the Columbia Supercomputer; Food for Thought: Five Lectures on Lattice Gauge Theory

Current quantization and fractal hierarchy in a driven repulsive lattice gas.

Science.gov (United States)

Rotondo, Pietro; Sellerio, Alessandro Luigi; Glorioso, Pietro; Caracciolo, Sergio; Cosentino Lagomarsino, Marco; Gherardi, Marco

2017-11-01

Driven lattice gases are widely regarded as the paradigm of collective phenomena out of equilibrium. While such models are usually studied with nearest-neighbor interactions, many empirical driven systems are dominated by slowly decaying interactions such as dipole-dipole and Van der Waals forces. Motivated by this gap, we study the nonequilibrium stationary state of a driven lattice gas with slow-decayed repulsive interactions at zero temperature. By numerical and analytical calculations of the particle current as a function of the density and of the driving field, we identify (i) an abrupt breakdown transition between insulating and conducting states, (ii) current quantization into discrete phases where a finite current flows with infinite differential resistivity, and (iii) a fractal hierarchy of excitations, related to the Farey sequences of number theory. We argue that the origin of these effects is the competition between scales, which also causes the counterintuitive phenomenon that crystalline states can melt by increasing the density.

Current quantization and fractal hierarchy in a driven repulsive lattice gas

Science.gov (United States)

Rotondo, Pietro; Sellerio, Alessandro Luigi; Glorioso, Pietro; Caracciolo, Sergio; Cosentino Lagomarsino, Marco; Gherardi, Marco

2017-11-01

Driven lattice gases are widely regarded as the paradigm of collective phenomena out of equilibrium. While such models are usually studied with nearest-neighbor interactions, many empirical driven systems are dominated by slowly decaying interactions such as dipole-dipole and Van der Waals forces. Motivated by this gap, we study the nonequilibrium stationary state of a driven lattice gas with slow-decayed repulsive interactions at zero temperature. By numerical and analytical calculations of the particle current as a function of the density and of the driving field, we identify (i) an abrupt breakdown transition between insulating and conducting states, (ii) current quantization into discrete phases where a finite current flows with infinite differential resistivity, and (iii) a fractal hierarchy of excitations, related to the Farey sequences of number theory. We argue that the origin of these effects is the competition between scales, which also causes the counterintuitive phenomenon that crystalline states can melt by increasing the density.

Thermal and non-thermal lattice gas models for a dimer-trimer surface catalytic reaction: a Monte-Carlo simulation study

International Nuclear Information System (INIS)

Iqbal, K.; Khand, P.A.

2012-01-01

The kinetics of an irreversible dimer-trimer reaction of the type 2 A/sub 3/ +3 B/sub 2/ -- 6 AB by considering the precursor motion of the dimer (B/sub 2) on a square, as well as on a hexagonal surface, by using a Monte Carlo simulation have been studied. When the movement of precursors is limited to the first nearest neighborhood, the model gives reactive window widths of the order of 0.22 and 0.29 for the square and the hexagonal lattices, respectively, which are quite large compared to those predicted by the LH model. In our model, the reactive window width for a square lattice increases significantly as compared to that for the LH models of the same system on square and hexagonal lattices. The width of the reactive region increases when the precursor motion is extended to the second and the third nearest neighborhood. The continuous transition disappears when the precursor motion is extended to the third nearest neighborhood. The diffusion of B atoms does not change the situation qualitatively for both the precursor and the LH models. However, desorption of the dimer changes the situation significantly; i.e., the width of the reactive window shows an exponential growth with respect to the desorption probability of the dimer for both the precursor and the LH models. In our opinion, the inclusion of precursors in the LH model of the dimer-trimer reactions leads to a better and more realistic description of the heterogeneous catalytic reactions. Consequently, further numerical and theoretical activity in this field will be very useful for understanding complex heterogeneous reactions. (orig./A.B.)

Lattice Boltzmann simulation of droplet formation in T-junction geometries

Science.gov (United States)

Busuioc, Sergiu; Ambruş, Victor E.; Sofonea, Victor

2017-01-01

The formation of droplets in T-junction configurations is investigated using a two-dimensional Lattice Boltzmann model for liquid-vapor systems. We use an expansion of the equilibrium distribution function with respect to Hermite polynomials and an off-lattice velocity set. To evolve the distribution functions we use the second order corner transport upwind numerical scheme and a third order scheme is used to compute the gradient operators in the force term. The droplet formation successfully recovers the squeezing, dripping and jetting regimes. We find that the droplet length decreases proportionally with the flow rate of the continuous phase and increases with the flow rate of the dispersed phase in all simulation configurations and has a linear dependency on the surface tension parameter κ.

Three Dimensional Simulations of Multiphase Flows Using a Lattice Boltzmann Method Suitable for High Density Ratios - 12126

Energy Technology Data Exchange (ETDEWEB)

Gokaltun, Seckin; McDaniel, Dwayne; Roelant, David [Applied Research Center, Florida International University, 10555 West Flagler Street, Suite 2100, Miami, FL 33174 (United States)

2012-07-01

Multiphase flows involving gas and liquid phases can be observed in engineering operations at various Department of Energy sites, such as mixing of slurries using pulsed-air mixers and hydrogen gas generation in liquid waste tanks etc. The dynamics of the gas phase in the liquid domain play an important role in the mixing effectiveness of the pulsed-air mixers or in the level of gas pressure build-up in waste tanks. To understand such effects, computational fluid dynamics methods (CFD) can be utilized by developing a three-dimensional computerized multiphase flow model that can predict accurately the behavior of gas motion inside liquid-filled tanks by solving the governing mathematical equations that represent the physics of the phenomena. In this paper, such a CFD method, lattice Boltzmann method (LBM), is presented that can model multiphase flows accurately and efficiently. LBM is favored over traditional Navier-Stokes based computational models since interfacial forces are handled more effectively in LBM. The LBM is easier to program, more efficient to solve on parallel computers, and has the ability to capture the interface between different fluid phases intrinsically. The LBM used in this paper can solve for the incompressible and viscous flow field in three dimensions, while at the same time, solve the Cahn-Hillard equation to track the position of the gas-liquid interface specifically when the density and viscosity ratios between the two fluids are high. This feature is of primary importance since the previous LBM models proposed for multiphase flows become unstable when the density ratio is larger than 10. The ability to provide stable and accurate simulations at large density ratios becomes important when the simulation case involves fluids such as air and water with a density ratio around 1000 that are common to many engineering problems. In order to demonstrate the capability of the 3D LBM method at high density ratios, a static bubble simulation is

Study of shear viscosity of SU(2)-gluodynamics within lattice simulation

Energy Technology Data Exchange (ETDEWEB)

Astrakhantsev, N.Yu. [Institute for Theoretical and Experimental Physics,Moscow, 117218 (Russian Federation); Moscow Institute of Physics and Technology,Dolgoprudny, 141700 (Russian Federation); Braguta, V.V. [Institute for Theoretical and Experimental Physics,Moscow, 117218 (Russian Federation); Institute for High Energy Physics NRC “Kurchatov Institute”,Protvino, 142281 Russian Federation (Russian Federation); Far Eastern Federal University, School of Biomedicine,Vladivostok, 690950 (Russian Federation); National Research Nuclear University MEPhI (Moscow Engineering Physics Institute),Kashirskoe highway, 31, Moscow, 115409 (Russian Federation); Kotov, A.Yu. [Institute for Theoretical and Experimental Physics,Moscow, 117218 (Russian Federation); National Research Nuclear University MEPhI (Moscow Engineering Physics Institute),Kashirskoe highway, 31, Moscow, 115409 (Russian Federation)

2015-09-14

This paper is devoted to the study of two-point correlation function of the energy-momentum tensor 〈T{sub 12}T{sub 12}〉 for SU(2)-gluodynamics within lattice simulation of QCD. Using multilevel algorithm we carried out the measurement of the correlation function at the temperature T/T{sub c}≃1.2. It is shown that lattice data can be described by spectral functions which interpolate between hydrodynamics at low frequencies and asymptotic freedom at high frequencies. The results of the study of spectral functions allowed us to estimate the ratio of shear viscosity to the entropy density η/s=0.134±0.057.

The computer simulation of 3d gas dynamics in a gas centrifuge

Science.gov (United States)

Borman, V. D.; Bogovalov, S. V.; Borisevich, V. D.; Tronin, I. V.; Tronin, V. N.

2016-09-01

We argue on the basis of the results of 2D analysis of the gas flow in gas centrifuges that a reliable calculation of the circulation of the gas and gas content in the gas centrifuge is possible only in frameworks of 3D numerical simulation of gas dynamics in the gas centrifuge (hereafter GC). The group from National research nuclear university, MEPhI, has created a computer code for 3D simulation of the gas flow in GC. The results of the computer simulations of the gas flows in GC are presented. A model Iguassu centrifuge is explored for the simulations. A nonaxisymmetric gas flow is produced due to interaction of the hypersonic rotating flow with the scoops for extraction of the product and waste flows from the GC. The scoops produce shock waves penetrating into a working camera of the GC and form spiral waves there.

The computer simulation of 3d gas dynamics in a gas centrifuge

International Nuclear Information System (INIS)

Borman, V D; Bogovalov, S V; Borisevich, V D; Tronin, I V; Tronin, V N

2016-01-01

We argue on the basis of the results of 2D analysis of the gas flow in gas centrifuges that a reliable calculation of the circulation of the gas and gas content in the gas centrifuge is possible only in frameworks of 3D numerical simulation of gas dynamics in the gas centrifuge (hereafter GC). The group from National research nuclear university, MEPhI, has created a computer code for 3D simulation of the gas flow in GC. The results of the computer simulations of the gas flows in GC are presented. A model Iguassu centrifuge is explored for the simulations. A nonaxisymmetric gas flow is produced due to interaction of the hypersonic rotating flow with the scoops for extraction of the product and waste flows from the GC. The scoops produce shock waves penetrating into a working camera of the GC and form spiral waves there. (paper)

Twisted mass lattice QCD

International Nuclear Information System (INIS)

Shindler, A.

2007-07-01

I review the theoretical foundations, properties as well as the simulation results obtained so far of a variant of the Wilson lattice QCD formulation: Wilson twisted mass lattice QCD. Emphasis is put on the discretization errors and on the effects of these discretization errors on the phase structure for Wilson-like fermions in the chiral limit. The possibility to use in lattice simulations different lattice actions for sea and valence quarks to ease the renormalization patterns of phenomenologically relevant local operators, is also discussed. (orig.)

Twisted mass lattice QCD

Energy Technology Data Exchange (ETDEWEB)

Shindler, A. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC

2007-07-15

I review the theoretical foundations, properties as well as the simulation results obtained so far of a variant of the Wilson lattice QCD formulation: Wilson twisted mass lattice QCD. Emphasis is put on the discretization errors and on the effects of these discretization errors on the phase structure for Wilson-like fermions in the chiral limit. The possibility to use in lattice simulations different lattice actions for sea and valence quarks to ease the renormalization patterns of phenomenologically relevant local operators, is also discussed. (orig.)

Entropic Lattice Boltzmann: an implicit Large-Eddy Simulation?

Science.gov (United States)

Tauzin, Guillaume; Biferale, Luca; Sbragaglia, Mauro; Gupta, Abhineet; Toschi, Federico; Ehrhardt, Matthias; Bartel, Andreas

2017-11-01

We study the modeling of turbulence implied by the unconditionally stable Entropic Lattice Boltzmann Method (ELBM). We first focus on 2D homogeneous turbulence, for which we conduct numerical simulations for a wide range of relaxation times τ. For these simulations, we analyze the effective viscosity obtained by numerically differentiating the kinetic energy and enstrophy balance equations averaged over sub-domains of the computational grid. We aim at understanding the behavior of the implied sub-grid scale model and verify a formulation previously derived using Chapman-Enskog expansion. These ELBM benchmark simulations are thus useful to understand the range of validity of ELBM as a turbulence model. Finally, we will discuss an extension of the previously obtained results to the 3D case. Supported by the European Unions Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under the Marie Sklodowska-Curie Grant Agreement No. 642069 and by the European Research Council under the ERC Grant Agreement No. 339032.

Morphology of Gas Release in Physical Simulants

Energy Technology Data Exchange (ETDEWEB)

Daniel, Richard C.; Burns, Carolyn A.; Crawford, Amanda D.; Hylden, Laura R.; Bryan, Samuel A.; MacFarlan, Paul J.; Gauglitz, Phillip A.

2014-07-03

This report documents testing activities conducted as part of the Deep Sludge Gas Release Event Project (DSGREP). The testing described in this report focused on evaluating the potential retention and release mechanisms of hydrogen bubbles in underground radioactive waste storage tanks at Hanford. The goal of the testing was to evaluate the rate, extent, and morphology of gas release events in simulant materials. Previous, undocumented scoping tests have evidenced dramatically different gas release behavior from simulants with similar physical properties. Specifically, previous gas release tests have evaluated the extent of release of 30 Pa kaolin and 30 Pa bentonite clay slurries. While both materials are clays and both have equivalent material shear strength using a shear vane, it was found that upon stirring, gas was released immediately and completely from bentonite clay slurry while little if any gas was released from the kaolin slurry. The motivation for the current work is to replicate these tests in a controlled quality test environment and to evaluate the release behavior for another simulant used in DSGREP testing. Three simulant materials were evaluated: 1) a 30 Pa kaolin clay slurry, 2) a 30 Pa bentonite clay slurry, and 3) Rayleigh-Taylor (RT) Simulant (a simulant designed to support DSGREP RT instability testing. Entrained gas was generated in these simulant materials using two methods: 1) application of vacuum over about a 1-minute period to nucleate dissolved gas within the simulant and 2) addition of hydrogen peroxide to generate gas by peroxide decomposition in the simulants over about a 16-hour period. Bubble release was effected by vibrating the test material using an external vibrating table. When testing with hydrogen peroxide, gas release was also accomplished by stirring of the simulant.

tmLQCD: a program suite to simulate Wilson twisted mass lattice QCD

Energy Technology Data Exchange (ETDEWEB)

Jansen, Karl [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany); Urbach, Carsten [Institut fuer Physik, Humboldt-Universitaet, Berlin (Germany)

2009-05-15

We discuss a program suite for simulating Quantum Chromodynamics on a 4-dimensional space-time lattice. The basic Hybrid Monte Carlo algorithm is introduced and a number of algorithmic improvements are explained. We then discuss the implementations of these concepts as well as our parallelisation strategy in the actual simulation code. Finally, we provide a user guide to compile and run the program. (orig.)

tmLQCD: a program suite to simulate Wilson twisted mass lattice QCD

International Nuclear Information System (INIS)

Jansen, Karl; Urbach, Carsten

2009-05-01

We discuss a program suite for simulating Quantum Chromodynamics on a 4-dimensional space-time lattice. The basic Hybrid Monte Carlo algorithm is introduced and a number of algorithmic improvements are explained. We then discuss the implementations of these concepts as well as our parallelisation strategy in the actual simulation code. Finally, we provide a user guide to compile and run the program. (orig.)

Critical slowing down and error analysis in lattice QCD simulations

Energy Technology Data Exchange (ETDEWEB)

Schaefer, Stefan [Humboldt-Universitaet, Berlin (Germany). Inst. fuer Physik; Sommer, Rainer; Virotta, Francesco [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC

2010-09-15

We study the critical slowing down towards the continuum limit of lattice QCD simulations with Hybrid Monte Carlo type algorithms. In particular for the squared topological charge we find it to be very severe with an effective dynamical critical exponent of about 5 in pure gauge theory. We also consider Wilson loops which we can demonstrate to decouple from the modes which slow down the topological charge. Quenched observables are studied and a comparison to simulations of full QCD is made. In order to deal with the slow modes in the simulation, we propose a method to incorporate the information from slow observables into the error analysis of physical observables and arrive at safer error estimates. (orig.)

Critical slowing down and error analysis in lattice QCD simulations

International Nuclear Information System (INIS)

Schaefer, Stefan; Sommer, Rainer; Virotta, Francesco

2010-09-01

We study the critical slowing down towards the continuum limit of lattice QCD simulations with Hybrid Monte Carlo type algorithms. In particular for the squared topological charge we find it to be very severe with an effective dynamical critical exponent of about 5 in pure gauge theory. We also consider Wilson loops which we can demonstrate to decouple from the modes which slow down the topological charge. Quenched observables are studied and a comparison to simulations of full QCD is made. In order to deal with the slow modes in the simulation, we propose a method to incorporate the information from slow observables into the error analysis of physical observables and arrive at safer error estimates. (orig.)

Study of Particle Rotation Effect in Gas-Solid Flows using Direct Numerical Simulation with a Lattice Boltzmann Method

Energy Technology Data Exchange (ETDEWEB)

Kwon, Kyung [Tuskegee Univ., Tuskegee, AL (United States); Fan, Liang-Shih [The Ohio State Univ., Columbus, OH (United States); Zhou, Qiang [The Ohio State Univ., Columbus, OH (United States); Yang, Hui [The Ohio State Univ., Columbus, OH (United States)

2014-09-30

A new and efficient direct numerical method with second-order convergence accuracy was developed for fully resolved simulations of incompressible viscous flows laden with rigid particles. The method combines the state-of-the-art immersed boundary method (IBM), the multi-direct forcing method, and the lattice Boltzmann method (LBM). First, the multi-direct forcing method is adopted in the improved IBM to better approximate the no-slip/no-penetration (ns/np) condition on the surface of particles. Second, a slight retraction of the Lagrangian grid from the surface towards the interior of particles with a fraction of the Eulerian grid spacing helps increase the convergence accuracy of the method. An over-relaxation technique in the procedure of multi-direct forcing method and the classical fourth order Runge-Kutta scheme in the coupled fluid-particle interaction were applied. The use of the classical fourth order Runge-Kutta scheme helps the overall IB-LBM achieve the second order accuracy and provides more accurate predictions of the translational and rotational motion of particles. The preexistent code with the first-order convergence rate is updated so that the updated new code can resolve the translational and rotational motion of particles with the second-order convergence rate. The updated code has been validated with several benchmark applications. The efficiency of IBM and thus the efficiency of IB-LBM were improved by reducing the number of the Lagragian markers on particles by using a new formula for the number of Lagrangian markers on particle surfaces. The immersed boundary-lattice Boltzmann method (IBLBM) has been shown to predict correctly the angular velocity of a particle. Prior to examining drag force exerted on a cluster of particles, the updated IB-LBM code along with the new formula for the number of Lagrangian markers has been further validated by solving several theoretical problems. Moreover, the unsteadiness of the drag force is examined when a

Lattice model of ionic liquid confined by metal electrodes

Science.gov (United States)

Girotto, Matheus; Malossi, Rodrigo M.; dos Santos, Alexandre P.; Levin, Yan

2018-05-01

We study, using Monte Carlo simulations, the density profiles and differential capacitance of ionic liquids confined by metal electrodes. To compute the electrostatic energy, we use the recently developed approach based on periodic Green's functions. The method also allows us to easily calculate the induced charge on the electrodes permitting an efficient implementation of simulations in a constant electrostatic potential ensemble. To speed up the simulations further, we model the ionic liquid as a lattice Coulomb gas and precalculate the interaction potential between the ions. We show that the lattice model captures the transition between camel-shaped and bell-shaped capacitance curves—the latter characteristic of ionic liquids (strong coupling limit) and the former of electrolytes (weak coupling). We observe the appearance of a second peak in the differential capacitance at ≈0.5 V for 2:1 ionic liquids, as the packing fraction is increased. Finally, we show that ionic size asymmetry decreases substantially the capacitance maximum, when all other parameters are kept fixed.

Simulating condensation on microstructured surfaces using Lattice Boltzmann Method

Science.gov (United States)

Alexeev, Alexander; Vasyliv, Yaroslav

2017-11-01

We simulate a single component fluid condensing on 2D structured surfaces with different wettability. To simulate the two phase fluid, we use the athermal Lattice Boltzmann Method (LBM) driven by a pseudopotential force. The pseudopotential force results in a non-ideal equation of state (EOS) which permits liquid-vapor phase change. To account for thermal effects, the athermal LBM is coupled to a finite volume discretization of the temperature evolution equation obtained using a thermal energy rate balance for the specific internal energy. We use the developed model to probe the effect of surface structure and surface wettability on the condensation rate in order to identify microstructure topographies promoting condensation. Financial support is acknowledged from Kimberly-Clark.

Finite-lattice-spacing corrections to masses and g factors on a lattice

International Nuclear Information System (INIS)

Roskies, R.; Wu, J.C.

1986-01-01

We suggest an alternative method for extracting masses and g factors from lattice calculations. Our method takes account of more of the infrared and ultraviolet lattice effects. It leads to more reasonable results in simulations of QED on a lattice

Multi-component Lattice Boltzmann simulation of the hydrodynamics in drip emitters

Directory of Open Access Journals (Sweden)

Giacomo Falcucci

2017-09-01

Full Text Available In this paper, we propose a fast and efficient numerical technique based on the Lattice Boltzmann method (LBM to model the flow through a reference drip emitter geometry. The aim of the study is to demonstrate the applicability of the LBM as a reliable simulation tool for the hydraulic optimisation of irrigation systems. Results for the water flow through a rectangular drip emitter are in good agreement with literature numerical and experimental data. Furthermore, we demonstrate the feasibility of the proposed model to simulate a multi-component flow that could be used to simulate the presence of additives, contaminants, and suspended particles.

Gas-liquid Relative Permeability Estimation in 2D Porous Media by Lattice Boltzmann Method: Low Viscosity Ratio 2D LBM Relative Permeability

Directory of Open Access Journals (Sweden)

Sadegh Mahmoudi

2013-04-01

Full Text Available This work is a primary achievement in studying the CO2 and N2–oil systems. To predict gas-liquid relative permeability curves, a Shan-Chen type multicomponent multiphase lattice Boltzmann model for two-phase flow through 2D porous media is developed. Periodic and bounce back boundary conditions are applied to the model with the Guo scheme for the external body force (i.e., the pressure gradient. The influence of relationship between cohesion and adsorption parameters and the interfacial tension values in Young's equation, pore structure (micro scan image derived porous media response is compared with corresponding porosity and permeability ideal sphere pack structure, and saturation distribution on relative permeability curves are studied with the aim to achieve the realistic stable condition for the simulation of gas-liquid systems with a low viscosity ratio.

Numerical Investigation of Cross Flow Phenomena in a Tight-Lattice Rod Bundle Using Advanced Interface Tracking Method

Science.gov (United States)

Zhang, Weizhong; Yoshida, Hiroyuki; Ose, Yasuo; Ohnuki, Akira; Akimoto, Hajime; Hotta, Akitoshi; Fujimura, Ken

In relation to the design of an innovative FLexible-fuel-cycle Water Reactor (FLWR), investigation of thermal-hydraulic performance in tight-lattice rod bundles of the FLWR is being carried out at Japan Atomic Energy Agency (JAEA). The FLWR core adopts a tight triangular lattice arrangement with about 1 mm gap clearance between adjacent fuel rods. In view of importance of accurate prediction of cross flow between subchannels in the evaluation of the boiling transition (BT) in the FLWR core, this study presents a statistical evaluation of numerical simulation results obtained by a detailed two-phase flow simulation code, TPFIT, which employs an advanced interface tracking method. In order to clarify mechanisms of cross flow in such tight lattice rod bundles, the TPFIT is applied to simulate water-steam two-phase flow in two modeled subchannels. Attention is focused on instantaneous fluctuation characteristics of cross flow. With the calculation of correlation coefficients between differential pressure and gas/liquid mixing coefficients, time scales of cross flow are evaluated, and effects of mixing section length, flow pattern and gap spacing on correlation coefficients are investigated. Differences in mechanism between gas and liquid cross flows are pointed out.

Quantum Simulation with Circuit-QED Lattices: from Elementary Building Blocks to Many-Body Theory

Science.gov (United States)

Zhu, Guanyu

Recent experimental and theoretical progress in superconducting circuits and circuit QED (quantum electrodynamics) has helped to develop high-precision techniques to control, manipulate, and detect individual mesoscopic quantum systems. A promising direction is hence to scale up from individual building blocks to form larger-scale quantum many-body systems. Although realizing a scalable fault-tolerant quantum computer still faces major barriers of decoherence and quantum error correction, it is feasible to realize scalable quantum simulators with state-of-the-art technology. From the technological point of view, this could serve as an intermediate stage towards the final goal of a large-scale quantum computer, and could help accumulating experience with the control of quantum systems with a large number of degrees of freedom. From the physical point of view, this opens up a new regime where condensed matter systems can be simulated and studied, here in the context of strongly correlated photons and two-level systems. In this thesis, we mainly focus on two aspects of circuit-QED based quantum simulation. First, we discuss the elementary building blocks of the quantum simulator, in particular a fluxonium circuit coupled to a superconducting resonator. We show the interesting properties of the fluxonium circuit as a qubit, including the unusual structure of its charge matrix elements. We also employ perturbation theory to derive the effective Hamiltonian of the coupled system in the dispersive regime, where qubit and the photon frequencies are detuned. The observables predicted with our theory, including dispersive shifts and Kerr nonlinearity, are compared with data from experiments, such as homodyne transmission and two-tone spectroscopy. These studies also relate to the problem of detection in a circuit-QED quantum simulator. Second, we study many-body physics of circuit-QED lattices, serving as quantum simulators. In particular, we focus on two different

Lattice Boltzmann Simulations in the Slip and Transition Flow Regime with the Peano Framework

KAUST Repository

Neumann, Philipp

2012-01-01

We present simulation results of flows in the finite Knudsen range, which is in the slip and transition flow regime. Our implementations are based on the Lattice Boltzmann method and are accomplished within the Peano framework. We validate our code by solving two- and three-dimensional channel flow problems and compare our results with respective experiments from other research groups. We further apply our Lattice Boltzmann solver to the geometrical setup of a microreactor consisting of differently sized channels and a reactor chamber. Here, we apply static adaptive grids to fur-ther reduce computational costs. We further investigate the influence of using a simple BGK collision kernel in coarse grid regions which are further away from the slip boundaries. Our results are in good agreement with theory and non-adaptive simulations, demonstrating the validity and the capabilities of our adaptive simulation software for flow problems at finite Knudsen numbers.

Comparative Study of Algorithms for the Numerical Simulation of Lattice QCD

International Nuclear Information System (INIS)

Luz, Fernando H. P.; Mendes, Tereza

2010-01-01

Large-scale numerical simulations are the prime method for a nonperturbative study of QCD from first principles. Although the lattice simulation of the pure-gauge (or quenched-QCD) case may be performed very efficiently on parallel machines, there are several additional difficulties in the simulation of the full-QCD case, i.e. when dynamical quark effects are taken into account. We discuss the main aspects of full-QCD simulations, describing the most common algorithms. We present a comparative analysis of performance for two versions of the hybrid Monte Carlo method (the so-called R and RHMC algorithms), as provided in the MILC software package. We consider two degenerate flavors of light quarks in the staggered formulation, having in mind the case of finite-temperature QCD.

Testing the holographic principle using lattice simulations

Directory of Open Access Journals (Sweden)

Jha Raghav G.

2018-01-01

Full Text Available The lattice studies of maximally supersymmetric Yang-Mills (MSYM theory at strong coupling and large N is important for verifying gauge/gravity duality. Due to the progress made in the last decade, based on ideas from topological twisting and orbifolding, it is now possible to study these theories on the lattice while preserving an exact supersymmetry on the lattice. We present some results from the lattice studies of two-dimensional MSYM which is related to Type II supergravity. Our results agree with the thermodynamics of different black hole phases on the gravity side and the phase transition (Gregory–Laflamme between them.

Realistic multisite lattice-gas modeling and KMC simulation of catalytic surface reactions: Kinetics and multiscale spatial behavior for CO-oxidation on metal (1 0 0) surfaces

Science.gov (United States)

Liu, Da-Jiang; Evans, James W.

2013-12-01

A realistic molecular-level description of catalytic reactions on single-crystal metal surfaces can be provided by stochastic multisite lattice-gas (msLG) models. This approach has general applicability, although in this report, we will focus on the example of CO-oxidation on the unreconstructed fcc metal (1 0 0) or M(1 0 0) surfaces of common catalyst metals M = Pd, Rh, Pt and Ir (i.e., avoiding regimes where Pt and Ir reconstruct). These models can capture the thermodynamics and kinetics of adsorbed layers for the individual reactants species, such as CO/M(1 0 0) and O/M(1 0 0), as well as the interaction and reaction between different reactant species in mixed adlayers, such as (CO + O)/M(1 0 0). The msLG models allow population of any of hollow, bridge, and top sites. This enables a more flexible and realistic description of adsorption and adlayer ordering, as well as of reaction configurations and configuration-dependent barriers. Adspecies adsorption and interaction energies, as well as barriers for various processes, constitute key model input. The choice of these energies is guided by experimental observations, as well as by extensive Density Functional Theory analysis. Model behavior is assessed via Kinetic Monte Carlo (KMC) simulation. We also address the simulation challenges and theoretical ramifications associated with very rapid diffusion and local equilibration of reactant adspecies such as CO. These msLG models are applied to describe adsorption, ordering, and temperature programmed desorption (TPD) for individual CO/M(1 0 0) and O/M(1 0 0) reactant adlayers. In addition, they are also applied to predict mixed (CO + O)/M(1 0 0) adlayer structure on the nanoscale, the complete bifurcation diagram for reactive steady-states under continuous flow conditions, temperature programmed reaction (TPR) spectra, and titration reactions for the CO-oxidation reaction. Extensive and reasonably successful comparison of model predictions is made with experimental

Numerical simulation of direct methanol fuel cells using lattice Boltzmann method

Energy Technology Data Exchange (ETDEWEB)

Delavar, Mojtaba Aghajani; Farhadi, Mousa; Sedighi, Kurosh [Faculty of Mechanical Engineering, Babol University of Technology, Babol, P.O. Box 484 (Iran)

2010-09-15

In this study Lattice Boltzmann Method (LBM) as an alternative of conventional computational fluid dynamics method is used to simulate Direct Methanol Fuel Cell (DMFC). A two dimensional lattice Boltzmann model with 9 velocities, D2Q9, is used to solve the problem. The computational domain includes all seven parts of DMFC: anode channel, catalyst and diffusion layers, membrane and cathode channel, catalyst and diffusion layers. The model has been used to predict the flow pattern and concentration fields of different species in both clear and porous channels to investigate cell performance. The results have been compared well with results in literature for flow in porous and clear channels and cell polarization curves of the DMFC at different flow speeds and feed methanol concentrations. (author)

Lattice gauge theories and Monte Carlo simulations

International Nuclear Information System (INIS)

Rebbi, C.

1981-11-01

After some preliminary considerations, the discussion of quantum gauge theories on a Euclidean lattice takes up the definition of Euclidean quantum theory and treatment of the continuum limit; analogy is made with statistical mechanics. Perturbative methods can produce useful results for strong or weak coupling. In the attempts to investigate the properties of the systems for intermediate coupling, numerical methods known as Monte Carlo simulations have proved valuable. The bulk of this paper illustrates the basic ideas underlying the Monte Carlo numerical techniques and the major results achieved with them according to the following program: Monte Carlo simulations (general theory, practical considerations), phase structure of Abelian and non-Abelian models, the observables (coefficient of the linear term in the potential between two static sources at large separation, mass of the lowest excited state with the quantum numbers of the vacuum (the so-called glueball), the potential between two static sources at very small distance, the critical temperature at which sources become deconfined), gauge fields coupled to basonic matter (Higgs) fields, and systems with fermions

Hamiltonian and potentials in derivative pricing models: exact results and lattice simulations

Science.gov (United States)

Baaquie, Belal E.; Corianò, Claudio; Srikant, Marakani

2004-03-01

The pricing of options, warrants and other derivative securities is one of the great success of financial economics. These financial products can be modeled and simulated using quantum mechanical instruments based on a Hamiltonian formulation. We show here some applications of these methods for various potentials, which we have simulated via lattice Langevin and Monte Carlo algorithms, to the pricing of options. We focus on barrier or path dependent options, showing in some detail the computational strategies involved.

Lattice Commissioning Strategy Simulation for the B Factory

International Nuclear Information System (INIS)

Lee, M.; Whittum, D.; Yan, Y.; Cai, Y.; Shoaee, H.

2011-01-01

To prepare for the PEP-II turn on, we have studied one commissioning strategy with simulated lattice errors. Features such as difference and absolute orbit analysis and correction are discussed. To prepare for the commissioning of the PEP-II injection line and high energy ring (HER), we have developed a system for on-line orbit analysis by merging two existing codes: LEGO and RESOLVE. With the LEGO-RESOLVE system, we can study the problem of finding quadrupole alignment and beam position (BPM) offset errors with simulated data. We have increased the speed and versatility of the orbit analysis process by using a command file written in a script language designed specifically for RESOLVE. In addition, we have interfaced the LEGO-RESOLVE system to the control system of the B-Factory. In this paper, we describe online analysis features of the LEGO-RESOLVE system and present examples of practical applications.

Simulation of bubble motion under gravity by lattice Boltzmann method

International Nuclear Information System (INIS)

Takada, Naoki; Misawa, Masaki; Tomiyama, Akio; Hosokawa, Shigeo

2001-01-01

We describe the numerical simulation results of bubble motion under gravity by the lattice Boltzmann method (LBM), which assumes that a fluid consists of mesoscopic fluid particles repeating collision and translation and a multiphase interface is reproduced in a self-organizing way by repulsive interaction between different kinds of particles. The purposes in this study are to examine the applicability of LBM to the numerical analysis of bubble motions, and to develop a three-dimensional version of the binary fluid model that introduces a free energy function. We included the buoyancy terms due to the density difference in the lattice Boltzmann equations, and simulated single-and two-bubble motions, setting flow conditions according to the Eoetvoes and Morton numbers. The two-dimensional results by LBM agree with those by the Volume of Fluid method based on the Navier-Stokes equations. The three-dimensional model possesses the surface tension satisfying the Laplace's law, and reproduces the motion of single bubble and the two-bubble interaction of their approach and coalescence in circular tube. There results prove that the buoyancy terms and the 3D model proposed here are suitable, and that LBM is useful for the numerical analysis of bubble motion under gravity. (author)

A new lattice Boltzmann equation to simulate density-driven convection of carbon dioxide

KAUST Repository

Allen, Rebecca; Reis, Tim; Sun, Shuyu

2013-01-01

-driven convection becomes an important transport process to model. However, the challenge lies in simulating this transport process accurately with high spatial resolution and low CPU cost. This issue can be addressed by using the lattice Boltzmann equation (LBE

Simulations of relativistic quantum plasmas using real-time lattice scalar QED

Science.gov (United States)

Shi, Yuan; Xiao, Jianyuan; Qin, Hong; Fisch, Nathaniel J.

2018-05-01

Real-time lattice quantum electrodynamics (QED) provides a unique tool for simulating plasmas in the strong-field regime, where collective plasma scales are not well separated from relativistic-quantum scales. As a toy model, we study scalar QED, which describes self-consistent interactions between charged bosons and electromagnetic fields. To solve this model on a computer, we first discretize the scalar-QED action on a lattice, in a way that respects geometric structures of exterior calculus and U(1)-gauge symmetry. The lattice scalar QED can then be solved, in the classical-statistics regime, by advancing an ensemble of statistically equivalent initial conditions in time, using classical field equations obtained by extremizing the discrete action. To demonstrate the capability of our numerical scheme, we apply it to two example problems. The first example is the propagation of linear waves, where we recover analytic wave dispersion relations using numerical spectrum. The second example is an intense laser interacting with a one-dimensional plasma slab, where we demonstrate natural transition from wakefield acceleration to pair production when the wave amplitude exceeds the Schwinger threshold. Our real-time lattice scheme is fully explicit and respects local conservation laws, making it reliable for long-time dynamics. The algorithm is readily parallelized using domain decomposition, and the ensemble may be computed using quantum parallelism in the future.

Monte Carlo simulation of the three-state vector Potts model on a three-dimensional random lattice

International Nuclear Information System (INIS)

Jianbo Zhang; Heping Ying

1991-09-01

We have performed a numerical simulation of the three-state vector Potts model on a three-dimensional random lattice. The averages of energy density, magnetization, specific heat and susceptibility of the system in the N 3 (N=8,10,12) lattices were calculated. The results show that a first order nature of the Z(3) symmetry breaking transition appears, as characterized by a thermal hysterisis in the energy density as well as an abrupt drop of magnetization being sharper and discontinuous with increasing of volume in the cross-over region. The results obtained on the random lattice were consistent with those obtained on the three-dimensional cubic lattice. (author). 12 refs, 4 figs

Finite-Size Scaling in a Two-Temperature Lattice Gas: a Monte Carlo Study of Critical Properties

DEFF Research Database (Denmark)

Larsen, Heine; Præstgaard, Eigil; Zia, R.K.P.

1994-01-01

We present computer studies of the critical properties of an Ising lattice gas driven to a non-equilibrium steady state by coupling to two temperature baths. Anisotropic scaling, a dominant feature near criticality, is used as a tool to extract the values of the critical temperature and some expo...

Lattice QCD on fine lattices

Energy Technology Data Exchange (ETDEWEB)

Schaefer, Stefan [DESY (Germany). Neumann Inst. for Computing

2016-11-01

These configurations are currently in use in many on-going projects carried out by researchers throughout Europe. In particular this data will serve as an essential input into the computation of the coupling constant of QCD, where some of the simulations are still on-going. But also projects computing the masses of hadrons and investigating their structure are underway as well as activities in the physics of heavy quarks. As this initial project of gauge field generation has been successful, it is worthwhile to extend the currently available ensembles with further points in parameter space. These will allow to further study and control systematic effects like the ones introduced by the finite volume, the non-physical quark masses and the finite lattice spacing. In particular certain compromises have still been made in the region where pion masses and lattice spacing are both small. This is because physical pion masses require larger lattices to keep the effects of the finite volume under control. At light pion masses, a precise control of the continuum extrapolation is therefore difficult, but certainly a main goal of future simulations. To reach this goal, algorithmic developments as well as faster hardware will be needed.

Lattice dynamics and molecular dynamics simulation of complex materials

International Nuclear Information System (INIS)

Chaplot, S.L.

1997-01-01

In this article we briefly review the lattice dynamics and molecular dynamics simulation techniques, as used for complex ionic and molecular solids, and demonstrate a number of applications through examples of our work. These computational studies, along with experiments, have provided microscopic insight into the structure and dynamics, phase transitions and thermodynamical properties of a variety of materials including fullerene, high temperature superconducting oxides and geological minerals as a function of pressure and temperature. The computational techniques also allow the study of the structures and dynamics associated with disorder, defects, surfaces, interfaces etc. (author)

Gluon gas viscosity in nonperturbative region

International Nuclear Information System (INIS)

Il'in, S.V.; Mogilevskij, O.A.; Smolyanskij, S.A.; Zinov'ev, G.M.

1992-01-01

Using the Green-Kubo-type formulae and the cutoff model motivated by Monte Carlo lattice gluodynamics simulations we find the temperature behaviour of shear viscosity of gluon gas in the region of deconfinement phase transition. 22 refs.; 1 fig. (author)

The properties of tagged lattice fluids: II. Velocity correlation functions

International Nuclear Information System (INIS)

Binder, P.M.; d'Humieres, D.; Poujol, L.

1988-01-01

We report preliminary measurements of the velocity autocorrelation function for a tagged particle in a lattice gas. These measurements agree with the Boltzmann-level theory. The Green-Kubo integration of these measurements agrees with theoretical predictions for the diffusion coefficient. To within the error bars of the simulations (3 /times/ 10/sup /minus/3/) we observe no long-time tails. 9 refs., 1 fig., 1 tab

An Ideal Gas Law Simulator for Atmospheric Gas Molecules ...

African Journals Online (AJOL)

The ideal gas law which is the equation of state of a hypothetical ideal gas that allows us to gain useful insights into the behavior of most real gases at low densities was utilized in this work to conceptualize, design and develop the ideal gas law simulator in a 3 dimensional space using Microsoft Visual Studio, Microsoft ...

Numerical simulation of jet breakup behavior by the lattice Boltzmann method

International Nuclear Information System (INIS)

Matsuo, Eiji; Koyama, Kazuya; Abe, Yutaka; Iwasawa, Yuzuru; Ebihara, Ken-ichi

2015-01-01

In order to understand the jet breakup behavior of the molten core material into coolant during a core disruptive accident (CDA) for a sodium-cooled fast reactor (SFR), we simulated the jet breakup due to the hydrodynamic interaction using the lattice Boltzmann method (LBM). The applicability of the LBM to the jet breakup simulation was validated by comparison with our experimental data. In addition, the influence of several dimensionless numbers such as Weber number and Froude number was examined using the LBM. As a result, we validated applicability of the LBM to the jet breakup simulation, and found that the jet breakup length is independent of Froude number and in good agreement with the Epstein's correlation when the jet interface becomes unstable. (author)

Simulation and detection of massive Dirac fermions with cold atoms in one-dimensional optical lattice

Energy Technology Data Exchange (ETDEWEB)

Yu Yafei, E-mail: yfyuks@hotmail.com [Laboratory of Nanophotonic Functional Materials and Devices, LQIT and SIPSE, South China Normal University, Guangzhou 510006 (China); Shan Chuanjia [Laboratory of Nanophotonic Functional Materials and Devices, LQIT and SIPSE, South China Normal University, Guangzhou 510006 (China); College of Physics and Electronic Science, Hubei Normal University, Huangshi 435002 (China); Mei Feng; Zhang Zhiming [Laboratory of Nanophotonic Functional Materials and Devices, LQIT and SIPSE, South China Normal University, Guangzhou 510006 (China)

2012-09-15

We propose a simple but feasible experimental scheme to simulate and detect Dirac fermions with cold atoms trapped in one-dimensional optical lattice. In our scheme, through tuning the laser intensity, the one-dimensional optical lattice can have two sites in each unit cell and the atoms around the low energy behave as massive Dirac fermions. Furthermore, we show that these relativistic quasiparticles can be detected experimentally by using atomic density profile measurements and Bragg scattering.

Direct Monte Carlo simulation of nanoscale mixed gas bearings

Directory of Open Access Journals (Sweden)

Kyaw Sett Myo

2015-06-01

Full Text Available The conception of sealed hard drives with helium gas mixture has been recently suggested over the current hard drives for achieving higher reliability and less position error. Therefore, it is important to understand the effects of different helium gas mixtures on the slider bearing characteristics in the head–disk interface. In this article, the helium/air and helium/argon gas mixtures are applied as the working fluids and their effects on the bearing characteristics are studied using the direct simulation Monte Carlo method. Based on direct simulation Monte Carlo simulations, the physical properties of these gas mixtures such as mean free path and dynamic viscosity are achieved and compared with those obtained from theoretical models. It is observed that both results are comparable. Using these gas mixture properties, the bearing pressure distributions are calculated under different fractions of helium with conventional molecular gas lubrication models. The outcomes reveal that the molecular gas lubrication results could have relatively good agreement with those of direct simulation Monte Carlo simulations, especially for pure air, helium, or argon gas cases. For gas mixtures, the bearing pressures predicted by molecular gas lubrication model are slightly larger than those from direct simulation Monte Carlo simulation.

Solutions for correlations along the coexistence curve and at the critical point of a kagomé lattice gas with three-particle interactions

Science.gov (United States)

Barry, J. H.; Muttalib, K. A.; Tanaka, T.

2008-01-01

We consider a two-dimensional (d=2) kagomé lattice gas model with attractive three-particle interactions around each triangular face of the kagomé lattice. Exact solutions are obtained for multiparticle correlations along the liquid and vapor branches of the coexistence curve and at criticality. The correlation solutions are also determined along the continuation of the curvilinear diameter of the coexistence region into the disordered fluid region. The method generates a linear algebraic system of correlation identities with coefficients dependent only upon the interaction parameter. Using a priori knowledge of pertinent solutions for the density and elementary triplet correlation, one finds a closed and linearly independent set of correlation identities defined upon a spatially compact nine-site cluster of the kagomé lattice. Resulting exact solution curves of the correlations are plotted and discussed as functions of the temperature and are compared with corresponding results in a traditional kagomé lattice gas having nearest-neighbor pair interactions. An example of application for the multiparticle correlations is demonstrated in cavitation theory.

The Linked Neighbour List (LNL) method for fast off-lattice Monte Carlo simulations of fluids

Science.gov (United States)

Mazzeo, M. D.; Ricci, M.; Zannoni, C.

2010-03-01

We present a new algorithm, called linked neighbour list (LNL), useful to substantially speed up off-lattice Monte Carlo simulations of fluids by avoiding the computation of the molecular energy before every attempted move. We introduce a few variants of the LNL method targeted to minimise memory footprint or augment memory coherence and cache utilisation. Additionally, we present a few algorithms which drastically accelerate neighbour finding. We test our methods on the simulation of a dense off-lattice Gay-Berne fluid subjected to periodic boundary conditions observing a speedup factor of about 2.5 with respect to a well-coded implementation based on a conventional link-cell. We provide several implementation details of the different key data structures and algorithms used in this work.

Recent progress in molecular simulation of nanoporous graphene membranes for gas separation

Science.gov (United States)

Fatemi, S. Mahmood; Baniasadi, Aminreza; Moradi, Mahrokh

2017-07-01

If an ideal membrane for gas separation is to be obtained, the following three characteristics should be considered: the membrane should be as thin as possible, be mechanically robust, and have welldefined pore sizes. These features will maximize its solvent flux, preserve it from fracture, and guarantee its selectivity. Graphene is made up of a hexagonal honeycomb lattice of carbon atoms with sp 2 hybridization state forming a one-atom-thick sheet of graphite. Following conversion of the honeycomb lattices into nanopores with a specific geometry and size, a nanoporous graphene membrane that offers high efficiency as a separation membrane because of the ultrafast molecular permeation rate as a result of its one-atom thickness is obtained. Applications of nanoporous graphene membranes for gas separation have been receiving remarkably increasing attention because nanoporous graphene membranes show promising results in this area. This review focuses on the recent advances in nanoporous graphene membranes for applications in gas separation, with a major emphasis on theoretical works. The attractive properties of nanoporous graphene membranes introduce make them appropriate candidates for gas separation and gas molecular-sieving processes in nanoscale dimensions.

Lattice strings

International Nuclear Information System (INIS)

Thorn, C.B.

1988-01-01

The possibility of studying non-perturbative effects in string theory using a world sheet lattice is discussed. The light-cone lattice string model of Giles and Thorn is studied numerically to assess the accuracy of ''coarse lattice'' approximations. For free strings a 5 by 15 lattice seems sufficient to obtain better than 10% accuracy for the bosonic string tachyon mass squared. In addition a crude lattice model simulating string like interactions is studied to find out how easily a coarse lattice calculation can pick out effects such as bound states which would qualitatively alter the spectrum of the free theory. The role of the critical dimension in obtaining a finite continuum limit is discussed. Instead of the ''gaussian'' lattice model one could use one of the vertex models, whose continuum limit is the same as a gaussian model on a torus of any radius. Indeed, any critical 2 dimensional statistical system will have a stringy continuum limit in the absence of string interactions. 8 refs., 1 fig. , 9 tabs

Lattice Boltzmann Simulations in the Slip and Transition Flow Regime with the Peano Framework

KAUST Repository

Neumann, Philipp; Rohrmann, Till

2012-01-01

We present simulation results of flows in the finite Knudsen range, which is in the slip and transition flow regime. Our implementations are based on the Lattice Boltzmann method and are accomplished within the Peano framework. We validate our code

A Parrinello-Rahman approach to vortex lattices

International Nuclear Information System (INIS)

Carretero-Gonzalez, R.; Kevrekidis, P.G.; Kevrekidis, I.G.; Maroudas, D.; Frantzeskakis, D.J.

2005-01-01

We present a framework for studying vortex lattice patterns and their structural transitions, using the Parrinello-Rahman (PR) method for molecular-dynamics (MD) simulations. Assuming an interaction between vortices derived from a Ginzburg-Landau field-theoretic context, we extract the ground-state of a 'vortex gas' using the PR-MD technique and find it to be a triangular pattern. Other patterns are also obtained for special initial conditions. Generalizations of the technique, such as the inclusion of external potentials or excitation of quadrupolar modes, are also commented upon

Circuit QED lattices: Towards quantum simulation with superconducting circuits

Energy Technology Data Exchange (ETDEWEB)

Schmidt, Sebastian [Institute for Theoretical Physics, ETH Zurich, 8093, Zurich (Switzerland); Koch, Jens [Department of Physics and Astronomy, Northwestern University, Evanston, IL, 60208 (United States)

2013-06-15

The Jaynes-Cummings model describes the coupling between photons and a single two-level atom in a simplified representation of light-matter interactions. In circuit QED, this model is implemented by combining microwave resonators and superconducting qubits on a microchip with unprecedented experimental control. Arranging qubits and resonators in the form of a lattice realizes a new kind of Hubbard model, the Jaynes-Cummings-Hubbard model, in which the elementary excitations are polariton quasi-particles. Due to the genuine openness of photonic systems, circuit QED lattices offer the possibility to study the intricate interplay of collective behavior, strong correlations and non-equilibrium physics. Thus, turning circuit QED into an architecture for quantum simulation, i.e., using a well-controlled system to mimic the intricate quantum behavior of another system too daunting for a theorist to tackle head-on, is an exciting idea which has served as theorists' playground for a while and is now also starting to catch on in experiments. This review gives a summary of the most recent theoretical proposals and experimental efforts. (copyright 2013 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Simulation of N{sub f} = 2 + 1 lattice QCD at realistic quark masses

Energy Technology Data Exchange (ETDEWEB)

Schierholz, Gerrit

2014-07-01

So far most lattice QCD simulations are performed neglecting electromagnetic effects. In order to compute physical observables to high precision, it is important to include and control contributions from QED. We have initiated a similar program, as the symmetry of the electromagnetic current is similar to that of the mass matrix mass m=(m{sub u}+m{sub d}+m{sub s})/3=constant versus e{sub u}+e{sub d}+e{sub s}=constant=0. In a follow-up project we shall use this expansion and complement our previous simulations by a fully dynamical simulation of QCD+QED. (orig.)

Mixed Precision Solver Scalable to 16000 MPI Processes for Lattice Quantum Chromodynamics Simulations on the Oakforest-PACS System

OpenAIRE

Boku, Taisuke; Ishikawa, Ken-Ichi; Kuramashi, Yoshinobu; Meadows, Lawrence

2017-01-01

Lattice Quantum Chromodynamics (Lattice QCD) is a quantum field theory on a finite discretized space-time box so as to numerically compute the dynamics of quarks and gluons to explore the nature of subatomic world. Solving the equation of motion of quarks (quark solver) is the most compute-intensive part of the lattice QCD simulations and is one of the legacy HPC applications. We have developed a mixed-precision quark solver for a large Intel Xeon Phi (KNL) system named "Oakforest-PACS", empl...

Lattice Boltzmann method used to simulate particle motion in a conduit

Directory of Open Access Journals (Sweden)

Dolanský Jindřich

2017-06-01

Full Text Available A three-dimensional numerical simulation of particle motion in a pipe with a rough bed is presented. The simulation based on the Lattice Boltzmann Method (LBM employs the hybrid diffuse bounce-back approach to model moving boundaries. The bed of the pipe is formed by stationary spherical particles of the same size as the moving particles. Particle movements are induced by gravitational and hydrodynamic forces. To evaluate the hydrodynamic forces, the Momentum Exchange Algorithm is used. The LBM unified computational frame makes it possible to simulate both the particle motion and the fluid flow and to study mutual interactions of the carrier liquid flow and particles and the particle–bed and particle–particle collisions. The trajectories of simulated and experimental particles are compared. The Particle Tracking method is used to track particle motion. The correctness of the applied approach is assessed.

Steady-state hydrodynamic instabilities of active liquid crystals: hybrid lattice Boltzmann simulations.

Science.gov (United States)

Marenduzzo, D; Orlandini, E; Cates, M E; Yeomans, J M

2007-09-01

We report hybrid lattice Boltzmann (HLB) simulations of the hydrodynamics of an active nematic liquid crystal sandwiched between confining walls with various anchoring conditions. We confirm the existence of a transition between a passive phase and an active phase, in which there is spontaneous flow in the steady state. This transition is attained for sufficiently "extensile" rods, in the case of flow-aligning liquid crystals, and for sufficiently "contractile" ones for flow-tumbling materials. In a quasi-one-dimensional geometry, deep in the active phase of flow-aligning materials, our simulations give evidence of hysteresis and history-dependent steady states, as well as of spontaneous banded flow. Flow-tumbling materials, in contrast, rearrange themselves so that only the two boundary layers flow in steady state. Two-dimensional simulations, with periodic boundary conditions, show additional instabilities, with the spontaneous flow appearing as patterns made up of "convection rolls." These results demonstrate a remarkable richness (including dependence on anchoring conditions) in the steady-state phase behavior of active materials, even in the absence of external forcing; they have no counterpart for passive nematics. Our HLB methodology, which combines lattice Boltzmann for momentum transport with a finite difference scheme for the order parameter dynamics, offers a robust and efficient method for probing the complex hydrodynamic behavior of active nematics.

Lattice Methods for Quantum Chromodynamics

CERN Document Server

DeGrand, Thomas

2006-01-01

Numerical simulation of lattice-regulated QCD has become an important source of information about strong interactions. In the last few years there has been an explosion of techniques for performing ever more accurate studies on the properties of strongly interacting particles. Lattice predictions directly impact many areas of particle and nuclear physics theory and phenomenology. This book provides a thorough introduction to the specialized techniques needed to carry out numerical simulations of QCD: a description of lattice discretizations of fermions and gauge fields, methods for actually do

Lattice Boltzmann Simulation of Collision between 2D Circular Particles Suspension in Couette Flow

Directory of Open Access Journals (Sweden)

Li-Zhong Huang

2013-01-01

Full Text Available Collision between 2D circular particles suspension in Couette flow is simulated by using multiple-relaxation-time based lattice Boltzmann and direct forcing/fictitious domain method in this paper. The patterns of particle collisions are simulated and analyzed in detail by changing the velocity of top and bottom walls in the Couette flow. It can be seen from the simulation results that, while the velocity is large enough, the number of collisions between particles will change little as this velocity varies.

Dynamically adaptive Lattice Boltzmann simulation of shallow water flows with the Peano framework

KAUST Repository

Neumann, Philipp

2015-09-01

© 2014 Elsevier Inc. All rights reserved. We present a dynamically adaptive Lattice Boltzmann (LB) implementation for solving the shallow water equations (SWEs). Our implementation extends an existing LB component of the Peano framework. We revise the modular design with respect to the incorporation of new simulation aspects and LB models. The basic SWE-LB implementation is validated in different breaking dam scenarios. We further provide a numerical study on stability of the MRT collision operator used in our simulations.

An integrated simulator of structure and anisotropic flow in gas diffusion layers with hydrophobic additives

Science.gov (United States)

Burganos, Vasilis N.; Skouras, Eugene D.; Kalarakis, Alexandros N.

2017-10-01

The lattice-Boltzmann (LB) method is used in this work to reproduce the controlled addition of binder and hydrophobicity-promoting agents, like polytetrafluoroethylene (PTFE), into gas diffusion layers (GDLs) and to predict flow permeabilities in the through- and in-plane directions. The present simulator manages to reproduce spreading of binder and hydrophobic additives, sequentially, into the neat fibrous layer using a two-phase flow model. Gas flow simulation is achieved by the same code, sidestepping the need for a post-processing flow code and avoiding the usual input/output and data interface problems that arise in other techniques. Compression effects on flow anisotropy of the impregnated GDL are also studied. The permeability predictions for different compression levels and for different binder or PTFE loadings are found to compare well with experimental data for commercial GDL products and with computational fluid dynamics (CFD) predictions. Alternatively, the PTFE-impregnated structure is reproduced from Scanning Electron Microscopy (SEM) images using an independent, purely geometrical approach. A comparison of the two approaches is made regarding their adequacy to reproduce correctly the main structural features of the GDL and to predict anisotropic flow permeabilities at different volume fractions of binder and hydrophobic additives.

Molecular dynamics simulations of the lattice thermal conductivity of thermoelectric material CuInTe{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Wei, J. [Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon Tong (Hong Kong); Liu, H.J., E-mail: phlhj@whu.edu.cn [Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Cheng, L.; Zhang, J.; Jiang, P.H.; Liang, J.H.; Fan, D.D.; Shi, J. [Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072 (China)

2017-05-10

Highlights: • A simple but effective Morse potential is constructed to accurately describe the interatomic interactions of CuInTe{sub 2}. • The lattice thermal conductivity of CuInTe{sub 2} predicted by MD agrees well with those measured experimentally, as well as those calculated from phonon BTE. • Introducing Cd impurity or Cu vacancy can effectively reduce the lattice thermal conductivity of CuInTe{sub 2} and thus further enhance its thermoelectric performance. - Abstract: The lattice thermal conductivity of thermoelectric material CuInTe{sub 2} is predicted using classical molecular dynamics simulations, where a simple but effective Morse-type interatomic potential is constructed by fitting first-principles total energy calculations. In a broad temperature range from 300 to 900 K, our simulated results agree well with those measured experimentally, as well as those obtained from phonon Boltzmann transport equation. By introducing the Cd impurity or Cu vacancy, the thermal conductivity of CuInTe{sub 2} can be effectively reduced to further enhance the thermoelectric performance of this chalcopyrite compound.

Numerical Simulations for Enhanced Methane Recovery from Gas Hydrate Accumulations by Utilizing CO2 Sequestration

Science.gov (United States)

Sridhara, Prathyusha

In 2013, the International Energy Outlook (EIA, 2013) projected that global energy demand will grow by 56% between 2010 and 2040. Despite strong growth in renewable energy supplies, much of this growth is expected to be met by fossil fuels. Concerns ranging from greenhouse gas emissions and energy security are spawning new interests for other sources of energy including renewable and unconventional fossil fuel such as shale gas and oil as well as gas hydrates. The production methods as well as long-term reservoir behavior of gas hydrate deposits have been under extensive investigation. Reservoir simulators can be used to predict the production potentials of hydrate formations and to determine which technique results in enhanced gas recovery. In this work, a new simulation tool, Mix3HydrateResSim (Mix3HRS), which accounts for complex thermodynamics of multi-component hydrate phase comprised of varying hydrate solid crystal structure, is used to perform the CO2-assisted production technique simulations from CH4 hydrate accumulations. The simulator is one among very few reservoir simulators which can simulate the process of CH4 substitution by CO2 (and N2 ) in the hydrate lattice. Natural gas hydrate deposits around the globe are categorized into three different classes based on the characteristics of the geological sediments present in contact with the hydrate bearing deposits. Amongst these, the Class 2 hydrate accumulations predominantly confirmed in the permafrost and along seashore, are characterized by a mobile aqueous phase underneath a hydrate bearing sediment. The exploitation of such gas hydrate deposits results in release of large amounts of water due to the presence of permeable water-saturated sediments encompassing the hydrate deposits, thus lowering the produced gas rates. In this study, a suite of numerical simulation scenarios with varied complexity are considered which aimed at understanding the underlying changes in physical, thermodynamic and

Computer simulation of trails on a square lattice. I. Trails at infinite temperature

International Nuclear Information System (INIS)

Lim, H.A.; Meirovitch, H.

1989-01-01

A trail is a random walk on a lattice for which two bonds are not allowed to overlap. However, the chain may cross itself and one may associate with each such intersection an attractive energy epsilon-c. We study trails at infinite temperature T = ∞ (i.e., trails without attractions) on a square lattice using the scanning simulation method. Our results for the radius of gyration and the end-to-end distance strongly suggest (as do previous studies) that the shape exponent is ν = 0.75, similar to that for self-avoiding walks (SAW's). We obtain significantly more accurate estimates than have been obtained before for the entropy exponent γ = 1.350 +- 0.012 and for the effective growth parameter μ = 2.720 58 +- 0.000 20 (95% confidence limit). The persistence length is found to increase with increasing chain length N and the data fit slightly better an exponential function N/sup w/ where w = 0.047 +- 0.009 than a logarithmic one. Guttmann [J. Phys. A 18, 567 (1985)] has shown exactly that trails and SAW's on the hexagonal lattice at T = ∞ have the same exponents. Our results suggest that this is true also for the square lattice

Piecewise parabolic negative magnetoresistance of two-dimensional electron gas with triangular antidot lattice

International Nuclear Information System (INIS)

Budantsev, M. V.; Lavrov, R. A.; Pogosov, A. G.; Zhdanov, E. Yu.; Pokhabov, D. A.

2011-01-01

Extraordinary piecewise parabolic behavior of the magnetoresistance has been experimentally detected in the two-dimensional electron gas with a dense triangular lattice of antidots, where commensurability magnetoresistance oscillations are suppressed. The magnetic field range of 0–0.6 T can be divided into three wide regions, in each of which the magnetoresistance is described by parabolic dependences with high accuracy (comparable to the experimental accuracy) and the transition regions between adjacent regions are much narrower than the regions themselves. In the region corresponding to the weakest magnetic fields, the parabolic behavior becomes almost linear. The observed behavior is reproducible as the electron gas density changes, which results in a change in the resistance by more than an order of magnitude. Possible physical mechanisms responsible for the observed behavior, including so-called “memory effects,” are discussed.

Upscaled Lattice Boltzmann Method for Simulations of Flows in Heterogeneous Porous Media

Directory of Open Access Journals (Sweden)

Jun Li

2017-01-01

Full Text Available An upscaled Lattice Boltzmann Method (LBM for flow simulations in heterogeneous porous media at the Darcy scale is proposed in this paper. In the Darcy-scale simulations, the Shan-Chen force model is used to simplify the algorithm. The proposed upscaled LBM uses coarser grids to represent the average effects of the fine-grid simulations. In the upscaled LBM, each coarse grid represents a subdomain of the fine-grid discretization and the effective permeability with the reduced-order models is proposed as we coarsen the grid. The effective permeability is computed using solutions of local problems (e.g., by performing local LBM simulations on the fine grids using the original permeability distribution and used on the coarse grids in the upscaled simulations. The upscaled LBM that can reduce the computational cost of existing LBM and transfer the information between different scales is implemented. The results of coarse-grid, reduced-order, simulations agree very well with averaged results obtained using a fine grid.

Upscaled Lattice Boltzmann Method for Simulations of Flows in Heterogeneous Porous Media

KAUST Repository

Li, Jun

2017-02-16

An upscaled Lattice Boltzmann Method (LBM) for flow simulations in heterogeneous porous media at the Darcy scale is proposed in this paper. In the Darcy-scale simulations, the Shan-Chen force model is used to simplify the algorithm. The proposed upscaled LBM uses coarser grids to represent the average effects of the fine-grid simulations. In the upscaled LBM, each coarse grid represents a subdomain of the fine-grid discretization and the effective permeability with the reduced-order models is proposed as we coarsen the grid. The effective permeability is computed using solutions of local problems (e.g., by performing local LBM simulations on the fine grids using the original permeability distribution) and used on the coarse grids in the upscaled simulations. The upscaled LBM that can reduce the computational cost of existing LBM and transfer the information between different scales is implemented. The results of coarse-grid, reduced-order, simulations agree very well with averaged results obtained using a fine grid.

Entanglement growth and simulation efficiency in one-dimensional quantum lattice systems

OpenAIRE

Perales, Alvaro; Vidal, Guifre

2007-01-01

We study the evolution of one-dimensional quantum lattice systems when the ground state is perturbed by altering one site in the middle of the chain. For a large class of models, we observe a similar pattern of entanglement growth during the evolution, characterized by a moderate increase of significant Schmidt coefficients in all relevant bipartite decompositions of the state. As a result, the evolution can be accurately described by a matrix product state and efficiently simulated using the...

New techniques and results for worldline simulations of lattice field theories

Science.gov (United States)

Giuliani, Mario; Orasch, Oliver; Gattringer, Christof

2018-03-01

We use the complex ø4 field at finite density as a model system for developing further techniques based on worldline formulations of lattice field theories. More specifically we: 1) Discuss new variants of the worm algorithm for updating the ø4 theory and related systems with site weights. 2) Explore the possibility of canonical simulations in the worldline formulation. 3) Study the connection of 2-particle condensation at low temperature to scattering parameters of the theory.

Improved local lattice Monte Carlo simulation for charged systems

Science.gov (United States)

Jiang, Jian; Wang, Zhen-Gang

2018-03-01

Maggs and Rossetto [Phys. Rev. Lett. 88, 196402 (2002)] proposed a local lattice Monte Carlo algorithm for simulating charged systems based on Gauss's law, which scales with the particle number N as O(N). This method includes two degrees of freedom: the configuration of the mobile charged particles and the electric field. In this work, we consider two important issues in the implementation of the method, the acceptance rate of configurational change (particle move) and the ergodicity in the phase space sampled by the electric field. We propose a simple method to improve the acceptance rate of particle moves based on the superposition principle for electric field. Furthermore, we introduce an additional updating step for the field, named "open-circuit update," to ensure that the system is fully ergodic under periodic boundary conditions. We apply this improved local Monte Carlo simulation to an electrolyte solution confined between two low dielectric plates. The results show excellent agreement with previous theoretical work.

Z{sub c}(3900): confronting theory and lattice simulations

Energy Technology Data Exchange (ETDEWEB)

Albaladejo, Miguel; Fernandez-Soler, Pedro; Nieves, Juan [Instituto de Fisica Corpuscular (IFIC), Centro Mixto CSIC-Universidad de Valencia, Institutos de Investigacion de Paterna, Valencia (Spain)

2016-10-15

We consider a recent T-matrix analysis by Albaladejo et al. (Phys Lett B 755:337, 2016), which accounts for the J/ψπ and D{sup *} anti D coupled-channels dynamics, and which successfully describes the experimental information concerning the recently discovered Z{sub c}(3900){sup ±}. Within such scheme, the data can be similarly well described in two different scenarios, where Z{sub c}(3900) is either a resonance or a virtual state. To shed light into the nature of this state, we apply this formalism in a finite box with the aim of comparing with recent Lattice QCD (LQCD) simulations. We see that the energy levels obtained for both scenarios agree well with those obtained in the single-volume LQCD simulation reported in Prelovsek et al. (Phys Rev D 91:014504, 2015), thus making it difficult to disentangle the two possibilities. We also study the volume dependence of the energy levels obtained with our formalism and suggest that LQCD simulations performed at several volumes could help in discerning the actual nature of the intriguing Z{sub c}(3900) state. (orig.)

SU (2) lattice gauge theory simulations on Fermi GPUs

International Nuclear Information System (INIS)

Cardoso, Nuno; Bicudo, Pedro

2011-01-01

In this work we explore the performance of CUDA in quenched lattice SU (2) simulations. CUDA, NVIDIA Compute Unified Device Architecture, is a hardware and software architecture developed by NVIDIA for computing on the GPU. We present an analysis and performance comparison between the GPU and CPU in single and double precision. Analyses with multiple GPUs and two different architectures (G200 and Fermi architectures) are also presented. In order to obtain a high performance, the code must be optimized for the GPU architecture, i.e., an implementation that exploits the memory hierarchy of the CUDA programming model. We produce codes for the Monte Carlo generation of SU (2) lattice gauge configurations, for the mean plaquette, for the Polyakov Loop at finite T and for the Wilson loop. We also present results for the potential using many configurations (50,000) without smearing and almost 2000 configurations with APE smearing. With two Fermi GPUs we have achieved an excellent performance of 200x the speed over one CPU, in single precision, around 110 Gflops/s. We also find that, using the Fermi architecture, double precision computations for the static quark-antiquark potential are not much slower (less than 2x slower) than single precision computations.

Lattice Gas Model Based Optimization of Plasma-Surface Processes for GaN-Based Compound Growth

Science.gov (United States)

Nonokawa, Kiyohide; Suzuki, Takuma; Kitamori, Kazutaka; Sawada, Takayuki

2001-10-01

Progress of the epitaxial growth technique for GaN-based compounds makes these materials attractive for applications in high temperature/high-power electronic devices as well as in short-wavelength optoelectronic devices. For MBE growth of GaN epilayer, atomic nitrogen is usually supplied from ECR-plasma while atomic Ga is supplied from conventional K-cell. To grow high-quality epilayer, fundamental knowledge of the detailed atomic process, such as adsorption, surface migration, incorporation, desorption and so forth, is required. We have studied the influence of growth conditions on the flatness of the growth front surface and the growth rate using Monte Carlo simulation based on the lattice gas model. Under the fixed Ga flux condition, the lower the nitrogen flux and/or the higher the growth temperature, the better the flatness of the front surface at the sacrifice of the growth rate of the epilayer. When the nitrogen flux is increased, the growth rate reaches saturation value determined from the Ga flux. At a fixed growth temperature, increasing of nitrogen to Ga flux ratio results in rough surface owing to 3-dimensional island formation. Other characteristics of MBE-GaN growth using ECR-plasma can be well reproduced.

Wilson Fermions and Axion Electrodynamics in Optical Lattices

International Nuclear Information System (INIS)

Bermudez, A.; Martin-Delgado, M. A.; Mazza, L.; Rizzi, M.; Goldman, N.; Lewenstein, M.

2010-01-01

We show that ultracold Fermi gases in optical superlattices can be used as quantum simulators of relativistic lattice fermions in 3+1 dimensions. By exploiting laser-assisted tunneling, we find an analogue of the so-called naive Dirac fermions, and thus provide a realization of the fermion doubling problem. Moreover, we show how to implement Wilson fermions, and discuss how their mass can be inverted by tuning the laser intensities. In this regime, our atomic gas corresponds to a phase of matter where Maxwell electrodynamics is replaced by axion electrodynamics: a 3D topological insulator.

Effect of capillary condensation on gas transport properties in porous media

Science.gov (United States)

Yoshimoto, Yuta; Hori, Takuma; Kinefuchi, Ikuya; Takagi, Shu

2017-10-01

We investigate the effect of capillary condensation on gas diffusivity in porous media composed of randomly packed spheres with moderate wettability. To simulate capillary phenomena at the pore scale while retaining complex pore networks of the porous media, we employ density functional theory (DFT) for coarse-grained lattice gas models. The lattice DFT simulations reveal that capillary condensations preferentially occur at confined pores surrounded by solid walls, leading to the occlusion of narrow pores. Consequently, the characteristic lengths of the partially wet structures are larger than those of the corresponding dry structures with the same porosities. Subsequent gas diffusion simulations exploiting the mean-square displacement method indicate that while the effective diffusion coefficients significantly decrease in the presence of partially condensed liquids, they are larger than those in the dry structures with the same porosities. Moreover, we find that the ratio of the porosity to the tortuosity factor, which is a crucial parameter that determines an effective diffusion coefficient, can be reasonably related to the porosity even for the partially wet porous media.

Classical and quantum simulations of many-body systems

International Nuclear Information System (INIS)

Murg, Valentin

2008-01-01

This thesis is devoted to recent developments in the fields of classical and quantum simulations of many-body systems. We describe new classical algorithms that overcome problems apparent in conventional renormalization group and Monte Carlo methods. These algorithms make possible the detailed study of finite temperature properties of 2-D classical and 1-D quantum systems, the investigation of ground states of 2-D frustrated or fermionic systems and the analysis of time evolutions of 2-D quantum systems. Furthermore, we propose new ''analog'' quantum simulators that are able to realize interesting models such as a Tonks-Girardeau gas or a frustrated spin-1/2 XY model on a trigonal lattice. These quantum simulators make use of optical lattices and trapped ions and are technically feasible. In fact, the Tonks-Girardeau gas has been realized experimentally and we provide a detailed comparison between the experimental data and the theoretical predictions. (orig.)

Simulations and measurements of adiabatic annular flows in triangular, tight lattice nuclear fuel bundle model

Energy Technology Data Exchange (ETDEWEB)

Saxena, Abhishek, E-mail: asaxena@lke.mavt.ethz.ch [ETH Zurich, Laboratory for Nuclear Energy Systems, Department of Mechanical and Process Engineering, Sonneggstrasse 3, 8092 Zürich (Switzerland); Zboray, Robert [Laboratory for Thermal-hydraulics, Nuclear Energy and Safety Department, Paul Scherrer Institute, 5232 Villigen PSI (Switzerland); Prasser, Horst-Michael [ETH Zurich, Laboratory for Nuclear Energy Systems, Department of Mechanical and Process Engineering, Sonneggstrasse 3, 8092 Zürich (Switzerland); Laboratory for Thermal-hydraulics, Nuclear Energy and Safety Department, Paul Scherrer Institute, 5232 Villigen PSI (Switzerland)

2016-04-01

High conversion light water reactors (HCLWR) having triangular, tight-lattice fuels bundles could enable improved fuel utilization compared to present day LWRs. However, the efficient cooling of a tight lattice bundle has to be still proven. Major concern is the avoidance of high-quality boiling crisis (film dry-out) by the use of efficient functional spacers. For this reason, we have carried out experiments on adiabatic, air-water annular two-phase flows in a tight-lattice, triangular fuel bundle model using generic spacers. A high-spatial-resolution, non-intrusive measurement technology, cold neutron tomography, has been utilized to resolve the distribution of the liquid film thickness on the virtual fuel pin surfaces. Unsteady CFD simulations have also been performed to replicate and compare with the experiments using the commercial code STAR-CCM+. Large eddies have been resolved on the grid level to capture the dominant unsteady flow features expected to drive the liquid film thickness distribution downstream of a spacer while the subgrid scales have been modeled using the Wall Adapting Local Eddy (WALE) subgrid model. A Volume of Fluid (VOF) method, which directly tracks the interface and does away with closure relationship models for interfacial exchange terms, has also been employed. The present paper shows first comparison of the measurement with the simulation results.

Study of physical properties, gas generation and gas retention in simulated Hanford waste

International Nuclear Information System (INIS)

Bryan, S.A.; Pederson, L.R.; Scheele, R.D.

1993-04-01

The purpose of this study was to establish the chemical and physical processes responsible for the generation and retention of gases within high-level waste from Tank 101-SY on the Hanford Site. This research, conducted using simulated waste on a laboratory scale, supports the development of mitigation/remediation strategies for Tank 101-SY. Simulated waste formulations are based on actual waste compositions. Selected physical properties of the simulated waste are compared to properties of actual Tank 101-SY waste samples. Laboratory studies using aged simulated waste show that significant gas generation occurs thermally at current tank temperatures (∼60 degrees C). Gas compositions include the same gases produced in actual tank waste, primarily N 2 , N 2 O, and H 2 . Gas stoichiometries have been shown to be greatly influenced by several organic and inorganic constituents within the simulated waste. Retention of gases in the simulated waste is in the form of bubble attachment to solid particles. This attachment phenomenon is related to the presence of organic constituents (HEDTA, EDTA, and citrate) of the simulated waste. A mechanism is discussed that relates the gas bubble/particle interactions to the partially hydrophobic surface produced on the solids by the organic constituents

Computer code for the atomistic simulation of lattice defects and dynamics

International Nuclear Information System (INIS)

Schiffgens, J.O.; Graves, N.J.; Oster, C.A.

1980-04-01

This document has been prepared to satisfy the need for a detailed, up-to-date description of a computer code that can be used to simulate phenomena on an atomistic level. COMENT was written in FORTRAN IV and COMPASS (CDC assembly language) to solve the classical equations of motion for a large number of atoms interacting according to a given force law, and to perform the desired ancillary analysis of the resulting data. COMENT is a dual-purpose intended to describe static defect configurations as well as the detailed motion of atoms in a crystal lattice. It can be used to simulate the effect of temperature, impurities, and pre-existing defects on radiation-induced defect production mechanisms, defect migration, and defect stability

Large scale simulations of lattice QCD thermodynamics on Columbia Parallel Supercomputers

International Nuclear Information System (INIS)

Ohta, Shigemi

1989-01-01

The Columbia Parallel Supercomputer project aims at the construction of a parallel processing, multi-gigaflop computer optimized for numerical simulations of lattice QCD. The project has three stages; 16-node, 1/4GF machine completed in April 1985, 64-node, 1GF machine completed in August 1987, and 256-node, 16GF machine now under construction. The machines all share a common architecture; a two dimensional torus formed from a rectangular array of N 1 x N 2 independent and identical processors. A processor is capable of operating in a multi-instruction multi-data mode, except for periods of synchronous interprocessor communication with its four nearest neighbors. Here the thermodynamics simulations on the two working machines are reported. (orig./HSI)

Lattice gauge theories

International Nuclear Information System (INIS)

Creutz, M.

1983-04-01

In the last few years lattice gauge theory has become the primary tool for the study of nonperturbative phenomena in gauge theories. The lattice serves as an ultraviolet cutoff, rendering the theory well defined and amenable to numerical and analytical work. Of course, as with any cutoff, at the end of a calculation one must consider the limit of vanishing lattice spacing in order to draw conclusions on the physical continuum limit theory. The lattice has the advantage over other regulators that it is not tied to the Feynman expansion. This opens the possibility of other approximation schemes than conventional perturbation theory. Thus Wilson used a high temperature expansion to demonstrate confinement in the strong coupling limit. Monte Carlo simulations have dominated the research in lattice gauge theory for the last four years, giving first principle calculations of nonperturbative parameters characterizing the continuum limit. Some of the recent results with lattice calculations are reviewed

Understanding nucleon structure using lattice simulations. Recent progress on three different structural observables

International Nuclear Information System (INIS)

Schroers, W.

2007-01-01

This review focuses on the discussion of three key results of nucleon structure calculations on the lattice. These three results are the quark contribution to the nucleon spin, J q , the nucleon-Δ transition form factors, and the nucleon axial coupling, g A . The importance for phenomenology and experiment is discussed and the requirements for future simulations are pointed out. (orig.)

Numerical analysis of interfacial growth and deformation in horizontal stratified two-phase flow by lattice Boltzmann method

International Nuclear Information System (INIS)

Ebihara, Ken-ichi

2005-03-01

Two-phase flow is one of the important phenomena in nuclear reactors and heat exchangers at nuclear plants. It is desired for the optimum design and safe operation of such equipment to understand and predict the two-phase flow phenomenon by numerical analysis. In the present, the two-fluid model is widely used for the numerical analysis of two-phase flow. The numerical analysis method using the two-fluid model solves macroscopic hydrodynamic equations, in which fluid is regarded as continuum, with the boundary conditions at the wall, the inlet and outlet, and the interface between two phases. Since the interfacial and the wall boundary conditions utilized by this method are given as the model, such as the flow regime map and correlation, which is usually constructed on the basis of experimental results, the accuracy of the two-phase flow analysis using the two-fluid model depends on that of the utilized model or the experiment result for modeling. Tremendous progress of the computer performance and the development of new computational methods make the numerical simulation of two-phase flow with the interfacial motion possible in resent years. In such circumstances, the lattice-gas method and the lattice Boltzmann method, which represent fluid by many particles or the particle distribution function on the spatial lattice, was proposed in 1990s and these methods are applied to the numerical simulation of two-phase flow. The main feature of the two-phase fluid model of those methods is the capability of the simulation of two-phase flow without the procedure for tracking the interfacial position and shape owing to the inlet-particle potential generating the interface. Therefore it is expected that the lattice-gas method and the lattice Boltzmann method possess the predictability of the experiment by the numerical analysis of two-phase flow as well as the possibility of giving the substitute of the flow regime map and the correlation used by the two-fluid model. In this

A partial entropic lattice Boltzmann MHD simulation of the Orszag-Tang vortex

Science.gov (United States)

Flint, Christopher; Vahala, George

2018-02-01

Karlin has introduced an analytically determined entropic lattice Boltzmann (LB) algorithm for Navier-Stokes turbulence. Here, this is partially extended to an LB model of magnetohydrodynamics, on using the vector distribution function approach of Dellar for the magnetic field (which is permitted to have field reversal). The partial entropic algorithm is benchmarked successfully against standard simulations of the Orszag-Tang vortex [Orszag, S.A.; Tang, C.M. J. Fluid Mech. 1979, 90 (1), 129-143].

Color-gradient lattice Boltzmann model for simulating droplet motion with contact-angle hysteresis.

Science.gov (United States)

Ba, Yan; Liu, Haihu; Sun, Jinju; Zheng, Rongye

2013-10-01

Lattice Boltzmann method (LBM) is an effective tool for simulating the contact-line motion due to the nature of its microscopic dynamics. In contact-line motion, contact-angle hysteresis is an inherent phenomenon, but it is neglected in most existing color-gradient based LBMs. In this paper, a color-gradient based multiphase LBM is developed to simulate the contact-line motion, particularly with the hysteresis of contact angle involved. In this model, the perturbation operator based on the continuum surface force concept is introduced to model the interfacial tension, and the recoloring operator proposed by Latva-Kokko and Rothman is used to produce phase segregation and resolve the lattice pinning problem. At the solid surface, the color-conserving wetting boundary condition [Hollis et al., IMA J. Appl. Math. 76, 726 (2011)] is applied to improve the accuracy of simulations and suppress spurious currents at the contact line. In particular, we present a numerical algorithm to allow for the effect of the contact-angle hysteresis, in which an iterative procedure is used to determine the dynamic contact angle. Numerical simulations are conducted to verify the developed model, including the droplet partial wetting process and droplet dynamical behavior in a simple shear flow. The obtained results are compared with theoretical solutions and experimental data, indicating that the model is able to predict the equilibrium droplet shape as well as the dynamic process of partial wetting and thus permits accurate prediction of contact-line motion with the consideration of contact-angle hysteresis.

Multispeed Lattice Boltzmann Model with Space-Filling Lattice for Transcritical Shallow Water Flows

Directory of Open Access Journals (Sweden)

Y. Peng

2017-01-01

Full Text Available Inspired by the recent success of applying multispeed lattice Boltzmann models with a non-space-filling lattice for simulating transcritical shallow water flows, the capabilities of their space-filling counterpart are investigated in this work. Firstly, two lattice models with five integer discrete velocities are derived by using the method of matching hydrodynamics moments and then tested with two typical 1D problems including the dam-break flow over flat bed and the steady flow over bump. In simulations, the derived space-filling multispeed models, together with the stream-collision scheme, demonstrate better capability in simulating flows with finite Froude number. However, the performance is worse than the non-space-filling model solved by finite difference scheme. The stream-collision scheme with second-order accuracy may be the reason since a numerical scheme with second-order accuracy is prone to numerical oscillations at discontinuities, which is worthwhile for further study.

Quantum Simulation of a Lattice Schwinger Model in a Chain of Trapped Ions

Directory of Open Access Journals (Sweden)

P. Hauke

2013-11-01

Full Text Available We discuss how a lattice Schwinger model can be realized in a linear ion trap, allowing a detailed study of the physics of Abelian lattice gauge theories related to one-dimensional quantum electrodynamics. Relying on the rich quantum-simulation toolbox available in state-of-the-art trapped-ion experiments, we show how one can engineer an effectively gauge-invariant dynamics by imposing energetic constraints, provided by strong Ising-like interactions. Applying exact diagonalization to ground-state and time-dependent properties, we study the underlying microscopic model and discuss undesired interaction terms and other imperfections. As our analysis shows, the proposed scheme allows for the observation in realistic setups of spontaneous parity- and charge-symmetry breaking, as well as false-vacuum decay. Besides an implementation aimed at larger ion chains, we also discuss a minimal setting, consisting of only four ions in a simpler experimental setup, which enables us to probe basic physical phenomena related to the full many-body problem. The proposal opens a new route for analog quantum simulation of high-energy and condensed-matter models where gauge symmetries play a prominent role.

Immiscible multicomponent lattice Boltzmann model for fluids with ...

Indian Academy of Sciences (India)

College of Mechanical Engineering, Tongji University, 4800# Cao'an Road, ... was developed from a discretized fluid model known as the lattice gas automata ... of two immiscible fluids, several lattice Boltzmann (LB) models have been ...

Direct numerical simulation of circular-cap bubbles in low viscous liquids using counter diffusion lattice Boltzmann method

Energy Technology Data Exchange (ETDEWEB)

Ryu, Seungyeob, E-mail: syryu@kaeri.re.kr [Korea Atomic Energy Research Institute (KAERI), 1045 Daeduk-daero, Yuseong-gu, Daejeon 305-353 (Korea, Republic of); Kim, Youngin; Yoon, Juhyeon [Korea Atomic Energy Research Institute (KAERI), 1045 Daeduk-daero, Yuseong-gu, Daejeon 305-353 (Korea, Republic of); Ko, Sungho, E-mail: sunghoko@cnu.ac.kr [Department of Mechanical Design Engineering, Chungnam National University, 220 Gung-dong, Yuseong-gu, Daejeon 305-764 (Korea, Republic of)

2014-01-15

Highlights: • We directly simulate circular-cap bubbles in low viscous liquids. • The counter diffusion multiphase lattice Boltzmann method is proposed. • The present method is validated through benchmark tests and experimental results. • The high-Reynolds-number bubbles can be simulated without any turbulence models. • The present method is feasible for the direct simulation of bubbly flows. -- Abstract: The counter diffusion lattice Boltzmann method (LBM) is used to directly simulate rising circular-cap bubbles in low viscous liquids. A counter diffusion model for single phase flows has been extended to multiphase flows, and the implicit formulation is converted into an explicit one for easy calculation. Bubbles at high Reynolds numbers ranging from O(10{sup 2}) to O(10{sup 4}) are simulated successfully without any turbulence models, which cannot be done for the existing LBM versions. The characteristics of the circular-cap bubbles are studied for a wide range of Morton numbers and compared with the previous literature. Calculated results agree with the theoretical and experimental data. Consequently, the wake phenomena of circular-cap bubbles and bubble induced turbulence are presented.

An international effort to compare gas hydrate reservoir simulators

Energy Technology Data Exchange (ETDEWEB)

Wilder, J.W. [Akron Univ., Akron, OH (United States). Dept. of Theoretical and Applied Math; Moridis, G.J. [California Univ., Berkely, CA (United States). Earth Sciences Div., Lawrence Berkely National Lab.; Wilson, S.J. [Ryder Scott Co., Denver, CO (United States); Kurihara, M. [Japan Oil Engineering Co. Ltd., Tokyo (Japan); White, M.D. [Pacific Northwest National Laboratory Hydrology Group, Richland, WA (United States); Masuda, Y. [Tokyo Univ., Tokyo (Japan). Dept. of Geosystem Engineering; Anderson, B.J. [National Energy Technology Lab., Morgantown, WV (United States)]|[West Virginia Univ., Morgantown, WV (United States). Dept. of Chemical Engineering; Collett, T.S. [United States Geological Survey, Denver, CO (United States); Hunter, R.B. [ASRC Energy Services, Anchorage, AK (United States); Narita, H. [National Inst. of Advanced Industrial Science and Technology, MEthane hydrate Research Lab., Sapporo (Japan); Pooladi-Darvish, M. [Fekete Associates Inc., Calgary, AB (Canada); Rose, K.; Boswell, R. [National Energy Technology Lab., Morgantown, WV (United States)

2008-07-01

In this study, 5 different gas hydrate production scenarios were modeled by the CMG STARS, HydateResSim, MH-21 HYDRES, STOMP-HYD and the TOUGH+HYDRATE reservoir simulators for comparative purposes. The 5 problems ranged in complexity from 1 to 3 dimensional with radial symmetry, and in horizontal dimensions of 20 meters to 1 kilometer. The scenarios included (1) a base case with non-isothermal multi-fluid transition to equilibrium, (2) a base case with gas hydrate (closed-domain hydrate dissociation), (3) dissociation in a 1-D open domain, (4) gas hydrate dissociation in a one-dimensional radial domain, similarity solutions, (5) gas hydrate dissociation in a two-dimensional radial domain. The purpose of the study was to compare the world's leading gas hydrate reservoir simulators in an effort to improve the simulation capability of experimental and naturally occurring gas hydrate accumulations. The problem description and simulation results were presented for each scenario. The results of the first scenario indicated very close agreement among the simulators, suggesting that all address the basics of mass and heat transfer, as well as overall process of gas hydrate dissociation. The third scenario produced the initial divergence among the simulators. Other differences were noted in both scenario 4 and 5, resulting in significant corrections to algorithms within several of the simulators. The authors noted that it is unlikely that these improvements would have been identified without this comparative study due to a lack of real world data for validation purposes. It was concluded that the solution for gas hydrate production involves a combination of highly coupled fluid, heat and mass transport equations combined with the potential for formation or disappearance of multiple solid phases in the system. The physical and chemical properties of the rocks containing the gas hydrate depend on the amount of gas hydrate present in the system. Each modeling and

Classical and quantum simulations of many-body systems

Energy Technology Data Exchange (ETDEWEB)

Murg, Valentin

2008-04-07

This thesis is devoted to recent developments in the fields of classical and quantum simulations of many-body systems. We describe new classical algorithms that overcome problems apparent in conventional renormalization group and Monte Carlo methods. These algorithms make possible the detailed study of finite temperature properties of 2-D classical and 1-D quantum systems, the investigation of ground states of 2-D frustrated or fermionic systems and the analysis of time evolutions of 2-D quantum systems. Furthermore, we propose new 'analog' quantum simulators that are able to realize interesting models such as a Tonks-Girardeau gas or a frustrated spin-1/2 XY model on a trigonal lattice. These quantum simulators make use of optical lattices and trapped ions and are technically feasible. In fact, the Tonks-Girardeau gas has been realized experimentally and we provide a detailed comparison between the experimental data and the theoretical predictions. (orig.)

Rarefield gas dynamics fundamentals, simulations and micro flows

CERN Document Server

Shen, Ching

2006-01-01

This book elucidates the methods of molecular gas dynamics or rarefied gas dynamics which treat the problems of gas flows when the discrete molecular effects of the gas prevail under the circumstances of low density, the emphasis being on the basis of the methods, the direct simulation Monte Carlo method applied to the simulation of non-equilibrium effects and the frontier subjects related to low speed microscale rarefied gas flows. It provides a solid basis for the study of molecular gas dynamics for senior students and graduates in the aerospace and mechanical engineering departments of universities and colleges. It gives a general acquaintance of modern developments of rarefied gas dynamics in various regimes and leads to the frontier topics of non-equilibrium rarefied gas dynamics and low speed microscale gas dynamics. It will be also of benefit to the scientific and technical researchers engaged in aerospace high altitude aerodynamic force and heating design and in the research on gas flow in MEMS.

Passive heat transfer in a turbulent channel flow simulation using large eddy simulation based on the lattice Boltzmann method framework

Energy Technology Data Exchange (ETDEWEB)

Wu Hong [National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, Beihang University, Beijing 100191 (China); Wang Jiao, E-mail: wangjiao@sjp.buaa.edu.cn [National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, Beihang University, Beijing 100191 (China); Tao Zhi [National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, Beihang University, Beijing 100191 (China)

2011-12-15

Highlights: Black-Right-Pointing-Pointer A double MRT-LBM is used to study heat transfer in turbulent channel flow. Black-Right-Pointing-Pointer Turbulent Pr is modeled by dynamic subgrid scale model. Black-Right-Pointing-Pointer Temperature gradients are calculated by the non-equilibrium temperature distribution moments. - Abstract: In this paper, a large eddy simulation based on the lattice Boltzmann framework is carried out to simulate the heat transfer in a turbulent channel flow, in which the temperature can be regarded as a passive scalar. A double multiple relaxation time (DMRT) thermal lattice Boltzmann model is employed. While applying DMRT, a multiple relaxation time D3Q19 model is used to simulate the flow field, and a multiple relaxation time D3Q7 model is used to simulate the temperature field. The dynamic subgrid stress model, in which the turbulent eddy viscosity and the turbulent Prandtl number are dynamically computed, is integrated to describe the subgrid effect. Not only the strain rate but also the temperature gradient is calculated locally by the non-equilibrium moments. The Reynolds number based on the shear velocity and channel half height is 180. The molecular Prandtl numbers are set to be 0.025 and 0.71. Statistical quantities, such as the average velocity, average temperature, Reynolds stress, root mean square (RMS) velocity fluctuations, RMS temperature and turbulent heat flux are obtained and compared with the available data. The results demonstrate great reliability of DMRT-LES in studying turbulence.

Monte Carlo simulation of diblock copolymer microphases by means of a 'fast' off-lattice model

DEFF Research Database (Denmark)

Besold, Gerhard; Hassager, O.; Mouritsen, Ole G.

1999-01-01

We present a mesoscopic off-lattice model for the simulation of diblock copolymer melts by Monte Carlo techniques. A single copolymer molecule is modeled as a discrete Edwards chain consisting of two blocks with vertices of type A and B, respectively. The volume interaction is formulated in terms...

Introduction to lattice gauge theory

International Nuclear Information System (INIS)

Gupta, R.

1987-01-01

The lattice formulation of Quantum Field Theory (QFT) can be exploited in many ways. We can derive the lattice Feynman rules and carry out weak coupling perturbation expansions. The lattice then serves as a manifestly gauge invariant regularization scheme, albeit one that is more complicated than standard continuum schemes. Strong coupling expansions: these give us useful qualitative information, but unfortunately no hard numbers. The lattice theory is amenable to numerical simulations by which one calculates the long distance properties of a strongly interacting theory from first principles. The observables are measured as a function of the bare coupling g and a gauge invariant cut-off ≅ 1/α, where α is the lattice spacing. The continuum (physical) behavior is recovered in the limit α → 0, at which point the lattice artifacts go to zero. This is the more powerful use of lattice formulation, so in these lectures the author focuses on setting up the theory for the purpose of numerical simulations to get hard numbers. The numerical techniques used in Lattice Gauge Theories have their roots in statistical mechanics, so it is important to develop an intuition for the interconnection between quantum mechanics and statistical mechanics. This will be the emphasis of the first lecture. In the second lecture, the author reviews the essential ingredients of formulating QCD on the lattice and discusses scaling and the continuum limit. In the last lecture the author summarizes the status of some of the main results. He also mentions the bottlenecks and possible directions for research. 88 refs

An Active Lattice Model in a Bayesian Framework

DEFF Research Database (Denmark)

Carstensen, Jens Michael

1996-01-01

A Markov Random Field is used as a structural model of a deformable rectangular lattice. When used as a template prior in a Bayesian framework this model is powerful for making inferences about lattice structures in images. The model assigns maximum probability to the perfect regular lattice...... by penalizing deviations in alignment and lattice node distance. The Markov random field represents prior knowledge about the lattice structure, and through an observation model that incorporates the visual appearance of the nodes, we can simulate realizations from the posterior distribution. A maximum...... a posteriori (MAP) estimate, found by simulated annealing, is used as the reconstructed lattice. The model was developed as a central part of an algorithm for automatic analylsis of genetic experiments, positioned in a lattice structure by a robot. The algorithm has been successfully applied to many images...

Lattice constants of pure methane and carbon dioxide hydrates at low temperatures. Implementing quantum corrections to classical molecular dynamics studies

Energy Technology Data Exchange (ETDEWEB)

Costandy, Joseph; Michalis, Vasileios K.; Economou, Ioannis G., E-mail: i.tsimpanogiannis@qatar.tamu.edu, E-mail: ioannis.economou@qatar.tamu.edu [Chemical Engineering Program, Texas A& M University at Qatar, P.O. Box 23874, Doha (Qatar); Tsimpanogiannis, Ioannis N., E-mail: i.tsimpanogiannis@qatar.tamu.edu, E-mail: ioannis.economou@qatar.tamu.edu [Chemical Engineering Program, Texas A& M University at Qatar, P.O. Box 23874, Doha (Qatar); Environmental Research Laboratory, National Center for Scientific Research NCSR “Demokritos,” 15310 Aghia Paraskevi, Attikis (Greece); Stubos, Athanassios K. [Environmental Research Laboratory, National Center for Scientific Research NCSR “Demokritos,” 15310 Aghia Paraskevi, Attikis (Greece)

2016-03-28

We introduce a simple correction to the calculation of the lattice constants of fully occupied structure sI methane or carbon dioxide pure hydrates that are obtained from classical molecular dynamics simulations using the TIP4PQ/2005 water force field. The obtained corrected lattice constants are subsequently used in order to obtain isobaric thermal expansion coefficients of the pure gas hydrates that exhibit a trend that is significantly closer to the experimental behavior than previously reported classical molecular dynamics studies.

A SIMULATION MODEL OF THE GAS COMPLEX

Directory of Open Access Journals (Sweden)

Sokolova G. E.

2016-06-01

Full Text Available The article considers the dynamics of gas production in Russia, the structure of sales in the different market segments, as well as comparative dynamics of selling prices on these segments. Problems of approach to the creation of the gas complex using a simulation model, allowing to estimate efficiency of the project and determine the stability region of the obtained solutions. In the presented model takes into account the unit repayment of the loan, allowing with the first year of simulation to determine the possibility of repayment of the loan. The model object is a group of gas fields, which is determined by the minimum flow rate above which the project is cost-effective. In determining the minimum source flow rate for the norm of discount is taken as a generalized weighted average percentage on debt and equity taking into account risk premiums. He also serves as the lower barrier to internal rate of return below which the project is rejected as ineffective. Analysis of the dynamics and methods of expert evaluation allow to determine the intervals of variation of the simulated parameters, such as the price of gas and the exit gas complex at projected capacity. Calculated using the Monte Carlo method, for each random realization of the model simulated values of parameters allow to obtain a set of optimal for each realization of values minimum yield of wells, and also allows to determine the stability region of the solution.

Software for natural gas pipeline design and simulation (gaspisim ...

African Journals Online (AJOL)

Software for natural gas pipeline design and simulation (gaspisim) ... This paper focuses on the development of software for optimum design and simulation of natural gas pipeline. General ... EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT

Fuel lattice design using heuristics and new strategies

Energy Technology Data Exchange (ETDEWEB)

Ortiz S, J. J.; Castillo M, J. A.; Torres V, M.; Perusquia del Cueto, R. [ININ, Carretera Mexico-Toluca s/n, Ocoyoacac 52750, Estado de Mexico (Mexico); Pelta, D. A. [ETS Ingenieria Informatica y Telecomunicaciones, Universidad de Granada, Daniel Saucedo Aranda s/n, 18071 Granada (Spain); Campos S, Y., E-mail: juanjose.ortiz@inin.gob.m [IPN, Escuela Superior de Fisica y Matematicas, Unidad Profesional Adolfo Lopez Mateos, Edif. 9, 07738 Mexico D. F. (Mexico)

2010-10-15

This work show some results of the fuel lattice design in BWRs when some allocation pin rod rules are not taking into account. Heuristics techniques like Path Re linking and Greedy to design fuel lattices were used. The scope of this work is to search about how do classical rules in design fuel lattices affect the heuristics techniques results and the fuel lattice quality. The fuel lattices quality is measured by Power Peaking Factor and Infinite Multiplication Factor at the beginning of the fuel lattice life. CASMO-4 code to calculate these parameters was used. The analyzed rules are the following: pin rods with lowest uranium enrichment are only allocated in the fuel lattice corner, and pin rods with gadolinium cannot allocated in the fuel lattice edge. Fuel lattices with and without gadolinium in the main diagonal were studied. Some fuel lattices were simulated in an equilibrium cycle fuel reload, using Simulate-3 to verify their performance. So, the effective multiplication factor and thermal limits can be verified. The obtained results show a good performance in some fuel lattices designed, even thought, the knowing rules were not implemented. A fuel lattice performance and fuel lattice design characteristics analysis was made. To the realized tests, a dell workstation was used, under Li nux platform. (Author)

Fuel lattice design using heuristics and new strategies

International Nuclear Information System (INIS)

Ortiz S, J. J.; Castillo M, J. A.; Torres V, M.; Perusquia del Cueto, R.; Pelta, D. A.; Campos S, Y.

2010-10-01

This work show some results of the fuel lattice design in BWRs when some allocation pin rod rules are not taking into account. Heuristics techniques like Path Re linking and Greedy to design fuel lattices were used. The scope of this work is to search about how do classical rules in design fuel lattices affect the heuristics techniques results and the fuel lattice quality. The fuel lattices quality is measured by Power Peaking Factor and Infinite Multiplication Factor at the beginning of the fuel lattice life. CASMO-4 code to calculate these parameters was used. The analyzed rules are the following: pin rods with lowest uranium enrichment are only allocated in the fuel lattice corner, and pin rods with gadolinium cannot allocated in the fuel lattice edge. Fuel lattices with and without gadolinium in the main diagonal were studied. Some fuel lattices were simulated in an equilibrium cycle fuel reload, using Simulate-3 to verify their performance. So, the effective multiplication factor and thermal limits can be verified. The obtained results show a good performance in some fuel lattices designed, even thought, the knowing rules were not implemented. A fuel lattice performance and fuel lattice design characteristics analysis was made. To the realized tests, a dell workstation was used, under Li nux platform. (Author)

A weighted multiple-relaxation-time lattice Boltzmann method for multiphase flows and its application to partial coalescence cascades

Science.gov (United States)

Fakhari, Abbas; Bolster, Diogo; Luo, Li-Shi

2017-07-01

We present a lattice Boltzmann method (LBM) with a weighted multiple-relaxation-time (WMRT) collision model and an adaptive mesh refinement (AMR) algorithm for direct numerical simulation of two-phase flows in three dimensions. The proposed WMRT model enhances the numerical stability of the LBM for immiscible fluids at high density ratios, particularly on the D3Q27 lattice. The effectiveness and efficiency of the proposed WMRT-LBM-AMR is validated through simulations of (a) buoyancy-driven motion and deformation of a gas bubble rising in a viscous liquid; (b) the bag-breakup mechanism of a falling drop; (c) crown splashing of a droplet on a wet surface; and (d) the partial coalescence mechanism of a liquid drop at a liquid-liquid interface. The numerical simulations agree well with available experimental data and theoretical approximations where applicable.

Three-dimensional lattice Boltzmann model for immiscible two-phase flow simulations.

Science.gov (United States)

Liu, Haihu; Valocchi, Albert J; Kang, Qinjun

2012-04-01

We present an improved three-dimensional 19-velocity lattice Boltzmann model for immisicible binary fluids with variable viscosity and density ratios. This model uses a perturbation step to generate the interfacial tension and a recoloring step to promote phase segregation and maintain surfaces. A generalized perturbation operator is derived using the concept of a continuum surface force together with the constraints of mass and momentum conservation. A theoretical expression for the interfacial tension is determined directly without any additional analysis and assumptions. The recoloring algorithm proposed by Latva-Kokko and Rothman is applied for phase segregation, which minimizes the spurious velocities and removes lattice pinning. This model is first validated against the Laplace law for a stationary bubble. It is found that the interfacial tension is predicted well for density ratios up to 1000. The model is then used to simulate droplet deformation and breakup in simple shear flow. We compute droplet deformation at small capillary numbers in the Stokes regime and find excellent agreement with the theoretical Taylor relation for the segregation parameter β=0.7. In the limit of creeping flow, droplet breakup occurs at a critical capillary number 0.35simulations and experiments. Droplet breakup can also be promoted by increasing the Reynolds number. Finally, we numerically investigate a single bubble rising under buoyancy force in viscous fluids for a wide range of Eötvös and Morton numbers. Numerical results are compared with theoretical predictions and experimental results, and satisfactory agreement is shown.

S/sub N/ computational benchmark solutions for slab geometry models of a gas-cooled fast reactor (GCFR) lattice cell

International Nuclear Information System (INIS)

McCoy, D.R.

1981-01-01

S/sub N/ computational benchmark solutions are generated for a onegroup and multigroup fuel-void slab lattice cell which is a rough model of a gas-cooled fast reactor (GCFR) lattice cell. The reactivity induced by the extrusion of the fuel material into the voided region is determined for a series of partially extruded lattice cell configurations. A special modified Gauss S/sub N/ ordinate array design is developed in order to obtain eigenvalues with errors less than 0.03% in all of the configurations that are considered. The modified Gauss S/sub N/ ordinate array design has a substantially improved eigenvalue angular convergence behavior when compared to existing S/sub N/ ordinate array designs used in neutron streaming applications. The angular refinement computations are performed in some cases by using a perturbation theory method which enables one to obtain high order S/sub N/ eigenvalue estimates for greatly reduced computational costs

Analysis of polytype stability in PVT grown silicon carbide single crystal using competitive lattice model Monte Carlo simulations

Directory of Open Access Journals (Sweden)

Hui-Jun Guo

2014-09-01

Full Text Available Polytype stability is very important for high quality SiC single crystal growth. However, the growth conditions for the 4H, 6H and 15R polytypes are similar, and the mechanism of polytype stability is not clear. The kinetics aspects, such as surface-step nucleation, are important. The kinetic Monte Carlo method is a common tool to study surface kinetics in crystal growth. However, the present lattice models for kinetic Monte Carlo simulations cannot solve the problem of the competitive growth of two or more lattice structures. In this study, a competitive lattice model was developed for kinetic Monte Carlo simulation of the competition growth of the 4H and 6H polytypes of SiC. The site positions are fixed at the perfect crystal lattice positions without any adjustment of the site positions. Surface steps on seeds and large ratios of diffusion/deposition have positive effects on the 4H polytype stability. The 3D polytype distribution in a physical vapor transport method grown SiC ingot showed that the facet preserved the 4H polytype even if the 6H polytype dominated the growth surface. The theoretical and experimental results of polytype growth in SiC suggest that retaining the step growth mode is an important factor to maintain a stable single 4H polytype during SiC growth.

Lattice QCD. A critical status report

Energy Technology Data Exchange (ETDEWEB)

Jansen, Karl

2008-10-15

The substantial progress that has been achieved in lattice QCD in the last years is pointed out. I compare the simulation cost and systematic effects of several lattice QCD formulations and discuss a number of topics such as lattice spacing scaling, applications of chiral perturbation theory, non-perturbative renormalization and finite volume effects. Additionally, the importance of demonstrating universality is emphasized. (orig.)

Lattice QCD. A critical status report

International Nuclear Information System (INIS)

Jansen, Karl

2008-10-01

The substantial progress that has been achieved in lattice QCD in the last years is pointed out. I compare the simulation cost and systematic effects of several lattice QCD formulations and discuss a number of topics such as lattice spacing scaling, applications of chiral perturbation theory, non-perturbative renormalization and finite volume effects. Additionally, the importance of demonstrating universality is emphasized. (orig.)

Effects of simulated flue gas on components of Scenedesmus raciborskii WZKMT.

Science.gov (United States)

Li, Xie-kun; Xu, Jing-liang; Guo, Ying; Zhou, Wei-zheng; Yuan, Zhen-hong

2015-08-01

Scenedesmus raciborskii WZKMT cultured with simulated flue gas was investigated. Cellular components, including total sugar, starch, chlorophyll, protein and lipid, were compared between simulated flue gas and 7% (v/v) CO2. Dissolution of SO2 and NO in simulated flue gas led to pH decrease and toxicity to microalgae cells. Furthermore, the death or aging of microalgae cells reduced the buffer capacity and caused decrease of simulated flue gas absorption. With 7% CO2, the highest total sugar and starch content could attain to 66.76% and 53.16%, respectively, which indicated S. raciborskii WZKMT is a desired feedstock candidate for bioethanol production. Microalgae growth and starch accumulation was inhibited, while cells produced more chlorophyll, protein and lipid when simulated flue gas was the carbon source. Fatty acids composition analysis indicated that there was no significant distinction on fatty acids relative content (fatty acid/TFA) between cells aerated using simulated flue gas and 7% CO2. Copyright © 2015 Elsevier Ltd. All rights reserved.

Water droplet dynamic behavior during removal from a proton exchange membrane fuel cell gas diffusion layer by Lattice-Boltzmann method

Energy Technology Data Exchange (ETDEWEB)

Molaeimanesh, Golamreza; Akbari, Mohammad Hadi [Shiraz University, Shiraz (Iran, Islamic Republic of)

2014-04-15

A major challenge in the application of proton exchange membrane fuel cells (PEMFCs) is water management, with the flooding of electrodes as the main issue. The Lattice-Boltzmann method (LBM) is a relatively new technique that is superior in modeling the dynamic interface of multiphase fluid flow in complex microstructures such as non-homogeneous and anisotropic porous media of PEMFC electrodes. In this study, the dynamic behavior of a water droplet during removal from gas diffusion layer (GDL) of a PEMFC electrode with interdigitated flow field is simulated using LBM. The effects of GDL wettability and its spanwise and transverse gradients on the removal process are investigated. The results demonstrate great influence of wettability and its spanwise and transverse gradients on the dynamic behavior of droplets during the removal process. Although increasing the hydrophobicity of GDL results in better droplet removal, its increase beyond a critical value does not show a significant effect.

Anomalous spreading of a density front from an infinite continuous source in a concentration-dependent lattice gas automaton diffusion model

CERN Document Server

Kuentz, M

2003-01-01

A two-dimensional lattice gas automaton (LGA) is used for simulating concentration-dependent diffusion in a microscopically random heterogeneous structure. The heterogeneous medium is initialized at a low density rho sub 0 and then submitted to a steep concentration gradient by continuous injection of particles at a concentration rho sub 1 >rho sub 0 from a one-dimensional source to model spreading of a density front. Whereas the nonlinear diffusion equation generally used to describe concentration-dependent diffusion processes predicts a scaling law of the type phi = xt sup - sup 1 sup / sup 2 in one dimension, the spreading process is shown to deviate from the expected t sup 1 sup / sup 2 scaling. The time exponent is found to be larger than 1/2, i.e. diffusion of the density front is enhanced with respect to standard Fickian diffusion. It is also established that the anomalous time exponent decreases as time elapses: anomalous spreading is thus not a timescaling process. We demonstrate that occurrence of a...

Computer simulations of low energy displacement cascades in a face centered cubic lattice

International Nuclear Information System (INIS)

Schiffgens, J.O.; Bourquin, R.D.

1976-09-01

Computer simulations of atomic motion in a copper lattice following the production of primary knock-on atoms (PKAs) with energies from 25 to 200 eV are discussed. In this study, a mixed Moliere-Englert pair potential is used to model the copper lattice. The computer code COMENT, which employs the dynamical method, is used to analyze the motion of up to 6000 atoms per time step during cascade evolution. The atoms are specified as initially at rest on the sites of an ideal lattice. A matrix of 12 PKA directions and 6 PKA energies is investigated. Displacement thresholds in the [110] and [100] are calculated to be approximately 17 and 20 eV, respectively. A table showing the stability of isolated Frenkel pairs with different vacancy and interstitial orientations and separations is presented. The numbers of Frenkel pairs and atomic replacements are tabulated as a function of PKA direction for each energy. For PKA energies of 25, 50, 75, 100, 150, and 200 eV, the average number of Frenkel pairs per PKA are 0.4, 0.6, 1.0, 1.2, 1.4, and 2.2 and the average numbers of replacements per PKA are 2.4, 4.0, 3.3, 4.9, 9.3, and 15.8

Numerical simulation of a lattice polymer model at its integrable point

International Nuclear Information System (INIS)

Bedini, A; Owczarek, A L; Prellberg, T

2013-01-01

We revisit an integrable lattice model of polymer collapse using numerical simulations. This model was first studied by Blöte and Nienhuis (1989 J. Phys. A: Math. Gen. 22 1415) and it describes polymers with some attraction, providing thus a model for the polymer collapse transition. At a particular set of Boltzmann weights the model is integrable and the exponents ν = 12/23 ≈ 0.522 and γ = 53/46 ≈ 1.152 have been computed via identification of the scaling dimensions x t = 1/12 and x h = −5/48. We directly investigate the polymer scaling exponents via Monte Carlo simulations using the pruned-enriched Rosenbluth method algorithm. By simulating this polymer model for walks up to length 4096 we find ν = 0.576(6) and γ = 1.045(5), which are clearly different from the predicted values. Our estimate for the exponent ν is compatible with the known θ-point value of 4/7 and in agreement with very recent numerical evaluation by Foster and Pinettes (2012 J. Phys. A: Math. Theor. 45 505003). (paper)

Critical point of Nf=3 QCD from lattice simulations in the canonical ensemble

International Nuclear Information System (INIS)

Li Anyi; Alexandru, Andrei; Liu, Keh-Fei

2011-01-01

A canonical ensemble algorithm is employed to study the phase diagram of N f =3 QCD using lattice simulations. We lock in the desired quark number sector using an exact Fourier transform of the fermion determinant. We scan the phase space below T c and look for an S-shape structure in the chemical potential, which signals the coexistence phase of a first order phase transition in finite volume. Applying Maxwell construction, we determine the boundaries of the coexistence phase at three temperatures and extrapolate them to locate the critical point. Using an improved gauge action and improved Wilson fermions on lattices with a spatial extent of 1.8 fm and quark masses close to that of the strange, we find the critical point at T E =0.925(5)T c and baryon chemical potential μ B E =2.60(8)T c .

Lattice Boltzmann simulations of the time-averaged forces on a cylinder in a sound field

International Nuclear Information System (INIS)

Haydock, David

2005-01-01

We show that lattice Boltzmann simulations can be used to model the radiation force on an object in a standing wave acoustic field and comparisons are made to theoretical predictions. We show how viscous effects change the radiation force and predict the motion of a particle placed near a boundary where viscous effects are important

Lattice Boltzmann simulations of the time-averaged forces on a cylinder in a sound field

Energy Technology Data Exchange (ETDEWEB)

Haydock, David [Unilever R and D Colworth, Sharnbrook, Bedford MK44 1LQ (United Kingdom); Department of Physics, Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP (United Kingdom)

2005-04-15

We show that lattice Boltzmann simulations can be used to model the radiation force on an object in a standing wave acoustic field and comparisons are made to theoretical predictions. We show how viscous effects change the radiation force and predict the motion of a particle placed near a boundary where viscous effects are important.

Improved real-time dynamics from imaginary frequency lattice simulations

Directory of Open Access Journals (Sweden)

Pawlowski Jan M.

2018-01-01

Full Text Available The computation of real-time properties, such as transport coefficients or bound state spectra of strongly interacting quantum fields in thermal equilibrium is a pressing matter. Since the sign problem prevents a direct evaluation of these quantities, lattice data needs to be analytically continued from the Euclidean domain of the simulation to Minkowski time, in general an ill-posed inverse problem. Here we report on a novel approach to improve the determination of real-time information in the form of spectral functions by setting up a simulation prescription in imaginary frequencies. By carefully distinguishing between initial conditions and quantum dynamics one obtains access to correlation functions also outside the conventional Matsubara frequencies. In particular the range between ω0 and ω1 = 2πT, which is most relevant for the inverse problem may be more highly resolved. In combination with the fact that in imaginary frequencies the kernel of the inverse problem is not an exponential but only a rational function we observe significant improvements in the reconstruction of spectral functions, demonstrated in a simple 0+1 dimensional scalar field theory toy model.

Improved real-time dynamics from imaginary frequency lattice simulations

Science.gov (United States)

Pawlowski, Jan M.; Rothkopf, Alexander

2018-03-01

The computation of real-time properties, such as transport coefficients or bound state spectra of strongly interacting quantum fields in thermal equilibrium is a pressing matter. Since the sign problem prevents a direct evaluation of these quantities, lattice data needs to be analytically continued from the Euclidean domain of the simulation to Minkowski time, in general an ill-posed inverse problem. Here we report on a novel approach to improve the determination of real-time information in the form of spectral functions by setting up a simulation prescription in imaginary frequencies. By carefully distinguishing between initial conditions and quantum dynamics one obtains access to correlation functions also outside the conventional Matsubara frequencies. In particular the range between ω0 and ω1 = 2πT, which is most relevant for the inverse problem may be more highly resolved. In combination with the fact that in imaginary frequencies the kernel of the inverse problem is not an exponential but only a rational function we observe significant improvements in the reconstruction of spectral functions, demonstrated in a simple 0+1 dimensional scalar field theory toy model.

Retained Gas Sampler Calibration and Simulant Tests

Energy Technology Data Exchange (ETDEWEB)

CRAWFORD, B.A.

2000-01-05

This test plan provides a method for calibration of the retained gas sampler (RGS) for ammonia gas analysis. Simulant solutions of ammonium hydroxide at known concentrations will be diluted with isotopically labeled 0.04 M ammonium hydroxide solution. Sea sand solids will also be mixed with ammonium hydroxide solution and diluent to determine the accuracy of the system for ammonia gas analysis.

Retained Gas Sampler Calibration and Simulant Tests

International Nuclear Information System (INIS)

CRAWFORD, B.A.

2000-01-01

This test plan provides a method for calibration of the retained gas sampler (RGS) for ammonia gas analysis. Simulant solutions of ammonium hydroxide at known concentrations will be diluted with isotopically labeled 0.04 M ammonium hydroxide solution. Sea sand solids will also be mixed with ammonium hydroxide solution and diluent to determine the accuracy of the system for ammonia gas analysis

Large-scale grid-enabled lattice-Boltzmann simulations of complex fluid flow in porous media and under shear

NARCIS (Netherlands)

Harting, J.D.R.; Venturoli, M.; Coveney, P.V.

2004-01-01

Well–designed lattice Boltzmann codes exploit the essentially embarrassingly parallel features of the algorithm and so can be run with considerable efficiency on modern supercomputers. Such scalable codes permit us to simulate the behaviour of increasingly large quantities of complex condensed

A new lattice Boltzmann equation to simulate density-driven convection of carbon dioxide

KAUST Repository

Allen, Rebecca

2013-01-01

The storage of CO2 in fluid-filled geological formations has been carried out for more than a decade in locations around the world. After CO2 has been injected into the aquifer and has moved laterally under the aquifer\\'s cap-rock, density-driven convection becomes an important transport process to model. However, the challenge lies in simulating this transport process accurately with high spatial resolution and low CPU cost. This issue can be addressed by using the lattice Boltzmann equation (LBE) to formulate a model for a similar scenario when a solute diffuses into a fluid and density differences lead to convective mixing. The LBE is a promising alternative to the traditional methods of computational fluid dynamics. Rather than discretizing the system of partial differential equations of classical continuum mechanics directly, the LBE is derived from a velocity-space truncation of the Boltzmann equation of classical kinetic theory. We propose an extension to the LBE, which can accurately predict the transport of dissolved CO2 in water, as a step towards fluid-filled porous media simulations. This is achieved by coupling two LBEs, one for the fluid flow and one for the convection and diffusion of CO2. Unlike existing lattice Boltzmann equations for porous media flow, our model is derived from a system of moment equations and a Crank-Nicolson discretization of the velocity-truncated Boltzmann equation. The forcing terms are updated locally without the need for additional central difference approximation. Therefore our model preserves all the computational advantages of the single-phase lattice Boltzmann equation and is formally second-order accurate in both space and time. Our new model also features a novel implementation of boundary conditions, which is simple to implement and does not suffer from the grid-dependent error that is present in the standard "bounce-back" condition. The significance of using the LBE in this work lies in the ability to efficiently

Elastic lattice in an incommensurate background

International Nuclear Information System (INIS)

Dickman, R.; Chudnovsky, E.M.

1995-01-01

We study a harmonic triangular lattice, which relaxes in the presence of an incommensurate short-wavelength potential. Monte Carlo simulations reveal that the elastic lattice exhibits only short-ranged translational correlations, despite the absence of defects in either lattice. Extended orientational order, however, persists in the presence of the background. Translational correlation lengths exhibit approximate power-law dependence upon cooling rate and background strength. Our results may be relevant to Wigner crystals, atomic monolayers on crystals surfaces, and flux-line and magnetic bubble lattices

Statistical thermodynamics of long straight rigid rods on triangular lattices: nematic order and adsorption thermodynamic functions.

Science.gov (United States)

Matoz-Fernandez, D A; Linares, D H; Ramirez-Pastor, A J

2012-09-04

The statistical thermodynamics of straight rigid rods of length k on triangular lattices was developed on a generalization in the spirit of the lattice-gas model and the classical Guggenheim-DiMarzio approximation. In this scheme, the Helmholtz free energy and its derivatives were written in terms of the order parameter, δ, which characterizes the nematic phase occurring in the system at intermediate densities. Then, using the principle of minimum free energy with δ as a parameter, the main adsorption properties were calculated. Comparisons with Monte Carlo simulations and experimental data were performed in order to evaluate the outcome and limitations of the theoretical model.

Gas permeation through a polymer network

International Nuclear Information System (INIS)

Schmittmann, B; Gopalakrishnan, Manoj; Zia, R K P

2005-01-01

We study the diffusion of gas molecules through a two-dimensional network of polymers with the help of Monte Carlo simulations. The polymers are modelled as non-interacting random walks on the bonds of a two-dimensional square lattice, while the gas particles occupy the lattice cells. When a particle attempts to jump to a nearest-neighbour empty cell, it has to overcome an energy barrier which is determined by the number of polymer segments on the bond separating the two cells. We investigate the gas current J as a function of the mean segment density ρ, the polymer length l and the probability q m for hopping across m segments. Whereas J decreases monotonically with ρ for fixed l, its behaviour for fixed ρ and increasing ldepends strongly on q. For small, non-zero q, J appears to increase slowly with l. In contrast, for q = 0, it is dominated by the underlying percolation problem and can be non-monotonic. We provide heuristic arguments to put these interesting phenomena into context

Simulation of the catalyst layer in PEMFC based on a novel two-phase lattice model

Energy Technology Data Exchange (ETDEWEB)

Zhang Jiejing; Yang Wei; Xu Li [School of Chemical Engineering and Technology, State Key Laboratory of Chemical Engineering, Tianjin Key Laboratory of Membrane Science and Desalination Technology, Tianjin University, Tianjin 300072 (China); Wang Yuxin, E-mail: yxwang@tju.edu.cn [School of Chemical Engineering and Technology, State Key Laboratory of Chemical Engineering, Tianjin Key Laboratory of Membrane Science and Desalination Technology, Tianjin University, Tianjin 300072 (China)

2011-08-01

Highlights: > We propose a novel two phase lattice model of catalyst layer in PEMFC. > The model features a catalyst phase and a mixed ionomer and pores phase. > Transport and electrochemical reaction in the lattice are simulated. > The model enables more accurate results than pore-solid two phase model. > Profiles of oxygen level and reaction rate across catalyst layer vary with cell current. - Abstract: A lattice model of catalyst layer in proton exchange membrane fuel cells (PEMFCs), consisting of randomly distributed catalyst phase (C phase) and mixed ionomer-pore phase (IP phase), was established by means of Monte Carlo method. Transport and electrochemical reactions in the model catalyst layer were calculated. The newly proposed C-IP model was compared with previously established pore-solid two phase model. The variation of oxygen level and reaction rate along the thickness of catalyst layer with cell current was discussed. The effect of ionomer distribution across catalyst layer was studied by comparing profiles of oxygen level, reaction rate and overpotential, as well as corresponding polarization curves.

Monte Carlo simulation of liquid bridge rupture: Application to lung physiology

Science.gov (United States)

Alencar, Adriano M.; Wolfe, Elie; Buldyrev, Sergey V.

2006-08-01

In the course of certain lung diseases, the surface properties and the amount of fluids coating the airways changes and liquid bridges may form in the small airways blocking the flow of air, impairing gas exchange. During inhalation, these liquid bridges may rupture due to mechanical instability and emit a discrete sound event called pulmonary crackle, which can be heard using a simple stethoscope. We hypothesize that this sound is a result of the acoustical release of energy that had been stored in the surface of liquid bridges prior to its rupture. We develop a lattice gas model capable of describing these phenomena. As a step toward modeling this process, we address a simpler but related problem, that of a liquid bridge between two planar surfaces. This problem has been analytically solved and we use this solution as a validation of the lattice gas model of the liquid bridge rupture. Specifically, we determine the surface free energy and critical stability conditions in a system containing a liquid bridge of volume Ω formed between two parallel planes, separated by a distance 2h , with a contact angle Θ using both Monte Carlo simulation of a lattice gas model and variational calculus based on minimization of the surface area with the volume and the contact angle constraints. In order to simulate systems with different contact angles, we vary the parameters between the constitutive elements of the lattice gas. We numerically and analytically determine the phase diagram of the system as a function of the dimensionless parameters hΩ-1/3 and Θ . The regions of this phase diagram correspond to the mechanical stability and thermodynamical stability of the liquid bridge. We also determine the conditions for the symmetrical versus asymmetrical rupture of the bridge. We numerically and analytically compute the release of free energy during rupture. The simulation results are in agreement with the analytical solution. Furthermore, we discuss the results in connection

Diffusion on unstructured triangular grids using Lattice Boltzmann

NARCIS (Netherlands)

Sman, van der R.G.M.

2004-01-01

In this paper, we present a Lattice Boltzmann scheme for diffusion on unstructured triangular grids. In this formulation there is no need for interpolation, as is required in other LB schemes on irregular grids. At the end of the propagation step, the lattice gas particles arrive exactly at

Dual simulation of the massless lattice Schwinger model with topological term and non-zero chemical potential

Science.gov (United States)

Göschl, Daniel

2018-03-01

We discuss simulation strategies for the massless lattice Schwinger model with a topological term and finite chemical potential. The simulation is done in a dual representation where the complex action problem is solved and the partition function is a sum over fermion loops, fermion dimers and plaquette-occupation numbers. We explore strategies to update the fermion loops coupled to the gauge degrees of freedom and check our results with conventional simulations (without topological term and at zero chemical potential), as well as with exact summation on small volumes. Some physical implications of the results are discussed.

Multi-step magnetization of the Ising model on a Shastry-Sutherland lattice: a Monte Carlo simulation

International Nuclear Information System (INIS)

Huang, W C; Huo, L; Tian, G; Qian, H R; Gao, X S; Qin, M H; Liu, J-M

2012-01-01

The magnetization behaviors and spin configurations of the classical Ising model on a Shastry-Sutherland lattice are investigated using Monte Carlo simulations, in order to understand the fascinating magnetization plateaus observed in TmB 4 and other rare-earth tetraborides. The simulations reproduce the 1/2 magnetization plateau by taking into account the dipole-dipole interaction. In addition, a narrow 2/3 magnetization step at low temperature is predicted in our simulation. The multi-step magnetization can be understood as the consequence of the competitions among the spin-exchange interaction, the dipole-dipole interaction, and the static magnetic energy.

Non-Newtonian particulate flow simulation: A direct-forcing immersed boundary-lattice Boltzmann approach

Science.gov (United States)

Amiri Delouei, A.; Nazari, M.; Kayhani, M. H.; Kang, S. K.; Succi, S.

2016-04-01

In the current study, a direct-forcing immersed boundary-non-Newtonian lattice Boltzmann method (IB-NLBM) is developed to investigate the sedimentation and interaction of particles in shear-thinning and shear-thickening fluids. In the proposed IB-NLBM, the non-linear mechanics of non-Newtonian particulate flows is detected by combination of the most desirable features of immersed boundary and lattice Boltzmann methods. The noticeable roles of non-Newtonian behavior on particle motion, settling velocity and generalized Reynolds number are investigated by simulating benchmark problem of one-particle sedimentation under the same generalized Archimedes number. The effects of extra force due to added accelerated mass are analyzed on the particle motion which have a significant impact on shear-thinning fluids. For the first time, the phenomena of interaction among the particles, such as Drafting, Kissing, and Tumbling in non-Newtonian fluids are investigated by simulation of two-particle sedimentation and twelve-particle sedimentation. The results show that increasing the shear-thickening behavior of fluid leads to a significant increase in the kissing time. Moreover, the transverse position of particles for shear-thinning fluids during the tumbling interval is different from Newtonian and the shear-thickening fluids. The present non-Newtonian particulate study can be applied in several industrial and scientific applications, like the non-Newtonian sedimentation behavior of particles in food industrial and biological fluids.

Phase transitions and steady-state microstructures in a two-temperature lattice-gas model with mobile active impurities

DEFF Research Database (Denmark)

Henriksen, Jonas Rosager; Sabra, Mads Christian; Mouritsen, Ole G.

2000-01-01

The nonequilibrium, steady-state phase transitions and the structure of the different phases of a two-dimensional system with two thermodynamic temperatures are studied via a simple lattice-gas model with mobile active impurities ("hot/cold spots'') whose activity is controlled by an external drive...... on the temperatures, microstructured phases of both lamellar and droplet symmetry arise, described by a length scale that is determined by the characteristic temperature controlling the diffusive motion of the active impurities....

Chiral Magnetic Effect and Anomalous Transport from Real-Time Lattice Simulations

International Nuclear Information System (INIS)

Müller, Niklas; Schlichting, Sören; Sharma, Sayantan

2016-01-01

Here, we present a first-principles study of anomaly induced transport phenomena by performing real-time lattice simulations with dynamical fermions coupled simultaneously to non-Abelian S U (N _c) and Abelian U (1) gauge fields. By investigating the behavior of vector and axial currents during a sphaleron transition in the presence of an external magnetic field, we demonstrate how the interplay of the chiral magnetic and chiral separation effect leads to the formation of a propagating wave. Furthermore, we analyze the dependence of the magnitude of the induced vector current and the propagation of the wave on the amount of explicit chiral symmetry breaking due to finite quark masses.

Ballistic magnetotransport in a suspended two-dimensional electron gas with periodic antidot lattices

Energy Technology Data Exchange (ETDEWEB)

Zhdanov, E. Yu., E-mail: zhdanov@isp.nsc.ru; Pogosov, A. G.; Budantsev, M. V.; Pokhabov, D. A.; Bakarov, A. K. [Siberian Branch of the Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics (Russian Federation)

2017-01-15

The magnetoresistance of suspended semiconductor nanostructures with a two-dimensional electron gas structured by periodic square antidot lattices is studied. It is shown that the ballistic regime of electron transport is retained after detaching the sample from the substrate. Direct comparative analysis of commensurability oscillations of magnetoresistance and their temperature dependences in samples before and after suspension is performed. It is found that the temperature dependences are almost identical for non-suspended and suspended samples, whereas significant differences are observed in the nonlinear regime, caused by direct current passage. Commensurability oscillations in the suspended samples are more stable with respect to exposure to direct current, which can be presumably explained by electron–electron interaction enhancement after detaching nanostructures from the high-permittivity substrate.

Lattice Boltzmann scheme for diffusion on triangular grids

NARCIS (Netherlands)

Sman, van der R.G.M.

2003-01-01

In this paper we present a Lattice Boltzmann scheme for diffusion on it unstructured triangular grids. In this formulation of a LB for irregular grids there is no need for interpolation, which is required in other LB schemes on irregular grids. At the end of the propagation step the lattice gas

Quantitative study of fluctuation effects by fast lattice Monte Carlo simulations: Compression of grafted homopolymers

International Nuclear Information System (INIS)

Zhang, Pengfei; Wang, Qiang

2014-01-01

Using fast lattice Monte Carlo (FLMC) simulations [Q. Wang, Soft Matter 5, 4564 (2009)] and the corresponding lattice self-consistent field (LSCF) calculations, we studied a model system of grafted homopolymers, in both the brush and mushroom regimes, in an explicit solvent compressed by an impenetrable surface. Direct comparisons between FLMC and LSCF results, both of which are based on the same Hamiltonian (thus without any parameter-fitting between them), unambiguously and quantitatively reveal the fluctuations/correlations neglected by the latter. We studied both the structure (including the canonical-ensemble averages of the height and the mean-square end-to-end distances of grafted polymers) and thermodynamics (including the ensemble-averaged reduced energy density and the related internal energy per chain, the differences in the Helmholtz free energy and entropy per chain from the uncompressed state, and the pressure due to compression) of the system. In particular, we generalized the method for calculating pressure in lattice Monte Carlo simulations proposed by Dickman [J. Chem. Phys. 87, 2246 (1987)], and combined it with the Wang-Landau–Optimized Ensemble sampling [S. Trebst, D. A. Huse, and M. Troyer, Phys. Rev. E 70, 046701 (2004)] to efficiently and accurately calculate the free energy difference and the pressure due to compression. While we mainly examined the effects of the degree of compression, the distance between the nearest-neighbor grafting points, the reduced number of chains grafted at each grafting point, and the system fluctuations/correlations in an athermal solvent, the θ-solvent is also considered in some cases

A new approach to the problem of dynamical quarks in numerical simulations of lattice QCD

International Nuclear Information System (INIS)

Luescher, M.

1993-11-01

Lattice QCD with an even number of degenerate quark flavours is shown to be a limit of a local bosonic field theory. The action of the bosonic theory is real and bounded from below so that standard simulation algorithms can be expected to apply. The feasibility of such calculations is discussed, but no practical tests have yet been made. (orig.)

Chiral and continuum extrapolation of partially quenched lattice results

Energy Technology Data Exchange (ETDEWEB)

C.R. Allton; W. Armour; D.B. Leinweber; A.W. Thomas; R.D. Young

2005-04-01

The vector meson mass is extracted from a large sample of partially quenched, two-flavor lattice QCD simulations. For the first time, discretization, finite-volume and partial quenching artifacts are treated in a unified chiral effective field theory analysis of the lattice simulation results.

Lattice simulations of QCD-like theories at finite baryon density

Energy Technology Data Exchange (ETDEWEB)

Scior, Philipp Friedrich

2016-07-13

The exploration of the phase diagram of quantum chromodynamics (QCD) is of great importance to describe e.g. the properties of neutron stars or heavy-ion collisions. Due to the sign problem of lattice QCD at finite chemical potential we need effective theories to study QCD at finite density. Here, we use a three-dimensional Polyakov-loop theory to study the phase diagrams of QCD-like theories. In particular, we investigate the heavy quark limit of the QCD-like theories where the effective theory can be derived from the full theory by a combined strong coupling and hopping expansion. This expansion can be systematically improved order by order. Since there is no sign problem for the QCD-like theories we consider, we can compare our results to data from lattice calculations of the full theories to make qualitative and quantitative statements of the effective theory's validity. We start by deriving the effective theory up to next-to-next-to leading-order, in particular for two-color and G{sub 2}-QCD where replace the three colors in QCD with only two colors or respectively replace the gauge group SU(3) of QCD with G{sub 2}. We will then apply the effective theory at finite temperature mainly to test the theory and the implementation but also to make some predictions for the deconfinement phase transition in G{sub 2} Yang-Mills theory. Finally, we turn our attention to the cold and dense regime of the phase diagram where we observe a sharp increase of the baryon density with the quark chemical potential μ, when μ reaches half the diquark mass. At vanishing temperature this is expected to happen in a quantum phase transition with Bose-Einstein-condensation of diquarks. In contrast to the liquid-gas transition in QCD, the phase transition to the Bose-Einstein condensate is continuous. We find evidence that the effective theories for heavy quarks are able to describe the qualitative difference between first and second order phase transitions. For even higher μ we

Lattice simulations of QCD-like theories at finite baryon density

International Nuclear Information System (INIS)

Scior, Philipp Friedrich

2016-01-01

The exploration of the phase diagram of quantum chromodynamics (QCD) is of great importance to describe e.g. the properties of neutron stars or heavy-ion collisions. Due to the sign problem of lattice QCD at finite chemical potential we need effective theories to study QCD at finite density. Here, we use a three-dimensional Polyakov-loop theory to study the phase diagrams of QCD-like theories. In particular, we investigate the heavy quark limit of the QCD-like theories where the effective theory can be derived from the full theory by a combined strong coupling and hopping expansion. This expansion can be systematically improved order by order. Since there is no sign problem for the QCD-like theories we consider, we can compare our results to data from lattice calculations of the full theories to make qualitative and quantitative statements of the effective theory's validity. We start by deriving the effective theory up to next-to-next-to leading-order, in particular for two-color and G_2-QCD where replace the three colors in QCD with only two colors or respectively replace the gauge group SU(3) of QCD with G_2. We will then apply the effective theory at finite temperature mainly to test the theory and the implementation but also to make some predictions for the deconfinement phase transition in G_2 Yang-Mills theory. Finally, we turn our attention to the cold and dense regime of the phase diagram where we observe a sharp increase of the baryon density with the quark chemical potential μ, when μ reaches half the diquark mass. At vanishing temperature this is expected to happen in a quantum phase transition with Bose-Einstein-condensation of diquarks. In contrast to the liquid-gas transition in QCD, the phase transition to the Bose-Einstein condensate is continuous. We find evidence that the effective theories for heavy quarks are able to describe the qualitative difference between first and second order phase transitions. For even higher μ we find the rise of the

Discrete Lattice effect of various forcing methods of body force on immersed Boundary-Lattice Boltzmann method

Energy Technology Data Exchange (ETDEWEB)

Son, Sung Wan; Ha, Man Yeong; Yoon, Hyun Sik [Pusan National University, Busan (Korea, Republic of); Jeong, Hae Kwon [POSCO, Pohang (Korea, Republic of); Balachandar, S. [University of Florida, Florida (United States)

2013-02-15

We investigate the discrete lattice effect of various forcing methods in the lattice Boltzmann method (LBM) to include the body force obtained from the immersed boundary method (IBM). In the immersed boundary lattice Boltzmann method (IB-LBM), the LBM needs a forcing method to involve the body force on a forcing point near the immersed boundary that is calculated by IBM. The proper forcing method in LBM is derived to include the body force, which appears to resolve problems such as multiphase flow, non-ideal gas behavior, etc. Many researchers have adopted different forcing methods in LBM to involve the body force from IBM, even when they solved similar problems. However, it is necessary to evaluate the discrete lattice effect, which originates from different forcing methods in LBM, to include the effect of the body force from IBM on the results. Consequently, in this study, a rigorous analysis of the discrete lattice effect for different forcing methods in IB-LBM is performed by solving various problems.

Discrete Lattice effect of various forcing methods of body force on immersed Boundary-Lattice Boltzmann method

International Nuclear Information System (INIS)

Son, Sung Wan; Ha, Man Yeong; Yoon, Hyun Sik; Jeong, Hae Kwon; Balachandar, S.

2013-01-01

We investigate the discrete lattice effect of various forcing methods in the lattice Boltzmann method (LBM) to include the body force obtained from the immersed boundary method (IBM). In the immersed boundary lattice Boltzmann method (IB-LBM), the LBM needs a forcing method to involve the body force on a forcing point near the immersed boundary that is calculated by IBM. The proper forcing method in LBM is derived to include the body force, which appears to resolve problems such as multiphase flow, non-ideal gas behavior, etc. Many researchers have adopted different forcing methods in LBM to involve the body force from IBM, even when they solved similar problems. However, it is necessary to evaluate the discrete lattice effect, which originates from different forcing methods in LBM, to include the effect of the body force from IBM on the results. Consequently, in this study, a rigorous analysis of the discrete lattice effect for different forcing methods in IB-LBM is performed by solving various problems.

Lattice Thermal Conductivity of Ultra High Temperature Ceramics ZrB2 and HfB2 from Atomistic Simulations

Science.gov (United States)

Lawson, John W.; Murray, Daw S.; Bauschlicher, Charles W., Jr.

2011-01-01

Atomistic Green-Kubo simulations are performed to evaluate the lattice thermal conductivity for single crystals of the ultra high temperature ceramics ZrB2 and HfB2 for a range of temperatures. Recently developed interatomic potentials are used for these simulations. Heat current correlation functions show rapid oscillations which can be identified with mixed metal-Boron optical phonon modes. Agreement with available experimental data is good.

KMCLib: A general framework for lattice kinetic Monte Carlo (KMC) simulations

Science.gov (United States)

Leetmaa, Mikael; Skorodumova, Natalia V.

2014-09-01

KMCLib is a general framework for lattice kinetic Monte Carlo (KMC) simulations. The program can handle simulations of the diffusion and reaction of millions of particles in one, two, or three dimensions, and is designed to be easily extended and customized by the user to allow for the development of complex custom KMC models for specific systems without having to modify the core functionality of the program. Analysis modules and on-the-fly elementary step diffusion rate calculations can be implemented as plugins following a well-defined API. The plugin modules are loosely coupled to the core KMCLib program via the Python scripting language. KMCLib is written as a Python module with a backend C++ library. After initial compilation of the backend library KMCLib is used as a Python module; input to the program is given as a Python script executed using a standard Python interpreter. We give a detailed description of the features and implementation of the code and demonstrate its scaling behavior and parallel performance with a simple one-dimensional A-B-C lattice KMC model and a more complex three-dimensional lattice KMC model of oxygen-vacancy diffusion in a fluorite structured metal oxide. KMCLib can keep track of individual particle movements and includes tools for mean square displacement analysis, and is therefore particularly well suited for studying diffusion processes at surfaces and in solids. Catalogue identifier: AESZ_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AESZ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 49 064 No. of bytes in distributed program, including test data, etc.: 1 575 172 Distribution format: tar.gz Programming language: Python and C++. Computer: Any computer that can run a C++ compiler and a Python interpreter. Operating system: Tested on Ubuntu 12

Computer code for the atomistic simulation of lattice defects and dynamics. [COMENT code

Energy Technology Data Exchange (ETDEWEB)

Schiffgens, J.O.; Graves, N.J.; Oster, C.A.

1980-04-01

This document has been prepared to satisfy the need for a detailed, up-to-date description of a computer code that can be used to simulate phenomena on an atomistic level. COMENT was written in FORTRAN IV and COMPASS (CDC assembly language) to solve the classical equations of motion for a large number of atoms interacting according to a given force law, and to perform the desired ancillary analysis of the resulting data. COMENT is a dual-purpose intended to describe static defect configurations as well as the detailed motion of atoms in a crystal lattice. It can be used to simulate the effect of temperature, impurities, and pre-existing defects on radiation-induced defect production mechanisms, defect migration, and defect stability.

Rahman Prize Lecture: Lattice Boltzmann simulation of complex states of flowing matter

Science.gov (United States)

Succi, Sauro

Over the last three decades, the Lattice Boltzmann (LB) method has gained a prominent role in the numerical simulation of complex flows across an impressively broad range of scales, from fully-developed turbulence in real-life geometries, to multiphase flows in micro-fluidic devices, all the way down to biopolymer translocation in nanopores and lately, even quark-gluon plasmas. After a brief introduction to the main ideas behind the LB method and its historical developments, we shall present a few selected applications to complex flow problems at various scales of motion. Finally, we shall discuss prospects for extreme-scale LB simulations of outstanding problems in the physics of fluids and its interfaces with material sciences and biology, such as the modelling of fluid turbulence, the optimal design of nanoporous gold catalysts and protein folding/aggregation in crowded environments.

Off-gas adsorption model and simulation - OSPREY

Energy Technology Data Exchange (ETDEWEB)

Rutledge, V.J. [Idaho National Laboratory, P. O. Box 1625, Idaho Falls, ID (United States)

2013-07-01

A capability of accurately simulating the dynamic behavior of advanced fuel cycle separation processes is expected to provide substantial cost savings and many technical benefits. To support this capability, a modeling effort focused on the off-gas treatment system of a used nuclear fuel recycling facility is in progress. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, an adsorption model has been developed within Multi-physics Object Oriented Simulation Environment (MOOSE) developed at the Idaho National Laboratory (INL). Off-gas Separation and Recovery (OSPREY) models the adsorption of offgas constituents for dispersed plug flow in a packed bed under non-isothermal and non-isobaric conditions. Inputs to the model include gas composition, sorbent and column properties, equilibrium and kinetic data, and inlet conditions. The simulation outputs component concentrations along the column length as a function of time from which breakthrough data can be obtained. The breakthrough data can be used to determine bed capacity, which in turn can be used to size columns. In addition to concentration data, the model predicts temperature along the column length as a function of time and pressure drop along the column length. A description of the OSPREY model, results from krypton adsorption modeling and plans for modeling the behavior of iodine, xenon, and tritium will be discussed. (author)

Efficient Monte Carlo Simulations of Gas Molecules Inside Porous Materials.

Science.gov (United States)

Kim, Jihan; Smit, Berend

2012-07-10

Monte Carlo (MC) simulations are commonly used to obtain adsorption properties of gas molecules inside porous materials. In this work, we discuss various optimization strategies that lead to faster MC simulations with CO2 gas molecules inside host zeolite structures used as a test system. The reciprocal space contribution of the gas-gas Ewald summation and both the direct and the reciprocal gas-host potential energy interactions are stored inside energy grids to reduce the wall time in the MC simulations. Additional speedup can be obtained by selectively calling the routine that computes the gas-gas Ewald summation, which does not impact the accuracy of the zeolite's adsorption characteristics. We utilize two-level density-biased sampling technique in the grand canonical Monte Carlo (GCMC) algorithm to restrict CO2 insertion moves into low-energy regions within the zeolite materials to accelerate convergence. Finally, we make use of the graphics processing units (GPUs) hardware to conduct multiple MC simulations in parallel via judiciously mapping the GPU threads to available workload. As a result, we can obtain a CO2 adsorption isotherm curve with 14 pressure values (up to 10 atm) for a zeolite structure within a minute of total compute wall time.

On the zero-crossing of the three-gluon Green's function from lattice simulations

Energy Technology Data Exchange (ETDEWEB)

Athenodorou, Andreas [Univ. of Cyprus, Nicosia, Cyprus; Boucaud, Philippe [Univ. Paris-Sud, Orsay (France); de Soto, Feliciano [Univ. Pablo de Olavide, 41013 Sevilla; Spain; Univ. of Granada (Spain); Rodriguez-Quintero, Jose [Universidad de Huelva, 21071 Huelva; Spain; Univ. of Granada (Spain); Zafeiropoulos, Savvas [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); College of William and Mary, Williamsburg, VA (United States); Heidelberg Univ. (Germany). Inst. for Theoretische Physik

2018-04-01

We report on some efforts recently made in order to gain a better understanding of some IR properties of the 3-point gluon Green’s function by exploiting results from large-volume quenched lattice simulations. These lattice results have been obtained by using both tree-level Symanzik and the standard Wilson action, in the aim of assessing the possible impact of effects presumably resulting from a particular choice for the discretization of the action. The main resulting feature is the existence of a negative log-aritmic divergence at zero-momentum, which pulls the 3-gluon form factors down at low momenta and, consequently, yields a zero-crossing at a given deep IR momentum. The results can be correctly explained by analyzing the relevant Dyson-Schwinger equations and appropriate truncation schemes.

Boundary Slip and Surface Interaction: A Lattice Boltzmann Simulation

International Nuclear Information System (INIS)

Yan-Yan, Chen; Hua-Bing, Li; Hou-Hui, Yi

2008-01-01

The factors affecting slip length in Couette geometry flows are analysed by means of a two-phase mesoscopic lattice Boltzmann model including non-ideal fluid-fluid and fluid-wall interactions. The main factors influencing the boundary slip are the strength of interactions between fluid-fluid and fluid-wall particles. Other factors, such as fluid viscosity, bulk pressure may also change the slip length. We find that boundary slip only occurs under a certain density (bulk pressure). If the density is large enough, the slip length will tend to zero. In our simulations, a low density layer near the wall does not need to be postulated a priori but emerges naturally from the underlying non-ideal mesoscopic dynamics. It is the low density layer that induces the boundary slip. The results may be helpful to understand recent experimental observations on the slippage of micro flows

Quantum Lattice-Gas Model for the Diffusion Equation

National Research Council Canada - National Science Library

Yepez, J

2001-01-01

.... It is a minimal model with two qubits per node of a one-dimensional lattice and it is suitable for implementation on a large array of small quantum computers interconnected by nearest-neighbor...

Slow quench dynamics of a one-dimensional Bose gas confined to an optical lattice.

Science.gov (United States)

Bernier, Jean-Sébastien; Roux, Guillaume; Kollath, Corinna

2011-05-20

We analyze the effect of a linear time variation of the interaction strength on a trapped one-dimensional Bose gas confined to an optical lattice. The evolution of different observables such as the experimentally accessible on site particle distribution are studied as a function of the ramp time by using time-dependent numerical techniques. We find that the dynamics of a trapped system typically displays two regimes: For long ramp times, the dynamics is governed by density redistribution, while at short ramp times, local dynamics dominates as the evolution is identical to that of an homogeneous system. In the homogeneous limit, we also discuss the nontrivial scaling of the energy absorbed with the ramp time.

Numerical simulation research on gas migration with Y type ventilation

Science.gov (United States)

Gou, Yanan; Han, Xuezheng

2018-01-01

The ventilation way of the working face has a great influence to goaf flow field and gas migration, the existing U-shaped ventilation face wind serious overrun, Y type ventilation mode is put forward, and the mathematic control equation of the gas moving rule is established. Put the Gaozhuang coal mine west five mining area as the model, set up calculation model. And the gas concentration is simulated, the simulation results show that the Y type ventilation ways can intercept goaf gas into the corner on the working plane and return air lane, effectively avoid the work of top corner gas accumulation.

Atmospheric dispersion simulations of volcanic gas from Miyake Island by SPEEDI

International Nuclear Information System (INIS)

Nagai, Haruyasu; Furuno, Akiko; Terada, Hiroaki; Umeyama, Nobuaki; Yamazawa, Hiromi; Chino, Masamichi

2001-03-01

Japan Atomic Energy Research Institute is advancing the study for prediction of material circulation in the environment to cope with environmental pollution, based on SPEEDI (System for Prediction of Environmental Emergency Dose Information) and WSPEEDI (Worldwide version of SPEEDI), which are originally developed aiming at real-time prediction of atmospheric dispersion of radioactive substances accidentally released from nuclear facility. As a part of this study, dispersion simulation of volcanic gas erupted from Miyake Island is put into practice. After the stench incident at the west Kanto District on 28 August 2000 caused by volcanic gas from Miyake Island, the following simulations dealing with atmospheric dispersion of volcanic gas from Miyake Island have been carried out. (1) Retrospective simulation to analyze examine the mechanism of the transport of high concentration volcanic gas to the west Kanto District on 28 August and to estimate the release amount of volcanic gas. (2) Retrospective simulation to analyze the mechanism of the transport of volcanic gas to Tokai and Kansai districts in a case of stench incident on 13 September. (3) Automated real-time simulation from the acquisition of meteorological data to the output of figures for operational prediction of the transport of volcanic gas to Tokai and Kanto districts. This report describes the details of these studies. (author)

Lattice overview

International Nuclear Information System (INIS)

Creutz, M.

1984-01-01

After reviewing some recent developments in supercomputer access, the author discusses a few areas where perturbation theory and lattice gauge simulations make contact. The author concludes with a brief discussion of a deterministic dynamics for the Ising model. This may be useful for numerical studies of nonequilibrium phenomena. 13 references

An improved lattice Boltzmann scheme for multiphase fluid with multi-range interactions

Energy Technology Data Exchange (ETDEWEB)

Maquignon, Nicolas; Duchateau, Julien; Roussel, Gilles; Rousselle, François; Renaud, Christophe [Laboratoire Informatique Signal et Image de la Côte d' Opale, 50 rue Ferdinand Buisson, 62100 Calais (France); Université du Littoral Côte d' Opale, 1 place de l' Yser, 59140, Dunkerque (France); Association INNOCOLD, MREI 1, 145 (France)

2014-10-06

Modeling of fluids with liquid to gas phase transition has become important for understanding many environmental or industrial processes. Such simulations need new techniques, because traditional solvers are often limited. The Lattice Boltzmann Model (LBM) allows simulate complex fluids, because its mesoscopic nature gives possibility to incorporate additional physics in comparison to usual methods. In this work, an improved lattice Boltzmann model for phase transition flow will be introduced. First, the state of art for Shan and Chen (SC) type of LBM will be reminded. Then, link to real thermodynamics will be established with Maxwell equal areas construction. Convergence to isothermal liquid vapor equilibrium will be shown and discussed. Inclusion of an equation of state for real fluid and better incorporation of force term is presented. Multi-range interactions have been used for SC model, but it hasn't been yet applied to real fluid with non-ideal equation of state. In this work, we evaluate this model when it is applied to real liquid-vapor equilibrium. We show that important differences are found for evaluation of gas density. In order to recover thermodynamic consistency, we use a new scheme for calculation of force term, which is a combination of multi range model and numerical weighting used by Gong and Cheng. We show the superiority of our new model by studying convergence to equilibrium values over a large temperature range. We prove that spurious velocities remaining at equilibrium are decreased.

Simulations of overall flow in gas centrifuge considering feed jet

International Nuclear Information System (INIS)

He Liang; Jiang Dongjun; Ying Chuntong

2010-01-01

A coupled method for the numerical solution of the flow in rapidly rotating gas centrifuge was presented. An iteration process of DSMC and CFD was performed to analyze the overall flow in radial direction, in which DSMC was adopted to simulate the rarefied region, and CFD was adopted to the counter-current of gas centrifuge to discrete the model equations. It was applied to simulate the 2D symmetrical flow model considering the rarefied region with the feed jet flow. A series of illustrative numerical examples were given. The flow structures of the feed jet in the rarefied gas flow region were shown. The results suggest that DSMC CFD coupled method is competent to the simulations of overall flow in a gas centrifuge. (authors)

Working Group Report: Lattice Field Theory

Energy Technology Data Exchange (ETDEWEB)

Blum, T.; et al.,

2013-10-22

This is the report of the Computing Frontier working group on Lattice Field Theory prepared for the proceedings of the 2013 Community Summer Study ("Snowmass"). We present the future computing needs and plans of the U.S. lattice gauge theory community and argue that continued support of the U.S. (and worldwide) lattice-QCD effort is essential to fully capitalize on the enormous investment in the high-energy physics experimental program. We first summarize the dramatic progress of numerical lattice-QCD simulations in the past decade, with some emphasis on calculations carried out under the auspices of the U.S. Lattice-QCD Collaboration, and describe a broad program of lattice-QCD calculations that will be relevant for future experiments at the intensity and energy frontiers. We then present details of the computational hardware and software resources needed to undertake these calculations.

Computer simulation of strain-induced ordering in interstitial solutions based on the b.c.c. Ta lattice

International Nuclear Information System (INIS)

Blanter, M.S.; Khachaturyan, A.G.

1980-01-01

A computer simulation is made of strain-induced ordering of interstitial atoms within octahedral interstices in the Ta host lattice. The calculation technique allows to take into account infinite-range strain-induced interaction. Computer simulation of ordering process enables to model the sequence of structure changes which occur during the ordering process and to find the equilibrium structure of the stable interstitial superstructures. The structures of high-temperature ordering phases obtained by the method of static concentration waves coincide with those obtained by means of computer simulation. However computer simulation enables to predict the structures of low-temperature ordered phases which cannot be obtained by the method of concentration waves. Comparison of computer simulation results and structures of observed ordered phases demonstrates good agreement. (author)

The Bond Fluctuation Model and Other Lattice Models

Science.gov (United States)

Müller, Marcus

Lattice models constitute a class of coarse-grained representations of polymeric materials. They have enjoyed a longstanding tradition for investigating the universal behavior of long chain molecules by computer simulations and enumeration techniques. A coarse-grained representation is often necessary to investigate properties on large time- and length scales. First, some justification for using lattice models will be given and the benefits and limitations will be discussed. Then, the bond fluctuation model by Carmesin and Kremer [1] is placed into the context of other lattice models and compared to continuum models. Some specific techniques for measuring the pressure in lattice models will be described. The bond fluctuation model has been employed in more than 100 simulation studies in the last decade and only few selected applications can be mentioned.

Moments of nucleon generalized parton distributions from lattice QCD

International Nuclear Information System (INIS)

Alexandrou, C.; Cyprus Institute, Nicosia; Carbonell, J.; Harraud, P.A.; Papinutto, M.; Constantinou, M.; Kallidonis, C.; Guichon, P.; Jansen, K.; Korzec, T.; Humboldt Univ. Berlin

2011-07-01

We present results on the lower moments of the nucleon generalized parton distributions within lattice QCD using two dynamical flavors of degenerate twisted mass fermions. Our simulations are performed on lattices with three different values of the lattice spacings, namely a=0.089 fm, a=0.070 fm and a=0.056 fm, allowing the investigation of cut-off effects. The volume dependence is examined using simulations on two lattices of spatial length L=2.1 fm and L=2.8 fm. The simulations span pion masses in the range of 260-470 MeV. Our results are renormalized nonperturbatively and the values are given in the MS scheme at a scale μ=2 GeV. They are chirally extrapolated to the physical point in order to compare with experiment. The consequences of these results on the spin carried by the quarks in the nucleon are investigated. (orig.)

Ultracold Dipolar Gases in Optical Lattices

OpenAIRE

Trefzger, C.; Menotti, C.; Capogrosso-Sansone, B.; Lewenstein, M.

2011-01-01

This tutorial is a theoretical work, in which we study the physics of ultra-cold dipolar bosonic gases in optical lattices. Such gases consist of bosonic atoms or molecules that interact via dipolar forces, and that are cooled below the quantum degeneracy temperature, typically in the nK range. When such a degenerate quantum gas is loaded into an optical lattice produced by standing waves of laser light, new kinds of physical phenomena occur. These systems realize then extended Hubbard-type m...

Quantum lattice problems

NARCIS (Netherlands)

de Raedt, Hans; von der Linden, W.; Binder, K

1995-01-01

In this chapter we review methods currently used to perform Monte Carlo calculations for quantum lattice models. A detailed exposition is given of the formalism underlying the construction of the simulation algorithms. We discuss the fundamental and technical difficulties that are encountered and

Axisymmetric multiphase lattice Boltzmann method for generic equations of state

NARCIS (Netherlands)

Reijers, S.A.; Gelderblom, H.; Toschi, F.

2016-01-01

We present an axisymmetric lattice Boltzmann model based on the Kupershtokh et al. multiphase model that is capable of solving liquid–gas density ratios up to 103. Appropriate source terms are added to the lattice Boltzmann evolution equation to fully recover the axisymmetric multiphase conservation

Compositional simulations of producing oil-gas ratio behaviour in low permeable gas condensate reservoir

OpenAIRE

Gundersen, Pål Lee

2013-01-01

Master's thesis in Petroleum engineering Gas condensate flow behaviour below the dew point in low permeable formations can make accurate fluid sampling a difficult challenge. The objective of this study was to investigate the producing oil-gas ratio behaviour in the infinite-acting period for a low permeable gas condensate reservoir. Compositional isothermal flow simulations were performed using a single-layer, radial and two-dimensional, gas condensate reservoir model with low permeabili...

Effect of disorder on condensation in the lattice gas model on a random graph.

Science.gov (United States)

Handford, Thomas P; Dear, Alexander; Pérez-Reche, Francisco J; Taraskin, Sergei N

2014-07-01

The lattice gas model of condensation in a heterogeneous pore system, represented by a random graph of cells, is studied using an exact analytical solution. A binary mixture of pore cells with different coordination numbers is shown to exhibit two phase transitions as a function of chemical potential in a certain temperature range. Heterogeneity in interaction strengths is demonstrated to reduce the critical temperature and, for large-enough degreeS of disorder, divides the cells into ones which are either on average occupied or unoccupied. Despite treating the pore space loops in a simplified manner, the random-graph model provides a good description of condensation in porous structures containing loops. This is illustrated by considering capillary condensation in a structural model of mesoporous silica SBA-15.

Simulation of sound waves using the Lattice Boltzmann Method for fluid flow: Benchmark cases for outdoor sound propagation

NARCIS (Netherlands)

Salomons, E.M.; Lohman, W.J.A.; Zhou, H.

2016-01-01

Propagation of sound waves in air can be considered as a special case of fluid dynamics. Consequently, the lattice Boltzmann method (LBM) for fluid flow can be used for simulating sound propagation. In this article application of the LBM to sound propagation is illustrated for various cases:

Cold collisions in dissipative optical lattices

International Nuclear Information System (INIS)

Piilo, J; Suominen, K-A

2005-01-01

The invention of laser cooling methods for neutral atoms allows optical and magnetic trapping of cold atomic clouds in the temperature regime below 1 mK. In the past, light-assisted cold collisions between laser cooled atoms have been widely studied in magneto-optical atom traps (MOTs). We describe here theoretical studies of dynamical interactions, specifically cold collisions, between atoms trapped in near-resonant, dissipative optical lattices. The extension of collision studies to the regime of optical lattices introduces several complicating factors. For the lattice studies, one has to account for the internal substates of atoms, position-dependent matter-light coupling, and position-dependent couplings between the atoms, in addition to the spontaneous decay of electronically excited atomic states. The developed one-dimensional quantum-mechanical model combines atomic cooling and collision dynamics in a single framework. The model is based on Monte Carlo wavefunction simulations and is applied when the lattice-creating lasers have frequencies both below (red-detuned lattice) and above (blue-detuned lattice) the atomic resonance frequency. It turns out that the radiative heating mechanism affects the dynamics of atomic cloud in a red-detuned lattice in a way that is not directly expected from the MOT studies. The optical lattice and position-dependent light-matter coupling introduces selectivity of collision partners. The atoms which are most mobile and energetic are strongly favoured to participate in collisions, and are more often ejected from the lattice, than the slow ones in the laser parameter region selected for study. Consequently, the atoms remaining in the lattice have a smaller average kinetic energy per atom than in the case of non-interacting atoms. For blue-detuned lattices, we study how optical shielding emerges as a natural part of the lattice and look for ways to optimize the effect. We find that the cooling and shielding dynamics do not mix

Lattice location of Tm in Si and Ge determined from ion channeling followed by Monte Carlo simulations

International Nuclear Information System (INIS)

Yamamoto, Y.; Wakaiki, M.; Ikeda, A.; Kido, Y.

1999-01-01

The lattice location of Tm implanted into Si(1 0 0) and Ge(1 1 1) with energy of 180 keV was determined precisely by ion channeling followed by Monte Carlo simulations of ion trajectories. The implantations were performed at 550 deg. C with a dose of 5 x 10 14 ions/cm 2 . In the case of Tm in Si, 25 at.% and 50 at.% of Tm are located in the tetrahedral interstitial site and in the random site, respectively and the rest takes the substitutional position. The assumption of the Gaussian distribution centered at the exact tetrahedral site with a standard deviation of 0.2 Angstroms reproduced the azimuth angular-scan spectrum around the [1 1 0] axis. However, the observed angular spectrum is significantly broader than the simulated one. This is probably due to the fact that there exist slightly different Tm lattice sites from the exact tetrahedral position. For Ge(1 1 1) substrates, 25 at.% of Tm occupied the tetrahedral interstitial site and the rest was located randomly

Kinetic Monte Carlo simulations of travelling pulses and spiral waves in the lattice Lotka-Volterra model.

Science.gov (United States)

Makeev, Alexei G; Kurkina, Elena S; Kevrekidis, Ioannis G

2012-06-01

Kinetic Monte Carlo simulations are used to study the stochastic two-species Lotka-Volterra model on a square lattice. For certain values of the model parameters, the system constitutes an excitable medium: travelling pulses and rotating spiral waves can be excited. Stable solitary pulses travel with constant (modulo stochastic fluctuations) shape and speed along a periodic lattice. The spiral waves observed persist sometimes for hundreds of rotations, but they are ultimately unstable and break-up (because of fluctuations and interactions between neighboring fronts) giving rise to complex dynamic behavior in which numerous small spiral waves rotate and interact with each other. It is interesting that travelling pulses and spiral waves can be exhibited by the model even for completely immobile species, due to the non-local reaction kinetics.

Fluctuating ideal-gas lattice Boltzmann method with fluctuation dissipation theorem for nonvanishing velocities.

Science.gov (United States)

Kaehler, G; Wagner, A J

2013-06-01

Current implementations of fluctuating ideal-gas descriptions with the lattice Boltzmann methods are based on a fluctuation dissipation theorem, which, while greatly simplifying the implementation, strictly holds only for zero mean velocity and small fluctuations. We show how to derive the fluctuation dissipation theorem for all k, which was done only for k=0 in previous derivations. The consistent derivation requires, in principle, locally velocity-dependent multirelaxation time transforms. Such an implementation is computationally prohibitively expensive but, with a small computational trick, it is feasible to reproduce the correct FDT without overhead in computation time. It is then shown that the previous standard implementations perform poorly for non vanishing mean velocity as indicated by violations of Galilean invariance of measured structure factors. Results obtained with the method introduced here show a significant reduction of the Galilean invariance violations.

Three-dimensional simulations of Bingham plastic flows with the multiple-relaxation-time lattice Boltzmann model

OpenAIRE

Song-Gui Chen; Chuan-Hu Zhang; Yun-Tian Feng; Qi-Cheng Sun; Feng Jin

2016-01-01

This paper presents a three-dimensional (3D) parallel multiple-relaxation-time lattice Boltzmann model (MRT-LBM) for Bingham plastics which overcomes numerical instabilities in the simulation of non-Newtonian fluids for the Bhatnagar–Gross–Krook (BGK) model. The MRT-LBM and several related mathematical models are briefly described. Papanastasiou’s modified model is incorporated for better numerical stability. The impact of the relaxation parameters of the model is studied in detail. The MRT-L...

Design of the SPEAR 3 magnet lattice

International Nuclear Information System (INIS)

Corbett, J.; Limborg, C.; Nosochkov, Y.; Safranek, J.

1998-01-01

The SPEAR 3 Upgrade Project seeks to replace the present 160 nm-rad FODO lattice with an 18 nm-rad double bend achromat (DBA) lattice. The new lattice must conform to the layout of the SPEAR racetrack tunnel and service the existing photon beamlines. Working within these constraints, the authors designed a lattice with 18 achromatic cells and 3 GeV beam energy. This paper reports on design of the main DBA cells, design of the matching cells leading into the 6.5 m racetrack straights, and simulation of the dynamic aperture. The new lattice has gradient dipoles, conventional quadrupoles, and provides horizontal dynamic aperture to ± 20 mm with conservative magnetic multipole errors

Application of the lattice Boltzmann model to simulated stenosis growth in a two-dimensional carotid artery

International Nuclear Information System (INIS)

Boyd, J; Buick, J; Cosgrove, J A; Stansell, P

2005-01-01

The lattice Boltzmann model is used to observe changes in the velocity flow and shear stress in a carotid artery model during a simulated stenosis growth. Near wall shear stress in the unstenosed artery is found to agree with literature values. The model also shows regions of low velocity, rotational flow and low near wall shear stress along parts of the walls of the carotid artery that have been identified as being prone to atherosclerosis. These regions persist during the simulated stenosis growth, suggesting that atherosclerotic plaque build-up creates regions of flow with properties that favour atherosclerotic progression

Thermodynamics of lattice QCD with 2 sextet quarks on Nt=8 lattices

International Nuclear Information System (INIS)

Kogut, J. B.; Sinclair, D. K.

2011-01-01

We continue our lattice simulations of QCD with 2 flavors of color-sextet quarks as a model for conformal or walking technicolor. A 2-loop perturbative calculation of the β function which describes the evolution of this theory's running coupling constant predicts that it has a second zero at a finite coupling. This nontrivial zero would be an infrared stable fixed point, in which case the theory with massless quarks would be a conformal field theory. However, if the interaction between quarks and antiquarks becomes strong enough that a chiral condensate forms before this IR fixed point is reached, the theory is QCD-like with spontaneously broken chiral symmetry and confinement. However, the presence of the nearby IR fixed point means that there is a range of couplings for which the running coupling evolves very slowly, i.e. it ''walks.'' We are simulating the lattice version of this theory with staggered quarks at finite temperature, studying the changes in couplings at the deconfinement and chiral-symmetry restoring transitions as the temporal extent (N t ) of the lattice, measured in lattice units, is increased. Our earlier results on lattices with N t =4, 6 show both transitions move to weaker couplings as N t increases consistent with walking behavior. In this paper we extend these calculations to N t =8. Although both transitions again move to weaker couplings, the change in the coupling at the chiral transition from N t =6 to N t =8 is appreciably smaller than that from N t =4 to N t =6. This indicates that at N t =4, 6 we are seeing strong-coupling effects and that we will need results from N t >8 to determine if the chiral-transition coupling approaches zero as N t →∞, as needed for the theory to walk.

Modelling and Simulation of Gas Engines Using Aspen HYSYS

Directory of Open Access Journals (Sweden)

M. C. Ekwonu

2013-12-01

Full Text Available In this paper gas engine model was developed in Aspen HYSYS V7.3 and validated with Waukesha 16V275GL+ gas engine. Fuel flexibility, fuel types and part load performance of the gas engine were investigated. The design variability revealed that the gas engine can operate on poor fuel with low lower heating value (LHV such as landfill gas, sewage gas and biogas with biogas offering potential integration with bottoming cycles when compared to natural gas. The result of the gas engine simulation gave an efficiency 40.7% and power output of 3592kW.

Tadpole-improved SU(2) lattice gauge theory

Science.gov (United States)

Shakespeare, Norman H.; Trottier, Howard D.

1999-01-01

A comprehensive analysis of tadpole-improved SU(2) lattice gauge theory is made. Simulations are done on isotropic and anisotropic lattices, with and without improvement. Two tadpole renormalization schemes are employed, one using average plaquettes, the other using mean links in the Landau gauge. Simulations are done with spatial lattice spacings as in the range of about 0.1-0.4 fm. Results are presented for the static quark potential, the renormalized lattice anisotropy at/as (where at is the ``temporal'' lattice spacing), and for the scalar and tensor glueball masses. Tadpole improvement significantly reduces discretization errors in the static quark potential and in the scalar glueball mass, and results in very little renormalization of the bare anisotropy that is input to the action. We also find that tadpole improvement using mean links in the Landau gauge results in smaller discretization errors in the scalar glueball mass (as well as in the static quark potential), compared to when average plaquettes are used. The possibility is also raised that further improvement in the scalar glueball mass may result when the coefficients of the operators which correct for discretization errors in the action are computed beyond the tree level.

Analysis of nanowire transistor based nitrogen dioxide gas sensor – A simulation study

Directory of Open Access Journals (Sweden)

Gaurav Saxena

2015-06-01

Full Text Available Sensors sensitivity, selectivity and stability has always been a prime design concern for gas sensors designers. Modeling and simulation of gas sensors aids the designers in improving their performance. In this paper, different routes for the modeling and simulation of a semiconducting gas sensor is presented. Subsequently, by employing one of the route, the response of Zinc Oxide nanowire transistor towards nitrogen dioxide ambient is simulated. In addition to the sensing mechanism, simulation study of gas species desorption by applying a recovery voltage is also presented.

Status and future of lattice gauge theory

International Nuclear Information System (INIS)

Hoek, J.

1989-07-01

The current status of lattice Quantum Chromo Dynamics (QCD) calculations, the computer requirements to obtain physical results and the direction computing is taking are described. First of all, there is a lot of evidence that QCD is the correct theory of strong interactions. Since it is an asymptotically free theory we can use perturbation theory to solve it in the regime of very hard collisions. However even in the case of very hard parton collisions the end-results of the collisions are bound states of quarks and perturbation theory is not sufficient to calculate these final stages. The way to solve the theory in this regime was opened by Wilson. He contemplated replacing the space-time continuum by a discrete lattice, with a lattice spacing a. Continuum physics is then recovered in the limit where the correlation length of the theory, say ξ. is large with respect to the lattice spacing. This will be true if the lattice spacing becomes very small, which for asymptotically free theories also implies that the coupling g becomes small. The lattice approach to QCD is in many respects analogous to the use of finite element methods to solve classical field theories. These finite element methods are easy to apply in 2-dimensional simulations but are computationally demanding in the 3-dimensional case. Therefore it is not unexpected that the 4-dimensional simulations needed for lattice gauge theories have led to an explosion in demand for computing power by theorists. (author)

Vortex lattices in a rotating Fermi superfluid in the BCS–BEC crossover with many Landau levels

International Nuclear Information System (INIS)

Song, Tie-ling; Ma, C.R.; Ma, Yong-li

2012-01-01

We present an explicit analytical analysis of the ground state of vortex lattice structure, based on a minimization of the generalized Gross–Pitaevskii energy functional in a trapped rotating Fermi superfluid gas. By a Bogoliubov-like transformation we find that the coarse-grained average of the atomic density varies as inverted parabola in three dimensional cases; the Fermi superfluid in the BEC regime enters into the lowest Landau level at fast rotation, in which the vortices form an almost regular triangular lattice over a central region and the vortex lattice is expanded along the radial direction in the outer region; the fluid in the unitarity and BCS regimes occupies many low-lying Landau levels, in which a trapped gas with a triangular vortex lattice has a superfluid core surrounded by a normal gas. The calculation is qualitatively consistent with recent numerical and experimental data both in the vortex lattice structure and vortex numbers and in the density profiles versus the stirring frequency in the whole BCS–BEC crossover. - Highlights: ► We present an analysis of vortex lattice in an interacting trapped rotating Fermi superfluid gas. ► Decomposing the vortex from the condensate, we can explain the vortex lattice. ► The calculation is consistent with numerical and experimental data. ► It can characterize experimentally properties in different regimes of the BCS–BEC crossover.

Phase diagram and Chiral Magnetic Effect in Dirac Semimetals from Lattice Simulation

Directory of Open Access Journals (Sweden)

Boyda D.L.

2018-01-01

Full Text Available Dirac Semimetals Na3Bi and Cd3As2 are recently discovered materials, which low energy electronic spectrum is described by two flavours of massless 3+1D fermions. In order to study electronic properties of these materials we formulated lattice field theory with rooted staggered fermions on anisotropic lattice. It is shown that in the limit of zero temporal lattice spacing this theory reproduces effective theory of Dirac semimetals. Using the lattice field theory we study the phase diagram of Dirac semimetals in the plane effective coupling constant - Fermi velocity anisotropy. We also measure conductivity of Dirac Semimetals within lattice field theory in external magnetic field. Our results confirm the existence of Chiral Magnetic Effect in Dirac Semimetals.

Numerical Simulation of Flows about a Stationary and a Free-Falling Cylinder Using Immersed Boundary-Finite Difference Lattice Boltzmann Method

Directory of Open Access Journals (Sweden)

Roberto Rojas

2013-03-01

Full Text Available The applicability of the immersed boundary-finite difference lattice Boltzmann method (IB-FDLBM to high Reynolds number flows about a circular cylinder is examined. Two-dimensional simulations of flows past a stationary circular cylinder are carried out for a wide range of the Reynolds number, Re, i.e., 1 ≤ Re ≤ 1×105. An immersed boundary-lattice Boltzmann method (IB-LBM is also used for comparison. Then free-falling circular cylinders are simulated to demonstrate the feasibility of predicting moving particles at high Reynolds numbers. The main conclusions obtained are as follows: (1 steady and unsteady flows about a stationary cylinder are well predicted with IB-LBM and IB-FDLBM, provided that the spatial resolution is high enough to satisfy the conditions of numerical stability, (2 high spatial resolution is required for stable IB-LBM simulation of high Reynolds number flows, (3 IB-FDLBM can stably simulate flows at very high Reynolds numbers without increasing the spatial resolution, (4 IB-FDLBM gives reasonable predictions of the drag coefficient for 1 ≤ Re ≤ 1×105, and (5 IB-FDLBM gives accurate predictions for the motion of free-falling cylinders at intermediate Reynolds numbers.

Simulation of ion beam scattering in a gas stripper

Energy Technology Data Exchange (ETDEWEB)

Maxeiner, Sascha, E-mail: maxeiner@phys.ethz.ch; Suter, Martin; Christl, Marcus; Synal, Hans-Arno

2015-10-15

Ion beam scattering in the gas stripper of an accelerator mass spectrometer (AMS) enlarges the beam phase space and broadens its energy distribution. As the size of the injected beam depends on the acceleration voltage through phase space compression, the stripper becomes a limiting factor of the overall system transmission especially for low energy AMS system in the sub MV region. The spatial beam broadening and collisions with the accelerator tube walls are a possible source for machine background and energy loss fluctuations influence the mass resolution and thus isotope separation. To investigate the physical processes responsible for these effects, a computer simulation approach was chosen. Monte Carlo simulation methods are applied to simulate elastic two body scattering processes in screened Coulomb potentials in a (gas) stripper and formulas are derived to correctly determine random collision parameters and free path lengths for arbitrary (and non-homogeneous) gas densities. A simple parametric form for the underlying scattering cross sections is discussed which features important scaling behaviors. An implementation of the simulation was able to correctly model the data gained with the TANDY AMS system at ETH Zurich. The experiment covered transmission measurements of uranium ions in helium and beam profile measurements after the ion beam passed through the He-stripper. Beam profiles measured up to very high stripper densities could be understood in full system simulations including the relevant ion optics. The presented model therefore simulates the fundamental physics of the interaction between an ion beam and a gas stripper reliably. It provides a powerful and flexible tool for optimizing existing AMS stripper geometries and for designing new, state of the art low energy AMS systems.

Cluster properties of the one-dimensional lattice gas: the microscopic meaning of grand potential.

Science.gov (United States)

Fronczak, Agata

2013-02-01

Using a concrete example, we demonstrate how the combinatorial approach to a general system of particles, which was introduced in detail in an earlier paper [Fronczak, Phys. Rev. E 86, 041139 (2012)], works and where this approach provides a genuine extension of results obtained through more traditional methods of statistical mechanics. We study the cluster properties of a one-dimensional lattice gas with nearest-neighbor interactions. Three cases (the infinite temperature limit, the range of finite temperatures, and the zero temperature limit) are discussed separately, yielding interesting results and providing alternative proof of known results. In particular, the closed-form expression for the grand partition function in the zero temperature limit is obtained, which results in the nonanalytic behavior of the grand potential, in accordance with the Yang-Lee theory.

Simulations of Micro Gas Flows by the DS-BGK Method

KAUST Repository

Li, Jun

2011-01-01

For gas flows in micro devices, the molecular mean free path is of the same order as the characteristic scale making the Navier-Stokes equation invalid. Recently, some micro gas flows are simulated by the DS-BGK method, which is convergent to the BGK equation and very efficient for low-velocity cases. As the molecular reflection on the boundary is the dominant effect compared to the intermolecular collisions in micro gas flows, the more realistic boundary condition, namely the CLL reflection model, is employed in the DS-BGK simulation and the influence of the accommodation coefficients used in the molecular reflection model on the results are discussed. The simulation results are verified by comparison with those of the DSMC method as criteria. Copyright © 2011 by ASME.

Designed defects in 2D antidot lattices for quantum information processing

DEFF Research Database (Denmark)

Pedersen, Jesper Goor; Flindt, Christian; Mortensen, Niels Asger

2008-01-01

We propose a new physical implementation of spin qubits for quantum information processing, namely defect states in antidot lattices defined in the two-dimensional electron gas (2DEG) at a semiconductor heterostructure. Calculations of the band structure of a periodic antidot lattice are presented...

Investigation of GDL compression effects on the performance of a PEM fuel cell cathode by lattice Boltzmann method

Science.gov (United States)

Molaeimanesh, G. R.; Nazemian, M.

2017-08-01

Proton exchange membrane (PEM) fuel cells with a great potential for application in vehicle propulsion systems will have a promising future. However, to overcome the exiting challenges against their wider commercialization further fundamental research is inevitable. The effects of gas diffusion layer (GDL) compression on the performance of a PEM fuel cell is not well-recognized; especially, via pore-scale simulation technique capturing the fibrous microstructure of the GDL. In the current investigation, a stochastic microstructure reconstruction method is proposed which can capture GDL microstructure changes by compression. Afterwards, lattice Boltzmann pore-scale simulation technique is adopted to simulate the reactive gas flow through 10 different cathode electrodes with dissimilar carbon paper GDLs produced from five different compression levels and two different carbon fiber diameters. The distributions of oxygen mole fraction, water vapor mole fraction and current density for the simulated cases are presented and analyzed. The results of simulations demonstrate that when the fiber diameter is 9 μm adding compression leads to lower average current density while when the fiber diameter is 7 μm the compression effect is not monotonic.

Simulation of granular and gas-solid flows using discrete element method

Science.gov (United States)

Boyalakuntla, Dhanunjay S.

2003-10-01

In recent years there has been increased research activity in the experimental and numerical study of gas-solid flows. Flows of this type have numerous applications in the energy, pharmaceuticals, and chemicals process industries. Typical applications include pulverized coal combustion, flow and heat transfer in bubbling and circulating fluidized beds, hopper and chute flows, pneumatic transport of pharmaceutical powders and pellets, and many more. The present work addresses the study of gas-solid flows using computational fluid dynamics (CFD) techniques and discrete element simulation methods (DES) combined. Many previous studies of coupled gas-solid flows have been performed assuming the solid phase as a continuum with averaged properties and treating the gas-solid flow as constituting of interpenetrating continua. Instead, in the present work, the gas phase flow is simulated using continuum theory and the solid phase flow is simulated using DES. DES treats each solid particle individually, thus accounting for its dynamics due to particle-particle interactions, particle-wall interactions as well as fluid drag and buoyancy. The present work involves developing efficient DES methods for dense granular flow and coupling this simulation to continuum simulations of the gas phase flow. Simulations have been performed to observe pure granular behavior in vibrating beds. Benchmark cases have been simulated and the results obtained match the published literature. The dimensionless acceleration amplitude and the bed height are the parameters governing bed behavior. Various interesting behaviors such as heaping, round and cusp surface standing waves, as well as kinks, have been observed for different values of the acceleration amplitude for a given bed height. Furthermore, binary granular mixtures (granular mixtures with two particle sizes) in a vibrated bed have also been studied. Gas-solid flow simulations have been performed to study fluidized beds. Benchmark 2D

Simulation of gas turbines operating in off-design condition

Energy Technology Data Exchange (ETDEWEB)

Walter, Arnaldo [Universidade Estadual de Campinas, SP (Brazil). Faculdade de Engenharia Mecanica. Dept. de Energia]. E-mail: walter@fem.unicamp.br

2000-07-01

In many countries thermal power plants based on gas turbines have been the main option for new investment into the electric system due to their relatively high efficiency and low capital cost. Cogeneration systems based on gas turbines have also been an important option for the electric industry. Feasibility studies of power plants based on gas turbine should consider the effect of atmospheric conditions and part-load operation on the machine performance. Doing this, an off-design procedure is required. A G T off-design simulation procedure is described in this paper. Ruston R M was used to validate the simulation procedure that, general sense, presents deviations lower than 2.5% in comparison to manufacturer's data. (author)

Two-dimensional simulation of intermediate-sized bubbles in low viscous liquids using counter diffusion lattice Boltzmann method

Energy Technology Data Exchange (ETDEWEB)

Ryu, Seungyeob, E-mail: syryu@kaeri.re.kr [Korea Atomic Energy Research Institute (KAERI), 1045 Daeduk-daero, Yuseong-gu, Daejeon 305-353 (Korea, Republic of); Kim, Youngin; Kang, Hanok; Kim, Keung Koo [Korea Atomic Energy Research Institute (KAERI), 1045 Daeduk-daero, Yuseong-gu, Daejeon 305-353 (Korea, Republic of); Ko, Sungho, E-mail: sunghoko@cnu.ac.kr [Department of Mechanical Design Engineering, Chungnam National University, 220 Gung-dong, Yuseong-gu, Daejeon 305-764 (Korea, Republic of)

2016-08-15

Highlights: • We directly simulate intermediate-sized bubbles in low viscous liquids. • The path instability and shape oscillation can be successfully simulated. • The motion of a pair bubble and bubble swarm is presented. • Bubbles with high-Reynolds-number can be simulated with under-resolved grids. • The counter diffusion multiphase method is feasible for the direct simulation of bubbly flows. - Abstract: The counter diffusion lattice Boltzmann method (LBM) is used to simulate intermediate-sized bubbles in low viscous liquids. Bubbles at high Reynolds numbers ranging from hundreds to thousands are simulated successfully, which cannot be done for the existing LBM versions. The characteristics of the path instability of two rising bubbles are studied for a wide range of Eotvos and Morton numbers. Finally, the study presented how bubble swarms move within the flow and how the flow surrounding the bubbles is affected by the bubble motions.

Lattice Boltzmann simulations for wall-flow dynamics in porous ceramic diesel particulate filters

Science.gov (United States)

Lee, Da Young; Lee, Gi Wook; Yoon, Kyu; Chun, Byoungjin; Jung, Hyun Wook

2018-01-01

Flows through porous filter walls of wall-flow diesel particulate filter are investigated using the lattice Boltzmann method (LBM). The microscopic model of the realistic filter wall is represented by randomly overlapped arrays of solid spheres. The LB simulation results are first validated by comparison to those from previous hydrodynamic theories and constitutive models for flows in porous media with simple regular and random solid-wall configurations. We demonstrate that the newly designed randomly overlapped array structures of porous walls allow reliable and accurate simulations for the porous wall-flow dynamics in a wide range of solid volume fractions from 0.01 to about 0.8, which is beyond the maximum random packing limit of 0.625. The permeable performance of porous media is scrutinized by changing the solid volume fraction and particle Reynolds number using Darcy's law and Forchheimer's extension in the laminar flow region.

Lattice distortion in hcp rare gas solids

Science.gov (United States)

Grechnev, A.; Tretyak, S. M.; Freiman, Yu. A.

2010-04-01

The lattice distortion parameter δ ≡c/a-√8/3 has been calculated as a function of molar volume for the hcp phases of He, Ar, Kr, and Xe. Results from both semi-empirical potentials and density functional theory are presented. Our study shows that δ is negative for helium in the entire pressure range. For Ar, Kr, and Xe δ changes sign from negative to positive as the pressure increases, growing rapidly in magnitude at higher pressures.

QCD with 2 light quark flavours: thermodynamics on a 163 x 8 lattice and glueballs and topological charge on a 163 x 32 lattice

International Nuclear Information System (INIS)

Bitar, K.M.; Edwards, R.; Gottlieb, S.; Heller, U.M.; Kennedy, A.D.; Kim, S.; Kogut, J.B.; Krasnitz, A.; Liu, W.; Ogilvie, M.C.; Renken, R.L.; Sinclair, D.K.; Sugar, R.L.; Teper, M.; Toussaint, D.; Wang, K.C.

1993-01-01

The HTMCGC collaboration has been simulating lattice QCD with two light staggered quarks with masses m q = 0.0125 and also m q = 0.00625 on a 16 3 x 8 lattice. We have been studying the behaviour of the transition from hadronic matter to a quark-gluon plasma and the properties of that plasma. We have been measuring entropy densities, Debye and hadronic screening lengths, the spacial string tension and topological susceptibility in addition to the standard order parameters. The HEMCGC collaboration has simulated lattice QCD with two light staggered quarks, m q = 0.025 and m q = 0.010 on a 16 3 x 32 lattice. We have measured the glueball spectrum and topological susceptibilities for these runs. (orig.)

QCD with 2 light quark flavours: Thermodynamics on a 163 x 8 lattice and glueballs and topological charge on a 163 x 32 lattice

International Nuclear Information System (INIS)

Sinclair, D.K.

1992-01-01

The HTMCGC collaboration has been simulating lattice QCD with two light staggered quarks with masses m q = 0.0125 and also m q = 0.00625 on a 16 3 x 8 lattice. We have been studying the behavior of the transition from hadronic matter to a quark-gluon plasma and the properties of that plasma. We have been measuring entropy densities, Debye and hadronic screening lengths, the spacial string tension and topological susceptibility in addition to the standard order parameters. The HEMCGC collaboration has simulated lattice QCD with two light staggered quarks,m q = 0.025 and m q = 0.010 on a 16 3 x 32 lattice. We have measured the glueball spectrum and topological susceptibilities for these runs

Group theory and lattice gauge fields

International Nuclear Information System (INIS)

Creutz, M.

1988-09-01

Lattice gauge theory, formulated in terms of invariant integrals over group elements on lattice bonds, benefits from many group theoretical notions. Gauge invariance provides an enormous symmetry and powerful constraints on expectation values. Strong coupling expansions require invariant integrals over polynomials in group elements, all of which can be evaluated by symmetry considerations. Numerical simulations involve random walks over the group. These walks automatically generate the invariant group measure, avoiding explicit parameterization. A recently proposed overrelaxation algorithm is particularly efficient at exploring the group manifold. These and other applications of group theory to lattice gauge fields are reviewed in this talk. 17 refs

Lattice Boltzmann simulation of flow around a confined circular cyclinder

International Nuclear Information System (INIS)

Ashrafizaadeh, M.; Zadehgol, A.

2002-01-01

A two dimensional lattice Boltzmann model (LBM) based on a single time relaxation BGK model has been developed. Several benchmark problems including the Poiseuille flow, the lid driven cavity flow and the flow around a circular cylinder have been performed employing a d2q9 lattice. The laminar flow around a circular cylinder within a channel has been extensively investigated using the present lattice Boltzmann model. Both symmetric and asymmetric placement configurations of the circular cylinder within the channel have been considered. A new treatment for the outlet velocity and pressure (density) boundary conditions has been proposed and validated. The present LBM results are in excellent agreement with those of the other existing CFD results. Careful examination of the LBM results and an appropriate calculation of the lift coefficient based on the rectangular lattice representation of the circular cylinder reveals that the periodic oscillation of the lift coefficient has a second harmonic when the cylinder is placed asymmetrically within the channel. The second harmonic could be associated with an asymmetrical shedding pattern of the vortices behind the cylinder from the upper and lower sides of the cylinder. (author)

Entropy favours open colloidal lattices

Science.gov (United States)

Mao, Xiaoming; Chen, Qian; Granick, Steve

2013-03-01

Burgeoning experimental and simulation activity seeks to understand the existence of self-assembled colloidal structures that are not close-packed. Here we describe an analytical theory based on lattice dynamics and supported by experiments that reveals the fundamental role entropy can play in stabilizing open lattices. The entropy we consider is associated with the rotational and vibrational modes unique to colloids interacting through extended attractive patches. The theory makes predictions of the implied temperature, pressure and patch-size dependence of the phase diagram of open and close-packed structures. More generally, it provides guidance for the conditions at which targeted patchy colloidal assemblies in two and three dimensions are stable, thus overcoming the difficulty in exploring by experiment or simulation the full range of conceivable parameters.

Numerical Study of the Ghost-Ghost-Gluon Vertex on the Lattice

International Nuclear Information System (INIS)

Mihara, A.; Cucchieri, A.; Mendes, T.

2004-01-01

It is well known that, in Landau gauge, the renormalization function of the ghost-ghost-gluon vertex Z-tilde1 (p2) is finite and constant, at least to all orders of perturbation theory. On the other hand, a direct non-perturbative verification of this result using numerical simulations of lattice QCD is still missing. Here we present a preliminary numerical study of the ghost-ghost-gluon vertex and of its corresponding renormalization function using Monte Carlo simulations in SU(2) lattice Landau gauge. Data were obtained in 4 dimensions for lattice couplings β = 2.2, 2.3, 2.4 and lattice sides N = 4, 8, 16

Numerical study of the ghost-ghost-gluon vertex on the lattice

International Nuclear Information System (INIS)

Mihara, A.; Cucchieri, A.; Mendes, T.

2004-01-01

It is well known that, in Landau gauge, the renormalization function of the ghost-ghost-gluon vertex Z∼ 1 1(p 2 ) is finite and constant, at least to all orders of perturbation theory. On the other hand, a direct non-perturbative verification of this result using numerical simulations of lattice QCD is still missing. Here we present a preliminary numerical study of the ghost-ghost-gluon vertex and of its corresponding renormalization function using Monte Carlo simulations in SU(2) lattice Landau gauge. Data were obtained in 4 dimensions for lattice couplings β= 2.2, 2.3, 2.4 and lattice sides N = 4, 8, 16. (author)

Influence of Boundary Conditions on the Simulation of a Diamond-Type Lattice Structure: A Preliminary Study

Directory of Open Access Journals (Sweden)

Patrick Terriault

2017-01-01

Full Text Available Emergent additive manufacturing processes allow the use of metallic porous structures in various industrial applications. Because these structures comprise a large number of ordered unit cells, their design using conventional modeling approaches, such as finite elements, becomes a real challenge. A homogenization technique, in which the lattice structure is simulated as a fully dense volume having equivalent material properties, can then be employed. To determine these equivalent material properties, numerical simulations can be performed on a single unit cell of the lattice structure. However, a critical aspect to consider is the boundary conditions applied to the external faces of the unit cell. In the literature, different types of boundary conditions are used, but a comparative study is definitely lacking. In this publication, a diamond-type unit cell is studied in compression by applying different boundary conditions. If the porous structure’s boundaries are free to deform, then the periodic boundary condition is found to be the most representative, but constraint equations must be introduced in the model. If, instead, the porous structure is inserted in a rigid enclosure, it is then better to use frictionless boundary conditions. These preliminary results remain to be validated for other types of unit cells loaded beyond the yield limit of the material.

Lattice Boltzmann simulations of pressure-driven flows in microchannels using Navier–Maxwell slip boundary conditions

KAUST Repository

Reis, Tim

2012-01-01

We present lattice Boltzmann simulations of rarefied flows driven by pressure drops along two-dimensional microchannels. Rarefied effects lead to non-zero cross-channel velocities, nonlinear variations in the pressure along the channel. Both effects are absent in flows driven by uniform body forces. We obtain second-order accuracy for the two components of velocity the pressure relative to asymptotic solutions of the compressible Navier-Stokes equations with slip boundary conditions. Since the common lattice Boltzmann formulations cannot capture Knudsen boundary layers, we replace the usual discrete analogs of the specular diffuse reflection conditions from continuous kinetic theory with a moment-based implementation of the first-order Navier-Maxwell slip boundary conditions that relate the tangential velocity to the strain rate at the boundary. We use these conditions to solve for the unknown distribution functions that propagate into the domain across the boundary. We achieve second-order accuracy by reformulating these conditions for the second set of distribution functions that arise in the derivation of the lattice Boltzmann method by an integration along characteristics. Our moment formalism is also valuable for analysing the existing boundary conditions. It reveals the origin of numerical slip in the bounce-back other common boundary conditions that impose conditions on the higher moments, not on the local tangential velocity itself. © 2012 American Institute of Physics.

Modelling of Dispersed Gas-Liquid Flow using LBGK and LPT Approach

Science.gov (United States)

Agarwal, Alankar; Prakash, Akshay; Ravindra, B.

2017-11-01

The dynamics of gas bubbles play a significant, if not crucial, role in a large variety of industrial process that involves using reactors. Many of these processes are still not well understood in terms of optimal scale-up strategies.An accurate modeling of bubbles and bubble swarms become important for high fidelity bioreactor simulations. This study is a part of the development of robust bubble fluid interaction modules for simulation of industrial-scale reactors. The work presents the simulation of a single bubble rising in a quiescent water tank using current models presented in the literature for bubble-fluid interaction. In this multiphase benchmark problem, the continuous phase (water) is discretized using the Lattice Bhatnagar-Gross and Krook (LBGK) model of Lattice Boltzmann Method (LBM), while the dispersed gas phase (i.e. air-bubble) modeled with the Lagrangian particle tracking (LPT) approach. The cheap clipped fourth order polynomial function is used to model the interaction between two phases. The model is validated by comparing the simulation results for terminal velocity of a bubble at varying bubble diameter and the influence of bubble motion in liquid velocity with the theoretical and previously available experimental data. This work is supported by the ``Centre for Development of Advanced Computing (C-DAC), Pune'' by providing the advanced computational facility in PARAM Yuva-II.

Simulation of Micro-Channel and Micro-Orifice Flow Using Lattice Boltzmann Method with Langmuir Slip Model

Directory of Open Access Journals (Sweden)

A. R. Rahmati

2016-12-01

Full Text Available Because of its kinetic nature and computational advantages, the Lattice Boltzmann method (LBM has been well accepted as a useful tool to simulate micro-scale flows. The slip boundary model plays a crucial role in the accuracy of solutions for micro-channel flow simulations. The most used slip boundary condition is the Maxwell slip model. The results of Maxwell slip model are affected by the accommodation coefficient significantly, but there is not an explicitly relationship between properties at wall and accommodation coefficient. In the present wok, Langmuir slip model is used beside LBM to simulate micro-channel and micro-orifice flows. Slip velocity and nonlinear pressure drop profiles are presented as two major effects in such flows. The results are in good agreement with existing results in the literature.

Lattice doped Zn–SnO{sub 2} nanospheres: A systematic exploration of dopant ion effects on structural, optical, and enhanced gas sensing properties

Energy Technology Data Exchange (ETDEWEB)

Baraneedharan, P. [Nanoscience and Technology, Anna University – BIT Campus, Tiruchirappalli 620024 (India); Alternative Energy and Nanotechnology Laboratory, Indian Institute of Technology Madras, Chennai 600036 (India); Imran Hussain, S. [Nanoscience and Technology, Anna University – BIT Campus, Tiruchirappalli 620024 (India); Department of Applied Science and Technology, Anna University, Chennai 600 025 (India); Dinesh, V.P. [Nanosensor Laboratory, PSG Institute of Advanced Studies, Coimbatore 641004 (India); Siva, C. [Nanoscience and Technology, Anna University – BIT Campus, Tiruchirappalli 620024 (India); Department of Physics and Nanotechnology, SRM University, Kattankulathur 603 203 (India); Biji, P. [Nanosensor Laboratory, PSG Institute of Advanced Studies, Coimbatore 641004 (India); Sivakumar, M., E-mail: muthusiva@gmail.com [Nanoscience and Technology, Anna University – BIT Campus, Tiruchirappalli 620024 (India)

2015-12-01

Graphical abstract: - Highlights: • A simple, novel and surfactant free hydrothermal route to prepare SnO{sub 2} nanospheres. • A systematic investigation of growth mechanism with the assist of time dependent HR-TEM images. • Incorporation of Zn ions into SnO{sub 2} lattices clearly elucidated with XRD and XPS spectrums. • Three fold time increased response in Zn–SnO{sub 2} nanospheres when compared to undoped SnO{sub 2}. - Abstract: A surfactant-free one step hydrothermal method is reported to synthesize zinc (Zn{sup 2+}) doped SnO{sub 2} nanospheres. The structural analysis of X-ray diffraction confirms the tetragonal crystal system of the material with superior crystalline nature. The shift in diffraction peak, variation in lattice constant and disparity in particle size confirm the incorporation of Zn{sup 2+} ions to the Sn host lattices. The lattice doped structure, the disparity in morphology, size and shape by the addition of Zn{sup 2+} ions are evident from X-ray photoelectron spectroscopic and electron microscopic analysis. Significant changes in the absorption edge and the band gap with increased doping concentration were observed in UV–vis absorption spectral analysis. The formation of acceptor energy levels with the incorporation of Zn{sup 2+} ions has a significant effect on the electrical conductivity of SnO{sub 2} nanospheres. Comparative tests for gas sensors based on Zn doped SnO{sub 2} nanospheres and SnO{sub 2} nanospheres clearly show that the former exhibited excellent NO{sub 2} sensing performance. The responses of Zn{sup 2+} ions incorporated SnO{sub 2} nanospheres sensor were increased 3 fold at trace level NO{sub 2} gas concentrations ranging from 1 to 5 ppm. The excellent sensitivity, selectivity and fast response make the Zn{sup 2+} doped SnO{sub 2} nanospheres ideal for NO{sub 2} sensing.

Chimera states in Gaussian coupled map lattices

Science.gov (United States)

Li, Xiao-Wen; Bi, Ran; Sun, Yue-Xiang; Zhang, Shuo; Song, Qian-Qian

2018-04-01

We study chimera states in one-dimensional and two-dimensional Gaussian coupled map lattices through simulations and experiments. Similar to the case of global coupling oscillators, individual lattices can be regarded as being controlled by a common mean field. A space-dependent order parameter is derived from a self-consistency condition in order to represent the collective state.

Hadronic vacuum polarization contribution to g-2 from the lattice

International Nuclear Information System (INIS)

Feng, X.; Jansen, K.; Renner, D.

2011-12-01

We give a short description of the present situation of lattice QCD simulations. We then focus on the computation of the anomalous magnetic moment of the muon using lattice techniques. We demonstrate that by employing improved observables for the muon anomalous magnetic moment, a significant reduction of the lattice error can be obtained. This provides a promising scenario that the accuracy of lattice calculations can match the experimental errors. (orig.)

Hadronic Vacuum Polarization Contribution to g-2 from the Lattice

Energy Technology Data Exchange (ETDEWEB)

Dru Renner, Xu Feng, Marcus Petschlies, Karl Jansen

2012-05-01

We give a short description of the present situation of lattice QCD simulations. We then focus on the computation of the anomalous magnetic moment of the muon using lattice techniques. We demonstrate that by employing improved observables for the muon anomalous magnetic moment, a significant reduction of the lattice error can be obtained. This provides a promising scenario that the accuracy of lattice calculations can match the experimental errors.

Hadronic vacuum polarization contribution to g-2 from the lattice

Energy Technology Data Exchange (ETDEWEB)

Feng, X. [High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki (Japan); Jansen, K. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Petschlies, M. [The Cyprus Institute, Nicosia (Cyprus); Renner, D. [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)

2011-12-15

We give a short description of the present situation of lattice QCD simulations. We then focus on the computation of the anomalous magnetic moment of the muon using lattice techniques. We demonstrate that by employing improved observables for the muon anomalous magnetic moment, a significant reduction of the lattice error can be obtained. This provides a promising scenario that the accuracy of lattice calculations can match the experimental errors. (orig.)

Correlation induced localization of lattice trapped bosons coupled to a Bose–Einstein condensate

Science.gov (United States)

Keiler, Kevin; Krönke, Sven; Schmelcher, Peter

2018-03-01

We investigate the ground state properties of a lattice trapped bosonic system coupled to a Lieb–Liniger type gas. Our main goal is the description and in depth exploration and analysis of the two-species many-body quantum system including all relevant correlations beyond the standard mean-field approach. To achieve this, we use the multi-configuration time-dependent Hartree method for mixtures (ML-MCTDHX). Increasing the lattice depth and the interspecies interaction strength, the wave function undergoes a transition from an uncorrelated to a highly correlated state, which manifests itself in the localization of the lattice atoms in the latter regime. For small interspecies couplings, we identify the process responsible for this cross-over in a single-particle-like picture. Moreover, we give a full characterization of the wave function’s structure in both regimes, using Bloch and Wannier states of the lowest band, and we find an order parameter, which can be exploited as a corresponding experimental signature. To deepen the understanding, we use an effective Hamiltonian approach, which introduces an induced interaction and is valid for small interspecies interaction. We finally compare the ansatz of the effective Hamiltonian with the results of the ML-MCTDHX simulations.

Parallel computer calculation of quantum spin lattices

International Nuclear Information System (INIS)

Lamarcq, J.

1998-01-01

Numerical simulation allows the theorists to convince themselves about the validity of the models they use. Particularly by simulating the spin lattices one can judge about the validity of a conjecture. Simulating a system defined by a large number of degrees of freedom requires highly sophisticated machines. This study deals with modelling the magnetic interactions between the ions of a crystal. Many exact results have been found for spin 1/2 systems but not for systems of other spins for which many simulation have been carried out. The interest for simulations has been renewed by the Haldane's conjecture stipulating the existence of a energy gap between the ground state and the first excited states of a spin 1 lattice. The existence of this gap has been experimentally demonstrated. This report contains the following four chapters: 1. Spin systems; 2. Calculation of eigenvalues; 3. Programming; 4. Parallel calculation

Molecular dynamics simulation of electron trapping in the sapphire lattice

International Nuclear Information System (INIS)

Rambaut, C.; Oh, K.H.; Fayeulle, S.; Kohanoff, J.

1995-10-01

Energy storage and release in dielectric materials can be described on the basis of the charge trapping mechanism. Most phenomenological aspects have been recently rationalized in terms of the space charge mode. Dynamical aspects are studied here by performing Molecular Dynamics simulations. We show that an excess electron introduced into the sapphire lattice (α -Al 2 O 3 ) can be trapped only at a limited number of sites. The energy gained by allowing the electron to localize in these sites is of the order of 4-5 eV, in good agreement with the results of the space charge model. Displacements of the neighboring ions due to the implanted charge are shown to be localized in a small region of about 5 A. Detrapping is observed at 250 K. The ionic displacements turn out to play an important role in modifying the potential landscape by lowering, in a dynamical way, the barriers that cause localization at low temperature. (author). 18 refs, 7 figs, 2 tabs

APS-U LATTICE DESIGN FOR OFF-AXIS ACCUMULATION

Energy Technology Data Exchange (ETDEWEB)

Sun, Yipeng; Borland, M.; Lindberg, R.; Sajaev, V.

2017-06-25

A 67-pm hybrid-seven-bend achromat (H7BA) lattice is being proposed for a future Advanced Photon Source (APS) multi-bend-achromat (MBA) upgrade project. This lattice design pushes for smaller emittance and requires use of a swap-out (on-axis) injection scheme due to limited dynamic acceptance. Alternate lattice design work has also been performed for the APS upgrade to achieve better beam dynamics performance than the nominal APS MBA lattice, in order to allow off-axis accumulation. Two such alternate H7BA lattice designs, which target a still-low emittance of 90 pm, are discussed in detail in this paper. Although the single-particle-dynamics performance is good, simulations of collective effects indicate that surprising difficulty would be expected accumulating high single-bunch charge in this lattice. The brightness of the 90-pm lattice is also a factor of two lower than the 67-pm H7BA lattice.

Lattice Boltzmann simulations of droplet formation in confined channels with thermocapillary flows

Science.gov (United States)

Gupta, A.; Sbragaglia, M.; Belardinelli, D.; Sugiyama, K.

2016-12-01

Based on mesoscale lattice Boltzmann simulations with the "Shan-Chen" model, we explore the influence of thermocapillarity on the breakup properties of fluid threads in a microfluidic T-junction, where a dispersed phase is injected perpendicularly into a main channel containing a continuous phase, and the latter induces periodic breakup of droplets due to the cross-flowing. Temperature effects are investigated by switching on-off both positive-negative temperature gradients along the main channel direction, thus promoting a different thread dynamics with anticipated-delayed breakup. Numerical simulations are performed at changing the flow rates of both the continuous and dispersed phases, as well as the relative importance of viscous forces, surface tension forces, and thermocapillary stresses. The range of parameters is broad enough to characterize the effects of thermocapillarity on different mechanisms of breakup in the confined T-junction, including the so-called "squeezing" and "dripping" regimes, previously identified in the literature. Some simple scaling arguments are proposed to rationalize the observed behavior, and to provide quantitative guidelines on how to predict the droplet size after breakup.

Coupled lattice Boltzmann method for numerical simulations of fully coupled heart and torso bidomain system in electrocardiology

OpenAIRE

Corre , Samuel; Belmiloudi , Aziz

2016-01-01

International audience; In this work, a modified coupling Lattice Boltzmann Model (LBM) in simulation of cardiac electrophysiology is developed in order to capture the detailed activities of macro- to micro-scale transport processes. The propagation of electrical activity in the human heart through torso is mathematically modeled by bidomain type systems. As transmembrane potential evolves, we take into account domain anisotropical properties using intracellular and extracellular conductivity...

A volume-preserving sharpening approach for the propagation of sharp phase boundaries in multiphase lattice Boltzmann simulations

KAUST Repository

Reis, T.

2011-07-01

Lattice Boltzmann models that recover a macroscopic description of multiphase flow of immiscible liquids typically represent the boundaries between phases using a scalar function, the phase field, that varies smoothly over several grid points. Attempts to tune the model parameters to minimise the widths of these interfaces typically lead to the interfaces becoming fixed to the underlying grid instead of advecting with the fluid velocity. This phenomenon, known as lattice pinning, is strikingly similar to that associated with the numerical simulation of conservation laws coupled to stiff algebraic source terms. We present a lattice Boltzmann formulation of the model problem proposed by LeVeque and Yee (1990) [3] to study the latter phenomenon in the context of computational combustion, and offer a volume-conserving extension in multiple space dimensions. Inspired by the random projection method of Bao and Jin (2000) [1] we further generalise this formulation by introducing a uniformly distributed quasi-random variable into the term responsible for the sharpening of phase boundaries. This method is mass conserving, gives correct average propagation speeds over many timesteps, and is shown to significantly delay the onset of pinning as the interface width is reduced. © 2010 Elsevier Ltd.

A volume-preserving sharpening approach for the propagation of sharp phase boundaries in multiphase lattice Boltzmann simulations

KAUST Repository

Reis, T.; Dellar, P.J.

2011-01-01

Lattice Boltzmann models that recover a macroscopic description of multiphase flow of immiscible liquids typically represent the boundaries between phases using a scalar function, the phase field, that varies smoothly over several grid points. Attempts to tune the model parameters to minimise the widths of these interfaces typically lead to the interfaces becoming fixed to the underlying grid instead of advecting with the fluid velocity. This phenomenon, known as lattice pinning, is strikingly similar to that associated with the numerical simulation of conservation laws coupled to stiff algebraic source terms. We present a lattice Boltzmann formulation of the model problem proposed by LeVeque and Yee (1990) [3] to study the latter phenomenon in the context of computational combustion, and offer a volume-conserving extension in multiple space dimensions. Inspired by the random projection method of Bao and Jin (2000) [1] we further generalise this formulation by introducing a uniformly distributed quasi-random variable into the term responsible for the sharpening of phase boundaries. This method is mass conserving, gives correct average propagation speeds over many timesteps, and is shown to significantly delay the onset of pinning as the interface width is reduced. © 2010 Elsevier Ltd.

Time-dependent perpendicular fluctuations in the driven lattice Lorentz gas

Science.gov (United States)

Leitmann, Sebastian; Schwab, Thomas; Franosch, Thomas

2018-02-01

We present results for the fluctuations of the displacement of a tracer particle on a planar lattice pulled by a step force in the presence of impenetrable, immobile obstacles. The fluctuations perpendicular to the applied force are evaluated exactly in first order of the obstacle density for arbitrarily strong pulling and all times. The complex time-dependent behavior is analyzed in terms of the diffusion coefficient, local exponent, and the non-Skellam parameter, which quantifies deviations from the dynamics on the lattice in the absence of obstacles. The non-Skellam parameter along the force is analyzed in terms of an asymptotic model and reveals a power-law growth for intermediate times.

Synthesizing lattice structures in phase space

International Nuclear Information System (INIS)

Guo, Lingzhen; Marthaler, Michael

2016-01-01

In one dimensional systems, it is possible to create periodic structures in phase space through driving, which is called phase space crystals (Guo et al 2013 Phys. Rev. Lett. 111 205303). This is possible even if for particles trapped in a potential without periodicity. In this paper we discuss ultracold atoms in a driven optical lattice, which is a realization of such a phase space crystals. The corresponding lattice structure in phase space is complex and contains rich physics. A phase space lattice differs fundamentally from a lattice in real space, because its coordinate system, i.e., phase space, has a noncommutative geometry, which naturally provides an artificial gauge (magnetic) field. We study the behavior of the quasienergy band structure and investigate the dissipative dynamics. Synthesizing lattice structures in phase space provides a new platform to simulate the condensed matter phenomena and study the intriguing phenomena of driven systems far away from equilibrium. (paper)

Equivalence of interest rate models and lattice gases.

Science.gov (United States)

Pirjol, Dan

2012-04-01

We consider the class of short rate interest rate models for which the short rate is proportional to the exponential of a Gaussian Markov process x(t) in the terminal measure r(t)=a(t)exp[x(t)]. These models include the Black-Derman-Toy and Black-Karasinski models in the terminal measure. We show that such interest rate models are equivalent to lattice gases with attractive two-body interaction, V(t(1),t(2))=-Cov[x(t(1)),x(t(2))]. We consider in some detail the Black-Karasinski model with x(t) as an Ornstein-Uhlenbeck process, and show that it is similar to a lattice gas model considered by Kac and Helfand, with attractive long-range two-body interactions, V(x,y)=-α(e(-γ|x-y|)-e(-γ(x+y))). An explicit solution for the model is given as a sum over the states of the lattice gas, which is used to show that the model has a phase transition similar to that found previously in the Black-Derman-Toy model in the terminal measure.

Towards the confirmation of QCD on the lattice. Improved actions and algorithms

International Nuclear Information System (INIS)

Krieg, Stefan F.

2009-01-01

Lattice Quantum Chromodynamics has made tremendous progress over the last decade. New and improved simulation algorithms and lattice actions enable simulations of the theory with unprecedented accuracy. In the first part of this thesis, novel simulation algorithms for dynamical overlap fermions are presented. The generic Hybrid Monte Carlo algorithm is adapted to treat the singularity in the Molecular Dynamics force, to increase the tunneling rate between different topological sectors and to improve the overall volume scaling of the combined algorithm. With this new method, simulations with dynamical overlap fermions can reach smaller lattice spacings, larger volumes, smaller quark masses, and therefore higher precision than had previously been possible. The second part of this thesis is focused on a large scale simulation aiming to compute the light hadron mass spectrum. This simulation is based on a tree-level Symanzik improved gauge and tree-level improved stout-smeared Wilson clover action. The efficiency of the combination of this action and the improved simulation algorithms used allows to completely control all systematic errors. Therefore, this simulation provides a highly accurate ab initio calculation of the masses of the light hadrons, such as the proton, responsible for 95% of the mass of the visible universe, and confirms Lattice QCD in the light hadron sector. (orig.)

Towards the confirmation of QCD on the lattice. Improved actions and algorithms

Energy Technology Data Exchange (ETDEWEB)

Krieg, Stefan F.

2009-07-01

Lattice Quantum Chromodynamics has made tremendous progress over the last decade. New and improved simulation algorithms and lattice actions enable simulations of the theory with unprecedented accuracy. In the first part of this thesis, novel simulation algorithms for dynamical overlap fermions are presented. The generic Hybrid Monte Carlo algorithm is adapted to treat the singularity in the Molecular Dynamics force, to increase the tunneling rate between different topological sectors and to improve the overall volume scaling of the combined algorithm. With this new method, simulations with dynamical overlap fermions can reach smaller lattice spacings, larger volumes, smaller quark masses, and therefore higher precision than had previously been possible. The second part of this thesis is focused on a large scale simulation aiming to compute the light hadron mass spectrum. This simulation is based on a tree-level Symanzik improved gauge and tree-level improved stout-smeared Wilson clover action. The efficiency of the combination of this action and the improved simulation algorithms used allows to completely control all systematic errors. Therefore, this simulation provides a highly accurate ab initio calculation of the masses of the light hadrons, such as the proton, responsible for 95% of the mass of the visible universe, and confirms Lattice QCD in the light hadron sector. (orig.)

Monte-Carlo simulations in a gas centrifuge

International Nuclear Information System (INIS)

Roblin, Ph.; Doneddu, F.

2000-01-01

This paper is associated with the centrifugation process for isotope separation, using the principle of a cylinder rotating at high speed in a vacuum casing. As in the most widely used configuration, the gas containing the isotope mixture is introduced by a fixed axial feed pipe and expands in the cylinder. It is subjected to high centrifugal acceleration, undergoes rigid body rotation and stratifies radially according to a barometric-type pressure law. By pressure diffusion, the heavier isotopes migrate to the cylinder wall and the lighter to the center. A temperature gradient on the wall and the presence of a scoop in the fluid, produce a vertical countercurrent which transforms the radial separation effect into an axial effect. The scoop extracts the gas depleted in light isotopes, called W, and another is used to recover the gas enriched in light isotopes, called P. Practically all the gas is governed by the Navier-Stokes equations in 2D axial symmetry. Due to the strong pressure stratification, continuous fluid equations are not valid in the whole cylinder, with or without linearization of the model. Consequently, an internal boundary separates the continuum domain from a rarefied domain in which the feed gas expands. The radial position of this cut-off then approaches the cylinder wall with increasing rotation speeds. In the rarefied domain, the Boltzmann equation is solved and a well suited numerical method is the Monte-Carlo method. A complete simulation of feed gas expansion and interaction with rotating gas, presented here with the DSMC (Direct Simulation Monte-Carlo) code, provides realistic boundary conditions for fluid flow calculations. The reference centrifuge is a hypothetical machine enabling the scientific community to compare results obtained for the optimization of separation performance. Its radius a is 6 cm, and its peripheral speed a is 600 m/s. The selected gas, containing the isotopes, is UF 6 . The gas pressure p(a) at the cylinder wall is

Three-Dimensional Neutral Transport Simulations of Gas Puff Imaging Experiments

International Nuclear Information System (INIS)

Stotler, D.P.; DIppolito, D.A.; LeBlanc, B.; Maqueda, R.J.; Myra, J.R.; Sabbagh, S.A.; Zweben, S.J.

2003-01-01

Gas Puff Imaging (GPI) experiments are designed to isolate the structure of plasma turbulence in the plane perpendicular to the magnetic field. Three-dimensional aspects of this diagnostic technique as used on the National Spherical Torus eXperiment (NSTX) are examined via Monte Carlo neutral transport simulations. The radial width of the simulated GPI images are in rough agreement with observations. However, the simulated emission clouds are angled approximately 15 degrees with respect to the experimental images. The simulations indicate that the finite extent of the gas puff along the viewing direction does not significantly degrade the radial resolution of the diagnostic. These simulations also yield effective neutral density data that can be used in an approximate attempt to infer two-dimensional electron density and temperature profiles from the experimental images

Frustrated lattices of Ising chains

International Nuclear Information System (INIS)

Kudasov, Yurii B; Korshunov, Aleksei S; Pavlov, V N; Maslov, Dmitrii A

2012-01-01

The magnetic structure and magnetization dynamics of systems of plane frustrated Ising chain lattices are reviewed for three groups of compounds: Ca 3 Co 2 O 6 , CsCoCl 3 , and Sr 5 Rh 4 O 12 . The available experimental data are analyzed and compared in detail. It is shown that a high-temperature magnetic phase on a triangle lattice is normally and universally a partially disordered antiferromagnetic (PDA) structure. The diversity of low-temperature phases results from weak interactions that lift the degeneracy of a 2D antiferromagnetic Ising model on the triangle lattice. Mean-field models, Monte Carlo simulation results on the static magnetization curve, and results on slow magnetization dynamics obtained with Glauber's theory are discussed in detail. (reviews of topical problems)

Potts ferromagnet correlation length in hypercubic lattices: Renormalization - group approach

International Nuclear Information System (INIS)

Curado, E.M.F.; Hauser, P.R.

1984-01-01

Through a real space renormalization group approach, the q-state Potts ferromagnet correlation length on hierarchical lattices is calculated. These hierarchical lattices are build in order to simulate hypercubic lattices. The high-and-low temperature correlation length asymptotic behaviours tend (in the Ising case) to the Bravais lattice correlation length ones when the size of the hierarchical lattice cells tends to infinity. It is conjectured that the asymptotic behaviours several values of q and d (dimensionality) so obtained are correct. Numerical results are obtained for the full temperature range of the correlation length. (Author) [pt

Lattice Boltzmann study of slip flow over structured surface with transverse slots

Science.gov (United States)

Chen, Wei; Wang, Kai; Wang, Lei; Hou, Guoxiang; Leng, Wenjun

2018-04-01

Slip flow over structured superhydrophobic surface with transverse slots is investigated by the lattice Boltzmann method. The Shan-Chen multiphase model is employed to simulate the flow over gas bubbles in the slots. The Carnahan-Starling equation of state is applied to obtain large density ratio. The interface thickness of the multiphase model is discussed. We find that the Cahn number Cn should be smaller than 0.02 when the temperature T = 0.5T c to restrict the influence of interface thickness on slip length. Influences of slot fraction on slip length is then studied, and the result is compared with single LB simulation of which the interface is treated as free-slip boundary. The slip length obtained by the multiphase model is a little smaller. After that, the shape of the liquid-gas interface is considered, and simulations with different initial protrusion angles and capillary numbers are performed. Effective slip length as a function of initial protrusion angle is obtained. The result is in qualitative agreement with a previous study and main features are reproduced. Furthermore, the influence of Capillary number Ca is studied. Larger Ca causes larger interface deformation and smaller slip length. But when the interface is concaving into the slot, this influence is less obvious.

Analytical approach for collective diffusion: one-dimensional lattice with the nearest neighbor and the next nearest neighbor lateral interactions

Czech Academy of Sciences Publication Activity Database

Tarasenko, Alexander

2018-01-01

Roč. 95, Jan (2018), s. 37-40 ISSN 1386-9477 R&D Projects: GA MŠk LO1409; GA MŠk LM2015088 Institutional support: RVO:68378271 Keywords : lattice gas systems * kinetic Monte Carlo simulations * diffusion and migration Subject RIV: BE - Theoretical Physics OBOR OECD: Atomic, molecular and chemical physics (physics of atoms and molecules including collision, interaction with radiation, magnetic resonances, Mössbauer effect) Impact factor: 2.221, year: 2016

Moving charged particles in lattice Boltzmann-based electrokinetics

Science.gov (United States)

Kuron, Michael; Rempfer, Georg; Schornbaum, Florian; Bauer, Martin; Godenschwager, Christian; Holm, Christian; de Graaf, Joost

2016-12-01

The motion of ionic solutes and charged particles under the influence of an electric field and the ensuing hydrodynamic flow of the underlying solvent is ubiquitous in aqueous colloidal suspensions. The physics of such systems is described by a coupled set of differential equations, along with boundary conditions, collectively referred to as the electrokinetic equations. Capuani et al. [J. Chem. Phys. 121, 973 (2004)] introduced a lattice-based method for solving this system of equations, which builds upon the lattice Boltzmann algorithm for the simulation of hydrodynamic flow and exploits computational locality. However, thus far, a description of how to incorporate moving boundary conditions into the Capuani scheme has been lacking. Moving boundary conditions are needed to simulate multiple arbitrarily moving colloids. In this paper, we detail how to introduce such a particle coupling scheme, based on an analogue to the moving boundary method for the pure lattice Boltzmann solver. The key ingredients in our method are mass and charge conservation for the solute species and a partial-volume smoothing of the solute fluxes to minimize discretization artifacts. We demonstrate our algorithm's effectiveness by simulating the electrophoresis of charged spheres in an external field; for a single sphere we compare to the equivalent electro-osmotic (co-moving) problem. Our method's efficiency and ease of implementation should prove beneficial to future simulations of the dynamics in a wide range of complex nanoscopic and colloidal systems that were previously inaccessible to lattice-based continuum algorithms.

Gas flows in the circumgalactic medium around simulated high-redshift galaxies

Science.gov (United States)

Mitchell, Peter D.; Blaizot, Jérémy; Devriendt, Julien; Kimm, Taysun; Michel-Dansac, Léo; Rosdahl, Joakim; Slyz, Adrianne

2018-03-01

We analyse the properties of circumgalactic gas around simulated galaxies in the redshift range z ≥ 3, utilizing a new sample of cosmological zoom simulations. These simulations are intended to be representative of the observed samples of Lyman α (Ly α) emitters recently obtained with the multi unit spectroscopic explorer (MUSE) instrument (halo masses ˜1010-1011 M⊙). We show that supernova feedback has a significant impact on both the inflowing and outflowing circumgalactic medium (CGM) by driving outflows, reducing diffuse inflow rates, and by increasing the neutral fraction of inflowing gas. By temporally stacking simulation outputs, we find that significant net mass exchange occurs between inflowing and outflowing phases: none of the phases are mass-conserving. In particular, we find that the mass in neutral outflowing hydrogen declines exponentially with radius as gas flows outwards from the halo centre. This is likely caused by a combination of both fountain-like cycling processes and gradual photoionization/collisional ionization of outflowing gas. Our simulations do not predict the presence of fast-moving neutral outflows in the CGM. Neutral outflows instead move with modest radial velocities (˜50 km s-1), and the majority of the kinetic energy is associated with tangential rather than radial motion.

Feedback control of atomic motion in an optical lattice

International Nuclear Information System (INIS)

Morrow, N.V.; Dutta, S.K.; Raithel, G.

2002-01-01

We demonstrate a real-time feedback scheme to manipulate wave-packet oscillations of atoms in an optical lattice. The average position of the atoms in the lattice wells is measured continuously and nondestructively. A feedback loop processes the position signal and translates the lattice potential. Depending on the feedback loop characteristics, we find amplification, damping, or an entire alteration of the wave-packet oscillations. Our results are well supported by simulations

A computer simulation of a potential derived from the gay-berne potential for lattice model

Directory of Open Access Journals (Sweden)

Habtamu Zewdie

2000-06-01

Full Text Available The lattice model of elongated molecules interacting via a potential derived from the Gay-Berne pair potential is proposed. We made a systematic study of the effect of varying the molecular elongation and intermolecular vector orientation dependence of the pair potential on the thermodynamic as well as the structural properties of liquid crystals. A Monte Carlo simulations of molecules placed at the site of a simple cubic lattice and interacting via the modified Gay-Berne potential with its nearest neighbours is performed. The internal energy, heat capacity, angular pair correlation function and scalar order parameter are obtained. The results are compared against predictions of molecular field theory, experimental results and that of other related simulations wherever possible. It is shown that for more elongated molecules the nematic-isotropic transition becomes stronger first order transition. For a given molecular elongation as the intermolecular vector orientation dependence becomes larger the nematic-isotropic transition becomes a stronger first order transition as measured by the rate of change of the order parameter and the divergence of the heat capacity. Scaling the potential well seems to have dramatic change on the effect of the potential well anisotropy on trends of nematic-isotropic transition temperature and divergence of the heat capacity. It is shown that the behaviour of many nematics can be described by proposed model with the elongation ratio of molecules and potential well anisotropy ranging from 3 to 5.

Detecting the BCS pairing amplitude via a sudden lattice ramp in a honeycomb lattice

Science.gov (United States)

Tiesinga, Eite; Nuske, Marlon; Mathey, Ludwig

2016-05-01

We determine the exact time evolution of an initial Bardeen-Cooper-Schrieffer (BCS) state of ultra-cold atoms in a hexagonal optical lattice. The dynamical evolution is triggered by ramping the lattice potential up, such that the interaction strength Uf is much larger than the hopping amplitude Jf. The quench initiates collective oscillations with frequency | Uf | /(2 π) in the momentum occupation numbers and imprints an oscillating phase with the same frequency on the order parameter Δ. The latter is not reproduced by treating the time evolution in mean-field theory. The momentum density-density or noise correlation functions oscillate at frequency | Uf | /(2 π) as well as its second harmonic. For a very deep lattice, with negligible tunneling energy, the oscillations of momentum occupation numbers are undamped. Non-zero tunneling after the quench leads to dephasing of the different momentum modes and a subsequent damping of the oscillations. This occurs even for a finite-temperature initial BCS state, but not for a non-interacting Fermi gas. We therefore propose to use this dephasing to detect a BCS state. Finally, we predict that the noise correlation functions in a honeycomb lattice will develop strong anti-correlations near the Dirac point. We acknowledge funding from the National Science Foundation.

Multiple scattering of low energy rare gas ions: a comparison of experiment and computer simulation

International Nuclear Information System (INIS)

Heiland, W.; Taglauer, E.; Robinson, M.T.

1976-01-01

Some aspects of ion scattering below a few keV have been interpreted by multiple scattering. This can partly be simulated by chain or string models, where the single crystal surface is replaced by a chain of atoms. The computer program MARLOWE allows a simulation of solid-ion interaction, which is much closer to reality, e.g. the crystal is three-dimensional, includes lattice vibrations, electronic stopping power, different scattering potentials, etc. It is shown that the energy of the reflected ions as a function of the primary energy, lattice constant, impact angle and scattering angle can be understood within the string model. These results of the string model are confirmed by the MARLOWE calculations. For an interpretation of the measured intensities the simple string model is insufficient, whereas with MARLOWE reasonable agreement with experimental data may be achieved, if the thermal vibrations of the lattice atoms are taken into account. The experimental data include Ne + →Ni, Ne + →Ag and preliminary data on Ne + →W. The screening parameters of the scattering potentials are estimated for these ion-atom combinations. The results allow some conclusions about surface Debye temperatures. (Auth.)

Phase transitions in cooperative coinfections: Simulation results for networks and lattices

Science.gov (United States)

Grassberger, Peter; Chen, Li; Ghanbarnejad, Fakhteh; Cai, Weiran

2016-04-01

We study the spreading of two mutually cooperative diseases on different network topologies, and with two microscopic realizations, both of which are stochastic versions of a susceptible-infected-removed type model studied by us recently in mean field approximation. There it had been found that cooperativity can lead to first order transitions from spreading to extinction. However, due to the rapid mixing implied by the mean field assumption, first order transitions required nonzero initial densities of sick individuals. For the stochastic model studied here the results depend strongly on the underlying network. First order transitions are found when there are few short but many long loops: (i) No first order transitions exist on trees and on 2-d lattices with local contacts. (ii) They do exist on Erdős-Rényi (ER) networks, on d -dimensional lattices with d ≥4 , and on 2-d lattices with sufficiently long-ranged contacts. (iii) On 3-d lattices with local contacts the results depend on the microscopic details of the implementation. (iv) While single infected seeds can always lead to infinite epidemics on regular lattices, on ER networks one sometimes needs finite initial densities of infected nodes. (v) In all cases the first order transitions are actually "hybrid"; i.e., they display also power law scaling usually associated with second order transitions. On regular lattices, our model can also be interpreted as the growth of an interface due to cooperative attachment of two species of particles. Critically pinned interfaces in this model seem to be in different universality classes than standard critically pinned interfaces in models with forbidden overhangs. Finally, the detailed results mentioned above hold only when both diseases propagate along the same network of links. If they use different links, results can be rather different in detail, but are similar overall.

Hybrid lattice Boltzmann finite difference simulation of mixed convection flows in a lid-driven square cavity

Energy Technology Data Exchange (ETDEWEB)

Bettaibi, Soufiene, E-mail: Bettaibisoufiene@gmail.com [UR: Rayonnement Thermique, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 Tunis (Tunisia); Kuznik, Frédéric [INSA-Lyon, CETHIL, F-69621 Villeurbanne (France); Université de Lyon, CNRS, UMR5008, F-69622 Villeurbanne (France); Sediki, Ezeddine [UR: Rayonnement Thermique, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 Tunis (Tunisia)

2014-06-27

Highlights: • Mixed convection heat transfer in 2D lid-driven cavity is studied numerically. • Hybrid scheme with multiple relaxation time lattice Boltzmann method is used to obtain the velocity field. • Finite difference method is used to compute the temperature. • Effect of both Richardson and Reynolds numbers for mixed convection is studied. - Abstract: Mixed convection heat transfer in two-dimensional lid-driven rectangular cavity filled with air (Pr=0.71) is studied numerically. A hybrid scheme with multiple relaxation time lattice Boltzmann method (MRT-LBM) is used to obtain the velocity field while the temperature field is deduced from energy balance equation by using the finite difference method (FDM). The main objective of this work is to investigate the model effectiveness for mixed convection flow simulation. Results are presented in terms of streamlines, isotherms and Nusselt numbers. Excellent agreement is obtained between our results and previous works. The different comparisons demonstrate the robustness and the accuracy of our proposed approach.

Quantum degenerate atomic gases in controlled optical lattice potentials

Science.gov (United States)

Gemelke, Nathan D.

2007-12-01

Since the achievement of Bose Einstein condensation in cold atomic gases, mean-field treatments of the condensed phase have provided an excellent description for the static and dynamic properties observed in experiments. Recent experimental efforts have focused on studying deviations from mean-field behavior. I will describe work on two experiments which introduce controlled single particle degeneracies with time-dependent optical potentials, aiming to induce correlated motion and nontrivial statistics in the gas. In the first experiment, an optical lattice with locally rotating site potentials is produced to investigate fractional quantum Hall effects (FQHE) in rotating Bose gases. Here, the necessary gauge potential is provided by the rotating reference frame of the gas, which, in direct analogy to the electronic system, organizes single particle states into degenerate Landau levels. At low temperatures the repulsive interaction provided by elastic scattering is expected to produce ground states with structure nearly identical to those in the FQHE. I will discuss how these effects are made experimentally feasible by working at small particle numbers in the tight trapping potentials of an optical lattice, and present first results on the use of photoassociation to probe correlation in this system. In the second experiment, a vibrated optical lattice potential alters the single-particle dispersion underlying a condensed Bose gas and offers tailored phase-matching for nonlinear atom optical processes. I will demonstrate how this leads to parametric instability in the condensed gas, and draw analogy to an optical parametric oscillator operating above threshold.

Numerical simulation of the flow field in pump intakes by means of Lattice Boltzmann methods

International Nuclear Information System (INIS)

Schneider, A; Conrad, D; Böhle, M

2013-01-01

Lattice Boltzmann Methods are nowadays popular schemes for solving fluid flow problems of engineering interest. This popularity is due to the advantages of these schemes: For example, the meshing of the fluid domain can be performed fully automatically which results in great simplicity in handling complex geometries. In this paper a numerical scheme for the flow simulation in pump intakes based on a Lattice Boltzmann large eddy approach is presented. The ability of this scheme to capture the flow phenomena of the intake flow at different operating conditions is analysed. For the operational reliability and efficiency of pumps and pump systems, the incoming flow conditions are crucial. Since the efficiency and reliability requirements of pumps are rising and must be guaranteed, the flow conditions in pump intakes have to be evaluated during plant planning. Recent trends show that pump intakes are built more and more compact, which makes the flow in the intake even more complex. Numerical methods are a promising technique for conduction flow analysis in pump intakes, because they can be realised rapidly and cheaply

Machines for lattice gauge theory

International Nuclear Information System (INIS)

Mackenzie, P.B.

1989-05-01

The most promising approach to the solution of the theory of strong interactions is large scale numerical simulation using the techniques of lattice gauge theory. At the present time, computing requirements for convincing calculations of the properties of hadrons exceed the capabilities of even the most powerful commercial supercomputers. This has led to the development of massively parallel computers dedicated to lattice gauge theory. This talk will discuss the computing requirements behind these machines, and general features of the components and architectures of the half dozen major projects now in existence. 20 refs., 1 fig

Compact lattice QED with staggered fermions and chiral symmetry breaking

International Nuclear Information System (INIS)

Hoferichter, A.; Mitrjushkin, V.K.; Mueller-Preussker, M.

1994-07-01

Different formulations of the 4d compact lattice QED with staggered fermions (standard Wilson and modified by suppression of lattice artifacts) are investigated by Monte Carlo simulations within the quenched approximation. We show that after suppressing lattice artifacts the system undergoes a phase transition from the Coulomb phase into a presumably weakly chirally broken phase only at (unphysical) negative β-values. (orig.)

Particle linear theory on a self-gravitating perturbed cubic Bravais lattice

International Nuclear Information System (INIS)

Marcos, B.

2008-01-01

Discreteness effects are a source of uncontrolled systematic errors of N-body simulations, which are used to compute the evolution of a self-gravitating fluid. We have already developed the so-called ''particle linear theory''(PLT), which describes the evolution of the position of self-gravitating particles located on a perturbed simple cubic lattice. It is the discrete analogue of the well-known (Lagrangian) linear theory of a self-gravitating fluid. Comparing both theories permits us to quantify precisely discreteness effects in the linear regime. It is useful to develop the PLT also for other perturbed lattices because they represent different discretizations of the same continuous system. In this paper we detail how to implement the PLT for perturbed cubic Bravais lattices (simple, body, and face-centered) in a cubic simulation box. As an application, we will study the discreteness effects--in the linear regime--of N-body simulations for which initial conditions have been set up using these different lattices.

Lattice quantum chromodynamics with approximately chiral fermions

International Nuclear Information System (INIS)

Hierl, Dieter

2008-05-01

In this work we present Lattice QCD results obtained by approximately chiral fermions. We use the CI fermions in the quenched approximation to investigate the excited baryon spectrum and to search for the Θ + pentaquark on the lattice. Furthermore we developed an algorithm for dynamical simulations using the FP action. Using FP fermions we calculate some LECs of chiral perturbation theory applying the epsilon expansion. (orig.)

Lattice quantum chromodynamics with approximately chiral fermions

Energy Technology Data Exchange (ETDEWEB)

Hierl, Dieter

2008-05-15

In this work we present Lattice QCD results obtained by approximately chiral fermions. We use the CI fermions in the quenched approximation to investigate the excited baryon spectrum and to search for the {theta}{sup +} pentaquark on the lattice. Furthermore we developed an algorithm for dynamical simulations using the FP action. Using FP fermions we calculate some LECs of chiral perturbation theory applying the epsilon expansion. (orig.)

Lattice QCD simulation of meson exchange forces

International Nuclear Information System (INIS)

Richards, D.G.; Sinclair, D.K.; Sivers, D.

1990-01-01

We present the formalism for investigating the bar Qq bar Qq system in lattice QCD. This system serves as a model for describing exchange forces between heavy, static hadrons. We use this formalism to calculate the exchange potential from gauge configurations which incorporate the effects of dynamical quarks. Our data can be interpreted as giving preliminary results on the range of the nuclear force

Gas Bubble Migration and Trapping in Porous Media: Pore-Scale Simulation

Science.gov (United States)

Mahabadi, Nariman; Zheng, Xianglei; Yun, Tae Sup; van Paassen, Leon; Jang, Jaewon

2018-02-01

Gas bubbles can be naturally generated or intentionally introduced in sediments. Gas bubble migration and trapping affect the rate of gas emission into the atmosphere or modify the sediment properties such as hydraulic and mechanical properties. In this study, the migration and trapping of gas bubbles are simulated using the pore-network model extracted from the 3D X-ray image of in situ sediment. Two types of bubble size distribution (mono-sized and distributed-sized cases) are used in the simulation. The spatial and statistical bubble size distribution, residual gas saturation, and hydraulic conductivity reduction due to the bubble trapping are investigated. The results show that the bubble size distribution becomes wider during the gas bubble migration due to bubble coalescence for both mono-sized and distributed-sized cases. And the trapped bubble fraction and the residual gas saturation increase as the bubble size increases. The hydraulic conductivity is reduced as a result of the gas bubble trapping. The reduction in hydraulic conductivity is apparently observed as bubble size and the number of nucleation points increase.

Concentration contours in lattics and grain boundary diffusion in a polycrystalline solid

International Nuclear Information System (INIS)

Kim, Yong Soo; Jae, Won Mok; El Saied, Usama; Olander, Donald R.

1995-01-01

Grain boundary diffusion plays significant role in the fission gas release, which is one of the crucial processes dominating nuclear fuel performance. Gaseous fission products such as Xe and Kr generated inside fuel pellet have to diffuse in the lattice and in the grain boundary before they reach open space in the fuel rod. In the mean time, the grains in the fuel pellet grow and shrink according to grain growth kinetics, especially at elevated temperature at which nuclear reactors are operating. Thus the boundary movement ascribed to the grain growth greatly influences the fission gas release rate by lengthening or shortening the lattice diffusion distance, which is the rate limiting step. Sweeping fission gases by the moving boundary contributes to the increment of the fission gas release as well. Lattice and grain boundary diffusion processes in the fission gas release can be studied by 'tracer diffusion' technique, by which grain boundary diffusivity can be estimated and used directly for low burn up fission gas release analysis. However, even for tracer diffusion analysis, taking both the intragranular grain growth and the diffusion processes simultaneously into consideration is not easy. Only a few models accounting for the both processes are available and mostly handle them numerically. Numerical solutions are limited in the practical use. Here in this paper, an approximate analytical solution of the lattice and stationary grain boundary diffusion in a polycrystalline solid is developed for the tracer diffusion techniques. This short closed form solution is compared to available exact and numerical solutions and turns out to be acceptably accurate. It can be applied to the theoretical modeling and the experimental analysis, especially PIE (post irradiation examination), of low burn up fission gas release

Vortex structure in abelian-projected lattice gauge theory

International Nuclear Information System (INIS)

Ambjoern, J.; Giedt, J.; Greensite, J.

2000-01-01

We report on a breakdown of both monopole dominance and positivity in abelian-projected lattice Yang-Mills theory. The breakdown is associated with observables involving two units of the abelian charge. We find that the projected lattice has at most a global Z 2 symmetry in the confined phase, rather than the global U(1) symmetry that might be expected in a dual superconductor or monopole Coulomb gas picture. Implications for monopole and center vortex theories of confinement are discussed

Computer simulations of a single-laser double-gas-jet wakefield accelerator concept

Directory of Open Access Journals (Sweden)

R. G. Hemker

2002-04-01

Full Text Available We report in this paper on full scale 2D particle-in-cell simulations investigating laser wakefield acceleration. First we describe our findings of electron beam generation by a laser propagating through a single gas jet. Using realistic parameters which are relevant for the experimental setup in our laboratory we find that the electron beam resulting after the propagation of a 0.8 μm, 50 fs laser through a 1.5 mm gas jet has properties that would make it useful for further acceleration. Our simulations show that the electron beam is generated when the laser exits the gas jet, and the properties of the generated beam, especially its energy, depend only weakly on most properties of the gas jet. We therefore propose to use the first gas jet as a plasma cathode and then use a second gas jet placed immediately behind the first to provide additional acceleration. Our simulations of this proposed setup indicate the feasibility of this idea and also suggest ways to optimize the quality of the resulting beam.

Simulation of pellet-cladding thermomechanical interaction and fission gas release

International Nuclear Information System (INIS)

Denis, Alicia; Soba, Alejandro

2003-01-01

This paper summarizes the present status of a computer code that describes some of the main phenomena occurring in a nuclear fuel rod throughout its life. Temperature distribution, thermal expansion, elastic and plastic strains, creep, mechanical interaction between pellet and cladding, fission gas release, gas mixing, swelling, and densification are modeled. The modular structure of the code allows for the incorporation of models to simulate different phenomena and material properties. Collapsible rods can be also simulated. The code is bidimensional, assumes cylindrical symmetry for the rod and uses the finite element method to integrate the differential equations. The stress-strain and heat conduction problems are nonlinear due to plasticity and to the temperature dependence of the thermal conductivity. The fission gas inventory is calculated with a diffusion model, assuming spherical grains and using a one-dimensional finite element scheme. Pressure increase, swelling and densification are coupled with the stress field. Good results are obtained for the simulation of the irradiation tests of the first argentine prototypes of MOX fuels, where the bamboo effect is clearly observed, and of the FUMEX series for the fuel centerline temperature, the inside rod pressure and the fractional gas release.

Gas kinematics in FIRE simulated galaxies compared to spatially unresolved H I observations

Science.gov (United States)

El-Badry, Kareem; Bradford, Jeremy; Quataert, Eliot; Geha, Marla; Boylan-Kolchin, Michael; Weisz, Daniel R.; Wetzel, Andrew; Hopkins, Philip F.; Chan, T. K.; Fitts, Alex; Kereš, Dušan; Faucher-Giguère, Claude-André

2018-06-01

The shape of a galaxy's spatially unresolved, globally integrated 21-cm emission line depends on its internal gas kinematics: galaxies with rotationally supported gas discs produce double-horned profiles with steep wings, while galaxies with dispersion-supported gas produce Gaussian-like profiles with sloped wings. Using mock observations of simulated galaxies from the FIRE project, we show that one can therefore constrain a galaxy's gas kinematics from its unresolved 21-cm line profile. In particular, we find that the kurtosis of the 21-cm line increases with decreasing V/σ and that this trend is robust across a wide range of masses, signal-to-noise ratios, and inclinations. We then quantify the shapes of 21-cm line profiles from a morphologically unbiased sample of ˜2000 low-redshift, H I-detected galaxies with Mstar = 107-11 M⊙ and compare to the simulated galaxies. At Mstar ≳ 1010 M⊙, both the observed and simulated galaxies produce double-horned profiles with low kurtosis and steep wings, consistent with rotationally supported discs. Both the observed and simulated line profiles become more Gaussian like (higher kurtosis and less-steep wings) at lower masses, indicating increased dispersion support. However, the simulated galaxies transition from rotational to dispersion support more strongly: at Mstar = 108-10 M⊙, most of the simulations produce more Gaussian-like profiles than typical observed galaxies with similar mass, indicating that gas in the low-mass simulated galaxies is, on average, overly dispersion supported. Most of the lower-mass-simulated galaxies also have somewhat lower gas fractions than the median of the observed population. The simulations nevertheless reproduce the observed line-width baryonic Tully-Fisher relation, which is insensitive to rotational versus dispersion support.

Simulations of Micro Gas Flows by the DS-BGK Method

KAUST Repository

Li, Jun

2011-01-01

For gas flows in micro devices, the molecular mean free path is of the same order as the characteristic scale making the Navier-Stokes equation invalid. Recently, some micro gas flows are simulated by the DS-BGK method, which is convergent

Numerical simulations of enhanced gas recovery at the Zalezcze gas field in Poland confirm high CO2 storage capacity and mechanical integrity

International Nuclear Information System (INIS)

Klimkowski, Lukasz; Nagy, Stanislaw; Papiernik, Bartosz; Orlic, Bogdan; Kempka, Thomas

2015-01-01

Natural gas from the Zalecze gas field located in the Fore-Sudetic Monocline of the Southern Permian Basin has been produced since November 1973, and continuous gas production led to a decrease in the initial reservoir pressure from 151 bar to about 22 bar until 2010. We investigated a prospective enhanced gas recovery operation at the Zalecze gas field by coupled numerical hydro-mechanical simulations to account for the CO 2 storage capacity, trapping efficiency and mechanical integrity of the reservoir, cap-rock and regional faults. Dynamic flow simulations carried out indicate a CO 2 storage capacity of 106.6 Mt with a trapping efficiency of about 43% (45.8 Mt CO 2 ) established after 500 years of simulation. Two independent strategies on the assessment of mechanical integrity were followed by two different modeling groups resulting in the implementation of field- to regional-scale hydro-mechanical simulation models. The simulation results based on application of different constitutive laws for the lithological units show deviations of 31% to 93% for the calculated maximum vertical displacements at the reservoir top. Nevertheless, results of both simulation strategies indicate that fault reactivation generating potential leakage pathways from the reservoir to shallower units is very unlikely due to the low fault slip tendency (close to zero) in the Zechstein cap-rocks. Consequently, our simulation results also emphasise that the supra- and sub-saliferous fault systems at the Zalecze gas field are independent and very likely not hydraulically connected. Based on our simulation results derived from two independent modeling strategies with similar simulation results on fault and cap-rock integrity, we conclude that the investigated enhanced gas recovery scheme is feasible, with a negligibly low risk of relevant fault reactivation or formation fluid leakage through the Zechstein cap-rocks. (authors)

Magnetic properties in kagomé lattice with RKKY interaction: A Monte Carlo study

Energy Technology Data Exchange (ETDEWEB)

Masrour, R., E-mail: rachidmasrour@hotmail.com [Laboratory of Materials, Processes, Environment and Quality, Cady Ayyed University, National School of Applied Sciences, 63, 46000 Safi (Morocco); Laboratoire de Magnétisme et Physique des Hautes Energies L.M.P.H.E.URAC 12, Université Mohammed V, Faculté des Sciences, B.P. 1014, Rabat (Morocco); Jabar, A. [Laboratoire de Magnétisme et Physique des Hautes Energies L.M.P.H.E.URAC 12, Université Mohammed V, Faculté des Sciences, B.P. 1014, Rabat (Morocco); Benyoussef, A. [Laboratoire de Magnétisme et Physique des Hautes Energies L.M.P.H.E.URAC 12, Université Mohammed V, Faculté des Sciences, B.P. 1014, Rabat (Morocco); Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco); Hamedoun, M. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco)

2016-03-01

The magnetic properties of the kagomé lattice have been studied with Ruderman–Kittel–Kasuya–Yosida (RKKY) exchange interactions in a spin-7/2 Ising model using Monte Carlo simulations. The RKKY interaction between the two magnetic layers is considered for different distances. The magnetizations and magnetic susceptibilities of this lattice are given for different triquadratic interactions around each triangular face. The critical temperature is obtained for a fixed size. The magnetic hysteresis cycle of kagomé lattice with RKKY interactions is obtained for different temperatures and for different crystal field with a fixed size of nonmagnetic layer. - Highlights: • We study the RKKY interaction in kagomé lattice using the Monte Carlo simulations. • The transition temperature is obtained for kagomé lattice with RKKY interaction. • The coercive field is obtained for kagomé lattice with RKKY interaction.

Continuous surface force based lattice Boltzmann equation method for simulating thermocapillary flow

International Nuclear Information System (INIS)

Zheng, Lin; Zheng, Song; Zhai, Qinglan

2016-01-01

In this paper, we extend a lattice Boltzmann equation (LBE) with continuous surface force (CSF) to simulate thermocapillary flows. The model is designed on our previous CSF LBE for athermal two phase flow, in which the interfacial tension forces and the Marangoni stresses as the results of the interface interactions between different phases are described by a conception of CSF. In this model, the sharp interfaces between different phases are separated by a narrow transition layers, and the kinetics and morphology evolution of phase separation would be characterized by an order parameter via Cahn–Hilliard equation which is solved in the frame work of LBE. The scalar convection–diffusion equation for temperature field is resolved by thermal LBE. The models are validated by thermal two layered Poiseuille flow, and two superimposed planar fluids at negligibly small Reynolds and Marangoni numbers for the thermocapillary driven convection, which have analytical solutions for the velocity and temperature. Then thermocapillary migration of two/three dimensional deformable droplet are simulated. Numerical results show that the predictions of present LBE agreed with the analytical solution/other numerical results. - Highlights: • A CSF LBE to thermocapillary flows. • Thermal layered Poiseuille flows. • Thermocapillary migration.

Continuous surface force based lattice Boltzmann equation method for simulating thermocapillary flow

Energy Technology Data Exchange (ETDEWEB)

Zheng, Lin, E-mail: lz@njust.edu.cn [School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); Zheng, Song [School of Mathematics and Statistics, Zhejiang University of Finance and Economics, Hangzhou 310018 (China); Zhai, Qinglan [School of Economics Management and Law, Chaohu University, Chaohu 238000 (China)

2016-02-05

In this paper, we extend a lattice Boltzmann equation (LBE) with continuous surface force (CSF) to simulate thermocapillary flows. The model is designed on our previous CSF LBE for athermal two phase flow, in which the interfacial tension forces and the Marangoni stresses as the results of the interface interactions between different phases are described by a conception of CSF. In this model, the sharp interfaces between different phases are separated by a narrow transition layers, and the kinetics and morphology evolution of phase separation would be characterized by an order parameter via Cahn–Hilliard equation which is solved in the frame work of LBE. The scalar convection–diffusion equation for temperature field is resolved by thermal LBE. The models are validated by thermal two layered Poiseuille flow, and two superimposed planar fluids at negligibly small Reynolds and Marangoni numbers for the thermocapillary driven convection, which have analytical solutions for the velocity and temperature. Then thermocapillary migration of two/three dimensional deformable droplet are simulated. Numerical results show that the predictions of present LBE agreed with the analytical solution/other numerical results. - Highlights: • A CSF LBE to thermocapillary flows. • Thermal layered Poiseuille flows. • Thermocapillary migration.

A Worm Algorithm for the Lattice CP(N-1) Model arXiv

CERN Document Server

Rindlisbacher, Tobias

The CP(N-1) model in 2D is an interesting toy model for 4D QCD as it possesses confinement, asymptotic freedom and a non-trivial vacuum structure. Due to the lower dimensionality and the absence of fermions, the computational cost for simulating 2D CP(N-1) on the lattice is much lower than the one for simulating 4D QCD. However to our knowledge, no efficient algorithm for simulating the lattice CP(N-1) model has been tested so far, which also works at finite density. To this end we propose and test a new type of worm algorithm which is appropriate to simulate the lattice CP(N-1) model in a dual, flux-variables based representation, in which the introduction of a chemical potential does not give rise to any complications.

Precision Light Flavor Physics from Lattice QCD

Science.gov (United States)

Murphy, David

In this thesis we present three distinct contributions to the study of light flavor physics using the techniques of lattice QCD. These results are arranged into four self-contained papers. The first two papers concern global fits of the quark mass, lattice spacing, and finite volume dependence of the pseudoscalar meson masses and decay constants, computed in a series of lattice QCD simulations, to partially quenched SU(2) and SU(3) chiral perturbation theory (chiPT). These fits determine a subset of the low energy constants of chiral perturbation theory -- in some cases with increased precision, and in other cases for the first time -- which, once determined, can be used to compute other observables and amplitudes in chiPT. We also use our formalism to self-consistently probe the behavior of the (asymptotic) chiral expansion as a function of the quark masses by repeating the fits with different subsets of the data. The third paper concerns the first lattice QCD calculation of the semileptonic K0 → pi-l +nul ( Kl3) form factor at vanishing momentum transfer, f+Kpi(0), with physical mass domain wall quarks. The value of this form factor can be combined with a Standard Model analysis of the experimentally measured K0 → pi -l+nu l decay rate to extract a precise value of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element Vus, and to test unitarity of the CKM matrix. We also discuss lattice calculations of the pion and kaon decay constants, which can be used to extract Vud through an analogous Standard Model analysis of experimental constraints on leptonic pion and kaon decays. The final paper explores the recently proposed exact one flavor algorithm (EOFA). This algorithm has been shown to drastically reduce the memory footprint required to simulate single quark flavors on the lattice relative to the widely used rational hybrid Monte Carlo (RHMC) algorithm, while also offering modest O(20%) speed-ups. We independently derive the exact one flavor action, explore its

Finite size effects in lattice QCD with dynamical Wilson fermions

Energy Technology Data Exchange (ETDEWEB)

Orth, B.

2004-06-01

Due to limited computing resources choosing the parameters for a full lattice QCD simulation always amounts to a compromise between the competing objectives of a lattice spacing as small, quarks as light, and a volume as large as possible. Aiming at pushing unquenched simulations with the standard Wilson action towards the computationally expensive regime of small quark masses, the GRAL project addresses the question whether computing time can be saved by sticking to lattices with rather modest numbers of grid sites and extrapolating the finite-volume results to the infinite volume (prior to the usual chiral and continuum extrapolations). In this context we investigate in this work finite-size effects in simulated light hadron masses. Understanding their systematic volume dependence may not only help saving computer time in light quark simulations with the Wilson action, but also guide future simulations with dynamical chiral fermions which for a foreseeable time will be restricted to rather small lattices. We analyze data from hybrid Monte Carlo simulations with the N{sub f} = 2 Wilson action at two values of the coupling parameter, {beta} = 5.6 (lattice spacing {alpha} {approx} 0.08 fm) and {beta} = 5.32144 ({alpha} {approx} 0.13 fm). The larger {beta} corresponds to the coupling used previously by SESAM/T{chi}L. The considered hopping parameters {kappa} = 0.1575, 0.158 (at the larger {beta}) and {kappa} = 0.1665 (at the smaller {beta}) correspond to quark masses of 85, 50 and 36% of the strange quark mass, respectively. At each quark mass we study at least three different lattice extents in the range from L = 10 to L = 24 (0.85-2.04 fm). Estimates of autocorrelation times in the stochastic updating process and of the computational cost of every run are given. For each simulated sea quark mass we calculate quark propagators and hadronic correlation functions in order to extract the pion, rho and nucleon masses as well as the pion decay constant and the quark mass

Simulation of Thermal Flow Problems via a Hybrid Immersed Boundary-Lattice Boltzmann Method

Directory of Open Access Journals (Sweden)

J. Wu

2012-01-01

Full Text Available A hybrid immersed boundary-lattice Boltzmann method (IB-LBM is presented in this work to simulate the thermal flow problems. In current approach, the flow field is resolved by using our recently developed boundary condition-enforced IB-LBM (Wu and Shu, (2009. The nonslip boundary condition on the solid boundary is enforced in simulation. At the same time, to capture the temperature development, the conventional energy equation is resolved. To model the effect of immersed boundary on temperature field, the heat source term is introduced. Different from previous studies, the heat source term is set as unknown rather than predetermined. Inspired by the idea in (Wu and Shu, (2009, the unknown is calculated in such a way that the temperature at the boundary interpolated from the corrected temperature field accurately satisfies the thermal boundary condition. In addition, based on the resolved temperature correction, an efficient way to compute the local and average Nusselt numbers is also proposed in this work. As compared with traditional implementation, no approximation for temperature gradients is required. To validate the present method, the numerical simulations of forced convection are carried out. The obtained results show good agreement with data in the literature.

Matlab/Simulink-based simulation for digital-control system of marine three-shaft gas-turbine

International Nuclear Information System (INIS)

Yu Youhong; Chen Lingen; Sun Fengrui; Wu Chih

2005-01-01

A gas-turbine plant model is required in order to design and develop its control system. In this paper, a simulation model of a marine three-shaft gas-turbine's digital-control system is presented. Acceleration processes are simulated via a Matlab/Simulink program. The effects of some of the main variables on the system's performance are analyzed and the optimum values of parameters obtained. A simulation experiment upon a real gas-turbine plant is performed using the digital-control model. The results show that the simulation model is reliable

Determining the scale in lattice QCD

Energy Technology Data Exchange (ETDEWEB)

Bornyakov, V.G. [Institute for High Energy Physics, Protvino (Russian Federation); Institute of Theoretical and Experimental Physics, Moscow (Russian Federation); Far Eastern Federal Univ., Vladivostok (Russian Federation). School of Biomedicine; Horsley, R. [Edinburgh Univ. (United Kingdom). School of Physics and Astronomy; Hudspith, R. [York Univ., Toronto, ON (Canada). Dept. of Physics and Astronomy; and others

2015-12-15

We discuss scale setting in the context of 2+1 dynamical fermion simulations where we approach the physical point in the quark mass plane keeping the average quark mass constant. We have simulations at four beta values, and after determining the paths and lattice spacings, we give an estimation of the phenomenological values of various Wilson flow scales.

Synthesis of spatially variant lattices.

Science.gov (United States)

Rumpf, Raymond C; Pazos, Javier

2012-07-02

It is often desired to functionally grade and/or spatially vary a periodic structure like a photonic crystal or metamaterial, yet no general method for doing this has been offered in the literature. A straightforward procedure is described here that allows many properties of the lattice to be spatially varied at the same time while producing a final lattice that is still smooth and continuous. Properties include unit cell orientation, lattice spacing, fill fraction, and more. This adds many degrees of freedom to a design such as spatially varying the orientation to exploit directional phenomena. The method is not a coordinate transformation technique so it can more easily produce complicated and arbitrary spatial variance. To demonstrate, the algorithm is used to synthesize a spatially variant self-collimating photonic crystal to flow a Gaussian beam around a 90° bend. The performance of the structure was confirmed through simulation and it showed virtually no scattering around the bend that would have arisen if the lattice had defects or discontinuities.

Interference patterns of Bose-condensed gases in a two-dimensional optical lattice

International Nuclear Information System (INIS)

Liu Shujuan; Xiong Hongwei; Xu Zhijun; Huang Guoxiang

2003-01-01

For a Bose-condensed gas confined in a magnetic trap and in a two-dimensional (2D) optical lattice, the non-uniform distribution of atoms in different lattice sites is considered based on the Gross-Pitaevskii equation. A propagator method is used to investigate the time evolution of 2D interference patterns after (i) only the optical lattice is switched off, and (ii) both the optical lattice and the magnetic trap are switched off. An analytical description on the motion of side peaks in the interference patterns is presented by using the density distribution in a momentum space

DSMC simulation of feed jet flow in gas centrifuge

International Nuclear Information System (INIS)

Jiang Dongjun; Zeng Shi

2011-01-01

Feed jet flow acts an important role for the counter-current in gas centrifuge. Direct simulation Monte-Carlo (DSMC) method was adopted to simulate the structure of the radial feed jet model. By setting the proper boundary conditions and the collision model of molecules, the flow distributions of the 2D radial feed jet were acquired under different feed conditions, including the wave structure of feed jet and the profile of the flow parameters. The analyses of the calculation results note the following flow phenomena: Near the radial outflow boundary, the obvious peaks of the flow parameters exist; higher speed of feed gas brings stronger influence on the flow field of the centrifuge; including the density, pressure and velocity of the gas, the distribution of the temperature is affected by the feed jet, at the outflow boundary, temperature to double times of the average value. (authors)

Second-principles method for materials simulations including electron and lattice degrees of freedom

Science.gov (United States)

García-Fernández, Pablo; Wojdeł, Jacek C.; Íñiguez, Jorge; Junquera, Javier

2016-05-01

We present a first-principles-based (second-principles) scheme that permits large-scale materials simulations including both atomic and electronic degrees of freedom on the same footing. The method is based on a predictive quantum-mechanical theory—e.g., density functional theory—and its accuracy can be systematically improved at a very modest computational cost. Our approach is based on dividing the electron density of the system into a reference part—typically corresponding to the system's neutral, geometry-dependent ground state—and a deformation part—defined as the difference between the actual and reference densities. We then take advantage of the fact that the bulk part of the system's energy depends on the reference density alone; this part can be efficiently and accurately described by a force field, thus avoiding explicit consideration of the electrons. Then, the effects associated to the difference density can be treated perturbatively with good precision by working in a suitably chosen Wannier function basis. Further, the electronic model can be restricted to the bands of interest. All these features combined yield a very flexible and computationally very efficient scheme. Here we present the basic formulation of this approach, as well as a practical strategy to compute model parameters for realistic materials. We illustrate the accuracy and scope of the proposed method with two case studies, namely, the relative stability of various spin arrangements in NiO (featuring complex magnetic interactions in a strongly-correlated oxide) and the formation of a two-dimensional electron gas at the interface between band insulators LaAlO3 and SrTiO3 (featuring subtle electron-lattice couplings and screening effects). We conclude by discussing ways to overcome the limitations of the present approach (most notably, the assumption of a fixed bonding topology), as well as its many envisioned possibilities and future extensions.

Lattice Thermal Conductivity from Atomistic Simulations: ZrB2 and HfB2

Science.gov (United States)

Lawson, John W.; Daw, Murray S.; Bauschlicher, Charles W.

2012-01-01

Ultra high temperature ceramics (UHTC) including ZrB2 and HfB2 have a number of properties that make them attractive for applications in extreme environments. One such property is their high thermal conductivity. Computational modeling of these materials will facilitate understanding of fundamental mechanisms, elucidate structure-property relationships, and ultimately accelerate the materials design cycle. Progress in computational modeling of UHTCs however has been limited in part due to the absence of suitable interatomic potentials. Recently, we developed Tersoff style parameterizations of such potentials for both ZrB2 and HfB2 appropriate for atomistic simulations. As an application, Green-Kubo molecular dynamics simulations were performed to evaluate the lattice thermal conductivity for single crystals of ZrB2 and HfB2. The atomic mass difference in these binary compounds leads to oscillations in the time correlation function of the heat current, in contrast to the more typical monotonic decay seen in monoatomic materials such as Silicon, for example. Results at room temperature and at elevated temperatures will be reported.

Lattice Quantum Chromodynamics

CERN Document Server

Sachrajda, C T

2016-01-01

I review the the application of the lattice formulation of QCD and large-scale numerical simulations to the evaluation of non-perturbative hadronic effects in Standard Model Phenomenology. I present an introduction to the elements of the calculations and discuss the limitations both in the range of quantities which can be studied and in the precision of the results. I focus particularly on the extraction of the QCD parameters, i.e. the quark masses and the strong coupling constant, and on important quantities in flavour physics. Lattice QCD is playing a central role in quantifying the hadronic effects necessary for the development of precision flavour physics and its use in exploring the limits of the Standard Model and in searches for inconsistencies which would signal the presence of new physics.

Three-dimensional simulations of Bingham plastic flows with the multiple-relaxation-time lattice Boltzmann model

Directory of Open Access Journals (Sweden)

Song-Gui Chen

2016-01-01

Full Text Available This paper presents a three-dimensional (3D parallel multiple-relaxation-time lattice Boltzmann model (MRT-LBM for Bingham plastics which overcomes numerical instabilities in the simulation of non-Newtonian fluids for the Bhatnagar–Gross–Krook (BGK model. The MRT-LBM and several related mathematical models are briefly described. Papanastasiou’s modified model is incorporated for better numerical stability. The impact of the relaxation parameters of the model is studied in detail. The MRT-LBM is then validated through a benchmark problem: a 3D steady Poiseuille flow. The results from the numerical simulations are consistent with those derived analytically which indicates that the MRT-LBM effectively simulates Bingham fluids but with better stability. A parallel MRT-LBM framework is introduced, and the parallel efficiency is tested through a simple case. The MRT-LBM is shown to be appropriate for parallel implementation and to have high efficiency. Finally, a Bingham fluid flowing past a square-based prism with a fixed sphere is simulated. It is found the drag coefficient is a function of both Reynolds number (Re and Bingham number (Bn. These results reveal the flow behavior of Bingham plastics.

Nucleon-nucleon interactions via Lattice QCD: Methodology. HAL QCD approach to extract hadronic interactions in lattice QCD

Science.gov (United States)

Aoki, Sinya

2013-07-01

We review the potential method in lattice QCD, which has recently been proposed to extract nucleon-nucleon interactions via numerical simulations. We focus on the methodology of this approach by emphasizing the strategy of the potential method, the theoretical foundation behind it, and special numerical techniques. We compare the potential method with the standard finite volume method in lattice QCD, in order to make pros and cons of the approach clear. We also present several numerical results for nucleon-nucleon potentials.

DFT-Assisted Polymorph Identification from Lattice Raman Fingerprinting.

Science.gov (United States)

Bedoya-Martínez, Natalia; Schrode, Benedikt; Jones, Andrew O F; Salzillo, Tommaso; Ruzié, Christian; Demitri, Nicola; Geerts, Yves H; Venuti, Elisabetta; Della Valle, Raffaele Guido; Zojer, Egbert; Resel, Roland

2017-08-03

A combined experimental and theoretical approach, consisting of lattice phonon Raman spectroscopy and density functional theory (DFT) calculations, is proposed as a tool for lattice dynamics characterization and polymorph phase identification. To illustrate the reliability of the method, the lattice phonon Raman spectra of two polymorphs of the molecule 2,7-dioctyloxy[1]benzothieno[3,2-b]benzothiophene are investigated. We show that DFT calculations of the lattice vibrations based on the known crystal structures, including many-body dispersion van der Waals (MBD-vdW) corrections, predict experimental data within an accuracy of ≪5 cm -1 (≪0.6 meV). Due to the high accuracy of the simulations, they can be used to unambiguously identify different polymorphs and to characterize the nature of the lattice vibrations and their relationship to the structural properties. More generally, this work implies that DFT-MBD-vdW is a promising method to describe also other physical properties that depend on lattice dynamics like charge transport.

Adaptive lattice decision-feedback equalizers - Their performance and application to time-variant multipath channnels

Science.gov (United States)

Ling, F.; Proakis, J. G.

1985-04-01

This paper presents two types of adaptive lattice decision-feedback equalizers (DFE), the least squares (LS) lattice DFE and the gradient lattice DFE. Their performance has been investigated on both time-invariant and time-variant channels through computer simulations and compared to other kinds of equalizers. An analysis of the self-noise and tracking characteristics of the LS DFE and the DFE employing the Widrow-Hoff least mean square adaptive algorithm (LMS DFE) are also given. The analysis and simulation results show that the LS lattice DFE has the faster initial convergence rate, while the gradient lattice DFE is computationally more efficient. The main advantages of the lattice DFE's are their numerical stability, their computational efficiency, the flexibility to change their length, and their excellent capabilities for tracking rapidly time-variant channels.

New simulated gas detector offers realistic training for mine rescue teams

Energy Technology Data Exchange (ETDEWEB)

Bealko, S.B.; Alexander, D.; Chasko, L.L. [National Inst. for Occupational Safety and Health, Pittsburgh, PA (United States). Office of Mine Safety and Health Research; Holtan, J. [LightsOn Safety Solutions, Spring, TX (United States)

2010-07-01

The National Institute for Occupational Safety and Health, together with LightsOn Safety Solutions, evaluated 2 versions of a multi-gas simulated gas monitor system (GMS) in separate field trials with mine rescue teams. This paper described the GMS wireless simulation tool along with its development and testing. It also described the GMS functions for the initial phase of testing as well as plans for the next phase of research which may introduce tracking and automation features. The GMS requires a personal computer and uses a wireless local area network. The GMS teaches mine rescue members about gas detection and helps them understand the importance of gas concentrations. In addition, it promotes decision-making actions by team members and offers a more realistic method of receiving gas concentration readings using a simulated hand-held gas detector. The purpose of the evaluation was to determine if the electronic placard in the GMS could be used by mine rescue teams instead of the currently used cardboard placards, and if the functionality of the device was suitable, reliable and practical. Results from the second field trial demonstrated improvements with the GMS over the original prototype technology, particularly with regards to wireless and connectivity issues. The GMS was successfully incorporated into the mine rescue exercises as planned, with very few problems encountered. 4 refs., 2 figs.

New simulated gas detector offers realistic training for mine rescue teams

International Nuclear Information System (INIS)

Bealko, S.B.; Alexander, D.; Chasko, L.L.

2010-01-01

The National Institute for Occupational Safety and Health, together with LightsOn Safety Solutions, evaluated 2 versions of a multi-gas simulated gas monitor system (GMS) in separate field trials with mine rescue teams. This paper described the GMS wireless simulation tool along with its development and testing. It also described the GMS functions for the initial phase of testing as well as plans for the next phase of research which may introduce tracking and automation features. The GMS requires a personal computer and uses a wireless local area network. The GMS teaches mine rescue members about gas detection and helps them understand the importance of gas concentrations. In addition, it promotes decision-making actions by team members and offers a more realistic method of receiving gas concentration readings using a simulated hand-held gas detector. The purpose of the evaluation was to determine if the electronic placard in the GMS could be used by mine rescue teams instead of the currently used cardboard placards, and if the functionality of the device was suitable, reliable and practical. Results from the second field trial demonstrated improvements with the GMS over the original prototype technology, particularly with regards to wireless and connectivity issues. The GMS was successfully incorporated into the mine rescue exercises as planned, with very few problems encountered. 4 refs., 2 figs.

Grand canonical Monte Carlo simulation study of capillary condensation between nanoparticles.

Science.gov (United States)

Kim, Seonmin; Ehrman, Sheryl H

2007-10-07

Capillary condensation at the nanoscale differs from condensation in the bulk phase, because it is a strong function of surface geometry and gas-surface interactions. Here, the effects of geometry on the thermodynamics of capillary condensation at the neck region between nanoparticles are investigated via a grand canonical Monte Carlo simulation using a two-dimensional lattice gas model. The microscopic details of the meniscus formation on various surface geometries are examined and compared with results of classical macromolecular theory, the Kelvin equation. We assume that the system is composed of a lattice gas and the surfaces of two particles are approximated by various shapes. The system is modeled on the basis of the molecular properties of the particle surface and lattice gas in our system corresponding to titania nanoparticles and tetraethoxy orthosilicate molecules, respectively. This system was chosen in order to reasonably emulate our previous experimental results for capillary condensation on nanoparticle surfaces. Qualitatively, our simulation results show that the specific geometry in the capillary zone, the surface-surface distance, and the saturation ratio are important for determining the onset and broadening of the liquid meniscus. The meniscus height increases continuously as the saturation ratio increases and the meniscus broadens faster above the saturation ratio of 0.90. The change of the radius of curvature of the particle surface affects the dimensions of the capillary zone, which drives more condensation in narrow zones and less condensation in wide zones. The increase of surface-surface distance results in the decrease of the meniscus height or even the disappearance of the meniscus entirely at lower saturation ratios. These effects are significant at the nanoscale and must be carefully considered in order to develop predictive relationships for meniscus height as a function of saturation conditions.

Lattice QCD evaluation of baryon magnetic moment sum rules

International Nuclear Information System (INIS)

Leinweber, D.B.

1991-05-01

Magnetic moment combinations and sum rules are evaluated using recent results for the magnetic moments of octet baryons determined in a numerical simulation of quenched QCD. The model-independent and parameter-free results of the lattice calculations remove some of the confusion and contradiction surrounding past magnetic moment sum rule analyses. The lattice results reveal the underlying quark dynamics investigated by magnetic moment sum rules and indicate the origin of magnetic moment quenching for the non-strange quarks in Σ. In contrast to previous sum rule analyses, the magnetic moments of nonstrange quarks in Ξ are seen to be enhanced in the lattice results. In most cases, the spin-dependent dynamics and center-of-mass effects giving rise to baryon dependence of the quark moments are seen to be sufficient to violate the sum rules in agreement with experimental measurements. In turn, the sum rules are used to further examine the results of the lattice simulation. The Sachs sum rule suggests that quark loop contributions not included in present lattice calculations may play a key role in removing the discrepancies between lattice and experimental ratios of magnetic moments. This is supported by other sum rules sensitive to quark loop contributions. A measure of the isospin symmetry breaking in the effective quark moments due to quark loop contributions is in agreement with model expectations. (Author) 16 refs., 2 figs., 2 tabs

Kondo length in bosonic lattices

Science.gov (United States)

Giuliano, Domenico; Sodano, Pasquale; Trombettoni, Andrea

2017-09-01

Motivated by the fact that the low-energy properties of the Kondo model can be effectively simulated in spin chains, we study the realization of the effect with bond impurities in ultracold bosonic lattices at half filling. After presenting a discussion of the effective theory and of the mapping of the bosonic chain onto a lattice spin Hamiltonian, we provide estimates for the Kondo length as a function of the parameters of the bosonic model. We point out that the Kondo length can be extracted from the integrated real-space correlation functions, which are experimentally accessible quantities in experiments with cold atoms.

Lattice Boltzmann simulation of immiscible fluid displacement in porous media: Homogeneous versus heterogeneous pore network

International Nuclear Information System (INIS)

Liu, Haihu; Zhang, Yonghao; Valocchi, Albert J.

2015-01-01

Injection of anthropogenic carbon dioxide (CO 2 ) into geological formations is a promising approach to reduce greenhouse gas emissions into the atmosphere. Predicting the amount of CO 2 that can be captured and its long-term storage stability in subsurface requires a fundamental understanding of multiphase displacement phenomena at the pore scale. In this paper, the lattice Boltzmann method is employed to simulate the immiscible displacement of a wetting fluid by a non-wetting one in two microfluidic flow cells, one with a homogeneous pore network and the other with a randomly heterogeneous pore network. We have identified three different displacement patterns, namely, stable displacement, capillary fingering, and viscous fingering, all of which are strongly dependent upon the capillary number (Ca), viscosity ratio (M), and the media heterogeneity. The non-wetting fluid saturation (S nw ) is found to increase nearly linearly with logCa for each constant M. Increasing M (viscosity ratio of non-wetting fluid to wetting fluid) or decreasing the media heterogeneity can enhance the stability of the displacement process, resulting in an increase in S nw . In either pore networks, the specific interfacial length is linearly proportional to S nw during drainage with equal proportionality constant for all cases excluding those revealing considerable viscous fingering. Our numerical results confirm the previous experimental finding that the steady state specific interfacial length exhibits a linear dependence on S nw for either favorable (M ≥ 1) or unfavorable (M < 1) displacement, and the slope is slightly higher for the unfavorable displacement

Lattice Boltzmann simulation of immiscible fluid displacement in porous media: Homogeneous versus heterogeneous pore network

Energy Technology Data Exchange (ETDEWEB)

Liu, Haihu, E-mail: haihu.liu@mail.xjtu.edu.cn [School of Energy and Power Engineering, Xi’an Jiaotong University, 28 West Xianning Road, Xi’an 710049 (China); James Weir Fluids Laboratory, Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow G1 1XJ (United Kingdom); Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Zhang, Yonghao [James Weir Fluids Laboratory, Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow G1 1XJ (United Kingdom); Valocchi, Albert J. [Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

2015-05-15

Injection of anthropogenic carbon dioxide (CO{sub 2}) into geological formations is a promising approach to reduce greenhouse gas emissions into the atmosphere. Predicting the amount of CO{sub 2} that can be captured and its long-term storage stability in subsurface requires a fundamental understanding of multiphase displacement phenomena at the pore scale. In this paper, the lattice Boltzmann method is employed to simulate the immiscible displacement of a wetting fluid by a non-wetting one in two microfluidic flow cells, one with a homogeneous pore network and the other with a randomly heterogeneous pore network. We have identified three different displacement patterns, namely, stable displacement, capillary fingering, and viscous fingering, all of which are strongly dependent upon the capillary number (Ca), viscosity ratio (M), and the media heterogeneity. The non-wetting fluid saturation (S{sub nw}) is found to increase nearly linearly with logCa for each constant M. Increasing M (viscosity ratio of non-wetting fluid to wetting fluid) or decreasing the media heterogeneity can enhance the stability of the displacement process, resulting in an increase in S{sub nw}. In either pore networks, the specific interfacial length is linearly proportional to S{sub nw} during drainage with equal proportionality constant for all cases excluding those revealing considerable viscous fingering. Our numerical results confirm the previous experimental finding that the steady state specific interfacial length exhibits a linear dependence on S{sub nw} for either favorable (M ≥ 1) or unfavorable (M < 1) displacement, and the slope is slightly higher for the unfavorable displacement.

A thermodynamic study of peptides binding to carbon nanotubes based on a hydrophobic-polar lattice model using Monte Carlo simulations

International Nuclear Information System (INIS)

Cheng, Y; Lu, C; Liu, G R; Li, Z R; Mi, D

2008-01-01

Carbon nanotubes (CNTs) are outstanding novel materials that have great potential for a variety of chemical and biomedical applications. However, the mechanism of their interactions with biomaterials is still not fully understood, and more insightful research work is needed. In this work, we use the 2D hydrophobic-polar lattice model and the Monte Carlo simulation method to study the interactions between model peptides and CNTs. The energy parameters of the coarse-grained lattice model are qualitatively determined based on experimental data and molecular dynamics simulation results. Our model is capable of reproducing the essential phenomena of peptides folding in bulk water and binding to CNTs, as well as providing new insights into the thermodynamics and conformational properties of peptides interacting with nanotubes. The results suggest that both the internal energy and the peptide conformational entropy contribute to the binding process. Upon binding to the CNTs, peptides generally unfold into their denatured structures before they reach the lowest-accessible energy states of the system. Temperature has a significant influence on the adsorption process

Improved thermal lattice Boltzmann model for simulation of liquid-vapor phase change

Science.gov (United States)

Li, Qing; Zhou, P.; Yan, H. J.

2017-12-01

In this paper, an improved thermal lattice Boltzmann (LB) model is proposed for simulating liquid-vapor phase change, which is aimed at improving an existing thermal LB model for liquid-vapor phase change [S. Gong and P. Cheng, Int. J. Heat Mass Transfer 55, 4923 (2012), 10.1016/j.ijheatmasstransfer.2012.04.037]. First, we emphasize that the replacement of ∇ .(λ ∇ T ) /∇.(λ ∇ T ) ρ cV ρ cV with ∇ .(χ ∇ T ) is an inappropriate treatment for diffuse interface modeling of liquid-vapor phase change. Furthermore, the error terms ∂t 0(T v ) +∇ .(T vv ) , which exist in the macroscopic temperature equation recovered from the previous model, are eliminated in the present model through a way that is consistent with the philosophy of the LB method. Moreover, the discrete effect of the source term is also eliminated in the present model. Numerical simulations are performed for droplet evaporation and bubble nucleation to validate the capability of the model for simulating liquid-vapor phase change. It is shown that the numerical results of the improved model agree well with those of a finite-difference scheme. Meanwhile, it is found that the replacement of ∇ .(λ ∇ T ) /∇ .(λ ∇ T ) ρ cV ρ cV with ∇ .(χ ∇ T ) leads to significant numerical errors and the error terms in the recovered macroscopic temperature equation also result in considerable errors.

Topological susceptibility in lattice QCD with unimproved Wilson fermions

International Nuclear Information System (INIS)

Chowdhury, Abhishek; De, Asit K.; De Sarkar, Sangita; Harindranath, A.; Mondal, Santanu; Sarkar, Anwesa; Maiti, Jyotirmoy

2012-01-01

We address a long standing problem regarding topology in lattice simulations of QCD with unimproved Wilson fermions. Earlier attempt with unimproved Wilson fermions at β=5.6 to verify the suppression of topological susceptibility with decreasing quark mass (m q ) was unable to unambiguously confirm the suppression. We carry out systematic calculations for two degenerate flavours at two different lattice spacings (β=5.6 and 5.8). The effects of quark mass, lattice volume and the lattice spacing on the spanning of different topological sectors are presented. We unambiguously demonstrate the suppression of the topological susceptibility with decreasing quark mass, expected from chiral Ward identity and chiral perturbation theory.

Monte Carlo algorithms for lattice gauge theory

International Nuclear Information System (INIS)

Creutz, M.

1987-05-01

Various techniques are reviewed which have been used in numerical simulations of lattice gauge theories. After formulating the problem, the Metropolis et al. algorithm and some interesting variations are discussed. The numerous proposed schemes for including fermionic fields in the simulations are summarized. Langevin, microcanonical, and hybrid approaches to simulating field theories via differential evolution in a fictitious time coordinate are treated. Some speculations are made on new approaches to fermionic simulations

APPLICATION OF A LATTICE GAS MODEL FOR SUBPIXEL PROCESSING OF LOW-RESOLUTION IMAGES OF BINARY STRUCTURES

Directory of Open Access Journals (Sweden)

Zbisław Tabor

2011-05-01

Full Text Available In the study an algorithm based on a lattice gas model is proposed as a tool for enhancing quality of lowresolution images of binary structures. Analyzed low-resolution gray-level images are replaced with binary images, in which pixel size is decreased. The intensity in the pixels of these new images is determined by corresponding gray-level intensities in the original low-resolution images. Then the white phase pixels in the binary images are assumed to be particles interacting with one another, interacting with properly defined external field and allowed to diffuse. The evolution is driven towards a state with maximal energy by Metropolis algorithm. This state is used to estimate the imaged object. The performance of the proposed algorithm and local and global thresholding methods are compared.

Summer Student Project: GEM Simulation and Gas Mixture Characterization

CERN Document Server

Oviedo Perhavec, Juan Felipe

2013-01-01

Abstract This project is a numerical simulation approach to Gas Electron Multiplier (GEM) detectors design. GEMs are a type of gaseous ionization detector that have proposed as an upgrade for CMS muon endcap. The main advantages of this technology are high spatial and time resolution and outstanding aging resistance. In this context, fundamental physical behavior of a Gas Electron Multiplier (GEM) is analyzed using ANSYS and Garfield++ software coupling. Essential electron transport properties for several gas mixtures were computed as a function of varying electric and magnetic field using Garfield++ and Magboltz.

Low-energy scattering on the lattice

International Nuclear Information System (INIS)

Bour Bour, Shahin

2014-01-01

In this thesis we present precision benchmark calculations for two-component fermions in the unitarity limit using an ab initio method, namely Hamiltonian lattice formalism. We calculate the ground state energy for unpolarized four particles (Fermi gas) in a periodic cube as a fraction of the ground state energy of the non-interacting system for two independent representations of the lattice Hamiltonians. We obtain the values 0.211(2) and 0.210(2). These results are in full agreement with the Euclidean lattice and fixed-node diffusion Monte Carlo calculations. We also give an expression for the energy corrections to the binding energy of a bound state in a moving frame. These corrections contain information about the mass and number of the constituents and are topological in origin and will have a broad applications to the lattice calculations of nucleons, nuclei, hadronic molecules and cold atoms. As one of its applications we use this expression and determine the low-energy parameters for the fermion dimer elastic scattering in shallow binding limit. For our lattice calculations we use Luescher's finite volume method. From the lattice calculations we find κa fd =1.174(9) and κr fd =-0.029(13), where κ represents the binding momentum of dimer and a fd (r fd ) denotes the scattering length (effective-range). These results are confirmed by the continuum calculations using the Skorniakov-Ter-Martirosian integral equation which gives 1.17907(1) and -0.0383(3) for the scattering length and effective range, respectively.

Electromagnetic form factors at large momenta from lattice QCD

Science.gov (United States)

Chambers, A. J.; Dragos, J.; Horsley, R.; Nakamura, Y.; Perlt, H.; Pleiter, D.; Rakow, P. E. L.; Schierholz, G.; Schiller, A.; Somfleth, K.; Stüben, H.; Young, R. D.; Zanotti, J. M.; Qcdsf/Ukqcd/Cssm Collaborations

2017-12-01

Accessing hadronic form factors at large momentum transfers has traditionally presented a challenge for lattice QCD simulations. Here, we demonstrate how a novel implementation of the Feynman-Hellmann method can be employed to calculate hadronic form factors in lattice QCD at momenta much higher than previously accessible. Our simulations are performed on a single set of gauge configurations with three flavors of degenerate mass quarks corresponding to mπ≈470 MeV . We are able to determine the electromagnetic form factors of the pion and nucleon up to approximately 6 GeV2 , with results for the ratio of the electric and magnetic form factors of the proton at our simulated quark mass agreeing well with experimental results.

Simulation for temperature changing investigation at RSG-GAS cooling system

International Nuclear Information System (INIS)

Utaja

2002-01-01

The RSG-GAS cooling system considers of primary and secondary system, is used for heat rejection from reactor core to the atmosphere. For temperature changing investigation cause by atmospherics condition changing or coolant flow rate changing, is more safe done by simulation. This paper describes the simulation for determine the RSG-GAS coolant temperature changing base on heat exchange and cooling tower characteristic. The simulation is done by computer programme running under WINDOWS 95 or higher. The temperature changing is based on heat transfer process on heat exchanger and cooling tower. The simulation will show the water tank temperature changing caused by the temperature and humidity of the atmosphere or by coolant flow rate changing. For example the humidity changing from 60% to 80% atmospherics temperature 30 oC and 32400 k Watt power will change the tank temperature from 37,97 oC to 40,03 oC