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Particle Dynamics (particle + dynamics)

Distribution by Scientific Domains

Engineering	33%

Selected Abstracts

Mesophase Separation of Diblock Copolymer Confined in a Cylindrical Tube Studied by Dissipative Particle Dynamics

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2006
Jian Feng
Abstract Summary: The morphologies of diblock copolymers confined in a cylindrical tube have been investigated by the dissipative particle dynamics (DPD) method. Results indicate that the morphology depends on the volume ratio of the immiscible blocks, the diameter of the cylindrical tube and the interactions between the blocks and between the confinement wall and blocks. For symmetric diblock copolymers, when the tube wall is uniform toward the two blocks, perpendicular lamellae or a stacked disk morphology are generally formed except when the diameter of the cylindrical tube is very small; in that case, a special bi-helix morphology forms because of the entropy effect. When the tube wall is non-uniform, as the diameter of the tube increases, perpendicular lamellae are first formed, then changing to parallel lamellae and, finally, back to perpendicular lamellae again. An intermediate morphology characterizing the transition between perpendicular and parallel lamellae is observed. If the non-uniformity of the wall is further enhanced, only parallel lamellae can be found. In the case of asymmetric diblock copolymers, more complex morphologies can be obtained. Multi-cylindrical micro-domains and a multilayer helical phase as well as other complex pictures are observed. Generally, the morphologies obtained could find their counterparts from experiments or Monte Carlo simulations; however, differences do exist, especially in some cases of asymmetric diblock copolymers. Bi-helix and stacked disks morphologies of A5B5 diblock copolymer confined in two different neutral nanocylinders. [source]

Clustering revealed in high-resolution simulations and visualization of multi-resolution features in fluid,particle models

CONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 2 2003
Krzysztof Boryczko
Abstract Simulating natural phenomena at greater accuracy results in an explosive growth of data. Large-scale simulations with particles currently involve ensembles consisting of between 106 and 109 particles, which cover 105,106 time steps. Thus, the data files produced in a single run can reach from tens of gigabytes to hundreds of terabytes. This data bank allows one to reconstruct the spatio-temporal evolution of both the particle system as a whole and each particle separately. Realistically, for one to look at a large data set at full resolution at all times is not possible and, in fact, not necessary. We have developed an agglomerative clustering technique, based on the concept of a mutual nearest neighbor (MNN). This procedure can be easily adapted for efficient visualization of extremely large data sets from simulations with particles at various resolution levels. We present the parallel algorithm for MNN clustering and its timings on the IBM SP and SGI/Origin 3800 multiprocessor systems for up to 16 million fluid particles. The high efficiency obtained is mainly due to the similarity in the algorithmic structure of MNN clustering and particle methods. We show various examples drawn from MNN applications in visualization and analysis of the order of a few hundred gigabytes of data from discrete particle simulations, using dissipative particle dynamics and fluid particle models. Because data clustering is the first step in this concept extraction procedure, we may employ this clustering procedure to many other fields such as data mining, earthquake events and stellar populations in nebula clusters. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Grid services for earthquake science

CONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 6-7 2002
Geoffrey Fox
Abstract We describe an information system architecture for the ACES (Asia,Pacific Cooperation for Earthquake Simulation) community. It addresses several key features of the field,simulations at multiple scales that need to be coupled together; real-time and archival observational data, which needs to be analyzed for patterns and linked to the simulations; a variety of important algorithms including partial differential equation solvers, particle dynamics, signal processing and data analysis; a natural three-dimensional space (plus time) setting for both visualization and observations; the linkage of field to real-time events both as an aid to crisis management and to scientific discovery. We also address the need to support education and research for a field whose computational sophistication is rapidly increasing and spans a broad range. The information system assumes that all significant data is defined by an XML layer which could be virtual, but whose existence ensures that all data is object-based and can be accessed and searched in this form. The various capabilities needed by ACES are defined as grid services, which are conformant with emerging standards and implemented with different levels of fidelity and performance appropriate to the application. Grid Services can be composed in a hierarchical fashion to address complex problems. The real-time needs of the field are addressed by high-performance implementation of data transfer and simulation services. Further, the environment is linked to real-time collaboration to support interactions between scientists in geographically distant locations. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Conservation properties of a time FE method.

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2005
Part IV: Higher order energy, momentum conserving schemes
Abstract In the present paper a systematic development of higher order accurate time stepping schemes which exactly conserve total energy as well as momentum maps of underlying finite-dimensional Hamiltonian systems with symmetry is shown. The result of this development is the enhanced Galerkin (eG) finite element method in time. The conservation of the eG method is generally related to its collocation property. Total energy conservation, in particular, is obtained by a new projection technique. The eG method is, moreover, based on objective time discretization of the used strain measure. This paper is concerned with particle dynamics and semi-discrete non-linear elastodynamics. The related numerical examples show good performance in presence of stiffness as well as for calculating large-strain motions. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A method for representing boundaries in discrete element modelling,part II: Kinematics

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2001
M. Kremmer
Abstract The application of the DEM to engineering problems involving the dynamic behaviour of discontinuous media has necessitated the introduction of moving boundary surfaces. In this paper a method is presented for modelling three-dimensional moving boundary surfaces within the discrete element framework. The surfaces of boundary objects are discretized into triangular planar surfaces using the finite wall method. Wall elements are grouped and each group is associated with a single discrete boundary object which may move independently. Movement comprises any combination of translation and rotation of wall element groups, subject to a given acceleration and velocity during a calculation cycle. The scheme is explicit due to rigidity of the wall elements which are stationary fixed in position and orientation over a time step. Any in-plane velocity is handled as a contact point velocity within a calculation cycle. The kinematic conditions at each calculation cycle may be pre-defined or returned from a separate calculation of rigid body motion of the boundary object. The method provides a means for coupling sphere-based particle dynamics with rigid body dynamics and structural analysis of boundary components. Copyright © 2001 John Wiley & Sons, Ltd. [source]

A meso-scale analysis of lipid bilayers with the dissipative particle dynamics method: Thermally fluctuating interfaces

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6-8 2007
Taisuke Sugii
Abstract We present a meso-scale simulation of lipid bilayers with the dissipative particle dynamics (DPD) method. The spectrums of the thermal undulation are analysed and the bending rigidity of the lipid bilayers is calculated. In order to define the position of the membrane, we apply a definition of the interface which has been newly proposed by Kikugawa et al. (Comput. Fluids 2007; 36:69,76). We show the applicability of this method to the lipid bilayer system. By means of this definition, the roughness of the extracted interface can be varied and this effect is investigated. The spectral intensity is shown as a function of the undulatory wavenumber q. The spectral intensity in large- q regions is affected by the roughness of the interface. However, we find that the spectral intensity in small- q regions, where the bending rigidity can be calculated, is hardly affected. Moreover, the undulation spectrums show q,4 behaviour in small- q regions, which agrees with the theoretical prediction. The effects of the size of the computational cell are also investigated. All spectrums obtained in the differently sized cells agree well, although the observable range of the wavenumber depends on the cell size. The bending rigidity calculated by spectral intensity from the largest cell is in good agreement with experiments and molecular dynamics simulations in the literature. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Simultaneous light and small-angle neutron scattering on aggregating concentrated colloidal suspensions

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2003
Sara Romer
A new sample environment has been developed in order to perform light and small-angle neutron scattering (SANS) simultaneously on colloidal systems. The combination of SANS and diffusing wave spectroscopy (DWS) is of particular use in the high-concentration regime. DWS provides information on the local dynamic properties of the individual particles, whereas SANS gives access to the structural properties on similar length scales. The combination of both methods thus allows one to obtain structural and dynamic information over a very large range of length and time scales. Using this new setup, the onset of aggregation and the sol,gel transition in concentrated destabilized polystyrene sphere suspensions have been investigated. At the gel point, a dramatic change of the particle dynamics from diffusion to a subdiffusive arrested motion is observed. However, while the DWS measurements indicate that dramatic changes in the local dynamics occur over a long period, the SANS pattern quickly reaches its final appearance. The SANS experiments thus indicate that a fluid-like structure is arrested in the course of the gel formation. The data are found to be in good qualitative agreement with computer simulations. [source]

Dissipative Particle Dynamics Simulations of Polymer Brushes: Comparison with Molecular Dynamics Simulations

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2006
Sandeep Pal
Abstract Summary: The structure of polymer brushes is investigated by dissipative particle dynamics (DPD) simulations that include explicit solvent particles. With an appropriate choice of the DPD interaction parameters , we obtain good agreement with previous molecular dynamics (MD) results where the good solvent behavior has been modeled by an effective Lennard,Jones potential. The present results confirm that DPD simulation techniques can be applied for large length scale simulations of polymer brushes. A relation between the different length scales and is established. Polymer brush at a solid,liquid interface. [source]