Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Topology optimization has undergone a tremendous development since its introduction in the seminal paper by Bendsoe and Kikuchi in 1988. By now, the concept is developing in many different directions, including “density”, “level set”, “topological derivative”, “phase field”, “evolutionary” and several others. The paper gives an overview, comparison and critical review of the different approaches, their strengths, weaknesses, similarities and dissimilarities and suggests guidelines for future research.

Topology optimization approaches: A comparative review

The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuations by means of straightforward atomistic Monte Carlo simulations based on a very accurate many-body interatomic potential for carbon. We find that ripples spontaneously appear due to thermal fluctuations with a size distribution peaked around 70 \AA which is compatible with experimental findings (50-100 \AA) but not with the current understanding of stability of flexible membranes. This unexpected result seems to be due to the multiplicity of chemical bonding in carbon.

Intrinsic ripples in graphene

Guided Lamb waves for identification of damage in composite structures: A review

Topology optimization is the process of determining the optimal layout of material and connectivity inside a design domain. This paper surveys topology optimization of continuum structures from the year 2000 to 2012. It focuses on new developments, improvements, and applications of finite element-based topology optimization, which include a maturation of classical methods, a broadening in the scope of the field, and the introduction of new methods for multiphysics problems. Four different types of topology optimization are reviewed: (1) density-based methods, which include the popular Solid Isotropic Material with Penalization (SIMP) technique, (2) hard-kill methods, including Evolutionary Structural Optimization (ESO), (3) boundary variation methods (level set and phase field), and (4) a new biologically inspired method based on cellular division rules. We hope that this survey will provide an update of the recent advances and novel applications of popular methods, provide exposure to lesser known, yet promising, techniques, and serve as a resource for those new to the field. The presentation of each method's focuses on new developments and novel applications.

/pdf/a-survey-of-structural-and-multidisciplinary-continuum-3lbeegkisv.pdf

A survey of structural and multidisciplinary continuum topology optimization: post 2000

Vibration-based model-dependent damage (delamination) identification and health monitoring for composite structures — a review

Introduction: Background Introduction to 3D FRP composites Manufacture of 3D Fibre Preforms: Weaving Braiding Knitting Stitching Preform Consolidation Liquid moulding techniques Resin selection Tooling Component quality. Micromechanics Models for Mechanical Properties: Fundamentals in micromechanics Unit cell models for 2D woven composites Models for 3D woven composites Unit cell models for braided and knitted composites. 3D Woven Composites: Microstructural properties of 3D woven composites In-plane mechanical properties of 3D woven composites Interlaminar fracture properties of 3D woven composites 3D woven distance fabric composites. Braided Composite Materials: In-plane mechanical properties Fracture toughness and damage performance Fatigue performance Modelling of braided composites. Knitted Composite Materials: In-plane mechanical properties Interlaminar fracture toughness Impact performance Modelling of knitted composites. Stitched Composites: The Stitching process Mechanical properties of stitched composites Interlaminar properties of stitched composites Stitched composite joints. Z-Pinned Composites Fabrication of Z-pinned composites Mechanical properties of Z-pinned composites Delamination resistance and damage tolerance of Z-pinned composites Z-Pinned sandwich composites.

3D Fibre Reinforced Polymer Composites

The main objective of this article is to present an overview of the modelling that has been proposed by various workers in the field of smart or intelligent structures. Before the main discussion o...

A Review on the Modelling of Piezoelectric Sensors and Actuators Incorporated in Intelligent Structures

Textile composite is one of the important materials used in industry and is made from textile substrates embedded in the matrices of different materials (see ref. 1 ). However, due to its complicated microstructure, understanding of mechanical properties of textile composite materials is still in its infant stage (see refs 2.3 ). Recently, many researchers have contributed to develop finite element analysis (FEA) and theoretical analysis models for predicting mechanical properties of textile composites, and to study the variation trends of mechanical property with major architectural parameters. In this paper, a review of recent developments and results in predicting mechanical properties of textile composites using finite element analysis and theoretical analysis methods, focusing on elastic behaviour for woven fabric composites, is presented. The predictive capability of various models, including earlier one-dimensional (1D) ‘mosaic model’ and more recent three-dimensional (3D) models, are discussed in this review.

Modelling for predicting the mechanical properties of textile composites : A review

Preface. 1. Introduction. 2. Stress Analysis Techniques. 3. Failure Criteria and Strength Prediction. 4. Damage Tolerance. 5. Optimum Design. 6. Effect of Transverse Stitching. 7. Selected Applications. References. Index.

Liyong Tong

Papers

Vibration-based model-dependent damage (delamination) identification and health monitoring for composite structures — a review

3D Fibre Reinforced Polymer Composites

A Review on the Modelling of Piezoelectric Sensors and Actuators Incorporated in Intelligent Structures

Modelling for predicting the mechanical properties of textile composites : A review

Analysis and design of structural bonded joints