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

Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (e.g., a high power density and a long cycle-life) (507 references).

A review of electrolyte materials and compositions for electrochemical supercapacitors

https://www.crm.sns.it/media/course/3060/miehe+hofacker+welschinger10.pdf

A phase field model for rate-independent crack propagation: Robust algorithmic implementation based on operator splits

The computational modeling of failure mechanisms in solids due to fracture based on sharp crack discontinuities suffers in situations with complex crack topologies. This can be overcome by a diffusive crack modeling based on the introduction of a crack phase-field. In this paper, we outline a thermodynamically consistent framework for phase-field models of crack propagation in elastic solids, develop incremental variational principles and consider their numerical implementations by multi-field finite element methods. We start our investigation with an intuitive and descriptive derivation of a regularized crack surface functional that Γ-converges for vanishing length-scale parameter to a sharp crack topology functional. This functional provides the basis for the definition of suitable convex dissipation functions that govern the evolution of the crack phase-field. Here, we propose alternative rate-independent and viscous over-force models that ensure the local growth of the phase-field. Next, we define an energy storage function whose positive tensile part degrades with increasing phase-field. With these constitutive functionals at hand, we derive the coupled balances of quasi-static stress equilibrium and gradient-type phase-field evolution in the solid from the argument of virtual power. Here, we consider a canonical two-field setting for rate-independent response and a time-regularized three-field formulation with viscous over-force response. It is then shown that these balances follow as the Euler equations of incremental variational principles that govern the multi-field problems. These principles make the proposed formulation extremely compact and provide a perfect base for the finite element implementation, including features such as the symmetry of the monolithic tangent matrices. We demonstrate the performance of the proposed phase-field formulations of fracture by means of representative numerical examples. Copyright © 2010 John Wiley & Sons, Ltd.

Thermodynamically consistent phase‐field models of fracture: Variational principles and multi‐field FE implementations

A new approach for modelling discrete cracks in meshfree methods is described. In this method, the crack can be arbitrarily oriented, but its growth is represented discretely by activation of crack surfaces at individual particles, so no representation of the crack's topology is needed. The crack is modelled by a local enrichment of the test and trial functions with a sign function (a variant of the Heaviside step function), so that the discontinuities are along the direction of the crack. The discontinuity consists of cylindrical planes centred at the particles in three dimensions, lines centred at the particles in two dimensions. The model is applied to several 2D problems and compared to experimental data. Copyright © 2004 John Wiley & Sons, Ltd.

Cracking particles: A simplified meshfree method for arbitrary evolving cracks

콘크리트궤도는 고속으로 이동하는 열차를 직접 지지하는 구조물로서 주어진 하중 조건에서 큰 손상 없이 제 기능을 발휘할 수 있도록 설계되어야 한다. 특히 열차하중이 반복적으로 작용하게 되므로 콘크리트 슬래브의 피로 파손에 대한 평가가 중요하 다. 피로 파손에 대비하기 위해서는 콘크리트 슬래브에 발생하는 인장응력의 크기와 변동 폭, 발생 위치 파악이 필요하다. 이때 슬래브에 발생하는 응력은 여러 가지 하중 조건과 슬래브의 형상, 교량부 및 토공부의 상이한 지지 조건 등과 같은 다양한 조 건에 따라 달라지므로 궤도 슬래브 설계 시부터 세심한 주의가 필요하다. 콘크리트 슬래브에 대한 연구는 1920년대 이전부터 활발히 수행되어 왔는데[1-6], 많은 연구자들은 차량하중과 같은 직접적 인 하중 외에 온도가 콘크리트 포장 성능에 영향을 미치는 중요한 환경적 요인이라고 밝혀 왔다[7]. 도로 및 공항 콘크리트 포 장에 대해 차량하중과 환경하중(온도), 그 외 주요설계 변수들을 반영하여 응력식을 산정하고 콘크리트의 피로 특성을 고려하 Abstract This study looked into the behavior of precast concrete track due to temperature variation and initial track deformation and examined the effect of initial deformation and deformation caused by temperature gradient on the stress distribution of slab under train load. In this paper, one of two papers in a series, a finite element analysis model for calculating deformation and stress of precast concrete track was proposed; the temperature distribution and displacements measured at the precast concrete track in the field were compared with the analytical results. The results show that the slab always curled up due to initial deformation; by comparing the measured displacements with the displacements calculated by taking measured temperatures at each depth as input, the effective built-in temperature (EBITD), the temperature difference between the top and bottom of the slab corresponding to the initial deformation, can be estimated. If EBITD is relevantly assumed, the calculated displacements correlate well with the measured ones.

Deformation and Stress Distribution of Discontinuous Precast Concrete Track Slab: I. Initial and Temperature Deformation

A stochastic computational method based on goal-oriented error estimation for heterogeneous geological materials

The experimental comparison of the uniaxial and biaxial flexural tensile strengths according to the size of specimens

This study developed and investigated a precast slab track system partially reinforced with glass fiber reinforced polymer (GFRP) rebars in the transverse direction, which mitigated the loss of track circuit current by reducing magnetic coupling between the rails and steel reinforcements. An electric analysis was conducted and the results of the analysis verified that the GFRP rebars mitigate the reduced current strength produced by electro-magnetic induction. In the study, a threedimensional finite element method and flexural experiments were used to study the mechanical behavior of the proposed slab track.

Goangseup Zi

Papers

Deformation and Stress Distribution of Discontinuous Precast Concrete Track Slab: I. Initial and Temperature Deformation

A stochastic computational method based on goal-oriented error estimation for heterogeneous geological materials

The experimental comparison of the uniaxial and biaxial flexural tensile strengths according to the size of specimens

A precast slab track partially reinforced with GFRP rebars

Optimum NDT using infrared thermography for defected concrete