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

An extended finite element method is applied to predict residual strength of cracked thin sheet plates. Two kinds of middle tension M(T) testings different in initial crack direction are simulated for stable crack growth process based on a crack tip opening angle criterion or a cohesive crack model. Crack growth direction is determined from direction of the maximum principal stress at the crack tip. Material follows plane-stress J2 plasticity with linear isotropic/kinematic hardening. The residual strength and crack propagation path obtained by the extended finite element method are compared to experimental measurement and show reasonable agreement.

https://iopscience.iop.org/article/10.1088/1757-899X/10/1/012063/pdf

Predicting residual strength of multi-cracked thin sheet plates based on CTOA or cohesive crack model using the extended finite element method

The utilization of red mud (RM) as an aluminosilicate precursor (AP) for geopolymer production is attracting increasing research interest. This use of RM offers a desirable outlet for the increasing RM inventory and provides a sustainable solution for the immobilization of heavy metals and the valorization of waste as eco-friendly building materials. However, the effect of RM and its caustic residue on geopolymerization remains uncertain because of the extremely varied characteristics of RM. This study investigates the potential of using RM supplied from a local alumina refinery as an AP. First, RM was used to partially replace fly ash (FA) and the strength activity index (SAI) of the RM was evaluated. Second, to gain a deeper insight into the effect of caustic residue on geopolymerization, performances of traditional FA-based geopolymer and red-mud–fly-ash (RMFA)–based geopolymer under different NaOH concentrations were investigated and compared. Third, based on alkali leaching tests, the effective molar ratios considering the reactive content of RM and FA were developed, compared with conventional nominal molar ratio, and verified intensively using scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS). 

Investigation on red mud and fly ash-based geopolymer: Quantification of reactive aluminosilicate and derivation of effective Si/Al molar ratio

콘크리트궤도의 합리적인 설계를 위해서는 콘크리트 슬래브에 발생하는 인장응력의 크기와 변동 폭, 발생 위치를 정확히 파 악해야 한다. 슬래브에 발생하는 응력은 여러 가지 하중 조건과 슬래브의 형상, 교량부 및 토공부의 상이한 지지 조건 등과 같 은 다양한 조건에 따라 달라지므로 주의가 필요하다. 특히 프리캐스트 콘크리트궤도는 4면이 구속되지 않은 상태이기 때문에 모서리와 코너부의 변형이 크게 발생하고, 응력 분포도 많은 차이를 보이게 된다. 본 연구는 콘크리트궤도 슬래브의 실제 손상 모드를 고려한 합리적인 설계법 개발을 위하여 콘크리트궤도 슬래브의 초기 변 형과 온도 경사에 의한 변형이 열차하중에 의한 슬래브의 응력 분포에 미치는 영향을 고찰하는 것을 목적으로 하며, 본 논문은 2개의 논문 중 두 번째 논문으로 앞서 첫 번째 논문[1]에서는 상용 구조해석 프로그램을 이용하여 프리캐스트 콘크리트궤도의 변형과 응력을 계산할 수 있는 유한요소 해석모델을 제시하였고, 현장에 부설된 프리캐스트 콘크리트궤도의 변형과 온도 분포 를 측정하였다. 그리고 측정된 깊이별 온도를 입력으로 하여 유한요소 해석에 의해 구한 슬래브 수직 변위와 현장에서 측정된 변위를 비교함으로써 슬래브 설치 후 발생한 초기 변형과 온도경사에 의한 슬래브의 변형 거동을 분석하였다. 본 논문에서는 첫 번째 논문에서 제시한 유한요소 해석모델과 분석 결과를 이용하여 초기 변형과 온도에 의한 변형이 발생한 상태에서 열차 Abstract In this paper, the effects of initial built-in deformation and temperature deformation on the stress distribution of discontinuous precast concrete track slab under train load were examined. According to the results, when train load is put on a precast concrete slab with initial built-in deformation and deformation due to temperature gradient, the maximum tensile stresses develop at the upper side of slab in the slab center, edge center and corner of shear pocket; the stress distribution is different from that of the case under train load only. Therefore, to accurately predict the actual weak points and failure modes, one should calculate the stress under train load considering the initial built-in and temperature deformation of the slab.

Deformation and stress distribution of discontinuous precast concrete track slab: II. Stress distribution

In this study, we conducted experiment and finite element analysis on the flexural behavior of the round concrete panels according to the evaluation method of biaxial flexural tensile strengths. The Round Panel Test (RPT) and the Biaxial Flexure Test (BFT) were used to determine the biaxial flexural strength of round plain concrete panels. In order to understand the stress distribution on the panels, we measured load-strain relationship at the center of the panels` bottom surface. Test results show that fracture pattern in RPT and BFT panels are similar, and the tensile stress distribution is uniform in all directions at the center of the bottom surface of the panels for both RPT and BFT. The distribution of stresses in two test specimens coincided with the analysis result. The average biaxial flexural strength of RPT is about 29% greater than those of the BFT. The coefficient of variations (COV) of the RPT and BFT for the biaxial flexure strength is 8%, 6%, respectively, which indicates that BFT method is useful and reliable for determining biaxial flexural strengths of the concrete.

/pdf/an-experimental-study-on-the-flexural-behavior-of-the-round-17x9ult68g.pdf

An Experimental Study on the Flexural Behavior of the Round Concrete Panels according to the Evaluation Method of Biaxial Flexural Tensile Strengths

https://www.koreascience.kr:443/article/JAKO201001660923738.pdf

Goangseup Zi

Papers

Predicting residual strength of multi-cracked thin sheet plates based on CTOA or cohesive crack model using the extended finite element method

Investigation on red mud and fly ash-based geopolymer: Quantification of reactive aluminosilicate and derivation of effective Si/Al molar ratio

Deformation and stress distribution of discontinuous precast concrete track slab: II. Stress distribution

An Experimental Study on the Flexural Behavior of the Round Concrete Panels according to the Evaluation Method of Biaxial Flexural Tensile Strengths

Analysis of Static Crack Growth in Asphalt Concrete using the Extended Finite Element Method