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

Basalt-based fiber-reinforced materials and structural applications in civil engineering

The use of empirical force fields is now a standard approach in predicting the properties of hydrated oxides which are omnipresent in both natural and engineering applications. Transferability of force fields to analogous hydrated oxides without rigorous investigations may result in misleading property predictions. Herein, we focus on two common empirical force fields, the simple point charge ClayFF potential and the core-shell potential to study tobermorite minerals, the most prominent family of Calcium-Silicate-Hydrates that are complex hydrated oxides. We benchmark the predictive capabilities of these force fields against first principles results. While the structural information seem to be in close agreement with DFT results, we find that for higher order properties such as elastic constants, the core-shell potential quantitatively improves upon the simple point charge model, and shows a larger degree of transferability to complex materials. In return, to remedy the deficiencies of the simple point charge potential for hydrated calcio-silicates, we suggest using both structural data and elasticity data for potential calibration, a new force field potential, CSH-FF. This re-parameterized version of ClayFF is then applied to simulating an atomistic model of cement (Pellenq et al., PNAS, 2009). We demonstrate that this force field improves the predictive capabilities of ClayFF, being considerably less computational intensive than the core-shell model.

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Transferability of empirical force fields for complex hydrated calcio-silicate layered materials

A review on durability of fiber reinforced polymer (FRP) bars reinforced seawater sea sand concrete

The paper recognizes that the introduction of polymers and advanced polymer composites in the civil engineering world has been a comparatively rapid process vis-s-vis other civil engineering materials when they were first introduced. Aerospace and marine industries have been first to utilize advanced polymer compounds, but recently there has been a growing interest among civil/structural engineers in the importance of the unique mechanical and in-service properties of these materials together with their customized fabrication technologies. The paper outlines the development stages of this exciting material and provides a look into the future prospects for it.

The evolution of and the way forward for advanced polymer composites in the civil infrastructure

Strength enhancement of recycled aggregate pervious concrete using a cement paste redistribution method

Fiber reinforced polymer (FRP) is widely used in concrete structures due to its high tensile strength and superior corrosion resistance. However, the FRP reinforced concrete (FRPRC) shows a less ductile behavior compared to the conventional steel reinforced concrete. In order to improve the strength and flexural ductility simultaneously, a hybrid reinforcement system composed of FRP and steel bars has been proposed and adopted in design recently. In hybrid FRPRC beams, FRP and steel reinforcements play different roles in improving strength and ductility. The hybrid reinforcement ratio between FRP and steel, Af/As, has a significant influence on the flexural performance of hybrid FRPRC beams as it affects the balance between strength and ductility in the flexural design. Here, the effect of hybrid reinforcement ratio on the flexural performance of concrete beams in both under- and over- reinforced scenarios is studied using three-dimensional finite element models. The results from the finite element models show that a preferable strength and ductility performance can be obtained through an appropriate design of hybrid reinforcement ratio. Such information helps us determine an appropriate range of hybrid reinforcement ratio and provide a design guideline for hybrid FRPRC beams for optimizing the strength and ductility performance.

Effect of reinforcement ratio on the flexural performance of hybrid FRP reinforced concrete beams

Adhesive bonding of fiber-reinforced polymers (FRP) to wood has been proven as a general way to achieve reinforcement and rehabilitation for wood structures. Although a significant mechanical enhancement can be acquired by using such approach, there exists a big concern about the long-term performance of the FRP–wood composite, especially under the effect of moisture. In this paper, both experimental and atomistic approaches are adopted for investigating the moisture effect on the entire FRP–wood composite system. Macroscopic mechanical tests show that its mechanical properties and its fracture behaviors notably change at different levels of ambient humidity. From an atomistic perspective, molecular dynamics (MD) simulations reveal that water molecules significantly reduce the adhesion energy between wood and epoxy. Results from experimental and numerical studies imply that the strength of the FRP–wood interface critically determines the mechanical performance of the entire system. The water molecules absorbed at the interface are crucial to the durability of multi-layer systems and a general mechanism governing the failure modes of such systems is found.

Ao Zhou

Papers

Strength enhancement of recycled aggregate pervious concrete using a cement paste redistribution method

Effect of reinforcement ratio on the flexural performance of hybrid FRP reinforced concrete beams

Effect of moisture on the mechanical properties of CFRP–wood composite: An experimental and atomistic investigation

Utilization of waste cathode ray tube funnel glass for ultra-high performance concrete

Long term performance and fire safety aspect of FRP composites used in building structures