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

비만아 부모의 돌봄 경험: q 방법론

In recent years, there has been an increasing interest in the adoption of emerging sensing technologies for instrumentation within a variety of structural systems. Wireless sensors and sensor networks are emerging as sensing paradigms that the structural engineering field has begun to consider as substitutes for traditional tethered monitoring systems. A benefit of wireless structural monitoring systems is that they are inexpensive to install because extensive wiring is no longer required between sensors and the data acquisition system. Researchers are discovering that wireless sensors are an exciting technology that should not be viewed as simply a substitute for traditional tethered monitoring systems. Rather, wireless sensors can play greater roles in the processing of structural response data; this feature can be utilized to screen data for signs of structural damage. Also, wireless sensors have limitations that require novel system architectures and modes of operation. This paper is intended to serve as a summary review of the collective experience the structural engineering community has gained from the use of wireless sensors and sensor networks for monitoring structural performance and health.

http://www-personal.umich.edu/~jerlynch/papers/SVDReview.pdf

A summary review of wireless sensors and sensor networks for structural health monitoring

Design-oriented stress–strain model for FRP-confined concrete

Performance and application of a design-oriented stress-strain model for FRP-confined concrete

New types of structural columns are being developed for new construction. They are made of concrete-encased fiber reinforced polymer (FRP) tubes. The concrete-filled FRP tubes are cast in place. The tube acts as formwork, protective jacket, confinement, and shear and flexural reinforcement. It can also be used to complement or replace conventional steel reinforcement of the column. This paper presents the results of experimental and analytical studies of the performance of concrete columns conbined with carbon and glass FRP composite tubes. Concrete-filled FRP tubes are instrumented and tested under uniaxial compressive load. Test variables include type of fiber, thickness of tube, and concrete compressive strength. Results show that external confinement of concrete by FRP tubes can significantly enhance the strength, ductility, and energy absorption capacity of concrete. Equations to predict the compressive strength and failure strain, as well as the entire stress-strain curve of concrete-filled FRP tubes were developed. A comparison between the experimental results and those of analytical results indicate that the proposed model provides satisfactory predictions of ultimate compressive strength, failure strain, and stress-strain response. The study shows that the available models generally overestimate the strength of concrete confined by FRP tubes, resulting in unsafe design.

Behavior of concrete columns confined with fiber reinforced polymer tubes

Concrete members reinforced with glass fiber-reinforced polymer (GFRP) bars exhibit large deflections and crack widths compared with concrete members reinforced with steel. This is due to the low modulus of elasticity of GFRP. Current design methods for predicting deflections at service load and crack widths developed for concrete structures reinforced with steel may not be used for concrete structures reinforced with GFRP. This paper presents methods for predicting deflections and crack widths in beams reinforced with GFRP. To use the effective moment of inertia for concrete beams reinforced with GFRP bars, the effect of the FRP reinforcement ratios and elastic modulus of FRP were incorporated in the exponent of Branson's equation. In addition, an equation based on flexural stiffness of GFRP reinforced concrete was developed to predict deflections. Based on this investigation and past studies, a theoretical correlation for predicting crack width was proposed. Six concrete beams reinforced with different GFRP reinforcement ratios were tested. Their measured deflections and crack widths were compared with the proposed models. The experimental results compared favorably with those predicted by the models.

Mohamed Saafi

Papers

Behavior of concrete columns confined with fiber reinforced polymer tubes

Flexural behavior of concrete beams reinforced with glass fiber-reinforced polymer (GFRP) bars

Effect of fire on FRP reinforced concrete members

Enhanced properties of graphene/fly ash geopolymeric composite cement

Multifunctional properties of carbon nanotube/fly ash geopolymeric nanocomposites