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

Additive manufacturing of metallic components – Process, structure and properties

/pdf/the-theory-of-industrial-organization-19bejph0ej.pdf

The Theory of Industrial Organization

Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

Additive manufacturing (AM) is poised to bring about a revolution in the way products are designed, manufactured, and distributed to end users. This technology has gained significant academic as well as industry interest due to its ability to create complex geometries with customizable material properties. AM has also inspired the development of the maker movement by democratizing design and manufacturing. Due to the rapid proliferation of a wide variety of technologies associated with AM, there is a lack of a comprehensive set of design principles, manufacturing guidelines, and standardization of best practices. These challenges are compounded by the fact that advancements in multiple technologies (for example materials processing, topology optimization) generate a "positive feedback loop" effect in advancing AM. In order to advance research interest and investment in AM technologies, some fundamental questions and trends about the dependencies existing in these avenues need highlighting. The goal of our review paper is to organize this body of knowledge surrounding AM, and present current barriers, findings, and future trends significantly to the researchers. We also discuss fundamental attributes of AM processes, evolution of the AM industry, and the affordances enabled by the emergence of AM in a variety of areas such as geometry processing, material design, and education. We conclude our paper by pointing out future directions such as the "print-it-all" paradigm, that have the potential to re-imagine current research and spawn completely new avenues for exploration. The fundamental attributes and challenges/barriers of Additive Manufacturing (AM).The evolution of research on AM with a focus on engineering capabilities.The affordances enabled by AM such as geometry, material and tools design.The developments in industry, intellectual property, and education-related aspects.The important future trends of AM technologies.

The status, challenges, and future of additive manufacturing in engineering

Blown-powder laser cladding is an efficient method for enhancing the surface properties of engineering components while preserving the properties of the base material. High power direct diode lasers (HPDDLs) offer wide beams with nearly uniform intensity distribution, allowing the deposition of wide clad tracks with flatter profiles than those produced with a Gaussian beam. In this work, a 4.0 kW HPDDL is used to perform blown-powder cladding on AISI 4140 and AISI 5150 steel shafts. The first part of the experiments concerns two-layer circumferential tracks created from two commonly used hardfacing alloys: Stellite 6 (Co-Cr alloy) and Nistelle 625 (Ni-Cr alloy). The effects of laser power and powder feed rate on the clad geometry are assessed. Increasing the powder feed rate and holding constant all other parameters decreases the track width-to-thickness aspect ratio. All tracks exhibit dendrite microstructures that are characteristic of powder-based clad tracks. The tracks exhibit no cracks or porosity. Energy dispersive X-ray (EDX) analysis reveals dilution of five percent or less between the clad and substrate materials. The second part of the experiments concerns overlapping of single-layer clad tracks in a continuous helical pattern on the substrate to form a layer that covers a large area. Clad layer thickness and inter-track porosity are measured to determine the optimum degree of overlap for producing a high-quality clad layer. The thickness of the resulting Stellite 6 and Nistelle 625 clad layers decreases as the overlap percentage decreases. No inter-track, interfacial, or bulk pores are present for any tests, comprising overlap percentages of 50% and lower.© 2007 ASME

Laser Cladding of Two Hardfacing Alloys Onto Cylindrical Low Alloy Steel Substrates With a High Power Direct Diode Laser

Intelligent systems

Peripheral milling process productivity or quality can be improved by controlling either cutting force or contour error. While each means for improvement is often addressed individually, efforts to...

https://journals.sagepub.com/doi/pdf/10.1177/0954405416654100

Adaptive robust control of machining force and contour error with tool deflection using global task coordinate frame

This paper deals with the spallation induced by shock wave propagation in targets during the laser shock peening process. Physical aspects concerning laser-matter interaction, shock wave propagation, and spallation are considered. A continuous kinetic model for the spallation process is included in a one-dimensional finite-difference hydrodynamic code using Lagrangian coordinates in order to calculate the laser-induced spallation phenomena. Shock wave propagation in solids is calculated and validated by experimental data. The spallation zone location is then calculated for various materials with different thickness of foils and various laser shock peening parameters. The numerical simulations are compared with previously reported experimental results and good agreement is obtained for the spallation threshold and damage zone location.

Shock Wave Propagation and Spallation Study in Laser Shock Peening

The approach of designing a discrete time optimal controller for a nonlinear system represented by a fuzzy model is presented in this paper. A fuzzy model with product inference engine, singleton fuzzifier, center average defuzzifier, and Gaussian membership functions is trained by the orthogonal least square (OLS) learning algorithm based on given input-output data pairs. An optimal control scheme is then formulated based on the fuzzy model. The numerical solution of the problem is achieved by use of a feasible-direction algorithm. To show the effectiveness of the proposed method, the simulation results of three nonlinear optimal control problems are presented. The results show that the performance of the proposed approach is quite similar to that of optimal control of the system represented by an explicit mathematical model, thus demonstrating the efficacy of the proposed scheme for optimal control of unknown nonlinear systems.

Yung C. Shin

Papers

Laser Cladding of Two Hardfacing Alloys Onto Cylindrical Low Alloy Steel Substrates With a High Power Direct Diode Laser

Intelligent systems

Adaptive robust control of machining force and contour error with tool deflection using global task coordinate frame

Shock Wave Propagation and Spallation Study in Laser Shock Peening

Nonlinear discrete time optimal control based on Fuzzy Models