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

A molecular dynamics investigation into the mechanisms of subsurface damage and material removal of monocrystalline copper subjected to nanoscale high speed grinding

Fly cutting in ultra-precision machining (UPM), termed ultra-precision fly cutting (UPFC), is an intermittent cutting process in which a diamond tool is mounted with a spindle to intermittently cut a workpiece. The process offers the high flexibility necessary for fabricating freeform, micro/nano-structural surfaces, as well as hybrid structural surfaces with sub-micrometric form error and nanometric surface roughness, and its constant cutting velocity provides uniform high surface quality. However, in addition to its low machining efficiency, UPFC’s intermittent cutting process results in distinctive surface generation mechanisms, covering intermittent tool-workpiece relative motion, tool geometry imprinted into a machined surface, and surface material separation and deformation. General factors, such as cutting conditions, tool geometry, material factors (material property change, material swelling and recovery, and material separation mechanism), kinematic and dynamic errors, assembling errors, cutting strategies, tool path, and workpiece geometry, are individual to UPFC and universal in UPM. Accordingly, this paper focuses on the current investigation of fly cutting applied into surface generation in UPM. Conclusions are reached and the challenges and opportunities for further studies are discussed.

A review of fly cutting applied to surface generation in ultra-precision machining

Aerostatic bearings design and analysis with the application to precision engineering: State-of-the-art and future perspectives

Molecular dynamics simulations of nanometric cutting mechanisms of amorphous alloy

Understanding the basic action of how material removing in nanoscale is a critical issue of producing well-formed components. In order to clarify thermal effects on material removal at atomic level, molecular dynamics (MD) simulations of nanometric cutting of mono-crystalline copper are performed with Morse, EAM and Tersoff potential. The effects of cutting speed on temperature distribution are investigated. The simulation results demonstrate that the temperature distribution shows a roughly concentric shape around shear zone and a steep temperature gradient lies in diamond tool, a relative high temperature is located in shear zone and machined surface, but the highest temperature is found in chip. At a high cutting speed mode, the atoms in shear zone with high temperature implies a large stress is built up in a local region.

Molecular dynamics simulations of thermal effects in nanometric cutting process

The temperature rise of an ultra-precision machine tool has a great impact on machining accuracy. Meanwhile, the hydrostatic spindle system is the main internal heat source of the machine tool, which consists of a hydrostatic spindle and a direct current motor. Therefore, it is very significant to study the thermal behaviors of the hydrostatic spindle system. In this paper, an integrated heat-fluid–solid coupling model of the hydrostatic spindle system is built to simulate the heat generation process and the fluid–structure conjugate heat transfer. Then a finite volume element method (FVEM) is proposed by combining the advantages of the finite volume method (FVM) and the finite element method (FEM) with consideration of the interaction of the temperature field, thermal deformation, and eccentricity. Based on the proposed model and method, the thermal characteristics of the hydrostatic spindle system are studied by the two-way heat-fluid–solid coupling analysis. The temperature variations obtained by the simulation agree well with the experimental results, which validate the proposed model and method.

Thermal analysis of the hydrostatic spindle system by the finite volume element method

This paper presents the design philosophy of an ultra-precision fly cutting machine tool from the machining material properties and the processing requirements points of view. Three configurations of the machine tool are proposed and compared from the aspect of the proposed design philosophy. The design philosophy has been applied to guide the development of the key machine components as well as an experimental prototype. In order to improve the dynamic performances of the machine tool, the influence of the main components on the tool–workpiece structural loop is analyzed, and the weak structural component is optimized. Preliminary machining trials have been carried out. The test results make a further proof and validate that the design philosophy proposed in this article can assure the high performance of the developed ultra-precision fly cutting machine tool for producing large diameter optics.

Design philosophy of an ultra-precision fly cutting machine tool for KDP crystal machining and its implementation on the structure design

The thermal error of an ultra-precision machine tool has a great influence on machining accuracy. In order to improve the machining accuracy, the thermal performance of the machine tool has to be improved. In this paper, the thermal behaviors of a machine tool are studied by the finite volume element method (FVEM) considering the influence of temperature rise, preload forces, contact surfaces, and gravity. Then, a new thermal optimization method is proposed to reduce the thermal error in the designing stage, which is the thermal displacement decomposition and counteraction method. By the thermal displacement decomposition method, the thermal behaviors of each part are studied, and the thermal displacement of the tool nose is decomposed. Meanwhile, the design variables are determined to carry out the thermal optimization of the machine tool. By the thermal displacement counteraction method, the thermal deformations of different parts are counteracted with each other by minimizing the proposed objective function. Finally, the machine tool optimized by the thermal performance is built, and the machining tests are carried out to validate the proposed thermal optimization method.

Lihua Lu

Papers

Aerostatic bearings design and analysis with the application to precision engineering: State-of-the-art and future perspectives

Molecular dynamics simulations of thermal effects in nanometric cutting process

Thermal analysis of the hydrostatic spindle system by the finite volume element method

Design philosophy of an ultra-precision fly cutting machine tool for KDP crystal machining and its implementation on the structure design

Thermal optimization of an ultra-precision machine tool by the thermal displacement decomposition and counteraction method