This paper studies the roughness effect combining with effects of rarefaction and compressibility by a lattice Boltzmann model for rarefied gas flows at high Knudsen numbers. By discussing the effect of the tangential momentum accommodation coefficient on the rough boundary condition, the lattice Boltzmann simulations of nitrogen and helium flows are performed in a two-dimensional microchannel with rough boundaries. The surface roughness effects in the microchannel on the velocity field, the mass flow rate and the friction coefficient are studied and analysed. Numerical results for the two gases in micro scale show different characteristics from macroscopic flows and demonstrate the feasibility of the lattice Boltzmann model in rarefied gas dynamics.
Quasicontinuum simulations were performed to study the processes of incipient plastic deformation on three FCC metals (Ag,Ni and Pd) under the action of a rigid indenter.Four widths (9.3,18.6,27.9 and 37.2 ) of the indenters were modelled for each metal specimen.A series of load-displacement responses and the strain energy versus displacement responses of the indenter were presented.It is shown that the abrupt drop of the load in the load-displacement response is triggered by the nucleation of dislocations in the metals.The critical load of each metal specimen increases with the increase of the indenter width,while the hardness of the metal specimen decreases as the indenter width increases.Furthermore,the microscopic mechanism of deformation in the films was analyzed.Two dislocations are nucleated respectively beneath the right and left sides of the indenter.Each dislocation successively decomposes into two Shockley partial dislocations after the first nucleation process.The distances between the two partial dislocations are equal for both sides of the indenter,which are in agreement with the theoretical values.
