Numerical analysis of confinement effect on crack propagation mechanism from a flaw in a pre-cracked rock under compression

In many situations rocks are subjected to biaxial loading and the failure process is controlled by the lateral confinement stresses. The importance of confinement stresses has been recognized in the literature by many researchers, in particular, its influence on strength and on the angle of fracture, but still there is not a clear description for the influence of confining stress on the crack propagation mechanism of rocks. This paper presents a numerical pro- cedure for the analysis of crack propagation in rock-like ma- terials under compressive biaxial loads. Several numerical simulations of biaxial tests on the rock specimen have been carried out by a bonded particle model （BPM） and the influ- ence of confinement on the mechanism of crack propagation from a single flaw in rock specimens is studied. For this purpose, several biaxial compressive tests on rectangular spec- imens under different confinement stresses were modeled in （2 dimensional particle flow code） PFC2D. The results show that wing cracks initiate perpendicular to the flaw and trend toward the direction of major stress, however, when the lat- eral stresses increase, this initiation angle gets wider. Also it is concluded that in addition to the material type, the initiation direction of the secondary cracks depends on confine- ment stresses, too. Besides, it is understood that secondary cracks may be produced from both tensile and shear mechanisms.

A Surface-Simplex Swarm Evolution Algorithm

In the paper,a particle surface-simplex search（PSSS） is designed based on particle surface-simplex and particle surface-simplex neighborhood.Using PSSS and an evolutionary strategy of multi-states swarm,a surface-simplex swarm evolution（SSSE） algorithm for numerical optimization is proposed.In the experiments,SSSE is applied to solve 17 benchmark problems and compared with the other intelligent optimization algorithms.In the application,SSSE is used to analyze the three intrinsic independent components of gravity earth tide.The results demonstrate that SSSE can accurately find optima or close-to-optimal solutions of the complex functions with high-dimension.The performance of SSSE is stable and efficient.

A hybrid multi-objective PSO algorithm with local search strategy for VLSI partitioning

Very large scale integration （VLSI） circuit par- titioning is an important problem in design automation of VLSI chips and multichip systems; it is an NP-hard combi- national optimization problem. In this paper, an effective hy- brid multi-objective partitioning algorithm, based on discrete particle swarm optimzation （DPSO） with local search strat- egy, called MDPSO-LS, is presented to solve the VLSI two- way partitioning with simultaneous cutsize and circuit delay minimization. Inspired by the physics of genetic algorithm, uniform crossover and random two-point exchange operators are designed to avoid the case of generating infeasible so- lutions. Furthermore, the phenotype sharing function of the objective space is applied to circuit partitioning to obtain a better approximation of a true Pareto front, and the theorem of Markov chains is used to prove global convergence. To improve the ability of local exploration, Fiduccia-Matteyses （FM） strategy is also applied to further improve the cutsize of each particle, and a local search strategy for improving circuit delay objective is also designed. Experiments on IS- CAS89 benchmark circuits show that the proposed algorithm is efficient.