Key Engineering Materials Vols. 306-308

Abstract: Ultra-precision positioning systems basically require high natural frequency and sufficient workspace. To cope with this requirement, flexure hinge mechanisms have been proposed. However, previous designs have difficulty satisfying the functional requirements of the system due to problems in the modeling and optimization process since they are coupled. Therefore, this paper performs optimum design of a planar 3-D ultra-precision positioning mechanism using a booster based on axiomatic design. Based on preliminary kinematic analysis and dynamic modeling of the system, an optimum design is conducted. To examine the effectiveness of the optimal parameters obtained by a theoretical approach, a simulation is performed by FEM. The simulation result shows that a natural frequency of 200.53Hz and a workspace of 200 μm x 200 μm can be ensured, which is in very close agreement with the specified goal of design.

Abstract: This paper present an analysis of the mechanics characters of a safety structure with steel liner under near blasting load, by the methods of numerical study. Through the ANSYS/LS-DYNA numerical analysis, we get the reasonable thickness and position location of steel. This paper put forward the curve of the steel at different thickness and position in the safety structure, that provide a reference to the designing of the safety structures and other relevant project.

Abstract: A shape design optimization of the boom system in high ladder vehicle modeled by 3-dimensional finite elements is carried out. The structural analysis is performed using 3-D FEA (Finite Element Analysis) giving the results of displacements, stresses and natural frequencies. The section height and width of the boom is controlled by the FEA result data. The subproblem approximation method is implemented for the optimal shape based on displacement and principal stress. In the meantime, Lanzcos algorithm method is implemented in order to find the natural frequency of the system. The optimal models obtained by three different optimization processes are compared with the initial model and evaluated for economic conditions respectively. It is found that the different shape optimization processes give the different shape optimization results, which suggest their unique optimal shapes under their necessary design condition.

Abstract: In this paper, a new Riemann-solver-free class of difference schemes are constructed to scalar nonlinear hyperbolic conservation laws in the three dimension (3D). We proved that these schemes had second order accuracy in space and time, and satisfied maximum principles (marked as MPs) under an appropriate CFL condition. This results in a second-order accuracy, MP schemes a natural extension of the one (two)-dimensional second-order. In addition, these schemes can still be extended to the vector system of conservation law. We yet prove that these schemes satisfied the scalar and vector maximum principle, and in the more general context of systems.

Abstract: The dynamic nature of marine environment is the major cause of fatigue failures in subsea gas pipeline structures. Since the severest loaded part of piping system is the free span, freespan inspection is performed periodically to ensure that no free span exceeds its critical length. The objective of this paper is to optimize free-span inspection interval by means of probabilistic fracture mechanics analysis. Simulation data is taken from previous work of Tronskar [1]. Stress intensity factors at the crack tip are calculated by crack closure technique. Fatigue crack growth is simulated by cycle-by-cycle integration technique. The fracture mechanics analysis is then expanded to probabilistic analysis to include stochastic input parameters. Probability of failure is computed by modified direct simulation method. Based on the result of direct simulation, the studied pipelines are recommended to be inspected every 3 years to make sure that no free span exceeds 30 m.

Abstract: SPH (Smoothed Particle Hydrodynamics) method is applied to impact crush/buckling problem of circular tube. It has been known that there are several kinds of buckling modes by axial impact load. First, elastic analyses of the crush/buckling are conducted, and three types of typical crush/buckling shape are obtained. Following the elastic analyses, elastic-plastic analyses were performed to improve the accuracy of the simulation. The shape of the buckling and the energy absorbed by circular tube are discussed.

Abstract: In order to solve the problem of web buckling for hot rolled I-beams without membrane subjected to concentrated load, a plastic mechanism analysis that involves consideration of the plastic hinges developing in the flanges and the yield lines forming in the web plate have been made, and a simple theoretical prediction of collapse loads have been developed. At the same time, wide ranges of finite element studies have been made. Based on the finite element results, certain approximations and empirical modifications are introduced because of the complex geometrical nature of the problem and the purpose to make the resulting design method simple enough for routine practical application. The theoretical results have been compared, and show close correlation, with the finite element results.

Abstract: To minimize the geometric error made in ground surface, the optimization of grinding parameters is essential. This paper focused on the parameter optimization of the surface grinding process based on Taguchi and response surface methods for minimizing the geometric error. Firstly, the effect of grinding parameters on the geometric error was evaluated and optimum grinding conditions were determined. Then, a second-order response model for predicting the geometric error was developed and the validation of the response surface model was examined with industrial constraints such as the surface roughness and the material removal rate. Finally, experimental verification was conducted at an optimal condition and two selected conditions to see accuracy of the developed response surface model.

Abstract: The main objective of this paper is to propose the buckling equations of the sea sheets under concentrated forces. Two different cases of the acting forces are considered in this paper and the buckling equations of them are deprived, respectively. Then, the dimensionless forms of these equations are given. Furthermore, by adopting a numerical method, two cases of different thickness of the ice sheet and different distances between sea structures are explored. On the basis of the buckling equations, the expressions of the critical load between sea ice and sea structures are obtained. Finally, the relationship between the critical load factor and the dimensionless radius are presented

Abstract: The formulation and implementation of three-dimensional element free Galerkin method (3D EFG) are developed. A simple and efficient scheme for a variable domain of influence stipulates that a constant number of nodal points are visible from each integration location is proposed. This method significantly increases the efficiency of the variable domain of influence by limiting the size of the least-square problem that is solved when computing approximate functions. The 3D EFG methods based on moving least square method use only nodal points to built local and global approximation. Discrete model of the 3D EFG for three-dimensional elastic problems is derived by least potential energy principle. Reference to the 2D EFG, in the 3D EFG, it is enforced to meet displacements boundary conditions by use of limiting nodal point number method and penalty method. The stress concentration of a small column-shaped cavity in a cube subjected to uniaxial uniform tension at two opposing faces in far field. Compared the approximation solutions with theory ones, the results indicate that the 3D EFG is validity in solving three-dimensional elastic problems and the limiting nodal point number method is validity.