Applied Mechanics and Materials Vols. 204-208

Abstract: Wiener series are the important functional series describing nonlinear system. If an input signal is the Gaussian white noise, the wiener kernels are estimated through calculating the cross-correlation functions of the input and output of a nonlinear system. In this paper, a single-DOF quadratic nonlinear system is identified by the Wiener series. The results show that the intensity of the nonlinear response can be expressed by the second-order kernel.

Abstract: We put forward a new specialty blasting method to solve drill-jamming based on stress concentration and stress wave theory. Drill-jamming accident of banji was successfully solved at the early 2006 through this method first: for this drill-jamming, study drilling tools and location of drill-jamming to find the weak position (Fig. 1); produce impact loading and form stress concentration (Fig. 3) at weak position by place well-designed explosive package at special position. Through many times controllable safe explosions and repeatedly impact loading, accurate fracture, separate sinker bar and the above parts from drill bit, this part raised up successfully (Fig. 7). The rest would be taken out after second reaming.

Abstract: In fluid mechanics, to obtain the multiple solutions in ordinary differential equations is always a concerned and difficult problem. In this paper, a novel RNA genetic algorithm (NRNA-GA) inspired by RNA molecular structure and operators is proposed to solve the parameter estimation problems of the multiple solutions in fluid mechanics. This algorithm has improved greatly in precision and the success rate. Multiple solutions can be found through changing accuracy and search coverage and multi-iterations of computer. At last, parameter estimation of the ordinary differential equations with multiple solutions is calculated. We found that the result has great accuracy and this method is practical.

Abstract: Meso-scale simulation is one of the important ways to study dynamic behaviors of concrete materials, while most of the simulation time is used to solve the sparse linear systems. Because the discrete grid is three dimensional and is of large scale, iterations are the best solutions. But the convergence depends on the distribution of the eigenvalues of the coefficient matrix, to make the eigenvalues distributed more closely each other, it is required to adopt preconditioning techniques. In this paper, with the characteristics of the sparse linear systems considered, there provides a coarse grid correction algorithm, which is based on domain decomposition preconditioners and aggregation of sub-domains, with each aggregated into a single super-node. A linear system with small scale size is formed, which contains the global information and the solution is used to correct the solution components of the original auxiliary linear system. For incomplete factorization preconditioner parallelized with block Jacobi, classic additive Schwarz, and factors combination techniques, the experiments show that the presented algorithm can improve the convergence rate and the efficiency.

Abstract: The Fourier analysis is employed to study the effect of non-constant terms on the convergence properties of SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm formulated on a staggered grid in two-dimension. The results indicate the non-constant items can broaden the convergence range of pressure relaxation factor for a given velocity under-relaxation factor. What’s more, the non-constant items do well to the damping of the lowest error and can accelerate the convergence rate.

Abstract: A high accuracy non-contact laser displacement measuring system is developed to obtain the surface deformation of the ice-like material. A speed measurement and positioning system is established for the moving air cushion load. The mechanical properties of the ice-like material and the pressure distribution of air cushion load are measured. Under different air cushion load and different speed, a series of experiments of the deformation of ice-like material are carried out in towing channel which the depth of water is variable. The maximum deformation of ice-like material can be caused when air cushion load moves at critical speed, and the ice-water resonance mechanism of ice-breaking by air cushion is revealed, which provides the basis of ice-breaking for practical air cushion vehicle.

Abstract: Abstract. On the basis of the nonlinear plate-shell and piezoelectric theory, the governing equations of motion for axisymmetrical piezoelectric delaminated cylindrical shell under hygrothermal conditions were derived. The governing equation of transverse motion was modified by contact force and thus the penetration between two delaminated layers could be avoided. The whole problem was resolved by using the finite difference method. In calculation examples, the effects of delamination length, depth and amplitude of load on the nonlinear dynamic response of the axisymmetrical piezoelectric delaminated shell under hygrothermal conditions were discussed in detail.

Abstract: The yield strength-to-tensile stress ratio (fy/fu) is considered to be an important material factor in the design of welded tubular joints. For instance CIDECT (2008) has set a limitation on fy of 0.8fu and for steels with nominal fy greater than 355Mpa and a reduction factor of 0.9 on all joint strength formulae to account for the relatively larger deformations that take place for joints with nominal fy of 450Mpa[1]. In this study a statistical analysis of an experimental database was carried in order to determine the influence of the chord fy/fu ratio on joint strength. A finite element study was also carried out in order to quantify this influence and a yield strength function was proposed. Results from the statistical analysis and finite element study both show that the static strength of unstiffened circular hollow section (CHS) K-gap joints under static axial loading is inversely proportional to the chord fy/fu ratio.

Abstract: In this paper, nonlinear forced vibration analysis for thin rectangular plate with four free edges on nonlinear elastic foundation is researched. Based on Hamilton variation principle, the equations of nonlinear vibration motion for the thin rectangular plate under period loads on nonlinear elastic foundation are established. In the case of four free edges, the suitable expressions of trial functions satisfied all boundary conditions for the problem are proposed. Then, we convert the equations to a system of nonlinear algebraic equations by using Galerkin method and they are solved by using harmonic balance method. In the analysis of numerical computations, the effect to the amplitude-frequency characteristic curve which due to change of the structural parameters of plate、the parameters of foundation and the parameters of excitation force are discussed.

Abstract: Deepwater risers play an important role in the exploration and production of oil and gas. Research of deepwater risers’ installation is so important in the field. This paper proposed a riser FEM models by commercial software ABAQUS, and then, the calculation result is analyzed and main conclusion are obtained.