The dynamic analysis of multibody systems is carried out in this paper based on Gauss constraint principle, for a family of multibody open loop chain structures. Gauss constraint method is used to derive the dynamic equation of multibody chain structures, in a symbolic derivation process, and the analytic expressions of the dynamic equation are obtained in closed form. By taking the rigid and flexible structures as examples, the time used for symbolic derivation of dynamic equations is analyzed for different analysis methods and degrees of freedom. It is shown that Gauss constraint method is more suitable for symbolic derivation of dynamic equations of multibody structures compared with Lagrange's method. Furthermore, the calculation advantage of Gauss constraint method increases with the increase of degrees of freedom.
The fatigue behavior of Low alloy steel in air and corrosion medium was studied by the fatigue tests. The S-N curves were obtained and the observations of flat surfaces and fatigue fractographs have been made. The results showed that the fatigue strength of Low alloy steel in corrosion medium was much lower than that in air. Fatigue cracks in air were initiated from the matrix of surface, while most of fatigue cracks in corrosion medium were initiated from pits. The typical feature of the fatigue crack propagation region in air was fatigue striations, while that in corrosion medium was intergranular crack characteristic. The fatigue limit in air could be predicted by empirical equation. The predicted fatigue limit was agreeable to the experimental fatigue limit.
The transport of different petroleum products through a single pipeline is known as batch transfer, which is the most common method in product transportation. A certain amount of mixing between products is called interface contamination. In order to ensure the quality of the products being transported, the mixing volume and the position of the mixing zone should be accurately predicted. This paper estimates the mixing volumes by using a two-dimensional model of convection-diffusion equation, which is solved by a two step method to obtain numerical solutions in laminar flow and turbulent flow, as a comparatively effective method. The results show that the mixing volume in turbulent flow is smaller than that in laminar flow, the distribution of the mean concentration in the cross section changes with time, and the diffusion coefficient influences the mixing volume in turbulent flow.
The meshless method for unsteady flow involving large-scale moving boundaries is studied in this paper. A criterion for whether the point is to be deleted is established, the cloud is rebuilt by a filling method, and the state of the new point is calculated by a linear interpolation method, which serves as the local reestablishment of cloud for dealing with large scale moving points. The algorithm for solving ALE equations based on the meshless method is developed. On the basis of clouds, the spatial derivatives are approximated by using local least-squares curve fitting and the numerical flux is calculated with HLLC scheme, and a multistage Runge-Kutta algorithm is used to advance the equation in time. As an example, a moving piston is simulated, and the numerical results agree well with exact results. In addition, the flow of airflow passing through a static column and the flow of a column moving in the static flow are simulated and compared with each other, and results indicate that the method is valid.