Effect of Track Irregularities on the Response of Two-Way Railway Tracks

In predicting the response of track from a moving train only one track is generally considered. However, the effect of ground vibrations from one track and its effect on the nearby tracks has not been studied completely. Therefore, in the present paper, the effect of track irregularities and speed on the prediction of two-way tracks response is investigated. For this purpose, a three-dimensional dynamic finite element (FE) model capable of simulating interactions between the train and track by using a nonlinear hertz contact method was developed. The model uses tensionless stiffness between the wheel and rail to couple them. The model components including the sleeper, ballast, and soil domain are represented by solid brick elements. The rails are modeled as 3D Euler–Bernoulli beam elements. An iterative numerical algorithm was established for the integrations of the train and track interface. A comparative analysis was performed at various speeds and rail surface irregularity wavelengths. With the increase in speed, the results showed a significant increase in the adjacent tracks response and can induce much larger track vibrations at high frequency.

A Representativeness Assessment of the Angell–Korshover 63-Station Network Sampling Based on Reanalysis Temperature Data

Global climate observations from ground stations require an evaluation of the effectiveness of a station network, which is often an assessment of the geometric distribution of [Formula: see text] points on a sphere. The representativeness of the Angell–Korshover 63-station network (AK-network) is assessed in this paper. It is shown that AK-network can effectively sample the January global average temperature data of the NCEP/NCAR Reanalysis from 1948 to 2015 when estimating inter-decadal variations, but it has large uncertainties for estimating linear trends. This paper describes a method for the assessment, and also includes an iterative numerical algorithm used to search for the locations of 63 uniformly distributed stations, named U63. The results of AK-63 and U63 are compared. The Appendix explains a problem of searching for the optimal distribution of [Formula: see text] points on a unit sphere in three-dimensional space under the condition of the maximum sum of the mutual distances among the points. The core R code for finding U63 is included. The R code can generate various interesting configurations for different [Formula: see text], among which one is particularly surprising: The configuration of 20 points is not a dodecahedron although the configurations for [Formula: see text], and 12 are tetrahedron, octahedron, cube, and icosahedron, respectively.

An iterative scheme for axisymmetric supercavitating flow

This article presents a numerical investigation of axisymmetric supercavitating flow. It is assumed that such a flow field could be estimated by a potential flow that neglects the viscosity effects and rotational motion of the fluid and assumes the flow as an irrotational flow field. One of the most adequate methods for modelling potential fields is the boundary element method, which is employed in this article. A novel iterative scheme is used to capture the free surface of an axisymmetric supercavity. This numerical algorithm is based on updating an initial guess for the cavity's boundary; the convergence criterion is the pressure amount on the free surface of the cavity, which converges to a constant value. To obtain finite lengths for supercavities, a cavity closure model is applied. The results are in good agreement with similar analytical and numerical solutions as well as the existing experimental data for supercavities characteristic properties and the drag coefficient on cavitators. The present iterative numerical algorithm is reliable for predicting the characteristics of a supercavitating flow. Moreover, the feasibility of the cavity capturing in a flow field with low cavitation number is especially attractive.

Computer Aided Synthesis of Rational Motion Under Kinematic Constraints of Spatial SS Open Chains

In this paper, we study the problem of rational motion interpolation under kinematic constraints of spatial SS open chains. The objective is to synthesize a smooth rational motion that interpolates a given set of end effector positions and satisfies the kinematic constraints imposed by spatial SS open chains. The kinematic constraints under consideration define a constraint manifold representing all the positions available to the end effector. By choosing dual quaternion representation for the displacement of the end effector, the problem is reduced to designing a smooth curve in the space of dual quaternions that is constrained to lie inside the constraint manifold of the spatial SS open chain. An iterative numerical algorithm is presented that solves this problem effectively. The results presented in this paper are extension of our previous work on the synthesis of piecewise rational planar and spherical motions for open and closed chains under kinematic constraints.