Fujie Xia

An inverse railway wagon model and its applications

An inverse wagon model was developed to estimate wheel–rail contact forces using only measurements of wagon body responses as inputs. The purpose of this work was to provide mathematical modelling to embed in low-cost devices that can be mounted on each freight wagon in a large wagon fleet. To minimize cost, complication, and the maintenance inconvenience of these devices, the constraint is imposed that transducers and connections are limited to locations on the wagon body. Inputs to the inverse model developed include only vertical and lateral translational accelerations and angular accelerations of roll, pitch, and yaw of the wagon body. The model combines the integration and partial modal matrix (PMM) techniques together to form an IPMM method. Besides wheel–rail contact forces some motion quantities such as the lateral and yaw displacements of wheelset are also predicted. Results from the inverse model were compared with data from full scale laboratory suspension tests for vertical suspension excitations. The inverse model was also compared with results from simulations completed in VAMPIRE® for more complicated track input profiles. The model results and the applications of the model are discussed.

Grey box-based inverse wagon model to predict wheel–rail contact forces from measured wagon body responses

A grey box-based inverse wagon model was developed to estimate wheel–rail contact forces using only measurements of wagon body responses as inputs. The project is based on a similar application using a deterministic inverse wagon model [F. Xia, C. Cole, and P. Wolfs, An inverse railway wagon model and its applications, Veh. Syst. Dyn. 45 (6) (2007), pp. 583–605]. The deterministic (i.e. white box) inverse wagon model has some limitations, one of which is that the high-frequency components of the forces at the wheel–rail interface cannot be predicted from the lower frequencies at the wagon body. They are effectively isolated by the suspension. To overcome this problem, the present research focuses on developing of a grey box-based inverse wagon. The high-frequency forces may be considered as the responses to random track irregularities with high frequency and appear as a random feature. The grey box-based inverse wagon is used to predict wheel–rail contact forces using only lateral and vertical accelerations, roll, pitch and yaw angular velocities measured on the wagon body.

A Method for Setting Wagon Speed Restrictions Based on Wagon Responses

This article presents a method to set wagon speed restrictions based on wagon body accelerations. For the specific locomotive, wagon conditions and track states, an individual wagon critical speed may be determined from its running stability. Furthermore, stability can be evaluated by a wheelset derailment index, which is determined by the ratio of lateral and vertical wheel–rail contact forces. Providing the information on the critical speed online has, without doubt, significant industrial application potentials. The research efforts in this article are focused on the estimation of wheel–rail contact forces using measured wagon body accelerations.

On the Motion of the Structure Varying Multibody Systems with Two-Dimensional Dry Friction

In the present paper the dynamics of the structure varying multibody systems caused by stick-slip motion with two-dimensional dry friction are analyzed. The methods to determine friction force both in stick and slip states are described. The direct method of considering the wagon bogie system as a structure varying system was used to consider two dimensional friction at the wheelset-side frame connection. The concept of friction direction angle used to determine the friction force components of two-dimensional dry friction both in the stick and slip motion states was used. A speed depended friction coefficient was used and described approximately by hyperbolic secant function. All switch conditions were derived and friction forces both for stick and slip states. Some simulation results are provided.

The effects of the friction between frame and adapters on the performance of three-piece truck

For the traditional three-piece truck there is no primary suspension and the connection between side frame and adapter (wheelset) is via direct contact with two-dimensional dry friction on the contact surfaces. The dry friction has two modes: stick and slip motion. Knowledge of the friction on the adapter surface is useful as it affects the wagon dynamic performance on both straight and curved track. In this paper we developed a friction element which can be used to describe two-dimensional dry friction with stick-slip modes. Static and kinematic friction coefficients can be used. The successfully implemented this new friction element in a complete wagon model. The model also includes two-dimensional friction on the surfaces of friction wedge dampers in the secondary suspension. Various friction coefficients are selected for the side frame/adapter contact and the dynamic performance of wagon on straight and curved track is investigated