In this paper, the use of the combined deterministic-stochastic subspace identification algorithm for the experimental modal analysis of mechanical structures is discussed. The algorithm requires artificial forces to be applied to the structure, so it can be used for experimental modal analysis (EMA). The algorithm can also be used for operational modal analysis (OMA), since the excitation level of the artificial force(s) can be low compared to the excitation level of the ambient forces. Both the modes that are artificially excited and those that are excited by the ambient forces are identified. This type of operational modal analysis is called an OMAX analysis (Operational Modal Analysis with eXogenous inputs) [1]. The main advantages of OMAX over OMA are that the modes that are excited by the artificial forces can be scaled to unity modal mass and that a higher number of modes can be identified.

Reference-based combined deterministic-stochastic subspace identification for experimental and operational modal analysis

Suspension components play key roles in the running behaviour of rail vehicles, and therefore, mathematical models of suspension components are essential ingredients of railway vehicle multi-body models. The aims of this paper are to review existing models for railway vehicle suspension components and their use for railway vehicle dynamics multi-body simulations, to describe how model parameters can be defined and to discuss the required level of detail of component models in view of the accuracy expected from the overall simulation model. This paper also addresses track models in use for railway vehicle dynamics simulations, recognising their relevance as an indispensable component of the system simulation model. Finally, this paper reviews methods presently in use for the checking and validation of the simulation model.

Modelling of suspension components in a rail vehicle dynamics context

Consideration of nonlinear wheel–rail contact forces for dynamic vehicle–bridge interaction in high-speed railways

This paper presents an investigation of dynamic interaction of long suspension bridges with running trains. A three-dimensional finite element model is used to represent a long suspension bridge. Each 4-axle vehicle in a train is modelled by a 27-degrees-of-freedom dynamic system. The dynamic interaction between the bridge and train is realized through the contact forces between the wheels and track. By applying a mode superposition technique to the bridge only and taking the measured track irregularities as known quantities, the number of degrees of freedom (d.o.f.) the bridge-train system is significantly reduced and the coupled equations of motion are efficiently solved. The proposed formulation and the associated computer program are then applied to a real long suspension bridge carrying a railway within the bridge deck. The dynamic response of the bridge-train system and the derail and offload factors related to the running safety of the train are computed. The results show that the formulation presented in this paper can well predict dynamic behaviors of both bridge and train with reasonable computation efforts. Dynamic interaction between the long suspension bridge and train is not significant.

Dynamic interaction of long suspension bridges with running trains

Rail vehicle dynamic simulation has progressed a long way from its origins as a research tool. Modern multibody software packages are used as an essential part of the design process for new vehicle ...

Challenges in simulation of rail vehicle dynamics

In recent years, different systems have been developed in order to improve the dynamic behaviour of railway vehicles when passing through turnouts. Some of these improvements consist in varying the...

Rail vehicle passing through a turnout: analysis of different turnout designs and wheel profiles

Constitutive Models for Rubber VIII

In this paper, a method of introducing falling friction coefficients into curving simulations for studying curve squeal noise is presented. Generation of squeal at the wheel of a railway vehicle in a curve is caused by unstable vibration, caused in turn by a lateral wheel/rail force which reduces with increasing lateral creepage. To model vehicle curve squeal, the wheel/rail tangential force in the curving simulation is calculated by a modified version of FASTSIM, which uses a sliding velocity-dependent friction characteristic. Using the falling friction characteristics, a UK passenger vehicle is modelled with SIMPACK. Curving behaviour is simulated for a range of curve radii and cant deficiencies. The wheel/rail contact properties are then obtained to study the possibility of the occurrence of squeal using a frequency-domain method. The methodology in this paper allows various curves, wheel/rail profiles, vehicle speeds and friction characteristics to be taken into account.

Introduction of falling friction coefficients into curving calculations for studying curve squeal noise

This paper deals with the solution of the non-steady state wheel-rail contact problem. Firstly, the existing models are analysed and it is concluded that none of them have the computational efficiency and/or accuracy characteristics required to be used in a railway simulation programme. Following this, a new solution is proposed to the problem that allows obtaining sufficiently accurate results with a relatively low computational cost. During the development of the proposed method it has been assumed that only one type of creepage is variable with respect to the time. Further work is necessary to extend it to more general cases.

Non-steady state modelling of wheel-rail contact problem for the dynamic simulation of railway vehicles

This article deals with the application of the FastSim algorithm to the solution of the tangential contact problem for non-elliptical contact areas. At first, the causes creating problems for the solution of non-hertzian contact areas with this algorithm shall be analyzed. Then, different currently existing methods shall be studied, analyzing their accuracy characteristics and computational cost to determine whether or not they are appropriate to use in dynamic simulations. Finally, a new strategy shall be proposed that, in the opinion of the authors, offers good characteristics of precision and computational cost.

Asier Alonso

Papers

Rail vehicle passing through a turnout: analysis of different turnout designs and wheel profiles

Constitutive Models for Rubber VIII

Introduction of falling friction coefficients into curving calculations for studying curve squeal noise

Non-steady state modelling of wheel-rail contact problem for the dynamic simulation of railway vehicles

Tangential problem solution for non-elliptical contact areas with the FastSim algorithm