Olivier Chiello

Propagation of vibrations due to a tramway line

Tramway traffic may produce vibrations propagating in soil leading to vibration annoyance for people living or working in neighbouring buildings. Thus vibration is an important parameter to be considered when planning new lines and dynamic performance evaluation of tramway tracks is necessary to validate or modify the existing means that reduce vibrations. This paper presents experimental and theoretical investigations of vibrations caused by tramway passages in Nantes, France. It focuses on the control of ground-borne vibrations for the whole system, taking into account important elements such as the dynamic vehicle characteristics, the track and the soil behaviour. A complete track-soil-ground model is proposed to predict ground-borne vibrations, so as to estimate a trouble gauge concerning - for example - the impact of a future tramway line.

Squeal noise generated by railway disc brakes: Experiments and stability computations on large industrial models

The squeal noise generated by railway disk brakes is an everyday source of discomfort for the passengers both inside and outside the trains in stations. The development of silent brake components is needed and requires a better characterisation and understanding of the phenomenon. This is the aim of the experimental and numerical investigations performed in the framework of the French AcouFren project and presented in this paper. The first part deals with the analysis of experimental data coming from bench tests in a lot of braking configurations including different brake pads. In the second part, the measurements are compared with the results of a large FE model of the brake taking into account the mechanical complexity of each component, especially the brake pads. Components models have been previously updated using experimental modal analysis but the whole model is a direct assembling of it, without updating. The assumption of unilateral contact and Coulomb friction at the pad/disc interface is sufficient to destabilize the sliding equilibrium of the brake and lead to self-sustained vibrations. Complex vibrating modes are computed in order to describe and understand the dynamic instabilities.

Numerical investigations into the squeal propensity of a railway disc brake

This paper comes within the scope of a research program concerning with the reduction of the squeal noise generated by high power railway disc brakes. It focuses on the numerical results provided by a finite element model of the brake including unilateral contact and Coulomb friction at the disc/pad interfaces. In particular, the dynamic stability of the sliding equilibrium is investigated by performing a complex eigenvalue analysis of the linearized equations verified by the structural displacement fields. Complex eigenvalues and complex modes are used to estimate the squeal propensity of the brake in a given frequency range. The effect of various mechanical and geometrical parameters is studied in order to better understand the mechanism leading to the system instability.

Dynamic wheel/rail forces induced by trams at low frequencies

This work is part of various experimental and theoretical investigations into the noise and the vibrations caused by trams in Nantes, France. It focuses on the problem of the low frequency vibrations induced in the track and the ground and particularly on the excitation mechanism at the wheel/rail interface. In order to estimate the corresponding dynamic wheel/rail forces, axle‐box vibrations have been measured on a carrying bogie in various vehicle and track configurations. Additionally, a specific instrument has been used to measure the rail unevenness at large wavelengths likely to excite the vehicle/track system in the low frequency range. Finally, the vertical receptance of the different tracks has been measured by using an impact hammer. In the paper, all these experimental results are presented and the validity of a simple vehicle/track interaction model is discussed.

A modal synthesis approach to investigate the influence of viscoelastic boundary conditions on the sound radiated from a plate backed cavity

In this paper an efficient formulation is proposed to calculate the sound radiation from a plate with edges viscoelastically restrained against translation and rotation and coupled to a cavity. The viscoelastic constants can be varied arbitrarily along the plate boundary and reproduce simply supported, clamped, free or guided edges as limiting cases. The formulation classically couples a modal expansion for the structure in vacuo and the cavity, using a coordinate transformation to calculate the fluid‐structure coupled modes. The modal basis associated with the structure in vacuo is determined using a free component mode synthesis technique considering the viscoelastic parameters as components with a residual flexibility only. This approach is appropriate to compute the coupled modes efficiently and to perform a parameter study. Numerical examples are presented in the case of a plate excited either mechanically or acoustically. The aim of the study is to determine which boundary parameters have an influen...

Experimental identification of mechanical joint dynamic properties

Large structures are often composed of substructures connected through mechanical joints. The dynamic behavior of these joints is generally difficult to characterize. In this paper, a method for identifying dynamic joint characteristics is presented. Joint properties are extracted directly from measured frequency responses of the assembled structure. Measurement points are not taken on the interface between the structure components. This feature is of practical importance since it is often difficult to directly attach a transducer on the joint. The method only requires the knowledge of the frequency responses of the substructures taken separately. These responses can be either measured, analytically calculated, or simulated by FEM. The presented approach allows for the determination of the joint properties as a function of frequency. The joint properties extracted from one assembled structure can be used to predict the behavior of another structure assembled with the same joint condition. The applicabilit...