Wolfgang Kropp

STRUCTURE-BORNE SOUND ON A SMOOTH TYRE

Abstract The vibration behaviour of tyres is the link between noise-generating mechanisms and radiated tyre noise. Although the problem has often been discussed, this paper goes more deeply into several aspects of the vibration of unloaded smooth tyres. Measurements on a stationary tyre are compared with a two-dimensional model, called the circular ring model. The characteristics discussed in this text are phase velocity and damping of waves along the circumference. The point admittance, measured in the radial direction, is compared with results which are calculated using the theoretical model. The influence of the area on which the force operates is analysed with respect to the admittance. It will be shown that the ‘local stiffness’ is of importance for noise-generating mechanisms such as roughness excitation and friction.

The modelling of the dynamic behaviour of tyre tread blocks

Abstract The interaction between tyre and road constitutes the dominant noise source for road vehicles at speeds above 50 km/h. The understanding and control of tyre/road noise generation mechanisms is still one of the main challenges in the field of acoustics, covering a wide area of topics, such as the structure-borne sound properties of tyres, the non-linear contact between tyre and road and the sound radiation from vibrating tyres. The work presented here only covers a small part of this complex field, the modelling of the tread blocks in order to incorporate the dynamic behaviour into a simulation model for a rolling tyre on a rough road. A finite element model is made for individual blocks in order to investigate their first eigenfrequencies and mode shapes. This information is used to build an equivalent model consisting of a simple mass and springs. The equivalent model has the advantage of being handier when coupling to a model of the tyre structure. The impedance coupling method is used. The results of the driving point mobility in the radial and tangential directions to the surface of the block are compared with measurements on tyres. The results show good agreement for the radial direction, while for the tangential direction, the agreement is poor. This is mainly due to the fact that the model for the tyre structure does not include in-plane motion. The results also show that, for the frequency range up to 3 kHz, the influence of the blocks depends strongly on their geometry. The geometry of the tread blocks determines the contact geometry as a kind of macro roughness. It also determines the eigenfrequencies, which for typical tread blocks are expected to be situated, at least, in the range above 2000 Hz.

Tyre/road noise prediction: A comparison between the SPERoN and HyRoNE models ‐ Part 1

The SPERoN and HyRoNE models predict the pass‐by tyre/road noise of a passenger car from intrinsic characteristics of the road surface. Both models are hybrid: they combine statistical laws with physical models. With a computing time of a few minutes (very quick compared to full physical models), they provide operational tools for tyre/road noise prediction. Particular fields of interest are road surface optimisation with respect to noise at the laboratory scale, conformity of production of a new surface and acoustic monitoring of roads. They are now implemented as user‐friendly stand‐alone applications. The presentation will address the principles of the models, their performances and their respective main fields of application. Part 1 will address the principles of the models and their respective fields of application.

City traffic noise - a local or global problem?

According to the EU Green Paper on Noise policy, approx. 20% of the EU population is exposed to outdoor noise levels exceeding 65 dB (equivalent A-weighted daytime levels) and a little more than 40% is exposed to levels between 55 and 65 dB. The main source is then city traffic noise caused by cars, trucks, buses, trams, and trains. The situation in other industrialised countries is very much similar. This actual situation should be compared to the longterm goal for maximum noise exposure of the citizens. These goals are in most cases formulated as outdoor equivalent levels; in some cases as 24 hour levels, in others in separate daytime and nighttime levels. In several countries in Europe the goal implies 24 hour levels of the order LAeq<55 dB. This corresponds to a situation where a substantial fraction of the population is judged to be annoyed or seriously annoyed by the noise. To achieve this goal, it is demanded to accomplish a typical noise reduction of the order of 10 dB or more. For dwellings facing main roads the necessary noise reduction is of the order 20 dB. For the covering abstract see IRRD E104312.

A fast time‐domain model for wheel/rail interaction demonstrated for the case of impact forces caused by wheel flats

The prediction of impact forces caused by wheel flats requires the application of time‐domain models that are generally more computationally demanding than are frequency‐domain models. In this paper, a fast time‐domain model is presented to simulate the dynamic interaction between wheel and rail, taking into account the non‐linear processes in the contact zone. Track and wheel are described as linear systems using impulse‐response functions that can be precalculated. The contact zone is modelled by non‐linear contact springs, allowing for loss of contact. This general model enables the calculation of the vertical contact forces generated by any kind of roughness excitation between wheel and rail. Here, the model is adapted to the excitation caused by wheel flats by introducing the irregular wheel shape as a form of extreme roughness. A brief parameter study is presented to demonstrate the functioning of the model. The results from the model are discussed and compared with results from literature.

Modelling of railway curve squeal including effects of wheel rotation

Railway vehicles negotiating tight curves may emit an intense high-pitch noise. The underlying mechanisms of this squeal noise are still a subject of research. Simulation models are complex since they have to consider the non-linear, transient and high-frequency interaction between wheel and rail. Often simplified models are used for wheel and rail to reduce computational effort, which involves the risk of over-simplifications. This paper focuses on the importance to include a rotating wheel instead of a stationary wheel in the simulation models. Two formulations for a rotating wheel are implemented in a previously published wheel/rail interaction model: a realistic model based on an Eulerian modal coordinate approach and a simplified model based on a rotating load and moving Green’s functions. The simulation results for different friction coefficients and values of lateral creepage are compared with results obtained for the stationary wheel. Both approaches for the rotating wheel give almost identical results for the rolling speed considered. Furthermore, it can be concluded that a model of a stationary flexible wheel is sufficient for both capturing the tendency to squeal and predicting the resulting wheel/rail contact forces.

Towards an engineering model for curve squeal

Curve squeal is a strong tonal noise that may arise when a railway vehicle negotiates a curve. The wheel/rail contact model is the central part of prediction models, describing the frictional instability occurring in the contact during squeal. A previously developed time-domain squeal model considers the wheel and rail dynamics, and the wheel/rail contact is solved using Kalker’s nonlinear transient CONTACT algorithm with Coulomb friction. In this paper, contact models with different degree of simplification are compared to CONTACT within the previously developed squeal model in order to determine a suitable contact algorithm for an engineering curve squeal model. Kalker’s steady-state FASTSIM is evaluated, and, without further modification, shows unsatisfying results. An alternative transient single-point contact algorithm named SPOINT is formulated with the friction model derived from CONTACT. Compared to the original model results, the SPOINT implementation results are promising and similar to results from CONTACT.

A Time Domain Model for Wheel/Rail Interaction Aiming to Include Non-linear Contact Stiffness and Tangential Friction

A time domain model is presented for the dynamic interaction between a railway wheel and rail, which takes into account the non-linear processes in the contact zone and aims at predicting both normal and tangential contact forces. The model follows an approach that has been used successfully, for instance for the modelling of the interaction between road and tyre. Track and wheel are described as linear systems by the means of impulse response functions. The contact zone is modelled by non-linear contact springs with stiffnesses depending on the roughness of rail and wheel. Here, the method of the area of real contact is applied in order to obtain the required spring characteristics. For the tangential contact, a characteristic function for the friction coefficient is applied. In a first stage, the approach is demonstrated for the calculation of normal contact forces. For validation, the results from the model are compared with an existing time domain model that itself has been validated by field testing. Very good agreement is found for different types of roughness excitation.

A time-domain model for coupled vertical and tangential wheel/rail interaction - a contribution to the modelling of curve squeal

Lateral forces due to frictional instability are seen as the main reason for the occurrence of curve squeal. Predicting squeal requires thus to describe the high-frequency wheel/rail interaction during curving including the coupling between vertical and lateral directions. In this article, a time-domain approach is presented which includes both vertical and lateral forces and takes into account the non-linear processes in the contact zone. Track and wheel are described as linear systems using pre-calculated impulse response functions. The non-linear, non-steady state contact model is based on an influence function method for the elastic half-space, includes a velocity-dependent friction coefficient and accounts for surface roughness. First results from the interaction model demonstrate the functioning of the approach.

Modeling of tangential contact forces

The main noise source from vehicles at speeds greater than 50 km/h is the tires. To reduce traffic noise it is therefore necessary to understand the noise generation mechanisms in the contact between tire and road. The paper presents an improvement of an earlier developed acoustic rolling model concerning a smooth tire rolling on a rough surface. This model consists of three steps. First, the radial contact forces between road and tire are calculated. These forces give the vibrations of the tire, which finally give the sound radiation from the tire. A method to include the tangential forces into the rolling model is the topic of this paper. To do this, the influence of the tread blocks on the force transmission from the road to the belt of the tire has to be known. A FEM‐model of one tread block is made in order to determine its dynamical properties. A simplified model of the block is established, by only taking into account the two lowest modes in the frequency range of interest (i.e., up to 3 kHz). This...