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WHEEL EIGENMODES INVOLVED IN SQUEAL
Chapters 3 and 4 provided a description of the key kinematic and vehicle dynamics parameters influencing the generation of squeal in the test curve.
To complete the experimental characterisation of squeal, the current chapter is concerned with identifying the wheel eigenmodes involved in squeal and establishing a relationship between the kinematic parameters found to be important to squeal and such eigenmodes.
The study of the wheel eigenmodes involved in squeal were conducted via modal analysis of wheel Types A and B of known diameter (916 mm) and mounted under an empty ore wagon. In addition the damping ratios of wheel modes with were also determined for the freely suspended wheelset for wheel Type A.
In addition finite element modal analysis was used to visualise the wheel modes identified as being involved in squeal. This also confirmed that such eigenmodes have significant out-of-plane vibration that can be linked to the high noise levels associated with squeal.
EXPERIMENTAL MODAL ANALYSIS
Due to the regular sinusoidal pattern in the circumferential direction of the mode shapes of the wheel, a detailed modal analysis was not used to identify the modes of vibration of the wheel responsible for squeal. Instead a simplified approach was followed to study the mode shapes of the mounted wheel.
Firstly, a modal analysis was conducted to identify the sinusoidal pattern of each mode in the circumferential direction around the wheel tread. The measurement grid encompassed nine measurement points spaced at unequal distances around a quarter of the wheel (see Figure 5-1).
The angular positions of grid points A to G and O were chosen to correspond with nodal diameters of the sine modes with 1 to 8 nodal diameters and aligned to have one of their nodal points at the wheel-rail contact point. Excitation was provided at grid point H, which was selected to not coincide with a nodal diameter of one of the 1 to 8 nodal diameter sine modes. The wheel was excited in the radial, axial and circumferential directions at the excitation point. Excitation in the radial direction was applied on the wheel tread, excitation in the axial direction on the field side of the wheel rim and excitation in the circumferential direction was applied via a small steel block rigidly mounted on the wheel tread.
For the modal analysis an instrumented hammer was used to provide the excitation and the response was measured using a single tri-axial accelerometer. A roving accelerometer approach was used to capture the wheel mode shape components in the radial, axial and circumferential directions at each measurement point. An average of three impacts was used for each measurement. The response, radial and circumferential excitation points on the wheel tread were chosen 105 mm from the back of the flange to correspond with the average of the contact positions identified for the inner squealing wheels via the results of the RsGeo simulations. The receptance for each input/output location was recorded and later used to extract the modal parameters of each mode using the least squares exponential curve fitting algorithm available in the Labview environment.
The eigenvectors representative of the different modes were normalised to unit modal mass.
An example of the results for sinusoidal pattern recognition is presented in Figure 5-2. The results are plotted for the unwrapped rim between 0° and 90°. Because the wheel-rail contact point fixes the location of the nodal diameters, the cosine modes could also be identified from the modal analysis.
1 INTRODUCTION
1.1 Background
1.2 Curve squea
1.3 Context of current study
1.4 Objectives of the study
1.5 Publications
1.6 Organisation of the dissertation
2 LITERATURE REVIEW.
2.1 Mechanisms of frictional self-excitation
2.2 Railway wheel squeal
2.2.1 Bogie curving
2.2.2 Sources of instability responsible for squeal .
2.2.3 Wheel dynamics.
2.2.4 Mechanisms responsible for curve squeal
2.3 Modelling squeal
2.4 Parameters influencing squeal generation
2.4.1 Wheelset angle-of-attack
2.4.2 Wheelset lateral displacement
2.4.3 Contact friction law/Friction characteristic
2.5 Field measurements related to squeal .
2.5.1 Key parameters accounted for during field measurements
2.5.2 Source identification of squealing wheel
2.5.3 Key findings of field measurement campaigns
2.6 Guidance from literature
3 EXPERIMENTAL CHARACTERISATION OF RAILWAY WHEEL SQUEAL OCCURRING IN LARGE RADIUS CURVES
3.1 Field measurements
3.1.1 Measurement setup
3.1.2 The Sishen-Saldanha railway line
3.2 Evaluation of field measurements
3.2.1 Source of squeal
3.2.2 Bogie curving characteristic
3.2.3 Longitudinal creepage present in wheel-rail contact of squealing wheel
3.3 Tracking condition of squealing bogies .
3.4 Squeal frequency versus wheel diameter
3.5 Top-of-rail friction modification
3.6 Flange throat squeal .
3.6.1 Flanging/squeal noise and bogie curving.
3.7 Discussion
3.7.1 Inner wheel squeal
3.7.2 Outer wheel squeal
4 CURVING BEHAVIOUR OF “SQUEALING” BOGIES
4.1 Vehicle dynamics simulations
4.1.1 Bogie curving performance
4.2 Operating point of squealing wheel on Adhesion curve
4.3 Discussion
5 WHEEL EIGENMODES INVOLVED IN SQUEAL
6 FREQUENCY DOMAIN MODEL FOR RAILWAY WHEEL SQUEAL RESULTING FROM UNSTEADY LONGITUDINAL CREEPAGE
7 FREQUENCY DOMAIN MODEL FOR RAILWAY WHEEL SQUEAL RESULTING FROM UNSTEADY SPIN CREEPAGE
8 SQUEAL MITIGATION
9 CONCLUSIONS AND RECOMMENDATIONS
10 REFERENCES .
