Rolling noise

The rolling noise results include calculated sound pressure levels, sound power levels, track decay rates and mobilities from the rolling noise calculations.

As a beta feature, if the option to include axlebox/bogie transfer functions is selected, then the velocity response at prescribed points on the bogie frame will also be calculated.

Sound pressure levels

The sound pressure prediction approach of the rolling noise calculation is a simplified version of the method used in the external noise calculation. The full pass-by of the train is not considered, but for each wheelset a single integration length of 20 metres is assumed, containing a total of 4 identical wheelsets. This should be accounted for when comparing sound pressure level predictions made between the two calculation types.

To view results, select the source data and the desired receivers in the panels to the left, and click “Refresh results”.

For more information about interacting with charts, see here: viewing results.

For the wheel, the values shown are a combined total of:

• axial modes,
• radial modes,
• rotational modes,

For the rail, the values shown are a combined total of:

• vertical propagating wave,
• vertical decaying wave,
• lateral propagating wave,
• lateral decaying wave.

For the sleeper, the values shown are due to vertical excitation.

The values for each of the respective wave/mode types above may be obtained from .csv files in the results folder. If you are interested in obtaining these specific values, please contact us for more info.

Sound power levels

The sound power results from the rolling noise calculation contain the sound power values of individual rolling components (i.e. wheel, rail, sleeper and total).

Similar to the sound pressure level values described above, the plotted sound power values are totals of each component’s respective wave/mode types. Data for the individual wave/mode types is provided in .csv files in the results folder (contact us for more info).

Track decay rates

The track decay rates used in the rolling noise calculation are also viewable in Train Noise Expert. These include the both the calculated values and the values provided in any track decay rate input data file.

By default, only the values actually used in the calculation are plotted. For example, if the calculation was set to use track decay rates from a supplied file, the calculated track decay rates will not be plotted. However, at times it can be useful to plot the calculated and file datasets together, for example to verify that the rail pad stiffness values used in the model are appropriate. To accommodate this, the ‘unused’ track decay rate data is still able to be plotted, but is greyed out in the source data panel to the left.

Track decay rates - quick calculation

Track decay rates can be quickly calculated and plotted (without requiring a full rolling noise calculation) by selecting Project > Rolling noise > Calculate TDR…

This can be helpful, for example, when tuning the railpad stiffness/damping parameters so that the calculated values match any measured data you may have.

From the plot window that appears, choose the track from the dropdown list. If you keep this window open and make any changes to your parameters in the model, select “Refresh” to replot with the updated parameters.

Mobilities

The calculated track component mobilities used in the rolling noise calculation are also viewable in Train Noise Expert, for vertical and lateral directions.

Both the magnitude and phase are presented. Due to the number of points present in the mobility data, the clarity of the plots may be improved by hiding the line markers; this can be accomplished through the legend’s right-click menu, see interacting with charts.

Output files

The rolling noise calculations each generate a collection of output files, which are used in plotting data in Train Noise Expert, and also as input data for external noise calculations. Some of this data may be of interest to users, and a description of the data contents is provided here.