Track
Track objects are used to group a number of parameters that relate to the rails, railpads, sleepers and ballast.
Overview
Due to the large number of track parameters, they are subdivided into the following:
Rolling sound powers from rolling sources are calculated according to the rolling noise procedure. When calculating the sound pressure levels using the external noise calculation, Train Noise Expert implements the following:
Wheel
Two equivalent point sources are used model the noise contribution from each wheel and they are both located at the wheel centre. The first one accounts for the acoustic power from radial vibration and has a monopole directivity. The second one accounts for the acoustic power from axial vibration and has a dipole directivity (with axis in the lateral direction). Each wheelset is composed of two wheels and both the wheels are present in the simulation (i.e. there are 4 point sources per wheelset).
Rail
There are two sources used to model the rail vibration due to the interaction with each wheel. The rail vertical vibration contribution is modelled with a point source having a monopole directivity. The lateral vibration is modelled with a point source with dipole directivity (orientated laterally). The position for rail sources is 0.07 m below the top of rail.
Sleeper
The sleeper acoustic power is represented by a monopole at 0.2 m directly below the top of rail. Note that this is a standard monopole that radiates in a whole sphere so that it can be reflected in the ground. There is one source on each side of the track for each wheelset.
Input Parameters
Global track properties
Global track properties for the 'track' model object.
| Name | Data type | Unit | Comment |
|---|---|---|---|
| Include track absorption (Beta feature) | Checkbox | - | Selects whether track absorption is considered for the calculations (only affects sound pressure results). This parameter actually belongs to the Situation but is shown here for convenience; it is therefore possible to use the same track in separate situations with track absorption turned on/off. Note that this is a Beta feature and this functionality may be changed in future releases. |
| Track | Lib. item | - | The library item for the track components. |
| Width between rail centres | Number | m | The separation between the centres of the two rails. |
| Roughness file | File | - | If the roughness input for the Situation has been selected to allow ‘separate rail/wheel roughness’, the roughness input file location for the Track is specified here (with ’.to’ file extension ). |
| Track decay rate | Choice | - | For rolling noise calculations, the track decay rate is used to calculate the radiated sound power of the rail and sleepers. This can be estimated from the other track properties, or you may specify the values to be taken from a file. |
| Track decay rate file | File | - | If the track decay rate has been specified to be taken from a file, the file location is specified here (with ’.to’ file extension ). |
| Track absorption file (Beta feature) | File | - | If track absorption is to be included in the calculation, the file location is specified here (with ’.to’ file extension ). |
| Absorption coverage ratio (Beta feature) | Number | 0-1 | The ratio of the track surface that should be assigned the data provided in the absorption file. All other parts of the track are assumed to be reflective. |
When specifying track decay rate input files, it is still necessary to ensure appropriate values are entered for the other track properties (for example railpad stiffness), as these values are still used in calculating the interaction between the various components.
Rail properties
Some default rail configurations can be selected, including UIC60, UIC54 and S49. Alternatively, rail properties can be user-defined.
Rail properties for the 'track' model object.
| Name | Data type | Unit | Comment |
|---|---|---|---|
| Height | Number | m | The height of the rail. |
| Rail type | Choice | - | A number of pre-defined rail types including UIC60, UIC54 and S49 are available, as well as a ‘user-defined’ option, which allows the user to manually define all of the following parameters. |
| Mass per unit length | Number | kg/m | The mass per unit length of the rail. |
| Young’s modulus | Number | Pa | The Young’s modulus of elasticity of the rail. This is in Pascals (i.e. 210 GPa = 2.1e+11 Pa). |
| Density | Number | kg/m3 | The density of the rail. |
| Poisson’s ratio | Number | - | The Poisson’s ratio of the rail. |
| Bending stiffness (vert) | Number | Nm2 | The bending stiffness of the rail in the vertical direction. |
| Bending stiffness (lat) | Number | Nm2 | The bending stiffness of the rail in the lateral direction. |
| Timo. shear coeff (vert) | Number | - | The Timoshenko shear coefficient of the rail in the vertical direction. |
| Timo. shear coeff (lat) | Number | - | The Timoshenko shear coefficient of the rail in the lateral direction. |
| Loss factor (vert) | Number | - | The damping loss factor of the rail in the vertical direction. |
| Loss factor (lat) | Number | - | The damping loss factor of the rail in the lateral direction. |
| Cross receptance factor | Number | - | The cross receptance factor of the rail. |
| Rail radiation file | File | - | The file location for the rail radiation is specified here (with ’.to’ file extension ). |
| Rail transverse radius | Number | m | The transverse radius of the rail at the contact point. Can be adjusted to simulate worn rail. |
Railpad properties
Railpad properties can have default stiffness values (high, medium, low and very low) and default damping values (high, medium and low), or have user-defined values. See below for the values used for the default conditions.
Railpad properties for the 'track' model object.
| Name | Data type | Unit | Comment |
|---|---|---|---|
| Stiffness type | Choice | - | A number of pre-defined stiffnesses are available, as well as a ‘user-defined’ option. See below for values. |
| Stiffness (vert) | Number | N/m | The acoustic stiffness of the railpad in the vertical direction. |
| Stiffness (lat) | Number | N/m | The acoustic stiffness of the railpad in the lateral direction. |
| Damping type | Choice | - | A number of pre-defined damping values are available, as well as a ‘user-defined’ option. See below for values. |
| Loss factor (vert) | Number | - | The damping loss factor of the railpad in the vertical direction. |
| Loss factor (lat) | Number | - | The damping loss factor of the railpad in the lateral direction. |
Sleeper properties
Sleeper properties for the 'track' model object.
| Name | Data type | Unit | Comment |
|---|---|---|---|
| Sleeper type | Choice | - | A number of pre-defined sleeper types are available, including mono-block, bi-block and timber sleepers, as well as ‘user-defined’ options. |
| Spacing between sleepers | Number | m | The distance between the centre of each sleeper. |
| Length per sleeper | Number | m | The length of each sleeper (across the track). For a normal sleeper, this will be the full length of the sleeper. For bi-block sleepers, this is the length of each bi-block sleeper. |
| Height at railseat | Number | m | The height of the sleeper at the railseat. |
| Height at centre | Number | m | The height of the sleeper at the centre. |
| Width at railseat top | Number | m | The width of the top of the sleeper at the railseat. |
| Width at railseat bottom | Number | m | The width of the bottom of the sleeper at the railseat. |
| Width at centre top | Number | m | The width of the top of the sleeper at the centre. |
| Width at centre bottom | Number | m | The width of the bottom of the sleeper at the centre. |
| Railseat dist. from end | Number | m | The distance of the railseat zone from the end of the sleeper. |
| Mass per rail* | Number | kg | The mass per rail of the sleeper. *Only used in calculations for user-defined bi-block sleepers. |
| Young’s modulus | Number | Pa | The Young’s modulus of elasticity of the sleeper/slab material. This is in Pascals (i.e. 41 GPa = 4.1e+10 Pa). |
| Density | Number | kg/m3 | The density of the sleeper/slab material. |
| Poisson’s ratio | Number | - | The Poisson’s ratio of the sleeper/slab material. |
| Timo. shear coefficient | Number | - | The Timoshenko shear coefficient of the sleeper/slab material. |
| Loss factor | Number | - | The damping loss factor of the sleeper/slab material. |
| Sleeper radiation model (Beta feature) | Choice | - | Choose classic ‘rectangular piston’ model, or a file that describes the radiation properties. |
| Sleeper radiation file (Beta feature) | File | - | The file location for the sleeper radiation is specified here (with ’.to’ file extension ). |
| Include under-sleeper pad | Checkbox | - | Specifies whether to include under-sleeper pads in the calculation of rolling noise. |
| Pad stiffness (vert) | Number | N/m | The acoustic stiffness provided by the under-sleeper pad in the vertical direction, per rail. |
| Pad loss factor (vert) | Number | N/m | The damping loss factor provided by the under-sleeper pad in the vertical direction. |
When running rolling noise calculations, the model used for the vertical resonse of mono-block sleepers is a modal model, which takes into account the sleeper dimensions and material parameters. The model used for bi-block sleepers (and for the lateral response of mono-block sleepers) uses a simplified mass of the sleeper in the calculations. If the base stiffness is to be provided with a file, then sleeper dimensions are additionally used to accommodate any differences in sleeper footprint area. The radiating area of the sleepers is calculated from the sleeper length and width of the top of the sleeper at the rail supports.
Base properties
Base properties for the 'track' model object.
| Name | Data type | Unit | Comment |
|---|---|---|---|
| Base type | Choice | - | A choice of base types are available, including ballast, slab or a ‘user-defined’ option. The parameter values for each of the pre-defined base types are shown below. |
| Vertical stiffness type | Choice | - | A choice of whether the vertical stiffness is constant with frequency (with loss factor or viscous damping), whether it is variable (see below for more explanation), or whether the vertical stiffness is specified for each frequency from a file.. |
| Stiffness file | File | - | If the vertical stiffness type has been specified to be taken from a file, the file location is specified here (with ’.to’ file extension ). Vertical stiffness and loss factor values will be read from this file. |
| Stiffness (vert) | Number | N/m | The stiffness of the base in the vertical direction, when evaluated over the area of the sleeper. |
| Stiffness (vert) file muliplier | Number | - | A multiplier to apply to the stiffness values given in the file. |
| Stiffness (lat) | Number | N/m | The stiffness of the base in the lateral direction, when evaluated over the area of the sleeper. |
| Variable frequency point | Number | Hz | The transition frequency point, when the vertical stiffness type has been specified as ‘variable’. |
| Loss factor (vert) file muliplier | Number | - | A multiplier to apply to the loss factor values given in the file. |
| Loss factor (vert) | Number | - | The damping loss factor of the base in the vertical direction. |
| Loss factor (lat) | Number | - | The damping loss factor of the base in the lateral direction. |
| Viscous damping (vert) | Number | N.s/m | The viscous damping of the base in the vertical direction when evaluated for a point on the sleeper (i.e. usually half a sleeper length is assumed). |
| Viscous damping (lat) | Number | N.s/m | The viscous damping of the base in the lateral direction when evaluated for a point on the sleeper (i.e. usually half a sleeper length is assumed). |