Rail tunnel-Tutorial 2

Previous (Rail tunnel-Tutorial 1)    | Back to Start    |    Next (Road tunnel-Tutorial 1)

Rail tunnel tutorial 2-Modifying a rail-tunnel system model

We will continue by extending the existing model of sample1 to include a platform with a ventilation shaft. The case should correspond to the available case

…\tunnel\samples\tunnel\sample2.idm.

1. Open the sample1 system (if not already open).
2. Delete the connection between the section and the right portal by placing the cursor on the connection line, then right click and select ‘Delete’.
3. Copy the platform with two portals from the side bar by clicking on its frame and then drag the components into the system form.

The connection of the platform to tunnel sections and ventilation shafts should be done via portal components (by default sharp-edged). This is already prepared in the side bar component library.

4. Copy one tunnel section component from the side bar and place to the left of the rightmost entry.
5. Copy one more portal to be used when connecting the ventilation shaft to the platform.
6. All components used so far have been taken from the Main library. Click on Common to get access to the ventilation shaft and shaft entry components and copy one of each to the system.
7. Connect the components as shown in Figure 19.

Figure 19. The system form

                An extra portal to put between the platform and the shaft can be copied from the ‘Platform’ part of the Rail library in the side bar. Note that portal’s connection points are colour-coded: the light-coloured one must be connected to a platform, while the darker-coloured one must be connected to a tunnel section or a shaft.

When connecting the extra portal between the platform and the shaft the Connect dialog (Figure 20) is shown.

Figure 20. The connect dialog

8. Press the OK button to confirm that the station interface of the portal is to be connected to tunnel interface 3 of the platform.
9. Double-click on the platform component to open the form of Figure 21.

Figure 21. A platform/hall form

10. Change the floor level in the platform to coincide with the level of the right hand side of the previous tunnel section, i.e. set hFloor equal to 10.

The air in the platform is assumed to be well mixed, so the condition is mainly described by scalar variables, e.g. air temperature, pressure, wall temperature, relative humidity and air fractions.

Note that the z-coordinate (height) at the neighboring end of the tunnel sections/ventilation shafts/escalator sections has to fall between floor level (hFloor) and floor level plus height of platform.

The activity and clothing levels of passengers on the platform is described by the MET and CLO parameters respectively. Passenger presence is specified in terms of maximum number of passengers nOcc and a possibly time dependent occupancy coefficient schedOcc.

The surrounding wall is specified in the same way as in the section model, which also seepage out of tunnel wall and drain flow properties are.

Particle filters are as in the section model described by contaminant removal effectiveness, filter efficiency and filter volume air flow.

            In section Platform  of the Tunnel Theory the mathematical models for mass and heat balance are presented.

11. Open the section component to the right of the platform. Click on the ‘Edit segment’ button and change the level of the tunnel section to 10 m, i.e. set Height equal to 10 at both ends of the section (see Figure 5 and Figure 6 ), creating a horizontal section 10 m above the reference height.
12. Press OK and close the section form.
13. Open the shaft component, click on the ‘Edit segment’ button to set the dimensions of the shaft. We want to model a vertical shaft with length 15 m and cross section area 15 m² from the roof of the platform (see Figure 22).

Figure 22. Edit segment dialog

14. The first row is marked in the pane under the heading ‘Points’. Below the heading ‘Data for selected object’ set Height equal to 20 (position of platform roof), set ‘Cross section area’ equal to 15 and ‘Hydraulic diameter’ equal to 3.
15. Click on the second row under the heading ‘Points’. To get a vertical shaft of length 15 m, enter 15 as Position and 35 as Height.
16. Press OK and close the shaft form.

The ventilation shaft component uses the same mathematical model as the tunnel section component. Likewise the shaft entry component and the entry/exit portal share the same mathematical description. Only the graphical symbol is different.

17. Click on one of the portals between platform and tunnel sections to open the form of Figure 23.

Figure 23. A portal form

            The thermally driven air flow is shown.

Loss coefficients kPos and kNeg determine the viscous losses of entering or exiting air. The given default values are valid for a sharp-edged portal. For a further explanation of selection of pressure coefficients,

                    see Section "Selected topics on physical modelling > Definition of pressure loss coefficients".

            In section 2.1.6 of the Theoretical Reference the mathematical model for air flow is presented.

18. To log the air flow VFAir (air volume flow out of tunnel) double click on the variable value and select ‘Log-to RESULTS’.
19. Log the air flow in all three portals.

 RESULTS is a predefined output file for logging time series of variables.

                    See section of Recording output time series for a more detailed description of how to log variables.

20. Reset to constant conditions as follows.
21. Click on the ‘…’ button to the  right of ‘Ambient’ button at the bottom of the system form (Figure 19).
22. Mark ‘Constant’ in the pane below heading ‘Insert new object’ and press OK.
23. Enter 20 ˚C as ambient temperature and 50 as relative humidity in the shown form and close the form.
24. Click on the Global tab of the system form.
25. Change parameter tauWall to 1 hours.
26. Return to Schematic tab.
27. Press the ‘Simulation data’ button at the bottom of the system form to get access to the Calculation tab of the Simulation data dialog (Figure 7).
28. Reset simulation time to 1 hour (Figure 24).

Figure 24. The Simulation data/Calculation tab

26. Click on the Advanced tab and set Maximal time step to 1.
27. Perform a simulation by pressing the ‘Run’ button on the tool menu.
28. Double click on RESULTS under the heading ‘Results:’ at the upper right corner of the system form to exhibit the computed portal air flows.

Figure 25. Computed portal air flows

Adding traffic to a tunnel

We want to add two routes in opposite directions between the two entry/exit portals.

31. First press the ‘Add route’ button,  , in the lower left corner of the system form; ‘Editing path’ window will appear (Figure 26)

Figure 26. Editing path for a route

32. Then define the route from left to right by clicking with cursor first on the left entry/exit and then on the right entry/exit. The route will be shown by green arrows and circles on the schematics (Figure 27)

Figure 27. Route shown on the schematics

It is also possible to define a route first by pressing the Shift key while clicking first on the left entry/exit and then on the right entry/exit, and to press ‘Add route’ button after that.

It is not necessary to mark all components passed as long as the route becomes unique; there is just one possibility to travel from the left portal to the right portal.

33. Add another route in the opposite direction.
34. At the top of the system form under heading ‘Route:’ two routes with names Route and Route1 now appear. Double clicking on one of them will open the Route form (Figure 28).

Figure 28. The Route form

Defaults are set to all parameters and variables defining the route, i.e. type of train running the route, schedule of trains and passengers with relevant data.

The properties of the train type running the route are accessed by clicking the ‘Details’ button to open the Train parameter form (see below).

Time interval between trains is not necessarily constant but can be bound to a time table by using the ‘Bind to…’ button.

                   The procedure of binding is further explained in Creating schedules and binding variables.

To disturb perfect adherence to time tables one can apply stochastic delays to train departures.

                    This is done by clicking the ‘Stoch. delay’  and selecting appropriate stochastic distribution (Stochastic train traffic)

nRun is the maximum number of trains allowed on the route simultaneously. If this parameter is too small the simulation will be interrupted by an error message.

rSeg.n is number of route segments. A default segmentation is defined by the presence of platforms (or sections marked to be platforms) along the route. However, the number of and size of segments can be manually edited.

Route segments are defined by a number, start position, length, maximum speed, end speed and dwell time (at stations).

rSeg.vCoast is the minimum coasting speed on the route. If the train speed should decrease at the end of a segment (i.e. the end speed is lower than the actual maximum speed) the deceleration is modelled as follows:

 - If coasting is allowed (checked) the train coasts until the speed decreases to the minimum coasting speed, then it starts breaking.

 - If coasting is not allowed or the train speed is lower than the minimum coasting speed, the train is only breaking.

The point where the train starts coasting and breaking is calculated automatically.

35. Clicking the ‘Details’ button to the right of the train type specification opens the Train parameter form (Figure ).

Figure 29. The Train parameter form

By default, a specific train type named X40 is defined. In the form, front area, drag factor and skin friction coefficient among other data are defined. For diesel trains some additional data are given. Parameters can be changed and saved for this train type by pressing the ‘Save’ button or saved with another name by using the ‘Save as…’ button.

                   The equations for vehicle drag and skin friction are presented in Rail tunnel section of the Tunnel theory.

The main part of the train parameters is used in the heat flow equations for the train presented in Train heat model and Train compartment heating and air conditioning and air quality equations of sections CO2 content, Humidity fraction, Particle content and CO, NO2 and HC contents of the Tunnel theory.

36. Close the Train parameter form

            In case of fire simulation, define the emergency traffic. To do this, press the ‘Emergency’ button and fill the emergency form, see section .

37. Close the Route form.

            An interesting measure of the air quality in a tunnel system is the mean age of air. To illustrate how it may vary we will log the platform age of air to a result object named ‘age’.

38. Select library tab ‘Utility’ by clicking on Utility.
39. Position the cursor on the OUTPUT-FILE object and drag to the system form (Note: not to the Results list).

            At the top of the system form under heading ‘Results:’ an output file with name ‘OUTPUT-FILE’ now appears.

40. Right click on ‘OUTPUT-FILE’ and select ‘Rename …’ from the list of options, write the new name ‘age’ and press OK.
41. Double click on the platform component. Position the cursor on the text ‘Mean age of air’ in the list of air fractions, right click and select Log-to, then select ‘age’.
42. Close the platform form.
43. Press the ‘Simulation data’ button at the bottom of the system form to get access to the Calculation tab of the Simulation data dialog (Figure ).
44. Extend the simulation time to 5 hours.
45. Click on the Global tab of the system form and change tauWall to 5 hours.
46. Perform a simulation by pressing the ‘Run’ button on the Tool bar.
47. Double click on ‘age’ under the heading ‘Results:’ at the upper right corner of the system form to inspect the computed station age of air.

Figure 30. Computed station age of air

This concludes the tutorial part of the Getting Started Guide.

Previous (Rail tunnel-Tutorial 1)    | Back to Start    |    Next (Road tunnel-Tutorial 1)