Entering Trains Upon Routes (Input Forms 8A, 8B)

Trains are placed into operation on the route at the train scheduling origin (Input Form 8A). The location of a train is defined to be the distance along the route coordinate system where the front of the train is located. The remainder of the train extends in the negative direction along the route coordinate system. The train scheduling origin (see Figure 7.1) may lie anywhere along the route — from the route origin to the forward end of the last track section which defines the end of the route. In the case of a route that originates outside of the tunnel system and enters the tunnel system through a portal, the train scheduling origin may be located in either the open air portion of the route or within the tunnel system.

Trains are placed in operation at the train scheduling origin according to the time schedule defined for the route in the dispatcher information. If implicit train performance (train performance Option 1 on Input Form 1C) is being used, the trains are placed in operation at zero speed and immediately begin to accelerate and travel along the route. If explicit train performance (train performance option 2 or 3 on Input Form 1C) is being used, the trains are placed into operation at the speed which is specified for time zero on the speed-time profile. Trains are removed from operation when the front of the train goes beyond the forward end of the last track section, or, in the case of explicit train performance only, when the front of the train goes beyond the last point of the speed-time profile.

A train is considered to be operational from the time that it is dispatched onto its route until it is removed from operation. Each train is assigned a train number by the program which is used to identify a particular train throughout its period of operation. Train numbers are assigned to trains in the sequential order in which they are created — the trains which are in operation at system initialization first, and then in

7-7 An attempt to exceed the maximum number of simultaneous operating trains during a simulation will result in a simulation error message. When this occurs, a new train will not be placed into operation until after a train has been removed from operation in order that the new train will not cause the limit of simultaneous operational trains to be exceeded. It should be noted, however, that by not placing this train into operation, the normal train scheduling is disrupted. If the user is analyzing the events in the system at stabilization, the disruption of the train schedule, which is a major forcing function of the system, will prevent the system from reaching stabilization and, in many cases, invalidate the results of the simulation.

A maximum of eight trains may be located in a line segment at one time, and these trains may be on the same route or on different routes. If the program limit of eight trains simultaneously located in a line segment is exceeded during a simulation, only eight of the trains will be considered to be in the segment for aerodynamic and thermodynamic calculations. The remaining trains will temporarily be considered to be outside of the tunnel system, and a simulation error message will be printed. When the number of trains in the line segment becomes eight or less, the error condition would no longer exist and the simulation would continue.

Minimum Coasting Velocity. For each route on which coasting is permitted, the user must specify the minimum speed that can be attained by the train. In addition, the user must indicate the coasting option, the trains mode of operation, should the minimum speed be reached. The user has the option of allowing the train to operate in a constant speed mode at the minimum speed, or to switch to an accelerating mode.

Train Dispatching and Scheduling. For each route which is being simulated, the user must provide the schedule by which trains are to be dispatched onto that route. When a train is dispatched, a new train is created with the characteristics of the train type which is indicated, it is assigned a train number by the program which can be used to identify the particular train, and the train is placed into operation at the train scheduling origin of its route. The train then proceeds to travel along its route in the positive direction.

A train group consists of one or more consecutive trains which are dispatched on the same route that are of the same type and the same headway. The train headway is defined as the time interval between trains on the same route. The headway for a given train is the elapsed time between the dispatching of the previous train on the given train's route and the time the given train was dispatched.

Since a train group consists only of trains with the same characteristics, if either the train type or headway changes, a new group is formed for that route.

The user must define the number of groups of trains that could enter the route. The first train group contains only one train, but the second and subsequent train groups can be composed of one or more trains of the same type and operating at the same headway. The first group, which is a special case, does not have a headway, rather it has a delay time before dispatching the first train. This is the time that the program is to wait after the beginning of the simulation before the first train is dispatched onto this route. After all the trains in a group have been dispatched, the program begins to dispatch trains from the next group.

Example 7.1 Figure 7.4 shows sample input for train scheduling data. The number of groups of trains that could be entered is 4, and the delay time before dispatching first train is 70 seconds. The first train type was entered as 3, and therefore the first train group consists of one train of Type 3 which is dispatched 70 seconds after the start of the simulation. In the case of the first train group, the number of trains is understood to be 1.

The second train group contains three trains of Type 1 which are operating at 100-second headway. They are dispatched at 170 seconds (70 plus 100), 270 seconds (170 plus 100), and 370 seconds (270 plus 100). The third group contains only one train of Type 3 which is operating at 150-second headway. It is dispatched at 520 seconds (370 plus 150).

Number of groups of trains that could enter route = 4.

Delay time before dispatching first train = 70 seconds.

Group Number

Number of Subway Trains

Train Type

Headway (Seconds)

Time Last Train in Group becomes Operational (Seconds)

1 1 3 70 70

2 3 1 100 370

3 1 3 150 520

4 5 1 100 1020

Figure 7.4 Example of Train Dispatching Data

The fourth train group contains five trains of Type 1 which are operating at 100- second headway. The first is dispatched at 620 seconds (520 plus 100), and the last is dispatched at 1020 seconds (520 plus 5 x 100).

In the above example only trains of Type 1 and 3 are being dispatched, and no trains of Type 2 are being dispatched onto this route. Type 2 trains may be dispatched on other routes, or they may not be dispatched at all. It is not incorrect to define additional train types that are not being used in a particular simulation provided the program array size limit for the number of train types, given as LMTRTP in Appendix A, is not exceeded. The additional train type might have been originally defined for another simulation, and the user did not wish to remove it from the data set since it was planned to be used in

7-9 system to become stabilized. A stabilized system is one in which all calculated values of parameters — airflow rate, temperature, and humidity — repeat at regular intervals. The interval over which this repetition occurs is usually the same interval over which the train dispatching repeats for all of the routes.

The user should define enough trains to be dispatched into the system such that the time at which the last train is to be dispatched is at least equal to, and preferably greater than, the maximum simulation time for the simulation. The maximum simulation time indicated on Input Form 13, which is used to control the program operation, defines the point at which the simulation is to be terminated. If the simulation is terminated before all the trains are dispatched into the system, the remaining trains will neither be dispatched nor simulated. If, on the other hand, the maximum run time was more than one headway greater than the time at which the last train on each route is to be dispatched, then the results of the simulation might not be meaningful. If this is the case, when there are no new trains entering the system, it will go into an aerodynamic “die-down” mode in which the airflows will decrease due to damping, and the temperatures within the system will approach the wall surface temperature. If the user is taking

summaries of the results, the results of the stabilized system and not of the system in “die-down” will usually be used.

It frequently occurs during a series of runs simulating a system then the length of the simulation must be increased. Users are cautioned that it is a common error to increase the “maximum simulation time” and to adjust the print controls accordingly, but to fail to adjust the train dispatcher data to reflect the longer simulation. This causes the system to die-down near the end of the simulation and possibly

invalidate the results. Other items which must be checked when a longer simulation is performed are fans and unsteady heat loads. Each ventilation shaft which contains a fan has associated with it a time at which the fan switches on, and a time at which the fan switches off. If the fan is to remain operational throughout the entire simulation, the time when the fan switches off must be greater than the maximum simulation time. Unsteady heat loads also have associated with them a time after which the load becomes active and a time after which the load becomes inactive. If the load is to remain active throughout the remainder of the simulation, the time after which the load becomes inactive must be greater than the maximum simulation time.