GasStationRefueling.cs

#region License Information
/*
 * This file is part of SimSharp which is licensed under the MIT license.
 * See the LICENSE file in the project root for more information.
 */
#endregion

using System;
using System.Collections.Generic;
using static SimSharp.Distributions;

namespace SimSharp.Samples {
  public class GasStationRefueling {
    /*
     * Gas Station Refueling example
     *
     * Covers:
     *  - Resources: Resource
     *  - Resources: Container
     *  - Waiting for other processes
     *
     * Scenario:
     *  A gas station has a limited number of gas pumps that share a common
     *  fuel reservoir. Cars randomly arrive at the gas station, request one
     *  of the fuel pumps and start refueling from that reservoir.
     *
     *  A gas station control process observes the gas station's fuel level
     *  and calls a tank truck for refueling if the station's level drops
     *  below a threshold.
     */
    private const int RandomSeed = 42;
    private const int GasStationSize = 200; // liters
    private const int Threshold = 10; // Threshold for calling the tank truck (in %)
    private const int FuelTankSize = 50; // liters
    private const int RefuelingSpeed = 2; // liters / second
    private static readonly Uniform InitialFuelLevel = UNIF(5, 26); // Level of fuel tanks (in liters)
    private static readonly TimeSpan TankTruckTime = TimeSpan.FromMinutes(10); // Minutes it takes the tank truck to arrive
    private static readonly UniformTime CarArrival = UNIF(TimeSpan.FromMinutes(30), TimeSpan.FromMinutes(300)); // Arrival distribution for cars
    private static readonly TimeSpan SimTime = TimeSpan.FromMinutes(3000); // Simulation time

    private IEnumerable<Event> Car(string name, Simulation env, Resource gasStation, Container fuelPump) {
      /*
       * A car arrives at the gas station for refueling.
       * 
       * It requests one of the gas station's fuel pumps and tries to get the
       * desired amount of gas from it. If the stations reservoir is
       * depleted, the car has to wait for the tank truck to arrive.
       */
      var fuelTankLevel = env.Rand(InitialFuelLevel);
      env.Log("{0} arriving at gas station at {1}", name, env.Now);
      using (var req = gasStation.Request()) {
        var start = env.Now;
        // Request one of the gas pumps
        yield return req;

        // Get the required amount of fuel
        var litersRequired = FuelTankSize - fuelTankLevel;
        if (litersRequired > fuelPump.Level && fuelPump.Level > 0) {
          var level = fuelPump.Level;
          yield return fuelPump.Get(level); // draw it empty
          yield return env.Timeout(TimeSpan.FromSeconds(level / RefuelingSpeed));
          yield return fuelPump.Get(litersRequired - level); // wait for the rest
          yield return env.Timeout(TimeSpan.FromSeconds((litersRequired - level) / RefuelingSpeed));
        } else {
          yield return fuelPump.Get(litersRequired);
          yield return env.Timeout(TimeSpan.FromSeconds(litersRequired / RefuelingSpeed));
        }
        env.Log("{0} finished refueling in {1} seconds.", name, (env.Now - start).TotalSeconds);
      }
    }


    private IEnumerable<Event> GasStationControl(Simulation env, Container fuelPump) {
      /*
       * Call the tank truck if the level falls below a threshold.
       */
      while (true) {
        yield return fuelPump.WhenAtMost(fuelPump.Capacity * (Threshold / 100.0));
        // We need to call the tank truck now!
        env.Log("Calling tank truck at {0}", env.Now);
        // Wait for the tank truck to arrive and refuel the station
        yield return env.Process(TankTruck(env, fuelPump));
      }
    }

    private IEnumerable<Event> TankTruck(Simulation env, Container fuelPump) {
      // Arrives at the gas station after a certain delay and refuels it.
      yield return env.Timeout(TankTruckTime);
      env.Log("Tank truck arriving at time {0}", env.Now);
      var amount = fuelPump.Capacity - fuelPump.Level;
      yield return fuelPump.Put(amount);
      env.Log("Tank truck finished refuelling {0} liters at time {1}.", amount, env.Now);
    }

    private IEnumerable<Event> CarGenerator(Simulation env, Resource gasStation, Container fuelPump) {
      // Generate new cars that arrive at the gas station.
      var i = 0;
      while (true) {
        i++;
        yield return env.Timeout(CarArrival);
        env.Process(Car("Car " + i, env, gasStation, fuelPump));
      }
    }

    public void Simulate(int rseed = RandomSeed) {
      // Setup and start the simulation
      // Create environment and start processes
      var env = new Simulation(DateTime.Now.Date, rseed);
      env.Log("== Gas Station refuelling ==");
      var gasStation = new Resource(env, 2) {
        QueueLength = new TimeSeriesMonitor(env, name: "Waiting cars", collect: true),
        WaitingTime = new SampleMonitor(name: "Waiting time", collect: true),
        Utilization = new TimeSeriesMonitor(env, name: "Station utilization"),
      };
      var fuelPump = new Container(env, GasStationSize, GasStationSize) {
        Fillrate = new TimeSeriesMonitor(env, name: "Tank fill rate")
      };
      env.Process(GasStationControl(env, fuelPump));
      env.Process(CarGenerator(env, gasStation, fuelPump));

      // Execute!
      env.Run(SimTime);
      env.Log(gasStation.QueueLength.Summarize());
      env.Log(gasStation.WaitingTime.Summarize());
      env.Log(gasStation.Utilization.Summarize());
      env.Log(fuelPump.Fillrate.Summarize());
    }
  }
}