چارچوب شبیه سازی برای مدیریت زمان واقعی ناوگان در سیستم های حمل و نقل داخلی

This paper presents a simulation framework incorporating traffic simulator with classical discrete event simulation model of internal transport systems. The objective behind this integration is to provide a simulation model in which traffic is captured in the internal haulage networks. For this purpose, the highly detailed microscopic traffic modelling approach is adopted. The developed simulator can reproduce the punctual trucks movement’s in the haulage network between pickup and delivery stations. Furthermore the complex traffic behaviour of platoon formation and congestion propagation is accurately emulated. This traffic behaviour is widely uncounted and criticized in the outdoor and internal transport system such as in container terminals and in surface mines applications. Experiments are conducted in two typical surface mines transportation systems. Results demonstrate that when the dispatching and routing problem is solved based on such detailed simulation model; the real-time truck fleet management is enhanced and the inherent traffic in the internal transport system is controlled.

The present work focuses on fleet management problems encountered in internal transportation systems. The main goal of fleet management is to maximize transporter (trucks, vehicle, etc.) efficiency by moving loads through the internal (i.e. within physical boundary) and shared haulage network as quickly as possible. This transportation between pickup and delivery stations is conducted under operational constraints. More precisely, this work addresses transportation activities taking place in the unpredictable, non-stationary, outdoor environment. Several applications in transportation belong to this class, including transportation of containers in transhipment terminals, transport of broken rock in surface mines or quarries, etc. Over the last decades many works have addressed the problematic of fleet management in such transportation systems. At the beginning, algorithms were proposed to deal with fleet dispatching under deterministic conditions i.e. constant travel time, no upset occurrence, etc. More recently a special emphasis is made to find better dynamic solutions to real-time fleet dispatching as well as to fleet routing under non-stationary system state. As stated in Van der Meer [1] this real-time fleet management can enhance the overall system performances as it takes into account the highly stochastic environment in which such internal transportations systems evolve. To reach this desired efficient real-time fleet management in internal transport systems, authors such as, Grunow et al. [2], Vis [3], Murty et al. [4], Burt and Caccetta [5] and Krzyzanowska [6], pointed out the importance of tracking the inherent traffic behaviour in the internal and often congested haulage networks. They explain that the used analytical or the simulation models have to take into account the unpredictable and highly variable travel time induced by truck bunched together in platoons and congestion appearance in the shared closed network. In this context, the purpose of this work is to provide a simulation framework incorporating traffic simulator with classical discrete event simulation model of internal transport systems. For this purpose, the microscopic traffic modelling paradigm is integrated with the classical object-oriented model formerly used to address the pickup and delivery problems arise in internal transport systems. The idea behind using a highly detailed microscopic approach to model the transportation comes from its successful use in the traffic engineering field, Barcelo et al. [7]. The herein provided model can capture the travel delays as well as congestion and platoon formation because the adopted microscopic approach uses equations designed to mimic punctual trucks movement and interactions through the haulage network. In this work, the conceptual model specification phase is conducted based on the Unified Modelling Language (UML) methodology. Its purpose is to show modifications needed on the classical models. In the classical models, trucks travelling in the haulage network between pickup/delivery stations used to be modelled as an activity processing with a specified time. This time is computed off-line and is based on stationary assumption. This classical modelling approach may be sufficient at an earlier design stage of the transportation system, but it is inadequate for real-time fleet management as it fails to reproduce the inherent complex behaviour of traffic flows. An implementation of the proposed conceptual model is also carried out with SIMAN/ARENA® simulation language, which is widely used in industrial applications. The purpose of this phase is to elucidate simulation model coding issues allowing capturing the longitudinal truck interaction along the haulage road segments. This longitudinal interaction is important as it is the source of platoons’ formation and the resulting congestion propagation in internal transport systems. Generally speaking, in internal transport system such as is surface mine haul road network as well as in the road network inside a container terminal, the movement of trucks is similar to vehicles in a one-lane scenario without overtaking. Thus, the travel time delay is dominated by this longitudinal interaction which induces platoons’ formation and congestion. Finally a proof of efficiency of the proposed framework is carried out through the use of the developed simulation model to solve the truck dispatching and routing problem in surface mine. For this purpose the simulation model is embedded as the kernel of a simulation-based control architecture. The role of this control architecture is to insure the real-time truck fleet management in the internal transport system. In literature many simulation-based control architecture were proposed [8]. The herein used architecture is inspired form the model-based predictive control and is developed by our research team [9]. Experiments are conducted on two realistic surface mines to assess the benefit of embedding the proposed highly detailed simulation model. In the first study, a common problem of route blockage in the traffic network is emulated. In the second experiment, the problem of heavy traffic congestion is considered. This paper is organized as follows. Section 2 reviews some previous applications which have considered the issue of traffic and discusses the traffic modelling approach used. Without a loss of generalization for internal transport applications, this review is restricted to the transport of containers at transhipment terminals and material transportation in surface mines. Section 3 deals with the specification phase of the conceptual model we propose. Section 4, details some important implementation issues of the simulation model. Section 5 includes experiments and discusses results. Finally, Section 6 summarizes the findings and the main conclusions.

This paper proposed a highly detailed simulation framework for internal transport system. This model explicitly integrates microscopic traffic approach in classical discrete event simulation model of internal transportation systems. A conceptual model, based on the object-oriented formalism, was proposed in order to allow its reusability and to elucidate important issues in traffic behaviour modelling. The implementation of this model in surface mine application is carried out. A demonstration study was conducted to test the capability of the developed simulation model to emulate trucks longitudinal interactions. This specific form of interaction is of great interest because the travel time delay in internal haulage network is dominated by the longitudinal truck–truck interaction. Results showed that in the developed simulation model this interaction is realistically reproduced and the complex traffic behaviour of platoon formation and congestion propagation is accurately emulated. Conducted experiments on two typical surface mines show the benefit of using the highly detailed simulation model to solve the truck dispatching and routing problem arising in internal transport system. Better real-time fleet management is achieved as the unproductive time of truck bunching is controlled. By improving truck fleet efficiency, a substantial loss of production is then prevented. Another advantage behind this detailed model is its use to analyze the internal traffic network and to assess the road occupancy level for congestion alleviation. Experiments results show that, under heavy traffic, real-time truck re-routing to less congested but longer path may greatly enhance the internal transport system performance. For future real implementation of the proposed model in surface mine or in container terminal systems, the corresponding calibration study must be carried out. The calibration phase of the microscopic traffic simulator has been identified as a complex issue for urban road networks. Generally speaking the larger the network is, the more complex collection of data for the calibration becomes. Nevertheless, as for the internal transportation application, the network is of limited boundary, this calibration may be less problematic. Furthermore, as the trucks are generally equipped with on-board positioning system, then each truck can be considered as a probe vehicle delivering the needed data for the calibration phase.