Giacomo Liotta

A network flow based heuristic approach for optimising AGV movements

Automated Guided Vehicles (AGVs) are driverless carriers that automatically navigate along planned paths by means of several guidance and control methods. This paper proposes an approach for solving the dispatching problem in an AGV system. The problem is modelled through a network by relying on the formulation of a Minimum Cost Flow Problem. In the defined graph, the nodes represent transportation tasks and AGVs while the arcs consider, through the associated weights, several system’s aspects such as pick, drop, and travel times, battery recharging, capacity constraints, congestion and error issues. Two objectives can be achieved: (i) minimisation of the average time for carrying out transportation tasks or (ii) maximisation of the utilisation degree of AGVs. The modelling and solution approach adopted has provided a novel Vehicle–Initiated dispatching rule and parameters settings for the dynamic assignments of transportation missions to AGVs. The decision making process concurrently and dynamically considers several factors. The results show a relevant reduction in the average time for transportation order fulfilment and a decrease in its variability. The proposed approach has been exploited for optimising the AGVs performance in a pharmaceutical production system.

Optimization and Simulation of Collaborative Networks for Sustainable Production and Transportation

Complex and delocalized manufacturing industries require high levels of integration between production and transportation in order to effectively implement lean and agile operations. There are, however, limitations in research and applications simultaneously embodying further sustainability dimensions. This paper presents a methodological framework based on optimization and simulation to integrate aggregate optimized plans for production and multimodal transportation with detailed dynamic distribution plans affected by demand uncertainty. The objective function of the optimization model considers supply, production, transportation, and CO2 emission costs, as well as collaboration over the multimodal network. Bill-of-materials and capacity constraints are included. A feedback between simulation and optimization is used to plan requirements for materials and components. Computational experiments are based on realistic instances. Results demonstrate that the framework can be effectively used to analyze cost-CO2 emission tradeoffs, effects of demand uncertainty, and collaborative distribution strategies on economic and environmental performance of the supply chain.

A simulation-based approach for estimating the commercial capacity of railways

Rail transport is expected to play a remarkable role for a sustainable mobility in Europe. This paper presents an approach for estimating the commercial capacity of railways. The commercial capacity is intended as the number of possible paths in a defined time window on a rail line, or part of it, considering a fixed path mix, with market-oriented quality. The capacity management is one of the most important tasks of railway Infrastructure Managers. The proposed simulation-based approach relies on the use of an optimizer and a simulator. The study has been developed for the rail line Verona-Brennero, located in the Italian part of the European Corridor Hamburg-Napoli. Computational results allowed to estimate the commercial capacity differences between the whole line and three important line sections within it. Other computational experiments showed the relevant estimated increase in commercial capacity that a reduction in time spacing between trains could imply.

Closing global material loops: Initial insights into firm-level challenges

Summary Sharing and exchanging waste materials between industrial actors, a practice known as industrial symbiosis (IS), has been identified as a key strategy for closing material loops. This article adopts a critical view on geographical proximity and external coordinators—two key enablers of IS. By “uncovering” a case where both enablers are absent, this study seeks to explore firm-level challenges of IS. We adopt an exploratory case-study approach at a cement manufacturer who engages in cross-border IS without the support of external coordinators. Our research presents insights into two key areas of IS: (1) setting up the initial IS exchange and (2) improving the performance of existing IS exchanges. Moreover, our research provides initial insights into the underlying nature of the related firm-level challenges and explores how internal coordination between manufacturing and purchasing may or may not act as a substitute for geographical proximity and external coordinators. In doing so, our insights into firm-level challenges of long-distance IS exchanges contribute to closing global material loops by increasing the number of potential circular pathways.

A simulation-based architecture for supporting strategic and tactical decisions in the apron of Rome-Fiumicino Airport

In this paper, we describe an architecture for the evaluation and optimization of aircraft ground movements in apron taxiways. The paper aims at providing an effective methodology for supporting the decision-makers involved in both the apron design and management phases. The purpose deriving from the utilization of the proposed approach consists in obtaining substantial improvements in the level of service with a reduction in congestion and ground delays within airports while considering safety aspects like aircraft separation. The methodology relies on a modular architecture. A simulation-based architecture, in which an optimization module is included, has been developed; an information feedback between simulation and optimization modules is enabled. The validation has been performed through the data of the apron of Rome-Fiumicino airport. The computational results show a reduction in aircraft flowtime and a relevant decrease in aircraft ground flows. Interesting issues related to strategic modification of system configuration are presented.

A comprehensive model for short-haul and long-haul transportation

In networked production environments and globalized economy an efficient, high quality and sustainable freight transport represents a crucial challenge nowadays. In this context, intermodality can reduce the environmental and social impacts of transportation operations. The paper faces the problem of freight transportation planning of logistics platforms in a multimodal network. Generally, these complex problems are approached in the literature through their decomposition into sub-problems that are individually solved. The paper presents a comprehensive model and a solution method based on Lagrangian relaxation in order to consider simultaneously the features and constraints related to short-haul and long-haul transportation. In the proposed approach a decision maker coordinates logistics platforms and aims at optimizing the transportation plans on a determined time horizon.

A model to realise sustainability in networked production and transportation

Cost optimisation in decentralised, make-to-order production systems requires tight integration with suppliers and transport operations as well as flexible network connections. Additionally, minimisation of environmental impacts of freight flows must be included in the industrial practice to realise sustainable growth. To these aims, the paper presents a model integrating production networks and sustainable freight transportation. The model includes Bill-of-Material constraints with alternative sources having different production and distribution costs. The objective function considers sourcing, production and transportation costs as well as environmental impacts of transport over a multimodal network. Due dates and time windows constraints for production and transportation management are included. Computational experiments are based on a real multimodal network. The optimisation model solved the case study instance. A sensitivity analysis proved the model robustness. The results demonstrate that the model can be effectively used in order to analyse cost-emissions trade-offs and the influence of links’ capacity on emissions.

Simulation of Supply-Chain Networks: A Source of Innovation and Competitive Advantage for Small and Medium-Sized Enterprises

Simulation is a method for tackling a problem by constructing a model of the related system. It starts with an abstraction process, from which a dynamic model of the system and its logic is built. Simulation software provides the development environment in which the model is implemented, verified, validated, and experimented with to evaluate different scenarios of interest, which depend on the goals of the simulation. Researchers and companies may create their own “in house” simulation tools, although commercial software is also available and is widely used in industry. Prices vary according to feature availability, software updates, maintenance, customer service, add-on capabilities, and user friendliness. The widespread use of simulation tools in large enterprises as well as in research institutions confirms its relevance and practical utility. However, this article emphasizes the increasing relevance of simulation in supply-chain network design and management and, more importantly, its relevance to small and mediumsized enterprises (SMEs) as a source of competitive advantage and predictive power in their decision making.

A NEW MODEL FOR ACHIEVING VALUE ADDED GOALS IN A COLLABORATIVE INDUSTRIAL SCENARIO

Nowadays, at industrial research level, seems to be recognised that the Collaboration among firms is becoming a relevant and effective way of operating. For the enterprises rather than compete on costs it could be necessary increase the product/service value added; this goal could be effectively achieved by collaborating with other firms in the value chain.

Carrier Selection for Multi-commodity Flow Optimization in Cooperative Environments

Freight transportation decisions are critical economic and environmental factors in the design and management of networked manufacturing systems at global scale. Multimodal transportation options in combination with cooperative models between transport operators and together with manufacturers can contribute to define more economically and environmentally sustainable operations. This work addresses the problem of the selection of carriers in an international production and distribution network. The aim is to minimize costs and environmental impacts of freight transport. A cooperative decision-making setting between carriers in response to transportation demand of manufacturers is adopted. An integrated optimization-simulation approach is proposed to model the process of defining the optimal combination of transportation services in a multimodal transport network. Experiments show that collaboration based on shared modal capacity between carriers can produce transport cost reduction and service level improvements.