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This paper formalises the evolution from decision problems to disjunctive optimisation problems based on several alternative Petri Net (PN) models. This copes with the general problem of Discrete Event Systems (DES) design and operation. A new type of PN called Alternatives Aggregation Petri Nets (AAPN) is presented as a promising tool to solve this general problem in an efficient way. AAPN are constructed by aggregating the alternative PN models, which are feasible solutions to the DES design. As a result, the optimisation problem can be solved by means of classical methods like exhaustive or heuristic search in a single phase. (2010) 'The alternatives aggregation Petri nets as a formalism to design discrete event systems', Int.

This paper proposes the integration of life cycle analysis within the production system models as a tool for decision making (whether at the strategic, tactical or operational levels) attending not only economic and technical criteria but also the environmental impact. This methodological proposal advances over the traditional approach of calculating the value of the environmental impact of a particular product, by proposing the use of models to determine the environmental impact of the product, according to the decisions made in the production system. That is, it does not provide an impact value of the product, but rather a model to determine the impact in terms of the decisions made in the production process; therefore, it can be used, especially by means of simulation, for the optimization of the production system, based on multiple criteria (including environmental impact). The methodological approach is exemplified by a case study, which is used to validate the proposal and to expose it more precisely and clearly, although the methodology is equally applicable to any production process, especially processes highly automated or with different alternative production techniques. This case study, based on the wine production sector of the Rioja Qualified Designation of Origin, in Spain, was made with actual data after several years of research in representative wineries; therefore, besides an application example, it is a support tool for sustainability in wineries, by reducing the environmental impact of wine production (especially in La Rioja and Spain, but generally throughout the world).

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This paper presents a study to evaluate the effect of the tool profile on friction stir welding (FSW) process in the aluminium AA 1050, using vibroacoustic signals. The vibroacoustic signals in Z and Y directions have been acquired by the AE instrument NI USB-9234. The characterisation in time and frequency domains and the statistical analysis of vibroacoustical signal have been carried out in order to correlate them with the design of two different tools. Statistical and temporal parameters of discomposed vibroacoustical signals using wavelet transform have been used for filtering vibration signal to eliminate the noise of the FSW machine and the extraction features of them. The analysis has confirmed that the vibroacoustical signals were significantly affected by changes in the tool profiles. Finally, it has been demonstrated that signals generated by this process can be effectively used to characterise the changes on tool design.

The construction, set-up and operation of many systems of interest in sectors such as industry, supply chains and communications are complex processes, which may require significant investment of resources. For this reason, the automation of the decision making for achieving the best design and operation of such systems, which may be regarded as discrete event systems (DESs), constitutes an active research field. In this paper, we present a methodology to cope with this process in an efficient way, optimizing not only the behaviour of the DES but also its structure. This kind of problem is usually associated with the so-called combinatorial explosion, since the number of alternative configurations for the DES might be huge. We present an improved algorithm to transform a set of alternative Petri nets, representing alternative structural configurations, into a more compact model called an alternatives aggregation Petri net. In real decision-making problems, where the different alternative structural configurations may share common subnets, this compact model may allow the development of a much more efficient optimization problem than the classic approach of ‘divide and conquer’. The achievement of this objective is performed by developing a single and compact model for all of the alternative structural configurations of the DES and the simulation of the most promising of them. In this paper, the mentioned methodology is introduced and its advantages and drawbacks are described in relation with the classic approach.

Petri nets (PN) paradigm is broadly used to model discrete event systems (DES). Thanks to both, its graphical and algebraic representations, PN provide a powerful and uniform tool, with an important theoretical support for modelling and formal analysis. On the other hand, genetic algorithms constitute a metaheuristics able to cope with complex problems of combinatorial optimisation. The use of genetic algorithms to solve optimisation problems based on PN models is a classical research line; nevertheless, it has been applied mainly to decision support systems related only to the operation of DES. In this paper a general statement of decision problems is proposed, including not only the operation but also the design process of the DES. This leads to a set of undefined parameters, classified according to their role in the PN model. Moreover, under certain circumstances, the PN model can appear as a disjunctive constraint. Alternatives aggregation PN are presented as a natural formalism to afford the transformation of the disjunctive constraint and to define a single solution space that allows genetic algorithms to perform a very efficient search of the best solution in a single process. A case-study is presented exhaustively, where the proposed methodology outperforms more classical approaches.