Net-Simulation: combining optimisation and simulation in the textile industry

Abstract

In this paper we present a new concept, NET-SIMULATION, that combines discrete optimisation and discrete event simulation techniques for the textile industry. Although the discrete optimisation and the discrete event simulation techniques are well known, in this article we present a scheme that improves the performance of the planning and decision making in a company by combining both techniques in an integrated form. The scheme consists in an optimisation module that optimises the production planning from a deterministic point of view and then sends this plan to a simulation module that validates or invalidates the plan, using the stochastic information of the production plant and the information of the orders and products that are in the production process. These two steps are done several times up to arrive to a convergent result. If the simulation invalidates one solution, then the optimisation has to use the constraints that the simulation has detected and use them to make a new plan. These constraints are the production machines, the laboratory resources to prepare the orders, the human resources, etc. The approach proposed in this paper has its correspondence in the continuous domain where optimisation and simulation is combined in order to optimal control, using predictive strategies, water distribution networks, sewer networks. In this field, optimisation and simulation are combined in order to generate optimal controls and the result of application to the real system is measured and used in the computation of following optimal controls (predictive control strategy) (Brdys, 1994) (Cembrano, 2000) (Cembrano, 2003). The idea or marrying simulation and optimisation is a field that has deserved attention of serveral authors as Morito (1999), Glover (1999), among others. The NET-SIMULATION concept is being developed in the European project TEXTERM Textile Extended Enterprise Resource management System (GRD1-2000-26817) and it is being applied to the dying textile company Gassol Color. At present, we are validating the scheme and testing the software in the Gassol Color plant in Salt (Girona-Spain).