This paper proposes a Systems Modeling Language (SysML)-based simulation model aggregation framework to develop aggregated simulation models with high accuracy. The framework consists of three major steps: 1) system conceptual modeling, 2) simulation modeling, and 3) additive regression model-based parameter estimation. SysML is first used to construct the system conceptual model for a generic seedling propagation system in terms of system structure and activities in a hierarchical manner (i.e. low, medium and high levels). Simulation models conforming to the conceptual model are then constructed in Arena. An additive regression model-based approach is proposed to estimate parameters for the aggregated simulation model. The proposed framework is demonstrated via one of the largest grafted seedling propagation systems in North America. The results reveal that 1) the proposed framework allows us to construct accurate but computationally affordable simulation models for seedling propagation system, and 2) model aggregation increases the randomness of simulation outputs.
INTRODUCTIONGrafting is a horticultural technique whereby tissues from one plant are joined with another to obtain a combination of rootstock and scion genotypes that are more desirable than those contained in a single plant. The advantage of the vegetable grafting is to improve fruit yield and quality as well as to reduce the environmental impact through reducing chemical fumigants utilized in traditional cropping systems. According to Kubota et al. (2008), many seedling propagators in North America have strong interests in introducing grafting into their seedling propagation systems. For a seedling propagation system, uncertainties and complexity involved in high resource (e.g. machines and labors) management and in environmental factors (e.g. humidity and temperature) make the system performance difficult to predict. Discrete event simulation has become one of the most used analysis tools for large scale systems like seedling propagation system because it is one of the few tools that can take randomness into account, and it can address aggregate as well as very detailed models. A simulation model representing a seedling propagation system can be used to predict system performance, supporting various decisions in design or operation (e.g. production scheduling in a peak season) of the seedling propagation system. In simulation, fidelity refers to the faithfulness with which model behavior reflects modeled system behavior (Kim, Mcginnis and Zhou 2012). It has been recognized that the level of detail of simulation has a significant impact on the fidelity (Persson 2002;Vasudevan and Devikar 2011;Venkateswaran and Son 2004). For example, Venkateswaran and Son (2004) demonstrated that the dynamics and inventory level of supply chain are highly dependent on the level of detail of simulation models even though the models simulate the same process. One principal challenge that we faced while developing a highly detailed simulation model (i.e. low level sim...