Perturbation analysis for continuous and discrete flow models: a study of the delivery time impact on the optimal buffer level

In this paper, a manufacturing system composed of a single-product machine, a buffer and a stochastic demand is considered. Two models are presented: continuous and discrete flow models including constant delivery times, machine failures and random demands. The objective is to determine the value of the optimal buffer level, for a hedging point policy which minimises the total average cost function. The cost function is the sum of inventory, transportation and lost sales costs. Infinitesimal perturbation analysis is used for optimisation of the failure-prone manufacturing system. The trajectories of buffer level are studied for the continuous and discrete cases and the infinitesimal perturbation analysis estimators are evaluated. These estimators are shown to be unbiased and then they are implemented in an optimisation algorithm which determines the optimal buffer level in the presence of constant delivery time. Numerical results are presented for continuous and discrete flow models and then compared in order to evaluate the application of the infinitesimal perturbation analysis on the discrete flow model.     

A simulation based continuous improvement approach for manufacturing based field repair service contracting

This paper develops and tests a novel extension to traditional supplier selection practice, with a particular focus on the concluding stages of a manufacturing-based field service. Action-based research was used to design and develop a discrete event simulation decision support for a large multinational manufacturing organisation with a significant after-sales service supply chain. The framework has been designed to identify and validate the value attributable to collaborative supplier contracting with built-in costed performance improvement targets. Use of the framework in the case organisation was found to produce greater cost savings over traditional practice, facilitating extended supply chain contracts. The results provide evidence of the high level of savings achievable while also improving customer delivery through targeted service improvements over the contracts life cycle. This framework advances beyond the prevalent practice of cost-focused short-term adversarial supply contracting and is innovative in terms of its continuous improvement simulation based framework design.     

Agent-based manufacturing control based on distributed bid selection and publish-subscribe messaging: a simulation case study

Bidding-based negotiation schemes play a major role in multi-agent manufacturing systems research. Despite some concerns with message congestion, researchers have been proposing and studying negotiation schemes based on the contract net protocol (CNP). On the other hand, research in robotics has considered a variant of CNP based on publish-subscribe messaging designed for multi-robot coordination. A distinct feature of this variant involves distributing the bid evaluation and selection functions among robot agents. This paper discusses our adaptation of this design variant for multi-agent manufacturing systems and examines its performance implications. Using discrete-event simulation, we study how the adapted CNP design can help address the message congestion problem by cutting down on negotiation slack time. Our case study results show that it can enhance the resilience of the agent negotiation process to message congestion, thereby contributing to the overall performance of a multi-agent manufacturing system.     

A simulation study on the US rehabilitation service process for patients with modest-to-severe traumatic brain injury

Traumatic brain injury (TBI) is a devastating injury with severe consequences. In this paper, we conduct a simulation study on the commonly implemented care delivery process for TBI rehabilitation in the US, which covers three care categories: inpatient acute, outpatient sub-acute and general residential care. Our investigation is focused on assessing how coverage duration of publicly funded rehabilitation impacts two key system outcomes: sub-acute rehabilitation readmission and total rehabilitation spending. We develop prediction models on the above two outcomes for patients of different conditions. We introduce the notions of forceful transition and medical necessity adjustment, and embed the notions in a state-transition simulation model. Our simulation results suggest that to minimise the care spending, the duration of publicly insured outpatient sub-acute rehab be set smaller than what is currently implemented but not to the point where coverage should be completely removed. Our sensitivity analysis justifies the robustness of our results under variations on model parameters.     

A study on the dust control effect of the dust extraction system in TBM construction tunnels based on CFD computer simulation technology

In order to control dust in a tunnel boring machine (TBM) construction tunnels, this paper, in combination with field measurements, applies CFD computer simulation technology to study the dust control effect of TBM construction tunnels under different dust extraction flow rates. Firstly, the dust extraction system is closed, and the result of the simulation show that the dust diffuses to the entire TBM working area within 181 s, indicating the necessity of having a dust extraction system in the tunnel. Secondly, the dust extraction system is open and under the original dust extraction flow rate of Q_e = 8 m³/s, the overall dust diffuses to the entire working area L_o = 130 m, and the full-face dust diffusion distance is L_f = 47.54 m. Then the study was carried out with the setting of 2 m³/s ≤ Q_e ≤ 14 m³/s. The results show that: when Q_e ≤ 8 m³/s, the full-face dust diffuses to 47.54–71.84 m; when Q_e > 8 m³/s, the full-face dust can be controlled at 42.81–46.34 m; and when Q_e = 8 m³/s, the full-face dust control effect is better, and the average dust concentration in the tunnel is as low as 12.25 mg/m³, indicating that the original dust extraction system has a better design. The field measurement results verify that the CFD computer simulation results are accurate.