4 research outputs found
Standalone closed-form formula for the throughput rate of asynchronous normally distributed serial flow lines
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Flexible flow lines use flexible entities to generate multiple product variants using the same serial routing. Evaluative analytical models for the throughput rate of asynchronous serial flow lines were mainly developed for the Markovian case where processing times, arrival rates, failure rates and setup times follow deterministic, exponential or phase-type distributions. Models for non-Markovian processes are non-standalone and were obtained by extending the exponential case. This limits the suitability of existing models for real-world human-dependent flow lines, which are typically represented by a normal distribution. We exploit data mining and simulation modelling to derive a standalone closed-form formula for the throughput rate of normally distributed asynchronous human-dependent serial flow lines. Our formula gave steady results that are more accurate than those obtained with existing models across a wide range of discrete data sets
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Constrained black box optimization for radioisotope thermal generator manufacturing
This thesis aims to optimize the conditions and policies used at Los Alamos National Laboratory for the manufacturing of Radioisotope Thermal Generators used for deep space exploration. This manufacturing faces unique and stringent constraints on their operations as well as extraordinarily rigorous quality control measures to ensure that products will work when deployed. Furthermore, this manufacturing process is new, and no historical data exists to prove the capability of the manufacturing system and what the expected operating costs will be. Through this analysis, a theoretical model is constructed to understand the system dynamics to arrive at a theoretical product throughput. A base case of the manufacturing system is created using values for the system as it is currently envisioned. From this case, the total cost, average total time per product, and the number of products completed are optimized. This optimization is achieved by changing the policies on how batches are formed and when operators should work to use resources most efficiently and ensure that no resource is under or over-utilized. It was discovered that the most efficient policy is to add a half working day on Saturdays which significantly reduces the cost by about 30,000 utilizing the optimized values. Finally, using cost estimation techniques, the total manufacturing cost including fringe benefits, maintenance, operating supplies, and supervisory labor is estimated to be around 3M per year. The results presented in this thesis can inform Los Alamos National Laboratory on the direction and policies that must be implemented to meet manufacturing targets. Furthermore, the methodology developed can be expanded and applied to other product lines throughout the lab to analyze throughput and stay cost efficient while meeting national security requirements.Mechanical Engineerin
Empirical study of the effect of stochastic variability on the performance of human-dependent flexible flow lines
Manufacturing systems have developed both physically and technologically, allowing production of innovative new products in a shorter lead time, to meet the 21st century market demand. Flexible flow lines for instance use flexible entities to generate multiple product variants using the same routing. However, the variability within the flow line is asynchronous and stochastic, causing disruptions to the throughput rate. Current autonomous variability control approaches decentralise the autonomous decision allowing quick response in a dynamic environment. However, they have limitations, e.g., uncertainty that the decision is globally optimal and applicability to limited decisions. This research presents a novel formula-based autonomous control method centered on an empirical study of the effect of stochastic variability on the performance of flexible human-dependent serial flow lines. At the process level, normal distribution was used and generic nonlinear terms were then derived to represent the asynchronous variability at the flow line level. These terms were shortlisted based on their impact on the throughput rate and used to develop the formula using data mining techniques. The developed standalone formulas for the throughput rate of synchronous and asynchronous human-dependent flow lines gave steady and accurate results, higher than closest rivals, across a wide range of test data sets. Validation with continuous data from a real-world case study gave a mean absolute percentage error of 5%. The formula-based autonomous control method quantifies the impact of changes in decision variables, e.g., routing, arrival rate, etc., on the global delivery performance target, i.e., throughput, and recommends the optimal decisions independent of the performance measures of the current state. This approach gives robust decisions using pre-identified relationships and targets a wider range of decision variables. The performance of the developed autonomous control method was successfully validated for process, routing and product decisions using a standard 3x3 flexible flow line model and the real-world case study. The method was able to consistently reach the optimal decisions that improve local and global performance targets, i.e., throughput, queues and utilisation efficiency, for static and dynamic situations. For the case of parallel processing which the
formula cannot handle, a hybrid autonomous control method, integrating the formula-based and an existing autonomous control method, i.e., QLE, was developed and validated.InnovateU
Advances in stochastic models of manufacturing and service operations
The special issue on advances in stochastic models of manufacturing and service operations presents state-of-the art research results in the area of stochastic models for the analysis, design, coordination, and control of manufacturing and service system operations. Although the title includes both "manufacturing" and "service" operations, the main emphasis is on manufacturing. The term "service system operations" is intended to refer mainly to functions that are supportive of manufacturing system operations. The volume includes thirteen state-of-the art articles that can be classified in three categories: stochastic modeling and analysis for design and optimization of manufacturing systems; production planning, management, and control; and analytical approaches to supply chain management