Scholarworks@UNIST
http://scholarworks.unist.ac.kr:80
The Repository digital repository system captures, stores, indexes, preserves, and distributes digital research material.2024-03-15T05:59:53ZModel-based safe reinforcement learning for nonlinear systems under uncertainty with constraints tightening approach
https://scholarworks.unist.ac.kr/handle/201301/81661
Title: Model-based safe reinforcement learning for nonlinear systems under uncertainty with constraints tightening approach
Author(s): Kim, Yeonsoo; Oh, Tae Hoon
Abstract: In chemical processes, the safety constraints must be satisfied despite any uncertainties. Reinforcement learning is an algorithm that learns optimal control policies through interaction with the system. Recently, studies have shown that well-trained controllers can improve the performance of chemical processes, but the actual application requires additional schemes to satisfy the constraints. In our previous work, we proposed a modelbased safe RL in which both state and input constraints can be considered by introducing barrier functions into the objective function. This study extends our previous model-based safe RL to consider the constraints with model-plant mismatches and stochastic disturbances. The Gaussian processes are employed to predict the expectation and variance of errors in constraints caused by uncertainties. Subsequently, these are further used to tighten the constraint by backoffs. With these adaptive backoffs, the safe RL can satisfy chance constraints and learn the optimal control policy of the uncertain nonlinear system.2024-03-31T15:00:00ZConceptual Design of an Energy-Efficient Process for Separating Aromatic Compounds from Naphtha with a High Concentration of Aromatic Compounds Using 4-Methyl-N-butylpyridinium Tetrafluoroborate Ionic Liquid
https://scholarworks.unist.ac.kr/handle/201301/81660
Title: Conceptual Design of an Energy-Efficient Process for Separating Aromatic Compounds from Naphtha with a High Concentration of Aromatic Compounds Using 4-Methyl-N-butylpyridinium Tetrafluoroborate Ionic Liquid
Author(s): Oh, Tae Hoon; Oh, Se-Kyu; Kim, Hosoo; Lee, Kyungmoo; Lee, Jong Min
Abstract: To obtain aromatic compounds from a crude mixture such as reformate or pyrolysis gasoline, three different processes are simulated with the realistic composition of reformate and product specification. Simulations were performed by Aspen Plus supported with COSMO-RS method to predict the physical and thermodynamic properties of ionic liquid. Furthermore, utility analysis and economic evaluation are presented. Conventionally, aromatic compounds are extracted from a crude mixture either by extraction or by extractive distillation using a solvent such as sulfolane and separated by a series of distillation columns. In this study, the sulfolane-based commercial process is first introduced, and two novel processes that use 4-methyl-N-butylpyridinium tetrafluoroborate ionic liquid as solvent are proposed. The second process shows that energy consumption has successfully decreased, but the high price of ionic liquid offset the cost advantage. The third process is therefore proposed to reduce the amount of ionic liquid using two extractions. A similar level of energy saving is achieved with reduced costs.2017-05-31T15:00:00ZGraph Neural Network-Based Detailed Placement Optimization Framework
https://scholarworks.unist.ac.kr/handle/201301/81659
Title: Graph Neural Network-Based Detailed Placement Optimization Framework
Author(s): Lim, Dho Ui; Park, Heechun2024-04-02T15:00:00ZDesign-Technology Co-Optimization with Standard Cell Layout Generator for Pin Configurations
https://scholarworks.unist.ac.kr/handle/201301/81658
Title: Design-Technology Co-Optimization with Standard Cell Layout Generator for Pin Configurations
Author(s): Yoon, Junghyun; Park, Heechun2024-04-02T15:00:00Z