Browsing by Author "Tu, Paul"
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- ItemOpen AccessCapacity and Operational Performance Optimization under External Constraints with Uncertainty(2016) Sabzevar, Nikoo; Enns, Van; Bergerson, Joule; Freiheit, Theodor; Silva, Emilson; Tu, Paul; Alp, OsmanThis thesis presents novel models to investigate the significant impacts of globalization, demand uncertainty, competition, and external emissions regulations on firms' profitability, operational performance, and decision-making processes. The models relax common simplifying assumptions (i.e., deterministic lead-times, exogenous emissions permit price) to better represent real market characteristics and applications. Specifically, these models are developed in the context of maritime shipments of fuels, such as Liquefied Natural Gas (LNG), to supply global energy markets. The transport capacity investment problem is studied in terms of a mixed integer nonlinear model to maximize a single firm's profit. Using a proposed heuristic algorithm, the model determines the optimal number and size of tankers to deliver a single product under demand uncertainty. The model incorporates economies of scale, lost sales penalties, and the possibility of leasing extra capacity. Results show that tanker size and capacity utilization decrease if demand uncertainty increases. Moreover, tanker sizes are found to decrease as economies of scale decrease. This model is extended to a duopoly setting under competition constrained by the cap-and-trade policy. It is treated as a nonlinear Cournot game and solved analytically to maximize firms' individual profits by determining their optimal production volumes. Furthermore, it provides a set of cap-and-trade policy characteristics (i.e., market cap, cap allocation rate, permit price) leading to the maximum total profit and increasing the trading possibility. Moreover, individual bounds on the ranges of these characteristics are determined within which trading occurs. This model is modified for the carbon tax policy and is further extended to an oligopoly natural gas (NG) market to satisfy price-sensitive NG demand in the Chinese power sector. The supplied NG volume replaces a fraction of the coal consumption for electricity generation to investigate the economic and environmental implications of replacing coal with imported NG in its life cycle through an integrated Cournot game and life cycle assessment approach. The model is able to find a carbon price range under various sources of uncertainty involved in the market at which the import of NG to generate electricity is economically preferred compared to the coal-dominant Chinese power mix outlook.
- ItemOpen AccessChatter Suppression in Boring Operations through Altering Tool Dynamics(2016) Alammari, Youssef; Park, Simon; Freiheit, Theodor; Dalton, Colin; Tu, Paul; Xue, DeyiIn machining, a phenomenon known as chatter, which is a self-excited excessive vibration, is considered one of the most limiting factors for productivity. Particularly in boring process, the long cantilevered structure of boring bar makes it the most flexible part of machine tool system. As a result, there is a high possibility for chatter to occur compared with other machine tool components. In this research, two methods were investigated to attenuate chatter and increase stability in boring operations by manipulating the boring bar structure dynamics. First, the effect of altering the boring bar’s natural frequency on chatter is investigated through varying the boring bar’s overall mass. Second, a tuned liquid column damper (TLCD) is developed to improve the dynamic stiffness for boring bars application for improving the overall stability. Several models and experiments are carried out for evaluating the performance of the proposed methods.
- ItemOpen AccessConcept and Methods for the Development of Blockchain based Cloud Manufacturing(2023-04-30) Wang, Binni; Tu, Paul; Li, Simon; Xue, Deyi; Thekinen, Joseph; Patterson, Raymond; Zeng, YongCloud manufacturing is seen as a promising improvement for networked manufacturing, with potential for achieving higher service quality at a lower cost, although the progress of its application has not met expectations. The main obstacle hindering its adoption is the reluctance of potential users to share data with cloud manufacturing due to concerns about data safety issues caused by central management. To address this drawback, the integration of a decentralized blockchain system has been proposed as a promising solution. However, the traceable data and provable system features of blockchain technology cannot guarantee data security, particularly for small or moving objects that lack the ability for data verification. Therefore, blockchain-based cloud manufacturing systems must have the ability to ensure data reliability. Moreover, the scalability problem must be addressed for the adoption of a blockchain-based system. This PhD thesis proposes a feasible architecture for a blockchain-based cloud manufacturing system and evaluates the reliability of perceived data through data similarity measurement. Firstly, the architecture of the system is outlined, with the use of rollup technology to address scalability issues. Second, the proper fee setting for the system is analyzed. For data similarity measurement, comparable data is selected using a modified clustering algorithm, and the data is described using polygon-based descriptions, including existing and proposed polygon descriptions. Finally, data similarity measurement is transformed into a similarity comparison of polygon descriptions, with methods such as multi-objective programming-based similarity comparison and overlap area-based similarity comparison applied for this purpose. The feasibility of the proposed methods is verified through a case study.
- ItemOpen AccessConcepts and Methods for the Development of Efficient Femtosecond Laser Micromachining Technology(2014-03-06) Chang, Gang; Tu, PaulThe femtosecond pulse laser is a useful tool for micro/nano-machining, which is a fundamental technology for fabricating micro 3D structure devices or components such as micro fluidic devices or micro optical components. However, it is a challenge to control the machining precision since the laser is a non-contact tool and the machining result is affected by various factors. To figure out the influence of these factors, the a concept of named asof laser ablation volume (LAV) is introduced in the thesis research work to describe the ‘shape’ of the laser machining tool. The spatial structure of LAV is investigated to provide the principle to about controling the resolution and the depth evolution in a micro machining process. The shape and the size of LAV are determined by the pre-designed parameters. A computational model based on the shape of LAV has been verified to deal with different combinations of the moving path and moving speed of LAV for the purpose to improve the machining accuracy. Furthermore, based on the concept of LAV, a closed loop control of the micro milling process has been successfully accomplished in which the laser triggered plasma is employed as a real-time feedback indicator.
- ItemOpen AccessContract Design for Cloud Logistics (CL) Based on Blockchain Technology (BT)(2020-04-28) Xu, Lan; Tu, Paul; Tang, QianPurpose. This paper aims to design the contract and present the profit distribution mechanism for CL platform, so as to realize the intelligent and automatic operation of the artificial intelligent- (AI-) based CL platform. Design/Methodology. A smart contract based on BT is designed for the AI-based CL platform. Profit distribution mechanism based on the Nash bargaining model for the CL platform is also put forward to coordinate different participators’ benefit relationship in CL. Findings. The AI-based CL platform and the proposed smart contract based on BT map the scenario which may be influenced by human factors and involve trust issues onto execution of codes. Practical Implications. The study will help CL practitioners in establishing effective profit mechanism and designing contracts on the platform, thus facilitating its sustainable operation. Originality/Value. The AI-based CL platform with BT smart contract can be totally free of human intervention, and hence, the problems of trust during CL platform’s operation are solved.
- ItemOpen AccessDesign Project Scheduling with Probabilistic Iterations: Optimization & Investigation of Robustness(2018-09-05) Ebufegha, Akposeiyifa Joseph; Li, Simon; Tu, Paul; Xue, Deyi; Sadeghpour, FarnazThis research focuses on reliable prediction of product development (PD) project duration within reasonable solution times. It is based on the model of PD projects presented by Smith and Eppinger which suggests that PD projects are akin to Markov reward chains. The research was divided into two phases; the development of a hybrid algorithm to minimize the problem’s solve time without compromising solution quality and the identification of features of a robust PD schedule. The first phase of the research shows that the hybrid algorithm yields similar quality solutions whilst reducing solve times by 50% - 97.4%. The second phase highlights four features that affect robust PD schedule as well as patterns observed in the schedule. In conclusion, this research demonstrates the utility of the developed hybrid algorithm and also illustrates the importance of examining expected project duration and the standard deviation in the results when developing robust PD schedules.