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<div><div>This thesis analyzed three fundamental fluid dynamics problems arising from multiphase flows that may be encountered in hydraulically fractured flow passages. During hydraulic fracturing (``fracking''), complex fluids laden with proppants are pumped into tight rock formations. Flow passages in these formation are naturally heterogeneous with geometric variations, which become even more pronounced due to fracking. Upon increasing the flow area (and, thus, the conductivity of the rock), crude oil, shale gas or other hydrocarbons can then flow out of the formation more easily. In this context, we encounter the following three fluid mechanical phenomena: fluid--fluid interfacial instabilities, flow-wise variation of the hydraulic conductivity, and particle migration in the pumped fluids. </div><div><br></div><div>First, we studied the (in)stability of the interface between two immiscible liquids in angled (tapered) Hele-Shaw cells, as model of a non-uniform flow passage. We derived an expression for the growth rate of perturbations to the flat interface and for the critical capillary number, as functions of the small gap gradient (taper). On this basis, we formulated a three-regime theory to describe the interface's stability. Specifically, we found a new regime in which the growth rate changes from negative to positive (converging cells), or from positive to negative (diverging cells), thus the interface's stability can change type at some location in the cell. We conducted three-dimensional OpenFOAM simulations of the Navier--Stokes equations, using the continuous surface force method, to validate the theory.</div><div><br></div><div>Next, we investigated the flow-wise variation of the hydraulic conductivity inside a non-uniformly shaped fracture with permeable walls. Using lubrication theory for viscous flow, in conjunction with the Beavers--Joseph--Saffman boundary condition at the permeable walls, we obtained an analytical expression for the velocity profile, conductivity, and wall permeation velocity. The new expression highlights the effects of geometric variation, </div><div>the permeability of the walls, </div><div>and the effect of flow inertia.</div><div>The theory was validated against OpenFOAM simulations of the Navier--Stokes equations subject to a tensorial slip boundary condition.</div><div><br></div><div>Finally, we extended the utility of phenomenological models for particle migration in shear flow using the physics-informed neural networks (PINNs) approach. We first verified the approach for solving the inverse problem of radial particle migration in a non-Brownian suspension in an annular Couette flow. Then, we applied this approach to both non-Brownian and Brownian suspensions in Poiseuille slot flow, for which a definitive calibration of the phenomenological migration model has been lacking. Using PINNs, we identified the unknown/empirical parameters in the physical model, showing that (unlike assumptions made in the literature) they depend on the bulk volume fraction and shear P\'eclet number. </div></div>

<div>Thermal barrier coatings (TBCs) made of low thermal conductivity ceramic topcoats have been extensively used in hot sections of gas turbine engines, in aircraft propulsion and power generation applications. TBC damage may occur during gas turbine operations, due to either time- and cycle-dependent degradation phenomena, external foreign object damage, and/or erosion. The damaged TBCs, therefore, need to be removed and repaired during engine maintenance cycles. Although several coating removal practices have been established which are based on the trial-and-error approach, a fundamental understanding of coating fracture mechanisms during the removal process is still limited, which hinders further development of the process.</div><div>The objective of the thesis is to develop a particle-based coating removal modeling framework, using both the smoothed particle hydrodynamics (SPH) and discrete element modeling (DEM) methods. The thesis systematically investigates the processing-property relationships in the TBC removal processes using a modeling approach, thus providing a scientific tool for process design and optimization.</div><div>To achieve the above-mentioned objective, the following research tasks are identified. First a comprehensive literature review of major coating removal techniques is presented in Chapter 2. Chapter 3 discusses an improved SPH model to simulate the high-velocity particle impact behaviors on TBCs. In Chapter 4, the abrasive water jet (AWJ) removal process is modeled using the SPH method. In Chapter 5, an SPH model of the cutting process with regular electron beam physical vapor deposition (EB-PVD) columnar grains is presented. In Chapter 6, a 3D DEM cutting model with regular EB-PVD column grains is discussed. In Chapter 7, a 2D DEM cutting model based on the realistic coating microstructure is developed. Finally, in Chapter 8, based on the particle-based coating removal modeling framework results and analytical solutions, a new fracture mechanism map is proposed, which correlates the processing parameters and coating fracture modes.</div><div>The particle-based modeling results show that: (1) for the SPH impact model, the impact hole penetration depth is mainly controlled by the vertical velocity component. (2) The SPH AWJ simulation results demonstrate that the ceramic removal rate increases with incident angle, which is consistent with the fracture mechanics-based analytic solution. (3) The SPH model with regular EB-PVD columnar grains shows that it is capable to examine the stress evolutions in the coating with columnar grain structures, which is not available if a uniform bulk coating model was used. Additional analysis reveals that the fracture of the columnar grains during the cutting process is achieved through deflection and fracture of the grains, followed by pushing against neighboring grains. (4) The 3D DEM model with regular coating columnar grains shows that, during the coating removal process, a ductile-to-brittle transition is identified which depends on the cutting depth. The transition occurs at the critical cutting depth, which is based on the Griffith fracture criterion. At small cutting depths, the ductile failure mode dominates the cutting process, leading to fine cut particles. As the cutting depth exceeds the critical cutting depth, a brittle failure mode is observed with the formation of chunk-like chips. (5) The 2D DEM model with the realistic coating microstructure shows that there are densification and fracture during the foreign object compaction process, which qualitatively agrees with the experimental observations. (6) The newly proposed coating fracture mechanism map provides guidance to predict three fracture modes, i.e., ductile brittle, and mixed ductile-brittle, as a function of processing parameters, including the cutting depth and cutting speed. The map can be used to determine the processing conditions based on required TBC removal operations: rough cut (brittle mode), semi-finish (mixed ductile-brittle mode), and finish (ductile mode).</div><div><br></div>

The master thesis deals with the design of the injection mold for the production of a plastic two-part worm which is part of the worm gear set in the sleeve. From the beginning, an analysis of the assigned component was performed, specifying its function and specifying the criteria that must be met by the component. In addition, design of the production technology (injection molding) was carried out, followed by theoretical analysis of plastic materials, injection molding technology and mold design. Subsequently, in the practical part, a complete design of the injection mold was made on the basis of simulations and technological calculations. On the basis of the parameters of the injection mold, a machine was chosen, on which production should be carried out according to the proposed technological procedure. The conclusion of the thesis contains a technical and economic evaluation of the proposed technology for the production of Plastics splatter component.

<p> An investigation into the impact of the Reynolds Bauxite Company, a decentralized industry in north-central Jamaica, on the spatial pattern of employment in the surrounding area. The spatial impact is simulated using the Polya-Eggenberger distribution. </p> / Thesis / Master of Arts (MA)

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Yes / To study the flexural behavior of Steel-FRP (Fiber-Reinforced Polymer) Composite Bars (SFCBs) reinforced Reactive Powder Concrete (RPC) frame beams, the flexural behavior of six frame beams with different types of concrete and reinforcement was simulated and analyzed using the finite element software ABAQUS. The strain behavior of concrete and reinforcement was simulated using real strain models, and the simulation results matched well with the experimental results. Based on the validated model, the effect of mechanical properties of concrete and SFCB, reinforcement ratio, and the dimensions of frame beam on the flexural behavior of frame beams was parametrically analyzed. The results showed that, compared with the steel-reinforced ordinary concrete (OC) frame beam, the ultimate deflection of SFCB-OC frame beam increased by 5%. Compared with the SFCB-OC frame beam, the bearing capacity and ultimate deflection of the SFCB-RPC frame beam increased by 16% and 22%, respectively. Improving the steel content of SFCB reduced the ultimate load and deformation of SFCB-RPC frame beam. The yield strength of SFCB core steel had a significant influence on the yield load of frame beam, but a small influence on the ultimate load and deformation. Enhancing the elastic modulus of SFCB out-wrapped FRP reduced the ultimate deformation of the frame beam. Improving the reinforcement ratio of SFCB increased the bearing capacity and reduced the deformation. When reinforced concrete frame beams had similar bearing capacity, the cross-sectional dimensions of steel-RPC frame beam, FRP-RPC frame beam, and SFCB-RPC frame beam are 90.1%, 61.5%, and 72.7%, respectively, of those of their corresponding respective reinforced OC frame beams. All reinforced RPC frame beams exhibited high bearing capacity, good deformation, ductility, and energy dissipation performance. This research can provide a reference for the design of SFCB-RPC frame beams. / High-End Foreign Experts Project of Ministry of Science and Technology, China (G2022014054L), the Science and Technology Project of Gansu Construction System (JK2021-19), the Science and Technology Project of Jiangsu Construction System (2018ZD047, 2021ZD06, 2023ZD104, 2023ZD105), the Science and Technology Cooperation Fund Project of Yangzhou City and Yangzhou University (YZ2022194), the Yangzhou Construction System Science and Technology Project (202309, 202312), the Research Project of Jiangsu Civil Engineering and Architecture Society (the Second Half of 2022). / The full-text of this article will be released for public view at the end of the publisher embargo on 27 Jan 2025.

一、研究目的： 華江橋台北端為一圓環，在交通尖峰時間，此一圓環容易發生壅塞，車輛通過頗為費時。由於華江橋圓環目前所有進出路口均為雙向行車，車輛進出皆無任何管制，假若吾人對進出華江橋圓環的車輛施予若干管制，其交通是否會獲得改善？針對這個問題，本研究之目的即為：(1)制訂華江橋圓環的交通管制策略。(2)建立華江橋圓環交通的模擬模式，以便進行各種交通管制策略之評估。 二、研究方法： 本研究制訂交通管制策略的方法是根據有關文獻的結論與建議，參酌實際上華江橋圓環的交通狀況而主觀訂定各種改善策略。由於每個圓環的幾何形狀與交通流量的情形不會完全相同，因此吾人必須將所訂定的策略加以評估。本研究所用的評估方法是固定時間增加的模擬分析法(Fixed-time Incremental Simulation Analysis) 三、研究內容： 本文共分六章。第一章介紹研究動機、目的、資料來源及研究方法。第二章為有關文獻之探討。第三章介紹系統模擬的基本概念及進行的步驟。第四章說明如何調查華江橋圓環的交通流量，並對調查結果作了必要的統計檢定。第五章建立了華江橋圓環模擬模式，並對所建立的模擬模式作了信度檢定。第六章為各種管制策略的模擬結果與分析，並選定一組較佳之華江橋圓環交通管制策略。 四、研究結果： 本研究之結果顯示，在尖峰時間內若禁止車輛從環河南街往西門町的路口離去，同時以各路口車輛到達數來控制車輛進入圓環，可以獲致良好的交通管制效果。

In order to cope with the turbulent environments in digital age, an enterprise should response to the changes quickly. Therefore, an enterprise must improve her ability of real-time decision-making. One way to increase the competence of real-time decision-making is to use Real-Time Decision Support Systems (RTDSS). A key feature for a Decision Support Systems (DSS) to successfully support real-time decision-making is to help decision-makers selecting the best models within deadline. This study focuses on developing methods to support the mechanism of model selection in DSS. There are five results in this study. Firstly, we have developed a time-based framework to evaluate models. This framework can help decision-makers to evaluate the quality and cost of model solutions. Secondly, based on the framework of models evaluation, we also developed three models selection strategies. These strategies can help decision-makers to select the best model within deadline. Thirdly, according the definitions of parameter value precision and model solution precision in this study, we conduct a simulation analysis to understand the impacts of the precision of parameter values to the precision of a model solution. Fourthly, in order to understand the interaction among the model selection variables, we also simulate the application of model selection strategies. The results of simulation indicate our study can support models selection well. Finally, we developed a structure-based model retrieval method to help decision-makers find alternative models from model base efficiently and effectively. In conclusion, the results of this research have drawn a basic skeleton for the development of models selection. This research also reveals much insight into the development of real-time decision support systems.