DSpace community: 工學院

Three-Dimensional Numerical Analysis of Thermal Field and Thermal Stress in β-????2??3 Crystal Growth Using the EFG Method

title: Three-Dimensional Numerical Analysis of Thermal Field and Thermal Stress in β-????2??3 Crystal Growth Using the EFG Method abstract: 在本論文中，建立了一個三維數值模型，用以分析採用邊界限定薄膜供料生長法（Edge-Defined Film-Fed Growth，EFG）生長 β-Ga?O? 晶體過程中的溫度場與熱誘發應力. 該模型是在穩態條件下建立, 並考慮了晶體沿 [010] 生長方向的各向異性熱導率, 同時假設結晶界面為平面. 透過電磁模擬獲得 EFG 系統內部的熱源分佈, 從而研究電磁加熱、溫度場以及晶體內熱應力形成之間的關係. 模擬結果顯示, 熱量主要在坩堝壁處產生, 並透過熱傳導與輻射傳遞至熔體與晶體, 進而形成軸向與徑向溫度梯度. 這些溫度梯度是熱應力產生的主要原因, 其中等效 von Mises 應力主要集中於靠近生長界面的晶體邊緣區域. 結果亦表明, 內部輻射對晶體內部的溫度分佈具有顯著影響, 而熔體流場對生長界面處的熱條件則未產生明顯影響. 此外, 本研究探討了在坩堝上方設置防護遮罩以改善熱傳條件並降低熱應力的效果. 結果顯示. 安裝遮罩可提高晶種區域的溫度, 減小軸向溫度梯度, 從而顯著降低熱應力. 進一步分析了晶體在生長過程中長度變化的影響, 結果顯示, 隨著晶體逐漸伸出高溫區, 溫度梯度與熱應力均呈現增加的趨勢. 總體而言, 本研究闡明了 EFG 法生長 β-Ga?O? 晶體過程中熱應力形成的機制, 並為優化系統設計與操作條件、降低熱應力及提升晶體品質提供了科學依據. ;In this thesis, a three-dimensional numerical model is developed to analyze the thermal field and thermally induced stress during the growth of β-Ga?O? crystals using the Edge-Defined Film-Fed Growth (EFG) method. The model is established under steady-state conditions and takes into account the anisotropic thermal conductivity of the crystal along the [010] growth direction, while the crystallization interface is assumed to be planar. The heat source distribution within the EFG system is obtained through electromagnetic simulations, allowing the relationship between electromagnetic heating, the thermal field, and thermal stress formation in the crystal to be examined. The simulation results show that heat is mainly generated at the crucible walls and transferred to the melt and the crystal through conduction and radiation, resulting in axial and radial temperature gradients. These temperature gradients are the primary cause of thermal stress, with the von Mises equivalent stress mainly concentrated near the crystal edges close to the growth interface. The results also indicate that internal radiation has a significant influence on the temperature distribution within the crystal, whereas the melt flow field has no noticeable effect on the thermal conditions at the growth interface. In addition, the effect of a protective shield placed above the crucible is investigated to improve heat transfer conditions and reduce thermal stress. The results demonstrate that the installation of the shield increases the temperature in the seed region, reduces the axial temperature gradient, and consequently leads to a significant reduction in thermal stress. Furthermore, the influence of crystal length during the growth process is examined, showing that as the crystal extends out of the hot zone, both temperature gradients and thermal stress tend to increase. Overall, this study provides insight into the mechanisms of thermal stress formation in β-Ga?O? crystals grown by the EFG method and offers a scientific basis for optimizing system design and operating conditions to reduce thermal stress and improve crystal quality.

以離散元素法探討岩坡崩塌能量與臨界斜交角

title: 以離散元素法探討岩坡崩塌能量與臨界斜交角 abstract: 岩坡穩定性受岩體不連續面位態及工程配置角顯著影響，其中坡面傾向（??s）與不連續面傾向（????）之交角，又稱斜交角（|???? ? ??s|, oblique angle）為控制岩坡穩定性與破壞模式轉換之關鍵參數。本文採用PFC3D（Particle Flow Code in Three Dimensions）離散元素法（Discrete Element Method, DEM），建立含單一不連續面之合成岩坡模型，模擬不同斜交角（|???? ? ??s|）與岩坡條件下的崩塌行為，並以崩塌能量為量化指標，探討摩擦角（?j）、坡角（βs）、坡高（H）及不連續面傾角（βj）對崩塌能量與臨界斜交角的影響。模型涵蓋順向坡至逆向坡之完整斜交角範圍，並輔以極限平衡法 RocTopple 進行比對分析，以驗證破壞趨勢之合理性。研究結果顯示：（1）本文依據 PFC3D 模擬結果，建立平面破壞崩塌能量與臨界斜交角之連續函數，得以評估破壞模態轉換與崩塌能量。（2）平面破壞不利因子包含低斜交角、高坡角、高坡高、中等不連續面傾角及低摩擦角；傾覆破壞則以高斜交角、高坡角、高坡高、高不連續面傾角及低摩擦角為主要不利因子，當多項不利因子同時存在時，傾覆破壞崩塌能量將顯著上升，其潛在崩塌規模不亞於平面破壞。（3）在一般岩坡條件下，平面破壞臨界斜交角（γ_(cr,p)）約為 20?，與工程實務經驗及《水土保持技術規範》之順向坡定義相符；當岩坡處於多重不利條件時，臨界斜交角可能提升至約 40?。（4）本文依據 PFC3D 模擬結果，提出傾覆破壞臨界斜交角（γ_(cr,t)）判別式，並驗證其可視為既有現地調查經驗式形式。整體而言，本文之模擬結果顯示斜交角對崩塌能量與破壞模式具有關鍵控制作用，其趨勢與 SMR 位態評分調整一致，並進一步指出既有岩坡分類系統未充分納入摩擦角與坡高等影響因子之侷限性，顯示數值模擬方法於岩坡穩定性評估與工程應用上具有重要價值。關鍵字：離散元素法、異向性岩體、崩塌能量、臨界斜交角、連續函數 ;Rock slope stability is strongly influenced by the orientation of rock mass discontinuities and engineering configuration angles. Among these factors, the angle between the slope face dip direction (??s) and the discontinuity dip direction (????), referred to as the oblique angle (|???? ? ??s|), is a key parameter governing slope stability and the transition of failure modes. In this study, the discrete element method (DEM) implemented in PFC3D (Particle Flow Code in Three Dimensions) is employed to construct three-dimensional synthetic rock slope models containing a single discontinuity. Slope failure behaviors under different oblique angles and slope conditions are simulated, and collapse energy is adopted as a quantitative indicator to investigate the effects of discontinuity friction angle (??), slope angle (β?), slope height (H), and discontinuity dip angle (β?) on collapse energy and critical oblique angles. The models cover the full range of oblique angles from dip slopes to anti-dip slopes, and limit equilibrium analyses using RocTopple are conducted for comparison to verify the rationality of the observed failure trends. The results indicate that: (1) based on PFC3D simulation outcomes, continuous functions describing collapse energy and critical oblique angles for plane failure are established, enabling the evaluation of failure mode transitions and collapse energy levels; (2) unfavorable factors for plane failure include low oblique angles, high slope angles, large slope heights, intermediate discontinuity dip angles, and low friction angles, whereas toppling failure is primarily associated with high oblique angles, high slope angles, large slope heights, steep discontinuity dip angles, and low friction angles. When multiple unfavorable factors coexist, the collapse energy associated with toppling failure increases significantly, and the potential collapse scale is comparable to that of plane failure; (3) under general slope conditions, the critical oblique angle for plane failure (γ_(cr,p)) is approximately 20?, which is consistent with engineering practice and the definition of dip slopes in the Soil and Water Conservation Technical Regulations. When multiple adverse conditions are present, the critical oblique angle may increase to approximately 40?; (4) using PFC3D simulation results, a discriminant equation for the critical oblique angle of toppling failure (γ_(cr,t)) is proposed and verified to be a generalized form of existing empirical relationships derived from field investigations. Overall, the simulation results demonstrate that the oblique angle plays a critical controlling role in collapse energy and failure mode development. The observed trends are consistent with the orientation adjustment logic adopted in the Slope Mass Rating (SMR) system. Furthermore, this study highlights the limitations of existing rock slope classification systems, which do not explicitly incorporate friction angles and slope height, and underscores the importance of numerical simulation as a complementary tool for rock slope stability assessment and engineering applications. Keywords: discrete element method; anisotropic rock mass; collapse energy; critical oblique angle; continuous equation.

應用實例分割與點雲配準於平面放置物件之機械手臂分揀系統開發;Development of a Robotic Arm Sorting System for Planar-Placed Objects by Applying Instance Segmentation and Point Cloud Registration

title: 應用實例分割與點雲配準於平面放置物件之機械手臂分揀系統開發;Development of a Robotic Arm Sorting System for Planar-Placed Objects by Applying Instance Segmentation and Point Cloud Registration abstract: 本研究針對醫療器械經清洗消毒後之回收處理流程，開發一套自動化分揀系統，旨在改善傳統人工作業仰賴人力判讀、易疲勞且效率受限之問題。在系統架構方面，硬體採用TM5-900協作型手臂搭配Ensenso N35立體相機，建立眼在手架構；針對扁平且金屬表面易滑動之器械特性，設計整合V型結構指夾與真空吸嘴的複合式末端執行器。軟體基於ROS2平台，整合YOLOv11實例分割與FastAPI後端介面，建構模組化的自動化控制系統。在技術方法上，提出「由粗至細」的配準策略。首先利用YOLOv11識別類別並生成遮罩以擷取目標點雲，接著利用FPFH(Fast Point Feature Histograms)特徵結合RANSAC(Random Sample Consensus)進行粗配準，最後透過點對平面ICP(Iterative Closest Point)演算法進行精細姿態修正，以計算器械在空間中的三維坐標。實驗結果顯示，針對高反光金屬器械，本系統之點雲配準平均適配度為0.969，均方根誤差控制在1.894 mm內。在隨機分類揀放實驗中，總共20個物件平均成功率為96.62%，平均處理耗時13.73秒。研究結果證實，本系統在定位準確度與作業效率上，已具備應用於醫療後勤自動化流程之可行性。 ;This study develops an automated pick-and-place system for the recycling process of medical instruments after cleaning and sterilization, aiming to address the efficiency limitations and fatigue issues associated with traditional manual sorting. Regarding the system architecture, the hardware integrates a TM5-900 collaborative robot with an Ensenso N35 stereo camera in an Eye-in-Hand configuration. A hybrid end-effector combining a V-shaped gripper and a vacuum nozzle was designed to handle flat instruments with slippery metal surfaces. The software is built on the ROS2 platform, integrating YOLOv11 instance segmentation and a FastAPI backend to establish a modular automated control system. For the technical methodology, a "Coarse-to-Fine" registration strategy is proposed. First, YOLOv11 is used to identify classes and generate masks to extract target point clouds. Then, FPFH(Fast Point Feature Histograms) features combined with RANSAC(Random Sample Consensus) are employed for coarse registration, followed by the Point-to-Plane ICP(Iterative Closest Point) algorithm for fine pose correction to calculate the 3D coordinates of the instruments. Experimental results indicate that for highly reflective metal instruments, the system achieved an average point cloud registration fitness of 0.969, with a Root Mean Square Error (RMSE) maintained within 1.894 mm. In random sorting and pick-and-place experiments involving 20 objects, the average success rate was 96.62%, with an average processing time of 13.73 seconds. These findings confirm that the system possesses the necessary positioning accuracy and operational efficiency for feasible application in automated medical logistics processes.

階梯型式微流道蒸發冷板流動沸騰性能研究

title: 階梯型式微流道蒸發冷板流動沸騰性能研究 abstract: 為了解決兩相蒸發冷卻技術應用於高發熱量電子元件散熱時所面臨的流動不穩定問題，並替代常用且具有高全球暖化潛勢（GWP = 1030）的冷媒 HFC-245fa，本研究提出了以階梯型式流道設計來改善微流道蒸發器之性能，並選用FMD-50為替代工作流體，其GWP值為7。相較於直線型流道，階梯型流道可有效降低冷板的壓降。其原因在於，當相同流量進入熱交換器時，流體於下游區域不再受限於狹窄的微流道空間，流道長度亦相對縮短，使流體不易受到幾何限制而產生過大的流動阻力，進而降低整體壓降。反觀直線型流道，由於流體受到流道幾何限制，導致其壓降相對較高。在階梯流道中，固定流道寬度為0.15mm，流道數量為80，並透過將鰭片高度為了解決兩相蒸發冷卻技術應用於高發熱量電子元件散熱時所面臨的流動不穩定問題，並替代常用且具有高全球暖化潛勢（GWP = 1030）的冷媒 HFC-245fa，本研究提出了以階梯型式流道設計來改善微流道蒸發器之性能，並選用FMD-50為替代工作流體，其GWP值為7。相較於直線型流道，階梯型流道可有效降低冷板的壓降。其原因在於，當相同流量進入熱交換器時，流體於下游區域不再受限於狹窄的微流道空間，流道長度亦相對縮短，使流體不易受到幾何限制而產生過大的流動阻力，進而降低整體壓降。反觀直線型流道，由於流體受到流道幾何限制，導致其壓降相對較高。在階梯流道中，固定流道寬度為0.15mm，流道數量為80，並透過將鰭片高度由3mm降低至1mm，以探討其對流動與熱傳特性的影響。以階梯型式流道來改善直線流道，在HFC-245fa中，可以將低13% 至68% 之壓降，然而其熱傳係數亦同時降低約 17% 至 20% 。在FMD-50中，無論階梯流道或是直線流道，其熱傳性能彼此間差異不大，但在壓降方面，只有在低流量中，直線流道之壓降高於階梯流道10% 至 70%，但在中、高流量中，兩者間的壓降差異不大。由3mm降低至1mm，以探討其對流動與熱傳特性的影響。以階梯型式流道來改善直線流道，在HFC-245fa中，可以將低13% 至68% 之壓降，然而其熱傳係數亦同時降低約 17% 至 20% 。在FMD-50中，無論階梯流道或是直線流道，其熱傳性能彼此間差異不大，但在壓降方面，只有在低流量中，直線流道之壓降高於階梯流道10% 至 70%，但在中、高流量中，兩者間的壓降差異不大。 ;To address the flow instability encountered in two-phase evaporative cooling applied to the thermal management of high–heat-flux electronic components, and to replace the commonly used refrigerant HFC-245fa with a high global warming potential (GWP = 1030), this study proposes a stepped-channel design to enhance the performance of microchannel evaporators and adopts FMD-50 as an alternative working fluid, with a global warming potential (GWP) value of 7. Compared with straight channels, the stepped-channel design effectively reduces the pressure drop of the cold plate. This improvement is attributed to the fact that, under the same inlet flow rate, the downstream region is no longer constrained by narrow microchannel geometry and the effective flow length is shortened. Consequently, the flow resistance induced by geometric confinement is alleviated, leading to a lower overall pressure drop. In contrast, straight channels impose continuous geometric constraints along the flow path, resulting in a relatively higher pressure drop. In the stepped-channel configuration, the channel width is fixed at 0.15 mm with a total of 80 channels, and the fin height is reduced from 3 mm to 1 mm to investigate its effects on flow and heat transfer characteristics.When HFC-245fa is used as the working fluid, the stepped-channel design reduces the pressure drop by approximately 13% to 68% compared with the straight-channel design; however, the heat transfer coefficient is simultaneously reduced by about 17% to 20%. For FMD-50, the heat transfer performance of the stepped and straight channels shows no significant difference. In terms of pressure drop, the straight-channel design exhibits a 10% to 70% higher pressure drop than the stepped-channel design under low flow rate conditions, whereas at medium and high flow rates, the pressure drop difference between the two configurations becomes negligible.