類別:http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/322026-04-04T04:03:21Z2026-04-04T04:03:21Z點吸式波浪發電裝置最佳化形狀之計算流體力學研究吳世煌Shih-Huang Wuhttp://tdr.lib.ntu.edu.tw/jspui/handle/123456789/986912025-08-18T16:07:01Z2025-01-01T00:00:00Z標題: 點吸式波浪發電裝置最佳化形狀之計算流體力學研究; A CFD Study on the Shape Optimization of Point-absorber Wave Energy Converters
作者: 吳世煌; Shih-Huang Wu
摘要: 本研究以開源計算流體力學軟體 OpenFOAM v8，基於雷諾平均納維-斯托克斯方程式，建立三維數值水槽，將起伏運動的能量擷取系統 (power take off system，PTO) 簡化成線性阻尼，模擬點吸式波浪發電裝置浮體的真實起伏運動， 並限制其他方向運動，以審視 Edwards and Yue (2022, Journal of Fluid Mechanics, 933, A1) 基於線性勢流理論和深水假設的點吸式波浪發電裝置浮體形狀優化框架中，只在起伏運動方向，並限制其他五個運動方向的圓柱和最佳化形狀 (no-kink-2nd-order) 所預測的發電效率及動態響應的差異。線性勢流理論雖廣泛應 用於浮體初步設計，但因未考慮黏滯力與水面上形狀等影響，對阻尼與動態響應的預測準確性有限。由模擬結果顯示，在深水二階斯托克斯波作用下，圓柱和最佳化形狀的發電效率相近，其運動響應約為波浪振幅的 0.7 倍，未達到理論預測的 3 倍，顯示線性勢流理論高估浮體動態響應。此外，本研究深入探討不同的參數改變對於發電效率的影響；第一為固定週期和水深，發現波高越小，無因次化後的發電效率越好；第二為固定波高和週期，發現圓柱在中間水深條件下之發電效率略低於深水條件，係因為其沒水深度較深，使底部所受到的能量相較於深水波還要小，而最佳化形狀由於沒水深度較淺，中間水深和深水所受到的波浪能量相當，所以發電效率表現較不敏感；第三為浮體密度變小，且圓柱和最佳化形狀的水下形狀與 Edwards and Yue (2022) 相同，發現兩浮體密度變小，發電效率會增加，尤其在浮體剛好不會被液體淹沒的時候，會有最好的發電效率，當密度再繼續降低，發電效率趨緩甚至不再增加；第四為 PTO 的線性阻尼變化，發現在未發生共振情況下，發電效率主要受到 PTO 線性阻尼係數的主導。當阻尼設定為自身輻射阻尼的 20 倍時，圓柱與最佳化形狀的發電效率分別提升約 3.7 倍與 4.5 倍，當線性阻尼係數繼續增加，發電效率因浮體起伏運動速度降低顯著而下降；最後本研究設計三種新浮體形狀，其沒水表面積與圓柱或是最佳化形狀相同且線性阻尼係數為自身的輻射阻尼係數，發現未產生共振現象，且新形狀之起伏運動振幅與圓柱和最佳化形狀相近，但新形狀有更大的輻射阻尼係數，因此發電效率較高，顯示在難以達成共振的情境下，選用輻射阻尼係數較高的浮體形狀能提升發電效率。綜合以上結果，顯示線性勢流理論在不考慮黏滯力和水面上形狀下，無法準確預測真實的動態響應，並難以反映浮體密度、波高、沒水深度等關鍵參數改變對發電效率的影響。本研究成果不僅揭示線性勢流理論的侷限性，更提供未來波浪發電裝置設計一具體、可行之數值分析與優化參考依據。; This study utilizes the open-source computational fluid dynamics software OpenFOAM v8, based on the Reynolds-Averaged Navier–Stokes equations, to establish a three-dimensional numerical wave tank. The power take-off system (PTO) in the heave mode of the point-absorber wave energy converter is simplified as a linear damping model to simulate the realistic heaving motion of the floating body, while constraining other degrees of freedom. This simulation aims to examine the differences in predicted power generation efficiency and dynamic response between the cylindrical and optimized (no-kink-2nd-order) shapes from Edwards and Yue (2022, Journal of Fluid Mechanics, 933, A1), which are based on linear potential flow theory and deep-water assumptions, specifically considering motion only in the heave direction and constraining the other five degrees of freedom. Although linear potential flow theory is widely used in preliminary floating body designs, its predictions regarding damping and dynamic response are limited due to neglecting viscous effects and the influence of above-water geometry. Simulation results show that under deep-water second-order Stokes waves, the power generation efficiencies of both the cylindrical and optimized shapes are similar, with their heave motion amplitudes approximately 0.7 times the wave amplitude, which falls short of the theoretically predicted factor of 3, indicating an overestimation of dynamic response by linear potential flow theory. Further parametric studies reveal the following: (1) with fixed wave period and water depth, power generation efficiency improves as wave height decreases; (2) with fixed wave height and period, the power of cylindrical shape generation efficiency in intermediate water depths is slightly lower than in deep water, due to its deeper draft causing less wave energy to reach its bottom compared to deep water; conversely, the optimized shape, with a shallower draft, captures wave energy effectively in both intermediate and deep water depths, making its efficiency less sensitive to water depth changes; (3) reducing the density of floating body while maintaining the underwater geometry consistent with Edwards and Yue (2022), the power generation efficiency increases and reaches its peak when the body is just barely not fully submerged by the liquid. Further reductions in density result in diminishing returns or stagnation in power generation efficiency; (4) variation in the linear damping coefficient of the PTO in the heave mode shows that, absent resonance, power generation efficiency is mainly governed by this coefficient. When the damping is set to twenty times the radiation damping coefficient, the cylindrical and optimized shapes achieve approximately 3.7 and 4.5 times improvements in power generation efficiency, respectively. However, further increases in the linear damping coefficient reduce efficiency due to significant decreases in the heave velocity of the floating body. Finally, three new floating body shapes with identical underwater surface areas to the cylindrical or optimized shapes were designed, and their PTO damping coefficients were set equal to their own radiation damping. These new shapes exhibited no resonance and showed heave motion amplitudes comparable to the cylindrical and optimized shapes. However, due to their larger radiation damping coefficients, the new shapes demonstrated higher power generation efficiencies. This indicates that in scenarios where resonance is difficult to achieve, selecting floating bodies with larger radiation damping coefficient can enhance power conversion performance. In summary, the results indicate that linear potential flow theory, neglecting viscous effects and above-water geometry, cannot accurately predict the real dynamic responses nor reflect the influence of key parameters such as floating body density, wave height, and draft on power generation efficiency. This study not only reveals the limitations of linear potential flow theory but also provides a concrete and feasible numerical analysis and optimization reference for future wave energy converter designs.2025-01-01T00:00:00Z黑潮發電機之模擬與實驗Po-Yu Chen陳柏宇http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/789382021-07-11T15:30:40Z2018-01-01T00:00:00Z標題: 黑潮發電機之模擬與實驗; Simulation and Experiment Kuroshio Current Generator
作者: Po-Yu Chen; 陳柏宇
摘要: 本篇論文提出400W黑潮直驅式永磁通部發電機之模擬與實驗，利用Ansys Maxwell以有限元速分析法進行模擬分析，模擬結果將會作為平台實驗與水槽實驗之實驗參考基礎，而實體發電機將會於平台進行實際性能測式，最後將會於本系上之實驗水槽進行水下實測。本計畫目的為在額定轉速150RPM時，發電機發出額定功率400W，以及裝置兩顆發電機的浮游試黑潮發電渦輪機組發出800W功率。; In this thesis, the simulation and experiment for 400W direct-drive permanent magnet synchronous generator of Floating Kuroshio Turbine is proposed. In order to analyze the 400W low-speed direct-drive generator, the PMSG is simulated by using the ANSYS Maxwell design tool which is finite element analysis software. The simulation results are used as the reference for the real experiments including platform experiment and towing tank experiment. After the fabrication of the generator, the real tests of the 400W low-speed direct-drive synchronous permanent magnet generator are carried out by the platform in order to test the performance of the designed PMSG. Finally, the towing tank experiments were conducted at National Taiwan University. The goal of this work is to obtain 800W generated by two 400W generators at the speed of 150 rpm.2018-01-01T00:00:00Z黏性效應對於半潛式浮式風機系統性能的影響蘇恆Heng Suhttp://tdr.lib.ntu.edu.tw/jspui/handle/123456789/956492024-09-15T16:18:41Z2024-01-01T00:00:00Z標題: 黏性效應對於半潛式浮式風機系統性能的影響; The Impact of Viscous Effect on the Performance of Semi-Submersible Floating Wind Turbine System
作者: 蘇恆; Heng Su
摘要: 本研究探討流體黏性對半潛式浮式風機系統性能的影響，分析三種半潛式浮 式風機系統(圓碟型、駁船型及圓柱型)在四種系統佈置方向(15°、45°、75°及 105°)下的性能表現，模擬場址為新竹外海，模擬條件包括額定風速條件(RC)、50 年回歸期風速條件(50C)及長期條件(LTC)。三種半潛式浮式風機皆為 35875 噸，搭 載 SNL 13.2 MW 風機，使用 3×3 繫纜系統。ANSYS AQWA 用於預測忽略流體黏 性的水動力特性，STAR-CCM+用於預測考慮黏性效應的水動力特性，ORCAFLEX 用於預測繫纜受力和葉片空氣動力，以及求解運動方程式獲得運動響應、發電機功 率及纜繩張力。假設波向和風向相同，風和浪分別以 API 風譜及 JONSWAP 波譜 描述，預測 RC(示性波高 1.7m、零上切週期 5.5s)、50C(示性波高 12.72m、零 上切週期 8.83s)及 LTC 在四個風向(45°、135°、225°及 315°)下浮式風機各項性 能，其中長期條件是基於新竹外海 2015 至 2021 年的統計結果。本研究結果顯示， 圓碟型浮式風機在 RC 下的最大傾角及平均傾角超過限制值，駁船型在 50C 下的 最大偏移量及纜繩張力超過限制值。圓柱型浮式風機在系統佈置為 105°時為最佳 設計，發電機容量因子 0.446，九條纜繩最大損傷為限制損傷的 26.97%。流體黏性 對性能標準差影響最大，對性能平均值影響最小。流體黏性對發電機容量因子影響 極小，最大差異僅 0.227%，駁船型浮式風機容量因子最大，圓柱型次之，圓碟型 最小，分別為理論容量因子的 98.08%、95.98%及 94.58%。流體黏性對纜繩疲勞損 傷影響顯著，差異在-35.70%至-63.42%之間，九條纜繩最大損傷以駁船型浮式風機 最小，圓柱型次之，圓碟型最大，分別為限制損傷量的 17.14%、26.97%及 97.47%。; This study investigates the impact of fluid viscosity on the performance of semi- submersible floating offshore wind turbine (FOWT) systems. Three types of semi- submersible floating platform (disk-, barge-, and column-type) are investigated in the Hsinchu offshore area under four system arrangement directions (15°, 45°, 75°, and 105°) and three simulation conditions: rated wind speed (RC), 50-year return period wind speed (50C), and long-term (LTC). The studied FOWTs all have a mass of 35,875 ton, a 3×3 mooring system, and an SNL 13.2-MW wind turbine. The hydrodynamic properties without fluid viscosity are predicted using AQWA based on potential flow theory, while the hydrodynamic properties considering viscous effects are predicted using STAR- CCM+. ORCAFLEX is employed to predict the mooring system forces and blade aerodynamics of the FOWT system and to solve the motion equations for obtaining the motion response, generator power, and mooring line tension. Assuming that the waves align with the wind direction, the wind and waves are described using the API wind spectrum and JONSWAP wave spectrum, respectively. Predictions are made for the performance evaluation of the FOWT system using a significant wave height of 1.7 m and a zero-up-crossing period of 5.5 s in the RC scenario, a significant wave height of 12.72 m and a zero-up-crossing period of 8.83 s in the 50C scenario, and four wind directions (45°, 135°, 225°, and 315°) in the LTC scenario. The LTC scenario is analyzed based on the statistical results from the Hsinchu offshore area from 2015 to 2021. The results indicate that the disk-type FOWT exceeds tilt angle limits under RC scenario. Under 50C scenario, the barge-type FOWT exceeds limits for maximum offset and mooring line tension. The column-type FOWT, with a system arrangement of 105°, is identified as the optimal design, where its capacity factor is 0.446 and the maximum damage is 26.97% of the allowable damage. The effect of viscosity is most pronounced on the standard deviation of performance metrics, particularly affecting the disk-type FOWT under RC scenario and the barge-type the under 50C scenario. The capacity factor is limited affected by viscosity, with a maximum difference of only 0.227% . The barge-type FOWT has the highest capacity factor (98.08%), followed by the column-type (95.98%) and disk-type ones (94.58%). The viscosity significantly impacts mooring line fatigue damage, with differences ranging from - 35.70% to -63.42%. The barge-type FOWT shows the least damage, followed by the column-type and disk-type ones, with damages of 17.14%, 26.97%, and 97.47% of the allowable damage, respectively.2024-01-01T00:00:00Z鯨豚聲音偵測研究Yin-Ying Fang方銀營http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/440422021-06-15T02:37:28Z2011-01-01T00:00:00Z標題: 鯨豚聲音偵測研究; Underwater Acoustic Detection and Classification for
Cetaceans’ Vocalizations
作者: Yin-Ying Fang; 方銀營
摘要: 被動聲學已被視為觀察海洋生物及進行長時間水下環境監測的一項重要工具，由於聲學的錄音資料量龐大，故需要即時有效的自動化偵測器，快速辨識聲音訊號、篩選重要數據。本研究之聲音偵測器，主要可分為「特徵萃取」和「分類」兩項模組；「特徵萃取」模組，利用熵偵測器搭配時域端點偵測法，截取重要音訊，並在其時域及頻域上萃取訊號的特徵參數；「分類」模組，運用倒傳遞類神經網路作為辨識工具，本研究樣本來源採集康乃爾大學網路資料庫並以臺灣東北海域及龜山島附近海域常出現之海洋哺乳動物聲音作為辨識對象。將所萃取的特徵參數作正規化及設定目標值後，輸入類神經網路作訓練，直到網路穩定收斂，再進行測試。
目前本方法可以獲得良好的正確判斷率，未來如能增進自動化偵測器之辨識準確度，還可應用於辨識其他未知音訊，透過自動化偵測及分類的能力，輔助專業人工辨識員，達到「省時、省工、省力」等多項優點。; Passive acoustics has been well recognized as an important tool for observing marine animals and long-term underwater environment monitoring. Since the amount of data is enormous, it is needed to have an effective auto-detector to select critical features and classify their patterns from the recorded acoustic signal. In this study, we had developed an automatic detector with both the feature extraction and classification modules. In the feature extraction module, we select features from the entropy and end-point of the time signal. Then, we normalized the extracted features as inputs for the classification module based on the theory of back propagation neural network (BPNN). The BPNN will be trained and tested using the cetaceans’ acoustic signals from database of Cornell University Macaulay Library Marine Collection until the network becomes stable and convergent. The selected samples are commonly found cetaceans from the northeastern offshore of Taiwan and Guishan Island.
Currently, our detector had obtained fairly good recognition rate for classifying cetaceans. In the future, our automatic detector can be applied to classify similar acoustic signals if we can improve the accuracy. We believe the proposed automatic detector will be a robust tool, which supersedes the experienced human operators due to less time consuming and low labor cost.2011-01-01T00:00:00Z