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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/1808

    Title: Random Walk方法對轉注射出成型充填過程中氣泡消長行為之數值模擬分;Random Walk Approach on Study of Void Formation in Resin Transfer Molding
    Authors: 施明憲;Ming-Sam Shih
    Contributors: 機械工程研究所
    Keywords: 轉注射出成型;蒙地卡羅法;亂向步進子;達西定律;門檻壓力;氣泡;Resin Transfer Molding (RTM);Monte Carlo;Rando
    Date: 2003-06-03
    Issue Date: 2009-09-21 11:32:15 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 在樹脂轉注成形(RTM)充填過程中,氣泡的生成與殘留直接影響了產品的機械性質。本研究將分為兩部份,以數值模擬法與實驗區分。第一部份:以蒙地卡羅亂向步進法,來分別探討氣泡生成的兩個主要階段:巨微觀流動面速度差異及氣泡崩解。以樹脂橫向流經纖維束為模型,第一階段,由於纖維束內、外區域滲透度的差異造成流動面運動快慢的不同,纖維束中的氣泡生成機構於是形成。主要的影響因數是纖維內外的滲透度比值和毛細力的影響,結果顯示當滲透度比值 ,則流動面的運動差異便足以於纖維束內形成初始氣泡。 第二階段,當初始氣泡形成後纖維束內的流動主要是毛細力主導的微觀流持續的向纖維束滲透,造成了初始氣泡的壓縮效應,液體表面張力與背壓會形成一門檻壓力值。壓縮初始氣泡的速率與門檻壓力之升高速率,為影響微小氣泡生成的主要因素; 結果顯示當毛細數 時,崩解的氣泡就會顯著增加。 第二部份:在探討氣泡生成的過程中,毛細效應是不可忽略的,本研究對毛細壓力的量測採用無因次參數 理論進行分析,並設計實驗取得毛細壓力與孔隙關連。 第一部份流動模型較複雜,由於傳統數值方法對氣泡崩解後的微小氣泡模擬有技術上的限制(自由面形狀定義的複雜性與隔點產生的困難性),因此第一部份數值法採用蒙地卡羅法(Monte Carlo method)及亂向步進子(Random walk)來預測流動面前進的位置,亂向步進子之位移機率強度,以 (壓力梯度)與 (可動性)乘積的修正來計算。 The presence of the void is harmful to the product’s mechanical properties. In the present study, a Monte-Carlo-like random walk model is firstly proposed for the simulation of void formation, namely, the voids of the first kind and the voids of the second kind, during the filling stage of RTM. The former is resulted from the kinetic difference along the free surface movement, and the latter is the product of the first type void. An obstacle in the flow field always tends to lift the potential on void entrapment. Results show that the void of the first kind is formed within the fiber bundle as the permeability ratio of the fiber mats to the fiber bundle is greater than 10. Once the first type voids are formed, the dissolution of that voids may occur due to the capillary action. That is, micro flow provides compression strength on the bubbles within the bundle to against the threshold pressure, such that some gas molecules were rejected out periodically to reach balance to the external pressure. Results show that, the content of second type voids increases as the decreases. The critical is found to be . Below which the number of the void is inversely proportional to in a parabolic trend. Based on the similarity of capillary rise, a centrifugal platform is conducted to perform the required data for the correlation between capillary pressure and other properties of the fibrous network proposed by theorem. A Monte-Carlo-like random walk approach is developed here to resolve the time-dependent, free-surface flows and to study the transport of tiny bubbles by tracing the paths of fictitious random walk, colored black or white. By using the strong correlation functions ( and ), the local displacing probability of random walks can be determined.
    Appears in Collections:[機械工程研究所] 博碩士論文

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