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題名 | Numerical Investigation of Hydrodynamic Forces Acting on Oscillating and Translating Bodies Submerged Under Free Surface=在波浪中前進沒水結構物的水動力精度分析 |
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作者姓名(中文) | 吳東明; | 書刊名 | 中國造船暨輪機工程學刊 |
卷期 | 18:1 1999.02[民88.02] |
頁次 | 頁19-32 |
分類號 | 443.1 |
關鍵詞 | 遠場動量法; 離散源點分佈法; 直接格林解析法; 前進速度效應; Classical integral equation; Discrete source distribution method; Direct green function method; Forward speed effect; |
語文 | 英文(English) |
中文摘要 | 本文中兩種數值計算方法被應用於預測在波浪中前進沒水結構物水動力負載。其 中速度函數採用離散源點分佈法及直接格林解析法等來計算,同時此二法經特別數學處理, 以提昇水動力計算成果的精度。 有關水動力阻尼係數的計算精度,上述二數值方法被廣泛用來檢核。關於水動力阻尼係數的 預測理論則採用能量法及直接積分法。在精度分析過程中,亦考慮元素使用量及物體沒水深 度等參數影響,其計算值相對誤差均小於 0.5%,並節省了相當計算時間。 在處理雙胴體結構問題時,採用源偶影像法來進行計算模擬。於實際數值計算時,配合數值 收歛及精度等需求,適當的無限數列項數被作取捨。文中並對波浪激振力及二階水動力等數 值解,進行計算精度檢核。其中二階水動力的預測則應用近場積分法及遠場動量法等來研究 討論。對於未考慮前進速度效應的三維穿液面橢圓體之水動力阻尼係數之計算精度分析亦有 討論。 |
英文摘要 | Two numerical methods have been reviewed to predict hydrodynamic loadings acting on oscillating and translating bodies submerged under the free surface. The velocity potentials are calculated by the discrete source distribution technique and the direct solution by the classical integral equation method. These approaches have been modified to improve numerical accuracy of hydrodynamic forces on submerged structures advancing in waves. This has been done by solving the logarithmic part of Green function analytically. Numerical accuracy of damping coefficients predicted by two modified methods is investigated comprehensively. The accuracy check is performed to predict damping coefficients by energy flux consideration in fluid domain and by direct pressure integration over body boundary contour. The accuracy check is also performed by varying the number of the discrete elements and for different depths of immersion. The relative errors in the estimation of damping coefficients are found within 0.5% and the computation time is cut down dramatically. For twin cylinders case the accuracy is also checked by varying the number of dipole images. In practical computation the infinite series can be truncated to a certain number of dipole images. Calculations are carried out on the number of terms required to be taken for numerical convergence. The accuracy of wave excitation forces and second order forces is investigated. Predicted results of second order horizontal and vertical forces by both near and far field approaches are studied and discussed extensively. Moreover an accuracy check of damping coefficients for a 3D surface piercing ellipsoid at zero speed is also performed to ensure the reliability of both numerical approaches. |
本系統之摘要資訊系依該期刊論文摘要之資訊為主。