嵌板受水下爆炸衝擊之數值分析研究

The Study of Numerical Analysis for Plate Panel Subjected to Underwater Explosion

本文以水下背面為空氣的嵌板，遭受水下爆炸衝擊所產生的塑性大變形以致破裂損壞的狀況為研究案例，探討以不同的數值模擬方式所得分析結果的差異與適切性。本文分別說明ALE（Arbitrary Lagrangian-Eulerian）演算法與炸藥模型、採用雙漸進近似法（DAA）運算的USA分析以及LS-DYNA所提供簡易估算水下爆炸衝擊結構反應的LOAD_SSA棋組三種數值模擬方法，並以Ramajecyathilagam & Vendha（2004）（以下簡稱為R&V 2004）的試驗模型為分析比較對象。其試驗目標板的長×寬×厚＝0.55m × 0.45m × 0.002m，四周有2.5cm厚板支撐並以螺栓鎖定於中空的厚鋼板箱，板未被厚板支撐的範圍，長與寬分別為0.30m與0.25m，爆炸距離0.15m，屬於近距離爆炸。嵌板分析採用非線性材料板殼元素，並考慮邊界螺栓的束制條件。分析過程板結構在爆震波衝擊下快速進入塑性範圍，亦考慮應變率對板結構之材料非線性變形的影響。本文將三種數值模擬方式所得分析結果與R&V 2004試驗值比較，包含碳板中心在不同爆震因子條件下產生的永久變位及沿中心線自邊界至中心的永久變形，同時也從嵌板吸收入射爆震波能量比例的角度比較三種數值分析的差異及其運算效率，並討論三種分析模式優劣與適切性。最後，將爆炸距離設為0.45m，為較遠距離爆炸，採用相同爆震因子，探討相同爆震因子下結構爆震反應在近距離爆炸與追距離爆炸之差異。 In this paper, the transient dynamic responses for large plastic deformation and damage states of an air-backed plate panel subjected to underwater explosion (UNDEX) has been investigated. Three different finite element models were used, which are the ALE (Arbitrary Lagrangian-Eulerian) method with 3D model of fluid domain and the explosive model, DAA(Doubly Asymptotic Approximation) method of USA (Underwater Shock Analysis) code and the LOAD_SSA Module supplied by LS-DYNA. The analyzed results were compared with the experimental results of Ramajecyathilagam & Vendha (2004). The target plate has the dimension of length x width x thickness = 0.55m x 0.45m x 0.002m, whose four edges are supported by 0.025m thicker plates and mounted on a strong steel box with bolts, the unsupported area of the target plate is 0.30mx 0.25m.The standoff distance was 0.15m, which belongsto short distance explosion impact. The dynamic responses of the target plate reached to large plastic deformation, under extremely high shock pressure of UNDEX, the non-linear material model with strain rate effect were en into consideration. Three FE-analyzed results were discussed and compared with the experiment results by Ramajecyathilagam & Vendha(2004) under different shock factors. The energy transferred from shockwave to plate and the computing efficiency of the numerical models were discussed. Furthermore, the comparative case study of farther detonation distance with the same shock factor was proceed to study the difference of plate responses between the cases of far and short standoff distance.