Calculation of shock wave transmission and reflection pressures at water-soil interface
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摘要: 冲击波在水土交界面的透射、反射压力计算尚缺乏可靠的计算理论,利用质量守恒方程、动量守恒方程以及水、土的状态方程,分别推导得到冲击波在水、土介质中传播的Hugoniot关系以及p-u曲线,进而从理论上解析得到冲击波在水土交界面处的透射和反射压力。分别建立了水中自由场、水-土分层介质场的二维数值计算模型,其中水、土参数与理论推导时采用的三相介质饱和土计算模型中的参数保持一致。计算结果表明,水土交界面透射、反射压力的理论解与数值解具有高度的一致性。采用80 g TNT炸药,距离水土交界面0.1~0.9 m(比例爆距为0.232~2.089 m/kg1/3)爆炸时,得到的透射、反射压力的理论解与数值解误差均小于7%,根据解析解得出反射压力与水中入射压力之比,反射压力系数在1.6~1.8范围内;距离水土交界面0.5 m时,饱和土的含气量在0~10%范围内变化,得到的透射、反射压力的范围为63.8~70.0 MPa,此时其反射压力系数在1.55~1.70范围内。推导得出的冲击波在水土交界面透射、反射压力的计算方法,物理意义明确、计算精度高,可为开展水下爆炸对水底土中工程结构的毁伤评估提供理论基础。Abstract: There is a lack of reliable calculation theory for the transmission and reflection pressures of shock waves at the water-soil interface. Using the mass conservation equation, momentum conservation equation, and the equations of state of water and soil, the Hugoniot relationship and p-u curve of the propagation of shock waves in water and soil medium are derived, and then the transmission and reflection pressures of the shock wave at the water-soil interface can be analyzed theoretically. Two-dimensional numerical models of the free field in water and water-soil layered medium field are established, in which the water and soil parameters are consistent with those in the three-phase medium saturated soil model used in the theoretical derivation. The calculation results show that the theoretical and numerical solutions of the water-soil interface transmission and reflection pressures are highly consistent. When using 80 g TNT explosives and exploding at 0.1–0.9 m from the water-soil interface (proportional burst distance of 0.232–2.089 m/kg1/3), the error of the theoretical and numerical solutions for transmission and reflection pressures is less than 7%, and the coefficient of the reflection pressure is in the range of 1.6–1.8 according to the analytical solution of the reflection pressure and the ratio of the incident pressure in the water. When exploding at 0.5 m from the water-soil interface and the gas content of the saturated soil varies in the range of 0–10%, the transmission and reflection pressures are 63.8–70.0 MPa, and the reflection pressure coefficients are in the range of 1.55–1.70 at this time. The calculation method for the shock wave transmission and reflection pressure at the water-soil interface has a clear physical meaning and high precision and can provide a theoretical basis for the soil damage assessment of engineering structures in submerged soil caused by underwater explosions.
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表 1 土的状态方程参数
Table 1. Equation of state parameters of the soil
c1/(m·s−1) c2/(m·s−1) c3/(m·s−1) ρ0/(kg·m−3) ρ1/(kg·m−3) ρ2/(kg·m−3) ρ3/(kg·m−3) 340 1 500 4 500 2 210 1.2 1 000 2 650 α1 α2 α3 k1 k2 k3 S0 0.001 0.3 0.699 1.4 3.0 3.0 1.92 表 2 水的参数
Table 2. Parameters of water
ρ/(kg·m−3) c/(m·s−1) γ0 α S1 S2 S3 E0/Pa 1025 1520 0.28 0 1.92 0 0 0 表 3 炸药参数
Table 3. Parameters of the explosive
ρ/(kg·m–3) pCJ/GPa A/GPa B/GPa R1 R2 ω E0/GPa 1 583 19.4 307 3.898 4.485 0.79 0.3 6.968 4 表 4 饱和土参数
Table 4. Saturated soil parameters
ρ/(kg·m−3) G/MPa K/MPa a0/MPa2 a1/MPa a2 pc/MPa ε1 ε2 2 210 2 693 9 659 3.339×10−7 0.2251 3.794 –6.9×10−3 0 –0.001 868 ε3 ε4 ε5 ε6 ε7 ε8 ε9 ε10 p1/MPa –0.003 276 –0.004 649 –0.005 887 –0.008 206 –0.009 398 –0.010 043 –0.012 787 –0.014 439 0 p2/MPa p3/MPa p4/MPa p5/MPa p6/MPa p7/MPa p8/MPa p9/MPa p10/MPa 7.2 16.8 26.4 35.2 52 60.8 65.6 86.4 99.2 表 5 80 g TNT对应不同爆距下的水中自由场峰值压力及偏差
Table 5. Free-field peak pressures and their deviations in water at different burst distances for 80 g TNT
爆距/m 计算结果/MPa 模拟结果/MPa 偏差/% 0.1 394.44 354.01 –10.3 0.2 124.74 132.66 6.3 0.3 78.73 78.90 0.2 0.4 56.88 54.44 –4.3 0.5 44.20 41.24 –6.7 0.6 35.97 32.98 –8.3 0.7 30.22 27.27 –9.8 0.8 25.99 23.05 –11.3 0.9 22.75 19.88 –12.6 表 6 不同爆距下的理论和模拟反射压力、偏差及反射系数
Table 6. Theoretical and simulated reflection pressures, deviations, and reflection coefficients at different blast distances
爆距/m 比例爆距/(m·kg–1/3) 入射压力/MPa 反射压力 反射系数 理论值/MPa 模拟值/MPa 相对偏差/% 0.1 0.232 354.01 632.8 589.90 –6.8 1.788 0.2 0.464 132.66 228.8 229.50 0.3 1.730 0.3 0.696 78.90 133.6 133.60 0 1.693 0.4 0.928 54.44 91.6 91.21 –0.4 1.683 0.5 1.160 41.24 68.8 68.82 0.2 1.668 0.6 1.392 32.98 54.4 53.49 –1.7 1.649 0.7 1.625 27.27 45.1 43.79 –3.0 1.654 0.8 1.857 23.05 37.6 36.75 –2.3 1.631 0.9 2.089 19.88 32.4 31.42 –3.1 1.630 -
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