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摘要:
为了得到二维功能梯度壁板热颤振的精确解并揭示颤振机理,根据经典薄板理论及一阶活塞理论,建立了超声速气流下二维功能梯度壁板的本征控制微分方程并求得了精确解,根据得到的本征根对颤振机理进行了分析。针对功能梯度材料(FGM)的不同体积分数,分别研究了壁板在恒温场及非线性温度场下的颤振边界随马赫数的变化规律,并比较了2种温度场下的结果。通过分析简支、固支及其组合边界情况下的壁板颤振特性,从数学角度发现颤振现象的发生是由于挠度的一阶导数导致刚度非对称,且功能梯度材料能够有效提高热环境下壁板的颤振边界,同时利用ABAQUS软件对功能梯度壁板的振动特性进行了模拟,进一步验证了所提方法的有效性。
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关键词:
- 超声速 /
- 功能梯度材料(FGM) /
- 热颤振 /
- 本征根 /
- 精确解
Abstract:For achieving the thermal flutter exact solutions of two-dimensional functionally graded panel and revealing the mechanism of the thermal flutter, based on the classical thin plate theory and the first-order piston theory, the characteristic governing differential equation of two-dimensional functionally graded panel in supersonic flow is established and exact solutions are obtained. Through the analysis of the eigenvalues, the mechanism of the panel flutter is investigated. According to different volume fraction of Functionally Graded Materials (FGM), the flutter boundary changes with Mach number in constant temperature field and nonlinear temperature field are studied respectively, and the results in two temperature fields are compared. By analyzing the flutter characteristics of panels with simply supported, fixed and integrated edges, it can be concluded that the flutter phenomenon is caused by the first-order derivative of deflection which leads to the asymmetry of system stiffness, and FGM can effectively improve the flutter boundary of the panel in the thermal environment. Meanwhile, the vibration properties of the FGM panel is simulated with ABAQUS, further validating the effectiveness of the present method.
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Key words:
- supersonic /
- Functionally Graded Materials (FGM) /
- thermal flutter /
- eigenvalue /
- exact solution
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表 1 简支和固支边界条件
Table 1. Boundary conditions for simple support and clamp
BCs(边界条件) x=0或x=a 简支(S) w=0, 固支(C) w=0, 表 2 二维壁板颤振频率方程和本征函数
Table 2. Eigensolutions of two-dimensional panel flutters
BCs 频率方程 本征函数的系数 简支-简支(SS)
ϕ(0)=0
ϕ(1)=0
ϕ″(0)=0
ϕ″(1)=0固支-固支(CC)
ϕ(0)=0
ϕ(1)=0
ϕ′(0)=0
ϕ′(1)=0简支-固支(SC)
ϕ(0)=0
ϕ″(0)=0
ϕ(1)=0
ϕ′(1)=04ϑα1β1sinh 2ϑ-β1(4ϑ2-α12-β12)sin α1cosh β1-α2(4ϑ2+α12+β12)cos α1sinh β1=0 表 3 功能梯度材料弹性常数
Table 3. Elastic constants of FGM
材料名称 组成成分 E/GPa υ ρ/(kg·m-3) 陶瓷金属 Si3N4(氮化硅陶瓷) 322 0.24 2 370 SUS304(不锈钢) 207 0.32 8 166 表 4 分层为5层时密度和弹性模量
Table 4. Density and modulus of elasticity for 5 layers
坐标方向 厚度方向坐标/(10-4m) 密度/(kg·m-3) 弹性模量/(1011Pa) z -8.000 8 165.942 2.070 z -4.000 8 151.916 2.073 z 0 7 984.875 2.106 z 4.000 7 191.866 2.263 z 8.000 4 743.520 2.749 表 5 分层为10层时密度和弹性模量
Table 5. Density and modulus of elasticity for 10 layers
坐标方向 厚度方向坐标/(10-4m) 密度/(kg·m-3) 弹性模量/(1011Pa) z -9.000 8 165.998 2.070 z -7.000 8 165.560 2.070 z -5.000 8 160.340 2.071 z -3.000 8 135.558 2.076 z -1.000 8 059.047 2.091 z 1.000 7 874.296 2.127 z 3.000 7 493.496 2.203 z 5.000 6 790.582 2.343 z 7.000 5 594.284 2.580 z 9.000 3 681.166 2.959 表 6 不同边界条件下FGM板频率
Table 6. Frequency of FGM plate under different boundary conditions
边界条件 模态阶数 频率/Hz 精确解 ABAQUS(5层) ABAQUS(10层) SS 1 131.679 3 129.345 7 131.010 7 2 523.997 7 517.596 2 521.925 4 CC 1 296.864 6 293.355 6 295.806 1 2 818.792 2 808.520 3 815.306 1 SC 1 204.444 7 202.048 4 203.851 7 2 663.293 8 654.707 9 660.551 3 表 7 本文解与Galerkin方法结果的对比
Table 7. Comparison of result between present method and Galerkin method
方法 固有频率(Ma=2) 颤振参数 ω1/Hz ω2 /Hz ωf /Hz Maf Galerkin 650.725 8 2 130.318 9 1 773.443 7 7.177 4 本文 651.975 4 2 130.663 1 1 759.928 3 6.989 6 表 8 不同边界下FGM板的临界颤振频率和临界动压的比较
Table 8. Comparison of flutter frequency and critical dynamic pressure of FGM plate under different boundary conditions
T/K n SS CC SC λ* ω* λ* ω* λ* ω* Tt=300
Tb=3001 434.22 26.0 788.45 41.7 594.19 33.3 5 388.51 21.1 719.89 34.1 548.49 27.3 50 354.23 19.0 651.33 30.6 491.35 24.5 Tt=500
Tb=3001 399.94 24.8 754.17 40.7 571.34 32.4 5 365.66 20.2 685.61 33.2 514.21 26.3 50 319.95 17.9 617.05 29.7 457.07 23.4 Tt=500
Tb=5001 365.66 23.4 708.46 39.3 525.63 30.9 5 331.38 18.9 639.90 31.9 479.93 25.1 50 285.67 16.6 571.34 28.5 422.79 22.3 -
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