Application of High-Order Isoparametric Elements in Free Vibration of Membrane Structures
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摘要: 薄膜结构是工程中广泛应用的结构之一,其自振特性的理论解与三角函数族有关,采用常规低阶单元分析时,有限元解精度不高. 虽然h型有限元法将结构的网格细化后可提高有限元解的精度,但是其前处理相对困难,如果细化网格时出现畸变网格,那么有限元解的精度可能降低. 基于p型有限元法构造两种用于研究薄膜结构自由振动特性的四边形高阶等参元,即节点数为16的Q16等参元和节点数为13的Q13等参元. 不同形状和不同边界条件的薄膜结构算例表明,所提单元较常规低阶等参元有较快的收敛速率和较高的精度及计算效率.Abstract: The membrane is one of the most widely used structures in engineering. Because the theoretical solution of the structure's natural vibration characteristics is related to the trigonometric function family, the accuracy of the finite element solution is not very high by the conventional low-order element analysis. Although the h-type finite element method can improve the accuracy of the finite element solution with refined meshing of the structure, the corresponding pre-processing is relatively difficult, and the accuracy of the finite element solution may be reduced if the refined mesh is distorted. Based on the p-type finite element method, 2 quadrilateral high order isoparametric elements, i.e., isoparametric element Q16 with 16 nodes and isoparametric element Q13 with 13 nodes, were constructed to study the free vibration characteristics of membranes. Examples of membranes with different shapes and different boundary conditions show that, the proposed elements have faster convergence rates, higher computational accuracies and efficiencies than conventional low-order isoparametric elements.
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Key words:
- membrane free vibration /
- p-type finite element /
- vibration characteristic
edited-byedited-by1) (我刊编委邓子辰来稿) -
表 1 三边固定一边自由方膜的前10阶自振频率(基于Q13、Q9、Q8和Q4)(单位: Hz)
Table 1. The 1st 10 natural frequencies of the 3-sides-fixed and one-side-free membrane based on Q13, Q9, Q8 and Q4 (unit: Hz)
N-F(m, n) element type Q13 Q9
Ne=100
(udof=380)Q8
Ne=100
(udof=280)Q4
Ne=900
(udof=870)exact[21] Ne=2
(udof=6)Ne=4
(udof=18)Ne=16
(udof=84)Ne=100
(udof=570)1(m=1, n=1) 0.342 0.340 0.340 0.340 0.340 0.340 0.340 0.340 2(m=2, n=1) 0.556 0.549 0.549 0.549 0.549 0.549 0.549 0.549 3(m=1, n=2) 0.647 0.631 0.627 0.627 0.627 0.627 0.628 0.627 4(m=2, n=2) 0.831 0.768 0.761 0.761 0.761 0.761 0.762 0.761 5(m=3, n=1) 0.904 0.829 0.820 0.819 0.820 0.820 0.821 0.819 6(m=1, n=3) 1.399 0.949 0.926 0.926 0.926 0.926 0.929 0.926 7(m=3, n=2) - 1.048 0.975 0.974 0.974 0.974 0.977 0.974 8(m=2, n=3) - 1.064 1.021 1.021 1.021 1.021 1.024 1.021 9(m=4, n=1) - 1.164 1.109 1.108 1.109 1.109 1.113 1.108 10(m=3, n=3) - 1.265 1.190 1.188 1.189 1.189 1.193 1.188 time cost /s 3.25 5.85 24.66 122.75 46.69 42.19 182.17 - 表 2 三边固定一边自由方膜的前10阶自振频率(基于Q16、Q9、Q8和Q4) (单位: Hz)
Table 2. The 1st 10 natural frequencies of the 3-sides-fixed and one-side-free membrane based on Q16, Q9, Q8 and Q4 (unit: Hz)
N-F(m, n) element type Q16 Q9
Ne=100
(udof=380)Q8
Ne=100
(udof=280)Q4
Ne=900
(udof=870)exact[21] Ne=2
(udof=12)Ne=4
(udof=30)Ne=16
(udof=132)Ne=100
(udof=870)1(m=1, n=1) 0.342 0.340 0.340 0.340 0.340 0.340 0.340 0.340 2(m=2, n=1) 0.550 0.549 0.549 0.549 0.549 0.549 0.549 0.549 3(m=1, n=2) 0.646 0.627 0.627 0.627 0.627 0.627 0.628 0.627 4(m=2, n=2) 0.776 0.761 0.761 0.761 0.761 0.761 0.762 0.761 5(m=3, n=1) 0.828 0.820 0.820 0.819 0.820 0.820 0.821 0.819 6(m=1, n=3) 0.993 0.926 0.926 0.925 0.926 0.926 0.929 0.926 7(m=3, n=2) 1.160 0.974 0.974 0.974 0.974 0.974 0.977 0.974 8(m=2, n=3) 1.282 1.021 1.021 1.021 1.021 1.021 1.024 1.021 9(m=4, n=1) 1.719 1.109 1.109 1.108 1.109 1.109 1.113 1.108 10(m=3, n=3) 1.804 1.189 1.189 1.188 1.189 1.189 1.193 1.188 time cost /s 9.55 19.37 77.45 428.38 46.69 42.19 182.17 - 表 3 裂缝薄膜的前5阶特征值(基于Q13、Q9、Q8和Q4单元)
Table 3. The 1st 5 eigenvalues of the cracked membrane based on Q13, Q9, Q8 and Q4
N-F element type Q13 Q9
Ne=225
(udof=855)Q8
Ne=225
(udof=630)Q4
Ne=900
(udof=855)exact Ne=2
(udof=6)Ne=4
(udof=15)Ne=16
(udof=78)Ne=64
(udof=348)1 8.842 2 8.726 3 8.539 2 8.454 6 8.563 7 8.580 8 8.464 7 8.371 3[22] 2 16.999 2 16.815 2 16.648 5 16.645 6 16.644 3 16.644 4 16.685 5 16.645 3[22] 3 31.107 5 28.807 3 27.996 6 27.977 9 27.979 7 27.979 7 28.098 2 27.977 7[5] 4 33.498 5 32.188 4 31.024 0 30.759 0 31.049 5 31.093 7 30.916 2 30.536 4[5] 5 63.512 3 44.514 7 42.798 4 42.551 3 42.696 7 42.718 2 42.845 3 42.447 9[5] time cost /s 3.42 5.53 19.91 77.70 244.89 125.58 178.03 表 4 裂缝薄膜的前5阶特征值(基于Q16、Q9、Q8和Q4单元)
Table 4. The 1st 5 eigenvalues of the cracked membrane based on Q16, Q9, Q8 and Q4
N-F element type Q16 Q9
Ne=225
(udof=855)Q8
Ne=225
(udof=630)Q4
Ne=900
(udof=855)exact Ne=2
(udof=12)Ne=4
(udof=27)Ne=16
(udof=126)Ne=64
(udof=540)1 8.652 0 8.597 0 8.476 5 8.423 8 8.563 7 8.580 8 8.464 7 8.371 3[22] 2 16.940 1 16.792 6 16.647 4 16.645 4 16.644 3 16.644 4 16.685 5 16.645 3[22] 3 29.159 8 28.500 7 27.994 8 27.977 8 27.979 7 27.979 7 28.098 2 27.977 7[5] 4 32.424 9 31.835 6 30.853 0 30.676 6 31.049 5 31.093 7 30.916 2 30.536 4[5] 5 45.050 7 43.884 1 42.725 3 42.513 4 42.696 7 42.718 2 42.845 3 42.447 9[5] time cost /s 9.20 17.15 66.36 269.39 244.89 125.58 178.03 表 5 环扇形薄膜的前10阶自振频率参数(基于Q13、Q9、Q8和Q4单元)
Table 5. The 1st 10 natural vibration frequency parameters of an annular membrane (based on Q13, Q9, Q8 and Q4)
N-F element type Q13 Q9
Ne=225
(udof=841)Q8
Ne=225
(udof=616)Q4
Ne=400
(udof=361)exact[7] Ne=4
(udof=10)Ne=8
(udof=22)Ne=12
(udof=49)Ne=25
(udof=121)Ne=36
(udof=181)Ne=64
(udof=337)1 6.842 6 6.842 3 6.814 1 6.813 8 6.813 8 6.813 8 6.813 9 6.813 9 6.826 0 6.814 0 2 8.313 3 8.301 0 8.267 3 8.266 8 8.266 7 8.266 7 8.266 9 8.266 8 8.291 6 8.267 0 3 10.338 0 10.237 7 10.191 6 10.190 2 10.189 4 10.189 0 10.189 8 10.189 6 10.257 0 10.189 0 4 12.537 2 12.407 7 12.323 0 12.320 4 12.314 5 12.311 9 12.314 5 12.314 1 12.467 2 12.311 0 5 13.281 4 13.270 6 12.929 4 12.855 7 12.855 6 12.855 5 12.856 2 12.855 8 12.916 8 12.856 0 6 14.330 5 14.168 6 13.816 7 13.742 7 13.742 4 13.742 3 13.743 1 13.742 6 13.809 4 13.742 0 7 15.739 4 14.739 1 14.546 8 14.576 8 14.516 6 14.505 1 14.511 6 14.511 0 14.802 0 14.502 0 8 16.943 0 15.710 6 15.198 1 15.112 3 15.110 6 15.110 1 15.111 4 15.110 7 15.207 8 15.110 0 9 20.438 0 17.245 1 16.806 1 16.829 1 16.794 4 16.715 3 16.727 9 16.727 0 17.017 1 16.706 0 10 24.941 9 17.922 7 16.987 4 16.854 1 16.845 1 16.841 8 16.844 7 16.843 8 17.216 0 16.841 0 time cost /s 28.13 55.09 83.25 174.13 257.67 462.43 447.65 333.32 104.52 - 表 6 环扇形薄膜的前10阶自振频率参数(基于Q16、Q9、Q8和Q4单元)
Table 6. The 1st 10 natural vibration frequency parameters of an annular membrane(based on Q16, Q9, Q8 and Q4)
N-F element type Q16 Q9
Ne=225
(udof=841)Q8
Ne=225
(udof=616)Q4
Ne=400
(udof=361)exact[7] Ne=4
(udof=22)Ne=8
(udof=46)Ne=12
(udof=85)Ne=25
(udof=196)Ne=36
(udof=289)Ne=64
(udof=529)1 6.842 2 6.842 2 6.814 1 6.813 8 6.813 8 6.813 8 6.813 9 6.813 9 6.826 0 6.814 0 2 8.300 3 8.300 0 8.267 1 8.266 8 8.266 7 8.266 7 8.266 9 8.266 8 8.291 6 8.267 0 3 10.233 1 10.228 9 10.190 6 10.190 1 10.189 3 10.189 0 10.189 8 10.189 6 10.257 0 10.189 0 4 12.412 6 12.355 9 12.317 8 12.320 0 12.314 4 12.311 9 12.314 5 12.314 1 12.467 2 12.311 0 5 13.267 0 13.267 1 12.929 4 12.855 7 12.855 6 12.855 5 12.856 2 12.855 8 12.916 8 12.856 0 6 14.114 2 14.114 1 13.815 0 13.742 6 13.742 4 13.742 3 13.743 1 13.742 6 13.809 4 13.742 0 7 14.667 0 14.549 7 14.522 7 14.574 9 14.516 1 14.505 1 14.511 6 14.511 0 14.802 0 14.502 0 8 15.460 1 15.457 0 15.182 3 15.111 1 15.110 3 15.110 0 15.111 4 15.110 7 15.207 8 15.110 0 9 17.101 6 16.762 2 16.803 9 16.823 3 16.792 9 16.715 2 16.727 9 16.727 0 17.017 1 16.706 0 10 17.270 9 17.220 1 16.917 5 16.848 8 16.843 9 16.841 7 16.844 7 16.843 8 17.216 0 16.841 0 time cost /s 72.13 144.05 214.37 444.51 661.42 1176.72 447.65 333.32 104.52 - -
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