RESEARCH ON EQUILIBRIUM AND CONFORMING THEORY OF THE FINITE ELEMENT METHOD IN ELASTICITY
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摘要: 有限元分析中的单元可以遵循不同的方法构造,该文提出以单元模型的平衡性与协调性进行分类,并对弹性力学平面问题中的几种经典单元进行了分析比较,总结了协调元、非协调元和超协调元的协调性方法,以及基于解析试函数法的平衡型方法。单元的协调性理论思路包含单纯形格式协调元和非单纯形格式协调元,以及相应的非协调和超协调元格式,关注的重点是单元边界的协调。单元的平衡性理论思路包含解析试函数和权函数的高阶完备性,关注的重点研究是单元内部及边界平衡性。研究表明:针对弹性力学中平衡性和协调性要求,两类理论给出的不同单元格式各具特点,而既能保证单元内部平衡性,又能考虑单元界面协调性的单元类型给出了更精确、合理的计算结果。Abstract: Element formulations in finite element analysis may follow different approaches. A classification of elements in equilibrium and compatibility is presented. Analysis and comparison of some classic plane elements show that, non-conforming, conforming and super conforming elements can be constructed based on the compatibility theory, and analytical trial functions can be employed to help the construction of equilibrium elements. The researches of compatibility focus on the boundary conforming between elements, which conform bases of simplex conforming, non-simplex conforming, non-conforming and super conforming elements. The researches of equilibrium focus on the equilibrium principle in element or between elements, which emphasize high-precise completeness of analytical trial functions and weight functions. The benchmark tests show that although all kinds of elements have their own advantages and shortcomings, elements that satisfy both the equilibrium inside elements and the compatibility between elements deliver generally better performance.
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表 1 三角形网格下各类单元的挠度精度分析(精确解为1.0000)
Table 1. Precision of triangular elements
网格数 2×2 2×4 2×8 2×16 CST 0.0128 0.0489 0.1654 0.4058 GT9 0.1045 0.3156 0.6371 0.8510 GT9M 0.1049 0.3191 0.6504 0.8692 TR3 0.9906 0.9903 0.9911 0.9961 表 2 网格畸变敏感性测试精度分析
Table 2. Precision in distorted mesh
d 5β 7β P-S ATF-GCQ4 ATF-Q4 0.0 1.0000 0.3151 1.0000 1.0000 1.0000 1.0 0.2670 0.1900 0.6290 0.5512 1.0000 2.0 0.1876 0.1574 0.5500 0.4386 1.0000 3.0 0.1911 0.1681 0.5470 0.4431 1.0000 4.0 0.2118 0.1701 0.5310 0.4297 1.0000 4.9 0.3496 0.1413 0.4980 0.4267 1.0000 表 3 网格畸变敏感性测试计算结果
Table 3. Precision in distorted mesh
网格 结果 Q8 HSF-Q8 1 $ {\sigma _x} $(A) 56.447 120.000 $ {\sigma _x} $(B) −74.863 −120.000 $w ({\rm C})$ −2.328 −12.000 2 $ {\sigma _x} $(A上) 13.665 120.000 $ {\sigma _x} $(A下) 5.262 120.000 $ {\sigma _x} $(B上) −5.665 −120.000 $ {\sigma _x} $(B下) −14.299 −120.000 $w ({\rm C})$ −0.477 −12.000 -
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