Isoparametric quadrilateral elements are widely used in the finite element method, but the accuracy of the isoparametric quadrilateral elements will drop obviously deteriorate due to mesh distortions. Spline functions...Isoparametric quadrilateral elements are widely used in the finite element method, but the accuracy of the isoparametric quadrilateral elements will drop obviously deteriorate due to mesh distortions. Spline functions have some properties of simplicity and conformality. Two 8-node quadrilateral elements have been developed using the trian- gular area coordinates and the B-net method, which can ex- actly model the quadratic field for both convex and concave quadrangles. Some appropriate examples are employed to evaluate the performance of the proposed elements. The nu- merical results show that the two spline elements can obtain solutions which are highly accurate and insensitive to mesh distortions.展开更多
The quadrilateral discrete Kirchhoff thin plate bending element DKQ is based on the isoparametric element Q8, however, the accuracy of the isoparametric quadrilateral elements will drop significantly due to mesh disto...The quadrilateral discrete Kirchhoff thin plate bending element DKQ is based on the isoparametric element Q8, however, the accuracy of the isoparametric quadrilateral elements will drop significantly due to mesh distortions. In a previous work, we constructed an 8-node quadrilateral spline element L8 using the triangular area coordinates and the B- net method, which can be insensitive to mesh distortions and possess the second order completeness in the Cartesian co- ordinates. In this paper, a thin plate spline element is devel- oped based on the spline element L8 and the refined tech- nique. Numerical examples show that the present element indeed possesses higher accuracy than the DKQ element for distorted meshes.展开更多
在自然条件下利用紫外灯补充紫外线B,模拟臭氧层破坏10%、20%后昆明地区增加的紫外线B强度2.5和5 k J/(m^2·d),研究了紫外线B增加对滇杨(Populus yunnanensis)(2 430 m)和川杨(P.szechuanica)(3 300 m)光合参数、暗呼吸速率、叶片...在自然条件下利用紫外灯补充紫外线B,模拟臭氧层破坏10%、20%后昆明地区增加的紫外线B强度2.5和5 k J/(m^2·d),研究了紫外线B增加对滇杨(Populus yunnanensis)(2 430 m)和川杨(P.szechuanica)(3 300 m)光合参数、暗呼吸速率、叶片厚度的影响。结果表明:与对照相比,2.5和5 k J/(m^2·d)紫外线B处理使滇杨的净光合速率(Pn)分别降低了32%和51%,川杨则降低了16%和39%;相反,2.5和5 k J/(m^2·d)紫外线B显著提高了暗呼吸速率(Rd)和叶片厚度;相关性分析表明:两种杨树的叶片净光合速率与水分利用效率均呈显著正相关,与暗呼吸速率呈显著的负相关(P<0.01)。此外,2.5 k J/(m^2·d)紫外线B强度对滇杨和川杨的气孔导度、暗呼吸速率及其与净光合效率比值的影响不同;且川杨的净光合速率、暗呼吸速率、叶片厚度都显著大于滇杨,这些差异反映出生长在高海拔环境下的川杨比生长在低海拔的滇杨对紫外线B增强具有更强的耐性。展开更多
基金supported by the National Natural Science Foundation of China(11001037,11102037 and 11290143)the Fundamental Research Funds for the Central Universities
文摘Isoparametric quadrilateral elements are widely used in the finite element method, but the accuracy of the isoparametric quadrilateral elements will drop obviously deteriorate due to mesh distortions. Spline functions have some properties of simplicity and conformality. Two 8-node quadrilateral elements have been developed using the trian- gular area coordinates and the B-net method, which can ex- actly model the quadratic field for both convex and concave quadrangles. Some appropriate examples are employed to evaluate the performance of the proposed elements. The nu- merical results show that the two spline elements can obtain solutions which are highly accurate and insensitive to mesh distortions.
基金supported by the National Natural Science Foundation of China(11001037,11102037,11290143)the Fundamental Research Funds for the Central Universities(DUT13LK07)
文摘The quadrilateral discrete Kirchhoff thin plate bending element DKQ is based on the isoparametric element Q8, however, the accuracy of the isoparametric quadrilateral elements will drop significantly due to mesh distortions. In a previous work, we constructed an 8-node quadrilateral spline element L8 using the triangular area coordinates and the B- net method, which can be insensitive to mesh distortions and possess the second order completeness in the Cartesian co- ordinates. In this paper, a thin plate spline element is devel- oped based on the spline element L8 and the refined tech- nique. Numerical examples show that the present element indeed possesses higher accuracy than the DKQ element for distorted meshes.
文摘在自然条件下利用紫外灯补充紫外线B,模拟臭氧层破坏10%、20%后昆明地区增加的紫外线B强度2.5和5 k J/(m^2·d),研究了紫外线B增加对滇杨(Populus yunnanensis)(2 430 m)和川杨(P.szechuanica)(3 300 m)光合参数、暗呼吸速率、叶片厚度的影响。结果表明:与对照相比,2.5和5 k J/(m^2·d)紫外线B处理使滇杨的净光合速率(Pn)分别降低了32%和51%,川杨则降低了16%和39%;相反,2.5和5 k J/(m^2·d)紫外线B显著提高了暗呼吸速率(Rd)和叶片厚度;相关性分析表明:两种杨树的叶片净光合速率与水分利用效率均呈显著正相关,与暗呼吸速率呈显著的负相关(P<0.01)。此外,2.5 k J/(m^2·d)紫外线B强度对滇杨和川杨的气孔导度、暗呼吸速率及其与净光合效率比值的影响不同;且川杨的净光合速率、暗呼吸速率、叶片厚度都显著大于滇杨,这些差异反映出生长在高海拔环境下的川杨比生长在低海拔的滇杨对紫外线B增强具有更强的耐性。
