Accuracy assessment to applying 20-node solid elements to pressurized composite shells

A factorial analysis is conducted to explore the impact of five factors — aspect ratio, radius-to-thickness ratio, material anisotropy, fiber angle and integration order on the finite element accuracy, with regard to the application of 20-node isoparametric solid elements to clamped composite cylindrical shells subjected to internal pressure. The maximum radial displacement at the central cross-section is employed as the indicator of accuracy. Results from finite element methods were compared with closed-form solutions. Aspect ratio, radius-to- thickness ratio, and integration order are significant main effects as predicted for isotropic materials. Material anisotropy shows no significant main effect, while the fiber angle does have strong impact on the finite element accuracy. In addition to four influential main effects, some multiple-factor interactions are shown to have significant influences on the finite element accuracy. The analysis is limited to the linear elastic range.     

换能器前辐射头与轴向相平行方向的弯曲振动

复合棒型换能器前面的变截面组件在工作时常伴有弯曲振动现象，这在一定程度上会影响换能器的工作性能；利用复合棒型换能器的纵向振动基频与前辐射头弯曲振动的恰当耦合，可展宽换能器的频带。本文用有限元法，研究了前辐射头在声换能器组成中的弯曲振动问题，与测试结果相吻合。     

On the localization of the antisymmetric flexural edge waves for obtuse angles

It is well known that the existence of edge waves is directly related to the localization of the acoustic field in the wedge. In this paper, it is shown experimentally and numerically that, for wedge angles smaller than about 100° (this angle may vary from one material to an other), the edge modes are confined in the tip of the wedge and may be considered as localized. For higher wedge angles, the analysis of the results shows a delocalization of the guided waves, which induces a new repartition of the acoustical energy in the wedge and a decrease in the amplitude of the wedge wave. This observation is numerically verified via an analysis in the time domain. Experiments realized on obtuse wedges demonstrate that the first ASF mode may be detected for wedge angles up to about 110°.     

Study on rectangular ultrasonic radiator of flexural resonant vibration in high modes

Based on the theory of coupling vibration and flexural vibration of thin rod of rectangular cross section, the fiexural vibration of rectangular thin plate was studied. The frequency equation was derived under the condition of freeboundaries. The normal modes and the relation between the normal modes and the resonant frequency were obtained. Experiments showed that the calculated resonant frequencies agree well with the measured results, and the rectangular thin plate in flexural vibration has abundant resonant frequencies. The radiator of flexural vibration used in ultrasonic cleaning and other techniques has the advantages of large acoustic radiating area, uniform acoustic field and easy adjustment of resonant frequencies, proving that it is a promising ultrasonic source.     

Mathematical Modeling of the Stress-Strain State of Adhesive Layers in Sandwich Structures

The studies on theoretical modeling of a sandwich shell (SS) and sandwich beam (SB) are presented in this paper. The displacements of adhesive layers are computed in the whole SS. The Euler-Ostrogradskii equations are used to derive the equations of equilibrium, which contain six 16th-order differential equations. The three-point bending of a sandwich beam is considered and the behavior of the adhesive layer of the SB is calculated.     

Existence theory for linearly elastic shells

We review existence and uniqueness results, recently obtained for three of the most important linear two-dimensional shell models: Koiter’s model, the bending model and the membrane model. They rely on a crucial lemma of J L Lions, used in an essential way for establishing in each case a generalized Korn’s inequality, which is then combined with a generalized rigid displacement lemma of a geometrical nature. Dedicated to the memory of Professor K G Ramanathan     

圆柱壳在径向冲击载荷作用下的弹性脉冲屈曲

当圆柱壳承受径向脉冲载荷时，如果其径厚比大于一特定值，圆柱壳将产生弹性动力屈曲．本文根据有关实验结果，假定变形模态，采用Ｌａｇｒａｎｇｅ方法分析了有限长薄圆柱壳（ａ／ｈ＝４８０）在余弦冲击载荷作用下的弹性脉冲动力屈曲．导出了动力屈曲方程组，借助数值方法求解方程，并与有关计算结果进行了比较．     

NONLINEAR THEORY OF MULTILAYER SANDWICH SHELLS AND ITS APPLICATION(III)──LARGE DEFLECTION AND POSTBUCKLING OF SHALLOW SHELLS

Exactsolutionsoflargedeflectionandpostbucklingofrectangularplatesaredifficultproblems.Usually,appropriateseriesofsolutionsbasedonspecificboundaryareassumedtosolvetheproblems['].LiuandChengl'lsolvedthenonlinearbendingproblemofsimplysuPPortedrectangularsand…     

A comparison of high-order time integrators for thermal convection in rotating spherical shells

A numerical study of several time integration methods for solving the three-dimensional Boussinesq thermal convection equations in rotating spherical shells is presented. Implicit and semi-implicit time integration techniques based on backward differentiation and extrapolation formulae are considered. The use of Krylov techniques allows the implicit treatment of the Coriolis term with low storage requirements. The codes are validated with a known benchmark, and their efficiency is studied. The results show that the use of high-order methods, especially those with time step and order control, increase the efficiency of the time integration, and allows to obtain more accurate solutions.