A layerwise finite element formulation for vibration and damping analysis of sandwich plate with moderately thick viscoelastic core

Abstract

Most previous studies of viscoelastic sandwich plates were based on the assumption that damping was only resulting from shear deformation in the viscoelastic core. However, extensive and compressive deformations in the viscoelastic core should also be considered especially for sandwich plates with moderately thick viscoelastic core. This paper presents a finite element formulation for vibration and damping analysis of sandwich plates with moderately thick viscoelastic core based on a mixed layerwise theory. The face layers satisfy the Kirchhoff theory while the viscoelastic core meets a general high-order deformation theory. The viscoelastic core is modeled as a quasi-three-dimensional solid where other types of deformation such as longitudinal extension and transverse compression are also considered. To better describe the distribution of the displacement fields, auxiliary points located across the depth of the sandwich plate are introduced. And based on the auxiliary points, the longitudinal and transverse displacements of the viscoelastic core are interpolated independently by Lagrange interpolation functions. Quadrilateral finite elements are developed and dynamic equations are derived by Hamilton’s principle in the variation form. Allowing for the frequency-dependent characteristics of the viscoelastic material, an iterative procedure is introduced to solve the nonlinear eigenvalue problem. The comparison with results in the open literature validates the remarkable accuracy of the present model for sandwich plates with moderately thick viscoelastic core, and demonstrates the importance of the higher-order variation of the transverse displacement along the thickness of the viscoelastic core for the improvement of the analysis accuracy. Moreover, the influence of the thickness and stiffness ratios of the viscoelastic core to the face layers on the damping characteristics of the viscoelastic sandwich plate is discussed.     

Production of eicosapentaenoic acid by a bacterium isolated from mackerel intestines

Optimization of culture conditions for the growth rate, 5,8,11,14,17-cis-Eicosapentaenoic acid (EPA) content and EPA productivity of a bacterium isolated from Pacific mackerel intestines was investigated by use of a culture medium containing 1.00 wt% peptone and 0.50 wt% yeast extract in an artificial sea water (ASW). Cultivation temperature affected the growth rate and cellular EPA content of the bacterium. The cellular EPA content at 8°C was as great as 16.8 mg/g of dry cells, which was more than two times greater than that at 25°C (7.3 mg/g of dry cells), although the growth rate showed a maximum at 25°C. Both the yield of bacterial cells and the cellular EPA content at 25°C reached maximum values when the pH of the culture medium was nearly 7.0 and when the concentration of ASW was 100% (v/v). Under optimum culture conditions [25°C pH 7.0 and 100% (v/v) ASW], the amount of EPA accumulated in the cellular lipids reached 45.6 mg/L of culture broth after 8 hr.     

再生中强型涤纶工业长丝技术的开发

采用化学醇解法制得的再生聚酯切片,经固相增黏后输送至纺丝系统,从而制备中强型涤纶工业长丝。针对再生基聚酯切片具有的熔点低、特性黏度不稳定、含有机杂质多等特性,对固相增黏工艺、熔体过滤系统、纺丝工艺等过程条件进行了探索和优化,最终制得断裂强度≥6.5 cN/dtex、断裂伸长率19.4%、干热收缩率6.49%的工业用中强型涤纶工业长丝。     

山东禹城污水处理厂主体工艺调试经验与分析

介绍了禹城污水处理厂的调试运行状况，并从培菌启动条件、设备配置、水力流态等方面对调试过程中出现的问题进行了分析与探讨，在此基础上提出了适合中小城镇污水处理厂面对进水水量波动较大，冲击负荷高的情况下的调试经验。     

小康住宅的电气设计技术

本文首先阐述了对小康住宅的电气设计技术提出的新概念与新要求,电气安全最受人们的重视和关注,包括防人身电击技术,防电气火灾技术,电涌防护技术,电气检修安全技术的保安技术等,介绍了适合于住宅小区的安全可靠的配电系统,讨论了小康住宅智能化的发展方向,在对住宅信息化,智能化的综合布线系统研究的基础上,分析了住宅小区智能化系统方案。     

一种脱盐水处理新工艺的应用

采用失效阳床和前置阴床给水处理新工艺,实现在一套装置上同时生产软水、浅除盐水和除盐水。该技术的应用对工厂扩容、降耗、增效起到了重要作用。     

仰韶酒微量组分的分析研究

甲烷菌、己酸菌二元复合菌发酵培养人工老窖技术提高了仰韶酒己酸乙酯的含量,丙酸菌的作用抑制了乳酸乙酯的生成,利用先进的毛细管气相色谱分析技术对仰韶酒微量组分进行深入分析     

应用己酸菌及人工培养窖泥提高浓香型青稞酒质量的研究

详细叙述了己酸菌及窖泥的培养方法,以及应用己酸菌及人工培养窖泥提高浓香型青稞酒质量的研究全过程     

Trefftz method applied to a moderately thick plate

This paper presents the Trefftz direct and indirect methods for analysing moderately thick plate bending problems based on an improved plate theory (IPT). By using a T‐complete set in the formulation, a non‐singular boundary integral equation is obtained. The results show that the present method is effective for both thin and thick plates. An alternative type of locking problem which is caused by the overflow of Trefftz functions has been observed and a so‐called variable‐reducing procedure for eliminating such a phenomenon is also discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

一株Pseudomonas sp.菌局部富集提高原油采收率机理

从某油田产出水中分离得到一株Pseudomonas sp．菌,主要代谢产物是糖脂类表活剂,同时产少量低分子有机酸。在菌体局部富集实验中可观察到细菌由于化学趋向性而在油水界面处富集;在代谢产物局部富集实验中,肉眼可观察到由于“在位繁殖”效应,油水界面处水相的颜色变化,在不同距离处分别取样定量测定得到产物浓度分布梯度;并且在微观仿真模型中做微生物驱油实验,观察到菌体在孔隙壁和油、水三相交界处富集,研究微生物及其代谢产物的驱油机理,得到了一些有价值的结论。