英国食品标准局 餐桌守护神

目前英国食品标准局发布报告,点名警告亨氏、雀巢等西方知名品牌在英国的产品致癌物升高,并提醒英国市民长期食用这些产品具有的风险。这个被称为“餐桌守护神”的部门,是英国政府为解决近年来日益严重的食品安全问题而专门设立的独立监督机构。成立十多年来,它不仅让英国没有再次面临“疯牛病”、“口蹄疫”的困扰,而且成了英国人食品安全的“实时预报员”。对于日益被食品安全“撕咬”着的中国民众来说,笔者不免对英国食品标准局的运作产生几分好奇,并于日前访问了位于伦敦市中心的英国食品标准局总部。     

爆炸复合板与轧制复合板界面结构的研究

用透射电镜、扫描电镜和能谱仪等手段对爆炸和轧制复合板界面组织、相结构和成分变化进行了研究。结果发现爆炸复合是由周期性熔化和非熔化构成的波状复合面，它比轧制扩散复合形成的平面积多１／３左右。两种复合方式都有越过界面的元素扩散，爆炸态扩散范围在２５μｍ左右；轧制态Ｆｅ、Ｎｉ、Ｃｒ元素扩散范围在５０μｍ左右，碳元素越过纯Ｎｉ层向不锈钢侧的扩散范围为１００μｍ左右，在此区域发现沿晶界连续析出有Ｍ２３Ｃ６型碳化物。     

柔性印版的变形分析

为了解决柔性版印刷过程中印刷图文存在的偏差问题,对印刷过程中出现的几种印版的变形进行了分析,通过对印版变形的印前预补偿处理,利用杜邦经验公式计算印版缩版尺寸等方法补偿印版尺寸的变化,最终获得质量较高的印刷品.     

Impact of plate design on the performance of welded type plate heat exchangers for sorption cycles

Numerical and experimental analysis was carried out to examine the heat transfer and pressure drop characteristics of welded type plate heat exchangers for absorption application using Computational Fluid Dynamics (CFD) technique. The simulation results based on CFD are compared with experimental results. A commercial CFD software package (FLUENT) has been used to predict the characteristics of heat transfer, pressure drop and flow distribution within the plate heat exchangers. In this paper, a welded plate heat exchanger with a plate of chevron embossing type was tested by controlling mass flow rate, solution concentration, and inlet/outlet temperatures. The working fluid is H₂O/LiBr solution with the LiBr concentration of 54–62% in mass. The numerical simulation examines the internal flow patterns, temperature distribution and the pressure distribution within the channel of the plate heat exchanger. Three plates of embossing types; chevron embossing, elliptic and round, are proposed and simulated in this paper. The simulation results show reasonably good agreement with the experimental results. Also, the numerical results show that the plate with the elliptical shape gives better performance than the plate of the chevron shape from the viewpoints of heat transfer and pressure drop.     

Dynamics of the bilinear Mindlin plate element

Plate and shell finite elements based upon Mindlin plate theory and evaluated by one-point quadrature are attractive because of their effectiveness for both thick and thin shells, at minimal computing cost. However, these elements are rank-deficient and must be stabilized to obtain reliable behaviour. Methods for achieving full rank of the stiffness and for stabilizing element behaviour in static analysis and in explicit dynamic calculations exist and are quite effective. This paper addresses the remaining issue of controlling spurious modes of response in vibration analysis and implicit dynamic solutions. Several alternatives for the element mass formulation are examined in detail. We show that non-physical dynamic modes present a potential problem with most mass matrix formulations, and that spurious modes other than the familiar hourglassing motion are possible. A combination of projection methods and reduced quadrature is suggested which eliminates these deficiencies and produces accurate numerical results. The remaining techniques investigated give rise to anomalous behaviour which make them unsuitable for general use.     

振动固定板结构体积位移的获取

在低频时控制振动板结构的体积位移是降低结构总声功率的一种有效策略.提出一种阵列式压电式传感器的设计方法测量固定板体积位移.通过对PVDF传感器阵列输出信号设计的加权系数,使PVDF传感器阵列输出信号为相应结构体积位移.结果表明这种阵列式PVDF传感器的加权系数与施加在振动板表面的外激励力性质(如激励力类型、位置等)无关.并且分析了影响阵列式PVDF传感器的各种因素及其适应性.     

A quadrilateral hybrid-Trefftz plate bending element for the inclusion of warping based on a three-dimensional plate formulation

A plate formulation, for the inclusion of warping and transverse shear deformations, is considered. From a complete thick and thin plate formulation, which was derived without ad hoc assumptions from the three-dimensional equations of elasticity for isotropic materials, the bending solution, involving powers of the thickness co-ordinate z, is used for constructing a quadrilateral finite plate bending element. The constructed element trial functions, for the displacements and stresses, satisfy, a priori, the three-dimensional Navier equations and equilibrium equations, respectively. For the coupling of the elements, independently assumed functions on the boundary are used. High accuracy for both displacements and stresses (including transverse shear stresses) can be achieved with rather coarse meshes for thick and thin plates.     

The decomposed form of the three-dimensional elastic plate

Summary. In 1992, Gregory [1] gave a rigorous proof about the decomposed form when stress is anti-symmetrical about the mid-plane. His proof is dependent on his previous works [3], [4], i.e., the Papkovich-Fadle eigenfunction expansion of bi-harmonic functions. In this paper, we give a new proof concisely and directly, which is independent of the Papkovich-Fadle expansion, when stress is anti-symmetrical about the mid-plane. The general state of stress in the plate can be decomposed into three parts: the interior state, the shear state and the Papkovich-Fadle state.     

Fundamental frequency of the CCCF composite sandwich plate

The analytical closed-form solution providing the value of fundamental frequency of the CCCF composite sandwich plate is proposed in this article. The variational equations of motion are derived using Hamilton’s principle in conjunction with the first-order shear deformation theory. The solution approach involves reduction of the governing equations of motion to a system of ordinary equations using Kantorovich procedure and subsequent application of the generalised Galerkin method. The analytical solution is verified using the finite element modal analysis. The comparisons of computational results have shown that the fundamental frequency of the CCCF sandwich plates can be calculated with sufficient accuracy using the analytical technique developed in this work.     

Stiffened plate bending analysis in terms of refined triangular laminated plate element

Based on the higher-order global–local theories, a finite element model is proposed to study the bending behavior of stiffened laminated plates. The proposed model treats the embedded stiffeners as the part of laminated plate, so that the compatibility of displacements and stresses between the plate and the stiffeners can be automatically satisfied. Distributions of the displacements and stresses through the thickness of laminates were also given for the first time, which can serve as references for future investigations as such information is lacking in the published literature. In addition, the impact of the stiffeners on the bending response of the stiffened laminated plates is also studied in terms of the quantity, the collocation and the geometry of stiffeners. Numerical results showed that the higher-order global–local theories are more suitable for predicting the bending response of thick and moderately thick stiffened laminated plates compared to the first order theory commonly used in engineering. By varying the quantity, the collocation and the geometry of stiffeners, the stiffness and the strength of stiffened laminated plates can be remarkably improved.     

Phononic plate waves

In the past two decades, phononic crystals (PCs) which consist of periodically arranged media have attracted considerable interest because of the existence of complete frequency band gaps and maneuverable band structures. Recently, Lamb waves in thin plates with PC structures have started to receive increasing attention for their potential applications in filters, resonators, and waveguides. This paper presents a review of recent works related to phononic plate waves which have recently been published by the authors and coworkers. Theoretical and experimental studies of Lamb waves in 2-D PC plate structures are covered. On the theoretical side, analyses of Lamb waves in 2-D PC plates using the plane wave expansion (PWE) method, finite-difference time-domain (FDTD) method, and finite-element (FE) method are addressed. These methods were applied to study the complete band gaps of Lamb waves, characteristics of the propagating and localized wave modes, and behavior of anomalous refraction, called negative refraction, in the PC plates. The theoretical analyses demonstrated the effects of PC-based negative refraction, lens, waveguides, and resonant cavities. We also discuss the influences of geometrical parameters on the guiding and resonance efficiency and on the frequencies of waveguide and cavity modes. On the experimental side, the design and fabrication of a silicon-based Lamb wave resonator which utilizes PC plates as reflective gratings to form the resonant cavity are discussed. The measured results showed significant improvement of the insertion losses and quality factors of the resonators when the PCs were applied.     

冷板冷藏车内冷板换热性能的研究

采用焓法的处理方法对冷板冷藏车内冷板的相变传热问题进行研究。通过数值模拟计算得到冷板的最佳厚度及管间距;保证当冷板外表面过热到-5℃时冷板内共晶冰全部融解,同时又能保证冷板尽可能蓄更多的冷量,为冷板车内冷板结构设计提供参考。     

多次水下爆炸作用下钢板与焊接钢板冲击损伤特性

为了研究舰船结构在多次水下爆炸载荷作用下的抗爆抗冲击能力,基于水下爆炸鼓胀试验分别开展了5 mm、12 mm的船用A32背空钢板及焊接板的多次水下爆炸试验,得到了钢板与焊接板的塑性变形历程,测量并计算了钢板与焊接板受冲击区域沿半径各点处的挠度及厚度减薄率,分析了钢板与焊接板的塑性变形规律。结果表明:多次水下爆炸载荷作用下,焊接板与钢板的塑性变形形貌呈类球冠形,二者的厚度减薄率从中心位置到边界处呈先减小再增大的趋势,但焊接板的挠度小于钢板的挠度。A32钢板的变形模式主要为弯曲和拉伸变形,焊接板以弯曲变形为主。持续增加的水下爆炸载荷导致钢板中心位置与边界处拉伸断裂,而焊接板的焊缝及其热影响区发生脆性断裂。     

Oscillatory flow around the edge of a flat plate

Summary The paper deals with oscillatory flow of an incompressible viscous fluid around the edge of a flat plate. The primary interest is, in connexion with the flow in open pipes near the edge due to acoustic standing waves, in the dissipation associated with the flow around the edge. Mathematically, the problem to find the flow around the edge can be formulated as an integral equation for a dipole distribution along the plate. This can be simplified by making use of the fact that the Stokes boundary layer is thin with respect to the characteristic length scale of the flow. The simplified equation is solved by a method used recently by Boersma. With the help of this solution the dissipation is calculated. The result is compared with exact, numerical, calculation by Disselhorst. Good agreement is found.