5000m~3拱顶油罐失稳原因分析

为了保证油罐使用中的安全性,油罐不仅要具有足够的强度,而且还应该具有可靠的稳定性。应用外压失稳理论分析某厂５０００ｍ３拱顶油罐失稳原因,结果表明,该油罐缺乏足够的稳定性设计;为了保证油罐的稳定性,油罐设计必须符合实际工况条件,油罐施工建造必须保证质量标准。     

Classical and variational multiscale LES of the flow around a circular cylinder on unstructured grids

The effects of numerical viscosity, subgrid scale (SGS) viscosity and grid resolution are investigated in LES and VMS-LES simulations of the flow around a circular cylinder at Re=3900 on unstructured grids. The separation between the largest and the smallest resolved scales in the VMS formulation is obtained through a variational projection operator and finite-volume cell agglomeration. Three different non-dynamic eddy-viscosity SGS models are used both in classical and in VMS-LES. The so-called small-small formulation is used in VMS-LES, i.e. the SGS viscosity is computed as a function of the smallest resolved scales. Two different grid resolutions are considered. It is found that, for each considered SGS model, the amount of SGS viscosity introduced in the VMS-LES formulation is significantly lower than in classical LES. This, together with the fact that in the VMS formulation the SGS viscosity only acts on the smallest resolved scales, has a strong impact on the results. However, a significant sensitivity of the results to the considered SGS model remains also in the VMS-LES formulation. Moreover, passing from classical LES to VMS-LES does not systematically lead to an improvement of the quality of the numerical predictions.     

基于WinXP的实时控制在某舵机电动缸加载中的研究和应用

以Windows XP为系统平台,采用双核计算机,实现了对电动缸输出载荷的实时控制,提出了Windows XP下实时控制的具体实现方法和对其实时性能的要求。经多次试验验证,介绍的方案在实时控制方面,运行稳定、结构简单、成本低廉,具有广泛应用前景。     

Measuring the coolness of interactive products: the COOL questionnaire

Coolness has recently started to be explored as a design goal for interactive products from practitioners as well as researchers within human–computer interaction (HCI), but there is still a need to further operationalise the concept and explore how we can measure it. Our contribution in this paper is the COOL questionnaire. We based the creation of the questionnaire on literature suggesting that perceived coolness is decomposed to outer cool (the style of a product) and inner cool (the personality characteristics assigned to it). In this paper, we focused on inner cool, and we identified 11 inner cool characteristics. These were used to create an initial pool of question items and 2236 participants were asked to assess 16 mobile devices. By performing exploratory and confirmatory factor analyses, we identified three factors that can measure the perceived inner coolness of interactive products: desirability, rebelliousness and usability. These factors and their underlying 16 question items comprise the COOL questionnaire. The whole process of creating the questionnaire is presented in detail in this paper and we conclude by discussing our work against related work on coolness and HCI.     

Inner approximations of completely positive reformulations of mixed binary quadratic programs: a unified analysis

Every quadratic programming problem with a mix of continuous and binary variables can be equivalently reformulated as a completely positive optimization problem, that is, a linear optimization problem over the convex but computationally intractable cone of completely positive matrices. In this paper, we focus on general inner approximations of the cone of completely positive matrices on instances of completely positive optimization problems that arise from the reformulation of mixed binary quadratic programming problems. We provide a characterization of the feasibility of such an inner approximation as well as the optimal value of a feasible inner approximation. In particular, our results imply that polyhedral inner approximations are equivalent to a finite discretization of the feasible region of the original completely positive optimization problem. Our characterization yields, as a byproduct, an upper bound on the gap between the optimal value of an inner approximation and that of the original instance. We discuss the implications of this error bound for standard and box-constrained quadratic programs as well as general mixed binary quadratic programs with a bounded feasible region.     

基于三端口双向DC/DC 储能变流器的电流内环控制策略研究

多端口双向DC/DC储能变流器是一种进行能量控制变换的电力电子装置,是一种新型前沿技术,在以风力发电、光伏发电、燃料电池发电多能互补的智能微电网系统以及电动汽车能量管理控制系统中有着良好发展前景。系统主拓扑结构是以三端口双向DC/DC变换器作为储能装置,分别连接负载端、超级电容器和蓄电池,所组成的电动汽车充放电能量管理系统。通过对三端口双向DC/DC 储能变流器的控制策略的深入研究,采用状态空间法和波特图的形式来研究电流内环控制策略,实现储能装置在发电系统及电动汽车能量管理系统中的稳定应用,改善电能的利用效率。     

发动机部件强度和刚度评价及疲劳分析

某汽油机开发阶段须对发动机各主要部件结构强度和刚度做全面评价,并且须考核缸盖缸体的高周疲劳性能.基于STAR-CCM+计算出水套内部气体温度和对流换热系数,将其映射到水套有限元网格表面上作为温度边界条件.得到整个机体的温度场分布以后,在考虑各部件接触非线性的基础上,得到机体各部件的应力和变形等结果并进行评价.在有限元分析结果的基础上考虑材料温度非线性,考察缸体缸盖疲劳安全因数.结果表明,缸盖局部应力偏大,下缸体与油底壳接触面局部间隙过大,缸体缸盖疲劳安全性能满足要求.     

Universal instability modes in internal and external flows

Two prototypical external and internal flows have been studied which display linear temporal instability followed by nonlinear saturation taking the flows to a new equilibrium state. Direct simulation results are obtained using a specific formulation and numerical methods with very high accuracy. These results are analyzed via proper orthogonal decomposition (POD), which reveal similar modes for flow past a circular cylinder and flow inside a lid-driven cavity, indicating universality of such modes. Unlike many other efforts on reduced order modeling via POD, here the emphasis has been on understanding the physical aspect of the flow instability which requires very high accuracy of the simulation. Then, the obtained POD modes are related to the instability modes (in the classical sense of defining the latter) and new generic types of instability modes are identified in the studied external and internal flows. These new modes have been reported for flow past a circular cylinder [Sengupta TK, Singh N, Suman VK. Dynamical system approach to instability of flow past a circular cylinder. J Fluid Mech 2010;656:82–115] which help one in understanding the instability sequence and the relative importance of these modes in the flow evolution starting from an impulsive start. Present comparative study, furthermore, reveals universality of such instability modes by showing their presence for the flow inside a lid-driven cavity as well. Despite seeming dissimilarities between these two flows, similarities between the instability portrait of these two flows suggest universality of such modes. From the equilibrium amplitude of vorticity time-series, we establish the presence of multiple modes and multiple bifurcation sequences for these flows in parameter space. Existing theory due to Landau and Stuart that considers only a single dominant mode and its self-interaction does not explain all these features. We invoke a multi-modal interaction model in the cited reference above, termed as Landau–Stuart–Eckhaus (LSE) equation in recognition of Eckhaus’ work in modifying the classical Stuart–Landau equation. We also show that the new instability modes do not follow either the classical Stuart–Landau or the newly proposed LSE model equations and for this reason we call these as anomalous modes. Two specific classes of anomalous modes are identified and classified in the present work. Empirical expressions for the evolution of these anomalous modes are presented and their unambiguous role during instabilities is discussed.     

Comparison of image reconstruction by using near‐field and far‐field data for an imperfect conductor

Image reconstruction by using near‐field and far‐field data for an imperfectly conducting cylinder is investigated. A conducting cylinder of unknown shape and conductivity scatters the incident wave in free space and the scattered near and far fields are measured. By using measured fields, the imaging problem is reformulated into an optimization problem and solved by the genetic algorithm. Numerical results show that the convergence speed and final reconstructed results by using near‐field data are better than those obtained by using far‐field data. This work provides both comparative and quantitative information. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 69–73, 2001.     

A new similarity computing method based on concept similarity in Chinese text processing

The paper proposes a new text similarity computing method based on concept similarity in Chinese text processing. The new method converts text to words vector space model at first, and then splits words into a set of concepts. Through computing the inner products between concepts, it obtains the similarity between words. The new method computes the similarity of text based on the similarity of words at last. The contributions of the paper include： 1） propose a new computing formula between words; 2） propose a new text similarity computing method based on words similarity; 3） successfully use the method in the application of similarity computing of WEB news; and 4） prove the validity of the method through extensive experiments.