通过辐射模态研究封闭空间结构声辐射及其有源控制

通过辐射模态研究了封闭空间的结构声辐射及其有源控制问题.分析了辐射模态的数学和物理意义并揭示了辐射模态与声腔模态之间的内在耦合关系,并通过声辐射模态建立了弹性封闭空间结构声辐射有源控制模型.针对辐射模态在有源控制中的应用实现问题,给出了一种新的控制策略,即将辐射模态按对应辐射效率或耦合强度从大到小排列,使前k阶声辐射模态声势能最小化.采用压电陶瓷作动器作为控制力源进行了封闭空间结构声辐射有源控制数值计算与分析研究.结果表明,辐射模态与声腔模态的耦合具有严格的选择性,各阶辐射模态的形状和与相耦合的主导声模态在耦合面上的形状非常相似;在低频范围内,一般只需最小化前三阶辐射模态声势能,在更低频或声模态频率附近,只需最小化前一阶最有效辐射模态声势能,便能和总声势能最小化策略控制效果基本一样.     

Optimal External Memory Planar Point Enclosure

In this paper we study the external memory planar point enclosure problem: Given N axis-parallel rectangles in the plane, construct a data structure on disk (an index) such that all K rectangles containing a query point can be reported I/O-efficiently. This problem has important applications in e.g. spatial and temporal databases, and is dual to the important and well-studied orthogonal range searching problem. Surprisingly, despite the fact that the problem can be solved optimally in internal memory with linear space and O(log N+K) query time, we show that one cannot construct a linear sized external memory point enclosure data structure that can be used to answer a query in O(log  _B N+K/B) I/Os, where B is the disk block size. To obtain this bound, Ω(N/B ^1−ε ) disk blocks are needed for some constant ε>0. With linear space, the best obtainable query bound is O(log ₂ N+K/B) if a linear output term O(K/B) is desired. To show this we prove a general lower bound on the tradeoff between the size of the data structure and its query cost. We also develop a family of structures with matching space and query bounds. An extended abstract of this paper appeared in Proceedings of the 12th European Symposium on Algorithms (ESA’04), Bergen, Norway, September 2004, pp. 40–52. L. Arge’s research was supported in part by the National Science Foundation through RI grant EIA–9972879, CAREER grant CCR–9984099, ITR grant EIA–0112849, and U.S.-Germany Cooperative Research Program grant INT–0129182, as well as by the US Army Research Office through grant W911NF-04-01-0278, by an Ole Roemer Scholarship from the Danish National Science Research Council, a NABIIT grant from the Danish Strategic Research Council and by the Danish National Research Foundation. V. Samoladas’ research was supported in part by a grant co-funded by the European Social Fund and National Resources-EPEAEK II-PYTHAGORAS. K. Yi’s research was supported in part by the National Science Foundation through ITR grant EIA–0112849, U.S.-Germany Cooperative Research Program grant INT–0129182, and Hong Kong Direct Allocation Grant (DAG07/08).     

轻型围护门式刚架普通钢结构厂房的优化设计分析

随着轻型围护材料的广泛应用和一些钢结构厂房工程的实践,在普通钢结构厂房中,用实腹式门式刚架代替传统采用的格构式刚架结构成为可能,但现有设计方法只是单纯采用普钢规范和凭借工程经验。为优化这种设计方法,控制用钢量并保证设计的可靠性,通过对我国现行钢结构相关规范、规程的对比分析,结合工程经验,提出了轻型围护门式刚架普通钢结构厂房的优化设计方法。最后用实际工程案例验证了该方法的可行性和优势,为今后同类型的厂房设计提供了一定的设计依据。     

BHP来实轻钢围护系统施工工艺

厦门某工业厂房采用BHP来实轻钢围护系统,屋面无搭接、无螺钉穿透、无压条,防漏可靠,排水能力极佳;并且防热胀冷缩性、隔热、防火、保温、吸声、通风效果好。BHP屋面及墙面的铺装有其特定的工艺和施工要点。在施工中对原设计还进行了部分改进,该厂房至今未出现变形与渗漏现象。     

Transient natural convection in 3D tilted enclosure heated from two opposite sides

In the present work, we investigate numerically the natural convection flow in 3D cubic enclosure tilted at an angle (γ) with respect to the vertical position. The enclosure is heated and cooled from the two opposite walls while the remaining walls are adiabatic. The numerical procedure adopted in this analysis yield consistent performance over a wide range of parameters. Simulations have been carried out for Rayleigh numbers Ra ranging from 10³ to 1.3 × 10⁵, Prandtl number, Pr, (0.71 ≤ Pr ≤ 75) and inclination angle γ (0° ≤ γ ≤ 90°). Particular attention is focused on the three-dimensional steady effects that can arise in such configuration that seem to be unknown in the literature, even for relatively small values of the Rayleigh number. The 3D flow characteristics and thermal fields are analyzed in terms of streamlines, isotherms and Nusselt numbers. A periodic behavior of the 3D flow has been observed at Ra = 8.5 × 10⁴ with a fundamental frequency of 8.27. The Hopf bifurcation is localized. In addition, time-dependent solutions reveal that the flow characteristics depend on the inclination angle γ. The effects of Prandtl number on heat transfer and fluid flow is significant for Pr ≥ 6.     

Effect of magnetic field on convection heat transfer inside a tilted square enclosure

Steady, laminar, natural-convection flow in the presence of a magnetic field in a tilted enclosure heated from below and cooled from top is considered. The enclosure is filled with liquid gallium. In our formulation of governing equations, mass, momentum and energy are applied to the enclosure. To solve the nonlinear governing differential equations a finite volume code based on PATANKAR's SIMPLER method is utilized. It is shown that for a given inclination angle (φ), as the value of Hartmann number (Ha) increases, the convection heat transfer reduces. Furthermore it is found that at Ra = 10⁴, value of Nusselt number depends strongly upon the inclination angle for relatively small values of Hartmann number. At Ra = 10⁵, the Nusselt number increases up to about φ = 45^o and then decrease as φ increases.     

泄漏条件下室内火灾烟气的自然充填过程

采用全尺寸实验的方法研究有泄漏条件下室内火灾烟气的自然充填过程.测量了室内外压差和温度分布.在对泄漏分布做一定假设的前提下,估算实验场所的泄漏面积及泄漏流量.对于实验中庭,其侧墙泄漏平均宽度约为0.038 m,顶棚泄漏面积约为0.65 m2由于泄漏面积较小,烟气充填过程中的泄漏流量远小于烟气羽流质量流量.泄漏的存在对烟气浓度、温度和沉降过程影响不大,但将在室内形成上正下负的内外压差分布及中性面.     

紧凑而可靠的新型126kV三相共筒型GIS

笔者介绍了一种紧凑而可靠的新型126 kV三相共筒型GIS,同时对产品的成本进行了分析。分析结果表明,新设计在基础材料成本、运输、运行、维护成本上均有一定的优势。     

Binary gas diffusivity estimates from transient,one-dimensional sublimation–diffusion experiments in a spherical enclosure

Binary gas diffusivities D_AB’s are extremely useful in the analysis/design of mass transfer systems and to develop correlations. This study used an unsteady experimental method to determine D_AB’s in gas pairs starting with a sublimating solid (A) such as naphthalene or camphor and air (B). The cumulative fractional mass transferred from the surface of a solid A sphere placed concentrically within an isothermal spherical enclosure was followed gravimetrically with time. The experimental D_AB,exp for the gas pair was determined by nonlinear regression using the solution to a transient, one-dimensional (radial) diffusion model. The model’s Case 1 option assumed impermeability (no flux of gas A) at the enclosure’s outer surface, while Case 2 assumed zero concentration of gas A at the same location. For naphthalene–air, D_AB,exp overestimated the literature values, the errors ranging from ?110 to ?185% for Case 1 and ?21 to ?65% for Case 2. For camphor–air, the error in D_AB,exp was ?36% for Case 1 and ?16% for Case 2. D_AB,exp for camphor in atmospheric air is herein reported for the first time. Potential improvements to the experiments include automation of the sphere melt-casting process and tighter control of the enclosure’s environmental conditions. Likewise, the theoretical model could be extended to three dimensions with multicomponent diffusion to assess the effect of air humidity on the transport of gas A. This is the first attempt to determine D_AB,exp for naphthalene–air and camphor–air from an unsteady sublimation–diffusion experiment and to model the results using rigorous mass transport theory.     

土钉加排桩复合围护结构的共同作用分析

土钉加排桩复合围护结构是新近出现的一种深基坑围护结构形式。在缺少类似工程经验的情况下,结合详细的现场监测数据,借助有限元软件对该复合围护结构进行计算,分析土钉和排桩各自的受力变形性状以及它们之间共同作用的特性。通过有限元计算与现场监测结果的对比,提出基于室内土工试验结果的同类硬黏土弹性模量的取值方法,并对复合围护结构中土钉与排桩的共同作用进行分析,给出设计和计算分析的实用方法。