集值映射空间上的Tightness和Fan Tightness

本文讨论了连续集值映射空间在赋予点态收敛拓扑和紧开拓扑下的tightness和fan tightness, 将关于连续单值映射空间的某些结果推广到连续集值映射空间.     

扇的倍图的邻点可区别边色数

设G(V,E)是阶数至少是3的简单连通图,若f是图G的k-正常边染色,使得对任意的uv∈E(G),C(u)≠C(v),那么称f是图G的k-邻点可区别边染色(k-ASEC),其中C(u)={f(uw)│uw∈E(G)},而χa′s(G)=min{k│存在G的一个k-ASEC},称为G的邻点可区别边色数.本文给出扇的倍图D(Fm)的邻点可区别边色数.     

Reduction of motor fan noise using CFD and CAA simulations

Motor fans used for cooling electric motors have long been recognized as one of the major noise sources. Current paper focuses on design of motor fan for electric motors that are used in submarines for pumping sea water. Noise reduction at source is very important and the critical task, for under water applications. An attempt has been made for reduction of motor fan noise by modification of noise sources. For this purpose computational fluid dynamics and computational aeroacoustics code FLUENT package is used to identify the noise sources and to know the overall sound pressure level of motor fan. From these results it is observed that aerodynamic noise is the dominate fan noise source. Aerodynamic noise of motor fan can be reduced by modifying fan geometry. The aerodynamic noise level of motor fan has been reduced by replacing the straight blades with various digits of NACA (National Advisory Committee for Aeronautics) 65 series airfoil sections. From the numerical results it is observed that the minimum sound pressure level for NACA 65-010 is 65.4 dB(A). These numerical results are compared with measurements in a semi-anechoic chamber. It is found that there is good agreement between numerical and experimental results.     

Aerodynamic damping of sidewall bounded oscillating cantilevers

As a result of their simplicity, low power consumption, and relative ease of implementation, oscillating cantilevers have been investigated for use in multiple applications. However, the in situ operation in many cases, requires oscillating near one or more solid walls. When the separation distance between the vibrating cantilever and the solid wall becomes small, damping from the surrounding fluid is increased, which in turn can increase the power required to maintain certain operational performance characteristics (e.g., vibration amplitude). This increase in damping is a well-studied phenomenon for certain configurations (e.g., microcantilevers in Atomic Force Microscopy, or AFM), but is largely unexplored for a cantilever sweeping across a solid wall, which has direct impact for many macro-based applications including electronics cooling and propulsion. In this paper, we experimentally investigate the aerodynamic damping as a function of the gap between two sidewalls parallel to the oscillating motion of the cantilever. Multiple voltage and frequency inputs are considered in addition to the magnitude of the wall to cantilever gap. Experiments performed across a range of operating conditions reveal that decreasing the distance between the walls and the oscillating cantilever can increase the aerodynamic damping as much as 5 times that of the isolated (i.e., without sidewalls) operation. The resonance frequency is also shown to decrease when the gap spacing is extremely small, suggesting the added mass of the fluid is also sensitive to this variable. However, this change is much smaller (~0.5%) compared to the change typically observed in damping. The findings in the paper help to quantify the overall effect of solid enclosure walls on the performance of an oscillating cantilever, which will better enable the designer to achieve the maximum operational effectiveness. The experimental findings also suggest viscous damping with sidewalls could be predicted from first principles in a similar manner to well accepted analytical models of a cantilever vibrating above a solid surface.     

离心风机子午通道内湍流场数值模拟

由进风口－叶轮－无叶扩压器－蜗壳等部件组成的离心风机通道内流分析是非常复杂的，目前还只能是分别计算各部件内的流场，但必须考虑部件间的相互影响。本文采用轴对称Ｎ－Ｓ方程，根据三维叶轮通道计算给出的叶片力分布，求解了考虑叶片力的进风口－叶轮－无叶扩压器组成的子午通道问题，所得结果可用来给出三维叶轮通道计算的进口条件，并可用于优化设计进风口及叶轮前、后盘形状。该方法已得到实践检验。     

某轴流送风机叶片断裂事故计算分析

本文是理论计算与工程实际相结合的典型例子．某电厂锅炉送风机，多次发生叶片断裂事故，严重影响了电厂生产的正常运行，受电厂委托，我所就风机动叶片断裂事故，采用有限元方法对转子、支承结构、壳体和动叶片均进行了一系列的计算分析，找出了故障原因，并提出了改进措施．     

核电站一回路用机械密封

机械密封在各类核电站的一回路中有大量应用.核电站一回路用机械密封是核电站的关键部件之一,其性能好坏很大程度上决定着核电站能否长周期安全可靠运行.本文以几种具有代表性的核电站反应堆堆型为例,对其一回路用机械密封进行了介绍,这些反应堆分别以水、氦气和液态金属为冷却剂并跨越第二代到第四代核电技术.首先介绍了压水堆核主泵机械密封,分别叙述了美式风格的流体静压型核主泵密封及欧式风格的流体动压型核主泵密封的结构特点、工作原理和最新的基础研究状况;随后介绍了高温气冷堆氦气轮机/氦气风机干气密封的结构特点、使用要求及相应的针对性设计;最后介绍了钠冷快堆钠泵机械密封,包括1种惰性气体缓冲、油膜润滑的三级串联式机械密封和1种直接以液态金属润滑的螺旋槽式机械密封.     

风机叶片噪声的有源消声研究

建立了风机转动时产生的动叶气动噪声和静叶干涉噪声的声学模型，推导了声功率的表达式，根据最小辐射声功率准则导出了有源消声控制方程，并探讨了次级声源的配置参数对消声效果的影响。     

Rank 72 high minimum norm lattices

Given a polarization of an even unimodular lattice and integer k?1, we define a family of unimodular lattices L(M,N,k). Of special interest are certain L(M,N,3) of rank 72. Their minimum norms lie in {4,6,8}. Norms 4 and 6 do occur. Consequently, 6 becomes the highest known minimum norm for rank 72 even unimodular lattices. We discuss how norm 8 might occur for such a L(M,N,3). Our method constructs such L(M,N,k) in dimensions 96, 120 and 128 with minimum norms 8.     

On quotients of generalized Euclidean group rings

Let R = ?[C] be the integral group ring of a finite cyclic group C. Dennis et al. [4 Dennis, K., Magurn, B., Vaserstein, L. (1984). Generalized Euclidean group rings. J. Reine Angew. Math. 351:113–128.[Web of Science ®] , [Google Scholar]] proved that R is a generalized Euclidean ring in the sense of Cohn [3 Cohn, P. M. (1966). On the structure of the GL₂ of a ring. Inst. Hautes Études Sci. Publ. Math. 30:5–53.[Crossref] , [Google Scholar]], i.e., SL_n(R) is generated by the elementary matrices for all n. We prove that every proper quotient of R is also a generalized Euclidean ring.