膨胀弯管在管道柔性设计中的定性分析

为防止管道因热胀冷缩、管道支撑或端点附加位移造成的应力问题,对管线中设置的膨胀弯管进行定性分析.通过2个参数的变化对膨胀弯管进行编号得到多种设计方案,用ANSYS建立管道的有限元模型,并分析各方案中膨胀管道的变形、应力和弯矩等;根据分析结果对膨胀弯管设计半径、设置位置和形状进行定性分析.该定性分析结果可为膨胀弯管概念设计和管道柔性设计提供参考.     

基于维间扩展和事务压缩的关联规则算法改进

Apriori是关联规则挖掘的经典算法,在利用该算法进行医疗数据挖掘的过程中,发现其频繁项集产生过程有一些不必要的开销,为此提出了改进算法Mypriori,利用维间扩展和事务压缩策略来提高频集发现的效率,并通过实验验证了算法的有效性.     

基于扇形领域扩展的同步双向A*算法

为提高航空器飞行的安全性和平滑性,解决传统A^*算法拐弯角度过大、搜索路径节点过多等问题,提出一种基于扇形领域扩展的同步双向A^*搜索算法。首先,根据栅格图法扩展危险区域边界;其次,设计了基于同步双向搜索的A^*算法,动态定义正反向搜索的目标节点。针对搜索角度有限问题,提出了在5×5领域内的扇形领域扩展策略,并设计了含有双重权重参数的评价函数以减少冗余点的产生。为验证改进算法的有效性,选取方形和不规则形状危险区进行仿真。结果表明改进的同步双向搜索算法搜索的路径更平滑;与传统双向A^*算法的结果相比,在不同形状的危险区域下,搜索路径长度分别减少了1.65%、13.16%,搜索路径节点个数减少了42.6%、46.81%,具有较强的搜索效率。     

Hybrid function projective synchronization of chaotic systems with uncertain time-varying parameters via Fourier series expansion

In this paper, the hybrid function projective synchronization (HFPS) of different chaotic systems with uncertain periodically time-varying parameters is carried out by Fourier series expansion and adaptive bounding technique. Fourier series expansion is used to deal with uncertain periodically time-varying parameters. Adaptive bounding technique is used to compensate the bound of truncation errors. Using the Lyapunov stability theory, an adaptive control law and six parameter updating laws are constructed to make the states of two different chaotic systems asymptotically synchronized. The control strategy does not need to know the parameters thoroughly if the time-varying parameters are periodical functions. Finally, in order to verify the effectiveness of the proposed scheme, the HFPS between Lorenz system and Chen system is completed successfully by using this scheme.     

Electrical conductivity,self-diffusion,and volume expansion of alkali halides at the melting point

In an earlier paper, Heisenberg's uncertainty principle was invoked at the melting point T _m of crystalline solids to provide fundamental justification for Lindemann's melting law and to compute diffusion coefficients of several alkali halides. The uncertainty principle defines breakdown of Debye zone boundary (ZB) phonons as valid collective excitations when phonon energies and line widths due to anharmonicity become comparable at T _m. Upon breakdown, random, high-frequency single-particle motion or partial decoupling of crystal ions sets in. Lifetimes of these single-particle ZB motions are determined from the minimum-uncertainty product inequality by assuming that it becomes an equality at T _m for ZB phonons. The present paper addresses improved formulation of that work and extended application to ionic electrical conductivities of 18 molten alkali halides at T _m. It is shown that use of the Debye model produces an approximate lower bound to the mean free time, not the unconstrained direct estimate previouslu implied. This feature is generally reflected in results for ionic conductivities and alkali halide diffusion coefficients for which comparison experimental data were found. However, in spite of this lower-bound formulation and the simple nature of the computation, the results compare favorably with experiment. A model of random single-particle harmonic motion superimposed on the lower-frequency collective motion is proposed to account for volume expansion accompanying the partial decoupling for hard-sphere ions. Experimental comparisons for 15 alkali halides show the decoupling volume change to account largely for the total volume change of melting (in the hard-sphere approximation), yielding a closer agreement with experiment than recent calculations aimed explicitly at the total volume change.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal expansion of molybdenum in the range 1500–2800 K by a transient interferometric technique

The linear thermal expansion of molybdenum has been measured in the temperature range 1500–2800 K by means of a transient (subsecond) interferometric technique. The molybdenum selected for these measurements was the Standard Reference Material SRM 781 (a high-temperature enthalpy and heat capacity standard). The results are expressed by the relation where T is in K and l ₀ is the specimen length at 20°C. The maximum error in the reported values of thermal expansion is estimated to be about 1% at 2000 K and not more than 2% at 2800 K.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Thermal expansion of Pyros from 20 to 1273 K

Pyros, which is a Ni-base alloy (82% Ni, 8% Cr, 4% W, 3% Mn, and 3% Fe), has been used extensively in France since 1926 as a temperature sensor and as a reference material for thermal expansion measurements. In this paper we present recent data on the expansion and expansivity of Pyros from 20 to 1273 K. Expansivity results, obtained by taking the derivative of a cubic-spline polynomial fitting performed to the L/L experimental data, show that Pyros is a stable material in the 20 to 1273 K temperature range. Furthermore, since the expansivity values are similar to those of steels, Pyros should be of special interest to laboratories which are concerned with expansion measurements on steels. Therefore, we suggest that Pyros be considered as a suitable reference material for thermal expansion measurements on steels, and until more accurate results are obtained, we propose our results as reference data between 20 and 1273 K.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

逆向工程中带孔洞的曲面对象三角剖分法研究

在分析现有的一些三角剖分方法的基础上，提出一种新的基于边界扩展的3D三角剖分方法，该方法首先采用一种空间栅格装点法来进行初始点云数据精简；再构造种子三角形，通过连接已剖分网格区域的边界边与最优扩展点来形成三角形网格从而向外扩展。该法可以对带有内孔等其他非凸壳的复杂曲面对象点云直接进行三角剖分，无需人工分区。实际应用表明采用该法可以快速、有效地从三维数据点集建立几何模型。     

微型涡喷发动机燃烧室全覆盖气膜冷却

为了延长微型涡喷发动机燃烧室的使用寿命,针对燃烧室壁面高温区进行全覆盖气膜冷却研究. 在KJ-66微型涡喷发动机试车实验的基础上,比较实际燃烧工况下,排布方式和燃烧室外环的扩张孔对气膜冷却效果及燃烧室整体性能的影响. 结果表明,在实际微型涡喷发动机模型中,顺排的平均综合冷却效率低于叉排,但对壁面的综合降温效果优于叉排. 随着扩张孔出口直径的增大,气膜冷却效果逐渐改善,但会影响燃烧室出口温度分布的均匀性. 由于燃烧室后排冷却孔的影响,二次流射入主流会发生偏转,提升了气膜的冷却效果. 整体而言,全覆盖气膜冷却在实际燃烧工况下对燃烧室壁面有着很好的冷却作用,扩张型气膜孔能够有效改善燃烧室外环的气膜冷却效果.     

Pathways to eliminate carbon emissions via renewable energy investments at higher education institutions

Higher education institutions are among the many public and private sector entities that have committed to long-term sustainability goals in response to the threat of climate change. A key challenge for these institutions is establishing a commitment to make targeted investments in renewable energy technologies in support of emissions reduction goals. Such strategies require a vision to simultaneously coordinate strategic investments in renewable energy technologies with tactical operational decisions to achieve the desired benefits. In this paper, we formulate and solve a least-cost renewable energy capacity investment planning model to determine pathways to achieve emissions reduction strategies. Specifically, we apply our model to Rutgers University to evaluate its target of 100 % carbon neutrality. Using these insights, we share recommendations on how these strategies can be executed. This research serves as a springboard for administrators to assess and deploy their emissions reduction strategies, while ensuring system and financial constraints are satisfied.