巧用二重积分求解定积分之例说

将高维数转化为低维数问题进行研究是数学解题教学中常见的策略之一,本文通过范例说明如何将高维定积分转化为二重积分求解,为定积分提供了一个计算技巧,同时也丰富了高等数学中低维数与高维数互化的数学思想方法。

基于稀疏子空间聚类的文本谱聚类算法研究

本文为解决传统文本谱聚类算法聚类纯度低的问题,提出了基于稀疏子空间聚类的文本谱聚类算法研究。通过提取文本谱特征,设计文本谱低维数据稀疏地线性表示矩阵,融合文本谱低维数据特征,构建文本谱特征向量稀疏子聚类空间,实现文本谱聚类算法。设计实例分析,结果表明,设计聚类算法的聚类纯度明显高于传统聚类算法。

Kruskal法在地质中的应用

Kruskal法就是将N个多维(P维)对象点,在近似的意义下,从P维约简到一个较低维数的空间内,寻求一个最佳的空间维数和空间标度,而近似地保存各对象点数据的原始关系。这种方法通常称为多维标度法。

基于多Agent的启动装置多类故障高效智能检测

传统检测方法只能对单个启动装置进行故障检测,无法实现多类故障智能检测,为了避免传统方法带来的弊端,提出了基于多Agent的多类故障高效智能检测方法。根据Agent功能划分结果,从实体状态信息中提取运行行为信息,定时查询相关变量,获取完整装置运行情况,并将其转化为状态信息。利用已有状态信息建立低维数特征空间,采用等能量分段方法提取相关特征,获取异常状态信息。利用决策Agent模糊理论融合技术对异常状态信息隶属度条件进行设定,获取最可能出现的故障种类,依据高效智能检测流程,实现启动装置多类故障检测。通过实验结果可知,该方法最小检测误差可达到0.005,为电力设备稳定运行奠定基础。

2D Model of Guide Vane for Low Head Hydraulic Turbine： Analytical and Numerical Solution of Inverse Problem

Low-head hydraulic turbines are the subjects to individual approach of design. This comes from the fact that hydrological conditions are not of a standard character. Therefore, the design method of the hydraulic turbine stage has a great importance for those who may be interested in such an investment. As a first task in a design procedure the guide vane is considered. The proposed method is based on the solution of the inverse problem within the flame of 2D model. By the inverse problem authors mean a design of the blade shapes for given flow conditions. In the paper analytical solution for the simple cylindrical shape of a guide vane is presented. For the more realistic cases numerical solutions according to the axis-symmetrical model of the flow are also presented. The influence of such parameters as the inclination of trailing edge, the blockage factor due to blade thickness, the influence of loss due to dissipation are shown for the chosen simple geometrical example.

Computational modeling of cavitating flows in liquid nitrogen by an extended transport-based cavitation model

Developing a robust computational strategy to address the rich physical characteristic involved in the thermcdynamic effects on the cryogenic cavitation remains a challenge in research. The objective of the present study is to focus on developing mod- elling strategy to simulate cavitating flows in liquid nitrogen. For this purpose, numerical simulation over a 2D quarter caliber hydrofoil is investigated by calibrating cavitation model parameters and implementing the thermodynamic effects to the Zwart cavitation model. Experimental measurements of pressure and temperature are utilized to validate the extensional Zwart cavi- tation model. The results show that the cavitation dynamics characteristic under the cryogenic environment ale different from that under the isothermal conditions： the cryogenic case yields a substantially shorter cavity around the hydrofoil, and the pre- dicted pressure and temperature inside the cavity are steeper under the cryogenic conditions. Compared with the experimental data, the computational predictions with the modified evaporation and condensation parameters display better results than the default parameters from the room temperature liquids. Based on a wide range of computations and comparisons, the extension- al Zwart cavitation model may predict more accurately the quasi-steady cavitation over a hydrofoil in liquid nitrogen by pri- marily altering the evaporation rate near the leading edge and the condensation rate in the cavity closure region.

Sound absorption performance of natural fibers and their composites

This research aimed to study the sound absorption properties of natural fibers and their reinforced composites.Sound absorption coefficients of three types of natural fibers,i.e.,ramie,flax and jute fibers and their composites were measured by the two-microphone transfer function technique in the impedance tube.The results were compared with synthetic fibers and their composites.It was found that both natural fibers and their composites had superior capability of noise reduction.The multi-scale and hollow lumen structures of natural fibers contributed to the high sound absorption performance.Moreover,the sound absorption properties of these natural fibers were also calculated by the Delany-Bazley and Garai-Pompoli models.They showed good agreement with the experimental data.It was concluded that multi-functional composite materials can be made by natural fibers so that both the mechanical and acoustical functions can be achieved.

Topological evolution of laminar juncture flows under different critical parameters

Horseshoe vortex topological structure has been studied extensively in the past,traditional"saddle of separation"and new"attachment saddle point"topologies found in literature both have theoretical basis and experimental and computational evidences for support.The laminar incompressible juncture flows at low Reynolds numbers especially are observed to have new topology.Studies concerning the existence of the new topology though found in literature,the topological evolution and its dependency on various critical flow parameters require further investigation.A Particle Image Velocimetry based analysis is carried out to observe the effect of aspect ratio,?*/D and shape of the obstacle on laminar horseshoe vortex topology for small obstacles.Rise in aspect ratio evolves the topology from the traditional to new for all the cases observed.The circular cross section obstacles are found more apt to having the new topology compared to square cross sections.It is noted that the sweeping effect of the fluid above the vortex system in which horseshoe vortex is immersed plays a critical role in this evolution.Topological evolution is observed not only in the most upstream singular point region of horseshoe vortex system but also in the corner region.The corner vortex topology evolves from the traditional type to new one before the topological evolution of the most upstream singular point,resulting in a new topological pattern of the laminar juncture flows"separation-attachment combination".The study may help extend the understanding of the three-dimensional boundary layer separation phenomenon.