内插中心斜杆换热管的换热性能

在热传递技术的被动改进中,在管中使用插入物是当今一种非常普遍并且具有很大实际作用的改进技术。内插中心斜杆换热管可以使管内实现类似于优化流场的多纵向涡旋流,使换热管在流动阻力增幅不大的情况下换热性能得到有效提升。利用数值模拟方法对内插中心斜杆的换热管进行研究,探求斜杆数目、节距、直径等参数的变化对换热、阻力特性的影响。结果发现:内插中心斜杆换热管的换热性能远优于光管的综合换热性能;内插中心斜杆换热管的努塞尔数随着斜杆数量的增多而在一定范围提高,压降随着斜杆数量的增多而增大,斜杆数量为3时,内插中心斜杆换热管的综合换热性能较好;努塞尔数和压降随着节距的增大而减小,斜杆节距为20 mm时,内插中心斜杆换热管的综合换热性能较好;努塞尔数和压降随着斜杆直径的增大而增加,斜杆直径为2.0 mm时,内插中心斜杆换热管的综合换热性能较好。     

Study of the damping characteristics of sectional flight vehicles of different length

The dependence of the damping characteristics of axisymmetric tri-sectional flight vehicles executing plane oscillations about the zero angle of attack on their geometric parameters is investigated on the supersonic range of uniform oncoming air flow Mach numbers. Systematic data are obtained using the least laborious approach, namely, by calculating the steady-state inviscid flow past equivalent bodies determined from the principle of the local similarity of force interaction. Ranges of the vehicle design parameters on which the dependence of the damping moment coefficient in pitch on the length of the conical or cylindrical-conical stabilizer of the vehicle is nonmonotonic are found. Typical viscosity effects on the characteristics under study are estimated using a method based on the assumptions of the linear theory for finite-thickness bodies. It is established that the damping coefficient increases monotonically with decreasing Reynolds number; moreover, even transition to oscillation antidumping regimes is possible when the sign of the damping coefficient changes.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, 2004, pp. 153–162. Original Russian Text Copyright © 2004 by Antonets and Shmanenkov.     

浅谈车床加工螺纹常见故障及解决方法

分析了车削螺纹时常见的故障,如牙型角不正确、螺距(或导程)不正确、表面粗糙度值大、乱牙、中径不正确等,针对故障产生的原因提出了相应的解决方法。     

聚甲基丙烯酸羟乙胆甾接枝共聚物(PHCEM)的合成、结构与性能研究 Ⅱ PHCEM的相态转变

本文通过偏光显微镜、DSC、X射线衍射及选择散射等手段,深入研究了甲基丙烯酸羟乙酯胆甾醇甲苯二异氰酸酯接枝共聚物的相态转变。在一定的条件下,侧链上的胆甾基团可自由取向,形成胆甾相液晶。     

变螺距螺杆加工的研究

本文主要对变螺距螺纹进行了数学、物理和成形机理的理论分析，给出了全新的变距加工系统设计。     

加工变螺距螺杆的一种改进设计

通过对变螺距螺纹进行了数学、物理和成形机理的理论分析，给出了基于普通车床上的一种加工系统设计．     

茶叶揉切机齿辊节距误差数理统计建模与分析

采用 χ2检验法对 CTC齿辊节距误差进行了数理统计建模研究 ,在此基础上对工件加工精度进行了定量分析 ,从而对生产起到了指导性作用     

Organic residue analysis of Neolithic pottery from North Greece

Organic residues associated with Neolithic pottery from two Late Neolithic sites, Paliambela and Makriyalos (Northern Greece), were analyzed by gas chromatography-mass spectrometry. The study aimed at identifying the origin of the tar used for waterproofing and gluing broken pots. Reference tars were prepared in laboratory conditions by pyrolysis of the bark from three tree species, namely from Betula pendula (silver birch), Ostrya carpinifolia (hop hornbeam) and Carpinus orientalis (Eastern hornbeam). The results suggest that mostly birch bark tar was used as glue for fixing broken pieces of the pots as well as for waterproofing close-shaped vessels. None of the archaeological tars derived from the two hornbeams. The analysis shows certain variability in the composition of birch bark tar, which is related to the production technique and to the re-use of tar. Of particular interest is the presence of characteristic diterpenoid biomarkers in several samples, which indicates that pine pitch was used for gluing and pine resin for waterproofing vessels for liquids. Correspondence: Sophia Mitkidou, Department of Science, School of Technological Applications, Technological Institute of Kavala, Greece     

ADCP方向谱估计的倾斜修正算法研究

声学多普勒流速剖面仪(ADCP)是用来测量不同深度上海水流速的仪器,在测流基础上可以通过速度测点组成阵列反演海洋表面波浪。当ADCP倾斜时,速度测点位置发生偏移,导致方向谱估计出现误差,为提高测量精度,有必要对测点位置进行修正。本文在引入旋转矩阵的基础上给出了当ADCP倾斜时的测点位置修正方法,通过仿真和实测数据分析表明,当ADCP倾斜时,方向谱估计误差不仅和俯仰角横滚角有关,同时与ADCP安放深度有关。该倾斜修正算法,同时考虑姿态角和安放深度,提高了ADCP倾斜状态下的方向谱估计精度。     

藏语语音基音周期检测

在藏语语音处理中基音周期的检测具有非常重要的意义．本文首先讨论了用自相关函数法进行基音周期检测的基本原理及其改进方法,进而研究了这种方法在藏语语音处理中的应用,并给出了相应的实例．