Study of the phase-change coefficients of the cavitation model in cavitation flow fields generated from cone cavitator

The influence of phase-change coefficients variations in the Singhal cavitation model on the calculation results has been numerically studied. By comparing the numerical results and experimental data, the relationship between the coefficients and cavitation numbers is obtained. The calculation results of 2d axisymmetrical cylinder with 45-degree cone cavitator show that under different cavitation numbers, there are three typical kind of cavities, which are respectively main cavity, secondary cavity and rear cavity. The coefficients variations have a great influence respectively on the three type cavities in shape, collapse position, collapse strength, etc, and different cavitation numbers are corresponding to different phase-change coefficients. The cavitation flow field can be divided into three typical zones according to the cavitation number: weak-cavitation zone, secondary-cavitation zone and supercavitation zone. For 45-degree cone cavitator cylinder, the evaporation coefficients will firstly decrease and then increase with the decrease of cavitation numbers in secondary-cavitation zone, while the condensation coefficients keep relatively lower and almost unchanged. In weak-cavitation zone, there only exists the smaller main cavity attached to the model head or there is no obvious cavity. In supercavitation zone, the secondary cavity attached to the model will fall off and merge into the new rear cavity.     

模型结构对通气超空泡影响的实验研究

在水洞中开展了模型结构对通气超空泡形态和水动力影响的系列模型实验研究。结果表明:空化器、通气碗、锥柱结合的模型主体、尾部收缩段以及模型支撑的截面形状和方式都会对空泡形态和模型水动力产生影响。在相同空泡数下,空化器直径越大,超空泡长度越大,并且在相同直径下,圆盘空化器比圆锥空化器产生的超空泡长度大;模型尺度越大,阻塞比越大,超空泡长度越大;锥柱结合的模型主体会产生滞后效应;模型支撑的截面形状应为流线型;前支撑、腹支撑和尾支撑适用于研究不同的超空泡特性,其中当模型采用前支撑方式时,空泡形态和水动力应采用有效空化器直径进行计算。     

超空泡射弹尾拍振动特性分析

为了研究超空泡射弹的尾拍振动特性,利用刚一柔耦合动力学方法,得到弹体横向振动的基频和一阶模态;并通过模拟计算,分析了弹体横向振动基频和模态与弹体转速、长细比、材料特性的关系．计算结果表明：弹体频率和模态随转速而变化;弹体的长细比的增加和材料特性的改变,使频率和模态随转速的变化更加显著;当长细比较小或者角速度小于50ra...     

楔体后部非定常超空泡长度预测

基于势流理论,采用积分方程方法,研究了薄楔体后部非定常自然超空泡流问题。应用时间有限差分离散化方法,得到了积分方程的数值解。预测了楔角和空化数作各种变化时,超空泡长度的非定常变化过程。楔角或空化数变化频率越高,空泡长度的变化越小,相对滞后时间越长。     

Deriving some further results from Tensile Stability Criterion in SPH

The linear form of the error propagation of SPH,which was obtained through perturbation method,has been employed to analyze the tensile instability in SPH.The sufficient condition for tensile instability,which was ever presented by Swegle,could also be derived from the eigenvalues of the linear form.Hence,the eigenvalues correspondingly yielded a tensile stability criterion.The criterion confirmed the Swegle’s statement that the tensile instability is induced by imaginary sound speed,and revealed the origins of imaginary sound speed and some details of CFL conditions.Moreover,a reasonable numerical sound speed,which accords with the one given by Monaghan through dimensional analysis,was also derived from the criterion.The kernel’s spatial derivatives,which are only with respect to the distance between particles,were found it was not accurate if the spatial derivatives of smoothing lengths were not trifle.     

Application of empirical mode decomposition in early diagnosis of magnetic memory signal

In order to eliminate noise interference of metal magnetic memory signal in early diagnosis of stress concentration zones and metal defects, the empirical mode decomposition method combined with the magnetic field gradient characteristic was proposed. A compressive force periodically acting upon a casing pipe led to appreciable deformation, and magnetic signals were measured by a magnetic indicator TSC-1M-4. The raw magnetic memory signal was first decomposed into different intrinsic mode functions and a residue, and the magnetic field gradient distribution of the subsequent reconstructed signal was obtained. The experimental results show that the gradient around 350 mm represents the maximum value ignoring the marginal effect, and there is a good correlation between the real maximum field gradient and the stress concentration zone. The wavelet transform associated with envelop analysis also exhibits this gradient characteristic, indicating that the proposed method is effective for early identifying critical zones.     

水下两相冲压喷射发动机性能的数值模拟研究

为了对水下两相冲压喷射发动机的性能进行理论研究,分别对扩张段、混合腔及喷管进行分析并建立了物理模型.基于双流体模型,采用变步长的Runge-Kutta法进行了喷管内泡状流计算.综合各部分计算结果求得发动机推力与推进效率.重点研究了混合腔与入口面积比(Am/Ai)、发动机入口面积(Ai)、通气量、航行速度及初始气泡半径对发动机推力及效率的影响.计算结果表明:发动机推力和效率均随着面积比Am/Ai的增大而增大;当Am/Ai保持不变时,推力和效率随入口面积Ai的增大而增大;推力随着通气量、航行速度的增大而增大,效率却随其增大而减小;气泡初始半径增大时,发动机推力及效率同时减小.这将为两相冲压喷射发动机设计提供一定依据.     

基于小波包与粗集的往复压缩机故障诊断方法

提出了基于小波包与粗集的往复压缩机故障诊断的新方法。该方法使故障特征提取及规则的提取都由计算机自动完成，经诊断实例表明，使用该方法可对往复压缩机进行有效的故障诊断。     

汽轮发机组状态监测与故障诊断系统的研制及其应用

介绍了一套汽轮发电机组状态监测及故障诊断系统ＭＭＭＤ－ⅢＡ，该系统使用了微机ＳＵＮ－２８６及ＳＴＤ总线工业控制机系统Ⅱ－５Ａ，实现了信号采集、信号处理、数据存储、报告、报警、自检、黑匣子及故障诊断等功能，最后给出该系统在电厂的应用实例。     

透平压缩机复杂故障诊断不确定知识的表示

本文以透平压缩机为研究对象，提出了复杂故障诊断知识预处理的概念。针对领域本身的特点，提出了利用重要度和清晰度、存在度和严重度来分别描述征兆、故障的不确定性关系。在此基础上，给出了适用于诊断经验知识描述的加权模糊产生式诊断规则的表示形式，并将诊断规则划分为广义充分规则、广义必要规则和广义充要规则等三种基本类型。