风筒叶片撞击瞬态响应的数值模拟

应用有限元方法对丢失的失效风机叶片撞击风筒的非线性瞬态响应进行了数值计算研究,模拟了叶片撞击风筒的过程,分析了撞击过程中叶片、风筒的变形、应力与能量变化.结果表明：有限元方法能较好地模拟风机叶片丢失后撞击风筒的过程,该型风机风筒对叶片具有包容性.     

风机叶片外物损伤的模拟与分析

采用有限元程序LS—DYNA对风机金属块撞击风机叶片的非线性瞬态响应进行了数值仿真研究，结果表明：接触冲击算法能较为真实反映风机叶片金属块撞击过程；金属块质量不同和在不同的进气速度条件下金属块撞击风机叶片时，叶片响应都有较大的差异。     

柔性杆多次撞击过程的瞬态动力学分析

对双柔性杆多次撞击过程,采用St.VENANT杆波动理论,提出应用瞬态波函数特征值展开法,分别求解多次撞击和分离过程瞬态波响应理论解.应用该理论解,由撞击过程中两杆组合结构的撞击界面应力,计算多次撞击力响应,从而实现了对多次撞击问题的分析.数值计算表明,该方法可以合理的分析多次撞击过程,较精确的计算多次撞击力响应和结构瞬态波响应,并可进一步研究"次撞击"和瞬态波传播等物理现象,以及研究系统参数对多次撞击过程的影响.研究结果可为柔性结构多次撞击过程的瞬态响应分析和结构安全评估提供参考.     

变截面叶片受飞射物强烈撞击的塑性动力响应

以涡轮发动机为背景,讨论了高速转动的涡轮叶片受到飞射物强烈撞击后的塑性动力响应问题。根据变截面叶片做高速旋转的特点,建立了新的力学模型,分析了叶片受撞击后的瞬态变形,包括质量比的影响,涡轮旋转所引起的离心力的影响以及输入能量的影响等。     

运动参数对叶片外物损伤的影响分析

采用终点弹道学弹丸侵彻原理,运用非正规撞击模型,建立了叶片受外物撞击的运动学模型.运用数值计算,得出了运动参数对叶片损伤的影响规律:叶片随机体的平移速度越大,或旋转的角速度越大,或撞击位置越靠近叶尖,叶片的损伤越大;初始安装角越大,叶片外物撞击时的接触撞击力越大,叶片的损伤越大;由于偏航角与倾斜角的存在,使得运动叶片与静止叶片外物损伤的模式有一定差异.其结果将对叶片抗外物撞击损伤的研究提供依据.     

航空发动机风扇叶片外物撞击识别方法研究

通过风扇叶片外物撞击试验平台来模拟真实发动机叶片受外物撞击的过程,使用基于叶尖定时原理的非接触式叶尖振动测量方法获取叶片叶尖振动信号。采用基于短时能量的方法对原始振动信号进行处理,获取风扇不同稳定转速状态所对应的叶尖振动参考短时能量值,经过反复试验及数据统计分析给定门限系数,依据在线检测原理获取外物撞击风扇叶片的检测门限值。对不同尺寸、质量外物撞击给定风扇转速的叶片振动数据进行分析,获取其对应的短时能量分布,进而准确判断出叶片发生外物撞击的时刻、次数。     

外物形状对发动机叶片中残余应力场的影响分析

综合运用显、隐式有限元算法对航空发动机叶片进气边受不同形状外物的撞击进行数值分析,在Ansys/LS-DYNA中进行不同形状外物撞击的瞬态显式分析,然后通过显—隐式算法的转换,获得受不同形状的外物撞击后叶片中的残余应力场分布。结果表明,外物的形状对叶片所受的损伤是有影响的,外物撞击部位的形状越尖锐,撞击叶片后叶片中分布的最大残余拉应力值越大,导致叶片的抗疲劳强度受削弱较大;几何外形相近的外物撞击后,叶片中的残余应力场分布趋势相近。     

粒子分离器涡形叶片金属块撞击损伤研究

研究粒子分离器涡形叶片受外物冲击损伤的规律,提高粒子分离器抗外物损伤设计能力,降低外物对航空涡轮轴发动机安全运行的影响。以冲击动力学为基础,通过冲击损伤试验方法,研究了金属块撞击粒子分离器涡形叶片的过程。采用瞬态响应测试系统,得到了金属块撞击涡形叶片的应变——时间历程;利用三坐标测量仪,获得了涡形叶片金属块撞击后的变形。对金属块撞击粒子分离器涡形叶片进行了数值仿真,对比分析了金属块撞击涡形叶片的试验结果与数值仿真结果。金属块(M6和M8螺栓)以0.2 Ma速度撞击涡形叶片时,涡形叶片的变形较小。     

流固耦合在涡轮叶片瞬态传热仿真中的应用

为真实模拟超高速转子的工作性能,必须对涡轮叶片进行流体-热-结构耦合分析。将有限元软件中提供的流固耦合仿真技术应用到涡轮叶片瞬态传热计算中,利用ANSYS CFX建立了涡轮叶片与高温燃气的流固耦合传热模型,该模型既包括了固体与固体之间的接触传热,也包括了流体与固体之间的耦合传热。以某涡轮转子为例进行了流-固-热耦合分析仿真计算,获得叶片的瞬态温度场分布和热应力。在此基础上结合整个涡轮叶片的实际工作状况对其模拟结果进行定性分析,验证其分析方法的可行性,为实际涡轮叶片设计优化提供了理论依据,有助于叶片加工工艺方法的改进。     

基于FMM方法的发动机失谐叶盘瞬态响应分析

基本失谐模型FMM(Fundamental Mistuning Model)是以一种基于失谐叶盘结构的单模态族子集为模态变换阵的减缩方法,采用该方法建立分析模型,可以容易识别出控制失谐响应的基本参数,基于该理论在不同描述框架和假设前提的若干典型简化形式,给出了若干分析应用实例,以及这些方法的瞬态响应分析。     

气冷涡轮叶片气热耦合数值模拟研究

采用气热耦合计算方法进行气冷涡轮气动性能-传热分析,这种方法无需指定对流换热系数和热流密度等经验参数,只须要给出气流与固体之间的流动换热物理条件.利用该方法对某三维涡轮导叶进行数值模拟,计算结果表明,气热耦合计算的叶片温度场更接近真实情况,针对该叶片尾缘烧蚀问题,利用气热耦合计算方法,研究了叶片尾缘冷却设计方案,通过对在尾缘开缝冷却方案的分析计算,结果表明,该设计方案可以使得尾缘最高温度下降了130K.     

单片钢板弹簧受短波冲击的瞬态响应研究

应用钢板弹簧的波动传递特性,在考虑钢板弹簧的具体结构的情况下,针对不同参数,对受短波冲击的钢板单自由度系统进行建模,与古典振动理论的建模方法进行比较,得到了五种方法的响应结果。并对它们的响应进行分析,探讨了钢板弹簧不同参数对瞬态响应的影响。为钢板弹簧高频振动建模提供参考。     

汽轮机叶片高温变形中数值模拟组织演化规律研究

针对叶片的锻造工艺成型和模具设计缺乏系统的、精确的理论分析手段,而主要依赖操作者的经验和反复试验的工艺现状;对某叶片用材料1Cr12Ni2W1Mo1V合金在高温变形中的组织演化规律进行了研究,计算包含变形温度、应变速率和变形量的函数,揭示了变形温度、等效应变和等效应变速率对晶粒尺寸演化的影响规律。将晶粒尺寸公式嵌入MSC.Marc软件的ugrain子程序来模拟热模拟压缩试验过程;结果表明:随着压头往下运动,晶粒逐步被细化,区域性分布逐步明显;随着应变速率的增大,晶粒尺寸分布越来越不平均,区域性越来越明显;随着温度的升高,晶粒尺寸逐渐增大。晶粒尺寸的随机选取点的预测值与测量值的平均相对误差为9.73%。     

基于FLUENT的叶轮机械三维紊流流场数值模拟

根据k—ε两方程模型构造了轴流泵三维流动的数学模型,并考虑了近壁面流动的处理方法。利用fluent软件数值模拟了叶轮机械内的三维流动,计算了静子和转子上的速度矢量和压力值。通过数值模拟结果来看,数值模拟方法能真实反映叶轮内部的复杂流动,为叶轮机械的设计和改进提供了理论依据。     

An analysis of the extrusion of bimetallic tubes by numerical simulation

This paper presents a numerical analysis of a high temperature extrusion process applied to bimaterial tubes made of two pre-bonded metallic materials with different plastic properties. The analysis has been carried out for different geometries and material combinations by using a FE code. An elasto-plastic behaviour with strain rate dependence has been assumed. A parameter related to the void growth rate at the bimaterial interface has been considered for fracture prediction during the extrusion operation.The influence of the different extrusion variables, namely the yield stress ratio, the location and relative thickness of the layers and the die angle, has been assessed. As a conclusion of the analysis, the yield stress ratio between the two materials turns out to be the most critical parameter of the process. Besides, the thickness fluctuations of the harder layer in the final product have been analysed for several material combinations. Those fluctuations can lead to an unacceptable geometrical heterogeneity under certain conditions. The results of the FE calculations are in reasonable agreement with the scarce data available from similar industrial operations.In short, the paper shows that use of FE calculations can be a pre-screening tool for the selection of material couples and extrusion conditions for the production of sound bimetallic tubes, before being engaged in very costly full-scaled trials.     

Kinematics analysis and numerical simulation of a manipulator based on virtual prototyping

Manipulator kinematics refers the analytical study of the motion of manipulator, such as positions, velocities, and accelerations of the links of a manipulator. As formulating the suitable kinematics models for a manipulator is very crucial for analyzing the behavior of manipulators and light weight design of manipulators, many researches have been focused on it in recent decades with a result of many valuable contributions. However, current researches always focus on rigid manipulator, while the manipulator is always a rigid-flexible coupling multibody system, which can affect the accuracy of kinematics analysis and numerical simulation. This paper proposed a model of kinematics analysis of manipulator based on rigid-flexible coupling virtual prototyping. After a model of manipulator kinematics based on the D-H method was proposed, rigid-flexible coupling virtual prototyping-based kinematics simulation and numerical simulation was then put forward. The kinematical experiment is carried out based on manipulator physical prototyping, which demonstrates that the accuracy of the kinematics calculation and the rationality of design based on rigid-flexible coupling virtual prototyping. The design of a five-degrees-of-freedom manipulator is given as an example, which demonstrates that the methodology is obviously helpful to manipulator design.     

Second-order spectra for quadratic nonlinear systems by Volterra functional series: Analytical description and numerical simulation

Higher-order spectral analysis techniques are often used to identify nonlinearities in complex dynamical systems. More specifically, the auto- and cross-bispectrum have proven to be useful tools in testing for the presence of quadratic nonlinearities based on knowledge of a system's input and output. In this paper, analytical expressions for the auto- and cross-bispectrum are developed using a Volterra functional approach under the assumption of a zero-mean, stationary Gaussian input; proper simplifications are presented when the whiteness of the input signal is also imposed. These formulae show the contributions of the bispectrum in terms of the system frequency response function and elementary physical properties of the system. Simulations based on a stochastic numerical integration technique accompany the analytical solutions for a mechanical mass–spring–damper system possessing quadratic damping and stiffness coefficients and subjected to Gaussian white noise excitation. Subsequent estimates of the bispectrum based on the simulated signals show excellent agreement with theory. These results show how modes may interact nonlinearly producing intermodulation components at the sum and/or difference frequency of the fundamental modes of oscillation. The presence and extent of nonlinear interactions between frequency components are identified. Advantages of using higher-order spectra techniques will be revealed and pertinent conclusions will be outlined.     

Reconstruction methodology of a Francis runner blade using numerical tools

Journal of Mechanical Science and Technology - In a hydraulic turbine, the search of a better energy exchange with the fluid has led to designs of runner blade of geometrical shapes so complex that...     

2009年一次连续性暴雨过程的诊断分析和数值模拟

利用WRF中尺度模式对湖南省2009-07-24～27的暴雨天气过程进行数值模拟和诊断分析,模拟结果为:暴雨中心位置以及雨强与实况基本一致,但降水范围较实际偏大。诊断分析WRF模式输出的物理量发现:强降水落区与假相当位温最大值区相对应;涡度(散度)的低层辐合、高层辐散的高低空配置为强降水提供了动力条件。结合NCEP分析场、分析能量场和水汽条件,假相当位温高值区和水汽通量散度最大辐合中心与暴雨的落区有很好的一致性,表明WRF中尺度模式和NCEP分析场对这场连续暴雨都有很好的指示意义。