柴油机机体模态分析与结构改进

为降低机体的表面结构振动和噪声辐射,采用ANSYS有限元分析软件建立了495型柴油机机体的有限元模型,对其进行自由模态分析,并对机体进行了试验模态分析。通过有限元结果和试验结果比较,验证了计算模型的准确性。根据模态分析结果,得出机体的固有振动特性。在该模型的基础上,增加了梯形加强板结构,使其固定于机体油底壳法兰底部。计算结果表明,铝制加强板能提高机体裙部刚度,抑制机体裙部的开合振动,有效地提高机体的固有频率。     

四缸内燃机机体结构模态分析

以某直立四缸柴油机为例 ,用 Pro/ Engineer软件在建立底部被约束的机体三维实体模型的基础上 ,对机体结构进行了约束模态的有限元分析 ,得出了机体结构的前 2 0阶约束模态的固有频率及相应振型 ,并与机体自由模态分析结果进行了比较。结果显示出了机体各部分结构振动的强弱分布以及抗振薄弱区 ,揭示了不同频率范围内机体结构振动模态的特点。同时 ,分析结果表明 :约束模态的固有频率及振型都与自由模态有显著的差别 ,因此考虑约束边界条件的机体模态分析对揭示机体结构的动力学特性是非常有必要的。     

柴油机机体模态分析与试验验证

建立某直列四缸柴油机机体三维模型,对其进行自由模态有限元分析,并提取前5阶机体的固有频率及对应的振型,分析机体各频率范围内的振动规律和抗振薄弱区。为了验证有限元分析模型的准确性,对机体进行自由悬挂试验模态分析。对比结果表明,计算和试验的低阶振型基本一致,固有频率最大相对误差为6.3%,说明有限元模型具有较高的精度,可以作为后续优化和动力学分析之用。     

485柴油机机体有限元模拟及结构改进

采用有限元法,利用hypermesh软件建立485柴油机机体的有限元网格模型;利用Ansys中的Block Lanczos法提取前20阶自由模态,通过计算模态和试验模态参数的对比,验证了结果的有效性,并分析了机体模态的规律,为发动机的结构优化提供了参考依据.采用梯形框结构加强机体底部的刚度,计算结果表明,机体相对变形最大值从0.38mm降低到0.29mm,效果明显.     

基于有限元的S385型柴油机机体自由和约束模态分析

根据S385型柴油机机体的结构特点,利用有限元分析方法对其进行了自由模态和约束模态的有限元分析.采用兰索斯法计算出了机体前十一阶自由模态和约束模态的固有频率及相应振型,通过振型分析找到了机体刚度的薄弱部位并提出了相应的修改措施,为机体结构的改进设计提供了理论依据.     

ZH195型柴油机机体有限元模态分析

针对ZH195型柴油机机体的结构特点,利用有限元分析方法对其进行了自由模态和约束模态的有限元分析.采用兰索斯法计算出了机体前十五阶自由模态和约束模态的固有频率及相应振型,通过振型分析找到了机体振动的薄弱部位并提出了相应的改进措施,为机体结构的改进设计及其动态响应分析提供了理论依据.     

SD11O5型柴油机机体结构试验模态分析及改进

本文对试验模态分析进行简要介绍，并针对原SD1105型柴油机机体结构所存在的问题，用试验模态分析方法对其进行了结构动态特性分析。根据分析结果对机体提出了结构改进方案，并对改进后的机体又进行一次试验模态分析和实际应用。结果表明，改进后机体的动态特性有较大的改善，解决了该机体结构所存在的问题，且机体重量也有所降低。     

EQ6100机体动态特性研究

本文分别用有限元分析法和测试模态法对ＥＱ６１００汽油机机体的模态进行了研究。并对这两种方法进行对比，计算结果与试验数据相符。表明两者达到比较高的精度。为进行机体动态特性优化及低噪声机体设计提供了有效的方法。     

EQ6100机体动态特性研究

本文分别用有限元分析法和测试模态法对ＥＱ６１００汽油机机体的模态进行了研究。并对这两种方法进行对比，计算结果与试验数据相符。表明两者达到比较高的精度。为进行机体动态特性优化及低噪声机体设计提供了有效的方法。     

TBD234V6型柴油机曲轴的试验模态研究

曲轴有限元模型是进行轴系多体系统动力学分析的主要部件,而试验模态是对有限元模型进行检验、补充和修正的重要手段.为获取准确的结构响应信息,基于试验模态分析的基本理论,对TBD234V6型曲轴进行了自由条件下的试验模态分析,并通过模态判定准则(MAC)检验模态识别结果.     

Effective thermal conductivity of common geometric shapes

This work explores the porous block paradigm based on replacing an actual heat sink by the volume of fluid that once enveloped the fins. Thermal equivalence is achieved by increasing the thermal conductivity of the lumped fluid above the base plate until the thermal resistance of the actual heat sink is matched. The popularity of the porous block model can be attributed to its ability to approximate the three-dimensional isotherms corresponding to a detailed heat sink. While previous investigations have focused on a numerically calculated, effective thermal property of the compact model, we employ a methodology leading to a closed-form alternative. The explicit solutions that we provide are not limited to the rectangular porous block models used in former studies. Rather, we extend the analysis to cover most fundamental body shapes and flow configurations under both free and forced convection modes. The exact or approximate formulations that we provide apply to most common Nusselt number correlations and obviate the need for guesswork or user-intervention to reach convergence.     

内燃机机体有限元模态分析

以某卧式单缸柴油机为例,利用美国SDRC公司的I-Deas软件的模态分析功能,在建立底部被约束的机体三维实体模型的基础上,对机体结构进行了约束模态的有限元分析。得到了机体结构的前10阶固有频率及相应振型,从中可看出机体各部分振动的大小,据此对机体结构提出了一些合理改进建议。     

Research on Marangoni condensation heat transfer for water and ethanol mixture vapor

A brass block was constructed as a test block to study the Marangoni condensation in this paper. The maximal temperature difference of the block surface on which pure steam condensed was 11^°C when the block was cooled by the normal temperature water. Regulations and modes of Marangoni condensation for mixture vapor with different mass fractions were studied when the speed of vapor was 0.3 m/s. As both temperature gradients and concentration gradients exist on the condensing surface, the experimental results indicate that the maximal heat transfer coefficient of mixture vapor can be 2.8 times that of pure steam when the Marangoni condensation of mixture vapor appears. The heat transfer coefficient of mixture vapor increases with the decrease of surface subcooling, and it appears a steep increase when the surface subcooling is small enough; the heat transfer flux has a maximum value as the surface subcooling rises; and the different modes of condensation are confirmed when the different ethanol concentration and different surface subcooling exist. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(8): 505–514, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20035     

铸造缺陷修补机在发动机铸件缺陷焊补方面的应用及分析

通过铸造缺陷修补机在灰铁250、球铁500及铝合金101三种材质试块上焊补效果的显微分析，以及对HT250发动机缸体、删气缸套、ZL101发动机缸体缺陷渗漏的焊补效果检测，说明铸造缺陷修补机在灰铁、球铁、铝合金三种材质上的焊补效果满足性能要求，是一种值得推广的新技术。     

Effect of surface free energy difference on steam-ethanol mixture condensation heat transfer

The condensation heat transfer of steam-ethanol mixture with different weight fractions was investigated experimentally at atmospheric pressure. The results indicate that the heat transfer coefficients (HTC) and condensation modes, i.e. filmwise condensation (FWC), transition state and dropwise condensation (DWC), varied with the mixture compositions and the vapor-surface temperature differences. The interface effect, in terms of equivalent surface free energy difference between condensate and ultra thin liquid film, was introduced to analyze the variation of condensation modes and heat transfer coefficient. The equivalent surface free energy differences under various vapor conditions and vapor-surface temperature differences are calculated quantitatively. The experimental results show that as equivalent surface free energy difference was gradually increased, the condensation mode alternates from filmwise to transition state and finally to dropwise condensation, with heat transfer coefficient simultaneously increasing. The effect of surface free energy difference was also introduced to analyze the data in literature, and the effect of subcooling on heat transfer coefficient was discussed from the perspective of interface effect. The results show that as the vapor-surface temperature difference was gradually increased, the surface free energy difference increase accordingly and then reaches its peak value. The heat transfer coefficient exhibits the same tendency as equivalent surface free energy.     

Measuring the Torsional Modal Frequencies of a 900 MW Turbogenerator

Transient torques exerted on the rotors of turbine generators can produce high stresses. This paper describes an investigation into the torsional properties of the shaft of a 1500 rpm steam turbine generator rated 900 MW and includes 1. prediction, by theoretical model of the shaft and rotor structure, of its undamped natural vibrations and natural modes; 2. determination, by measurements and subsequent modal analysis, of the complex natural vibrations (free and damped) and natural modes. For the measurements the rotor was torqued by shock torques applied by the turning gear, as well as by harmonic sinusoidal torques of variable frequency applied by a shaker. Vibrations were measured by accelerometers on the shaft and on some selected turbine blades. Two modal analysis computer programs were used to process the signals. The results obtained by theoretical predictions and by measured modal analysis verify that the theoretical characterization of the rotor structure is indeed valid for calculating the values of the natural frequencies. However, the damping factors measured by the two modal programs differ significantly.