随机瞬态温度场分析

研究随机瞬态温度场响应的数字特征问题.考虑导热中物理参数和边界条件的随机性,并将随机参数用随机因子的形式表示.从结构温度场响应的近似表达式出发,利用求解随机变量函数数字特征的代数综合法,导出具有随机参数温度场响应的均值和方差的拟解析计算表达式.通过算例考察各参数的随机性对温度场响应随机性的影响.该方法具有只进行一次随机温度场分析便可以获得其响应数字特征,且可以考察任意参数的随机性对温度场响应的影响的优点.     

随机参数刚架结构的平稳随机位移响应动力可靠性分析

研究物理参数具有随机性的刚架结构的平稳随机位移响应动力可靠性的计算方法。考虑结构的物理参数具有随机性，从结构随机响应的频域表达式出发，利用求解随机变量数字特征的代数综合法和矩法，导出随机参数刚架结构在平稳随机激励下的位移及速度响应均方值的数字特征，再由动力可靠性的Poisson公式导出结构动力可靠度的计算公式。通过算例就各参数的随机性对结构动力可靠度的影响进行分析，验证本文方法的可行性。     

基于概率的桁架结构随机振动响应分析研究

研究了具有随机物理参数和几何参数的桁架结构在随机振动激励下的动力响应问题.从结构在随机振动激励下其振动响应在频率域上的表达式出发,利用求解随机变量函数矩的方法和求解随机变量数字特征的代数综合法,导出了桁架结构的位移响应均方值和应力响应均方值的均值、方差和变异系数的计算表达式.通过算例分析了结构物理参数和几何参数的随机性对桁架结构在随机振动激励下动力响应随机性的影响,得出了若干有用的结论,为随机桁架结构的动力设计奠定了基础.     

镗铣加工中心主轴箱热特性仿真及试验研究

对镗铣加工中心主轴箱进行三维建模,依据工况确定热源,计算得出热源发热量并作为热载荷,以计算得出的各换热面对流换热系数作为边界条件,对主轴箱温度场进行了模拟分析,得到温度场分布以及稳态、瞬态温度场变化规律。依据温度场模拟结果,进行了热-结构耦合分析得到主轴箱热变形。通过主轴箱温度测试实验对温度场模拟结果进行了验证,并对实验与仿真结果的误差进行了分析。研究结果为建立热特性分析模型以及热误差的补偿提供参考。     

基于扫描法的轧辊瞬态温度场准三维建模与仿真

为了准确预报和控制轧辊瞬态热行为,对轧辊瞬态温度场进行了分析和研究。针对轧辊的工作特点,采用基于扫描法的准三维建模方法,从局部二维温度场出发拓展出全局三维温度场。该方法可以准确全面刻画出轧辊温度场的分布,最大限度地对计算过程进行了简化,为轧辊温度场研究提供了合理方案。应用该方法对1450轧机工作辊温度场进行仿真,取得了很好的效果。     

齿轮初期啮合瞬态热胶合研究

针对传统热胶合计算闪温法和积分温度法的不足,在考虑齿轮初期啮合和实际工况的条件下,运用有限元方法和传热学理论建立直齿圆柱齿轮模型、加载边界条件并对其瞬态温度场进行仿真,得到了轮齿瞬态温度场的分布云图,研究了温度场的分布规律,得到了轮齿瞬态温度,最后对比了轮齿瞬态温度与闪温理论值。结果表明:闪温法偏于保守,考虑初期啮合的瞬态热胶合分析结果更符合实际工况,为指导齿轮靠性设计热胶合、热应力、热变形等提供了重要依据。     

带式制动器瞬态温度场的有限元分析

依据传热学理论和带式制动器的结构特点,建立了制动带瞬态温度场数值模拟三维有限元计算模型,用有限元分析软件MSC.Marc进行了紧急制动工况下瞬态温度场的分析计算,获得了内部温度场分布规律;分析了摩擦片不同性能参数对温度场分布规律的影响,为带式制动器的优化设计提供参考。     

离合器内片支架激光焊接温度场仿真分析

针对激光焊接过程中焊接件结构失效的问题,开展了焊接过程中瞬态温度场的仿真分析。以某离合器内片支架与花键轴为研究对象,借助于SYSWELD有限元软件建立激光焊接模型对焊接过程进行了数值模拟,得到了焊接过程中瞬态温度场分布图和特征节点的热循环曲线及相演变情况。仿真结果表明:激光焊接时间为2.5s时,温度场进入准稳态;距离焊缝线0～3.5mm的焊接区域内,峰值温度过高,焊接件容易发生热变形;冷却后的焊缝区域显微组织主要为马氏体,焊接接头具有较好的强度和韧性。     

某直升机主减换向锥齿轮传动系统瞬态热分析

直升机传动系统无油状态下的温度场分布是直升机工业普遍关注的问题,本文以直升机主减中换向锥齿轮传动系统为研究对象,基于热网络法建立了该系统的温度场计算模型;编程计算了该系统各部件的热源、各部件与滑油和油雾空气之间的对流换热系数以及各部件之间的热阻;求解了该系统的稳态温度场,以稳态温度场为基础,提出了换向锥齿轮传动系统瞬态温度场的计算方法,并依据此方法建立了瞬态温度场计算模型,最终得到了该系统的瞬态温度场分布。     

高温物体快速冷却时瞬态温度场的确定

物体在快速加热或快速冷却时,瞬态温度场的计算由于热传导常数难于确定而遇到困难.本文运用实验和分析相结合的办法,利用逼近法确定Δt 时间内的热流量 q,得到较好的瞬态温度场的计算结果.此方法对工程计算有实用价值.     

Topology design and analysis of compliant mechanisms with composite laminated plates

To improve the small deformation and high stress level in hinge zones of compliant mechanisms with isotropic material, a topology optimization method of compliant mechanisms with composite laminated plates was proposed. Based on the anisotropy and designability of composite laminated plates, a topology optimization model of compliant mechanisms with composite laminated plates was built to maximize the deformable capability. Numerical examples of designing compliant inverters and grippers were investigated to demonstrate the effectiveness of the proposed method. The influence mechanism of layer sequences on topologic shapes, deformation and loading capability were also discussed. The results showed that the deformable capability and stress levels of compliant mechanisms with composite laminated plates were further improved by a reasonable configuration of layer sequences.

     

Thermally induced buckling of functionally graded hybrid composite plates

In this paper, thermal buckling analysis is performed on hybrid functionally graded plates (FGPs) with an arbitrary initial stress. The governing equations are derived using the average stress method, including the effect of transverse shear deformation. Then, an eigenvalue problem is formed to evaluate thermal buckling temperatures for simple supported initially stressed ceramic-FGM-metal plates. The effects of functionally graded material (FGM) layer thickness, volume fraction index, layer thickness ratio, thickness ratio, aspect ratio and initial stress on the thermal buckling temperature of hybrid FGPs are investigated. The results reveal that the volume fraction index, initial stresses and FGM layer thickness have significant influence on the thermal buckling of hybrid FGPs.     

Mg/Al复合板波纹轧模拟及变形区微观组织演变分析

通过建立Mg/Al复合板波纹轧热力耦合有限元模型并进行轧卡实验,分析了应力、应变及温度对金属变形以及微观组织演变的影响。结果表明,当波纹轧初始轧制温度为400 ℃、平均压下率为35%时,复合板在变形区靠近出口位置实现复合,复合界面波谷处扩散层厚度为3.3 μm,波峰处扩散层为2.7 μm;等效应变和温度的增加促进了镁合金的变形晶粒发生动态再结晶,其微观组织主要包括等轴晶、孪晶以及动态再结晶晶粒,界面波谷处晶粒平均尺寸为3.71 μm,波峰处为6.92 μm。     

约束阻尼板双线性材料插值法拓扑动力学优化

为减小阻尼板质量并提高减振性能,研究了结构动力学优化技术。构建了以移动常数与模态损耗因子差值为目标、阻尼层单元密度为拓扑变量、阻尼层体积用量及振动模态频率为约束的阻尼板优化模型。利用序列凸规划法构造目标函数的凸性逼近式,采用拉格朗日乘子法解算逼近函数,以获取全局优化的阻尼层布局。利用模态损耗因子与模态应变能的本构关系推导目标函数关于拓扑设计变量的灵敏度,基于K-T条件构造拓扑变量迭代式。引入双线性插值函数惩罚拓扑变量并使其值聚集于0或1,编写并实现了悬臂阻尼板优化程序。当阻尼层体积用量控制在50%时,1阶模态损耗因子增大52.29%,灰度单元占比1.78%。阻尼板谐响应分析表明优化构形具良好减振特性。双线性插值优化既能充分发挥阻尼层的耗能效力又可大幅减少灰度阻尼单元数。     

炭/炭复合材料在空间光学遥感器热控制中的应用

提出在金属表面粘贴炭/炭复合材料来解决空间光学遥感器光机结构材料导热率低、温度梯度较大的问题.概述了炭/炭复合材料的基本特点并建立了钢板表面粘贴炭/炭复合材料的热传导数学模型.对钢板的裸板和单面分别贴0.5mm和2 mm复合材料的3种状态进行了理论分析与温度测试试验,获得了钢板在3种状态下的等效热导率.利用IDEAS-TMG有限元软件对模型进行了仿真分析并对钢板在上述3种状态下的传热性能进行了比较.对比结果显示,粘贴炭/炭复合材料能很好地改善钢板的传热性能.最后,将0.5 mm厚的炭/炭复合材料应用于低热导率的星敏感器安装支架(材料为TC4)的热控,并对星敏感器支架粘贴炭/炭复合材料前后两种情况进行了温度测试试验.试验结果显示,表面粘贴炭/炭复合材料后,星敏感器支架测点温差由28℃减小为5℃,提高了星敏感器支架温度均匀性,表明该措施对改善空间光学遥感器上低热导率结构件的温度梯度很有意义.     

A method of increasing hard-alloy wear resistance via aerodynamic impact

The paper presents the effect of an increase in wear resistance after several operating cycles of hard-alloy plates is investigated and the results of investigations. The plate is heated to one-third of the melting temperature and subjected to air fluctuations with frequencies of 160–800 Hz. A hypothesis on how aerodynamic impacts occur on hard alloy surfaces is presented. An experimental way to strengthen the surface layer of metal cutting plates is described. It is revealed that under industrial condition the mean time between failures for the plates processed by mentioned procedure is 1.8–2.2 times higher than for the standard delivery plates.     

Determination of the energy of a relativistic electron beam by measuring the thickness of the colored layer in glass

A method for determining the energy of relativistic electrons, which was used in the investigation of electromagnetic fields in plasma and dielectric structures, is described. The electron energy was determined by the extrapolated track of electrons in glass, which was estimated by the thickness of the colored (darkened) layer formed by electrons. The density distribution of the colored layer along the direction of electron motion makes it possible to record the width of the beam energy spectrum and the beam position relative to the axis of the transit channel. A stack of glass plates on which the beam is incident can be installed in the transit channel of the dielectric structure or in plasma. Each plate in the stack is placed in parallel to the beam axis. After irradiation of the plates with relativistic electrons, the colored layer depth and the density distribution are determined. Examples of determining the electron energy of a pulsed relativistic electron beam are presented. The method is insensitive to electromagnetic noise, is inexpensive, simple, and easy to use.     

A study on the merging position of frozen layers in injection-molded disks and rectangular plates

Thermal and flow simulations of center-gated disks and rectangular plates molded under different process conditions are presented. The process variables were melt temperature, mold temperature, injection speed and packing pressures which have been varied systematically. The input pressure data were taken from the experimental traces, if possible. In particular, we have focused on the effect of process conditions on the growth of, so called, a fronzen layer We found that the frozen layer started to merge at about 0.75 ^R from the center for the center-gated disks and about 0.25–0.35^L from the gate for the rectangular plates for most of process conditions. The present result would help to understand the mechanism how the packing process affects the limited portion in overpacked injection-molded parts.     

A design-experiment study of nonlinear properties of coal-plastic

A design-experiment method of estimating and forecasting nonlinear deformation of unidirectional and layered coal-plastic with different angles of layers placed under quasi-static loading is proposed. The elastic properties of a layer were determined on the basis of test results of crossing-reinforced flat samples under stretching. It was assumed that the nonlinearity of a layer and of a stack with multiple layers stowed at different angles is determined by nonlinear deformation of the layer at shear in the layer’s plane, which was described with the help of a piecewise-linear approximation. To construct the defining relations of the pack, the theory of laminated plates was used. The investigation results showed a satisfactory agreement of calculated and experimental data.     

高效薄层色谱法分析茶叶中高效氯氟氰菊酯和联苯菊酯农药残留

建立了茶叶中高效氯氟氰菊酯和联苯菊酯残留的高效薄层色谱分析法。样品用乙酸乙酯机械振荡提取,活性炭固相萃取柱和氟罗里硅土固相萃取柱串联净化。采用半自动点样仪将待测样品溶液点样到高效薄层板上,用展开剂[正己烷:二氯甲烷=6:4(v:v)混合溶液]单向上行展开,高效薄层色谱扫描仪于230nm处检测。结果表明,在该色谱条件下高效氯氟氰菊酯(比移值Rf=0.42)和联苯菊酯(比移值Rf=0.63)的最小检测限分别为10ng和20ng,茶叶中高效氯氟氰菊酯和联苯菊酯的添加回收率分别为82.1%～105%和75.2%～98.6%(添加浓度为0.50～10.0mg/kg),相对标准偏差分别为3.59%～12.0%和6.94%～13.3%。该分析方法的准确性、精确性、灵敏度和重现性均达到了农药残留分析的要求。