三沟槽锥球头铣刀的新型虚拟模型研究

分析了与经线、轴线成定角以及等螺距的传统回转铣刀刃口设计存在的设计制造难题,提出了一种新型刃口设计方法,给出了相应的刃口应当满足的通用微分方程,并以第三沟槽的锥球头铣刀为例,建立了新型的刃口设计、沟槽设计相关模型,还给出了二轴联动制造锥球头铣刀中的主干数学模型,给出了二轴联动加工中的进给速度公式,并结合与工厂合作的实践,指出解决其相关问题的方法,从而为这种新型设计与相应制造提供了整套虚拟模型,可供同类研究参考。     

变参量Wiggler FEL的三维非线性理论

本文建立了变参量Wiggler自由电子激光放大器的三维自洽非线性理论。考虑电磁波、电子注和Wiggler场三者均在三维空间中变化,忽略电子注的自身场和空间电荷效应,导出了带有变参量双绕螺旋Wiggler场和轴向导引磁场的矩形波导,轴对称电子注自由电子激光器的非线性互作用微分方程组。数值模拟表明:在适当位置逐渐减小Wiggler场的幅值或周期均能有效地提高电子注的能量转换效率。     

Ductile-brittle transition mechanisms of amorphous glass subjected to taper grinding experiment

Taper grinding experiments were conducted in this paper to investigate the continuous and complete ductile-brittle transition process of two kinds of amorphous glass: high purity fused silica (HPFS) which is silica rich glass and soda-lime silica glass (SLSG) which is low silica glass. The grinding force, ground surface morphology, surface roughness, and subsurface damage depth induced during different stages of taper grinding were all analyzed. A mathematical model describing the cutting force of a grit and micro-crack length was established to clarify the ductile-brittle transition mechanisms of isotropic material. The model revealed that material removal mechanisms and grinding force were mainly determined by the crack equivalent length in front of the grit and its equivalent cutting force. The ground surface roughness and subsurface damage depth were mainly affected by the cutting force of the grit and length of cracks behind it. The ductile machinability of SLSG was better than that of HPFS due to the bonding of metallic atoms in SLSG with nonbridging oxygens, as well as their packing into free volume in SiO₂ network.     

镗削活塞锥形销孔的气液压刀具补偿系统

精镗销孔是活塞加工中保证精度的关键工序之一。由于销孔尺寸、形状和位置精度及粗糙度的要求都很高,一般都需要设计并制造高精度的镗头。本文介绍了镗削活塞锥形销孔的气液压刀具补偿系统的工作原理,并介绍了气液压刀具补偿系统的应用实例。     

圆锥轴承套圈车削自动线的研制

ZZX-01圆锥轴承套圈自动车削生产线具有高精度、高效率、高可靠性及大批量生产等优点,文章介绍了其现代设计方法、研制规划及工作原理.     

Driver responses to differing urban work zone configurations

This study reports the results of a simulator-based assessment of driver response to two different urban highway work zone configurations. One configuration represented an existing design which was contrasted with a second configuration that presented a reduced taper length prototype work zone design. Twenty-one drivers navigated the two different work zones in two different conditions, one with and one without a lead vehicle; in this case a bus. Measures of driver speed, braking, travel path, and collision frequency were recorded. Drivers navigated significantly closer to the boundary of the work area in the reduced taper length design. This proximity effect was moderated by the significant interaction between lead vehicle and taper length and such interactive effects were also observed for driver speed at the end of the work zone and the number of collisions observed within the work zone itself. These results suggest that reduced taper length poses an increase in risk to both drivers and work zone personnel, primarily when driver anticipation is reduced by foreshortened viewing distances. Increase in such risk is to a degree offset by the reduction of overall exposure to the work zone that a foreshortened taper creates. The benefits and limitations to a simulation-based approach to the assessment and prediction of driver behavior in different work zone configurations are also discussed.     

反向映射法在双列圆锥滚子汽车轮毂轴承设计中的应用

通过对比分析国内外双列圆锥滚子汽车轮毂轴承产品系列的结构特征和参考目前国内(单列)圆锥滚子轴承设计方法,分析了反向映射法在双列圆锥滚子汽车轮毂轴承结构设计中的应用。     

Wind-induced coupled motion of tall buildings with varying square plan with height

One characteristic of many tall buildings is that their building shapes vary with height, implying that the distribution of their structural components may also vary with height. Response analyses have been conducted for tall buildings with square plans with height variations using high-frequency force balance data, focusing on comparing the total accelerations of the various building shapes based on the shapes themselves, and not on different natural frequencies. The variation trends of total accelerations are different between mass and rigidity center eccentricity, and the acceleration of the square model is the largest, and the differences among models increase with eccentricity. For the setback and tapered models, although the across-wind acceleration is larger than that of the square model, the along-wind and torsional accelerations are smaller than those of the square model, resulting in smaller total rms acceleration response. However, the increase in torsional response for the tapered and setback buildings when the offsets lie in the windward diagonal direction may enhance building occupants' awareness of the motion even if the total rms accelerations become small.     

Multi-objective crashworthiness optimization of tapered thin-walled tubes with axisymmetric indentations

In this paper, the effects of tapering and introducing axisymmetric indentations on the crash performances of thin-walled tubes are investigated. The crash performances of the tubes are evaluated using two metrics: the crush force efficiency (CFE, the ratio of the average crushing load to the peak load), and the specific energy absorption (SEA, absorbed energy per unit mass). The optimum values of the number of the axisymmetric indentations, the radius of the indentations, the taper angle and the tube thickness are sought for maximum CFE and maximum SEA using surrogate based optimization. In addition, multi-objective optimization of the tubes is performed by maximizing a composite objective function that provides a compromise between CFE and SEA. The CFE and SEA values at the training points of surrogate models (metamodels) are computed using the finite element analysis code LS-DYNA. Polynomial response surfaces, radial basis functions, and Kriging are the different surrogate models used in this study. Surrogate based optimization of the tubes showed that the tubes with indentations have better crush performance than tubes without indentations. It is found that maximum CFE requires large number of indentations with high radius, small thickness, and medium taper angle, while maximum SEA requires small number of indentations with low radius, large thickness and small taper angle. It is also found that the globally most accurate surrogate model does not necessarily lead to the optimum.     

圆柱型阵机载雷达杂波抑制新方法

圆柱型阵天线相对于常规的平面阵天线具有空间全方位扫描、搜索跟踪方式灵活和波束方向性好等优点。该文首先从圆柱型阵机载雷达杂波协方差矩阵特征值分布和杂波功率谱距离向分布两个方面分析了圆柱型阵列与均匀平面阵列之间的区别,得到杂波功率谱随距离变化的结论。然后根据圆柱型阵机载雷达杂波分布特点提出了两种不同的杂波抑制方法,它们能够很好地解决圆柱型阵机载雷达杂波距离向分布非均匀的问题。最后通过仿真实验验证了该文方法的正确性。