线接触脂润滑弹流润滑分析

工程中大多数滚动轴承采用脂润滑,但是润滑脂具有非牛顿体特性和润滑过程的时效性,较难准确地建模分析其润滑特性。通过总结脂润滑弹流的理论分析与实验研究进展,基于Ostwald本构模型建模,用Gauss-Seidel迭代法和Jacobi双极子迭代法分析脂润滑条件下的润滑膜厚度分布和压力分布;探讨不同流变指数、不同载荷和不同卷吸速度对脂润滑弹流特性的影响。结果表明:载荷和卷吸速度对润滑脂膜厚和压力的影响与油润滑相似;稳定后的脂润滑膜厚接近相应工况基础油润滑膜厚的1/2;润滑脂的非牛顿特性越显著,则膜厚越小,压力分布越接近Hertz接触应力分布。

Comprehensive analyses of initiation and failure mechanisms of the 2017 Xinmo catastrophic rockslide

The failure of the 2017 Xinmo catastrophic rockslide in Maoxian County, Sichuan, Southwest China was a combined effect of long-term and shortterm triggering factors. Field investigation, historical data collection, laboratory tests, chemical and microstructure analysis and numerical simulations were adopted herein to reveal the initiation and failure mechanism of the Xinmo rockslide. The analytical results showed that this failure involved the coupling of several triggering factors. The initial cracks in the rock mass were induced by historical earthquakes due to the convex topography and the direction effect. Rock masses from the source area of the Xinmo rockslide contain water-sensitive minerals, i.e., albite and chamosite, and the easily oxidized chemical element Fe, resulting in obvious strength deterioration under the action of water. The scanning electron microscopy(SEM) experimental results indicated that the internal structure of the rock mass is conducive to weathering. The compressive and shear strengths of the rock mass were reduced due to freeze-thaw cycles and weathering. The antecedent rainfall further deteriorated the stability of the slope, and stress and deformation accumulated continually in the locked section. Finally, the locked section sheared out, and the slope failed. An entrainment effect was observed in the Xinmo rockslide due to the presence of old landslide deposits and the antecedent rainfall, resulting in an amplification of the catastrophic rockslide. A simplified three dimensional analysis model was established in this study to reveal the influence of the triggering factors on the failure mechanism of the Xinmo rockslide.

Numerical investigation of the interaction of the turbulent dual-jet and acoustic propagation

In order to study the interaction between two independent jets, a three-dimensional（3D） transient mathematical model is developed to investigate the flow field and acoustic properties of the two-stream jets. The results are compared with those of the single-stream jet at Mach number 0.9 and Reynolds number 3600. The large eddy simulation（LES） with dynamic Smagorinsky sub-grid scale（SGS） approach is used to simulate the turbulent jet flow structure. The acoustic field is evaluated by the Ffowcs Williams–Hawkings（FW-H） integral equation. Considering the compressibility of high-speed gas jets, the density-based explicit formulation is adopted to solve the governing equations. Meanwhile, the viscosity is approximated by using the Sutherland kinetic theory. The predicted flow characteristics as well as the acoustic properties show that they are in good agreement with the existing experimental and numerical results under the same flow conditions available in the literature. The results indicate that the merging phenomenon of the dual-jet is triggered by the deflection mechanism of the Coanda effect, which sequentially introduces additional complexity and instability of flow structure. One of the main factors affecting the dual-jet merging is the aperture ratio, which has a direct influence on the potential core and surrounding flow fluctuation. The analysis on the noise pollution reveals that the potential core plays a fundamental role in noise emission while the additional mixing noise makes less contribution than the single jet noise. The overall sound pressure level（OASPL） profiles have a directive property, suggesting an approximate 25° deflection from the streamwise direction, however, shifting toward lateral direction of about 10° to 15° in the dual-jet. The conclusion obtained in this study can provide valuable data to guide the development of manufacturing-green technology in the multi-jet applications.

Design of the Airbag Inflation System Applicable to Conventional and Autonomous Vehicles

The emergency transformation of various aspects of life and business these days requires prompt evaluation of autonomous vehicles.One of the primary reassessments deals with the applicability of the vehicle passive safety system to the protec-tion of arbitrarily positioned passengers.To mitigate possible risks caused by the simultaneous deployment of several big airbags,a new principle of their operation is required.Herein,the aspirated inflator for a driver airbag is developed that can provide 50L-airbag inflation within 30-40 ms.As a result,about 3/4 of the air is to be entrained into an airbag from the vehicle compartment.The process is initiated by a supersonic pulse jet(1/3 air volume)generated pyrotechnically.Then the Prandtl-Meyer problem formulation enables guiding linear and angular dimensions of the essential parts of the device.Accordingly,a family of experimental models of varied geometry is fabricated and tested to determine their operational effectiveness in a range of motive pressure within~3-7 MPa.Experiments are performed on a specially designed facility equipped with compressed-air tanks and a high-speed valve to mimic the inflator operation with the pyrotechnic gas generator.The aspirated inflator operability is characterized using multivariate measurements of pressure fields,high-speed video-recording of the airbag inflation process,and evaluation of aspiration(entrainment)ratio.The average volume aspiration ratio measured at 300 K is found to reach 2.8 and it’s expected to almost double at 1200 K.