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排序方式: 共有124条查询结果,搜索用时 78 毫秒
121.
采用大涡模拟数值方法,模拟了具有工程应用背景的二维超声速湍流混合层,通过非线性时间序列分析伪相图、关联维数和Lyapunov指数,得到了混合层发展情况的混沌特性.结果表明,混合层中心线沿流向位置的压力伪相图可定性地表示混合层的稳定性,关联维数分布可定量描述混合层经历的线性失稳、非线性失稳和涡合并阶段等发展情况,最大Lyapunov指数分布作为关联维数分析结果的验证.对于相应的超声速混合层实验,采用非线性时间序列分析方法研究混合层发展情况具有通用性. 相似文献
122.
《防务技术》2020,16(5):1019-1038
This article makes the first attempt in assessing the influence of active constrained layer damping (ACLD) treatment towards precise control of frequency responses of functionally graded skew-magneto-electro-elastic (FGSMEE) plates by employing finite element methods. The materials are functionally graded across the thickness of the plate in terms of modest power-law distributions. The principal equations of motion of FGSMEE are derived via Hamilton’s principle and solved using condensation technique. The effect of ACLD patches are modelled by following the complex modulus approach (CMA). Additionally, distinctive emphasis is laid to evaluate the influence of geometrical skewness on the attenuation capabilities of the plate. The accuracy of the current analysis is corroborated with comparison of previous researches of similar kind. Additionally, a complete parametric study is directed to understand the combined impacts of various factors like coupling fields, patch location, fiber orientation of piezoelectric patch in association with skew angle and power-law index. 相似文献
123.
渗硫层对网格化激光淬火表面摩擦磨损性能的影响 总被引:1,自引:0,他引:1
利用低温离子渗硫技术在CrMoCu合金铸铁网格化激光淬火表面制备了渗硫层,分析了其形貌组成与结构,考察了渗硫激光复合表面的摩擦学性能。结果表明:渗硫层表面疏松多孔,在淬火区域硫化物颗粒细小,结构致密,其相组成主要为FeS;在干摩擦条件下,渗硫层能降低网格化激光淬火表面的摩擦因数,提高其耐磨性能,其主要原因是硫化物及摩擦化学反应生成的氧化物能在摩擦表面形成边界润滑膜,抑制了磨粒磨损和粘着磨损,有效减弱了网格化激光淬火表面"摩擦台阶"效应。 相似文献
124.
《防务技术》2020,16(1):43-49
The temperature difference between the exposed surface of an underground silo and the surrounding soil surface is significant, which means a silo can be easily found by infrared detection. We designed an infrared camouflage cloak consisting of an imitative layer and an insulation layer for the silos. The imitative layer is used to imitate the thermal response of the soil to the surrounding environment. The insulation layer is used to weaken the impact of the internal temperature field of the silo on the lower boundary of the imitative layer. A silo model including surrounding soil and a soil model without silo were established, and the influences of the material and thickness of each layer on the infrared camouflage effect were analyzed. The results show that when using a silicone rubber containing alumina powder with a volume fraction of 3.18% as the imitative material, its thermal inertia is in consistent with that of the soil. Meanwhile, it was found that the thickness of the imitative layer doesn’t need to be greater than its thermal penetration depth to achieve the infrared camouflage, and the absence of the insulation layer will cause hot spots on the silo surface in winter to weaken the camouflage effect. The optimized thicknesses of the imitative layer and the insulation layer are 22 cm and 4 cm respectively. The simulations indicate that with the application of the cloak, the maximum value of the absolute values of the temperature differences between the average temperatures of the silo surface and the surrounding soil surface temperatures drops from 1.59 °C to 0.31 °C in summer and from 1.92 °C to 0.21 °C in winter. This designed cloak can achieve an all-weather and full-time passive infrared camouflage. 相似文献