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This research is intended to provide academic reference and design guidance for further studies to determine the most effective means to reduce a ship’s resistance through an air-cavity. On the basis of potential theory and on the assumption of an ideal and irrotational fluid, this paper drives a method for calculating air cavity formation using slender ship theory then points out the parameters directly related to the formation of air cavities and their interrelationships. Simulations showed that the formation of an air cavity is affected by cavitation number, velocity, groove geometry and groove size. When the ship’s velocity and groove structure are given, the cavitation number must be within range to form a steady air cavity. The interface between air and water forms a wave shape and could be adjusted by an air injection system. 相似文献
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Runoff and soil erosion from highway construction spoil deposits: A rainfall simulation study 总被引:3,自引:0,他引:3
Jianzhi DongKeli Zhang Zhongling Guo 《Transportation Research Part D: Transport and Environment》2012,17(1):8-14
To measure soil loss from these road construction spoils, 30 rainfall simulations involving five rainfall intensities were conducted to study runoff and soil erosion processes on a road in China. Twenty-five of the rainfall simulations were carried out on loose materials five different slopes. Another five rainfall simulations were conducted on compacted road materials with a slope of 30.6%. The results show that soil bulk density has a positive effect on runoff rate, and the effect of slope on runoff rate changes with rainfall intensity. Higher soil bulk density increases soil loss under low rainfall intensity, but decreases soil loss when rainfall intensity is high. Soil loss is positively related to slope, but the relationship differs from that in prior studied of croplands and disturbed lands. Equations for predicting soil erosion from loose materials and compacted road are developed. 相似文献
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为了降低泵喷推进器的辐射噪声,借鉴航空发动机"处理机匣"技术,在泵喷推进器导管内壁上开设凹槽结构,达到降低泵喷推进器转子梢涡强度、抑制梢涡空化的目的。针对某型泵喷推进器,采用结构化网格,对比分析了无凹槽和有凹槽喷泵喷推进器的梢涡强度,结果显示,导管凹槽能够有效削弱梢涡强度;分析了湍流模型、网格数量和时间步长对计算结果的影响,初步建立了导管凹槽梢涡抑制效果的数值计算方法,研究结果为泵喷推进器梢涡控制提供了新的技术路径和技术支撑。 相似文献
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文章在均质平衡多相流模型的基础上耦合输运方程型空化模型,通过求解混合介质的RANS方程、RNG k-ε湍流输运方程以及各相的质量输运方程,采用通用CFD软件—FLUENT数值模拟了水洞中带圆盘空化器航行体模型的定常通气空泡流动,研究了圆形截面闭式空泡水洞中洞壁效应对通气空化数和压力场的影响。得到的阻塞空化数线性正比于圆盘水洞直径比,且与三维圆盘自然空泡流的势流近似解基本一致,分析了洞壁效应作用下空化流场内的压力分布特点,并根据计算结果拟合了一定适用条件下通气空泡长度、最大直径和模型阻力系数的近似公式。 相似文献
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Visual imagery of costal morphological change processes must be accompanied by supporting information to make change processes understandable. We explored the influence of supporting information (graphs and numeric values) on perceptions of coastal morphological change processes through an experiment delivered to coastal recreationists. Supporting information was presented alongside four imagery types: human perspective digital elevation models (DEMs), human perspective digital photographs, aerial views of DEMs and aerial photography. We found neither the use of graphs nor numeric values influenced respondents' perceptions of coastal environmental change. However, perceptions varied significantly across imagery type; human perspective digital photographs and aerial photographs yielded higher ratings compared to human perspective DEMs and aerial views of DEMs. The results suggest supporting information representing increasingly severe rates of beach erosion and shoreline movement does not translate into perceptions of increasingly dramatic geophysical processes; this is consistent with previous empirical findings. The results also suggest individuals perceive coastal change processes as more severe when those processes are presented through photographs, particularly aerial photographs. Scientists, educators and coastal land use managers struggling to communicate the magnitude and severity associated with coastal geophysical processes are advised to use comparative aerial photography when possible. 相似文献