排序方式: 共有51条查询结果,搜索用时 15 毫秒
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Simulations of free surface flows with implementation of surface tension and interface sharpening in the two-fluid model 总被引:2,自引:0,他引:2
Two-fluid model used for free surface flows with large characteristic scales is improved; the smeared interface is sharpened with conservative level set method and the surface tension force with wetting angle is implemented. Surface tension force is split between two phases with several models. Detailed analysis showed the splitting of surface tension force with volume averaging as the most appropriate. The improved two-fluid model with interface sharpening and implemented surface tension is validated on several test cases. The pressure jump over a droplet interface test case showed that the pressure jump in simulation converges with grid refinement to the analytical one. The parasitic currents in simulation are one order of magnitude larger than in simulation with volume of fluid model. In the oscillating droplet test case the time period of oscillating droplet with initially ellipsoid or square shape is similar to the analytical time period. In the rising bubble test case, the rising bubble position, terminal velocity, and circularity are similar to the one observed in simulations with level set model. The wetting angle is implemented in the two-fluid model with interface sharpening and surface tension force. Model is tested in the simulation of droplet in contact with wall with different wetting angles. 相似文献
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多项式结构设计方法是主瓣指向可调宽带波束形成器设计的一类重要方法。多项式结构的阶数是有限的,导致主瓣实际指向与期望指向之间存在偏差,因而影响了波束形成器的指向性指数。针对这一问题,该文提出了一种基于插值点优化的多项式结构宽带波束形成器设计方法。首先,引入多项式结构插值点处阵列响应的空间导数约束,以减小主瓣指向偏差;进而利用粒子群优化算法对多项式结构中的插值点进行优化,以充分利用插值点位置提供的自由度进一步提升多项式结构宽带波束形成器的性能。优化设计结果表明,与现有设计方法相比,该文提出的方法不仅降低了主瓣的指向偏差,同时也提高了指向性指数,有效改善了多项式结构宽带波束形成器的性能。 相似文献
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阐述了非线性铁氧体传输线的工作机理,并给出了等阻抗的设计方法。针对已有重复频率脉冲功率源输出脉冲特点,设计了工作重复频率可达10kHz的铁氧体传输线,并可实现将前沿ns级的高压脉冲陡化至几百ps。采用多种NiZn铁氧体磁芯开展陡化实验,研究了磁芯参数、铁氧体传输线长度及外加励磁场等因素对陡化效果的影响,得出采用高饱和磁化强度的磁芯可以获得更快的脉冲前沿;采用小磁芯可以加快输出脉冲前沿,但需要的铁氧体长度更长;外加轴向励磁对陡化前沿也具有促进作用,但励磁场并非越大越好,而是存在一个最佳范围。目前,根据实验结果优化后,经铁氧体传输线可将脉冲前沿从4ns陡化至450ps,且输出脉冲电压峰值39kV,基本实现了高重复频率、高功率及快脉冲输出。 相似文献
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Multi-Beam Echo-Sounders (MBES) designed for seafloor-mapping applications are today a major tool for ocean exploration and monitoring. Concerns have been raised about their impact towards marine life and especially marine mammals, although their inherent characteristics (high frequencies, short signals and narrow transmitting lobes) actually minimize this possibility. The present paper proposes an analysis of MBES radiation characteristics (pulse design, source level and radiation directivity pattern) accounting for the various geometries met today and expressed according to the metrics used for acoustical impact assessment (maximum Sound Pressure Level, and cumulative Sound Exposure Level). A detailed radiation model is proposed, including the transmission through directivity sidelobes, and applied to three typical MBES examples. A simplified radiation model is then defined, in order to extend it to the case of the cumulative insonification by a MBES moving along a survey line. An approximated analytical model is proposed for the accumulated intensity, showing good agreement with the complete simulation of insonification; it is applied to the worst-case configuration of a low-frequency (12 kHz) multi-sector system. The computation of ranges corresponding to impact thresholds accepted today shows that impacts in terms of injury are negligible for both SPL and SEL; however behavioural response impacts cannot be excluded, and should require specific experimentation. 相似文献
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The furry regions of ultrasound images are to be enhanced for good quality visual perception. This paper proposes a contourlet transform (CT) based sharpening technique (ST) for contrast enhancement in ultrasound (US) images. While sharpening, noise emphasize is the drawback of the classical ST methods. The proposed ST is operated on the multiscale, multidirectional CT decomposition of the underlying US image. The new ST not only sharpens the US image but also control the noise effect with tunable parameters. The results are compared with common unsharp masking and recently proposed nonlinear unsharp masking. The parameters like enhancement measure, structural similarity, and blind image quality measure evaluate the improved performances of the proposed technique. 相似文献
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