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Study on the Shear Effect on Dye Patches Diffused in Wall-Bounded Shear Flow

Open Journal of Fluid Dynamics 2016年第4期6卷 438-452页

作者： Qianqian Shao Takahiro Tsukahara Yasuo Kawaguchi Department of Mechanical Engineering Tokyo University of Science Chiba Japan

This paper focuses on the high intensity filaments (dye patches) embedded in dye plumes in a wall-bounded shear flow, to investigate the shear effect on the dye patch distribution. Motivated by the widely concerned inverse estimation of the source location, we try extracting useful information to know the source location from down-stream dye patches. Accordingly, we changed the dye injection location at different distances from the wall and made observations at different downstream (diffusion) distances from the source. The orientation angle and roundness of dye patches were concerned to examine the shear effect and dye patch characteristics. To capture the dye plume images, a planar laser induced fluorescence (PLIF) technique was used. The orientation and roundness of each dye patch were calculated by least-square fitting. The statistics of both the orientation angle and the roundness were compared with those in homogeneous turbulent cases to reveal the shear effect. Different from uniformly-orientated dye patches in the homogeneous flow, larger occurrence probabilities with positive orientation angles of dye patches are observed in wall-bounded shear flow, in particular, when the injection location is near the wall. As with information extraction for the inverse estimation of source location, it is found that the orientation distribution of dye patches is independent of the diffusion distance, but related with the injection location from the wall. While for the homogeneous flow cases, a strong dependence on the diffusion distance is observed in the orientation distribution profiles. As for the roundness, similar aspects are found regarding the dependencies on the injection location in shear flow and on diffusion distance in homogeneous flow.

关键词： Dye Patch Image Processing Inverse Problem least-square fitting Passive Scalar Shear Flow Source Estimation Point-Source Diffusion Wall Turbulence

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Baseline correction for digital strong-motion records by using the pre-event portion

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Geodesy and Geodynamics 2011年第1期2卷 43-46页

作者： Li Heng Yao Yunsheng Zheng Shuiming Cai Yongjian Lei Dongning Institute of Seismology China Earthquake Administration Wuhan 430071 China Wuhan Institute of Earthquake Engineering Wuhan 430071 China

Baseline offset in digital strong-motion acceleration record and initial velocity can produce unrealistic results for ground velocity and displacement derived from the acceleration by integration. A new method is proposed for the baseline correction and initial velocity calculation. It is based on linear least-squares fitting of the pre-event portion of velocity derived from the uncorrected acceleration data. Compared with the conventional method,which is based on removing the mean values of the pre-event portions of the acceleration and velocity traces,this method has clearer physical meaning and better stability.

关键词： baseline offset correction acceleration records initial velocity least-square fitting

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