Research on the Movement Patterns of Bed-load Streaky Structure Transport and the Mechanism of Fluid-solid Coupling
The movement of sediment particles driven by specific water flow intensities gradually forms streaky structure in bed surfaces, a phenomenon that underscores the intricate interplay between sediment dynamics and fluid mechanics. These bed surface structures once formed, exert a profound influence on...
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Editorial Department of Journal of Sichuan University (Engineering Science Edition)
2024-01-01
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| Series: | 工程科学与技术 |
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| Online Access: | http://jsuese.scu.edu.cn/thesisDetails#10.12454/j.jsuese.202400672 |
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| author | YAO Jiateng XIE Xiaoxi WANG Hao ZHAO Lin XIE Haonan ZHEN Rongtian |
| author_facet | YAO Jiateng XIE Xiaoxi WANG Hao ZHAO Lin XIE Haonan ZHEN Rongtian |
| author_sort | YAO Jiateng |
| collection | DOAJ |
| description | The movement of sediment particles driven by specific water flow intensities gradually forms streaky structure in bed surfaces, a phenomenon that underscores the intricate interplay between sediment dynamics and fluid mechanics. These bed surface structures once formed, exert a profound influence on the sediment transport process and the coherent structures of the water flows, indicating a reciprocal and intricate relationship. However, despite the significance of this interplay, quantitative research on their mutual influence remains somewhat sparse, necessitating a deeper understanding of the mechanisms involved. In this context, studying the interaction among turbulent coherent structures, bedload motion, and bed surface topography emerges as a critical area of study. To address this gap, the present study built upon previous research by conducting bedload equilibrium sediment transport experiments under medium to low flow conditions (<italic>Θ</italic> = 0.068~0.096). These experiments aimed to unravel the complexities of sediment transport, bed surface morphology and bursting events. During the experiments, captured images of sediment movement underwent rigorous preprocessing to ensure accuracy. Top-hat transformation was employed to mitigate the impact of uneven illumination, enhancing the clarity of the images. Histogram equalization was then applied to bolster the contrast between sediment particles and the background, thereby facilitating the extraction of particle characteristics. Grayscale subtraction was subsequently used to process adjacent frames of particle movement images, allowing for the identification of motion regions and their respective characteristics. To further refine the data, gaussian filtering was utilized to reduce noise interference, ensuring that only relevant information was retained. Binarization was then performed to obtain the centroids of moving sediment particles, which served as the foundation for subsequent tracking and analysis. The particle tracking velocimetry (PTV) matching probability method was adopted to track particles effectively and acquire velocity information, providing valuable insights into the dynamics of sediment transport. Based on the located centroids and vector velocities of bedload particles, the Kalman filter algorithm was employed to calculate both measured and predicted values under the given conditions. Through update recursion, subsequent particle motion positions were obtained, ultimately achieving the tracking of bedload moving particles with unprecedented precision. In addition to particle tracking, the present study also leveraged the structure from motion (SFM) method for three-dimensional reconstruction of the scouring topography. Utilizing the open-source program on the VisualSFM platform, images containing control points were processed to yield post-scouring terrain conditions, providing a comprehensive view of the bed surface morphology. With the bed surface morphology and particle tracking data in hand, the study then turned its focus to the flow fields at sand troughs and sand ridges. To visualize these flow fields, hollow glass microspheres were selected as tracer particles, and the particle image velocimetry (PIV) method was utilized to measure the two-dimensional instantaneous flow fields within the terrains. The flow fields were then calculated by using a multi-grid iterative image deformation algorithm, yielding detailed results at different locations. A modified quadrant analysis method was employed to delve deeper into the turbulent bursting events within the flow field results. This analysis included the occurrence ratios of ejection and sweep events, as well as the variation patterns of corresponding characteristic parameters along the water depth. These insights provided a clearer understanding of the turbulent dynamics within the flow field and their impact on sediment transport. By combining the laws of sediment motion, the three-dimensional bed topography, and the bursting phenomena corresponding to these topographies, the study aimed to unravel the coupling relationship among turbulent coherent structures, sediment particle motion, and bed surface topography. The conclusions drawn from this study offer valuable insights into the intricate interplay between these components: 1)Under medium to low flow intensities (<italic>Θ</italic> = 0.068~0.096), both the intensity distribution of particle motion and the bed surface topography exhibited a streaky structure distribution. Bedload motion was more intense in the middle of the flume, gradually weakening towards the sides. Correspondingly, larger-scale sand band structures formed in the middle of the bed surface, while smaller and more blurred structures were observed on both sides. As the flow intensity increased, the scale of these streaky structures continually enlarged, with a corresponding decrease in the number of streaky structures. When 0.068 < <italic>Θ</italic> < 0.096, the streaky structures were most pronounced, becoming blurred outside this range. 2)The normalized curves of particle motion quantity and topographic elevation revealed a clear correlation between bedload motion intensity and bed surface morphology. Areas with higher bedload motion intensity corresponded to sand troughs, while areas with lower bedload motion intensity corresponded to sand ridges. This finding underscores the impact of sediment transport on bed surface morphology. 3) The flow field results at sand troughs and sand ridges indicated that within the near-wall region, compared with the ridge areas, the occurrence ratio, duration, maximum shear force, and transported momentum values of the sweep event in the trough areas are all larger, but the period value is smaller. These differences in flow field characteristics resulted in more intense particle motion at sand troughs and smoother motion at sand ridges, ultimately leading to the formation of sand troughs and sand ridges on the bed surface. 4)Analysis of the streaky structures of bedload motion intensity, sand trough and ridge structures, and bursting phenomena in corresponding topographies showed that the results aligned with the large-scale streamwise vortex model hypothesis rather than the secondary flow hypothesis. This finding suggests that turbulent coherent structures, bedload motion, and topography interact and mutually constrain each other, resulting in the phenomenon of time-averaged sand band structures. In conclusion, this stduy provides a comprehensive understanding of the coupling relationship between turbulent structures, sediment motion, and riverbed structures. By studying these interactions, the study offers valuable insights into the dynamics of water and sediment transport, paving the way for future research in this field. |
| format | Article |
| id | doaj-art-1c4c158610a6434284a5dbcd758fec8a |
| institution | DOAJ |
| issn | 2096-3246 |
| language | English |
| publishDate | 2024-01-01 |
| publisher | Editorial Department of Journal of Sichuan University (Engineering Science Edition) |
| record_format | Article |
| series | 工程科学与技术 |
| spelling | doaj-art-1c4c158610a6434284a5dbcd758fec8a2025-08-20T02:47:35ZengEditorial Department of Journal of Sichuan University (Engineering Science Edition)工程科学与技术2096-32462024-01-0111276207578Research on the Movement Patterns of Bed-load Streaky Structure Transport and the Mechanism of Fluid-solid CouplingYAO JiatengXIE XiaoxiWANG HaoZHAO LinXIE HaonanZHEN RongtianThe movement of sediment particles driven by specific water flow intensities gradually forms streaky structure in bed surfaces, a phenomenon that underscores the intricate interplay between sediment dynamics and fluid mechanics. These bed surface structures once formed, exert a profound influence on the sediment transport process and the coherent structures of the water flows, indicating a reciprocal and intricate relationship. However, despite the significance of this interplay, quantitative research on their mutual influence remains somewhat sparse, necessitating a deeper understanding of the mechanisms involved. In this context, studying the interaction among turbulent coherent structures, bedload motion, and bed surface topography emerges as a critical area of study. To address this gap, the present study built upon previous research by conducting bedload equilibrium sediment transport experiments under medium to low flow conditions (<italic>Θ</italic> = 0.068~0.096). These experiments aimed to unravel the complexities of sediment transport, bed surface morphology and bursting events. During the experiments, captured images of sediment movement underwent rigorous preprocessing to ensure accuracy. Top-hat transformation was employed to mitigate the impact of uneven illumination, enhancing the clarity of the images. Histogram equalization was then applied to bolster the contrast between sediment particles and the background, thereby facilitating the extraction of particle characteristics. Grayscale subtraction was subsequently used to process adjacent frames of particle movement images, allowing for the identification of motion regions and their respective characteristics. To further refine the data, gaussian filtering was utilized to reduce noise interference, ensuring that only relevant information was retained. Binarization was then performed to obtain the centroids of moving sediment particles, which served as the foundation for subsequent tracking and analysis. The particle tracking velocimetry (PTV) matching probability method was adopted to track particles effectively and acquire velocity information, providing valuable insights into the dynamics of sediment transport. Based on the located centroids and vector velocities of bedload particles, the Kalman filter algorithm was employed to calculate both measured and predicted values under the given conditions. Through update recursion, subsequent particle motion positions were obtained, ultimately achieving the tracking of bedload moving particles with unprecedented precision. In addition to particle tracking, the present study also leveraged the structure from motion (SFM) method for three-dimensional reconstruction of the scouring topography. Utilizing the open-source program on the VisualSFM platform, images containing control points were processed to yield post-scouring terrain conditions, providing a comprehensive view of the bed surface morphology. With the bed surface morphology and particle tracking data in hand, the study then turned its focus to the flow fields at sand troughs and sand ridges. To visualize these flow fields, hollow glass microspheres were selected as tracer particles, and the particle image velocimetry (PIV) method was utilized to measure the two-dimensional instantaneous flow fields within the terrains. The flow fields were then calculated by using a multi-grid iterative image deformation algorithm, yielding detailed results at different locations. A modified quadrant analysis method was employed to delve deeper into the turbulent bursting events within the flow field results. This analysis included the occurrence ratios of ejection and sweep events, as well as the variation patterns of corresponding characteristic parameters along the water depth. These insights provided a clearer understanding of the turbulent dynamics within the flow field and their impact on sediment transport. By combining the laws of sediment motion, the three-dimensional bed topography, and the bursting phenomena corresponding to these topographies, the study aimed to unravel the coupling relationship among turbulent coherent structures, sediment particle motion, and bed surface topography. The conclusions drawn from this study offer valuable insights into the intricate interplay between these components: 1)Under medium to low flow intensities (<italic>Θ</italic> = 0.068~0.096), both the intensity distribution of particle motion and the bed surface topography exhibited a streaky structure distribution. Bedload motion was more intense in the middle of the flume, gradually weakening towards the sides. Correspondingly, larger-scale sand band structures formed in the middle of the bed surface, while smaller and more blurred structures were observed on both sides. As the flow intensity increased, the scale of these streaky structures continually enlarged, with a corresponding decrease in the number of streaky structures. When 0.068 < <italic>Θ</italic> < 0.096, the streaky structures were most pronounced, becoming blurred outside this range. 2)The normalized curves of particle motion quantity and topographic elevation revealed a clear correlation between bedload motion intensity and bed surface morphology. Areas with higher bedload motion intensity corresponded to sand troughs, while areas with lower bedload motion intensity corresponded to sand ridges. This finding underscores the impact of sediment transport on bed surface morphology. 3) The flow field results at sand troughs and sand ridges indicated that within the near-wall region, compared with the ridge areas, the occurrence ratio, duration, maximum shear force, and transported momentum values of the sweep event in the trough areas are all larger, but the period value is smaller. These differences in flow field characteristics resulted in more intense particle motion at sand troughs and smoother motion at sand ridges, ultimately leading to the formation of sand troughs and sand ridges on the bed surface. 4)Analysis of the streaky structures of bedload motion intensity, sand trough and ridge structures, and bursting phenomena in corresponding topographies showed that the results aligned with the large-scale streamwise vortex model hypothesis rather than the secondary flow hypothesis. This finding suggests that turbulent coherent structures, bedload motion, and topography interact and mutually constrain each other, resulting in the phenomenon of time-averaged sand band structures. In conclusion, this stduy provides a comprehensive understanding of the coupling relationship between turbulent structures, sediment motion, and riverbed structures. By studying these interactions, the study offers valuable insights into the dynamics of water and sediment transport, paving the way for future research in this field.http://jsuese.scu.edu.cn/thesisDetails#10.12454/j.jsuese.202400672image processingbed loadstreaky structureturbulent coherent structurestreamwise vortex model |
| spellingShingle | YAO Jiateng XIE Xiaoxi WANG Hao ZHAO Lin XIE Haonan ZHEN Rongtian Research on the Movement Patterns of Bed-load Streaky Structure Transport and the Mechanism of Fluid-solid Coupling 工程科学与技术 image processing bed load streaky structure turbulent coherent structure streamwise vortex model |
| title | Research on the Movement Patterns of Bed-load Streaky Structure Transport and the Mechanism of Fluid-solid Coupling |
| title_full | Research on the Movement Patterns of Bed-load Streaky Structure Transport and the Mechanism of Fluid-solid Coupling |
| title_fullStr | Research on the Movement Patterns of Bed-load Streaky Structure Transport and the Mechanism of Fluid-solid Coupling |
| title_full_unstemmed | Research on the Movement Patterns of Bed-load Streaky Structure Transport and the Mechanism of Fluid-solid Coupling |
| title_short | Research on the Movement Patterns of Bed-load Streaky Structure Transport and the Mechanism of Fluid-solid Coupling |
| title_sort | research on the movement patterns of bed load streaky structure transport and the mechanism of fluid solid coupling |
| topic | image processing bed load streaky structure turbulent coherent structure streamwise vortex model |
| url | http://jsuese.scu.edu.cn/thesisDetails#10.12454/j.jsuese.202400672 |
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