一种无干扰全流程水深测试方法及其在溃坝水流试验研究中的应用
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摘要
基于MATLAB图像处理和计算机视觉模块函数库,开发了一种无干扰全流程水深测试方法:首先利用Camera Calibration工具箱标定摄像机以得到标定代码;其次,将记录水流运动的视频文件逐帧保存,利用标定代码消除每帧图片中由于广角镜头产生的桶形畸变,并对图片灰度化和二值化,同时加入中值滤波消除噪声;最后,读取二值图黑色像素点,将其转换为实际水深,从而获取其时空分布特性。运用该方法对强非恒定流–溃坝水流进行了试验测量,研究工况为上游水深500 mm,水深比(初始时刻下游与上游水深之比)为0～0.9。观测发现,溃坝水流可大致分为3种演进模式:简单波(水深比为0)、间断波(水深比为0～0.4)、起伏波(水深比为0.4～1.0)。分别选取3种典型工况(水深比为0、0.3、0.6)数据与波高仪测量结果进行了对比,结果表明,除上下游静水区二者数据吻合良好外,下游水面光滑平顺的渐变流区、激波前锋与下游出现强间断的激波区及水面起伏明显的起伏波区,波高仪较图像技术都有不同程度的壅高,水流演进越剧烈,壅高越明显。本文建立的测量方法无需在水流中安放测量仪器,具有无侵入性,对流场无干扰,不仅能够获取全流程水深数据、重现水流完整演进过程,还能很好地捕捉到诸如水流跃起、翻滚、波动、空气卷吸等流态细节。另外,试验中保持稳定光照及染色浓度,有助于降低图片噪点、改善图片质量,从而进一步提高测量结果的精度。
Based on MATLAB image processing and computer vision module, this study developed a non-intrusive method to measure full-field water depth. First, the Camera Calibration toolbox was used to calibrate the camera to obtain the calibration code; Second, the experimental video which recorded water flow movement was saved frame by frame and the barrel distortion of each image caused by wide angle lens was eliminated by calibration code. Then the images were grayed and binarized, and the median filter was added to eliminate image noise; Finally, the number of black pixels in binary images was counted and converted to actual water depth to obtain its spatial and temporal distribution characteristics.This method was applied to experiment of intensively unsteady flow–dam-break flows, in which the upstream water depth was 500 mm and the depth ratio(ratio of initial downstream to upstream water depth) was from 0 to 0.9. The observation showed that dam-break flows could be roughly divided into three modes: simple wave(depth ratio was 0), discontinuity wave(depth ratio was from 0 to 0.4) and undulation wave(depth ratio was from 0.4 to 1.0). Three typical conditions(depth ratio was 0, 0.3, 0.6) were chosen to compare with the results of wave probe. The results showed that wave probe had larger values of water level when compared with image processing data in the gradually varying flow area with smooth water surface, the shock wave area with discontinuous water flowing between downstream and front of wave, and the rolling wave area with obvious fluctuations on water surface, except for the upstream and downstream areas where both results agreed well with each other. The more intensive the water flow was, the larger the differences were. There was no need to install intrusive measuring instruments in water channel by using this method, it could not only obtain full-field water depth and water evolution process completely, but also capture water details such as leap, tumbling, fluctuations and air entrainment. In addition, the stable lighting and dyeing concentration in the experiment could help reduce the image noise and improve the image quality, thus further improve the accuracy of measurement results.
Based on MATLAB image processing and computer vision module, this study developed a non-intrusive method to measure full-field water depth. First, the Camera Calibration toolbox was used to calibrate the camera to obtain the calibration code; Second, the experimental video which recorded water flow movement was saved frame by frame and the barrel distortion of each image caused by wide angle lens was eliminated by calibration code. Then the images were grayed and binarized, and the median filter was added to eliminate image noise; Finally, the number of black pixels in binary images was counted and converted to actual water depth to obtain its spatial and temporal distribution characteristics.This method was applied to experiment of intensively unsteady flow–dam-break flows, in which the upstream water depth was 500 mm and the depth ratio(ratio of initial downstream to upstream water depth) was from 0 to 0.9. The observation showed that dam-break flows could be roughly divided into three modes: simple wave(depth ratio was 0), discontinuity wave(depth ratio was from 0 to 0.4) and undulation wave(depth ratio was from 0.4 to 1.0). Three typical conditions(depth ratio was 0, 0.3, 0.6) were chosen to compare with the results of wave probe. The results showed that wave probe had larger values of water level when compared with image processing data in the gradually varying flow area with smooth water surface, the shock wave area with discontinuous water flowing between downstream and front of wave, and the rolling wave area with obvious fluctuations on water surface, except for the upstream and downstream areas where both results agreed well with each other. The more intensive the water flow was, the larger the differences were. There was no need to install intrusive measuring instruments in water channel by using this method, it could not only obtain full-field water depth and water evolution process completely, but also capture water details such as leap, tumbling, fluctuations and air entrainment. In addition, the stable lighting and dyeing concentration in the experiment could help reduce the image noise and improve the image quality, thus further improve the accuracy of measurement results.
引文
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[15]Chen Qiang,Zhu Lixin,Xia Deshen,et al.Image binarization based on canny’s operator[J].Journal of Computer-Aided Design&Computer Graphics,2005,17(6):1302-1306.[陈强,朱立新,夏德深,等.结合C-anny算子的图像二值化[J].计算机辅助设计与图形学学报,2005,17(6):1302-1306.]
[16]Lauber G,Hager W H.Experiments to dam-break wave:horizontal channel[J].Journal of Hydraul Research,1998,36(3):291-308.
[2]Zhou Zepei,Zeng Kankan,Wu Xiang,et al.Current situation and development of dam-break model experiment[J].Architectural Engineering Technology and Besign,2015(16):2192-2192.[周泽沛,曾侃衎,吴祥,等.溃坝模型试验研究的现状与发展[J].建筑工程技术与设计,2015(16):2192-2192.]
[3]Li Yun,Li Jun.Review of experimental study on dambreak[J].Advances in Water Science,2009,20(2):304-310.[李云,李君.溃坝模型试验研究综述[J].水科学进展,2009,20(2):304-310.]
[4]Liu Wenjun,Wang Bo,Zhang Jianmin,et al.Experimental study on dam-break flow under different upstream and downstream initial water depth[J].Advanced Engineering Sciences,2019,51(2):1-9.[刘文军,王波,张建民,等.上下游初始水深比对溃坝水流传播的影响研究[J].工程科学与技术,2019,51(2):1-9.]
[5]Song Jiajun,Wang Bo,Liu Wenjun,et al.Experimental study on up-downstream water depth and discharge characteristics of instantaneous collapse of gate[J].Water Resources and Power,2018,36(4):77-81.[宋家俊,王波,刘文军,等.水槽中闸门瞬时溃决时上下游水深及流量特性试验研究[J].水电能源科学,2018,36(4):77-81.]
[6]Aureli F,Maranzoni A,Mignosa P,et al.An image processing technique for measuring free surface of dam-break flows[J].Experiments in Fluids,2010,50(3):665-675.
[7]Soares-Fraz?o S.Experiments of dam-break wave over a triangular bottom sill[J].Journal of Hydraul Research,2007,45(Extra Issue):19-26.
[8]Stansby P K,Chegini A,Barnes T C D.The initial stages of dam-break flow[J].Journal of Fluid Mechanics,1998,374(370):407-424.
[9]Jouzdani A,Kabirisamani A R.Application of image processing method in experimental modeling of one dimension-al dam break wave[J].Advances in Applied Mechanics Research,2012:1193-1199.
[10]Kocaman S,Guzel H,Ozmen-Cagatay H.Investigation of dam-break flood waves in a dry channel with a hump[J].Journal of Hydro-Environment Research,2014,8(3):304-315.
[11]董长虹,赖志国,余啸海,等.Matlab图像处理与应用[M].北京:国防工业出版社,2004.
[12]Zhang Xi,Huang Liang,Xu Yang,et al.Application of camera calibration based on MATLAB calibration toolbox[J].Image Processing and Multimedia Technology,2011,30(14):31-33.[张曦,黄亮,徐洋,等.基于MATLAB中calibration toolbox的相机标定应用研究[J].图形、图像与多媒体,2011,30(14):31-33.]
[13]章毓晋.图象理解与计算机视觉[M].北京:清华大学出版社,2000.
[14]Sun Jinguang,Zhang Wenbin,Zhu Shian,et al.The realization and method of image gray processing[J].Journal of Liaoning Technical University(Natural Science),2002,21(3):340-341.[孙劲光,张文斌,朱世安,等.图象灰度的处理方法及实现[J].辽宁工程技术大学学报(自然科学版),2002,21(3):340-341.]
[15]Chen Qiang,Zhu Lixin,Xia Deshen,et al.Image binarization based on canny’s operator[J].Journal of Computer-Aided Design&Computer Graphics,2005,17(6):1302-1306.[陈强,朱立新,夏德深,等.结合C-anny算子的图像二值化[J].计算机辅助设计与图形学学报,2005,17(6):1302-1306.]
[16]Lauber G,Hager W H.Experiments to dam-break wave:horizontal channel[J].Journal of Hydraul Research,1998,36(3):291-308.
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