| CHENG Yongzhou,WANG Yongxue,JIANG Changbo,CHEN Chun. 2007. An experimental investigation of the velocity field under cnoidal waves over the asymmetric rippled bed. Acta Oceanologica Sinica, (1):130－139 |
| An experimental investigation of the velocity field under cnoidal waves over the asymmetric rippled bed |
| An experimental investigation of the velocity field under cnoidal waves over the asymmetric rippled bed |
| Received:May 20, 2006 Revised:October 25, 2006 |
| DOI： |
| Key words:ripple cnoidal wave velocity vortex |
| 中文关键词: ripple cnoidal wave velocity vortex |
| 基金项目: |
| Author Name | Affiliation | E-mail | | CHENG Yongzhou | State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China
Department of River and Ocean Engineering, Changsha University of Science and Technology, Changsha 410076, China | chengyongzhou@163.com | | WANG Yongxue | State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China | | | JIANG Changbo | Department of River and Ocean Engineering, Changsha University of Science and Technology, Changsha 410076, China | | | CHEN Chun | Department of River and Ocean Engineering, Changsha University of Science and Technology, Changsha 410076, China | |
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| Abstract: |
| The evolution of an initially flat sandy bed is studied in a laboratory wave flume under cnoidal waves and acoustic Doppler velocimeter (ADV) was utilized in the detailed velocity measurements at different positions.The ripple formation and evolution have been analyzed by CCD images and the asymmetric rippled bed is induced by the nonlinear wave flow.The flow structure and a complete process of vortex formation, evolvement and disappearance were observed on the asymmetric rippled bed under cnoidal waves.With the increasing nonlinearity of waves, which is an important factor in the sand ripple formation, the vortex intensity becomes stronger and shows different characteristics on both sides of the ripple crest.The vorticity and wave velocity reach their maximum values at different phase angles.The vortex value reaches the maximum value at a small phase angle with the increasing Ursell number.The near bed flow patterns are mainly determined by the ripple forms and the averaged longitudinal velocity over a wave period above the ripple trough and crest are positive, which indicates the possibility of significant onshore sediment transport and a corresponding ripple drift.The phase averaged vertical velocity has noticeable positive values near the bottom of the ripple crest and trough.Sediments may be lifted from the ripple surface, picked up in suspension by the local velocity, and deposited over the crest and on the lee of the ripples. |
| 中文摘要: |
| The evolution of an initially flat sandy bed is studied in a laboratory wave flume under cnoidal waves and acoustic Doppler velocimeter (ADV) was utilized in the detailed velocity measurements at different positions.The ripple formation and evolution have been analyzed by CCD images and the asymmetric rippled bed is induced by the nonlinear wave flow.The flow structure and a complete process of vortex formation, evolvement and disappearance were observed on the asymmetric rippled bed under cnoidal waves.With the increasing nonlinearity of waves, which is an important factor in the sand ripple formation, the vortex intensity becomes stronger and shows different characteristics on both sides of the ripple crest.The vorticity and wave velocity reach their maximum values at different phase angles.The vortex value reaches the maximum value at a small phase angle with the increasing Ursell number.The near bed flow patterns are mainly determined by the ripple forms and the averaged longitudinal velocity over a wave period above the ripple trough and crest are positive, which indicates the possibility of significant onshore sediment transport and a corresponding ripple drift.The phase averaged vertical velocity has noticeable positive values near the bottom of the ripple crest and trough.Sediments may be lifted from the ripple surface, picked up in suspension by the local velocity, and deposited over the crest and on the lee of the ripples. |
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