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Mechanism of back siltation in navigation channel in Dinh An Estuary, Vietnam

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Water Science and Engineering 2013年第2期6卷 178-188页

作者： Viet-Thanh NGUYEN jin-hai zheng Ji-sheng ZHANG State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai University College of Harbor Coastal and Offshore Engineering Hohai University Faculty of Civil Engineering University of Transport and Communications

The Dinh An Estuary is one of the Nine Dragon estuaries of the Mekong River. An international navigation channel was built in the estuary for vessels traveling from the South China Sea to the southwestern area of Vietnam and then to Phnom Penh, Cambodia. The morphological evolution of the navigation channel is complicated and unstable. The back siltation intensity in the navigation channel has largely increased and been concentrated in the curvature segments of the channel since 1980. In this study, based on simulation results and measured data, five key factors that influence the back siltation in the navigation channel were systematically analyzed. These factors included the increasing elevation gap between the channel and the nearby seabed, the disadvantageous hydrodynamic conditions, sediment transport, mixing of saltwater and freshwater, and wave effects in the navigation channel. It is shown that the back siltation to a large extent results from the low current velocity of the secondary ocean circulation, which often occurs in the curvature segments of the channel. Suspended sediment also settles in the channel due to the decrease of the current velocity and the sediment transport capacity when flow passes through the channel. The changes of hydrodynamic conditions are responsible for the majority of the severe siltation in the curvature segments of the navigation channel.

关键词： back siltation hydrodynamics navigation channel, sediment transport Dinh An Estuary

Numerical simulation of typhoon-induced storm surge along Jiangsu coast,PartⅡ:Calculation of storm surge

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Water Science and Engineering 2017年第1期10卷 8-16页

作者： jin-hai zheng jin-cheng Wang Chun-yan Zhou Hong-jun Zhao Sang Sang Key Laboratory of Coastal Disaster and Defence(Hohai University) Ministry of EducationNanjing 210098China College of Harbor Coastal and Offshore Engineering Hohai UniversityNanjing 210098China

The Jiangsu coastal area is located in central-eastern China and is well known for complicated dynamics with large-scale radial sand ridge systems. It is therefore a challenge to simulate typhoon-induced storm surges in this area. In this study, a two-dimensional astronomical tide and storm surge coupling model was established to simulate three typical types of typhoons in the area. The Holland parameter model was used to simulate the wind field and wind pressure of the typhoon and the Japanese 55-year reanalysis data were added as the background wind field. The offshore boundary information was provided by an improved Northwest Pacific Ocean Tide Model. Typhoon-induced storm surges along the Jiangsu coast were calculated based on analysis of wind data from 1949 to 2013 and the spatial distribution of the maximum storm surge levels with different types of typhoons, providing references for the design of sea dikes and planning for control of coastal disasters.

关键词： Jiangsu coast Typhoon-induced storm surge Numerical simulation Holland parameter model ADCIRC

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Actuator line method flow structures and morphology interaction around a monopile-supported tidal stream turbine using the actuator line–Sediment transport coupling simulation

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Journal of Hydrodynamics 2024年第4期36卷 693-705页

作者： Xiang-feng Lin Ji-sheng Zhang jin-hai zheng Da-wei Guan Xu Deng College of Harbor Coastal and offshore EngineeringHohai UniversityNanjing210098China Key Laboratory of Coastal Disaster and Defence Ministry of EducationHohai UniversityNanjing210098China

Marine turbines have been extensively utilized to harness tidal stream energy from free-flowing tides and currents. However, the assessment of the influences of these marine structures on the surrounding environment is still in its early stage. In this study, a numerical model that couples hydrodynamics and sediment transport is developed to simulate the scour processes around a monopile-supported horizontal axial tidal stream turbine under steady currents. The flow characteristics are calculated by solving the 3-D Navier-Stokes equations with the k -ω shear stress transport (SST) turbulence model for closure. The simulation of sediment bed elevation is achieved by solving the Exner equation. The turbine rotor is parameterized using the actuator line method. The developed model is validated against wake velocity and scour depth measurement obtained from previous literature, showing a good agreement. Subsequently, the effects of tip clearance on the flow characteristics around the turbine model on a rigid flatbed are examined. Finally, the scour processes of the turbine model are presented, along with the vortex system within the scour hole. The numerical model proposed in this study has the potential to contribute to the understanding of the scour mechanism of the tidal stream turbines.

关键词： Tidal stream turbines hydrodynamics sediment transport numerical simulation

Preface for special issue on local scour and soil liquefaction around offshore windfarm foundations

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Water Science and Engineering 2022年第1期15卷 1-2页

作者： jin-hai zheng Ya-kun Guo Ji-sheng Zhang Da-wei Guan Key Laboratory of Ministry of Education for Coastal Disaster and Protection Hohai UniversityNanjing 210098China College of Harbour Coastal and Offshore EngineeringHohai UniversityNanjing 210098China Department of Civil and Structural Engineering University of BradfordBradford BD71DPUK

The offshore wind industry has been Hourishing globally over the past few decades because of the increasing demand for renewable *** types of foundations have been adopted,including monopiles,gravity・based structures,tripods,jackets,and pile groups for traditional offshore wind-farm foundations,as well as drag-embedment anchors(DEAs)with associated subsea structures(i.e.,tensioners,clump weights,and chains)for foundations of floating *** scour and liquefaction issues are significant to the security of offshore windfarm foundations and foundation stability(Guan et al.,2019;Whitehouse et al.,2011;Zhu et al.,2018).

关键词： scour offshore soil

The visualization of turbulent coherent structure in open channel flow

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Journal of Hydrodynamics 2019年第2期31卷 266-273页

作者： Xiao-dong Bai Wei Zhang Qing-he Fang Yong Wang jin-hai zheng An-xin Guo Ministry of Education Key Laboratory of Coastal Disaster and Defence Hohai UniversityNanjing 210098China College of Harbor Coastal and Offshore EngineeringHohai UniversityNanjing 21009China Science and Technology on Water Jet Propulsion Laboratory Marine Design and Research Institute of ChinaShanghai 200011China Ministry of Education Key Laboratory of Structural Dynamic Behavior and Control School of Civil EngineeringHarbin Institute of TechnologyHarbin 150090China Max Planck Institute for Dynamics and Self-Organization GottingenGermany

Due to its multiscale and multi-layer natures,the coherent structures of turbulent in the open channel flow is complex and difficult to be visualized for understanding its *** this paper,five types of methods for the vortical structure in the fluids,namely the Q-criterion,the vorticity,the Omega method,the velocity-vorticity correlation structures(VVCS)as well as the most recent Rortex method,are adopted to visualize the turbulent flow in the open *** the free surface modelled as a free slip boundary,a direct numerical simulation(DNS)is carried out to study the multi-layered flow structure characteristics under the free *** visualization results by the Q-criterion,the vorticity,the Omega method and the Rortex are firstly *** the turbulent flow layers near the free surface are identified with corresponding anisotropy ***,the VVCS within various turbulence layers are visualized *** research indicates that the VVCS can straightforwardly show the geometry information of the cohere nt structures of turbulent in different layers for the ope n channel flow.

关键词： Open channel flow flow visualization velocity-vorticity coherent structure direct numerical simulation(DNS)

Field observation of wave overtopping at sea dike using shore-based video images

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Journal of Hydrodynamics 2021年第4期33卷 657-672页

作者： Shan-hang Chi Chi Zhang Ti-ti Sui Zhu-bin Cao jin-hai zheng Jiang-shan Fan State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai UniversityNanjing210098China Key Laboratory of Ministry of Education for Coastal Disaster and Protection Hohai UniversityNanjing210098China College of Harbour Coastal and Offshore EngineeringHohai UniversityNanjing210098China Rizhao Port Group Co. Ltd.Rizhao276826China

Wave overtopping at a sea dike was observed using video images during a storm in July 2018 at Rizhao Coast,China.A shore-based video monitoring system was mounted to collect coastal images with a sample frequency of 1 Hz in the beginning 10 min of each hour during daylight.A method to extract the frequency,location,width and duration of individual overtopping events based on the shore-based video monitoring system was developed.A total of 6252 individual overtopping events were detected over a 360m long sea dike during the storm of 10 h in a safe and labor-saving way,enabling a detailed analysis of the temporal and spatial variation of wave *** temporal variation of overtopping duration,frequency and volume is basically in sync with the change of tidal level(R=0.87,0.82 and 0.76,respectively).The increase of wave height increases the overtopping frequency *** found a high correlation between the hourly observed data and the predicted results of two commonly used *** the previous field measurements of overtopping that were limited in a single location,significant spatial variation of overtopping in the alongshore direction is *** overtopping volume varies with a factor of 6 within the range of several wave *** is further revealed that the spatial variation of overtopping is highly correlated with the alongshore variation of surf zone width with a correlation coefficient of *** present study suggests the feasibility of shore-based video monitoring technique to capture the main features of wave overtopping at coastal dikes,providing new possibilities to monitor wave overtopping in the field and to improve prediction tools.

关键词： Wave overtopping coastal video monitoring field measurement temporal and spatial variations storm events

Remarks on Representations of Finite Groups over an Arbitrary Field of Characteristic Zero

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Journal of Mathematical Research and Exposition 2011年第3期31卷 437-442页

作者： jin Ke hai zheng Xing LI College of Mathematics Qingdao University Shandong 266071 P. R: China

Let G be a finite group and K a field of characteristic *** is well-known that if K is a splitting field for G,then G is abelian if and only if any irreducible representation of G has degree *** this paper,we generalize this result to the case that K is an arbitrary field of characteristic zero（that is,K need not be a splitting field for G）,and we also obtain the orthogonality relations of irreducible K-characters of G in this *** results generalize some well-known theorems.

关键词： ΓK-action ΓK-classes orthogonality relations.

Countermeasures for local scour at offshore wind turbine monopile foundations:A review

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Water Science and Engineering 2022年第1期15卷 15-28页

作者： Zi-hao Tang Bruce Melville Naresh Singhal Asaad Shamseldin jin-hai zheng Da-wei Guan Liang Cheng Department of Civil and Environmental Engineering The University of AucklandAuckland 1010New Zealand State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai UniversityNanjing 210098China College of Harbor Coastal and Offshore EngineeringHohai UniversityNanjing 210098China School of the Environment and Safety Engineering Jiangsu UniversityZhenjiang 212013China

Local scour at monopile foundations of offshore wind turbines is one of the most critical structural stability *** article reviews the contemporary methods of scour countermeasures at monopile *** methods include armouring countermeasures(e.g.,riprap protection)to enhance the anti-scour ability of the bed materials and flow-altering countermeasures(e.g.,collars and sacrificial piles)to reduce downflow or change flow patterns around the *** number and size-selection equations for riprap armour layers are summarised and ***,other alternative methods to riprap are briefly introduced and presented.A typical graph of the scour depth reduction with different collar sizes and elevations under specific test conditions is summarised and compared with a plot for a pile founded on a *** rates for different flow-altering countermeasures,including the collar,are listed and compared.A newly developed soil improvement method,namely microbially induced calcite precipitation(MICP),is also reviewed and introduced as a scour protection *** a popular bio-soil treatment method,MICP has a good potential as a scour countermeasure ***-soil treatment methods and traditional armouring methods are defined as active and passive soil enhancement scour countermeasures,respectively.

关键词： Wind turbine foundation Scour countermeasures Armouring countermeasures Flow-altering countermeasures MICP method

Hydrodynamic and morphological processes in Yangtze Estuary:State-of-the-art research and its applications by Hohai University

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Water Science and Engineering 2012年第4期5卷 383-398页

作者： jin-hai zheng Yi-xin YAN Chao-feng TONG Zhi-yi LEI Chi ZHANG State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai University College of Harbor Coastal and Offshore EngineeringHohai University

This paper presents a review of the state-of-the-art research and its applications developed at Hohai University relating to the hydrodynamic and morphological processes in the Yangtze Estuary. Longitudinal, lateral, and horizontal flow circulations have been revealed based on the measurements with acoustic Doppler current profilers （ADCP）. The hydrodynamic mechanism at diversion points as well as the changing patterns of flow and sediment flux in the Yangtze Estuary has been investigated through long-term data analysis. A field survey has been carried out to detect the saltwater intrusion from the North Branch to South Branch. Different numerical models of flow motion, sediment transport, and saltwater intrusion have been developed to simulate the complicated processes and to evaluate the effects of engineering projects. The morphological processes of wetlands over a time scale of decades have been analyzed with an established database. Ideas for further research on the bio-geomorphological model system and long-term evolution mechanisms are put forward.

关键词： Yangtze Estuary hydrodynamic process morphological process saltwater intrusion,Hohai University