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  • 1.
    Bilal, Ahmed
    et al.
    College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing, China.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    The Numerical Study of Open Channel Junctions with Extreme Confluence Angles for Surface Flow Without Wall Roughness2019Inngår i: E-proceedings of the 38th IAHR World Congress, International Association for Hydro-Enviroment Engineering and Research (IAHR) , 2019, s. 3620-3626Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Confluences exist not only in nature, like in streams or rivers but also constructed environment like the structures for sewage and urban rainfall drainage canals. In the natural environment, two tributaries join at an angle from 30° to 135°. Existing related research focuses on tributary angels within this mentioned range. However, in the constructed environment, channel junctions with its angle beyond this range may occur. Hydrodynamic data from a 90-degree flume confluence is taken from experiments, available in the literature. The information is used to build a numerical model on Delft 3D. The similar flow parameters are used, with the comparable cross-sectional dimensions, with three confluence geometries. Firstly, two confluences with a junction-angle of 0°, and then with an angle of 180° are studied, each with three flow cases. Free slip condition is supplied to elude the effect of wall roughness on flow behavior. Interesting results have been found and presented. It is noticed that geometries affect the location of vertical velocity and velocity distribution in the confluence area. The 180° confluence shows a big stagnation zone in the angled tributary. This study improves the understanding of the interaction between flow dynamics and confluence angles better.

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  • 2.
    Bilal, Ahmed
    et al.
    College of Water Conservancy and Hydropower Engineering, Hohai University (HHU), Nanjing 210098, China.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Zhai, Yanyan
    Division of Fluid Mechanics, Coastal and Maritime Engineering, Technical University of Denmark (DTU), 2800 Kgs, 2800 Lyngby, Denmark .
    Flow, Sediment, and Morpho-Dynamics of River Confluence in Tidal and Non-Tidal Environments2020Inngår i: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 8, nr 8, artikkel-id 591Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    River confluences are the key features of the drainage basins, as their hydrological, geomorphological, and ecological nature strongly influences the downstream river characteristics. The river reaches near the coastal zones, which also makes them under the influence of tidal currents in addition to their runoff. This causes a bi-directional flow and makes the study of confluences more interesting and complex in these areas. There is a reciprocal adjustment of flow, sediment, and morphology at a confluence, and its behaviors, differ greatly in tidal and non-tidal environments. Existing studies of the river junctions provide a good account of information about the hydrodynamics and bed morphology of the confluent areas, especially the unidirectional ones. The main factors which affect the flow field include the angle of confluence, flow-related ratios (velocity, discharge, and momentum) of the merging streams, and bed discordance. Hydraulically, six notable zones are identified for unidirectional confluences. However, for bi-directional (tidal) junctions, hydrodynamic zones always remain in transition but repeat in a cycle and make four different arrangements of flow features. This study discusses the hydrodynamics, sediment transport, morphological changes, and the factors affecting these processes and reviews the recent research about the confluences for these issues. All of these studies provide insights into the morpho-dynamics in tidal and non-tidal confluent areas.

    Fulltekst (pdf)
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  • 3.
    Burman, Anton
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andersson, Anders G.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ecohydraulical Applications and Limitations of Calibrated Numerical 2D Models2022Inngår i: Proceedings of the 39th IAHR World Congress: From Snow To Sea / [ed] Miguel Ortega-Sánchez, International Association for Hydro-Environment Engineering and Research (IAHR) , 2022, s. 1557-1564Konferansepaper (Fagfellevurdert)
    Fulltekst (pdf)
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  • 4.
    Dai, Wenhong
    et al.
    State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing China; College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing, China; National Engineering Research Center of Water Resources Efficient Utilization and Engineering Safety, China.
    Bilal, Ahmed
    College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing, China.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ahmad, Ijaz
    Centre of Excellence in Water Resources Engineering, University of Engineering and Technology, Lahore, Pakistan.
    Joshi, Ishwar
    Hydro Lab, Lalitpur, Nepal.
    Numerical Modeling for Hydrodynamics and Near-Surface Flow Patterns of a Tidal Confluence2020Inngår i: Journal of Coastal Research, ISSN 0749-0208, E-ISSN 1551-5036, Vol. 36, nr 2, s. 295-312Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Because of the flow influx of tributaries, a confluence forms a unique environment carrying interesting hydrodynamic features and other attributes. The understanding of flow behavior here is important, particularly if it is on a tidally influenced channel in a harbor metropolitan. Because of communal requirements, there is a possibility of building wading structures, which may interplay with the flow in this zone. The knowledge of unidirectional river or flume confluences so far is not readily applicable for similar features in channels near coastal areas that have tidal flow in addition to river runoff. In this study, a tidal confluence that has a highly dynamic bidirectional flow is investigated. Near-surface flow patterns in a tidal cycle are simulated by using a numerical model. A field survey provides the bathymetry, time-series boundary conditions, and corresponding verification data. Good agreement is reached between calculated and measured results. Based on the condition of tidal current, four scenarios are selected for which confluence flow patterns are observed, both spatially and temporally. The results indicate that at least one recirculation is always in the tidal confluence for all flow conditions, which rotates counterclockwise for the ebb flow and clockwise for the flood flow. In addition, there is no absolute slack water condition at the tidal junction in the study area. The study also finds that the flows of all three connected channels at the confluence change in a looped pattern with respect to one another. Furthermore, the study reports unique relationships among the ratios of different flows.

    Fulltekst (pdf)
    fulltext
  • 5.
    Dai, Wenhong
    et al.
    College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China. State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing 210098, China.
    Ding, Wei
    College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China.
    Lu, Chuanteng
    State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing 210098, China. Nanjing Hydraulic Research Institute, Nanjing 210029, China.
    Luo, Xiaofeng
    State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing 210098, China. Nanjing Hydraulic Research Institute, Nanjing 210029, China.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Field Investigations of Underwater Mounds Formed by Hopper Dredge Discharges in a Coastal Environment2020Inngår i: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 8, nr 6, artikkel-id 395Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In a coastal environment, this paper investigated the formation process and the cumulative shape of subaqueous mounds formed by hopper dredged discharges. Hydrological observations and field tests were performed to examine the flow features and ultimately generated morphology characteristics. A high-precision digital elevation model (DEM) was established by multi-beam depth sweeping (MBDS) in the experiment. Particular attention was paid to the formation of the mounds, the three-dimensional shape and the influence factors. The field measurements showed that the mounds were roughly symmetrical in space, and the tidal current, though of weak strength, played a certain role in shaping the profiles. Cone and volcanic cone mound tops were observed, featuring the main top shapes. The height and covered area of the mounds were proportional to the amount of dumped sediment, and they were also affected a lot by the water depth. The results of superimposed tests showed that the second placement over the existing mound resulted in a similar overall shape, but there was pronounced movement around the mound; additional discharged volumes at the same location mainly increased the mound height. The field tests provided a reference for understanding the sediment dumping in other similar coastal areas.

    Fulltekst (pdf)
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  • 6.
    Ding, Wei
    et al.
    Nanjing Hydraulic Research Institute, Nanjing 210029, China.
    Lu, Chuanteng
    Nanjing Hydraulic Research Institute, Nanjing 210029, China; State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing 210098, China.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Luo, Xiaofeng
    Nanjing Hydraulic Research Institute, Nanjing 210029, China; State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing 210098, China.
    Zhang, Gongjin
    Nanjing Hydraulic Research Institute, Nanjing 210029, China.
    Understanding the Settling Processes of Dredged Sediment Disposed in Open Waters through Experimental Tests and Numerical Simulations2022Inngår i: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 10, nr 2, artikkel-id 220Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During dredging for subsea tunnels and pipelines, the dredged soil is typically dumped in a designated area. Understanding the settling behaviors of the dumped particles is essential for an accurate prediction of the resulting morphology. This study dealt with the settling processes in the open-water column by means of experimental tests and numerical simulations. Both quiescent and ambient current conditions were taken into account. Particular attention was paid to the induced flow patterns, descent sediment movement features and the resulting topography. Regarding the diffusion width and settling velocity, three key effect factors, i.e., dumped volume, particle size and ambient flow strength, were considered. The results show that the dumped sediment in the water forms a particle cloud, and two vortices with opposite rotations occur on both sides of the cloud. During settlement, three stages corresponding to convective descent, dynamic collapse and passive diffusion are observed. Most of the descending sediment is incorporated in a spherical vortex, resembling an upside-down mushroom cloud, and some sediment is also contained in an irregular trailing stem. The dumped particles exhibit initial acceleration, and then they slow down to converge to a fixed value. Subjected to the ambient currents, the initial acceleration phase is prolonged, and the vortex is somewhat distorted; the particle cloud is also advected downstream with a velocity roughly equal to the ambient current.

    Fulltekst (pdf)
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  • 7.
    Li, Shicheng
    et al.
    Department of Civil and Architectural Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Yang, James
    Department of Civil and Architectural Engineering, KTH Royal Institute of Technology, Stockholm, Sweden; Vattenfall AB, R&D Hydraulic Laboratory, Älvkarleby, Sweden .
    Daily suspended sediment forecast by an integrated dynamic neural network2022Inngår i: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 604, artikkel-id 127258Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Suspended sediment is of importance in river and dam engineering. While, due to its high nonlinearity and stochasticity, sediment prediction by conventional methods is a challenging task. Consequently, this paper establishes a new hybrid model for an improved forecast of suspended sediment concentration (SSC). It is a nonlinear autoregressive network with exogenous inputs (NARX) integrated with a data pre-processing framework (denoted as INARX). In this model, wavelet transformation (WT) is used for time series decomposition and multigene genetic programing (MGGP) for details scaling. The two incorporated modules improve time and frequency domain analysis, allowing the network to unveil the embedded characteristics and capture its non-stationarity. At a hydrological station on the upper reaches of the Yangtze River, the records of daily water stage, flow discharge and suspended sediment are collected and refer to a nine-year period during 2004-2012. The data are used to evaluate the models. Several wavelets are explored, showing that the Coif3 leads to the most accurate prediction. Compared to the sediment rating curve (SRC), the conventional MGGP, multilayer perceptron neural network (MLPNN) and NARX, the INARX demonstrates the best forecast performance. Its mean coefficient of determination (CD) increases by 7.7%-38.6% and the root mean squared error (RMSE) reduces by 15.1%-54.5%. The INARX with the Coif3 wavelet is further evaluated for flood events and multistep forecast. Under flood conditions, the model generates satisfactory results, with CD > 0.83 and 84.7% of the simulated data falling within the ±0.1 kg/m3 error. For the multistep forecast, at a one-week lead time, the network also yields predictions with acceptable accuracy (mean CD = 0.78). The model performance deteriorates if the lead time becomes larger. The established framework is robust and reliable for real-time and multistep SSC forecast and provides reference for time series modeling, e.g. streamflow, river temperature and salinity.

  • 8.
    Ren, Weichen
    et al.
    College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China.
    Wei, Jie
    Power China Zhongnan Engineering Corporation Limited, Changsha 410014, China.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Miao, Baoguang
    Power China Zhongnan Engineering Corporation Limited, Changsha 410014, China.
    Wang, Lijie
    Power China Zhongnan Engineering Corporation Limited, Changsha 410014, China.
    Experimental and Numerical Investigations of Hydraulics in Water Intake with Stop-Log Gate2020Inngår i: Water, E-ISSN 2073-4441, Vol. 12, nr 6, artikkel-id 1788Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A stop-log gate, installed in water intake of hydropower project, has become an effective facility in achieving selective withdrawal and temperature control for the sake of benefiting downstream ecosystems. Hence, it is of great importance to comprehensively explore the water intake hydraulics with the gate, not limited to some specific case studies. This study deals, through laboratory experiments and numerical simulations, with flow features of such a gate-functioned intake. The physical model test is used to validate the numerical simulation. Subsequently, a series of numerical cases considering different hydraulic and geometric conditions are performed to help look into the behaviors. Particular attention is paid to the flow regimes, head loss and flow velocity distributions. The results showcase the effect of the gate on the intake flow regime, and in terms of head loss and flow velocity distribution, the influences of the upstream water head, intake chamber width and withdrawal depth are revealed in detail. An empirical expression, with regard to the coefficient of head loss, is derived and validated by data from the available literature. Moreover, it is found that the maximum velocity at trash rack section is dependent exclusively on the relative withdrawal depth and always occurs at a certain height range above the gate. These results may provide a meaningful reference for the research of water intake with similar situations.

    Fulltekst (pdf)
    fulltext
  • 9.
    Teng, Penghua
    et al.
    Resources, Energy & Infrastructure, Royal Institute of Technology, 10044 Stockholm, Sweden.
    Yang, James
    Concrete Structures, Royal Institute of Technology, 10044 Stockholm, Sweden. Vattenfall AB, R&D Hydraulic Laboratory, 81426 Älvkarleby, Sweden..
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Improving Energy Dissipation of a Spillway with Structural Modifications2019Inngår i: E-proceedings of the 38th IAHR World Congress, International Association for Hydro-Enviroment Engineering and Research (IAHR) , 2019, s. 2531-2538Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The stilling basin of Rusfors spillway comprised a concrete frame with two supporting plates and a cover, which was probably constructed for timber floating but was not in use anymore. Abrasion damages occurred in the basin bottom due to the sediment carried by the bottom current. To safely discharge the updated design flood, removal of the structure was suggested to avoid further deterioration of the operation conditions. Physical model tests and CFD modelling were performed to help understand the flow behaviors in the basin. The studies show that, due to the concrete frame, strong surface currents prevail in the basin, with inefficient energy dissipation and accordingly large water-level fluctuations downstream. The supporting plates also lead to skewed bottom currents, which are the cause of the bottom damages. Together with the detruncation of the spillway crest, the removal of the frame results favorably in a typical hydraulic jump. As shown from both the physical and numbering modelling, the basin flow pattern and energy dissipation become satisfactory at the design flood.

    Fulltekst (pdf)
    fulltext
  • 10.
    Wang, Mingyang
    et al.
    School of Engineering and Materials Science, Queen Mary, University of London, UK.
    Avital, Eldad
    School of Engineering and Materials Science, Queen Mary, University of London, UK.
    Chen, Qingsheng
    College of Water Conservancy and Hydropower Engineering, Hohai University, China.
    Williams, John
    School of Engineering and Materials Science, Queen Mary, University of London, UK.
    Mi, Shuo
    School of Engineering and Materials Science, Queen Mary, University of London, UK.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    A Numerical Study on Suspended Sediment Transport in a Partially Vegetated Channel Flow2021Inngår i: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 599, artikkel-id 126335Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Turbulent structures generated by vegetation patches play a dominant role in the dispersion of suspended sediment, which in turn is of great significance for ecosystem cycling and river geomorphology development. High fidelity Large Eddy Simulations (LES) coupled with the Discrete Phase Method (DPM) were used to explore the particle distribution and its variance (the non-uniformity in temporal and spatial space) in a partially vegetated straight channel. The novel findings and conclusions are outlined here. Firstly, the contour of the vertical vorticity component coincides well with particle preferential gatherings in the outer edge of the mixing layer in the near-bed region. Large-scale turbulent structures grow in mixing layer along the side of a vegetation patch (VP), which deplete particles away from the mixing layer into the neighbouring region. Also, higher vegetation densities (Dn) promote this depletion trend. Secondly, the Probability Density Function (PDF) and its variance were defined to quantify these phenomena, illustrating that the VP continuously interrupts the flow condition and promotes higher non-uniformity of particle distribution among the vegetated and non-vegetated regions. The variance of the PDF in the non-vegetated region is significantly higher than that in the neighbouring vegetated region located in the same streamwise location. The particle parcels are highly unevenly located along the periphery of the large eddies and are exchanged by the mixing flow between the non-vegetated and vegetated regions. Finally, the vertical entrainment of particles occurs in the vegetated region of the present cases. This is because the horseshoe structures provide an upwards velocity for the current Dn conditions (Dn<0.1) and an increase of Dn (Dn<0.1) accelerates the upward suspension. These findings complete our understanding of particles’ transportation in both spanwise and vertical directions.

  • 11.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Field Measurements and Numerical Simulations of Sediment Transport in a Tidal River2019Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In a coastal area, an alluvial lowland river has a free connection with the open sea and its flow is bidirectional. The river basin is often highly urbanized since it hosts valuable ecosystems and natural resources. Along with the growing population, climate change and human activities (e.g., industrialization, agricultural expansion, and fishery industry) pose a significant threat to the health of the river, leading to an unbalance of the flow and the sedimentation and also a considerable degradation of water quality.

    With long-term alluvial processes, the river often displays patterns such as meandering, braided, straight, wandering and anastomosing. In addition to the irregular geometry and bathymetry, a tidal river is typically influenced by the freshwater-saltwater interplay, which makes the hydrodynamic processes and sediment transport patterns extremely complicated. For many tidal river systems, cohesive sediment transported with the tides plays an important role. This is not only because of its interaction with flow but also due to its link to bed deformation.

    In this thesis, field measurements and numerical simulations of flow and sedimentation in a system, including a confluence and a meandering reach are presented and discussed. The numerical simulations are performed with the Delft3D package, which allows a coupling between complex river geometry, the bathymetry, the flow and the sediment boundaries in one module. Two morpho-dynamic models, a 2D depth-averaged model for the confluence and a 3D model for the meandering reach, are set up to disclose the fluvial processes in respective area.

    The objective of this thesis is, by means of extensive field measurements and numerical simulations, investigate flow features and sediment movement patterns in a tidal river. A comparatively long-term river-bed change, including a scour-hole at the confluence and asymmetric cross-sections at the bends, are also examined. Based on the perturbation theory, an improved sediment carrying capacity formula is also derived being suitable for calculations in a tidal environment. This study explores the variability of sediment transport, and reveals the relationship between the flow velocity and suspended load influenced by both the run-off and the tides. Their interactions also generate a different morphological regime as compared to a non-tidal river reach.

    This research may support a decision‐making process when considering the integrated tidal river management and it also provides a reference for other similar situations. The calibrated and validated model may therefore be a powerful tool for managers or researchers.

    Fulltekst (pdf)
    fulltext
  • 12.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Field Measurements and Predictions of River Flow, Sediment Transport and Morphological Changes2021Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In an alluvial lowland river, sediment is transported in the form of suspended and bed loads. The fluvial process is the macroscopic view and long-term consequence of sediment movement. The river frequently adjusts its cross-section, longitudinal profile, course of flow and pattern through the natural process of sediment transport, scour and deposition. Anthropogenic factors, e.g., river damming, channelization and other wading projects, also modify the natural processes. With long-term alluvial changes, the river often exhibits patterns such as meandering, braiding and wandering. If the river course has a free connection with open sea, its flow is often bi-directional. The river is typically influenced by the interplay between the runoff and tides, which makes the behaviours of flow and sediment transport extremely complicated.

    By combining field measurements, numerical simulations, physical model tests and machine learning techniques, this research investigates the fluvial river dynamics and processes, paying attention to the flow patterns, bed shear stresses, steady and unsteady sediment transport and morphological changes. Measurements of flow and sediment, and mapping of bathymetry in both tidal and non-tidal river systems, are presented and discussed. Based on field data, 2D and 3D numerical simulations are performed with the open source code Delft3D, allowing a couped modelling between complex river geometry, bathymetry, and flow and sediment boundaries. A hybrid approach of physical and numerical simulations is adopted for examination of reservoir sedimentation issues, in which both suspended and bed load transport are taken into account. A machine learning method is also applied for predications of suspended load in a river.  

    In a tidal river including a confluence and meander reach, the research elucidates the interplay between freshwater flows and tidal currents. This discloses the circulatory patterns of suspended load transport during the tidal rising and falling. From the interplay also the bed scour changes of hole at the confluence and asymmetric cross-sectional changes at the bends are illustrated. In addition, it is shown that the shifting tidal directions result in a migration of erosion and deposition in both directions, which does not exist in unidirectional runoff flows. The flood tides govern sediment transport and deposition, while the ebb tides with run-offs lead to erosion. Based on the perturbation theory, an improved sediment carrying capacity formula is also derived, suitable for calculations in a tidal environment.

    At a diffluence-confluence unit, the flow and sediment characteristics and the resulting bed changes are examined. The results indicate that incoming flow variations have a bearing on the diffluence flow partition. Secondary flow structures are found to be more influenced by the thalweg curvature than the flow division. The ‘inlet step’ or differential topography contributes to the unequal flow division. In the confluence, a two-cell flow structure coexists, which may diminish along with the dynamical adjustment of the two merging flows. The classical bed discordance is also observed.

    Based on extensive recorded hydrologic data and surveyed bathymetries, the sedimentation of the 500-km Lower Yangtze River reach is elucidated before and after the commissioning of the Three Gorges dam. The analyses demonstrate that the impoundment modulates the seasonal flow discharges and traps an appreciable amount of sediment, resulting in enhanced erosion potential and coarsening of sediment. The reach has not yet achieved a hydro-morphological equilibrium; the riverbed down-cutting is supposed to continue for some years and the noticeable sediment reduction from upstream is the extrinsic cause for the bed erosion. 

    Some river training measures, e.g., training wall at the diffluence and guide vanes in the reservoir, are employed to modify flow patterns and sediment transport. With proper training wall layout, acceptable flow patterns are achieved in the diffluence and the branch flow efficiently is increased. With respect to the layout of the vanes, 15º‒20º is suitable under typical operating conditions. The vanes modify effectively the flow patterns and suppress the flow circulations, leading to less sedimentation and enhancing the sediment flushing efficiency. 

    In overall, this research provides support a decision-making process when considering the integrated river management and it also provides reference for other similar situations. 

    Fulltekst (pdf)
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  • 13.
    Xie, Qiancheng
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Joshi, Ishwar
    Hydro Lab, 21093 Lalitpur, Nepal.
    Yang, James
    Concrete Structures, Royal Institute of Technology, 10044 Stockholm, Sweden.Vattenfall AB, R&D Hydraulic Laboratory, 81426 Älvkarleby, Sweden.
    River-Bed Down-Cutting Equilibrium of a Reach on Yangtze River2019Inngår i: E-proceedings of the 38th IAHR World Congress, International Association for Hydro-Enviroment Engineering and Research (IAHR) , 2019, s. 1850-1857Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The Three Gorges Project (TGP) introduces significant flow and sediment variations after its impoundment, due to which remarkable geomorphic adjustments prevail in the Jingjiang reach of the middle Yangtze River. The present study deals with the hydro-morphological equilibrium, considering both the dam operation and large-scale bank protection works along the reach. Based on available data, the equilibrium is, by means of a regime-based approach of maximum flow efficiency, analysed for the reach. The study shows that the flow discharge of the reach has not changed considerably after the TGP impoundment in 2003. After the impoundment, the suspended load into the reach descends drastically and but comes to a relatively stable level after 2006. The reach had not come at a hydro-morphological equilibrium before 2012; there is seemingly a tendency to reach a new equilibrium with time. The maximum flow efficiency method is useful to explore equilibrium conditions of a large river if flow and sediment conditions are modified.

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  • 14.
    Xie, Qiancheng
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Yang, J.
    Division of Resources, Energy and Infrastructure, Royal Institute of Technology (KTH), Stockholm, Sweden; Vattenfall AB, Research and Development (R and D), Älvkarleby Laboratory, Älvkarleby, Sweden.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Dai, W.
    College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing, China.
    Understanding morphodynamic changes of a tidal river confluence through field measurements and numerical modeling2018Inngår i: Water, E-ISSN 2073-4441, Vol. 10, nr 10, artikkel-id 1424Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A confluence is a natural component in river and channel networks. This study deals, through field and numerical studies, with alluvial behaviors of a confluence affected by both river run-offand strong tides. Field measurements were conducted along the rivers including the confluence. Field data show that the changes in flow velocity and sediment concentration are not always in phase with each other. The concentration shows a general trend of decrease from the river mouth to the confluence. For a given location, the tides affect both the sediment concentration and transport. A two-dimensional hydrodynamic model of suspended load was set up to illustrate the combined effects of run-offand tidal flows. Modeled cases included the flood and ebb tides in a wet season. Typical features examined included tidal flow fields, bed shear stress, and scour evolution in the confluence. The confluence migration pattern of scour is dependent on the interaction between the river currents and tidal flows. The flood tides are attributable to the suspended load deposition in the confluence, while the ebb tides in combination with run-offs lead to erosion. The flood tides play a dominant role in the morphodynamic changes of the confluence. 

  • 15.
    Xie, Qiancheng
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Yang, James
    Vattenfall AB, Älvkarleby; Royal Institute of Technology, Stockholm, Sweden.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Field Studies and 3D Modelling of Morphodynamics in a Meandering River Reach Dominated by Tides and Suspended Load2019Inngår i: Fluids, E-ISSN 2311-5521, Vol. 4, nr 1, artikkel-id 15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Meandering is a common feature in natural alluvial streams. This study deals with alluvial behaviors of a meander reach subjected to both fresh-water flow and strong tides from the coast. Field measurements are carried out to obtain flow and sediment data. Approximately 95% of the sediment in the river is suspended load of silt and clay. The results indicate that, due to the tidal currents, the flow velocity and sediment concentration are always out of phase with each other. The cross-sectional asymmetry and bi-directional flow result in higher sediment concentration along inner banks than along outer banks of the main stream. For a given location, the near-bed concentration is 2−5 times the surface value. Based on Froude number, a sediment carrying capacity formula is derived for the flood and ebb tides. The tidal flow stirs the sediment and modifies its concentration and transport. A 3D hydrodynamic model of flow and suspended sediment transport is established to compute the flow patterns and morphology changes. Cross-sectional currents, bed shear stress and erosion-deposition patterns are discussed. The flow in cross-section exhibits significant stratification and even an opposite flow direction during the tidal rise and fall; the vertical velocity profile deviates from the logarithmic distribution. During the flow reversal between flood and ebb tides, sediment deposits, which is affected by slack-water durations. The bed deformation is dependent on the meander asymmetry and the interaction between the fresh water flow and tides. The flood tides are attributable to the deposition, while the ebb tides, together with run-offs, lead to slight erosion. The flood tides play a key role in the morphodynamic changes of the meander reach.

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  • 16.
    Xie, Qiancheng
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Yang, James
    Vattenfall AB, R&D Hydraulic Laboratory, 81426 Älvkarleby, Sweden; Department of Civil and Architectural Engineering, Royal Institute of Technology, 10044 Stockholm, Sweden.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Chen, Jieren
    College of Water Conservancy and Hydropower Engineering, Hohai University, 210098 Nanjing, China.
    Hybrid Modeling for Solutions of Sediment Deposition in a Low-Land Reservoir with Multigate Sluice Structure2022Inngår i: Applied Sciences, E-ISSN 2076-3417, Vol. 12, nr 18, artikkel-id 9144Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    At the multigate sluice structure on a fluvial river, undesired sediment deposition affects the normal operation of the reservoir in question. Physical and numerical models are hybridized to help explore flow and sedimentation patterns. Field and laboratory investigations show that the deposition is attributable to the formation of large recirculation zones at low and medium discharges. As a potential countermeasure, an array of guide vanes is recommended to cope with the concern. Their attack angle with the flow is a dominant parameter that needs to be evaluated. Tests in the fixed-bed model demonstrate that the vanes bend the reservoir flow towards the sluice and suppress the circulation zones along both banks. The favorable range of attack angle is 15–20°. With the examination of sedimentation of both bed and suspended loads, the numerical modeling indicates that the sediment-removal efficiency increases with an increase in attack angle. By weighing the flushing efficiency and the risk of local scouring at the vanes, the 15° vane layout is recommended. This study is expected to provide a reference for guide-vane design in similar situations.

    Fulltekst (pdf)
    fulltext
  • 17.
    Xie, Qiancheng
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Yang, James
    Department of Civil and Architectural Engineering, Royal Institute of Technology, Stockholm, Sweden. Vattenfall AB, R&D Hydraulic Laboratory, Älvkarleby, Sweden.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Flow and Sediment Behaviours and Morpho-dynamics of a Diffluence−Confluence Unit2020Inngår i: Rivers Research and Applications: an international journal devoted to river research and management, ISSN 1535-1459, E-ISSN 1535-1467, Vol. 36, nr 8, s. 1515-1528Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A diffluence‐confluence unit is an elementary component within a river system and presents a complex yet linked pattern of both flow and sediment transport in between. This study deals, by means of field investigations and numerical modelling, with morpho‐dynamics of such a unit on the lower Yangtze River reaches. The unit comprises, looking downstream, a secondary (left) course and a main (right) course. Field surveys are performed for measurements of flow discharge, sediment loads at selected locations and river bathymetry at certain intervals. The field data show that the reach is mainly composed of suspended load, whose amount exhibits a declining trend with the elapse of time. Simulations in 3D are made to complement the field data and clarify the basic features of the unit, especially the partitioning of flow and suspended sediment in the diffluence and their subsequent reciprocal adjustment in the confluence. The results indicate that approach flow variations have a bearing on the diffluence flow partition. To augment flow discharge in the left branch, a training wall is devised in the diffluence to modify the intake flow. Secondary flow structures are found to be more influenced by the thalweg curvature than the flow division. The “inlet step” or differential topography contributes to the unequal flow division. In the confluence, a two‐cell flow structure coexists, which may diminish along with the dynamical adjustment of the two waters. The classical bed discordance is also observed. With the typical flow and sediment features, the main course is prone to slight erosion, while the secondary branch faces up with gradual siltation. These findings contribute to the understanding of the alluvial behaviours of such units, and provide reference for studies in similar situations and river management.

  • 18.
    Xie, Qiancheng
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Yang, James
    Concrete Structures, Royal Institute of Technology; Vattenfall AB, R&D Hydraulic Laboratory.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Perturbation Theory and Sediment Carrying Capacity of Suspended Load in a Tidal River2019Konferansepaper (Fagfellevurdert)
    Fulltekst (pdf)
    fulltext
  • 19.
    Xie, Qiancheng
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Yang, James
    R&D Hydraulic Laboratory, Vattenfall AB, 81426, Älvkarleby, Sweden; Civil and Architectural Engineering, Royal Institute of Technology, 10044, Stockholm, Sweden.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sediment and morphological changes along Yangtze River’s 500 km between Datong and Xuliujing before and after Three Gorges Dam commissioning2021Inngår i: Scientific Reports, E-ISSN 2045-2322, Vol. 11, artikkel-id 13662Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The impoundment of the Three Gorges Dam on the Yangtze River begins in 2003 and a full pool level is first attained in 2010. This process leads to reciprocal adjustments in flow discharge, sediment transport and morphology downstream of the dam. Based on 26-year recorded hydrologic data 1990–2015 and surveyed bathymetries 1998, 2010 and 2015, this study elucidates, before and after the commissioning of the dam, the alterations along the 500-km reach of the river. Two-dimensional numerical simulations are performed to predict future morphological changes by 2025. The analyses demonstrate that the impoundment modulates the seasonal flow discharges and traps an appreciable amount of sediment, resulting in enhanced erosion potential and coarsening of sediment. On a multi-year basis, the maximum discharge varies by a factor of 1.3 and the corresponding suspended load concentration and transport rate differ by a factor of 3.0 and 3.8, respectively. Combinations of surveyed and simulated bathymetries reveal its morphological responses to the changes. A general pattern of erosion is observed along the reach. In its upper 120 km, the process slows down towards 2025. In the middle 200 km, the erosion shifts, following the gradual impounding, to slight deposition, which then shifts back to erosion around September 2018. In the final 180 km, erosion continues without any sign of de-escalation, which is presumedly ascribed to tidal actions. The reach has not yet achieved a hydro-morphological equilibrium; the riverbed down-cutting is supposed to continue for a while. The combination of the field and numerical investigations provides, with the elapse of time, insight into the morpho-dynamics in the 500 km river reach.

    Fulltekst (pdf)
    fulltext
  • 20.
    Yang, James
    et al.
    Vattenfall AB, Research & Development (R & D), Hydraulic Laboratory, Älvkarleby, Sweden;Division of Resources, Energy & Infrastructure, Royal Institute of Technology, Stockholm, Sweden.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Vattenfall AB, Research & Development (R & D), Hydraulic Laboratory, Älvkarleby, Sweden.
    Teng, Penghua
    Division of Resources, Energy & Infrastructure, Royal Institute of Technology, Stockholm, Sweden.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    The Past and Present of Discharge Capacity Modeling for Spillways: A Swedish Perspective2019Inngår i: Fluids, E-ISSN 2311-5521, Vol. 4, nr 10, artikkel-id 4010010Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most of the hydropower dams in Sweden were built before 1980. The present dam-safety guidelines have resulted in higher design floods than their spillway discharge capacity and the need for structural upgrades. This has led to renewed laboratory model tests. For some dams, even computational fluid dynamics (CFD) simulations are performed. This provides the possibility to compare the spillway discharge data between the model tests performed a few decades apart. The paper presents the hydropower development, the needs for the ongoing dam rehabilitations and the history of physical hydraulic modeling in Sweden. More than 20 spillways, both surface and bottom types, are analyzed to evaluate their discharge modeling accuracy. The past and present model tests are compared with each other and with the CFD results if available. Discrepancies do exist in the discharges between the model tests made a few decades apart. The differences fall within the range −8.3%–+11.2%. The reasons for the discrepancies are sought from several aspects. The primary source of the errors is seemingly the model construction quality and flow measurement method. The machine milling technique and 3D printing reduce the source of construction errors and improve the model quality. Results of the CFD simulations differ, at the maximum, by 3.8% from the physical tests. They are conducted without knowledge of the physical model results in advance. Following the best practice guidelines, CFD should generate results of decent accuracy for discharge prediction.

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  • 21.
    Yang, James
    et al.
    Division of Resources, Energy & Infrastructure, Royal Institute of Technology (KTH), Stockholm, SwedenDivision of Resources, Energy & Infrastructure, Royal Institute of Technology (KTH), Stockholm, Sweden. Vattenfall R&D, Älvkarleby Hydraulic Laboratory, Älvkarleby, Sweden.
    Teng, Penghua
    Division of Resources, Energy & Infrastructure, Royal Institute of Technology (KTH), Stockholm, Sweden.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Modelling of air demands of a spillway aerator with two-phase flow models2018Inngår i: E-proceedings of the 2nd International Symposium on Hydraulic Modelling and Measuring Technology Congress, International Association for Hydro-Enviroment Engineering and Research (IAHR) , 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Air demand is an issue of concern for a spillway aerator. To numerically map its air-water flow behavior has a bearing on its design. The recently completed spillway at Bergeforsen features a 35-m wide chute aerator with 13 air vents. With this in background, CFD modelling is performed with three commonly used two-phase flow models, i.e. the Volume-of-Fluid (VOF) Model, Two-Fluid Model and Mixture Model. The purpose is to evaluate these models in terms of water-air flow properties. The simulations have shown that the VOF Model generates the lowest air demand, while the Two-Fluid Model points to a 34% higher value, which is attributable to the differences in the two-phase flow formulations. The resulting air pressure in the air cavity including the air groove leads also to considerable discrepancy in the vent air-flow distribution across the chute and spatial air concentration. Evaluations of two-phase models are necessary, so that a reliable model is adopted for engineering design.

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    fulltext
  • 22.
    Yang, James
    et al.
    Vattenfall, R&D Hydraulic Laboratory, Älvkarleby, Sweden; Civil and Architectural Engineering, Royal Institute of Technology, Stockholm, Sweden .
    Teng, Penghua
    Civil and Architectural Engineering, Royal Institute of Technology, Stockholm, Sweden .
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Li, Shicheng
    Civil and Architectural Engineering, Royal Institute of Technology, Stockholm, Sweden .
    Understanding Water Flows and Air Venting Features of Spillway: a Case Study2020Inngår i: Water, E-ISSN 2073-4441, Vol. 12, nr 8, artikkel-id 2106Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For safe spillway discharge of floods, attention is paid to the water flow. The resulting air flow inside the facility, an issue of personnel security, is sometimes disregarded. The spillway in question comprises two surface gates and two bottom outlet gates lying right below. Air passages to the outlet gates include an original gallery and a recently constructed vertical shaft. To understand water-air flow behavior, 3D CFD modelling is performed in combination with the physical model tests. The simulations are made with fully opened radial gates and at the full pool water level (FPWL). The results show that the operation of only the bottom outlets leads to an air supply amounting to ~57 m3/s, with the air flow rates 35 and 22 m3/s to the left and right outlets. The air supply to the right outlet comes from both the shaft and the gallery. The averaged air velocity in the shaft and the gallery are approximately 5 and 7 m/s. If only the surface gates are fully open, the water jet impinges upon the canal bottom, which encloses the air space leading to the bottom outlets; the air flow rate fluctuates about zero. If all the four gates are open, the total air demand is limited to ~10 m3/s, which is mainly attributable to the shear action of the meeting jets downstream. The air demand differs significantly among the flow cases. It is not the simultaneous discharge of all openings that results in the largest air demand. The flood release from only the two outlets is the most critical situation for the operation of the facility. The findings should provide reference for spillways with the same or similar layout

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