Secondary Currents

The open-source finite-element system Telemac has been applied to simulate various complex hydrodynamic and morphodynamic situations including waterways, curved channels, recirculating flows and wave-induced littoral transport. In the applications presented here, the sediment transport model is mainly restricted to the transport of non-cohesive sediments, which relies on classical semi-empirical concepts including sand grading effects, parameterization of secondary currents and wave effects. In comparison with other comprehensive modeling systems (Delft-3D, Mike-21, etc.), the main originality lies in the efficiency and flexibility of the finite elements. Thanks to the optimization of numerical schemes, parallelism, as well as tremendous progress in the performance of computers, bed evolution can be calculated on basin scale (10-100 km) and for the medium term (years to decades), without the use of hydrodynamic filtering methods. As a novelty in release 6.0, we present a method of feedback for the bed roughness, which reduces uncertainty in the prediction of both transport rates and flow velocities.

A culvert is a covered channel designed to pass water through an embankment. The adverse ecological impacts of road crossings on upstream fish passage have driven the development of new design guidelines with a focus on small-bodied native fish species and juveniles of larger fish. Recent studies recommended the usage of low velocity zones (LVZ) in the culvert for upstream fish passage. To date, there is a limited knowledge on the hydrodynamics in the LVZ, particularly the turbulence characteristics, despite its relevance to fish kinematics. New research was carried out to study the turbulence and secondary motion in low velocity zone in a rectangular culvert. Detailed turbulence measurements were undertaken in a near full-scale box culvert barrel. Velocity and Reynolds stress measurements showed some strong secondary motion of Prandtl's second kind. The turbulent characteristics, including burst events and secondary currents, were carefully detailed, presenting a novel insight into the turbulence of fish's preferential swimming zone.

Quantifying turbulent fluxes and secondary structures in shallow channel flows is important for predicting momentum and mass transfer in rivers as well as channel capacity and associated water levels. Here, we focus on the flow over a lateral bed-roughness variation with very low relative submergence of the roughness elements, h∕k = {3, 2, 1.5} , where h is the flow depth and k is the roughness height. Measurements were performed in a 1.1 m wide and 26 m long glass flume whose bed was fitted with cubes arranged in two regular side-by-side patterns with frontal densities f = 0.2 and 0.4 to create a rough-to-rougher variation. Measurements were performed using stereoscopic PIV in two orthogonal planes, in a vertical transverse plane spanning the two roughness types, and in a longitudinal one at the interface between the roughness types. The results show that the bulk velocity difference between the two sides of the channel increases with decreasing h/k. Also, contrary to what is observed at high relative submergence with smooth-to-rough transitions, higher bulk velocities occur on the side with higher roughness. This difference is increasing as the flow becomes shallower and is shown to be due to increasing effective depths ratios, leading to increasingly lower friction factor ratios with lower friction factors on the high-velocity but rougher side. Although increasing streamwise momentum transfer at the interface is needed as h/k decreases, the turbulent and secondary circulation transfer of momentum is increasingly inhibited. A globally-driven secondary-circulation at h∕k = 3 ceases for lower h/k and roughness-scale circulation becomes dominant. Also, even the increased global shear does not lead to large-scale Kelvin Helmholtz instabilities structures. However, the relative importance of the roughness difference on the flow is augmented as the flow becomes shallower and momentum transfer due to lateral dispersive stresses increases.

Ramos and all others who not been specifically mentioned here. Special thanks to Carla Teixeira and to Maria da Luz Sousa for being not only good professionals but also good persons willing always to help and to listen. The last months were not easy for me…being far away from my beloved husband and daughter and finishing the PhD thesis, but I could always count on my friends Andrey Lyubchik and his gorgeous wife Elena Lygina. I'm very grateful to them for helping me with my daily problems in this difficult period of my life, for supporting and understanding. I would also like to express my deep gratitude to my parents in-law for their encouragement and believing in me. Undoubtely, the completion of this research would not have been possible without their support. At last but not least I would like to thank my husband Sergej for his love and care, patience, responsibility and understanding. Thank you for being tolerant when I was in a bad mood. You are the best husband and I'm so lucky to have you! Я тебя люблю! Very special thanks to my daughter Anastacia. When you smile my day becomes brighter and happier. You are my little sunshine. Thank you for being such a wonderful daughter! I love you, my beautiful princess Anastacia! iii

A culvert is a covered channel designed to pass water through an embankment. The adverse ecological impacts of road crossings on upstream fish passage has driven the development of new culvert design guidelines with a focus on small-bodied native fish species and juveniles of larger fish. Previous literatures focused on the usage of baffles and macro-roughness, although these can drastically reduce the discharge capacity of the culvert. Such approaches have raised concerns in relation to the total costs of these structures. Hence, new research was carried out with the aim of developing fish friendly box culverts without altering the design capacity. The study focused on the low velocity zones conducive of upstream fish passage. Detailed turbulence measurements were undertaken in a near full-scale box culvert barrel. Velocity and Reynolds stress measurements showed some strong secondary motion of Prandtl's second kind. The channel boundaries and bottom corners contributed to the occurrence of low-velocity zones. The characteristics of these low-velocity zones were carefully detailed. The results demonstrated how the bottom corners in standard box culvert barrel can induce a strong flow three-dimensionality, conducive of successful upstream passage of small-bodied fish.

To better understand the influence of non-uniform flow in coarse-bed streams with a submerged vegetation strip on flow characteristics, data were collected from experiments in a laboratory flume and field investigations in a cobblebed river reach in central Iran. The results of the experiments and field observations showed that the velocity profiles for non-uniform flows in cobble-bed streams with vegetation strips can be divided into either two or three sub-zones. The velocity profiles of non-uniform flows in the laboratory flume and cobble-bed stream deviated from the log law in the wake and mixing zones, but fitted approximately in the log-law layer zone. The distribution of Reynolds stress for non-uniform flows was influenced by the vegetation strip and showed a non-concave shape. Near the channel bed, sweep motion occurred more frequently than the ejection process. Close to the top of vegetation strip, the correlation coefficient (r u 0 w 0) was negative, indicating downward momentum transport due to sweep and ejection processes. However, r u 0 w 0 was positive near the water surface, indicating upward momentum by the vegetation strip due to inward and outward interactions. The study shows that laboratory results cannot be easily applied to natural rivers without considerable assumptions. Water Management Non-uniform flow over cobble bed with submerged vegetation strip Afzalimehr, Barahimi and Sui

Quantifying turbulent fluxes and secondary structures in shallow channel flows is important for predicting momentum and mass transfer in rivers as well as channel capacity and associated water levels. Here, we focus on the flow over a lateral bed-roughness variation with very low relative submergence of the roughness elements, h∕k = {3, 2, 1.5} , where h is the flow depth and k is the roughness height. Measurements were performed in a 1.1 m wide and 26 m long glass flume whose bed was fitted with cubes arranged in two regular side-by-side patterns with frontal densities f = 0.2 and 0.4 to create a rough-to-rougher variation. Measurements were performed using stereoscopic PIV in two orthogonal planes, in a vertical transverse plane spanning the two roughness types, and in a longitudinal one at the interface between the roughness types. The results show that the bulk velocity difference between the two sides of the channel increases with decreasing h/k. Also, contrary to what is observed at high relative submergence with smooth-to-rough transitions, higher bulk velocities occur on the side with higher roughness. This difference is increasing as the flow becomes shallower and is shown to be due to increasing effective depths ratios, leading to increasingly lower friction factor ratios with lower friction factors on the high-velocity but rougher side. Although increasing streamwise momentum transfer at the interface is needed as h/k decreases, the turbulent and secondary circulation transfer of momentum is increasingly inhibited. A globally-driven secondary-circulation at h∕k = 3 ceases for lower h/k and roughness-scale circulation becomes dominant. Also, even the increased global shear does not lead to large-scale Kelvin Helmholtz instabilities structures. However, the relative importance of the roughness difference on the flow is augmented as the flow becomes shallower and momentum transfer due to lateral dispersive stresses increases.

Discharge determination in open channels is of great interest for water engineering. In compound channels, discharge determination raises the issue of the link between the measured velocity and the mean velocity. To do so, Computational Fluid Dynamics is used as a tool to determine the velocity distribution in compound channels. The purpose of this study is to compare through numerical simulations the most common turbulence models such as k-ω and RSM to LES that is rarely used in this field in order to investigate the efficiency of the LES model to reproduce the velocity distribution.

Pure sine wave transformers are very important nowadays when it comes to using ds power sources for both low and high-power applications. These inverters not only increase the efficiency of the power system but also prevent electrical components from damaging. Much work has been done in the field of pure sine wave inverter but for a waveform with low number of harmonics along with high efficiency is still an open challenge. There are techniques available to do this, but the need to adapt to a solution that is easy to implement as well as specifically for low energy applications. In this paper, a multi-vibration technique is used to generate a square wave which is then split into two square waves of the same frequency by the 4017-decade counter to hold the H-bridge inverter. The output of the H-bridge inverter contains harmonics that are filtered using a low pass filter. Thus, we get a pure sin wave in the output.

The open-source finite-element system Telemac has been applied to simulate various complex hydrodynamic and morphodynamic situations including waterways, curved channels, recirculating flows and wave-induced littoral transport. In the applications presented here, the sediment transport model is mainly restricted to the transport of non-cohesive sediments, which relies on classical semi-empirical concepts including sand grading effects, parameterization of secondary currents and wave effects. In comparison with other comprehensive modeling systems (Delft-3D, Mike-21, etc.), the main originality lies in the efficiency and flexibility of the finite elements. Thanks to the optimization of numerical schemes, parallelism, as well as tremendous progress in the performance of computers, bed evolution can be calculated on basin scale (10-100 km) and for the medium term (years to decades), without the use of hydrodynamic filtering methods. As a novelty in release 6.0, we present a method of feedback for the bed roughness, which reduces uncertainty in the prediction of both transport rates and flow velocities.

Based on direct numerical simulations, the paper investigates momentum fluxes and hydrodynamic stresses within and above a mobile granular bed in a turbulent open-channel flow laden with monodisperse spherical particles. Two simulation scenarios are considered: one with partially mobilized particles ("heavy" particles) and another with all particles in motion ("light" particles). The momentum fluxes were computed as temporal and spatial averages following the double-averaging methodology for rough-bed flows. The analysis, hence, allows the DNS data to be convoluted in a rigorous way to provide detailed description and quantification of the physical mechanisms involved in momentum exchanges. In particular, it was found that heavy particles create streamwise bedforms causing heterogeneity in the spanwise direction. This yields significant form-induced momentum fluxes that cannot be neglected. For both scenarios, the mobile particles take up a substantial amount of the momentum supplied, which ultimately increases the hydraulic resistance of the channel. These effects enhance and stabilize secondary flows in the channel.

A tidal bore is an unsteady flow motion generated by the rapid water level rise at the river mouth during the early flood tide when the tidal range exceeds 4 to 6 m, the estuary bathymetry amplifies the tidal wave and the freshwater level is low. The tidal bore is an abrupt rise in water depth associated with a discontinuity in water depth and velocity at the bore front. The present study examines the turbulence and turbulent mixing generated by the passage of an undular tidal bore in a short channel constriction such as a set of bridge piers. Some new experiments were conducted in a large rectangular prismatic channel. Then a short channel constriction that was a 1/20 scale model of the Pont Aubaud on the Sélune River in the Baie du Mont Saint Michel was installed. The free-surface properties of undular tidal bores were carefully documented for both configurations. The analysis of the parametric relationship between momentum function and specific energy showed that the undular flow properties were restricted to the subcritical branch of the ME diagram, while the quantitative results indicated that the effects of streamline curvature could not be ignored. The freesurface undulation profiles exhibited a quasi-periodic shape, but both field measurements and laboratory observations demonstrated that neither the linear wave theory nor the Boussinesq equation theory captured the fine details of the free-surface profiles. An analysis of the potential energy of the undular tidal bore showed that the potential energy of the free-surface undulations represented up to 30% of the potential energy of the tidal bore. The presence of the channel constriction had a major impact on the free-surface properties. In the channel throat, the wave motion was three-dimensional, pseudo-chaotic and energetic and the undular bore lost nearly one third of its potential energy per surface area as it propagated through the channel constriction. The velocity data sets suggested the upstream advection of energetic turbulent events and vorticity behind the bore front. It is proposed that these energetic turbulent events were some macroturbulence generated by secondary currents. With the channel constriction, some intense large-scale turbulence was further produced by the constriction. The proposed mechanism was consistent with some field observations in the Daly River tidal bore in 2003. Overall the presence of a channel constriction (e.g. bridge piers) does impact onto the bore propagation. It is associated with some energy loss and the development of large-scale coherent structures, and these processes might induce some river bed scour on the vicinity of the bridge piers. The technical report is supported by a digital appendix (Appendix B) containing five movies available at the University of Queensland institutional open access repository UQeSpace {http://espace.library.uq.edu.au/}.

Tidal Bores, aegir and pororoca are a surge of waters propagating upstream as the tidal flow turns to rising and the flood tide rushes into a funnel shaped river mouth. The bore forms during the spring tides when the tidal range exceeds 4 to 6 m and the rising tide waters are confined to the narrow funnelled estuary during the dry season. Herein the author aims to share his enthusiasm and passion for these geophysical wonders by explaining the basic theory, supported by field and laboratory observations. Behind the bore, some strong turbulent kinetic energy is produced next to the boundaries and some macro-turbulence is advected behind the tidal bore front. Transient fronts may also develop behind a bore inducing further secondary circulation. The paper intends to bridge the gap between the general knowledge, engineering practice and scientific expertise on the tidal bores.

In this study, to find the best location to cultivate the trees for river bank protection, some experimental tests were performed. One row of trees were cultivated at five different distances from the main channel/floodplain interface in a rectangular compound open channel. In experimental model for simulating the trees, some cylindrical wood rods were attached to the bed of flood plain. The three-dimensional flow velocity of flow in a cross-section between the trees were measured in 149 nodal points using Micro-acoustic Doppler velocimeter (ADV) velocity meter. At each nodal point, 6000 velocity data for each direction were stored in a computer. From the analysis of the experimental data, it was concluded that upon cultivating trees at 10% distance of flood plain width from the edge of main channel, the minimum streamwise velocity occurred near main channel/floodplain interface, while the maximum streamwise velocity occurred far from the edge of floodplain. Therefore, the best location for cultivating the trees was found to be at 10% of floodplain width and it is suggested for river bank protection in practical applications.

An analysis of flow was carried out in this study to find the effects of trees on flow structure in a straight compound open channel. To resemble the vegetation stem, two rows of vertical rods were installed on the floodplain of an asymmetrical compound channel. Two dimensional flow velocity was measured using Particle Image Velocimetry (PIV). The results showed a decreasing trend in turbulent kinetic energy and turbulent intensity along the floodplain. At low flow depth, significant decrease in mean velocity and kinetic energy was observed. Similar reduction was observed at the inter section of floodplain and main channel and around the stems. Under this condition, the direction of velocity vectors changed from floodplain to the main channel. However, this trend was reversed at higher flow depths. This reversal was due to changes in momentum transfer and shear stress at the intersection of floodplain and main channel. Additionally, numerical analysis showed that vortices are formed at the junction of the floodplain and main channel.

In this study a comparison of three turbulence closure models (two isotropic and one anisotropic) with experimental data is performed. The interaction between the main channel (MC) flow and the floodplain (FP) generates a complex flow structure. A shallow mixing layer develops between the MC flow and the slower FP flow generating a high horizontal shear layer, streamwise and vertical vortices, momentum transfer and other phenomena, related to velocity retardation and acceleration. This phenomenon dissipates part of the kinetic energy and contributes to the reduction of the velocity differences between the MC and the FP. The large scale vortices that are generated in the shear layer are anisotropic, provoking the formation of secondary flow cells that influence the primary velocity distribution. These threedimensional turbulent structures can be reasonable well reproduced by a simple anisotropic model (Algebraic Stress Model). The isotropic models are capable of simulating the bounda...

During flood, movement of water occurs from main river stream to its both adjacent flood plains and vice versa. If the river has only one flood plain either side of it, then it is called as asymmetric compound channel. The difference in hydraulic resistances between the main channel and flood plain subsections causes the exchange of momentum between them. In recent centuries, a great deal of experimental investigations has been carried out in order to understand the complex turbulent flow structure in compound channel flow. The article reports the turbulence measurements undertaken in an asymmetric compound channel flow in the hydraulics laboratory, NIT, Rourkela. This experimental facility is designed in such a way that it characterizes a model of a river system with roughened floodplains. The principal focus in this study is on the nonlinear nature of flow structures in the shear layer region between the main channel and flood plain. The variation of secondary flow in lateral dire...

Multi-section flow visualization technique and Mass-Consistent model are employed to picture the vortical structures and their behavior in a comparatively wide single-flood plain channel. Repeated cycles of photography enables us to calculate both mean and instantaneous flow characteristics. Investigations of vortical structures have revealed that in the main channel, close to the bed, vortices with axes in the spanwise direction

Vegetation plays an important role in the physical, ecological, and hydraulic functions of streams, rivers and many other water bodies and can affect the transport of water, sediment and nutrients both within the channel and to or between the riparian zones. This research studied the momentum and passive contaminant transport mechanism in a vegetated channel with a floodplain. Three dimensional numerical simulation and physical experimentations were conducted for turbulent flow in the presence of model vegetation. A non-linear k-ε model with a vegetation model for turbulent flow and an algebraic flux model (DH model) for contaminant transport were adopted. An in-house code developed by the authors was implemented for numerical simulations. Model vegetation zones were prepared in the channel to predict the mixing mechanism. The numerical results were compared with corresponding experimental observations. A good agreement between the simulated and experimental results was observed in terms of pollutant concentration.

Uniform flow in compound channels has been studied in terms of a numerical model, called the NKE model. The model uses the three dimensional Navier-Stokes equations in conjunction with the non-linear k-ε turbulence model. The latter is used for the calculation of the Reynolds stress components responsible for the generation of the secondary currents. This model is based on the SIMPLE technique, and computes the six parameters U, V, W, P, k, and ε using wall functions on a Cartesian grid. The NKE model was used to simulate the compound open channel flows of the UK Flood Channel Facility run 080301 . The Reynolds Stress Model (RSM) of FLUENT was also used as a comparison. The results obtained have shown that the NKE and RSM models can reasonably predict the primary mean velocity and secondary currents. Although agreement is certainly not perfect in every detail, the main features of the flow are reproduced. The bulging of the contours at the bottom corner of the main channel, the inclination of the contours near the free surface towards the channel centre, and the depression of the maximum velocity below the free surface can be seen. These are consistent with the pattern of the secondary flows, which are mainly formed by two vortices, namely the main channel vortex and flood plain vortex. These vortices, which originate near the main channel-flood plain junction, can be reproduced by the NKE and RSM models. KEY WORDS: Compound Channel, Navier-Stokes Equation, Non-linear k-ε Turbulence Model, Reynolds Stress Model (RSM), Velocity Distribution, Secondary Currents. F. Othman, E. M. Valentine: NUMERICKÉ MODELOVANIE ROZDELENIA RÝCHLOSTI V ZLOŽENOM KORYTE. Vodohosp. Čas., 54, 2006, 3; 25 lit., 7 obr.

Uniform flow in compound channels has been studied in terms of a numerical model, called the NKE model. The model uses the three dimensional Navier-Stokes equations in conjunction with the non-linear k-ε turbulence model. The latter is used for the calculation of the Reynolds stress components responsible for the generation of the secondary currents. This model is based on the SIMPLE technique, and computes the six parameters U, V, W, P, k, and ε using wall functions on a Cartesian grid. The NKE model was used to simulate the compound open channel flows of the UK Flood Channel Facility run 080301 (Shiono and Knight, 1989). The Reynolds Stress Model (RSM) of FLUENT was also used as a comparison. The results obtained have shown that the NKE and RSM models can reasonably predict the primary mean velocity and secondary currents. Although agreement is certainly not perfect in every detail, the main features of the flow are reproduced. The bulging of the contours at the bottom corner of t...

A complete research work can never be the work of anyone alone. The contributions of many different people, in their different ways, have made this possible. One page can never suffice to express the sense of gratitude to those whose guidance and assistance was indispensable for the completion of this project. I would like to express my special appreciation and thanks to my supervisors Professor Dr. Kishanjeet Kumar Khatua and Professor Dr. Kanhu Charan Patra, you both have been tremendous mentors for me. I would like to thank you for encouraging my research and for allowing me to grow as a research scholar. Your advices on both researches as well as on my career have been priceless. I would also like to thank my committee members, Professor, Nagendra Roy; Head of the Civil Department. And also I am sincerely thankful to Prof. Ramakar Jha, and Prof. A. Kumar for their kind cooperation and necessary advice. I also want to thank you for letting my seminars be an enjoyable moment, and for your brilliant comments and suggestions, thanks to you. I wish to express my sincere gratitude to Dr. S K Sarangi, Director, NIT, Rourkela for giving me the opportunities and facilities to carry out my research work. A special words of thanks to Mr. Swayam Bikash Mishra Ph.D. scholar of Production Engineering and Mrs. Bandita Naik, Manaswinee Patnaik, Laxmipriya Mohanty Ph.D. scholar of Civil Engineering Department, for his suggestions, comments and entire support throughout the project work. I express to my special iii thanks to my dear friends Monalisa, Ellora, Aparupa, Chita, Bibhuti, Arpan, B. Mohan Kumar for their continuous support, suggestions and love. Last but not least I would like to thanks to my father Mr. Arjun Chandra Mohanta and mother Mrs. Sabita Mohanta, who taught me the value of hard work by their own example. Thanks a lot for your understanding and constant support, and to my sister Priyanka Mohanta and brother in law Sailendra Mohanta for his encouragement. They rendered me enormous support during the whole tenure of my study at NIT Rourkela. Words cannot express how grateful I am to my Father, Mother, Sister, Brother in law and my little nephew Pragyan for all of the sacrifices that you have made on my behalf. Your prayer for me was that sustained me thus far.

ABSTRACT
In the light of prevailing power cuts in the country, there is a sudden rise of a need to come up with backup power solutions. The most common backup supply systems available on the market are Automotive Generator Sets (convert mechanical energy to electrical energy by means of burning fossil fuel) and UPS (Uninterrupted power supply). Even though all these backup supply systems turn to perform their said functions to some extent, they turn to pose some challenges. Some of the limitations of using generator as alternative or additional source of electricity are mostly noisy during its operation, which causes disturbances in the neighborhood. The carbon mono-oxide and the black oil from the generator pose threats to the environment as air and soil or water pollutant making it non-environmentally friendly. The cost of maintenance turns to be expensive since they run on fuel, compared to an Inverter. This makes it quite unaffordable by people with low income. The 600VA DC-AC power inverter is designed to produce backup power that runs on 12V DC batteries which are ecofriendly to produce backup power for a longer period of time. This project would increase the knowledge on power inverter application by constructing a 12V DC to 220V AC with output power rating at 600VA with frequency varying between 49.95Hz, which is approximately 50 Hz. The traditional square wave derived from a stable multi-vibrator would be substituted for modified sine wave oscillator which would be designed by the combination of a timer and a flip-flop. The signal from the flip-flop is fed to a dual input Class AB pull-push amplifier to produce an alternating output with the same waveform but with a higher power enough to power up any equipment in the power rating of the system. The parallel state built by the RFP40N10 (N-Channel Mosfets) is to conduct large amount of power through the primary of the transformer to oscillate thereby generating an output at the secondary of the transformer.

ABSTRACT
In the light of prevailing power cuts in the country, there is a sudden rise of a need to come up with backup power solutions. The most common backup supply systems available on the market are Automotive Generator Sets (convert mechanical energy to electrical energy by means of burning fossil fuel) and UPS (Uninterrupted power supply). Even though all these backup supply systems turn to perform their said functions to some extent, they turn to pose some challenges. Some of the limitations of using generator as alternative or additional source of electricity are mostly noisy during its operation, which causes disturbances in the neighborhood. The carbon mono-oxide and the black oil from the generator pose threats to the environment as air and soil or water pollutant making it non-environmentally friendly. The cost of maintenance turns to be expensive since they run on fuel, compared to an Inverter. This makes it quite unaffordable by people with low income. The 600VA DC-AC power inverter is designed to produce backup power that runs on 12V DC batteries which are ecofriendly to produce backup power for a longer period of time. This project would increase the knowledge on power inverter application by constructing a 12V DC to 220V AC with output power rating at 600VA with frequency varying between 49.95Hz, which is approximately 50 Hz. The traditional square wave derived from a stable multi-vibrator would be substituted for modified sine wave oscillator which would be designed by the combination of a timer and a flip-flop. The signal from the flip-flop is fed to a dual input Class AB pull-push amplifier to produce an alternating output with the same waveform but with a higher power enough to power up any equipment in the power rating of the system. The parallel state built by the RFP40N10 (N-Channel Mosfets) is to conduct large amount of power through the primary of the transformer to oscillate thereby generating an output at the secondary of the transformer.

In the present study, vortices were generated in open channel flow with a cross-flow cylinder installed horizontally near the bed. Sediment pickup rates were then measured over the channel bed downstream the cylinder using a sediment lift. The experimental data show that the pickup rate increases exponentially in the presence of vortices. Two different relationships can be clearly observed between the pickup rate and the maximum root-mean-square (rms) value of the streamwise velocity fluctuation, one for the cylinder-obstructed flow and the other for the unobstructed flow. The results imply that the vortex-induced sediment pickup cannot be explained based on the traditional boundary layer theory.

In this study a comparison of three turbulence closure models (two isotropic and one anisotropic) with experimental data is performed. The interaction between the main channel (MC) flow and the floodplain (FP) generates a complex flow structure. A shallow mixing layer develops between the MC flow and the slower FP flow generating a high horizontal shear layer, streamwise and vertical vortices, momentum transfer and other phenomena, related to velocity retardation and acceleration. This phenomenon dissipates part of the kinetic energy and contributes to the reduction of the velocity differences between the MC and the FP. The large scale vortices that are generated in the shear layer are anisotropic, provoking the formation of secondary flow cells that influence the primary velocity distribution. These threedimensional turbulent structures can be reasonable well reproduced by a simple anisotropic model (Algebraic Stress Model). The isotropic models are capable of simulating the boundary layer, especially the model base in k-ω equations, but cannot simulate the shear layer that develops at the interface.

In this study a comparison of three turbulence closure models (two isotropic and one anisotropic) with experimental data is performed. The interaction between the main channel (MC) flow and the floodplain (FP) generates a complex flow structure. A shallow mixing layer develops between the MC flow and the slower FP flow generating a high horizontal shear layer, streamwise and vertical vortices, momentum transfer and other phenomena, related to velocity retardation and acceleration. This phenomenon dissipates part of the kinetic energy and contributes to the reduction of the velocity differences between the MC and the FP. The large scale vortices that are generated in the shear layer are anisotropic, provoking the formation of secondary flow cells that influence the primary velocity distribution. These threedimensional turbulent structures can be reasonable well reproduced by a simple anisotropic model (Algebraic Stress Model). The isotropic models are capable of simulating the boundary layer, especially the model base in k-ω equations, but cannot simulate the shear layer that develops at the interface.

In this study the results of Baseline Explicit Algebraic Reynolds Stress model (BSL EARSM), Baseline Reynolds Stress model (BSL RSM) and Speziale-Sarkar-Gatski Reynolds Stress model (SSG RSM) of turbulent flow in an asymmetric compound channel are presented. The numerical results are validated with experimental measurements of Tominaga & Nezu (1991).

In this study the results of Baseline Explicit Algebraic Reynolds Stress model (BSL EARSM), Baseline Reynolds Stress model (BSL RSM) and Speziale-Sarkar-Gatski Reynolds Stress model (SSG RSM) of turbulent flow in an asymmetric compound channel are presented. The numerical results are validated with experimental measurements of Tominaga & Nezu (1991).

In this study the results of Baseline Explicit Algebraic Reynolds Stress model (BSL EARSM), Baseline Reynolds Stress model (BSL RSM) and Speziale-Sarkar-Gatski Reynolds Stress model (SSG RSM) of turbulent flow in an asymmetric compound channel are presented. The numerical results are validated with experi-mental measurements of Tominaga & Nezu (1991).

Characteristics of open channel flows can be significantly modified in the presence of secondary flows. In this study, cellular secondary flows were artificially generated with alternate rough and smooth bed strips, which were aligned longitudinally in an open channel. Flow measurements were conducted with a two-dimensional Laser Doppler Anemometer system. Experimental results show that the distributions of the primary velocity and streamwise Reynolds shear stress that are altered in the presence of the secondary flows clearly deviate from those observed for two-dimensional open channel flows. The modified streamwise velocity can be represented by a function proposed in the log-wake form but varying periodically in the lateral direction. This study also demonstrates that the flow field can be linearized so that a flow quantity can be generally decomposed into two components, one being related to the average base flow and the other symbolizing the perturbation caused by the bed configuration. This perturbation-based approach finally provides an analytical description of the altered Reynolds shear stress distribution that differs from the linear profile used for two-dimensional open channel flows.

Uniform flow in compound channels has been studied in terms of a numerical model, called the NKE model. The model uses the three dimensional Navier-Stokes equations in conjunction with the non-linear k-? turbulence model. The latter is used for the calculation of the Reynolds stress components responsible for the generation of the secondary currents. This model is based on the SIMPLE technique, and computes the six parameters U, V, W, P, k, and ? using wall functions on a Cartesian grid. The NKE model was used to simulate the compound open channel flows of the UK Flood Channel Facility run 080301 (Shiono and Knight, 1989). The Reynolds Stress Model (RSM) of FLUENT was also used as a comparison. The results obtained have shown that the NKE and RSM models can reasonably predict the primary mean velocity and secondary currents. Although agreement is certainly not perfect in every detail, the main features of the flow are reproduced. The bulging of the contours at the bottom corner of the main channel, the inclination of the contours near the free surface towards the channel centre, and the depression of the maximum velocity below the free surface can be seen. These are consistent with the pattern of the secondary flows, which are mainly formed by two vortices, namely the main channel vortex and flood plain vortex. These vortices, which originate near the main channel-flood plain junction, can be reproduced by the NKE and RSM models.

The paper detailed a water quality modelling study of a hyper-tidal estuary, undertaken to assess the impact of various bacteria input loads on the receiving waters in a coastal basin in the UK, by using the model developed in previous study of the same authors enterococci, used as the indicators for bathing water quality under the new European Union (EU) Bathing Water Directive, were numerically modelled using a hydro-environmental model. In particular, the numerical model used in this study includes the effects of sediment on bacteria transport processes in surface water. Finally, the importance of sediment bacteria inputs on the bathing water quality was also investigated under different weather and tidal condition. During spring tide, the bacteria input from the bed sediments are dominant for both wet and dry weather conditions. During neap tides and during dry weather conditions the inputs of bacteria from the bed sediment were still dominant, but during wet weather conditions the inputs from river were dominant. Under different tidal flow conditions some parameters had a more significant role than others. During high flow conditions the sediment re-suspensions processes were dominant, therefore the bed bacteria concentrations played a dominant role on the overall bacteria concentration levels in the water column. In contrast, during low flow conditions sediment deposition prevails and bacteria are removed from the water column. The partition coefficient was found to be more important than the bed bacteria concentrations, during low flow conditions.

Apparent shear stress, which is presented in forms of roughness ratio, width ratio and depth ratio between main channel and flood plain, is quite important in the compound channel flows with the behaviors of momentum transfer on control works for both soil material and contaminate transports. The analytical solutions of apparent shear stress for symmetric-straight compound channel flows both in main channel and flood plain are derived and compared with the results of experimental and numerical outputs. The acceptable tendencies and agreements are presented. The significances of the ratios on roughness, width and depth are discussed for the characteristics of apparent shear stress.

"Abstract
A large-eddy simulation study has been undertaken to investigate the turbulent structure of open-channel flow in an asymmetric compound channel. The dynamic sub-grid scale model has been employed in the model, with the partial cell treatment being implemented using a Cartesian grid structure to deal with the floodplain. The numerical model was used to predict the: primary velocity and secondary currents, boundary shear stress, turbulence intensities, turbulent kinetic energy, and Reynolds stresses. These parameters were compared with experimental measurements published in the literature, with relatively close agreement being obtained between both sets of results. Furthermore, instantaneous flow fields and large-scale vortical structures were predicted and are presented herein. These vortical structures were found to be responsible for the significant lateral exchange of mass and momentum in compound channels."