Search

In this work is described a research project, which central objective was to reduce scouring depth in shorts and vertical abutments of bridges, so in this it was analyzed at trough of a physical model reduced, the scouring depth that generate an water flow in a system performed by a short and vertical abutment of bridge, in a sand channel of hydraulic engineering laboratory of ESIA Zacatenco United, in Mexico; the abutment was modified in his geometry (with wings to 45, 30 y 20º), in order to determine experimentally its influence in local scouring that was generated, with some flow condition; and in the way of essay‐error to reduce the local erosion. In this project, the local erosion depth generated by the original abutment was reduced in a 98 %. [ABSTRACT FROM AUTHOR]

Successive earthquakes can drive landscape evolution. However, the mechanism and pace with which landscapes respond remain poorly understood. Offset channels in the Carrizo Plain, California, capture the fluvial response to lateral slip on the San Andreas Fault on millennial time scales. We developed and tested a model that quantifies competition between fault slip, which elongates channels, and aggradation, which causes channel infilling and, ultimately, abandonment. Validation of this model supports a transport-limited fluvial response and implies that measurements derived from present-day channel geometry are sufficient to quantify the rate of bedload transport relative to slip rate. Extension of the model identifies the threshold for which persistent change in transport capacity, obliquity in slip, or advected topography results in reorganization of the drainage network. [ABSTRACT FROM AUTHOR]

Deep-water coarse-grained channels are embedded within a polygonal fault tier, and the polygonal faults (PFs) present non-polygonal geometries rather than classic polygonal geometry in plan view. However, PFs present differences when they encounter deep-water (coarse-grained vs. fine-grained) channels with different lithology, which has not been further studied to date. 3D seismic data and a drilling well from Beijiao sag of Qiongdongnan basin, South China Sea were utilized to document the plan view and cross-sectional properties of the PFs and their differences and genetic mechanism were investigated. Results show that, first, PFs can be divided morphologically into channel-segmenting PFs and channel-bounding PFs in plan view. The former virtually cuts or segments the axes of channels in high- and low-amplitudes, and the latter nearly parallels the boundaries of the channels. Both are approximately perpendicular to each other. Secondly, channel-bounding PFs that related to low-amplitude channels are much longer than those of high-amplitude ones; channel-segmenting PFs related to low-amplitude channels are slightly longer than the counterparts related to high-amplitude channels. Lastly, the magnitudes (e.g., heights) of the PFs are proportional to the scales (e.g., widths and heights) of low-amplitude channels, whereas the magnitudes of the PFs are inversely proportional to the scales of high amplitude channels. Coarse-grained (high amplitude) channels act as a mechanical barrier to the propagation of PFs, whereas fine-grained (low-amplitude) channels are beneficial to the propagation and nucleation of PFs. Additionally, the genetic mechanism of PFs is discussed and reckoned as combined geneses of gravitational spreading and overpressure hydrofracture. The differences of the PFs can be used to reasonably differentiate coarse-grained channels from fine-grained channels. This study provides new insights into understanding the different geometries of the PFs related to coarse-grained and fine-grained channels and their genetic mechanism. [ABSTRACT FROM AUTHOR]

Abstract Channels with parabola-shaped cross-section are widely used in water conservancy and hydropower engineering, agricultural irrigation and drainage engineering, so it is necessary to determine the accurate normal depth values for design of open channels, operation management and analysis of gradually varied flow. However, the governing equations are nonintegrable for cubic and semi-quintic parabola-shaped channels in terms of the wetted perimeters. In this study, the Simpson's numerical integral method is introduced to approximate the two nonintegrable wetted perimeters for cubic and semi-quintic parabola-shaped channels which can meet the requirements of engineering design well in the commonly using range of engineering. Subsequently, the approximate wetted perimeters are substituted into the uniform flow equation and the uniform flow equation deforms optimal model identically. The optimal model parameters are determined by the 1stOpt software based on Marquardt algorithm and two explicit calculation formulas for the normal depths of cubic and semi-quintic channels are proposed. At the same time, two direct calculation formulas for normal depths of semi-cubic and quadratic parabola-shaped channels are presented as well. Four sets of formulas for normal depths of parabola-shaped channels are presented and their maximum relative errors are 0.52%, − 0.37%, − 0.22% and 0.57%, respectively, which have wide range of application, high precision, concise form and can provide some better guidance for engineering design and operation management. Highlights • The Simpson's numerical integral method is firstly introduced to approximate the two nonintegrable wetted perimeters for cubic and semi-quintic parabola-shaped channels accurately. • Two explicit formulae for normal depths of cubic and semi-quintic parabola-shaped channels are obtained with high precision, wide range of application firstly. • Two explicit formulae for normal depths of semi-cubic and quadratic parabola-shaped channels are obtained with higher precision, wider range of application than those of former studies. [ABSTRACT FROM AUTHOR]

Abstract A Two-stage compound channel section is commonly used in ecological channel design. This paper presents the geometric properties of the compound section and the formulae for calculating the cross-section area, wetted perimeter are obtained. Then, the explicit equations of the best hydraulic section for design are derived. Results show the best width-depth ratio of the compound section is related to some geometric parameters. Furthermore, this type of best hydraulic section is compared with the rectangular and trapezoidal sections. Results indicate that the cross-section area and wetted perimeter are less than those of rectangular and trapezoidal sections for a given flow discharge when the ratios of the compound section's roughness coefficient to those of rectangular and trapezoidal sections are less than 1.017 and 0.855, respectively. It means less lining and excavation cost is required for construction. Highlights • Geometric properties of the two-stage compound channel section are presented. • Formulae for calculating the cross-section area, wetted perimeter of the compound section are obtained. • The explicit equations of the best hydraulic section of the compound section for design are derived. • This type of best hydraulic section is compared with the rectangular and trapezoidal sections. • Quantitative values are obtained used to determine the more efficient section of the compound section. [ABSTRACT FROM AUTHOR]

Characteristics of turbulent flow around a braided bar are much more complex as compared to the straight and meandering rivers. The impact of a mid-channel bar on the turbulent flow structure has been investigated in this research. A new dominance function [S.sub.i,H] is proposed in this study as a measure of the relative dominance of ejection and sweep events in turbulent flow structure. Occurrence of the kolk-boil phenomenon is observed due to interaction of ejection and sweep events. The kolk-boil phenomenon generates negative pressure gradients which result in suspension of bed sediment particles in the flow domain. The transition probability of bursting event movements is computed using the first Markov chain. A new parameter movement ratio is formulated in this study, which is found to faithfully reflect the fluvial processes of sedimentation and scouring on the channel bed. Acceleration of flow is seen to occur at adjoining regions close to the upstream end of the bar. Due to the presence of the bar, the flow area in its proximity decreases which has caused increment in the velocity at sections located near the upstream end of the mid-channel bar. For model runs with bars, a distinct bulge in the turbulent intensity graph is observed. The mid-channel bar effect is mainly discernible in the lower layers of flow. Key words: kolk-boil phenomenon, bursting events, mid-channel bar, transitional movements, hole size, fluid-bar interaction. Les caracteristiques de l'ecoulement turbulent autour d'un banc anastomose sont beaucoup plus complexes que celles des rivieres droites et sinueuses. Dans le cadre de cette recherche, l'impact du banc median d'alluvionnement sur la structure de l'ecoulement turbulent a ete etudie. Une nouvelle fonction de dominance [S.sub.i,H] est proposee comme mesure de la dominance relative des evenements d'ejection et de balayage dans la structure de l'ecoulement turbulent. Le phenomene d'ebullition du << kolk >> est observe en raison de l'interaction des evenements d'ejection et de balayage. Le phenomene d'ebullition du kolk genere des gradients de pression negatifs qui entrainent la suspension de particules de sediments du lit dans le domaine d'ecoulement. La probabilite de transition des mouvements d'evenements d'eclatement est calculee a l'aide de la premiere chaine de Markov. Un nouveau parametre, soit le rapport de mouvement, est formule et s'avere refleter fidelement les processus fluviaux de sedimentation et d'affouillement sur le lit du canal. L'acceleration de l'ecoulement se produit dans les regions adjacentes pres de l'extremite en amont du banc. En raison de la presence du banc, la zone d'ecoulement dans sa proximite diminue, ce qui entraine une augmentation de la vitesse dans les sections situees pres de l'extremite amont du banc median d'alluvionnement. Pour les analyses de modele avec des bancs, un gonflement distinct dans le graphique d'intensite turbulente est observe. L'effet du banc median d'alluvionnement est principalement perceptible dans les couches inferieures de l'ecoulement. [Traduit par la Redaction] Mots-cles : phenomene d'ebullition de << kolk >>, evenements d'eclatement, banc median d'alluvionnement, mouvements de transition, taille de trou, interaction fluide-banc., Introduction There exist in nature several patterns of river planforms such as meandering and braiding. The flow structure and secondary currents in the meandering channels have been studied by many [...]

Channels are important sedimentary features in hydrocarbon plays either as targets for drilling or geohazards that should be avoided, depending on burial depth and fluid-fill. Either way, for well design purposes it is important to image channels before drilling. Shearlet transform, as a multi-scale and multi-directional transformation, is capable of detecting anisotropic singularities in two and higher dimensional data. In this study, the complex-valued shearlet-based edge measure was implemented for the aim of channel boundary detection. The method was applied to synthetic seismic time-slices containing channels with different signal-to-noise ratios as well as a real time-slice from the South Caspian Sea. The performance of the shearlet-based algorithm was compared both qualitatively and quantitatively with well known gradient-based edge detectors such as Sobel and Canny, resulting in successfully localising edges and detecting less false positives. Channel detection plays a significant role in seismic interpretation. Shearlet transform as a multi-scale and multi-directional transformation is capable of detecting anisotropic singularities. We applied complex-valued shearlet edge measure to synthetic and real seismic time-slices from the South Caspian Sea. The proposed algorithm outperformed both Sobel and Canny edge detectors. [ABSTRACT FROM AUTHOR]

Highlights • A new approach is applied to estimate the bank profile shape of a stable channel. • Most influential parameters on channel geometry are studied. • A wide-ranging field dataset are used to evaluate the models. • An explicit expression for practical engineering is provided. • The proposed method can be used as an alternative in practical applications. Abstract Accurate prediction of the long-term average dimensions of alluvial stable channels is a significant problem in river engineering. The goal of this research is to investigate the effect of flow discharge (Q), mean sediment size (d 50) and Shields parameter (τ∗) on the stable channel dimensions by employing non-linear regression (NLR) and two Artificial Intelligence (AI) methods, including: Generalized Structure of Group Method of Data Handling (GS-GMDH) neural network and Gene Expression Programming (GEP). Discharge, grain size and Shields parameter from 85 gaging stations situated in three stable Iranian rivers were used as input data for the three methods to estimate the water-surface width (W), average flow depth (D) and longitudinal slope (S) of the rivers. Based on the results, it was found that the GS-GMDH produced more accurate results for simulating the channel width with a Mean Absolute Relative Error (MARE) value of 0.055; and GEP produced better estimations for channel depth and slope with MARE values of 0.035 and 0.03, respectively. Furthermore, by employing Artificial Intelligence (AI) methods (GS-GMDH and GEP), the RMSE values decreased by 22%, 25% and 75% in predicting width, depth, and slope, respectively, compared to NLR method. The overall results showed that the AI methods generally produced better estimations than the non-linear regression method. To determine the effect of each input variable (Q, d 50 , τ∗) on the target variables (W, D, S), a sensitivity analysis comprising various combinations of input variables was conducted. Based on the results, the flow discharge had a dominant role on depth and width estimation of stable channels. In slope estimation, the most important parameter was τ∗ and then d 50 , while the discharge had a weak effect on slope prediction. In general, the Shields parameter was the most effective parameter in depth and specially slope estimation of stable channels. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • We created an intermediate complexity model for simulating channel evolution at watershed scales. • The model matches physical understanding of channel change. • It can also predict erosion processes in accordance with field data sets. • The model is useful for predicting channel evolution and answering relevant management questions. Abstract Excessive river erosion and sedimentation threatens critical infrastructure, degrades aquatic habitat, and impairs water quality. Tools for predicting the magnitude of erosion, sedimentation, and channel evolution processes are needed for effective mitigation and management. We present a new numerical model that simulates coupled river bed and bank erosion at the watershed scale. The model uses modified versions of Bagnold's sediment transport equation to simulate bed erosion and aggradation, as well as a simplified Bank Stability and Toe Erosion Model (BSTEM) to simulate bank erosion processes. The model is mechanistic and intermediate complexity, accounting for the dominant channel evolution processes while limiting data requirements. We apply the model to a generic test case of channel network response following a disturbance and the results match physical understanding of channel evolution. The model was also tested on two field data sets: below Parker Dam on the lower Colorado River and the North Fork Toutle River (NFTR) which responded dramatically to the 1980 eruption of Mount St. Helens. It accurately predicts observed channel incision and bed material coarsening on the Colorado River, as well as observations for the upstream 18 km of the NFTR watershed. The model does not include algorithms for extensive lateral migration and avulsions and therefore did not perform well in the lower NFTR where the channel migrated across a wide valley bottom. REM is parsimonious and useful for simulating network scale channel change in single thread systems responding to disturbance. [ABSTRACT FROM AUTHOR]

Abstract A channel head is the upstream-most point of concentrated water flow and sediment transport between definable banks with a longitudinally continuous channel downstream. A channel head can be a relatively diffuse feature, the identification of which is subjective, or a very discrete and prominent break in the surface associated with a headcut. As the formal start of the channel network, channel heads reflect the location of process thresholds and thus differentiate geomorphic process domains for water, solute, and sediment fluxes. Stream order derives from mapped channel networks and the accuracy of stream ordering thus depends on the accuracy of identifying channel heads and associated first-order streams. In the absence of mapped channel heads, remote methods that under- or over-estimate the contributing area necessary to form a channel head can significantly over- or under-estimate, respectively, the extent of first-order streams and erroneously estimate drainage density. This paper reviews the current state of knowledge of the processes that form channel heads, the influences on channel head stability, and the methods used to identify the location of channel heads within a landscape unit. Individual channel heads can result from distinctly different processes, including surface fluvial erosion, surface colluvial erosion, subsurface erosion, or the intersection of subsurface preferential flow with the surface. The location of any channel head over a period of years to decades and longer is best understood as an average location that can and does change through time. The magnitude of change in the location of a channel head over time periods of years to decades will reflect the disturbance regime of the hillslope and the speed with which hillslope-channel processes recover following disturbance. If channel heads form where overland flow exerts a boundary shear stress that exceeds the critical value for substrate erosion, the channel initiation threshold, C , can be expressed as the product of contributing catchment area, A , and hillslope gradient, S : AS α ≥ C. An inverse relation between source area A and local slope S is present to a greater or lesser degree across diverse regions. Substantial variability in values of A and S reflects the influence of factors such as vegetation, slope aspect, surface versus subsurface flow paths, and substrate grain size. Analyses of published data suggest that channel head locations can be predicted with reasonable accuracy where surface runoff dominates channel initiation. Subsurface processes strongly influence the locations of many channel heads, however, and the area-slope relations for these channel heads are much less consistent and predictable. The challenges of channel heads are three-fold for any given drainage basin or portion of a drainage basin: to identify their geographic location, to predict their geographic location, and to determine the relative importance of potential control variables on the multiple processes that can create channel heads. In order to effectively address these challenges, additional research is needed to predict the regional characteristics likely to result in channel heads created by predominantly surface versus subsurface flow; develop envelope curves of A-S relations for different regions; compare channel head locations predicted based on hillslope curvature versus actual channel head locations; evaluate the spatial consistency of channel heads through time; and develop A-S relations for channel heads in little studied regions, including arid and hyperarid environments, karst and permafrost terrains, and grassland and savanna environments. [ABSTRACT FROM AUTHOR]

A 2D tidal-dispersion model is implemented to simulate the morphodynamics of marsh channels and their response to changes in Sea Level Rise (SLR) rate and sediment supply. The model is applied to the mesotidal marshes of Plum Island Estuary (MA, USA). The peak tidal flow predicted by the model agrees with that measured in a channel for different spring-neap conditions. The model also reproduces the present channel geometry, which is characterized by a spatially variable width to depth ratio. The model suggests that an increase in sediment supply during colonial times (17th century) narrowed the channels of the existing fringing marshes. This narrowing was however temporary, and channels returned to their pre-disturbed width by the end of the 19th century. The model highlights that Suspended Sediment Concentration (SSC) within the channels did not respond uniformly to the changes in sediment supply, and that gradients in SSC can be used to infer sediment input to or export from the marsh. The model also reproduces the spatial patterns of channel widening that occurred since the beginning of the 20th century as a result of the increase in SLR rate from ∼1 to ∼2.6 mm/yr. Under the present SLR rate and sediment supply, the largest channels (>20 m wide) in Plum Island Estuary are predicted to widen by 5–10 m over the next centuries. Both an increase in SLR rate and a drop in sediment supply will increase the amount of widening, but will create different widening fingerprints: the latter will cause more spatially variable widening than the former. As such, spatial patterns of channel widening might theoretically be used to infer whether marsh loss is mainly driven by an increase in SLR rate or a decrease in sediment supply. [ABSTRACT FROM AUTHOR]

Summary: The purpose of this paper is to demonstrate cross‐Channel exchange of calcareous sandstone‐type whetstones derived from the Weald (Sussex, UK) in the Roman period. The presence of this particular type of whetstone at several Roman sites on the Continent – more specifically, in Belgium, France and the Netherlands – is reported for the first time. The morphology, geological provenance, petrographic characteristics and distribution patterns are discussed, based on a comparative analysis with archaeological and geological reference material. The geological analysis identifies a common geological source for the Continental finds: the very fine‐grained, thin‐bedded, flagstone‐like calcareous sandstone beds of the Lower Cretaceous Wealden Clay Formation. These sandstones were, most probably, extracted in the north‐western part of the Weald area. The distribution pattern of the archaeological material implies the importance of personal mobility, with potential military affinities. [ABSTRACT FROM AUTHOR]

In this paper, the thermo-hydrodynamics of Al 2 O 3 -water nanofluid in a wavy U-turn channel with hot walls is numerically investigated by means of lattice Boltzmann modeling. At first, the numerical technique is validated by simulating fluid flow in a (non-)wavy straight channel. Then, the effects of various active parameters, e.g. pressure gradient in the channel, nanoparticles volume fraction, and number of sinusoidal waves along the channel, on the flow field and heat transfer is studied. Furthermore, the thermal–hydraulic performance factor is determined to investigate whether heat transfer enhancement outweighs the greater frictional losses caused by both complex wavy wall geometry and nanoparticles. The results show that the heat transfer rises by increasing pressure gradient in the channel while drops by increasing number of waves. Also, the effect of nanoparticles volume fraction on dimensionless Nusselt number becomes more pronounced at higher pressure gradients. The results indicate that the thermal–hydraulic performance factor grows by increasing nanoparticles volume fraction or decreasing the number of waves. [ABSTRACT FROM AUTHOR]

The transition flow regime is the most complicated domain for modeling since the transition regime is a varying mixture of different transport mechanisms. Modeling the Navier-Stokes equations with the appropriate second order slip boundary condition at high Knudsen numbers is further explored in this paper. The general models proposed by one of the authors are validated against extensive numerical and experimental data in the literature. It is noteworthy that the geometry and the partial momentum accommodation are taken into account by the models. The present work provides a markedly simple way to compute quantities of engineering interest in microchannels and nanochannels of various cross sections over the full transition flow regime that is estimated to be accurate to 10%, with most data within 5%. As in the transition regime no data exist for most various geometries, this proposed engineering model fills this void. This paper further explores and validates working engineering macro models that can be easily implemented in applications. [ABSTRACT FROM AUTHOR]

Studying solute dispersion in channel flows is of significance for environmental and industrial applications. Two-dimensional concentration distribution for a most typical case of a point source release on the free water surface in a channel flow with bed absorption is presented by means of Chatwin’s long-time asymptotic technique. Five basic characteristics of Taylor dispersion and vertical mean concentration distribution with skewness and kurtosis modifications are also analyzed. The results reveal that bed absorption affects both the longitudinal and vertical concentration distributions and causes the contaminant cloud to concentrate in the upper layer. Additionally, the cross-sectional concentration distribution shows an asymptotic Gaussian distribution at large time which is unaffected by the bed absorption. The vertical concentration distribution is found to be nonuniform even at large time. The obtained results are essential for practical implements with strict environmental standards. [ABSTRACT FROM AUTHOR]

Experimental investigation into flow boiling critical heat flux (CHF) characteristics in narrow rectangular channels was performed under rotating state using distilled water as working fluids. The effects of mass velocity, inlet temperature and heating orientation on CHF under dynamic load were analyzed and discussed in this paper. The results show that the dynamic load obviously influences the CHF through enhancing two-phase mixing up and bubble separating. The greater the dynamic load, the higher the CHF values. The CHF values increase with the increase of mass velocity and inlet subcooling in the experimental range. The magnitude of CHF increase with the dynamic load for bottom heating is greater than that for up heating. The present study and its newly correlation may provide some technical supports in designing the airborne vapor cycle system. [ABSTRACT FROM AUTHOR]

In this study, we report large eddy simulations of turbulent flow in a periodic compound meandering channel for three different depth conditions: one in-bank and two overbank conditions. The flow configuration corresponds to the experiments of Shiono and Muto (1998). The predicted mean streamwise velocities, mean secondary motions, velocity fluctuations, turbulent kinetic energy as well as mean flood flow angle to meandering channel are in good agreement with the experimental measurements. We have analyzed the flow structure as a function of the inundation level, with particular emphasis on the development of the secondary motions due to the interaction between the main channel and the floodplain flow. Bed shear stresses have been also estimated in the simulations. Floodplain flow has a significant impact on the flow structure leading to significantly different bed shear stress patterns within the main meandering channel. The implications of these results for natural compound meandering channels are also discussed. [ABSTRACT FROM AUTHOR]

In this paper, we study the achievable throughput of batched temporal network coding in multi-hop erasure channels, where network coding is applied only within small coding blocks and each communication hop is modeled as a Gilbert–Elliott (GE) packet erasure channel. The GE channel is a 2-state Markov model that is commonly used for channels with memory. While channel memory does not affect the end-to-end capacity of multi-hop erasure channels, we show that it degrades the end-to-end throughput, when batched network coding with finite batch size is applied, due to the higher variance in erasures within one coding block. On the other hand, if the initial channel state information is available, the channel variance can be significantly reduced. We show that this fact can be utilized for improving the efficiency of the recoding operations at the intermediate nodes, and hence improve the end-to-end throughput of batched network coding schemes. Specifically, we propose adaptive recoding operations, where the network coded packets are adaptively generated based on the number of received packets and the initial channel state for each coding block. The simulation results show that the proposed adaptive recoding scheme significantly enhances the end-to-end throughput of batched network coding over multi-hop GE channels. [ABSTRACT FROM PUBLISHER]

This study uses continuous-recording load cell pressure sensors in four, high-elevation (1500–1800 m), Sierra Nevada headwater streams to collect high-temporal-resolution, bedload-movement data for investigating the channel bed movement patterns within these streams for water years 2012–2014. Data show an annual pattern where channel bed material in the thalweg starts to build up in early fall, peaks around peak snow melt, and scours back to baseline levels during hydrograph drawdown and base flow. This pattern is punctuated by disturbance and recovery of channel bed material associated with short-term storm events. A conceptual model, linking sediment sources at the channel margins to patterns of channel bed fill and scour in the thalweg, is proposed building on the results of Martin et al. (2014). The material in the thalweg represents a balance between sediment supply from the channel margins and sporadic, conveyor-belt-like downstream transport in the thalweg. The conceptual model highlights not only the importance of production and transport rates but also that seasonal connectedness between the margins and thalweg is a key sediment control, determining the accumulation rate of sediment stores at the margins and the redistribution of sediment from margins to thalweg that feeds the conveyor belt. Disturbance and recovery cycles are observed at multiple temporal scales; but long term, the channel beds are stable, suggesting that the beds act as short-term storage for sediment but are in equilibrium interannually. The feasibility of use for these sensors in forested mountain stream environments is tested. Despite a high failure rate (50%), load cell pressure sensors show potential for high-temporal-resolution bedload measurements, allowing for the collection of channel bed movement data to move beyond time-integrated change measurements — where many of the subtleties of bedload movement patterns may be missed — to continuous and/or real-time measurements. This type of high-temporal-resolution data provides insight into short-term cycles of bedload movement in high gradient, forested mountain streams. [ABSTRACT FROM AUTHOR]

This work presents the results of an experimental study of thermohydraulic performance of rectangular channel having discrete V-pattern baffle attached on the broad wall. Measurements have been carried out for the aspect channel ratio of 10, Reynolds number from 3000 to 21000, relative baffle height value of 0.50, relative baffle pitch value of 1.5, relative gap width value of 1.0, flow attack angle value of 60°, and relative discrete distance values of 0.26 to 0.83. The heat transfer and friction factor data obtained were compared with the data obtained from a smooth wall channel under similar operating conditions. In comparison to the smooth wall channel the discrete V-pattern baffle channel enhanced the Nusselt number and friction factor by 3.89 and 6.08 times, respectively. The overall thermal performance parameter is found superior for the relative discrete distance of 0.67. Discrete V-pattern baffle roughness shape has also been shown to be overall thermal performance higher in comparison to other continuous (without discrete) V-pattern baffle shape rectangular channel. [ABSTRACT FROM AUTHOR]

This paper focuses on simulation and analysis of the Houston Ship Channel vessel traffic and operation, through a discrete event model in Arena. The model is applied to mitigate the consequences of the channel closure for constructing a new bridge over the waterway. To evaluate different closure scenarios, real world data is analyzed, and a single factor ANOVA is used to find significant vessel waiting time differences. In addition, Fisher pairwise comparison method is applied to specify the best closure alternative. The results reveal that the best closure scenario will decrease waiting time up to 70%. The model can be used for assessing the performance of the system under different decision making frameworks. [ABSTRACT FROM AUTHOR]

Experimental study on mixed convection in the entrance region of a one-side-heated narrow rectangular channel has been carried out. We have performed a series of experiments under natural circulation conditions with Re ranging from 1000 to 3000 and inclination angle ranging from 0° to 30°. Meanwhile, we conducted flow visualization experiments to identify secondary flow driven by temperature difference between the lower, heated and upper, unheated plate of the channel. It is found that thermal instability can be enhanced by increasing the inclination angle of the channel. The secondary flow induces the onset of thermal instability (OTI) while increasing in Re delays the OTI. A sudden increase of hear transfer coefficient and friction factor has been observed after the OTI. The traditional identification criteria for mixed convection are not suitable for the inclined, narrow rectangular channel with a heated lower side. However, transverse Richardson number can identify mixed convection in the channel. The experiment results, together with image data for the flow condition in the inclined narrow rectangular channel, offer valuable data to improve the engineering design of plate-type fuel assembly and similar heat exchangers. [ABSTRACT FROM AUTHOR]

In this paper, the flow in the vicinity of rectangular side orifices placed in main channels is estimated by means of the FLOW-3D model. To reconstruct the flow free surface, the volume of fluid (VOF) approach is utilized. In addition, the standard k-ε and RNG k-ε turbulence models are employed to predict turbulence flow. According to the results obtained from the numerical modeling, the RNG k-ε turbulence model has higher accuracy than the standard k-ε. The analysis of the numerical modeling results proved that this model forecasts the discharge coefficient of side weirs with suitable accuracy. On the other hand, the mean absolute percent error (MAPE) is calculated equal to 12.204%. Also, the maximum pressure is simulated near the main channel bed. Moreover, the minimum pressure is estimated near the flow free surface. Regarding the numerical simulations, the maximum turbulence energy state occurs near the inlet of the side orifice and by increasing the side orifice dimensions the flow field turbulence energy value increases. [ABSTRACT FROM AUTHOR]

In streams where water availability is limited, conservative flow ranges are often adopted by water managers to ensure that streamflow is available to meet the ecological requirements of aquatic organisms. However, a variety of natural and anthropogenic disturbances can influence stream channel morphology and in-stream wood characteristics through time, potentially altering the availability of habitat at a given flow level. Using a 2D hydrodynamic modelling approach incorporating 45 years of detailed channel morphology data from Carnation Creek, British Columbia, this paper examines relationships between legacy (forestry-driven) watershed disturbance, changes to channel morphology, and habitat availability for juvenile coho salmon (Oncorhynchus kisutch) under nine flow levels. Results indicate that substantial variability in the abundance of salmonid habitat is present through time, even when modelled flow levels are held constant. Additionally, trade-offs were observed between availability of habitat types as discharge increased. Finally, modelling results indicate that habitat availability is reduced following historical harvesting. These findings suggest that legacy watershed disturbances affecting stream channel form and function are worth considering when allocating streamflow. Dans les cours d'eau ou la disponibilite d'eau est limitee, des fourchettes de debit axees sur la conservation sont souvent adoptees par les gestionnaires de l'eau afin d'assurer la disponibilite d'un ecoulement suffisant pour repondre aux besoins ecologiques d'organismes aquatiques. Diverses perturbations naturelles et d'origine humaine peuvent toutefois influencer la morphologie du chenal d'un cours d'eau et les caracteristiques du bois dans le cours d'eau au fil du temps, modifiant ainsi potentiellement la disponibilite d'habitats a un debit donne. En utilisant une approche de modelisation hydrodynamique en 2D qui integre 45 annees de donnees detaillees sur la morphologie du chenal pour le ruisseau Carnation (ColombieBritannique), l'article examine les relations entre les perturbations passees (causees par l'exploitation forestiere) du reseau hydrographique, les changements de la morphologie du chenal et la disponibilite d'habitats pour les saumons cohos (Oncorhynchus kisutch) juveniles pour neuf niveaux de debit. Les resultats revelent une variabilite considerable de l'abondance d'habitats de salmonides au fil du temps, meme quand les debits modelises sont maintenus constants. Des compromis entre la disponibilite de differents types d'habitats sont en outre observes a mesure qu'augmentent les debits. Enfin, les resultats de la modelisation indiquent que la disponibilite d'habitats baisse apres des coupes passees. Ces constatations donnent a penser qu'il est pertinent de tenir compte, au moment d'etablir les debits a allouer, des perturbations passees du reseau hydrographique qui ont une incidence sur la forme et la fonction du chenal. [Traduit par la Redaction], Introduction The quality and quantity of aquatic habitat supporting juvenile salmonids can be conceptualized as a product of five primary components in stream channels and in the broader surrounding landscape: [...]

The velocity distribution in natural channels is of considerable interest for streamflow measurements to obtain information on discharge and flow resistance. This study focuses on the comparison of theoretical velocity distributions based on 1) entropy theory, and 2) the two-parameter power law. The analysis identifies the correlation between the parameters of the distributions and defines their dependence on the geometric and hydraulic characteristics of the channel. Specifically, we investigate how the parameters are related to the flow resistance in terms of Manning roughness, shear velocity and water surface slope, and several formulae showing their relationships are proposed. Velocity measurements carried out in the past 20 years at Ponte Nuovo gauged section along the Tiber River, central Italy, are the basis for the analysis. [ABSTRACT FROM AUTHOR]

Sharp-crested weirs are frequently used for discharge measurements in open channels. They offer a simple, reliable and accurate flow measurement approach if they are properly installed and maintained. Suppressed weirs can be installed in channels with different shapes. The standard suppressed rectangular weir is well documented in the literature. The current research is conducted to achieve an accurate and simple formula for flow through the suppressed, sharp-crested weir located at the end of circular, open channels. The discharge equation of a suppressed, circular weir ends up as incomplete elliptic integrals of the first and second kinds, which are not very suitable for practical purposes owing to their complexity. In this study, a simple and accurate theoretical discharge equation has been presented for this weir. A series of laboratory experiments (244 runs) are also performed to investigate the discharge coefficient of sharp-crested weirs located at the end of two horizontal, circular, open channels. Using the data collected from two pipes of diameters 19·1 and 30·1 cm, a suitable discharge coefficient equation with an average relative error of less than 2·3% is presented; thus actual discharge through the channel can be simply estimated using the proposed equations. [ABSTRACT FROM AUTHOR]

The present study combines numerical and experimental approaches to investigate cross flow problems in the entrance channel of a harbor. The combined numerical-experimental approach is illustrated by an application to Lanshan Port (Shandong, China) where large tidal ranges and a newly planned harbor layout may give rise to strong cross flow in the entrance channel of the planned harbor. The resulting flow field with the numerical prediction shows that the layout of newly planned harbor has a major impact on the cross flow speeds in the entrance channel. This will affect the navigation safety of ship entering or leaving the harbor. A corresponding protective scheme related to breakwaters was put forward. A series of physical model experiments under the given flow provided by the numerical approach, were conducted to design the length and crest elevation of a previously proposed breakwater. Results from a series of laboratory model tests show a significant reduction of flow velocities across the entrance channel with longer breakwater length and higher crest elevation. However, a longer or higher breakwater obviously can expand the cross flow influenced zone into the entrance channel. The acceptable breakwater length and crest elevation were determined by taking account the maximum cross flow speed and cross flow influenced zone in addition to the construction cost. [ABSTRACT FROM AUTHOR]

In narrow water channels, ship traffic may be affected by water flows and ship interactions. Studying their effects can help maritime authorities to establish appropriate management strategies. In this study, a two-lane cellular automation model is proposed. Further, the behavior of ship traffic is analyzed by setting different water flow velocities and considering ship interactions. Numerical experiment results show that the ship traffic density-flux relation is significantly different from the results obtained by classical models. Furthermore, due to ship interactions, the ship lane-change rate is influenced by the water flow to a certain degree. [ABSTRACT FROM AUTHOR]

Lagrangian and Eulerian statistics are obtained from a water-channel experiment of an idealized two-dimensional urban canopy flow in neutral conditions. The objective is to quantify the Eulerian $$(T^{\mathrm{E}})$$ and Lagrangian $$(T^{\mathrm{L}})$$ time scales of the turbulence above the canopy layer as well as to investigate their dependence on the aspect ratio of the canopy, AR, as the latter is the ratio of the width ( W) to the height ( H) of the canyon. Experiments are also conducted for the case of flat terrain, which can be thought of as equivalent to a classical one-directional shear flow. The values found for the Eulerian time scales on flat terrain are in agreement with previous numerical results found in the literature. It is found that both the streamwise and vertical components of the Lagrangian time scale, $$T_\mathrm{u}^\mathrm{L} $$ and $$T_\mathrm{w}^\mathrm{L} $$ , follow Raupach's linear law within the constant-flux layer. The same holds true for $$T_\mathrm{w}^\mathrm{L} $$ in both the canopies analyzed $$(AR= 1$$ and $$AR= 2$$ ) and also for $$T_\mathrm{u}^\mathrm{L} $$ when $$AR = 1$$ . In contrast, for $$AR = 2$$ , $$T_\mathrm{u}^\mathrm{L} $$ follows Raupach's law only above $$z=2H$$ . Below that level, $$T_\mathrm{u}^\mathrm{L} $$ is nearly constant with height, showing at $$z=H$$ a value approximately one order of magnitude greater than that found for $$AR = 1$$ . It is shown that the assumption usually adopted for flat terrain, that $$\beta =T^{\mathrm{L}}/T^{\mathrm{E}}$$ is proportional to the inverse of the turbulence intensity, also holds true even for the canopy flow in the constant-flux layer. In particular, $$\gamma /i_\mathrm{u} $$ fits well $$\beta _\mathrm{u} =T_\mathrm{u}^\mathrm{L} /T_\mathrm{u}^\mathrm{E} $$ in both the configurations by choosing $$\gamma $$ to be 0.35 (here, $$i_\mathrm{u} =\sigma _\mathrm{u} / \bar{u} $$ , where $$\bar{u} $$ and $$\sigma _\mathrm{u} $$ are the mean and the root-mean-square of the streamwise velocity component, respectively). On the other hand, $$\beta _\mathrm{w} =T_\mathrm{w}^\mathrm{L} /T_\mathrm{w}^\mathrm{E} $$ follows approximately $$\gamma /i_\mathrm{w} =0.65/\left( {\sigma _\mathrm{w} /\bar{u} } \right) $$ for $$z > 2H$$ , irrespective of the AR value. The second main objective is to estimate other parameters of interest in dispersion studies, such as the eddy diffusivity of momentum $$(K_\mathrm{{T}})$$ and the Kolmogorov constant $$(C_0)$$ . It is found that $$C_0$$ depends appreciably on the velocity component both for the flat terrain and canopy flow, even though for the latter case it is insensitive to AR values. In all the three experimental configurations analyzed here, $$K_\mathrm{{T}}$$ shows an overall linear growth with height in agreement with the linear trend predicted by Prandtl's theory. [ABSTRACT FROM AUTHOR]

Maximum and average shear stress in rectangular channels can be estimated using the percentage of shear force carried by walls (%SFw), which is a parameter obtained using semi-empirical methods. The radial basis function (RBF) and Modified Structure RBF (MS-RBF) models are employed in this study to estimate %SFw. The two types of models performed well but an MS-RBF model with correlation coefficient (R2) of .9596 indicated better function than the RBF model withR2of .9462. Moreover, sensitivity analyses of the parameters affecting %SFwwere carried out based on two statistical parameters using the MS-RBF models. Fifteen MS-RBF models with different input combinations were investigated and the best model with the lowest error values was selected. Subsequently, this optimum model was compared with three linear regression equations presented for rough and smooth rectangular channels and two equations suggested by other researchers for smooth ducts. The MS-RBF model withR2of .9743 made the best %SFwpredictions compared with the other equations. [ABSTRACT FROM PUBLISHER]

Open channel flow through a line of vertically oriented circular rods, designed to represent idealized bankline vegetation, is studied. Bankline vegetation is a common feature in rivers and streams and yet has not received as much attention as fully vegetated flows. Particular focus is placed on the effect of vegetation diameter on the flow resistance which is quantified via a drag coefficient. A large number of laboratory experiments of uniform flow through one-line of vegetation were carried out and drag coefficients were calculated via a momentum balance. Experimentally obtained drag coefficients are then compared to those calculated using a number of empirical expressions that have been proposed in the literature. Good agreement is generally observed. The results show that varying the diameter of the rigid emergent vegetation affects flow resistance, and that the drag coefficient of in-line vegetation exhibits limited sensitivity to the stem Reynolds number. [ABSTRACT FROM PUBLISHER]

In order to study the impact of an expanding conjunction (with a divergent conjunction or with an abruptly expanding conjunction) between a stilling basin and the downstream channel on the height after jump, systematic experimental studies were carried out with different divergent angles and different abrupt expansion ratios at the conjunction. The link between the conjunction type and the height after jump is explored. The height after jump without an expanding conjunction is larger than that with a divergent conjunction, while the height after a jump without an expanding conjunction is larger than that with the abrupt expanding conjunction. Furthermore, with a larger divergent angle or larger expansion ratio, the impact on the height after jump becomes more variable. It is proposed that the existing formula which is used to calculate the height after jump in a straight channel is not appropriate for a jump with an expanding conjunction. This paper proposes a corrected formula to calculate the height after jump with an expanding conjunction, which is suggested for application in the engineering design process. [ABSTRACT FROM AUTHOR]

A hydraulic jump is the rapid transition from a supercritical to subcritical flow. This transition is characterized by large-scale turbulence and energy dissipation. Despite the importance of understanding the hydraulic jump to design hydraulic structures, few studies have aimed on hydraulic jumps in U-shaped channels. In this paper, the 3D pattern of hydraulic jumps in U-shaped channels is studied numerically. The variations of the flow free surface are predicted using the volume of fluid scheme. Also, the flow field turbulence is simulated using the standard $$k-\varepsilon $$ and RNG $$k-\varepsilon $$ turbulence models. According to the numerical modeling results, the standard $$k-\varepsilon $$ turbulence model estimates the flow characteristics with more accuracy. A comparison between the laboratory and numerical results shows that the numerical model simulates the flow field characteristics with good accuracy. For example, in the hydraulic jump model with a relative discharge $$({q=Q/{\sqrt{( {gD^{5}})}}})$$ equal to 0.321 and a Froude number $$({{F}_1})$$ equal to 4.85, the values of MAPE, RMSE and $${R}^{2}$$ are calculated 7.617, 0.022 and 0.989, respectively. Next, 45 numerical models are simulated in different hydraulic conditions and some relationships are provided for calculating the sequent depth $$({{h_2 }/{h_1 }})$$ , hydraulic length $$({{L_\mathrm{j}}/{h_1}})$$ and roller length $$({{L_\mathrm{r} }/{h_1}})$$ ratios by analyzing their results. [ABSTRACT FROM AUTHOR]

Evaluation of flow conditions in strongly curved open-channels is of vital importance in studying a variety of water engineering problems such as sedimentation, erosion, and contaminant transport. This work presents the impact of middle vanes on the water depth changes (super-elevation) in sharp bends. The behavior of these vanes while extending the up- and downstream channels is also investigated. Various experiments are conducted to verify the laboratory model, guarantee homogeneity of the data, and minimize the systematic errors. Accordingly, the water depth values are measured for three $$30{^{\circ }}$$ , $$60{^{\circ }}$$ , and $$90{^{\circ }}$$ bends with various inlet discharges for gauging sections throughout and after the bend. It is found that, unlike mild bends, super-elevation in sharp bends is nonlinear. Moreover, the vanes shift the location of the maximum and minimum depths from the bisector toward the end of the bends. Vanes are able to decrease the super-elevation while their efficiency can be improved up to 90% by extending them into the up- and downstream channels. A new equation is also proposed to determine the maximum water depth gradients. [ABSTRACT FROM AUTHOR]

This paper experimentally investigates the effects of rotation, turning vane, trailing edge ejection, and channel orientation on heat transfer (HT) in a typical turbine blade three-passage internal cooling test model. The cross section of the first and second passage are rectangular with aspect ratio 1:1 (AR = 1) and 2:1 (AR = 2) respectively, while the third passage is wedged shaped with slot discharge configuration to simulate the trailing edge ejection design. The flow direction in the first passage is radial outward, after the 180° tip turn, the flow turns radial inward at the second passage. The flow finally redirected to radial outward by the 180° hub turn and discharges through the slot configuration at the third passage. Data measurements are conducted in the second and third passages (includes the hub turn regions). The first passage is not instrumented and serves as flow inlet only. The effects of rotation on the heat transfer coefficients (HTC) were investigated at rotation numbers ( Ro ) up to 0.32 and Reynolds numbers ( Re ) from 10,000 to 40,000. This study concludes that the rotating utilizes a positive and negative effect on HT on the radial inward flow leading and trailing surfaces respectively. A reverse trend is concluded for radial outward flow. Rotation also suppresses HT in the turn portion. The effect is most severe at the hub turn side wall. The effect of turning vane slightly reduces and increases HT on all interested surfaces in radial inward and outward flow passages respectively. The turning vane effect is diluted in the hub turn area under rotation. Radial outward flow (third passage) HT is substantially impacted by the channel orientation. Combine with the discharge configuration, under rotating scheme, HT levels in β = 45° is significant lower then β = 90°. Regional HTCs are correlated with rotation numbers for multi-pass rectangular smooth channel with hub turning vane and trailing edge ejection. [ABSTRACT FROM AUTHOR]

Open water systems such as irrigation canals are used to transport and deliver water from the source to the user. Water loss in these systems by seepage, leakage, evaporation, or unknown water offtakes can be large. If this loss is unknown to the model used, it will not be considered by the controller and create a real system model mismatch. This mismatch will affect the water level directly and create an offset from the reference set point of the water level. A control configuration for open water canals, model predictive control (MPC) based on moving horizon estimation (MHE-MPC), to deal with offset problems resulting from real system-model mismatch is described in this paper. MHE uses the past predictions of the model and the past measurements of the system to estimate unknown disturbances and systematically removes the offset in the controlled water level. This control configuration is numerically tested on an accurate hydrodynamic model of the Control Algorithms Test Canal of the Technical University of Catalonia (UPC-PAC). The results presented in this paper show that MHE-MPC can realize offset-free control and the results are better than those of the well-known disturbance modelling offset-free control scheme. [ABSTRACT FROM AUTHOR]

An analytical solution of nondimensional hydraulic energy equation is derived in cosine form for the flow in rectangular open channels considering nonhydrostatic pressure and nonuniform velocity distributions across flow depth and friction and turbulent losses. The new inverted energy equation is a single equation describing all the three roots of the nondimensional hydraulic energy equation. The energy losses due to turbulence and bed shear are also implicitly accounted. Only two roots out of the three roots are practically significant, which denote the two alternate depths and are distinguishable for subcritical and supercritical flow, respectively. These equations yield direct determination of alternate depths in a single step, avoiding an iterative procedure. The use of the new equations is illustrated through worked-out examples. The new single-term analytical inverted equations are computationally simple and useful for academicians, field engineers, and practitioners in directly solving in a single step the problems of energy-equation inversion often encountered when dealing with transitions in a channel section, and flows over a dam-spillway and under a sluice gate, with correction-factors and loss coefficients estimated or known. [ABSTRACT FROM AUTHOR]

Side orifice is a hydraulic structure provided in the walls of a channel to divert flow from the main channel to another channel. It is used widely in environmental engineering and irrigation engineering. In the present study, numerical simulation has been performed to analyze the flow characteristics of a rectangular side orifice using the CFD program with ANSYS-CFX code. Finite volume method is used to solve the governing equations of the standard k-ε turbulence model in prismatic channels. The CFD model developed has been verified with the available experimental studies of Hussain and his associates. On comparing with experimental observations; it is found that the CFD model simulates the flow through the orifice with good accuracy. Flow pattern for a side orifice has also been analyzed for streamline pattern, velocity distribution, velocity contours. Further, a reverse flow in the main channel has been noticed near the vicinity of the orifice in the main channel. [ABSTRACT FROM AUTHOR]

For a given width, a labyrinth weir has a developed crest length, thereby increasing the flow capacity for a given upstream headwater. This paper experimentally studies the flow over labyrinth weirs with semicircular and sinusoidal configurations in a rectangular channel under a wide range of flow discharges. The effects of headwater ratio (HT/P), length of weir (L/P), arc radius ratio (R/P) and the number of cycles (N) on the discharge coefficient of semicircular and sinusoidal labyrinth weirs are investigated. Experimental results indicated the decreasing trend of Cd for HT/P>0.35 which is probably related to the progressive development of local submergence. Despite the effects of local submergence, the labyrinth weirs have nearly the same discharge coefficient as broad-crested weirs, and the flow discharge exceeded the linear weirs efficiency by ∼30. Additionally, reliable equations for estimating the discharge coefficient of labyrinth weirs with semicircular and sinusoidal configurations are presented. [ABSTRACT FROM AUTHOR]

The occurrence of local scour around bridge piers or abutments is one of the major reasons for the destruction of bridges. Therefore, this phenomenon should be prevented or at least minimized using some methods, namely using collars in recent years. In the present paper, by proposing a new approach and developing an experimental model of partial collars (collars not fully encircling the abutment), the effect of length and width of collars on reducing scouring and sedimentation pattern around the bridge abutments with vertical walls were investigated under different conditions. Moreover, the obtained results were compared with the results of models with full collars. The results revealed that collar dimensions could have a great impact on its efficiency. In partial collars, if only the upstream face of the abutment is protected and there is no protrusion toward the downstream, there will be no high and acceptable efficiency. However, increasing length and width, its positive efficiency will be enhanced. Although increasing the length of a collar of this type to more than 0.6 times the length of the abutment diminishes the scouring around the bridge abutment, increasing its width not only does reduce the scour depth but also produces a much greater effect on the location of the scouring hole to be farther away from the downstream of the abutment. Furthermore, the efficiency of full collars is also enhanced as their length and width increase. Comparison of the results shows that the efficiency of full collars is less than that of partial collars, despite their greater cross-sectional area. Therefore, partial collars are more cost-effective than full collars due to their lower cross-sectional areas. The average percentage of scour depth reduction for all four flows for different models in the erodible bed and at the base point ranged from 24 to 68% and 24 to 97%, respectively. [ABSTRACT FROM AUTHOR]

Broad-crested weirs (BCW) are commonly used elements of stormwater systems and different open-channel hydraulic structures. Specific features of stormwater drainage channels are small width, low flow depths and, accordingly, small overflow heads at weirs. Dependences of the discharge coefficient of narrow (b = 0.224 m) rectangular sharp-edged broad-crested weirs with vertical walls, threshold height of 0.05 m and threshold length of 0.05-0.2 m were obtained experimentally. The experimental values of the discharge coefficient were approximated by the power-law functions of relative length of the weir. At large values of the relative length of the threshold (L/h> 10), for all weirs was obtained the same tendency of decreasing the discharge coefficient with increasing L/h ratio that can be explained by the enlargement of the hydraulic friction along the weir with increasing L/h ratio. [ABSTRACT FROM AUTHOR]