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Understanding the flow characteristics of rivers in both their inbank and overbank flow conditions is an important task for engineers. So far, many studies have been carried out in compound channels with prismatic and non-prismatic floodplains. However, we still don't understand the effect of the floodplain's side slope on the flow field in compound channels. This paper presents the results of experiments on compound channels with skewed and inclined floodplains (lateral slope of 0.075). Velocity and boundary shear stress were measured at various experimental sections for different relative depths and two skew angles of 3.81º and 11.31º. Using the measured data, the secondary currents pattern, the apparent shear forces at the vertical interface between the main channel and floodplains, and the discharge distribution in the main channel and the floodplains along the flume have been investigated. The results of the experiments were then compared to the experimental data of the skewed compound channel with flat floodplains. The research shows that due to lateral flow and momentum exchange between flume subsections, the flow velocity, bed shear stress, and percentage discharge on the diverging floodplain are greater than those on the converging floodplain with the same cross-sectional geometry. [ABSTRACT FROM AUTHOR]

This study numerically investigates and compares the secondary currents, velocity dips, turbulence properties, and boundary shear stresses in supercritical narrow open channel flows (OCFs) and in narrow duct flows (DFs) using an updated Launder–Reece–Rodi Reynolds stress model in OpenFOAM, which was validated previously for supercritical flows using experimental data. Six steady state simulations were performed at a bulk velocity of 2.31 m/s covering Reynolds numbers from 3.08×105 to 6.16×105 and aspect ratios (width to flow depth) of 1.0. 1.25, and 2.0, which in combination with the observed Froude numbers from 1.65 to 2.33 for OCFs are comparable to sediment bypass tunnel flows. Although free surface produces greater maximum secondary flows, the top wall in DFs creates stronger bulging of the longitudinal velocity above the velocity dips, which generates marginally higher maximum longitudinal velocity and significantly higher velocity fluctuations compared to OCFs. Two pairs of corner vortices are observed in each half width for DFs. However, such vortices differ in OCFs, in which the reduction of aspect ratio develops intermediate vortices. Such differences in the secondary currents are interrelated to the observed variations in the distributions of longitudinal velocity and Reynolds stresses. Higher average bed and sidewall shear stresses are obtained for DFs than for OCFs. The bottom vortices undulate the bed shear stress distributions. Similarly, the sidewall corner vortices (for DFs) or intermediate vortices and inner secondary vortices (for OCFs) undulate the wall shear stress distributions. These undulations are further influenced by the aspect ratio. Moreover, the flow characteristics below the mid depth observed for OCFs are comparable to those obtained for DFs, especially for the square cross sections with aspect ratio of 1.0. [ABSTRACT FROM AUTHOR]

A compound channel's discharge capacity and boundary shear force can be predicted as a sum of the discharge capacity of different sub-regions once the apparent shear stress of the dividing line is reasonably quantified. The apparent shear stress was usually expressed as a coefficient multiplied by the difference between two squared velocities of two adjacent regions. This study investigated the range of the coefficient values and their influencing factors. Firstly, the optimal values of the coefficient were obtained based on experimental data. Then, comparisons between the optimal values and several parameters used in quantifying the apparent shear stress were conducted. The results show that the coefficient is mainly related to a morphological parameter of the floodplain and the ratio of resistance coefficients between the floodplain and the main channel. An empirical formula to calculate the coefficient was developed and introduced to calculate the flow discharge and boundary shear stress. Experimental data, including 142 sets of test data of symmetric-floodplain cases and 104 sets of one-floodplain cases, have been used to examine the prediction accuracy of discharges and boundary shear stress. For all these tests, the ranges of water depth of the main channel and the total width of the compound cross-section are about 0.05~0.30 m and 0.3~10 m, respectively; the Q range and the range of Froude numbers of the main channel flow are about 0.0033~1.11 m3/s and 0.3~2.3, respectively. Comparison with other methods and experimental data from both rigid and erodible compound channels indicated that the proposed method not only provided acceptable accuracy for the computation of discharge capacity and boundary shear stress of compound channels in labs but also gave insights for calculating discharge capacity in natural compound channels. [ABSTRACT FROM AUTHOR]

The present study discusses and analyses the influence of composite roughness on the stage-discharge relationships and flow characteristics in compound channels with different channel roughness. An analytical solution to predict depth-averaged velocity, non-dimensional coefficient, integration constants and composite roughness is developed by considering the shear forces acting on the channel beds and walls. The model was applied to three different new experiments and two previous experiments. It indicates that the composite roughness is the key flow resistance parameter that influences the depth-averaged velocity, boundary shear stress distributions, and stage-discharge relationships. The result shows that, in a rough bed, the boundary shear stress in the floodplain was significantly higher than in a heterogeneous and smooth bed. The error analysis is also discussed, and the present model error is the least. Thus, the present analytical solution gives a good prediction of the stage-discharge relationships when compared with experimental data. [ABSTRACT FROM AUTHOR]

The present study has studied a model to predict depth-averaged velocity distribution and boundary shear stress in compound channels with different floodplain widths. The model was verified against three different data sets of the present experiments and two data used in the literature. The results indicate that the present model can predict the depth-averaged velocity and shear stress distributions, promising to simulate the flow field and related characteristics better. The results show that the non-dimensional coefficient plays a dominant role in portraying the variation of depth-averaged velocity and shear stress distributions in compound channels with different floodplain widths. In addition, the apparent shear forces were examined by dividing the channel cross-section into seven parts, and each element carried shear forces and acted on the horizontal and vertical interfaces for three different width-to-depth ratios were discussed and analyzed. In all configurations, the horizontal interface was negative, indicating that the upper region of flow accelerates the flow in the lower main channel. In contrast, the vertical interfaces were positive, suggesting that the slower floodplain flows retards the faster main channel flows. [ABSTRACT FROM AUTHOR]

This paper presents experimental results of overbank flow in compound channels with converging and inclined floodplains. Velocity and boundary shear stress distributions at different selected sections along the narrowing part of the flume for two convergence angles of 3.81° and 11.31° were measured. The study indicated that the velocity and boundary shear stress increase along the flume, especially in the second half of the converging part of the flume. It was shown that the maximum velocity at the end of the converging transition can be over than twice as much as at the beginning section. By using the experimental data and force–momentum balance, the apparent shear forces at the vertical interface between the main channel and floodplains were investigated. The apparent shear forces at the vertical interface of the flume subsections increased with the increase of the convergence angle and relative depth, reached a peak at the relative depth of 0.4, and then decreased. [ABSTRACT FROM AUTHOR]

Discharge and channel geometry control velocity and bed shear stress within a reach. Channel roughness (e.g., riffles, pools) and ice cover in winter moderates velocity and shear stress at the bed. This study evaluated velocity profiles across a channel segment with variable bed roughness (e.g., riffles, pools) to determine changes in the position of maximum velocity, maximum velocity magnitude, and resulting bed shear stress estimates when ice cover was present. Using acoustic doppler velocimeter (ADV) and acoustic doppler current profiler (ADCP) high resolution velocity profiles were collected during ice cover, open water, and open water with significant increases in vegetation cover through a riffle‐pool sequence in a low‐order channel in southern Ontario Canada in the first half of 2021. Key findings were that in five of the seven cross‐sections, flow direction was significantly different when ice was present. Additionally, maximum velocities were closer to the bed during ice cover, a common finding in modelling and experimental work, and is confirmed in this field setting. Although maximum velocity magnitudes were not significantly different, derived bed shear stress values under ice were larger. Specifically, under ice conditions, riffle bed shear stress ranged 0–16 N/m2 compared to 0–9 N/m2 in ice free conditions. In the pool, bed shear stress ranged 0–6 N/m2 under ice cover, and 0–5 N/m2 in ice free conditions. Further, as flow levels increased through the spring and summer, this coincided with increased in‐stream vegetation cover, which decreased flow velocities near the bed, and thus decreased bed shear stresses to less than 1 N/m2 in both the riffle and pool sections. The findings indicate that channel evolution processes may be more intense during lower‐stage winter flows when ice is present and has significant implications for channel design, restoration and management strategies used in small channels impacted by ice cover. [ABSTRACT FROM AUTHOR]

A model for stage–discharge relationship in two-stage wide meandering channels, devised by statistical analysis of new experimental boundary shear data and some published shear data, is presented. By evaluating the measured boundary shear percentage on floodplains of unequal length on either side along with corresponding wetted area percentage for sinuous channels, it is seen that different but particular empirical relationships exist between shear percentage and percentage flow area due to various flow mechanisms occurring on floodplains lying on either side of the bend. The empirical relationships obtained for left floodplain shear is an exponential function while that for total floodplain is a power function. Expressions for average zonal velocity and hence for zonal discharge are then estimated by 1D analysis to compute the H–Q rating curve for such channels. This method is validated through its application to different published data sets with discharge prediction error lying close to ±10% on most occasions. The method when compared with some other well-known 1D approaches is found to perform reasonably well as evident from error analysis. The method when tested for predicting flow distribution, the error percentage is again within 10% for available limited data series. [ABSTRACT FROM AUTHOR]

Measurement of bed shear stress is always a challenging task for engineers. In river engineering, bed shear is a fundamental variable and is important in estimating flow resistance and sediment transport. In this study, experiments are carried out in diverging compound channel with smooth bed (perspex sheet) and rough bed (Gravel) conditions to determine the effect of roughness. The shear velocity is estimated from universal logarithmic law. The effect of geometry and roughness on Von-Karman constant, eddy viscosity coefficient, friction factor is studied. The mass conservation and momentum conservation equations are used to derive apparent shear forces at interface of main channel and floodplain. A genetic algorithm model is developed to predict percentage of shear force (%Sfp) carried by sub-sections. To perform better with less and unseen data K-Fold cross-validation technique is used. The model is compared with available models in literature and it is observed that developed model gave better predictions with low MAPE. [ABSTRACT FROM AUTHOR]

Conventional methods for measuring local shear stress on the wetted perimeter of open channels are related to the measurement of the very low velocity close to the boundary. Measuring near-zero velocity values with high fluctuations has always been a difficult task for fluid flow near solid boundaries. To solve the observation problems, a new model was developed to estimate the distribution of boundary shear stress from the velocity distribution in open channels with different cross-sectional shapes. To estimate the shear stress at a point on the wetted perimeter by the model, the velocity must be measured at a point with a known normal distance to the boundary. The experimental work of some other researchers on channels with various cross-sectional shapes, including rectangular, trapezoidal, partially full circular, and compound shapes, was used to evaluate the performance of the proposed model. Optimized exponent coefficients for the model were found using the multivariate Newton method with the minimum of the mean absolute percentage error (MAPE) between the model and experimental data as the objective function. Subsequently, the calculated shear stress distributions along the wetted perimeter were compared with the experimental data. The most important advantage of the proposed model is its inherent simplicity. The mean MAPE value for the seven selected cross-sections was 6.9%. The best results were found in the cross-sections with less discontinuity of the wetted perimeter, including the compound, trapezoidal, and partially full circular pipes. In contrast, for the rectangular cross-section with an angle between the bed and walls of 90°, MAPE increased due to the large discontinuities.

The estimation of boundary shear stress distribution in a channel is a challenge in some hydraulic or environment investigations. A new partition model of a trapezoidal cross-section in a prismatic channel with composite roughness has been introduced based on a concept of a standardized cross-section using the "zero-shear stress" division lines. Based on this new model, an "equal local-region velocity" assumption, which can be regarded as an improvement of Einstein's (1942) "equal velocity" assumption, has been proposed that is based on a discussion on the mechanism of energy transfer and velocity distribution at two sides of a dividing line. This assumption along with some empirical treatments have been employed to establish a new method to estimate the boundary shear stress of a side-wall or bed. Comparisons show that the proposed method can be applied to composite roughness cases and provides better prediction performance compared to other methods. [ABSTRACT FROM AUTHOR]

The use of apparent shear stress at the interface between the adjacent subregions of a cross section to represent the effect of momentum transfer is a common method for the one-dimensional calculation of compound open-channel flow. The apparent shear stress of the dividing lines is affected by the compound geometry and boundary conditions. The expressions of the apparent shear stress established with previous studies are very different. Empirical treatment was proposed in this study to simplify the expressions based on a momentum transfer–equivalent states assumption, in which (1) the apparent shear stress was assumed to be the difference of the momentum transfer from two sides of a dividing line, and (2) two assumed equivalent states were employed to define the equivalent value of the momentum transfer. The apparent shear stress could be calculated based on the deviation of the momentum transfer from its equivalent value. The new expressions were used to calculate the discharges and the boundary shear force. Comparisons between the calculated results based on different methods and the measured data showed that the proposed method improved the calculation of the subregion boundary shear force and the discharges in the compound cross sections. [ABSTRACT FROM AUTHOR]

Compound channels are consisting of two hydraulic sections namely main channel and floodplain. In meandering rivers, with the passage of time and lateral movement of the meanders, the external bending progression and the sinusoidal or curvature is increased. The curvature of meandering sections can be defined by a dimensionless parameter as the sinusoidal number which is the ratio of meandering length of main channel to the floodplain length. In this research work, the hydraulic characteristics of flow including the velocity magnitude, boundary shear stress, turbulence intensity and turbulence energy of the main channel along the meandering compound channel have been investigated numerically, regarding changes in the sinusoidal ratio for six types of channels with different sinusoidal ratios. In order to investigate the effect of sinusoidal ratio in meandering compound channels on the hydraulic characteristics of the flow, the FLOW3D software is applied. Numerical simulation results show that by increasing the channel sinusoidal number from 1 to 1.641, the velocity and bed shear stress decrease and the turbulence intensity and energy increases. So that the maximum value of the above parameters occurs in the inner arc.

The presence of spherical solid particles immersed in an incompressible turbulent flow was numerically investigated from the perspective of the particle mass fraction (PMF or Φm), a measure of the particle-to-fluid mass ratio. Although a number of different changes have been reported to be obtained by the presence of solid particles in incompressible turbulent flows, the present study reports the findings of varying Φm in the the turbulent behaviour of the flow, including aspects such as: turbulent statistics, skin-friction coefficient, and the general dynamics of a particle-laden flow. For this purpose, a particle-laden turbulent channel flow transporting solid particles at three different friction Reynolds numbers, namely Reτ = 180, 365, and 950, with a fixed particle volume fraction of Φv = 10-3, was employed as conceptual flow model and simulated using large eddy simulations. The value adopted Φv for allowed the use of a two-way coupling approach between the particles and the flow or carrier phase. Three different values of Φm were explored in this work Φm ≈ 1, 2.96, and 12.4. Assessment of the effect of Φm was performed by examining changes of mean velocity profiles, velocity fluctuation profiles, and a number of other relevant turbulence statistics. Our results show that attenuation of turbulence activity of the carrier phase is attained, and that such attenuation increases with Φm at fixed Reynolds numbers and Φv. For the smallest Reynolds number case considered, flows carrying particles with higher Φm exhibited lower energy requirements to sustain constant fluid mass flow rate conditions. By examining the flow velocity field, as well as instantaneous velocity components contours, it is shown that the attenuation acts even on the largest scales of the flow dynamics, and not only at the smaller levels. These findings reinforce the concept of a selective stabilising effect induced by the solid particles, particularly enhanced by high values of Φm, which could eventually be exploited for improvement of energetic efficiency of piping or equivalent particles transport systems. [ABSTRACT FROM AUTHOR]

An analytical model was developed to predict the boundary shear stress and the depth-averaged streamwise velocity in the breach. A more general expression of the depth-integrated form of the streamwise Reynolds averaged Navier-Stokes (RANS) equation was rewritten by considering the secondary flow effects. It accounts for secondary flow effects via the dimensionless secondary flow parameters k1 and k2. The averaged lateral shear stress, the bottom shear stress and the depth-averaged streamwise velocity of the breach was obtained. According to sensitivity analysis of parameters, it is obtained that the secondary flow parameter k2 has a great influence on the averaged lateral shear stress, but few influences on the bottom shear stress and the depth-averaged streamwise velocity. The dimensionless streamwise velocity variation parameter c1 has great influences on the averaged lateral shear stress, bottom shear stress and the depth-averaged streamwise velocity. Comparison of the analytical results with experimental data shows that the proposed model predicts the averaged lateral shear stress and the bottom shear stress well. [ABSTRACT FROM AUTHOR]

An unsteady flow and heat transfer problem with viscous dissipation of a third order fluid placed within two long parallel flat porous walls is studied in present work. The governing equations are non-dimensionalized and finally a non-linear coupled system of partial differential equation is obtained. An approximated solution is obtained using finite difference method of fully implicit form. With help of high speed MATLAB programming numerical solution is procured and presented graphically. Investigation is made on effect of different physical parameters on flow and heat profile. The notable finding in the current work is that for smaller values of visco-elastic parameter ®, the velocity rises with raising the values of ®. But for larger visco-elastic parametric values of ®, a reversed effect is seen on velocity field. Also with the increase of viscous-dissipation parameter, more viscous-dissipation heat generated that increases the temperature field. [ABSTRACT FROM AUTHOR]

In the present investigation, the roughness characteristics of the gravel bed is tested and modelled for the no-load condition. A straight trapezoidal channel having gravel bed surface of grain size D50 as 13.5 mm for no-load condition is used to carry out the investigation. Depth averaged velocity (DAV) and boundary shear stress (BSS) have been measured for five different depths. An improved model for prediction of friction factor is derived as the function of corresponding hydraulic radius and average diameter of the gravel. This improved model is validated with the models of past investigators. Furthermore, BSS is then calculated using Shiono and Knight Method (SKM), which is dependent on the following hydraulic parameters, such as friction factor f, coefficient of eddy viscosity λ and secondary flow term Г. Since friction factor is modelled for the given channel, same model is used to calculate the value of f over the bed, which tests the reliability of the model while using numerical method. The lateral distribution of DAV and BSS is shown for five different flow depths, which elaborate the bed friction due to the no-load condition. Finally, friction factor model is corroborated on two reaches of the natural river. [ABSTRACT FROM AUTHOR]

Gravel bed flow is so generic condition that its study becomes fascinating as well as critical to apprehend flow characteristic. In this particular study, no bed load movement was maintained using grains of 13.5 mm (D50 value) characterised as no load condition. Depth Average Velocity (DAV) and the Boundary Shear Stress (BSS) has been experimentally estimated for five different depths for the prevailing no load condition. Furthermore, the distribution of streamwise depth-averaged velocity and boundary shear stress at different flow depths of gravel bed are also calculated using different hydraulic software packages such as CES & ANSYS FLUENT. These numerical simulation results have shown reasonably good agreement with experimental data over main channel in inbank flow. Finally, results obtained are corroborated through error analysis. The overall idea of this study was to understand flow characteristic and behaviour of gravel bed having inbank flow through experimental and numerical simulation techniques. [ABSTRACT FROM AUTHOR]

In this work, we have considered and compared two molecular dynamics schemes widely used when studying a thin fluid film confined between solid surfaces and undergoing boundary shear. In the first approach, the non-equilibrium simulations are performed on a confined fluid explicitly connected to bulk reservoirs. In the second one, non-equilibrium simulations are carried out on the confined fluid only, in which the average density is deduced from a prior simulation in the grand canonical ensemble. We have found that the apparent properties (average density and effective viscosity) of a strongly confined Lennard-Jones liquid are significantly different using one scheme or the other when the solid surfaces induce a strong structure in the whole fluid, i.e., for small separations between the solid surfaces. Furthermore, the shear velocity dependence of the friction force has been found to be as well very sensitive to the approach chosen and can be well understood in terms of the fluid structure, which can even lead to a visco-plastic behavior of the fluid in some cases. Finally, it is shown that the first scheme is the only one usable to explore the history-dependence of the friction force as observed in experiments. [ABSTRACT FROM AUTHOR]

Abstract The Shiono and Knight Method (SKM) is widely used to predict the lateral distribution of depth-averaged velocity and boundary shear stress for flows in compound channels. Three calibrating coefficients need to be estimated for applying the SKM, namely eddy viscosity coefficient (λ), friction factor (f) and secondary flow coefficient (k). There are several tested methods which can satisfactorily be used to estimate λ, f. However, the calibration of secondary flow coefficients k to account for secondary flow effects correctly is still problematic. In this paper, the calibration of secondary flow coefficients is established by employing two approaches to estimate correct values of k for simulating asymmetric compound channel with different side slopes of the internal wall. The first approach is based on Abril and Knight (2004) who suggest fixed values for main channel and floodplain regions. In the second approach, the equations developed by Devi and Khatua (2017) that relate the variation of the secondary flow coefficients with the relative depth (β) and width ratio (α) are used. The results indicate that the calibration method developed by Devi and Khatua (2017) is a better choice for calibrating the secondary flow coefficients than using the first approach which assumes a fixed value of k for different flow depths. The results also indicate that the boundary condition based on the shear force continuity can successfully be used for simulating rectangular compound channels, while the continuity of depth-averaged velocity and its gradient is accepted boundary condition in simulations of trapezoidal compound channels. However, the SKM performance for predicting the boundary shear stress over the shear layer region may not be improved by only imposing the suitable calibrated values of secondary flow coefficients. This is because difficulties of modelling the complex interaction that develops between the flows in the main channel and on the floodplain in this region.

There is always an exchange of momentum between the deep main channel and its shallow floodplains of a compound channel section. When rivers have single side floodplains, they are known as asymmetric compound channels. Momentum transfer phenomenon has the effect of increasing floodplain shear and decreasing the main channel shear. In symmetrical compound channels, the momentum transfer occurs from both sides of the main channel to the floodplains whereas, for an asymmetrical compound channel, there is a stronger interaction takes place as compared to the symmetrical case. This causes more non-uniform boundary shear stress distribution as compared to the symmetrical cases. Experiments are conducted to measure the boundary shear stress distribution of an asymmetric compound channel that helps to quantify the momentum transfer in terms of apparent shear stress at the interface. Analysis of the apparent shear is useful in deciding the choice of appropriate interface planes for stage–discharge relationship of a compound channel. In the present work, an improved expression to predict the apparent shear stress, especially in an asymmetrical compound channel is developed. The strength of the new expression to predict apparent shear stress is also found to be better than the models of other investigators. [ABSTRACT FROM AUTHOR]

Gravel bed can be categorised into three bed load conditions, i.e. no load, moderate and intense. An experimental investigation was carried out in an open channel flow with gravel bed surface of grain size of D50 values 6.5 mm intense load conditions. The investigation of the roughness characteristics of gravel bed open channel flows under intense load conditions over various discharges and flow depths are presented. Variation of friction factor for the roughness conditions for different flow depths is estimated. The intensity of the bed load is calculated with the help of sediment transport rate. The bed load transport rate for the intense load conditions is also determined from experimentation on gravel beds of 6.5 mm gravel size for different flow depths. Using the data-set of other researchers and present experimental data, a new model as a function of intensity of the bed load transport with respect to Shield's parameter is formulated. The modified model gives satisfactory results as compared to previous works, which is displayed through error analysis. [ABSTRACT FROM AUTHOR]

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A culvert is a covered channel to pass streams and floodwaters through an embankment. The ecological impact of culverts has been recognised, in particular in terms of stream connectivity, but existing guidelines lead often to un-economical culvert design. Herein, a small triangular corner baffle system was tested physically in a near-full-scale fish-friendly facility of a box culvert barrel. Experiments were repeated with several configurations to characterise the flow properties for a range of less-than-design flows, baffle sizes and spacings. In presence of triangular corner baffles, the flow was asymmetrical, owing to the wake behind each baffle. The presence of triangular corner baffles had a moderate effect on the flow resistance and discharge capacity, albeit the data indicated the combined effect of relative baffle height and spacing on the friction factor. With triangular baffles, the surface area of slow velocity regions increased by a factor of two to three. Such low velocity regions are preferential swimming zones for fish, beneficial to small-bodied fish passage. Testing with small-bodied fish showed that fish preferred to swim upstream in slow-velocity regions, typically next to the sidewalls and in the left corner where the triangular baffles were located. The presence of small triangular baffles facilitated substantially the upstream passage of small fish, including in terms of endurance, compared to a smooth un-baffled box culvert barrel, when the baffle size was comparable to the fish length. The present findings highlighted the importance of physical modelling at near full-scale for the development of fish-friendly culvert designs. [ABSTRACT FROM AUTHOR]

The method of determining concrete fracture energy recommended by RILEM has an obvious size effect, so determining fracture energy that is unaffected by size of the test specimen is difficult. In this study, 60 high-strength concrete single-edge notched beams (SENBs) of different sizes, crack length-to-depth ratios, and span-to-depth ratios were subjected to the three-point loading test as recommended by RILEM. Then, the influences of the boundary effect on the fracture energy were identified. Based on the SENB boundary effect model, a piecewise function of the interrelationships between the experimental test fracture energy Gf, the local fracture energy gf, and the fracture energy unaffected by specimen size GF was established. The applicability of the boundary effect model was verified using the test results from this study and from the previously published research. The results show that the local fracture energy distribution in the boundary influence region was nonuniform. The smaller the local fracture energy was, the closer it was to the rear boundary of the specimen. The influence length al∗ of the boundary increased with the increasing specimen size. Based on the bilinear distribution model of the local fracture energy gf, the fracture energy unaffected by beam size GF can be obtained according to the fracture energy Gf measured for laboratory-scale small-sized SENB specimens. Furthermore, the model predictions are in good agreement with experimental observations. [ABSTRACT FROM AUTHOR]

Depth-averaged hydrodynamic models are predominantly used in numerical simulations of compound channel flows. One of the most popular methods for the depth-averaged simulation is Shiono and Knight method (SKM). This method accounts for the effects of bed friction, lateral turbulence and secondary flows, via three key parameters f, λ and Γ, respectively. The conventional expressions that are developed to calibrate these parameters are generally based on experiments in compound channels with wide floodplains. In this study, the application of SKM to an asymmetric compound channel with a narrow floodplain is examined in terms of the calibration requirements. Two sets of experiments that have smooth and rough floodplains are conducted and then simulated by SKM. In smooth floodplain cases, the results reveal that SKM model with the conventional calibration expressions of f, λ and Г is reasonably capable of predicting the distributions of depth-averaged velocity and boundary shear stress in the main channel. However, in the floodplain region, the expressions recommended for calibrating Г need to be modified to improve the predicted results in that region. In cases of the rough floodplain, the results indicate that only the values of λ in the main channel need to be changed from its conventional values to improve the predictions. [ABSTRACT FROM AUTHOR]

Highlights • Measurements of flow, bed sediment and bed load below a large gravel bed river bend. • Sediment transport processes contributing to stability of meanders are identified. • Equal threshold of movement of sediment is achieved across the bend point-bar. • Bed surface armoring and bed structuring might increase stability of the pool. • Processes sustaining stability in straight reaches operate also in meander bends. Abstract A new data set of bed load measurements in a cross-section at the exit of a river bend is presented. Data are analyzed to identify processes that contribute to the morphodynamic stability of gravel bed meanders. It is shown that boundary shear stress and bed material texture are strongly coupled, resulting in an almost equal mobility at incipient motion over the bend point bar in relation to channel flow stage. Conversely, for conditions above bankfull an excess of fine sediment towards the inner-bank, likely related to more intense crosswise flux and grain size sorting, results in size selective transport in relation to the local bed material. We suggest that bed armoring and structuring, as well as crosswise sediment flux, add stability to the outer-bank pool, while the point bar is eroded by large floods and restored by moderate flows. Results reveal the strong feedback of processes at different scales promoting stability at bends of gravel bed rivers. [ABSTRACT FROM AUTHOR]

Plumes generated by vertically distributed sources of buoyancy have been observed to have substantially lower entrainment coefficients than their equivalent-geometry constant buoyancy flux plumes. Two differences between distributed and localized sources of buoyancy are the presence of a wall shear stress at the source and that non-ideal source conditions are distributed over the whole height of the enclosure for a vertically distributed source. Herein the impact of non-ideal source and boundary conditions on vertically distributed plumes is analysed. It is shown that, at small heights, the plume volume flow rate is significantly influenced by the wall-source volume flux. At larger heights the wall-source buoyancy is greater than the mean plume buoyancy, creating a non-self-similar horizontal buoyancy distribution within the plume. Recent experiments into the behaviour of a vertically distributed source of buoyancy in a confined region have also shown that the plume partially detrains in the stratified region of the enclosure. This detrainment has not been observed for constant buoyancy flux plumes in a confined region. Although models have been proposed to quantify the detrainment process, it is still unclear why vertically distributed buoyancy sources detrain while constant buoyancy flux plumes do not in the same physical geometry. The impact of source and boundary effects on previously published experiments on vertically distributed plumes are reviewed and the possible implications for plume entrainment and detrainment are discussed. [ABSTRACT FROM AUTHOR]

An equation of screw dislocations in a thin film is derived for arbitrary boundary conditions. The boundary conditions can be the free surface, the fixed surface or the gradient loading imposed on the surface. The new equation makes it possible to study changes in the dislocation structure under various gradient stress applied to the surface. The rigidity and mobility of screw dislocations in a thin film are explored by using the equation. It is found that the screw dislocation core in a thin film is like a Hookean body with a specific shear stress applied to the surface. Free-surface effects on the Peierls stress are investigated and compared with previous studies. An abnormal behavior of the Peierls stress of screw dislocations in a soft-inclusion film between two rigid films is predicted theoretically. [ABSTRACT FROM AUTHOR]

A novel instrument named Micro-Electro-Mechanical System (MEMS) flexible hot-film shear stress sensor was used to study the boundary shear stress distribution in the generalized natural meandering open channel, and the mean sidewall shear stress distribution along the meandering channel, and the lateral boundary shear stress distribution in the typical cross-section of the meandering channel was analysed. Based on the measurement of the boundary shear stress, a semi-empirical semi-theoretical computing approach of the boundary shear stress was derived including the effects of the secondary flow, sidewall roughness factor, eddy viscosity and the additional Reynolds stress, and more importantly, for the first time, it combined the effects of the cross-section central angle and the Reynolds number into the expressions. Afterwards, a comparison between the previous research and this study was developed. Following the result, we found that the semi-empirical semi-theoretical boundary shear stress distribution algorithm can predict the boundary shear stress distribution precisely. Finally, a single factor analysis was conducted on the relationship between the average sidewall shear stress on the convex and concave bank and the flow rate, water depth, slope ratio, or the cross-section central angle of the open channel bend. The functional relationship with each of the above factors was established, and then the distance from the location of the extreme sidewall shear stress to the bottom of the open channel was deduced based on the statistical theory. [ABSTRACT FROM AUTHOR]

General equations for predicting depth-averaged velocity in open channels are not well suited for trapezoidal open channels. In this study, an innovative method is developed for predicting the depth-averaged velocity distributions in smooth trapezoidal open channels with the best hydraulic section. Depth-averaged velocity was obtained using the boundary shear stress obtained in the present study. To calibrate the present analytical results, an experimental investigation was also performed. Analytical results compared well with the experimental data.

This paper describes the hysteresis in the torque for Taylor-Couette flow in the turbulent flow regime for different shear Reynolds numbers, aspect ratios and boundary conditions. The hysteresis increases with decreasing shear Reynolds number and becomes more pronounced as the aspect ratio is increased from 22 to 88. Measurements conducted in two different Taylor-Couette set-ups depict the effect of the flow conditions at the ends of the cylinders on the flow hysteresis by showing reversed hysteresis behaviour. In addition, the flow structure in the different branches of the hysteresis loop was investigated by means of stereoscopic particle image velocimetry. The results show that the dominant flow structures differ in shape and magnitude depending on the branch of the hysteresis loop. Hence, it can be concluded that the geometry could have an effect on the hysteresis behaviour of turbulent Taylor-Couette flow, but its occurrence is related to a genuine change in the flow dynamics. [ABSTRACT FROM AUTHOR]

A new prediction model was proposed to give the critical cutting condition of serrated chip in high speed machining, including cutting speed, depth of cut, and rake angle. Firstly, a critical criterion of serrated chip in high speed machining was obtained through the linear stability analysis of balance equations of continuum mechanics for primary deformation zone, which considers the influence of compression stress through stress equivalent. Secondly, the model of deformation in the primary deformation zone was proposed to build the corresponding relationships between the cutting conditions and the deformation conditions based on the model of parallel boundary shear zone. Lastly, the critical cutting condition of serrated chip in high speed machining can be predicted by combining the critical criterion and the calculation of deformation conditions in the primary deformation zone. For the validation of model, the critical cutting conditions of serrated chip on AISI 1045 steel were predicted and an orthogonal cutting experiment was performed for comparing with the prediction results. The comparison shows that the prediction results agree well with that of experiment. Therefore, the proposed model is available. This is very useful for the optimization of cutting parameters and precision control of high speed machining. [ABSTRACT FROM AUTHOR]

We investigate the process of shear melting and resolidification of a colloidal glass, directly after loading (preyielding) and after a series of consecutive strain sweeps (postyielding). The postyielding glass shows a significant softening compared with the preyielding glass, together with the absence of history effects in successive shear melting protocols, indicating a reproducible process of fluidisation and resolidification into a glass state unaffected by residual stresses. However, a significant hysteresis characterizes strain sweeps with increasing or decreasing strain amplitude. The appearance of history and hysteresis effects coincides with the formation of a glass state, whereas it is not observed in the liquid. We can describe the onset of shear melting over a broad range of volume fractions and frequencies using a recently developed model which describes the yielding process in terms of loss of long-lived nearest neighbors. [ABSTRACT FROM AUTHOR]

The serrated chip is a typical characteristic of high-speed cutting due to the occurrence of adiabatic shear. Based on an adiabatic shear sensitivity index proposed via linear perturbation analysis, which considers the pressure-shear condition in machining, the relationship of adiabatic shear and cutting conditions is established. The corresponding relation between the cutting conditions and the deformation conditions is established based on the model of a parallel boundary shear zone. The influence of cutting parameter on adiabatic shear is analysed and the results show that the adiabatic shear in high speed machining tends to occur under the condition of higher cutting speed, greater depth of cut and smaller rake angle. An orthogonal cutting experiment was performed to validate the proposed model. Furthermore, the influence mechanism of cutting conditions on adiabatic shear is discussed in detail and one application of the model is introduced. [ABSTRACT FROM AUTHOR]

Experimental investigations were carried out to investigate turbulent flow characteristics in non-uniform sand bed channels for both no seepage and seepage flow. Steady flows over non-uniform sand bed channel were simulated experimentally with downward seepage applied through the boundary. Measures of turbulent parameters such as velocity, Reynolds shear stresses, thickness of roughness sub layer and shear velocities were found increasing with seepage. The turbulent diffusivity and mixing length decrease in presence of seepage. The quadrant analysis suggests that the relative contributions of bursting events increased throughout the flow layer and the thickness of the zone of dominance of sweep event increases with seepage which is responsible for increment in bed material transport. The mean time of occurrence of ejections and sweeps in downward seepage are more persistent than those in no seepage. The analysis of third order moments states that an upward downstream flux of turbulent kinetic energy is observed over the near bed surface giving rise to sweeps with seepage. The turbulent kinetic energy fluxes increase in presence of seepage within the near bed flow. The increased in bed load transport with seepage associated with an increase in flow turbulence production corresponds with decrease in turbulent kinetic energy dissipation, pressure energy diffusion and turbulent diffusion. The traversing length decreases and size of eddies increases with seepage. [ABSTRACT FROM AUTHOR]

A complete and accurate method for determining the stresses and displacements of a lined arbitrary shaped tunnel excavated in orthogonal anisotropic rock mass is proposed. The method is based on an analytical method, the complex variable method, and the power series method. The basic equations can be obtained according to the stress boundary conditions along the inner boundary of the lining and the stress and displacement continuity conditions along the lining-rock interface. Based on the method, the tangential stresses along the excavation boundary, the inner and outer boundaries of the lining, and the normal and shear stresses along the lining-rock interface are given. Results show that, when the number of terms of the series is large enough, solutions with high accuracy can be obtained. The positions of the tangential stress concentration, the effect of the displacement release coefficient, and the angle of the rock layers on the tangential stresses along the excavation boundary and both boundaries of the lining are discussed. [ABSTRACT FROM AUTHOR]

This paper investigates the hydrodynamic and heat transfer effects on the dissipation and dispersion of entropy waves in non-reactive flows. These waves, as advected density inhomogeneities downstream of unsteady flames, may decay partially or totally before reaching the exit nozzle, where they are converted into sound. Attenuation of entropy waves dominates the significance of the subsequent acoustic noise generation. Yet, the extent of this decay process is currently a matter of contention and the pertinent mechanisms are still largely unexplored. To resolve this issue, a numerical study is carried out by compressible large eddy simulation of thewave advection in a channel subject to convective and adiabatic thermal boundary conditions. The dispersion, dissipation, and spatial correlation of thewave are evaluated by post-processing of the numerical results. This includes application of the classical coherence function as well as development of nonlinear quantitative measures of wave dissipation and dispersion. The analyses reveal that the high frequency components of the entropy wave are always strongly damped. The survival of the low frequency components heavily depends on the turbulence intensity and thermal boundary conditions of the channel. In general, high turbulence intensities and particularly heat transfer intensify the decay and destruction of the spatial coherence of entropywaves. In some cases, they can even result in the complete annihilation of the wave. The current work can therefore resolve the controversies arising over the previous studies of entropy waves with different thermal boundary conditions. [ABSTRACT FROM AUTHOR]

The long noncoding RNAs (lncRNAs), which constitute a large portion of the transcriptome, have gained intense research interest because of their roles in regulating physiological and pathophysiological functions in the cell. We identified from RNA-Seq profiling a set of lncRNAs in cultured human umbilical vein endothelial cells (HUVECs) that are differentially regulated by atheroprotective vs. atheroprone shear flows. Among the comprehensively annotated lncRNAs, including both known and novel transcripts, LINC00341 is one of the most abundant lncRNAs in endothelial cells. Moreover, its expression level is enhanced by atheroprotective pulsatile shear flow and atorvastatin. Overexpression of LINC00341 suppresses the expression of vascular cell adhesion molecule 1 (VCAM1) and the adhesion of monocytes induced by atheroprone flow and tumor necrosis factor-alpha. Underlying this anti-inflammatory role, LINC00341 guides enhancer of zest homolog 2, a core histone methyltransferase of polycomb repressive complex 2, to the promoter region of the VCAM1 gene to suppress VCAM1. Network analysis reveals that the key signaling pathways (e.g., Rho and PI3K/AKT) are co-regulated with LINC00341 in endothelial cells in response to pulsatile shear. Together, these findings suggest that LINC00341, as an example of lncRNAs, plays important roles in modulating endothelial function in health and disease. [ABSTRACT FROM AUTHOR]

Total resistance of a compound channel may be ascribed to channel roughness, geometry and flow characteristics and is exhibited in the form of tangential stress from point to point along the periphery, known as boundary shear stress. This paper reports the boundary shear stress distribution of compound channels with asymmetric flood plains. Due to the scarcity of data sets in asymmetric compound channel as evident from the previous literatures, wide ranges of data sets have been generated by application of SKM. New expression for predicting boundary shear distribution is found to give better results as compared to other models. Using the new expression, a modified flow prediction approach in a two-stage asymmetric compound channel has been presented. The approach has been tested with asymmetric flood channel facility experimental data, other investigators data and with natural river data sets. The efficacy of the model has been proved from the error analysis. [ABSTRACT FROM AUTHOR]

In prismatic compound channels, the water level remains uniform throughout the length of the channel. But in case of non-prismatic compound channels, the flow becomes non-uniform and complex. This paper examines the use of Lateral Distribution Method (LDM) and its modifications in the computation of depth-averaged velocity and boundary shear stress distribution in a compound channel for both prismatic and non-prismatic floodplains. The modification of LDM has been done considering the friction slope and secondary current effect. Finite difference scheme has been used for discretizing the Modified LDM using MATLAB tool. For the present study, different prismatic and non-prismatic compound channels having converging flood plains have been considered to evaluate the strength of Modified LDM over other numerical approaches like LDM and Conveyance and Afflux Estimation system. [ABSTRACT FROM AUTHOR]

A numerical analysis of the ridges on the bed of wide, open channels and their effects on the distribution of secondary currents and wall shear is undertaken using CFD (Computational Fluid Dynamics). The presence of the lines of boil, consisting of low speed streaks, periodically in the transverse direction, is reported in the literature due to the presence of the ridges. In the present work, simulations are run on channel sections with varying the number of ridges on the bed and the size of these ridges. The effect of these variations on the flow structures and shear stress distribution in wide open channels is reported. The results offer an interesting insight into the 3D (Three-Dimensional flow structures involved and the link between flow structures and bed morpho-dynamics in prismatic channels.