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Lang, Shinan, Ben Xu, Xiangbin Cui, Kun Luo, Jingxue Guo, Xueyuan Tang, Yiheng Cai, Bo Sun et Martin J. Siegert. « A self-adaptive two-parameter method for characterizing roughness of multi-scale subglacial topography ». Journal of Glaciology 67, no 263 (24 février 2021) : 560–68. http://dx.doi.org/10.1017/jog.2021.12.
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AbstractDuring the last few decades, bed-elevation profiles from radar sounders have been used to quantify bed roughness. Various methods have been employed, such as the ‘two-parameter’ technique that considers vertical and slope irregularities in topography, but they struggle to incorporate roughness at multiple spatial scales leading to a breakdown in their depiction of bed roughness where the relief is most complex. In this article, we describe a new algorithm, analogous to wavelet transformations, to quantify the bed roughness at multiple scales. The ‘Self-Adaptive Two-Parameter’ system calculates the roughness of a bed profile using a frequency-domain method, allowing the extraction of three characteristic factors: (1) slope, (2) skewness and (3) coefficient of variation. The multi-scale roughness is derived by weighted-summing of these frequency-related factors. We use idealized bed elevations to initially validate the algorithm, and then actual bed-elevation data are used to compare the new roughness index with other methods. We show the new technique is an effective tool for quantifying bed roughness from radar data, paving the way for improved continental-wide depictions of bed roughness and incorporation of this information into ice flow models.
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Faruque, Md Abdullah Al, et Ram Balachandar. « Roughness effects on turbulence characteristics in an open channel flow ». Canadian Journal of Civil Engineering 37, no 12 (décembre 2010) : 1600–1612. http://dx.doi.org/10.1139/l10-098.
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A comprehensive study was carried out to understand the effect of roughness on the turbulence characteristics of flow in an open channel. To this end, tests were conducted with four different types of bed surface conditions at two different Reynolds number (Re = 47 500 and 31 000). This includes the use of an impermeable smooth bed, impermeable rough bed, permeable sand bed, and an impermeable bed with distributed roughness. The roughness is generated using sand grains of median diameter 2.46 mm. The effect of bed roughness is seen to have penetrated through most of the flow depth, disputing the conventional "wall similarity" hypothesis. The results show that the distributed roughness generates the largest roughness effect. The differences in the characteristics as noted by the velocity triple products exceed 200% between the flow over the smooth and rough beds. Although the same sand grain is used to create the different rough bed conditions, there are differences in turbulence characteristics, which is an indication that specific geometry of the roughness has an influence. A quadrant analysis indicates that roughness increases the contribution of the extreme turbulent events that produce very large instantaneous Reynolds shear stress and consequently influence the flow.
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A.Merry, Marwa. « EXPERIMENTAL STUDY FOR DETERMINE MANNING'S COEFFICIENT WITH DIFFERENT SLOPES AND CHANNEL BED MATERIALS ». Kufa Journal of Engineering 8, no 3 (12 novembre 2017) : 76–88. http://dx.doi.org/10.30572/2018/kje/8031160.
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Water resources and hydraulic engineering projects have been upward rapidly in all over the world, accordingly the prediction of roughness coefficient is essential criteria to design open channels, and related hydraulic structures. The aims of this research are to find out the effect of changing beds materials and discharge on coefficient of roughness (n), the beds that used in the tests are smooth which represented by original channel bed (steel plate), rough bed material which is a gravel bed and waved bed .The experimental work was performed in a rectangular flume with dimension of (15 m* 0.3 m* 0.45 m) long, wide and deep, respectively with different value of slope (1:200 and 1:500) to analyze slope effect on coefficient of roughness in addition to the effect of channel bed material. The experimental work showed that The coefficient of roughness reduced when the discharge increases for specified slope and channel bed, The slope of the channel and bed roughness is the main factors affected on determining coefficient of roughness and when the channel slope increases the coefficient of roughness increases, the coefficient of roughness is decreased when using smooth bed and it is increased when channel bed is waved. The percentage change in the Manning coefficient due to changing in slope and channel bed is (112.6%) when slope equal to (1/200) and the channel bed changed from smooth to rough , (184%) when the bed changed from rough to waved, and (33.6%) when channel bed changed from rough to waved. And for (1/500) slope, the percentage change in the Manning coefficient equal to (33.5%) when the bed changed from smooth to rough, (80%) when changed from smooth to waved, and (33.1%) when changed from rough to waved.
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Irzooki, Raad Hoobi, et Ayad Saoud Najem. « Experimental Investigation for Free Overfall of Flow in Semi-circular Channels ». IOP Conference Series : Earth and Environmental Science 1120, no 1 (1 décembre 2022) : 012010. http://dx.doi.org/10.1088/1755-1315/1120/1/012010.
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Abstract In the present paper, the effects of diameter, bed slopes, and bed roughness on free overfall flow of semi-circular channels were investigated experimentally. For this purpose, three models of semi-circular channels with free overfall were built and installed in a 6m long laboratory flume. These three models were 250 cm long and had varying diameters 160, 200, and 250 mm. Four different bed slopes (S) were used in each of these models (0, 0.004, 0.008, and 0.012). For each bed slope, three sand particle sizes were used to roughen the bed (1.18mm, 2.36mm, and 4.75mm). For each model, the experimental testing program contained sixteen series of experiments. They were divided into two categories: four smooth beds and twelve rough beds. Different rates of discharge (Q) were examined in a total of 192 tests. According to the experimental results of all models, the Froude number (F r ) of flow decreases as the end depth ratio ( y b / y c ) increases for various bed roughnesses. For varying bed slopes and bottom roughness, a simple linear formula was developed to relate the brink depth ( y b ) with the critical depth ( y c ). For various bed slopes and roughness conditions, simple empirical equations for the flow over the free overfall in semi-circular channels were found. The results demonstrate a good level of agreement.
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Nikora, Vladimir I., Derek G. Goring et Barry J. F. Biggs. « On gravel-bed roughness characterization ». Water Resources Research 34, no 3 (mars 1998) : 517–27. http://dx.doi.org/10.1029/97wr02886.
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Majeed, Hayder Q., Ali M. Ghazal et Basheer Al-Hadeethi. « Experimental and Numerical Study of Open Channel Flow with T-Section Artificial Bed Roughness ». Mathematical Modelling of Engineering Problems 9, no 6 (31 décembre 2022) : 1589–95. http://dx.doi.org/10.18280/mmep.090619.
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Experimental and numerical studies have been conducted on the effects of bed roughness elements such as cubic and T-section elements that are regularly half-channel arrayed on one side of the river on turbulent flow characteristics and bed erosion downstream of the roughness elements. The experimental study has been done for two types of bed roughness elements (cubic and T-section shape) to study the effect of these elements on the velocity profile downstream the elements with respect to different water flow discharges and water depths. A comparison between the cubic and T-section artificial bed roughness showed that the velocity profile downstream the T-section increased in smooth side from the river and decrease in the rough side from it compared with the case when a cubic artificial bed roughness is used. By comparing the results for the element shapes, it can be notices that the T-section bed roughness element more effective compared to cubic shape for both sides of the channel. The numerical method has been done using Computational Fluid Dynamic (CFD) method. A validation for the CFD model with the experimental study have been carried out for a specific flow discharge and water depth. The results indicated that the velocity distribution profiles downstream the bed roughness elements in both sides shown very good agreement for manning coefficients between the numerical and experimental studies. The range of errors between the experimental and numerical study have been calculated using Root Mean Square Error (RMSE) approach, which is found that the RMSE is approximately equal to 1 in case of cubic bed roughness and the RMSE is about 1.5 in case of T-section bed roughness for both smooth and rough sides. Furthermore, the influence of the velocity profile and the bed erosion downstream of the T-section element under the effect of tides have been investigated using the CFD method, which is commonly happened in Shat al-Arab south of Iraq. The results show that the tide of the flow has a reverse effect on the velocity profiles for both sides. Since the velocity profile downstream of bed roughness region increase in the rough side and decrease in the smooth side compared with the normal flow of the river.
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FALCINI, FRANCESCA A. M., DAVID M. RIPPIN, MAARTEN KRABBENDAM et KATHERINE A. SELBY. « Quantifying bed roughness beneath contemporary and palaeo-ice streams ». Journal of Glaciology 64, no 247 (13 septembre 2018) : 822–34. http://dx.doi.org/10.1017/jog.2018.71.
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ABSTRACTBed roughness is an important control on ice-stream location and dynamics. The majority of previous bed roughness studies have been based on data derived from radio-echo sounding (RES) transects across Antarctica and Greenland. However, the wide spacing of RES transects means that the links between roughness and flow are poorly constrained. Here, we use Digital Terrain Model/bathymetry data from a well-preserved palaeo-ice stream to investigate basal controls on the behaviour of contemporary ice streams. Artificial transects were set up across the Minch Palaeo-Ice Stream (NW Scotland) to mimic RES flight lines over Institute and Möller Ice Streams (Antarctica). We then explored how different data-resolution, transect orientation and spacing, and different methods, impact roughness measurements. Our results show that fast palaeo-ice flow can occur over a rough, hard bed, not just a smooth, soft bed, as previous work has suggested. Smooth areas of the bed occur over both bedrock and sediment covered regions. Similar trends in bed roughness values were found using Fast Fourier Transform analysis and standard deviation methods. Smoothing of bed roughness results can hide important details. We propose that the typical spacing of RES transects is too wide to capture different landform assemblages and that transect orientation influences bed roughness measurements in both contemporary and palaeo-ice-stream setting.
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Fredsøe, J., B. M. Sumer, T. S. Laursen et C. Pedersen. « Experimental investigation of wave boundary layers with a sudden change in roughness ». Journal of Fluid Mechanics 252 (juillet 1993) : 117–45. http://dx.doi.org/10.1017/s0022112093003696.
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This study deals with turbulent oscillatory boundary-layer flows over a plane bed with a sudden spatial change in roughness. Two kinds of ‘change in the roughness’ were investigated: in one, the roughness changed from a smooth-wall roughness to a roughness equal to 4.8 mm, and in the other, it changed from a roughness equal to 0.35 mm to the same roughness as in the previous experiment (4.8 mm). The free-stream flow was a purely oscillating flow with sinusoidal velocity variation. Mean flow and turbulence properties were measured. The Reynolds number was 6 × 106 for the major part of the experiments, with a maximum velocity of approximately 2 m/s and the stroke of the motion about 6 m. The response of the boundary layer to the sudden change in roughness was found to occur over a transitional length of the flow. The bed shear stress over this transitional length attains a peak value over the bed section with the larger roughness. It was found that the amplification in the bed shear stress due to this peak could be up to 2.5 times its asymptotic value. Also, it was found that the turbulence is quantitatively different in the two half periods; a much stronger turbulence is experienced in the half period where the flow is towards the less-rough section. The present experiments further showed that a constant streaming occurs near the bed in the neighbourhood of the junction between the two bed sections. This streaming is directed towards the section with the larger roughness.
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Devi, Kalpana, Prashanth Reddy Hanmaiahgari, Ram Balachandar et Jaan H. Pu. « A Comparative Study between Sand- and Gravel-Bed Open Channel Flows in the Wake Region of a Bed-Mounted Horizontal Cylinder ». Fluids 6, no 7 (1 juillet 2021) : 239. http://dx.doi.org/10.3390/fluids6070239.
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In nature, environmental and geophysical flows frequently encounter submerged cylindrical bodies on a rough bed. The flows around the cylindrical bodies on the rough bed are very complicated as the flow field in these cases will be a function of bed roughness apart from the diameter of the cylinder and the flow velocity. In addition, the sand-bed roughness has different effects on the flow compared to the gravel-bed roughness due to differences in the roughness heights. Therefore, the main objective of this article is to compare the mean velocities and turbulent flow properties in the wake region of a horizontal bed-mounted cylinder over the sand-bed with that over the gravel-bed. Three experimental runs, two for the sand-bed and one for the gravel-bed with similar physical and hydraulic conditions, were recorded to fulfil this purpose. The Acoustic Doppler Velocimetry (ADV) probe was used for measuring the three-dimensional (3D) instantaneous velocity data. This comparative study shows that the magnitude of mean streamwise flow velocity, streamwise Reynolds normal stress, and Reynolds shear stress are reduced on the gravel-bed compared to the sand-bed. Conversely, the vertical velocities and vertical Reynolds normal stress are higher on the gravel-bed than the sand-bed.
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Kashefipour, Seyed Mahmood, Mehdi Daryaee et Mehdi Ghomeshi. « Effect of bed roughness on velocity profile and water entrainment in a sedimentary density current ». Canadian Journal of Civil Engineering 45, no 1 (janvier 2018) : 9–17. http://dx.doi.org/10.1139/cjce-2016-0490.
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In this study, the effect of bed roughness on velocity profile and water entrainment in a sedimentary density current for Richardson numbers of 1.2–7 (subcritical flow conditions) was investigated. Experiments were carried out in a tilting flume with four different bed slopes, four roughness heights, and two fluid densities of sedimentary density currents. The results showed that bed roughness significantly affects the general shapes of velocity profiles, especially in the wall region. Two empirical equations were developed as the functions of the relative roughness for the wall and jet regions of velocity profile using the measured velocities of density currents. Water entrainment was also affected by bed roughness and an empirical equation was developed describing the relationship of this phenomenon with the Richardson number and relative roughness. Sensitivity analysis of this equation by using elasticity coefficient method showed that the effectiveness of the Richardson number is 3.9 times more than the effect of relative roughness on water entrainment.
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Khechiba, Haroun, Ali Ghomri, Djamel Besser, Ibtissam Herri et Salim Khechana. « Experimental study of the sequent depths ratio of the hydraulic jump in a rectangular compound channel with rough main and minor beds and zero slope ». STUDIES IN ENGINEERING AND EXACT SCIENCES 6, no 1 (8 janvier 2025) : e13139. https://doi.org/10.54021/seesv6n1-003.
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Hydraulic jumps, the rapid transitions from supercritical to subcritical flow, are crucial for energy dissipation in flood management structures. This study aims to address this knowledge gap by experimentally analyzing the effect of bed roughness on the sequent depth ratio of hydraulic jumps in a rectangular compound channel. Laboratory experiments were conducted in a rectangular compound channel with two distinct roughness zones: the primary bed (main channel) and the secondary bed (floodplain). Uniform plastic granules were used to simulate varying roughness conditions. Results indicated a significant reduction in the sequent depth ratio in rough channels compared to smooth ones. Increased bed roughness enhances momentum transfer, leading to higher energy dissipation and a lower sequent depth ratio. This effect is further amplified by the shortening of the roller length, which limits the increase in downstream water depth. Figure 10 illustrates this phenomenon, showing a more pronounced reduction in the sequent depth ratio in the shallower secondary bed (0 < h2 < 15.5 cm), where relative roughness (ε/b) has a greater influence than in the deeper primary bed (15.5 < h2 < 28 cm). The increased roughness in the secondary bed results in greater energy dissipation and a smaller downstream depth (h2). Empirical equations were derived from a comprehensive dataset to predict the sequent depth ratio as a function of the Froude number and relative roughness. These equations provide valuable tools for designing energy dissipation structures.
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Bertin, Stephane, Jane Groom et Heide Friedrich. « Grain and bedform roughness properties isolated from gravel-patch DEMs ». E3S Web of Conferences 40 (2018) : 04005. http://dx.doi.org/10.1051/e3sconf/20184004005.
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Remote sensing of gravel-bed patches and resulting high-resolution digital elevation models (DEMs) allow for the identification of various spatial scales of surface roughness. Thus far, dimensions relating to grain and bedform roughness scales have been determined using semivariograms or equivalent structure/autocorrelation functions. However, it is difficult to clearly differentiate roughness scales and separate analysis of roughness properties is not possible. This study examines the use of moving-window detrending on gravel-patch DEMs for isolating grain and bedform roughness and their respective topographic signatures. An extensive dataset of water-worked gravel surfaces collected in both laboratory and field environments is used. The measured bed topography is separated into two distinct DEMs: one representing grains, the other representing bedforms, and roughness properties are determined separately for grain and bedform DEMs. The results show that both roughness scales are controlled by the size of the coarse sediment forming the bed surface, with positive linear relationships connecting bed composition and vertical roughness. Coarse sediment is controlling bedform development by forming humps on the surface, in the lee of which finer sediment is sheltered. We present synthesis relationships connecting vertical roughness of gravel patches to the vertical roughness of grains and bedforms.
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Ding, Lei, et Qing-He Zhang. « LATTICE BOLTZMANN SIMULATION TO CHARACTERIZE ROUGHNESS EFFECTS OF OSCILLATORY BOUNDARY LAYER FLOW OVER A ROUGH BED ». Coastal Engineering Proceedings 1, no 32 (30 janvier 2011) : 3. http://dx.doi.org/10.9753/icce.v32.sediment.3.
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The 3-D lattice Boltzmann method was applied to characterize roughness effects of oscillatory boundary layer flow over a rough bed. The direct numerical simulation was carried out and the flow resistance of the flat and fixed bed was investigated. The position of the theoretical bed, equivalent roughness height and the behavior of friction factor at small values of relative roughness were obtained using the log-fit method.
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Humbyrd, Chelsea Joy, et Ole Secher Madsen. « PREDICTING MOVABLE BED ROUGHNESS IN COASTAL WATERS ». Coastal Engineering Proceedings 1, no 32 (29 janvier 2011) : 6. http://dx.doi.org/10.9753/icce.v32.sediment.6.
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Accurately predicting movable bed roughness is essential to the analyses of transport processes, but when the bottom is rippled, as it commonly is in the coastal environment, characterizing the roughness is less straightforward than when the bottom is flat. The common method of predicting roughness, while effective, unnecessarily predicts ripple geometry and requires a model-dependent factor, which varies widely, relating ripple geometry and bottom roughness. We have therefore developed an alternative, more direct method of predicting bed roughness in the ripple regime: the wave energy dissipation factor is predicted from flow and sediment information and then any desired theoretical friction factor model is used to back-calculate the roughness. This paper describes the common and proposed methods of predicting roughness and presents results of preliminary testing of the methods with field data. Both methods adequately predict current velocities in wave-current field flows, with the proposed method yielding the smaller RMS-error of 3.1 cm/s. Remaining questions concerning the appropriate near-bottom orbital velocity required to describe field conditions must be resolved when additional field data becomes available.
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Chen, Yifan, Feifeng Cao, Weiping Cheng et Bin Liu. « Enhancing the Accuracy of Water-Level Forecasting with a New Parameter-Inversion Model for Estimating Bed Roughness in Hydrodynamic Models ». Applied Sciences 13, no 7 (3 avril 2023) : 4551. http://dx.doi.org/10.3390/app13074551.
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The accurate and efficient estimation of bed roughness using limited historical observational data is well-established. This paper presents a new parameter-inversion model for estimating bed roughness in hydrodynamic models that constrains the roughness distribution between river sections. The impact of various factors on the accuracy of inversed roughness was analyzed through a numerical experiment with the number of measurement stations, observed data amount, initial bed roughness, observational noise, and the weight of the regularization term. The results indicate that increasing the number of measurement stations and the amount of observed data significantly improves the robustness of the model, with an optimal parameter setting of 3 stations and 30 observed data. The initial roughness had little impact on the model, and the model showed good noise resistance capacity, with the error significantly reduced by controlling the smoothness level of inversed roughness using a small weight of the regularization term (i.e., 100). An experiment conducted on a real river using the calibrated model parameters shows a forecasted water level RMSE of 0.041 m, 31% less than that from the Federal Emergency Management Agency. The proposed model provides a new approach to estimating bed roughness parameters in hydrodynamic models and can help in improving the accuracy of water-level forecasting.
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López, Raúl, et Javier Barragán. « Equivalent Roughness of Gravel-Bed Rivers ». Journal of Hydraulic Engineering 134, no 6 (juin 2008) : 847–51. http://dx.doi.org/10.1061/(asce)0733-9429(2008)134:6(847).
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Wu, Weiming, et Sam S. Y. Wang. « Movable Bed Roughness in Alluvial Rivers ». Journal of Hydraulic Engineering 125, no 12 (décembre 1999) : 1309–12. http://dx.doi.org/10.1061/(asce)0733-9429(1999)125:12(1309).
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Hager, Willi H., Giuseppe Del Giudice, Weiming Wu et Sam S. Y. Wang. « Movable Bed Roughness in Alluvial Rivers ». Journal of Hydraulic Engineering 127, no 7 (juillet 2001) : 627–29. http://dx.doi.org/10.1061/(asce)0733-9429(2001)127:7(627).
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Wiberg, Patricia L., et David M. Rubin. « Bed roughness produced by saltating sediment ». Journal of Geophysical Research 94, no C4 (1989) : 5011. http://dx.doi.org/10.1029/jc094ic04p05011.
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Gallagher, Edith L., E. B. Thornton et T. P. Stanton. « Sand bed roughness in the nearshore ». Journal of Geophysical Research : Oceans 108, no C2 (février 2003) : n/a. http://dx.doi.org/10.1029/2001jc001081.
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Rippin, D. M., D. G. Vaughan et H. F. J. Corr. « The basal roughness of Pine Island Glacier, West Antarctica ». Journal of Glaciology 57, no 201 (2011) : 67–76. http://dx.doi.org/10.3189/002214311795306574.
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AbstractWe assess basal roughness beneath Pine Island Glacier (PIG), West Antarctica, based on a recent airborne radio-echo sounding dataset. We identify a clear relationship between faster ice flow and decreased basal roughness in significant parts of PIG. The central portion and two of its tributaries are particularly smooth, but the majority of the tributaries feeding the main trunk are rougher. We interpret the presence of a smooth bed as being a consequence of the deposition of marine sediments following disappearance of the West Antarctic ice sheet in the Pliocene or Pleistocene, and, conversely, a lack of marine sedimentation where the bed is rough. Importantly, we also identify a patchy distribution of marine sediments, and thus a bed over which the controls on flow vary. While there is a notable correspondence between ice velocity and bed roughness, we do not assume a direct causal relationship, but find that an indirect one is likely. Where low basal roughness results in low basal resistance to flow, a lower driving stress is required to produce the flux required to achieve mass balance. This, in turn, means that the surface in that area will be lower than surrounding areas with a rougher bed, and this will tend to draw flow into the area with low bed roughness. Since our studies shows that bed roughness beneath the tributaries of the trunk varies substantially, there is a strong likelihood that these tributaries will differ in the rate at which they transmit current velocity changes on the main trunk into the interior of the glacier basin.
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Balachandar, Ram, et V. C. Patel. « Flow over a fixed rough dune ». Canadian Journal of Civil Engineering 35, no 5 (mai 2008) : 511–20. http://dx.doi.org/10.1139/l08-004.
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Using a laser Doppler velocimeter (LDV) system, experiments were carried out to obtain detailed information on the flow over a long train of fixed two-dimensional rough-wall dunes. The experiments provide quantitative data on conventionally averaged velocity and turbulence parameters, as well as insights on the flow structures that play a crucial role in sediment transport. The results indicate that the shape of the dunes has a major influence on the flow features, whereas the effect of near-bed roughness is limited to the wall region extending to a distance of about 80% of the dune height about the crest. However, the length of the separation eddy seems to be influenced by the near-bed roughness. As in flow over a smooth dune, the turbulence data reveal large peaks along a line roughly coinciding with the shear layer emanating from the separation at the crest. However, the location of the peak turbulence is farther extended into the flow away from the bed with increasing bed roughness. Moreover, with increasing roughness the magnitude of the peak is also reduced. A secondary peak in the streamwise turbulence profiles is noticed at some distance from the bed. This feature is not influenced by the near-bed roughness and indicates sustenance of turbulence generated by the previous dune and relates to the convection of the upstream flow history. Based on the results obtained at several stations between two successive dune crests, one can conclude that the quantitative effect of roughness itself is limited to the near-bed region in the measurements at all levels.
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Katopodis, C., et H. K. Ghamry. « Hydrodynamic and physical assessment of ice-covered conditions for three reaches of the Athabasca River, Alberta, Canada ». Canadian Journal of Civil Engineering 34, no 6 (1 juin 2007) : 717–30. http://dx.doi.org/10.1139/l07-026.
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Water is needed for oil sand developments in the lower Athabasca River basin of northern Alberta, Canada, and is also a key consideration from an ecological and fish habitat perspective, particularly in winter when river flows are at their lowest. Efforts to establish an appropriate flow management regime for the lower Athabasca included revision of River2D, a fixed bed, depth-averaged finite element model, available from www.river2d.ca, to predict hydraulics with a partial or total ice cover. Hydrometric surveys from three reaches of the Athabasca River were used to test the model, assess different model calibration methods, and simulate hydrodynamics for ice-covered conditions. Calibrating bed roughness from ice-free data, assuming the same bed roughness for ice-covered conditions, or the reverse, provided a close fit to the surveyed water surface elevations. The applied ice and composite roughness heights differed according to the applied method of calibration. This may have implications for local velocity estimates possibly affecting fish habitat suitability. A range of bed and composite grain roughness heights, corresponding to different bed substrates and ratios of bed and composite roughness heights to water depths, are provided for model calibration purposes. Key words: hydrodynamics, hydraulics, ice, ecology, environment, fish habitat, winter, oil sands.
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Warmink, J. J. « Dune dynamics and roughness under gradually varying flood waves, comparing flume and field observations ». Advances in Geosciences 39 (7 août 2014) : 115–21. http://dx.doi.org/10.5194/adgeo-39-115-2014.
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Abstract. Accurate forecasts of bed forms and their roughness during a flood wave are essential for flood management. Bed forms remain dynamic even under steady discharge and are subject to a continuous process of creations and destructions of individual bed forms. Dune evolution during the rising limb of a flood wave is quite well understood and can be modeled. However, dune evolution during the falling limb remains poorly understood. The objective of this paper is to explain the bed form evolution and roughness during the receding limb of fast flood waves. Therefore, bed profiles of two flume experiments were analyzed in detail and individual dune creations and destructions were classified. The results showed that for fast flood waves in subcritical water flow: (1) dune length grows during both rising and falling limb due to amalgamation of bed forms, (2) dune length has a longer adaptation time than dune height, resulting in short, high dunes during the peak discharge, and (3) this hysteresis difference between dune height and length results in a larger roughness than predicted by equilibrium bed form dimension equations, which may result in a larger roughness of the main channel during floods than expected.
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Domhof, Boyan C. A., Koen D. Berends, Aukje Spruyt, Jord J. Warmink et Suzanne J. M. H. Hulscher. « Discharge and location dependency of calibrated main channel roughness : Case study on the River Waal ». E3S Web of Conferences 40 (2018) : 06038. http://dx.doi.org/10.1051/e3sconf/20184006038.
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To accurately predict water levels, river models require an appropriate description of the hydraulic roughness. The bed roughness increases as river dunes grow with increasing discharge and the roughness depends on differences in channel width, bed level and bed sediment. Therefore, we hypothesize that the calibrated main channel roughness coefficient is most sensitive to the discharge and location in longitudinal direction of the river. The roughness is determined by calibrating the Manning coefficient of the main channel in a 1D hydrodynamic model. The River Waal in the Netherlands is used as a case study. Results show that the calibrated roughness is mainly sensitive to discharge. Especially the transition from bankfull to flood stage and effects of floodplain compartmentation are important features to consider in the calibration as these produce more accurate water level predictions. Moreover, the downstream boundary condition also has a large effect on the calibrated roughness values near the boundary.
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Lau, Kok-Tee, Mastura Mohammad Taha, Syahibudil Ikhwan Abdul Kudus et See Ern Chung. « EFFECT OF PRINT BED’S HEAT FLOW ON CURLING AND SURFACE ROUGHNESS OF FDM-PRINTED ABS SAMPLE ». Jurnal Teknologi 85, no 2 (23 février 2023) : 211–22. http://dx.doi.org/10.11113/jurnalteknologi.v85.18610.
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The optimization of printing parameters, in particular the print bed aspect, is essential for the further improvement of print quality. This paper investigates the effect of the print bed’s heat flow and surface properties (i.e. materials and surface roughness) on the curling defect and surface roughness of the ABS-based dog bone designed print. The print bed temperature is varied, and the corresponding heat flow is measured using a portable heat flow meter. The maximum z deflection (curling) of the print is characterized using Geomagic Control X metrology software by measuring the dimension deviation of the 3D scanned print compared with the CAD drawing. The surface roughness in terms of the Ra and Rz of the print are obtained by a stylus-based contact profilometer. The measured heat flow data have a positive linear correlation with the print bed temperature, which is confirmed by our theoretical calculation. The surface roughness of the print is higher when printed on the zinc plate-overlaid print bed, compared with the standard (unmodified) print bed. Furthermore, the applied heat flow has a large positive correlation with the print’s roughness but no correlation with the maximum z deflection. The roughness and z-deflection behaviour are attributed to the curling at the grip section of the print, resulting in a shorter interaction time with the print bed surface compared with the gage section that remains in physical contact throughout the 3D printing.
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MIGNOT, EMMANUEL, D. HURTHER et E. BARTHELEMY. « On the structure of shear stress and turbulent kinetic energy flux across the roughness layer of a gravel-bed channel flow ». Journal of Fluid Mechanics 638 (7 octobre 2009) : 423–52. http://dx.doi.org/10.1017/s0022112009990772.
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This study examines the structure of shear stress and turbulent kinetic energy (TKE) flux across the roughness layer of a uniform, fully rough gravel-bed channel flow (ks+ ≫ 100, δ/k = 20) using high-resolution acoustic Doppler velocity profiler measurements. The studied gravel-bed roughness layer exhibits a complex random multi-scale roughness structure in strong contrast with conceptualized k- or d-type roughness in standard rough-wall flows. Within the roughness layer, strong spatial variability of all time-averaged flow quantities are observed affecting up to 40% of the boundary layer height. This variability is attributed to the presence of bed zones with emanating bed protuberances (or gravel clusters) acting as local flow obstacles and bed zones of more homogenous roughness of densely packed gravel elements. Considering the strong spatial mean flow variability across the roughness layer, a spatio-temporal averaging procedure, called double averaging (DA), has been applied to the analysed flow quantities. Three aspects have been addressed: (a) the DA shear stress and DA TKE flux in specific bed zones associated with three classes of velocity profiles as previously proposed in Mignot, Barthélemy & Hurther (J. Fluid Mech., vol. 618, 2009, p. 279), (b) the global and per class DA conditional statistics of shear stress and associated TKE flux and (c) the contribution of large-scale coherent shear stress structures (LC3S) to the TKE flux across the roughness layer. The mean Reynolds and dispersive shear structure show good agreement between the protuberance bed zones associated with the S-shape/accelerated classes and recent results obtained in standard k-type rough-wall flows (Djenidi et al., Exp. Fluids, vol. 44, 2008, p. 37; Pokrajac, McEwan & Nikora, Exp. Fluids, vol. 45, 2008, p. 73). These gravel-bed protuberances act as local flow obstacles inducing a strong turbulent activity in their wake regions. The conditional statistics show that the Reynolds stress contribution is fairly well distributed between sweep and ejection events, with threshold values ranging from H = 0 to H = 8. However, the TKE flux across the roughness layer primarily results from the residual shear stress between ejection and sweep of very high magnitude (H = 10–20) and of small turbulent scale. Although LC3S are seen to penetrated the interfacial roughness layer, their TKE flux contribution is found to be negligible compared to the very energetic small-scale sweep events. These sweeps are dominantly produced in the bed zones of local gravel protuberances where the velocity profiles are inflexional of S-shape type and the mean flow properties are of mixing-layer flow type as previously shown in Mignot et al. (2009).
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Kee, Choong Pei, Deepak T. J et Raman Bai. « Determining Coefficient of Discharge and Coefficient of Roughness for Short Grass Bed and Concrete Bed ». International Journal of Trend in Scientific Research and Development Special Issue, Special Issue-ICAEIT2017 (30 novembre 2018) : 23–33. http://dx.doi.org/10.31142/ijtsrd19119.
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Ratul, Das, et Nizar Sinan. « Influence of bed roughness on near-bed turbulent flow characteristics ». International Journal of Water Resources and Environmental Engineering 12, no 3 (31 juillet 2020) : 47–56. http://dx.doi.org/10.5897/ijwree2015.0624.
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Akutina, Yulia, Frédéric Moulin, Maxime Rouzes et Olivier Eiff. « Flow structures in a shallow channel with lateral bed-roughness variation ». E3S Web of Conferences 40 (2018) : 02051. http://dx.doi.org/10.1051/e3sconf/20184002051.
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Highly heterogeneous floodplains can give rise to secondary flow structures responsible for the bulk of lateral momentum exchange. Quantifying the redistribution of momentum is required to predict lateral profiles of flow velocity and the associated water level in a river. In the work herein, we focus on studying secondary flow structures and the momentum redistribution associated with a lateral bed-roughness variation in a channel with low relative submergence of the roughness elements, h=k = 3, 2 and 1.5, where h is the flow depth and k is the roughness height. A series of laboratory experiments were performed in a flume containing rows of cubes. They were arranged in two types of regular patterns, with higher and lower frontal density, and placed side by side such that the bed roughness varies in the lateral direction. The measurements were performed using stereoscopic PIV in a vertical cross plane spanning between the two roughness types. The time-averaged and turbulence statistics of the three components of the velocity field were analyzed. First, we focus on the intensity of the secondary currents. As the flow becomes shallower (lower relative submergence), the cross-stream velocity normalized by the streamwise velocity increases. A large-scale secondary current at the border between the two roughnesses as observed in [1] (though in their case between smooth and rough regions) appears for h=k = 3. As h=k decreases, this structure reaches to the same size as the secondary flow generated by the roughness elements. Also, the discharge distribution between the two sides of the channel becomes less uniform with decreasing h=k. In this sense, the relative importance of the roughness difference increases with decreasing water depth. Moreover, higher discharge is observed on the side with higher equivalent sand roughness, contrary to what is observed for smooth-to-rough transition [1, 2]. Time series of the streamwise velocity fluctuations are calculated using Taylor’s “frozen turbulence” hypothesis. In this representation, streamwise velocity streaks are apparent for h=k = 3, but they appear to lose coherence for the most shallow case of h=k=1.5.
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Rippin, David M. « Bed roughness beneath the Greenland ice sheet ». Journal of Glaciology 59, no 216 (2013) : 724–32. http://dx.doi.org/10.3189/2013jog12j212.
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AbstractThe roughness of the bed beneath ice streams exerts an important control on their dynamics. Here the first in-depth analysis of roughness beneath the Greenland ice sheet is presented. Much of the interior is underlain by a smooth bed, while the margins are much rougher; this is particularly pronounced in the east where more mountainous topography dominates and fast-flow features are laterally constrained in deep narrow valleys. In contrast, fast flow in the west is much less laterally constrained and areas of high roughness are less extensive and pronounced. It is proposed that there is a major geological control on the distribution of bed variability since a significant thrust-fault coincides approximately with the boundary between rough terrain in the east and the smooth central region. Furthermore there is an abrupt change in roughness approximately coinciding with the crossing of this fault line. This suggests a limiting factor on the extent of fast flow in the east, which is lacking in the west. The size of many glaciers draining Greenland makes their local bed conditions difficult to determine with great confidence. However, the much larger Petermann Glacier lies in a deep trough characterized by a smooth bed that extends some distance into the ice sheet. The smooth bed may be due to deformable marine sediments which facilitate faster flow, although smoothing could also result from ice dynamics and subglacial erosion. That the smooth bed of Petermann Glacier extends some considerable distance raises concerns about the possible stability of this feature, and perhaps others in Greenland too.
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Nikora, V. I., T. Stoesser, S. M. Cameron, M. Stewart, K. Papadopoulos, P. Ouro, R. McSherry, A. Zampiron, I. Marusic et R. A. Falconer. « Friction factor decomposition for rough-wall flows : theoretical background and application to open-channel flows ». Journal of Fluid Mechanics 872 (13 juin 2019) : 626–64. http://dx.doi.org/10.1017/jfm.2019.344.
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A theoretically based relationship for the Darcy–Weisbach friction factor $f$ for rough-bed open-channel flows is derived and discussed. The derivation procedure is based on the double averaging (in time and space) of the Navier–Stokes equation followed by repeated integration across the flow. The obtained relationship explicitly shows that the friction factor can be split into at least five additive components, due to: (i) viscous stress; (ii) turbulent stress; (iii) dispersive stress (which in turn can be subdivided into two parts, due to bed roughness and secondary currents); (iv) flow unsteadiness and non-uniformity; and (v) spatial heterogeneity of fluid stresses in a bed-parallel plane. These constitutive components account for the roughness geometry effect and highlight the significance of the turbulent and dispersive stresses in the near-bed region where their values are largest. To explore the potential of the proposed relationship, an extensive data set has been assembled by employing specially designed large-eddy simulations and laboratory experiments for a wide range of Reynolds numbers. Flows over self-affine rough boundaries, which are representative of natural and man-made surfaces, are considered. The data analysis focuses on the effects of roughness geometry (i.e. spectral slope in the bed elevation spectra), relative submergence of roughness elements and flow and roughness Reynolds numbers, all of which are found to be substantial. It is revealed that at sufficiently high Reynolds numbers the roughness-induced and secondary-currents-induced dispersive stresses may play significant roles in generating bed friction, complementing the dominant turbulent stress contribution.
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Nielsen, Peter, et Paul A. Guard. « VERTICAL SCALES AND SHEAR STRESSES IN WAVE BOUNDARY LAYERS OVER MOVABLE BEDS ». Coastal Engineering Proceedings 1, no 32 (26 janvier 2011) : 1. http://dx.doi.org/10.9753/icce.v32.sediment.1.
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Unified scaling rules are provided for smooth and rough wave boundary layers. It is shown that the rough equivalent of the smooth, or viscous, vertical scale , the Stokes’ length, is a function of r, the Nikuradse roughness and A, the near-bed semi excursion of the wave motion. Realizing this equivalence of viscous and rough scales a unified description in the style of Colebrook’s (1939) formulae for steady flow friction can be devised based on the unified vertical scale. That is, unified smooth and rough wave friction factor formulae can be used with adequate accuracy. A general procedure is given for deriving the unified vertical scale from velocity data including data from mobile bed experiments, which enable determination of the equivalent Nikuradse roughness from these experiments. Presently available sheet flow data show a velocity structure, which corresponds to a Nikuradse roughness r of the order 50 to 100 grain diameters. Instantaneous shear stresses derived through the usual momentum integral from sheet flow experiments show that the shear stress varies strongly through the sheet flow layer with the value at the lowest level of sediment motion being 2 to 3 times the value at the undisturbed bed level. The corresponding Nikuradse roughnesses are about 2.5d50 corresponding to the undisturbed bed level and 100d50 for the stress at the lowest level of sediment motion. With this strong variation of the shear stress through the layer of moving sediment, it is not at all obvious what should be understood by THE BED SHEAR STRESS in the context of wave sediment transport.
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Penna, Nadia, Francesco Coscarella, Antonino D’Ippolito et Roberto Gaudio. « Bed Roughness Effects on the Turbulence Characteristics of Flows through Emergent Rigid Vegetation ». Water 12, no 9 (26 août 2020) : 2401. http://dx.doi.org/10.3390/w12092401.
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During floods, the riparian vegetation in a watercourse significantly changes the velocity distribution and the turbulence structures of the flow. However, a certain influence on them is always exerted by the bed sediments. The aim of the present work is to study the bed roughness effects on the turbulence characteristics in an open-channel flow with rigid and emergent vegetation. Toward this end, an experimental campaign was conducted and consisted of three runs with different bed roughness conditions. The study is based on the analysis of the velocity, Reynolds shear stress, and viscous stress distributions. The results show that, in the region below the free surface region, the flow is strongly influenced by the vegetation. However, moving toward the bed, the flow is affected by a combined effect of vegetation, firstly, and bed roughness, secondly. This flow zone becomes more extended, as the size of the bed sediments increases. The shear stress distributions confirm the distinction between the two flow regions. In fact, the shear stresses are practically negligible in the upper zone of the water depth influenced by vegetation, whereas, owing to the bed roughness, they reach the maximum value near the bed surface. Finally, the analysis of the turbulent kinetic energy (TKE) revealed high values below the crest level and in the near-bed flow zone in the streamwise direction, whereas a strong lateral variation of TKE from the flume centerline to the cylinder occurred in the intermediate region.
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Cooper, Michael A., Thomas M. Jordan, Dustin M. Schroeder, Martin J. Siegert, Christopher N. Williams et Jonathan L. Bamber. « Subglacial roughness of the Greenland Ice Sheet : relationship with contemporary ice velocity and geology ». Cryosphere 13, no 11 (26 novembre 2019) : 3093–115. http://dx.doi.org/10.5194/tc-13-3093-2019.
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Abstract. The subglacial environment of the Greenland Ice Sheet (GrIS) is poorly constrained both in its bulk properties, for example geology, the presence of sediment, and the presence of water, and interfacial conditions, such as roughness and bed rheology. There is, therefore, limited understanding of how spatially heterogeneous subglacial properties relate to ice-sheet motion. Here, via analysis of 2 decades of radio-echo sounding data, we present a new systematic analysis of subglacial roughness beneath the GrIS. We use two independent methods to quantify subglacial roughness: first, the variability in along-track topography – enabling an assessment of roughness anisotropy from pairs of orthogonal transects aligned perpendicular and parallel to ice flow and, second, from bed-echo scattering – enabling assessment of fine-scale bed characteristics. We establish the spatial distribution of subglacial roughness and quantify its relationship with ice flow speed and direction. Overall, the beds of fast-flowing regions are observed to be rougher than the slow-flowing interior. Topographic roughness exhibits an exponential scaling relationship with ice surface velocity parallel, but not perpendicular, to flow direction in fast-flowing regions, and the degree of anisotropy is correlated with ice surface speed. In many slow-flowing regions both roughness methods indicate spatially coherent regions of smooth beds, which, through combination with analyses of underlying geology, we conclude is likely due to the presence of a hard flat bed. Consequently, the study provides scope for a spatially variable hard- or soft-bed boundary constraint for ice-sheet models.
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Hoobi, Raad, et Ayad Saoud Najem. « Study the Affecting Factors on Free overfall Flow and Bed Roughness in Semi-Circular Channels by Artificial Neural Network ». Tikrit Journal of Engineering Sciences 29, no 4 (25 décembre 2022) : 69–78. http://dx.doi.org/10.25130/tjes.29.4.8.
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One of the significant problems facing the water resource engineer is calculating the coefficient of roughness for subsequent design calculations of the discharge amount of a channel or river. In this study, experiments were conducted in a semi-circular, straight channel to investigate the factors affecting bed roughness and flow discharge using Artificial Neural Network (ANN). For this purpose, three semi-circular channel models with free overfall were constructed and installed in a 6-meter-long laboratory flume. The length of these models was 2.50 m with three different diameters (D= 150, 187, and 237mm) and three bed slopes (S=0.004, 0.008, and 0.012). Three sand particle sizes (ds) were used for each semi-circular channel to roughen the bed. The results showed that the Manning roughness coefficient obtained using a rough bed surface was higher than the channel with a smooth bed surface. Also, the results revealed that the Manning roughness coefficient and the Froude number were inversely related. (ANN) analysis showed a good agreement between the experimental and predicted results of flow and roughness. The bring depth (yb) had an 85.8% impact percentage on the free overfall discharge for semi-circular channels, while the bottom slope (S) had only 1.1%.
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Nardone, Paride, et Katinka Koll. « Velocity field and drag force measurements of a cube and a hemisphere mounted on an artificial bed surface roughness ». E3S Web of Conferences 40 (2018) : 05022. http://dx.doi.org/10.1051/e3sconf/20184005022.
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Quantification of the resistance in complex roughness situations, when both bed surface and form roughnesses contribute to the total resistance, as well as partitioning of the two contributions is still unsolved. Studies about form resistance of single elements focused on obstacles mounted on smooth bed surfaces, and only few considered a rough bed surface. In order to define an approach for shear stress partitioning in open channel flows, the effect of flow conditions, the geometrical characteristics of the obstacle, and the effect of the bed surface need to be studied. This paper contributes to the topic presenting results of experiments investigating the flow field around a cube and a hemisphere mounted on a bed surface with wake interference roughness. The velocity field and the drag force exerted on the obstacles were measured with a 3D Laser Doppler Anemometer and a drag force sensor, respectively. The double averaging methodology (DAM) was applied to define the characteristic region influenced by the cube and the hemisphere, and to analyse the streamwise velocities. DAM was developed for canopy flow, thus, the methodology needed to be adapted for isolated obstacle situations. A dependency of the drag coefficient on the relative submergence is observed and analysed.
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Zwolenik, Monika, et Bogusław Michalec. « Effect of water surface slope and friction slope on the value of the estimated Manning’s roughness coefficient in gravel-bed streams ». Journal of Hydrology and Hydromechanics 71, no 1 (4 février 2023) : 80–90. http://dx.doi.org/10.2478/johh-2022-0041.
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Abstract The aim of the study was to assess the possibility of using the empirical formulas to determine the roughness coefficient in gravel-bed streams, the bed slopes of which range from 0.006 to 0.047. Another aim was to determine the impact of taking into account the conditions of non-uniform flow on the application of these formulas and to develop the correlation relationships between the roughness coefficient and water surface slope and also between the roughness coefficient and friction slope in order to estimate the roughness coefficient n in gravel-bed streams. The studies were conducted in eight measuring sections of streams located in the Kraków-Częstochowa Upland, southern Poland. The roughness coefficient n 0 for these sections was calculated from the transformed Bernoulli equation based on the results of surveys and hydrometric measurements. The values of n 0 were compared with the calculation results obtained from fourteen empirical formulas presenting the roughness coefficient as a function of slope. The Lacey, Riggs, Bray and Sauer formulas were found to provide an approximate estimate of the n value, while the best roughness coefficient estimation results were obtained using the Riggs formula. It was also found that taking into account the non-uniform flow and using the friction slope in the formulas instead of the bed slope or water surface slope did not improve the estimated values of the roughness coefficient using the tested formulas. It was shown that the lack of differences in the RMSE and MAE error values calculated for the developed correlation equations between the roughness coefficient and the friction slope or with the water surface slope also indicate no influence of the assumed friction slope or water surface slope on the value of the estimated roughness coefficient.
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Berends, Constantijn J., Roderik S. W. van de Wal, Tim van den Akker et William H. Lipscomb. « Compensating errors in inversions for subglacial bed roughness : same steady state, different dynamic response ». Cryosphere 17, no 4 (12 avril 2023) : 1585–600. http://dx.doi.org/10.5194/tc-17-1585-2023.
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Abstract. Subglacial bed roughness is one of the main factors controlling the rate of future Antarctic ice-sheet retreat and also one of the most uncertain. A common technique to constrain the bed roughness using ice-sheet models is basal inversion, tuning the roughness to reproduce the observed present-day ice-sheet geometry and/or surface velocity. However, many other factors affecting ice-sheet evolution, such as the englacial temperature and viscosity, the surface and basal mass balance, and the subglacial topography, also contain substantial uncertainties. Using a basal inversion technique intrinsically causes any errors in these other quantities to lead to compensating errors in the inverted bed roughness. Using a set of idealised-geometry experiments, we quantify these compensating errors and investigate their effect on the dynamic response of the ice sheet to a prescribed forcing. We find that relatively small errors in ice viscosity and subglacial topography require substantial compensating errors in the bed roughness in order to produce the same steady-state ice sheet, obscuring the realistic spatial variability in the bed roughness. When subjected to a retreat-inducing forcing, we find that these different parameter combinations, which per definition of the inversion procedure result in the same steady-state geometry, lead to a rate of ice volume loss that can differ by as much as a factor of 2. This implies that ice-sheet models that use basal inversion to initialise their model state can still display a substantial model bias despite having an initial state which is close to the observations.
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Alwan, Iman A., et Riyadh Z. Azzubaidi. « Investigations on Large-Scale Geometric Roughness Elements in Open Channels with Different Heights ». Association of Arab Universities Journal of Engineering Sciences 28, no 1 (31 mars 2021) : 07–14. http://dx.doi.org/10.33261/jaaru.2021.28.1.002.
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Large-scale geometric roughness elements is one of the solutions that is used to protect openchannels from erosion. It is use to change the hydraulic characteristics of the flow. It may be concrete blocksor large stone placed at the bed of the channel to impose more resistance in the bed. The height of theseroughness elements is an important parameter that can affect the hydraulic characteristics of the flow. Usinga series of tests of T-shape roughness elements at three different heights, 3, 4.5, and 6cm, arranged in thefully rough configuration in order to investigate the velocity distributions along the flume. ANSYSParametric Design Language, APDL, and Computational Fluid Dynamics, CFD, were used to simulate theflow in an open channel with roughness elements. This simulation helps to find the best height of roughnesselements that can be used to change the hydraulic characteristics of the flow. The results showed that thevelocity values are decreased near the bed by about 61%, 58%, and 64% in case of 3cm, 4.5cm, and 6cmroughness heights consequently compared with the velocity of the control case. The velocity values areincreased near the free surface by about 32% and 19% in case of roughness elements height 6cm comparedwith 3cm and 4.5cm roughness heights respectively. The case of 6cm roughness height is considered to bethe effective case for decreasing the velocity values near the bed of the flume.
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Irzooki, Raad, et Safa Hasan. « Characteristics of flow over the free overfall of triangular channel ». MATEC Web of Conferences 162 (2018) : 03006. http://dx.doi.org/10.1051/matecconf/201816203006.
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In the present paper, the effects of side slopes, bed slopes and bed roughness on the flow over free overfalls in triangular channels have been studied experimentally. For this purpose, three models of triangular channels with free overfalls have been constructed and fixed in a 6m length laboratory flume. These three models had length of 244cm with different values of side slopes (Z) (0.8(H):1(V), 1:1 and 1.33:1). Each one of these models had four different bed slopes (S) (0, 0.0041, 0.0082 and 0.0123). For each bed slope, the bed was roughened with three particle sizes of sand (ds) (1.18mm, 2.36mm, and 4.75mm). The experimental testing program included sixteen series of experiments for each model. Four of them were for smooth beds and twelve for rough beds. A total of forty eight experiments were tested for different rates of discharge (Q). Experimental results of all models showed that Froude number (Frb) of flow decreases with the increasing of end depth ratio values (yb/yc) for different bed roughness, different bed slopes. The relations between the brink depth (yb) and the critical depth (yc) were found to be a simple linear formula for various bottom slope and different bottom roughness. An empirical expression was obtained for the flow over the free overfall in triangular channels for different bed slopes and roughness. The results of the present study have been compared with studies were obtained by other investigators, the comparison shows a very good agreement between them.
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Zhou, Yin-jun, Jin-you Lu, Li Chen et Jie Ren. « Bed roughness adjustments determined from fractal measurements of river-bed morphology ». Journal of Hydrodynamics 30, no 5 (14 septembre 2018) : 882–89. http://dx.doi.org/10.1007/s42241-018-0101-y.
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Matoušek, Václav, et Jan Krupička. « On equivalent roughness of mobile bed at high shear stress ». Journal of Hydrology and Hydromechanics 57, no 3 (1 septembre 2009) : 191–99. http://dx.doi.org/10.2478/v10098-009-0018-9.
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On equivalent roughness of mobile bed at high shear stressThe friction conditions at the top of a mobile bed are discussed for flows in the upper-plane-bed regime, i.e. for the flows with values of the bed Shields parameter larger than approximately 0.6. A special attention is devoted to flows of the bed Shields parameter bigger than 2. Experimental data for flows at high bed shear are collected from literature and new data are added from own measurements of flows of a 1.36-mm sand slurry in the 100-mm pipe loop of the Institute of Hydrodynamics. The database represents flows of very different solids and covers friction conditions within a broad range of Shields parameters up to the maximum value of about 23. The paper analyses the data in order to evaluate a relationship among the equivalent roughness of the top of the bed and other relevant parameters. A semi-empirical formula is proposed that relates the equivalent roughness to the bed Shields parameter, the ratio of flow velocity and particle settling velocity, and the ratio of flow hydraulic radius and particle diameter. The formula is applicable primarily to flows of combined load (contact- and suspended loads together).
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Smart, Graeme, Jochen Aberle, Maurice Duncan et Jeremy Walsh. « Measurement and analysis of alluvial bed roughness ». Journal of Hydraulic Research 42, no 3 (janvier 2004) : 227–37. http://dx.doi.org/10.1080/00221686.2004.9728388.
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Bertin, Stephane, Jane Groom et Heide Friedrich. « Isolating roughness scales of gravel-bed patches ». Water Resources Research 53, no 8 (août 2017) : 6841–56. http://dx.doi.org/10.1002/2016wr020205.
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Bicudo, J. R., et M. F. Giorgetti. « The Effect of Strip Bed Roughness on the Reaeration Rate Coefficient ». Water Science and Technology 23, no 10-12 (1 mai 1991) : 1929–39. http://dx.doi.org/10.2166/wst.1991.0649.
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Measurements are presented for the rate of atmospheric reaeration in open-channel flow under different conditions of depth and bed roughness. A 2k factorial design was employed for the estimation of both depth and bed resistance factor effects upon stream reaeration. Consistent results indicated that stream reaeration is primarily controlled by water shear, but that different modes of instability generated by a combination of depth and strip roughness levels might prevail for different boundary roughness conditions, and as a consequence, differently affect the reaeration coefficient.
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Cai, Yiheng, Fuxing Wan, Shinan Lang, Xiangbin Cui et Zijun Yao. « Multi-Branch Deep Neural Network for Bed Topography of Antarctica Super-Resolution : Reasonable Integration of Multiple Remote Sensing Data ». Remote Sensing 15, no 5 (28 février 2023) : 1359. http://dx.doi.org/10.3390/rs15051359.
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Bed topography and roughness play important roles in numerous ice-sheet analyses. Although the coverage of ice-penetrating radar measurements has vastly increased over recent decades, significant data gaps remain in certain areas of subglacial topography and need interpolation. However, the bed topography generated by interpolation such as kriging and mass conservation is generally smooth at small scales, lacking topographic features important for sub-kilometer roughness. DeepBedMap, a deep learning method combined with multiple surface observation inputs, can generate high-resolution (250 m) bed topography with realistic bed roughness but produces some unrealistic artifacts and higher bed elevation values in certain regions, which could bias ice-sheet models. To address these issues, we present MB_DeepBedMap, a multi-branch deep learning method to generate more realistic bed topography. The model improves upon DeepBedMap by separating inputs into two groups using a multi-branch network structure according to their characteristics, rather than fusing all inputs at an early stage, to reduce artifacts in the generated topography caused by earlier fusion of inputs. A direct upsampling branch preserves large-scale subglacial landforms while generating high-resolution bed topography. We use MB_DeepBedMap to generate a high-resolution (250 m) bed elevation grid product of Antarctica, MB_DeepBedMap_DEM, which can be used in high-resolution ice-sheet modeling studies. Moreover, we test the performance of MB_DeepBedMap model in Thwaites Glacier, Gamburtsev Subglacial Mountains, and several other regions, by comparing the qualitative topographic features and quantitative errors of MB_DeepBedMap, BEDMAP2, BedMachine Antarctica, and DeepBedMap. The results show that MB_DeepBedMap can provide more realistic small-scale topographic features and roughness compared to BEDMAP2, BedMachine Antarctica, and DeepBedMap.
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Daneshfaraz, Rasoul, Amir Ghaderi, Aliakbar Akhtari et Silvia Di Francesco. « On the Effect of Block Roughness in Ogee Spillways with Flip Buckets ». Fluids 5, no 4 (16 octobre 2020) : 182. http://dx.doi.org/10.3390/fluids5040182.
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In this study, the effect of the presence of bed-block roughness in an ogee spillway on energy dissipation and jet length is investigated. A series of experimental and numerical tests were conducted using an ogee spillway with block roughness on the bed without a flip bucket and with a flip bucket at different take-off angles (32 °C and 52 °C). To model the free-flow surface, the volume-of-fluid (VOF) method and turbulence model from RNG k–ε were used. Results indicated that the numerical model is fairly capable of simulating a free-flow surface over an ogee spillway; using block roughness on the spillway chute without a bucket, relative energy dissipation increased by 15.4% compared to that in the spillway with a smooth bed, while for the spillway with 32 °C and 52 °C buckets, it increased by 9.5%. The jet length for a spillway with a flip bucket and roughened bed decreased by 8% to 58% compared to that in a smooth bed. Lastly, the relationships for the estimation of relative energy dissipation and jet length are presented.
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Schönfeldt, Hans-Jürgen. « On the aeolian saltation bed shear stress and saltation roughness length ». Meteorologische Zeitschrift 15, no 3 (10 juillet 2006) : 307–15. http://dx.doi.org/10.1127/0941-2948/2006/0126.
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Zhang, Zeng, et S. Samuel Li. « Large Eddy Simulation of Near-Bed Flow and Turbulence over Roughness Elements in the Shallow Open-Channel ». Water 12, no 10 (27 septembre 2020) : 2701. http://dx.doi.org/10.3390/w12102701.
Texte intégralRésumé :
Turbulent flows in rough open-channels have complex structures near the channel-bed. The near-bed flow can cause bed erosion, channel instability, and damages to fish habitats. This paper aims to improve our understanding of the structures. Transverse square bars placed at the channel-bed form two-dimensional roughness elements. Turbulent flows over the bars are predicted using large eddy simulation (LES). The predicted flow quantities compare well with experimental data. The LES model predicts mean-flow velocity profiles that resemble those in the classic turbulent boundary layer over a flat plate and profiles that change patterns in the vicinity of roughness elements, depending on the pitch-to-roughness height ratio λ/k. The relative turbulence intensity and normalized Reynolds shear stress reach maxima of 15% and 1.2%, respectively, at λ/k = 8, compared to 9% and 0.2% at λ/k = 2. The predicted bottom boundary layers constitute a large portion of the total depth, indicating roughness effect on the flow throughout the water column. Fluid exchange between the roughness cavity and outer region occurs due to turbulence fluctuations. The fluctuations increase in intensity with increasing λ/k ratio. This ratio dictates the number of eddies in the cavity as well as their locations and shapes. It also controls turbulence stress distributions. LES can be used to explore strategies for erosion control, channel restoration, and habitat protection.