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In this study, a depth-averaged numerical model was employed to investigate the two-dimensional flow features of transitional open-channel flows from a supercritical to a subcritical state. Compared to a shallow-water model, the proposed model incorporates supplementary terms to account for the effects of non-uniform velocity and non-hydrostatic pressure distributions. The model equation was solved numerically by means of the Adams–Bashforth–Moulton scheme. A wide variety of transitional open-channel flow problems such as hydraulic jumps was considered for assessing the suitability of the numerical model. The results of the model for the free-surface profile, pressure distribution, and characteristics of the first wave of an undular jump were compared with the experimental data, and the agreement was found to be satisfactory. Despite the effects of the three-dimensional characteristics of the flow and the bulking of the flow caused by air entrainment, the model performed reasonably well with respect to the simulations of the mean flow characteristics of the curvilinear turbulent flow problems. Furthermore, the results of this investigation confirmed that the model is more suitable for analyzing near-critical turbulent flow problems without cross-channel shock waves.
Yebegaeshet T. Zerihun. Non-Hydrostatic Transitional Open-Channel Flows from a Supercritical to a Subcritical State. Slovak Journal of Civil Engineering 2021, 29, 39 -48.
AMA StyleYebegaeshet T. Zerihun. Non-Hydrostatic Transitional Open-Channel Flows from a Supercritical to a Subcritical State. Slovak Journal of Civil Engineering. 2021; 29 (2):39-48.
Chicago/Turabian StyleYebegaeshet T. Zerihun. 2021. "Non-Hydrostatic Transitional Open-Channel Flows from a Supercritical to a Subcritical State." Slovak Journal of Civil Engineering 29, no. 2: 39-48.
A number of studies have considered the effects of weir design variations on the free- and submerged-flow characteristics of trapezoidal broad-crested weirs. It appears that the hydraulics of short-crested weir flows have received little attention; thus, the current knowledge is incomplete. By systematically analyzing a large set of experimental data, the present study aims to fill in this knowledge gap and to provide a complete description of the discharge characteristics of trapezoidal-shaped weirs, including the salient features of two-dimensional weir flows. The analysis of the axial free-surface profiles for short-crested weir flows attested that the location of the nearest station for the correct measurement of the overflow depth under free-flow conditions is at η0 from the heel of the weir, where η0 is the upstream free-surface elevation. Additionally, an empirical equation for the free-flow discharge coefficient is proposed as being valid for a trapezoidal-shaped weir with varying upstream- and downstream-face slopes. The results of this investigation reveal that the streamline curvature and the slopes of the upstream and downstream weir faces significantly affect the streamwise flow patterns and, hence, the free-flow discharge.
Yebegaeshet T. Zerihun. Free Flow and Discharge Characteristics of Trapezoidal-Shaped Weirs. Fluids 2020, 5, 238 .
AMA StyleYebegaeshet T. Zerihun. Free Flow and Discharge Characteristics of Trapezoidal-Shaped Weirs. Fluids. 2020; 5 (4):238.
Chicago/Turabian StyleYebegaeshet T. Zerihun. 2020. "Free Flow and Discharge Characteristics of Trapezoidal-Shaped Weirs." Fluids 5, no. 4: 238.
Most of the existing models for analyzing unconfined flows in hillslope aquifers are based on the Boussinesq (1877) equation. In the development of these models, the assumption of negligible bed-normal velocity was employed, thus restricting their application to shallow groundwater-flow situations. On the basis of a non-hydrostatic pressure approach, a ground-water-flow model that considers the effects of the vertical curvature of the flow streamlines and the three-dimensional geometry of the underlying bedrock was proposed. A dissipative two-four finite-difference scheme was utilized to discretize and solve the model equation. The applicability of the model was assessed by conducting numerical experiments on transient unconfined flows in convergent- and divergent-type hillslope aquifers with non-uniform bedrock slopes. The numerical results for the phreatic-surface profiles and outflow discharges were compared to the experimental data, and a good agreement was obtained. The results of the comparison attested that the dynamics of the hillslope drainage processes were accurately portrayed by the proposed model. This study highlights the necessity of considering the effects of the plan shape and the profile curvature of complex hillslopes in order to improve the overall performance of the computational model.
Yebegaeshet T. Zerihun. A Numerical Investigation of Transient Groundwater Flows with a Phreatic Surface Along Complex Hillslopes. Slovak Journal of Civil Engineering 2020, 28, 11 -19.
AMA StyleYebegaeshet T. Zerihun. A Numerical Investigation of Transient Groundwater Flows with a Phreatic Surface Along Complex Hillslopes. Slovak Journal of Civil Engineering. 2020; 28 (1):11-19.
Chicago/Turabian StyleYebegaeshet T. Zerihun. 2020. "A Numerical Investigation of Transient Groundwater Flows with a Phreatic Surface Along Complex Hillslopes." Slovak Journal of Civil Engineering 28, no. 1: 11-19.
In an open-channel, the transition of a flow from a subcritical to a supercritical state may occur as a result of a lateral inflow or outflow that produces a streamwise discharge variation. Apparently, such a transition cannot be modeled accurately by a conventional hydrostatic pressure approach. In this study, a depth-averaged model that accounts for the effects of a spatially-varied discharge and a non-hydrostatic pressure distribution was developed and applied to simulate the transcritical flow in a lateral-spillway channel and the subcritical flow in a main channel fitted with side weirs. The model results for the axial free-surface profile and variation of discharge in the main channel were compared with the results of a shallow-flow model and experimental data, thereby resulting in a closer match to the measurements than the shallow-flow model. Overall, the investigation results confirmed the efficiency and validity of the non-hydrostatic depth-averaged model in simulating the mean flow characteristics of the subcritical and transcritical free-surface flows with spatially increasing or decreasing discharges, thus demonstrating its potential to be used as a numerical tool in engineering practice.
Yebegaeshet T. Zerihun. On Steady Two-dimensional Free-surface Flows with Spatially-varied Discharges. Slovak Journal of Civil Engineering 2019, 27, 1 -11.
AMA StyleYebegaeshet T. Zerihun. On Steady Two-dimensional Free-surface Flows with Spatially-varied Discharges. Slovak Journal of Civil Engineering. 2019; 27 (3):1-11.
Chicago/Turabian StyleYebegaeshet T. Zerihun. 2019. "On Steady Two-dimensional Free-surface Flows with Spatially-varied Discharges." Slovak Journal of Civil Engineering 27, no. 3: 1-11.
The classical Dupuit–Forchheimer approach, commonly used in analysing unconfined groundwater-flow systems, relies on the assumption of a negligible vertical component of the flow. This approximation is valid only when the convergence of streamlines is very limited and the drawdown of the phreatic surface is small, or the thickness of the horizontal layer of the heterogeneous aquifers is sufficiently small. In this study, a higher-order one-dimensional model is proposed for groundwater-flow problems with significant inclination and curvature of the phreatic surface. The model incorporates non-hydrostatic terms that take into account the effects of the vertical velocity of the flow, and was solved with an implicit finite-difference scheme. The accuracy of the proposed model was demonstrated by simulating various unconfined seepage- and groundwater-flow problems with moderate curvilinear effects. The computational results for steady-state flows were compared with the results of the full two-dimensional potential-flow methods and experimental data, resulting in a reasonably good agreement. In general, the comparison results exhibited the efficiency and validity of the model in simulating complex unconfined flows over curved bedrock and curvilinear flows over planar bedrock with a steep slope.
Yebegaeshet T. Zerihun. Extension of the Dupuit–Forchheimer Model for Non-Hydrostatic Flows in Unconfined Aquifers. Fluids 2018, 3, 42 .
AMA StyleYebegaeshet T. Zerihun. Extension of the Dupuit–Forchheimer Model for Non-Hydrostatic Flows in Unconfined Aquifers. Fluids. 2018; 3 (2):42.
Chicago/Turabian StyleYebegaeshet T. Zerihun. 2018. "Extension of the Dupuit–Forchheimer Model for Non-Hydrostatic Flows in Unconfined Aquifers." Fluids 3, no. 2: 42.
This study describes the results of a numerical investigation aimed at developing and validating a non-hydrostatic depth-averaged model for flow problems where the horizontal length scales close to flow depth. For such types of problems, the steep-slope shallow-water equations are inadequate to describe the two-dimensional structure of the curvilinear flow field. In the derivation of these equations, the restrictive assumptions of negligible bed-normal acceleration and bed curvature were employed, thus limiting their applicability to shallow flow situations. Herein, a Boussinesq-type model is deduced from the depth-averaged energy equation by relaxing the weakly-curved flow approximation to deal with the non-hydrostatic steep flow problems. The proposed model is solved with an implicit finite difference scheme and then applied to simulate steady free-surface flow problems with strong curvilinear effects. The numerical results are compared to experimental data, resulting in a reasonable overall agreement. Further, it is shown that the discharge characteristics of free flow over a round-crested weir are accurately described by using a Boussinesq-type approximation, and the drawbacks arising from a standard hydrostatic approach are overcome. The suggested numerical method to determine the discharge coefficient can be extended and adopted for other types of short-crested weirs.
Yebegaeshet T. Zerihun. A Non-Hydrostatic Depth-Averaged Model for Hydraulically Steep Free-Surface Flows. Fluids 2017, 2, 49 .
AMA StyleYebegaeshet T. Zerihun. A Non-Hydrostatic Depth-Averaged Model for Hydraulically Steep Free-Surface Flows. Fluids. 2017; 2 (4):49.
Chicago/Turabian StyleYebegaeshet T. Zerihun. 2017. "A Non-Hydrostatic Depth-Averaged Model for Hydraulically Steep Free-Surface Flows." Fluids 2, no. 4: 49.
The flow field of many practical open channel flow problems, e.g. flow over natural bed forms or hydraulic structures, is characterised by curved streamlines that result in a non-hydrostatic pressure distribution. The essential vertical details of such a flow field need to be accounted for, so as to be able to treat the complex transition between hydrostatic and non-hydrostatic flow regimes. Apparently, the shallow-water equations, which assume a mild longitudinal slope and negligible vertical acceleration, are inappropriate to analyse these types of problems. Besides, most of the current Boussinesq-type models do not consider the effects of turbulence. A novel approach, stemming from the vertical integration of the Reynolds-averaged Navier-Stokes equations, is applied herein to develop a non-hydrostatic model which includes terms accounting for the effective stresses arising from the turbulent characteristics of the flow. The feasibility of the proposed model is examined by simulating flow situations that involve non-hydrostatic pressure and/or nonuniform velocity distributions. The computational results for free-surface and bed pressure profiles exhibit good correlations with experimental data, demonstrating that the present model is capable of simulating the salient features of free-surface flows over sharply-curved overflow structures and rigid-bed dunes.
Yebegaeshet T. Zerihun. A Numerical Study of Non-hydrostatic Shallow Flows in Open Channels. Archives of Hydro-Engineering and Environmental Mechanics 2017, 64, 17 -35.
AMA StyleYebegaeshet T. Zerihun. A Numerical Study of Non-hydrostatic Shallow Flows in Open Channels. Archives of Hydro-Engineering and Environmental Mechanics. 2017; 64 (1):17-35.
Chicago/Turabian StyleYebegaeshet T. Zerihun. 2017. "A Numerical Study of Non-hydrostatic Shallow Flows in Open Channels." Archives of Hydro-Engineering and Environmental Mechanics 64, no. 1: 17-35.
This study addresses a particular phenomenon in open channel flows for which the basic assumption of hydrostatic pressure distribution is essentially invalid, and expands previous suggestions to flows where streamline curvature is significant. The proposed model incorporates the effects of the vertical curvature of the streamline and steep slope, in making the pressure distribution non-hydrostatic, and overcomes the accuracy problem of the Saint-Venant equations when simulating curvilinear free surface flow problems. Furthermore, the model is demonstrated to be a higher-order one-dimensional model that includes terms accounting for wave-like variations of the free surface on a constant slope channel. Test results of predicted flow surface and pressure profiles for flow in a channel transition from mild to steep slopes, transcritical flow over a short-crested weir and flow with dual free surfaces are compared with experimental data and previous numerical results. A good agreement is attained between the experimental and computed results. The overall simulation results reveal the satisfactory performance of the proposed model in simulating rapidly varied gravity-driven flows with predominant non-hydrostatic pressure distribution effects. This study suggests that a higher-order pressure equation should be used for modelling the pressure distribution of a curvilinear flow in a steeply sloping channel.
Yebegaeshet T. Zerihun. Modelling free surface flow with curvilinear streamlines by a non-hydrostatic model. Journal of Hydrology and Hydromechanics 2016, 64, 281 -288.
AMA StyleYebegaeshet T. Zerihun. Modelling free surface flow with curvilinear streamlines by a non-hydrostatic model. Journal of Hydrology and Hydromechanics. 2016; 64 (3):281-288.
Chicago/Turabian StyleYebegaeshet T. Zerihun. 2016. "Modelling free surface flow with curvilinear streamlines by a non-hydrostatic model." Journal of Hydrology and Hydromechanics 64, no. 3: 281-288.
Venturi flumes are one of the most important flow-measuring structures commonly investigated by physical model tests in the past. The solutions to the Venturi flume flow problems were generally found on the basis of empirical equations arising from such tests. Nonetheless, the overall accuracy and range of applicability of these equations rely on the scope of the tests. Additionally, the hydraulic characteristics of free flows in short-throated flumes cannot be modelled by the conventional hydrostatic pressure approaches. In this study, a one-dimensional model, which incorporates a higher-order dynamic pressure correction for the effects of the sidewalls and streamline vertical curvatures, is applied to simulate such flows and elucidate relevant flow features. The model equations are discretised and solved using the finite difference scheme. The computed results for free surface profiles, pressure distributions at different sections and discharge characteristics are compared to measured data. The computational results exhibit good agreement with measured data. Overall, it is shown that the developed model is capable of accurately simulating the curvilinear flows in short-throated flumes with rounded transition and bottom humps. The results also highlight the detailed dependence of the discharge characteristics of the critical-flow flumes under free flow conditions on the curvature of the streamlines.
Yebegaeshet T. Zerihun. A Numerical Study on Curvilinear Free Surface Flows in Venturi Flumes. Fluids 2016, 1, 21 .
AMA StyleYebegaeshet T. Zerihun. A Numerical Study on Curvilinear Free Surface Flows in Venturi Flumes. Fluids. 2016; 1 (3):21.
Chicago/Turabian StyleYebegaeshet T. Zerihun. 2016. "A Numerical Study on Curvilinear Free Surface Flows in Venturi Flumes." Fluids 1, no. 3: 21.