Journal of Hydraulic Engineering

The aim of this paper is the experimental characterization of a ball valve under steady and unsteady conditions, based on experimental tests carried out in a pressurized pipe system assembled at Instituto Superior Técnico. Data analysis showed that the response of the valve under steady-state conditions depends not only on the valve geometry and closure percentage, but also on the flow regime (i.e., Reynolds number); the comparison with values published in literature confirmed that typical valve head loss curves presented in manuals and textbooks refer to turbulent flows. The behavior under unsteady conditions was also analyzed based on transient pressure head measurements showing that the valve effective closure time varies between 4 and 10% of the total time of the maneuver. Two mathematical functions (hyperbolic and sigmoidal) are proposed to describe the discharge variation as a function of the total time of the maneuver and of the initial steady-state discharge; the most appropriate function depends on the simplifications imposed on the hydraulic transient simulator. A computational fluid dynamics (CFD) model was used to support the observed experimental behavior and to highlight the effect of the pipe length on the discharge variation.

In transport-limited alluvial streams, the suspended sediment concentration $C$ exhibits power functional relationships with the flow discharge $Q$ at a given station. Once the power-law $C\text{-}Q$ relationships at multiple stations along a stream are compiled, these relationships either systematically lag in the downstream direction (i.e., decreasing $C$ downstream for a constant $Q$) or overlap each other (i.e., similar $C$ for a constant $Q$ anywhere along the stream). It has been claimed that the mode of downstream $C\text{-}Q$ (lag or overlap) is associated with the downstream channel geometry. This poses a fundamental question as to whether different modes of downstream $C\text{-}Q$ relationships are the mechanistic consequences of channel hydraulics functions induced by different channel geometries or distinct channel geometries are the signatures of adaptation to the varying $C\text{-}Q$ relationships. This question is investigated in this study with theoretical streams by applying a numerical model which solves sediment flux and shallow water equations simultaneously. Simulation results are consistent with observations from natural rivers in many respects, such as power-law at-a-station and downstream hydraulic geometry relationships. Lagged $C\text{-}Q$ relationships are reproduced whereas the degree of a lag depends on the imposed channel geometry. This agrees with field observations and can be explained through the downstream increase rate in the bed shear stress. These findings imply that the downstream lag in $C\text{-}Q$ relationships is the resultant feature of a given channel geometry.

Targeted and proactive pipeline condition assessment is critical for cost-effective maintenance of aging water transmission and distribution systems. The current research proposes a fast inverse transient analysis (ITA) with a head-based method of characteristics (HBMOC) and a flexible computational grid for condition assessment of long pressurized pipelines. Compared with conventional ITA, the key innovations of the proposed method include (1) the development and use of an innovative forward-modeling scheme HBMOC to enhance computational efficiency; and (2) use of a flexible characteristics grid to avoid the need for interpolation and hence enhance the accuracy by satisfying the Courant condition in all iterations of forward modeling. To examine and verify the proposed method, numerical simulations are conducted in a pipeline with multiple sections of deterioration (simulated by changes in wavespeed). Both the conventional ITA and proposed ITA are applied to the numerical pipe model, and the wavespeeds estimated by different ITA approaches are compared. It is concluded that the proposed ITA is more accurate and four times more computationally efficient than the conventional ITA. The impact of neglecting friction in the proposed approach is shown to be insignificant given that the proposed ITA was aimed at condition assessment of transmission mains, and only transient pressures that cover the pipe section of interest are analyzed.

A key assumption in the use of numerical sediment transport models is the selection and application of an equation to describe sediment transport capacity. This assumption introduces uncertainty in the model predictions because all sediment transport equations are simplifications of the physical processes. Bayesian model averaging (BMA) is a statistical method that characterizes the uncertainty due to the mathematical structure of a model and allows predictions from multiple models to be combined. In this paper, BMA is applied to quantify how the uncertainty originating from the transport equation affects the predictions from a sediment transport model. To apply BMA in this context, the likelihood function is modified to allow consideration of multiple model output variables. In addition, BMA’s assumption that the uncertainty associated with each model remains constant between the calibration and forecast periods is relaxed. The proposed multivariate BMA model is applied to transport equations included in the sedimentation and river hydraulics—one dimension (SRH-1D) model. For two flume experiments, the multivariate BMA model provides improved predictions over the individual transport equations and univariate BMA models, and it provides more realistic descriptions of the predictive uncertainty.

Both the profile and orientation of an intake entrance basically determine the characteristics of the flow (especially the velocity distribution and therefore the hydraulically developed subsurface depressions) toward the intake. The profile and orientation of the intake affect (1) the process of accumulation and growth of vorticity (circulation) along the pathway axis of the swirling vortex from the free surface to the intake; (2) position of the pathway of the swirling-vortex filament; and (3) location of the point of entry of the free-surface or subsurface vortex at the entrance of the intake. Test results indicate that the intake-entrance profile has limited effects on the occurrence of the air-core vortex and critical submergence. Regardless of the profile of the intake entrance, one common physical mechanism exists for development of free vortices occurring at intake entrances of different profiles. It is proven that spherical sink surface sectors (SSSSs) are essential for the vortex to exist.

This study used fully spatially distributed three-dimensional (3D) velocity data for the improved calibration of a 3D hydrodynamic model. The conventional calibration methods do not account for the spatial distribution of the fully 3D flow field. This study compared the results of the proposed calibration approach with those in the literature to show how choosing different calibration methods can change the model predictive capability. The proposed calibration approach can advance the model prediction of 3D flow complexity; consequently, it enhances the potential for the estimation of river processes such as channel morphodynamics and contaminant mixing. To test the proposed methodology, a tortuously natural meandering river was simulated using the Delft3D hydrodynamic model. The spatially intensive acoustic Doppler current profiler (ADCP) velocity data collected throughout the river model domain provided the fully 3D distributed velocities for the model calibration. For the accurate and realistic comparison of the fully 3D predicted velocities and the measured velocities, an algorithm was developed to match the location of each ADCP bin with the 3D model grid points. The results of this study demonstrated that the fully 3D calibration method led to a calibrated model parameterization that was different from that obtained from conventional calibration approaches. The t-test analysis illustrated that with or without implementation of the horizontal large eddy simulation (HLES) model option, the model results were sensitive to the user input background horizontal eddy viscosity, confirming the importance of an appropriate calibration of the developed 3D model. The results of various calibration approaches were validated using the 3D velocity data collected at a bend section in the river using an acoustic Doppler velocimeter (ADV). It was shown that the proposed 3D calibration approach resulted in the best model performance. The results of this study suggest that the proposed methodology can provide a better calibration potential for the simulation of natural meandering rivers with complex geometry.

Hydraulic losses of a low specific speed centrifugal pump originate in the friction and turbulent dissipations in all components between the suction and discharge nozzles as well as fluid recirculation mainly caused by momentum transfer between different parts of fluid zones. The best hydraulic efficiency of centrifugal pumps can reach 85–95% when operating at their designed condition. Shut-off conditions or low flow rates cause the greatest bulk of energy consumption. This study tests 11 distinct centrifugal pumps to calculate disk friction, mechanical losses (ignoring leakage losses due to their very insignificant values for the selected pumps), and hydraulic efficiency after energy balance. Temperature rise of the working fluid is also measured during operation at part load conditions. A theoretically analyzed experimental relation is derived for the temperature difference of suction and discharge. The proposed relation is used to evaluate hydraulic efficiency directly from the temperature rise value and other hydraulic characteristics of the centrifugal pump. The relation accuracy is examined by implementing several centrifugal pumps and it leads to satisfactory results.

Engineering activities, such as disposal of dredged materials or land reclamation, produce sediment clouds that can be characterized by a descending thermal and a trailing stem resulting from an instantaneous release. The mass loss from the trailing stem during the descent induces turbidity in the water column and this is investigated in this study. The experimental data of trailing stems from previous studies were reanalyzed to derive a relationship between the mass loss to the trailing stem and the sediment release conditions. The normalized trailing stem length and the cumulative mass distribution within the stem were then obtained. Finally, an application of the model to estimate the sediment loss to the ambient during sediment disposal is given.

This paper presents a mathematical model for analyzing the emptying process in a pipeline using pressurized air. The rigid water column model (RWCM) is used to analyze the transient phenomena that occur during the emptying of the pipeline. The air-water interface is also computed in the proposed model. The proposed model is applied along a 271.6-m-long PVC-steel pipeline with a 232-mm internal diameter. The boundary conditions are given by a high-pressure air tank at the upstream end and a manual butterfly valve at the downstream end. The solution was carried out in a computer modeling program. The results show that comparisons between both the computed and measured water flow oscillations and gauge pressures are very similar; hence, the model can effectively simulate the transient flow in this system. In addition, the results indicate that the proposed model can predict both the water flow and gauge pressure better than previous models.

Levee breaches have resulted in significant damage and loss of life in recent years. Although this area has been of considerable interest to researchers, procedures are not available to compute the breach outflow accurately, which are needed for flood mitigation and emergency preparedness. In this work, the outflow discharge through a levee breach with constant cross section is computed by using two different models: the first solves the one-dimensional spatially varied flow equation, and the second numerically solves the two-dimensional Saint-Venant equation. Both models are applied to a breach in rectangular and trapezoidal channels. Different cases are simulated by varying the breach width, submergence ratio, and inflow discharge. It is found that the effect of breach width on the outflow is less than that caused by the submergence ratio. Breach outflows computed by a spatially varied flow model are higher than that by the two-dimensional model. A new relationship is proposed to correct the breach outflows calculated using the one-dimensional model.