Journal of Hydraulic Engineering

An analytic model (AM) describes the dynamical behavior of a Newtonian fluid that is suddenly released to the atmosphere from a pressurized vessel. The discharge process is a very fast transient phenomenon in which the liquid transits from rest to a highly turbulent motion, constituting a two-phase flow with a liquid–air interface. The AM has a number of parameters that can be adjusted to conform to experimental or simulation data. This AM is then used to assess the ability of some relevant computational fluid dynamics (CFD) turbulence models to simulate the fast transient behavior described by the AM. The detached eddy simulation (DES) $k-\omega$ shear-stress-transport with scale-adaptive-simulation (SSTSAS) turbulence model provides an acceptable agreement with the AM because it can reproduce the intense wall friction generated in the transient motion. The CFD results suggest that deceleration plays a very prominent role in generating turbulence near the wall. The cross-section velocity and turbulence fields profiles for the CFD model are also discussed.

Density currents generated by marine brine discharges, e.g., from desalination plants, can have a negative impact on marine ecosystems. It is therefore important to accurately predict their behavior. Predictions are often made using computational hydrodynamic models, which should be validated using field or laboratory measurements. This paper focuses on the setup and validation of three-dimensional (3D) models for estimating the transport and mixing processes that occur in these types of flows. Through a comprehensive sensitivity analysis based on the reproduction of several laboratory-generated density currents, a set of recommendations are made regarding the modeling aspects, including the domain discretization, the treatment of momentum at the density current source, the hydrostatic hypothesis and the selection of turbulence closure models. Finally, the proposed numerical model setup is validated using different experimental data showing good agreement in terms of the main variables considered: errors of less than 1.3% for dilution and of 6% for velocity. This study serves as a first step toward the full validation of these 3D hydrodynamic models for the simulation of field-scale density currents.

In this paper, the pipeline leak localization problem using transient data is investigated. Signal processing techniques that proved successful in wireless communications and acoustics are adapted and tested for leak identification. More specifically, Bartlett’s beamforming (BF) (also known as conventional BF, matched field, or phased array), Capon’s BF (also known as the minimum variance distortionless response filter), Lagunas’ BF, and multiple signal classification (MUSIC) methods are used. The localization is realized by a one-dimensional search for the leak location along the pipe, where one-dimensional search means that the wave model used includes one leak only. The one-dimensional search is advantageous in that it involves low computational cost. The performance of the different techniques in the cases of a single leak and multiple leaks is discussed. In the single-leak case, the proposed spectral methods accurately localize the leak even for a high level of noise. For the multiple-leak case, the proposed spectral methods are able to localize all leaks provided that the leak-to-leak distance is of the same order or larger than half the shortest probing wavelength. However, the localization deteriorates when the leaks are too close together because a model with a single leak is being used to identify multiple leaks. Although not accurate, the application of the one-dimensional search to multiple leaks is still valuable because it provides a fast initial estimate of the leak locations, which serves as prior information for more precise but computationally expensive multidimensional search techniques.

The transfer matrix method was applied to detect partial blockages in liquid pipelines using the first four harmonics of the pressure oscillations produced by sinusoidal opening and closing of a downstream valve. Unlike most available methods, which use a large number of harmonics to analyze the pattern of the frequency response diagram, this study uses only the first few harmonics to investigate the effect of a partial blockage on the amplitude of pressure head oscillations. A relationship between the relative blockage location and the amplitude of the pressure head oscillation was determined for each lower harmonic in the steady-oscillatory flow. The effect of steady and unsteady friction is discussed. The results of the current approach are compared with those obtained in the time domain by using the method of characteristics and with the experimental data reported in the literature; there is a satisfactory agreement.

A geotextile mattress with sloping curtain (GMSC) was introduced to protect underwater pipelines from scour in steady currents. GMSC is a newly developed countermeasure against river and estuarine scour. To better understand the beneficial effects of GMSC on seepage flow under pipelines, dye was injected to determine the hydraulic gradients across the pipeline in a series of verification tests. Hydraulic gradients across the pipeline with and without a GMSC were quantified for different curtain angles, curtain heights of the GMSC, and distances between the pipeline and the GMSC, and installing GMSCs with or without sand-pass openings, which are openings to allow bottom flow with a high concentration of sediment to pass. The results of the experiments show that a GMSC is capable of protecting a pipeline against scour in a steady current by effectively reducing the hydraulic gradient in the bed soil below the pipeline. The hydraulic gradient across the pipeline decreases nonlinearly with the increase of curtain height and angle of the GMSC. The effect of sand-pass openings on the hydraulic gradient across the pipeline is not significant. The hydraulic gradient decreases nonlinearly with decreasing distance between the pipeline and the GMSC. When the distance decreases below a critical point, the seepage flow under the pipeline reverses. The GMSC may provide an optimum protection effect on the pipeline when the distance between the pipeline and the GMSC is about 6 times the obstacle height of the GMSC ($H_c\sin \alpha$) by reducing the flow velocity approaching the pipeline close to zero.

Dam-break waves are commonly used throughout the field of hydraulic engineering. Given the availability of several well-developed analytical solutions, as well as the relative ease with which they can be implemented as a numerical or physical boundary condition, dam-break waves have been used to examine various phenomena. This study employs a smoothed particle hydrodynamics (SPH) model to examine the influence of the gate opening on characteristics of the wave propagation. First, the model was extensively validated using experimental results from tests which employed swing and lift gates. Generally, any dam-break gate should open or be removed as fast as possible to allow the formation of a perfect dam break wave. However, cost-benefit considerations and technical design constraints, particularly for gates fitted on large-scale test facilities, result in less than instantaneous gate motions because the complexity and associated cost of the gate increases exponentially with increasing drive capacity. Larger gate weights installed in wide flumes require an improved understanding of the errors involved with slower opening times of both types of gate mechanisms. The study found that the influence of the gate opening time decreased with time elapsed from impounded water release, as well as with the downstream distance from the gate. The study also provides an estimate of the errors associated with the gate opening time to help engineers and researchers in the process of planning to generate such waves.

A two-dimensional (2D) flux-form Eulerian-Lagrangian method (FFELM) on unstructured grid is proposed for solving the advection equation in free-surface scalar transport models. The scalar concentrations of backtracking points are combined with time-interpolated cell-face velocities to evaluate cell-face advective fluxes. A G-correction is defined as an additional mechanism to eliminate potential nonphysical oscillations by correcting the cell-face advective fluxes. A flux-form cell update is finally carried out to obtain new cell concentrations. The role of the G-correction in the FFELM is clarified using a test of scalar transport in unsteady open-channel flows. A solid-body rotation test, a laboratory bend-flume test, and a real river test (using a 600-km river reach of the upper Yangtze River) are used to demonstrate the FFELM. The FFELM is revealed in tests to achieve almost the same accuracy as a pure Eulerian-type method [the subcycling finite-volume method (SCFVM)] and a conservative ELM [the finite-volume ELM (FVELM)]. Relative to explicit Eulerian methods, the FFELM uses the information of backtracking points over an extended upwind dependence domain in evaluating cell-face advective fluxes, and allows larger time steps for which the Courant-Friedrichs-Lewy number (CFL) is greater than 1. In the real river test, stable and accurate FFELM simulations can be achieved at a time step for which the CFL is as large as 5. Efficiency issues of the FFELM are clarified using the bend-flume test (193,536 cells) and the real river test (213,363 cells). In solving a transport problem (using 1–32 kinds of scalars and 16 cores), a parallel run using the FFELM is 1.0–3.3 times faster than a parallel run using the SCFVM. The FFELM has a computational cost slightly less (15%–17%) than that of the FVELM. Moreover, the implementation of the FFELM is much easier than that of the FVELM, and extension of the 2D FFELM to its one-dimensional (1D) and three-dimensional (3D) versions is straightforward.

In this study, a theoretical formula for a one-dimensional longitudinal dispersion coefficient was developed using the lateral distribution equation for depth-averaged streamwise velocity derived from the Shiono and Knight model. A set of experimental results that included detailed velocity and tracer concentration data acquired from natural rivers was used to verify the developed dispersion formula. Additionally, the developed formula was compared with existing empirical equations for the longitudinal dispersion coefficient. From this comparison, it could be seen that the results of this study showed a close approximation to the observed dispersion coefficient, although the agreement was not best. The developed equation could be used in cases where the dispersion coefficient must be determined based only on topographic or hydraulic information rather than detailed flow data.