Journal of Hydraulic Engineering

An implicit dual time-stepping method (DTS) is applied to a Godunov-type finite-volume model for two-dimensional (2D) shallow-water flows on unstructured grids to improve run-time efficiency. In this model, an implicit nonlinear lower–upper symmetric Gauss–Seidel (LU-SGS) solution algorithm is used as an inner iteration solver for DTS. To relieve the quantity nonconservation problem of DTS, a water quantity conservation correction method is presented. Five extensive test cases including two analytical benchmark cases and experimental and actual dam-break cases have been applied to validate the proposed model and to demonstrate its performance by comparison with an explicit scheme. The presented results show that DTS can reduce the run time from 55 to 78% without or with a minimal loss of accuracy. The overall performance demonstrates that the proposed model is accurate and efficient for simulating shallow water in practical applications.

Peak discharges during large floods can often result in submerged orifice flow (also called “pressure flow”), or embankment and bridge overtopping flow, in which the embankment and abutment foundation of a bridge are subjected to severe scour and possible failure. In this study, abutment scour experiments were carried out in a wide, laboratory compound channel to investigate the characteristics of abutment scour for the three flow types of free, submerged orifice, and weir (overtopping) for an erodible but riprap-protected embankment and abutment. Detailed bed contours and three-dimensional (3D) velocities and turbulence quantities were measured with acoustic Doppler velocimeters. The results show that the contracted flow around an abutment (due to lateral or vertical flow contraction) and the local turbulent structures near the downstream face of the bridge are the main features of the flow field responsible for the maximum scour depth near the abutment. Experimental results for combined abutment and contraction scour depth are presented in terms of the theoretical long contraction scour for all three types of flow. The experimental results for maximum scour depth are compared with those of other investigators, and it is shown that the erosional strength of the embankment defines an upper and lower bound for maximum scour depth for a solid abutment versus a riprap-protected embankment and abutment.

Sediment-laden flows are a complex solid-fluid interaction process. This study presents a multimode morphodynamic model system combined with shallow water theory and a nonequilibrium assumption for sediment transport. The model system aims to simulate the morphological change caused by sediment-laden flows with various sediment transport modes. It involves three modules: a hydrodynamic module, a sediment transport module, and a morphological evolution module. The hydrodynamic model is governed by modified shallow water equations considering the interaction effects of flow and sediment. A flexible sediment transport model is presented that incorporates a weight coefficient. The model can adaptively choose an appropriate transport mode according to local, real-time flow conditions. Bedload, suspended load, and total mixed sediment load are all involved. The model is solved by a second-order Godunov-type finite-volume method that is robust and accurate. Validation is demonstrated through a series of test cases. The results indicate that the model can attain good agreement with measured data, thereby demonstrating the capabilities of the multimode morphodynamic model system in predicting sediment-laden flows and resulting morphological change.

Radio frequency identification (RFID) technology enables bidirectional, remote communication between a reader and a transponder (or tag) with a unique ID via an excitation antenna. This study provides a framework for estimating the burial depth of a transponder from a fixed location as a means of assessing scour depth or for other riverine applications. In doing so, a low frequency (LF), passive RFID system is used, which operates at a resonance frequency of 134.2 kHz and can penetrate through saturated sediments. The objective of this research is the development and validation of a semitheoretical expression that relates the decay of the received input voltage (VIN) at the reader with the transponder burial depth or detection distance, $d$, through a series of well-controlled experiments. This study examines the correspondence between $V_{IN}$ and $d$ in air, as well as in water, gravel, and sand, and assesses the role of transponder orientation (perpendicular and parallel with respect to the excitation antenna) on the received $V_{IN}$. It is found that $V_{IN}$ exhibits a universal behavior as a function of $d$ as it decays inversely with the cube of the distance ($\sim d^{-3}$) not only for air but also for water, gravel, and sand. More importantly, it is shown that the orientation angle between the excitation and the transponder miniature antennas as well as the sediment-bed composition/texture (e.g., sand, clay, gravel) surrounding the transponder can have a significant effect on the magnitude of the $V_{IN}$ and on the decay rate of the $V_{IN}$ versus $d$ curve. A change in the transponder orientation from perpendicular to parallel reduces the $V_{IN}$ by one order of magnitude and the maximum detection $d$ by 26–76% for the different media. The greatest reduction in $V_{IN}$ occurs for sand, likely due to its smaller void ratio that causes excessive defragmentation of the RF waves. These promising findings allow a relatively accurate, remote estimation of $d$ using the inexpensive LF, passive RFID technology and warrant future research and development on this topic.

This paper discusses the ability of the two-dimensional (2D) shallow water equations to model meandering flows in shallow rectangular reservoirs. Four meandering flows of various shallowness were modeled using an academic flow model that includes a depth-averaged $k\text{-}ϵ$ model accounting for the horizontal and vertical turbulent length-scales. Different roughness heights were considered for modeling the bottom friction. A proper orthogonal decomposition (POD) was applied to the simulation results to extract the behavior of the main structures responsible for the meandering flow. The same POD analysis was also performed for the reference experimental flow fields, obtained by large-scale particle image velocimetry. The first two POD modes obtained from the numerical simulations assuming a smooth bottom are in good agreement with the experimental modes in terms of energy, as well as temporal and spatial variations, whatever the shallowness. In contrast, the remaining simulated modes are not well rendered. The effect of an increased roughness height in the simulations is finally discussed. It leads to an improved reproduction of the first two modes and of the following modes, except when significant viscous effects govern in the flow.

A numerical model of a hydraulic system with a closed surge tank is developed for evaluating the thermodynamic behavior during slow transients in the air pocket. The numerical model is used to evaluate the polytrophic equation against a Modified Rational Heat Transfer (MRHT) method, and the results are compared to field observations. The original RHT method considers heat transfer to walls and water as a lumped quantity, and the method is modified in this work to evaluate these two processes separately. The field observation dataset contains pressure and water level measurements from a $\mathrm{3,050}{\mathrm{m}}^3$ closed surge tank during a pressure increase from 805 to 1543 kPa over 40 min, thus providing a unique opportunity to investigate the thermodynamic behavior during slow transients. This paper will show how the accuracy of modeling slow transient events in a closed surge tank may be improved by applying the MRHT method, which accounts for heat transfer to enclosing media.

A one-dimensional (1D) system and three-dimensional (3D) component cosimulation method based on the method of characteristic (MOC) and computational fluid dynamics (CFD) was proposed to study the interaction between valve-induced water hammer and pump during the rapid closing of the valve. In a long pipeline system, the pump was treated as a 3D CFD model using Fluent code, whereas the remaining system models (e.g., pipe, valve) were represented by 1D components using MOC. The numerical coupling and integration of both models were realized by a coupled code written using Visual Basic. The coupling theory and procedure were described in detail. MOC-CFD steady coupling in the case of the fully open state of the valve was first conducted. The corresponding results showed that the steady cosimulation can accurately determine the operating conditions. A transient cosimulation for the rapid closing procedure of the valve was conducted to study the interaction. The relative dynamic behavior obtained by MOC-CFD cosimulation was compared with that using MOC calculation alone. Transient simulation demonstrated that MOC-CFD coupling analysis was closer to real conditions because of considering the effect of fluid inertia. The effect was further explained through a comparison of internal and external characteristics between the transient and quasi-steady assumptions.

The present study focuses on riprap protection at single piers under live-bed conditions. The riprap mattress is displayed so that its top is leveled with the surrounding river bed, for ease in the construction process. Over 48 laboratory experiments have been carried out to understand the trend of the required riprap mattress width to protect single piers against edge and bedform undermining failures. The influence of bedform height on the required width is emphasized. A simple expression is given to calculate the required riprap mattress width; for low sediment transport rates the expressions given in the literature for clear-water conditions are recovered.

This paper develops an analytical approach to evaluate the mean boundary shear stress in rectangular ice-covered channels. The flow cross section was divided into an upper ice layer and a lower bed layer at the plane of zero shear stress, determined analytically from an order of the Boussinesq approximation involving the eddy viscosity concept, together with Prandtl’s mixing length theory. The conformal mapping procedure was used to obtain the functional relationships for the division curves within each flow layer. Based on the force balance in each flow subregion, an analytical model for the average bed, ice, and side-wall shear stresses was developed. The two-power law for describing vertical velocity profiles in asymmetric channels was adopted to determine the location of zero shear stress and its parameters, determined using coupled equations for the flat-bed friction factor and an empirical relationship for the bed-form friction factor. A comparison between the results of the present model and the collected data from literature shows that the proposed method does well in predicting the mean boundary shear stress in rectangular ice-covered channels.