Journal of Hydraulic Engineering

This paper presents the application of the adaptive response surface approach to the reliability analysis of water distribution networks. In this case, the response of the system is approximated by an analytical solution (response surface) and then the reliability problem is solved using first-order reliability methods. This approach is then extended to the analysis of networks that may have to work under several different configurations. This can be a consequence of repairing operations or some other unexpected event, for example. Finally, two numerical examples are presented to discuss the main aspects of the proposed approach.

Gravity currents from instantaneous sources down a slope were modeled with classic thermal theory, which has formed the basis for many subsequent studies. Considering entrainment of ambient fluid and conservation of total buoyancy, thermal theory predicted the height, length, and velocity of the gravity current head. In this study, the problem with direct numerical simulations was re-investigated, and the results compared with thermal theory. The predictions based on thermal theory are shown to be appropriate only for the acceleration phase, not for the entire gravity current motion. In particular, for the current head forms on a 10° slope produced from an instantaneous buoyancy source, the contained buoyancy in the head is approximately 58% of the total buoyancy at most and is not conserved during the motion as assumed in thermal theory. In the deceleration phase, the height and aspect ratio of the head and the buoyancy contained within it may all decrease with downslope distance. Thermal theory relies on the increase in the mass of the current head through entrainment as the major mechanism for deceleration and, therefore, tends to underpredict the front velocity in the deceleration phase.

Flood propagation over urban areas can cause an interaction between the free-surface flow and large underground pipe networks used for sewage and storm drainage, causing outflows and inflows at the bed. The waves resulting from these bed discharges may collide with each other and the surface waves, increasing water depths, velocities and accelerations, and their interaction thus affects flood risk. The authors previously introduced a one-dimensional (1D) shallow-water model for simulating free-surface interaction with the flows issuing vertically through finite gaps, referred to as efflux. This model used a modified wave propagation algorithm and was validated by comparing results with the full Navier-Stokes equation solver (STAR-CD) based on the volume-of-fluid method, which models free-surface motion quite generally, although at considerable computational expense. The present paper extends the shallow-water scheme to two dimensions, including source terms for pipe outflow/inflow (efflux/influx) and bed friction and bathymetry gradients. A general pipe network solver for full flow is coupled with the free-surface flow. The methodology is first tested with idealized cases. Two-dimensional (2D) dam-break flow over a complex bed profile without efflux/influx at the bed is first modeled. Next, efflux discharge is modeled in isolation over a dry bed and then with dam-break interaction, comparing with 3D STAR-CD results. Results for these idealized cases are in good agreement. Finally dam-break interaction with a pipe network of 25 nodes demonstrates the complex bore interaction.

This paper presents equations developed by using genetic algorithms (GA) to estimate decay coefficients for instantaneous acceleration–based (IAB) unsteady friction models in order to predict energy dissipation following sudden valve closures in simple elastic pipe systems. The GA searched for the optimum combination of IAB coefficients to reproduce pressure history at the valve location using the normalized root mean-squared error (NRMSE) as the minimization criteria. The measured results comprise nine downstream and five upstream sudden-valve-closure experiments performed in five laboratories around the globe. Three IAB unsteady models are compared: a one-coefficient model, a two-coefficient model discretizing the unsteady friction term using finite-difference approximations, and a new two-coefficient model that includes the unsteady friction term in the method of characteristics. The two-coefficient models produced a better match with the experimental data than the one-coefficient models. A new equation for the estimation of the decay coefficient of one-equation models, as well as average values for the decay coefficients for the two-coefficient models, is presented.

This paper shows an advanced application of the smoothed particle hydrodynamics (SPH) method to the numerical modeling of noncohesive sediment flushing aiming at the setup of a reliable engineering tool for the prediction of the coupled water-sediment dynamics at the bottom of an artificial reservoir. Both liquid and granular materials are modeled as weakly compressible viscous fluids, whose motion results from the numerical solution of the continuity and momentum equations discretized according to standard SPH formulation. The effect of two alternative erosion criteria on the description of the failure mechanism of bottom sediments is analyzed. These criteria are based, respectively, on Mohr-Coulomb yielding criterion and Shields theory. A sensitivity analysis is performed in order to assess, for both criteria, the influence of the model parameters on the simulation of the erosion process; the method is eventually validated by comparing numerical results with the experimental data obtained in a two-dimensional (2D) laboratory test.

A total variation diminishing Runge-Kutta discontinuous Galerkin finite element method for the solution of one-dimensional (1D) shallow water flow equations for natural channels is presented. The hydrostatic pressure force and the wall pressure force terms are combined to simplify the calculations and prevent unphysical flow attributable to improper treatment of the bottom slope term. The treatment of the combined term that appropriately accounts for the momentum flux is given. HLL and Roe Riemann solvers are assessed for the mass and momentum flux terms. Numerical tests are conducted using prismatic rectangular and nonrectangular channels as well as non prismatic channels and natural channel for dam break, supercritical flow, transcritical flow, and dry-bed problems. Slope limiters based on flow cross section area, water surface, and water depth are evaluated. The tests show that HLL and Roe solvers provide similar accuracy. However, the slope limiter based on flow area provides more accurate solutions for tests in nonrectangular and natural channels.

In this study, six different types of flow-altering countermeasures against pier scour were evaluated experimentally. The selected countermeasures were submerged vanes, bed sill, transverse sacrificial piles, collar, threading, and pier slot. Laboratory tests were performed in clear-water conditions with flow intensity slightly below the threshold of sediment motion. Tests were designed on the basis of the best configurations recommended in previous studies by different authors to obtain the maximum efficiency in terms of scour depth reduction. Results showed that some countermeasures, which were recommended as highly efficient in the literature, do not perform well under other test conditions; in particular, literature tests carried out with low flow intensity or short duration or in narrow-channel conditions are criticized. The efficiency of bed sill, submerged vanes, and threading was found to be less than 20%, whereas collar, pier slot, and transverse sacrificial piles reduced the maximum scour depth of approximately 35% or less. Finally, design of a pier slot is discussed, and an optimum configuration is proposed.