Journal of Hydraulic Engineering

The transient flow phenomenon in a pipeline accounts for the flow variations with time and space. The transient energy analysis (TEA) overlooks the process as it sums the energy of the entire pipe domain and reports it at each moment. The current research takes advantage of this approach to investigate different influential factors in water pipelines, including steady friction, unsteady friction, and pipe wall viscoelasticity, to figure out the energy conversion and dissipation during a transient flow process. To this end, energy expressions are derived and compared for both elastic and viscoelastic pipeline systems. Two different viscoelastic materials—oriented polyvinyl chloride (PVC-O) and high-density polyethylene (HDPE)—are applied in the analysis to compare the proportions of the energy dissipation by different influential factors. The results reveal that at small transient perturbations, the influence of the steady friction is dominant in the energy dissipation, and the impact of viscoelasticity grows with the excitation intensity and valve’s oscillation frequency. Besides, spatial variations of energy dissipation (per unit of length) along the pipeline have been investigated in single and branched systems, demonstrating significant deviations by distance from the excitation source.

The detached eddy simulation model and volume of fluid (VOF) method were combined to simulate the pressure fluctuations in the downstream region of an aerator in a spillway tunnel, which often lead to hydraulic structure failure. The predictions were compared to experimental data to validate the model. Satisfactory agreement was obtained between the simulation and experimental results. The root mean square and fluctuation coefficient exhibited single-peak distribution, with the maximum values attained in the impact zone. The ranges of fluctuations of the pressure coefficient in the impact and stable zones were 3.31%–7.08% and 0.96%–3.15%, respectively. The probability density distribution obeyed a normal distribution law and presented a positive skew. The pressure fluctuation characteristics were primarily controlled by large-scale coherent eddies. The flow in the downstream region was a typical low-frequency fluctuation flow. The turbulent kinetic energy spectrum of the flow was congruent with Kolmogorov’s –5/3 law. Our method is convenient for engineers to analyze pressure fluctuation characteristics and propose the shape of a hydraulic structure with superior hydraulic characteristics.

The Serre–Green–Naghdi (SGN) theory is used widely in maritime hydraulics for the computation of water waves from shallow to intermediate water depths. However, it has been largely ignored in problems of open-channel hydraulics. This research applies the SGN theory to compute shallow flows over curved beds, focusing on round-crested control structures. A systematic and complete analysis is presented, including the solution of both the unsteady and steady versions of the SGN theory. A new steady SGN solver is presented, allowing for automatic computation of the rating curves of the structures, thereby avoiding tedious trial and error iterations. The SGN theory is applied to a wide portfolio of obstacle shapes used in practice, resulting in agreement with experimental evidence within the shallowness limit determined. A higher-order approach is discussed, pointing to a possible path to increase the validity of SGN-type solvers in high overflow problems.

A multilayer model is proposed to calculate time-dependent sediment velocity and concentration profiles with the resulting sediment transport. The model is developed here for the wave boundary layer. Measurable quantities are considered, namely, the values of transport during the wave crest and the wave trough, as well as total and net sediment transport values (averaged over the wave period) resulting from the summation and subtraction of their absolute values, respectively. The calculated value of the maximum stress at the bed during the wave period is verified by direct stress measurements. The model is tested for mixed sediments with different grain size distributions including semiuniform and poorly sorted grains. Transport calculations are carried out for acceleration-skewed oscillatory flows and waves described by Stokes’ first and second approximations. Comparison with the available small- and full-scale data from flumes and oscillating tunnels yields agreement typically within plus/minus a factor of two of the measurements.

Several methods have been developed to estimate critical shear stress ${\tau }_c$ and the erodibility coefficient $k_d$ for cohesive stream banks/beds. This research compares estimates of these parameters between an in situ minijet device and a laboratory pressurized conduit flume. Estimates for ${\tau }_c$ between the two devices for the same soils were in general agreement compared with $k_d$, especially for shear magnitudes greater than 5 Pa and consolidated soil with moisture contents greater than 20%. However, $k_d$ erodibility estimates between devices were significantly different. Operation of the minijet device applied a unique multiple-pressure setting (MPS) procedure that accounts for the change in soil properties with depth from the bank face. Both the minijet MPS approach and a conduit flume appeared to reduce the effect of surface subaerial process on erodibility parameter measurements, where ${\tau }_c$ and $k_d$ estimates were more similar compared with single-pressure test estimates using the Blaisdell, iterative solution, and scour depth solution computational procedures. Findings suggest ${\tau }_c$ and $k_d$ estimates are dependent on the device hydraulics, computational method, and soil properties.

The feasibility of pier nose extensions as an environmentally acceptable alternative to reduce local pier scour for a nontypical pier geometry was investigated using a 1:30 Froude-scaled movable-bed model. The movable-bed characteristics were investigated using Shields scaling to the $D_{90}$ grain. The study was conducted for a site-specific location, the Burlington Northern Santa Fe (BNSF) Railway crossing on the Santa Ana River near Corona, California. Local scour behavior was evaluated in the model for the estimated worst-case hydrodynamic conditions with and without the pier nose extensions. When aligned with the approach flow, the pier extensions reduced the local pier scour. They produce a reduction of 53% compared with the existing pier configuration without extensions. Historically, pier nose extensions have been used for the passage of debris and to increase the conveyance in lined channels. This study extends the possible engineering applicability of pier nose extensions as a countermeasure for local scour.