Journal of Hydraulic Engineering

Parallel pumping systems may operate with excessive vibrations as a result of complex hydraulic excitation sources. To remove excessive vibrations, it is essential to understand the relationships between inner hydraulic excitations and outer vibration characteristics. In this investigation, experiments that included pressure and vibration measurements were performed in a parallel operating pumping system. A computational method was evaluated to determine its ability to reproduce the experimental results. The experimental results show that a large-amplitude vibration may occur under two specific conditions. One is when intrinsic single frequencies in pumps fall into the range of the broadband frequencies. The other is the beat phenomenon, which can occur if the blade passing frequencies (BPFs) from different pumps have a slight difference. The resonance condition is most likely satisfied on the floor slab of the pump house because the natural frequencies of the floor slab are relatively close to the BPF. The computational strategy is proven to be appropriate for resonance checks and risk assessment of high-level vibrations at the design stage.

An approach combining the Brunone unsteady friction model and first- and second-order Godunov-type scheme (GTS) is developed to simulate transient pipe flow. The exact solution to the Riemann problem calculates the mass and momentum fluxes while implicitly considering the Brunone unsteady friction factor. The boundary cells can either be computed by applying the Rankine–Hugoniot condition or through virtual boundary cells adapted to achieve a uniform solution for both interior and boundary cells. Predictions of the proposed model are compared both with experimental data and with method of characteristics (MOC) predictions. Results show the first-order GTS and MOC scheme have identical accuracy, but both approaches sometimes produce severe attenuation when used with small Courant numbers. The presented second-order GTS numerical model is more accurate, stable, and efficient, even for Courant numbers less than one, a particularly important attribute for unsteady-friction simulations, which inevitably create numerical dissipation in both the MOC and proposed first-order Godunov-type schemes. In fact, even with a coarse discretization, the new second-order GTS Brunone model accurately reproduces the entire experimental pressure oscillations including their physical damping in all transient flows considered here.

The backscatter strength provided by multifrequency acoustic systems is frequently used to characterize suspended elements in water courses in the entire water column on a short time scale with high temporal and spatial resolution. However, in estuarine waters with highly concentrated suspended matter, sound attenuation may hinder the ability of the acoustic method to obtain grain size profiles. This article presents a novel acoustic technique to overcome this limitation by estimating the sound attenuation caused by both fine and coarse suspended matter fractions through an iterative process that starts by introducing discrete values of suspended particle concentration and size obtained from a conventional diffractometer. Results were compared with those obtained by the traditional two frequency method to highlight the substantial improvement achieved. The main advantage of the proposed methodology is the rapid detection of changes in the concentration and size profiles, which remain hidden when measurements are made with instruments that provide discrete values and require longer times. The technique was applied to obtain the particle size and concentration distributions along a cross section of an estuary characterized by zones where a massive convective process of sedimentation occurs.

In-stream boulders significantly affect local flow hydrodynamics, sediment transport, and aquatic habitats. This study experimentally investigates the Reynolds shear stress (RSS) profiles and turbulent events around an intermediately submerged boulder under a wake interference flow regime. The frequency of turbulent events and their contribution to the RSS are quantified at two specific submergence ratios of 1.56 and 1.90 around the boulder in the near-bed and top-boulder regions. Ejection and sweep events were generally dominant in the near-bed and top-boulder regions. The dominance of turbulent events around the boulder varied as the submergence level changed. Relationships are proposed to predict the contribution of the near-bed turbulent events to the RSS around the boulder.