Journal of Hydraulic Engineering

Abstract

Accurate prediction of pressure caused by plunging jets of high spillways is essential for assessing the bed rock scour initiation and expansion. The hydrodynamic pressure characteristics at plunge pools’ bottom and inside rock joints are assessed based on the experimental results and the analysis of extensive available library experimental data. A new empirical model of mean dynamic pressure coefficient, the $C_P$, and pressure fluctuation, the $C_P^{\prime }$, for core and developed jets at stagnation point are presented. The effects of jet break-up ratio ($L/L_b$), the jet’s fall height $L$ to the jet break-up length $L_b$ ratio, on $C_P$ and $C_P^{\prime }$ at the pool bottom and inside the rock joints are assessed. The maximum $C_P$ at pool bottom and inside rock joint occurs in $L/L_b\le 1.2$ range while the maximum $C_P^{\prime }$ occurs within $0.85<L/L_b<1.2$ range at pool bottom. Transient dynamic pressures inside the rock joint generates a stress field inside the rock joint, which highly depends on the joint length, and it is characterized by the stress intensity factor. The effects of joint length on pressure filed and the stress intensity factor are assessed to determine the fluid resistance due to joint elongation and to formulate the stress intensity factor. A new data set of dynamic pressure measurements inside rock joints at different lengths is presented. Experimental results indicate that the stress intensity factor inside the rock joint reaches its maximum values when the joint length reaches 4 times the initial formed rock joint length in rock mass.

Practical Applications

Determining the pressure characteristics is essential when assessing the rock joint stability and the scour geometry at plunge pools. In this study, the hydrodynamic pressure characteristics at the bottom of plunge pools and inside rock joints are investigated, and a new empirical model of mean dynamic pressure coefficient, $C_P$, and pressure fluctuation, $C_P^{\prime }$, for the core and developed jets is presented. The effects of joint length and the jet break-up ratio ($L/L_b$) on the pressure field and the stress intensity factor are assessed. The stress intensity factor inside the rock joint is modified to accurately assess the hydraulic fracturing of the rock joint and scour geometry development.

A brand-new type of multislot and pool–weir combined fishway (MSWF) is firstly proposed in this paper. In fact, six MSWF configurations (MSWF-1 to MSWF-6) are designed and compared, and numerical results demonstrate that MSWF-5 (i.e., weir height $h=0.6\mathrm{m}$ and the vertical-slot width $b_s=0.62\mathrm{m}$) has the best performance at a flow discharge (i.e., $Q$) of $600\mathrm{L}/\mathrm{s}$ in terms of flow topology, velocity distribution, and turbulent kinetic energy among all the eight fishways considered. The introduction of the weir in MSWF not only contributes to improving the flow regime, but also offers an extra fish-passage channel for fishes. Moreover, the general superiority of MSWF-5 over the vertical-slot fishway (VSF) is exhibited by providing the numerical results at $Q=600$, 800, 1,000, and $\mathrm{1,200}\mathrm{L}/\mathrm{s}$. Additionally, fish-passage tests are carried out in a physical model (including the MSWF-5 part and the VSF part) with the aid of juvenile grass carps. As expected, the recommended MSWF-5 does outperform VSF with respect to passage success rate, mean fish transit time, entry efficiency, and mean entrance time, matching its excellent hydraulic properties.

This study examines the instability of sand waves (dunes and antidunes) from both linear and weakly nonlinear perspectives. The linear and weakly nonlinear analyses use the standard linearization and the center manifold-projection technique, respectively. The mathematical framework includes the depth-averaged continuity and momentum equations, the advection–diffusion equation for suspended sediment concentration, and Exner’s equation for bed evolution. The streamline curvature is treated using the Boussinesq approximation. The model considers the departure of the pressure distribution from the hydrostatic law. Both modes of sediment transport, as bedload and as suspended load, are taken into consideration. The perturbations characterize the maximum growth rate for a selected wave number, called the resonant wave number, which is the most favorable wave number for the formation of sand waves. As the flow Froude number and the relative roughness number increase, the dimensionless resonant wave number decreases. The dimensionless amplitude of sand waves increases as the flow Froude number and the relative roughness number increase to achieve a maximum, and subsequently it decreases. The predicted wave number and amplitude of sand waves satisfactorily match the available experimental data.

Bubble screens are used at sea locks to mitigate salt intrusion into inland water systems. In this paper the effectiveness of a bubble screen in delaying the mixing of salt and freshwater via lock exchange was studied. Laboratory-scale experiments investigating the flow field and mixing caused by a bubble screen are presented. The tests include both the homogeneous situation of freshwater on both sides of the screen and the inhomogeneous situation where there is an initial density difference across the screen, which leads to a density current after the lock gate is removed or opened. Optical measurement techniques were applied, giving spatially detailed flow velocities and densities. The parameters varied between tests are the airflow discharge and the bubble size. The results show that the bubble size in the screen had a significant effect with a screen with bubbles of 1–2 mm being more effective at generating a surface flow in the homogeneous case but less effective at keeping the fresh and salt sides separated in the inhomogeneous case, when compared with a screen of 4–6 mm bubbles. The point of maximum effectiveness for separating salt and fresh sides was also shown to be dependent on bubble size.

During the discharge of floodwater from a hydropower station, a significant number of water droplets in motion are created in the downstream space. These droplets vary in size and velocity, causing challenges in determining the particle size and velocity distribution of the flood discharge atomized droplets. Currently, the particle-size distribution and velocity distribution of atomized droplets are considered to be independent, and the gamma function is used to describe the particle-size distribution and velocity distribution of droplets separately. However, a joint distribution of atomized droplet size and velocity is lacking. This paper uses the basic theory of maximum entropy to study the combined distribution of droplet size and velocity in the atomized flow caused by jet overflow. The present model was in a good agreement with experimental data, providing a method for the theoretical study of droplet size and velocity distribution in flood discharge atomization.

Abstract

Sudden displacement of large volumes of liquid–granular mixtures in nature (dam-breaks, landslides, floods, etc.) are often reported to be deadly and destructive. The flow behavior of those mixtures is complex and depends on a large variety of parameters, e.g., size distribution of the solid phase, viscosity of the fluid, predisplacement packing conditions, ratio of solid to liquid phase, and geometry of the domain. Because of the multitude of parameters and the large displacements involved, the numerical modeling of these phenomena is complex. A two-phase double-point material point method formulation in Anura3D, a particle-based continuum numerical method, was tested against two experimental cases. Model simulations showed that simple constitutive models such as Mohr-Coulomb (MC) with perfect plasticity can be sufficient to accurately model bulk granular flow behavior. However, with slightly different initial conditions, these flows can exhibit more complex features such as progressive block failures, which necessitates a more advanced solid constitutive model such as MC strain softening. Further, other simulation parameters like wall friction boundary conditions and fluidization threshold are also crucial in these types of numerical simulations. The ability of such models to capture complex failure modes is critical to assess dam safety.

Practical Applications

The sudden release of a mixture of granular materials and water, for example, after failure of a tailings dam, can have devastating consequences on downstream infrastructure and communities. We investigated how such flows can be accurately predicted using the computer model Anura3D, which uses a special technique, where material points separately represent the water and the grains because those points can efficiently represent the large deformations that these types of granular flows exhibit. We found that, at higher water content, a simple model of the mechanical properties of the granular and water mixture suffices. However, at lower water content, the more complex behavior of the granular flow requires a specific model that takes into account the local history of deformations. This study is relevant to the analyses of dam safety, post-wild fire hillslope debris flows, and landslides.

A novel coupled approach to modeling various stages of waves generated by different types of landslides (e.g., subaerial to submerged) through divergence-free incompressible smoothed particle hydrodynamics (ISPH) was developed in this study. In this approach, coexisting fluid and granular modules interact with each other through an interaction force pair, which necessitates the accurate transfer of information related to the fluid stress tensor and velocity vectors of the complementary module. A support domain centering each particle of both phases along with specific corrective treatments caters to the averaging of information from the complementary module. The model was tested against three scenarios (with limiting criteria such as suspended load transport and hindrance to porosity conceptualization) ranging from subaerial to submerged granular slides and resulting water surface fluctuations.

Abstract

In recent decades, the Inner Mongolia Reach of the Yellow River (IMRYR) in China has experienced new characteristics in terms of ice conditions due to human activities and climate change. It is crucial to develop a comprehensive river ice model for this reach that reflects the changing physical characteristics of ice events. However, simulating river ice process in the IMRYR using numerical model is challenging due to the scarcity of observed data on river geometry, hydrology, meteorology, and river ice conditions. With latest field measurements, this study examined the spatiotemporal variations of ice conditions in the IMRYR. In the development of river ice model, this study tackled various challenges such as incomplete river geometry, insufficient tributary flow information, and the identification of ice bridge locations. By improving the one-dimensional river ice model, the study simulated the ice development process during the 2012–2013 ice flood season in the IMRYR. A comparative analysis was conducted between the simulated and observed water temperature, ice cover thickness, ice front locations, and flows, showing a good agreement. This study analyzed and determined the ice hydrodynamics, thermodynamics, and relevant river parameters, providing a deeper understanding of the intricate interactions and dynamics associated with the formation and behavior of river ice in the Yellow River. This research can provide scientific basis and methodological support for ice disaster prevention and control in the Yellow River, as well as insights and technical means for simulating comprehensive river ice processes in natural rivers and artificial channels.

Practical Applications

The Yellow River is one of the rivers in China that experiences frequent ice-related disasters, with the main occurrences happening in the Inner Mongolia Reach (IMR). In recent decades, the IMR has faced new challenges in ice evolution, including changing climatic conditions, severe channel siltation, and expanded ice-related channel storage, making the understanding of ice conditions more complex. The China Institute of Water Resources and Hydropower Research, commissioned by the Hydrographic Bureau of the Yellow River Conservancy Commission, conducted numerical simulations of the ice processes in the IMR. Based on the new characteristics of ice conditions in the Yellow River, a mathematical model was proposed to simulate the development of winter ice conditions in data-scarce regions. The one-dimensional river ice process model was enhanced to enable dynamic simulations of the ice processes in the IMR, and accurately capturing the evolution of winter water temperature, ice cover thickness, ice front progression, flow rate, and water level. This study provides valuable scientific basis for ice forecasting, ice control operations, and disaster prevention in the Yellow River. The improved model has been adopted by the Hydrographic Bureau of the Yellow River Conservancy Commission, and additional categories and sampling frequencies of hydrological and meteorological data have been tailored for the Inner Mongolia Reach considering specific data requirements for the model.