Journal of Hydraulic Engineering

Abstract

An innovative numerical model called the Modified Two-Component Pressure Approach (MTPA) is proposed to better capture the physics of column separation in conduit systems. Based on the Two-Component Pressure Approach (TPA), the MTPA calculates both cavitating and pressurized flow using a single set of equations that governs unsteady flow in open channel flow. As opposed to shock-fitting-based models, in which a complex algorithm is needed to keep track of the interfaces separating the cavitating and liquid zones, the proposed model can capture both flow phases automatically. The first-order Godunov type finite volume method is utilized to numerically solve the equations. A customized Harten, Lax and Van Leer (HLL) Riemann solver is employed to calculate the fluxes at the computational cell boundaries and to dissipate potential post-shock oscillations generated when the cavity is collapsed and the open channel flow beneath the cavity is switched back to pressurized flow. The numerical results are shown to be in good agreement with both experimental data and the results obtained from the Discrete Gas Cavity Model (DGCM). A hypothetical test case is also presented to demonstrate the unique feature of the proposed model, which is the ability to simultaneously account for waterhammer, cavitation, and open channel flow regimes, a feature making the model even superior to the DGCM.

Practical Applications

Several numerical approaches are available to successfully calculate the induced waterhammer pressures following column separation. Existing 1D models based on these numerical approaches can help engineers quantify the impacts of column separation and design measures to protect the pipe system against this phenomenon. Nevertheless, most of the existing models used in the industry exclusive work with pipe systems that remain fully pressurized during transient flow. However, column separation may occur in pipe systems carrying concurrent open channel and pressurized flows. Examples of such systems and operating conditions are sewer conveyance and pipe system collection, intermittent water distribution systems, pump power failure in self-draining pumped pipelines, and pipeline filling and draining. To fill part of this gap, this paper presents a numerical open channel-based 1D model that can treat concurrent transient open channel, pressurized flow, and column separation. The model is validated using experimental data, numerical results from other models, and a hypothetical example. The results reveal that the model is accurate enough to be used in practical applications. The model can also calculate the shape and spread of vapor cavities across the pipe system, a feature that makes the proposed model superior to counterpart models.

Quantification of sediment transport rates is necessary for river management but remains difficult due to large volumes of sediment in motion, spatiotemporal heterogeneity in discharge, depth, and morphology, the need for expensive equipment, and personnel costs. During efforts to quantify sediment bed load in the Mississippi (MS) River near Vicksburg, MS, US, the US Army Corps of Engineers-Engineer Research and Development Center (USACE-ERDC) collected acoustic multibeam topographic data during the 2011 MS River flood. Bed topography data were analyzed to quantify the effect of changing flow rates on bed topography. Bedforms were much higher and longer in the center section than near either bank, and superimposed bedforms were found during the falling limb of the 2011 flood hydrograph. Bedform amplitudes and lengths were positively correlated with flow depths, but amplitudes were typically higher and lengths shorter than predicted in previous research. Topography data from three lower flows are included to illustrate the morphometric variation induced by a wide range of discharges.

This work presents the design of controls for a pressure-reducing valve considering stability and robustness issues and preserving the classical linear proportional-integral-derivative (PID) structure included in, nowadays, industrial controllers. Due to only the outlet pressure being measured for control purposes, other variables, flow and inlet pressure, are included in the uncertainty of the system. The theory of Lyapunov allows for validating the linear PID proposal even considering the nonlinear relation between inlet pressure and flow with the behavior of pressure-reducing valves. A brief robustness analysis demonstrates how the proposal can cope with the uncertainties of the system. Finally, experimental and simulated results indicate the good performance of the control.

The mean velocity distribution of open channel flows with fully submerged two-layered vegetation can be divided into three zones. Zone 1 represents the lower region of short vegetation, where the flow has high drag because of highly dense vegetation, Zone 2 represents the middle flow zone from the edge of the short vegetation to the top of the tall one, and Zone 3 denotes the upper region with the free surface flow. A new analytical model is developed based on the momentum equation of vegetated flow, where turbulent eddy viscosity is approximated as a linear relationship with local velocity. The analytical model was evaluated using seven experimental data sets under different flow conditions with distinctive densities and formations of vegetation. Three sets of data available from other researchers were also used to check the applicability of the proposed model. An agreement between the analytical model and experimental data indicates the validity and robustness of the model.

This study evaluates the laser in situ scattering and transmissometry (LISST) instrument LISST-SL2, a laser diffraction instrument for suspended sediment sampling in rivers, with concurrent physical measurements of suspended sediment concentration (SSC) and particle size distribution (PSD) as well as velocity measurements by an acoustic Doppler current profiler (ADCP). We collected 136 LISST-SL2 samples along with 61 physical samples for SSC measurement, of which 24 physical samples included PSD measurement during 2018–2020 from 11 sites in Washington state and Virginia. An effective density is required to convert the measured volumetric SSC by the LISST-SL2 into a reported mass SSC, and by default the LISST-SL2 assumes a value of $2.65\mathrm{g}/\mathrm{mL}$. From our data set, we computed effective densities (mass SSC/volumetric SSC) that ranged from 0.5 to $5.4\mathrm{g}/\mathrm{mL}$, with a best-fit value of $2.05\mathrm{g}/\mathrm{mL}$. Additionally, the LISST-SL2 was not able to measure the finest sediment sizes in suspension, which affects the resulting PSD. Therefore, we propose some adjustments of the LISST-SL2 data with a supporting physical sample to account for these effective density and PSD issues. When doing so, we were able to reduce the root-mean square relative error (RMSRE) to 18% from 117% for SSC, and to 26% from 78% for PSD. LISST-SL2 velocities were generally higher than ADCP velocities with a 21% RMSRE. Our results and guidance will allow for more accurate sampling by the LISST-SL2, which has potential for studying spatial and temporal variation of suspended sediment characteristics in rivers.

The objective of this study was to improve the design criteria of rock-ramp fish passes by better describing the physics of frictional phenomena such as the impact of the deformation of the free surface or the bed shear stress due to the presence of obstacles. Experiments on square-shaped obstacles were performed in a scale model. A new analysis of the old and current measurements allowed us to specify the calibration coefficient of the drag and bottom friction forces. For a given water depth, the flow rate accuracy was about 10% by using only three parameters per shape. Thus, a more precise comparison of the flows according to the shape of the obstacles could be carried out. This plays an important role for the specification of projects of equipment of river dams. The theoretical advantages of each shape were highlighted, such as the significant reduction of the maximum velocity for the configuration with square obstacles.