Journal of Hydraulic Engineering

Control valves are commonly used for the operation of water distribution systems. Modeling these devices typically requires that their operating states are known, or that a computationally expensive search is undertaken over all possible operating states. This paper presents a novel method of modeling control valves (including flow control, pressure sustaining, pressure reducing and check valves) in extended-period simulations of water distribution systems. Instead of the normal discrete control problem formulation, it is approached with the Karush-Kuhn-Tucker equations for an optimization problem with constraints. The proposed method does not prerequire the operating state (open, closed, active) of each valve to be determined, as this is done implicitly. Pipe and valve flow rates and nodal heads are determined by: (1) minimizing deviations from targets at control valves, and (2) satisfy the state equations (conservation of mass and energy) by solving a constrained least-squares problem. Sensitivity equations with respect to the control variables (valve settings) are derived from the state equations, and the control variables are updated using Levenberg-Marquardt iterations. The results of simple problems and case studies are presented to demonstrate the effectiveness of the approach.

This study presents the results from detailed experiments of the two-phase pressurized flow behavior during the rapid filling of a large-scale pipeline. The physical scale of this experiment is close to the practical situation in many industrial plants. Pressure transducers, water-level meters, thermometers, void fraction meters, and flow meters were used to measure the two-phase unsteady flow dynamics. The main focus is on the water–air interface evolution during filling and the overall behavior of the lengthening water column. It is observed that the leading liquid front does not entirely fill the pipe cross section; flow stratification and mixing occurs. Although flow regime transition is a rather complex phenomenon, certain features of the observed transition pattern are explained qualitatively and quantitatively. The water flow during the entire filling behaves as a rigid column as the open empty pipe in front of the water column provides sufficient room for the water column to occupy without invoking air compressibility effects. As a preliminary evaluation of how these large-scale experiments can feed into improving mathematical modeling of rapid pipe filling, a comparison with a typical one-dimensional rigid-column model is made.

Water column separation during rapid pipeline filling is numerically explored using a one-dimensional (1D) model that employs the method of characteristics to solve the governing equations and the well-known discrete gas cavity model (DGCM) to represent column separation. Extensive numerical experiments helped to identify the conditions under which column separation may occur during the rapid filling and to gain a physical sense of when the local rejoining pressures can be most severe. The major findings are that local $V$-shaped pipeline profiles following knee points are prone to the occurrence of water column separation and that the magnitude of the resultant overpressures markedly depends on the geometrical and hydraulic characteristics of the profile. Significantly, the propagation and reflection of the first pressure spike following column rejoining at a knee point can cause the onset of column separation in other parts of the pipe system. It is also found that short pipes must usually be steep to give rise to column separation during rapid filling, whereas longer pipes require much milder slopes; however, potential overpressures are significantly higher in short, steep pipes. Overall, the paper seeks to provide a physical interpretation of the numerical results to provide design and operational insight into this potentially important phenomenon.

Bubble characteristics in free hydraulic jumps for inflow Froude numbers ranging from 2.0 to 6.7 were measured using a single-tip optical probe, with a focus on mean and turbulent bubble velocities. It was found that the mean bubble velocity $u_b$, to a large extent, is able to reflect the water-phase flow structure in a jump. In the boundary layer of the channel bed, $u_b$ follows the $1/7$th power law in the vertical direction, and it follows a Gaussian distribution beyond that up to the water surface. Dimensionless maximum bubble velocity was found to be smaller than that for the classical wall jet up to a characteristic distance in the longitudinal direction; beyond that, however, they agree well with each other. Turbulence intensity of bubble velocity was found to first increase and then decrease with the vertical distance from the bed. The maximum value of turbulence intensity is 33% of the inflow velocity, which is comparable to that of the water-phase. Exponential relations are proposed to describe the variation of the maximum bubble velocity and maximum turbulence intensity of bubbles, in the longitudinal direction.

The purpose of this study was to explore the applicability of terrestrial laser scanning (TLS) in determining floodplain ground level and vegetation properties for hydraulic analyses. The field investigations were conducted in a two-stage channel containing five differently vegetated test reaches established to represent conditions from bare soil to grasses and $\sim 1\mathrm{m}$ tall willows. Comparing TLS to manual cross-sectional and vegetation surveys brought new insight into the reliability of TLS as a method to determine the vegetation characteristics and floodplain ground level for different seasons and variable vegetation cover. The detected ground level had a mean absolute error (MAE) of 2–14 cm in the grassy test reaches with 50 cm window size. In spring the reach-averaged MAE was 4 cm and increased to 8 cm for the late growing season. For the densely vegetated test reaches, increasing the point cloud density from $\mathrm{50,000}{\mathrm{pts}/\mathrm{m}}^2$ did not considerably improve the ground-level estimate. For deriving spatial information about physically based vegetation characteristics such as the height distribution and the volumetric blockage factor, a digital surface model of 1 cm in resolution appeared suitable.

A distorted physical model, based on Ürkmez Dam in Izmir, Turkey, was built to study sudden partial dam break flows. The distorted model had a horizontal scale of $1/150$ and a vertical scale of $1/30$, containing dam reservoir, dam body, and downstream area—from dam body to Ürkmez urban area until the sea coast. In the model, the reservoir is approximately $12{\mathrm{m}}^3$, the dam body has a width of 2.84 m and a height of 1.07 m, and the downstream area is nearly $200{\mathrm{m}}^2$. The Ürkmez Dam was chosen because Ürkmez Town is located right at its downstream area, allowing the study of dam break flows in an urban area. Furthermore, the dimensions were suitable such that it allowed the construction of a physical model (dam reservoir, dam body, and downstream area) having a horizontal scale of $1/150$ in the available space of $300{\mathrm{m}}^2$. The features creating roughness such as buildings, bridge, and roads were also reflected in the physical model. The dam break flow was investigated for sudden partial collapse, which was simulated by a trapezoidal breach on the dam body. The water depths at downstream area were measured at eight different locations by using $e+$ WATER L (level) sensors. The velocities were measured at four different locations by ultrasonic velocity profiler (UVP) transducers. The propagation of the flood was recorded by a high-defnition camera. The experimental results show that the Ürkmez area can be flooded in a matter of minutes, at depths reaching up to 3 m in residential areas in 4 min. The flood wave front can reach the residential areas in 2 min and to the sea coast in 4 min. Flow velocities can reach $70.9\mathrm{km}/\mathrm{h}$ in sparse residential areas, close to dam body. Away from the dam body in the sparse buildings part of the town, the velocities can reach $27.7\mathrm{km}/\mathrm{h}$. In dense residential areas of the town, the velocities are too low ($2.8\mathrm{km}/\mathrm{h}$) but flow depths can reach 3 m. Velocity profiles show similar behavior like unsteady and nonuniform open channel flow in nonresidential areas close to the dam body. In residential areas away from the dam body, the velocity profiles are more uniform, having lower velocity values. Vertical variations of velocities show markedly different behavior during rising and recession stages. The profiles are smooth during the rising stage in sparse residential area, yet it shows fluctuating behavior during the recession stage.