Open Channel Flow Model Research Articles

Approximate modelling of 2D curvilinear open channel flows

The common treatment of open channel flow involves the hydrostatic pressure approach. However, many flows are curvilinear and a higher-order approach is needed to deal with the non-hydrostatic pressure distribution. The current models are based on linear relationships for the variation of streamline curvature and inclination along the equipotential curves of the flow net, yet this approach is not verified with 2D results. In the present study typical 2D free surface flow nets are analysed to investigate the variations of streamline curvature and inclination. From the detailed 2D information, approximate relationships describing the curvature and inclination are proposed. It was found that streamline curvature and inclination do not vary linearly in general. The higher-order energy and momentum curvilinear equations are improved with this approach, thereby approximating the real flow net geometry. The implications of these findings on curvilinear flow modelling are discussed using several test cases.

Modeling Unsteady Open-Channel Flow for Controller Design

An approximated linear model of unsteady open-channel flow is necessary to design the water-level controller for irrigation open channels. Toward this end, this paper presents the matrix approach to derive the linear model of open-channel system in analytical form mainly according to the Saint Venant equations and the backwater profile at the steady state of open channel. The hydraulic model of the check structure at the downstream end of open channel is also incorporated into the linear model. A practical example indicates that the frequency response of the open-channel system can be accurately analyzed with the linear model. The simulation results in the time domain show that the dynamic behavior of the linear model approximates to that of the nonlinear model of the open-channel system. Finally, the limitations of the linear model are discussed.

Flow Discharge Modeling in Open Canals Using a New Fuzzy Modeling Technique (SMRGT)

AbstractThe main goal of this study was to research the answer to two important questions in flow modeling; i) how to optimally design the cross‐section of an open channel for a given flow, and ii) in the case of selecting the fuzzy method for modeling, how to construct the membership functions (MFs) and fuzzy rules (FRs) such that the system yields the best results. The first question is answered in order to minimize difficulties in excavation and related costs by using the appropriate flow velocity. To provide the best answer researchers use several methods. The second question is answered in order to minimize model error. For this aim, there are many algorithms proposed by researchers in the literature. In this paper, the fuzzy logic method was used for open canal flow modeling. Furthermore, a simple membership function and fuzzy rule generation technique (SMRGT) is introduced, and used for fuzzy modeling. Two fuzzy models, each for different cross‐sectional shape, are presented in this study as an application of SMRGT. The comparison depends on various statistics, mean absolute relative error, and contour maps showed that the fuzzy models were successful in open channel flow modeling and SMRGT is useful for MF (membership function) and FR (fuzzy rule) generation.

Fuzzy logic adaptive Kalman filtering in the control of irrigation canals

AbstractA fuzzy logic adaptive Kalman filtering methodology was developed for the automatic control of an irrigation canal system under unknown disturbances (water withdrawals) acting in the canal. Using a linearized finite difference model of open channel flow, the canal operation problem was formulated as an optimal control problem and an algorithm for gate opening in the presence of arbitrary external disturbances (changes in flow rates) was derived. Based on the linear optimal control theory, the linear quadratic regulator (LQR), assuming all the state variables (flow depths and flow rates) were available, was designed to generate control input (optimal gate opening). As it was expensive to measure all the state variables (flow rates and flow depths) in a canal system, a fuzzy logic adaptive Kalman filter and traditional Kalman filter were designed to estimate the values for the state variables that were not measured but were needed in the feedback loop. The performances of the state estimators designed using the fuzzy logic adaptive Kalman filter methodology and the traditional Kalman filtering technique were compared with the results obtained using the LQR (target loop function). The results of the present study indicated that the performance of the fuzzy logic adaptive Kalman filter was far superior to the performance of the observer design based upon the traditional Kalman filter approach. The obvious advantages of the fuzzy logic adaptive Kalman filter were the prevention of filter divergence and ease of implementation. As the fuzzy logic adaptive Kalman filter requires smaller number of state variables for the acceptable accuracy therefore, it would need less computational effort in the control of irrigation canals. Copyright © 2009 John Wiley & Sons, Ltd.

Riemann 해법을 이용한 1차원 개수로 수리해석 - 자연하도 적용

Riemann 해법을 이용한 1차원 개수로 수리해석 - 자연하도 적용

A novel application of a multi-objective evolutionary algorithm in open channel flow modelling

The Shiono and Knight method (SKM) is a simple depth-averaged flow model, based on the RANS equations which can be used to estimate the lateral distributions of depth-averaged velocity and boundary shear stress for flows in straight prismatic channels with the minimum of computational effort. However, in order to apply the SKM, detailed knowledge relating to the lateral variation of the friction factor (f), dimensionless eddy viscosity (λ) and a sink term representing the effects of secondary flow (Γ) are required. In this paper a multi-objective evolutionary algorithm is used to study the lateral variation and value of these parameters for simple trapezoidal channels over a wide range of aspect ratios through the model calibration process. Based on the available experimental data, four objectives are selected and the NSGA-II algorithm is applied to several datasets. The best answer for each set is then selected based on a proposed methodology. Rules relating f, λ and Γ to the wetted parameter ratio (Pb/Pw) for a variety of situations have been developed which provide practical guidance for the engineer on choosing the appropriate parameters in the SKM model.

Towards an ecohydrology-based restoration of the Usangu wetlands and the Great Ruaha River, Tanzania

An open channel flow model, calibrated against field data, suggests that cattle intrusion in the eastern Usangu wetlands, as well as both dry and wet weather irrigation upstream, are responsible for the seasonal drying out of the Great Ruaha River (GRR) downstream. This human-induced change has severe socio-economic implications downstream, including hindering hydroelectricity production, as well as a devastating impact on the Ruaha National Park (RNP) ecosystem that is now shifting from wet tropics to dry tropics. To ensure sustainable development, governance is urgently needed for the Usangu catchment in a way that is compatible with ecohydrology principles for the sustainable use of water resources. In order to do that, perennial flow must be restored to the GRR. For this to happen this study suggests that all the livestock must be removed from the eastern Usangu wetlands and dry weather irrigators must return at least 25% (∼4 m3 s−1) of the water to the river.

Numerical modeling of open channel flows with moving fronts using a variable boundary formulation

Modeling flows in open channels with explicit family of schemes is constrained by the choice of time step, which is limited by the Courant Friedrichs Lewy stability condition. For simulations over large spatial domains or long time durations, this limitation reflects in increased computational time. To address this limitation, in this work the affect of using varying boundary locations at both the upstream and downstream ends in the numerical code is investigated. The location of the two boundaries in this approach is an evolving function with time and not fixed as in the standard implementations. Such a formulation will aid in solving the flow equations over reduced number of nodes at every time, thus accelerating the solution to the desired state. The performance of this approach for modeling transient and stationary waves for mixed flow conditions is investigated. The results indicate that this approach can significantly accelerate the solution with out affecting its accuracy.

Turbulence modeling of compound open-channel flows with and without vegetation on the floodplain using the Reynolds stress model

A Reynolds stress model for the numerical simulation of compound open-channel flows with vegetation on the floodplain is described. The Reynolds stress model consists of various sub-models such as Speziale et al.’s model, Mellor and Herring’s model, and Rotta’s model for the pressure–strain correlation term, the turbulent diffusion term, and the dissipation term, respectively. For validation of the model, plain compound open-channel flows are simulated. The computed results were compared with measured data by [Tominaga A, Nezu I. Turbulent structure in compound open-channel flows. J Hydraul Eng, ASCE 1991;117(1):21–41] and the results show that the Reynolds stress model successfully simulates the mean flow and turbulence structure of plain compound channel flows. The model was then applied to compound open-channel flows with vegetated floodplains. Good agreement between the simulated results and data from an algebraic stress model by [Naot D, Nezu I, Nakagawa H. Hydrodynamic behavior of partly vegetated open channels. J Hydraul Eng, ASCE 1996;122(11):625–33] was found. However, it was shown that the RSM is capable of predicting the velocity dip and lateral shift in the maximum streamwise velocity, which were not observed in the data from algebraic stress modeling. Finally, a depth-averaged analysis of the streamwise momentum equation was performed to investigate the lateral momentum transfer in compound channel flows with vegetated floodplains. Compared with components by the secondary currents and Reynolds stress, the drag force due to the presence of vegetation appears to be a factor in reducing the bottom shear stress in both main channel and floodplain.

Extraordinary Flood Response of a Small Urban Watershed to Short-Duration Convective Rainfall

Abstract The 9.1 km2 Moores Run watershed in Baltimore, Maryland, experiences floods with unit discharge peaks exceeding 1 m3 s−1 km−2 12 times yr−1, on average. Few, if any, drainage basins in the continental United States have a higher frequency. A thunderstorm system on 13 June 2003 produced the record flood peak (13.2 m3 s−1 km−2) during the 6-yr stream gauging record of Moores Run. In this paper, the hydrometeorology, hydrology, and hydraulics of extreme floods in Moores Run are examined through analyses of the 13 June 2003 storm and flood, as well as other major storm and flood events during the 2000–03 time period. The 13 June 2003 flood, like most floods in Moores Run, was produced by an organized system of thunderstorms. Analyses of the 13 June 2003 storm, which are based on volume scan reflectivity observations from the Sterling, Virginia, WSR-88D radar, are used to characterize the spatial and temporal variability of flash flood producing rainfall. Hydrology of flood response in Moores Run is characterized by highly efficient concentration of runoff through the storm drain network and relatively low runoff ratios. A detailed survey of high-water marks for the 13 June 2003 flood is used, in combination with analyses based on a 2D, depth-averaged open channel flow model (TELEMAC 2D) to examine hydraulics of the 13 June 2003 flood. Hydraulic analyses are used to examine peak discharge estimates for the 13 June flood peak, propagation of flood waves in the Moores Run channel, and 2D flow features associated with channel and floodplain geometry.

Modelling the water mass exchange through navigational channels connecting adjacent coastal basins - application to the Channel of Potidea (North Aegean Sea)

Abstract. The research objective is the detection of the mechanism of the water mass exchange through a navigational channel connecting two adjacent coastal basins. The research involves the application of a mathematical model in parallel to in-situ measurements. The hydrodynamic circulation in the greater area of the NW Aegean Sea is modeled by means of a barotropic circulation model. Wind, Coriolis and Tide are the main forcings taken into account. The flow through the channel is resolved at a subgrid scale by means of a local open channel flow model. The comparison between field measurements, recorded during a limited period, and the model results supports the model verification. The study is integrated by an operational application of the model under various realistic forcings. The results help to gain a better understanding of the mechanisms regulating the water mass exchange and the consequent interaction between two adjacent connected coastal basins. From the case study of the Potidea channel it is revealed that the water mass exchange under mean wind forcing is of the same order as the one induced by the tidal forcing.

3D numerical simulation of compound open-channel flow with vegetated floodplains by reynolds stress model

This paper presents a Reynolds stress modeling of compound open-channel flows with vegetation on the floodplain. In the Reynolds stress model, we use the SSG model by Spezialeet al., for the pressure-strain correlation term, Mellor and Herring's model for the turbulent diffusion term, and Hanjalic and Launder's model for the dissipation term. In order to take into account the anisotropy of turbulence due to the free surface, the combination of Shir's model and Gibson and Launder's model is included in the pressure-strain correlation model. Model validations are carried out for the compound open-channel flows without vegetation. Then, the model is applied to the compound open-channel flows with vegetated floodplains. The mean flow and turbulence structures are simulated and the impact of vegetation on the floodplains is investigated.

Frequency Modeling of Open-Channel Flow

A good model is necessary to design automatic controllers for water distribution in an open-channel system. The frequency response of a canal governed by the Saint-Venant equations can be easily obtained in the uniform case. However, in realistic situations, open-channel systems are usually far from the uniform regime. This paper provides a new computational method to obtain a frequency domain model of the Saint-Venant equations linearized around any stationary regime (including backwater curves). The method computes the frequency response of the Saint-Venant transfer matrix, which can be used to design controllers with classical automatic control techniques. The precision and numerical efficiency of the proposed method compare favorably with classical numerical schemes (e.g., Runge–Kutta). The model is compared in nonuniform situations to the one given by a finite difference scheme applied to Saint-Venant equations (Preissmann scheme), first in the frequency domain, then in the time domain. The proposed ...

A multiple grid algorithm for one-dimensional transient open channel flows

Numerical modeling of open channel flows with shocks using explicit finite difference schemes is constrained by the choice of time step, which is limited by the CFL stability criteria. To overcome this limitation, in this work we introduce the application of a multiple grid algorithm to the field of computational hydraulics. By coupling this algorithm to a second-order accurate MacCormack scheme, we demonstrate that the solution can be accelerated to the desired transient state. The present formulation has been tested to simulate shocks arising from sudden closure of a sluice gate and for flows accompanied with a hydraulic jump. The close agreement between the obtained results and the theoretical findings indicates the reliability of the proposed algorithm.

Time of Opening of Irrigation Canal Gates

A criterion for the time of opening of irrigation canal gates is developed based on hydrodynamic principles. An analytical model of unsteady open-channel flow is used to calculate the attenuation of small-amplitude surface transients. Wave attenuation is expressed in terms of a dimensionless parameter containing both steady and unsteady components. The developed criterion is shown to be in agreement with actual field practice in the Imperial Valley, Calif.

Flood simulation in the coastal lowlands of northern Jiangsu, China

The coastal lowlands in northern Jiangsu Province, China, is characterized by low relief and low water surface gradient in streams. The flooding stages are commonly lower than the high-tide level and the tidal range is relatively small. All these factors prohibit rapid discharge of floodwater and make the flood regimes here extremely sensitive to the sea level rise. The 1991 Plum Rain was examined, when precipitation was significantly higher than normal. The one-dimensional open-channel non-conservative flow model was used to simulate the stream flow in the channel network of studied area. GIS technology was used to delineate the maximum in undated area by analyzing the DEMs.

Experimental Evaluation of 2-D Entropy Model for Open-Channel Flow

The purpose of this technical note is to investigate the applicability of the Principle of Maximum Entropy in hydrodynamics, particularly in velocity distribution in open channels, by comparing the predictions of two 2-D models with measured data. Both models use a curvilinear coordinate system, but whereas the first uses logarithmic law for velocity distribution, the second is derived by the principle of maximum entropy. The computed values are then compared to 1,832 point velocity measurements by means of laser-Doppler velocimetry in five experiments with rectangular smooth-wall flumes. The results show that the entropy model performs better than the logarithmic model not only in general terms (mean absolute error 12.8% versus 19.1%), but in practically all flow regions, especially in those near the channel bed (absolute error 23.8% versus 55.3%). Because the models disregard secondary flow, velocity predictions in the upper region of near-side walls are relatively poor.

HYDRAULIC CHARACTER OF FLOOD DRAINAGE SYSTEMS PART 1: HYDRAULIC BASIS

The wealth of professional experience gained in recent years clearly confirms hydraulic intuition that flood drainage systems (FDS) often display distinct hydraulic characters. This seems remarkable in a background where the FDS configurations are potentially unlimited owing to (a) geomorphological diversity and hydrometric complexity and (b) multi-purpose utilitarian functions and subsequent attributes (such as land use, environment, public perception). Since conflicts are inevitable in these systems, a problem-solving procedure based on hydraulic modelling and holistic appraisals has been developed. This paper argues that such a problem-solving procedure may be enriched by identification of hydraulic characters to offer a sense of direction for obtaining insights into the complexities of the FDS. Together with the case studies presented in the companion paper (Paper 11321), this paper presents a review of prevailing hydraulic characters in the background of current open channel flow modelling practices. Based on the dominance of spatially-distributed storage and dynamic effects and features such as distributive and locally-governed effects, the following hydraulic characters were identified: attenuating, storing, responsive, retarding, spatially-distributed, inertial, distributive and locally-governed systems.

Channel Routing with Flow Losses

A technique is developed and implemented within the NWS FLDWAV model to account for the effect of flow-volume losses in one-dimensional (1D) open-channel unsteady flow modeling. A functional form for the loss-induced lateral outflow is derived based on a specified total-volume distribution along the reach in which the loss occurs. The flow-loss–enhanced FLDWAV model is capable of modeling unsteady flow with any specified amount of flow loss between any two cross sections along the routing reach.

The use of a one-dimensional depth-averaged moment of momentum equation for the nonhydrostatic pressure condition

A depth-averaged model formulated in the Cartesian coordinate system for curved open-channel flows is extended to solve problems where the effects of nonhydrostatic pressure distribution and nonuniform velocity distribution are significant. The nonhydrostatic pressure condition is added to the z-direction momentum equation assuming that the pressure deviation from the hydrostatic condition at the channel bed decreases linearly to the water surface. The pressure-effect terms are modified in both the moment of momentum and momentum equations. The resulting system of nonlinear equations is solved by a finite-element method. The derived model is then applied to four sophisticated nonuniform flow experiments from the literature. A comparison of the actual experimental results with their numerical prediction results, as calculated with the model, is presented. Generally speaking, a fairly good agreement for the depth-averaged velocities as well as reasonable perturbation profiles were obtained from this comparison. Therefore, it can be said that the depth-averaged model for open-channel flow is reasonably accurate under the given conditions. Key words: open-channel flow, depth-averaged method, finite-element method, nonhydrostatic pressure, nonuniform flow.