Selahattin Kocaman

Dam-Break Flow in the Presence of Obstacle: Experiment and CFD Simulation

Abstract The aim of this paper is to present an experimental and numerical investigation of dam-break flow over initially dry bed with a bottom obstacle. This test case highlights not only the bottom slope effects but also those of abrupt change in channel topography. Dam-break flow was applied in a smooth prismatic channel of rectangular cross-section over a trapezoidal bottom sill on the downstream bed. The present study scrutinized the formation and propagation of negative bore behind the sill. The flow was numerically simulated by the VOF-based commercially available CFD program, Flow-3D, solving the Reynolds Averaged Navier Stokes equations with the k-ε turbulence model (RANS) and the Shallow Water Equations (SWE). To validate CFD models an experiment was carried out. Using an advanced measuring technique, digital image processing, the flow was recorded simply through the glass walls of channel; thus, continuous free surface profiles were acquired synchronously with three cameras along the channel. The adopted measuring technique is non-intrusive and yields accurate and valuable results without flow disturbances. Comparison of the computed results with experimental data shows that RANS model reproduces the flow under investigation with reasonable accuracy while simple SWE model indicates some discrepancies particularly in predicting the negative wave propagation.

Dam-break flows during initial stage using SWE and RANS approaches

Experimental and numerical results relating to dam-break flows are compared. Dam-break waves were generated by the quasi-instantaneous removal of a plate in a smooth prismatic channel of rectangular cross-section over horizontal dry and wet beds. The laboratory experiments were conducted to determine the initial stages of the free surface profiles using digital image processing. The flow characteristics were detected by applying an adequate, simple and economical measuring technique. The experimental results were compared with the results of a commercially available CFD program, solving the Reynolds-averaged Navier–Stokes (RANS) equations with the k–ϵ turbulence model involving the shallow-water equations. Measured and computed free surface profiles during the initial dam-break stages indicate that although both models predict the dam-break flow with a reasonable accuracy, the agreement using the RANS model is better.

Artificial neural network approaches for prediction of backwater through arched bridge constrictions

This paper presents the findings of laboratory model testing of arched bridge constrictions in a rectangular open channel flume whose bed slope was fixed at zero. Four different types of arched bridge models, namely single opening semi-circular arch (SOSC), multiple opening semi-circular arch (MOSC), single opening elliptic arch (SOE), and multiple opening elliptic arch (MOE), were used in the testing program. The normal crossing (@f=0), and five different skew angles (@f=10^o, 20^o, 30^o, 40^o, and 50^o) were tested for each type of arched bridge model. The main aim of this study is to develop a suitable model for estimating backwater through arched bridge constrictions with normal and skewed crossings. Therefore, different artificial neural network approaches, namely multi-layer perceptron (MLP), radial basis neural network (RBNN), generalized regression neural network (GRNN), and multi-linear and multi-nonlinear regression models, MLR and MNLR, respectively were used. Results of these experimental studies were compared with those obtained by the MLP, RBNN, GRNN, MLR, and MNLR approaches. The MLP produced more accurate predictions than those of the others.

3D model for prediction of flow profiles around bridges

Computational fluid dynamics models have become well established as tools for simulating free surface flow over a wide range of structures. This study is an assessment and comparison of the performance of a commercially available three-dimensional numerical software, which solves the Reynolds-averaged Navier–Stokes equations, to predict the free surface profiles from up- to downstream of four different bridge types with and without piers in a compound channel. The model results were compared with the available experimental data. Comparisons indicate that the model provides a reasonably good description of free surface profiles under both gradually and rapidly varied flow conditions in the bridge vicinity, respectively.

3D Numerical Modelling of Flow Around Skewed Bridge Crossing

Abstract This study investigates the performance of commercially available three-Dimensional (3D) numerical software, FLOW-3D, on the prediction of the water surface profiles using a series of experimental data obtained in a two stage channel with skewed bridge crossing. The experiments were carried out for four different types of bridge models with two different skew angles of ø = 30° and ø = 45°. FLOW-3D, which solves the Reynolds-averaged Navier - Stokes equations, was applied to experimental data for the prediction of water surface profiles along the compound channel from upstream to downstream. The comparison of free surface profiles of 3D model showed good agreement with the experimental data. Notably, the measured and computed afflux values are found to be almost identical.

Prediction of Backwater Profiles due to Bridges in a Compound Channel Using CFD

With the advancements in computing power, computational fluid dynamics (CFD) analysis has emerged as a powerful hydraulics design tool. This study aims to assess the performance of CFD via commercially available software (FLOW-3D) in the prediction of backwater surface profiles for three different types of bridges with or without piers in a compound channel. A standard two-equation turbulence model (k-ε) was used to capture turbulent eddy motion. The numerical model results were compared with the available experimental data and the comparisons indicate that the CFD model provides reasonably good description of backwater surface profiles upstream of the bridges. Notably, the computed and measured afflux values are found to be almost identical.

ANN approaches for the prediction of bridge backwater using both field and experimental data

This paper presents the findings of laboratory model testing of arched bridge constrictions in a rectangular open-channel flume whose bed slope was fixed at zero. Four different types of arched bridge models, namely single-opening semi-circular arch, multiple-opening semi-circular arch, single-opening elliptic arch, and multiple-opening elliptic arch, were used in the testing program. The normal crossing (φ  =  0) and five different skew angles (φ  =  10°, 20°, 30°, 40°, and 50°) were tested for each type of arched bridge model. Recently, a major coverage of backwater field data obtained from the medieval arched bridge constrictions was published by the Hydraulic Research Wallingford in the UK (Brown, P.M., 1985. Hydraulics of bridge waterways: Interium report. Wallingford, UK: Hydraulic Research Wallingford, Report SR 60; Brown, P.M., 1987. Afflux at arch bridges: second interium report. Wallingford, UK: Hydraulic Research Wallingford, Report SR 115; Brown, P.M., 1988. Afflux at arch bridges. Wallingford, UK: Hydraulic Research Wallingford, Report SR 182). These data were also used in the analysis. The main aim of this study is to develop a suitable model for estimating backwater through arched bridge constrictions with normal and skewed crossings using both experimental and field data. Therefore, different artificial intelligence approaches, namely multi-layer perceptron (MLP), radial basis neural network (RBNN), generalized regression neural network (GRNN), and multi-linear and multi-nonlinear regression models, MLR and MNLR, respectively were used. The comparison between these developed models and one of the most commonly used traditional methods (Biery, P.F. and Delleur, J.W., 1962. Hydraulics of single span arch bridge constrictions. ASCE Journal of the Hydraulics Division, 88, 75–108) has been made. The test results showed that the MLP model gave highly accurate results than those of Biery and Delleur, MLR, MNLR, and GRNN and gave similar results with the RBNN model when applied to both field and experimental data.

EXPERIMENTAL AND NUMERICAL COMPARISION OF 3D DAM-BREAK FLOOD WAVE PROPAGATION

Dam-break flood wave is an irregular, time-dependent and rapidly varying free surface open channel flow and therefore, is one of the complex and difficult problems. The research for solving this problem is mainly directed at experimental and numerical studies due to the difficulties in collecting field data. Despite that, the experimental and numerical studies on 3-dimensional dam-break problem are limited in the literature. In this study, the propagation of expanding dam-break flood wave in the downstream direction is investigated using a vertical plate placed in front of a reservoir built in the laboratory. The propagation of the wave front was observed using high speed camera and obtained results were compared with FLOW-3D numerical model which uses 3D RANS equations. The results were in quite good agreement.