Search

A three-dimensional buoyancy-extended version of k--[epsilon] turbulence model was developed for simulating the turbulent flow and heat transport in a curved open channel. The density-induced buoyant force was included in the model, and the influence of temperature stratification on flow field was considered. The flow and temperature fields were simulated simultaneously. The model was validated by comparison with laboratory measurements, and the simulated fields were generally in good agreement with experimental data. A comparison of velocity fields in thermal and isothermal flow in curved open channel is presented and the effects of channel curvature and buoyant force on the velocity fields are also discussed. DOI: 10.1061/(ASCE)0733-9429(2009)135:7(554) CE Database subject headings: Temperature distribution; Open channel flow; Turbulence; Simulation; Heat transfer.

To improve knowledge of the flow and scour processes associated with spur dikes, three-dimensional flow velocities were measured at 2,592 points using an acoustic Doppler velocimeter over a fixed flat bed with a trapezoidal shaped submerged spur dike in a laboratory flume. General velocity distribution and detailed near field flow structures were revealed by the measurements and numerical simulations performed using a free surface turbulent flow model with a k-[epsilon] closure scheme. The three- dimensional flow separation characterized in this study was found to yield forces on the bed that were significantly different from nonsubmerged vertical obstructions that have been measured in other studies. Values of bed shear stress derived from both measured and simulated values were similar but indicated that local scour would be initiated in one rather than in the two locations of initial local scour measured in previous experiments with a similar flow. CE Database subject headings: Three-dimensional flow; Turbulent flow; Flow patterns; Three-dimensional models; Dikes; Flow measurement; Simulation.

The characteristics of fully developed turbulent flow in a hybrid domain channel, which consists of a clear fluid region and a porous bed, are examined numerically using a model based on the macroscopic Reynolds-averaged Navier-Stokes equations. By adopting the classical continuity interface conditions, the present model treats the hybrid domain problem with a single domain approach, and the simulated results are noted to coincide with the existing experimental data and microscopic data. The effects of porosity [PHI] and Darcy number Da on the flow properties over and inside the porous bed are further investigated in the selected ranges of 0.6 [less than or equal] [PHI] [less than or equal] 0.8, and 1.6 X [10.sup.-4] [less than or equal] Da [less than or equal] 1.6 x [10.sup.-2]. It has been demonstrated that the presence of the porous bed causes the significant reduction of the flow velocities inside the clear fluid region relative to that of a smooth impermeable bed, and also reduces the magnitude of the integral constant B of the velocity logarithmic distributions from its traditional value 5.25. Moreover, turbulent shear stress within the upper part of the porous bed increases significantly with the porosity [PHI] and Darcy number Da. The thickness of turbulence penetration remains proportional to the values of porosity [PHI] and Darcy number Da. DOI: 10.1061/(ASCE)0733-9429(2007)133:6(610) CE Database subject headings: Turbulent flow; Porous media; Open channel flow; Channel beds.

A quasi-three-dimensional coastal area morphological (Q3DCAM) model has been developed using the process-based approach. It is for simulating complex multiscale coastal processes, primarily morphodynamic changes of the seabed. This software package has integrated three key submodels for simulating irregular wave deformations, nearshore currents, and morphological processes. The quasi-three-dimensional capability of the depth-averaged model has been developed to consider the vertical flow structure inside the surf zone and the cross-shore movement mechanisms of nearshore currents, e.g., undertow and mass flux. To this end, the calculations of the radiation stresses inside the surf zone have been improved by introducing the nonsinusoidal wave model for surface roller effects due to the breaking wave. To predict accurately the wave field and the morphological processes near coastal structures, the wave diffraction effects were included in a multidirectional spectral wave transformation model. The morphodynamic change was modeled by considering the sediment transport due to the combinations of waves and currents. These three submodels were validated by simulating three laboratory experimental cases in regard to: (1) irregular wave deformations over a shoal; (2) longshore currents in a wave basin; and (3) moveable bed evolutions around an offshore breakwater under attack of an incident wave. The numerical results of the morphological modeling confirmed that the Q3DCAM model consisting of the diffraction effects and the surface roller effects is capable of predicting waves, currents, and morphodynamic changes more accurately than before. Therefore, this validated model can be applied to simulate more realistic morphological processes in coastal zones including structures. DOI: 10.1061/(ASCE)0733-950X(2006) 132:6(462) CE Database subject headings: Coastal processes; Numerical models; Wave diffraction; Nearshore circulation; Coastal morphology; Three-dimensional models.

A three-dimensional numerical model was developed for simulating the phosphorus concentration in shallow lakes. In this model, the computational domain was divided into two parts: the water column and the bed sediment layer. The processes of mineralization, settling, adsorption, desorption, bed release (diffusion), growth, and death of phytoplankton were taken into account, and the concentration of organic phosphorus, phosphate, and related water quality constituents was simulated. The concentrations of adsorbed (particulate) and dissolved phosphate due to adsorption-desorption were calculated using two formulas derived based on the Langmuir equation. The release rate of phosphorus from the bed sediment layer was calculated by considering the effects of the concentration gradient across the water-sediment interface, pH, temperature, dissolved oxygen concentration, and flow conditions. The adsorption and desorption of phosphate from sediment particles, as well as its release from bed sediment, were verified using laboratory experimental data. The model was calibrated and applied to Deep Hollow Lake in the Mississippi alluvial plain. The simulated trends and magnitudes of phosphorus concentration were compared with field observations. The simulation results show that there are strong interactions between sediment-related processes and phosphorus concentration. CE Database subject headings: Phosphorus; Numerical models; Lakes; Sediment.

To improve navigation conditions for barges passing through river channels, many submerged weirs (SWs) have been installed along the bendways of many waterways by the U.S. Army Corps of Engineers. This paper presents results from three-dimensional numerical simulations that were conducted to study the helical secondary current (HSC) and the near-field flow distribution around one SW. The simulated flow fields around a SW in a scale physical model were validated using experimental data. The three-dimensional flow fields around a SW, the influence of the SW on general HSC, and the implication of effectiveness of submerged weirs to realign the flow field and improve navigability in bendways were analyzed. The numerical simulations indicated that the SW significantly altered the general HSC. Its presence reduced a skewed pressure difference cross its top and a triangular-shaped recirculation to the downstream side. The over-top flow tends to realign toward the inner bank and therefore improves conditions for navigation. DOI: 10.1061/(ASCE)0733-9429(2005) 131:8(682) CE Database subject headings: Numerical analysis: Flow simulation: Secondary flow: Turbulent flow: Three-dimensional models: Channel bends: Hydraulic structures: Weirs.

A numerical method based on optimal control theories for identifying Manning's roughness coefficients (Manning's n) in modeling of shallow water flows is presented. The coefficients are difficult to be determined especially when the spatial variation is significant, and are usually estimated empirically. The present methodology is applied to determine the optimal values of the spatially distributed parameters, which give least overall discrepancies between simulations and measurements. Through a series of systematic studies to identify the n values in both a hypothetical open channel and a natural stream stretch, several identification procedures based on unconstrained and constrained minimizations are analyzed. It is found that the limited-memory quasi-Newton method has the advantages of higher rate of convergence, numerical stability and computational efficiency. Although the identification of Manning's n is chosen as an example, the identification methods can be applied to numerical simulations of various flow problems. CE Database subject headings: Parameters; Shallow water; Roughness coefficient; Identification; River flow.

The scouring process in a plunge pool of loose bed with uniform bed-materials due to a two-dimensional plane impinging jet was simulated computationally. The finite-element-based unsteady three-dimensional model, CCHE3D, with k-[Epsilon] turbulence closure was employed to solve the flow field. It has long been recognized that the unsteady behavior of the turbulent jet fluctuation plays an important role in scouring and transporting sediment in the plunge pool. In order to model this phenomenon realistically, one has to consider the effects of both shear stress and the life force on sediment particles due to pressure fluctuation. The latter has been taken into account by using empirical relationships of flume data. Both of these effects have been incorporated in the nonequilibrium sediment transport model consisting of sediment pickup rate and step length adopted for the jet scour problem. The model constant relating to the fluctuating lift force was calibrated using an empirical equation to predict the quasi-equilibrium scour depth. The results simulated by the model proposed here agree reasonably well with experimental data.