Copyright (c) 2013 University of Iowa All rights reserved. http://ir.uiowa.edu/iihr_pubs Recent documents in Iowa Institute of Hydraulic Research (IIHR) - Hydroscience & Engineering Publications en-us Thu, 16 May 2013 15:16:55 PDT 3600 http://ir.uiowa.edu/iihr_pubs/27 http://ir.uiowa.edu/iihr_pubs/27 Tue, 13 Sep 2011 20:22:41 PDT Presents details of the experiments on flow at a 90-degree open-channel junction. Occurrence of two open channels in hydraulic structures; Factors that influence flow characteristics; Characteristics of a sharp-edged, open-channel junction flow; Comparison of depth ratios across an open-channel junction.

]]> Larry J. Weber et al. http://ir.uiowa.edu/iihr_pubs/26 http://ir.uiowa.edu/iihr_pubs/26 Tue, 13 Sep 2011 20:22:40 PDT High levels of dissolved gas downstream of Wanapum Dam on the Columbia River have required Public Utility District Number 2 of Grant County (the District) to investigate various approaches to reduce gas supersaturation levels. To evaluate the effectiveness of flow deflectors mounted on the spillway face the District had a physical model built of three bays of the Wanapum Spillway. The model was used to both qualitatively and quantitatively assess the performance of the flow deflectors. The qualitative evaluation was performed by visual observations of the flow patterns generated by each flow deflector downstream of the spillway. Whereas, the quantitative evaluation was performed by collecting an extensive data set describing velocity fields and bubble distributions. This data set was then analyzed numerically to predict the downstream concentration of gas supersaturation. The purpose of this paper is to describe the physical model study and the qualitative evaluation of the flow deflectors. A companion paper by Orlins and Gulliver (1996) describes the numerical model developed to analyze the velocity and bubble data.

]]> Larry J. Weber et al. http://ir.uiowa.edu/iihr_pubs/25 http://ir.uiowa.edu/iihr_pubs/25 Tue, 13 Sep 2011 20:22:38 PDT Recently, numerical models have been used more frequently in hydraulic design projects. This is particularly true in the design of fish passage facilities. Advances in numerical modeling methodologies and the ability to collect high-resolution position data of salmonids within a reservoir have led to interesting issues of numerical model calibration. Presently, more emphasis is being placed on higher-order hydrodynamics, such as accelerations, turbulence and energy dissipation. Therefore, it has become subsequently more important to understand the ability of a numerical model to predict such quantities accurately. The purpose of the paper is to describe the detailed approach taken to calibrate a fully three-dimensional numerical model of two main stem Columbia and Snake River dams, namely Rocky Reach Dam and Lower Granite Lock and Dam. The paper presents detailed calibration methods that show validation of the numerical model to field and physical model velocities; field measurements of velocity fluctuations due to unsteadiness as well as turbulence; and the effect of surface roughness. Additionally, data will be presented showing the impact of scaling factors and limitations of spatial boundaries from physical models used to provide validation data. The paper concludes by discussing the need for accepted standards for numerical model validation. Copyright ASCE 2004.

]]> Larry J. Weber et al. http://ir.uiowa.edu/iihr_pubs/24 http://ir.uiowa.edu/iihr_pubs/24 Tue, 13 Sep 2011 20:22:37 PDT Larry J. weber http://ir.uiowa.edu/iihr_pubs/23 http://ir.uiowa.edu/iihr_pubs/23 Tue, 13 Sep 2011 20:22:36 PDT Larry J. Weber http://ir.uiowa.edu/iihr_pubs/22 http://ir.uiowa.edu/iihr_pubs/22 Tue, 13 Sep 2011 20:22:35 PDT High summer water temperatures have caused increased juvenile fish stress in fish passage facilities at McNary Dam. The need to better understand the main mechanisms that generate high temperatures and result in subsequent harmful stress to downstream migrating fish motivates this study. Most numerical studies of temperature dynamics in reservoirs are based on one- or two-dimensional models. McNary Dam forebay is characterized by complex three-dimensional flow patterns and unsteady heat exchange between the atmosphere and water. An unsteady three-dimensional non-hydrostatic model is used in this paper to predict the hydrodynamics and thermal dynamics in the forebay and turbine intakes of McNary Dam. This model is based on the Reynolds Average Navier-Stokes equations, using a Boussinesq approach, with a standard k- model to solve the flow field. The thermal model takes into account the short and long wave radiation and heat convection at the free surface, which is function of air temperature and wind velocity. The predicted temperature is compared against a 24 h field data set for a warm day in 2004. Simulated and measured temperature profiles in the forebay and within the gatewells show reasonable agreement. An additional simulation studies the inclusion of a thermal curtain upstream of the turbine intakes. Numerical results indicate that the thermal curtain reduces gatewell temperatures potentially increasing survival for migratory salmonids at the dam. 2007 Elsevier B.V. All rights reserved.

]]> Marcela Politano et al. http://ir.uiowa.edu/iihr_pubs/21 http://ir.uiowa.edu/iihr_pubs/21 Tue, 13 Sep 2011 20:22:34 PDT Because of the high homologous temperature at which ice is normally found, creep deformation is a mechanism that is often observed when ice is loaded. However, it is not clear to what extent creep crack growth (growth of a crack under constant, creep, loading) occurs in ice, if indeed it does. A preliminary series of experiments have been performed to determine the extent of creep crack growth in freshwater ice. The results of these experiments are presented, and the implications of these results are discussed.

]]> wilfrid A. Nixon et al. http://ir.uiowa.edu/iihr_pubs/20 http://ir.uiowa.edu/iihr_pubs/20 Tue, 13 Sep 2011 20:22:32 PDT Construction in remote Arctic locations is made more difficult and expensive by the need to bring to site bulky building materials. This need can be reduced by the use of ice-soil mixtures. The strength of this reinforced ice is a function of the percentage of reinforcing soil mixed with the ice. To determine this function, beams of sand-reinforced ice were made, with volume percentage reinforcement of sand between 1.4 and 66.9%. The beams were loaded in bending, at a crosshead displacement rate of 50 mm/min and a temperature of -5C. All samples failed in a brittle manner. The bending strength increased with increasing reinforcement. This behavior is explained by a simple model, extending the work of Nixon and Weber (1991), which assumes that failure arises from the propagation of flaws within the ice matrix. The model, which is semiempirical, describes the observed bending strength behavior very well. Further work is required to refine the model and account quantitatively for the effect of unfrozen water on the beam strength.

]]> wilfrid A. Nixon et al. http://ir.uiowa.edu/iihr_pubs/19 http://ir.uiowa.edu/iihr_pubs/19 Tue, 13 Sep 2011 20:22:31 PDT This paper presents the research performed to define the current abilities and limits of PIV in measuring air concentration and velocity in spillway plunging jets. The research concluded that PIV measurement methods can successfully measure velocity and air concentration in a stilling basin environment. It was shown that laser-light sheet intensity, special seeding such as florescence and camera filters, and size discrimination techniques can be used to separate images of fluid marking particles and bubbles. It was shown that PIV can efficiently provide a detailed measurement of average velocity for a stilling basin flow field. It was also shown that PIV can measure turbulence and vortex structures.

]]> Kevin D. Nielsen et al. http://ir.uiowa.edu/iihr_pubs/18 http://ir.uiowa.edu/iihr_pubs/18 Tue, 13 Sep 2011 20:22:30 PDT Numerous studies have been performed to determine the discharge coefficient for orifices. These studies have included a variety of shapes, sizes, and configurations. The values developed typically ranges from about 0.6 to 0.85. However, specific discharge coefficient values for a particular configuration often appear contradictory. This is probably a result of variations in testing methods and operating conditions. The effect of submergence is also not specifically identified as a parameter for determining the discharge coefficient. Therefore, it is difficult to confidently select a discharge coefficient value from the available literature for an orifice operating under different levels of submergence. For this reason, a physical model was constructed at the Iowa Institute of Hydraulic Research to determine the effect of submergence on a rectangular orifice with partially suppressed contractions. The model results demonstrated that the discharge coefficient varies from about 0.6 to 0.85 depending on the magnitude of the submergence. Copyright ASCE 2004.

]]> Kevin D. Nielsen et al. http://ir.uiowa.edu/iihr_pubs/17 http://ir.uiowa.edu/iihr_pubs/17 Tue, 13 Sep 2011 20:22:29 PDT Acoustic Doppler Velocimeters (ADV) are an established method of measuring three dimensional velocity components. However, when bubbles are present in the measurement area the quality of the measurement decreases rapidly. At high concentrations of bubbles, the ADV is mainly measuring the bubble velocity rather than the velocity of the water or nothing at all. Bubbles are often present for a free-discharging jet entering a body of water. This makes it difficult to measure the velocity distribution of the jet as it disperses in the water body. This paper describes a method to separate the measurements on bubbles from those on water so that the water velocity can be extracted from the ADV output files.

]]> Kevin D. Nielsen et al. http://ir.uiowa.edu/iihr_pubs/16 http://ir.uiowa.edu/iihr_pubs/16 Tue, 13 Sep 2011 20:22:28 PDT The recent digital-electronic revolution has helped experimental hydraulics benefit from a new generation of acoustic-, laser-, and imaging-based instrumentation. These newly developed techniques are not only of superior accuracy, but they have also expedited data collection. Powerful visualization software has been used increasingly to present and interpret experimental results. In addition, numerical models have become increasingly available in some cases providing turnkey solutions to complex flows. The outcome of this intensive development is powerful computer-based research tools that allow an unprecedented interaction between physical and numerical experiments. This integrated approach is considerably improving our understanding of numerous aspects and practical consequences of flow mechanics and allows a comprehensive treatment of space-time processes in fluid flows which is difficult to obtain using alternative means. This holistic experimental-numerical approach is readily available for integration as expertsystems or decision-making programs in hydroinformatics systems. The present paper discusses the beneficial synergy between laboratory measurements and computational models of different levels of complexity. A study, conducted at the Iowa Institute of Hydraulic Research (IIHR) is presented herein as an example to demonstrate the interaction among the three investigation components, namely, laboratory measurements, the kinematic model, and the hydrodynamic model, as well as the benefits and limitations of each of them. The laboratory velocity measurements were made using three-component Acoustic-Doppler Velocimeters. A simple numerical model based exclusively on flow kinematics was used to empower results visualization and to provide insight in several flow features. The kinematic model feedback was used to optimize the data acquisition scheme for the ensuing measurements. The detailed hydrodynamic flow analysis for regions with complex three-dimensional flows was obtained by a numerical model that solves the Reynolds Averaged Navier-Stokes (RANS) equations in general curvilinear coordinates.

]]> Marian Muste et al. http://ir.uiowa.edu/iihr_pubs/15 http://ir.uiowa.edu/iihr_pubs/15 Tue, 13 Sep 2011 20:22:27 PDT A three-dimensional numerical model is developed to resolve the flow in natural rivers, in particular in the vicinity of hydraulic structures. The model solves the Reynolds Averaged Navier Stokes (RANS) equations in generalized curvilinear coordinates. It is currently being applied to a river reach approximately seven kilometers (four and half miles) long in Columbia River, WA, immediately upstream of Wanapum Dam. The model has been calibrated against field measurements for two flow discharges. The higher discharge (5390 m3s) is split between the powerhouse and the spillway, while the lower discharge (2559 m3s) is released only through the powerhouse. The field measurements are collected at six cross sections. At each vertical velocity-station, three velocity components were measured at 0.2, 0.4, and 0.8 of the flow depth. A comparison between the numerical solutions and the field data is presented, and a good agreement is observed. The obtained level of agreement indicates that the numerical model produces results that are quite satisfactory for practical purposes.

]]> Ehab A. Meselhe et al. http://ir.uiowa.edu/iihr_pubs/14 http://ir.uiowa.edu/iihr_pubs/14 Tue, 13 Sep 2011 20:22:25 PDT The flow hydrodynamics in a straight open channel containing a multiple-embayment groyne field on one of its sides is investigated numerically using large eddy simulation. The vertical groynes are fully emerged. The mean flow depth in the groyne region is about half that of the main channel and the length and width of the embayments are much larger than the mean depth in the embayment region. The model is validated using mean velocity and turbulent fluctuations data collected at the free surface in a previous experimental study. It is found that despite the fact that the flow inside the main recirculation eddy in the embayments can be characterized as being quasi-two dimensional, the flow inside the mixing layer region between the embayments and the channel is strongly nonuniform over the depth. As this region controls the mass exchange processes between the groyne field and the main channel, a three-dimensional description of the flow in this area is essential. The large-scale eddies that populate the mixing layer can penetrate the embayment region over lateral distances of the order of the channel depth. These eddies advect with them channel fluid inside the embayment. Eventually, the channel fluid is mixed with the embayment fluid by the small scales. The other main mixing mechanism is due to the injection of patches of high-vorticity mixing-layer fluid near the tip of the downstream groyne and their subsequent convection in the form of a wall-attached jet-like flow into the embayment, first parallel to the downstream groyne face and then to the sidewall. It is shown that on average, most of the fluid leaves the embayment region via the top layer of the embayment-channel interface (upstream half) and enters the embayment region at levels situated around the middepth (practically over the whole length of the embayment) of the interface surface. This explains why the mass exchange coefficients are overestimated when predicted using methods that employ floating particles as a tracer. The instantaneous bed shear stress inside the cavity is found to peak close to the downstream groyne face of each embayment and to show a high variability around the mean values due to the interaction of the mixing layer eddies with the tip of the groynes and the formation of the jet-like flow parallel to the droyne face. 2008 ASCE.

]]> Andrew McCoy et al. http://ir.uiowa.edu/iihr_pubs/13 http://ir.uiowa.edu/iihr_pubs/13 Tue, 13 Sep 2011 20:22:24 PDT This paper presents a numerical method for free surface flows that couples the incompressible Navier-Stokes equations with the level set method in the finite element framework. The implicit characteristic-Galerkin approximation together with the fractional four-step algorithm is employed to discretize the governing equations. The schemes for solving the level set evolution and reinitialization equations are verified with several benchmark cases, including stationary circle, rotation of a slotted disk and stretching of a circular fluid element. The results are compared with those calculated from the level set finite volume method of Yue et al. (Int. J. Numer. Methods Fluids 2003; 42:853-884), which employed the third-order essentially non-oscillatory (ENO) schemes for advection of the level set function in a generalized curvilinear coordinate system. The comparison indicates that the characteristic Galerkin approximation of the level set equations yields more accurate solutions. The second-order accuracy of the Navier-Stokes solver is confirmed by simulation of decay vortex. The coupled system of the Navier-Stokes and level set equations then is validated by solitary wave and broken dam problems. The simulation results are in excellent agreement with experimental data. Copyright 2005 John Wiley Sons, Ltd.

]]> Ching-Long Lin et al. http://ir.uiowa.edu/iihr_pubs/12 http://ir.uiowa.edu/iihr_pubs/12 Tue, 13 Sep 2011 20:22:23 PDT The free surface flow of two conceptual fish passage designs are investigated numerically by a level-set finite-element method. One design has a right-angled entrance from the reservoir to the fish passage chute, and the other has a curved-shaped entrance. The numerical results are validated with hydraulic experiments through comparison of the free surface location and the pressure distribution in the spillway. It is found that the right-angled design yields a curved free surface and pressure distribution in the vicinity of the entrance due to large strains, whereas the curved-shaped design yields a smooth flow transition with small strains. The negative pressure distributions near the ogee crest for both designs exhibit similar characteristics. Further downstream the free surface is elevated near the wall and is associated with counterrotating vortices. It is concluded that the curved-shaped design is favorable for fish passage because of the feature of a smooth flow transition with small strains. [ABSTRACT FROM AUTHOR]; Copyright of Journal of Hydraulic Engineering is the property of American Society of Civil Engineers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

]]> Haegyun Lee http://ir.uiowa.edu/iihr_pubs/11 http://ir.uiowa.edu/iihr_pubs/11 Tue, 13 Sep 2011 20:22:21 PDT Larry J. weber http://ir.uiowa.edu/iihr_pubs/10 http://ir.uiowa.edu/iihr_pubs/10 Tue, 13 Sep 2011 20:22:20 PDT A three-dimensional numerical method, without the hydrostatic assumption, is developed to solve flow problems in hydraulic engineering. This method adopts an unstructured grid technology that is applicable to arbitrarily shaped cells and offers the potential to unify many grid topologies into a single formulation. It solves the three-dimensional turbulent flow equations and utilizes a collocated and cell-centered storage scheme with a finite-volume discretization. In Part I, the technical details of the method are presented, along with its verification and validation by computing a benchmark open channel flow. Meshes of hexahedral, tetrahedral, and prismatic shapes are employed, and results are compared with experimental data and among different meshes. Accuracy estimates and error analyses are also developed and discussed. Our companion paper applies the method to two practical problems: Flow in a hydroturbine draft tube, and flow in the forebay of Rocky Reach Dam for design of a fish passage facility.

]]> Yong G. Lai et al. http://ir.uiowa.edu/iihr_pubs/9 http://ir.uiowa.edu/iihr_pubs/9 Tue, 13 Sep 2011 20:22:19 PDT A three-dimensional computational method, without the use of hydrostatic assumption, is developed to solve fluid flows for hydraulic applications. Numerical algorithms and verification of the nonhydrostatic model are described in our companion paper. The model employs unstructured grid technology with arbitrarily shaped cells, offering the potential to unify many grid topologies into a single formulation. Herein, the model is applied to two practical steady hydraulic flows to provide further validation of the model and demonstrate its use in practical flows. The flows in a hydroturbine draft tube and in the forebay of Rocky Reach Dam for the fish passage facility design are simulated. Comparison with experimental data in the former and physical and field measurements in the latte establish the scope of the model.

]]> Yong G. Lai et al. http://ir.uiowa.edu/iihr_pubs/8 http://ir.uiowa.edu/iihr_pubs/8 Tue, 13 Sep 2011 20:22:18 PDT Natural river flows are mostly unsteady in nature due to seasonal variation of flow discharge and controlled operation of hydraulic structures. Often this unsteadiness leads to complex flow pattern changes and the flow characteristics may be quite different from that of steady-state flows. Unsteadiness is particularly important during flooding events and when submerged islands exist immediately upstream or downstream of hydraulic structures. In the past, however, unsteadiness has not been modeled in most projects involving fully three-dimensional computational fluid dynamic modeling. The purpose of this paper is to address the issue of unsteadiness in the context of fully three-dimensional numerical modeling. Particularly, effort is directed at developing the unsteady capability associated with the wetting and drying processes for a reach of a natural river. Validation and application were performed with a forebay reach of the Columbia River at the Rock Island Dam. The computational results are reported and discussed. Copyright ASCE 2004.

]]> Yong G. Lai et al.