Doctor of Philosophy / Department of Biological and Agricultural Engineering / Naiqian Zhang / An optical sensor for determining water velocity in natural open channels like creeks and rivers has been designed and tested. The sensor consists of a plastic body which is shaped so that water flows through a U-shaped channel into which are mounted LEDs and matching phototransistors at various angles. A small amount of dye is injected into the water just upstream of two sets of LEDs and phototransistors which are spaced 4 cm apart. The time delay between the dye’s effects on these signals depends on water velocity and is determined using a biased cross correlation calculation. In addition to providing velocity, the LEDs and phototransistors can also be used to estimate soil sediment concentration. A previous version of the sensor was tested in enclosed flow to confirm that the general design of the sensor, including LEDs, phototransistors, dye and electronics, would indeed work to detect the velocity of water flowing through the sensor. Although the conditions for the test were unlike those experienced in natural open channels, the ability to catch all the fluid flowing through the sensor provided a simple confirmation of the velocity estimate that was not available in field settings. Further testing in the field then confirmed that the sensor worked in the field but also identified several areas needing improvement. Computational fluid dynamics was used to improve the sensor body. The electronics and program running the sensor were also redesigned. After making these improvements, a new version of the sensor was produced. The testing of the new version of the sensor confirmed its ability to accurately detect velocity in natural open channels. The velocity measurements from this sensor were compared to the commercially available Flowtracker velocity sensor. A regression analysis on the measurements from the two sensors found that the velocity measurements from each sensor were nearly identical across a range of velocities. Other tests established that the electronics and programming running the sensor performed as designed. The development and testing of this sensor has resulted in a system which works in natural open channels like creeks and rivers.

Este trabalho representa a continuidade de estudos envolvendo a problemática dos escoamentos com superfície livre, contemplando a análise do fenômeno transiente em canais, a partir do modelo matemático unidimensional de Saint-Venant. Para tanto, é desenvolvido um modelo computacional em linguagem FORTRAN, capaz de avaliar o comportamento do escoamento não permanente. As equações hidrodinâmicas completas são discretizadas por um esquema completamente implícito de diferenças finitas e aplicadas no modelo computacional para a avaliação de dois casos. O modelo é previamente testado para um caso simples, cujos resultados são analisados viabilizando o modelo. No primeiro caso, o modelo é aplicado ao canal de alimentação da Usina Hidrelétrica Monjolinho em São Carlos-SP, para avaliar a necessidade de vertedouro quando se dá o fechamento brusco da turbina, e a ocorrência da entrada de ar na mesma quando da sua abertura repentina. No segundo caso, procurou-se avaliar o desenvolvimento do escoamento no Canal do Trabalhador, responsável pelo abastecimento da cidade de Fortaleza-CE. Com manobras de enchimento e esvaziamento do sistema, é possível determinar o tempo de antecedência de liga-desliga do sistema de recalque a partir das alturas dágua e velocidades de ocorrência, permitindo também a automação para as operações de controle. Em ambos os casos o modelo reproduziu resultados que ilustram com coerência os conceitos pré-estabelecidos, constituindo numa ferramenta útil para análise do fenômeno transiente nos escoamentos em condutos livres. / This work presents a computational model developed in FORTRAN language for the study of unsteady open-channel flows with the use of Saint-Venant one-dimensional equation. The discretization of hydrodynamic equations are presented in a completely implicit method of finite differences and applied in the model for the investigation of two cases, besides the one used previously to test the model. In the first case, the model is applied for a channel that supplies the Monjolinho hydroelectric plant in Sao Carlos SP, aiming to evaluate the need of a spillway when the turbine is closed and the flow abruptly stopped, as well as the occurrence of air entering the turbine when it is opened instantaneously. In the second case, the model simulates the development of the flow in the Trabalhador channel, responsible for the water supply in the city of Fortaleza - CE, in order to make possible the automation of operational control, based on data of flow velocity and water level. In both cases the model is presented as a useful tool for the analysis of unsteady open-channel flows, showing results and coherency with theory.

The depth-averaged Saint-Venant equations, which are used for most computational flow models, are adequate in simulating open channel flows with insignificant curvatures of streamlines. However, these equations are insufficient when applied to flow problems where the effects of non-hydrostatic pressure distribution are predominant. This study provides a comprehensive examination of the feasibility of a simple one-dimensional Boussinesq-type model equation for such types of flow problems. This equation, which allows for curvature of the free surface and a non-hydrostatic pressure distribution, is derived using the momentum principle together with the assumption of a constant centrifugal term at a vertical section. Besides, two Boussinesq-type model equations that incorporate different degrees of corrections for the effects of the curvature of the streamline are investigated in this work. One model, the weakly curved flow equation model, is the simplified version of the flow model based on a constant centrifugal term for flow situations that involve weak streamline curvature and slope, and the other, the Boussinesq-type momentum equation linear model is developed based on the assumption of a linear variation of centrifugal term with depth.

The depth-averaged Saint-Venant equations, which are used for most computational flow models, are adequate in simulating open channel flows with insignificant curvatures of streamlines. However, these equations are insufficient when applied to flow problems where the effects of non-hydrostatic pressure distribution are predominant. This study provides a comprehensive examination of the feasibility of a simple one-dimensional Boussinesq-type model equation for such types of flow problems. This equation, which allows for curvature of the free surface and a non-hydrostatic pressure distribution, is derived using the momentum principle together with the assumption of a constant centrifugal term at a vertical section. Besides, two Boussinesq-type model equations that incorporate different degrees of corrections for the effects of the curvature of the streamline are investigated in this work. One model, the weakly curved flow equation model, is the simplified version of the flow model based on a constant centrifugal term for flow situations that involve weak streamline curvature and slope, and the other, the Boussinesq-type momentum equation linear model is developed based on the assumption of a linear variation of centrifugal term with depth.

The optimum values for the section variables like channel side slope,bottom width,depth and radius for triangular,rectangular, trapezoidal and circular channels are computed by minimizing the cost of the channel section.Manning &rsquo / s uniform flow formula is treated as a constraint for the optimization model.The cost function is arranged to include the cost of lining,cost of earthwork and the increment in the cost of earthwork with the depth below the ground surface.The optimum values of section variables are expressed as simple functions of unit cost terms.Unique values of optimum section variables are obtained for the case of minimum area or minimum wetted perimeter problems.

Sharp crested rectangular weirs used for discharge measurement purposes in open channel hydraulics are investigated experimentally. A series of experiments were conducted by measuring discharge and head over the weir for different weir heights for full width weir. It is seen that after a certain weir height, head and discharge relation does not change. Hence a constant weir height is determined. For that height / discharge and head over the weir are measured for variable weir width, starting from the full width weir to slit weir. Description of the discharge coefficient valid for the full range of weir widths and an empirical expression involving dimensionless flow variables is aimed. Experimental data obtained for this purpose and the results of the regression analysis performed are represented.

A comprehensive understanding of the hydrodynamics in vegetated open-channels and flow-vegetation interaction is of high interest to researchers and practitioners alike for instance in the content of river and coastal restoration schemes. The focus of this study was to investigate the effect of the presence of vegetation on flow resistance, turbulence statistics, and the instantaneous flow in open channels by performing three-dimensional computational-fluid-dynamics (CFD) simulations. Firstly, fully developed turbulent flow in fully-vegetated channel was analyzed by employing the method of high-resolution Large-Eddy Simulation (LES). Flow through a staggered array of rigid, emergent cylinders was simulated and the LES was validated through experiments. After validation, numerical simulations were performed at an extended parameter range of two different cylinder Reynolds numbers (ReD = 500 and 1340) and three different vegetation densities (φ = 0.016, 0.063, and 0.251). Flow structures and statistics were analyzed on the instantaneous flow and the effect of the vegetation density and cylinder Reynolds number was assessed. Moreover, drag forces exerted on the cylinders were calculated explicitly, and the effect of both ReD and φ on the drag coefficient was quantified. Secondly, two new alternative simulation strategies, a RANS based strategy with a vegetative closure model and a low-resolution Large-Eddy Simulation, were devised. They were evaluated by simulating several experimental cases with diverse conditions of the cylinder arrangement (i.e., staggered vs. random distribution), vegetation densities (φ = 0.016, 0.022, 0.063, 0.087, 0.091, 0.150, and 0.251), and cylinder Reynolds number (ReD = 170 - 1700). For the RANS based strategy, the importance of a-priori knowledge was assessed, and for the low-resolution LES, the efficiency and accuracy was demonstrated. Finally, a numerical strategy based on a porosity approach was developed and applied to open-channel flow through a natural plant. The simulated velocities were compared with experimentally acquired ones and results showed reasonable agreement. The results obtained in this research contribute to the understanding of fundamental mechanism of flow-vegetation interaction in vegetated open-channels, resolving turbulent flow-vegetation interaction explicitly. In addition, the new numerical strategies developed as part of this research are expected to allow describing the behavior of turbulent flow through artificial and natural vegetation with high efficiency and accuracy.

Extreme hydrological events associated with global warming are likely to produce an increasing number of flooding scenarios resulting in significant bridge inundation and associated damages. During large floods, the presence of a bridge in an open channel triggers a highly turbulent flow field including 3D complex coherent structures around bridge structures. These turbulence structures are highly energetic and possess high sediment entrainment capacity which increases scouring around the bridge foundation and consequently lead to structural stability problems or even failure of the structure. Hence, understanding the complex turbulent flow field for these extreme flow conditions is crucial to estimate the failure risks for existing bridges and better design of future bridges. This research employs the method Large Eddy Simulation (LES) to predict accurately the 3D turbulent flow around bridge structures. The LES code is refined with a novel free surface algorithm based on the Level Set Method (LSM) to determine the complex water surface profiles. The code is used to analyze the hydrodynamics of compound channel flow with deep and shallow overbanks, free flow around a bridge abutment, pressure flow with a partially submerged bridge deck and bridge overtopping flow. All simulations are validated with data from complementary physical model tests under analogous geometrical and flow conditions. Primary velocity, bed shear stress, turbulence characteristics and 3D coherent flow structures are examined thoroughly for each of the flow cases to explain the hydrodynamics of these complex turbulent flows.

An experimental research was performed to study the effects of surface roughness on the characteristics of separated and reattached turbulent flows in an open channel. A backward facing step was used to induce flow separation. The rough surfaces comprised wire mesh grit-80 and sand grains of average diameter 1.5 mm. In each experiment, the Reynolds number based on the step height and freestream velocity of approach flow was fixed at 3240 and the Reynolds number based on the approach flow depth and freestream velocity was kept constant at 25130. Particle image velocimetry (PIV) technique was used to measure the flow velocity. The results showed that roughness effects on the mean and turbulent quantities are evident only in the recovery region. Moreover, roughness effects on the flow dynamics are dependent on the specific roughness element.

Simulation of fresh concrete flow has spurged with the advent of Self-Compacting Concrete, SCC. The fresh concrete rheology must be compatible with the reinforced formwork geometry to ensure complete and reliable form filling with smooth concrete surfaces. Predicting flow behavior in the formwork and linking the required rheological parameters to flow tests performed on the site will ensure an optimization of the casting process. In this thesis, numerical simulation of concrete flow and particle behaviour is investigated, using both discrete as well as a continuous approach. Good correspondence was achieved with a Bingham material model used to simulate concrete laboratory tests (e.g. slump flow). It is known that aggregate properties such as size, shape and surface roughness as well as its grading curve affect fresh concrete properties. An increased share of non-spherical particles in concrete increases the level of yield stress, τ0, and plastic viscosity, µpl. The yield stress level may be decreased by adding superplasticizers, however, the plastic viscosity may not. An explanation for the behaviour of particles is sought after experimentally, analytically and numerically. Bingham parameter plastic viscosity is experimentally linked to particle shape. It was found that large particles orient themselves aligning their major axis with the fluid flow, whereas small particles in the colloidal range may rotate between larger particles. The rotation of crushed, non-spherical fine particles as well as particles of a few microns that agglomorate leads to an increased viscosity of the fluid. Generally, numerical simulation of large scale quantitative analyses are performed rather smoothly with the continuous approach. Smaller scale details and phenomena are better captured qualitatively with the discrete particle approach. As computer speed and capacity constantly evolves, simulation detail and sample volume will be allowed to increase. A future merging of the homogeneous fluid model with the particle approach to form particles in the fluid will feature the flow of concrete as the physical suspension that it represents. One single ellipsoidal particle in fluid was studied as a first step. / <p>QC 20150326</p>