Browsing by Author "Petrie, John"

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Application of the grid convergence index to a laminar axisymmetric sudden expansion flow
(Universidad de Cuenca, 2014) Carrillo Serrano, Verónica Margarita; Petrie, John; Pacheco Tobar, Esteban Alonso
The use of numerical models to represent natural processes is increasingly common. The development of advanced numerical tools allows a more physically-based representation of complex flow phenomena. While more advanced systems can be solved, the uncertainty of the accuracy of the solutions obtained remains. The mere comparison between experiments and simulations is not enough proof of strength of the results. The Grid Convergence Index (GCI) methodology has been proposed with the aim to provide a mechanism to calculate and report discretization errors estimates in computational fluid dynamics (CFD) simulations. It permits the quantification of the uncertainty present in grid convergence. This method uses a grid convergence error estimator that is obtained by applying the generalized Richardson Extrapolation theory. The process is applied to an axisymmetric sudden expansion laminar flow case. Experimental results are used to verify the numerical simulation and GCI outcome. As a result of the application of this method the order of accuracy of the numerical scheme was verified. Additionally, comparing the numerical results with the experimental values, a maximum error of 6% was obtained. Finally, considering the two finest meshes, it can be concluded that the asymptotic range has been reached and that a finer Mesh won’t improve the accuracy of the solution when considering the increased numerical cost.
Characterization of bedload sediment transport in high slope rivers using hydraulic geometry theory
(Asce library, 2019) Cisneros Espinoza, Felipe Eduardo ; Petrie, John; Pacheco Tobar, Esteban Alonso; Timbe Castro, Luis Manuel; Carrillo Serrano, Verónica Margarita
In Ecuador, steep rough-bedded channels constitute the main component of mountainous drainage system. They provide sediment to milder-slope downstream channels. Thus, sediment transport represents a driving process in natural drainage system. Namely, it defines river morphology evolution. To quantify and to understand the magnitude and effect of this process in the surrounding environment, the understanding and knowledge of bedload transport must be improved. The study of sediment transport in steeper channels with coarser material is a complex process. The continuously changing environment results in a high uncertainty in the quantification of sediment transport rates. Some equations have been proposed to quantify the rates. However the lack of actual measured data does not allow proper quantification and verification. On the other hand, hydraulic geometry (HG) theory has been applied to generate elements for a consistent monitoring of rivers behavior. Dimensionless HG relations that replicate what is observed in rivers have been obtained. Parameters such as top width, mean flow depth, mean velocity, and suspended sediment load of several gravel-bed rivers have been related with liquid discharge. The present study proposes the characterization of bedload sediment transport of steep gravel-bed rivers in terms of dimensionless HG relations. Measurements in various reaches along a river of bedload transport rate are performed to determine the parameters (exponents and coefficients) of the HG relations. The results represent a contribution that allows the reduction of the lack of field-measured data as well as the application of a theory generally used to characterize hydraulic-geometric parameters to characterize bedload sediment transport.
Using a statistical efficiency methodology for predictors’ selection in the bedload transport problem: a high gradient experimental channel case
(2021) Cisneros Espinoza, Felipe Eduardo ; Carrillo Serrano, Verónica Margarita; Timbe Castro, Luis Manuel; Mendoza, Daniel E.; Petrie, John; Matovelle Carrillo, Pedro Andres; Torres Flores, Sebastián Eugenio; Pacheco Tobar, Esteban Alonso
Bedload transport rates for high-gradient gravel bed rivers has been studied through a physical model that replicated the typical features of these channels. A stepwise regression was performed to identify the best predictors from a set of independent variables. As independent variables channel slope, the ratio of area occupied by large particles to the total plan area, flow discharge, mean flow depth, mean flow velocity, water surface velocity, boundary shear stress, and shear velocity were considered. Different characteristic diameters (d16, d50, d84, and d90) were used to nondimensionalize the variables as well as to test the influence of grain size. A linear and a potential model were obtained for each characteristic diameter. Based on the correlation coefficients (R2) with the data used to build the models, the d50 and d84 linear and potential models were selected to perform further analysis. A set of independent data was used to verify the selected models. Better performance was observed for the potential models with 96% of the data falling within ½ order of the magnitude bands both for d50 and d84. R2 for the d50 and d84 potential models were 0.63 and 0.76, respectively. Therefore, the d84 potential model can be selected as the present study representative model.