Spelling suggestions: "subject:"themathematical models"" "subject:"appeal.mathematical models""
1 
Distributed approach of coupling basin scale hydrology with atmospheric processesMahanama, Sarith Prasad Panditha. January 2000 (has links)
published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

2 
Modelling streamflow response to hydroclimatic variables in the Upper Mkomazi River, South AfricaOyebode, Oluwaseun Kunle 13 June 2014 (has links)
Submitted in fulfillment of the requirements of the Degree of Master of Technology: Civil Engineering, Durban University of Technology, 2014. / Streamflow modelling remains crucial to decisionmaking especially when it concerns planning and management of water resources systems in waterstressed regions. This study proposes a suitable method for streamflow modelling irrespective of the limited availability of historical datasets. Two datadriven modelling techniques were applied comparatively so as to achieve this aim. Genetic programming (GP), an evolutionary algorithm approach and a differential evolution (DE)trained artificial neural network (ANN) were used for streamflow prediction in the upper Mkomazi River, South Africa. Historical records of streamflow and meteorological variables for a 19year period (1994 2012) were used for model development and also in the selection of predictor variables into the input vector space of the models. In both approaches, individual monthly predictive models were developed for each month of the year using a 1year lead time. Two case studies were considered in development of the ANN models. Case study 1 involved the use of correlation analysis in selecting input variables as employed during GP model development, while the DE algorithm was used for training and optimizing the model parameters. However in case study 2, genetic programming was incorporated as a screening tool for determining the dimensionality of the ANN models, while the learning process was further finetuned by subjecting the DE algorithm to sensitivity analysis. Altogether, the performance of the three sets of predictive models were evaluated comparatively using three statistical measures namely, Mean Absolute Percent Error (MAPE), Root MeanSquared Error (RMSE) and coefficient of determination (R2).
Results showed better predictive performance by the GP models both during the training and validation phases when compared with the ANNs. Although the ANN models developed in case study 1 gave satisfactory results during the training phase, they were unable to extensively replicate those results during the validation phase. It was found that results from case study 1 were considerably influenced by the problems of overfitting and memorization, which are typical of ANNs when subjected to small amount of datasets. However, results from case study 2 showed great improvement across the three evaluation criteria, as the overfitting and memorization problems were significantly minimized, thus leading to improved accuracy in the predictions of the ANN models. It was concluded that the conjunctive use of the two evolutionary computation methods (GP and DE) can be used to improve the performance of artificial neural networks models, especially when availability of datasets is limited. In addition, the GP models can be deployed as predictive tools for the purpose of planning and management of water resources within the Mkomazi region and KwaZuluNatal province as a whole.

3 
A procedure for the determination of a flow duration curve at an ungaged basinAhn, Taejin, 1957 January 1987 (has links)
The purpose of this study is to develop a method for predicting monthly flow duration curves for ungaged basins that are suitable for estimating average annual flow, and installed capacity and average annual energy generation at potential sites for hydropower development. The procedures were tested by developing monthly rainfall duration curves for five sample watersheds and then developing flow duration curves from the rainfall data. The methods were evaluated by comparing the predicted monthly flow duration curves to daily and monthly flow duration curves based on field data from the selected sites because a plant's potential energy output can be computed directly from a flow duration curve. The methods tested fit duration curves based on field data reasonably well and are suitable for preliminary evaluation of hydropower developments in ungaged basins.

4 
Investigations of streamaquifer interactions using a coupled surfacewater and groundwater flow modelVionnet, Leticia Beatriz, Maddock, Thomas, III, Goodrich, David C. 01 1900 (has links)
A finite element numerical model is developed for the modeling of coupled
surfacewater flow and groundwater flow. The mathematical treatment of subsurface
flows follows the confined aquifer theory or the classical Dupuit approximation for
unconfined aquifers whereas surfacewater flows are treated with the kinematic wave
approximation for open channel flow. A detailed discussion of the standard approaches to
represent the coupling term is provided. In this work, a mathematical expression similar
to Ohm's law is used to simulate the interacting term between the two major hydrological
components. Contrary to the standard approach, the coupling term is incorporated
through a boundary flux integral that arises naturally in the weak form of the governing
equations rather than through a source term. It is found that in some cases, a branch cut
needs to be introduced along the internal boundary representing the stream in order to
define a simply connected domain, which is an essential requirement in the derivation of
the weak form of the groundwater flow equation. The fast time scale characteristic of
surfacewater flows and the slow time scale characteristic of groundwater flows are
clearly established, leading to the definition of three dimensionless parameters, namely, a
Peclet number that inherits the disparity between both time scales, a flow number that
relates the pumping rate and the streamflow, and a Biot number that relates the
conductance at the riveraquifer interface to the aquifer conductance.
The model, implemented in the Bill Williams River Basin, reproduces the observed
streamflow patterns and the groundwater flow patterns. Fairly good results are obtained
using multiple time steps in the simulation process.

5 
Investigation of streamaquifer interactions using a coupled surface water and groundwater flow model.Vionnet, Leticia Beatriz, Vionnet, Leticia Beatriz January 1995 (has links)
A finite element numerical model is developed for the modeling of coupled surfacewater flow and groundwater flow. The mathematical treatment of subsurface flows follows the confined aquifer theory or the classical Dupuit approximation for unconfined aquifers whereas surfacewater flows are treated with the kinematic wave approximation for open channel flow. A detailed discussion of the standard approaches to represent the coupling term is provided. In this work, a mathematical expression similar to Ohm's law is used to simulate the interacting term between the two major hydrological components. Contrary to the standard approach, the coupling term is incorporated through a boundary flux integral that arises naturally in the weak form of the governing equations rather than through a source term. It is found that in some cases, a branch cut needs to be introduced along the internal boundary representing the stream in order to define a simply connected domain, which is an essential requirement in the derivation of the weak form of the groundwater flow equation. The fast time scale characteristic of surfacewater flows and the slow time scale characteristic of groundwater flows are clearly established, leading to the definition of three dimensionless parameters, namely, a Peclet number that inherits the disparity between both time scales, a flow number that relates the pumping rate and the streamflow, and a Biot number that relates the conductance at the riveraquifer interface to the aquifer conductance. The model, implemented in the Bill Williams River Basin, reproduces the observed streamflow patterns and the groundwater flow patterns. Fairly good results are obtained using multiple time steps in the simulation process.

6 
Frequency analysis of low flows: comparison of a physically based approach and hypothetical distribution methodsMattejat, Peter Paul January 1985 (has links)
Several different approaches are applied in low flow frequency analysis. Each method's theory and application is explained. The methods are (1) physically based recession model dealing with time series, (2) logPearson type III and mixed logPearson type III using annual minimum series, (3) Double Bounded pdf using annual minimum series, (4) Partial Duration Series applying truncated and censored flows.
Each method has a computer program for application. One day low flow analysis was applied to 15 stations, 10 perennial streams and 5 intermittent streams. The physically based method uses the exponential baseflow recession with duration, initial recession flow, and recharge due to incoming storm as random variables, and shows promise as an alternative to black box methods, and is appealing because it contains the effect of drought length. LogPearson is modified to handle zero flows by adding a point mass probability for zero flows. Another approach to zero flows is the Double Bounded probability density function which also includes a point mass probability for zero flows. Maximum likelihood estimation is used to estimate distribution parameters. Partial Duration Series is applied due to drawbacks of using only one low flow per year in annual minimum series. Two approaches were used in Partial Duration Series (i) truncation, and (ii) censorship which represent different low flow populations. The parameters are estimated by maximum likelihood estimation. / M.S.

7 
RANS and LES predictions of turbulent scalar transport in dead zones of natural streamsDrost, Kevin J. 04 June 2012 (has links)
Natural stream systems contain a variety of ﬂow geometries which contain ﬂow
separation, turbulent shear layers, and recirculation zones. This work focuses on
streams with dead zones. Characterized by slower ﬂow and recirculation, dead
zones are naturally occurring cutouts in stream banks. These dead zones play an
important role in stream nutrient retention and solute transport. Previous experimental work has focused on idealized dead zone geometries studied in laboratory
ﬂumes. This work explores the capabilities of computational ﬂuid dynamics (CFD)
to investigate the scaling relationships between ﬂow parameters of idealized geometries and the time scales of transport. The stream geometry can be split into two
main regions, the main stream ﬂow and the dead zone. Geometric parameters of
the dead zone as well as the bulk stream velocity were varied to determine a scaling relationship for the transport time scales. These ﬂow geometries are simulated
using the RANS turbulence model with the standard kω closure. The standard
ﬁrst order dead zone model is expanded to a two region model to accommodate the
multiple time scales observed in the simulation results. While this model currently
has limited predictive capability, it provides physical insight into the functional
dependence of the dead zone time scales. LES is used to evaluate the performance
of the Reynolds Averaged NavierStokes (RANS) turbulence model and to describe
the anisotropic turbulence characteristics. The differences between the time averaged ﬂow ﬁeld for Large Eddy Simulation (LES) and RANS was determined to
have a significant impact on passive scalar transport. / Graduation date: 2012

8 
A new Lagrangian model for the dynamics and transport of river and shallow water flowsDevkota, Bishnu Hari January 2005 (has links)
This study presents a new Lagrangian model for predicting dynamics and transport in rivers and shallow water flows. A hydrostatic model is developed for the prediction of rivers and floodplain flow and lateral interactions between them. The model is extended to the Boussinesq weakly nonlinear, nonhydrostatic model for the simulation of solitary waves and undular bores. A model for advectiondiffusion transport of tracers in open channel flow is also presented. The simulation results are compared against an analytical solution and published laboratory data, field data and theoretical results. It is demonstrated that the Lagrangian moving grid eliminates numerical diffusion and oscillations; the model is dynamically adaptive, providing higher resolution under the wave by compressing the parcels (grid). It also allows flow over dry beds and moving boundaries to be handled efficiently. The hydrostatic model results have shown that the model accurately simulates wave propagation and nonlinear steepening until wave breaking. The model is successfully applied to simulate flow and lateral interactions in a compound channel and flood wave movement in a natural river. The nonhydrostatic model has successfully reproduced the general features of solitary waves such as the balance between nonlinearity and wave dispersion and nonlinear interactions of two solitary waves by phaseshift. Also, the model successfully reproduced undular bores (high frequency short waves) from a long wave and the predicted maximum height of the leading wave agreed very well with the published results. It is shown that the simple second order accurate Lagrangian scheme efficiently simulates dispersive waves without any numerical diffusion. Lagrangian modeling of advectiondiffusion transport of Gaussian tracer distributions, top hat tracer distributions and steep fronts (step function) in steady, uniform flow has provided exact results and has shown that the scheme allows the use of a large time step without any numerical diffusion and oscillations, including for the advection of steep fronts. The scheme can handle large Courant numbers (results are presented for Cr = 0 to 20) and the entire range of grid Peclet numbers from zero to infinity. The model is successfully applied to tracer transport due to flow induced by simple waves, solitary waves and undular bores

9 
Modeling of GroundWater Flow and Surface/GroundWater Interaction for the San Pedro River Basin Part I Mexican Border to Fairbank, ArizonaVionnet, Leticia Beatriz, Maddock, Thomas January 1992 (has links)
Many hydrologic basins in the southwest have seen their perennial streamflows
turn to ephemeral, their riparian communities disappear or be jeopardized, and their
aquifers suffer from severe overdrafts. Under management of ground water exploitation
and of conjunctive use of surface and ground waters are the main reasons for these
events.

Page generated in 0.103 seconds