Thesis (MScEng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This work investigates methods to theoretically determine the lateral velocity distribution across a river from which factors may be derived to translate a single point velocity into average velocity for the river as a whole. A wide range of field data from vanous nvers was analysed. This produced over a hundred velocity distributions with which to compare theoretical distribution results. Four theoretical approaches were considered: the one-dimensional method (Manning's equation), a two-dimensional flow formula solved as an initial-value-problem, a two dimensional flow formula solved as a boundary-value-problem and an empirical method developed from energy principles. The one-dimensional and initial-value-problem approaches were unsuccessful. The boundary-value and empirical approach did however produce promising results. Surprisingly the analysis of the field data revealed patterns of similarity which could produce accurate results without the need of a theoretical approach. / AFRIKAANSE OPSOMMING: Metodes word ondersoek om teoreties 'n laterale snelheidsverspreiding oor 'n rivier te bepaal en sodoende 'n faktor te vind waarmee 'n gemete enkelpuntsnelheid in die rivier omgeskakel kan word na 'n gemiddelde snelheid vir die rivier in geheel. Vloeimeetdata van verskeie nviere IS geanaliseer. Sodoende is meer as 100 snelheidsverspreidings gegenereer waarmee die teorie vergelyk kon word. Vier teoretiese benaderings is gevolg: Manning se een-dimensionele vloeivergelyking, 'n twee dimensionele vloei-vergelyking opgelos met behulp van 'n beginwaarde, 'n twee dimensionele vloei-vergelyking opgelos met behulp van randwaardes, en 'n empiriese metode ontwikkel vanuit energie beginsels. Die een-dimensionele- en beginwaarde-benaderings was me suksesvol me. Die randwaarde- en empiriese benaderings het wel belowende resultate gelewer. Selfs verwerking van die gemete stroommetings het waardevolle inligting gelewer: daar bestaan duidelike ooreenkomste in die snelheidsverspreidings wat gebruik kan word om die verspreidingsfaktor mee te bereken sonder om teoretiese oplossings te soek.

<p>Simulation of the planing hull in waves has been addressed during the last 25 years and basically been approached by strip methods. This work follows that tradition and describes a time-domain strip model for simulation of the planing hull in waves. The actual fluid mechanical problem is simplified through the strip approach. The load distribution acting on the hull is approximated by determining the section load at a number of hull sections, strips. The section-wise 2-dimensional calculations are expressed in terms of added mass coefficients and used in the formulations of both inertia and excitation forces in the equations of motions. The modeling approach starts from the hypothetic assumption that the transient conditions can be modeled based on those section-wise calculations. The equation of motion is solved in the time-domain. The equation is up-dated at each time step and every iteration step with respect to the momentary distribution of section draught and relative incident velocity between the hull and water and catches the characteristic non-linear behavior of the planing craft in waves.</p><p>The model follows the principles of the pioneering work of E. E. Zarnick differing on model structure and in details such as the modeling of the lift in the transom area. A major part of the work is concerned with experiments and evaluation of simulations with respect to performed model tests and to published experiment data. Simulations of model tests have been performed and comparisons have been made between measured and simulated time series. The link between simulation and experiment is a wave model which is based on a wave height measurement signal. It is developed and evaluated in the thesis.</p><p>The conclusions are in favor of the 2-dimensional approach to modeling the conditions for the planing hull in waves and among further studies is evaluation of simulated loads and motions to full-scale trial measurement data.</p>

Durban is the busiest container port in Africa and there are plans for significant expansion during the next few years. This expansion includes the widening of the port entrance channel to accommodate larger "post-panamax" vessels. Complex crosscurrents near the port entrance, coupled with severe wind and wave conditions, may lead to the intermittent closure of the port which in turn could lead to significant economic implications. Information on the nature of the crosscurrents and how they affect the ships could assist harbour pilots in developing their skills and reduce the risks associated with steering ships into the port. The research involved a case study to develop an innovative new method for directly measuring the effect of wind, waves and crosscurrents on ships entering the port. The technology is based on the application of digital image processing to track the position of ships as they manoeuvre in the port approach channel. The key innovation of this research is the extraction of the heading direction of the ship from the image data. The angle between this heading direction and the true velocity vector (the "crab angle") is then a direct measure of the cross-track drift velocity (CTDV) due to the combined effects of wind, waves and currents. The crosscurrents are usually the main contributing factor to the cross-track drift. The aim of this research was to develop a fully automated image processing system for real-time ship monitoring, and to determine cross-track drift within a wide range of weather conditions and ship parameters. The methodology presented in this research allows the spatial structure of the CTDV along the harbour approach channel to be studied. The relationship of the CTDV to local surface winds was analysed. For deep draught vessels, measured CTDVs were found to be poorly correlated to surface winds. The spatial structure of the measured CTDVs shows distinct regions along the approach channel where vessels experience significantly larger drift velocities. In summary, with the software tools developed by this research, digital images can be captured automatically and analysed to produce ship tracks and crab angles. From this information an extensive database for ship manoeuvring in the approach channel can be developed and the safety and efficiency of port operations improved. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2002.

In the past decades, engineers have started to realize the importance of the interaction between vegetation, biota and water flow, in riverine and marine environments; a discipline that has been named “Eco-Hydraulics”. Scientists have valued this coupled phenomenon for much longer than their engineering colleagues. As early as 1970, marine researchers presented the evidence that colonies of micro-organisms might alter the stability of fine cohesive sediments (Neuman et al., 1970). However traditional models of sediments transport (e.g. Shields, 1936) have been derived using abiotic sediments and did not consider that most wet surfaces would soon be colonized by micro-organisms and their extracellular polymeric substances (EPS), a combination called “biofilm” (Lock, 1993). Scientists during the 1990s, after observing this phenomenon in the field, coined the term “biostabilization”. During this period they showed that colonies of cyanobacteria and diatoms coating fine sand or cohesive sediments can increase their stability by up to 960% compared to abiotic sediments (Grant and Gust, 1987; Dade et al, 1990; Paterson 1997). Only recently have engineers started to take into consideration the effect of such increased cohesion and adhesion due to biogenic forces within the sediment transport model (Righetti and Lucarelli, 2007); yet all of those studies have low applicability because they are linked to specific environmental conditions. Moreover no data are available on the effect of biofilm on larger sediments (e.g. coarse sand and gravel). The present thesis provides experimental data carried out in a flume laboratory pertaining to biostabilization of non-cohesive coarse sand and gravels at a scale representation of a real river system (from 0.2m to 1m). Four sediment substratum (glass spheres of D50 = 1.09mm and 2.00mm; sand of D50 = 1.20mm and gravel of D50 = 2.20mm) were colonized under unidirectional flow by a cyanobacterium (Phormidium sp.) for between 1 and 10 weeks. The increase in erosion threshold for biotic sediment is then investigated using a series of different methods ranging from traditional sediment transport techniques (e.g. Yalin, 1972), to image thresholding and particle image velocimetry (PIV) assessments of flow modification due to biofilm presence. Moreover, tensile strength analysis of ex-situ biofilm/substratum specimens will be presented to understand better the mechanical property of this composite material. Data indicates that: i) biostabilization of sediments in the range of coarse sand and gravel occurs (9%-150% more shear stress required to induce entrainment compared to abiotic sediments) but to a lower extent compared to critical entrainment thresholds for fine sand and cohesive sediments (Paterson, 1997); ii) flume experimentation can be employed to control specific variables affecting biostabilization and could help to unfold the complicated interactions between environmental variables, and the affect of flow on the growth and strength of biofilm colonization over sediments; iii) strong biofilm growth generated a more uniform velocity field, with reduction in shear stress (up to 82% compared with abiotic sediments) and decreases in roughness length of the bed (up to 94% compared to abiotic sediments); iv) Composite biofilm/substratum specimens presented a clear elastic behaviour when tensile tested; v) Conventional models of sediment transport (e.g. Wiberg and Smith, 1987) do not consider the presence of biofilm and will not work in the case of bio-mats smoothing the surface of the bed; hence the need for new models which include the biofilm elasticity and the bio-mat smoothing process. This thesis suggests two theoretical examples where the biofilm action is considered at a grain to grain and bio-mat scale.

This thesis takes an interdisciplinary approach to the problem of the aleatory uncertainty manifest in the design of engineering structures that are subject to random loading, with specific application to continuous gust loading on aircraft and wave loading on offshore structures. The main focus is on aircraft gust loading because this is the area in which more significant progress is made. A review of the literature on gust loading is carried out to evaluate the sufficiency of existing methods and the possibility of a unified certification model is discussed. In order to obtain reliable probabilistic design loads using conventional stochastic simulation techniques, a large number of simulations are required to derive probability distributions that have adequately low sampling variability in the area of interest. A novel method, called the Efficient Threshold Upcrossing method, is developed that reduces the required number of simulations by at least 2 orders of magnitude. The method is initially developed for the efficient derivation of short-term offshore structural response statistics and is subsequently applied to the modelling of aircraft response to continuous turbulence. The ETU method was successfully extended to take into account long-term statistics of nonlinear aircraft response and it was shown that reliable design exceedance curves can be obtained by as little as 4\% of the computational cost of the conventional method. The current methods for the computation of design loads for nonlinear aircraft are limited to discrete, `1~-~cosine' gust encounters as the continuous turbulence models are only applicable to linear aircraft response. However, the most significant outcome of this thesis is that this is no longer the case, because the ETU method provides a way to calculate nonlinear response statistics in the time domain at a significantly lower computational cost. Mathematical models of a simple offshore structure, and both linear and nonlinear aircraft, are developed and a more robust technique is introduced for simulating patches of continuous turbulence. These models, which have the ability to generate random inputs, are used to derive response probability distributions for each of the test structures. The results obtained by applying the new approaches to these data sets show that they offer a marked improvement in performance.

The exploitation of small horizontal axis wind turbines provides a clean, prospective and viable option for energy supply. Although great progress has been achieved in the wind energy sector, there is still potential space to reduce the cost and improve the performance of small wind turbines. An enhanced understanding of how small wind turbines interact with the wind turns out to be essential. This work investigates the aerodynamic design and analysis of small horizontal axis wind turbine blades via the blade element momentum (BEM) based approach and the computational fluid dynamics (CFD) based approach. From this research, it is possible to draw a series of detailed guidelines on small wind turbine blade design and analysis. The research also provides a platform for further comprehensive study using these two approaches. The wake induction corrections and stall corrections of the BEM method were examined through a case study of the NREL/NASA Phase VI wind turbine. A hybrid stall correction model was proposed to analyse wind turbine power performance. The proposed model shows improvement in power prediction for the validation case, compared with the existing stall correction models. The effects of the key rotor parameters of a small wind turbine as well as the blade chord and twist angle distributions on power performance were investigated through two typical wind turbines, i.e. a fixed-pitch variable-speed (FPVS) wind turbine and a fixed-pitch fixed-speed (FPFS) wind turbine. An engineering blade design and analysis code was developed in MATLAB to accommodate aerodynamic design and analysis of the blades. The linearisation for radial profiles of blade chord and twist angle for the FPFS wind turbine blade design was discussed. Results show that, the proposed linearisation approach leads to reduced manufacturing cost and higher annual energy production (AEP), with minimal effects on the low wind speed performance. Comparative studies of mesh and turbulence models in 2D and 3D CFD modelling were conducted. The CFD predicted lift and drag coefficients of the airfoil S809 were compared with wind tunnel test data and the 3D CFD modelling method of the NREL/NASA Phase VI wind turbine were validated against measurements. Airfoil aerodynamic characterisation and wind turbine power performance as well as 3D flow details were studied. The detailed flow characteristics from the CFD modelling are quantitatively comparable to the measurements, such as blade surface pressure distribution and integrated forces and moments. It is confirmed that the CFD approach is able to provide a more detailed qualitative and quantitative analysis for wind turbine airfoils and rotors. With more advanced turbulence model and more powerful computing capability, it is prospective to improve the BEM method considering 3D flow effects.

The purpose of this research is to develop a 3-D numerical model on the Lower Mississippi River to simulate hydrodynamics and non-cohesive sediment transport. The study reach extends from Bonnet Carré Spillway (RM 127) to Head of Passes (RM 0). Delft3D with sigma coordinates was selected as the river modeling tool. This model River domain is characterized by a complex distributary system that connects the Mississippi River to the Gulf of Mexico. The boundary conditions were: water levels in the Gulf and Head of Passes; and discharges upstream. For the calibration, there are observed data for both types of boundary conditions. Several periods of high discharge were simulated to compare water level, discharge, velocity profiles and sediment transport with measurements and accomplish calibration and validation of the model. A calibrated 3-D model has been developed with the following %RMSE: 5% for stage; 6% for discharge; and 5% for sand load.

The stratified flow of the lower Mississippi River due to density gradients is a well documented phenomenon. This stratification of fresh and saline water manifests itself as a heavier wedge of saline water that extends upriver and a buoyant fresh water plume extending into the Gulf of Mexico past the Southwest Pass jetties. The maximum absolute distance of saltwater intrusion observed anywhere in the world occurred on the Mississippi River in 1939 and 1940 when saltwater was observed approximately 225 km upstream from the mouth of Southwest Pass. The U. S. Army Corps of Engineers now prevents the wedge from migrating upstream by constructing a subaqueous barrier in the river channel. A curvilinear grid was constructed representative of the modern Mississippi River delta. Boundary conditions were developed for the drought year of 2012 and the grid was tested in order to evaluate the salinity intrusion and sediment transport abilities of the Cartesian Z-coordinate Delft3D code. The Z-model proved to have the ability to propagate the saline density current as observed in the prototype. The effect of salinity on fine sediment transport is evaluated by manipulation of the settling velocity through a cosine function provided in the model code. Manipulation of the fine sediment fall velocity through the cosine function was an effective means to simulate the re-circulation of flocculated sediments in the saline wedge turbidity maxima. In addition, the Z-model capably reproduced the fine sediment concentration profiles in a fully turbulent shear flow environment. With the ability to reproduce the seasonal saline density current and its effect on sedimentation within the turbidity maxima as well as sedimentation characteristics in a fully turbulent shear flow, a model capable of analyzing all of the major processes affecting fine sediment transport within the Mississippi River salt wedge estuary has been developed.

A aplicação de modelagem numérica para análise acidentes envolvendo derrames de óleo se tornou uma das principais ferramentas para o estudo deste tipo de impacto ambiental, auxiliando na previsão do deslocamento e permitindo maior eficácia nas formas de atuação nos processos de contingência do deslocamento da mancha. Estes pressupostos dão impulso ao desenvolvimento de pesquisa aplicada neste caso específico de estudo, ou seja, de modelação hidrodinâmica no Canal de São Sebastião em vários cenários através da utilização do módulo hidrodinâmico do software MIKE 21 da DHI, e da avaliação dos resultados gerados pela simulação através de comparação com o acompanhamento de eventos reais de espalhamento de manchas de óleo em acidentes antigos e com uma imagem de satélite simultânea a um derramamento. Foram avaliados sete eventos distintos onde ocorreram vazamentos de óleo no Canal de São Sebastião e a eles comparados às simulações hidrodinâmicas geradas pelo modelo em diferentes condições ambientais. Os resultados obtidos mostram que o deslocamento da mancha de óleo está condicionado preferencialmente pelo regime de ventos, estando bem correlacionados com os padrões hidrodinâmicos encontrados. A partir das diferentes situações apresentadas nas simulações, é possível estimar o sentido do deslocamento em acidentes futuros, dando subsídios nas ações de contenção dos efeitos deste tipo de acidente. / The application of numeric models for analysis of oil spill in the coastal environments becomes one of the most important ways to understand the behavior of the oil in this case of impact, giving subsides to the prediction of the displacement of the patches and allowing best efficiency in the control of the extension of the impact agent. These assumptions give thrust to the development of applied research in this work, which is defined by the knowledge of the different hydrodynamic conditions that compose the oceanographic structure in the São Sebastião Channel, by the utilization of the software MIKE 21 of the DHI (Danish Hydrodynamic Institute) and the comparison with historic cases of spill described in the literature. A satellite image was processed showing the real conditions of the spill, considering the physic-chemical changes and compared with the other data improve the evaluation process. Seven oil spills were studied and compared to the simulations, and there were generated six scenarios in different environmental conditions. The results show that the most important forcing of the environmental conditions of the oil patch is the wind, and the simulations agree well with the real processes. The hydrodynamic module of Mike 21 reveals an applicable tool for this kind of studies, giving sufficient information to reduce the impact of oil spill improving the oil spill contention.

This thesis examines the application of two evolutionary computation techniques to two different aspects of open channel flow. The first part of the work is concerned with evaluating the ability of an evolutionary algorithm to provide insight and guidance into the correct magnitude and trend of the three parameters required in order to successfully apply a quasi 2D depth averaged Reynolds Averaged Navier Stokes (RANS) model to the flow in prismatic open channels. The RANS modeled adopted is the Shiono Knight Method (SKM) which requires three input parameters in order to provide closure, i.e. the friction factor (\(f\)), dimensionless eddy viscosity (λ) and a sink term representing the effects of secondary flow (Γ). A non-dominated sorting genetic algorithm II (NSGA-II) is used to construct a multiobjective evolutionary based calibration framework for the SKM from which conclusions relating to the appropriate values of \(f\), λ and Γ are made. The framework is applied to flows in homogenous and heterogeneous trapezoidal channels, homogenous rectangular channels and a number of natural rivers. The variation of \(f\), λ and Γ with the wetted parameter ratio (\(P_b\)/\(P_w\)) and panel structure for a variety of situations is investigated in detail. The situation is complex: \(f\) is relatively independent of the panel structure but is shown to vary with P\(_b\)/P\(_w\), the values of λ and Γ are highly affected by the panel structure but λ is shown to be relatively insensitive to changes in \(P_b\)/\(P_w\). Appropriate guidance in the form of empirical equations are provided. Comparing the results to previous calibration attempts highlights the effectiveness of the proposed semi-automated framework developed in this thesis. The latter part of the thesis examines the possibility of using genetic programming as an effective data mining tool in order to build a model induction methodology. To this end the flow over a free overfall is exampled for a variety of cross section shapes. In total, 18 datasets representing 1373 experiments were interrogated. It was found that an expression of form \(h_c\)=A\(h_e\)\(^{B\sqrt S_o}\), where \(h_c\) is the critical depth, \(h_e\) is the depth at the brink, \(S_o\) is the bed slope and A and B are two cross section dependant constants, was valid regardless of cross sectional shape and Froude number. In all of the cases examined this expression fitted the data to within a coefficient of determination (CoD) larger than 0.975. The discovery of this single expression for all datasets represents a significant step forward and highlights the power and potential of genetic programming.