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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Some effects of Langmuir circulation on suspended particles in lakes and reservoirs

Buranathanitt, T. January 1979 (has links)
The quantitative extent to which the large-scale organised water motion in the surface waters of lakes and reservoirs, known as Langmuir circulation, affects the distribution and settling of suspended particles, especially the algae, is not known and has been ignored in the conventional modelling of water quality. Since the settling of these particles is an important process in determining water quality, the present study investigates the Langmuir circulation effect by means of a mathematical model, based on the two-dimensional advection-diffusion mass transport equation describing the temporal and spatial distribution of suspended particles in a typical Langmuir cell. The Langmuir circulation flow field and turbulent diffusion coefficients are empirically modelled by relating these variables to the environmental parameters. It has been shown that Langmuir circulation does affect particle distribution and settling. For particles with small sinking speeds, the circulation causes intense mixing, resulting in essentially uniform distribution of particles over the Langmuir cell. For particles with high sinking velocities, aggregation of particles can occur, giving rise to considerable reduction in sinking losses. Two preliminary laboratory experiments have been performed. The wind-wave tank experiment suggests that the Langmuir circulation scale of motion is dependent on the significant height of the surface waves, thus providing an empirical means of determining the size of Langmuir cells from environmental variables. The particle-settling tank experiment holds promise as a means of studying the effect of circulating flows on the distribution and settling of particles.

Integrated modelling of hydrodynamic processes, faecal indicator organisms and related parameters with Improved accuracy using parallel (GPU) computing

Boye, Brian A. January 2014 (has links)
Environmental problems and issues are not limited by artificial boundaries created by man. Usually there are different teams or individuals working on the catchments, estuaries, rivers and coastal basins in different countries using different parameters and formulations for various processes. However, the system is a natural one and as such no boundaries exist. When a rain drop of water moves from a catchment to a stream, river or estuary and to the sea, it does not know at any stage whether it is in the catchment, river, estuary or sea. In recent years there has been growing concern about the impact of diffuse source pollution on river, estuarine and coastal water quality and particularly with regard to non-compliance of bathing waters. Hydro-environmental impact assessment modelling studies are generally regarded as having several fundamental shortcomings in model simulations, which can lead to erroneous environmental impact assessment outcomes. These shortcomings were addressed in this project and included: 1. Applying a Cloud to Coast (C2C) approach to modelling flow and solute transport processes in river, estuarine and coastal waters; 2. Improving the computational linking of catchment, river and estuarine-coastal models; 3. Improving the kinetic decay process representation in deterministic models, to include the impacts of salinity, solar irradiance, turbidity and temperature, and; 4. Using parallel (GPU based) computing to enhance the computational speed in executing bathing water quality models. In this research study, the Ribble Estuary and Fylde Coast model was refined to more accurately predict bathing water quality and use parameters which give a better representation of the existing physical and bio-chemical processes. A Cloud to Coast (C2C) approach to modelling was implemented by using common input parameters and formulations in both the 1-D and 2-D domains of the Ribble Estuary and Fylde Coast model. An empirical formulation linking the mortality (decay) rate of bacterial water quality indicators to environmental conditions such as solar irradiation, turbidity, temperature and salinity was added to the numerical code. The linked boundary between the 1-D and 2-D domains of the numerical model was improved by removing the large overlapped linked region. An existing numerical code was rewritten to take advantage of the parallel computing capability of the Graphics Processing Unit (GPU). This was tested on the Ribble Estuary and the Thames Estuary model. Thames Estuary models of varying mesh density were prepared in this research study using lots of bathymetric data (over 80 million points) and tested on the GPU. This research study improved the ability to predict bathing water quality accurately by introducing more realistic representation of environmental conditions and using parallel computing. This improved the ability to carry real time forecasting of bathing water quality and hence prevent failure to meet the requirements of the EU Bathing Water Directive.

Stochastic analysis of saturated soils using finite elements

Onisiphorou, Christakis January 2000 (has links)
This thesis has investigated the static liquefaction failure, during construction, of the Nerlerk underwater berm. This hydraulically-placed sandfill structure was designed to form part of an artificial caisson island, intended for use as a year-round exploration drilling platform in the Canadian Beaufort Sea. The aim of the investigation has been to examine how liquefaction was possible in a fill which, according to CPT data, was predominantly dilative; in particular, to study the influence, on stability, of 'pockets' of liquefiable material in the sandfill. Instead of a conventional deterministic approach, based on mean strengths, a stochastic type of approach has been necessary, in order to accurately model material heterogeneity. For this research, the double-hardening constitutive model Monot has been used, this being capable of modelling a wide range of material behaviour, from liquefiable to strongly dilative. The material parameters have been calibrated from an extensive laboratory database and expressed in terms of density via the state parameter for sands. The state parameter statistics have been derived, based on a detailed statistical evaluation of an extensive CPT database from the Tarsiut and Nerlerk island sites. These statistics were used for generating uni-variate random fields of state parameter, from which the Monot material parameters could then be backfigured, in order to model the spatial variability in the fill (i.e. heterogeneity). A number of sophisticated stochastic investigations have been performed, using an advanced two-dimensional finite element algorithm encompassing Monot. The results have shown that liquefaction of the Nerlerk berm is consistent with CPT data: i.e. it may be possible for a predominantly dilative fill to liquefy, under static loading conditions, due to the presence of semi-continuous loose zones arising from deposition-induced anisotropy. For such problems, in which material anisotropy is present, a deterministic approach is not appropriate and can be misleading, as this was shown to represent an upper bound response to the stochastic simulations.

Impulsive overtopping of vertical seawalls under oblique wave conditions

Napp, Nicolas January 2004 (has links)
There is no guidance available for either mean or wave-by-wave overtopping discharges over vertical seawalls subject to oblique and impulsive wave attack.  Impulsive wave attack (i.e. waves break onto the structure) may lead to substantially higher overtopping volumes than pulsating wave attach and can arise at relatively low water levels. Mean and wave-by-wave overtopping discharges represent important quantities in the design of coastal structures. The not only affect the structural safety and determine the capacity of the drainage system behind the structure, but also pose a hazard to communications, buildings, and members of the public. Previous work has shown that impulsive overtopping can substantially increase overtopping volumes and velocities, thus underlining the importance of robust prediction tools. This PhD thesis describes experiments and analysis to provide design guidance in wave overtopping of vertical seawalls under oblique and impulsive wave attach. The guidance extends existing design tools for wave overtopping which cover both wave conditions under oblique wave attack. Special attention is given to the transition from impulsive to reflecting wave conditions, which goes along with a significant reduction in overtopping towards higher obliquities. For moderate obliquities (15° and 30°) a new intermediate wave condition is defined as the “impact-like” condition, which – in terms of overtopping – has still to be treated as impulsive. Contrary to a few previous investigations on sloping walls, no increase in overtopping could be found at small obliquities (15°). Spatial variability, however, could be measured along the seawall and has been considered in the design guidance offered in this thesis.

Design of hydraulic structures with plane intermediate filters

Farouk, Mohamed Ismail January 2000 (has links)
Hydraulic structures should be secured against uplift pressure and piping. Design engineers, therefore, may provide these structures with different features such as intermediate filters to establish safer and/or more economic structures. One or more intermediate filters can be built within the floor. In this research, the problem of seepage flow beneath hydraulic structures with two plane intermediate filters over a homogenous soil has been deduced analytically using the conformal mapping technique. The solutions include the potential heads at both key and stagnation points, the hydraulic exit gradient just downstream the floor, and the location of the stagnation points. The results have been used to create design charts over a wide range of variables. Then, the general steady-state seepage problem beneath a floor of hydraulic structure having any shape provided with any number of filters and cut-offs located anywhere over a heterogeneous soil has been obtained using a finite element model. After calibrating the model, it has been applied to solve the same problem studied analytically using conformal mapping to confirm both solutions and to determine the adequacy of the numerical solution for potential heads, exit gradient and location of the stagnation points. Good agreement between both solutions has been obtained confirming the accuracy of the numerical solution. Then the model has been used to check the stability against uplift and piping for New Esna Barrage on Nile River in Egypt as one of the existing barrage, which has been provided with one intermediate filter. After the stability of the barrage against these forces has been confirmed, many alternative designs for its floor have been studied to investigate where the exist solution from the optimum one. These alternative designs include different lengths and location for the filter and an upstream cut-off with different depths. Finally the finite element model has been applied over a wide range of variables for a comparison study between the effect of using one and two plane filters upon uplift pressures, hydraulic exit gradients and seepage discharges

Field investigation of discolouration material accumulation rates in live drinking water distribution systems

Cook, Dominic January 2007 (has links)
Discolouration is the biggest cause of aesthetic customer contacts in the water industry. This project was designed to develop new insight and understanding into discolouration, by investigating the impact ofdifferent factors on discolouration material accumulation rates and the effectiveness of traditionaJly used mains cleaning and rehabilitation methods, through detailed studies of live distribution systems. Analysis ofdiscolouration customer contacts and burst incidents covering a five year period for two water companies and pipe asset data base for a water company's entire region, at the District Meter Area (DMA) level, shows little correlation between the number ofdiscolouration events and pipe properties, indicating complex inter relationships between a number offactors. Discolouration accumulation rates were investigated through repeat full zonal flushing in two DMAs. Discolouration material was seen to accumulate at the same rate in all areas ofthe networks, as a factor ofwater quality, until equilibrium was reached between accumulation and erosion rates. This equilibrium was as a factor ofdaily conditioning shear stress, whereby pipes affected by a low daily conditioning shear stress continued to accumulate material longer than pipes with a higher daily conditioning shear stress and thicker layers ofdiscolouration material were fonned. Long tenn turbidity monitoring in five DMAs has showed that the amplitude ofa daily turbidity cycle, based on resuspension and corrosion processes, can be used to assess the effectiveness of network rehabilitation. A greater improvement in the reduction ofdiscolouration potential was seen in the full zonal flush DMAs, than in DMAs that were rehabilitated under the Distribution Operation and Maintenance Strategy (DOMS), at far greater cost. Using the principles of change in shear the methodology for a simple modelling tool was designed and field tested to predict the discolouration response to valve movements, to enable valve operations to be managed to reduce discolouration risk.

Risk and the designer : an investigation into what affects risk-taking and errors in the design of hazardous offshore installations using an experience sampling methodology

Beesley, Nicholas John January 2008 (has links)
This exploratory piece of work has disclosured certain predictive affects associated with a designer's use of risky protocols ('Risky') and cognitive error ('Error'). The implication of this organisational study on risk and cognitive error (Simon, Hillson & Newland, 1997) rests in the potential for theory development in the role of the offshore designer. The focus of this research has been to investigate how designers of hazardous installations, in particular offshore platforms, might influence the design end users' safety performance. The risk paradigm provided the conceptual framework for making sense ofthe designer's attitude to risk. This exploratory research investigates if individual personality differences and the individual perception of risk and other constructs affect cognitive error and the use of certain risky design protocols. This study has extended the use of the Experience Sampling Methodology (ESM) into the complex design enivironment. A sample population of 167 design engineers from 55 design teams was assessed in situ, up to four times per day over four working weeks. The sample that participated in this organisational study was drawn from industrial sectors that involved the high hazard nuclear and offshore oil and gas industry. This research has been conducted in a number of stages, applying both conventional questionnaires and the novel electronic diary based techniques. Questionnaires were used to measure stable factors through individual maturity, such as personality, and an experience sampling methodology, using personal digital assistants that were used to record momentary data. The stable factors were analysed using exploratory factor analysis to derive 14 emergent factors from the six constructs examined. Multilevel hierarchical linear modelling, using HLM6, was applied to these factors and the momentary diary data. Whilst the research was primarily interested in the individual designer, there were certain interactions between the sample units that characterised the multilevel structure of the investigation. The momentary data nested within individuals, and within design teams showed that personality is significant in predicting cognitive error reports and the use of risky design protocols. Analyses indicated that emotionally stable individuals commit fewer errors, whereas extraverted, open and agreeable personality traits and the key job characteristic of job autonomy and the organisational safety climate are significant predictors in the use of risky design protocols.

A study of shock wave transmission in pipe lines with particular reference to surge tanks

Hawkins, Peter January 1953 (has links)
No description available.

Analysis of multicomponent VSP data for shear-wave anisotropy

Campden, David A. January 1990 (has links)
Propagation characteristics of split shear-waves are studied to gain an understanding of the effects of attenuation anisotropy. It is shown that, compared to velocity anisotropy, attenuation anisotropy is a more difficult quantity to measure, being dependent on the attenuation of the faster split shear-wave and the velocity anisotropy. Measuring changes in attenuation anisotropy from repeated shear-wave experiments is also considered, with a view to monitoring EOR processes. Three automatic methods for measuring shear-wave splitting parameters are developed and tested on a synthetic VSP data set contaminated with different amounts of random noise. Standard signal processing techniques are investigated using the synthetic data, to determine whether they distort or improve observations on shear-wave splitting. VSPs from a North Sea gas field and the Geysers geothermal zone, California, are analysed for shear-wave splitting. The North Sea VSP consisted of four wide offset source locations, relying on <i>P</i>-waves being mode-converted to <i>SV</i>-waves at the top of the cap-rock overlying the gas saturated reservoir sands. Fast shear-wave polarizations and time delays are measured from shear-waves in the reservoir region using the three automatic techniques previously developed. Results suggest a predominant crack orientation of N47<SUP>o</SUP>W agreeing with maximum horizontal stress directions found from earthquake focal mechanisms and borehole breakout data. One of the main problems associated with these North Sea VSPs was that the source to borehole azimuths were very nearly parallel to the crack strike, resulting in poor observations of shear-wave splitting.

Application of two-dimensional cellular automaton lattice-gas models to the simulation of hydrodynamics

Wylie, Brian J. N. January 1990 (has links)
Hydrodynamic equations are notoriously difficult to solve, both analytically and computationally, therefore less complicated methods, drawing on the power of cellular automata and lattice-gases, are introduced. Their combined ability to capture the fundamental properties of fluid dynamics in an inherently simple manner is discussed. The <i>FHP7</i> cellular automation lattice-gas model of Frisch, Hasslacher and Pomeau, which will form the basis for the subsequent simulations, is described in detail, with a more general covering of the associated models. The scalable and flexible computational power of the transputer-based ECS multicomputer, and how this may be applied to the lattice-gas simulations at hand is addressed. The distributed multiprocessor architecture provides unique challenges, such that the implementation might achieve its potential. It is found that a straightforward one-dimensional geometric decomposition of the lattice, in conjunction with the loosely-synchronous nature of the distributed update, provides a natural load-balancing, and highly scalable efficiency. Visualisation of the development of the hydrodynamic features captured by the simulations, such that their content may be clearly extracted is also addressed. Many interesting transient and dynamic features, often occurring on time-scales which make their analysis by other methods difficult, are easily identified. Those occasionally found to be the result of artifacts, perhaps in the initialisation of the simulation are quickly identified, such that the simulations may be refined. Elementary static systems and flows are designed, such that the ability of the <i>FHP7</i> lattice-gas to model incompressible hydrodynamics, and its multicomputer implementation, are verified against the theoretically and experimentally expected behaviour. Subsequently, more complex flow configurations involving obstructions and jets, generally beyond the limits of current analytic techniques are constructed, and found to qualitatively match experimental visualisations. No lattice-gases are currently known to accurately model compressible fluid dynamics completely, and the ultimate cause of this limitation still requires clarification. The behaviour of the <i>FHP7</i> lattice-gas, in réimes where compressibility effects are expected to be important, is investigated with the aim of identifying those aspects of its microdynamics which cause breakdown of its macrodynamics.

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