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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.
61

Multiscale modelling of snow depth over an agricultural field in a small catchement in southern ontario, canada.

Neilly, R. Michael A. January 2011 (has links)
Snow is a common overlying surface during winter-time and the redistribution of snow by wind is a very important concept for any hydrological research project located within the cryosphere. Wind redistributes snow by eroding it from areas of high wind speed, such as ridge tops and windward slopes, and deposits it in areas of lower wind speeds, such as the lees of ridge tops, vegetation stands, and topographic depressions. The accurate modelling of blowing snow processes such as erosion, deposition, and sublimation have proven to be rather problematic. The largest issue that many modellers must deal with is the accurate collection of solid precipitation throughout the winter season. Without this, incorrect energy and mass balances can occur. This thesis makes use of a new method of acquiring solid precipitation values through the use of an SR50a ultrasonic snow depth sensor and then incorporates it into a version of the Cold Regions Hydrological Model (CRHM) which includes the Prairie Blowing Snow Model (PBSM) and the Minimal Snowmelt Model (MSM) modules. The model is used to simulate seasonal snow depth over an agricultural field in southern Ontario, Canada and is driven with half-hourly locally acquired meteorological data for 83 days during the 2008-2009 winter season. Semi-automated snow surveys are conducted throughout the winter season and the collected in situ snow depth values are compared to the simulated snow depth values at multiple scales. Two modelling approaches are taken to temporally and spatially test model performance. A lumped approach tests the model‟s ability to simulate snow depth from a small point scale and from a larger field scale. A distributed approach separates the entire field site into three hydrological response units (HRUs) and tests the model‟s ability to spatially discretize at the field scale. HRUs are differentiated by varying vegetation heights throughout the field site. Temporal analysis compares the simulated results to each day of snow survey and for the entire field season. Model performance is statistically analyzed through the use of a Root Mean Square Difference (RMSD), Nash-Sutcliffe coefficient (NS), and Model Bias (MB). Both the lumped and distributed modelling approaches fail to simulate the early on-set of snow but once the snow-holding capacities are reached within the field site the model does well to simulate the average snow depth during the latter few days of snow survey as well as throughout the entire field season. Several model limitations are present which prevent the model from incorporating the scaling effects of topography, vegetation, and man-made objects as well as the effects from certain energy fluxes. These limitations are discussed further.
62

A study of water turbine power efficiency suitable for periodical ocean current in Penghu sea region

Lin, Chang-ching 06 September 2010 (has links)
This thesis investigates a horizontal water turbine blade designed to suit the periodical ocean current in Penghu sea region. Blade element momentum theory is exploited to design blade profiles. Then, CFD software, Fluent, is used to obtain such simulation result for torque, power, and efficiency. Firstly, performance of turbines with various cross-sectional profiles is discussed. Then, we use quasi-steady method to simulate power output of turbines from periodical ocean current and estimate how much ocean current energy we can obtain per day. Further, the performance of a turbine installed for different immersed depth from the surface is investigated. Our studies show that airfoil profile NACA6409 can outperform others in terms of high lift/drag ratio under low Reynolds number, and better hydrodynamic properties help the water turbine obtain higher torque and power output. A water turbine designed by using NACA6409, at R=1 m, at uniform velocity=2 m/s is estimated to generate 5KW output power. On condition of periodical current flow, the ebb tidal current can rotate water turbine, but power output is only 0.54 times of flood tidal current. The water turbine can generate more power when it is sited in deeper water, and less torque when it is sited near the water surface.
63

A Systematic Investigation of Shear Connections Between Full-Depth Precast Panels and Precast Prestressed Bridge Girders

Brey, Robert W. 2010 May 1900 (has links)
Full-depth precast panels are used in concrete bridges to provide several benefits such as faster construction, lower cost and reduced constructional hazard. However, one construction drawback is that connectors are required to transmit horizontal shear across the interface between the girder and deck. Shear connector performance is characterized by a series of experiments performed on part of a bridge system that mimics a full-depth precast deck on concrete girder with a pocket-connector-haunch system. Following initial breakaway of the adhesive bond within the haunch region, the specimens slide with frictional resistance provided by the clamping force of the anchor bolt. This leads to bolt yield with an observed sliding friction coefficient of 0.8 (+/- 20%) with lower values occurring at higher displacements. It is concluded that for a viable connector system to be developed a key feature is to have sufficient stirrups in the neighborhood of the anchor bolt to form a non-contact splice and to ensure the high pull-out force can be sustained without leading to premature beam failure. The successful implementation of a full-depth precast deck-panel system requires the use of a viable design methodology that properly accounts for system behavior. The design of a deck-haunch-girder system uses a truss modeling approach to design for the shear forces created by service loading. The truss model approach is considered more suitable for a concrete member due to the premise that the member will be substantially cracked at an ultimate limit state and that traditional beam theory does not account for the decreased ability of shear stresses to transfer across open cracks. Experimental results from Chapter II, such as the friction coefficient mu, are used along with a previously developed crack angle model to layout the geometry of the truss within a deck-panel span. Design solutions are presented utilizing the Rock Creek Bridge in Parker County, Texas as an example structure.
64

Sensitivity Study of the Effects of Mineral Dust Particle Nonsphericity and Thin Cirrus Clouds on MODIS Dust Optical Depth Retrievals and Direct Radiative Forcing Calculations

Feng, Qian 2010 August 1900 (has links)
A special challenge posed by mineral dust aerosols is associated with their predominantly nonspherical particle shapes. In the present study, the scattering and radiative properties for nonspherical mineral dust aerosols at violet-to-blue (0.412, 0.441, and 0.470 μm) and red (0.650 μm) wavelengths are investigated. To account for the effect of particle nonsphericity on the optical properties of dust aerosols, the particle shapes for these particles are assumed to be spheroids. A combination of the T-matrix method and an improved geometric optics method is applied to the computation of the single-scattering properties of spheroidal particles with size parameters ranging from the Rayleigh to geometric optics regimes. For comparison, the Mie theory is employed to compute the optical properties of spherical dust particles that have the same volumes as their nonspherical counterparts. The differences between the phase functions of spheroidal and spherical particles lead to quite different lookup tables (LUTs) involved in retrieving dust aerosol properties. Moreover, the applicability of a hybrid approach based on the spheroid model for the phase function and the sphere model for the other phase matrix elements is demonstrated. The present sensitivity study, employing the Moderate Resolution Imaging Spectroradiometer (MODIS) observations and the fundamental principle of the Deep Blue algorithm, illustrates that neglecting the nonsphericity of dust particles leads to an underestimate of retrieved aerosol optical depth at most scattering angles, and an overestimate is noted in some cases. The sensitivity study of the effect of thin cirrus clouds on dust optical depth retrievals is also investigated and quantified from MODIS observations. The importance of identifying thin cirrus clouds in dust optical depth retrievals is demonstrated. This has been undertaken through the comparison of retrieved dust optical depths by using two different LUTs. One is for the dust only atmosphere, and the other is for the atmosphere with overlapping mineral dust and thin cirrus clouds. For simplicity, the optical depth and bulk scattering properties of thin cirrus clouds are prescribed a priori. Under heavy dusty conditions, the errors in the retrieved dust optical depths due to the effect of thin cirrus are comparable to the assumed optical depth of thin cirrus clouds. With the spheroidal and spherical particle shape assumptions for mineral dust aerosols, the effect of particle shapes on dust radiative forcing calculations is estimated based on Fu-Liou radiative transfer model. The effect of particle shapes on dust radiative forcing is illustrated in the following two aspects. First, the effect of particle shapes on the single-scattering properties of dust aerosols and associated dust direct radiative forcing is assessed, without considering the effect on dust optical depth retrievals. Second, the effect of particle shapes on dust direct radiative forcing is further discussed by including the effect of particle nonsphericity on dust optical depth retrievals.
65

Guiding the Eye: A Non-photorealistic Solution for Controlling Viewer Interest

Piedra, Pedro A. 2010 December 1900 (has links)
In film and still photography, depth of field control is often employed to control viewer interest in an image. This technique is also used in computer animation, but, in a medium where artists have near infinite control, must we rely on replicating photorealism? This research is a viable, non-photorealistic solution to the problem of directing viewer interest. Vision is directed by reducing superfluous visual information from parts of the image, which do not directly affect the depictive meaning of that image. This concept is applied to images and animations rendered from three-dimensional, computergenerated scenes, where detail is defined as visual information pertaining to the surface properties of a given object. A system is developed to demonstrate this concept. The system uses distance from a user-defined origin as the main mechanism to modulate detail. This solution is implemented within a modeling and shading environment to serve as a non-photorealistic, functional alternative for depth of field. This approach is conceptually based on a model of human vision, specifically, the relationship between foveal and peripheral vision, and is artistically driven by various works in the disciplines of painting and illustration, that through the careful manipulation of detail, control interest and understanding within the image. The resulting images and animations produced by this system provide viable evidence that detail modulation can be used to control effectively viewer interest in an image eliminating the need to use photographic techniques like depth of field.
66

Simulation and Economic Screening of Improved Oil Recovery Methods with Emphasis on Injection Profile Control Including Waterflooding, Polymer Flooding and a Thermally Activated Deep Diverting Gel

Okeke, Tobenna 2012 May 1900 (has links)
The large volume of water produced during the extraction of oil presents a significant problem due to the high cost of disposal in an environmentally friendly manner. On average, an estimated seven barrels of water is produced per barrel of oil in the US alone and the associated treatment and disposal cost is an estimated $5-10 billion. Besides making oil-water separation more complex, produced water also causes problems such as corrosion in the wellbore, decline in production rate and ultimate recovery of hydrocarbons and premature well or field abandonment. Water production can be more problematic during waterflooding in a highly heterogeneous reservoir with vertical communication between layers leading to unevenness in the flood front, cross-flow between high and low permeability layers and early water breakthrough from high permeability layers. Some of the different technologies that can be used to counteract this involve reducing the mobility of water or using a permeability block in the higher permeability, swept zones. This research was initiated to evaluate the potential effectiveness of the latter method, known as deep diverting gels (DDG) to plug thief zones deep within the reservoir and far from the injection well. To evaluate the performance of DDG, its injection was modeled, sensitivities run for a range of reservoir characteristics and conditions and an economic analysis was also performed. The performance of the DDG was then compared to other recovery methods, specifically waterflooding and polymer flooding from a technical and economic perspective. A literature review was performed on the background of injection profile control methods, their respective designs and technical capabilities. For the methods selected, Schlumberger's Eclipse software was used to simulate their behavior in a reservoir using realistic and simplified assumptions of reservoir characteristics and fluid properties. The simulation results obtained were then used to carry out economic analyses upon which conclusions and recommendations are based. These results show that the factor with the largest impact on the economic success of this method versus a polymer flood was the amount of incremental oil produced. By comparing net present values of the different methods, it was found that the polymer flood was the most successful with the highest NPV for each configuration followed by DDG.
67

none

Lee, Tai-long 22 August 2006 (has links)
Abstract The broadcast industry is the non-profit organization, with disseminates the news, provides the entertainment, may change audience's manner and the behavior, widespread also is profound to society's influence, therefore, broadcasts the organization to have specially to emphasize the specialty, regarding each kind of specialized talented person's demand is earnest. How however has the series to gather broadcasts the organization complex specialized talented people, and obeys leader's command, unitedly aims at a common goal struggle, broadcasts the leader to have to be skilled in the leadership series imperial method and the skill. Moreover, because the broadcast frequency channel is open, each kind of broadcasting station sets up one after another, forms hundred school of thought contends the situation, the broadcast industry must survive in the competition management environment, and has the competitive advantage, the leader must grasp the current situation pulsation, effectively carries on the organization to transform. Broadcasts the leader to be supposed to relate from the crowd embarks, understanded the solution organization team characteristic, nimbly utilizes theleadership management the technology and the main point, can displaythe team strength, strengthens the staff achievements, achieves continues forever the development goal, then has the frontageinfluence to the national society. Although the broadcast industry is suitable the crowd relations which organizes to the enterprise, but broadcasts the training and the common business management which the leader receives alien, they also must consider the broadcast industry because the dissemination science and technology unceasingly progresses, brings each kind of impact and faces each challenge. Therefore, this research specially by the home well-known five broadcasting station's manager, the department manager and the basic unit staff, the altogether twenty artificial research objects, and with the depth document interview method, carries on time the transformation from the broadcast organization, discusses the leader special characteristic and the team interaction and the team and the member achievements connection and so on the subject, even influence which develops to the whole organization, hoped takes advantage of this describes the broadcast industry management and the management strategy and the blueprint, provides individual or the social reform, and is ambitious the investment broadcast enterprise development direction. But this research discovery, broadcasts the leader to be allowed because the person, because of events, to adopt the different condition leadership way as circumstances permit, but like can unfold the transformation leadership the special characteristic, regardless of to the team strength display also or the team and the staff achievements, all has reveals the influence effect. Essential character:¡GThe organization transforms, The leadership, The team, The achievements, Depth interview.
68

Using Eddy Current Testing Method to Evaluate the Depth of the Defects in the Heat Exchanger Tubes

Jong, Ming-hsiung 29 August 2006 (has links)
For the evaluation of non-ferrous heat exchanger tube, there are many non-destructive testing methods; however, the eddy current testing (ECT) method is the most popular one. By using of ECT, you may find out the defects existing inside or outside the tube wall, diagnose the heat exchanger system and find out the latent problems. The problem is that an improper signal analysis will result in error in the range of 15〜25% of the tube wall thickness, or even over 40% error. This is a great discouragement to the ECT inspectors, and will reduce the confidence of the proprietors of power plants or petro-chemical industries to the use of ECT. Therefore, in this thesis, the study is mainly focus on the problems of the aluminum brass tubes in condenser using ECT method. This thesis will analyze the causes of error of aluminum brass tubes when using ECT, prepare calibration and reference tubes, and test them using eddy current instruments. The relationship among the raw data with volts, phase angle and depth has been found. Two data evaluation methods are developed, one is the defect depth modification equation and the other is the auxiliary evaluation curve. The new methods are proved to be more accurate and practical in the evaluation of heat exchanger tube after more than one year of verification by field testing in the power plant. The results obtained in this thesis are very helpful to reduce the probability of tube failure.
69

The application of The Depth-from-Focus Techniques

PAN, JIA-WEI 12 July 2000 (has links)
Three different topics associated with their respective applications are proposed in this thesis. The first application is the implementation of a PC-Based Vision Inspecting Machine. The Second topic is to carry out a advanced Auot-focusing technology. And the third topic is focused on the implementation of a Depth-from-Focus Technology.
70

A Preliminary Study of Carbonate Chemistry in the Kuroshio regime off the Eastern Taiwan

Li, Fu-Shiang 26 June 2003 (has links)
In order to understand the input of South China Sea Water (SCSW) onto the Kuroshio and the distributions of carbonate parameters in Kuroshio Water (KW), the temperature, salinity, pH and TCO2 were measured for the seawater samples collected from the Kuroshio regime off eastern Taiwan during the cruise ORI 650 in July 2002. The distributions of temperature and salinity show that a front existed approximately along 123.5ºE, which separated the influenced KW by SCSW from typical KW. East of this front the water is characterized by temperature and salinity of KW, while west of it the water was mainly a mixture of the SCSW and the KW. After flowing out from the Luson Straint, the SCSW deflected northward along the east cost of Taiwan, and continuously mixed with the KW. The mixing of SCSW with KW could be traced northward as far as 22ºN and reach as deep as 1250m. Based on the measured carbonate data, the calculated IC/OC ratio ranges from 22% to 23% in the deep water of the Kuroshio region. Additionally, the penetration depth of anthropogenic CO2 was estimated to be about 1200m by using Chen¡¦s equation (Chen et al., 1986). Furthermore, the difference of pCO2 between atmosphere and surface seawater was evaluated to be about -5matm, indicating that the surface water in the study area was nearly saturated with pCO2 during the sampling period.

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