Detailed current profiles between the sediment-water interface and 20 cm above it reveal a viscous sublayer in the bottom boundary layer on the Oregon continental shelf. Data from three field experiments are used to test fundamental assumptions about boundary layer flow in the ocean. The first study, discussed in Chapter 1, evaluates the hypothesis that, in the absence of the obvious influence of topographic irregularities, the flow behaves like a universally similar, neutrally-buoyant flow over a smooth wall. The second study, discussed in Chapter 2, evaluates the influence which irregular small-scale topography may have on the near-bed flow, while the third, discussed in Chapter 3, examines streamwise velocity fluctuations in the viscous Sublayer and buffer layer and evaluates the hypothesis that spectra from the viscous sublayer and buffer layer of laboratory and geophysical boundary layer flows can be reduced to universal forms. although the thickness of the viscous sublayer scales with v/u, as required by universal similarity, the non-dimensional sublayer thickness is not as constant as in neutrally-buoyant laboratory flows. Even in the absence of the obvious effects of bottom irregularities, the near-bed flow is not as simple as smooth-walled boundarylayer flows in the laboratory. In the second study, it is shown that when the near-bed flow experiences resistance due to form drag as well as skin friction, the constant stress boundary layer assumption is not valid close to the sediment-water interface. Th the third study, it is shown that non-dimensionalized spectra of streamwise velocity fluctuations in the viscous sublayer and buffer layer at the ocean floor are very similar to those found in the laboratory. / Graduation date: 1982

No description available.

An experimental investigation of transition in boundary layer flows under the influence of various freestream conditions is described. Velocity profiles are obtained automatically by means of a stepper-motor driven traverse mechanism which carries a hot wire probe connected to a constant temperature anemometer and associated instrumentation. This was achieved by use of a data acquisition and control facility centred around a microcomputer with a Eurocard rack mounted extension. The automatic boundary layer traverse is software controlled and the data obtained is stored in a disc file for subsequent analysis and graphical display. As an integral part of this facility a successful method of obtaining reliable intermittency values from a hot wire signal was developed. The influence of freestream turbulence and pressure gradient upon transition within a boundary layer developing on a flat plate is elucidated by a series of controlled experiments. From the data accumulated, the concept of statistical similarity in transition regions is extended to include moderate non-zero pressure gradients, with the streamwise mean intermittency distribution described by the normal distribution function. An original correlation which accounts for the influence of freestream turbulence in zero pressure gradient flows, and the combined influence of freestream turbulence and pressure gradient in adverse pressure gradient flows, on the transition length Reynolds number R, is presented. (The limited amount of favourable pressure gradient data precluded the extension of the correlation to include favourable pressure gradient flows). A further original contribution was the derivation of an intermittency weighted function which describes the development of the boundary layer energy thickness through the transition region. A general boundary layer integral prediction scheme based on existing established integral techniques for the laminar and turbulent boundary layers with an intermittency modelled transition region, has been developed and applied successfully to a range of test data.

No description available.

No description available.

No description available.

The work addresses an important question of whether a discontinuity in wall curvature can cause boundary layer separation at transonic speeds. Firstly an inviscid transonic flow in the vicinity of a curvature break is analysed. Depending on the ratio of the curvatures, several physically different regimes can exist, including a special type of supersonic flows which decelerate to subsonic speeds without a shock wave, transonic Prandtl-Meyer flow and supersonic flows with a weak shock. It is shown that if the flow can be extended beyond the limiting characteristic, it subsequently develops a shock wave. As a consequence, a fundamental link between the local and the global flow patterns is observed in our problem. From an asymptotic analysis of the Karman-Guderley equation it follows that the curvature discontinuity leads to singular pressure gradients upstream and downstream of the break point. To find these gradients, we perform computations and employ both the hodograph method and the phase portrait technique. The focus is then turned to analysing how the given pressure distribution affects the boundary layer. It is demonstrated that the singular pressure gradient, which appears to be proportional to the inverse cubic root of the distance form the curvature break, corresponds to a special resonant case for the boundary layer upstream of the singularity. Consequently, the boundary layer approaches the interaction region in a pre-separated form. This changes the background on which the viscous-inviscid interaction develops, allowing to construct an asymptotic theory of the incipient viscous-inviscid interaction for our particular problem. The analysis of the interaction which takes place near a weak curvature discontinuity leads to a typical three-tier structure. It appears to be possible to obtain analytical solutions in all the tiers of the triple deck when the curvature break is small. As a result, the interaction equation may be derived in a closed form. The analytical solution of the interaction equation reveals a local minimum in the skin friction distribution, suggesting that a local recirculation zone can develop near the curvature break. In fact, the recirculation zone is formed when the ratio of the curvatures is represented as a series based on negative powers of the logarithm of the Reynolds number. This proves that a discontinuity in wall curvature does evoke boundary layer separation at transonic speeds. The result is fundamentally different from the effect of a curvature break at subsonic and supersonic speeds, as no separation takes place in these two regimes (Messiter & Hu 1975).

Lakes represent a major topographic feature in southern Manitoba, having a direct meteorological influence on a number of communities, including Winnipeg. Therefore, it is crucial that we have an understanding of the characteristics of lake breezes in the region and the influence that they can have on local weather. The Effects of Lake Breezes on Weather in Manitoba (ELBOW-MB) project in 2013 sought to fill in the gaps in our current knowledge of lake breezes in southern Manitoba. The primary research objectives of this thesis are to: (1) provide a radar-based climatology of lake breeze frequency and characteristics and, (2) to characterize the detailed thermodynamic and kinematic properties of lake breezes and lake-breeze fronts. The two results papers presented within this thesis represent the first detailed analysis of lake breezes in southern Manitoba and help to fill important gaps in our knowledge about the occurrence and characteristics of lake-breeze circulations. / February 2016

Approved for public release; distribution is unlimited. / One of the major problems with a Limited Area Model is the introduction of error from the lateral boundaries. The boundary condition provides a source of forcing to the interior of the model. This forcing typically originates from a global model such as NOGAPS. The transition at the boundary from one model to another invariably produces errors. Traditionally, the way to minimize boundary error is to move the boundary as far away from the area of interest as possible. In this way, the errors do not have time to infest the LAM with "bad" information. Moving the boundary far away from the area of interest increases the computational forecast load and decreases its timeliness. This study looks at how close the lateral boundary can be to minimize computational time and still maintain a forecast that is useful. It was found that when the entire inner COAMPS nest was analyzed, the differences between the control forecast and the test forecast where within the natural variability of the control grid. It was also found that there where localized areas within the model domain that differed between the control domain and the test domain by up to 20 mb for the sea level pressure after a six day forecast. / Lieutenant, United States Navy

Chu Shun Yin. / "August 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (p. 55-60). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.