Thesis (Ph. D)--University of Washington, 1999. / Vita. Includes bibliographical references (p. 291-296).

A new buoyant jet model is presented in this thesis to simulate the trajectory and dilution of a fluid from a single port or line source. The new features include: A generalised derivation of the governing equations so that buoyant jets discharged from a source of any shape can be modelled within the one framework, and the effects of high-frequency internal waves on the motion of the buoyant jet. Past buoyant jet models were constructed for specific cases and their application is necessarily restricted. In this thesis, a new model is developed in a Lagrangian framework that can be applied to buoyant jet discharges at any angle into ambient waters that may be stratified or unstratified, flowing or stagnant. The model is validated using both laboratory and field data. Furthermore, the model is applicable to the continuous discharge of a buoyant jet from line, axisymmetric or elliptic sources and to the instantaneous discharge of a spherical puff. No previously published model is capable of unifying and solving all of these problems within the one framework. Transforming the governing equations to their non-dimensional form shows that the trajectory and dilution of discharges from line or axisymmetric sources or of spherical puffs into a flowing, stratified ambient environment are uniquely specified using three parameters. These are: the non-dimensional size of the outlet port, the relative importance of the initial fluxes of momentum and buoyancy, and the number of orthogonal planes through which entrainment can occur. This is a significant advance in the understanding of the processes affecting buoyant jets. When high-frequency internal waves are present in the receiving waters they can have significant effects on the buoyant jet. These effects are incorporated into the present model. Using data obtained from an experiment conducted off Sydney the effects of internal waves on the height of rise and dilution of the buoyant jet were found to exceed a factor of two. Consequently, it is important that the effects of internal waves (when present) be incorporated into any buoyant jet model.

In the event of a small break loss of coolant accident (SBLOCA) in a nuclear reactor, cold fluid is injected through the reactor system high pressure injector to compensate for the coolant loss. When this flow rate is less than a critical value, however, the hot fluid in the cold leg penetrates into the vertical injection line in a process called buoyant backflow. Because the resulting penetrations induce thermal stresses in the pipe, the presence of backflow in the injection lines is potentially significant. Since these penetrations could potentially damage the pipe, it was the purpose of this study to evaluate the backflow behavior. To this end, both the critical injection conditions and the subcritical penetration depth were experimentally determined through flow simulation in a 1/5 scale model. In addition, the experimental trends wi-re modeled theoretically. By matching the theoretical results to the experimental data, it was determined that backflow began below a critical Froude number of .65 and increased in depth with the negative logarithm of the injection velocity. The agreement between theory and experiment was excellent. For a certain class of reactor systems, the full scale Froude numbers were then compared to the critical value obtained in the analysis. For the systems involved in this comparison, the full scale Froude numbers were shown to be less than .65 for all practical flow rates. As a consequence, buoyant backflow is expected within the injection lines of these reactors, under safety injection conditions. / Graduation date: 1991

The buoyancy (or density = mass volume-1) of marine larval fish is influenced by their nutritional status, starved larvae being less dense than fed larvae of like age. Buoyancy has, therefore, been proposed as an indicator by which to assess the nutritional condition of marine fish larvae in experiments and in situ. It has also been hypothesized that larval fish experiencing advanced starvation will exhibit increased density due to water loss resulting from osmoregulatory breach and failure. The magnitude of osmoregulation-related changes in density has not been examined and its influence on interpretations of nutritional condition and vertical distributions are unknown. Through a series of controlled laboratory experiments performed on larvae of cod (Gadus morhua L.), I developed evidence that osmoregulatory breach and failure has a strong positive effect on the density of larval fish, and that this effect on density is not limited to larvae experiencing advanced stages of starvation. These effects of osmotic breach and failure are sufficient to obscure effects resulting exclusively from nutritionally caused changes in density. Hence, if not identified and controlled these osmotically driven density changes can bias parameterization of buoyancy-related condition indices. I developed methods for isolating nutritional and osmotic effects. This facilitated the calibration of a nutritionally based density index with which to evaluate the nutritional state of cod larvae. Comparison of the calibrated density assay with a suite of widely used indices of condition (morphometric, behavioural and biochemical) showed density to be superior in its capacity to correctly classify larvae with respect to their nutritional state. The density index was also less subject to bias resulting from uncontrolled changes in larval size. A linear regression model based on these findings was developed to assess the relationship between density as an index of condition and near-term larval

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Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Civil Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 269-271. / Ph.D.

No description available.

No description available.

The purpose of this study was to examine the conceptual understandings of 55 elementary preservice teachers for the concept of buoyancy. This study used Ausubel’s Assimilation Theory (Ausubel, 1963) as a framework for a 15-week intervention that used pre/post concept maps (Cmaps), pre/post face-to-face semi-structured interviews, and drawings as evidences for change of formation of cognitive structures. Using a convergent parallel design and mixed methods approach, preservice teachers’ conceptions were analyzed using these evidences. Results of the study show that preservice teachers held both scientific conceptions and misconceptions about buoyancy as a force before and after an instructional intervention. Of importance were the existence of robust misconceptions about buoyancy that included inaccurate scientific knowledge about the foundational concepts of gravity, weight, mass, and density. The largest gains in scientific knowledge included the concepts of gravity, surface area, opposing forces, and the buoyant force. These concepts were consistently supported with evidence from post-concept maps, post, semi-structured interviews, and drawings. However, high frequencies of misconceptions were associated with these same aforementioned concepts as well as additional misconceptions about buoyancy-related concepts (i.e., weight, density, displacement, and sinking/floating). A paired t test showed a statistically significant difference (t = -3.504, p = .001) in the total number of scientifically correct concepts for the pre-concept maps (M = 0.51, SD = .879) and post-concept maps (M = 1.25, SD = 1.542). The Cohen’s d effect size was small, .47. Even through gains for the pre/post concept maps were noted, a qualitative analysis of the results indicated that not only were there serious gaps in the participant’s scientific understanding of buoyancy, after the instructional intervention an increased number of misconceptions were presented alongside the newly learned concepts. A paired t test examining misconceptions showed that there was a statistically significant difference (t = -3.160, p = .003) in the total number of misconceptions for the pre-concept maps (M = 2.709, SD = 1.449) and post-concept maps (M = 3.363, SD = 2.094) after the intervention. The Cohen’s d effect size was small, .43. Taken together, these results revealed that, in general, the preservice teachers had understandings of buoyancy that align with children in preschool and elementary school (Biddulph and Osborne, 1983; Grimellini-Tomasini et al., 1990; Halford, Brown & Thompson, 1986; Hsin and Wu, 2011; Kohn, 1993; Rappolt-Schlichtmann et al., 2007; Yin et al., 2008). Based on these findings, implications for this study suggest that elementary preservice teacher candidates should be carefully screened to ensure they have mastered foundational scientific knowledge that they are expected to teach to children. As such knowledge is a prerequisite to the development of pedagogical content knowledge, it is unlikely that large numbers of robust misconceptions will be significantly reduced or eliminated during a science methods course that is designed to focus on pedagogical content knowledge.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1982 / Includes bibliographical references. / by Paul Douglas Symolon. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Mechanical Engineering