Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, September 2003. / Thesis advisor(s): Wendell A. Nuss, David S. Brown. Includes bibliographical references (p. 65-66). Also available online.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution. / Includes bibliographical references (p. 186-188).

Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Isaac Kaminer, Vladimir Dobrokhodov. Includes bibliographical references (p. 67). Also available online.

Gap, outflow, or Squamish wind, is the cold low level seaward flow of air through fjords which dissect the coastal mountain barrier of northwestern North America. These flows, occurring mainly during winter, can be strong, threatening safety, economic activity and comfort. Howe Sound gap winds were studied using a combination of observations and several types of models. Observations of winds in Howe Sound showed that gap wind strength varied considerably along the channel, across the channel and vertically. Generally, winds increase down the channel, are strongest along the eastern side, and are below 1000 m depth. Observations were unable to answer all questions about gap winds due to data sparseness, particularly in the vertical direction. Therefore, several modelling approaches were used. The modelling began with a complete 3-dimensional quasi-Boussinesq model (CSURAMS) and ended with the creation and testing of models which are conceptually simpler, and more easily interpreted and manipulated. A gap wind simulation made using RAMS was shown to be mostly successful by statistical evaluation compared to other mesoscale simulations, and by visual inspection of the fields. The RAMS output, which has very high temporal and spatial resolution, provided much additional information about the details of gap flow. In particular, RAMS results suggested a close analogy between gap wind and hydraulic channel flow, with hydraulic features such as supercritical flow and hydraulic jumps apparent. These findings imply gap wind flow could potentially be represented by much simpler models. The simplest possible models containing pressure gradient, advection and friction but not incorporating hydraulic effects, were created, tested, and found lacking. A hydraulic model, which in addition incorporates varying gap wind height and channel geometry, was created and shown to successfully simulate gap winds. Force balance analysis from RAMS and the hydraulic model showed that pressure gradient and advection are the most important forces, followed by friction which becomes an important force in fast supercritical flow. The sensitivity of gap wind speed to various parameters was found from sensitivity tests using the hydraulic model. Results indicated that gap wind speed increases with increasing boundary layer height and speed at the head of channel, and increasing synoptic pressure gradient. Gap wind speed decreases with increasing friction, and increasing boundary layer height at the seaward channel end. Increasing temperature dilterences between the cold gap wind air and the warmer air aloft was found to increase the variability of the flow — higher maximum but lower mean wind speeds.

No description available.

High frequency turbulent temperature measurements were performed above clipped grass in the lower atmospheric surface layer in conjunction with three-dimensional turbulent velocities. Measurements were also made of turbulent temperature inside a corn canopy and at the canopy top. The 500Hz temperature time series were collected over periods of varying intervals, to a maximum of 24 hours. / The multifractal analysis was performed on several datasets. First scaling properties of the temperature and the velocity fields were examined. Our results suggest that scaling is not observed throughout the entire range but on different regimes. The physically related regimes corresponding to the clipped grass experiment include the inertial subrange, the trend for diurnal peak, and a range between them, all together featuring the existence of the hourly gap. In the canopy experiment, except for the above feature, the effects of the presence of plant objects are also reflected by the presence of two regimes different from those for clipped grass field. / The double trace moment technique was performed on the inertial subrange of the temperature and velocity fields measured over clipped grass to obtain the parameters characterizing the multifractal fields. The variability of the parameters with the atmospheric stability was investigated and no apparent difference between stable and unstable conditions was found. The results reveal that those fields are universal multifractals with the characteristic parameters $ alpha$ near 1.7 and C$ sb1$ ranging from 0.04 to 0.12, implying that the fields can be modeled by a log-Levy process with unbounded singularities. We also found that the critical moment q$ rm sb{s}$ for the multifractal phase transition is close to 4.

Previous numerical and theoretical results based on constant diapycnal diffusivity suggested the abyssal meridional overturning circulation (MOC) should weaken as winds over the Southern Ocean intensify. We corroborate this result in a simple ocean model, but find it does not hold in more complex models. First, models with a variable eddy transfer coefficient and simple yet dynamic atmosphere and sea-ice models show an increase, albeit slightly, of the abyssal MOC under increasing winds. Second, the abyssal MOC significantly strengthens with winds when diapycnal diffusivity is parameterized to be energetically supported by the winds. This tests the emerging idea that a significant fraction of the wind energy input to the large-scale ocean circulation is removed by mesoscale eddies and may then be transferred to internal lee waves, and thence to bottom-enhanced diapycnal mixing. A scaling theory of the abyssal MOC is extended to incorporate this energy pathway, corroborating our numerical results. / Graduate / 0415 / gstanley@uvic.ca

Due to their small size, relative covertness, and high maneuverability, micro rotorcraft are ideal for a plethora of civilian and military applications in an urban environment such as, surveillance, monitoring, mapping, and search and rescue. It is envisioned that these vehicles will operate indoors confined complex spaces, and outside near the ground—among buildings and other obstacles. The aerodynamic velocity fields in these areas are notoriously complex with the mean winds varying spatially and temporally with sharp changes in wind magnitude and direction over small distances. This results in velocity perturbations which are on the same order of magnitude as the maximum flight speeds of micro rotorcraft leading to stall, large attitude perturbations, and loss of control; thus preventing micro rotorcraft from carrying out even the most basic missions. This dissertation starts to fill the void in the literature on this topic by assessing how to design a micro coaxial helicopter with improved gust response in complex urban environments. Both experimental flight tests and modeling and simulation tools are developed and executed to analytically understand the challenges and potential solutions to enable rotorcraft to operate efficiently and robustly in urban environments. A set of performance metrics were developed to provide a framework to assess mission-level performance of micro rotorcraft in both flight experiments and simulation trade studies. A high fidelity dynamic model of a coaxial helicopter was developed to accurately simulate vehicle response to urban wind disturbances. The model was validated using flight experiments in a motion capture facility. Additionally, a dynamic inversion based Gust Rejection Control architecture was developed for the dynamic simulation which included a novel wind estimation algorithm that was utilized to improve controller performance and create a flight envelope protection scheme. The high fidelity dynamic model was employed to perform a variety of trade studies to: analyze vehicle response to prototypical urban wind kernels, understand the affect of wind estimation on the control architecture, assess the level of model fidelity required to adequately simulate vehicle response to urban winds, and identify key platform design parameter trends to improve wind disturbance capabilities. Overall the results show the challenges micro rotorcraft face in urban environments while highlighting some trends that can be helpful for future design and analysis efforts.

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 158-159). / xv, 159 leaves, bound ill., maps 29 cm

Bibliography: leaves 117-130 / xii, 130 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1989