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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.
51

Experimental and computational aerodynamic analysis of ice fragments shed from aircraft surfaces

Jacob, Joel 12 1900 (has links)
Icing can pose problems due to both accretions on aircraft aerodynamic surfaces as well as through shedding of large ice particles from aircraft surfaces. The shed ice causes damage by impacting downstream aerodynamic surfaces and on ingestion by aft mounted engines. Present ice trajectory simulation tools have limited capabilities due to the lack of experimental aerodynamic force and moment data for ice fragments and the large number of variables that can affect the trajectories of ice particles in the aircraft flowfield like the particle shape, size, mass, initial velocity, particle shedding location and orientation during shedding. A comprehensive literature review of experimental studies related to "random-shape" bluff body aerodynamics was conducted to support the development of a list of ice fragments for consideration in this research effort. Recommendations were also obtained from aircraft engine manufacturers and industry partners in developing the ice fragment list. Fifteen ice shapes were identified for aerodynamic testing and they were prioritized based on input from industry. The top three were selected for the present wind tunnel study. The ice fragments selected included a rectangular slab, a semicircular shell and a hemispherical shell. The literature review of experimental studies yielded a variety of methods employed by other investigators in obtaining force and moment data for randomshape bodies. However, in most previous experimental investigations force and moment data were obtained for infinite aspect ratio (2D) fragments. The research described in this thesis was performed to establish 3D six degree of freedom experimental force and moment data in the WSU 7-ft by 10-ft wind tunnel facility. The data obtained will be used in the probabilistic trajectory simulation methods of "random-shape" ice fragments employed at WSU. Experimental results are presented for five ice fragment configurations and include lift, drag and side force coefficients. In certain cases, the pitching, yawing and rolling moment coefficients are also provided. The data was reduced from the balance body axis system to the wind axis system. Transformations were developed to obtain the force and moment data at the model resolving center from the balance virtual center. The forces and moments were resolved by the WSU external balance at the virtual center. Detailed discussions are provided on the effects on the aerodynamic force and moment data due to the test mount, test section wall, model-mount interference, aspect-ratio, ice fragment shape and the associated Reynolds number. Moreover, the flowfield about selected ice fragments was computed using simulation tools like FLUENT (a Navier-Stokes solver) and GAMBIT (meshing preprocessor) to elucidate flow behavior and sting-model interference effects. Results from the computational effort are presented and include pressure coefficient contours and velocity colored streamlines. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering. / "December 2006." / Includes bibliographic references (leaves 134-140)
52

Computational Ice Dynamics and Hydraulics : Towards a Coupling in the Ice Sheet Code ARCTIC-TARAH

Holmgren, Hanna January 2012 (has links)
Numerical ice sheet modeling is a rather young discipline: it started in the 1950s. The "first generation" models developed at that time are currently being replaced by "new generations" ones, such as e.g. ARCTIC-TARAH. ARCTIC-TARAH is a Bert Bolin Center for Climate Research spin-off from the Pennsylvania State University Ice sheet model (PSUI). When the Bolin Center received PSUI for subsequent independent development and adaption of the code to Arctic settings in 2010, an initial inspection of the source code suggested that PSUI also contained a module that allows for the treatment of glacial hydraulics. A numerical ice sheet model including coupling of ice dynamics and hydraulics is an extremely important tool in testing new hypotheses of former geological events. E.g., based on the recent finding that Arctic Ocean sediments contain a very distinct signature, it has been suggested that ice dammed lakes at the south-eastern margin of the late Weichselian Eurasian ice sheet drained into the Arctic Ocean in a catastrophic event around 55.000 years ago. The aim of this thesis is to perform a reconnaissance analysis of the glacio-hydraulic algorithms in ARCTIC-TARAH, as "inherited" (but never with published record of functionality) from PSUI. The work is carried out in two steps: first the routines and algorithms describing the hydraulics are located and explored, and then these routines are tested and verified by performing experiment simulations. The investigation of the program code reveals the presence of two hydraulics related modules in ARCTIC-TARAH. The main tasks of the module Water are to initiate lakes and oceans and to adjust hydrostatic pressure in each lake. Further, with the module Move Water activated, transportation of water (e.g. in rivers) is possible. Results from idealized experiment simulations verify the functionality of the routines in the module Water. An in-depth analysis of the module Move Water suggests that there is a mismatch in time units when solving the equations describing flow of water. Experiment simulations also support this flaw detected in the flow model. Preliminary adjustments were made to the source code  of the module Move Water, which made it possible to simulate the transportation of water both under an ice sheet and in rivers on land. However, these adjustments do not solve the problem of mismatching time scales, and the numerical solutions obtained from the experiments were observed to be unstable and, therefore, possibly incorrect. To be able to perform more advanced simulations in support of the above mentioned hypothesis, the flow model in the module Move Water needs to be improved or replaced. One solution to the problem with mismatching time scales, could be to use a so called multiscale solution in time.
53

Integration of higher-order physics in the community ice sheet model scientific and software concerns /

Bocek, Timothy Joseph. January 2009 (has links)
Thesis (MS)--University of Montana, 2009. / Contents viewed on December 19, 2009. Title from author supplied metadata. Includes bibliographical references.
54

The fluid mechanics of ice-shelf buttressing

Pegler, Samuel Santeri January 2013 (has links)
No description available.
55

Characterization of Suspended Frazil and Surface Ice in Rivers Using Sonars

Ghobrial, Tadros I.R. Unknown Date
No description available.
56

Internal stress in a floating cover of sea ice

Wright, B. D. January 1974 (has links)
No description available.
57

Idealised models of sea ice thickness dynamics

Godlovitch, Daniel 10 September 2013 (has links)
Thickness distributions of sea ice (g(h)) display a ubiquitous exponential decay (’tail’) in ice above approximately 2 meters thick. This work uses idealised models to examine the root causes of the exponential tail of the sea ice thickness distribution. The ice of thickness greater than 2 meters is formed through the fracture and piling of ice caused by interactions between floes, driven by winds and currents. The material properties of sea ice are complex and mathematical descriptions of the relationship between force and deformation of a floe are still a topic of study. Smoluchowski Coagulation Models (SCMs) are used to develop an abstract representation of redistribution dynamics. SCMs describe populations whose members of fixed size combine at size-dependent rates. SCMs naturally produce exponential or quasi-exponential distributions. An SCM coupled with a thermodynamic component produces qualitatively realistic g(h) under a wide range of conditions. Using the abstract representation of redistribution dynamics from SCMs, a model developed from physical processes specific to sea ice is introduced. Redistribution events occur at rates dependent on the change in potential energy. This model is demonstrated to produce qualitatively realistic g(h). Sensitivity analysis shows that primary model sensitivities are to the relative strengths of the dynamic and thermodynamic components of the model; and to the relative occurrence of ice ridging, shearing and rafting. The exact relationship between the rate of redistribution events and the energy they consume is shown to be of lesser importance. We conclude that the exponential tail of g(h) is a mathematical consequence of the coagulative nature of the ice thickness redistribution process, rather than the material properties of sea ice. These model results suggest the strongest controls on the form of the tail are the relative strengths of thermodynamic and dynamic action, and the relative occurrence of ice ridging, shearing and rafting. / Graduate / 0415 / 0768
58

Estimation of ice-sheet topography and motion using interferometric synthetic aperture radar /

Joughin, Ian. January 1995 (has links)
Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [177]-182).
59

Theoretical and experimental investigations for measuring interfacial bonding strength between ice and substrate /

Javan-Mashmool, Mandana, January 2005 (has links)
Thèse (M.Ing.) -- Université du Québec à Chicoutimi, 2006. / Bibliogr.: f. 123-127. Document électronique également accessible en format PDF. CaQCU
60

High latitude coupled sea-ice-air thermodynamics /

Swick, William A. January 2004 (has links) (PDF)
Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, Sept. 2004. / Thesis advisor(s): Roland W. Garwood. Includes bibliographical references (p. 71-73). Also available online.

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