Several problems concerning wave propagation in a stratified fluid under the influence of gravity are considered. These may be divided into two major groups: the first group considered pertaining to the motions of the earth's atmosphere resulting from explosive disturbances, the second pertaining to the dissipation of energy of waves generated by bodies moving within an incompressible fluid. For the first group of problems attention is concentrated on the properties of the created wave motions, whereas for the second group attention is concentrated on the energy losses experienced by a moving body which are known to correspond to the generation of gravity waves within the fluid. The first three chapters are a study of wind effects upon acoustic-gravity waves caused by atmospheric nuclear explosions. In Chapter I experimental evidence is presented which shows that winds have a pronounced effect on groundpressure waves. Chapter II contains a derivation of a theoretical expression for ground-pressure waves from a point source in a particular type of model atmosphere containing winds. In Chapters II and III computations based on this expression are presented, some theoretical aspects of the results are considered, and comparison is made between theoretical wave-trains and actual microbarographic recordings associated with nuclear explosions. In Chapter IV is considered the determination of the vertical wave energy flux due to a disturbance at ground level in an atmosphere containing winds, An expression is derived for vertical energy flux and numerical estimates are presented for a particular case. Problems in the aforementioned second group are studied in Chapters V and VI, The motion of a body in a medium which may be regarded as the superposition of two uniform semi-infinite layers of fluid of differing densities is considered in Chapter V. The energy lost at the fluid interface is determined for a body which moves steadily through the medium at various inclinations and speeds and in various directions. Some numerical results are presented in connection with the motion of a body which is caused to oscillate freely at the interface. In Chapter VI wave resistances to the steady motion of a body through a fluid of varying density are presented for various inclinations of the body and various speeds and directions of the motion. The work described in this thesis was done at the Department of Mathematics, Imperial College of Science and Technology, under the supervision of Professor R.S. Scorer between October 1965 and January 1968. Computer calculations were performed at the Institute of Computer Science of the University of London. Here the author wishes to express his gratitude to Dr. P.W.G. Warren, Imperial College, for his guidance and encouragement during the preparation of this thesis, Any merit possessed by the work presented herein is a result of the many hours he gave to discussions with the author. Acknowledgment is gladly given to R.A. Hamilton, former Superintendent, Kew Observatory for his invaluable aid in providing the author with the opportunity to study the microbarographic records of the Meteorological Office. The author is also grateful to the Director, Meteorological Services of Eire and to Cmdr. Thoday of the Science Museum for their cooperation. During his studies the author was recipient of a scholarship from the Defence Research Board of Canada.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:623081 |
| Date | January 1968 |
| Creators | MacKinnon, Robert Francis |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/15961 |
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