University of Illinois Urbana-Champaign

Hydroballistic calculations of rise and water exit of buoyant bodies

Robertson, J.M.

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https://hdl.handle.net/2142/111861

Description

Title
Hydroballistic calculations of rise and water exit of buoyant bodies
Author(s)
Robertson, J.M.
Issue Date
1959-11
Keyword(s)
  • Hydroballistics
  • Water Exit
  • Buoyant Bodies
Abstract
Problems associated with the vertical rise and passage through a water-air interface of small buoyancy-propelled bodies are considered. In general the methods of analysis are approximate, and sometimes even crude, but the results are considered indicative of what may occur. Calculations are limited to consideration of prolate ellipsoids and usually to those of fineness ratio equal to 4. The terminal velocity and length of rise distance required to approach it closely are calculated in Chapters II and III. Comparison with experiment indicates fair agreement. It is further shown that above a diameter of 2 in. the Froude number no longer increases appreciably with body size. A rough analysis of the added-mass variation of ellipsoidal bodies as they pass through the free surface is developed in Chapter IV. This later estimate is used to indicate the expected velocity and acceleration changes of exiting bodies in Chapter V. These are shown to diverge somewhat from those found experimentally. Besides the effect of added-mass variation, buoyancy and drag changes as the body exits are also shown to have an important effect on the velocity-distance and acceleration-distance profiles. Finally, in Chapter VI the effect of entrained water, as has been experimentally observed, is considered. Calculations of the displacement volume of the boundary layer on the body are shown to be in fair agreement with the measured entrained-water volumes. This permits some consideration of this entrainment effect at other scales of water exit occurrence – the effects of Reynolds number and transition from laminar to turbulent boundary-layer flow are shown to be significant. Consideration of this estimate of the of the entrained water permits a revision in the calculated velocity and acceleration profiles; in Chapter VI this is shown to lead to closer agreement with observation. The entrained water is thus found to have an important effect on the water exit behavior of the bodies, a fact which has been suspected since the first observations of this occurrence.
Publisher
Department of Theoretical and Applied Mechanics. College of Engineering. University of Illinois at Urbana-Champaign
Series/Report Name or Number
  • TAM R 153
  • 1967-0449
ISSN
0073-5264
Type of Resource
text
Language
eng
Permalink
http://hdl.handle.net/2142/111861
Sponsor(s)/Grant Number(s)
Office of Naval Research, Contract Nonr 1834 (10), Project NR 062-202
Copyright and License Information
Copyright 1959 Board of Trustees of the University of Illinois

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