Report discussed measures to cushion impact on body falling into water. Heavy loads are generated by impact and by pressures of water cavity collapsing onto the body

Madden, R.

Remington, P. J.

Wright, H. A.

English

NASA Technical Reports Server

December 1975	 B75-10311 
NASA TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
The Impact of Water on Free-Falling Bodies 
.
A report has been published which discusses 
measures to cushion the impact on a body falling into 
water. Heavy loads are created during the impact 
which may damage instrumentation inside the body 
(e.g., rocket components, meteorological instrumen-
tation, air-dropped cargo, and the like). When the 
body drops into the water two effects occur: First, 
heavy loads are generated due to the impact, and 
second, additional loads are created by pressures of 
the water cavity collapsing onto the body. 
An effective method to cushion the impact is to use 
screens around the body. These have to be contoured 
to the body shape. Several arrangements varying in 
the number and spacing of the screens were tested and 
discussed in the report. A 1-in. (2.5-cm) sphere is 
used as the laboratory model of the body dropping 
into a flat water surface (e.g., no waves). The flat 
water surface has been selected because it creates the 
largest impact forces on the falling body. 
Preliminary results show that the screens substan-
tially attenuate the peak loading occurring during the 
impact. They first reduce the velocity of the impacting 
water and second aerate the water to provide 
additional cushioning. 
Next in the report the physics of the water-cavity 
collapse is discussed. A mathematical model is 
presented to permit the approximation of peak cavity 
collapse loads. One important observation in the 
laboratory tests is that entrapped air plays an 
instrumental role in cushioning the impact of the 
collapsing water onto the body. An important
conclusion from this analysis is that in subscale model 
tests realistic cavity collapse pressures can be obtained 
only when the environment is pressure scaled. In other 
words, additional pressure effects come into play 
when large bodies are studied. 
The study has wider implications. For example, the 
concepts discussed are also useful in protecting dikes, 
levees, and similar structures that are subject to wave 
damage during large storms. 
Note: 
Requests for further information may be made in 
writing to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code ATO1 
Marshall Space Flight Center, Alabama 35812 
Reference: B75-10311 
Patent status: 
Inquiries concerning rights for the commercial use 
of this invention should be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code CCO1 
Marshall Space Flight Center, Alabama 35812 
Source: H. A. Wright, P. J. Remington, 
and R. Madden of

Bolt Beranek and Newman, Inc.
(MFS-23310) 
Categories: 06 (Mechanics) 
03 (Physical Sciences) 
This document was prepared under the sponsorship of the National
	
Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
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The impact of water on free-falling bodies

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