LECTURE 10 
SCALE-MODEL STUDY OF PROPAGATION IN SHALLOW SEAS: 
A VISUAL METHOD OF REPRESENTATION OF LOW-INTENSITY 
SOUND FIELDS 
A.B. Wood 
Admiralty Research Laboratory 
Teddington, Middlesex, England 
10.1. INTRODUCTION 
It has long been recognized in engineering practice that the considerable 
cost and bulk of the structures with which the engineer is concerned frequently 
make comprehensive research upon them extremely laborious and prohibitively 
expensive. The conditions of operation of such full-scale structures also are not 
conducive to the acquisition of reliable information. On the other hand, experi- 
ments with small scale models have shown that they are capable of demonstrat - 
ing physical effects of a general character and of providing data which can be 
applied with some confidence in full-scale practice [1]. Aeronautics, naval 
architecture, hydrodynamics, and building acoustics have long furnished examples 
of successful small-scale research, and it is increasingly evident that the ex- 
perimental scale-model technique can be applied to a much wider range of 
subjects than interests the civil or mechanical engineer. A model can be con- 
structed for a very small fraction of the cost of its full-scale counterpart, and 
it need only include those features whichare known to influence the effects under 
consideration. A model is easy to manipulate, and its cost in labor and time is 
relatively low. Further, success is more likely to be achieved under controlled 
conditions in the laboratory. Many of the variable physical quantities which af- 
fect a particular problem can be simulated in a laboratory experiment and are 
capable of adequate, and in some cases separate, control. On a model scale 
modifications of apparatus or method can be made with an ease and rapidity 
which is quite unattainable at full scale. Model apparatus is also ideal for check- 
ing novel theories and data predicted theoretically. These advantages of model 
over full-scale research techniques are, of course, nowcommon knowledge. The 
alternative, a purely mathematical treatment of a problem, is within certain 
limitations often a possibility, but in some practical cases is either very dif- 
ficult or quite intractable. In acoustical problems, as is well known, it is often 
advantageous to consider analogous optical cases [2,3] when the wavelengths and 
linear dimensions involved can be suitably scaled. 
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