where n^ and m^ can take on any integer value independently. 

 The set n^(n , n 3 , n 3 ) designates the particular mode of 

 oscillation; a fundamental mode of oscillation corresponds 

 to the particular set (1, 1, 1). The second of relations (50) 

 demands that K^ be pure imaginary and hence 



n t \ (5D 



Moreover, for an inviscid fluid c is real and hence Q must 

 be negative so that the temporal attenuation factor co£ is 

 zero and the eigenfrequencies of the system are given by 



tt o j (^ ll x f + (n 3 fig f + (n 3 H 3 ? I 2 (52) 



Rectangular Cavity with Soft Walls 



The opposite extreme of the previous case is a cavity 

 for which complete pressure release occurs at the bounda- 

 ries. The pressure is readily evaluated in terms of the 

 relation 



p = -\ 7 • s (53) 



if the displacement components s^ , s 2 , s 3 are known. 

 Using (45) the relation for p is 



P = -^(^^jUsinhCr^ + H)^^ (54) 



46 



