Thus the maximum displacement of the particle is 0.45 feet which is small 

 when compared with the deepwater height, H^ = 10.45 feet. 



************************************* 



2.236 Subsurface Pressure . Subsurface pressure under a wave is the 

 summation of two contributing components, dynamic and static pressures, 

 and is given by 



coshl27r(z + d)/L] H /27rx 27rt\ 



P = '^ cosh (2.d/L) 2 ^°^ \y~^l ' '^" ^ ^^ ' ^'-'^^ 



where p' is the total or absolute pressure, p^^ is the atmospheric 

 pressure and p = w/g is the mass density of water (for saltwater, 

 p = 2.0 lbs sec2/ft'+= 2.0 slugs/ft^; for fresh water, p = 1.94 slugs/ft^). 

 The first term of Equation 2-26 represents a dynamic component due to 

 acceleration, while the second term is the static component of pressure. 

 For convenience, the pressure is usually taken as the gage pressure 

 defined as 



cosh[27r(z+d)/L] H /27rx 27rt\ 



^=^'-^a = P% eosh(2.d/L) 2 '^"^ I^IT "^ T"]" '^' ' ^'"''^ 



Equation 2-27 can be written as 



cosh[27r(z+d)/L] 



p = Pgr? Pgz , (2-28) 



cosh (27Td/L) 



since 



The ratio 



H /27rx 27rtl 



7? = — cos I — 



2 \ L T ; 



cosh[27r(z+d)/L] 



K = -^-^ . (2-29) 



^ cosh(27rd/L) 



is termed the pressure response factor. Hence, Equation 2-28 can be 

 written as 



p = pg(rjK -z) . (2-30) 



2-22 



