The new value of W from Equation 7-34 is 



^M^ 2.0 r2.0) 



W = = ^ = 0.33 , 



CjyH 1.2(10) 



and the new values of <j)^ and a^ are, 



K - 0-15 , 

 and 



a^ = 0.093 . 



Therefore, from Equation 7-35, 



(Pm)2'diam. = <A^wC^H^D , 



{^m)2' diam. ^ 0.15 (64) (1.2) (10)^ (2) = 2,300 lbs.. 



and from Equation 7-36, 



[^m)2'diam. ^ "mWC^H^Dd , 



say 



{^m)2'diam. = 0.093 (64) (1.2) (10)^ (2) (100) = 142,800 Ib.-ft., 

 {^m)2'diam. ^ 143,000 Ib.-ft. 



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



7o314 Transverse Forces Due to Eddy Shedding [Lift Forces) . In addition 

 to drag and inertia forces that act in the direction of wave advance, 

 transverse forces may arise. Because they are similar to aerodynamic 

 lift force, transverse forces are often termed lift forces, although 

 they do not act vertically but perpendicular to both wave direction and 

 the pile axis. Transverse forces result from vortex or eddy shedding on 

 the downstream side of a pile. Eddies are shed alternately from one side 

 of the pile and then from the other resulting in a laterally oscillating 

 force. 



Laird, et al . (1960) and Laird (1962) studied transverse forces on 

 rigid and flexible oscillating cylinders. In general, lift forces were 

 found to depend on the dynamic response of the structure. For structures 

 with a natural frequency of vibration about twice the wave frequency, a 

 dynamic coupling between the structure motion and fluid motion occurs, 

 resulting in large lift forces. Transverse forces have been observed 

 4.5 times greater than the drag force. 



For rigid structures, however, transverse forces equal to the drag 

 force is a reasonable upper limit. This upper limit pertains only to 

 rigid struotures. Larger lift forces can occur when tnere is dynamic 

 interaction between waves and the structure. For a discussion see Laird 

 (1962). The design procedure and discussion that follow pertain only to 

 rigid structures. 



7-95 



