2. Bowley Wave Barrier . 



The wave barrier concept developed by Bowley (1974) consists of modular 

 units which can be deployed in various arrays to form a system capable of 

 attenuating waves. This active concept (dynamic system) is based on the 

 principle that a desired wave field can be developed from incident waves 

 superposed on radiated point sources of mass or momentum. The multiple-point 

 sources are emitters of circular or elliptical wave fronts which interact with 

 the incoming wave train to produce a resultant wave field substantially atten- 

 uated from the incident conditions. The linear character of the wave equation 

 allows these systems to be modeled mathematically in an exacting manner. This 

 system involves an array of wave-excited modules which acts as a source of a 

 series of elliptical wave fronts (Fig. 193) , where the wave is generated by 

 the pitching motion of the module. Figure 194 is a schematic of the wave 

 pattern generated by the Bowley wave barrier. This wave pattern is elliptical 

 in shape because the motion about the pitch axis causes the module collar to 

 activate larger amounts of water in proportion to the distance from the 

 axis. The envelope of the emanating elliptical wave fronts is roughly linear 

 traveling seaward and shoreward, but the waves are high enough to trigger 

 instabilities in the incident waves which result in partial or complete 

 breaking. 



Bowley (1974) used a large amount of documented experience in the area of 

 large sea buoys, mooring lines, durability of materials, etc., to develop a 

 dynamic system capable of attenuating wave trains with a minimum of energy 

 dissipation within the system itself. Flexibility for performance tuning of 

 the system was obtained by several techniques. Various module anchoring 

 patterns can be used, and the length of the system can be altered simply by 

 the addition of module rows. The counterweight size and position can be 

 varied to change the pitching period, and the size of collar and air can 

 diameter is adjustable, as well as the collar position at the Stillwater 

 level. The module is simple enough for construction by unskilled labor with 

 inexpensive materials; the system array can be installed by a barge-tug system 

 which eliminates the need for any special machinery. Hence, the parameters of 

 the system will fit a variety of installation criteria. 



INCOMING WAVES 



=^S.W.L. 



Figure 193. Bowley wave barrier concept of floating 

 breakwater (after Bowley, 1974). 



253 



