unresolved questions regarding the influence of scale effects. Thus, 

 the Reynolds number is modeled by the length scale l^/^J in a Froude 

 model; this lack of Reynolds similarity may affect the energy dissipa- 

 tion on the seaward slope of the structure as well as the dissipation 

 within the structure. These problems associated with scale-model tests 

 should not be interpreted to mean that model tests are of no value. 

 They are mentioned here merely to point out that even accurately con- 

 ducted model tests have their sources of errors which should be consid- 

 ered in the interpretation of the test results. 



Although scale-model tests have weaknesses, model tests are believed 

 to present the best solution to the problem of wave interaction with 

 porous structures. However, a simple analytical model, although approx- 

 imate, does offer possibilities for performing a reasonably sound preliminary 

 design which may then be subjected to a model study to add the final 

 touch to the design. This procedure will reduce the significant cost 

 associated with the performance of model tests. For this reason this 

 investigation approaches the problem of wave transmission through and 

 reflection from a porous structure on an analytical basis. An analytical 

 treatment of this complex problem must be based on several simplifying 

 assumptions. The basic assumptions are: 



(a) Incident waves are periodic, relatively long, and normally 

 incident . 



(b) Fluid motion is adequately described by the linearized 

 governing equations. 



(c) Waves do not break on the seaward slope of the structure. 



Since the design wave conditions for most breakwaters correspond to 

 relatively long waves, i.e., waves of a length exceeding say ten times 

 the depth of water, the first assumption is physically reasonable with 

 the assumption of normal incidence being made for simplicity. From the 

 assumption of linearized governing equations, it is, in principle, 

 possible to generalize the solution to cover the conditions corresponding 

 to incident waves prescribed by their amplitude spectrum. With the 

 present lack of knowledge about the mechanics of wave breaking the third 

 assumption is dictated by necessity. This third assumption may seem 

 unrealistic. However, most porous structures have steep seaward slopes 

 on which relatively long incident waves may remain stable. 



With these assumptions, an analytical solution to the problem of 

 wave transmission through and reflection from a porous structure is 

 sought. The solution technique is based on the fundamental argument 

 that the problem of reflection from and transmission through a structure 

 may be regarded as one of determining tlie partition of incident wave 

 energy among reflected, transmitted, and dissipated energy. The problem 

 is in accounting for this partition and, in particular, in evaluating 

 the energy dissipation associated with the wave structure interaction. 



12 



