Reflection and transmission characteristics of porous rubble-mound breakwaters / by Ole Secher Madsen and Stanley M. White.

Abstract

ed In Block 20, If dlllerent horn Report) 18. SUPPLEMENTARY NOTES 19. KEY WORDS (Co Breakwaters Energy dissipation Empirical relationships Wave reflection sary and Identity by block number) Friction factor Reflection coefficient Hydraulics Rubble-mound breakwater Porous material Transmission coefficient Wave transmission 20. ABSTRACT (Conltnu aide If neceeaary and Identify by block number)This report presents the results of a study of the reflection and transmission characteristics of porous rubble-mound breakwaters.An attempt was made at making the procedures entirely self-contained by introducing empirical relationships for the hydraulic characteristics of the porous material and by establishing experimentally an empirical relationship for the friction factor that expresses energy dissipation on the seaward slope of a breakwater. DD 1473 EDITION OF I NOV 6S IS OBSOLETE SECURITY CLASSIFICATtOM OF THIS PAGE (When Data Entered) PREFACEThis report is published to provide coastal engineers with the re^ô f research on the reflection and transmission characteristics of porous rubble-mound breakwaters. The work was carried out under the coastal processes program of the U.S. Army Coastal Engineering Research Center

The modelling of wave action on and in coastal structures

“…The friction coefficient f can be estimated using the empirical formula from Madsen and White (1975) for fully turbulent flow on a uniform sloping breakwater.…”

“…The stones (DEQ) varied between 0.20 m and 0.34 m. Wave heights and wave periods varied between respectively 0.55-1.15 m and 2.8-11.3 s. The surf similarity parameters ~o varied between 0.7 and 6.3. The depth in front of the structure was 4.58 m. For the friction coefficient f, the empirical formula from Madsen and White (1975) for fully rough turbulent flow on a uniform slope has been used: For the maximum run-up level R the value 1.5 times the wave height was used as an approximation. The depth in front of the structure d~ = 4.58 m was the same for all tests.…”

“…Therefore, modelling as a homogeneous structure has been applied. The friction factor, depending on the roughness of the surface and the flow characteristics, was derived by using the empirical formula of Madsen and White (1975) about equal to the wave height for which 0.175 was used. For the angle of the slope, the angle from the berm section was taken (cotc~ = 5).…”

“…The friction coefficient fwas estimated using the formula from Madsen and White (1975) for fully turbulent flow on a uniform sloping breakwater (f= 0.15). The wave height was 0.20 m, the wave period was 1.5 s and the still water-level was set at 0.80 m. The value of A for the minimum water depth in the hydraulic model during the computation was set at 0.005 m, see also Fig.…”

Model Testing of Low-Crested Breakwaters

“…It was determined that transmission due to overtopping was, as with Goda (1969), strongly dependent upon the relative freeboard of the structures studied. In addition, transmission through the structure was found to be predicted reasonably well by a computer model written by Madsen and White (1976), but no simple design equation was proposed. Ahrens (1987aAhrens ( , 1987b In the present study, many of the same kinds of tests are performed, but with different ranges of conditions.…”