studies) are seldom required for model studies of these structures. Sta- 

 tistics of the wave dimensions, directions, and frequency of occurrence 

 of local, wind-generated waves are the type of wave data needed for these 

 studies. Some floating breakwater studies may require wave spectra data. 

 However, wave data of significant wave dimensions should be adequate for 

 most studies of pneumatic and hydraulic breakwaters. Information con- 

 cerning the densities and weight distribution of the materials used to 

 construct the breakwater, together with details of the geometry and 

 dimensions of the structure is needed for calculation of the mass moments 

 of inertia for both the transverse and longitudinal axes. Data are also 

 needed concerning the mooring cables (length, diameter, mass density, and 

 modulus of elasticity) and the cable assembly (number of cables and the 

 positions of attachment to the structure) . 



The conduct of stability models of rubble-mound breakwaters, jetties, 

 wave absorbers, seawalls, and the rubble-mound bases of composite break- 

 waters requires details of the structures' overall geometery and the 

 characteristics of the armor units, underlayer rock, and core material. 

 For some studies, it can be determined before the model study whether 

 quarrystones of sufficient size and density to withstand the attack of 

 the largest expected waves are available at competitive prices. Model 

 tests are necessary in other studies to determine whether quarrystones 

 are adequate as armor units, or whether concrete armor units of special 

 shape are required. For quarrystone armor units, the expected shapes, 

 the densities, and the estimated percentages of different size stone that 

 will be obtained from the quarrying of selected rock formations within 

 shipping or hauling distances of the prototype site are required; for 

 concrete armor units, the shape of unit and density of concrete are re- 

 quired. Information is also needed as to the extent and frequency of 

 damage that the structure can tolerate, and the economical and social 

 consequences if damage were to occur to the point of failure. The latter 

 information can affect the selection of design waves, and indicate the 

 desirability of conducting tests in which the wave height is correlated 

 with the amount of damage to the structure. The cost of repair versus 

 the cost of constructing a breakwater or seawall that is not expected to 

 be damaged can then be estimated from the test results, the construction 

 and repair costs, and the interest rates during the economic life of the 

 structure. 



The normal water depths at the structure site and the range of water 

 surface elevations about the selected Stillwater level are important vari- 

 ables in the design of coastal structures (especially rubble-mound, com- 

 posite, and vertical-wall structures), selection of design waves, and 

 selection of model test conditions. Thus, statistical data of tidal 

 ranges, wind setup, or storm surge are necessary for the design and effi- 

 cient operation of stability models for all types of coastal structures. 



b. Selection of Linear Scale , in the design of coastal structure 

 models, it is desirable to obtain dynamic similarity with an accuracy 

 sufficient for the needs of the design engineer, at the least possible 

 cost of construction, operation, and analysis of test results. The 



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