for proposed prototype installations. The range of wave dimensions and 

 water depths, and the wave gage position for measuring the transmitted 

 wave heights, should be the same as those suggested for the pneumatic 

 breakwater tests (Sec. VI, 3, b). The test procedures should be according 

 to equation (6-21) (Sec. VI, 2, g). 



c. Scale Effects . For complete dynamic similarity between model and 

 prototype, the ratio of inertia forces of the two systems must be equal 

 to the ratio of the resultant of all forces acting on the two systems 

 (eq. 2-6) , the ratio of the inertia forces of the two systems must be 

 equal to the ratio of individual component forces (eq. 2-7) , and the two 

 systems must be geometrically similar. These conditions of similitude 

 cannot be met completely as explained below and in Section II. The de- 

 viations of model test results from corresponding prototype behavior, 

 caused by the lack of complete dynamic similarity, are known as scale 

 effects. For coastal structure models the predominant force involved 

 is usually gravity, and the models are designed and operated based on 

 Froude's law. Thus, the scale effects to be considered when the test 

 results are analyzed and transferred to prototype values are caused by 

 the lack of similarity, model-to-prototype, of the other forces involved; 

 i.e., viscous, surface tension, and elastic forces. 



The conditions for similitude discussed above are imposed on the 

 laboratory engineer by the laws of fluid dynamics. Other factors that 

 influence the accuracy of model test results (and must be considered in 

 addition to those due to scale effects) in model design and operation 

 are: 



(a) Type of wave generator and the distance between the 

 generator and the test structure. 



(b) Distance between the test structure and the wave 

 absorber lised in the shoreward end of the wave flume. 



(c) Reflection coefficient of the wave absorber. 



(d) Type, magnitude, and duration of attack of the 

 test waves. 



(e) Stillwater level selected for testing. 



(f) Manner of determining the amount of damage to the 

 test section when it is a rubble-mound structure. 



(g) Accuracy with which the wave dimensions are measured. 



(h) Other test conditions that must be selected by the 

 laboratory engineer based on available prototype data and 

 experience with similar model studies previously conducted. 



Fan and Le Mehaute (1969) refer to the similitude relations dictated by 

 the laws of mechanics as conditions of similitude, and conditions that 

 can be specified by the laboratory engineer as criteria of similitude. 



339 



