RESULTS 



The results of the wave force measurements are tabulated in Table 3. 

 The difference among 100, 200, and 300 series data is model orientation. 

 The 100 series tests were conducted with the higher drag sides of models 

 facing on-coming waves. The models were turned 90° for 200 series and 

 180° for 300 series. The values of phase lags were obtained from the 

 oscillogram records by measuring the difference in phase angle between 

 the wave peak and the force peak. 



The objectives of the 200 series test were to observe the lift forces 

 (force normal to flow) on the non-symmetric models and to provide more 

 drag data on circular models. The noise to signal ratio was large in the 

 lift force recordings of the non-symmetric models and their peak force 

 and phase lag could not be determined accurately. Drag forces on these 

 geometries were of little interest. Consequently, these data were not 

 included in Table 3. A qualitative analysis of the force records of the 

 non-symmetric models indicates that large net lift forces cannot be produced 

 by orienting the long axis of the model cross-section in parallel to the 

 on-coming wave direction. 



The absolute values of positive (direction of wave propagation) and 

 negative peak forces on the circular, semi-circular, and crescent shaped 

 models are plotted against the wave steepness (ratio of wave height to 

 length) for the 100 series tests in Figures 16, 17 and 18. A family of 

 curves is shown in each plot with wave length as a parameter. The wave 

 force increases with increasing wave length and wave steepness. Figure 19 

 shows the wave peak forces on crescent shaped model in 300 series tests. 

 By comparing Figure 19 with Figure 18, it can be shown that the major 

 difference is the change in signs of the wave forces. The 300 series 

 data indicate the larger forces are negative forces whereas the 100 series 

 data indicate the larger forces are positive forces. 



The net differential peak forces, the difference between positive and 

 negative peaks, are plotted against wave heights and are presented in Figures 

 20, 21, and 22 for the three models. The circular model data in Figure 20 

 are wide spread about a mean value of zero. The semi-circular model 

 experiences no net negative forces in either orientation as shown in 

 Figure 21. However, the wave forces are much smaller when the model is 

 mounted with the circular side facing the on-coming waves. For the crescent 

 shaped model net negative peak forces are clearly shown in Figure 22 when 

 waves approach from the convex side. There are, however, several data 

 points which fall about the axis. This apparent discrepancy could be 

 caused by zero drift in the force gauge calibration which was found after 

 the tests were completed. The spread of the rest of data is small enough 

 to determine a mean which is sensitive to wave height. 



A study of the lag angle between the peak force and the wave peak 

 reveals whether the drag or the inertia force predominates. For a 90° 

 or 270° lag, the wave force is in phase with the water particle acceleration 

 and is, therefore, mainly due to inertia effects. A lag of 0° or 180° 

 indicates the wave force is in phase with the water particle velocity, 

 and is, therefore, controlled by drag. Figures 23, 24, and 25 are measured 



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