Wave-Induced Eddies and "Lift" Forces on Circular Cylinders 



Bidde reported he was not able to compare his results direct- 

 ly with those of Chang (1964), as Chang gave his results graphically 



as ( c l) max vs N KC and ( C l) max vs N R with no values o£ 

 ( C D) max- How ever, Chang' s graph of (C L ) max vs N RC showed 

 (Cl) ma x t° a PP^oach zero for Nj^c of about 5, and approach a 

 value of 1.0 at about Nj^q = 20. 



" Lift" Forces (Present Study) 



The work of Bidde described above was continued by the wri- 

 ters, to determine the effect of large values of Nj^q on the ratio of 

 "lift" forces to longitudinal forces. The results for the 1-5/8 inch 

 (0. 14 ft. ) pile are reported herein. Tests were made for conditions 

 that approximately modeled large scale tests which will be described 

 subsequently. The pile was carefully checked to determine its sen- 

 sitivity to direction and location of resultant force through a series 

 of calibrations. 



Aluminium powder and flour were sprinkled on the water 

 surface to help in visualizing eddies. However, owing to the high 

 values of Nj^q (15 to 90) and high Nr , the wake was very tur- 

 bulent and no distinct eddies were observed. 



The crest to through distances for thirty consecutive "lift" 

 forces were measured, while the crest to trough distances for only 

 four consecutive longitudinal forces were measured as the longitu- 

 dinal forces were quite uniform. The ratios of the averages of these 

 two sets of data were plotted on Figure 8 (labeled UCB 1972), and 

 tabulated in Table 2. 



The Coastal Engineering Research Center ( CERC ; formerly 

 the Beach Erosion Board, BEB ) , U.S . Army Corps of Engineers, 

 kindly lent to the writers the original records of forces exerted by 

 waves on a vertical pile that were obtained by Ross (195 9) in their 

 large wave tank (635 feet long by 15 feet wide by 20 feet deep). The 

 active section of the test pile was 3. feet, with a dummy pile below 

 and above the active section (Figure 9). The outside diameter of the 

 pile was 1. 06 feet. Data were not plotted in the form shown in Fi- 

 gure 7, as the minimum wave height used in these tests was greater 



*Run numbers on original data rolls and those reported in T. M. 

 Ill are not the same. See letter of 16 September 1971 from John C. 

 Fairchild of CERC to Robert L. Wiegel of UCB for code. 



775 



