WAVE FORCES 



2008 In an analysis of the forces exerted on structures by waves, a 

 division should be made between the action of breald.ng waves, non-rbreaking 

 waves, and broken waves. Pressures due to non-brealdng waves wi.!]: be 

 essentially hj^drostatiCa Broken and brealdng waves on the other hand, exert 

 additional pressures due to the dynamic effects of the turbulent water in 

 motion and the coripression of entrapped air pocketso These pressures may 

 be much greater than those due entirely to hydrostatic forcese Therefore 

 structures located in an area in which storm waves may break, should be 

 designed to withstand much greater forces and moments than those structures 

 vrhich would be attacked only by non-breaking waves „ 



201, Determination of Breaker Depths and Heights » «= Depths at wbJ-ch waves 

 may break, may be determined, given deep water wave conditions, from the curves 

 of Figure 18 o A note of caution is in order on the use of these cujrvese 

 Rarely are storm waves so regular that the depth of breaking ms^r be precisely 

 determinede Storm wave heights and lengths are extremelj'" variable if the 

 generating area is not far removed from the point of observations 



202» The curve labelled U,,Go, because of the controlled nature of the 

 model wave parameters used in the construction of tte curve, probably re- 

 presents a lower limit of the range of breaker depth to deep water height 

 ratios wMch would be found in nature for any one wave conditions If d, as 

 found from this curve is less than, the depth of water along a shore structure, 

 it should not be immediately assumed that these waves would not break on the 

 structure* For safety, waves must be assiimed to be capable of breaking in a 

 depth of water d, greater than the d, found from the curve, or if the ratio 

 d/d, - 1»5. Breaker heights may be determined from the curves of Figure 17 

 labelled U»C, For structures in shallow water, when deep water conditions 

 are not knox-m. or when the design wave determined from deep water conditions 

 would break before reaching tte structure, the height of the maximum wave 

 which would break on the structure can be found approximately from the rela- 

 tionship d, = 1,3H, 



203 (. Non-brealdng Waves , - Ordinarily, a shore structure would be so 

 located that storm waves would break in the depth in which the structure is 

 foundede However, in protected regions or in areas where the available fetch 

 is limited, non~breaJd.ng wave conditions may occ-ar» The most commonly used 

 method for the determination of pressures due to these waves in that of 

 M, Sainflou* 



20I4.. Sainflou I-fethod; Forces Due to Non-breaking Waves , - If a wave 

 of length L and height H strikes the vertical face of the wall AG, a standing 

 wave or clapotis will be set up» (See Figure 7^1- )o The point A is the 

 maximum elevation of the crest, ard point G is the minimum elevation of the 

 trough of the clapotis The mean level or orbit center is above the still 

 water level D a distance 



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