and this approximation is identical to Stokes* wave theory extended to the 

 same order. The theory represents the irrotational divergenceless flow. 

 Work also has been under way on preparation of a table of the values of 

 coefficients used in this theory. 



(g) Equilibrium Profile and Model Scale Effect Studies. 



Testing was continued in a small tank utilizing low specific gravity 

 material (crushed coal) to study the effect of scale on movable bed models 

 under wave action. The specific gravity of the coal was chosen so as to 

 model the settling velocity of the sand used in the large-scale tests. 

 Profiles derived from these tests bear basic resemblance to the profiles 

 obtained with the large (up to 5.5-foot) waves on a sand beach, although 

 things seem to happen sooner than expected in the small-scale tests. 



(h) Rubble Mound Stability. 



Large-scale (7.5 to 1) tests on stability of rubble-mound structures 

 under wave action were continued to spot check the results of the small- 

 scale test program at the Waterways Experiment Station. Previous tests have 

 involved entirely non-breaking waves. Since it was felt that somewhat 

 greater damage might be caused by fully breaking waves having the same in- 

 cident deep water height as the non-breaking waves, a 1 on 10 concrete beach 

 slope was installed in front of the test breakwater to permit generation of 

 a breaking wave on the breakwater base. These tests were carried out for 

 the 1 on 1-1/2 slope rubble breakwater using approximately 1-foot diameter, 

 160-pound stone. The tests did show that initiation of damage to the break- 

 water occurred with breaking waves having smaller offshore te ights than for 

 the non-breaking waves. Calibration of the tank to obtain a precise deter- 

 mination of the wave heights at the structure location without the structure 

 in place has been carried out and is essentially completed. Complete analy- 

 sis of the data obtained on rubble mound stability must await completion of 

 these calibration tests. The next tests will utilize a four-legged concrete 

 shape, a quadripod. This shape is somewhat similar to a tetrapod with a 

 flat base. A supply of these (weight, 75 pounds each) has been contracted 

 for, and is currently being delivered. 



(i) Wave Measurements and Analysis. 



Wave records continue to be taken at the five ocean gage stations 

 (Atlantic City, New Jersey; Palm Beach and Naples, Florida; Huntington Beach 

 and Port Hueneme, California). The gage at Naples was destroyed during 

 Hurricane Donna in September 1960, but has been replaced. Additional tape 

 recorded wave data for both Atlantic City and Port Hueneme were obtained and 

 further spectral analyses of some of these were made on the analyzer. Manual 

 and computer computation of the spectra for some of these were continued for 

 comparison with those obtained from the analyzer. A report describing the 

 spectrum analyzer, its uses, and the analyses presented by it was completed, 

 and presented at an NAS-ONR conference on wave spectra. A study has been 



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