6 Harbor Oscillations 



To evaluate harbor resonance characteristics, the HARBD numerical model 

 was run for the existing harbor and all alternative plans. Incident long wave 

 periods ranged from 25 sec to 1,000 sec in very fine increments, as discussed in 

 Chapter 4. These evaluations were included because oscillations are an impor- 

 tant part of interpreting the existing harbor wave response (as evidenced by gage 

 data in the harbor), and modifications to the harbor can potentially lead to 

 increased operational problems due to harbor oscillations. Amplification factor 

 results are presented in the following section. Additional results more closely 

 related to operational performance criteria are given in the final section. 



Amplification Factors 



Amplification factors for 

 the long waves involved in 

 harbor oscillation behave 

 differently than those for 

 wind waves and swell. Long 

 waves, because of their 

 length relative to harbor 

 dimensions and their 

 reflectivity from harbor 

 boundaries, form standing 

 wave patterns in the harbor. 

 Standing wave behavior in a 

 simple closed basin of 

 uniform depth is illustrated in 

 Figure 52. In the funda- 

 mental mode of oscillation, 

 antinodes occur at both basin 

 walls and a node midway 

 between walls. Second and 

 third modes of oscillation are 

 also illustrated. Antinodes 

 always occur at the walls. 

 Additional antinodes and 

 nodes occur at regular 



(I) Fundamental Mode 

 (First Harmonic) 



Node J 

 •Antinodes 



(2) Second Mode 



(Second Harmonic) 



3) Third Mode 



(Third Harmonic) 



Figure 52. Harbor oscillation 

 definitions 



Chapter 6 Harbor Oscillations 



77 



