In the second case, a distinct development of bimodal seas can be seen. This 

 occurred for Runs 31 to 36 from 0755 to 13^0 on 18 May I982. A generally decaying 

 swell came from north-northwest (330-350 degrees). Over the same period of time, 

 wind driven waves grew as they came from the south (l80 degrees). The energy in 

 the wind waves continued to grow and the period increased, until they ultimately 

 approached and surpassed the swell energy in Run 36. The increasing period of the 

 wind waves can also he seen in the graphs of mean directions, as the waves from the 

 south begin to shift to the middle frequency range. 



CONCLUDING REMARKS 



Throughout the trial the wave measurements of the WAVEC and Wave-Track buoys 

 agree in energy and modal period. There is a slightly greater difference between 

 the modal wave periods than the significant wave heights, as measured by the two 

 buoys. The measurements of the mean wave direction, associated with the modal 

 period, were fairly consistent between the two buoys. However, there was an offset 

 between the two, possibly due to magnetic influences or difficulties in an elec- 

 tronic coordinate resolution. The spectral densities, mean directions, and 

 spreading angles are also presented for the two directional sensing wave buoys for 

 most of the runs. The spectral density distributions of the two buoys agreed well 

 in most cases. The agreement was not as clear, however, for the mean directions. 

 The middle and upper frequency directions generally agreed, but the lower frequency 

 directions measured by the Wave-Track buoy changed too much. The spreading of wave 

 energy, as measured by the WAVEC buoy, was less than that for the Wave-Track buoy. 

 This may be due in part to a side effect orbital wave velocities have on the sub- 

 mersed stem of the Wave-Track buoy. 



Two cases of changing wave conditions were also measured. In one case, two 

 growing wave systems from different directions combined to a common frequency 

 range. The system aligned with the wind grew more quickly. In the other case, a 

 distinct bimodal wave system was evident. The swell from one direction slowly 

 degraded, while the wind driven sea from another direction increased in energy and 

 period. 



While the Delft buoy was also used to gather wave data, the results are not 

 included here. The authors did not have access to the raw data, and the results 

 available were calculated using a different method than for the results presented 

 here for the other two buoys. 



12 



