• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.2
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• pp.122-138
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• 2001

It is well known that whcn waves propagating on a shallow water suddenly encounter a much deeper water they do not propagate further but are reflected. If we apply this phenomenon to a harbor by making the harbor depth much greater than outside, we could improve the harbor tranquillity by making the waves impinging into the harbor be reflected at the harbor entrance. In the present paper, first we apply the numerical models based' on the mild-slope equation and extended mild-slope equation to calculate the long wave resonances in a rectangular harbor with a very large depth discontinuity at its entrance to find that the difference between the models is almost negligible. By applying the numerical model to a realistic model harbor whose inside is entirely dredged, it is found that the effect of dredging is insignificant when the inside depth is twice the outside one but tripled inside depth significantly reduces the long waves of period of one to five minutes whieh may exert a bad influence on ship motion. Moreover, even when only a portion of the harbor basin is dredged, the cffect of dredging in the dredged area is found to be comparable to that of entire dredging, showing that the dredging of harbor basin can be a countenncasure for harbor resonance.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.3
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• pp.226-235
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• 2011

Field measurements of the winds and waves were carried out for one year at multiple locations inside and outside of the Pohang New Harbor in order to clarify the reason of downtimes frequently occurring at most of the harbor quays and to establish an efficient countermeasure. In addition, the downtime records of the quays and precipitation data provided by Korea Meteorological Agency were acquired for mutual comparison and comprehensive analysis of the cause of downtimes. Except the influence of precipitation, it was found that the downtimes occurred when the height of waves entering into the harbor incurred by either one of swell, wind seas, or mixture of both, exceeded a threshold. The seiche whose period ranges from 5 to 80 minutes, which was suspected as a possible cause of the downtimes, is shown to have no direct relation with the downtimes. Meanwhile, the height of far-infra-gravity waves whose period ranges between 0.5 and 3 minutes, propagating to the harbor mouth forced by short period waves, showed almost proportional relationship with the height of short period waves. Based on the result of this study, it is concluded that the downtime problems of Pohang New Harbor can be greatly improved by effectively preventing the entrance of short period waves such as swell or wind seas.

• The Journal of the Acoustical Society of Korea
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• v.13 no.6
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• pp.75-82
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• 1994

The ray paths and travel times of sound wave in the ocean depend on the physical properties of the propagating media. Ocean Acoustic Tomography(OAT), which is inversely estimate the travel time variations between fixed sources and receivers the physical properties of the corresponding media can he understood. To apply ocean survey technology by using the OAT, the tomographic procedure requires forward problem that variation of the travel times be identified with the variability of the medium. Also, received signals must be satisfied the necessary conditions of ray path stability, identification and resolution in order for OAT to work. The canonical ocean has been determined based on the historical data and its travel time and ray path are used as reference values. The sound speed of canonical ocean in the East Sea is about 1523 m/s at the surface and 1458 m/s at the sound channel axis(400m). Sound speeds in the East Sea are perturbed by warm eddy whose horizontal extension is more than 100 km with deeper than 200 m in depth scale. In this study, an acoustic source and receiver are placed at the depth above the sound channel axis, 350 m, and are separated by 200 km range. Ray paths are identified by the ray theory methed in a range dependent medium whose sound speeds are functions of a range and depth. The eigenray information obtained from interpolation between the rays bracketing the receiver are used to simulate the received signal by convolution of source signal with the eigenray informations. The source signal is taken as a 400 Hz rectangular pulse signal, bandwidth is 16 Hz and pulse length is 64 ms. According to the analysis of the received signal and identified ray path by using numerical model of underwater sound propagation, simulated signals satisfy the necessary conditions of OAT, applied in the East Sea.

• Journal of Climate Change Research
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• v.1 no.2
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• pp.133-145
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• 2010

This study examined the characteristics of tropical cyclone(TC) activity over the western North Pacific(WNP) in 2009. Twenty-two TCs formed in 2009, which is slightly below normal(1979~2009 average: 25.8) and most of these occurred during the months of July to October. Most TCs in 2009 was formed over the northern Philippines and the eastern part of the WNP and they moved towards the South China Sea and the east of Japan, resulting in less TC affecting the East China Sea and Korea. The TC activity in 2009 is modulated by the large-scale circulations induced by the El $Ni{\tilde{n}}o$ and vigorous convection activity over the WNP. As the general characteristics of El $Ni{\tilde{n}}o$ year, the difference in sea surface temperature between the central Pacific and the eastern Pacific causes an anomalous westerly winds, expanding the WNP monsoon trough farther eastward. Accordingly, TC formation has relatively increased in the east part of the WNP. Active convection activities over the subtropical western Pacific excite a Rossby wave propagating from the South China Sea to mid-latitudes, resulting in an anomalous easterly steering flow in the South China, anomalous northwesterly over the East China Sea and Korea, and anomalous southwesterly over the east of Japan. Summing up, the TCs cannot enter the East China Sea and Korean region and instead they move towards the South China Sea or south-east of Japan. There were no effects of TCs in Korea in 2009. It is anticipated that this study which analyzed unusual TC activity and large-scale circulations in 2009 would help the predictability of TC effects to increase according to climate change in the East Asia.