• Journal of the Korean Society for Precision Engineering
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• v.5 no.2
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• pp.33-42
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• 1988

In a large scale oil hydraulic system having repeatedly operated actuator, such as a large scale forging press, pressure surges often due to the recombination of oil column in a return line attached to the downstream side of a directional control valve. Expecially, the pressure surges appear very severe ones at a certain valve operating frequency. These pressure surges restrict the operating frequency of the hydraulic system. But related reports on the above mentioned phenomenon are rarely to be found. In this study, therefore, the authors investigate the exact reason why such severe pressure surges occur at a certain range of valve operating frequency. The study is performed by experiment and numerical computation on the relationship between pressure surges and valve operating frequency.

• Atmosphere
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• v.28 no.4
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• pp.383-392
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• 2018

This study investigates synoptic characteristics of cold surges over South Korea during winter season (December-February). A total of 63 cold events are selected by quantile regression analysis using daily mean temperature observations from 11 KMA stations for 38 years (1979/80-2016/17). Large-scale pressure pattern during the cold surges is well characterized by high over Siberia and low over Aleutian regions, which elucidates cold advection over the Korean peninsula. However, the large-scale pattern cannot successfully explain the observed sudden decrease of temperature during the cold surges. Composite analyses reveal that a synoptic-scale cyclone developing over the northern Japan is a key feature that significantly contribute to the enhancement of cold advection by increasing pressure gradient over the Korean peninsula. Enhanced sensible and latent heat fluxes are observed over the southern ocean of Korea and Japan during the cold surges due to temperature and humidity differences between the near surface and the lower atmosphere over the ocean. The evaporated water vapor transported toward the center of the surface cyclone and condenses in the lower-to-middle troposphere. The released energy likely promotes the development of the surface cyclone by inducing positive PV near the surface of the heating region.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.1
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• pp.41-48
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• 2014

To analyze the surface elevation data of Typhoon Bolaven, simple analytical models are employed to investigate major causes of the storm surges in the west coast of Korea. Although the simple models cannot reproduce the storm surges by Typhoon Bolaven accurately, they are able to provide sufficient evidence of physical processes involved in the storm surges. Surges in islands located at deeper water were mainly driven by typhoon low pressure rather than associated winds. In contrast, bigger storm surge heights more than 1m were recorded in shallow coastal areas during low tide, which were dominantly produced by typhoon winds.

• International Journal of Fluid Machinery and Systems
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• v.9 no.1
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• pp.1-16
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• 2016

Behaviors of surges appearing near the stall stagnation boundaries in various fashions in systems of a single-stage compressor and flow-path systems were studied analytically and were tried to put to order. Deep surges, which enclose the stall point in the pressure-mass flow plane, tend to have either near-resonant surge frequencies or subharmonic ones. The subharmonic surge is a multiple-loop one containing, for example, in a (1/2) subharmonic one, a deep surge loop and a mild surge loop, the latter of which does not enclose the stall point, staying only within the stalled zone. Both loops have nearly equal time periods, respectively, resulting in a (1/2) subharmonic surge frequency as a whole. The subharmonic surges are found to appear in a narrow zone neighboring the stall stagnation boundary. In other words, they tend to appear in the final stage of the stall stagnation process. It should be emphasized further that the stall stagnation initiates fundamentally at the situation where a volume-modified reduced resonant-surge frequency becomes coincident with that for the stagnation boundary conditions, where the reduced frequency is defined by the acoustical resonance frequency in the flow-path system, the delivery flow-path length and the compressor tip speed, modified by the sectional area ratio and the effect of the stalling pressure ratio. The real surge frequency turns from the resonant frequency to either near-resonant one or subharmonic one, and finally to stagnation condition, for the large-amplitude conditions, caused by the non-linear self-excitation mechanism of the surge.

• 한국해양학회지
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• v.6 no.2
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• pp.92-98
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• 1971

Storm surges caused by typhoon Billie, 28 Aug. ∼ 2 Sep. 1970, on the west and south coasts of Korea are studied with the tidal data. Tracks and frequencies of the typhoons which affected the Korean peninsula and the yearly maximum tidal deviation at tide stations for the past twelve years are also reviewed. It is assumed that most of the typhoons affecting the Korea peninsula cause variations of sea level along almost all of the coast of Korea. Maximum storm surges at each tide station on the south coast appeared to be caused by typhoons during the summer, and by the north westerly monsoon and extraordinary cyclones on the west coast during spring and winter. In the coastal waters of the west coast where depths are shallower and the bottom configuration is flat, sea level variation is mostly caused by atmospheric pressure and wind effect. When a typhoon travels as in case of typhoon Billie, sea level ascends generally on the south coast and it descends on the west coast before the typhoon approaches near to the coasts. Considering the large tidal range on the western and southern coasts, it is assumed that the extraordinary destructive surges can be occurred when the tide is high water. Reviewing the monthly mean sea level variations on the each coast, hazards to be caused by storm surges can more fluently occur during the summer.

• 한국해양학회지
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• v.25 no.4
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• pp.161-181
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• 1990

A numerical model is established in order to simulate the storm surges which were observed in the seas around Korea during typhoon and winter storm periods. The typhoons are Brenda (1985), Vera (1986) and Thelma (1987). the winter storm period is January 1-6, 1986. The simulated surges for the typhoon periods show good agreements with the recorded ones for the periods at the Korean coasts, but those for the winter storm show fair agreements in general tendencies, not in details. The model simulation in open sea shows a positive sea level near the typhoon center and a native sea level behind the typhoon. the positive surge seems to be due to the low pressure near a typhoon center and the negative on due to the wind stresses of the typhoon. The negative sea level is usually in the form of an elongated gyre. In the gyre, there is a cyclonic circulation of sea water, in which the pressure gradient force induced by the circular depression of the sea surface is balanced by the Coriolis force in readjusting stage.

• Journal of the Society of Disaster Information
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• v.11 no.4
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• pp.493-505
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• 2015

Based on the typhoon paths landed on the southern coast of Korea, the distribution of typhoon moving directions follow the Beta probability density function and that of pressure drops in typhoon eyes follow the Rayleigh probability density function. Consequently, the extreme typhoon simulation scenarios for six landing positions are determined as most probable one in moving direction and extreme one of Typhoon Maemi level in pressure drop. The variation of storm surges in Masan bay associated with simulated typhoon landing position is analyzed through the numerical experiments in the next paper as the second part.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.27 no.5
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• pp.594-604
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• 1994

The storm surges caused by the typhoon Brenda in 1985 were studied by analysing tidal observation data at 7 stations along the south coast of the Korean peninsula. The tidal deviation at these stations along the coast are discussed in association with meteorological data. The sea level anomalies were studied by means of the Empirical Orthogonal Function (EOF) analysis and the Fast Fourier Transform(FFT) method. From the result of EOF analysis, the temporal and spatial variations of storm surge were described by the first mode of EOF, which is $73\%$ of the total variances during the passage of typhoon Brenda. From the results of FFT spectral analysis, the peak energy of the autospectrum for surge, atmospheric pressure, and wind stress appeared in the low frequency fluctuations band. The result of FFT analysis showed that the typhoon surge was related chiefly to the atmospheric pressure change in an open bay such as Cheju and Keomundo harbor, while it was influenced mainly by the wind stress in the semi-enclosed waters of Yeosu, Chungmu and Kadukdo.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.205-206
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• 2006

The surges caused by the typhoon of Korea are analysed in Kwangyang Bay. The deviations of the high water level were $74{\sim}185cm$ and the maximum deviations of the water level (maximum surges) were $151{\sim}240cm$ in Kwangyang Bay during the typhoon. The major parameters of the maximum deviations of the water level are as follows : Analysis shows that the pressure drop increased the sea level by $43{\sim}59cm$, the flood of the Sumjin River by $4{\sim}5cm$ and the external surge propagation and wind setup by $97{\sim}192cm$.

• Journal of the Korean earth science society
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• v.25 no.4
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• pp.277-288
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• 2004

In this study, state of sea surface were analyzed comparatively for cases of low atmospheric pressure, which occurred in the middle area of China and moved eastward to the Korean Peninsula across the Yellow sea during April 9-12, 1999, and typhoons 'NEIL' May 1999 and 'OLGA' July 1999, which moved northward along the west coast of the Korean Peninsula. In cases of low pressure, wind speeds and phases were respectively stronger and faster in the center area than in the surrounding areas. The wave heights seem to a somewhat differing tendency from that of the wind speeds due to the influences of geometry. On the other hand, wave heights were lower under typhoon weather than under low pressures, except the instance of wave height over 5 m on Chilbal when typhoon Olga pass northward from the southern area. Storm surges also showed larger amplitudes under low pressures than under typhoons. The results suggest that wave sand storm surges may be larger for a slow passing synoptic low pressures than for a fast passing local typhoon.