• Journal of Korean Society for Atmospheric Environment
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• v.15 no.4
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• pp.441-455
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• 1999

Meteorological characteristics of three high-ozone episodes in the Greater Seoul Area, selected on the basis of morning-average wind direction and speed for the 1990~1997 period, were investigated. Three high-ozone episodes thus selected were seven days of July 3~9, 1992, nine days of July 21~29, 1994, and three days of August 22~24, 1994. Along with surface meteorological data from the Seoul Weather Station, surface and 850-hPa wind fields over the Northest Asia around the Korean Peninsula were used for the analysis. In the July 1992 episode, westerly winds were most frequent as a result of the influence of a high-pressure system in the west behind the trough. In contrast, in the July 1994 episode, easterly winds were most frequent due to the effect of a typhoon moving north from the south of Japan. Despite different prevailing wind directions in the two episodes, the peak ozone concentration of each episode always occurred when a sea-land breeze developed in association with weak synoptic forcing. The August 1994 episode, selected as being representative of calm conditions, was another typical example in which peak ozone concentration rose to 322 ppb under the well-developed sea-land breeze. All three high-ozone episodes were terminated by precipitation, and subsequent rises in ozone concentrations were also suppressed by a series of precipitation afterwards. In particular, two heavy rainfalls were the main reason why the August 1994 episode, with the highest and second-highest ozone concentrations during the 1990~1997 period, lasted for only a few days.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1875-1880
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• 2003

Measurements of wind flow and pressure fluctuations induced by train passing on station platform have been conducted. Test conventional trains have a different nose shapes - bluff nose and wedged nose. The bluff nose train influence peak value of pressure fluctuations on station platform three times more than the wedged nose train for train speed of 108 km/h. Also, air flow induced by the bluff nose train passing is three times more than the wedged nose train passing. Current study shows that the gust induced by the bluff nose conventional train may threaten a passenger's safety on station platform in proximity to train passage.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.3
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• pp.1-7
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• 2002

An experimental study was conducted to investigate the effects of leading edge extension(LEX) on the surface prssure distribution over a delta wing in a subsonic wind tunnel. Freestream velocity was 40m/sec and Reynolds number per meter was 1.7x$10^6$ with total pressure of 101Pa and total temperature of 278K. LEX changed the surface pressure distribution on the wing dramatically. Comparing with the results without LEX, the peak of pressure distribution decreased on the front chordwise location but it turned to increase on the rear chordwise location with increase of the angle of attaci. The spanwise gradient of the pressure distribution also increased in the rear chordwise location. Without LEX, the peak of pressure distribution increased and decreased irregularly with increase of the angle of attack at each chordwise location, but LEX made it increased almost linearly with increase of the angle of attack at all of the chordwise locations.

• 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.

• Wind and Structures
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• v.17 no.5
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• pp.479-494
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• 2013

The vehicle-induced aerodynamic loads bring vibrations to some of the highway sound barriers, for they are designed in consideration of natural wind loads only. As references to the previous field experiment, the vehicle-induced aerodynamic loads is investigated by numerical and theoretical methodologies. The numerical results are compared to the experimental one and proved to be available. By analyzing the flow field achieved in the numerical simulation, the potential flow is proved to be the main source of both head and wake impact, so the theoretical model is also validated. The results from the two methodologies show that the shorter vehicle length would produce larger negative pressure peak as the head impact and wake impact overlapping with each other, and together with the fast speed, it would lead to a wake without vortex shedding, which makes the potential hypothesis more accurate. It also proves the expectation in vehicle-induced aerodynamic loads on Highway Sound Barriers Part1: Field Experiment, that max/min pressure is proportional to the square of vehicle speed and inverse square of separation distance.

• Wind and Structures
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• v.16 no.1
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• pp.93-115
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• 2013

This paper describes a study of the influence of a dynamically flexible building structure on pressures inside and net pressures on the roof of low-rise buildings with a dominant opening. It is shown that dynamic interaction between the flexible roof and the internal pressure results in a coupled system that is similar to a two-degree-of-freedom mechanical system consisting of two mass-spring-damper systems with excitation forces acting on both the masses. Two resonant modes are present, the natural frequencies of which can readily be obtained from the model. As observed with quasi-static building flexibility, the effect of increased dynamic flexibility is to reduce the first natural frequency as well as the corresponding peak value of the admittance, the latter being the result of increased damping effects. Consequently, it is found that the internal and net roof pressure fluctuations (RMS coefficients) are also reduced with dynamic flexibility. This model has been validated from experiments conducted using a cylindrical model with a leeward end flexible diaphragm, whereby good match between predicted and measured natural frequencies, and trends in peak admittances and RMS responses with flexibility, were obtained. Furthermore, since significant differences exist between internal and net roof pressure responses obtained from the dynamic flexibility model and those obtained from the quasi-static flexibility model, it is concluded that the quasi-static flexibility assumption may not be applicable to dynamically flexible buildings. Additionally, since sensitivity analyses reveal that the responses are sensitive to both the opening loss coefficient and the roof damping ratio, careful estimates should therefore be made to these parameters first, if predictions from such models are to have significance to real buildings.

• Korean Journal of Agricultural and Forest Meteorology
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• v.7 no.1
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• pp.35-44
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• 2005

Microclimate of Gwangneung forest watershed is characterized by analyzing wind, radiation, profiles of air temperature and humidity, soil and bole temperature, precipitation and soil water content measured at and around the flux tower from April 2000 to September 2003. Mountain-valley wind was prevalent due to the topographic effect with dominant wind from east during daytime and relatively weak wind from west during nighttime. Air temperature reaches its peak in July-August whereas monthly-averaged incoming shortwave radiation shows its peak in May due to summer monsoon. Albedo ranges from 0.12 to 0.16 during the growing season. Monthly-averaged bole temperature is in phase with monthly- averaged air temperature which is consistently higher. Monthly-averaged soil temperature lags behind air temperature and becomes higher with leaf fall. With the emergence of leafage in April, maximum temperature level during midday shifts from the ground surface to the crown level of 15-20m in May. Profiles of water vapor pressure show a similar shift in May but the ground surface remains as the major source of water. Vapor pressure deficit is highest in spring and lowest in winter. Monthly averaged surface soil temperatures range from 0 to 20℃ with a maximum in August. Monthly averaged trunk temperatures of the dominant tree species range from -5.8 to 21.6℃ with their seasonal variation and the magnitudes similar to those of air temperature. Annual precipitation amount varies significantly from year to year, of which >60% is from July and August. Vertical profiles of soil moisture show different characteristics that may suggest an important role of lateral movement of soil water associated with rainfall events.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.8-15
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• 2005

Aerodynamic sounds generated by a uniform flow around a two-dimensional circular cylinder at Re=150 are simulated by applying the finite difference lattice Boltzmann method. Thethird-order-accurate up-wind scheme (UTOPIA) is used for the spatial derivatives, and the second-order-accurate Runge-Kutta scheme is applied for the time marching. We have succeed in capturing very small pressure fluctuations with the same frequency of the Karman vortex street compared with the pressure fluctuation around a circular cylinder. The propagation velocity of the acoustic waves shows that the points of peak pressure are biased upstream due to the Doppler effect in the uniform flow. For the downstream, on the other hand, it is faster. It is also apparent that the amplitude of sound pressure is proportional to r /sup -1/2/,r being the distance from the center of the circular cylinder. To investigate the effect of the lattice dependence, furthermore, 2D computations of the tone noises radiated by a square cylinder and NACA0012 with a blunt trailing edge at high incidence and low Reynolds number are also investigate.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.5
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• pp.717-727
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• 2004

In this study, we simulate the aerodynamic sounds generated by a two-dimensional circular cylinder in a uniform flow are simulated by applying the finite difference lattice Boltzmann method (FDLBM). The third-order-accurate up-wind scheme (UTOPIA) is used for the spatial derivatives. and the second-order-accurate Runge-Kutta scheme is applied for the time marching. The results show that we successively capture very small acoustic pressure fluctuations with the same frequency of the Karman vortex street compared with the Pressure fluctuation around a circular cylinder The propagation velocity of the acoustic waves shows that the points of peak pressure are biased upstream due to the Doppler effect in the uniform flow For the downstream. on the other hand. it quickly Propagates. It is also apparent that the amplitude of sound Pressure is Proportional to $r^{-1/2}$, r being the distance from the center of the circular cylinder. To investigate the effect of the lattice dependence furthermore a 2D computation of the tone noise radiated by a NACA0012 with a blunt trailing edge at high incidence and low Reynolds number is also investigated.

• Journal of Integrative Natural Science
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• v.1 no.2
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• pp.89-114
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• 2008

Interrelationship between heavy rainfalls and related with low-level jets(LLJ) is analyzed by using fifty cases of heavy rainfall events occurred over the Korean peninsula from 1992 to 2001. Those cases are classified with four synoptical features. There are 32% chances that the low pressure exist in heavy rainfall over than 150 mm per day case by case. Secondly Changma front and front zone account for 28% of all cases. The ratio of marine tropical boundary type and trough type record 22% and 18% respectively. The moist and warm south-westerly winds associated with low-level jets have been induced convective instability and baroclinic instability. Therefore, heavy rainfall due to the approach of a low pressure occurred at September and before Changma. During the period of Changma, this type has been happened heavy rainfall when low pressure and stationary front has vibrated south and north. Changma type has longer the duration time of precipitation than other types. Third type, located with marine Tropical boundary, have mainly rained in August and September. The last trough case locally downpoured in short time with developing cell. The occurrence low-level jets related to heavy rainfall has increased over 12.5 m/s wind speed. The result is that 43 heavy rainfalls out of 50 cases reach peak at the time of maximum precipitation intensity. Also, the variation of wet number and K-index corresponded with the variation of wind speed. It is found that the number of frequency of low-level jets with southwestward direction has been increased and these jets are mainly passed from the southwest toward to the northeast of the Korean peninsula in that time.