• 한국환경과학회지
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• 제30권6호
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• pp.475-485
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• 2021

This research investigated the characteristics of fine particles during cold front passage in Busan, on March 19, 2020. The cold front speed was 17.4 m/s (about 63k km/hr), moving from the northwest to the southeast, and with a width of about 64 km. The backward trajectory analysis showed that a southern sea air parcel flowed into Busan before the cold front passage, carrying continental materials from China transported into Busan after cold front passage. The PM₁₀ concentration in Busan showed a rapid increase after passing through the cold front, with PM_2.5 showing a high concentration during cold front passage. The PM_2.5/PM₁₀ ratio was 0.10 - 0.30. When the cold front passed, SO₄^2-, NO₃^-, Ca²⁺, NH₄⁺, Na⁺, and K⁺ in PM_2.5 showed a rapid increase, with SO₄^2- showing the most significant increase. These results indicated that understanding the characteristics of fine particles during cold front passage in Busan could provide insight into establishing a strategy to control urban air quality.

• 한국환경과학회지
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• 제31권12호
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• pp.1069-1078
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• 2022

This study investigated the weather conditions, fine particle concentration, and ion components in PM_2.5 when two cold fronts passed through Busan in succession on February 1 and 2, 2021. A analysis of the surface weather chart, AWS, and backward trajectory revealed that the first cold front passed through the Busan at 0900 LST on February 1, 2021, with the second cold front arriving at 0100 LST on February 2, 2021. According to the PM₁₀ concentration of the KMA, the timing of the cold front passage had a close relationship with the occurrence of the highest concentration of fine particles. The transport time of the cold front from Baengnyeongdo to Mt. Gudeok was approximately 11 hours . The PM₁₀ and PM_2.5 concentrations in Busan started to increase after the first cold front had passed, and the maximum concentration occurred two hours after the second cold front passed. The SO₄^2-, NO₃^-, and NH₄⁺ concentration in PM_2.5 started to increase from 1100 to 1200 LST on February 1, after the first cold front passed, and peaked at 0100 LST to 0300 LST on February 2. However, the highest Ca²⁺ concentration was recorded 2-3 hours after the second cold front had passed.

• 소성∙가공
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• 제30권5호
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• pp.236-241
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• 2021

This study describes the cold stamping process design procedure to secure the formability and dimensional accuracy of the automotive structural component fabricated by 1.5GPa grade ultra-high strength steel sheet. The target product is selected as the front side rear lower member which is the most important energy absorption part in the frontal impact condition. To secure the product quality, an intermediate product shape is added while considering the low elongation and high strength characteristics of 1470Mart. The sequential optimization procedure of the intermediate product shape, the fine dimensional quality is then achieved without any crack or wrinkling. The cold stamping method with ultra-high strength steel sheets is validated by conducting the die tryout of the front side rear lower member.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.527-530
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• 1997

An automated process planning system for cold forging of non-axisymmetric parts of comparatively simple shape was developed in this study. Programs for the system have been written with Visual LISP in the AutoCAD using a personal computer and are composed of four main modules such as input module, shape cognition and shape expression module, material diameter determination module and process planning module. The design rules and knowledges for th system are extracted from the plasticity theories. handbook, relevant reference and empirical knowledge of field experts. Generally, in forging, only front view is needed for expression of axisymmetric parts, but non-axisymmetric parts are needed both front view and plane. At the plane, this system cognizes the external shape of non-axisymmetric parts - number of sides of regular polygon and radius of a circle circumscribing the polygon of n sides. At the front view, the system perceives diameter of axisymmetric portions and hight of primitive geometries such as polygon, cylinder, cone, concave, convex, etc.

• 한국군사과학기술학회지
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• 제12권4호
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• pp.415-423
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• 2009

To investigate low frequency acoustic transmissions in the Sub-Polar Front(SPF) of the East Sea, numerical experiments are conducted with Range dependent Acoustic Model(RAM) using Circulation Research of the East Asian Marginal Seas(CREAMS) data and Autonomous Profiling Explorer(APEX)) data. Significant seasonal variations of sea water properties are existed across the Sub-Polar Front(SPF) region from the north and the south. The model results show that Transmission Loss(TL) decrease(about 20dB) with ideal front in the warm region whereas TL increase(about 25dB) with ideal front in the cold region. Regardless of season(both in summer and winter), when the sound source is located in the cold region of the SPF, the model results show weak TL, compared to the case of the source in the warm region(Maximum difference of TL reaches 28dB). This difference between the cases when the source is located in the cold region and the warm region, is accounted for from the different vertical profiles of sound speed in both regions.

• 한국정밀공학회지
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• 제30권12호
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• pp.1295-1301
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• 2013

The cause of flow mark defect is known as non-uniform temperature of mold surface when the flow front meets the cold cavity. The exact definition and classification of Flow mark is not clear because the mechanism of flow mark is not figured out till now. Any injection molding analysis software can not predict the flow mark phenomena. To solve weldline and flow mark defects, the gate thickness is reduced to increase the melt front velocity and the melt front velocity of the flow mark area is increased from 82.3mm/s to 104.7mm/s. In addition, the bulk temperature of the flow mark area is increased from $178.3^{\circ}C$to $215.2^{\circ}C$ by adding a cold slug well. The flow mark phenomena can be greatly reduced by increasing the flow front velocity and elevating the bulk temperature.

• 한국수산과학회지
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• 제31권5호
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• pp.749-759
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• 1998

1996년 11월 동해에 형성된 전선역에서 동물플랑크톤의 분포를 살펴본 바, 그 양은 한수역보다는 작지만 난수역 보다는 큰 것으로 나타났고, 종 조성은 매우 풍부한 것으로 나타났다. 전선역의 동물플랑크톤 군집은 양적으로는 한류수의 영향을, 종류는 난류수의 영향을 받는 것으로 나타났다. 난수역과 한수역에서는 각 해역의 서로 다른 두 정점간에 채집 시간이 낮과 밤으로 차이가 있음에도 출현하는 동물플랑크톤의 종 조성과 분포 양상이 비슷하였지만, 전선역 두 정점에서는 하루중 비슷한 시간대에 채집되었음에도 종 조성과 분포 양상에 차이가 있었다. 이는, 전선역의 수괴 혼합 진행 정도를 반영하는 지리적 차이가 동물플랑크톤의 종 조성과 분포에 영향을 주고 있음을 의미한다. 한수역의 대표적인 요각류 Metri-dia pacinca 만이 주목할 만한 일주수직이동 양상을 보였으며, 이 종의 분포가 전체 동물플랑크톤의 분포 양상을 크게 좌우하였다. 그밖의 대부분 종들은 일주 수직이동이 매우 미약하였다. 수온이 동물플랑크톤의 분포에 큰 영향을 미치는 것으로 나타났다. 수온과 주요 우점 동물플랑크톤 분포량의 상관 관계는 난수역에서는 대체로 양의 상관관계를, 한수역에서는 매우 약한 음의 상관관계를, 그리고 전선역에서는 대부분 통계적 유의성이 없는 결과를 보였다.

• 해양환경안전학회지
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• 제15권4호
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• pp.289-296
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• 2009

본 연구는 장기 해양관측(1966-1995)자료, 위성관측자료 및 수치모델기법을 이용하여 한국 남서해역에서 하계에 형성되는 조석전선괴 저수온역의 시공간적 변화를 파악하였다. 한국 남서 연안해역에서는 6월과 8월에 대흑산도~진도간 해역의 표면에서 주변 해역보다 $2{\sim}3^{\circ}C$ 낮은 저수온역이 분포하면서 조석전선역이 형성됨을 확인할 수 있었다. 수온수평경도가 $0.3^{\circ}C$/km 이상인 조석전선은 성층계수 2.0~2.5 범위이며, $0.03^{\circ}C$/km 이상인 저수온역은 성층계수 2.5~3.0의 범위와 일치하였다. 소조시에서 대조시까지 조석주기가 변하는 동안 조석전선의 위치변동은 전선은 25~75km, 저수온역의 범위는 60~90km로 조류의 세기에 정비례하여 이동 범위가 커지는 것으로 나타났다. 또한, 남서쪽 외해역으로 저수온역이 확장되는 원인은 진도 남서쪽으로 향하는 10cm/s 이상의 강한 조석잔차류에 의한 것으로 판단된다.

• Journal of the korean society of oceanography
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• 제32권3호
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• pp.93-102
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• 1997

Coastal circulations during the (surface condition of an) idealized cold-air outbreak are numerically investigated with two-dimensional, non-hydrostatic model in which a constant bottom-slope exists. The atmospheric forcing during a cold-air outbreak is incorporated as the surface cooling and the wind stress. When the offshore angle of the wind-stress vector, defined as the angle measured from the alongshore axis, is smaller than 45 degrees, a strong downwelling circulation develops near the coast. A sharp density front, which separates the vertically homogeneous region from the offshore stratified region, is formed near the coast and propagates offshore with time. Onshore side of the density front, small-scale circulation cells which are aligned in the direction perpendicular to the bottom begin to develop as the near-coast homogeneous region broadens. The surface cooling enhances greatly the development of the surface mixed layer by convective motions due to hydrostatic instability. The convective motions reach far below the hydrostatically unstable layer which is attached to the surface. The small-scale circulation cells are appreciably modified by the convetion cell and the density front develops far offshore compared to the case of no surface cooling. As to the effect of the bottom slope, the offshore distance of the density front increases (decreases) as the bottom slope decreases (increases), which results from the fact that the onshore volume-transport (Ekman transport) of the low-density upper seawater remains almost constant when the wind-stress is maintained constant. It is shown that the bottom slope is an essential factor for the formation of both the density front and the alongshore current when the surface cooling is the only forcing.

• 한국해양학회지:바다
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• 제8권3호
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• pp.327-339
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• 2003

겨울철인 1998년 2월과 1999년 1월, 4월에 남해와 동중국해 북부해역에서 형성되는 전선의 분포와 구조를 파악하기 위하여 광역의 종합해양관측을 수행하였다. 관측해역에서 구분된 수계들은 대마난류기원 고온수, 황해냉수(북부냉수 혹은 중앙냉수) 그리고 남해저온수로 분류된다. 황해남부 해역에서는 제주도 서쪽을 우회하여 제주해협으로 유입하는 대마난류기원 고온수가 '┍'자 형태의 기본적 전선을 이루며 대흑산도 남쪽에 황해중앙냉수와 그리고 양자천퇴 동부에서 황해북부냉수와 만나고 있다. 이 전선은 고온수가 황해 북서부로 확장하는 세기에 의해 전선 모서리 형태와 위치가 달라진다. 양자천퇴 부근과 한반도 남서단 외측에서의 전선위치와 구조도 관측시기에 따라 변화한다 남해 전선에서는 연안 저온수가 국지적 냉각에 의해 독립적으로 형성된 수계로서 해저사면을 따라 침강한다. 이러한 겨울철 전선분포의 변화와 전선구조가 변화되는 과정은 탁월풍에 의한 순풍류 및 역풍류, 해수면을 통한 열수지 그리고 전선사이의 밀도차이에 의한 것으로 설명되었다.