• 천문학회지
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• 제53권3호
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• pp.77-85
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• 2020

In the molecular cloud G33.92+0.11A, massive stars are forming sequentially in dense cores, probably due to interaction with accreted gas. Cold dense gas, which is likely the pristine gas of the cloud, is traced by DCN line and dust continuum emission. Clear chemical differences were observed in different source locations and for different velocity components in the same line of sight. Several distinct gas components coexist in the cloud: the pristine cold gas, the accreted dense gas, and warm turbulent gas, in addition to the star-forming dense clumps. Filaments of accreted gas occur in the northern part of the A1 and A5 clumps, and the velocity gradient along these features suggests that the gas is falling toward the cloud and may have triggered the most recent star formation. The large concentration of turbulent gas in the A2 clump seems to have formed mainly through disturbances from the outside.

• 한국어류학회지
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• 제11권1호
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• pp.72-85
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• 1999

전선역 주변해역의 자치어 종 조성에 관한 조사가 대한해협을 대상으로 1993년 8월에 실시되었다. 북위 $35{\sim}36^{\circ}$의 대륙사면 주변해역에 전선이 형성되어있었다. 총 125 종류의 자치어가 출현하였다. 우점종은 멸치와 앨퉁이였으며 두 종의 출현량 비율은 각각 84.3%와 7.7%였다. 출현 빈도가 높은 종은 망둑어과, 돛양태과 그리고 자리돔과 둥이다. 위의 5종은 크게 모든 조사해역에서 출현하는 멸치와 돛양태과, 전선역을 경계로하여 수온이 높은 전선역의 남부해역에 주로 출현하는 망둑어과와 자리돔과 그리고 전선역을 포함한 전선역의 북부해역에 주로 출현하는 앨퉁이로 크게 구분되었다. 본 연구해역에서 자치어의 종 조성과 지리적인 분포는 어류의 종별 산란생태 뿐만 아니라 대마난류수와 동해고유수의 접촉으로 형성된 전선의 지리적인 분포와 구조등과 같은 물리적인 영향을 받는 것으로 판단된다.

• 한국해양학회지
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• 제7권1호
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• pp.19-23
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• 1972

온난한 해면위를 비교적 한냉한 대기가 통과할 때 공기와 수면 사이의 열교환량을 알기 위하여서는 해면에서의 현열방출량과 증발량을 측정하여야 하나, 이것들을 직접 측정하기란 현상 자체가 미세하고 측정범위가 너무나 광범위 하기 때문에 매우 어려운 점이 많다. 이런 점들을 극복하기 위하여 Jacobs91949, 1951)와 Manabe(1958)는 기온, 풍속, 증기압과 표면해수온도만을 사용하여 열교환량을 추정할 수 있는 실험식을 구하였다. 이 실험식들은 기온과 표면해수온도와의 차가 크면 클수록 열교환량이 증가함을 나타냈다. 겨울철에 우리나라 동해는 cP기단의 영향으로 한파의 내습이 빈번하고 강한 북서풍이 상존하기 때문에 대기와 해면 사이에 열교환이 왕성한 것은 기정사실이며, 이것에 대한 연구는 Matsumoto(1948, 1967), Manabe(1957, 1958), Kondo(1964), Fujita and Honda(1966)등 여러명의 일본 기상학자들이 관심을 갖고 다루어 왔으나, 이들은 한결같이 동해에서의 열수지 보다 물수지에 관심이 많았고, 일본본토의 강설량과 상관관계를 주로 연구하였다. 본 논문에서는 한국과 일본에서 이미 관측된 해양 및 기상자료를 이용하여 혹한을 동반한 1963년 1월과 난동의 1964년 1월, 그리고 평년의 1965년 1월의 열수지를 계산 비교하고, 이에 따른 여름철의 냉수괴의 세력을 비교 검토하여 보았다.

• Design & Manufacturing
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• 제6권2호
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• pp.54-58
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• 2012

A counter shaft gear is an important part in the transmission system of vehicle. Its shape is relatively complicated and should meets high strength. Traditionally it has been manufactured as follows; the counter shaft gear has consisted of a clutch and helical body with teeth which are forged and machined for teeth respectively and then attached by frictional welding. In this study, a new hot forging process was proposed and designed so that the counter shaft gear is formed as one body without divide it into two parts. Furthermore, the precision forging process has been developed for the clutch teeth without additional grinding.

• Design & Manufacturing
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• 제6권2호
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• pp.6-11
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• 2012

A counter shaft gear is an important part in the transmission system of vehicle. Its shape is relatively complicated and should meets high strength. Traditionally the counter shaft gear has been manufactured as follows; a spline body is firstly machined for teeth and then attached to the main gear body by frictional welding, and finally is finished by grinding. Therefore it is necessary to develop a new manufacturing technology eliminating both frictional welding and grinding processes. In this study, a new hot forging process was proposed and designed so that the spline body with teeth and main gear body are formed as one body. Finite element simulations and experimental works were peformed for design of forging processes to get the quality final precision-forged product. Consequently the most suitable blocker process could be obtained.

• 동력기계공학회지
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• 제16권2호
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• pp.17-23
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• 2012

The steady three-dimensional computational thermal flow analysis using standard k-${\varepsilon}$ turbulence model was carried out to investigate the heat transfer characteristics of a cabin cooler for a commercial vehicle. The heat exchanging method of this cabin cooler is to use the cooling effect of a thermoelectric module. In view of the results so far achieved, the air system resistance of a cabin cooler is about 12.4 Pa as a static pressure, and then the operating point of a cross-flow fan considering in this study is formed in the comparatively low flowrate region. The air temperature difference obtained from the cold part of an thermoelectric module is about $26^{\circ}C$, and the cooling water temperature difference obtained from the hot part of an thermoelectric module is about $3.5^{\circ}C$.

• Steel and Composite Structures
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• 제30권6호
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• pp.551-565
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• 2019

A total of 36 carbon steel and stainless steel bolted connections subjected to shear loading at different strain rates was experimentally investigated. The connection specimens were fabricated from carbon steel grades 1.20 mm G500 and 1.90 mm G450, as well as cold-formed stainless steel types EN 1.4301 and EN 1.4162 with nominal thickness 1.50 mm. The connection tests were conducted by displacement control test method. The strain rates of 10 mm/min and 20 mm/min were used. Structural behaviour of the connection specimens tested at different strain rates was investigated in terms of ultimate load, elongation corresponding to ultimate load and failure mode. Generally, it is shown that the higher strain rate on the bolted connection specimens, the higher ultimate load was obtained. The ultimate loads were averagely 2-6% higher, while the corresponding elongations were averagely 8-9% higher for the test results obtained from the strain rate of 20 mm/min compared with those obtained from the lower strain rates (1.0 mm/min for carbon steel and 1.5 mm/min for stainless steel). The connection specimens were generally failed in plate bearing of the carbon steel and stainless steel. It is shown that increasing the strain rate up to 20 mm/min generally has no effect on the bearing failure mode of the carbon steel and stainless steel bolted connections. The test strengths and failure modes were compared with the results predicted by the bolted connection design rules in international design specifications, including the Australian/New Zealand Standard (AS/NZS4600 2018), Eurocode 3 - Part 1.3 (EC3-1.3 2006) and North American Specification (AISI S100 2016) for cold-formed carbon steel structures as well as the American Specification (ASCE 2002), AS/NZS4673 (2001) and Eurocode 3 - Part 1.4 (EC3-1.4 2015) for stainless steel structures. It is shown that the AS/NZS4600 (2018), EC3-1.3 (2006) and AISI S100 (2016) generally provide conservative predictions for the carbon steel bolted connections. Both the ASCE (2002) and the EC3-1.4 (2015) provide conservative predictions for the stainless steel bolted connections. The EC3-1.3 (2006) generally provided more accurate predictions of failure mode for carbon steel bolted connections than the AS/NZS4600 (2018) and the AISI S100 (2016). The failure modes of stainless steel bolted connections predicted by the EC3-1.4 (2015) are more consistent with the test results compared with those predicted by the ASCE (2002).

• 소성∙가공
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• 제29권4호
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• pp.194-202
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• 2020

In this paper, experimental and numerical study on a combined sheet metal forming and plate forging of a seal part of a passenger car's hub bearing is conducted to develop the new process of which target is to remove machining process by plate forging and to achieve near-net shape manufacturing. The previous process of a sheet metal forming inevitably needed a machining process for making stepped sheet after conventional sheet metal forming in a progressive way. The stepped sheet is intended to be formed by plate forging in this study. Through the systematic way of developing the combined forming process using solid elements based-elastoplastic finite element method (FEM), several conceptual designs are made and an optimized process design in terms of geometric dimensioning and tolerance of straightness of the thin part is found, which is exposed to bending in metal forming of axisymmetric part. The predicted straightness measured by the slope angle of the tilted thin region is compared with the experimental straightness, showing that they are in a good agreement with each other. Through this study, a systematic approach to optimal process design, based on elastoplastic FEM with solid elements, is established, which will contribute to innovating the conventional small-scaled sheet metal forming processes which can be dealt with by solid elements.

• 한국수산과학회지
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• 제16권4호
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• pp.401-409
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• 1983

1981년과 1982년 $4{\sim}6$월에 한국 남해와 서해 연근해에서 채집된 멸치의 난치어 및 해양관측 자료를 사용하여 수괴배치에 따른 멸치의 난치어의 분포를 분석하였다. 온도전선은 남해에서는 제주도와 대마도를 잇는 선상에서 한국남안연안수와 대마난류간에 형성되었고 서해에서는 태안반도이남해역과 해안선과 평행하게 남북으로 한국서안연안수와 황해냉수간에 형성되었다. 한국남해에서 멸치난은 온도전선 내측인 연안측에서, 멸치 치어는 온도전선을 중심으로 연안측과 외해측으로 분리되어 출현하였다. 그러나 한국서해에서 멸치난과 치어는 온도전선내측과 온도전선역인 $12^{\circ}C$ 이상의 해역에서만 출현하였다. 치어의 체장조성을 보면 남해에서는 연안측에서 전기자어가, 외해측에서 후기자어 및 치어기의 멸치가 주로 출현하였으나, 서해에서는 남부해역에서는 전기자어가 북부해역에서는 후기자어가 주로 출현하였다. 또한 온도전선의 경도가 큰 1981년에는 1982년에 비하여 난과 치어의 분포범위가 크게 제한을 받으므로서 전선의 강약은 난과 치어의 분포에 큰 영향을 주는 것으로 추정된다.

• 소성∙가공
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• 제17권2호
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• pp.124-129
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• 2008

Net shape forging technologies give many effects into the costs and qualities for the finished products. So, the studies to reduce the additional machining amount are very important in forging industry. Specially, there are two main topics in cold forging industry, such as, tool life and precision forging. In this study, new forging technique was proposed to eliminate the machining process for fixing up the length and improve the lead accuracy of gear. The luck-up hub is manufactured through many processes, such as upsetting, piercing and direct extrusion. The gear is formed in direct extrusion process; however, lead accuracy of the gear is over allowance limit. Therefore, the additional sizing process must be added. In this study, process design for closed-die forging of a lock-up hub used for a component of automobile transmission was made using three-dimensional finite element simulations, and the strain distributions and velocity distributions are investigated through the post processor. The rigid-plastic finite-element method for back pressure forging has been used in order to reduce development time and die cost. Using the FEM simulation, we found the optimum value of back pressure. The prototypes of lock-up hub parts were forged into the net-shape. In the experiment, lead precision of tooth are measured by the CCMM(Contact Coordinate Measuring Machine). The dimensional accuracy of forged part was improved up to the 40% when back press was applied.