• 한국자원식물학회지
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• 제36권2호
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• pp.122-132
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• 2023

한국산 며느리밥풀속(Melampyrum L.) 6분류군(M. roseum, M. roseum var. japonicum, M. roseum var. ovalifolium, M. setaceum, M. setaceum var. nakaianum, and M. koreanum)을 대상으로 외부형태학적 형질을 관찰하였다. 조사 결과, 잎의 형태, 포의 형태, 포 가장자리 강모의 분포 위치와 수는 유용한 검색형질로 확인되었으며, 줄기의 횡단면 형태와 털의 분포, 포의 기부 형태, 꽃받침 열편과 정단부 돌기의 형태, 화관의 색과 길이는 유용한 검색형질로 나타났다. 이러한 외부형태학적 형질을 바탕으로 한국산 며느리밥풀속의 검색표를 제시하였다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
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• pp.370-376
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• 2005

Magnesium alloys are becoming important material for light weight car body, due to their low specific density but high specific strength. However they have a poor weldability, caused high oxidization tendency and low vapor temperature. In this study, the welding performance of magnesium alloys was investigated for automobile application. The materials were rolled magnesium alloy sheet contains Al and Zn such as AZ3l , AZ6l and AZ9l. Three types of welding process were studied, that were GTAW, Laser beam welding and FSW. To evaluate the weldability, we examined the appearance of welding bead. Also we checked bead shape and internal defects such as crack and porosity on cross section of welding bead. The mechanical property was measured for welded specimen by tensile test. For determination of the strength change by welding process, the hardness profile across the welding center was measured. For the results, the tensile properties of welded specimen were decreased obviously on all welding process. For the fusion welding process such as GTAW and laser beam welding, the surface of the welding bead was covered with oxidized magnesium dust but it was removed by simple cleaning work as wipe-out with tissue. Also under cut, that caused vaporization of base metal was occurred. for the friction stir welding, there was no oxidation, under-cut or internal defects. However it had poor weld performance, the reason was cleavage fracture occurred at plastic deformation zone. For welding of magnesium alloy, the laser beam welding process was recommended.

• 소성∙가공
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• 제27권3호
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• pp.154-159
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• 2018

In the rectangular bar multi-stage drawing process, the cross-section dimensional accuracy of the rectangular bar varies depending on the aspect ratio and process conditions. It is very important to predict the dimensional error of the cross-section occurring in the multi-stage drawing process according to the aspect ratio of the rectangular bar and the half die angle of each pass. In this study, a process map for improving the dimensional accuracy according to the aspect ratio was derived in the drawing process of a rectangular bar. FE-simulation of the multi-stage shape drawing process was carried out with four types of rectangular bar. The results of the FE-simulation were trained to the nonlinear relationship between the shape parameters using an Artificial Neural Network (ANN), and the process maps were derived from them. The optimum half die angles were determined from the process maps on the dimensional accuracy. The validity of the suggested process map for aspect ratios 1.25~2:1 were verified through FE-simulation and experimentation.

• Wind and Structures
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• 제21권1호
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• pp.63-84
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• 2015

The shape of a tall building has significant impact on wind force generation and wind-induced dynamic response. To study the effect of recessed cavities, wind excitations on a wind-tunnel model of an H-section tall building were compared with those on a square-section building model. Characteristics of the fluctuating wind pressures on the side faces of the two tall buildings and their role in the generation of crosswind forces on the buildings were investigated with the space-time statistical tool of proper orthogonal decomposition (POD). This paper also compares the use of different pressure data sets for POD analysis in situations where pressures on two different surfaces are responsible for the generation of a wind force. The first POD mode is found to dominate the generation of crosswind excitation on the buildings.

• 수산해양기술연구
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• 제34권3호
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• pp.283-286
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• 1998

활주선 선형을 갖는 고속어선의 저항특성을 체계적으로 연구하기 위한 제 1단계로서 단면형상 및 장-폭비와 저항특성과의 관계에 대한 실험적 연구를 수행하였다. 본 연구는 새로운 고속 활주형 어선을 개발하기 위한 초기연구로서 다음의 내용을 포함하고 있다. - 4가지 단면형상에 대한 저항 특성 - 4가지 장-폭비에 대한 저항 특성

• Steel and Composite Structures
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• 제43권2호
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• pp.271-278
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• 2022

Buckling is one of the most critical phoneme in the design of steel structures. Lateral torsional buckling (LTB) is particularly significant for slender beams generally subjected to loading in plane. The web distortion effects on LTB are not addressed explicitly in standards for flexural design of steel I-section members. Hence, the present study is focused to predict the influence of the web distortion on the elastic (L_r) limiting lengths given in American Institute of Steel Construction (AISC) code for the lateral torsional buckling (LTB) behavior of steel beams due to no provision in the code for consideration of web distortion. For this aim, the W44x335 beam is adopted in the buckling analysis carried out by the ABAQUS finite element (FE) program since it is one of the most critical sections in terms of lateral torsional buckling (LTB). The strain results at mid-height of the web at mid-span of the beam are taken into account as the monitoring parameters. The web strain results are found to be relatively greater than the yield strain value when L/L_r is equal to 1.0. In other words, the ratio of L/L_r is estimated from the numerical analysis to be about 1.5 when the beam reaches its first yielding at mid-span of the beam at mid-height of the section. Due to the effect of web distortion, the elastic limiting length (L_r) from the numerical analysis is obtained to be considered as greater than the calculated length from the code formulation. It is suggested that the formulations of the limiting length proposed in the code can be corrected considering the influence of the web distortion. This correction can be a modification factor or a shape factor that reduces sectional slenderness for the LTB formulation in the code.

• 대한조선학회논문집
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• 제55권4호
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• pp.330-340
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• 2018

In the present works, the High-speed Cavitation Tunnel (HCT) has been designed and manufactured to have the large test section to conduct various supercavitation experiments. The large amount of air ventilated behind a cavitator produces lots of tiny bubbles, which prevent clear observation of supercavitation at the test section. To collect small bubbles effectively, a bubble collecting section of large volume is equipped upstream of the test section. HCT has the test section dimension of $0.3^H{\times}0.3^W{\times}3.0^L\;m^3$ and provides maximum flow speed of 20.4 m/s at the test section. The blockage and Froude effects on the ventilated supercavitation are investigated successfully at the test section. The basic studies such as the supercavitation evolution, drag measurements and cavity shape extraction with air flow rate are also carried out in HCT.

• 식물분류학회지
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• 제38권4호
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• pp.433-458
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• 2008

한국산 꿩의다리속 식물에 대해 뿌리, 잎, 화서, 꽃, 수술, 암술, 열매 등 형태 형질의 종합적인 검토를 통하여 형질의 분류학적 가치를 논하고, 이에 따라 새로운 종 검색표를 작성하였다. 연구 결과, 특수화된 줄기 및 뿌리는 수근형, 괴경을 갖는 수근형, 괴근형, 팽미근형(tuberoid), 지하경, 지상경으로 구분되었다. 줄기는 능선의 유무 또는 털의 유무에 따라 구분되었으며, 잎은 일반적으로 2-3회 3출엽이며, 엽선, 엽저, 탁엽의 모양, 열편의 수로 구분되었다. 화서는 산방화서와 원추화서로 구분되고, 꽃은 양성화이다. 꽃잎이 없으며, 개화시 꽃받침이 있는 것과 없는 것으로 구분되고, 다양한 형태를 하고 있어 종을 동정하는데 중요한 형질로 나타났다. 특히 수술은 약의 모양과 정단모양, 약의 털, 수술대의 팽창정도, 수술대의 표피형태 등에 따라 구분되며, 암술은 주두의 모양, 자방의 선모유무, 심피자루의 길이 등에 따라 구분되었다. 열매는 수과의 형태를 가지며, 수과의 모양, 수과의 능선 또는 날개의 유무, 과병의 길이 등에 따라 구분되었다. 조사된 형질 중 절을 구별하는 데는 수술대의 확장정도, 약의 모양, 수과의 날개와 능선, 수과의 팽창 정도 등이 식별형질이 사용되었으며 종 동정을 하기 위한 유용한 형질은 뿌리, 잎의 모양, 수술과 암술의 모양, 수과의 부리 및 과병의 길이, 수과와 잎의 털 등으로 나타났다.

• 한국재난정보학회 논문집
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• 제14권3호
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• pp.379-386
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• 2018

연구목적: 본 연구는 I-Shape 단면형상을 가지고 있는 곡선교량의 지진파 불확실성에 따른 안전성 분석을 위해 확률론적 기반 취약도 평가를 목적으로 한다 연구방법: 상용유한요소해석 프로그램(ABAQUS, ANSYS)구축된 모델의 검증을 위해 토크와 집중하중을 적용하여 정적해석에 따른 해석결과와 이론해를 곡선 보의 1/4L, 2/4L, 3/4L 지점에서 휨 모멘트를 비교한 결과 모든 지점에서 1%내로 오차가 발생하는 것으로 나타나 3차원 유한요소 모델에 대한 신뢰성을 확보 하였다. 곡선교량 구조물의 지진파의 불확실성을 위해 경주 및 포항 지진을 포함하여 세계각지에서 발생한 20개의 지진파를 0.2g부터 1.5g까지 5개의 Scale로 변화시켜 시간이력해석을 수행하였으며, Monte-Carlo Simulation을 기반으로 지진 취약도 평가를 수행하였다. 연구결과: 지진 취약도 분석결과 한계상태를 190MPa로 하였을 때 0.2g를 넘어가면서 파괴가 발생하나 한계상태를 315MPa로 하였을 경우 0.6g를 넘어서면서 파괴가 발생하는 것으로 나타났다. 결론: 본 연구에서 이론해와 수치해석 모델을 비교함으로써 유한요소 모델을 검증하였으며 구축된 I-Shape 곡선 보 모델의 경우 고주파수 영역에 민감성을 보이며, 추후 연구에서 곡선 보의 주요 매개변수인 단면형상에 따른 지진 취약도 평가를 수행하고자 한다.

• 식물분류학회지
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• 제48권3호
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• pp.153-162
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• 2018

Lespedeza maximowiczii C. K. Schneid. (Fabaceae) is a deciduous shrub which is known to be distributed in the temperate forests of China, Korea and on Tsushima Island of Japan. Due to severe morphological variations within species, numerous examinations have been conducted for Korean L. maximowiczii. However, the morphology of Chinese plants has not been studied as thoroughly, despite doubts about their taxonomy. To clarify this taxonomic issue, we investigated morphological characters and undertook a Bayesian clustering analysis with microsatellite markers. The morphological and genetic traits of Chinese individuals varied considerably from those of typical L. maximowiczii growing in Korea. For example, petals of the former had a different shape and bore long claws, while the calyx lobes were diverged above the middle and the upper surface of the leaflet was pubescent. Their terete buds and spirally arranged bud scales were distinct from those within the series/section Heterolespedeza, which includes L. maximowiczii. Our Bayesian clustering analysis additionally included L. buergeri as an outgroup. Those results indicated that the Chinese samples clustered into a lineage separated from L. maximowiczii (optimum cluster, K = 2), despite the fact that the latter is grouped into the same lineage with L. buergeri. Therefore, we treat those Chinese plants as a new species with the name L. pseudomaximowiczii.