• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.51 no.2
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• pp.203-211
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• 2015

The purpose of this study is to identify the flow resistance of the bottom pair trawl nets. The bottom pair trawl nets being used in fishing vessel (100G/T, 550ps) was selected as a full-scale net, and 1/10, 1/25 and 1/50 of the model nets were made. Converted into the full-scale net by Tauti's modeling rule and Kim's modeling rule, when resistance coefficient k of each net was calculated by substituting into above equation for flow resistance R and wall area of nets S values of each net ${\upsilon}$. Because resistant coefficient k decreases exponentially according as flow velocity ${\upsilon}$ increases to make $k=c{\upsilon}^{-m}$, c and m values of each net were compared. As a result, as the model was smaller, c and m values was smaller in the two rule into standard of 1/10 model value, decrease degree of 1/25 model was almost same in the two rule, decrease degree of 1/50 model was very big in Tauti's modeling rule. Therefore, in the result of experiment, because average of c and m values for similarly 1/10 and 1/25 model were given $c=4.9(kgf{\cdot}s^2/m^4)$ and m=0.45, R (kgf) of bottom pair trawl net could show $R=4.9S{\upsilon}^{1.55}$ using these values. As in the order of cod-end, wing and bag part for 1/25 and 1/50 model net were removed in turn, measured flow resistance of each, converted into the full-scale, total resistance of the net and the resistance of each part net were calculated. The resistance ratio of each part for total net was not same in 1/25 and 1/50 model each other, but average of two nets was perfectly same area ratio of each part as the wing, bag and cod-end part was 43%, 45% and 12%. However, the resistance of each part divided area of the part, calculated the resistance of per unit area, wing and bag part were not big difference each other, while the resistance of cod-end part was very large.

• Applied Chemistry for Engineering
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• v.19 no.4
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• pp.413-420
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• 2008

Over the past decade, there have been significant advancement in the field of electrospinning area. This study has focused on preparing yarn using polycarbonate (PC) nanofibers including modified multi-walled carbon nanotube (mMWNT) by solution electrospinning process using the mixture of solvents consisting of tretrahydronfuran (THF) and N,N-dimethylformamide (DMF). In order to enhance the dispersion, MWNT was chemically modified. TEM analysis for the prepared PC/mMWNT nanofibers reveals that mMWNT was well-dispersed into the PC nanofiber matrix. Also with increasing contents of mMWNT, thermal stability of PC/mMWNT nanofibers was improved than that of PC nanofibers. Moreover when 3 to 5 wt% of mMWNT was added, the nanofibers showed good electrical properties expecting antistatic effect, ranging 109.1~109.5 ${\Omega}$. It was confirmed that the multi-filament fibers using PC/mMWNT had $60{\sim}100{\mu}m$ in diameter and 4~5 cm in length.

• Korean Journal of Food Science and Technology
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• v.39 no.6
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• pp.701-707
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• 2007

Anti-diabetic effect of Platycodi radix (PR) extract fractions was determined if vitro by investigating insulin-like action, insulin sensitizing action, glucose-stimulated insulin secretion, gene expression related to ${\beta}-cell$ function and mass, and ${\alpha}$-glucoamylase suppressing action. Insulin-like activity was not promoted by the treatment of PR methanol factions in 373-L1 fibroblast. However, treatment with 0, 20 and 100% PR methanol fractions along with 1 ng/mL insulin increased insulin-stimulated glucose uptake in 373-L1 adipocytes. In addition, the treatment of 0% and 100% methanol fractions along with differentiation inducers significantly increased the differentiation of 373-L1 fibroblasts to adipocytes. These fractions may contain insulin sensitizer. The 20%, 80% and 100% methanol fractions enhanced glucose-stimulated insulin secretion in Min6 cells, insulin secreting cell line. This was related to the mechanism to promote glucose sensing and ${\beta}-cell$ proliferation, which was regulated by the induction of IRS-2, glucokinase and PDX-1 genes. As expected, 20, 80 and 100% methanol fractions increased mRNA levels of IRS-2, glucokinase and PDX-1 genes. However, PR fractions did not affect the ${\alpha}-glucoamylase$ activity in vitro. These data suggested that PR extract fractions have anti-diabetic actions through improving insulin sensitization, glucose-stimulated insulin secretion, and ${\beta}-cell$ proliferation. Therefore, PR extracts can be beneficial for anti-diabetic treatment in lean diabetic patients.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.4
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• pp.221-231
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• 2011

Thinner and lighter structural members can be designed by utilizing the high stiffness and toughness, and high compressive strength of UHPC(ultra high performance concrete), which reaches up to 200MPa. The punching shear capacity of UHPC was investigated in this paper aiming for the application of UHPC to bridge decks. Six square slabs were fabricated and punching shear test was performed under fixed boundary condition. Different thicknesses of test slabs, which were 40mm and 70mm, were selected. The shape ratio of loading plates were ranged between 1.0~2.5. 40mm thickness slabs showed longer softening region after the peak load and, on the other hand, 70mm thickness slabs revealed a more brittle shear failure. Experimental results were analyzed using various existing punching shear predicting equations. Ductal$^{(R)}$ equation and JSCE equation better predicted for 40mm slabs, and Harajli et al. equation and ACI-Ductal$^{(R)}$ equation better suited for 70mm slabs. Nevertheless generally they didn't well predict the test results. A new punching shear equation which was derived based on the actual failure mechanism was proposed. The proposed equation appeared to better predict the punching shear strength of UHPC than other available equations.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.87-87
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• 2018

다이아몬드 상 탄소(diamond-like carbon, DLC)는 상당량의 $sp^3$ 결합을 가지는 비정질 탄소(a-C) 또는 수소화 비정질 탄소(a-C:H)로 이루어진 준안정 형태의 탄소이다. DLC는 전기 저항과 굴절률이 높고 화학적으로 다른 물질과 반응하지 않으며, 마찰계수가 낮고 경도가 높아 자기 디스크, 광학 소자 등의 다양한 분야에서 적용되고 있다[1,2]. 또한 다이아몬드에 비해 상온에서 성장이 가능할 정도로 합성온도가 낮아 적용 기판의 제한이 거의 없고, 증착 방법과 조건에 따라 탄소 결합의 다양성과 비정질성이 변화하기 때문에 넓은 범위의 특성을 얻을 수 있는 장점이 있다. 지금까지 DLC 박막의 광학적 특성, 특히 굴절률, 광학적인 에너지 밴드 갭, 자외선과 적외선 투과성에 대해서는 많은 연구가 진행되었으나 가시광선의 투과성에 대한 연구는 제한적이며[4], 가시광선 투과도 개선에 대한 연구는 전무하다. 본 연구에서는 ITO 기판 위에 DLC를 합성하고 기계적 특성과 가시광선 영역 투과도를 조사하였다. RF-PECVD(radio frequency plasma enhanced chemical vapor deposition) 방법에 의해서 $C_2H_2+Ar$ 혼합 가스 비율과 $C_2H_2+N_2$ 혼합 가스 비율을 변화시켜 ITO 기판 위에 DLC 박막을 합성하였다. 공정 압력과 rf-power, 증착시간, 기판온도는 0.2 torr, 40 W, 5 분, $50^{\circ}C$로 고정하고, 공정 가스는 $C_2H_2+Ar$과 $C_2H_2+N_2$가 200 sccm이 되도록 비율을 변화하였다. $C_2H_2:Ar$과 $C_2H_2:N_2$의 비율은 180 : 20, 160 : 40, 140 : 60, 120 : 80, 100 : 100이 되도록 가스의 유량을 조절하였다. 투과도는 가시광선(380 ~ 780 nm) 범위에서 측정하였고 두께와 표면조도는 AFM으로 측정하였다. 투과도는 $C_2H_2+Ar$의 Ar 가스 비율이 증가할수록 증가해 140 : 60일 때 최댓값을 나타낸 후 다시 감소하였다. $C_2H_2+N_2$ 투과도는 $N_2$ 가스 비율이 증가할수록 감소하는 경향을 나타내었다. 표면 거칠기는 $C_2H_2+Ar$ 혼합 가스를 사용한 경우의 Ar의 가스 비율이 증가할수록 증가하였다. 그러나 $C_2H_2+N_2$ 혼합 가스를 사용한 경우에는 $N_2$ 가스의 혼합 비율이 증가할수록 감소하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.106-106
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• 2018

해양환경용 선박재료는 전기화학적인 부식을 발생시키는 염소이온($Cl^-$)이 다량 포함된 부식 환경에 장기간 노출되어 있어 부식에 대해 취약하다. 따라서 우수한 내식성 및 내침식성을 가진 재료를 선정하는 것은 매우 중요하다. 알루미늄 합금은 충분한 강도와 부동태 피막 형성으로 인해 내식성이 우수하여 해양환경용 선박 재료로서 널리 이용되고 있으며, 이에 따른 부식 특성에 관한 연구도 활발히 이뤄지고 있다. 그러나 선박에서는 부식에 의한 손상뿐만 아니라 전식에 의한 부식 손상도 발생할 수 있다. 특히 선미 부분은 프로펠러의 동합금과 알루미늄 합금의 이종금속 간 전위차에 의한 전식이 발생하여 선체의 다른 부위에 비해 부식이 더 심하게 진행될 수도 있다. 또한 전식은 해안 부두에 접안된 선박의 용접 시미주전류(stray current)에 의한 부식손상이 발생할 수 있으나 이에 대한 연구는 미미한 실정이다. 따라서 본 연구는 해양환경에서의 전식을 인위적으로 모사할 수 있는 부식 정전류 시험법을 이용하여 다양한 크기의 전식 손상을 유발시켰으며, 해양환경 하에서 선박재료로 주로 사용되는 알루미늄 합금인 Al5083-H321, Al5052-O, Al6061-T6에 대한 전식 특성을 비교, 분석하였다. 실험 방법으로 작동전극은 각 재료의 시험편을 $2cm{\times}2cm$ 으로 절단하여 sand paper # 2000 번까지 연마 후 아세톤과 증류수로 세척하고 건조하였으며, 제작된 시험편은 자체 제작한 홀더를 이용하여 $1cm^2$만 노출시킨 후 정전류 가속 실험을 실시하였다. 기준전극은 은/염화은(Ag/AgCl) 전극을, 대응전극은 백금(Pt) 전극을 사용하였다. 정전류 가속 조건은 $0.001mA/cm^2$, $0.1mA/cm^2$, $1mA/cm^2$, $5mA/cm^2$, $10mA/cm^2$의 전류 밀도를 천연해수에서 30분간 인가하였다. 각 재료에 대한 전식 특성은 실험 전후의 무게 감소량으로 전식의 저항 특성을 확인하였다. 그리고 3D 현미경으로 표면 손상 경향과 깊이를 측정하였으며, 주사전자현미경 (SEM)을 통해 표면 형상을 미시적으로 관찰하였다. 부식 정전류 시험 결과 모든 시편에서 $0.01mA/cm^2$에서 미세한 국부적인 부식이 일어났으며, 전류밀도가 증가할수록 표면 전반에 부식이 진행되고 성장하였다. 그리고 모든 인가 전류밀도의 조건에서 Al6061-T6가 5000계열(Al5083-H321, Al5052-O)보다 더 우수한 내식성을 나타났다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.6
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• pp.21-30
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• 2013

As increasing number of large-size earthquake, the social interest of seismic retrofitting of RC structure is growing. Especially, the RC columns that are not reflected seismic design can not resist lateral loads by the earthquake. The brittle fracture of Non-seismic designed columns lead to full collapse of the building. Thus, the emergency columns reinforcement method is needed. That have a fast construction time, do not cause damage to the column. In the past, cross-sectional expansion method, a steel plate reinforcing method is applied mainly, but in recent years, carbon fiber sheet taking advantage of FRP (Fiber Reinforced Polymer) is widely used. In this study, retrofitting effect of seismic performance of FRP seismic reinforcement, which is possible to emergency construction, was examined. Reinforced concrete specimens were constructed to experimental study. The seismic performence of specimes retrifitted with FRP seismic reinforcement were evaluated. As a result, the seismic performance of specimen reinforced with FRP seismic reinforcement has been improved.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.147-157
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• 2018

The basis of capacity design has been explicitly or implicitly regulated in most bridge design specifications. It is to guarantee ductile failure of entire bridge system by preventing brittle failure of pier members and any other structural members until the columns provides fully enough plastic rotation capacity. Brittle shear is regarded as a mode of failure that should be avoided in reinforced concrete bridge pier design. To provide ductility behavior of column, the one of important factors is that flexural hinge of column must be detailed to ensure adequate and dependable shear strength and deformation capacity. Eight small scale circular reinforced concrete columns were tested under cyclic lateral load with 4.5 aspect ratio. The test variables are longitudinal steel ratio, transverse steel ratio, and axial load ratio. Eight flexurally dominated columns were tested. In all specimens, initial flexural-shear cracks occurred at 1.5% drift ratio. The multiple flexural-shear crack width and length gradually increased until the final stage. The angles of the major inclined cracks measured from the vertical column axis ranged between 42 and 48 degrees. In particular, this study focused on assessing transverse reinforcement contribution to the column shear strength. Transverse reinforcement contribution measured during test. Each three components of transverse reinforcement contribution, axial force contribution and concrete contribution were investigated and compared. It was assessed that the concrete stresses of all specimen were larger than stress limit of Korea Bridge Design Specifications.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.176-182
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• 2018

The purpose of this study was to investigate the safety and rationality of buckling strength and length coefficient by comparing with the design standards of domestic and foreign compression materials based on the buckling test results of circular steel pipe with ball joints. The types of round steel pipes selected for buckling performance evaluation were ø$48.6{\times}2.8t$, ø$60.5{\times}3.2t$ and ø$76.3{\times}3.2t$. For the design of domestic and foreign compression materials, Korea 's Load Resistance and Factor Design, Japan' s Limit State Design, and British Standard BS5950 standard were applied. In this study, we compared and analyzed the buckling performance between the experimental results of the previous research and the domestic and foreign design standards. The results were summarized as follows. As a result of applying the full length of the member to the buckling length in the compression materials design standards of each country, it was 64-89% of the buckling strength by the experiment. Therefore, it is deemed desirable to perform the member design according to the current design standard formula for safety. Experimental results show that the measured buckling strength was 1.02-1.43 times higher than the buckling strength of pure cylindrical steel tubes in the design standards of Korea, Japan and the United Kingdom compression materials. Consequently, it seemed that the buckling strength of individual member in the design of space frame structure should be considered buckling coefficient as the length of pure round steel pipe rather than the length of inter-node.

• The Journal of Engineering Geology
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• v.26 no.2
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• pp.207-221
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• 2016

As greater numbers of fill dams and reservoirs become old, the risks of damage or embankment collapse increases. However, few studies have considered the deterioration and hazard classification of the internal core layers of fill dams. This study reports the results of geotechnical investigations of 13 earth-cored fill dams in Korea, based on no-water borehole drilling, Standard Penetration Test, and 2D and 3D electrical resistivity surveys along with in situ and laboratory testing. High-capacity no-water boring minimized core layer disturbance while providing continuous core sample recovery. The results allow the classification of potential hazards related to the existing core layers based on both visual inspection of the recovered samples and the results of engineering surveys and tests. Four types of potential hazard are classified: locally fluidized core with a high water content, rapid water inflow to a borehole, cores with granular materials, and relatively low stiffness of core. Among these, the locally fluidized core is the most critical hazard that requires remedial action because it is related to the potential internal flow path and internal erosion. The other three hazard types are of medium importance and require careful monitoring and regular inspection. Of note, there was no correlation between age and core deterioration. The results are expected to aid the safe management and potential upgrading of aging cored fill dams.