• International Journal of Highway Engineering
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• v.14 no.1
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• pp.73-83
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• 2012

Effective use of traffic marking can lead to driver's safer driving by speed management and visibility enhancement. One of the critical factors in designing traffic marking is how to incorporate human factor issues into the design process. This study presented a methodology for evaluating the effectiveness of Hi-pass marking on Korean freeways based on kansei engineering. Hi-pass marking scenarios made by a virtual reality tool were used to evaluate the user's perceptions. Various combination of chevron angles and peripheral transverse(PT) bars were used for the evaluation. The results show that the most effective scenario is a combination of 60 degree chevron angle and an askew parallelogramshaped PT bar shaped. It is expected that the proposed method and outcome will be useful for making safer driving maneuvers.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.410-413
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• 2005

The results of an experimental and analytical study of composite pressure hull on buckling pressure are presented for LRN 300. Composite tensile test was done to know the composite material properties applied FE analysis for URN composite. We predicted the buckling and post buckling analysis of composite laminated cylindrical panels under external compression by using ABAQUS /Standard[Ver 6.4]. To obtain nonlinear static equilibrium solutions for unstable problems, where the load-displacement response can exhibit the type of nonlinear buckling behavior, during periods of the response, the load and/or the displacement may decrease as the solution evolves, used the modified Riks method. The modified Riks method is an algorithm that allows effective solution of such cases [7]. Experiments were conducted to verify the validation of present analysis for cross-ply laminated shells. The shells considered in the study have two different lamination patterns, $[{\pm}45/0/90]_{18s\;and}\;[/0/90]_{18s}$. Cylindrical panel of experiment and analysis have the radius of 200mm, length of 210mm and 60 degree of cutting angle. The critical load from experiment is $69\%$ of that of numerical analysis, because the fracture of matrix was generated before buckling. So URN 300 is not proper to use at the condition under high external pressue.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.34 no.3
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• pp.1-8
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• 2002

The object of this study was to determine the surface energy of hydrophobically modified micro-crystalline cellulose (MCC) with AKD and evaluate the effect of surface energy of the solid particles dispersed in aqueous medium on flotation efficiency. Especially to eliminate the complication derives from the diverse parameters of solid particles including particle size, type, etc. MCC's modified with AKD have been used. The surface energy Parameters were calculated from advancing contact angles of apolar and polar liquids on MCC pellets using the Lifshitz-van der Waals acid-base (LW:AB) approach. Total surface energy of hydrophobic MCC ranged from 46.19 mN/m to 48.60 mN/m. The contribution of the acid-base components to the total surface energy ranged form 13% to 17% for hydrophobic MCC's. The effect of surface characteristics on the flotation efficiency was evaluated. It was shown that there exist critical values of surface energies to increase flotation efficiency. Total surface energy and polar component of solid particles should be lower than 47 mN/m and 7 mN/m, respectively, for effective removal in the flotation process.

• Advances in aircraft and spacecraft science
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• v.7 no.6
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• pp.553-570
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• 2020

To address the problems caused by the strong coupling of an airbreathing hypersonic vehicle's airframe and propulsion to the integrated control system design, an integrated airframe-propulsion model is established, and the coupling characteristics between the aircraft and engine are analyzed. First, the airframe-propulsion integration model is established based on the typical nonlinear longitudinal dynamical model of an air-breathing hypersonic vehicle and the one-dimensional dual-mode scramjet model. Thrust, moment, angle of attack, altitude, and velocity are used as transfer variables between the aircraft model and the engine model. The one-dimensional scramjet model can accurately reflect the working state of the engine and provide data to support the coupling analysis. Second, owing to the static instability of the aircraft model, the linear quadratic regulator (LQR) controller of the aircraft is designed to ensure attitude stability and height tracking. Finally, the coupling relationship between the aircraft and the engine is revealed through simulation examples. The interaction between vehicle attitude and engine working condition is analyzed, and the influence of vehicle attitude on engine safety is considered. When the engine is in a critical working state, the attitude change of the aircraft will not affect the engine safety without considering coupling, whereas when coupling is considered, the attitude change of the aircraft may cause the engine unstart, which demonstrates the significance of considering coupling characteristics.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.323-324
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• 2011

현재 많은 blue LED소자의 제작 공정과 소자 표면에 texturing하는 과정이 보고되어 있다. 그 중n층이 위로 올라오는 수직형 LED 구조로 인해 표면 texturing 기술은 빛의 발광 효율을 증가 시킬 수 있는 중요한 기술 중 하나가 되었다. 1 이 연구에서, 우리는 InGaN을 바탕으로 한 LED 소자의 표면 roughening을 건식과 습식 공정을 모두 거치는 과정을 통하여 소자의 발광 효율을 높이는 시도를 하였다. 최근 전도성 물질 기판 위에 증착 되어 있는 수직형 LED 소자 2,3,4는 과거의 사파이어 기판 위에 증착 되어 있는 형태의 LED 소자에 비해 우수한 소자 특성을 보인다. 이는 과거 사파이어 기판을 사용함으로써 낮은 열적 특성과 더불어 전기 정도성에 몇 가지 제약을 초래하게 되었기 때문이다. 반면, 전도성 기판은 LED 구조의 back side ohmic contact을 가능하게 하였고, 더 나은 확산 특성을 보여 주었고 작동 전압 또한 감소 하였다. N층이 위에 있는 수직형 LED 소자는 KrF pulsed excimer laser로 인해 실현 되었다. 이 laser 빛이 투명한 사파이어 기판을 통해 얇은 GaN층에 입사되면, 기판과 GaN가 분리된다. 이 레이저 기술은 laser lift-off(LLO)로 성장된 기판으로부터 LED 구조를 분리하는데 성공하게 하였다. 우리는 건식 식각 공정을 이용하여 n 층이 위에 올라와 있는 구조인 수직형 LED 소자에 roughening을 주고 다시 이 표면에 습식 식각 공정을 적용하여 거친 부분의 거칠기를 또 한번 증가시켰다. 그리고 이 거칠어진 표면은 이 공정이 진행 되기 전의 소자에 비해 빛의 발광 효율이 증가 되었다. 이 두 공정을 포함한 식각 공정은 두 가지 장점이 생겼는데, 한가지는 GaN에서 외부로 방출할 수 있는 표면 지역이 증가되었고, 다른 한가지는 가파른 거칠기 특성으로 인해 critical angle을 증가시킨 것이다.

• Magazine of the Korean Society of Agricultural Engineers
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• v.34 no.3
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• pp.33-42
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• 1992

The shear strength of cohesionless Soils results from particle-to-particle friction and structural resistance by interlocking. And, the shear strength of soils is subjected to vary depending on the internal states and external condtions. If the volume change occurring in the soils and stress-strain relationships under the internal and external changes can accrurately he described, it is possible to predict the behaviors of soils. To accomplish these objectives a series of drained triaxial compression tests and isotropic compression test was performed on the Banwol sand at different relative densities ranging from 20% to 80% and different confining pressures ranging from 0.4kgf/cm$^2$ to l2kgf/cm$^2$. The results and main conclusions of the study are summarized as follows; 1.When the relative density or the confining pressure is increased, the maximum deviator stress is increased. The ratio of the maximum deviator stress and the confining pressure is linearly proportional to the relative density. 2.It is observed that the dilatancy depends not only upon its relative density but also the confining stress, and that the maximum deviator stress is obtained after the diatancy occurs. 3.The volume of sands undergoes initial contraction prior to the dilatancy occurred by strain softening. The dilatancy rate eventually approaches the critical state or a constant volume. 4.At lower strains, Poisson's ratio approaches a certain minimum value regadless of the state of materials. At larger strains, however, the ratio is increased as the relative density is increased. 5.It is observed that the modulus of elasticity is linearly proportional to the relative density and the pressure. 6.When the relative density is increased, the friction angle of sands is linearly increased. 7.When the relative density is increased, the expansion index and the compression index are linearly decreased, and the ratio of the two is about 1/3.

• Journal of Biosystems Engineering
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• v.29 no.3
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• pp.217-224
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• 2004

This research was conducted to test the feasibility of utilizing high-pressure water jets of over 1.0㎫ as a means of breaking and peeling garlic bulbs. High-pressure plunger pumps and flat-spray nozzles of varying orifice diameters and spray angles were utilized to supply water jets into a prototype peeling chamber made of transparent acrylic plates. Water jets were discharged from a total of six nozzles installed in such a way that three parallel nozzles face the other three. The cross-sectional area of the peeling chamber and the installation angle of the nozzles had critical effects on peeling performance. Small cross-sectional area was required so that total impact force of water jets on garlic could be increased. The optimum installation angles were around 4, 8, and 16$^{\circ}$ for the nozzles having 15, 40, and 65$^{\circ}$ spray angles, respectively. Best performance with 61.4% of completely-peeled garlics was obtained at a pressure of 1.94㎫ and a flow rate of 9.07 $\ell$/min for each nozzle. The peeling efficiency of the system was generally unsatisfactory due to the limited flow rate of the plunger pumps utilized. For better performance, it is recommended to increase flow rate while reducing operating pressure by utilizing other type of pumps.

• Explosives and Blasting
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• v.34 no.3
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• pp.10-16
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• 2016

Recently, transition from open pit to underground mining in limestone mines is an increasing trend in Korea due to environmental issues such as noise, dust and vibrations caused by crushers and equipment. The severe damages in the surrounding rock mass of underground opening caused by explosive blasting may lead to rock fall hazards or casualties. It is well known that variables which mainly affect blast-induced rock falls in underground mining are: blast vibration level, joint orientation and distribution and shape of the cross sections of underground structures. In this study, UDEC program, which is a DEM code, is used to simulate blast vibration-induced rock fall in underground openings. Variation of joint space, joint angle and joint normal stiffness was considered to investigate the effect of joint characteristics on the blast vibration-induced rock fall in underground opening. Finally, jointed rock mass models considering blast-induced damage zone were examined to simulate the critical blast vibration value which may cause rock falls in underground opening.

• Journal of Power System Engineering
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• v.20 no.5
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• pp.46-51
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• 2016

The TMCP steel has expanded in the marine structure during manufacturing process because of its excellent weld-ability and impact toughness. In the case of merchant ships, coverage of TMCP steel has been used widely on over DH36 Classifications material. The line heating process is applied to the outer surface of the steel plate for the shipbuilding. In this study, We compared between TMCP and normalizing steel for shipbuilding by analyzing some basic data through performing the natural cooling after the line heating. The experimental results show the angular misalignment changes in line heating. Heated surface of normalizing steel material expanded to $-0.3^{\circ}$ and reduced to $+0.2^{\circ}$ after cooling. And during cooling at $194^{\circ}C$ for 1,500 seconds, Angular Misalignment began from - direction to + direction, passed the critical point to the default at 2,200 seconds and did not take place any more at $103^{\circ}C$ after the 2,700 seconds. Angular Misalignment results of TMCP steels and Normalizing steel material show same angular misalignment lasted 1,200 seconds, TMCP steel has given more expansion and contraction angle which is $0.2^{\circ}$ than that of the Normalizing steel. Length difference between expansion and contraction is about 0.3 mm.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.182-185
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• 2004

In this work, the effect of chemical treatments on surface properties of SiC was investigated in mechanical interfacial properties of carbon fibers-reinforced composites. The surface properties of the SiC were determined by acid/base values and contact angles. The thermal stabilities of carbon fibers-reinforced composites were investigated by thermogravimetric analysis (TGA). Also, the mechanical interfacial properties of the composites were studied in interlaminar shear strength (ILSS) and critical strain energy release rate mode II $(G_{IIC})$ measurements. As a result, tile acidically treated SiC (A-SiC) had higher acid value than that of untreated SiC (V-SiC) or basically treated SiC (B-SiC). According to the contact angle measurements, it was observed that chemical treatments led to an increase of surface free energy of the SiC surfaces, mainly due to the increase of the specific (polar) component. The mechanical interfacial properties of the composites, including ILSS and $(G_{IIC})$, had been improved in the specimens treated by chemical solutions. These results were explained that good wetting played an important role in improving the degree of adhesion at interfaces between SiC and epoxy resin matrix.