• Journal of Korean Society of Steel Construction
• /
• v.25 no.1
• /
• pp.47-59
• /
• 2013

This study that is a successive secondary study right after the primary bending strength test of a new form of U-shape hybrid composite beam is a cyclic seismic test of U-shape hybrid composite beam and column conncetion. Three specimens are built for the variables which are kinds of columns, depth of beam, continuity or discontinuity of upper plate of beam, and a number of steel bars of end-beam. Kinds of columns are a reinforcement concrete column and a ACT column of CFT shape, and beam depth are 300, and 500 mm. Detail of connection is bolt connection with using a short bracket that is commonly use. As the result, deformability of 2~4% is ensured the floor displacement angle. If it is the negative moment, the maximum moment shows that its capacity is above the nominal moment.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.10a
• /
• pp.301-301
• /
• 2003

In current study, Nanocomposites are reinforced with carbon nanofiber, carbon nanotube and SiC, etc. Since the nano reinforcements have the excellent mechanical, thermal and electrical properties compared with that of existing composites, it has lately attracted considerable attention in the various areas. Cu have been widely used as signal transmission materials for electrical electronic components owing to its high electrical conductivity. However, it's size have been limited to small ones due to its poor mechanical properties. Until now, strengthening of the copper alloy was obtained either by the solid solution and precipitation hardening by adding alloy elements or the work hardening by deformation process. Adding the alloy elements lead to reduction of electrical conductivity. In this aspect, if carbon nanofiber is used as reinforcement which have outstanding mechanical strength and electric conductivity, it is possible to develope Cu matrix nanocomposite having almost no loss of electric conductivity. It is expected to be innovative in electric conducting material market. The unidirectional alignment of carbon nanofiber is the most challenging task developing the cooer matrix composites of high strength and electric conductivity. In this study, the unidirectional alignment of carbon nanofibers which is used reinforced material are controlled by drawing process and align mechanism as well as optimized drawing process parameter are verified via numerical analysis. The materials used in this study were pure copper and the nanofibers of 150nm in diameter and of 10∼20$\mu\textrm{m}$ in length. The materials have been tested and the tensile strength was 75MPa with the elongation of 44% for the copper. it is assumed that carbon nanofiber behave like porous elasto-plastic materials. Compaction test was conducted to obtain constitutive properties of carbon nanofiber Optimal parameter for drawing process was obtained by analytical and numerical analysis considering the various drawing angles, reduction areas, friction coefficient, etc. The lower drawing angles and lower reduction areas provides the less rupture of co tube is noticed during the drawing process and the better alignment of carbon nanofiber is obtained.

• Journal of Advanced Marine Engineering and Technology
• /
• v.32 no.8
• /
• pp.1149-1156
• /
• 2008

The principle of self clamping friction clutch is presented in this paper and the transmitted torque capacity is also calculated. In order to enlarge the friction force, a part of rotating force of driving side is converted to normal force of friction materials by clamping arm. The increased normal force of friction materials assures the large friction force and the transmitted torque capacity of clutch becomes large. The self clamping friction clutch is adopted in the tube type air pressure clutch and the condition of stability is investigated. It is proven that the inclined angle of clamping arm and the friction factor of friction materials are the essential elements in stability and torque capacity of self clamping friction clutch. The transmitted torque capacity of self clamping friction clutch is compared with air pressure clutch. The normal force of friction lining is magnified by 1/(1-k) and the transmitted torque capacity is also magnified with same proportion comparing with air pressure clutch. The larger the friction factor of friction lining, the larger the magnification factor. The longer the clamping arm, the smaller the magnification factor. It must be also noted that the value of k=${\mu}Y/X$ is the criterion of stability. If the value of k=${\mu}Y/X$ is greater than or equal to 1, the self clamping friction clutch is unstable and it can not be used as clutch.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.14 no.4
• /
• pp.339-345
• /
• 2008

The stratified flow can be seen in the oil and gas pipelines as well as pipelines related to ship's fluid machineries. Numerous theories and correlations have also been proposed in the past for the prediction of stratified flow in horizontal or slightly inclined pipe. The previous researches are mostly about the effects of physical properties, viscosity, phases densities and pipe geometries on the stratified flow. Very few study outcomes exist on the effect of gravity magnitude and large slop angle of pipe inclinations on the occurring condition of stratified flow. In this study, therefore, analytical procedures were conducted about the effect of both the change in the gravity magnitude and pipe inclinations on the stratified flow occurring conditions. From the analytical results, it was found that stratified flow occurred at the vertical upward inclination and at very low liquid phase flowrates in 0.17g and 0.33g conditions.

• 한국태양에너지학회:학술대회논문집
• /
• 2008.11a
• /
• pp.245-250
• /
• 2008

This study is on the availability of solar thermal energy in Korean high-rise apartment complex depending on the installation type of solar collectors to roof or facade of building. Firstly, solar access evaluation on the roof and the facade of apartment buildings was carried out. The total thermal load of each apartment unit and building was investigated and matched with the energy which was produced by solar thermal systems on the facade. The considered layout patterns of apartment buildings were '一type', 'alternative 一type', 'ㄱtype' and 'ㅁtype' and that was analyzed in prior studies. Extensive dynamic hourly energy simulations with the solar thermal system were Performed with the TRNSYS of SEL. We assumed that the apartment complex is composed of 9 buildings and located in Daejeon. The collectors are the heat-pip evacuated tube collectors and the number of collectors are 45 tubes We assumed that the collectors are installed on the balcony of each unit and the angle of incilnation is $90^{\circ}$. As a result, the supply amount of solar thermal systems is about 4,850,086kJ/hr and the solar fraction is about 66%. The solar fraction according to each azimuth is about 66% on the south, 62% on the south-east $30^{\circ}$ and 56% on the south-east $60^{\circ}$. So, we quantitatively got a line on the optimal azimuth for installing the solar thermal systems. The solar fraction has differences from 5% to 15% of each floor, 6th, 12th and 20th and those tendencies are same in analyzed each 4 types of the apartment complexes.

• Journal of the Institute of Electronics Engineers of Korea SP
• /
• v.37 no.6
• /
• pp.9-16
• /
• 2000

The perception of flicker on the computer display devices depends upon the temporal waveform of the phosphor decay characteristic, the frame rate, and the display size. The lowest frequency at which flicker is not perceived is called the critical fusion frequency or critical frequency. Critical fusion frequency is evaluated by the display illuminance and the modulation (m) defined as the ratio of the amplitude of first harmonic frequency to the DC of the waveform. In this paper, we analyze the relationship bet ween the critical fusion frequency, relating to the decay characteristic of the phosphors and luminance on the monitor, and the frame frequency. Also under considering the viewing angle, we presented the frame frequency that is less sensitive to the full size of the display device.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.5
• /
• pp.24-31
• /
• 2002

The effects of vortex generators, in the form of small delta-shaped tabs or thin tapes at an axi-symmetric supersonic nozzle exit, on the characteristics of supersonic jet flowfields are investigated by Schlieren images and Pitot-tube measurements. Small tabs as small as 1 % of the nozzle exit area can introduce streamwise vortices and produce a significant effect on the jet flowfield downstream of the nozzle. The effect is stronger for the cases of under-expanded jet than over- and perfect-expanded cases, introducing a larger flow entrainment. The effects of the angle of tabs with respect to the flow direction are also investigated, and for over-expanded jet cases, it is found that the tabs bended toward upstream can weaken the interaction strength and remove the Mach disc in the jet flowfield. Introduction of small proturbances inside the nozzle surface by attachment of thin tapes is also found to change the pressure distribution in the circumferential direction of the flowfield. Its effect is also found to be dependent on the jet expansion ratio.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.9 s.252
• /
• pp.921-928
• /
• 2006

Wake-induced boundary-layer transition on a NACA0012 airfoil with zero angle of attack is experimentally investigated in periodically passing wakes under the moderate level of free-stream turbulence. The periodic wakes are generated by rotating circular cylinders clockwise or counterclockwise around the airfoil. The free-stream turbulence is produced by a grid upstream of the rotating cylinder, and its intensities $(Tu_{\infty})$ at the leading edge of the airfoil are 0.5 and 3.5%, respectively. The Reynolds number (Rec) based on chord length (C) of the airfoil is $2.0{\times}10^5$, and Strouhal number (Stc) of the passing wake is about 1.4. Time- and phase-averaged streamwise mean velocities and turbulence fluctuations are measured with a single hot-wire probe, and especially, the corresponding wall skin friction is evaluated using a computational Preston tube method. The patch under the high free-stream turbulence $(Tu_{\infty}=3.5%)$ grows more greatly in laminar-like regions compared with that under the low turbulence $(Tu_{\infty}=0.5%)$ in laminar regions. The former, however, does not greatly change the turbulence level in very near-wall region while the latter does it. At further downstream, the former interacts vigorously with high environmental turbulence inside the pre-existing transitional boundary layer and gradually loses its identification, whereas the latter keeps growing in the laminar boundary layer. The calmed region is more clearly observed under the lower free-stream turbulence level and with the receding wakes.

• International Journal of Highway Engineering
• /
• v.15 no.4
• /
• pp.127-133
• /
• 2013

PURPOSES : The impact performance of flexible barrier system such as structural response, vehicular motion and occupant safety vary depending on the impact point. Thus, to properly evaluate the performance of a flexible barrier system, impact should be made to a point which will lead to the worst possible results. This point is called the Critical Impact Point (CIP). This paper presents the way to determine the CIP for a SB2 class flexible barrier system which is consisted of Thrie-Beam rail and circular hollow tube post of 2m span. METHODS: Barrier VII simulations were made for impact points; Case 1 at a post, Case 2 at 1/3 span downstream from a post, Case 3 at middle of the span, Case 4 at 2/3 span downstream from a post. For the structural performance (deflections), impact simulation of 8000kg-65km/h-15degree was used, and for vehicle motion and occupant safety, simulation of 1300kg-80km/h-20degree impact was made and analysed. RESULTS: Case 1 gave the largest dynamic deflection of 75.72cm and also gave the largest snag value of 44.3cm. Occupant safety and exit angle of the vehicle after the impact were not sensitive to the impact point and were all below the allowable limit. CONCLUSIONS : For the SB2 class flexible barrier system's CIP can be regarded as a post which is sufficiently away from the end of Length of Need in order to avoid the end-effect of the barrier system. It can be more economic in the long run because the normal concrete pavement material is likely to cost more due to higher probability of maintenance and repair and higher social cost due to traffic accident, etc.

• Journal of Korean Society of Steel Construction
• /
• v.26 no.4
• /
• pp.311-322
• /
• 2014

Concrete filled tubular structure should be installed diaphragms for moment connection. However internal and through diaphragm should be special welded when connected to column tube. The other hand, that has become increase of stress concentration and extend of construction error. Therefore, In this study the seismic performance of beam to column connections with External Diaphragms and implement cycle loading experiment. we had evaluated seismic performance with mentioned experiment which is concrete filled or not, variable shapes, to be welded or not of diaphragm. Also, formula of strength of external diaphragm was analyzed and looked into adequacy with regard to formula of tension strength.