• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.4
• /
• pp.354-361
• /
• 2008

Cold rolled steel sheet for automotive was treated by Ar/$O_2$ atmospheric pressure plasma to improve the adhesive bonding strength. Through the contact angle test and calculation of surface free energy for cold rolled steel sheet, the changes of surface properties were investigated before and after plasma treatment. The contact angle was decreased and surface free energy was increased after plasma treatment. And the change of surface roughness and morphology were observed by AFM(Atomic Force Microscope). The surface roughness of steel sheet was slightly changed. Based on Taguchi method, single lap shear test was performed to investigate the effect of experimental parameter such as plasma power, treatment time and flow rate of $O_2$ gas. Results shows that the bonding strength of steel sheet treated in Ar/$O_2$ atmospheric pressure plasma was improved about 20% compared with untreated sheet.

• Journal of computational fluids engineering
• /
• v.13 no.4
• /
• pp.66-71
• /
• 2008

This research computes the viscous flow field and aerodynamics around the model of a commercial passenger airplane, Boeing 747-400, which cruises in transonic speed. The configuration was realized through the reverse engineering based on the photo scanning measurement. In results, the pressure coefficients at the several wing section on the wing surface of the airplane was described and discussed to obtain the physical meaning. The lift coefficient increased almost linearly up to $17^{\circ}$. Here the maximum lift occurred at $18^{\circ}$ according to the angle of attack. And the minimum drag is expected at $-2^{\circ}$. The maximum lift coefficient occurred at the Mach number 0.89, and the drag coefficient rapidly increased after the Mach number of 0.92. Also shear-stress transport model predicts slightly lower aerodynamic coefficients than other models and Chen's model shows the highest aerodynamic values. The aerodynamic performance of the airplane elements was presented.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.11 no.2
• /
• pp.144-151
• /
• 2008

An experimental study has been conducted to investigate the effects of circular damage hole on the characteristics of airfoil performance. The damage on a wing created from a hit by anti-air artillery was modeled as a circular hole. Force balance measurements and static pressure measurements on the wing surface were carried out for the cases of having damage holes of 10% chord size at quarter chord and/or half chord positions. All experiments were conducted at Reynolds number of $2.85\times10^5$ based on the chord length. The surface pressure data show big pressure alterations near the circular damage holes. This abnormal surface pressure distribution produces shear stress that could lead to the acceleration of the structural degradation of the wing around the circular damage hole. However, in spite of the existence of circular damage holes, the measured force data indicated the only a slight decrease in lift accompanied by increase in drag compared to the results of undamaged one. The influence of damage hole on the aerodynamic performance was increased as the location of damage moved to the leading edge. The effect on the control force was insignificant when the damaged size was not large.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.11 no.6
• /
• pp.9-17
• /
• 2007

This experimental study has been conducted to investigate the effect of the recirculation zone on the multi-slot film cooling in the ramjet combustor. The recirculation zone which is generated by the protrusion tip on the entrance of the coolant flow path affects on the first slot. Velocity fields, dimensionless temperature fields and adiabatic film cooling effectiveness on the downstream wall of the slot exit are measured. The results show that the film cooling performance is rapidly decreased after the slot exit by shear layer and high turbulence intensity between separated flows and coolant flows.

• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.2648-2653
• /
• 2007

Recently, increasing demand on not only lighter but also extremely mobile battery make micro fuel cell device very attractive alternative. By reducing the size of fuel cell, surface tension becomes dominant factor with minor gravitational effect. Therefore, it is very difficult to detach the $CO_2$ bubble generating on a cathode side in ${\mu}DMFC$ (micro direct methanol fuel cell). The degassing of a $CO_2$ bubble has drawn quite attention especially for ${\mu}DMFC$ due to its considerable effect on overall machine performance. Our attention has been paid to the dynamic behavior of immiscible bubble attached to the one side of the wall on 2D rectangular channel subject to external shear flow. We use Level Contour Reconstruction Method (LCRM) which is simplified version of front tracking method to track the bubble interface motion. Effects of Reynolds number, Weber number, advancing/receding contact angle and property ratio on bubble detachment characteristic has been numerically identified.

• Journal of Ocean Engineering and Technology
• /
• v.26 no.3
• /
• pp.39-45
• /
• 2012

This paper investigates the strength characteristics and stress-strain behaviors of waste fishing net (WFN)-added lightweight soil. The lightweight soil, which consisted of dredged soil, crumb rubber, and cement, was reinforced with WFN in order to increase its shear strength. Glue treated WFN was also added to lightweight soil to improve the interlocking between the soil mixture and WFN. Three kinds of test specimens were prepared: unreinforced lightweight soil, reinforced lightweight soil without glue treatment, and reinforced lightweight soil with glue treatment. Several series of laboratory tests were carried out, including flow value tests, unconfined compression tests, and SEM analyses. From the experimental results, it was found that the peak strength of the reinforced lightweight soil with glue treatment was increased by the increased interlocking between the soil mixture and WFN, which was induced from the bonding effect. The stress-strain relation of the reinforced lightweight soil, irrespective of the glue treatment, showed a more ductile behavior than that of the unreinforced lightweight soil.

• Polymer(Korea)
• /
• v.39 no.3
• /
• pp.441-452
• /
• 2015

Twin-screw kneader is an efficient polymer processing equipment. In this paper, the mixing performance of one novel intermeshing counter-rotating twin-screw kneader with different tip angles of the male rotor is simulated using the mesh superimposition technique (MST). Statistical analysis is carried out for the flow field using particle tracking technique, and distributive mixing performance is evaluated using the residence time distribution and segregation scale, while the dispersive mixing performance is estimated using the parameters such as shear rate, stretching rate and mixing index. The results show that the best distributive mixing performance is achieved when the tip angle is 0o, while the optimal dispersive mixing performance is obtained when the tip angle is 20o. The results in this paper provide a data basis for the selection of parameters and optimization of the performance for the screw rotors.

• Journal of computational fluids engineering
• /
• v.20 no.2
• /
• pp.37-45
• /
• 2015

A parametric study on the shapes of bobsleigh bumpers has been performed to reduce the aerodynamic drag. Effects of geometric parameters, such as leading angle of leading bumper, the ratio of minimum width to maximum width of leading bumper, the ratio of leading bumper length to trailing bumper length, trailing angle of trailing bumper, and the ratio of bumper height to installation location of bumper from the bottom of bobsleigh, on the aerodynamic performance of the bobsleigh were estimated using 3-D Reynolds-averaged Navier-Stokes equations. The turbulence was analyzed using the shear stress turbulence model. Reynolds number based on the hydraulic diameter of the external flow channel was in the range of 150,000~1,000,000. Numerical results for drag coefficient were validated compared to experimental data. Ranges of the five geometric parameters were determined according to the rule of Federation Internationale de Bobsleigh et de Tobaganning. The aerodynamic performance of the bobsleigh sled was most sensitive to the leading angle of leading bumper and the ratio of minimum width to maximum width of leading bumper.

• Journal of Environmental Impact Assessment
• /
• v.16 no.3
• /
• pp.187-194
• /
• 2007

It started road constructions around river in 1990s. These maintenances concentrate on city river. Because river lives no living things and men don't come near there. But in spite of these river environment go to rack, river maintenances still keep on using preexistence method since 1990s. Only a part of city river environment maintenances consider environmental ability of passive river, river maintenance of a purpose of flood control still don't consider in the concrete. Because propulsion device that consider environment ability of passive river and possible application techniques don't complete. In accordance, A natural river maintenance needs absolutly a series of river projects. Because a natural river maintenance prevents a damage of environment ability. This study is to assume the flood really happened and to carry out the flood damage simulation needed in overflow simulation about the inundated zone. Also, This study examine unstable part about the hydraulic characteristic as velocities, stream power, shear, hydraulic depth, flow area in basin. And this study applied the HEC-RAS(river analysis system) model to predict flood overflow in youngsan river basin. Project flood is used the return period 100 year and inputed data that was calculated in intensity figures of illumination.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.24 no.1
• /
• pp.23-28
• /
• 2012

In the present work, numerical analyses of air flow in HVAC duct have been carried out for enhancement of cooling/heating performance. For the analyses, three-dimensional Reynolds-averaged Navier-Stokes equations have been solved with the shear stress transport turbulence model. The numerical results were validated in comparison with the experimental data. Based on the numerical results, the HVAC duct was designed to reduce the pressure loss. The modified duct geometry shows largely reduced pressure drop in comparison with the reference geometry. And, through modified duct shape, the performance of air conditioning has been enhanced.