• Journal of the Optical Society of Korea
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• v.13 no.4
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• pp.416-422
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• 2009

We have demonstrated a highly efficient cladding-pumped ytterbium-doped fiber laser, generating $>$2.1 kW of continuous-wave output power at 1.1 μm with 74% slope efficiency with respect to launched pump power. The beam quality factor ($M^2$) was better than 1.2. The maximum output power was only limited by available pump power, showing no evidence of roll-over even at the highest output power. We present data on how the beam quality depends on the fiber parameter, based on our current and past fiber laser developments. We also discuss the ultimate power-capability of our fiber in terms of thermal management, Raman nonlinear scattering, and material damage, and estimate it to 10 kW.

• Corrosion Science and Technology
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• v.3 no.4
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• pp.172-177
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• 2004

Biaxially oriented polyethylene terephthalate copolymer(BO - PET)film laminated aluminiums have been applied for chip condenser case. The BO PET film is characterized by high molecular which gives high corrosion resistance, good adhesion and high heat resistance. The higher orientation lowers formability of the film. So, optimum orientation has to be controlled during the laminating process. And to confirm the adhesion between BO PET and aluminium and to guarantee the formability of PET laminated aluminums, we have controlled the chromium oxides weight on the aluminium and laminating condition ( laminating temperature, soaking temperature and lag time after nip roll and quenching conditions) This paper discusses the effect of the laminating conditions on the formability of laminated aluminums. As results, it is clear that the orientation of the BO PET film decreased with an increase in the strip temperature. When the film temperature is over the melting point of the film, its orientation drastically decreased.

• International Journal of Naval Architecture and Ocean Engineering
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• v.2 no.2
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• pp.57-67
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• 2010

Experimental investigations were carried out on an Axi-symmetric Body Model fitted with Pump-jet Propulsor (PJP) in the Cavitation Tunnel at Naval Science and Technological Laboratory (NSTL). The tests were intended for evaluating the propulsion characteristics of the body and propulsor. The self propulsion point of the model for two configurations was determined after finding the corrections for tunnel blockage effects and differences in model length at zero trim. The results were found to match closely with the towing tank results. The rotor and stator torques also matched closely over full range of experiment. Further experiments were carried out on the body at $4.5^{\circ}$ angle of trim to investigate the propulsive performance and assess the operational difficulties in the sea. The results indicated an increase in resistance and decrease in rotor thrust; but the balance of torques between the rotor and stator was undisturbed, causing no concern to vehicle roll.

• International Journal of Control, Automation, and Systems
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• v.2 no.4
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• pp.494-500
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• 2004

The wing rock phenomenon is a high angle of attack aerodynamic motion manifested by limit cycle roll oscillations. Experimental studies reveal that direct control and manipulation of leading edge vortices, through the use of 'blowing' techniques is effective in the suppression of wing rock. This paper presents the design of a robust controller for the experimental implementation of one such 'blowing' technique - recessed angle spanwise blowing (RASB), to achieve wing rock suppression over a range of operating conditions. The robust controller employs Takagi - Sugeno fuzzy system, which is fine-tuned by experimental simulations. Performance of the controller is assessed by real-time wind tunnel experiments with an 80 degree swept back delta wing. Robustness is demonstrated by the suppression of wing rock at a range of angles of attack and free stream velocities. Numerical simulation results are used to further substantiate the experimental findings.

• Journal of Ocean Engineering and Technology
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• v.24 no.3
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• pp.11-20
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• 2010

The purpose of this study is the investigation of the wave interaction with the rectangular floating breakwater. The flow profile obtained by PIV technique is represented to understand the vortical flow due to the wave interaction with a rectangular floating breakwater in the roll motion and the fixed condition. Also, the transmission coefficients are compared in both conditions over the extensive wave periods, which represent the performance of breakwater to attenuate the incoming waves. These results would be applied to design the floating breakwater having the mooring system to improve its performance for a certain wave period.

• Current Optics and Photonics
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• v.3 no.5
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• pp.445-450
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• 2019

The influence of high-power laser diode (HPLD) emitter width on the device performance is investigated for 975-nm (In,Ga)(As,P)/(Al,Ga)As broad-area HPLDs, using self-consistent electro-thermal-optical simulation. To guarantee the simulation's accuracy, simulated results are matched with the measured results for a sample HPLD with fitting parameters. The influences of HPLD emitter width on temperature distribution, output power, and the beam product parameter (BPP) are analyzed for three different emitter widths of 50, 70, and $90{\mu}m$. It is found that a device with smaller emitter width exhibits both thermal rollover and thermal blooming at lower output power, but smaller BPP.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.10 no.3
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• pp.185-219
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• 1981

To analyze two dimensional incompressible laminar natural convection in a rectangular enclosure heated from below and cooled by a horizontal ceiling and two vertical walls, he primitive Navier-Stokes equations and the energy equation were solved numerically in time dependent form by a marker and cell method. A successive over-relaxation method for the elliptic portion of the problem and an explicit method for the parabolic portion were applied for the range of Grashoff number of $5{\times}10^3\;to\;5{\times}10^4$ to get the transient and steady state dimensionless temperature and velocity profiles. For the range of aspect ratio $L/H{\leqq}2.4$ in which only a pair of convection rolls exists mean Nusselt number calculated are as follows : $$N_{NU}0.89\;N_{Gr}^{0.2}(H/L)^{0.45}$$ By path lines drawn by marker particle trajectories roll number of cellular motion were observed for various aspect ratio of the enclosure.

• Journal of the Korean Society for Precision Engineering
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• v.9 no.4
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• pp.13-21
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• 1992

Standards concerning the determination of positioning accuracy and repeatability of numerically controlled(NC) machine tools have been published relentlessly over the last 20 years. Since the publication in 1988 of the International Standard 230-2 there has been a pronounced move, both at national and international standards level, to embrace further test procedures for a complete machine tool performance assessment. For example, measurements of angular (pitch, roll, and yaw) and straightness errors along linear axes are now commonplace and complement the existing positioning accuracy and repeatablity tests. More recently the subject of circularity evalutaion has also gained considerable interest. Here dynamic tests, using a kinematic ballbar or circular masterpiece, give an instant overview of the contouring ability of the machine in two axes at specific feedrates. This information is extremely important in optimising machining accuracy. This paper describes moves to complete the machine calibration package in national and international standardis- ation for the assessment of machine tool performance.

• Bulletin of the Korean Mathematical Society
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• v.61 no.4
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• pp.1107-1119
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• 2024

Consider a two dimensional smooth convex body with a marked point on the boundary of it, sitting tangentially at the marked point over a base curve in 𝔼², ℍ² or 𝕊² and the image of this body by the reflection with respect to the tangent line of the base curve at the marked point. When we roll these two bodies simultaneously along the base curve, the trajectories of the marked point bound a closed region. We show that the area of the closed region is independent of the shape of the base curve if the base curve is not highly curved with respect to the boundary curve of the convex body.

• Journal of the Korean Electrochemical Society
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• v.24 no.2
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• pp.28-33
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• 2021

Many researchers have increased the loading level of electrodes to improve the energy density of secondary batteries. In this study, high-loading NCM523 (LiNi_0.5Co_0.2Mn_0.3O₂) positive electrode is manufactured using a polytetrafluoroethylene (PTFE) binder, not the conventional polyvinylidene fluoride (PVdF) binder, which has been commonly used in lithium-ion batteries. Through the kneading process using PTFE suspension, not the conventional slurry process using PVdF solution in N-methyl-2-pyrrolidinone (NMP), thick electrodes with high loading are easily manufactured. When the PTFE and PVdF-based electrodes are prepared at a loading level of 5.0 mAh/cm², respectively, the PTFE-based electrode shows better cycle performance and rate capability than those of PVdF-based electrodes. The electrode manufactured by the kneading process using a PTFE binder has high electrode porosity due to insufficient roll-press, but the porosity can be lowered by high temperature roll-press over 120℃. However, there is no significant difference in cycle performance according to the roll press temperature. In addition, the cycle performance of the high loading electrode is slightly improved by increasing the content of the conductive material. Overall, the PTFE binder can improve the performance of the high loading electrode, but additional solutions will be needed.