• Journal of Korean Society for Quality Management
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• v.32 no.2
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• pp.154-167
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• 2004

The TOC/DBR and Six Sigma are the most attention-getting concepts for managing manufacturing companies in Korea. Using the ideas and methods of the TOC/DBR, companies can achieve a large reduction of work-in-process and finished-good inventories, significant improvement in scheduling performance, and substantial earnings increase. The Six Sigma approach derives the overall process of selecting the right projects based on their potential to improve performance metrics and selecting/training the right people to get the business results. These two concepts have different backgrounds and different viewpoints for production systems. So, if the two concepts collaborate each other, the synergy effects to innovate production systems can be expected. This paper proposes a new approach to implement the TOC/DBR concepts in production systems. This approach uses some concepts of Six Sigma which stresses educations, project approaches (step by step procedure using a Roadmap), and improvement philosophy.

• International Journal of Precision Engineering and Manufacturing
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• v.2 no.2
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• pp.17-25
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• 2001

In this paper, a theoretical study has been made to reduce the residual stress and birefringence in the injection-molded parts. An optimization program has been used to minimize the residual stresses and birefringence calculated from a simulation program. The thermally induced stress has been calculated using a linear viscoelasticity model. The flow stress and birefringence has been calculated using the Leonov's viscoelasticity model. This has been applied to the injection molding of a circular disc and a plate. the optimization has been done either by changing process variables while maintaining the mold temperature constant or by varying the mold-wall temperature with time. This study shows the significant reduction in residual stress and birefringence is possible through the optimization of processing conditions.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.166-171
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• 2004

Direct numerical simulations are peformed to investigate the physics of a spatially developing turbulent boundary layer flow suddenly subjected to spanwise oscillating electro-magnetic forces in the near-wall region. The Reynolds number based on the inlet momentum thickness and free-stream velocity is $Re_\theta=300$. A fully-implicit fractional step method is employed to simulate the flow. The mean flow properties and the Reynolds stresses are obtained to analyze the near-wall turbulent structure. It is found that skin-friction and turbulent kinetic energy can be reduced by the electro-magnetic forces. Instantaneous flow visualization techniques are used to observe the response of streamwise vortices to spanwise oscillating forces. The near-wall vortical structures are clearly affected by spanwise oscillating electro-magnetic forces.

• Proceedings of the KIEE Conference
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• 2003.04a
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• pp.221-223
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• 2003

This paper presents a new hybrid control method of asymmetrical/symmetrical half-bridge converter (AHBC/SHBC) with low voltage stress of the diodes. The proposed new control scheme is executed by using feedback of the input voltage and then can decide operation of the converter is divided into two ranges, which are asymmetrical control and symmetrical control, So the proposed control scheme has many advantages such as a low rated voltage of the secondary diodes, and low conduction loss according to the low voltage drop. The proposed control scheme is verified by simulated results.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.379-381
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• 1994

This paper is concerned with a zero-voltage soft-switching PWM DC-DC high-pelter converter using IGBTs, which Bakes the most of the parastic LC parameters of high-voltage transformer link, for diagnostic X-Ray power generator. The converter circuit basically utilizes phase-shift pulse width modulated series resonant full-bridge PWM DC-DC high-Power converter operating at a constant frequency:20kHz. This technique brings about dramatic decreases in the switching losses of power devices and their electrical stresses as compared with the commonly-used hard-switching PWM DC-DC power converter. The high-frequency switching operation of the converters has some effective advantages, which consist in the physical reduction in size and weight and lowered acoustic noise.

• The Journal of Korean Medicine
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• v.27 no.4
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• pp.125-134
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• 2006

During the prenatal period, the development of the individual is influenced by a host of environmental factors. Exposure to noise stress during pregnancy was determined to result in the retardation of growth, a reduction in neurogenesis, and an impairment of spatial learning ability in the rat pups. In the present study, we have attempted to characterize the effects of prenatal treatment with Cnidium officinale Makino on spatial memory and neurogenesis in the hippocampus of rat pups born from maternal rats exposed to noise stress during pregnancy. Prenatal treatment with Cnidium officinale Makino was shown to increase neurogenesis and enhanced spatial learning ability in rat pups born from maternal rats exposed to noise stress. In this study, we have determined that prenatal treatment with Cnidium officinale Makino can stimulate spatial development and neurogenesis in the brain of the fetuses exposed to prenatal stresses.

• Journal of Electrical Engineering and Technology
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• v.8 no.6
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• pp.1337-1344
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• 2013

This paper presents a simplified modulation strategy for the three-leg VSI fed two-winding induction motor. The strategy provides independent unbalanced voltage control for the main and auxiliary windings. This make the motor can be reversed rotation through the range of motor speed operation without limitation of voltage boost of the auxiliary winding. To study the advantages of the proposed drive, the experimental results such as voltage stresses, hysteresis band of the currents in locus, and also acoustic noise levels of the three-leg VSI are compared with those of the conventional two-leg topology. The results obviously show that the proposed technique achieves superior performance compared with the traditional scheme in case of dramatic increase of DC bus utilization, effective reduction of harmonic voltages content, and also significant enhancement of motor efficiency.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.11
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• pp.1645-1654
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• 2003

When vortex shedding is locked-on to a single frequency oscillatory flow, the variations of vortex dynamics are investigated using a time-resolved PIV system. Wake regions of recirculation and vortex formation, dynamic behavior of the shed vortices and the Reynolds stress fields are measured in the wake-transition regime at the Reynolds number 360. In the lock-on state, reduction of the wake region occurs and flow energy distributed downstream moves upstream being concentrated near the cylinder base. To observe the dynamic behavior of the shed vortices, the trajectory of the vortex center extended to the inside of the wake bubble is considered, which describes well the formation and evolution processes. The Reynolds stresses and their contributions to overall force balance on the wake bubble manifest the increase of the drag force by the lock-on.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1760-1765
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• 2007

This paper shows a derating design approach for LED reliability improvement. The LED is widely used in display devices or circuits. The main failure of interest is defined as 100% reduction of the light output intensity of LED resulting from corrosion due to stresses, i.e. temperature and humidity. The lifetime is varied according to the stress levels under where the LED operates so that correlation of the lifetime to these stress levels over time is modeled through accelerated life testings. A derating design approach to accomplish a required reliability level of LED is proposed to determine adequate the stress levels. In the approach, $B_{10}$ life, Failure rate, Sensitivity Analysis of LED are used as a reliability metric.

• Proceedings of the KAIS Fall Conference
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• 2011.05b
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• pp.679-682
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• 2011

The effects of heat input(1.5~3.6kJ/mm) and postweld heat treatment(PWHT, $600^{\circ}C$, 40hr.) on the TMCP HSB600 steel weldments made by GMAW process were investigated. The tensile strength and CVN impact energy of as-welded specimens decreased with increasing heat input. The fine-grained acicular ferrite was mainly formed in the low heat input while polygonal and side plate ferrites were dominated in the high inputs. Meanwhile, tensile strength and hardness of PWHT weldments decreased due to the coarsening of microstructure and reduction of residual stresses.