• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.3
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• pp.283-288
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• 2013

This paper describes development of a high speed Doppler OFDI system for non-invasive vascular imaging. Doppler OFDI (optical frequency domain imaging) is one of the phase-resolved second generation OCT (optical coherence tomography) techniques for high resolution imaging of moving elements in biological tissues. To achieve a phase-resolved imaging, two temporally separated measurements are required. In a conventional Doppler OCT, a pair of massively oversampled successive A-lines is used to minimize de-correlation noise at the expense of significant imaging speed reduction. To minimize a de-correlation noise between targeted two measurements without suffering from significant imaging speed reduction, several methods have been developed such as an optimized scanning pattern and polarization multiplexed dual beam scanning. This research represent novel imaging technique using frequency multiplexed dual beam illumination to measure exactly same position with aimed time interval. Developed system has been verified using a tissue phantom and mouse vessel imaging.

• Structural Engineering and Mechanics
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• v.50 no.1
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• pp.19-36
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• 2014

This paper focuses on a model order reduction (MOR) for large-scale rotordynamic systems by using finite element discretization. Typical rotor-bearing systems consist of a rotor, built-on parts, and a support system. These systems require careful consideration in their dynamic analysis modeling because they include unsymmetrical stiffness, localized nonproportional damping, and frequency-dependent gyroscopic effects. Because of this complex geometry, the finite element model under consideration may have a very large number of degrees of freedom. Thus, the repeated dynamic analyses used to investigate the critical speeds, stability, and unbalanced response are computationally very expensive to complete within a practical design cycle. In this study, we demonstrate that a Krylov subspace-based MOR via moment matching significantly speeds up the rotordynamic analyses needed to check the whirling frequencies and critical speeds of large rotor systems. This approach is very efficient, because it is possible to repeat the dynamic simulation with the help of a reduced system by changing the operating rotational speed, which can be preserved as a parameter in the process of model reduction. Two examples of rotordynamic systems show that the suggested MOR provides a significant reduction in computational cost for a Campbell diagram analysis, while maintaining accuracy comparable to that of the original systems.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.1105-1108
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• 2005

In oder to develope a train system for parcel service of high speed railway, which had been proposed for the operation of a high speed train, its conceptual design was build. Through this system, we are able to expect the fulfillment of customer needs for high speed rail market segments, and enhancement for cost-effective rail network operation of the mixed traffic on infrastructure cost-reduction in national logistics.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.821-824
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• 1999

In distributed arithmetic-based architecture for an inner product between two length-N vectors, the size of the ROM increases exponentially with N. Moreover, the ROMs are generally the bottleneck of speed, especially when their sire is large. In this paper, a ROM size reduction technique for DA (Distributed Arithmetic) is proposed. The proposed method is based on modified OBC (Offset Binary Coding) and control circuit reduction technique. By simulations, it is shown that the use of the proposed technique can result in reduction in the number of gates up to 50%.

• Journal of Advanced Marine Engineering and Technology
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• v.8 no.2
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• pp.74-80
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• 1984

In the reduction gears for marine propulsion engine such as turbine or high speed diesel engine, the standard involute double helical gears are generally used. However the addendum modification gear can be used in the reduction gear as it has flexibility for gear design on the tooth strength, scoring and operating noise. In this case, the determination of gear shaft bearing load is difficult by the alternation of operating pressure angle. In this paper, the formulas of bearing load according to the arrangements of the reduction gears are derived and the diagrams of operating pressure angle according to the modification coefficient are presented.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.11
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• pp.1279-1287
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• 2011

Weather strip is a functional component of a car body and doors for leaking protection, isolating outside noise and vibration reduction. Insert metal inserted to the weather strip plays a key role to keep the shape of the weather strip and increase its strength. Insert metal is mainly produced by a press process, which has low productivity and 40% material loss due to the scraps. To solve the problems, a high-speed rolling process for manufacturing the insert metal of weather strip is being attempted. In this study, the insert metal is manufactured by a high-speed rolling process, and its process variables: reduction, relative velocity of rollers and the number of passes, are optimized by using the FEA and the actual tests. The prototype was manufactured by the optimal process.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.4
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• pp.31-38
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• 2008

Under the recent situation that there increase the efforts to facilitate DFS(driver feedback sign) in school zones and children's protection areas caused by severity of traffic impact on children, the current study aims at predictively evaluating how and to what extent the reduced car speed is influential to the reduction of traffic accidents in elementary schools located in Buchon city by analyzing the velocity variation before and after DFS installation including its reduction ratio in traffic accidents as well as related literature survey. It, furthermore, aims at identifying applicable effectiveness in DFS operation for elementary schoolers in Buchon based on the data collected.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.12
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• pp.4036-4043
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• 1996

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study tested the effect of porous walls on the compression wave propagating into a model tunnel. Experimental results were obtained using a shock tube with an open end. The results showed that the cavity/porous wall is very effective for the compression wave with a large nonlinear effect. The porosity of 30% is most effective for attenuation and pressure gradient reduction of the compression wave front. Also the impulsive noise reduction increases with increasing the length and height of the cavity, compared with the tunnel equivalent diameter.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.6
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• pp.101-112
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• 2016

The characteristic analysis and fundamental test of a plasma generator is performed for drag reduction of a high speed vehicle. In high pressures, thermal plasmas is suitable for generating plasmas. The appropriate plasma torch is selected and used to generate thermal plasmas. The plasma torch, which can emit high-speed and high-pressure plasma jet, is suitable for generating plasma counterflow jet. In this study, the fundamental test and analysis for the plasma torch is summarized. Results show that supplying gas pressures and electrode gap of plasma torch are considered as critical parameters for generating plasma jets.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.443-449
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• 2010

Recently underwater systems moving at hyper-speed such as a super-cavitating torpedo have been studied for their practical advantage of the dramatic drag reduction. In this study we are focusing our attention on super-cavitating flows around axisymmetric cavitators. A numerical method based on inviscid flow is developed and the results for several shapes of the cavitator are presented. First using a potential based boundary element method, we find the shape of the cavitator yielding a sufficiently large enough cavity to surround the body. Second, numerical predictions of super-cavity are validated by comparing with experimental observations carried out in a high speed cavitation tunnel at Chungnam National University (CNU CT).