• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1529-1535
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• 2011

Improvement of the thermal efficiency in operation and maintenance of low- and medium-speed engines is a kind of never-ending requirement in the maritime power plant business. For the purpose of improving engine management efficiency, a principal factor that represents the fitness of the engine should be identified. Gas pressure, gas temperature, and vibration have all been used as this factor. However, they have limitations in terms of response speed and diagnosis accuracy. The EFR (engine fitness ratio) is suggested as a new diagnostic factor in this paper. The EFR is defined as the ratio of particular frequencies in the frequency domain and represents the fitness of an engine. It is calculated from the fluctuation pattern of the crankshaft angular speed. The EFR was verified using an experimental method for a low-speed engine and an analytic method for a medium-speed engine.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.5
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• pp.357-365
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• 2013

In this study, forces and moments were measured on a projectile which consisted of a missile configuration body(shell) and a head installed control fins. The shell and the head were separated each other and the shell was rotated by an electric motor. The head rotated reversely against the rotational direction of the shell. The rotational force on the head was obtained from a couple of fixed fins of which angular displacement were set to the rotational direction equally. The air velocity was 40m/s on the experiment and the Reynolds number based on the diameter of head was $1.3{\times}10^5$. The other couple of fins were used to control the position and direction of the projectile by changing the angular displacement. From this experiment, the variation of force and moment were measured on the rotating projectile, and the effective amplitude and frequency were obtained through the FFT analysis.

• Journal of Sasang Constitutional Medicine
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• v.29 no.2
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• pp.95-103
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• 2017

Objectives This study was aimed to analyze characteristics of facial shapes in adult women by sasang constitution using hyungsang classification. Methods Using a digital camera, we took a picture of 1,011 women who participated in clinical study on menstrual pain and acquired their 3D facial images with a face-only scanner. They filled out SSCQ-P(sasang constitution questionnaire for patient) for the diagnosis of sasang constitution. Based on the above photographs and 3D images, one of the hyungsang medicine specialist diagnosed according to five diagnostic criteria. The sasang constitution was diagnosed by referring to questionnaires and photographs. Frequency analysis was performed using the statistical analysis system version 9.4 and chi-square test was performed for validity evaluation. Results In taeeumin, the wide face shape(n=261, 74.36%) was much more than the narrow shape(n=90, 25.64%) and the convex face profile(n=164, 85.86%) was much more than the concave profile(n=27, 14.14%). Regardless of sasang constitution, angular face shape(n=501, 50%) was the most, followed by oval shape(n=317, 31.64%). Subjects with big ears(n=291, 29.19%) were the most, while big eyes(n=104, 10.43%) were the least. Subjects with eyes and nose tip upward(n=615, 78.05%) were the most, while eyes and nose tip downward(n=22, 2.79%) were the least. Conclusions Most Korean adult women have angular face, such as square or diamond, with slanted eyes and upturned nose. Taeeumin women have wide facial shape and convex profile.

• International Journal of Fluid Machinery and Systems
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• v.3 no.1
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• pp.67-79
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• 2010

Severe flexural vibration of the rotor shaft of a Francis turbine runner was experienced in the past. It was shown that the vibration was caused by the fluid forces and moments on the backshroud of the runner associated with the leakage flow through the back chamber. The aim of the present paper is to study the self-excited rotor vibration caused by the fluid force moments on the backshroud of a Francis turbine runner. The rotor vibration includes two fundamental motions, one is a whirling motion which only has a linear displacement and the other is a precession motion which only has an angular displacement. Accordingly, two types of fluid force moment are exerted on the rotor, the moment due to whirl and the moment due to precession. The main focus of the present paper is to clarify the contribution of each moment to the self-excited vibration of an overhung rotor. The runner was modeled by a disk and the whirl and the precession moments on the backshroud of the runner caused by the leakage flow were evaluated from the results of model tests conducted before. A lumped parameter model of a cantilevered rotor was used for the vibration analysis. By examining the frequency, the damping rate, the amplitude ratio of lateral and angular displacements for the cases with longer and shorter overhung rotor, it was found that the precession moment is more important for smaller overhung rotors and the whirl moment is more important for larger overhung rotors, although both types of moment due to the leakage flow can cause self-excited vibration of an overhung rotor.

• International Journal of Automotive Technology
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• v.7 no.4
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• pp.469-475
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• 2006

In this paper, an optimal suspension system with preview of the road input is synthesized for a half tracked vehicle. The main goal of this research is to improve the ride comfort characteristics of a fast moving tracked vehicle in order to maintain the driver's driving capability. Several different kinds of preview control algorithms are evaluated with active or semi-active suspension systems. The road information estimated from the motion of the 1st road-wheel is adequate to make the best use of the preview control algorithm for tracked vehicles. The ride-comfort characteristics of the tracked vehicle are more dependent on pitching angular acceleration than heaving acceleration. The pitching motion is reduced by the suspension system with hard outer suspensions and soft inner suspensions. Simulation results show that the performance of sky-hook algorithms for ride comfort nearly follow that of full state feedback algorithms.

• Journal of electromagnetic engineering and science
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• v.3 no.2
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• pp.133-139
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• 2003

The nonuniqueness of a mathematically rigorous solution to 2-dimensional inverse scattering problems is explained in a limiting view of the numerical calculations based on the spectral-domain moment method. It is illustrated that its theoretical uniqueness cannot be assured even by performing additional measurements of the scattered fields not only along multiple lines but also with angular/frequency-diversities. In a real situation, however, computational error and measurement noise are inevitable. Those limitations render it meaningless to controvert the existence of a theoretically rigorous solution. Hence the most practical issue is how to remedy the instability of its practically approximate solution.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3015-3020
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• 2007

An experimental study of the dynamic characteristics of the free rising oblate spherical bubble is investigated. As noted by Saffman, the characteristics of the spiral motion are defined with parameters of the spiral frequency, spiral radius, and rising velocity. High speed camera recorded every detail information of free rising bubble. The spiral number, the bubble rise velocity, and the angular velocities were measured for the bubble size between 1.0mm to 20.0mm in diameter. In order to make clear trajectory, we employed the Fast Fourier Transformation for the normal digital camera data to synchronize with the high speed camera data. It was found that the spiral number suggested here was monotonically decreased as the bubble size increases. The present observation, however tells us that previous Saffman's formulation shows a good agreement with the trend, but over estimated spiral number. Therefore, it is recommended that Saffman's theoretical study is needed to be improved.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1927-1929
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• 2004

현재 널리 쓰이는 고밀도 플라즈마 장치의 식각 시뮬레이션은 식각 패턴으로는 level set method이며 바이어스가 인가된 sheath model로는 Riley sheath model 이 보편적으로 받아들여지고 있다. 이러한 식각 시뮬레이션은 RF(Radio Frequency) sheath로부터 가속된 이온이 단위 입체각당 특정 지점에 이온 플럭스 분포함수, 이온 에너지 분포함수와, 중성종의 수송모델로 etch rate을 결정하는 과정과 level set method을 이용하여 식각 형태를 계산하는 과정으로 구성되어있다. 본 연구는 식각 형태 계산 이전의 단계로서 $Ar^+,\;Cl_2{^+},\;Cl^+$이온의 유동속도와 밀도를 장치의 radial방향으로 불균일하게 가정하였고, 가정한 값으로 이온 플럭스와 에너지 플럭스에 대한 영향을 알아보았다.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.3
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• pp.41-47
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• 2005

This paper deals with a squeal noise in a brake system. It has been proved that the squeal noise is influenced by the angular misalignment of a disk, disk run-out, with the previously experimental study. In this study, a cause of the noise is examined by using FE analysis program(SAMCEF) and numerical analyses with a derived analytical equation of the disk based on the experimental results. The FE analyses and numerical results show that the squeal noise is due to the disk run-out as the experimental results and the frequency component of the noise equals to that of a disk's bending mode arising from the Hopf bifurcation.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.4
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• pp.117-122
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• 2006

Maximum efficiency control scheme in a stator flux-oriented induction motor drive is proposed for minimizing input dc power. Flux level is decreased in steps for searching the minimum input dc power. In addition, Torque equation, slip angular frequency, and decoupling compensation current considering iron loss resistance is used. Simulation and experimental results verify the effectiveness of the proposed method.