• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.297-303
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• 2001

This research presents an analytical model to characterize the ball bearing vibration due to the waviness in a rigid rotor supported by multi-row ball bearings considering centrifugal force and gyroscopic moment of ball. The effects of centrifugal force and gyroscopic moment are introduced to the kinematic constraints and force equilibrium equations. The waviness of ball and races is modeled by the superposition of sinusoidal function and it is introduced to position vectors of race curvature center to use the Hertzian contact theory in order to calculate the elastic deflection and nonlinear contact force resulting from the waviness while the rotor has translational and angular motion. They can be determined by solving the nonlinear equations of motion with five degrees of freedom by using the Runge-Kutta-Fehlberg algorithm. The accuracy of this research is validated by comparing with the results of the prior researches. It characterizes the vibration frequencies resulting from the various kinds of waviness in rolling elements, the harmonic frequencies resulting from the nonlinear load-deflection characteristics of ball bearing resulting from the waviness interaction.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.11
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• pp.1133-1143
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• 2009

Vibro-acoustic characteristics of a simplified disk-brake rotor containing a narrow radial slot are studied using a semi-analytical procedure. First, modal sound radiations for flexural and radial modes of a generic annular disk having identical key dimension and slot(with free boundaries) are defined using pre-developed analytical solutions based on the modal vibrations from finite element model. The analytical solutions are validated by fully computational methods. Second, sound radiation from a simplified brake rotor simulated using sound radiation solution of the generic disk based on the rotor eigensolutions computed using a finite element code. Predictions by the semi-analytical method matched well numerical calculations using finite element and boundary element method. Finally, sound radiation and vibration characteristics for the example rotor due to a harmonic excitation fixed to the rotor or rotating around the rotor are also obtained.

• Journal of environmental and Sanitary engineering
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• v.12 no.1
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• pp.59-68
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• 1997

The main purpose of this study was to determine effects of BS-SBR compared with SBR on the removal of soluble organics and sludge separation. In the BS-SBR process, soluble organics were removed by suspended activated sludge as well as biological fixed films and these two processes occurred simultaneously in one tank. The removal efficiency of soluble COD in the BS-SBR, approximately 97% in both 1 and 3-cycle/d was higher than for SBR. The BS-SBR process was very efficient for SS removal. The averaged SS concentration were 4.8 mg/l over the operation period, the daily SS values were consistently below 10 mg/l in both of 1-cycle and 3-cycle a day. The sludge settling characteristics in BS-SBR were totally different from SBR's. The sludge, dark brown, was well flocculated and its floc size was visible larger than the SBR's.

• Current Industrial and Technological Trends in Aerospace
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• v.5 no.2
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• pp.23-32
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• 2007

헬리콥터 주 로터 시스템은 헬리콥터 전체 성능을 좌우하고, 비행특성을 결정하는 핵심 구성품이다. 주 로터 시스템은 회전하면서 추력 및 조종력을 발생시키기 때문에 동적 밸런싱을 맞추는 것도 중요한 개발단계업무 중에 하나이다. 주 로터 시스템의 개발 과정에서 헬리콥터 비행시제 장착 전에 동적 밸런스 시험, 성능시험, 안정성 시험 등을 포함하는 훨시험(whirl test)을 수행하게 된다. 이 시험 수행을 위해 제작되는 시험장치가 훨타워(whirl tower)이다. 세계 유수 헬리콥터 회사들은 주 로터 훨시험을 위한 설비인 훨타워를 보유하고 있으며, 지속적으로 성능 개량 등을 통해 최신의 기술 및 장비를 적용하여 운영하고 있다. 본 논문에서는 대표적으로 사용되고 있는 해외 헬리콥터 회사들의 훨타워의 사례를 설명하고 설비의 기능을 기술함으로써 기술적 동향에 대하여 살펴보았다. 현재 한국형헬기개발사업(KHP)에서 구축중인 다목적 의 WTTF(whirl tower test facility) 요구조건 및 설계 현황에 대해서도 기술하였다. 당 연구원의 WTTF는 한국형기동헬기(KUH)의 주 로터 훨시험 및 내구성 시험을 위해 구축되고 있다. 본 시험설비는 연구개발용 시험과 양산용 시험을 모두 수행할 수 있도록 다목적으로 개발될 예정이다. 본 설비는 기존 해외 설비와는 차별화되어 다목적 시험을 할 수 있도록 설계가 진행중이며, 2008년12월에 구축 완료 예정이다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.837-842
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• 2009

The efficient dynamic modeling of a satellite with flexible solar arrays is established by using the component mode synthesis technique. A flexible satellite model can be defined as the assembly of two sub-structures, central body and solar array. The reduced models of each substructure, which are expressed in each local frame, are coupled with respect to the satellite reference frame. The dynamic modeling method is applied to the numerical example of a satellite with a single solar array, and is verified by investigating the transfer function results with considering the solar array rotation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.11
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• pp.1028-1035
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• 2007

this study, forced vibration analysis was performed on the composite main wing structure of a small scale WIG craft which is equipped two-stroke pusher type reciprocating engine. The structural vibration analysis based on the finite element method was performed using a commercial FEM code, MSC/NASTRAN. Excitations for the frequency response analysis were assumed as the H-mode(horizontal mode), the V-mode(vertical mode) and the X-mode(twisted mode) which are typical main vibration modes of engine. And excitations for the transient response analysis were assumed as the L-mode(longitudinal mode) with the oscillating propeller thrust which occurs.

• Journal of Advanced Marine Engineering and Technology
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• v.6 no.1
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• pp.25-33
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• 1982

The characteristics of the stator current and torque of a small three- phase squirrel cage induction motor and studied experimentally under the situation of a single-phase operation due to various causes. Through the experiments, the torque-slip and current-slip curve of single-phase circuit as well as three-phase circuit are obtained and the needed constants are determined. The stator current and torque are calculated by the current and torque equations derived by the unbalanced circuit theory. The numerical values obtained from the above methods are compared with the experimental values under the same conditions. The results of the study are summerized as follow; 1) The values computed by the unbalanced circuit theory generally come to approach the values recorded through experiments. 2) Near the rated load, speed drop is less than 1.2 per cent of the speed of three-phase induction motor and torque reduces less than 3 per cent of it of three-phase induction motor when three-phase induction motor is run under a single-phase. On the other hand, the stator current in a single-phase circuit is more than 1.9 times of it in three-phase circuit. 3) The stalling torque in a single-phase circuit is reduced to about 41 per cent of it in three-phase circuit while the corresponding slip is moved toward the synchroneous speed and the corresponding stator current is increased.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1303-1309
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• 2003

This paper presents the static and dynamic measurements for the strength and motion characteristics as well as the improved procedures to assess strength of wheel loaders. Two scenarios for static measurement were decided by which cylinder was actuating. The dynamic measurement was performed for two types of motion, that is, simple reciprocation of the working devices and actual working motion including traveling, digging and dumping. The measured items were stresses, cylinder pressures and strokes. Stress induced by bucket working showed higher level than that by boom working. The measured cylinder speeds were relatively superior to the design speeds. Working stress histories were thought to be closer to static rather than dynamic. A fully assembled FE model was prepared for structural analysis. In this paper, a more simple method was suggested to avoid nonlinearity caused by heave of rear frame under digging forces. Also how brake affected on structural behavior and digging force was examined closely in relation with tire pressure. It was confirmed that the overall stress level of wheel loader during turning traveling with loaded bucket was far lower than the yield stress of material.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.2
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• pp.158-162
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• 2004

The magnetic levitator is the device which can float a magnetic material at the midair by electromagnetic force and it's principle can be applied to the high speed magnetic bearing or magnetic levitation train. There are many difficulties to control, because the magnetic levitator is basically a nonlinear and unstable system. In this paper, this system is modeled assuming that it is a linear system nearby an operating point, and a proportional and derivative(PD) position controller is designed to carry out the variable position control. The performance of position control response is shown through simulation and experiment. A prototype magnetic levitator is constructed using PWM converter and DSP(Digital Signal Processor) based control board.

• Journal of Korean Society of Steel Construction
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• v.15 no.5 s.66
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• pp.551-559
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• 2003

In steel frames, the analysis and design techniques are based on either idealized fixed or pinned connections. In this case, it has the advantage that the structural analysis and the design procedure were simplified, but there could be given different results of analysis between the real steel frame connections and the idealized fixed and pinned connection. This is because the real connections would be analyzed by semi-rigid, and have some transfer of moment and rotational constraint about the loads. In this study, structural analysis program with considered connections that have joint rigidity of fixed, pinned and semi-rigid, was developed. Then, the effects of joint rigidity on strength and displacement. in steel frames subjected to lateral forces and axial forces, were investigate, and the results were compared with those of the Midas Gen. w program.