• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.848-854
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• 2006

In this study, a computational analysis system has been developed in order to investigate flow-induced vibration(FIV) phenomenon for general stator-rotor cascade configurations. Relative movement of the rotor with respect to stator is reflected by modeling independent two computational domains. Fluid domains are modeled using the unstructured grid system with dynamic moving and local deforming methods. Unsteady, Reynolds-averaged Navier-Stokes equations with one equation Spalart-Allmaras and two-equation SST $k-\omega$ turbulence models are solved for unsteady flow problems. A fully implicit time marching scheme based on the Newmark direct integration method is used flow computing the coupled governing equations of the fluid-structure interaction problem. Detailed FIV responses for different flow conditions are presented with respect to time and vibration characteristics are also physically investigated in the time domain.

• 한국정밀공학회지
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• 제23권2호
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• pp.88-96
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• 2006

A gerotor pump is suitable for oil hydraulics of machine tools, automotive engines, compressors, constructions and other various applications. Especially the pump is an essential machine element of an automotive engine to feed lubricant oil. The subject of this paper is the theoretical analysis of the internal lobe pump which is a particular type of positive displacement pump. The main components of the pump are rotors; usually the outer rotor profile is characterized by lobes with circular shape, while the inner rotor profile is determined as conjugate as the outer rotor profile. For this reason the topic presented here is the definition of the geometry of the rotors starting from the design parameters. The choice of these parameters is subject to some limitations in order to avoid cusp and loop between rotors. And the integrated system which is composed of three main modules has been developed through AutoLISP & Visual Basic and CAD considering various design parameters. It generates automatically an designed model for a general type of a gerotor pump and allows us to calculate two performances indexes commonly used for the study of positive displacement pumps: the flow rate and flow rate irregularity. Results obtained using the system enable the designer and manufacturer of oil pump to be more efficient in this field.

• 대한기계학회논문집
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• 제16권6호
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• pp.1141-1149
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• 1992

본 연구에서는 Davison이 제안한 견실 제어이론을 응용하여, 자기베어링에 의 해서 지지되는 로터계를 위한 중앙 집중식 서보제어기를 설계하였다. 삼각함수 형태 의 외란과 지령치에 대한 완벽한 영향회피와 추적을 위하여, 일반적 서보보상기(serv- ocompensator)를 MIMO 제어기에 내장하였다. 또한, 상기 제어기의 일부분(subset)으 로서, 중앙집중식 PID 제어기를 제안하였다. 제2장에 자기베어링에 의해 지지되는 강체 로터계의 동적 모델을 요약하였으며, 제3장에서 제어기법의 구축을 설명하고, 두 가지 형태의 제어기에 대한 성능 비교와 견실성의 한계를 보여주는 시뮬레이션 결과를 제 4장에 제시하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.1127-1128
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• 2008

In this paper, we propose a control method to improve control performance for a Quad-rotor Unmanned Aerial Vehicle's stabilization. The proposed method is the Fuzzy+I control that contains a fuzzy controller which processes signals from the error and the change of error, and generates the control signal by summing up fuzzy output signal and integral signal. We simulated and experimented on the fuzzy+I control method by implementing Quad-rotor UAV that is able to hovering, for the purpose of verifying the effectiveness of the proposed fuzzy+I control method in comparison with general PID control, and we found out that fuzzy+I controller improved control performance of the system.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.735-741
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• 2008

Identification of asymmetry and anisotropy of rotor system is important for diagnosis of rotating machinery. Directional frequency response functions (dFRFs) are known to be a powerful tool in effectively detecting the presence of asymmetry or anisotropy. In this paper, an input noise effect of dFRFs for rotors is estimated, when both asymmetry and anisotropy are present. The normalized random errors of the dFRFs are calculated to verify the validity of the method, which is demonstrated by numerical simulation with a simple rotor model.

• 한국소음진동공학회논문집
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• 제12권2호
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• pp.116-123
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• 2002

Applying a general coupled lateral and torsional vibration finite element model of gear pair element, this paper intends to look into in detail the coupled lateral and torsional vibration characteristics of a turbo-chiller rotor bearing system, having a bull-pinion speed increasing gear. Investigations have been carried out systematically by comparing the uncoupled and coupled natural frequencies and their mode shapes upon varying the gear mesh stiffness with considerations on rotating speeds, and also by comparing the strain energies of lateral and torsional vibration modes. Results hale shown that some modes may hale the coupled lateral and torsional mode characteristics as the gear mesh stiffness Increases over a certain value, and moreover that their associated dominant modes may be different from their initial modes, j.e., a certain dominant mode may change from an initial torsional one to a lateral one or from an initial lateral one to a torsional one.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.162.5-162
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• 2001

This paper presents a indirect vector control system for induction motors using an adaptive fuzzy logic(AFL) speed estimator. The proposed speed estimator is based on the MRAS(Mode Referece Adaptive System) scheme. In general, the MRAS speed estimation approaches are more simple than any other strategies. However, there are some difficulties in the scheme, which are strong sensitivity to the motor parameters variations and necessity to detune the estimator gains caused by different speed area. In this paper, the AFL speed estimator is proposed to solve the problems. The structure of the proposed AFL is very simple. The input of the AFL is the rotor flux error difference between reference and adjustable model, and the output is the estimated incremental rotor speed. Moreover, the back propagation algorithm is combined to adjust the parameters of the fuzzy logic to the most appropriate values during the operating the system. Finally, the validity of the ...

• 한국항공우주학회지
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• 제31권4호
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• pp.99-104
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• 2003

본 논문은 헬리콥터 로터 시스템 설계시 고려해야 할 구조동역학 분야와 차세대 저진동 블레이드를 설계하는 과정을 소개하였다. 일반적으로 로터 시스템 설계시 허브 하중 최소화, 지상공진 방지 및 저진동 특성 등을 만족하도록 고유 진동수 범위를 정하게 된다. 먼저 로터 시스템에 대한 회전수별 고유 진동수 도표를 통해 로터 회전 속도와 공진영역이 생기지 않도록 설계하며 다음으로 동체에 전달되는 진동 하중 크기를 예측하기 위해 회전시 블레이드에서 발생되는 하중을 허브 중심의 비회전계 좌표축 성분으로 전환한다. 헬리콥터 전진 비행속도에 따라 동체에 전달되는 하중 크기를 구하고 동체를 강체로 모델링하여 조종속에서 발생되는 가속도를 계산함으로써 저진동 특성을 예측하였다. 본 설계기법은 현재 수행중인 차세대 로터 시스템 개발에 적용되고 있으며 향후 국내 개발 로터 시스템에 유용하게 적용될 것이다.

• Tribology and Lubricants
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• 제30권3호
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• pp.131-138
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• 2014

This study investigates the effects of the slopes of the rotational axis and bearing preloads on the natural frequencies and onset speeds of the instability of a rotor supported on gas foil bearings (GFBs). The predictive model for the rotating system consists of a rigid rotor supported on two gas foil journal bearings (GFJBs) and a pair of gas foil thrust bearings (GFTBs). Each GFJB supports approximately half the rotor weight. As the slope of the rotational axis increases from $0^{\circ}$(horizontal rotor operation) to $90^{\circ}$(vertical rotor operation), the applied load on the GFJB owing to the rotor weight decreases. The predictions show that the natural frequency and onset speed of instability decrease significantly with an increase in the slope of the rotational axis. In a parametric study, the nominal radial clearance and preload for the GFJB were changed. In general, a decrease in the nominal radial clearance lead to an increase in the natural frequency and onset speed of instability. For constant assembly clearance, the decrease in the preload changed the natural frequency and onset speed of instability with insignificant improvements in the rotordynamic stability. The present predictions can be used as design guidelines for GFBs for oil-free high-speed rotating machinery with improved rotordynamic performance.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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• pp.600-605
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• 2009

A general purpose viscous flow solver Ansys CFX is used to study a Savonius type wave energy converter in a 3D numerical viscous wave tank. This paper presents the results of a computational fluid dynamics (CFD) analysis of the effect of blade configuration on the performance of 3 bladed Savonius rotors for wave energy extraction. A piston-type wave generator was incorporated in the computational domain to generate the desired incident waves. A complete OWC system with a 3-bladed Savonius rotor was modeled in a three dimensional numerical wave tank and the hydrodynamic conversion efficiency was estimated. The flow over the rotors is assumed to be two-dimensional (2D), viscous, turbulent and unsteady. The CFX code is used with a solver of the coupled conservation equations of mass, momentum and energy, with an implicit time scheme and with the adoption of the hexahedral mesh and the moving mesh techniques in areas of moving surfaces. Turbulence is modeled with the k.e model. Simulations were carried out simultaneously for the rotor angle and the helical twist. The results indicate that the developed models are suitable to analyze the water flows both in the chamber and in the turbine. For the turbine, the numerical results of torque were compared for all the cases.