• 한국소음진동공학회논문집
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• 제11권8호
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• pp.338-348
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• 2001

A hybrid self-hearing motor, which Is a functional combination of general permanent magnet (PM) motor and hybrid active magnetic bearing(AMB), was proposed a few years ago. In this paper the hybrid self-bearing motor is modified to a disk type, in which one of two magnetic hearings was substituted for a thin yoke to make the system more compact. An outer rotors in this self-hearing motor is actively controlled only in two radial directions while the ocher motions are passively salable owing to the disk-type structure. Main advantages of the proposed self-hearing motor are simple control mechanism, low power consumption and smart structure. Mathematical model for the magnetic force Is built wish consideration of the radial displacement of the rotor. The model helps us not only to design a levitation controller but also to expect the system performance. Some experimental results show good capability and feasibility of the Proposed self-bearing motor.

• JSTS:Journal of Semiconductor Technology and Science
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• 제7권4호
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• pp.260-266
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• 2007

Analytical compact form models for the signal transients and crosstalk noise of inductive-effect-prominent multi-coupled RLC lines are developed. Capacitive and inductive coupling effects are investigated and formulated in terms of the equivalent transmission line model and transmission line parameters for fundamental modes. The signal transients and crosstalk noise expressions of two coupled lines are derived by using a waveform approximation technique. It is shown that the models have excellent agreement with SPICE simulation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.283-288
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• 2006

This study developes the vibration model to estimate the vibration energy of damper/spring assembly(mainbase assembly) for car CD player, and this model is verified by experiment. From frequency response, response, we investigate the natural frequency and mode shape in the up/down direction. In order to determine the analysis frequency band, we investigate the excitation frequency from the vehicle test. As the characteristics of damper and spring is changed, we carry out the vibration test(transmissibility) and investigate the change of transmissibility.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.783-786
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• 2002

The unsteady turbulent flow characteristics of NACA4406 airfoil at close proximity to the pound are numerically investigated, especially focused on the noise generation mechanism near the blunt trailing edge. The unsteady two-dimensional compressible Wavier-Stokes equations with a Spalart-Allmaras turbulence closure model are solved by the 6th-order compact scheme and the 4th-order Runge-Kutta scheme. The computation shows a noise generation by a feedback mechanism at the blunt tailing edge, where the acoustic-fluidic coupling occurs between the wall-reflected sound waves and the periodically disturbed turbulent shear layer.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.434-440
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• 2011

Oscillating airfoil haw been challenged for the dynamic stalls of airfoil am wind turbines at high angle of attach. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance am safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed for the oscillating airfoil at high angle of attack around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.2 and Reynolds number of $1.2{\times}10^4$. The lift, drag, pressure distribution, etc. are analyzed according to the pitching oscillation. Unsteady velocity field, periodic vortex shedding, the unsteady pressure distribution, and the acoustic fields are analyzed. The effects of these unsteady characteristics in the aerodynamic coefficients are analyzed.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 추계 학술대회논문집
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• pp.152-157
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• 2003

As computer capacity has been progressed continuously, the studies of the flow characteristics have been performing by the numerical methods actively. Recent numerical simulation has a tendency to require the higher-order accuracy in time, as well as in space. This tendency is more true in LES and acoustic noise simulation. In this study, 3-dimensional unsteady Incompressible Navier-Stokes equation was solved by numerical method using the fractional step method with the fourth order compact pade scheme to achieve high accuracy To validate the present code and algorithm, 3D flow-field around a cylinder was simulated. The drag coefficient and lift coefficient were computed and, then, compared with experiment. The present code will be tailored to LES simulation for more accurate turbulent flow analysis.

• 한국소음진동공학회논문집
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• 제17권12호
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• pp.1208-1216
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• 2007

Turbomachinery such as turbines, pumps and compressors, which are installed in transportation systems, including aircrafts, ships, and space vehicles, etc., often perform crucial missions and are exposed to potential dangerous impact environments such as base-transferred shock forces. To protect turbomachinery from excessive shock forces, it may be needed to accurately analyze transient responses of their rotors, considering the dynamics of mount designs to be applied. In this study a generalized FE transient response analysis model, introducing relative displacements, is proposed to accurately predict transient responses of a flexible rotor-bearing system with mount systems to base-transferred shock forces. In the transient analyses the state-space Newmark method of a direct time integration scheme is utilized, which is based on the average velocity concept. Results show that for the identical mount systems considered, the proposed FE-based detailed flexible rotor model yields more reduced transient vibration responses to the same shocks than a conventional simple model, obtained by treating a rotor as concentrated lumped mass, equivalent spring and a damper or Jeffcott rotor model. Hence, in order to design a rotor-bearing system with a more compact light-weighted mount system, preparing against any potential excessive shock, the proposed FE transient response analysis model herein is recommended.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.474-478
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• 2006

It is becoming more significant to develop a rotary voice coil motor(VCM) type's actuator for small form factor (SFF) optical disk drive(ODD), as portables are getting more and more popularized nowadays. The actuator which is applicable to small-sized ODD with a compact flash(CF) II card size was developed and fabricated. The experimental results showed that the finite element(FE) model is different from the fabricated model. And so flexible mode frequencies did not satisfy specifications of small-sized ODD, and tuning. Tuning procedures were required to improve dynamic characteristics of the fabricated actuator through finite difference method(FDM). At first, design variables were extracted through parameter study and the tuned FE model was improved by design of experiment(DOE). Consequently, It was confirmed that the improved model was applicable to SFF ODD.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.387-392
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• 2007

Turbomachinery such as turbines, pumps and compressors, which are installed in transportation systems such as warships, submarines and space vehicles, etc., often perform crucial missions and are exposed to potential dangerous impact environments such as base-transferred shock forces. To protect turbomachinery from excessive shock forces, it may be needed to accurately analyze transient responses of rotors, considering the dynamics of mount designs to be applied with. In this study a generalized FE transient response analysis model, introducing relative displacements, is firstly proposed to accurately predict transient responses of a flexible rotor-bearing system with mount systems to base-transferred shock forces. In the transient analyses the state-space Newmark method of a direct time integration scheme is utilized, which is based on the average velocity concept. Results show that for the identical mount systems considered, the proposed FE-based detailed flexible rotor model yields more reduced transient vibration responses to the same shocks than a conventional simple model or a Jeffcott rotor. Hence, in order to design a rotor-bearing system with a more compact light-weighted mount system, preparing against any potential excessive shock, the proposed FE transient response analysis model herein is recommended.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.414-419
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• 2011

Missile am fighter aircraft have been challenged by low restoring nose-down pitching moment at high angle of attach. The consequence of weak nose-down pitching moment can be resulting in a deep stall condition. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance and safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed at high angle of attack up to 60 degrees around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.3 and Reynolds number of $10^5$. The lift, drag, pressure distribution, etc. are analyzed according to the angle of attack. The results at a low angle of attack are compared with other results before a stall condition. From a certain high angle of attack, the strong vortex formed by the leading edge are flowing downstream as like Karman vortex around a circular cylinder. Unsteady velocity field, periodic vortex shedding, the unsteady pressure distribution on the airfoil surface, and the acoustic fields are analyzed. The effects of these unsteady characteristics in the aerodynamic coefficients are analyzed.